Quantitative structural assessment of graded receptor agonism.

Ligand-receptor interactions, which are ubiquitous in physiology, are described by theoretical models of receptor pharmacology. Structural evidence for graded efficacy receptor conformations predicted by receptor theory has been limited but is critical to fully validate theoretical models. We applied quantitative structure-function approaches to characterize the effects of structurally similar and structurally diverse agonists on the conformational ensemble of nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ). For all ligands, agonist functional efficacy is correlated to a shift in the conformational ensemble equilibrium from a ground state toward an active state, which is detected by NMR spectroscopy but not observed in crystal structures. For the structurally similar ligands, ligand potency and affinity are also correlated to efficacy and conformation, indicating ligand residence times among related analogs may influence receptor conformation and function. Our results derived from quantitative graded activity-conformation correlations provide experimental evidence and a platform with which to extend and test theoretical models of receptor pharmacology to more accurately describe and predict ligand-dependent receptor activity.

Deciphering PPARγ activation in cardiometabolic syndrome: studies by in silico and in vivo experimental assessment.

Cardiometabolic syndrome (CMetS) is a consolidation of metabolic disorders characterized by insulin resistance, dyslipidemia and hypertension. Curcumin, a natural bioactive compound, has been shown to possess notable anti-oxidant activity and it has also been included as a super natural herb in the super natural herbs database. Most of the beneficial effects of Curcumin are possibly due to activation of the nuclear receptor, peroxisome proliferator-activated receptor gamma (PPARγ). The present study investigates molecular interactions of curcumin with PPARγ protein through molecular docking and molecular dynamics (MD) simulation studies. Further, effect of curcumin on high fat diet induced CMetS was studied in rats along with western blot for PPARγ and nuclear factor-κB (NF-κB) expressions and histopathological studies. Computational studies presented several significant molecular interactions of curcumin including Ser289, His323, His449 and Tyr473 of PPARγ. The in vivo results further confirmed that curcumin was able to ameliorate the abnormal changes and also, increased PPARγ expressions. The results confirm our hypothesis that activation of PPARγ by curcumin possesses the therapeutic potential to ameliorate the altered levels of metabolic changes in rats in the treatment of CMetS. This is the first report of CMetS treatment by curcumin and study of its underlying mechanism through in silico as well as in vivo experiments.

Non-clinical safety evaluation and risk assessment to human of aleglitazar, a dual PPAR α/γ agonist, and its major human metabolite.

The non-clinical safety profile of aleglitazar, a peroxisome proliferator activated receptor alpha/gamma agonist, and its major human metabolite M6 was studied in a complete package consisting of drug metabolism and pharmacokinetics characterization, safety pharmacology, genotoxicity, repeat dose toxicity, reproductive toxicity and carcinogenicity studies. These studies identified the following main targets similar to other PPAR agonists: red blood cell parameters, liver, heart, kidney, ovaries, testes, bone marrow, adipose tissue, and fluid accumulation. Additionally, and in the 12-month monkey study only, an increased incidence of generalized hair loss/thinning was observed in all groups including controls. In the rat carcinogenicity study there was no statistically significant increase in tumors. In the mouse carcinogenicity study, there was an increased incidence of angiomatous tumors and there were three males with gallbladder adenoma. No relevant compound-related effects were observed in safety pharmacology, genotoxicity, and a 28-day immunotoxicity rat study. Effects observed in reproductive toxicity studies were similar to those known for other PPARγ agonists. Separate studies with the human metabolite M6 did not reveal findings that would prevent human dosing. Overall, the results from the non-clinical safety studies conducted with aleglitazar and the human metabolite M6 were considered to support the clinical Phase 3 program.

PPAR agonists stimulate adipogenesis at the expense of osteoblast differentiation while inhibiting osteoclast formation and activity.

Drugs used in the treatment of type 2 diabetes and cardiovascular disease, specifically peroxisome proliferator-activated receptor (PPAR) agonists, have been reported to affect bone cell function and fracture risk. In this study, we assessed the direct effects of PPAR-γ agonists (rosiglitazone and troglitazone), used in the treatment of diabetes, and a PPAR-α agonist (fenofibrate), used to treat hyperlipidaemia, on the function of primary osteoblasts and osteoclasts. Formation of 'trabecular' bone structures by rat calvarial osteoblasts was reduced by up to 85% in cultures treated with rosiglitazone and by 45% in troglitazone-treated or fenofibrate-treated cultures; at the same time, lipid droplet formation was increased by 40-70%. The expression of key osteogenic markers was similarly downregulated in cultures treated with PPAR agonists, whereas adipogenesis markers were upregulated. Formation of osteoclasts in cultures derived from mouse marrow diminished with fenofibrate treatment, whereas both glitazones reduced resorptive activity without affecting osteoclast number. Metformin, although not a PPAR agonist, is also commonly used in the treatment of type 2 diabetes. Here, metformin was found to have no effect on bone cell function. Taken together, these data suggest that PPAR-γ agonists may enhance bone loss via increased adipogenesis at the expense of osteoblast formation. In contrast, PPAR-α agonists may prevent bone loss. Given that the prevalence of diabetes and cardiovascular disease is expected to rise significantly, greater attention may need to be paid to the effects of PPAR agonists on bone homeostasis.

Assessment of cardiac safety for PPARγ agonists in rodent models of heart failure: a translational medicine perspective.

PPARγ-modulators, a class of anti-diabetic drugs as represented by thiazolidinediones (TZD), have been associated with cardiovascular risks in type-2 diabetes in humans but a similar liability has not been demonstrated in preclinical models. This gap between clinical and preclinical observations may reflect the lack of a translational model for cardiac safety assessment because preclinical efficacy for glycemic control for PPARγ-modulators is routinely conducted in animals with diabetic background while drug safety study is performed in young and health animals with little risk of heart failure, in contrast to the complex pathophysiological conditions of patients subjected to the treatment of TZDs. Therefore, some key steps are important to address this translational gap. First, it is essential to use an appropriate translational model that mimics most of human pathophysiology for the assessment of cardiovascular safety for TZDs. Second, it calls for the discovery of a translational biomarker (most likely a collection of biomarkers due to multiple risk factors contributed to the complex disease) to be able to sensitively detect the disease progression and in response to therapy. Specific examples are provided in this review for the use of a rodent model of myocardial infarction-induced heart failure to address the cardiac safety concern in response to chronic treatment of rosiglitazone. Multiple biomarkers, including physiological, biochemical, pharmacogenomic and imaging biomarkers, were applied to assess the cardiovascular risk in this heart failure model. The data and strategic approach are discussed from translational medicine perspectives.

Pioglitazone modulates vascular inflammation in atherosclerotic rabbits noninvasive assessment with FDG-PET-CT and dynamic contrast-enhanced MR imaging.

OBJECTIVES: We sought to determine the antiatherosclerotic properties of pioglitazone using multimethod noninvasive imaging techniques. BACKGROUND: Inflammation is an essential component of vulnerable or high-risk atheromas. Pioglitazone, a peroxisome proliferator-activated receptor-gamma agonist, possesses potent anti-inflammatory properties. We aimed to quantify noninvasively the anti-inflammatory effects of pioglitazone on atheroma using (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET)/computed tomography (CT) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI). METHODS: Atherosclerotic plaques were induced in the aorta of 15 New Zealand white rabbits by a combination of a hyperlipidemic diet and 2 balloon endothelial denudations. Nine rabbits continued the same diet, whereas 6 rabbits received pioglitazone (10 mg/kg orally) in addition to the diet. Twelve animals underwent (18)F-FDG-PET/CT, and 15 animals underwent DCE-MRI at baseline, 1 month, and 3 months after treatment initiation. Concomitantly, serum metabolic parameters were monitored. After imaging was completed, aortic histologic analysis and correlation analysis were performed. RESULTS: The (18)F-FDG-PET/CT imaging detected an increase in average standardized uptake value in the control group (p < 0.01), indicating progressive inflammation, whereas stable standardized uptake values were observed in the treatment group, indicating no progression. The DCE-MRI analysis detected a significant decrease in the area under the curve for the pioglitazone group (p < 0.01). Immunohistologic examination of the aortas demonstrated a significant decrease in macrophage and oxidized phospholipid immunoreactivity in the pioglitazone group (p = 0.04 and p = 0.01, respectively) with respect to control animals, underlining the imaging results. Serum metabolic parameters showed no difference between groups. Strong positive correlations between standardized uptake value and macrophage density and between area under the curve and neovessels were detected (r(2) = 0.86 and p < 0.0001, and r(2) = 0.66 and p = 0.004, respectively). CONCLUSIONS: Both (18)F-FDG-PET/CT and DCE-MRI demonstrate noninvasively the anti-inflammatory effects of pioglitazone on atheroma. Both imaging methods seem suited to monitor inflammation in atherosclerosis.

Assessment of the environmental fate and effects of the PPARgamma receptor agonist, pioglitazone.

The environmental fate and effects of pioglitazone prescribed for the treatment of type 2 diabetes were evaluated in an environmental risk assessment following the European Medicines Agency (EMA) "Guideline on the Environmental Risk Assessment of Medicinal Products for Human Use"; EMEA/CHMP/SWP/4447/00. A predicted environment concentration (PEC) for surface water was estimated at 0.023µgL(-1), (action limit of 0.01µgL(-1)) triggering a comprehensive battery of laboratory evaluations. Pioglitazone and its major metabolites were determined not to significantly adsorb to sewage solids, were not persistent in the aquatic environment, did not bioaccumulate and were non-toxic to aquatic organisms. Pioglitazone does not pose an unacceptable risk to groundwater supplies, with concentrations not anticipated to be a risk to aquatic organisms or human drinking water supplies. Pioglitazone does not pose a risk of secondary poisoning.

Plasma stability-dependent circulation of acyl glucuronide metabolites in humans: how circulating metabolite profiles of muraglitazar and peliglitazar can lead to misleading risk assessment.

Muraglitazar and peliglitazar, two structural analogs differing by a methyl group, are dual peroxisome proliferator-activated receptor-α/γ activators. Both compounds were extensively metabolized in humans through acyl glucuronidation to form 1-O-ß-acyl glucuronide (AG) metabolites as the major drug-related components in bile, representing at least 15 to 16% of the dose after oral administration. Peliglitazar AG was the major circulating metabolite, whereas muraglitazar AG was a very minor circulating metabolite in humans. Peliglitazar AG circulated at lower concentrations in animal species than in humans. Both compounds had a similar glucuronidation rate in UDP-glucuronic acid-fortified human liver microsomal incubations and a similar metabolism rate in human hepatocytes. Muraglitazar AG and peliglitazar AG were chemically synthesized and found to be similarly oxidized through hydroxylation and O-demethylation in NADPH-fortified human liver microsomal incubations. Peliglitazar AG had a greater stability than muraglitazar AG in incubations in buffer, rat, or human plasma (pH 7.4). Incubations of muraglitazar AG or peliglitazar AG in plasma produced more aglycon than acyl migration products compared with incubations in the buffer. These data suggested that the difference in plasma stability, not differences in intrinsic formation, direct excretion, or further oxidation of muraglitazar AG or peliglitazar AG, contributed to the observed difference in the circulation of these AG metabolites in humans. The study demonstrated the difficulty in doing risk assessment based on metabolite exposure in plasma because the more reactive muraglitazar AG would not have triggered a threshold of concern based on the recent U.S. Food and Drug Administration guidance on Metabolites in Safety Testing, whereas the more stable peliglitazar AG would have.

Hepatobiliary disposition of troglitazone and metabolites in rat and human sandwich-cultured hepatocytes: use of Monte Carlo simulations to assess the impact of changes in biliary excretion on troglitazone sulfate accumulation.

This study examined the hepatobiliary disposition of troglitazone (TGZ) and metabolites [TGZ sulfate (TS), TGZ glucuronide (TG), and TGZ quinone (TQ)] over time in rat and human sandwich-cultured hepatocytes (SCH). Cells were incubated with TGZ; samples were analyzed for TGZ and metabolites by liquid chromatography-tandem mass spectrometry. SCH mimicked the disposition of TGZ/metabolites in vivo in rats and humans; TGZ was metabolized primarily to TS and to a lesser extent to TG and TQ. In human SCH, the biliary excretion index (BEI) was negligible for TGZ and TQ, approximately 16% for TS, and approximately 43% for TG over the incubation period; in rat SCH, the BEI for TS and TG was approximately 13 and approximately 41%, respectively. Hepatocyte accumulation of TS was extensive, with intracellular concentrations ranging from 132 to 222 microM in rat SCH; intracellular TGZ concentrations ranged from 7.22 to 47.7 microM. In human SCH, intracellular TS and TGZ concentrations ranged from 136 to 160 microM and from 49.4 to 84.7 microM, respectively. Pharmacokinetic modeling and Monte Carlo simulations were used to evaluate the impact of modulating the biliary excretion rate constant (K(bile)) for TS on TS accumulation in hepatocytes and medium. Simulations demonstrated that intracellular concentrations of TS may increase up to 3.1- and 5.7-fold when biliary excretion of TS was decreased 2- and 10-fold, respectively. It is important to note that altered hepatobiliary transport and the extent of hepatocyte exposure may not always be evident based on medium concentrations (analogous to systemic exposure in vivo). Pharmacokinetic modeling/simulation with data from SCH is a useful approach to examine the impact of altered hepatobiliary transport on hepatocyte accumulation of drug/metabolites.

Assessment of dose proportionality of muraglitazar after repeated oral dosing in rats via a sparse sampling methodology.

Muraglitazar is an alpha/gamma-dual peroxisome proliferator-activated receptor (PPAR) agonist. This study evaluated the single- and multiple-dose oral toxicokinetics of muraglitazar in rats at doses of 3, 30 and 300 mg/kg/day. In total, 15 rats/gender/dose group received muraglitazar every day for 1 month. On both day 1 and day 28, blood samples were obtained at 0.5, 2, 4, 6, 8 and 24 h post-dose, followed by LC/MS analysis. In order to minimize blood loss in the rats, a sparse sampling approach was used to delineate the toxicokinetics. The peak plasma concentration (C(max)) and area under the plasma concentration-time curve (TAUC(0-t)) values for muraglitazar increased in a proportion less than the increment in dose. As the dose increased in the ratio 1:10:100, the C(max) for muraglitazar in male and female rats increased in the ratio of 1:10.3:58.6 and 1:15.3:75.3 on day 1, and 1:5.9:28.1 and 1:13.3:37.3 on day 28, respectively. The corresponding TAUC(0-t) values for males and females were in the ratio of 1:10.2:131 and 1:12.4:131 on day 1, and 1:9.5:93.4 and 1:11.8:94.3 on day 28, respectively. The results indicate that muraglitazar exhibits a dose dependent toxicokinetics in rats and the systemic exposure of muraglitazar was decreased on day 28 compared with day 1.

Muraglitazar (Bristol-Myers Squibb/Merck).

Bristol-Myers Squibb and Merck & Co are co-developing muraglitazar, a dual peroxisome proliferator-activated receptor-alpha/gamma agonist, for the potential treatment of type 2 diabetes and other metabolic disorders. In November 2004, approval was anticipated as early as mid-2005.