Effects of Valsartan and Valeryl 4-Hydroxy Valsartan on Human Platelets: A Possible Additional Mechanism for Clinical Benefits

Development and validation of a sensitive and simple LC-MS/MS method for simultaneous quantitation of valsartan, sacubitril and sacubitrilat in pediatric population

Pediatric heart failure (HF) is an important clinical disease with high hospitalization rates, morbidity, mortality and medical costs. Sacubitril/valsartan (also known as Entresto), was approved for the treatment of adult HF and is recently used in pediatrics. However, clinical therapy on children is more challenging than adults, and the pharmacokinetics of Entresto in children are still largely unknown and urgently needed. Herein, we aim to develop a simple and sensitive analytic method to monitor Entresto in pediatric patients, which is of great importance for individualized safe medication in children. Specifically, a liquid chromatography tandem mass spectrometry method for simultaneously quantification of valsartan, sacubitril and its bio-active metabolite sacubitrilat in human plasma has been developed and validated in pediatric patients. Plasma samples were pretreated with acetonitrile for protein precipitation. Elution was performed on X Select HSS T3 column (2.1 × 100 mm, 5 µm; Waters) column using an isocratic mobile phase process consisting of 0.1% formic acid aqueous solution and 0.1% formic acid acetonit rile with a total run time of 3.0 min. Valsartan-d3, sacubitrilin-d4 and sacubitrilat-d4 were used as the corresponding deuterium internal standards. According to the Bioanalytical Method Validation Guidance for Industry, the method was validated in the range of 0.5-5000 ng/mL. Intra- and inter-day accuracy of sacubitril,valsartan and sacubitrilat ranged from 93%- 108%, 98%- 109%, 91%- 102%, respectively, with relative standard deviation of precision ranging from 2.0% to 5.1%, 2.4%- 7.5%, 1,3%- 7.4%. The proposed method demonstrated good accuracy, precision and linearity. The matrix factors normalized by internal standard meet the acceptance criteria. The method was fully validated and applied in 39 children. Trough concentration of the three substances to be measured were: valsartan (11.3-938.0 ng/mL), sacubitril (0.5-395.5 ng/mL) and sacubitrilat (522.1-4890.0 ng/mL). Overall, this is the first study to simultaneously determined the plasma valsartan, sacubitril and sacubitrilat concentrations in children, which is believed to facilitate the clinical management of pediatric HF.

Biotransformation: Impact and Application of Metabolism in Drug Discovery

Biotransformation has a huge impact on the efficacy and safety of drugs. Ultimately the effects of metabolism can be the lynchpin in the discovery and development cycle of a new drug. This article discusses the impact and application of biotransformation of drugs by mammalian systems, microorganisms, and recombinant enzymes, covering active and reactive metabolites, the impact of the gut microbiome on metabolism, and how insights gained from biotransformation studies can influence drug design from the combined perspectives of a CRO specializing in a range of biotransformation techniques and pharma biotransformation scientists. We include a commentary on how biology-driven approaches can complement medicinal chemistry strategies in drug optimization and the in vitro and surrogate systems available to explore and exploit biotransformation.

The Role of Sartans in the Treatment of Stroke and Subarachnoid Hemorrhage: A Narrative Review of Preclinical and Clinical Studies

Background: Delayed cerebral vasospasm (DCVS) due to aneurysmal subarachnoid hemorrhage (aSAH) and its sequela, delayed cerebral ischemia (DCI), are associated with poor functional outcome. Endothelin-1 (ET-1) is known to play a major role in mediating cerebral vasoconstriction. Angiotensin-II-type-1-receptor antagonists such as Sartans may have a beneficial effect after aSAH by reducing DCVS due to crosstalk with the endothelin system. In this review, we discuss the role of Sartans in the treatment of stroke and their potential impact in aSAH. Methods: We conducted a literature research of the MEDLINE PubMed database in accordance with PRISMA criteria on articles published between 1980 to 2019 reviewing: "Sartans AND ischemic stroke". Of 227 studies, 64 preclinical and 19 clinical trials fulfilled the eligibility criteria. Results: There was a positive effect of Sartans on ischemic stroke in both preclinical and clinical settings (attenuating ischemic brain damage, reducing cerebral inflammation and infarct size, increasing cerebral blood flow). In addition, Sartans reduced DCVS after aSAH in animal models by diminishing the effect of ET-1 mediated vasoconstriction (including cerebral inflammation and cerebral epileptogenic activity reduction, cerebral blood flow autoregulation restoration as well as pressure-dependent cerebral vasoconstriction). Conclusion: Thus, Sartans might play a key role in the treatment of patients with aSAH.

Potential Protective Role of Blood Pressure-Lowering Drugs on the Balance between Hemostasis and Fibrinolysis in Hypertensive Patients at Rest and During Exercise

In patients with hypertension, the triad represented by endothelial dysfunction, platelet hyperactivity, and altered fibrinolytic function disturbs the equilibrium between hemostasis and fibrinolysis and translates into a hypercoagulable state, which underlies the risk of thrombotic complications. This article reviews the scientific evidence regarding some biological effects of antihypertensive drugs, which can protect patients from the adverse consequences of hypertensive disease, improving endothelial function, enhancing antioxidant activity, and restoring equilibrium between hemostatic and fibrinolytic factors. These protective effects appear not to be mediated through blood pressure reduction and are not shared by all molecules of the same pharmacological class.

AGI-1067, a novel vascular protectant, anti-inflammatory drug and mild antiplatelet agent for treatment of atherosclerosis

Oxidation-sensitive signals play an important role in platelet activation. AGI-1067 is a novel, phenolic, intra- and extracellular antioxidant that inhibits the expression of a number of proinflammatory genes involved in atherosclerosis. AGI-1067 is the metabolically stable monosuccinic acid ester of probucol, and a potent phenolic antioxidant representing a novel class of orally bioavailable compounds termed vascular protectants. AGI-1067 exhibits antioxidant activity equipotent to probucol. In addition, animal studies have demonstrated dual pharmacological activities of AGI-1067: the ability to block the expression of oxidation-sensitive inflammatory genes including genes that code for vascular cell adhesion molecule-1 and monocyte chemotactic protein-1. Importantly, AGI-1067 also exhibits mild antiplatelet properties inhibiting surface expression of various key platelet receptors, the formation of platelet monocyte microparticles and PAR-1 thrombin receptors. AGI-1067 is currently being tested in the late trials, and if proven to improve clinical outcomes (ARISE trial), the drug will ultimately be used in patients with different manifestations of atherosclerosis and atherothrombosis.

Effect of aliskiren and valsartan combination versus aliskiren monotherapy on hemostatic biomarkers in hypertensive diabetics: Aliskiren and Valsartan Impact in Diabetics pilot trial

Valsartan is known to inhibit platelet activity in both in vitro and ex vivo clinical setting, whereas aliskiren in vitro modulates antithrombin-III in plasma. The authors tested how aliskiren and valsartan combination versus aliskiren monotherapy will affect hemostatic biomarkers in mild-to-moderate hypertensive diabetics in the frame of the Aliskiren and Valsartan Impact in Diabetics (AVID) trial. A total of 52 patients with type 2 diabetes and mild-to-moderate hypertension were equally randomized to aliskiren (150-300 mg/d) and valsartan (160 mg/d) versus aliskiren (150-300 mg/d) alone for 4 weeks. A total of 25 biomarkers were serially measured, of which 16 are related to platelet function, 6 to coagulation, and 3 to fibrinolysis. Aliskiren monotherapy has no significant impact on any of the assessed biomarkers. In contrast, valsartan on top of aliskiren provided significant inhibition of ADP-induced platelet aggregation (P=0.032), decreased shear-induced activation measured with PFA-100 analyzer (P=0.041), and diminished expression of GP IIb/IIIa activity (P=0.027) measured by PAC-1 antibody, GP Ib (CD42b, P=0.033), vitronectin receptor (CD51/61, P=0.046), P-selectin (CD62p, P=0.026), lysosome-associated membrane protein (CD107a, P=0.042), and CD40-ligand (CD154, P=0.048). In AVID trial, valsartan in combination with aliskiren mildly but significantly inhibited platelets, confirming previous observations. In contrast, aliskiren monotherapy does not enhance antithrombin activity, suggesting that previous data probably represent a laboratory artifact. Importantly, these randomized data were generated on top of low-dose daily aspirin, supporting extra benefit for combination use of angiotensin receptor blockers and renin inhibitors in high-risk diabetic population.

The in vitro effects of Xancor, a synthetic astaxanthine derivative, on hemostatic biomarkers in aspirin-naïve and aspirin-treated subjects with multiple risk factors for vascular disease

Astaxanthine is a polar carotenoid metabolite derived from a proprietary prodrug, Xancor, which aligns parallel with the membrane phospholipids exhibiting potent antioxidant, anti-inflammatory, and cell protective properties, although the precise mechanism of action is unknown. This prodrug is currently under development for hepatic, neurologic, and vascular disease indications. Considering established links between heart disease and stroke with platelets, coagulation cascade, and fibrinolysis, the aim of the study was to assess the effect of asthaxantine on human biomarkers of hemostasis. The rationale was to test a hypothesis that the drug may diminish activation of hemostasis, making it a potentially attractive addition to treat patients with vascular disease. In vitro effects of whole blood preincubation with escalating concentrations of asthaxantine (0.3 microM, 1 microM, 3 microM, 10 microM, 30 microM, and 100 microM) were assessed from 12 aspirin-naïve and eight aspirin-treated volunteers with multiple risk factors for vascular disease. A total of 25 biomarkers were measured, of which 12 were related to platelet function, 10 to coagulation, and three to fibrinolysis. Platelet aggregation induced by ADP, collagen, and arachidonic acid and expression of CD31, CD41, GP IIb/IIIa, CD51/61, P-selectin, CD63, CD107a, CD151+CD14, and CD154 were not affected. Coagulation indices such as aPTT, prothrombin time, thrombin time, fibrinogen, antithrombin III (antigen and activity), Protein C, Protein S (free and activity), and von Willebrand factor remained unchanged after incubation with astaxanthine. Fibrinolytic activity biomarkers such as plasminogen, D-dimer, and FDP were also not affected after in vitro pretreatment of blood samples with astaxanthine. In the projected subclinical (less than 1 microM), therapeutic (3 microM to 30 microM), and supratherapeutic concentration (100 microM), astaxanthine in vitro does not affect platelet, coagulation, or fibrinolytic indices in either aspirin-naïve or aspirin-treated subjects. These results are important for the assessment of the safety profile, but remain to be confirmed preclinically, in vivo, and ultimately in the clinic.

Effect of fluvastatin and valsartan, alone and in combination, on postprandial vascular inflammation and fibrinolytic activity in patients with essential hypertension

Postprandial hypertriglyceridemia is associated with a series of atherogenic abnormalities, including a prothrombotic state and inflammation. Hypertensive patients have exaggerated postprandial triglyceride response. The benefit of combined treatment of statin and angiotensin II type 1 receptor blocker (ARB) has been demonstrated in diabetic patients. The aim of this investigation was to explore the effect of a statin, fluvastatin, and the ARB valsartan, alone and in combination, on fibrinolytic activity and inflammation after a high-fat meal in patients with essential hypertension (EHP). A total of 53 EHP patients were studied. The concentrations of plasma lipid profiles, soluble P-selectin, tissue plasminogen activator (t-PA) and plasminogen activator inhibitor type I (PAI-1) antigens were measured in fasting state and at 4 hours after a single high-fat meal (800 calories; 50 g fat). Patients randomly accepted placebo, fluvastatin 40 mg/day, valsartan 80 mg/day, or both for 1 week. Then a high-fat meal and assay of plasma samples were repeated. The postprandial plasma triglyceride, soluble P-selectin, PAI-1, and t-PA antigen concentrations significantly increased after a high-fat meal. Postprandial plasma concentration of triglyceride was significantly correlated with that of soluble P-selectin and PAI-1 antigen, respectively (P<0.001). The postprandial increase in plasma P-selectin, PAI-1, and t-PA antigen levels was attenuated by 1-week fluvastatin-alone and valsartan-alone treatments; their combination is more effective on both fasting and postprandial P-selectin, plasma PAI-1, and t-PA antigen levels. The improvement of these plasma variables was not significantly related to the changes of plasma lipids and blood pressure. In conclusion, postprandial hypertriglyceridemia induces postprandial fibrinolytic dysfunction and vascular inflammation in patients with essential hypertension after a high-fat meal. Short-term combined treatment with fluvastatin and valsartan more effectively inhibits this postprandial atherogenic change in plasma than monotherapy.

The in vitro effects of a novel vascular protectant, AGI-1067, on platelet aggregation and major receptor expression in subjects with multiple risk factors for vascular disease

Oxidation-sensitive signals are important in platelet activation. The novel, phenolic, intracellular and extra-cellular antioxidant AGI-1067 inhibits the expression of a number of proinflammatory genes involved in atherosclerosis. The effect of AGI-1067 on human platelets was evaluated. Blood obtained from 20 aspirin-naïve volunteers with multiple risk factors for vascular disease was preincubated with escalating concentrations of AGI-1067 for the assessment of its ex vivo effects on platelet aggregation and expression of major surface receptors flow cytometry, evaluated by flow cytometry. AGI-1067 resulted in significant inhibition of a variety of activation-dependent platelet biomarkers in healthy volunteers, including adenosine diphosphate-induced platelet aggregation and decreased surface platelet expression of glycoprotein IIb/IIIa antigen, activity with PAC-1 antibody, and glycoprotein Ib (CD42b). The effect of AGI-1067 differs from other known antiplatelet agents, suggesting opportunities for therapeutic combination. These data need to be confirmed in subjects receiving orally dosed AGI-1067 to be clinically relevant.

Platelet inhibition beyond conventional antiplatelet agents: expanding role of angiotensin receptor blockers, statins and selective serotonin reuptake inhibitors

Aspirin, dipyridamole, cilostazol, thienopyridines and glycoprotein IIb/IIIa inhibitors represent the classical examples of the established antiplatelet agents commonly used for the secondary prevention in patients after vascular events. Obviously, the era of expanding antiplatelet regimens and indications may require new agents as the substitutes, or additions to the available strategies. However, recent results of the majority of antiplatelet trials strongly suggest boarder line advantages in clinical outcomes, and higher associated bleeding risks with the novel antiplatelet agents or/and regimens. Moreover, unexpected failures, such as lack of efficacy of clopidogrel and aspirin combination for ischaemic stroke prevention (MATCH), or use of the same antiplatelet regimen for the primary vascular prevention (CHARISMA) raise legitimate concerns that the concept 'the more the better' may not be valid. Broad use of statins, angiotensin receptor blockers and selective serotonin reuptake inhibitors may be in part responsible for the lack of impressive results with the antiplatelet therapy because each of these drug classes per se inhibits platelets. In this review, we discuss the available evidence and potential clinical significance of these findings.

Angiotensin II type 1 receptors and the intestinal microvascular dysfunction induced by ischemia and reperfusion

The acute phase of intestinal ischemia-reperfusion (I/R) injury is mediated by leukocytes and is characterized by oxidative stress and blood cell recruitment. Upregulation of angiotensin II type 1 receptors (AT1-R) has been implicated in the pathogenesis of conditions associated with oxidative stress. The AT1-R-antagonist Losartan (Los) attenuates leukocyte recruitment following I/R. However, the role of AT1-R in intestinal I/R injury and the associated platelet-leukocyte interactions remains unclear. The objective of this study was to define the contribution of AT1-R to I/R-induced blood cell recruitment in intestinal venules. Leukocyte and platelet adhesion were quantified by intravital microscopy in the small bowel of C57Bl/6 [wild-type (WT)] mice exposed to sham operation or 45 min of ischemia and 4 h of reperfusion. A separate WT group received Los for 7 days before gut I/R (WT-I/R + Los). AT1-R bone marrow chimeras that express AT1-R on the vessel wall but not blood cells also underwent I/R. Platelet and leukocyte adhesion as well as AT1-R expression in the gut microvasculature were significantly elevated after I/R. All of these responses were attenuated in the WT-I/R + Los group, compared with untreated I/R mice. A comparable abrogation of I/R-induced blood cell adhesion was noted in AT1-R bone marrow chimeras. I/R-induced platelet adhesion was unaltered in mice overexpressing Cu,Zn-SOD or mice deficient in NAD(P)H oxidase. These data suggest that although gut I/R upregulates endothelial expression of AT1-R, engagement of these angiotensin II receptors on blood cells is more important in eliciting the prothrombogenic and proinflammatory state observed in postischemic gut venules, through a superoxide-independent pathway.

The action of dipyridamole to prevent thrombosis: practical implications for the treatment and prevention of stroke

Aggrenox (Boehringer Ingelheim, Ingelheim, Germany), a novel combination of low-dose aspirin with dipyridamole, represents a safe and promising combination alternative for mild but sustained platelet inhibition, and reduction of both arterial and venous thrombi occurrences. In a large, well-controlled randomized trial (ESPS-2 ) evaluating antiplatelet agents for stroke prevention, Aggrenox was twice as effective as monotherapy with either aspirin or dipyridamole. There is an increasing body of evidence that a delicate strategy with Aggrenox provides modest inhibition of platelet activity, especially in a chronic, long-term setting. Mild platelet inhibition beyond conventional aggregation may represent a substantial advantage over aggressive antiplatelet regimens for the treatment, and especially for secondary prevention, of cerebrovascular ischemic events. Although there is no doubt that the concept of inhibiting platelets is vital for the treatment of vascular ischemic disease in general and ischemic stroke and transient ischemic attack (TIA) in particular, the optimal degree of such inhibition still remains an unsolved mystery. It seems that the concepts of "the more, the better" and "one size fits all" may no longer be valid for ideal antiplatelet protection in such high-risk populations. Without routine individual laboratory assessment of platelet function, mild regimens have the advantage of being more suitable for the majority of patients and will contribute substantially to the success of dipyridamole. Conversely, if we can determine baseline platelet status and intelligently apply therapy based on platelet activity in each particular patient, clinical outcomes may be better. Avoiding excessive bleeding risks after aggressive strategies in patients with normal or already decreased platelet function, but targeting those who exhibit activated platelets, may improve risk stratification and save lives. Therefore, Aggrenox should be considered a drug of choice to prevent the second stroke. Eliminating, or at least minimizing, the most frequent side effect, namely transitory headaches at the beginning of therapy with Aggrenox, will benefit patients and increase the use of this agent. Should the PRoFESS (Prevention Regimen For Effectively avoiding Second Strokes) trial show an advantage in event reduction with Aggrenox over clopidogrel, the increase will be especially dramatic. In short, based on current evidence most guidelines include Aggrenox as a first-line option for secondary prevention of ischemic stroke or TIA, and some recent versions suggest it may be preferable in other clinical scenarios.

Escitalopram, but not its major metabolites, exhibits antiplatelet activity in humans

BACKGROUND

Clinical depression has been identified as an independent risk factor for increased mortality during follow-up in patients suffered from acute coronary events, whereas increased platelet activity has been proposed as one of the mechanisms for this association. Some evidence suggests that selective serotonin reuptake inhibitors and/or their metabolites exhibit potent antiplatelet properties.

METHODS

We assessed the in vitro effects of preincubation with escalating (50-200 nmol/L) concentrations of escitalopram (ESC) S-desmethyl-citalopram (S-DCT), and S-di-desmethyl-citalopram, (S-DCT) on platelet aggregation through the expression of major surface receptors using flow cytometry and quantitatively using platelet function analyzers in 20 healthy volunteers.

RESULTS

Pretreatment of blood samples with ESC with ESC resulted in a significant inhibition of platelet aggregation induced by ADP (P = 0.0001) and by collagen with the highest dose (P = 0.001). Surface platelet expressions of glycoprotein Ib (CD42) (P = 0.04), lysosome associated membrane protein-3 (CD63) (P = 0.02), and GP37 (CD165) (P = 0.03) was decreased in the ESC-pretreated samples. Closure time by the Platelet Function Analyzer-100 analyzer was prolonged for the 200 nmol/L dose (P = 0.02), indicating platelet inhibition under high shear conditions. Two major metabolites of ESC, namely S-DCT and S-DDCT, did not affect platelet activity.

CONCLUSION

Escitalopram, but not its metabolites, exhibited selective inhibition of human platelet properties. The direct antiplatelet effect of ESC requires further prospective or ex vivo testing to determine the possible clinical advantage of this finding.

Selective serotonin reuptake inhibitors and increased bleeding risk: are we missing something?

PURPOSE

Selective serotonin reuptake inhibitors (SSRIs) are first line agents to treat clinical depression. Although these medications exhibit a favorable safety profile, there are multiple case reports, registries, and uncontrolled studies suggesting that use of SSRIs might be associated in the increased risk of bleeding events. There is also emerging evidence that these side effects of SSRIs are due to blockade of serotonin reuptake in platelets and subsequent platelet dysfunction.

METHODS

The analysis of evidence linking SSRIs with bleeding episodes to define the prevalence, specific clinical characteristics, and estimated risk when SSRIs are used in combination with antiplatelet agents or/and anticoagulants.

RESULTS

There are over 120 MEDLINE-cited peer-reviewed research papers and more than 50000 Web pages devoted to SSRI-related bleeding events.

CONCLUSION

Independently of the brand, use of SSRIs is indeed associated with increased bleeding risk. Although such complications are rare, their frequency is growing, and physicians should be aware of SSRI-induced hemorrhages, especially in patients with hereditary platelet defects, and those treated with antiplatelet agents. Prospective studies are urgently needed to determine whether SSRIs will yield additional bleeding risks when used long term concomitantly with aspirin or clopidogrel.

Dipyridamole Decreases Protease-Activated Receptor and Annexin-V Binding on Platelets of Poststroke Patients with Aspirin Nonresponsiveness

BACKGROUND

Although controversial, the phenomenon of aspirin resistance (AR) has been correlated in some small studies with poor clinical outcomes in patients with coronary artery disease. Even less is known regarding the role of AR in the post stroke population. The reason for and the underlying mechanism of AR is unknown. We hypothesized that excessive formation of thrombin on the platelet surface may contribute to this phenomenon and assessed how dipyridamole affects multiple platelet and thrombin generation biomarkers in AR patients after ischemic stroke.

METHODS

Whole blood samples from 20 post stroke AR patients were pretreated with dipyridamole, simulating the therapeutic range, and then incubated for 45 min at 37 degrees C. Platelet characteristics were assessed by aggregometry, cartridge-based analyzer, and receptor expression by flow cytometry. Markers of thrombin generation were measured in the autologous plasma by ELISA.

RESULTS

Pretreatment of blood with dipyridamole resulted in 22-26% diminished expression of intact PAR-1 receptor (p=0.021 and p=0.024) and 28-31% decrease of annexin V binding (p=0.031 and p=0.02) after incubation with 2 microg/ml and 4 microg/ml of dipyridamole, respectively. Platelet aggregation and thrombin generation markers were not affected in vitro by dipyridamole.

CONCLUSIONS

Dipyridamole may be capable of overcoming increased prothrombinase complex formation and be in part able to compensate for AR in patients with moderate carotid stenosis. This phenomenon may explain the clinical advantages of Aggrenox, known to reduce ischemic events in post stroke patients as proven in clinical trials, though an additional antithrombotic benefit beyond the platelet inhibition by aspirin alone.

Valsartan inhibits platelet activity at different doses in mild to moderate hypertensives: Valsartan Inhibits Platelets (VIP) trial

BACKGROUND

Previous in vitro studies have suggested that valsartan produces significant inhibition of human platelets, probably targeting angiotensin I platelet receptors. To test whether valsartan inhibits platelet activity in mild to moderate hypertensives we conducted the randomized Valsartan Inhibits Platelets (VIP) trial.

METHODS AND RESULTS

Seventy-five patients with mild to moderate hypertension were randomized to valsartan 80 (n = 25), valsartan 160 (n = 29), or valsartan 320 mg/d (n = 21) for 9 weeks. Platelet function was assessed at baseline, week 5, and week 9 by aggregometry, flow cytometry, and cartridge-based analyzer. Independently of dose and duration, valsartan provided early sustained significant inhibition of adenosine diphosphate-induced platelet aggregation, decreased shear-induced activation measured with PFA-100 analyzer, and diminished expression of GP IIb/IIIa activity measured by PAC-1 antibody, GPIb (CD42b), vitronectin receptor (CD51/61), P-selectin (CD62p), lysosome-associated membrane protein (CD107a), and CD40-ligand (CD154). The antiplatelet properties of valsartan were more profound in patients with diabetes (n = 28) when compared with the nondiabetic group (n = 47). In subgroup analyses of patients with diabetes there appeared to be stronger inhibition of the platelet receptors, a significant decrease of adenosine diphosphate- and collagen-induced platelet aggregation, and more profound inhibition of GP IIb/IIIa activity.

CONCLUSIONS

In the randomized VIP trial, valsartan produced sustained inhibition of platelet aggregation and major platelet receptors. The antiplatelet properties of valsartan were not dose or time dependent. In subgroup analyses patients with diabetes with mild to moderate hypertension tended to have greater platelet inhibition, a finding which, if confirmed in future studies suggests possible additional advantages for using valsartan in this high-risk population.

Molecular-specific effects of angiotensin II antagonists: clinical relevance to treating hypertension?

Angiotensin II receptor blockers (ARBs) may produce a number of molecule-specific effects that appear to be independent of interaction with the angiotensin II type 1 (AT1)-receptor. These include antagonism of the thromboxane A2 receptor, inhibition of platelet aggregation, induction of peroxisome proliferator- activated receptor gamma (PPARgamma) activity, and reduction of serum uric acid levels. However, definitive evidence is lacking that these molecule-specific effects give rise to a therapeutic advantage of one ARB over another. Currently, the possibility of a link between a molecule-specific effect of an ARB and an improvement in clinical outcomes is best illustrated by a reduction in serum uric acid levels with losartan. Data from Losartan Intervention For Endpoint reduction in hypertension (LIFE) study suggest a treatment-induced decrease in serum uric acid may contribute to the treatment benefit of a losartan-based versus atenolol-based therapy on the composite endpoint (death, myocardial infarction, or stroke). This finding should prompt further studies to investigate the long-term cardioprotective benefits issue of reducing hyperuricaemia in hypertensive patients.

Do angiotensin II antagonists provide benefits beyond blood pressure reduction?

Hypertension is a powerful risk factor for cardiovascular (CV) morbidity and mortality; therefore, blood pressure (BP) lowering plays a central role in reducing the cardiovascular complications of hypertension, including stroke. Recent outcomes studies--Losartan Intervention For Endpoint reduction in hypertension, Reduction of Endpoints in Non-insulin-dependent Diabetes Mellitus with the Angiotensin II Antagonist Losartan, and the Irbesartan Type 2 Diabetic Nephropathy Trial--suggest that some angiotensin II antagonists are associated with CV and renal effects beyond their ability to lower BP in patients with hypertension or diabetic nephropathy and may play a role in the prevention of new-onset type 2 diabetes. Angiotensin II antagonists are associated with a wide variety of vascular, cardiac, and renal effects, as well as molecule-specific effects independent of those induced by the angiotensin-I receptor. These actions may offer a mechanistic explanation for the outcome benefits observed in patients with hypertension or diabetic nephropathy. Angiotensin-converting enzyme inhibitors and calcium-channel blockers may also have effects that are not completely explained by differences in the antihypertensive response to these agents, but the evidence is less robust. Collectively, these findings suggest that management of patients with hypertension, with or without diabetes or renal disease, should no longer be viewed as simply a matter of correcting elevated BP. Antihypertensive agents that possess CV benefits beyond their BP-reducing effects should be used to prevent the development of end-organ damage.