Angiotensin II receptor antagonism: losartan - sites and mechanisms of action

Effect of CYP2C9 genetic polymorphism and breviscapine on losartan pharmacokinetics in healthy subjects

1. Breviscapine was an active ingredient of flavonoid glycosides. Our present study was conducted to evaluate the impact of breviscapine on the pharmacokinetics of losartan and its active metabolite E-3174, and that relationship with the gene polymorphism of CYP2C9 in healthy Chinese volunteers, to provide a basis for clinical rational drug use.2. The genotypes of 217 healthy Chinese subjects were determined using PCR-RFLP. Twelve healthy subjects were selected and were known CYP2C9 genotypes (six CYP2C9*1/*3 and six CYP2C9*1/*1) in a two-phase randomised crossover design study. These subjects were given daily doses of 120 mg (40 mg, three times a day) of breviscapine or a placebo for 14 days, followed by 50 mg losartan on day 15.3. Compared with individuals carrying the CYP2C9*1/*1 genotype, the CYP2C9*1/*3 genotype showed an increase in the AUC_(0-36) (833.6 ± 379.8 ng h ml^-1 vs. 526.1 ± 140.1 ng h ml^-1, p < 0.05) and a decrease in the MR (the metabolic ratio of losartan, AUC_E-3174/AUC_losartan) (2.67 ± 1.40 vs. 4.56 ± 0.83, p < 0.05) of losartan during the placebo treatment phase. Individuals with genotype CYP2C9*1/*3 showed a significant increase in AUC_(0-36) (2335 ± 851.8 ng h ml^-1 vs. 1927 ± 949.5 ng h ml^-1, p < 0.05) and AUC_(0-∞) (2363 ± 875.6 ng h ml^-1 vs. 1966 ± 966.1 ng h ml^-1, p < 0.05) of E-3174 after breviscapine treatment compared to the placebo group.4. In healthy subjects, breviscapine had no significant effect on the pharmacokinetics of losartan. The activity of CYP2C9 enzyme to losartan metabolism was more significant in subjects with CYP2C9*1/*3 than those with CYP2C9*1/*1 genotype.

Evaluation of the losartan solubility in the biowaiver context by shake-flask method and intrinsic dissolution

This study aimed at evaluating the shake-flask use as a universal method to evaluate drug solubility in a biowaiver context as proposed by FDA, EMA and ANVISA. The solubility of losartan was determined in three buffers using the shake-flask method, intrinsic dissolution (ID) and Quantum Chemistry. Moreover, the evaluation of a losartan dissolution profile from coated tablets was conducted. The losartan low solubility in pH 1.2 and high solubility in pH 6.8 were observed using the shake-flask method. However, the solubility results using ID demonstrated its high solubility in pH 1.2 and 6.8. It was not possible to find conclusive results regarding the solubility of the drug in pH 4.5. The studies conducted by Quantum Chemistry provide molecular and electronic data that helped understand the losartan solvation in different pH values. Our experimental results defined that losartan can be classified as a low-solubility drug. In addition, this work shows that shake-flask cannot be a universal method of solubility studies in biowaiver context. Individual analysis will be necessary. The intrinsic dissolution should be considered as a complementary method.

Understanding electrostatic and steric requirements related to hypertensive action of AT(1) antagonists using molecular modeling techniques

AT1 receptor is an interesting biological target involved in several important diseases, such as blood hypertension and cardiovascular pathologies. In this study we investigated the main electrostatic and steric features of a series of AT1 antagonists related to hypertensive activity using structure and ligand-based strategies (docking and CoMFA). The generated 3D model had good internal and external consistency and was used to predict the potency of an external test set. The predicted values of pIC50 are in good agreement with the experimental results of biological activity, indicating that the 3D model can be used to predict the biological property of untested compounds. The electrostatic and steric CoMFA maps showed molecular recognition patterns, which were analyzed with structure-based molecular modeling studies (docking). The most and the least potent compounds docked into the AT1 binding site were subjected to molecular dynamics simulations with the aim to verify the stability and the flexibility of the ligand-receptor interactions. These results provided valuable insights on the electronic/structural requirements to design novel AT1 antagonists.

Effects of ticlopidine on pharmacokinetics of losartan and its main metabolite EXP-3174 in rats

AIM

Losartan and antiplatelet agent ticlopidine can be prescribed concomitantly for prevention or therapy of cardiovascular diseases. Hence, the effects of ticlopidine on the pharmacokinetics of losartan and its active metabolite EXP-3174 were evaluated in rats.

METHODS

Ticlopidine (4 or 10 mg/kg po) was administered 30 min before administration of losartan (9 mg/kg po or 3 mg/kg iv). The activity of human CYP2C9 and 3A4 were measured using the CYP inhibition assay kit. The activity of P-gp was evaluated using rhodamine-123 retention assay in MCF-7/ADR cells.

RESULTS

Ticlopidine (10 mg/kg) significantly increased the areas under the plasma concentration-time curves (AUCs) and peak plasma concentration (C(max)) of oral losartan (9 mg/kg), as well as the AUCs of the active metabolite EXP-3174. Ticlopidine (10 mg/kg) did not significantly change the pharmacokinetics of intravenous losartan (3 mg/kg). Ticlopidine inhibited CYP2C9 and 3A4 with IC₅₀ values of 26.0 and 32.3 μmol/L, respectively. The relative cellular uptake of rhodamine-123 was unchanged.

CONCLUSION

The significant increase in the AUC of losartan (9 mg/kg) by ticlopidine (10 mg/kg) could be attributed to the inhibition of CYP2C9- and 3A4-mediated losartan metabolism in small intestine and/or in liver. The inhibition of P-gp in small intestine and reduction of renal elimination of losartan by ticlopidine are unlikely to be causal factors.

The paradox of dopamine and angiotensin II-mediated Na(+), K(+)-ATPase regulation in renal proximal tubules

Accumulated studies reported that the natruretic dopamine (DA) and the anti-natruretic angiotensin II (Ang II) represent an important mechanism to regulate renal Na(+) and water excretion through intracellular secondary messengers to inhibit or activate renal proximal tubule (PT) Na(+), K(+)-ATPase (NKA). The antagonistic actions were mediated by the phosphorylation of different position of NKA α₁-subunit and different Pals-associated tight junction protein (PATJ) PDZ domains, the different protein kinase C (PKC) isoforms (PKC-β, PKC-ζ), the common adenylyl cyclase (AC) pathway, and the crosstalk and balance between DA and Ang II to NKA regulation. Besides, Ang II-mediated NKA modulation has bi-phasic effects.

Inhibition of angiotensin II receptor 1 limits tumor-associated angiogenesis and attenuates growth of murine melanoma

PURPOSE

We evaluated the involvement of angiotensin II (AngII)-dependent pathways in melanoma growth, through the pharmacological blockage of AT1 receptor by the anti-hypertensive drug losartan (LOS).

RESULTS

We showed immunolabeling for both AngII and the AT1 receptor within the human melanoma microenvironment. Like human melanomas, we showed that murine melanomas also express the AT1 receptor. Growth of murine melanoma, both locally and at distant sites, was limited in mice treated with LOS. The reduction in tumor growth was accompanied by a twofold decrease in tumor-associated microvessel density and by a decrease in CD31 mRNA levels. While no differences were found in the VEGF expression levels in tumors from treated animals, reduction in the expression of the VEGFR1 (Flt-1) at the mRNA and protein levels was observed. We also showed downregulation of mRNA levels of both Flt-4 and its ligand, VEGF-C.

CONCLUSIONS

Together, these results show that blockage of AT1 receptor signaling may be a promising anti-tumor strategy, interfering with angiogenesis by decreasing the expression of angiogenic factor receptors.

Losartan in cardiovascular disease

Hypertension is a major risk factor for the development of cardiovascular disease. Numerous placebo-controlled trials have demonstrated that treatment of hypertension results in substantial reduction of hypertension-related vascular events. The benefit of specific therapies beyond their effect on blood pressure is well established. Losartan is an orally-active, selective, nonpeptide, angiotensin II type 1-receptor antagonist (ARB), and it was the first in this class to be marketed. Several large-scale clinical trials have demonstrated that losartan and other ARBs have benefits in preventing cardiovascular disease. The Losartan Intervention For End point reduction in hypertension (LIFE) study demonstrated improved outcomes with losartan as compared with atenolol-based therapies in hypertensive patients with left ventricular hypertrophy, mainly because of stroke prevention. The Reduction of End points in Non-insulin-dependent diabetes mellitus with the Angiotensin II Antagonist Losartan (RENAAL) study demonstrated that losartan prevented the progression of diabetic nephropathy. In this review, evidence from these and other clinical trials with losartan shall be discussed. The pharmacodynamic and pharmacokinetic properties of losartan are described to explain its mechanisms of action. Among the ARB class, losartan possesses certain unique properties, which may enhance its cardiovascular protective effects. These include an increase of urinary uric acid excretion and antiatherothrombotic properties. Potential future roles for losartan and other ARBs shall be discussed, in addition to emphasizing areas in which evidence is currently lacking or indecisive, including head-to-head comparisons of ARBs and the effects of combining an ARB with angiotensin-converting-enzyme inhibitors.

Angiotensin II directly stimulates activity and alters the phosphorylation of Na-K-ATPase in rat proximal tubule with a rapid time course

We present evidence that Na-K-ATPase in the rat proximal tubule is directly activated by ANG II much faster than previously observed. Specifically, we show that a 2-min exposure to 0.1 and 1 nM ANG II slowed the rate of intracellular sodium accumulation in response to an increase in extracellular sodium added in the presence of gramicidin D. From these data, we show that ANG II directly stimulates Na-K-ATPase activity at rate-limiting concentrations of intracellular sodium. Under these same conditions, exposing proximal tubules to ANG II altered the amount of 32P incorporated into multiple phosphopeptides generated from a tryptic digest of the alpha-subunit of Na-K-ATPase. Na-K-ATPase was isolated from whole cell lysates by means of a ouabain-affinity column and then separated into its individual subunits by SDS-PAGE. Na-K-ATPase bound to the column in its E2 conformation and was eluted by altering its conformation to E1 using Na+ATP. Na-K-ATPase isolated from cells treated with ANG II eluted more easily from the ouabain-affinity column than Na-K-ATPase isolated from control cells, suggesting that ANG II decreased the affinity of Na-K-ATPase for ouabain. Thus ANG II rapidly stimulated the activity of Na-K-ATPase in 2 min or less by a mechanism that could involve changes in phosphorylation and conformation of Na-K-ATPase. We suggest that the physiological role for rapid direct activation of Na-K-ATPase is greater control of intracellular sodium during sodium reabsorption.

Pharmacokinetics and pharmacodynamics of irbesartan in patients with hepatic cirrhosis

The effect of hepatic impairment on the clinical pharmacology of the angiotensin II (AII) receptor antagonist irbesartan was assessed by comparing pharmacokinetic and pharmacodynamic parameters in 10 patients with hepatic cirrhosis with a matched group of 10 healthy volunteers. The pharmacokinetics and pharmacodynamics of irbesartan, 300 mg taken orally once daily, were evaluated after single- and multiple-dose (7 consecutive days) administration to normotensive subjects in an open-label, multiple-dose, parallel group study. Pharmacokinetic data obtained after administration of single and multiple doses of irbesartan showed no significant difference between the two groups in time to maximum observed plasma concentration of drug (tmax), half-life (t1/2), area under the plasma concentration-time curve (AUC), apparent oral clearance (Cl(t)/F), renal clearance (Cl(r)), and accumulation index (AI). Steady-state levels of irbesartan were reached within 3 days in both treatment groups. After irbesartan administration on day 1, mean increases from baseline in plasma AII levels and plasma renin activity (PRA) were greater in the group with cirrhosis than in the control group. On day 7, mean increases from baseline in PRA were greater in the control group than in the group with cirrhosis. No discontinuations or serious adverse events occurred during the study. The pharmacokinetics of irbesartan after repeated oral administration were not significantly affected in patients with mild-to-moderate cirrhosis of the liver. No dosage adjustment is necessary in patients with hepatic insufficiency.

Role of angiotensin in renal sympathetic activation in nephrotic syndrome

The effect of type 1 angiotensin II receptor antagonist treatment (losartan) on cardiac baroreflex regulation of renal sympathetic nerve activity (RSNA) and renal sodium handling in rats with nephrotic syndrome was examined. After intravenous losartan administration, with arterial pressure normalized by intravenous methoxamine, basal RSNA was decreased 14 +/- 3% in arterial baroreceptor-intact rats and by 21 +/- 5% in arterial baroreceptor-denervated rats. Intracerebroventricular losartan, which did not affect arterial pressure, decreased basal RSNA activity by 15 +/- 1%. Both intravenous and intracerebroventricular losartan augmented the renal sympathoinhibitory response to acute volume loading, and this was associated with an enhanced natriuretic response to the acute volume load. In nephrotic syndrome, acute losartan administration improved cardiac baroreflex regulation of RSNA, which was associated with improved ability to excrete acute sodium loads.