Angiotensin II receptor antagonists and treatment of hypertension and renal disease

Molecular mechanisms of proteinuria in diabetes

The epidemic of Type 2 diabetes, and the parallel rising incidence of end-stage renal disease, is progressively increasing worldwide. Kidney disease is one of the major chronic microvascular complications of diabetes, and both metabolic and haemodynamic perturbations participate in its development and progression towards end-stage renal disease. Hypertension and poor metabolic control seem to interact in causing the relentless decline in renal function seen in diabetic patients. Both high circulating glucose levels and increased glomerular capillary pressure act in conjunction in stimulating the different cellular pathways leading to kidney disease. It has been suggested that mechanical forces at the glomerular level may aggravate the metabolic insult by stimulating excessive cellular glucose uptake by up-regulating the facilitative GLUT-1 (glucose transporter-1). We propose the existence of a self-maintaining cellular mechanism whereby a haemodynamic stimulus on glomerular cells induces the up-regulation of GLUT-1, an event followed by greater glucose uptake and activation of intracellular metabolic pathways, resulting in excess TGF-beta1 (transforming growth factor-beta1) production. TGF-beta1, one of the major prosclerotic cytokines in diabetic kidney disease, maintains the up-regulation of GLUT-1, perpetuating a series of cellular events that result, as their ultimate effect, in increased extracellular matrix synthesis and altered permeability of the glomerular filtration barrier. Mechanical and metabolic coupling could represent an important mechanism of injury in the diabetic kidney.

High-affinity interaction of sartans with H+/peptide transporters

Sartans are very effective drugs for treatment of hypertension, heart failure, and other cardiovascular disorders. They antagonize the effects of angiotensin II at the AT(1) receptor and display p.o. bioavailability rates of 13 to 80%. Because some sartans sterically resemble dipeptide derivatives, we investigated whether they are transported by peptide transporters. We first assessed the effects of sartans on [(14)C]glycylsarcosine uptake into Caco-2 cells expressing H(+)/peptide transporter (PEPT) 1 and into SKPT cells expressing PEPT2. Losartan, irbesartan, valsartan, and eprosartan inhibited [glycine-1-(14)C]glycylsarcosine ([(14)C]Gly-Sar) uptake into Caco-2 cells in a competitive manner with K(i) values of 24, 230, 390, and >1000 microM. Losartan and valsartan also strongly inhibited the total transepithelial flux of [(14)C]Gly-Sar across Caco-2 cell monolayers. In SKPT cells, [(14)C]Gly-Sar uptake was inhibited with K(i) values of 2.2 microM (losartan), 65 microM (irbesartan), 260 microM (valsartan), and 490 microM (eprosartan). We determined by the two-electrode voltage-clamp technique whether the compounds elicited transport currents by PEPT1 or PEPT2 when expressed in Xenopus laevis oocytes. No currents were observed for any of the sartans, but the compounds strongly and reversibly inhibited peptide-induced currents. Uptake of valsartan, losartan, and cefadroxil was quantified in HeLa cells after heterologous expression of human PEPT1 (hPEPT1). In contrast to cefadroxil, no PEPT1-specific uptake of valsartan and losartan was found. We conclude that the sartans tested in this study display high-affinity interaction with PEPTs but are not transported themselves. However, they strongly inhibit hPEPT1-mediated uptake of dipeptides and cefadroxil.

The link between Glut-1 and hypertension in diabetic nephropathy

Nephropathy is a major diabetic microvascular complication; both metabolic and hemodynamic perturbations play critical roles in its occurrence and progression toward end-stage renal disease. Improvements in metabolic and blood pressure control have been shown to confer protection from this diabetic complication. In this article, we review the facilitative glucose transporter Glut-1, its regulation, and its potential role in linking metabolic and hemodynamic perturbations in the pathophysiologic processes that lead to kidney injury in diabetes. We propose that an auto-maintaining mechanism of hemodynamic perturbations and increased tissue angiotensin II may be involved in the initiation and maintenance of a loop in which transforming growth factor beta1 and Glut-1 upregulation play important roles in the pathophysiology of diabetic-induced kidney lesions. The understanding of the molecular mechanisms that link glomerular hypertension and excessive glucose metabolism may provide insight into new therapeutic strategies for the treatment of diabetic renal disease.

Erythropoiesis-stimulating protein therapy and the decline of renal function: a retrospective analysis of patients with chronic kidney disease

BACKGROUND/AIMS

Previous studies have hinted at possible associations between anemia and progression of renal disease. The study objective was to determine whether treatment with erythropoiesis-stimulating proteins (ESPs) can curb the rate of decline in renal function in predialysis patients with chronic kidney disease (CKD).

METHODS

Observational, before/after analysis using electronic medical records from the Veterans Administration (VA). Included patients had at least two measurements of serum creatinine levels before and after ESP treatment initiation. The Cockcroft-Gault formula was used to derive estimates of glomerular filtration rate (GFR). Rate of renal function decline prior to and following initiation of therapy were compared.

RESULTS

One hundred and twenty two patients with renal impairment levels of Stage 3 (moderate) or Stage 4 (severe) at ESP treatment initiation were identified. Over 80% of patients initiated therapy with either Grade 1 or Grade 2 anemia. The rate of renal function decline was calculated as the slope of the least-squares linear regression line of the inverse serum creatinine over time during the pre-treatment initiation and post-treatment initiation time periods. Overall, patients experienced a slowing in the rate of renal function decline after treatment was initiated (mean pretreatment initiation rate of -0.094 dL/mg/yr versus mean post-treatment initiation rate of -0.057 dL/mg/yr).

CONCLUSION

Renal function declined at a slower rate following ESP initiation. Results are consistent with prior studies indicating delayed dialysis initiation in patients treated with ESPs. Analyses were limited by the observational study design and lack of information regarding some potential confounders. Longer-term, prospective trials are needed to determine whether ESPs slow progression of renal disease and the potential magnitude of such an effect.

GLUT-1 overexpression: Link between hemodynamic and metabolic factors in glomerular injury?

Mesangial matrix deposition is the hallmark of hypertensive and diabetic glomerulopathy. At similar levels of systemic hypertension, Dahl salt-sensitive but not spontaneously hypertensive rats (SHR) develop glomerular hypertension, which is accompanied by upregulation of transforming growth factor beta1 (TGF-beta1), mesangial matrix expansion, and sclerosis. GLUT-1 is ubiquitously expressed and is the predominant glucose transporter in mesangial cells. In mesangial cells in vitro, GLUT-1 overexpression increases basal glucose transport, resulting in excess fibronectin and collagen production. TGF-beta1 has been shown to upregulate GLUT-1 expression. We demonstrated that in hypertensive Dahl salt-sensitive (S) rats fed 4% NaCl (systolic blood pressure [SBP]: 236+/-9 mm Hg), but not in similarly hypertensive SHR (SBP: 230+/-10 mm Hg) or their normotensive counterparts (Dahl S fed 0.5% NaCl, SBP: 145+/-5 mm Hg; and Wistar-Kyoto, SBP: 137+/-3 mm Hg), there was an 80% upregulation of glomerular GLUT-1 protein expression (P< or =0.03). This was accompanied by a 2.7-fold upregulation of TGF-beta1 protein expression in glomeruli of DSH compared with DSN rats (P=0.02). TGF-beta1 expression was not upregulated and did not differ in the glomeruli of Wistar-Kyoto and SHR rats. As an in vitro surrogate of the in vivo hemodynamic stress imposed by glomerular hypertension, we used mechanical stretching of human and rat mesangial cells. We found that after 33 hours of stretching, mesangial cells overexpressed GLUT-1 (40%) and showed an increase in basal glucose transport of similar magnitude (both P< or =0.01), which could be blocked with an anti TGF-beta1-neutralizing antibody. These studies suggest a novel link between hemodynamic and metabolic factors that may cooperate in inducing progressive glomerular injury in conditions characterized by glomerular hypertension.

Long-term effects of losartan on proteinuria and renal function in patients with renal amyloidosis

OBJECTIVE

To investigate the effect of the angiotensin II receptor antagonist losartan on proteinuria in secondary amyloidosis cases.

MATERIAL AND METHODS

Sixteen patients with renal biopsy-proven AA amyloidosis with proteinuria were included in the study. All the patients had received colchicine treatment for at least 18 months. The patients were divided into two groups with similar age and gender distributions. Eight patients were given losartan at a dose of 50 mg/day for 12 months and the other 8 patients served as controls. Mean arterial blood pressure, proteinuria, serum albumin level and renal function were determined at the initiation of the study and after 1 and 12 months.

RESULTS

There were no significant differences in proteinuria, serum albumin level, renal function or mean arterial blood pressure at the initiation of the study. In the losartan group daily proteinuria decreased significantly from 5.2 +/- 0.7 g at the initiation of the study to 3.9 +/- 1.2 g at 1 month and 3.6 +/- 0.8 g at 12 months, while in the control group it changed from 4.6 +/- 1.0 g to 4.7 +/- 1.0 g and 6.1 +/- 1.2 g, respectively. The increment at 12 months was significant. After 12 months of treatment with losartan, proteinuria was significantly lower in comparison to the degree of proteinuria in the control group. Serum albumin level increased significantly in the losartan group but was unchanged in the control group. In the control group, creatinine clearance showed a significant decrease. There was no significant difference in mean arterial blood pressure measurements, serum creatinine levels, total protein, albumin and creatinine clearance levels between the two groups.

CONCLUSIONS

Losartan seemed to prevent an increase in proteinuria without altering the creatinine clearance level in patients with amyloidosis type AA during a 12-month period. This indicates that losartan may be used to decrease proteinuria in this patient group. However, our results are only preliminary and need to be confirmed by larger studies.

Olmesartan medoxomil: an angiotensin II-receptor blocker

BACKGROUND

Regulation of the activity of the renin-angiotensin-aldosterone system has become important in the management of cardiovascular disease. Olmesartan medoxomil (CS-866) is the newest selective angiotensin II-receptor blocker (ARB) to be approved for the treatment of hypertension.

OBJECTIVE

This review describes the mechanism of action, pharmacokinetics, adverse-effect profile, drug-interaction potential, and dosing of olmesartan medoxomil. The results of relevant clinical efficacy and safety trials are also discussed.

METHODS

This review is based on data from published clinical efficacy and safety trials and abstracts of conference presentations. To identify appropriate English-language publications for review, MEDLINE (1966-October 2002) and EMBASE (1990-2002) were searched using the terms olmesartan medoxomil, CS-866, angiotensin II-receptor blocker, and hypertension.

RESULTS

Olmesartan medoxomil has been reported to be an effective agent for the treatment of hypertension. Its blood pressure-lowering effects were comparable to those of other antihypertensive agents and other ARBs. Effects were seen as early as 2 weeks and persisted when olmesartan medoxomil was administered long term (for 1 year). The maximum recommended daily dose is 40 mg, except in the presence of severe renal insufficiency (creatinine clearance <20 mL/min) or moderate hepatic insufficiency (Child-Pugh score 7-9), when the daily dose should not exceed 20 mg. Olmesartan medoxomil was well tolerated. The most commonly reported adverse effect occurring significantly more often with olmesartan medoxomil than with placebo was dizziness (seen in approximately 3% of patients). The occurrence of clinically significant drug interactions was minimal.

CONCLUSIONS

Based on the available literature, olmesartan medoxomil is an effective ARB for the treatment of hypertension, with a favorable adverse-effect and drug-interaction profile.

Angiotensin-II receptor antagonist losartan reduces microalbuminuria in hypertensive renal transplant recipients

In recent years, it has been demonstrated that losartan lowers macroproteinuria in diabetic or non-diabetic renal transplant recipients (RTx) similar to angiotensin converting enzyme (ACE) inhibitors. Microalbuminuria (MAU) may reflect subclinical hyperfiltration damage of the glomerulus. It could be a marker of kidney dysfunction in renal transplantation. The aim of the study was to assess the efficacy of losartan in hypertensive RTx with MAU. This study was conducted in 17 (M/F: 4/13) stable RTx. No change was made in the medical treatment of the patients. All cases received 50 mg/day losartan therapy for 12 wk. Renal functions and MAU were determined 12 and 6 wk and just before the treatment as well as sixth and twelfth week of the treatment in all patients. Losartan satisfactorily lowered systemic blood pressure. A significant reduction in MAU was observed from 103 +/- 53 microg/min at the beginning to 59 +/- 25 microg/min in the sixth week and 47 +/- 24 microg/min in the twelfth week (p=0.0007 and 0.0005, respectively). From the sixth week of the treatment, the therapy significantly decreased hemoglobin, hematocrit and erythrocyte levels but did not change mean leukocyte and platelet counts, urea, creatinine levels and creatinine clearances. No serious side-effect was observed during the study. In conclusion, we found that losartan decreased MAU in hypertensive RTx. For that reason, it might be considered as the first choise antihypertensive agent for the renoprotection in selected patients.

Routine renin-angiotensin system blockade in renal transplantation?

There is ample evidence to support the recommendation of renin-angiotensin system blockade therapy as the standard of care for strategies aimed at preserving renal function in chronic renal disease. Nevertheless, despite the well established antihypertensive effects of these drugs, the use of renin-angiotensin system blockers in renal transplantation has been quite limited so far, nephrologists being afraid of the possibility of inducing renal insufficiency in patients with a single kidney transplant. However, current knowledge of the ability of these agents to control blood pressure and urinary protein excretion, as well as post-transplant erythrocytosis, effectively in kidney transplant recipients suggests that it is now time to apply renin-angiotensin system blockers to the field of renal transplantation.

Pharmacotherapy of systolic heart failure: a review of recent literature and practical applications

Since the publication of the Agency for Health Care Policy and Research Guidelines for treatment of heart failure, a number of new agents have been investigated for this indication. beta-Blockers have now been shown to improve outcomes in mild to moderate heart failure when added to standard therapy. Angiotensin II receptor antagonists have also been investigated and show promise. In general, calcium channel blockers are second- or third-line agents in patients refractory to other therapy. Investigational agents including spironolactone may also hold promise for future therapy.