Modulators of dyslipidaemia

Nonhuman primates and other animal models in diabetes research

Animal models are important for determining the pathogenesis of and potential treatments for obesity and diabetes. Nonhuman primates (NHPs) are particularly useful for studying these disorders. As in humans, type 2 diabetes mellitus is the most common form of diabetes in NHPs and occurs more often in older obese animals, with a metabolic progression from insulin resistance (IR) and impaired glucose tolerance to overt diabetes. Histopathologic changes in pancreatic islets are also similar to those seen in humans with diabetes. Initially, there is islet hyperplasia with abundant insulin production to compensate for IR, followed by insufficient insulin production with replacement of islets with islet-associated amyloid. Diabetic NHPs also have adverse changes in plasma lipid and lipoprotein concentrations, biomarkers of obesity, inflammation, and oxidative stress, and protein glycation that contribute to the numerous complications of the disease. Furthermore, sex hormones, pregnancy, and environmental factors (e.g., diet and stress) affect IR and can also contribute to diabetes progression in NHPs. Additionally, due to their similar clinical and pathologic characteristics, NHPs have been used in many pharmacological studies to assess new therapeutic agents. For these reasons, NHPs are particularly valuable animal models of obesity and diabetes for studying disease pathogenesis, risk factors, comorbidities, and therapeutic interventions.

A selective peroxisome proliferator-activated receptor alpha agonist, CP-900691, improves plasma lipids, lipoproteins, and glycemic control in diabetic monkeys

Peroxisome proliferator-activated receptors (PPARs) are involved in the regulation of lipid and glucose metabolism. PPARgamma agonists improve insulin sensitivity and hyperglycemia and are effective in treating type 2 diabetes mellitus (T2DM), whereas PPARalpha agonists are used to treat dyslipidemia and atherosclerosis. The goal here was to examine the efficacy of a selective PPARalpha agonist {(S)-3-[3-(1-carboxy-1-methyl-ethoxy)-phenyl]-piperidine-1-carboxylic acid 4-trifluoromethyl-benzyl ester; CP-900691} on lipid, glycemic, and inflammation indices in 14 cynomolgus monkeys with spontaneous T2DM maintained on daily insulin therapy. Monkeys were dosed orally with either vehicle (n = 7) or CP-900691 (3 mg/kg, n = 7) daily for 6 weeks. CP-900691 treatment increased plasma high-density lipoprotein cholesterol (HDLC) (33 +/- 3 to 60 +/- 4 mg/dL, p < 0.001) and apolipoprotein A1 (96 +/- 5 to 157 +/- 5 mg/dL, p < 0.001), reduced plasma triglycerides (547 +/- 102 to 356 +/- 90 mg/dL, p < 0.01), and apolipoprotein B (62 +/- 3 to 45 +/- 3 mg/dL, p < 0.01), improved the lipoprotein index (HDL to non-HDLC ratio; 0.28 +/- 0.06 to 0.79 +/- 0.16, p < 0.001), decreased body weight (p < 0.01) and C-reactive protein (CRP) (1700 +/- 382 to 304 +/- 102 ng/ml, p < 0.01), and increased adiponectin (1697 +/- 542 to 4242 +/- 1070 ng/ml, p < 0.001) compared with baseline. CP-900691 treatment reduced exogenous insulin requirements by approximately 25% (p < 0.04) while lowering plasma fructosamine from 2.87 +/- 0.09 to 2.22 +/- 0.17 mM (p < 0.05), indicative of improved glycemic control. There were no changes in any of the aforementioned parameters in the vehicle group. Because low HDLC and high triglycerides are well established risk factors for cardiovascular disease, the marked improvements in these parameters, and in glycemic control, body weight, and CRP, suggest that CP-900691 may be of benefit in diabetic and obese or hyperlipidemic populations.

Aminopyrrolidineamide inhibitors of site-1 protease

The discovery and efficacy of a series of potent aminopyrrolidineamide-based inhibitors of sterol regulatory element binding protein site-1 protease is described.

Three-dimensional quantitative structure-activity relationship analysis of human CYP51 inhibitors

CYP51 fulfills an essential requirement for all cells, by catalyzing three sequential mono-oxidations within the cholesterol biosynthesis cascade. Inhibition of fungal CYP51 is used as a therapy for treating fungal infections, whereas inhibition of human CYP51 has been considered as a pharmacological approach to treat dyslipidemia and some forms of cancer. To predict the interaction of inhibitors with the active site of human CYP51, a three-dimensional quantitative structure-activity relationship model was constructed. This pharmacophore model of the common structural features of CYP51 inhibitors was built using the program Catalyst from multiple inhibitors (n = 26) of recombinant human CYP51-mediated lanosterol 14alpha-demethylation. The pharmacophore, which consisted of one hydrophobe, one hydrogen bond acceptor, and two ring aromatic features, demonstrated a high correlation between observed and predicted IC(50) values (r = 0.92). Validation of this pharmacophore was performed by predicting the IC(50) of a test set of commercially available (n = 19) and CP-320626-related (n = 48) CYP51 inhibitors. Using predictions below 10 microM as a cutoff indicative of active inhibitors, 16 of 19 commercially available inhibitors (84%) and 38 of 48 CP-320626-related inhibitors (79.2%) were predicted correctly. To better understand how inhibitors fit into the enzyme, potent CYP51 inhibitors were used to build a Cerius(2) receptor surface model representing the volume of the active site. This study has demonstrated the potential for ligand-based computational pharmacophore modeling of human CYP51 and enables a high-throughput screening system for drug discovery and data base mining.

The effect of HMG-CoA reductase inhibitors on chronic allograft rejection

Hydroxy-methyl-glutaryl coenzyme A (HMG-CoA) reductase inhibitors have pleiotropic actions that affect many systems other than lowering blood cholesterol concentrations. Hypercholesterolaemia is an adverse effect of immunosuppressive drug therapy and hence it is a common finding after organ transplantation. HMG-CoA reductase inhibitors lower cholesterol concentrations in transplant recipients but they also offer additional benefits. Since they impair the production of mevalonate, they reduce the concentrations of downstream products including farnesyl and geranyl phosphate. These isoprenoid moieties are required for protein prenylation and HMG-CoA reductase inhibitors impair this function in some cells. This action affects the immune system, especially in patients taking cyclosporin, and has been proposed as the mechanism whereby these drugs increase the half-life of transplanted organs. Other mechanisms have also been proposed including an increase in the free fraction of cyclosporin and a reduction in the time that low density lipoprotein (LDL) spends in blood. The latter effect reduces the extent of oxidation of LDL and hence reduces the damage caused by oxidised LDL. Chronic rejection is poorly understood but appears to involve both immune and non-immune processes. HMG-CoA reductase inhibitors affect both processes. At present, the evidence of benefit from statin prescription is confined to heart and kidney transplant recipients but it is likely that recipients of other organ transplants would also benefit. Drug interactions between cyclosporin and HMG-CoA reductase inhibitors are a limiting factor to their use. Pravastatin appears to be the best HMG-CoA reductase inhibitor for organ transplant recipients because of its lesser potential to interact with cyclosporin and hence cause myositis, which may thus allow higher doses to be used. Other, non-immunosuppressive drugs (including diltiazem and ketoconazole) have been shown to reduce transplant organ damage by unknown mechanisms and are widely prescribed in some transplant centres. More specific inhibitors of protein prenylation may afford useful immunosuppression, thereby prolonging transplant organ half-lives and also reducing the risk of cancer.

Pharmacokinetics, pharmacodynamics, and safety of a lipid-lowering adenosine A1 agonist, RPR749, in healthy subjects

RPR749 and its methylated metabolite are orally active and selective adenosine A(1) agonists that can inhibit lipolysis and lower plasma triglyceride levels in a variety of animal models. RPR749 also appears to lower free fatty acid (FFA) and insulin levels and may have additional lipid-modifying effects. This double-blind, single increasing-dose, placebo-controlled, parallel group, randomized study, the first done in humans, evaluated the safety, pharmacokinetics, and pharmacodynamics (effect on FFA) after a single oral dose of up to 200 mg RPR749 or placebo. Six parallel groups of 8 healthy men (6 active and 2 placebo/group) were enrolled in the study. Plasma samples were collected for up to 72 hours post-dose. RPR749 and its metabolite RPR772 concentrations were measured by a validated LC/MS/MS method with a minimal quantifiable limit of 1 ng/mL. RPR749 was safe and well tolerated as a single oral dose up to 200 mg. The mean plasma concentrations of RPR749 were approximately 30-fold higher than the mean RPR772 plasma concentrations. The mean terminal half-life (t(1/2)) of RPR749 and RPR772 were similar (approximately 16.4 hours). Mean values for serum insulin, triglycerides, glycerol, and blood glucose remained within normal ranges. Mean FFA concentrations in serum decreased in all treatment groups with the maximal decrease in the 200-mg dose group. In conclusion, RPR749 has the ability to reduce circulating levels of FFA that can be related to plasma RPR749 concentrations and thus possesses pharmacological properties that may be beneficial in treating coronary artery diseases and hyperlipidemia.

CP-346086: an MTP inhibitor that lowers plasma cholesterol and triglycerides in experimental animals and in humans

A microsomal triglyceride transfer protein (MTP) inhibitor, CP-346086, was identified that inhibited both human and rodent MTP activity [concentration giving half-maximal inhibition (IC50) 2.0 nM]. In Hep-G2 cells, CP-346086 inhibited apolipoprotein B (apoB) and triglyceride secretion (IC50 2.6 nM) without affecting apoA-I secretion or lipid synthesis. When administered orally to rats or mice, CP-346086 lowered plasma triglycerides [dose giving 30% triglyceride lowering (ED30) 1.3 mg/kg] 2 h after a single dose. Coadministration with Tyloxapol demonstrated that triglyceride lowering was due to inhibition of hepatic and intestinal triglyceride secretion. A 2 week treatment with CP-346086 lowered total, VLDL, and LDL cholesterol and triglycerides dose dependently with 23%, 33%, 75%, and 62% reductions at 10 mg/kg/day. In these animals, MTP inhibition resulted in increased liver and intestinal triglycerides when CP-346086 was administered with food. When dosed away from meals, however, only hepatic triglycerides were increased. When administered as a single oral dose to healthy human volunteers, CP-346086 reduced plasma triglycerides and VLDL cholesterol dose dependently with ED50s of 10 mg and 3 mg, and maximal inhibition (100 mg) of 66% and 87% when measured 4 h after treatment. After a 2 week treatment (30 mg/day), CP-346086 reduced total and LDL cholesterol and triglycerides by 47%, 72%, and 75%, relative to either individual baselines or placebo, with little change in HDL cholesterol. Together, these data support further evaluation of CP-346086 in hyperlipidemia.

F 12511, a novel ACAT inhibitor, and atorvastatin regulate endogenous hypercholesterolemia in a synergistic manner in New Zealand rabbits fed a casein-enriched diet

F 12511, a novel ACAT inhibitor, lowers plasma cholesterol levels in New Zealand rabbits fed a cholesterol-free casein-rich diet. In rabbits endogenous hypercholesterolemia pre-established for 8 weeks was used to compare treatments with F 12511 and atorvastatin for a further 8-week period, and to determine whether both agents act synergistically. F 12511 appears to be 3-4-fold more potent than atorvastatin in reducing total plasma cholesterol (active doses ranging from 0.16 to 2.5 and from 1.25 to 10 mg/kg per day, respectively) while the hypocholesterolemic efficacy of both compounds at 2.5 mg/kg per day amounted to 70 and 45%, respectively. A reduction by as much as 75% of esterified cholesterol in liver mediated by F 12511 could account for the decrease of plasma VLDL, LDL and apo B-100, whereas a reduction of the LDL production rate has been described as the main mechanism underlying the atorvastatin effect. F 12511 modified adrenal cholesterol balance only at the largest dose studied. In a further experiment the co-administration of threshold doses of F 12511 and atorvastatin (0.63 and 1.25 mg/kg per day, respectively) lowered plasma total cholesterol and apo B-100 containing lipoproteins to a greater extent and more rapidly than either agent alone. In the liver a decrease by atorvastatin in free cholesterol substrate for ACAT may amplify the effect of F 12511 on cholesteryl ester content leading to a diminution, in at least an additive manner, of the assembly and secretion of atherogenic lipoproteins in New Zealand rabbits which have developed an endogenous hypercholesterolemia. Thus, the combination of the ACAT inhibitor F 12511 with atorvastatin can represent a better approach than either agent alone to regulate lipoprotein metabolism in certain pathophysiological situations.

Lack of toxic effects of F 12511, a novel potent inhibitor of acyl-coenzyme A: cholesterol O-acyltransferase, on human adrenocortical cells in culture

Inhibition of acyl-coenzyme A: cholesterol O-acyltransferase (EC 2.3.1.26; ACAT) reduces intracellular cholesteryl esters that are substrates for steroidogenesis in adrenal cells. The adrenal side effects of ACAT inhibitors remain a key point for their development as antiatherosclerotic agents. The aim of this study was to characterize the effects of a novel and powerful ACAT inhibitor, F 12511 (S)-2',3',5'-trimethyl-4'-hydroxy-alpha-dodecylthio-phenylacetanilide, on the NCI-H295R cell line, which has functional properties comparable to those of normal human adrenal cells. F 12511 incubated with cultured cells for 4-72 hr strongly inhibited cholesteryl oleate formation. The concentrations required to produce 50% inhibition (IC50) values) ranged from 20 to 50 nM; in the presence of low-density lipoproteins (LDL), this effect was paralleled by a decrease in cholesteryl ester mass and an increase in intracellular free cholesterol. At concentrations 100-fold larger than the IC(50) value for up to 48 hr, F 12511 reduced neither the basal release of cortisol and aldosterone nor the production of cortisol stimulated by forskolin. F 12511 did not modify the mRNA levels of the steroidogenic enzyme genes cytochrome P450 cholesterol side-chain cleavage (P450scc), cytochrome P450 17alpha-hydroxylase (P450c17), or cytochrome P450 21-hydroxylase (P450c21) or those of the LDL receptor and high-density lipoprotein scavenger receptor class B, type I (SR-BI) genes, either in the presence or absence of adenosine 3',5'-cyclic monophosphate stimulation for 24 hr. Exposure to F 12511 at up to 3 microM for 24 or 48 hr did not result in significant change in morphological and ultrastructural characteristics; the cytoplasm contained large numbers of mitochondria with intact crystae, and the same typical features of secretory activity were observed in NCI-H295R control cells. Exposure to 3 microM of F 12511 for 96 hr also did not affect cell viability. These data demonstrate that reduction of the substrate for steroidogenesis by the ACAT inhibitor F 12511 impairs neither steroid production nor transcription of genes involved in steroidogenesis and lipoprotein uptake in the pluripotent human adrenal cell line NCI-H295R.