Carlos A. Taira

Chronic infusion of angiotensin-(1–7) improves insulin resistance and hypertension induced by a high-fructose diet in rats

The current study was undertaken to determine whether Ang-(1-7) is effective in improving metabolic parameters in fructose-fed rats (FFR), a model of metabolic syndrome. Six-week-old male Sprague-Dawley rats were fed either normal rat chow (control) or the same diet plus 10% fructose in drinking water. For the last 2 wk of a 6-wk period of either diet, control and FFR were implanted with subcutaneous osmotic pumps that delivered Ang-(1-7) (100 ng.kg(-1).min(-1)). A subgroup of each group of animals (control or FFR) underwent a sham surgery. We measured systolic blood pressure (SBP) together with plasma levels of insulin, triglycerides, and glucose. A glucose tolerance test (GTT) was performed, with plasma insulin levels determined before and 15 and 120 min after glucose administration. In addition, we evaluated insulin signaling through the IR/IRS-1/PI3K/Akt pathway as well as the phosphorylation levels of IRS-1 at inhibitory site Ser(307) in skeletal muscle and adipose tissue. FFR displayed hypertriglyceridemia, hyperinsulinemia, increased SBP, and an exaggerated release of insulin during a GTT, together with decreased activation of insulin signaling through the IR/IRS-1/PI3K/Akt pathway in skeletal muscle, liver, and adipose tissue, as well as increased levels of IRS-1 phospho-Ser(307) in skeletal muscle and adipose tissue, alterations that correlated with increased activation of the kinases mTOR and JNK. Chronic Ang-(1-7) treatment resulted in normalization of all alterations. These results show that Ang-(1-7) ameliorates insulin resistance in a model of metabolic syndrome via a mechanism that could involve the modulation of insulin signaling.

Efavirenz-loaded polymeric micelles for pediatric anti-HIV pharmacotherapy with significantly higher oral bioavailability

UNLABELLED Children constitute the most challenging population in anti-HIV/AIDS pharmacotherapy. Efavirenz (EFV; aqueous solubility 4 microg/ml, bioavailability 40-45%) is a first-line agent in the pediatric therapeutic cocktail. The liquid formulation of EFV is not available worldwide, preventing appropriate dose adjustment and more convenient administration. The bioavailability of liquid EFV is lower than that of the solid formulation. Improving the bioavailability of the drug would reduce the cost of treatment and enable less affluent patients to access this drug. AIM To encapsulate EFV in polymeric micelles to improve the aqueous solubility and the the oral bioavailability of the drug. METHODS EFV was incorporated into the core of linear and branched poly(ethylene oxide)-poly(propylene oxide) block copolymer micelles. The size and size distribution of the drug-loaded aggregates were characterized by dynamic light scattering and the morphology by transmission electron microscopy. The bioavailability of the EFV-loaded micellar system (20 mg/ml) was assessed in male Wistar rats (40 mg/kg) and compared to that of a suspension prepared with the content of EFV capsules in 1.5% carboxymethylcellulose PBS solution (pH 5.0), and an EFV solution in a medium-chain triglyceride (Miglyol 812). RESULTS This work demonstrates that the encapsulation of EFV, which is poorly water soluble, into polymeric micelles of different poly(ethylene oxide)-poly(propylene oxide) block copolymers significantly improves the oral bioavailability of the drug, and reduces the interindividual variability. CONCLUSION This strategy appears a very promising one towards the development of a liquid aqueous EFV formulation for the improved pediatric HIV pharmacotherapy.

Recent advances in obesity pharmacotherapy.

Obesity is considered a worldwide epidemic. Weight reduction by means of lifestyle changes is difficult to achieve, and pharmacotherapy is frequently needed. Although all currently approved anti-obesity agents have proven to be effective to achieve some degree of weight reduction and improve cardiometabolic risk factors, different compounds differ in their mechanism of action and safety profile. However, it is still difficult to achieve and maintain therapeutic objectives along time. The aim of the present article is to summarize the main characteristics of available anti-obesity agents and to explore novel agents that may provide significant clinical benefits in the future.

Paclitaxel-loaded PCL–TPGS nanoparticles: In vitro and in vivo performance compared with Abraxane®

The purpose of this work was to develop Cremophor(®) EL-free nanoparticles (NPs) loaded with Paclitaxel (PTX) in order to improve the drug i.v. pharmacokinetic profile and to evaluate its activity against commercially available formulations such as Taxol(®) and Abraxane(®). PTX-loaded poly(ε-caprolactone)-alpha tocopheryl polyethylene glycol 1000 succinate (PCL-TPGS) NPs were prepared using three different techniques: (i) by nanoprecipitation (NPr-method), (ii) by emulsion-solvent evaporation homogenized with an Ultra-Turrax(®) (UT-method) and (iii) by emulsion-solvent evaporation homogenized with an ultrasonicator (US-method). The NPs prepared by US-method showed the smallest size and the highest drug content. The NPs exhibited a slow and continuous release of PTX. The in vitro anti-tumoral activity was assessed using two human breast cancer cell lines (MCF-7 and MDA-MB-231) with the WTS assay. Cytotoxicity studies with both cell lines showed that PTX-loaded PCL-TPGS NPs exhibited better anti-cancer activity compared to PTX solution and the commercial formulation Abraxane(®) at different concentrations. Importantly, in the case of triple negative MDA-MB-231 breast cancer cells, the IC50 value for PTX-loaded PCL-TPGS NPs was 7.8 times lower than Abraxane(®). Finally, in vivo studies demonstrated that PTX-loaded PCL-TPGS NPs exhibited longer systemic circulation time and slower plasma elimination rate than Taxol(®) and Abraxane(®). Therefore, the novel NPs investigated might be an alternative nanotechnological platform for PTX delivery system in cancer chemotherapy.

Angiotensin-(1-7) improves cardiac remodeling and inhibits growth-promoting pathways in the heart of fructose-fed rats.

The present study examined whether chronic treatment with angiotensin (ANG)-(1-7) reduces cardiac remodeling and inhibits growth-promoting signaling pathways in the heart of fructose-fed rats (FFR), an animal model of insulin resistance. Sprague-Dawley rats were fed either normal rat chow (control) or the same diet plus 10% fructose in drinking water. For the last 2 wk of a 6-wk period of the corresponding diet, control and FFR were implanted with osmotic pumps that delivered ANG-(1-7) (100 ng.kg(-1).min(-1)). A subgroup of each group of animals (control or FFR) underwent a sham surgery. We determined heart weight, myocyte diameter, interstitial fibrosis, and perivascular collagen type III deposition as well as the phosphorylation degree of ERK1/2, JNK1/2, and p38MAPK. FFR showed a mild hypertension that was significantly reduced after ANG-(1-7) treatment. Also, FFR displayed higher ANG II circulating and local levels in the heart that remained unaltered after chronic ANG-(1-7) infusion. An increased heart-to-body weight ratio, myocyte diameter, as well as left ventricular fibrosis and perivascular collagen type III deposition were detected in the heart of FFR. Interestingly, significant improvements in these cardiac alterations were obtained after ANG-(1-7) treatment. Finally, FFR that received ANG-(1-7) chronically displayed significantly lower phosphorylation levels of ERK1/2, JNK1/2, and p38MAPK. The beneficial effects obtained by ANG-(1-7) were associated with normal values of Src-homology 2-containing protein-tyrosine phosphatase-1 (SHP-1) activity in the heart. In conclusion, chronic ANG-(1-7) treatment ameliorated cardiac hypertrophy and fibrosis and attenuated the growth-promoting pathways in the heart. These findings show an important protective role of ANG-(1-7) in the heart of insulin-resistant rats.

Nimodipine restores the altered hippocampal phenytoin pharmacokinetics in a refractory epileptic model

The present work was undertaken to examine the central pharmacokinetics of phenytoin (PHT) in an experimental model of epilepsy, induced by administration of 3-mercaptopropionic acid (MP), and possible participation of P-glycoprotein in this model of epilepsy. Repeated seizures were induced in male Wistar rats by injection of 3-MP (45 mg kg(-1), i.p.) during 10 days. Control rats (C) were injected with saline solution. In order to monitor extracellular PHT levels, either a shunt microdialysis probe or a concentric probe was inserted into carotid artery or hippocampus, respectively. All animals were administered with PHT (30 mg kg(-1), i.v.) 30 min after intraperitoneal administration of vehicle (V) or nimodipine (NIMO, 2 mg kg(-1)). No differences were found in PHT plasma levels comparing all experimental groups. In pre-treated rats with V, hippocampal PHT concentrations were lower in MP (maximal concentration, C(max): 2.7+/-0.3 microg ml(-1), p<0.05 versus C rats) than in C animals (C(max): 5.3+/-0.9 microg ml(-1)). Control rats pre-treated with NIMO showed similar results (C(max): 4.5+/-0.8 microg ml(-1)) than those pre-treated with V. NIMO pre-treatment of MP rats showed higher PHT concentrations (C(max): 6.8+/-1.0 microg ml(-1), p<0.05) when compared with V pre-treated MP group. Our results indicate that central pharmacokinetics of PHT is altered in MP epileptic rats. The effect of NIMO on hippocampal concentrations of PHT suggests that P-glycoprotein has a role in reduced central bioavailability of PHT in our epileptic refractory model.

The Mas receptor mediates modulation of insulin signaling by angiotensin-(1-7).

Angiotensin (Ang)-(1-7) stimulates proteins belonging to the insulin signaling pathway and ameliorates the Ang II negative effects at this level. However, up to date, receptors involved and mechanisms behind these observations remain unknown. Accordingly, in the present study, we explored the in vivo effects of antagonism of the Ang-(1-7) specific Mas receptor on insulin signal transduction in rat insulin-target tissues. We evaluated the acute modulation of insulin-stimulated phosphorylation of Akt, GSK-3β (Glycogen synthase kinase-3β) and AS160 (Akt substrate of 160kDa) by Ang-(1-7) and/or Ang II in the presence and absence of the selective Mas receptor antagonist A-779 in insulin-target tissues of normal rats. Also using A-779, we determined whether the Mas receptor mediates the improvement of insulin sensitivity exerted by chronic Ang-(1-7) treatment in fructose-fed rats (FFR), a model of insulin resistance, dyslipidemia and mild hypertension. The two major findings of the present work are as follows; 1) Ang-(1-7) attenuates acute Ang II-mediated inhibition of insulin signaling components in normal rats via a Mas receptor-dependent mechanism; and 2). The Mas receptor appears to be involved in beneficial effects of Ang-(1-7) on the phosphorylation of crucial insulin signaling mediators (Akt, GSK-3β and AS160), in liver, skeletal muscle and adipose tissue of FFR. These results shed light into the mechanism by which Ang-(1-7) exerts its positive physiological modulation of insulin actions in classical metabolic tissues and reinforces the central role of Akt in these effects.

Angiotensin-(1-7) inhibits the angiotensin II-enhanced norepinephrine release in coarcted hypertensive rats.

Since it has been suggested that angiotensin (Ang) (1-7) functions as an antihypertensive peptide, we studied its effect on the Ang II-enhanced norepinephrine (NE) release evoked by K+ in hypothalami isolated from aortic coarcted hypertensive (CH) rats. The endogenous NE stores were labeled by incubation of the tissues with 3H-NE during 30 min, and after 90 min of washing, they were incubated in Krebs solution containing 25 mM KCl in the absence or presence of the peptides. Ang-(1-7) not only diminished the K+-evoked NE release from hypothalami of CH rats, but also blocked the Ang II-enhanced NE release induced by K+. Ang-(1-7) blocking action on the Ang II response was prevented by [D-Ala7]Ang-(1-7), an Ang-(1-7) specific antagonist, by PD 123319, an AT2-receptor antagonist, and by Hoe 140, a B2 receptor antagonist. Ang-(1-7) inhibitory effect on the Ang II facilitatory effect on K+-stimulated NE release disappeared in the presence of Nomega-nitro-L-arginine methylester and was restored by L-arginine. Our present results suggest that Ang-(1-7) may contribute to blood pressure regulation by blocking Ang II actions on NE release at the central level. This inhibitory effect is a nitric oxide-mediated mechanism involving AT2 receptors and/or Ang-(1-7) specific receptors and local bradykinin generation.

Involvement of angiotensin-(1-7) in the hypothalamic hypotensive effect of captopril in sinoaortic denervated rats.

The role of anterior hypothalamic angiotensin-(1-7) (Ang-(1-7)) on blood pressure regulation was studied in sinoaortic denervated (SAD) rats. Since angiotensin-converting enzyme inhibitors increase endogenous levels of Ang-(1-7), we addressed the involvement of Ang-(1-7) in the hypotensive effect induced by captopril in SAD rats. Wistar rats 7 days after SAD or sham operation (SO) were anaesthetized and the carotid artery was cannulated for monitoring mean arterial pressure (MAP). A needle was inserted into the anterior hypothalamus for drug administration. Intrahypothalamic administration of Ang-(1-7) (5 pmol) was without effect in SO rats but reduced MAP in SAD rats by 15.5+/-3.2 mm Hg and this effect was blocked by 250 pmol [D-Ala(7)]-Ang-(1-7), a Mas receptor antagonist. Angiotensin II (Ang II) induced an increase in MAP in both groups being the effect greater in SAD rats (DeltaMAP=15.8+/-1.4 mm Hg) than in SO rats (DeltaMAP=9.6+/-1.0 mm Hg). Ang-(1-7) partially abolished the pressor response caused by Ang II in SAD rats. Whilst the captopril intrahypothalamic injection did not affect MAP in SO animals, it significantly reduced MAP in SAD rats (DeltaMAP=-13.3+/-1.9 mm Hg). Either [D-Ala(7)]-Ang-(1-7) or an anti-Ang-(1-7) polyclonal antibody partially blocked the MAP reduction caused by captopril. In conclusion, whilst Ang-(1-7) does not contribute to hypothalamic blood pressure regulation in SO normotensive animals, in SAD rats the heptapeptide induces a reduction of blood pressure mediated by Mas receptor activation. Although Ang-(1-7) is not formed in enough amount in the AHA of SAD animals to exert cardiovascular effects in normal conditions, our results suggest that enhancement of hypothalamic Ang-(1-7) levels by administration of captopril is partially involved in the hypotensive effect of the ACE inhibitor.

Issues in drug metabolism of major antihypertensive drugs: β-blockers, calcium channel antagonists and angiotensin receptor blockers

Several first-line antihypertensive drugs, including calcium channel blockers, β-adrenergic blockers and angiotensin receptor blockers, undergo metabolism through different CYP isoforms. As a consequence of CYP-dependent metabolism, wide interindividual variability of plasma concentrations of antihypertensive drugs has been found in clinical practice compromising blood pressure lowering response and clinical outcomes. Several factors, including aging, hepatic impairment, drug interactions, conditions affecting hepatic blood supply and polymorphisms, contribute to changes in oral and systemic clearance affecting drug exposure during antihypertensive therapy and cardiovascular response. Considering that the degree of blood pressure reduction is related to antihypertensive drug plasma concentrations, a greater knowledge of the sources of pharmacokinetic variability of hepatically eliminated antihypertensive drugs and the applicability of an individualized approach in hypertension management by means of pharmacokinetic/pharmacodynamic modeling and pharmacogenetic testing could enhance blood pressure lowering response to pharmacological therapy. The aim of the present review is to discuss the relevance of drug metabolism in the treatment of hypertension.