Christian Höcht

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.

Intranasal administration of antiretroviral-loaded micelles for anatomical targeting to the brain in HIV

AIM To investigate the intranasal administration of poly(ethylene oxide)-poly(propylene oxide) polymeric micelles loaded with high payloads of the first-line antiretroviral drug efavirenz for targeting to the CNS. METHODS & MATERIALS The effect of micellar size and composition and drug payload was assessed, employing simple micelles made of a highly hydrophilic copolymer, poloxamer F127, loaded with 20 mg/ml drug and mixed micelles containing 75% of a poloxamine of intermediate hydrophobicity, T904, and 25% F127 loaded with 20 and 30 mg/ml drug. F127 confers high physical stability, while T904 substantially improves the encapsulation capacity of the micelles. RESULTS The bioavailability of the drug in the CNS was increased fourfold and the relative exposure index (ratio between the area under the curve in the CNS and plasma) was increased fivefold with respect to the same system administered intravenously. CONCLUSION These findings demonstrate the potential of this scalable and cost-viable strategy to address the HIV sanctuary in the CNS.

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.

Efavirenz is a substrate and in turn modulates the expression of the efflux transporter ABCG2/BCRP in the gastrointestinal tract of the rat.

The oral bioavailability of the antiretroviral efavirenz (EFV) undergoes high inter and intra-individual variability, this fact supporting its therapeutic drug monitoring. Previously, it was demonstrated that the encapsulation of EFV within polymeric micelles increases the oral bioavailability of the drug. The breast cancer resistant protein (BCRP, ABCG2) is known to be inhibited by EFV in vitro. Since ABCG2 is profusely expressed in the gastrointestinal tract, the aim of the present work was to thoroughly investigate whether the intestinal permeability of EFV is modulated by ABCG2. The functional role of ABCG2 in mediating the transport of EFV at the intestinal level was consistent with the following findings: (a) an ABCG2 inhibitor, fumitremorgin C (5-10μM), significantly potentiated the mucosal-to-serosal permeation of the drug in everted gut sacs; (b) a five-day oral treatment with 20mg/kg EFV promotes the over-expression of ABCG2 in about 100%, this phenomenon being accompanied by a clear decline in the intestinal permeability of the antiretroviral and (c) the normalization of the ABCG2 expression within 24h after the last administration of EFV was coincident with the recovery of the ability of the drug to permeate through the small intestine wall. Interestingly, no interactions between EFV and P-glycoprotein (ABCB1) were apparent. Since the intestinal permeability of a drug could be associated with its in vivo absorbability, we suggest that the oral absorption of EFV is affected by modifications in the ABCG2 intestinal expression contributing to the intra-individual bioavailability variations.

Episcleral implants for topotecan delivery to the posterior segment of the eye.

Purpose. Intravenous or periocular topotecan has been proposed as new treatment modality for patients with advanced intraocular retinoblastoma, but systemic topotecan lactone exposure induced by both approaches may cause toxicity. The purpose of this study was to develop a topotecan-loaded ocular delivery system to minimize systemic exposure and achieve selective transscleral penetration. Methods. Biocompatible polymer implants containing low (0.3 mg) or high (2.3 mg) topotecan load were manufactured and characterized in vitro. Adrenaline (500 mug) was coloaded to induce local vasoconstriction in vivo in 2 of 4 animal groups. Implants were inserted into the episclera of rabbits, and topotecan (lactone and total) concentrations in ocular tissues and plasma were determined over a period of 48 hours. Results. In vitro, implants released 30% to 50% of the loaded drug within 48 hours and 45% to 70% by day 10. In vivo, topotecan lactone was highly accumulated in locally exposed ocular tissues (ranging from 10(5) to 10(6) ng/g in sclera and choroid and 10(2) to10(3) ng/g in retina) over 48 hours with all the formulations studied. Low vitreous topotecan lactone levels (approximately 5 ng/mL) were found in animals receiving concomitant local vasoconstriction and high load implants. Topotecan lactone concentrations in plasma and in contralateral eyes were minimal or undetectable as a marker of tissue selectivity of the proposed strategy. Conclusions. These studies may contribute to improving the efficacy and safety of chemotherapy treatments for retinoblastoma and may support the role of the local vasculature and tissues promoting drug clearance and local accumulation during transscleral drug delivery.

A Highly Concentrated and Taste-Improved Aqueous Formulation of Efavirenz for a More Appropriate Pediatric Management of the Anti-HIV Therapy

Pediatric HIV is scarce in developed countries; 90% of pediatric HIV patients are in developing countries. In contrast, children represent 15% of the new infections in poor countries. Approximately 90% of the HIV-positive children do not have access to antiretrovirals (ARVs). Without treatment, 50% of the patients die before the 2 years of age. Efavirenz (EFV, aqueous solubility approximately 4 microg/mL, 40-45% bioavailability), a non-nucleoside reverse transcriptase inhibitor (NNRTI), is a first-choice pediatric ARV. To assure therapeutic plasma concentrations, the low oral bioavailability demands the administration of relatively high EFV doses. Aqueous EFV irritates the oral mucosa, causing a Burning Mouth Syndrome (BMS). A triglyceride-based liquid formulation of EFV (30 mg/mL) is not commercially available worldwide, making the appropriate dose adjustment and the swallowing difficult. More importantly, clinical trials indicated that the oral bioavailability of this oily solution is lower than that of the solid one. Moreover, a relatively high inter-subject variability has been found. The present work reports the development and full characterization of a concentrated (20 mg/mL, 2%) and taste-masked aqueous formulation of EFV for a more appropriate management of the pediatric anti-HIV therapy. Formulations displayed high physicochemical stability over time under regular storage conditions. Release assays in vitro showed a burst effect (2 h) and zero-order kinetics later on (between 2 and 24 h), compatible with the oral administration route and release. Finally, taste tests performed by adult healthy volunteers indicated that the unique combination of flavors and sweeteners employed (i) reduced the intensity of the BMS and (ii) shortened its duration significantly. Overall results indicate that the cost-effective and scalable nanotechnological strategy proposed could enable the more convenient and compliant administration of lower EFV doses. Due to a better pharmacokinetic profile, this would result in similar plasma levels than higher doses administered in solid or triglyceride-soluble form. In this context, some reduction of the treatment cost can be envisioned. This could improve the access of less affluent pediatric patients to medication in poor countries.

Blood Pressure Variability: Prognostic Value and Therapeutic Implications

Blood pressure variability (BPV) is considered nowadays a novel risk factor for cardiovascular disease. Early findings in sinoaortic denervated rats have clearly shown that enhanced fluctuation of blood pressure induced left ventricular hypertrophy, vascular stiffness, and renal lesion. A large number of clinical trials confirm that short-term and long-term blood pressure variability independently contributes to target organ damage, cardiovascular events, and mortality not only in hypertensive patients but also in subjects with diabetes mellitus and chronic kidney disease. Therefore, amelioration of BPV has been suggested as an additional target of the treatment of cardiovascular diseases. Preliminary evidence obtained from meta-analysis and controlled clinical trials has shown that antihypertensive classes differ in their ability to control excessive BP fluctuations with an impact in the prevention of cardiovascular events. Calcium channel blockers seem to be more effective than other blood pressure lowering drugs for the reduction of short-term and long-term BPV. In order to increase actual knowledge regarding the prognostic value and therapeutic significance of BPV in cardiovascular disease, there is a need for additional clinical studies specifically designed for the study of the relevance of short-term and long-term BPV control by antihypertensive drugs.