Effects of thromboxane synthetase inhibitor (OKY-046) on urinary prostaglandin excretion and renal function in streptozotocin-induced diabetic rat

Renal endothelial dysfunction in diabetic nephropathy

Endothelial dysfunction has been posited to play an important role in the pathogenesis of diabetic nephropathy (DN). Due to the heterogeneity of endothelial cells (ECs), it is difficult to generalize about endothelial responses to diabetic stimuli. At present, there are limited techniques fordirectly measuring EC function in vivo, so diagnosis of endothelial disorders still largely depends on indirect assessment of mediators arising from EC injury. In the kidney microcirculation, both afferent and efferent arteries, arterioles and glomerular endothelial cells (GEnC) have all been implicated as targets of diabetic injury. Both hyperglycemia per se, as well as the metabolic consequences of glucose dysregulation, are thought to lead to endothelial cell dysfunction. In this regard, endothelial nitric oxide synthase (eNOS) plays a central role in EC dysfunction. Impaired eNOS activity can occur at numerous levels, including enzyme uncoupling, post-translational modifications, internalization and decreased expression. Reduced nitric oxide (NO) bioavailability exacerbates oxidative stress, further promoting endothelial dysfunction and injury. The injured ECs may then function as active signal transducers of metabolic, hemodynamic and inflammatory factors that modify the function and morphology of the vessel wall and interact with adjacent cells, which may activate a cascade of inflammatory and proliferative and profibrotic responses in progressive DN. Both pharmacological approaches and potential regenerative therapies hold promise for restoration of impaired endothelial cells in diabetic nephropathy.

Intermittent administration of a sustained-release prostacyclin analog ONO-1301 ameliorates renal alterations in a rat type 1 diabetes model

Diabetic nephropathy is the most common pathological disorder predisposing end-stage renal disease. ONO-1301 is a novel sustained-release prostacyclin analog possessing thromboxane (TX) synthase inhibitory activity. Here, we aimed to investigate the therapeutic efficacies of ONO-1301 in a rat type 1 diabetic nephropathy model. Streptozotocin (STZ)-induced diabetic rats received injections of slow-release form of ONO-1301 (SR-ONO) every 3 weeks. Animals were sacrificed at Week 14. SR-ONO significantly suppressed albuminuria, glomerular hypertrophy, mesangial matrix accumulation, glomerular accumulation of monocyte/macrophage, increase in glomerular levels of pro-fibrotic factor transforming growth factor (TGF)-beta1 and the number of glomerular alpha-smooth muscle actin (SMA)(+) cells in diabetic animals. The glomerular levels of hepatocyte growth factor (HGF) were significantly increased in SR-ONO-treated diabetic animals. Taken together, these results suggest the potential therapeutic efficacy of intermittent administration of SR-ONO in treating diabetic nephropathy potentially via inducing HGF, thus counteracting the pro-fibrotic effects of TGF-beta1.

Eicosanoids and renal damage in cardiometabolic syndrome

BACKGROUND

Obesity, hypertension and Type 2 diabetes are major contributing factors to the increase in the number of patients that have chronic kidney disease. The clustering of visceral obesity and cardiovascular risk factors has been designated metabolic syndrome or cardiometabolic syndrome. Cardiometabolic syndrome is associated with a complex systemic inflammatory state that has been implicated in medically important complications, including endothelial dysfunction. Inflammation, endothelial dysfunction and insulin resistance are interrelated and have reciprocal relationships that link cardiovascular and metabolic diseases. Ultimately, cardiometabolic syndrome increases the risk for cardiovascular events and end-organ damage. Although the number of patients with cardiometabolic syndrome is escalating, therapeutic approaches have not been developed that provide protection to the kidney.

OBJECTIVE

The objective of this review is to provide an overview of the contribution of eicosanoids to renal damage in cardiometabolic syndrome.

RESULTS/CONCLUSION

Eicosanoids are altered in cardiometabolic syndrome and contribute to the progression of renal injury. The antihypertensive and anti-inflammatory actions of epoxides and soluble epoxide hydrolase inhibitors make these attractive eicosanoid therapeutic targets for chronic kidney disease in patients with cardiometabolic syndrome.

Renal prostaglandin E2 receptor (EP) expression profile is altered in streptozotocin and B6-Ins2Akita type I diabetic mice

The homeostatic function of prostaglandin E(2) (PGE(2)) is dependent on a balance of EP receptor-mediated events. A disruption in this balance may contribute to the progression of renal injury. Although PGE(2) excretion is elevated in diabetes, the expression of specific EP receptor subtypes has not been studied in the diabetic kidney. Therefore, the purpose of this study was to characterize the expression profile of four EP receptor subtypes (EP(1-4)) in 16-wk streptozotocin (STZ) and B6-Ins2(Akita) type I diabetic mice. In diabetic mice, the ratio of kidney weight to body weight was increased twofold compared with controls, blood glucose was elevated, but urine albumin was only increased in B6-Ins2(Akita) mice. The excretion of PGE(2) and its metabolite was augmented two- to fourfold as determined by enzyme immunoassay. Accordingly, renal cyclooxygenases were also increased in diabetic mice, with isoform-specific and regional differences in each model. Finally, there was altered EP(1-4) receptor expression in diabetic kidneys, with significant differences between STZ and B6-Ins2(Akita) mice (fold-control). In STZ mice, cortical EP(1) increased by 1.6, EP(3) increased by 2.3, and EP(4) decreased by 0.63; yet in B6-Ins2(Akita) mice, cortical EP(1) increased by 2.4, but there was a general decrease in the remaining subtypes. Similarly, in the STZ medulla EP(3) increased by 3.6, but both EP(1) and EP(3) increased by 5.5 and 1.95, respectively, in B6-Ins2(Akita) mice. Therefore, knowing the pattern of change in relative EP receptor expression in the kidney could be useful in identifying specific EP targets for the prevention of various components of diabetic kidney disease.

Eicosanoids and renal vascular function in diseases

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

The effect of N-acetylcysteine on cardiac contractility to dobutamine in rats with streptozotocin-induced diabetes

We examined if myocardial depression at the acute phase of diabetes (3 weeks after injection of streptozotocin, 60 mg/kg i.v.) is due to activation of inducible nitric oxide synthase and production of peroxynitrite, and if treatment with N-acetylcysteine (1.2 g/day/kg for 3 weeks, antioxidant) improves cardiac function. Four groups of rats were used: control, N-acetylcysteine-treated control, diabetic and N-acetylcysteine-treated diabetic. Pentobarbital-anaesthetized diabetic rats, relative to the controls, had reduced left ventricular contractility to dobutamine (1-57 microg/min/kg). The diabetic rats also had increased myocardial levels of thiobarbituric acid reactive substances, immunostaining of inducible nitric oxide synthase and nitrotyrosine, and similar baseline 15-F2t-isoprostane. N-acetylcysteine did not affect responses in the control rats; but increased cardiac contractility to dobutamine, reduced myocardial immunostaining of inducible nitric oxide synthase and nitrotyrosine and level of 15-F2t-isoprostane, and increased cardiac contractility to dobutamine in the diabetic rats. Antioxidant supplementation in diabetes reduces oxidative stress and improves cardiac function.

Altered kidney CYP2C and cyclooxygenase-2 levels are associated with obesity-related albuminuria

OBJECTIVE

To determine cytochrome P450 (CYP450) and cyclooxygenase (COX) expression and metabolite regulation and renal damage in the early stages of obesity-related hypertension and diabetes.

RESEARCH METHODS AND PROCEDURES

Obese and lean Zucker rats at 10 to 12 weeks of age were studied. Blood pressure was measured in the conscious state using radiotelemetry. Blood glucose levels and body weight were measured periodically. Protein expression of CYP450 and COX enzymes in the kidney cortex, renal microvessels, and glomeruli was studied. The levels of CYP450 and COX metabolites in urine were measured, and urinary albumin excretion, an indicator of kidney damage, was measured.

RESULTS

Body weight and blood glucose averaged 432 +/- 20 grams and 105 +/- 5 mg/dl, respectively, in obese Zucker rats as compared with 320 +/- 8 grams and 91 +/- 5 mg/dl, respectively, in age-matched 10- to 12-week-old lean Zucker rats. Renal microvascular CYP4A and COX-2 protein levels were increased 2.3- and 17.0-fold, respectively, in obese Zucker rats. The protein expression of CYP2C11 and CYP2C23 was decreased 2.0-fold in renal microvessels isolated from obese Zucker rats when compared with lean Zucker rats. The urinary excretion rate of thromboxane B(2) was increased significantly in obese Zucker as compared with lean Zucker rats (22.0 +/- 1.8 vs. 13.4 +/- 1.0 ng/d). Urinary albumin excretion, an index of kidney damage, was increased in the obese Zucker rat at this early age.

DISCUSSION

These results suggest that increased CYP4A and COX-2 protein levels and decreased CYP2C11 and CYP2C23 protein levels occur in association with microalbuminuria during the onset of obesity-related hypertension and type 2 diabetes.

Early oxidative stress in the diabetic kidney: effect of DL-alpha-lipoic acid

Oxidative stress is implicated in the pathogenesis of diabetic nephropathy. The attempts to identify early markers of diabetes-induced renal oxidative injury resulted in contradictory findings. We characterized early oxidative stress in renal cortex of diabetic rats, and evaluated whether it can be prevented by the potent antioxidant, DL-alpha-lipoic acid. The experiments were performed on control rats and streptozotocin-diabetic rats treated with/without DL-alpha-lipoic acid (100 mg/kg i.p., for 3 weeks from induction of diabetes). Malondialdehyde plus 4-hydroxyalkenal concentration was increased in diabetic rats vs. controls (p <.01) and this increase was partially prevented by DL-alpha-lipoic acid. F(2) isoprostane concentrations (measured by GCMS) expressed per either mg protein or arachidonic acid content were not different in control and diabetic rats but were decreased several-fold with DL-alpha-lipoic acid treatment. Both GSH and ascorbate (AA) levels were decreased and GSSG/GSH and dehydroascorbate/AA ratios increased in diabetic rats vs. controls (p <.01 for all comparisons), and these changes were completely or partially (AA) prevented by DL-alpha-lipoic acid. Superoxide dismutase, glutathione peroxidase, glutathione reductase, glutathione transferase, and NADH oxidase, but not catalase, were upregulated in diabetic rats vs. controls, and these activities, except glutathione peroxidase, were decreased by DL-alpha-lipoic acid. In conclusion, enhanced oxidative stress is present in rat renal cortex in early diabetes, and is prevented by DL-alpha-lipoic acid.

Cyclooxygenase-2 inhibitor blocks expression of mediators of renal injury in a model of diabetes and hypertension

BACKGROUND

We previously reported that renal cortical cyclooxygenase (COX-2) expression increased following subtotal nephrectomy, and chronic treatment with a selective COX-2 inhibitor, SC58236, reduced proteinuria and retarded the development of glomerulosclerosis. The present studies were designed to examine the effects of COX-2 inhibition in a model of diabetic nephropathy.

METHODS

Rats were divided into three groups: control, diabetic (streptozotocin-induced diabetic animals with superimposed DOCA/salt hypertension; right nephrectomy and DOCA treatment), and treated (administration of the selective COX-2 inhibitor, SC58236, to a subset of diabetic/DOCA/salt rats). Insulin was administered to maintain blood glucose in the 200 to 300 mg/dL range.

RESULTS

Systolic blood pressure in the two diabetic groups was elevated within one week and remained elevated until sacrifice at six weeks (control, 108 +/- 2 mm Hg; diabetic, 158 +/- 4 mm Hg; treated, 156 +/- 7 mm Hg). When measured at six weeks, immunoreactive COX-2 expression in the renal cortex of the diabetic rats was 2.5 +/- 0.3-fold of control animals (N = 7). Immunohistochemical localization indicated increased expression in macula densa and surrounding cortical thick ascending limb of Henle (cTALH). The COX-2 inhibitor decreased COX-2 expression in diabetic rats to 1.3 +/- 0.1-fold control. In addition, SC58236 decreased expression of PAI-1 (diabetic vs. treated, 3.2 +/- 0.5 vs. 1.7 +/- 0.2-fold control, N = 7, P < 0.05), vascular endothelial growth factor (VEGF; 2.0 +/- 0.2 vs. 1.2 +/- 0.2; N = 7, P < 0.05), fibronectin (2.4 +/- 0.3 to 1.3 +/- 0.1; N = 7, P < 0.05) and transforming growth factor-beta (TGF-beta; 2.1 +/- 0.2 vs. 1.3 +/- 0.2; N = 7, P < 0.05). Proteinuria at six weeks was decreased in the SC58236-treated rats (149 +/- 8 vs. 92 +/- 8 mg/24 h; N = 7, P < 0.01). The mesangial sclerosis index, defined as increases in extracellular matrix within the mesangial space, was determined at six weeks; the control group had an index of 0.06 +/- 0.01, the diabetic group was 2.7 +/- 0.04 and the treated group was 0.6 +/- 0.03 (P < 0.0001 compared to the diabetic group).

CONCLUSIONS

These results suggest that in an experimental model of diabetes and hypertension, inhibition of COX-2 expression decreases potential mediators of glomerular and tubulointerstitial injury and also decreases biochemical, functional and structural markers of renal injury.

Roles of prostaglandin E receptors in mesangial cells under high-glucose conditions

BACKGROUND

High glucose reportedly stimulates prostaglandin (PG) E2 production and DNA synthesis in mesangial cells (MCs). However, the pathophysiological significance of PGE2 in MCs has remained unclear.

METHODS

The effects of prostanoids on [3H]-thymidine uptake and cAMP production in rat MCs cultured with 5.6 mM glucose, 25 mM glucose, or 5.6 mM glucose supplemented with 19.4 mM mannitol were examined. The gene expression of PGE2 receptor (EP) subtypes in MCs was analyzed with Northern blotting techniques.

RESULTS

Northern blotting indicated EP1 and EP4 gene expression in MCs. EP1 agonists and PGE2 stimulated [3H]-thymidine uptake in MCs. EP1 antagonists dose dependently attenuated high-glucose-induced [3H]-thymidine uptake, which suggests EP1 involvement, by an increase in intracellular Ca2+, in DNA synthesis of MCs. On the other hand, forskolin, db-cAMP, and 11-deoxy-PGE1, an EP4/EP3/EP2 agonist, significantly decreased DNA synthesis in MCs. These inhibitory effects are thought to be mediated via EP4 as a result of an increase in cAMP synthesis. The effects via EP4 seem to be particularly important because PGE2-induced cAMP synthesis was significantly attenuated in the high-glucose group compared with the mannitol group, in which [3H]-thymidine uptake did not increase in spite of augmented PGE2 production.

CONCLUSION

The increase in DNA synthesis in MCs under high-glucose conditions can be explained, at least in part, by the high-glucose-induced inhibition of cAMP production via EP4, which augments EP1 function in conjunction with the overproduction of PGE2.

Reduced expression of a novel peptide, prostacyclin-stimulating factor, in the kidneys of streptozotocin-induced diabetic rats

Prostacyclin (PGI2) produced by vascular endothelial cells (ECs) is a potent vasoactive prostanoid involved in maintenance of vessel wall homeostasis. Reduced PGI2 synthesis by vascular ECs could be a mechanism of pathogenesis in the development of vascular lesions such as diabetic angiopathy. Recently, we purified and cloned a novel bioactive peptide, PGI2-stimulating factor (PSF), which stimulates PGI2 production by vascular ECs. PSF may act on vascular ECs in a paracrine and/or autocrine fashion to regulate PGI2 synthesis. Decreased PSF production in the vessel wall may result in an imbalance of prostanoid synthesis, leading to the development of vascular lesions such as diabetic angiopathy. Our immunohistochemical study demonstrated that PSF is located in vascular resident cells such as vascular smooth muscle cells (SMCs) and ECs, as well as in bronchial SMCs. Moreover, PSF mRNA was found to be expressed in various tissues in Wistar rats, particularly in the kidneys and lungs. The present study demonstrated that streptozotocin (STZ)-induced diabetic rats showed less PSF mRNA expression in the kidneys (PSF mRNA/28S rRNA ratio; STZ versus control; 1.7+/-0.2 versus 2.5+/-0.2, p < 0.05) and reduced immunohistochemical staining for PSF in arteries in the kidney. However, in the lungs, there were no changes in tissue PSF mRNA expression (STZ versus control; 10.9+/-0.9 versus 11.5+/-1.0, NS) or in the extent of PSF staining in bronchial SMCs of STZ-induced diabetic rats. These findings suggest that decreased expression of PSF in renal vessels of STZ-induced diabetic rats may cause an imbalance of prostanoid synthesis, leading to the development and progression of vascular damage in the kidney.

Prostaglandins and diabetic nephropathy

Abnormalities of renal prostaglandins (PGs) contribute to the pathogenesis of diabetic nephropathy through changes in renal hemodynamics. Our recent studies have demonstrated that urinary excretion ratio of 6-keto-PGF1 alpha (6KF) to TXB2 is decreased in patients with non-insulin-dependent diabetes mellitus (NIDDM). In the present study, we evaluated the clinical effects of some drugs on renal PG metabolism and diabetic nephropathy. Ozagrel, a specific thromboxane synthetase inhibitor, reduced urinary TXB2 excretion, resulting in the improvement of the decreased urinary 6KF/TXB2 ratio in NIDDM patients. Urinary albumin excretion was decreased and creatinine clearance (Ccr) was increased during ozagrel administration. The similar beneficial effect was also found in the administration of cilostazol, a phosphodiesteraase inhibitor, whereas a stable analogue of PGI2, berprost sodium, reduced urinary albumin excretion in relation to the reduction of platelet aggregation rate. In conclusion, the drugs modulating renal and platelet PGs metabolism with direction to an increase in 6KF/TXB2 ratio and an inhibition against platelet function might be beneficial for the treatment of diabetic nephropathy.