CS-866, a New Angiotensin II Type 1 Receptor Antagonist, Ameliorates Glomerular Anionic Site Loss and Prevents Progression of Diabetic Nephropathy in Otsuka Long-Evans Tokushima Fatty Rats

Simultaneous Quantitative Analysis of Olmesartan Medoxomil and Amlodipine Besylate in Plasma by High-performance Liquid Chromatography Technique

A rapid, simple and sensitive high-performance liquid chromatography (HPLC) method has been developed for quantification of olmesartan medoxomil (OLM) and amlodipine besylate (AM) in plasma. The assay enables the measurement of OLM and AM for therapeutic drug monitoring with a minimum detectable limit of 2 ng mL. The method involves a simple, one-step extraction procedure and analytical recovery was above 50%. The separation was performed on an analytical 250 × 4.6 mm Eurospher 100^-5 C18 column. The wavelength was set at 239 nm. The mobile phase was a mixture of acetonitrile:0.05 M ammonium acetate buffer: 0.1 mL triethylamine at pH 6.8 was selected at a flow rate of 1.0 mL min. The calibration curve for the determination of OLM and AM in plasma was linear over the range 2–2500 and 8–10,000 ng mL AM and OLM. The coefficients of variation for interday and intraday assay were found to be <15%. The method can be applied to a pharmacokinetic and pharmacodynamic study of OLM and AM in a combined dosage form.

Application of smart spectrophotometric methods and artificial neural network for the simultaneous quantitation of olmesartan medoxamil, amlodipine besylate and hydrochlorothiazide in their combined pharmaceutical dosage form

Background

New, simple and specific spectrophotometric methods and artificial neural network (ANN) were developed and validated in accordance with ICH guidelines for the simultaneous estimation of Olmesartan (OLM), Amlodipine (AML), and Hydrochlorothiazide (HCT) in commercial tablets.

Results

For spectrophotometric methods: First, Amlodipine (AML) was determined by direct spectrophotometry at 359 nm and by application of the ratio subtraction, the AML spectrum was removed from the mixture spectra. Then Hydrochlorothiazide (HCT) was determined directly at 315 nm without interference from Olmesartan medoxamil (OLM) which could be determined using the isoabsorptive method. The calibration curve is linear over the concentration range of 5–40, 2.5-40 and 2–40 μg mL^-1 for AML, OLM and HCT, respectively. ANN (as a multivariate calibration method) was also applied for the simultaneous determination of the three analytes in their combined pharmaceutical dosage form using spectral region from 230–340 nm.

Conclusions

The proposed methods were successfully applied for the assay of the three analytes in laboratory prepared mixtures and combined pharmaceutical tablets with excellent recoveries. No interference was observed from common pharmaceutical additives. The results were favorably compared with those obtained by a reference spectrophotometric method. The methods are validated according to the ICH guidelines and accuracy, precision and repeatability are found to be within the acceptable limit.

Angiotensin receptor blocker protection against podocyte-induced sclerosis is podocyte angiotensin II type 1 receptor-independent

In the present study, we tested the hypothesis that the renoprotective effect of an angiotensin receptor blocker depends on the angiotensin II type 1 (AT(1)) receptor on podocytes. For this purpose, we generated podocyte-specific knockout mice for the AT(1) gene (Agtr1a) and crossed with NEP25, in which selective podocyte injury can be induced by immunotoxin, anti-Tac(Fv)-PE38. Four weeks after the addition of anti-Tac(Fv)-PE38, urinary albumin:creatinine ratio was not attenuated in Agtr1a knockout/NEP25 mice (n=18) compared with that in control NEP25 mice (n=13; 8.08+/-2.41 in knockout versus 4.84+/-0.73 in control). Both strains of mice showed similar degrees of sclerosis (0.66+/-0.17 versus 0.82+/-0.27 on a 0 to 4 scale) and downregulation of nephrin (5.78+/-0.45 versus 5.65+/-0.58 on a 0 to 8 scale). In contrast, AT(1) antagonist or an angiotensin I-converting enzyme inhibitor, but not hydralazine, remarkably attenuated proteinuria and sclerosis in NEP25 mice. Moreover, continuous angiotensin II infusion induced microalbuminuria similarly in both Agtr1a knockout and wild-type mice. Thus, angiotensin inhibition can protect podocytes and prevent the development of glomerulosclerosis independent of podocyte AT(1). Possible mechanisms include inhibitory effects on AT(1) of other cells or through mechanisms independent of AT(1). Our study further demonstrates that measures that directly affect only nonpodocyte cells can have beneficial effects even when sclerosis is triggered by podocyte-specific injury.

Quantitative determination of olmesartan in human plasma and urine by liquid chromatography coupled to tandem mass spectrometry

A specific, sensitive and fast method based on high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) was developed for the determination of olmesartan in human plasma and urine. Solid-phase extraction (SPE) was used to isolate the compounds from biological matrix followed by injection of the extracts onto a C(18) column with isocratic elution. The method was validated over the concentration range of 0.2-1000 and 5-10,000 ng/mL for olmesartan in human plasma and urine, respectively. The method was applied to the pharmacokinetic study of olmesartan medoxomil in healthy Chinese male and female subjects.

Agents in development for the treatment of diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease, and accounts for significant morbidity and mortality in patients with diabetes. Diabetic nephropathy seems to occur as a result of an interaction between metabolic and haemodynamic factors, which activate common pathways that lead to renal damage. In the past, the treatment of diabetic nephropathy has focused on the control of hyperglycaemia. Newer targets, some of which are linked to glucose-dependent pathways, appear to be a major focus of new treatments directed against the development and progression of renal damage as a result of diabetes. It is anticipated that additional therapeutic approaches that inhibit both metabolic and haemodynamic pathways will include strategies that target growth factors, cytokines and intracellular second messengers. Such an approach is expected to lead to improved therapies for the treatment of diabetic nephropathy.

AGEs activate mesangial TGF-beta-Smad signaling via an angiotensin II type I receptor interaction

BACKGROUND

The renin-angiotensin system (RAS) and the accumulation of advanced glycation end products (AGEs) have been implicated in the pathogenesis of diabetic nephropathy. Whether there is a functional interaction between the RAS and AGEs in diabetic nephropathy is not known. In this study, we investigated whether AGEs could activate autocrine angiotensin II (Ang II) signaling and subsequently induce transforming growth factor-beta (TGF-beta)-Smad signaling in cultured rat mesangial cells.

METHODS

The intracellular formation of reactive oxygen species (ROS) was detected using the fluorescent probe CM-H2DCFDA. Ang II was measured by radioimmunoassay. TGF-beta released into media was quantitatively analyzed in an enzyme-linked immunosorbent assay (ELISA). Smad2, p27(Kip1) (p27), fibronectin, and receptor for AGEs (RAGE) protein expression were determined by Western blot analysis. TGF-beta-inducible promoter activity was analyzed by a luciferase assay. DNA synthesis was evaluated by 5-bomo-2'-deoxyuridine (BrdU) incorporation and de novo protein synthesis was determined by [3H]leucine incorporation.

RESULTS

AGEs increased intracellular ROS generation in mesangial cells, and this effect was significantly inhibited by an antiserum against RAGE. AGEs also were found to stimulate Ang II production in a time- and dose-dependent manner, which was completely prevented by an antioxidant, N-acetylcysteine (NAC). AGE-induced TGF-beta overproduction was completely blocked by candesartan, an Ang II type 1 receptor (AT1R) antagonist. Both candesartan and neutralizing antibody against TGF-beta completely prevented AGEs-induced Smad2 phosphorylation and TGF-beta-inducible promoter activity. Furthermore, AGEs were found to inhibit DNA synthesis and to stimulate de novo protein synthesis and fibronectin production in association with up-regulation of p27. All of these phenomena were completely prevented by candesartan or a polyclonal antibody against TGF-beta.

CONCLUSION

The present study suggests that AGE-RAGE-mediated ROS generation activates TGF-beta-Smad signaling and subsequently induces mesangial cell hypertrophy and fibronectin synthesis by autocrine production of Ang II. This pathway may provide an important link between metabolic and haemodynamic factors in promoting the development and progression of diabetic nephropathy.

Temporary angiotensin II blockade at the prediabetic stage attenuates the development of renal injury in type 2 diabetic rats

Whether temporary angiotensin II (AngII) blockade at the prediabetic stage attenuates renal injury in type 2 diabetic OLETF rats later in life was investigated. OLETF rats were treated with an AT(1) receptor antagonist (olmesartan, 0.01% in food), angiotensin-converting enzyme inhibitor (temocapril, 0.01% in food), a combination of the two, or hydralazine (25 mg/kg per d) at the prediabetic stage (4 to 11 wk of age) and then monitored without further treatment until 50 wk of age. At 11 wk of age, blood glucose levels and urinary protein excretion (U(protein)V) were similar between OLETF and control LETO rats. However, OLETF rats showed higher kidney AngII contents and type IV collagen mRNA expression than LETO rats at this age. These decreased with olmesartan, temocapril, and a combination of these but not with hydralazine. At 50 wk of age, diabetic OLETF rats showed higher BP, U(protein)V, and intrarenal AngII levels than LETO rats. Temporary AngII blockade did not affect glucose metabolism or the development of hypertension in OLETF rats but significantly suppressed proteinuria and ameliorated glomerular injury. However, no parameters were affected by temporary hydralazine treatment. The present study demonstrated that intrarenal AngII and type IV collagen expression are already augmented long before diabetes becomes apparent in OLETF rats. Furthermore, temporary AngII blockade at the prediabetic stage attenuates the progression of renal injury in these animals. These data suggest that early AngII blockade could be an effective strategy for preventing the development of type 2 diabetic renal injury later in life.

The role of vascular endothelial growth factor (VEGF) in renal pathophysiology

Vascular endothelial growth factor (VEGF) is an endothelial-specific growth factor that promotes endothelial cell proliferation, differentiation and survival, mediates endothelium-dependent vasodilatation, induces microvascular hyperpermeability and participates in interstitial matrix remodeling. In the kidney, VEGF expression is most prominent in glomerular podocytes and in tubular epithelial cells, while VEGF receptors are mainly found on preglomerular, glomerular, and peritubular endothelial cells. The role of VEGF in normal renal physiology is essentially unknown. The absence of prominent effects of VEGF blockade in normal experimental animals suggests a limited function during homeostasis, although a role in the formation and maintenance of glomerular capillary endothelial fenestrations has been suggested. VEGF and its receptors are up-regulated in experimental animals and humans with type 1 and type 2 diabetes. Inhibition of VEGF has beneficial effects on diabetes-induced functional and structural alterations, suggesting a deleterious role for VEGF in the pathophysiology of diabetic nephropathy. VEGF is required for glomerular and tubular hypertrophy and proliferation in response to nephron reduction, and loss of VEGF is associated with the development of glomerulosclerosis and tubulointerstitial fibrosis in the remnant kidney. No firm conclusions on the role of VEGF in minimal change or membranous glomerulonephritis can be drawn. VEGF may be an essential mediator of glomerular recovery in proliferative glomerulonephritis. Glomerular and tubulointerstitial repair in thrombotic microangiopathy and cyclosporin nephrotoxicity may also be VEGF-dependent. In conclusion, VEGF is required for growth and proliferation of glomerular and peritubular endothelial cells. While deleterious in some, it may contribute to recovery in other forms of renal diseases.

[Pharmacological profiles and clinical effects of olmesartan medoxomil, a novel angiotensin II receptor blocker]

Olmesartan medoxomil is a new angiotensin II receptor blocker (ARB) indicated for the treatment of hypertension. Olmesartan medoxomil is a pro-drug that is converted to the active metabolite olmesartan. Olmesartan does not undergo further metabolism and does not interact with cytochrome P450 enzymes. Olmesartan is a potent ARB with high selectivity for the type 1 (AT(1)) receptor subtype and shows insurmountable antagonism against the AT(1) receptor in vascular tissues. This antagonistic mode, which could be attributed to tight binding of this drug to the receptor, would underlie the potent and persistent action of olmesartan medoxomil in vivo. In fact, oral administration of olmesartan medoxomil produces a potent and long-lasting antihypertensive action without inducing tachycardia. The preventive effects of olmesartan medoxomil on end-organ damage in the kidney, heart, and blood vessels have been demonstrated in various animal models. In clinical studies, olmesartan medoxomil is shown to be well tolerated and have an excellent safety profile that is comparable to that of placebo. Head-to-head comparisons with other ARBs (losartan, valsartan, irbesartan, and candesartan cilexetil) conducted in the United States and Europe have revealed that olmesartan medoxomil is superior to these other ARBs in lowering blood pressure. These facts suggest that olmesartan medoxomil would be beneficial for the treatment of hypertension and other end-organ diseases.

Antiproteinuric effect of RAS blockade: New mechanisms

Experimental and clinical studies have shown that blockade of the renin-angiotensin system (RAS) is effective in reducing proteinuria in conditions such as diabetes by reducing systemic and intraglomerular hydrostatic pressure. However, increasing evidence suggests that nonhemodynamic effects, such as preservation of the podocyte slit diaphragm structure and function, may also mediate the antiproteinuric effects of RAS blockade. In this review, we analyze in detail the evidence for known and novel mechanisms considered to play important roles in mediating the antiproteinuric effect of RAS blockers, with a particular focus on diabetic nephropathy.

RENAL EFFECTS OF 26-WEEK ADMINISTRATION OF OLMESARTAN MEDOXOMIL/HYDROCHLOROTHIAZIDE IN RATS

The combination of an angiotensin II type 1 receptor blocker (ARB) and a diuretic is effective clinically in treatment of hypertension. As a non-clinical safety evaluation of a combination of the ARB olmesartan medoxomil (OM) and the diuretic hydrochlorothiazide (HCTZ), male and female normotensive rats were administered OM/HCTZ (fixed ratio of 8 : 5) orally by gavage for 26 weeks at dose levels of 0, 4.88, 16.25, 48.75, 162.5, 487.5, or 1625 mg/kg/day. Additional groups were given 1000 mg/ kg/day OM or 625 mg/kg/day HCTZ. Statistically significant and marked decreases in urinary protein excretion were observed in males and females given doses of 16.25 mg/kg/day or higher compared to vehicle-control groups. Increases in blood urinary nitrogen (BUN) were observed in males and females given doses of 16.25 and 162.5 mg/kg/day or higher, respectively. Increased incidence of chronic progressive nephropathy (CPN), a rat-specific spontaneous renal lesion, was observed in males and females given doses of 48.75 mg/kg/day or higher. An additional mechanistic study, consisting of male and female rats given 0, or 162.5 mg/kg/day OM/HCTZ, was conducted to clarify the toxicological significance of the increases in BUN and the increased incidence of CPN described above. This additional study clearly demonstrated that saline-supplementation through free access to saline in the drinking water ameliorated the elevation in BUN and also ameliorated the incidence of CPN. Consequently, the effects on BUN and CPN observed in the first study can be explained by the hemodynamic disturbances caused by the large doses and an exaggerated pharmacological action in volume-depleted normotensive animals. Importantly, the marked decreases in urinary protein were not affected by the saline-supplementation, and indicated that OM/HCTZ elicited a renoprotective effect, probably by an effect on the glomeruli. An additional toxicokinetic study revealed no drug interactions between OM and HCTZ. In conclusion, OM/HCTZ induced a renoprotective effect as well as changes probably attributed to the exaggerated pharmacological action of the ARB with diuretic in normotensive rats. These results suggest that OM/HCTZ may have renoprotective effects in clinical treatment of hypertensive patients.