8-Aminopurines in the Cardiovascular and Renal Systems and Beyond

Screening of compounds comprising 8-substituted guanine revealed that 8-aminoguanosine and 8-aminoguanine cause diuresis/natriuresis/glucosuria, yet decrease potassium excretion. Subsequent investigations demonstrated that 8-aminoguanosine's effects are mediated by its metabolite 8-aminoguanine. The mechanism by which 8-aminoguanine causes diuresis/natriuresis/glucosuria involves inhibition of PNPase (purine nucleoside phosphorylase), which increases renal interstitial inosine levels. Additional evidence suggests that inosine, via indirect or direct adenosine A2B receptor activation, increases renal medullary blood flow which enhances renal excretory function. Likely, 8-aminoguanine has pleiotropic actions that also alter renal excretory function. Indeed, the antikaliuretic effects of 8-aminoguanine are independent of PNPase inhibition. 8-Aminoguanine is an endogenous molecule; nitrosative stress leads to production of biomolecules containing 8-nitroguanine moieties. Degradation of these biomolecules releases 8-nitroguanosine and 8-nitro-2'-deoxyguanosine which are converted to 8-aminoguanine. Also, guanosine and guanine per se may contribute to 8-aminoguanine formation. 8-Aminoinosine, 8-aminohypoxanthine, and 8-aminoxanthine likewise induce diuresis/natriuresis/glucosuria, yet do not reduce potassium excretion. Thus, there are several pharmacologically active 8-aminopurines with nuanced effects on renal excretory function. Chronic treatment with 8-aminoguanine attenuates hypertension in deoxycorticosterone/salt rats, prevents strokes, and increases lifespan in Dahl salt-sensitive rats on a high salt diet and attenuates the metabolic syndrome in rats; 8-aminoguanosine retards progression of pulmonary hypertension in rats and anemia and organ damage in sickle cell mice. 8-Aminoguanine reverses age-associated lower urinary tract dysfunction and retinal degeneration. 8-Aminopurines represent a new class of agents (and potentially endogenous factors) that have beneficial effects on the cardiovascular system and kidneys and may turn back the clock in age-associated diseases.

Relaxin Inhibits Ventricular Arrhythmia and Asystole in Rats With Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) leads to right ventricular cardiomyopathy and cardiac dysfunctions where in the clinical setting, cardiac arrest is the likely cause of death, in ~70% of PAH patients. We investigated the cardiac phenotype of PAH hearts and tested the hypothesis that the insulin-like hormone, Relaxin could prevent maladaptive cardiac remodeling and protect against cardiac dysfunctions in a PAH animal model. PAH was induced in rats with sugen (20 mg/kg), hypoxia then normoxia (3-weeks/each); relaxin (RLX = 0, 30 or 400 μg/kg/day, n ≥ 6/group) was delivered subcutaneously (6-weeks) with implanted osmotic mini-pumps. Right ventricle (RV) hemodynamics and Doppler-flow measurements were followed by cardiac isolation, optical mapping, and arrhythmia phenotype. Sugen-hypoxia (SuHx) treated rats developed PAH characterized by higher RV systolic pressures (50 ± 19 vs. 22 ± 5 mmHg), hypertrophy, reduced stroke volume, ventricular fibrillation (VF) (n = 6/11) and bradycardia/arrest (n = 5/11); both cardiac phenotypes were suppressed with dithiothreitol (DTT = 1 mM) (n = 0/2/group) or RLX (low or high dose, n = 0/6/group). PAH hearts developed increased fibrosis that was reversed by RLX-HD, but not RLX-LD. Relaxin decreased Nrf2 and glutathione transferases but not glutathione-reductase. High-dose RLX improved pulmonary arterial compliance (measured by Doppler flow), suppressed VF even after burst-pacing, n = 2/6). Relaxin suppressed VF and asystole through electrical remodeling and by reversing thiol oxidative stress. For the first time, we showed two cardiac phenotypes in PAH animals and their prevention by RLX. Relaxin may modulate maladaptive cardiac remodeling in PAH and protect against arrhythmia and cardiac arrest.

Long-Term Dipeptidyl Peptidase 4 Inhibition Worsens Hypertension and Renal and Cardiac Abnormalities in Obese Spontaneously Hypertensive Heart Failure Rats

Background The long-term effects of dipeptidyl peptidase 4 (DPP4) inhibitors on blood pressure and cardiovascular and renal health remain controversial. Herein, we investigated the extended (>182 days) effects of DPP4 inhibition in a model of spontaneous hypertension, heart failure, diabetes mellitus, obesity and hyperlipidemia. Methods and Results Adult obese spontaneously hypertensive heart failure rats (SHHF) were implanted with radio transmitters for measurement of arterial blood pressures. Two weeks later, SHHF were randomized to receive either a DPP4 inhibitor (sitagliptin, 80 mg/kg per day in drinking water) or placebo. At the end of the radiotelemetry measurements, renal and cardiac function and histology, as well as other relevant biochemical parameters, were assessed. For the first 25 days, mean arterial blood pressures were similar in sitagliptin-treated versus control SHHF; afterwards, mean arterial blood pressures increased more in sitagliptin-treated SHHF (P<0.000001). The time-averaged mean arterial blood pressures from day 26 through 182 were 7.2 mm Hg higher in sitagliptin-treated SHHF. Similar changes were observed for systolic (8.6 mm Hg) and diastolic (6.1 mm Hg) blood pressures, and sitagliptin augmented hypertension throughout the light-dark cycle. Long-term sitagliptin treatment also increased kidney weights, renal vascular resistances, the excretion of kidney injury molecule-1 (indicates injury to proximal tubules), renal interstitial fibrosis, glomerulosclerosis, renal vascular hypertrophy, left ventricular dysfunction, right ventricular degeneration, and the ratios of collagen IV/collagen III and collagen IV/laminin in the right ventricle. Conclusions These findings indicate that, in some genetic backgrounds, long-term DPP4 inhibitor treatment is harmful and identify an animal model to study mechanisms of, and test ways to prevent, DPP4 inhibitor-induced pathological conditions.

Complex III Inhibition-Induced Pulmonary Hypertension Affects the Mitochondrial Proteomic Landscape

The mitochondria play a vital role in controlling cell metabolism and regulating crucial cellular outcomes. We previously demonstrated that chronic inhibition of the mitochondrial complex III in rats by Antimycin A (AA) induced sustained pulmonary vasoconstriction. On the metabolic level, AA-induced mitochondrial dysfunction resulted in a glycolytic shift that was reported as the primary contributor to pulmonary hypertension pathogenesis. However, the regulatory proteins driving this metabolic shift with complex III inhibition are yet to be explored. Therefore, to delineate the mechanisms, we followed changes in the rat lung mitochondrial proteome throughout AA treatment. Rats treated with AA for up to 24 days showed a disturbed mitochondrial proteome with significant changes in 28 proteins (p < 0.05). We observed a time-dependent decrease in the expression of key proteins that regulate fatty acid oxidation, the tricarboxylic acid cycle, the electron transport chain, and amino acid metabolism, indicating a correlation with diminished mitochondrial function. We also found a significant dysregulation in proteins that controls the protein import machinery and the clearance and detoxification of oxidatively damaged peptides via proteolysis and mitophagy. This could potentially lead to the onset of mitochondrial toxicity due to misfolded protein stress. We propose that chronic inhibition of mitochondrial complex III attenuates mitochondrial function by disruption of the global mitochondrial metabolism. This potentially aggravates cellular proliferation by initiating a glycolytic switch and thereby leads to pulmonary hypertension.

DPP4 Inhibition, NPY1-36, PYY1-36, SDF-1α, and a Hypertensive Genetic Background Conspire to Augment Cell Proliferation and Collagen Production: Effects That Are Abolished by Low Concentrations of 2-Methoxyestradiol

By reducing their metabolism, dipeptidyl peptidase 4 inhibition (DPP4I) enhances the effects of numerous peptides including neuropeptide Y_1–36 (NPY_1–36), peptide YY_1–36 (PYY_1–36), and SDF-1α. Studies show that separately NPY_1–36, PYY_1–36 and SDF-1α stimulate proliferation of, and collagen production by, cardiac fibroblasts (CFs), preglomerular vascular smooth muscle cells (PGVSMCs), and glomerular mesangial cells (GMCs), particularly in cells isolated from genetically hypertensive rats. Whether certain combinations of these factors, in the absence or presence of DPP4I, are more profibrotic than others is unknown. Here we contrasted 24 different combinations of conditions (DPP4I, hypertensive genotype and physiologic levels [3 nM] of NPY_1–36, PYY_1–36, or SDF-1α) on proliferation of, and [³H]-proline incorporation by, CFs, PGVSMCs, and GMCs. In all three cell types, the various treatment conditions differentially increased proliferation and [³H]-proline incorporation, with a hypertensive genotype + DPP4I + NPY_1–36 + SDF-1α being the most efficacious combination. Although the effects of this four-way combination were similar in male versus female CFs, physiologic (1 nM) concentrations of 2-methoxyestradiol (2ME; nonestrogenic metabolite of 17β-estradiol), abolished the effects of this combination in both male and female CFs. In conclusion, this study demonstrates that CFs, PGVSMCs, and GMCs are differentially activated by various combinations of NPY_1–36, PYY_1–36, SDF-1α, a hypertensive genetic background and DPP4I. We hypothesize that as these progrowth conditions accumulate, a tipping point would be reached that manifests in the long term as organ fibrosis and that 2ME would obviate any profibrotic effects of DPP4I, even under the most profibrotic conditions (i.e., hypertensive genotype with high NPY_1–36 + SDF-1α levels and low 2ME levels).

Estradiol Metabolism: Crossroads in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a debilitating and progressive disease that predominantly develops in women. Over the past 15 years, cumulating evidence has pointed toward dysregulated metabolism of sex hormones in animal models and patients with PAH. 17β-estradiol (E2) is metabolized at positions C2, C4, and C16, which leads to the formation of metabolites with different biological/estrogenic activity. Since the first report that 2-methoxyestradiol, a major non-estrogenic metabolite of E2, attenuates the development and progression of experimental pulmonary hypertension (PH), it has become increasingly clear that E2, E2 precursors, and E2 metabolites exhibit both protective and detrimental effects in PH. Furthermore, both experimental and clinical data suggest that E2 has divergent effects in the pulmonary vasculature versus right ventricle (estrogen paradox in PAH). The estrogen paradox is of significant clinical relevance for understanding the development, progression, and prognosis of PAH. This review updates experimental and clinical findings and provides insights into: (1) the potential impacts that pathways of estradiol metabolism (EMet) may have in PAH; (2) the beneficial and adverse effects of estrogens and their precursors/metabolites in experimental PH and human PAH; (3) the co-morbidities and pathological conditions that may alter EMet and influence the development/progression of PAH; (4) the relevance of the intracrinology of sex hormones to vascular remodeling in PAH; and (5) the advantages/disadvantages of different approaches to modulate EMet in PAH. Finally, we propose the three-tier-estrogen effects in PAH concept, which may offer reconciliation of the opposing effects of E2 in PAH and may provide a better understanding of the complex mechanisms by which EMet affects the pulmonary circulation–right ventricular interaction in PAH.

Experimental intravascular hemolysis induces hemodynamic and pathological pulmonary hypertension: association with accelerated purine metabolism

Pulmonary hypertension (PH) is emerging as a serious complication associated with hemolytic disorders, and plexiform lesions (PXL) have been reported in patients with sickle cell disease (SCD). We hypothesized that repetitive hemolysis per se induces PH and angioproliferative vasculopathy and evaluated a new mechanism for hemolysis-associated PH (HA-PH) that involves the release of adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) from erythrocytes. In healthy rats, repetitive administration of hemolyzed autologous blood (HAB) for 10 days produced reversible pulmonary parenchymal injury and vascular remodeling and PH. Moreover, the combination of a single dose of Sugen-5416 (SU, 200 mg/kg) and 10-day HAB treatment resulted in severe and progressive obliterative PH and formation of PXL (Day 26, right ventricular peak systolic pressure (mmHg): 26.1 ± 1.1, 41.5 ± 0.5 and 85.1 ± 5.9 in untreated, HAB treated and SU+HAB treated rats, respectively). In rats, repetitive administration of HAB increased plasma ADA activity and reduced urinary adenosine levels. Similarly, SCD patients had higher plasma ADA and PNP activity and accelerated adenosine, inosine, and guanosine metabolism than healthy controls. Our study provides evidence that hemolysis per se leads to the development of angioproliferative PH. We also report the development of a rat model of HA-PH that closely mimics pulmonary vasculopathy seen in patients with HA-PH. Finally, this study suggests that in hemolytic diseases released ADA and PNP may increase the risk of PH, likely by abolishing the vasoprotective effects of adenosine, inosine and guanosine. Further characterization of this new rat model of hemolysis-induced angioproliferative PH and additional studies of the role of purines metabolism in HA-PH are warranted.

Dual A1/A2B Receptor Blockade Improves Cardiac and Renal Outcomes in a Rat Model of Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is prevalent and often accompanied by metabolic syndrome. Current treatment options are limited. Here, we test the hypothesis that combined A1/A2B adenosine receptor blockade is beneficial in obese ZSF1 rats, an animal model of HFpEF with metabolic syndrome. The combined A1/A2B receptor antagonist 3-[4-(2,6-dioxo-1,3-dipropyl-7H-purin-8-yl)-1-bicyclo[2.2.2]octanyl]propanoic acid (BG9928) was administered orally (10 mg/kg/day) to obese ZSF1 rats (n = 10) for 24 weeks (from 20 to 44 weeks of age). Untreated ZSF1 rats (n = 9) served as controls. After 24 weeks of administration, BG9928 significantly lowered plasma triglycerides (in mg/dl: control group, 4351 ± 550; BG9928 group, 2900 ± 551) without adversely affecting plasma cholesterol or activating renin release. BG9928 significantly decreased 24-hour urinary glucose excretion (in mg/kg/day: control group, 823 ± 179; BG9928 group, 196 ± 80) and improved oral glucose tolerance, polydipsia, and polyuria. BG9928 significantly augmented left ventricular diastolic function in association with a reduction in cardiac vasculitis and cardiac necrosis. BG9928 significantly reduced 24-hour urinary protein excretion (in mg/kg/day: control group, 1702 ± 263; BG9928 group, 1076 ± 238), and this was associated with a reduction in focal segmental glomerulosclerosis, tubular atrophy, tubular dilation, and deposition of proteinaceous material in the tubules. These findings show that, in a model of HFpEF with metabolic syndrome, A1/A2B receptor inhibition improves hyperlipidemia, exerts antidiabetic actions, reduces HFpEF, improves cardiac histopathology, and affords renal protection. We conclude that chronic administration of combined A1/A2B receptor antagonists could be beneficial in patients with HFpEF, in particular those with comorbidities such as obesity, diabetes, and dyslipidemias.

SIRT3-AMP-Activated Protein Kinase Activation by Nitrite and Metformin Improves Hyperglycemia and Normalizes Pulmonary Hypertension Associated With Heart Failure With Preserved Ejection Fraction

BACKGROUND

Pulmonary hypertension associated with heart failure with preserved ejection fraction (PH-HFpEF) is an increasingly recognized clinical complication of metabolic syndrome. No adequate animal model of PH-HFpEF is available, and no effective therapies have been identified to date. A recent study suggested that dietary nitrate improves insulin resistance in endothelial nitric oxide synthase null mice, and multiple studies have reported that both nitrate and its active metabolite, nitrite, have therapeutic activity in preclinical models of pulmonary hypertension.

METHODS AND RESULTS

To evaluate the efficacy and mechanism of nitrite in metabolic syndrome associated with PH-HFpEF, we developed a 2-hit PH-HFpEF model in rats with multiple features of metabolic syndrome attributable to double-leptin receptor defect (obese ZSF1) with the combined treatment of vascular endothelial growth factor receptor blocker SU5416. Chronic oral nitrite treatment improved hyperglycemia in obese ZSF1 rats by a process that requires skeletal muscle SIRT3-AMPK-GLUT4 signaling. The glucose-lowering effect of nitrite was abolished in SIRT3-deficient human skeletal muscle cells, and in SIRT3 knockout mice fed a high-fat diet, as well. Skeletal muscle biopsies from humans with metabolic syndrome after 12 weeks of oral sodium nitrite and nitrate treatment (IND#115926) displayed increased activation of SIRT3 and AMP-activated protein kinase. Finally, early treatments with nitrite and metformin at the time of SU5416 injection reduced pulmonary pressures and vascular remodeling in the PH-HFpEF model with robust activation of skeletal muscle SIRT3 and AMP-activated protein kinase.

CONCLUSIONS

These studies validate a rodent model of metabolic syndrome and PH-HFpEF, suggesting a potential role of nitrite and metformin as a preventative treatment for this disease.

Effect of dipeptidyl peptidase 4 inhibition on arterial blood pressure is context dependent

Because the effects of dipeptidyl peptidase 4 (DPP4) inhibitors on blood pressure are controversial, we examined the long-term effects of sitagliptin (80 mg/kg per day) on blood pressure (radiotelemetry) in spontaneously hypertensive rats (SHR), Wistar-Kyoto rats, and Zucker Diabetic-Sprague Dawley rats (metabolic syndrome model). In SHR, chronic (3 weeks) sitagliptin significantly increased systolic, mean, and diastolic blood pressures by 10.3, 9.2, and 7.9 mm Hg, respectively, a response abolished by coadministration of BIBP3226 (2 mg/kg per day; selective Y1-receptor antagonist). Sitagliptin also significantly increased blood pressure in SHR treated with hydralazine (vasodilator; 25 mg/kg per day) or enalapril (angiotensin-converting enzyme inhibitor; 10 mg/kg per day). In Wistar-Kyoto rats, chronic sitagliptin slightly decreased systolic, mean, and diastolic blood pressures (-1.8, -1.1, and -0.4 mm Hg, respectively). In Zucker Diabetic-Sprague Dawley rats, chronic sitagliptin decreased systolic, mean, and diastolic blood pressures by -7.7, -5.8, and -4.3 mm Hg, respectively, and did not alter the antihypertensive effects of chronic enalapril. Because DPP4 inhibitors impair the metabolism of neuropeptide Y1-36 (NPY1-36; Y1-receptor agonist) and glucagon-like peptide (GLP)-1(7-36)NH2 (GLP-1 receptor agonist), we examined renovascular responses to NPY1-36 and GLP-1(7-36)NH2 in isolated perfused SHR and Zucker Diabetic-Sprague Dawley kidneys pretreated with norepinephrine (to induce basal tone). In Zucker Diabetic-Sprague Dawley kidneys, NPY1-36 and GLP-1(7-36)NH2 exerted little, if any, effect on renovascular tone. In contrast, in SHR kidneys, both NPY1-36 and GLP-1(7-36)NH2 elicited potent and efficacious vasoconstriction.

IN CONCLUSION

(1) The effects of DPP4 inhibitors on blood pressure are context dependent; (2) The context-dependent effects of DPP4 inhibitors are due in part to differential renovascular responses to DPP4’s most important substrates (NPY1–36 and GLP-1(7–36)NH2) [corrected]; (3) Y1 receptor antagonists may prevent the prohypertensive and possibly augment the antihypertensive effects of DPP4 inhibitors.

Abstract 555: The Effect Of Dipeptidyl Peptidase 4 Inhibition On Arterial Blood Pressure Is Context Dependent

Dipeptidyl peptidase 4 (DPP4) inhibitors decrease the metabolism of endogenous glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) agonists, such as GLP-1(7-36)NH 2 , and GLP-1R agonists are antihypertensive. However, DPP4 inhibitors also impair the metabolism of endogenous Y 1 receptor (Y 1 R) agonists, such as neuropeptide Y 1-36 (NPY 1-36 ), and Y 1 R agonists are pro-hypertensive. Consequently, the long-term effect of DPP4 inhibition on blood pressure may be context dependent. To test this, we conducted radiotelemetry studies under highly controlled conditions to quantify the effects of chronic sitagliptin (80 mg/kg/day; DPP4 inhibitor) on blood pressure in spontaneously hypertensive rats (SHR), Wistar-Kyoto rats (WKY) and Zucker Diabetic-Sprague Dawley rats (ZDSD; model of the metabolic syndrome developed by PreClinOmics). In SHR, chronic (3 weeks) administration of sitagliptin significantly increased systolic, mean and diastolic blood pressures by 10.3, 9.2 and 7.9 mmHg, respectively (p<0.01). Sitagliptin also significantly (p<0.01) increased blood pressure in SHR treated with hydralazine (vasodilator; 25 mg/kg/day) or enalapril (ACE inhibitor; 10 mg/kg/day). Co-administration of BIBP3226 (2 mg/kg/day; Y 1 R antagonist) abolished the pro-hypertensive effects of sitagliptin in SHR. In WKY, chronic sitagliptin slightly decreased (p<0.01) systolic, mean and diastolic blood pressures (-1.8, -1.1 and -0.4 mmHg, respectively). In ZDSD, chronic sitagliptin markedly decreased systolic, mean and diastolic blood pressures (-7.7, -5.8, -4.3 mmHg, respectively). In isolated, perfused ZDSD kidneys pretreated with norepinephrine to induce basal tone, NPY 1-36 and GLP-1(7-36)NH 2 exerted little effect on renovascular tone. In contrast, in isolated SHR kidneys, both NPY 1-36 and GLP-1(7-36)NH 2 elicited potent and efficacious vasoconstriction (increased perfusion pressure by 171 and 132 mmHg, respectively).

Conclusions: 1) The effects of DPP4 inhibitors on blood pressure are context dependent; 2) The context-dependent effects of DPP4 inhibitors are due in part to differential renovascular responses to its most important substrates (NPY 1-36 and GLP-1(7-36)NH 2 ); 3) Y 1 R antagonists may augment the beneficial effects of DPP4 inhibitors.

Gender, sex hormones and pulmonary hypertension

Most subtypes of pulmonary arterial hypertension (PAH) are characterized by a greater susceptibility to disease among females, although females with PAH appear to live longer after diagnosis. While this "estrogen paradoxȍ of enhanced female survival despite increased female susceptibility remains a mystery, recent progress has begun to shed light upon the interplay of sex hormones, the pathogenesis of pulmonary hypertension, and the right ventricular response to stress. For example, emerging data in humans and experimental models suggest that estrogens or differential sex hormone metabolism may modify disease risk among susceptible subjects, and that estrogens may interact with additional local factors such as serotonin to enhance the potentially damaging chronic effects of estrogens on the pulmonary vasculature. Regardless, it remains unclear why not all estrogenic compounds behave equally, nor why estrogens appear to be protective in certain settings but detrimental in others. The contribution of androgens and other compounds, such as dehydroepiandrosterone, to pathogenesis and possibly treatment must be considered as well. In this review, we will discuss the recent understandings on how estrogens, estrogen metabolism, dehydroepiandrosterone, and additional susceptibility factors may all contribute to the pathogenesis or potentially to the treatment of pulmonary hypertension, by evaluating current human, cell-based, and experimental model data.

Bosentan inhibits oxidative and nitrosative stress and rescues occlusive pulmonary hypertension

Pulmonary arterial hypertension (PH) is a fatal disease marked by excessive pulmonary vascular cell proliferation. Patients with idiopathic PH express endothelin-1 (ET-1) at high levels in their lungs. As the activation of both types of ET-1 receptor (ETA and ETB) leads to increased generation of superoxide and hydrogen peroxide, this may contribute to the severe oxidative stress found in PH patients. As a number of pathways may induce oxidative stress, the particular role of ET-1 remains unclear. The aim of this study was to determine whether inhibition of ET-1 signaling could reduce pulmonary oxidative stress and attenuate the progression of disease in rats with occlusive-angioproliferative PH induced by a single dose of SU5416 (200 mg/kg) and subsequent exposure to hypoxia for 21 days. Using this regimen, animals developed severe PH as evidenced by a progressive increase in right-ventricle (RV) peak systolic pressure (RVPSP), severe RV hypertrophy, and pulmonary endothelial and smooth muscle cell proliferation, resulting in plexiform vasculopathy. PH rats also had increased oxidative stress, correlating with endothelial nitric oxide synthase uncoupling and NADPH oxidase activation, leading to enhanced protein nitration and increases in markers of vascular remodeling. Treatment with the combined ET receptor antagonist bosentan (250 mg/kg/day; day 10 to 21) prevented further increase in RVPSP and RV hypertrophy, decreased ETA/ETB protein levels, reduced oxidative stress and protein nitration, and resulted in marked attenuation of pulmonary vascular cell proliferation. We conclude that inhibition of ET-1 signaling significantly attenuates the oxidative and nitrosative stress associated with PH and prevents its progression.

Endogenous adenosine contributes to renal sympathetic neurotransmission via postjunctional A1 receptor-mediated coincident signaling

Adenosine A(1) receptor antagonists have diuretic/natriuretic activity and may be useful for treating sodium-retaining diseases, many of which are associated with increased renal sympathetic tone. Therefore, it is important to determine whether A(1) receptor antagonists alter renal sympathetic neurotransmission. In isolated, perfused rat kidneys, renal vasoconstriction induced by renal sympathetic nerve simulation was attenuated by 1) 1,3-dipropyl-8-p-sulfophenylxanthine (xanthine analog that is a nonselective adenosine receptor antagonist, but is cell membrane impermeable and thus does not block intracellular phosphodiesterases), 2) xanthine amine congener (xanthine analog that is a selective A(1) receptor antagonist), 3) 1,3-dipropyl-8-cyclopentylxanthine (xanthine analog that is a highly selective A(1) receptor antagonist), and 4) FK453 (nonxanthine analog that is a highly selective A(1) receptor antagonist). In contrast, FR113452 (enantiomer of FK453 that does not block A(1) receptors), MRS-1754 (selective A(2B) receptor antagonist), and VUF-5574 (selective A(3) receptor antagonist) did not alter responses to renal sympathetic nerve stimulation, and ZM-241385 (selective A(2A) receptor antagonist) enhanced responses. Antagonism of A(1) receptors did not alter renal spillover of norepinephrine. 2-Chloro-N(6)-cyclopentyladenosine (highly selective A(1) receptor agonist) increased renal vasoconstriction induced by exogenous norepinephrine, an effect that was blocked by 1,3-dipropyl-8-cyclopentylxanthine, U73122 (phospholipase C inhibitor), GF109203X (protein kinase C inhibitor), PP1 (c-src inhibitor), wortmannin (phosphatidylinositol 3-kinase inhibitor), and OSU-03012 (3-phosphoinositide-dependent protein kinase-1 inhibitor). These results indicate that adenosine formed during renal sympathetic nerve stimulation enhances the postjunctional effects of released norepinephrine via coincident signaling and contributes to renal sympathetic neurotransmission. Likely, the coincident signaling pathway is: phospholipase C → protein kinase C → c-src → phosphatidylinositol 3-kinase → 3-phosphoinositide-dependent protein kinase-1.

Diabetic nephropathy and long-term treatment effects of rosiglitazone and enalapril in obese ZSF1 rats

Diabetic nephropathy (DN) is a major cause of end-stage renal disease. Yet the pathogenic mechanisms underlying the development of DN are not fully defined, partially due to lack of suitable models that mimic the complex pathogenesis of renal disease in diabetic patients. In this study, we describe early and late renal manifestations of DN and renal responses to long-term treatments with rosiglitazone or high-dose enalapril in ZSF1 rats, a model of metabolic syndrome, diabetes, and chronic renal disease. At 8 weeks of age, obese ZSF1 rats developed metabolic syndrome and diabetes (hyperglycemia, glucosuria, hyperlipidemia, and hypertension) and early signs of renal disease (proteinuria, glomerular collagen IV deposition, tubulointerstitial inflammation, and renal hypertrophy). By 32 weeks of age, animals developed renal histopathology consistent with DN, including mesangial expansion, glomerulosclerosis, tubulointerstitial inflammation and fibrosis, tubular dilation and atrophy, and arteriolar thickening. Rosiglitazone markedly increased body weight but reduced food intake, improved glucose control, and attenuated hyperlipidemia and liver and kidney injury. In contrast, rosiglitazone markedly increased cardiac hypertrophy via a blood pressure-independent mechanism. High-dose enalapril did not improve glucose homeostasis, but normalized blood pressure, and nearly prevented diabetic renal injury. The ZSF1 model thus detects the clinical observations seen with rosiglitazone and enalapril in terms of primary and secondary endpoints of cardiac and renal effects. This and previous reports indicate that the obese ZSF1 rat meets currently accepted criteria for progressive experimental diabetic renal disease in rodents, suggesting that this may be the best available rat model for simulation of human DN.

Estrogens and development of pulmonary hypertension: interaction of estradiol metabolism and pulmonary vascular disease

Severe pulmonary arterial hypertension (PAH) is characterized by clustered proliferation of endothelial cells (ECs) in the lumina of small size pulmonary arteries resulting in concentric obliteration of the lumina and formation of complex vascular structures known as plexiform lesions. This debilitating disease occurs more frequently in women, yet both animal studies in classical models of PAH and limited clinical data suggest protective effects of estrogens: the estrogen paradox in pulmonary hypertension. Little is known about the role of estrogens in PAH, but one line of evidence strongly suggests that the vascular protective effects of 17β-estradiol (estradiol; E2) are mediated largely by its downstream metabolites. Estradiol is metabolized to 2-hydroxyestradiol (2HE) by CYP1A1/CYP1B1, and 2HE is converted to 2-methoxyestradiol (2ME) by catechol-O-methyl transferase. 2ME is extensively metabolized to 2-methoxyestrone, a metabolite that lacks biologic activity, but which may be converted back to 2ME. 2ME has no estrogenic activity, and its effects are mediated by estrogen receptors–independent mechanism(s). Notably, in systemic and pulmonary vascular ECs, smooth muscle cells, and fibroblasts, 2ME exerts stronger antimitotic effects than E2 itself. E2 and 2ME, despite having similar effects on other cardiovascular cells, have opposing effects on ECs; that is, in ECs, E2 is promitogenic, proangiogenic, and antiapoptotic, whereas 2ME is antimitogenic, antiangiogenic, and proapoptotic. This may have significant ramifications in severe PAH that involves uncontrolled proliferation of monoclonal apoptosis-resistant ECs. Based on its cellular effects, 2ME should be expected to attenuate the progression of disease and provide protection in severe PAH. In contrast, E2, due to its mitogenic, angiogenic, and antiapoptotic effects (otherwise desirable in normal quiescent ECs), may even adversely affect endothelial remodeling in PAH, and this may be even more significant if the E2's effects on injured endothelium are not opposed by 2ME (eg, in the event of reduced E2 conversion to 2ME due to hypoxia, inflammation, drugs, environmental factors, or genetic polymorphism of metabolizing enzymes). This review focuses on the effects of estrogens and their metabolites on pulmonary vascular pathobiology and the development of experimental PAH and offers potential explanation for the estrogen paradox in PAH. Furthermore, we propose that unbalanced estradiol metabolism may lead to the development of PAH. Recent animal data and studies in patients with PAH support this concept.

Dose-dependent therapeutic effects of 2-Methoxyestradiol on Monocrotaline-Induced pulmonary hypertension and vascular remodelling

2-Methoxyestradiol (2ME) is a major non-oestrogenic metabolite of oestradiol. Our previous studies, performed in several models of cardiac and/or vascular injury, suggest that 2ME strongly inhibits both pressure-dependent and pressure-independent cardiac and vascular remodelling. Furthermore, recently we have shown that in male rats 2ME attenuates the development and retards the progression of monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH); and in female rats 2ME eliminates the exacerbation of PAH and increased mortality due to ovariectomy. In the present study we compared the therapeutic effects of three different doses of 2ME (3, 10 and 30 microg/kg/hour; 2ME-3, 2ME-10 and 2ME-30, respectively) in male rats with MCT-induced PAH. The animals were also monitored for plasma 2ME levels and potential oestrogenic effects. Treatments were initiated 12 days after administration of MCT (60 mg/kg, i.p.). Twenty-eight days post MCT, right ventricular peak systolic pressure (RVPSP) was measured and morphometric analysis was conducted. All three doses of 2ME produced beneficial therapeutic effects in pulmonary hypertensive animals, i.e. reduced pulmonary artery pressure and right ventricular hypertrophy, attenuated pulmonary vascular remodelling and inflammatory response, and had favourable effects on survival. Notably, none of the three doses had any effect on plasma testosterone levels or on seminal vesicle or testicle weight. Dose-dependent increases in 2ME plasma levels were observed only with 2ME-3 and 2ME-10; 2ME-30 produced 2ME plasma levels similar to those seen with 2ME10. Nonetheless, 2ME-30 was significantly more efficacious than 2ME-3 or 2ME-10 and eliminated the high mortality (34%) induced by MCT. In summary, the present study indicates that 2ME, used in doses that produce plasma levels similar to those seen in the last trimester of pregnancy (1000-3000 pg/ml), is effective and safe (i.e. has no oestrogenic effects) in experimental PAH. These data also suggest that 2ME disposition, rather than plasma concentration, determines the therapeutic effects of 2ME in PAH.

Adenosine deaminase-adenosine pathway in hemolysis-associated pulmonary hypertension

Hemolysis-associated pulmonary hypertension (HA-PH) is a serious clinical complication of various hemolytic disorders, and pulmonary hypertension (PH) is considered the greatest risk factor for death in patients with a hemolytic disorder. It is now well established that hemolysis causes the release of soluble hemoglobin and arginase from injured erythrocytes into plasma. This leads to nitric oxide (NO) deficiency, oxidative stress and a state of endothelial dysfunction that is associated with clinical development of PH. We challenge this concept and propose that in addition to the NO-arginase pathway, the adenosine deaminase-adenosine pathway plays a significant role in HA-PH and that modulation of this pathway may offer protective/therapeutic effects in HA-PH. Our preliminary data suggest that in HA-PH adenosine deaminase (ADA) is released from injured erythrocytes into plasma and that metabolic conversion of adenosine (ADO) to inosine by ADA reduces extracellular ADO levels. Adenosine, mainly via activation of adenosine A(2A) receptors, mediates a number of biological responses that may reduce hemolysis-induced vasculopathy and the risk of PH. Hypoxia is the strongest stimulus for ADO synthesis, and this increased ADO production counteracts some of the tissue/vascular injury caused by hypoxia itself. Unfortunately, under hypoxic conditions (anemia, vasoconstriction, and vaso-occlusion) in HA-PH, this "ADO negative-feed back" is abolished and the vascular protective effects of ADO are severely diminished by ADA released from injured erythrocytes. We hypothesize that in hemolytic anemia the repetitive release of ADA increases the risk for vaso-occlusive events and PH. We also propose that increase in extracellular ADO levels or activation of adenosine A(2A) receptors attenuates HA-PH, and we suggest further preclinical and clinical investigation of ADA inhibitors and ADO agonists in HA-PH.

Plasmin activates epithelial Na+ channels by cleaving the gamma subunit

Proteolytic processing of epithelial sodium channel (ENaC) subunits occurs as channels mature within the biosynthetic pathway. The proteolytic processing events of the alpha and gamma subunits are associated with channel activation. Furin cleaves the alpha subunit ectodomain at two sites, releasing an inhibitory tract and activating the channel. However, furin cleaves the gamma subunit ectodomain only once. A second distal cleavage in the gamma subunit induced by other proteases, such as prostasin and elastase, is required to release a second inhibitory tract and further activate the channel. We found that the serine protease plasmin activates ENaC in association with inducing cleavage of the gamma subunit at gammaLys194, a site distal to the furin site. A gammaK194A mutant prevented both plasmin-dependent activation of ENaC and plasmin-dependent production of a unique 70-kDa carboxyl-terminal gamma subunit cleavage fragment. Plasmin-dependent cleavage and activation of ENaC may have a role in extracellular volume expansion in human disorders associated with proteinuria, as filtered plasminogen may be processed by urokinase, released from renal tubular epithelium, to generate active plasmin.

Renal and metabolic effects of tempol in obese ZSF1 rats--distinct role for superoxide and hydrogen peroxide in diabetic renal injury

Oxidative stress, that is, overproduction of reactive oxygen species and reduced antioxidant system activity, is implicated in the pathogenesis of diabetic complications; and therefore, superoxide dismutase (SOD) mimetic tempol should be protective in diabetic kidney. However, the effects of tempol in metabolic syndrome-associated renal injury have not been thoroughly examined. In this study, we examined the effects of 9 weeks of treatment with tempol on metabolic status, renal oxidative stress, and kidney function and structure in obese, diabetic, hypertensive ZSF(1) rats and their nondiabetic, hypertensive, lean littermates. The obese rats had significantly reduced total SOD and catalase activity, increased peroxidase activity and lipid peroxidation, and higher level of protein oxidation in renal cortical tissue compared with their lean littermates. These changes were accompanied by renal injury (proteinuria; reduced excretory function; and markedly increased glomerular and interstitial inflammation, proliferation, and collagen IV synthesis). Tempol treatment slightly increased total SOD activity, significantly reduced lipid peroxidation and peroxidase activity, but had no effect on catalase and protein oxidation. Tempol had no effects on blood pressure, renal hemodynamics and excretory function, and proteinuria in obese rats, yet improved insulin sensitivity and reduced renal inflammatory, proliferative, and fibrotic changes. Because tempol possesses no catalase activity and, in diabetes, not only SOD but also catalase is inhibited, it is possible that the toxicity of hydrogen peroxide (H(2)O(2)) remains unaltered under tempol treatment. This study suggests that superoxide and H(2)O(2) may have distinct roles in the pathogenesis of diabetic renal injury, with superoxide mainly being involved in inflammatory, proliferative, and fibrotic changes, and H(2)O(2) in glomerular hemodynamics and proteinuria.

Cellular distribution of the renal bumetanide-sensitive Na-K-2Cl cotransporter BSC-1 in the inner stripe of the outer medulla during the development of hypertension in the spontaneously hypertensive rat

1. The renal bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1) is expressed only in the thick ascending limb and selectively traffics from intracellular vesicles (IVs) to apical plasma membranes (PMs), where BSC-1 regulates sodium reabsorption. We showed previously that in kidneys from adult spontaneously hypertensive rats (SHR; model of essential hypertension) total protein expression of BSC-1 was higher compared with kidneys from normotensive Wistar-Kyoto (WKY) rats. However, whether this change is associated with an increased trafficking of BSC-1 from IVs to PMs is unknown. The goal of the present study was to test the hypothesis that the increase in total renal BSC-1 protein expression in SHR is accompanied by an augmented distribution of BSC-1 from IVs to PMs. 2. To test the hypothesis, we obtained renal tissue from the inner stripe of the outer medulla (ISOM; enriched in thick ascending limbs) and isolated IVs and PMs from this tissue by differential centrifugation. Total BSC-1 protein expression in ISOM and BSC-1 protein expression in ISOM IVs and PMs were measured by semiquantitative western blotting in SHR and aged-matched WKY rats at different ages and stages of hypertension. 3. At 5 weeks of age, SHR were prehypertensive (mean arterial blood pressure (MABP) 97 mmHg). At this age, both the total abundance and cellular distribution of BSC-1 were similar in ISOM from SHR and WKY rats. 4. As SHR aged, their hypertension progressed (MABP 137 and 195 mmHg at 8 and 14 weeks of age, respectively). Associated with the increase in MABP was an increase in both steady state protein levels of ISOM BSC-1 and the distribution of ISOM BSC-1 to PMs (four- and sixfold increases at 8 and 14 weeks of age, respectively, compared with age-matched WKY rats; P < 0.001). 5. Using semiquantitative reverse transcription-polymerase chain reaction, BSC-1 mRNA was measured and was found not to differ between SHR and WKY rat ISOM at any age or level of MABP. 6. We conclude that as SHR transition from prehypertensive to established hypertension, there is a marked increase in the total expression of BSC-1 in ISOM that is not related to increases in steady state levels of BSC-1 mRNA and therefore unlikely to be due to changes in either the rate of BSC-1 gene transcription or the stability of BSC-1 mRNA. This suggests changes in either translational efficiency or BSC-1 protein stability in SHR. 7. We also conclude that the age/hypertension-related increase in BSC-1 protein levels in ISOM is accompanied by an equally marked increased trafficking of BSC-1 to PMs in SHR ISOM.

Early renal injury induced by caffeine consumption in obese, diabetic ZSF1 rats

Our previous studies indicate that prolonged caffeine consumption exacerbates renal failure in nephropathy associated with the metabolic syndrome. Reduced activity of the antioxidant defense system and beneficial effects of antioxidant therapy have been reported in diabetic rats and humans. The purpose of this study was to examine the early renal effects of caffeine consumption and the effects of concomitant antioxidant therapy in young obese, diabetic ZSF1 rats. Eleven-week-old male ZSF1 rats were randomized to drink tap water, caffeine (0.1%), tempol (1 mmol/L), or a solution containing caffeine and tempol for nine weeks. Caffeine significantly reduced body weight and glycosuria (weeks 2-9), improved glucose tolerance (week 9), had no effect on elevated plasma triglycerides, plasma cholesterol (week 9) and blood pressure (week 9), and significantly increased plasma cholesterol level (weeks 5 and 9). Yet, as early as after two weeks, caffeine greatly augmented proteinuria and increased renal vascular resistance (RVR) and heart rate (HR: week 9). Tempol had no effects on metabolic status and development of proteinuria, did not alter caffeine-induced metabolic changes and early proteinuria, and attenuated caffeine-induced increase in HR and RVR. Immunohistochemical analysis revealed significant glomerular and interstitial inflammation, proliferation, and fibrosis in control animals. Caffeine augmented the influx of glomerular and interstitial macrophages (ED1+ cells) influx, glomerular and tubular proliferative response, and glomerular collagen IV content. Tempol abolished the exacerbation of renal inflammation, proliferation, and fibrosis induced by caffeine. In conclusion, in nephropathy associated with the metabolic syndrome, caffeine--most likely through the interaction with adenosine receptors and interference with anti-inflammatory and/or glomerular hemodynamic effects of adenosine--augments proteinuria and stimulates some of the key proliferative mechanisms involved in glomerular remodeling and sclerosis. Tempol does not prevent early renal injury (i.e., proteinuria) induced by caffeine, yet abolishes late renal inflammatory, proliferative, and fibrotic change induced by chronic caffeine consumption in obese ZSF1 rats.

PPAR? agonists improve renal preservation in kidneys subjected to chronic in vitro perfusion: interaction with mannitol

We developed methods for prolonged (12 h), sterile, normothermic perfusion of rat kidneys and screened compounds for renal preservation including: mitochondrial transition pore inhibitor (decylubiquinone); caspase inhibitor (Z-VAD); peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists (gemfibrozil, WY-14643); antioxidants (trolox, luteolin, quercetin); growth factors (HGF, PDGF, EGF, IGF-1, VEGF, transferrin); calpain inhibitor (Z-Val-Phe-CHO); calmodulin inhibitor (W7); K(ATP) opener (minoxidil, minoxidil sulfate); PARP inhibitor (3-aminobenzamide); calcium channel blocker (verapamil); V(2) agonist (DDAVP); diuretics (acetazolamide, hydrochlorothiazide, furosemide, mannitol); peroxisome proliferator-activated receptor-beta agonist (L-165041); dopamine agonist (dopamine); essential fatty acid (linolenic acid); beta-NAD; urea; uric acid; and aldosterone. In pilot studies, only PPARalpha agonists and mannitol provided promising results. Accordingly, these agents were investigated further. Fifteen rat kidneys were perfused for 12 h with L-15 media at 37 degrees C in the absence or presence of mannitol, gemfibrozil, gemfibrozil + mannitol or WY-14643. Chronic perfusion in untreated kidneys caused destruction of glomerular and tubular architecture (light and electron microscopy), disappearance of Na(+)-K(+)-ATPase-alpha(1) (Western blotting), and apoptosis (Apoptag staining). Gemfibrozil and WY-14643 marginally improved some biomarkers of renal preservation. However, the combination of gemfibrozil with mannitol markedly improved all parameters of renal preservation. We conclude that PPARalpha agonists, particularly when combined with mannitol, protect organs from normothermic, perfusion-induced damage.

The pancreatohepatorenal cAMP-adenosine mechanism

Stimulation of adenylyl cyclase causes cellular efflux of cAMP, and cAMP (unlike adenosine) is stable in blood. Therefore, it is conceivable that cAMP could function as a circulating adenosine prohormone by local target-organ conversion of distally released cAMP to adenosine via the sequential actions of ectophosphodiesterase and ecto-5'-nucleotidase (cAMP==> AMP==> adenosine; called the cAMP-adenosine pathway). A possible specific representation of this general concept is the pancreatohepatorenal cAMP-adenosine mechanism. The pancreas secretes glucagon into the portal circulation, and glucagon is a stimulant of hepatic adenylyl cyclase. Therefore, we hypothesize that the pancreas, via glucagon, stimulates hepatic cAMP production, which provides circulating cAMP for conversion to adenosine in the kidney via the cAMP-adenosine pathway. In normal rats, intravenous cAMP increased urinary and renal interstitial (assessed by renal microdialysis) cAMP and adenosine. Intraportal infusions of glucagon increased plasma cAMP 10-fold, it did not affect plasma adenosine, and it increased urinary and renal interstitial cAMP and adenosine. Local renal interstitial blockade (by adding inhibitors directly to the microdialysis perfusate) of ectophosphodiesterase (using 3-isobutyl-1-methylxanthine or 1,3-dipropyl-8-p-sulfophenylxanthine) or ecto-5'-nucleotidase (using alpha,beta-methyleneadenosine-5'-diphosphate) prevented the cAMP-induced and glucagon-induced increases in renal interstitial adenosine, but not cAMP. In ZSF1 rats with the metabolic syndrome, an oral glucose load increased plasma glucagon and urinary cAMP and adenosine excretion. We conclude that circulating cAMP is a substrate for local conversion to adenosine via the cAMP-adenosine pathway. A specific manifestation of this is the pancreatohepatorenal cAMP-adenosine mechanism (pancreas==> portal glucagon==> liver==> circulating cAMP==> kidney==> local cAMP-adenosine pathway).

2-Methoxyestradiol and 2-Ethoxyestradiol Retard the Progression of Renal Disease in Aged, Obese, Diabetic ZSF1 Rats

The metabolic syndrome is a main cause for cardiovascular disease and for the accelerating epidemic of chronic renal failure. Previous studies show that 2-hydroxyestradiol (2-HE), an estradiol metabolite with little estrogenic activity, decreases obesity and arterial blood pressure and attenuates the development of renal disease in young, obese, diabetic ZSF1 rats. In humans, however, diabetic renal disease is more frequent and severe in older patients. In vivo, 2-HE is readily converted to 2-methoxyestradiol (2-ME), an estradiol metabolite with no estrogenic activity. Accordingly, one purpose of this study was to determine whether 2-ME would provide benefit in aged rats with a very severe form of diabetic renal disease. Another objective was to determine whether synthetic analogs of estradiol metabolites might be beneficial in diabetic renal disease. To achieve these objectives we examined the effects of 2-ME and its analog 2-ethoxyestradiol (2-EE) in aged (35-week-old), obese ZSF1 rats. Animals were treated for 9 weeks with vehicle (PEG-400, 0.5 microL per hour), 2-ME or 2-EE (18 microg/kg per hour). Metabolic and renal function were measured at weeks 0, 3, 6, and 9, and renal hemodynamics and excretory function were assessed at week 9. Aged ZSF1 rats had elevated levels of glycosylated hemoglobin; increased renal cortical expression of proliferating cell nuclear antigen (PCNA), nuclear factor kappa B (NF-kappaB), and vascular endothelial growth factor (VEGF); glycosuria, hypertension; and proteinuria. 2-ME and 2-EE did not affect obesity or hypertension and had variable effects on glucose homeostasis, yet they attenuated proteinuria; increased renal blood flow and glomerular filtration; and reduced renal cortical expression of PCNA, NFkappaB, and VEGF. We conclude that 2ME and 2EE are strikingly renoprotective even in aged animals with severe diabetic renal disease. The present study warrants further investigation of 2-ME and analogs of estradiol metabolites for treatment of kidney disease associated with the metabolic syndrome.

2-Methoxyestradiol mediates the protective effects of estradiol in monocrotaline-induced pulmonary hypertension

When exposed to chronic hypoxia or toxin monocrotaline (MCT), female animals develop less severe pulmonary arterial hypertension (PH) compared to males; ovariectomy (OVX) exacerbates PH, and OVX animals treated with estradiol (E2) develop less severe disease. There is a line of evidence suggesting that cardiovascular protective effects of E2 are mediated by its major metabolite, 2-methoxyestradiol (2ME). Recently, we have shown that 2ME attenuates the development and retards the progression of MCT-induced pulmonary hypertension in male rats. We hypothesized that the protective effects of E2 in experimental PH are mediated by 2ME. Subsets of intact and OVX female rats were injected saline (Cont and OXV groups) or MCT (60 mg/kg; MCT and OVX-MCT groups) and some of OVX-MCT animals were treated with 2ME (10 microg/kg/h via osmotic minipumps; OVX-MCT+2ME). After 28 days, MCT caused PH, i.e., increased right ventricular peak systolic pressure (RVPSP) and right ventricle/left ventricle+septum (RV/LV+S) ratio, induced inflammatory response in the lungs and caused media hypertrophy (media thickness and % media index) and adventitia widening of small size pulmonary arteries. Ovariectomy exacerbated the disease, i.e., further increased RVPSP, and RV/LV+S ratio, and augmented vascular remodeling and inflammatory response. In diseased OVX rats, treatment with 2ME prevented the worsening of PH and attenuated the inflammatory response and vascular remodeling. No mortality was recorded in the OVX-MCT+2ME group vs. 10% and 36% mortality in the MCT and OVX-MCT group, respectively. This study suggests that 2-methoxyestradiol (a major non-estrogenic metabolite of E2) may mediate the protective effects of estradiol in MCT-induced PH, and warrants further evaluation of 2ME for treatment of PH.

Estradiol metabolites attenuate monocrotaline-induced pulmonary hypertension in rats

Pulmonary arterial hypertension (PH) is a deadly disease characterized by pulmonary arterial vasoconstriction and hypertension, pulmonary vasculature remodeling, and right ventricular hypertrophy. Our previous in vivo studies, performed in several models of cardiac, vascular, and/or renal injury, suggest that the metabolites of 17beta-estradiol may inhibit vascular and cardiac remodeling. The goal of this study was to determine whether 2-methoxyestradiol (2ME), major non-estrogenic estradiol metabolite, prevents the development and/or retards the progression of monocrotaline (MCT)-induced PH. First, a total of 27 male Sprague Dawley rats were injected with distillated water (Cont, n=6) or monocrotaline (MCT; 60 mg/kg, i.p.; n=21). Subsets of MCT animals (n=7 per group) received 2ME or its metabolic precursor 2-hydroxyestradiol (2HE; 10 microg/kg/h via osmotic minipumps) for 21 days. Next, an additional set (n=24) of control and MCT rats was monitored for 28 days, before right ventricular peak systolic pressure (RVPSP) was measured. Some pulmonary hypertensive animals (n=8) were treated with 2ME (10 microg/kg/h) beginning from day 14 after MCT administration. MCT caused pulmonary hypertension (ie, increased right ventricle/left ventricle+septum [RV/LV+S] ratio and wall thickness of small-sized pulmonary arteries, and elevated RVPSP) and produced high and late (days 22 to 27) mortality. Pulmonary hypertension was associated with strong proliferative response (PCNA staining) and marked inflammation (ED1+cells) in lungs. Both metabolites significantly attenuated the RV/LV+S ratio and pulmonary arteries media hypertrophy and reduced proliferative and inflammatory responses in the lungs. Furthermore, in diseased animals, 2ME (given from day 14 to 28) significantly decreased RVPSP, RV/LV+S ratio and wall thickness, and reduced mortality by 80% (mortality rate: 62.5% vs. 12.5%, MCT vs. MCT+2ME day 14 to 28). This study provides the first evidence that 2ME, a major non-estrogenic, non-carcinogenic metabolite of estradiol, prevents the development and retards the progression of monocrotaline-induced pulmonary hypertension. Further evaluation of 2ME for management of pulmonary arterial hypertension is warranted.

Estradiol Metabolites Attenuate Renal and Cardiovascular Injury Induced by Chronic Nitric Oxide Synthase Inhibition

Our previous studies in rodent models of nephropathy demonstrate that 2-hydroxyestradiol (2HE), an estradiol metabolite with little estrogenic activity, exerts renoprotective effects. In vivo, 2HE is readily converted to 2-methoxyestradiol (2ME), a major estradiol metabolite with no estrogenic activity. The goal of this study was to determine whether 2ME has renal and cardiovascular protective effects in vivo. First, the acute (90 minutes) and chronic (14 days) effects of 2ME (10 microg/kg/h) on blood pressure and renal function were examined in normotensive and spontaneously hypertensive rats (SHR). Second, a rat model of cardiovascular and renal injury induced by chronic nitric oxide synthase inhibition (N-nitro-L-arginine; 40 mg/kg/d; LNNA group) was used to examine the protective effects of estradiol metabolites. Subsets of LNNA-treated rats were administered either 2HE or 2ME (10 microg/kg/h via osmotic minipump; LNNA+2ME and LNNA+2HE groups, respectively. 2-Methoxyestradiol had no acute or chronic effects on blood pressure or renal function in normotensive animals or on hypertension in SHR. Prolonged, 5-week NOS inhibition induced severe cardiovascular and renal disease and high mortality (75%, LNNA group). 2ME, but not 2HE, significantly decreased elevated blood pressure and attenuated the reduction in GFR. 2HE delayed the onset of proteinuria, whereas no proteinuria was detected in the 2-ME group. 2HE and 2ME reduced mortality rate by 66% and 83%, respectively (P < 0.001). In the kidney, 2HE and 2ME abolished LNNA-induced interstitial and glomerular inflammation, attenuated glomerular collagen IV synthesis, and inhibited glomerular and tubular cell proliferation. In the heart, 2HE and 2ME markedly reduced vascular and interstitial inflammation and reduced collagen synthesis and vascular/interstitial cell proliferation. This study provides the first evidence that, in a model of severe cardiovascular and renal injury, 2-methoxyestradiol (a major nonestrogenic estradiol metabolite) exerts renal and cardiovascular protective effects and reduces mortality.

Increased expression of the sodium transporter BSC-1 in spontaneously hypertensive rats

The purpose of this study was to compare the expression of BSC-1 (bumetanide-sensitive Na+-K+-2Cl- cotransporter) in kidneys of spontaneously hypertensive rats (SHR) versus Wistar-Kyoto (WKY) rats by immunoblotting and reverse transcription-polymerase chain reaction. To determine the specificity of any observed changes in BSC-1 expression, we also compared expression of the thiazide sensitive Na+-Cl- cotransporter (TSC), the type-3 Na+-H+ exchanger (NHE-3), Na+-K+-ATPase-alpha1, the inwardly rectifying K+ channel (ROMK-1), the type-1 Na+-HCO3- cotransporter (NBC-1), aquaporin-1, and aquaporin-2. Analyses were performed on outer cortex, outer medulla, and inner medulla. BSC-1 protein was detected in outer medulla and was markedly (6-fold) higher in SHR. TSC protein was detected in the cortex and was not overexpressed in SHR. Aquaporin-1 protein was detected in all three regions and was not overexpressed in SHR. Aquaporin-2 and ROMK-1 proteins were detected in all three regions, but were moderately elevated (2-fold) only in the SHR inner medulla. Na+-K+-ATPase and NHE-3 proteins were detected in all three regions. Na+-K+-ATPase-alpha1 was modestly (25%) increased in SHR outer and inner medulla, whereas NHE-3 was moderately (2-fold) increased in the SHR cortex and inner medulla. NBC-1 protein was detected only in the cortex and was higher (2-fold) in SHR. mRNA levels of BSC-1, aquaporin-2, and ROMK-1 were not elevated in SHR, indicating a post-translational mechanism of protein overexpression. High-dose furosemide increased fractional sodium excretion more in SHR than WKY (3-fold). We conclude that increased expression of BSC-1, and to a lesser extent, aquaporin-2, ROMK-1, NHE-3, and NBC-1 may contribute to the pathogenesis of hypertension in the SHR.

Cardiovascular Pharmacology of Estradiol Metabolites

A discussion of the role of endogenous estradiol metabolites in mediating important biological actions of estradiol is essentially nonexistent in standard textbooks of pharmacology and endocrinology. Indeed, the prevailing view is that all biological effects of estradiol are initiated by binding of estradiol per se to estrogen receptors and that estradiol metabolites are more or less irrelevant. This orthodox view, which is most likely incorrect, is the fundamental premise (an estrogen is an estrogen is an estrogen) underlying the design of important clinical trials such as the Heart and Estrogen/Progestin Replacement Study and the Women's Health Initiative Study. Accumulating data provide convincing evidence that some metabolites of estradiol, the major estrogen secreted by human ovaries, are biologically active and mediate multiple effects on the cardiovascular and renal systems that are largely independent of estrogen receptors. More specifically, metabolites of estradiol, particularly catecholestradiols and methoxyestradiols, induce multiple estrogen receptor-independent actions that protect the heart, blood vessels, and kidneys from disease. These protective effects are mediated in part by the inhibition of the ability of vascular smooth muscle cells, cardiac fibroblasts, and glomerular mesangial cells to migrate, proliferate, and secrete extracellular matrix proteins, as well as by an improvement in vascular endothelial cell function. The purpose of this review is to highlight the cardiovascular and renal pharmacology of catecholestradiols and methoxyestradiols. The take home message is simple: that when it comes to cardiovascular and renal protection, the concept that all estrogenic compounds are created equal may not be true.

Moderate hypothermia may be detrimental after traumatic brain injury in fentanyl-anesthetized rats

OBJECTIVES

To determine whether transient, moderate hypothermia is beneficial after traumatic brain injury in fentanyl-anesthetized rats.

DESIGN

Prospective, randomized study.

SETTING

University-based animal research facility.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

All rats were intubated, mechanically ventilated, and anesthetized with fentanyl (10 microg/kg intravenous bolus and then 50 microg.kg(-1).hr(-1) infusion). Controlled cortical impact was performed to the left parietal cortex, followed immediately by 1 hr of either normothermia (brain temperature 37 +/- 0.5 degrees C) or hypothermia (brain temperature 32 +/- 0.5 degrees C). Hypothermic rats were rewarmed gradually over 1 hr. Fentanyl anesthesia and mechanical ventilation were continued in both groups until the end of rewarming (2 hrs after traumatic brain injury).

MEASUREMENTS AND MAIN RESULTS

Histologic assessment performed 72 hrs after traumatic brain injury was the primary outcome variable. Secondary outcome variables were physiologic variables monitored during the first 2 hrs after traumatic brain injury and plasma catecholamine and serum fentanyl concentrations measured at the end of both hypothermia and rewarming (1 and 2 hrs after traumatic brain injury). Contusion volume was larger in hypothermic vs. normothermic rats (44.3 +/- 4.2 vs. 28.6 +/- 4.0 mm, p <.05), but hippocampal neuronal survival did not differ between groups. Physiologic variables did not differ between groups. Plasma dopamine and norepinephrine concentrations were increased at the end of hypothermia in hypothermic (vs. normothermic) rats (p <.05), indicating that hypothermia augmented the systemic stress response. Similarly, serum fentanyl concentrations were higher in hypothermic (vs. normothermic) rats at the end of both hypothermia and rewarming (p <.05), demonstrating that hypothermia reduced the clearance and/or metabolism of fentanyl.

CONCLUSIONS

Moderate hypothermia was detrimental after experimental traumatic brain injury in fentanyl-anesthetized rats. Since treatment with hypothermia has provided reliable benefit in experimental traumatic brain injury with inhalational anesthetics, these results indicate that the choice of anesthesia/analgesia after traumatic brain injury may dramatically influence response to other therapeutic interventions, such as hypothermia. Given that narcotics commonly are administered to patients after severe traumatic brain injury, this study may have clinical implications.

Type IV phosphodiesterase inhibition improves cardiac contractility in endotoxemic rats

Type IV phosphodiesterase inhibitors have a potential role in treating human sepsis. We examined the cardiac performance effects of type IV phosphodiesterase inhibition in vivo, in the absence and presence of catecholamines. Rats were randomized to receive either 4-(3-Butoxy-4-methoxybenzyl)imidazolidin-2-one (Ro 20-1724) at 0 (vehicle), 2 or 10 microg/kg/min. Utilizing a left ventricular catheter to measure cardiac performance, each animal received each of the two catecholamines, epinephrine and norepinephrine, in randomized order. Rats then received intravenous endotoxin and additional infusions of catecholamines. Ro 20-1724 at 2 microg/kg/min protected cardiac contractility during endotoxemia, and at 10 microg/kg/min increased cardiac contractility and protected cardiac function during endotoxemia. Neither dose interfered with the maximal contractile response to catecholamines. Type IV phosphodiesterase inhibition with Ro 20-1724 exerts beneficial effects on cardiac performance during septicemia in an in vivo animal model. Clinical studies of type IV phosphodiesterase inhibitors in critically ill patients are indicated.

2-Hydroxyestradiol attenuates renal disease in chronic puromycin aminonucleoside nephropathy

It has been previously shown that 2-hydroxyestradiol (2-OHE) attenuates the development of renal disease in genetic nephropathy associated with obesity and the metabolic syndrome. The purpose of this study was to test the hypothesis that 2-OHE, irrespective of its effects on metabolic status and/or obesity, exerts direct renoprotective effects in vivo. First, the effects of increasing doses of 2-OHE on mesangial cell growth, proliferation, and collagen synthesis in isolated rat glomerular mesangial cells were evaluated in vitro. Second, the effects of 12-wk administration of 2-OHE (10 micro g/h per kg) on renal function and structure in chronic puromycin aminonucleoside (PAN)-induced nephropathy in rats were evaluated in vivo. 2-OHE concentration-dependently (0.001 to 1 micro mol/L; P < 0.001) inhibited serum (2.5%)-induced cell growth ((3)H-thymidine incorporation), collagen synthesis ((3)H-proline incorporation), and cell proliferation (cell number). Importantly, the inhibitory effects of 2-OHE (0.1 micro mol/L) were not blocked by ICI182780 (50 micro mol/L), an estrogen receptor antagonist. In vivo, chronic administration of PAN (75 mg/kg + 5 x 20 mg/kg) over 12 wk induced severe chronic renal disease. Chronic treatment with 2-OHE significantly (P < 0.05) attenuated PAN-induced decrease in glomerular filtration, reduced proteinuria, and the elevated BP, and it had no effect on PAN-induced increase in plasma cholesterol and triglycerides levels. 2-OHE had no effects on plasma testosterone levels in male nephropathic animals. Immunohistochemical staining for collagen IV and proliferating cell nuclear antigen (PCNA) in glomeruli and transforming growth factor-beta (TGF-beta) in renal tubular cells were significantly higher in PAN nephropatic rats versus control animals with intact kidneys. PAN also markedly increased glomerular and interstitial macrophage infiltration (ED1(+) cells). 2-OHE had no effects on renal tubular cell TGF-beta, but it significantly reduced glomerular PCNA and collagen IV and glomerular and interstitial macrophage infiltration. In summary, this study provides the first evidence that 2-OHE exerts direct renoprotective effects in vivo. These effects are mediated by estrogen receptor-independent mechanisms and are due, at least in part, to the inhibition of some of the key proliferative mechanisms involved in glomerular remodeling and sclerosis.

Expression of adenosine receptors in the preglomerular microcirculation

The purpose of this study was to systematically investigate the abundance of each of the adenosine receptor subtypes in the preglomerular microcirculation vs. other vascular segments and vs. the renal cortex and medulla. Rat preglomerular microvessels (PGMVs) were isolated by iron oxide loading followed by magnetic separation. For comparison, mesenteric microvessels, segments of the aorta (thoracic, middle abdominal, and lower abdominal), renal cortex, and renal medulla were obtained by dissection. Adenosine receptor protein and mRNA expression were examined by Western blotting, Northern blotting, and RT-PCR. Our results indicate that compared with other vascular segments and renal tissues, A1 and A2B receptor protein and mRNA are abundantly expressed in the preglomerular microcirculation, whereas A2A and A3 receptor protein and mRNA are barely detectable or undetectable in PGMVs. We conclude that, relative to other vascular and renal tissues, A1 and A2B receptors are well expressed in PGMVs, whereas A2A and A3 receptors are notably deficient. Thus A1 and A2B receptors, but not A2A or A3 receptors, may importantly regulate the preglomerular microcirculation.

Long-term caffeine consumption exacerbates renal failure in obese, diabetic, ZSF1 (fa-fa(cp)) rats

BACKGROUND

Our preliminary studies indicate that chronic caffeine consumption has adverse renal effects in nephropathy associated with high blood pressure and insulin resistance. The purpose of this study was to investigate the effects of early (beginning at 8 weeks of age) and long-term (30 weeks) caffeine treatment (0.1% solution) on renal function and structure in obese, diabetic ZSF1 rats.

METHODS

Metabolic and renal function measurements were performed at six-week intervals and in a subset of animals (N = 6 per group) heart rate (HR) and mean arterial blood pressure (MABP) were monitored by a radiotelemetric technique. At the end of the study acute, measurements of renal hemodynamics and excretory function were conducted in anesthetized animals.

RESULTS

Caffeine produced a very mild increase (4 to 5%) of MABP and HR, but greatly augmented proteinuria (P < 0.001), reduced creatinine clearance (P < 0.05) and had a mixed effect on metabolic status in obese ZSF1 rats. Caffeine significantly reduced body weight, glycosuria, fasting glucose and insulin levels and improved glucose tolerance, had no effect on elevated plasma triglycerides levels and significantly increased plasma cholesterol level (P < 0.001). Acute measurements of renal function revealed increased renal vascular resistance (95.1 +/- 11 vs. 50.7 +/- 2.4 mm Hg/mL/min/g kidney, P < 0.01) and decreased inulin clearance (0.37 +/- 0.11 vs. 0.97 +/- 0.13 mL/min/g kidney, P < 0.002) in caffeine-treated versus control animals, respectively. Caffeine potentiated the development of more severe tubulointerstitial changes (P < 0.05) and increased focal glomerulosclerosis (14.7 +/- 1.7 vs. 6.5 +/- 0.9%, caffeine vs. control, P < 0.002).

CONCLUSION

The present study provides the first evidence that caffeine (despite improving insulin sensitivity) exacerbates renal failure in obese, diabetic ZSF1 rats. Further mechanistic studies of adverse renal effects of caffeine in chronic renal failure associated with metabolic syndrome are warranted.

A(1) receptor blockade induces natriuresis with a favorable renal hemodynamic profile in SHHF/Mcc-fa(cp) rats chronically treated with salt and furosemide

Our goal was to test the hypothesis that A(1) receptor blockade induces diuresis/natriuresis with a favorable renal hemodynamic/cardiac profile in aged, lean SHHF/Mcc-fa(cp) rats, a rodent model of hypertensive dilated cardiomyopathy. Thirteen-month-old SHHF/Mcc-fa(cp) rats were pretreated for 72 h before experiments with furosemide (100 mg/kg by gavage 72, 48, and 24 h before experiments) to mimic the clinical setting of chronic diuretic therapy and were given 1% NaCl as drinking water to reduce dehydration/sodium depletion. Animals were instrumented for measurement of systemic and renal hemodynamics, renal excretory function, and cardiac performance, and baseline values were obtained during a 30-min clearance period. Animals then received either vehicle (n = 9), BG9719 [the S-enantiomer of 1,3-dipropyl-8-[2-(5,6-epoxynorbornyl)] xanthine (also called CVT-124)] (highly selective A(1) receptor antagonist; 0.1 mg/kg bolus + 10 microg/kg/min; n = 9) or furosemide (loop diuretic; 30 mg/kg; n = 8) and measurements were repeated during four subsequent clearance periods. Both BG9719 and furosemide increased urine volume and absolute and fractional sodium excretion. BG9719 increased renal blood flow and glomerular filtration rate, but did not affect fractional potassium excretion. Furosemide decreased renal blood flow and glomerular filtration rate and increased fractional potassium excretion. Neither drug altered afterload; however, furosemide, but not BG9719, decreased preload (central venous pressure and ventricular end diastolic pressure). Neither drug altered systolic function (+dP/dt(max)); however, furosemide, but not BG9719, attenuated diastolic function (decreased -dP/dt(max), increased tau). In the setting of left ventricular dysfunction, chronic salt loading and prior loop diuretic treatment, selective A(1) receptor antagonists are effective diuretic/natriuretic agents with a favorable renal hemodynamic/cardiac performance profile.

2-Hydroxyestradiol attenuates the development of obesity, the metabolic syndrome, and vascular and renal dysfunction in obese ZSF1 rats

A pandemic of obesity is contributing importantly to the prevalence of the metabolic syndrome characterized by hypertension, insulin resistance, and hyperlipidemia. In turn, the metabolic syndrome is contributing to vascular disease and the accelerating epidemic of chronic renal failure. Currently, pharmacological approaches to attenuate obesity and its cardiovascular/renal sequelae are limited. The purpose of this study was to determine the effects of 2-hydroxyestradiol, a metabolite of 17beta-estradiol with minimal estrogenic activity, on the development of obesity, the metabolic syndrome, and heart, vascular, and renal dysfunction in obese ZSF1 rats, a well-characterized genetic model of obesity and the metabolic syndrome with concomitant heart, vascular, and kidney disease. ZSF1 rats were treated, beginning at 12 weeks of age, for 26 weeks with vehicle or 2-hydroxyestradiol (10 microg/kg/h). At baseline and after 24 weeks of treatment, animals were placed in metabolic cages, and food intake, water intake, urine output, and urinary excretion of proteins and glucose were determined. Next, in fasting animals, plasma cholesterol was measured, an oral glucose tolerance test was conducted, and total glycated hemoglobin levels were determined. At the end of the study, animals were anesthetized and instrumented for assessment of heart performance, renal hemodynamics, and mesenteric vascular reactivity. 2-Hydroxyestradiol attenuated the development of obesity and improved endothelial function, decreased nephropathy, decreased the severity of diabetes, lowered arterial blood pressure, and reduced plasma cholesterol. 2-Hydroxyestradiol may be an important lead for the development of safe and effect drugs to attenuate obesity and its metabolic, vascular, and renal sequelae.

Inhibition of adenosine deaminase attenuates endotoxin-induced release of cytokines in vivo in rats

The purpose of this study was to investigate in vivo the effects of modulating the adenosine system on endotoxin-induced release of cytokines and changes in heart performance and neurohumoral status in early, profound endotoxemia in rats. Time/pressure variables of heart performance and blood pressure were recorded continuously, and plasma levels of tumor necrosis factor alpha (TNFalpha), interleukin 1-beta (IL-1beta), plasma renin activity (PRA), and catecholamines were determined before and 90 min after administration of endotoxin (30 mg/kg of lipopolysaccharide, i.v.). Erythro-9[2-hydroxyl-3-nonyl] adenine (EHNA; an adenosine deaminase inhibitor) had no effects on measured time-pressure variables of heart performance under baseline conditions and during endotoxemia, yet significantly attenuated endotoxin-induced release of cytokines and PRA. Pretreatment with the non-selective adenosine receptor antagonist DPSPX not only prevented the effects of EHNA but also increased the basal release of cytokines and augmented PRA. At baseline, caffeine (a non-selective adenosine receptor antagonist) increased HR, +dP/dtmax, heart rate x ventricular pressure product (HR x VPSP) and +dP/dtmax normalized by pressure (+dP/dtmax/VPSP), and these changes persisted during endotoxemia. Caffeine attenuated endotoxin-induced release of cytokines and augmented endotoxin-induced increases in plasma catecholamines and PRA. Pretreatment with propranolol abolished the effects of caffeine on heart performance and neurohumoral activation during the early phase of endotoxemia. 6N-cyclopentyladenosine (CPA; selective A1 adenosine receptor agonist) induced bradicardia and negative inotropic effects, reduced work load (i.e., decreased HR, VPSP, +dP/dtmax, +dP/dtmax/VPSP and HR x VPSP) and inhibited endotoxin-induced tachycardia and renin release. CGS 21680 (selective A2A adenosine receptor agonist) decreased blood pressure under basal condition but did not potentiate decreases in blood pressure during endotoxemia. CGS 21680 completely inhibited endotoxin-induced release of TNFalpha, augmented sympathetic activity and PRA, and increased +dP/dtmax and +dP/dtmax/VPSP in the absence and presence of endotoxin. The present study provides strong evidence that inhibition of adenosine deaminase reduces cytokine release in vivo without producing significant hemodynamic and cardiac effects during the early phase of profound endotoxemia in rats. The augmented neurohumoral activation induced by caffeine is associated with decreased cytokine release induced by endotoxin. Further studies are warranted to determine the impact of these effects on cardiac function and hemodynamics in the late phase of endotoxemia.

Renal and metabolic effects of caffeine in obese (fa/fa(cp)), diabetic, hypertensive ZSF1 rats

In Western society, the triad of hypertension, metabolic syndrome and obesity (which caries a high risk for renal disease) is increasing, as is the intake of caffeine. However, no information is available regarding the metabolic or renal consequences of caffeine consumption in this complex disease entity. The purpose of this study was to investigate the effects of chronic caffeine consumption on renal function and metabolic status in obese ZSF1 rats, an animal model of obesity, hypertension and the metabolic syndrome. Fifteen, 18-week-old male, obese ZSF1 rats were randomized to drink tap water (Cont, n = 8) or 0.1% solution of caffeine (Caff, n = 7) for 8 weeks. Metabolic and renal function measurements were performed at baseline and after 4 and 8 weeks of treatment. Caffeine treatment significantly (p < 0.05) reduced body weight, food, and fluid consumption and improved insulin sensitivity (fasting insulin 129.6+/-8.1 vs 97.5+/-3.6 microIU/mL; fed insulin 146.3+/-8.5 vs 110.6+/-3.4 microIU/mL; fasting glucose 138.7+/-13.4 vs 145+/-8.0 mg/dL; fed glucose 373+/-19.4 vs 283.3+/-19.6 mg/dL, Cont vs Caff, respectively). After 8 weeks of caffeine treatment, animals were less glycosuric as compared with control group. Area under glucose curves (AUC-glucose) in oral glucose tolerance test did not differ between the two groups (AUC- glucose: 592.5+/-42.7 vs 589.5+/-20.5 mg/dL x h, Cont vs Caff), whereas caffeine treatment significantly decreased AUC of insulin (AUC-insulin: 257.77+/-12.9 vs 198.0+/-5.9 microIU/mL x h, Cont vs. Caff, p<0.05). No differences were found with regard to plasma triglycerides and glycerol levels; however, caffeine significantly increased cholesterol levels after 4 and 8 weeks (2F-Anova, p<0.001). Moreover, caffeine significantly decreased creatinine clearance after 4 and 8 weeks (CrCl, Cont: 3.5+/-0.4, Caff: 2.2+/-0.2 L/kg/day, p<0.05) and increased protein/CrCl ratio (Cont: 323+/-30, Caff: 527+/-33 mg/L/day). Caffeine treatment for 8 weeks tended to increase plasma norepinephrine levels (p<0.06), but the two groups did not differ with regard to plasma renin activity, blood pressure, renal blood flow or and renal vascular resistance. The study indicates that caffeine improves insulin sensitivity but increases plasma cholesterol levels and impairs renal function in obesity with the metabolic syndrome and hypertension. Our results imply that the health consequences of chronic caffeine consumption may depend heavily on underlying pathophysiology process.

Renal function and structure in diabetic, hypertensive, obese ZDFxSHHF-hybrid rats

The obese ZDFxSHHF-fa/fa(cp) model was developed by crossing lean female Zucker Diabetic Fatty (ZDF +/fa) and lean male Spontaneously Hypertensive Heart Failure (SHHF/Mcc-fa(cp), +/fa) rats. The purpose of the present study was to determine renal function and morphology, hemodynamics, and metabolic status in ZDFxSHHF rats. Two sets of experiments were conducted. First, we evaluated heart and kidney function and metabolic status in aged (46 weeks old) male obese ZDFxSHHF and age matched obese SHHF rats, lean Spontaneously Hypertensive (SHR) and lean normotensive Wistar Kyoto (WKY) rats. In the second set of experiments, renal function and structure as well as metabolic and lipid status were determined in lean (LN) and obese (OB) adult (29-weeks of age) ZDFxSHHF rats. At 46 weeks of age ZDFxSHHF rats are hypertensive expressing marked cardiac hypertrophy associated with diastolic dysfunction and preserved contractile function. Fasted hyperglycemia and hyperinsulinemia are accompanied by moderate hypercholesterolemia and hypertriglyceridemia. Obese aged ZDFxSHHF have marked renal hypertrophy, a 3-8 fold decrease in creatinine clearance (compared with SHHF, SHR and WKY), a high percent of segmental + global glomerulosclerosis (59.8%+/-10.8), and severe tubulointerstitial and vascular changes. Obese ZDFxSHHF rats die at an early age (approximately 12 months) from end-stage renal failure. Studies conducted in 29-week animals showed that, although both LN and OB 29-week old animals are hypertensive, OB animals have more severely compromised renal function and structure as compared with lean litter-mates (kidney weight: 2.56+/-0.16 vs. 1.61+/-0.12 g; creatinine clearance: 0.42+/-0.04 vs. 1.24+/-0.13 L/g kid/day; renal vascular resistance 12.39+/-1.4 vs. 6.14+/-0.42 mmHg/mL/min/g kid; protein excretion: 556+/-16 vs. 159+/-9mg/day/g kid, p < 0.05, OB vs. LN, respectively). Obesity is also associated with hyperglycemia (424+/-37 vs. 115+/-11 mg/dL), hyperinsulinemia (117.2+/-8.8 vs. 42.3+/-3.5 microU/mL), hypertriglyceridemia (5200+/-702 vs. 194+/-23 mg/dL), hypercholesterolemia (632+/-39 vs. 109+/-4mg/dL), and presence of segmental + global glomerulosclerosis (20.1+/-3.2% vs. 0.1+/-0.1%) with prominent tubular and interstitial changes (p < 0.05, OB vs. LN, respectively). In summary, the present study indicates that the crossing of rat strains of nephropathy produces hybrids that carry a high risk for severe renal dysfunction. The ZDFxSHHF rats express insulin resistance, hypertension, dislipidemia and obesity and develop severe renal dysfunction. In addition, the hybrids do not develop some of the complications (hydronephrosis or congestive heart failure) common for the parental strains that may compromise studies of renal function and structure. Therefore, the ZDFxSHHF rat may be a useful model fore valuating risk factors and pharmacological interventions in chronic renal failure.

Inhibition of cytokine release by and cardiac effects of type IV phosphodiesterase inhibition in early, profound endotoxaemia in vivo

1. In rats, inhibition of type IV phosphodiesterase (PDE4) attenuates acute renal failure and early (hours) mortality induced by high-dose endotoxin. Because it is unlikely that protection of renal function accounts for improved early survivability, most likely PDE4 inhibition exerts multiple beneficial effects in endotoxaemia and the purpose of the present study was to test this hypothesis. 2. In study 1, we determined, in anaesthetized rats, the effects of endotoxin (30 mg/kg, i.v.) on cardiac performance parameters (heart rate (HR), ventricular peak systolic pressure (VPSP), maximum positive change in left ventricular pressure with respect to time (+dP/dt), maximum negative change in left ventricular pressure with respect to time (-dP/dtmax), ventricular end-diastolic pressure (VEDP), ventricular minimum diastolic pressure (VMDP) and HR-pressure product), plasma catecholamine levels, plasma renin activity (PRA) and plasma levels of inflammatory cytokines (tumour necrosis factor (TNF)-alpha and interleukin (IL)-lbeta). 3. In study 2, we determined, in anaesthetized rats, whether inhibition of PDE4 attenuates lipopolysaccharide (LPS)-induced changes in the aforementioned parameters of heart performance and neurohumoral status. We compared the changes in these parameters induced by endotoxaemia in animals treated with either RO 20-1724 (10 microg/kg per min; a selective PDE4 inhibitor) or its vehicle (DMSO; 1.35 microL/min). 4. At 90 min postadministration, endotoxin significantly increased HR and reduced -dP/dtmax and VEDP and caused a several-fold increase in plasma levels of TNF-alpha, IL-1beta, noradrenaline, adrenaline and PRA. RO20-1724 significantly blunted the endotoxin-induced reduction in -dP/dtmax and decreased endotoxin-induced increases in TNF-alpha and IL-1beta without significantly altering endotoxin-induced changes in HR, VEDP, catecholamine levels and PRA. 5. Results from these studies indicate that, in addition to preserving renal function, PDE4 inhibition attenuates inflammatory cytokine release caused by high-dose endotoxin and may have protective effects on diastolic function in early profound endotoxaemia.

Caffeine augments proteinuria in puromycin-aminonucleoside nephrotic rats

Several studies indicate that increased intrarenal adenosine concentrations may attenuate puromycin-aminonucleoside (PAN)-induced nephropathy in rats. The purpose of this study was to investigate the chronic effects of caffeine, a nonselective adenosine receptor antagonist, on renal function and structure in PAN-induced nephropathy. Animals were randomized to receive drinking water or 0.1% caffeine solution. PAN was administered in two doses to a subset from each group at 1 week (100 mg/kg, s.c.; Purom-1) and 15 wks (80 mg/kg, s.c.; Purom-2) after initiating caffeine treatment (PAN and CAFF-PAN groups). The remaining animals served as time controls (CON and CAFF groups). Renal excretory function was followed for 23 wks. Caffeine consumption significantly augmented PAN-induced proteinuria after both PAN injections (Purom-1 and Purom-2, p<0.05 and p<0.001 respectively; CAFF-PAN vs. PAN). In addition, caffeine potentiated the transient reduction in creatinine clearance (CrCl) induced by PAN. Caffeine consumption for 23 wks significantly reduced CrCl in conscious nephrotic animals (4.76 +/- 0.98 vs. 8.51 +/- 1.55 L/kg/day, CAFF-PAN vs. PAN). Seven days after both PAN injections, increased plasma renin activity was detected in animals that were consuming caffeine as compared with corresponding control groups (CAFF and CAFF + PAN vs CON and PAN, respectively). Eight weeks after the second injection of PAN, acute measures of renal hemodynamic and excretory function were compared in anesthetized animals and renal samples were analyzed for histological changes. In PAN-rats, caffeine treatment for 23 weeks significantly reduced inulin clearance (0.28 +/- 0.09 vs. 0.57 +/- 0.12 mL/min/gr kidney. CAFF-PAN vs PAN, p<0.05), tended to increase renal vascular resistance (59.0 +/- 9.5 vs. 42.9 +/- 5.5 mmHg/mL/min/gr kidney, CAFF-PAN vs. PAN, p < 0.06), potentiated the development of more severe tubulointerstitial damage (tubular atrophy, presence of proteinaceous material, tubular dilatation, interstitial inflammation, interstitial fibrosis), and tended to increase glomerulosclerosis. In conclusion, this study indicates that caffeine adversely affects renal function in PAN-nephrotic rats, and that this effect may be due, in part, to increased activity of the renin angiotensin system.