Improved lipid lowering activity of bezafibrate following continuous gastrointestinal administration: pharmacodynamic rationale for sustained release preparation of the drug

Optimizing the Pharmacological Profile of New Bifunctional Antihyperlipidemic/Antioxidant Morpholine Derivatives

Among the causal risk factors directly promoting the development of coronary and peripheral atherosclerosis are reactive oxygen species and elevated low-density lipoprotein plasma levels. We hereby designed new potent squalene synthase (SQS) inhibitors that may simultaneously tackle the oxidative stress induced by lipid peroxidation. Using previously developed morpholine derivatives as a starting point, we conducted extensive structural changes by either substituting or modifying the morpholine ring, aiming at an optimal SQS-antioxidant pharmacological profile. Compounds 2, 3, and 7 emerged as the most potent bifunctional analogues, displaying IC₅₀ values for SQS inhibition of 0.014, 0.16, and 0.51 μΜ, respectively, and further significantly decreasing lipid peroxidation of hepatic microsomal membranes. The aforementioned activities were also confirmed in vivo since the most promising derivative 2 exhibited a remarkable antihyperlipidemic and antioxidant effect. In conclusion, rational drug design accompanied by structure-activity relationship studies led to compounds combining improved antioxidant and antihyperlipidemic activity that may serve as multifunctional agents against atherosclerosis.

Bezafibrate administration improves behavioral deficits and tau pathology in P301S mice

Peroxisome proliferator-activated receptors (PPARs) are ligand-mediated transcription factors, which control both lipid and energy metabolism and inflammation pathways. PPARγ agonists are effective in the treatment of metabolic diseases and, more recently, neurodegenerative diseases, in which they show promising neuroprotective effects. We studied the effects of the pan-PPAR agonist bezafibrate on tau pathology, inflammation, lipid metabolism and behavior in transgenic mice with the P301S human tau mutation, which causes familial frontotemporal lobar degeneration. Bezafibrate treatment significantly decreased tau hyperphosphorylation using AT8 staining and the number of MC1-positive neurons. Bezafibrate treatment also diminished microglial activation and expression of both inducible nitric oxide synthase and cyclooxygenase 2. Additionally, the drug differentially affected the brain and brown fat lipidome of control and P301S mice, preventing lipid vacuoles in brown fat. These effects were associated with behavioral improvement, as evidenced by reduced hyperactivity and disinhibition in the P301S mice. Bezafibrate therefore exerts neuroprotective effects in a mouse model of tauopathy, as shown by decreased tau pathology and behavioral improvement. Since bezafibrate was given to the mice before tau pathology had developed, our data suggest that bezafibrate exerts a preventive effect on both tau pathology and its behavioral consequences. Bezafibrate is therefore a promising agent for the treatment of neurodegenerative diseases associated with tau pathology.

Pharmacokinetic-pharmacodynamic analysis of the glucose-lowering effect of metformin in diabetic rats reveals first-pass pharmacodynamic effect

Metformin, a commonly used antidiabetic drug, exerts its glucose-lowering effect due to metabolic activities at several sites of action (biophases), including liver, intestine, muscle cells, and adipocytes. The relative contribution of the individual biophases to the overall glucose-lowering effect is not known. Thus, the aims of this investigation were to study the influence of mode of drug administration on the kinetics of glucose-lowering action of metformin in diabetic rats and identify the contribution of different sites of action to the overall response. Streptozotocin diabetic rats received metformin in crossover fashion via intraduodenal, intravenous, and intraportal routes as bolus dose or infusion regimens designed to yield similar pharmacokinetic profiles. Metformin plasma concentrations and blood glucose levels were measured following each mode of administration. Despite the similarity in the concentration-time profiles obtained for different routes of metformin administration, intraduodenal administration produced larger response than intraportal metformin infusion, and lowest response was observed following intravenous administration. This finding indicates that a significant "first-pass" pharmacodynamic effect, which occurs in the presystemic sites of action (liver and the gastrointestinal wall), contributes to the overall glucose-lowering response of metformin. We applied a combined pharmacokinetic-pharmacodynamic modeling approach to study the nature of the first-pass pharmacodynamic effect. The observed data were successfully described by a novel integrated indirect response pharmacokinetic-pharmacodynamic model that revealed a correlation between the temporal metformin concentrations that transit the portal vein and through the gut wall rather than with drug concentrations that accumulated in the liver and the intestinal wall.

Preclinical evaluation of pharmacokinetic-pharmacodynamic rationale for oral CR metformin formulation

We examined the pharmacokinetic (PK) and pharmacodynamic (PD) rationales to develop controlled release (CR) formulations of metformin. Unrestrained diabetic rats received the drug as intravenous bolus (i.v.), oral solution (p.o.), intra-duodenal bolus, 4-h infusion, or intra-colonic bolus. In addition, we developed two CR-gastroretentive dosage forms (CR-GRDF) that released the drug over 3 or 6 h (in vitro), and retained in the rats' stomach for 8-10 h. Metformin exhibited flip-flop PK. The colonic absorption was low but sustained and was associated with highly variable glucose-lowering effects, thus providing a PK rationale to develop CR-GRDF. In addition, the glucose-lowering effect was greater following p.o. vs. i.v. administration, despite equivalent AUC, indicating a first pass PD effect, thus, adding a PD rationale to develop metformin CR-GRDF. When administered to the diabetic rats, CR-GRDFs produced bioavailability and extent of glucose-lowering effects that were similar to those of the duodenal infusion and p.o. metformin administration. These findings are attributed to the adsorption of metformin to the intestine that yields slow and prolonged absorption even following p.o. administration of drug solution. The data indicates that unless the CR formulation could significantly extend the absorption period, it is not likely to improve glucose-lowering efficacy.

Pharmacodynamic effects of bezafibrate and niacin combination: implications of the mode of administration

The goal of this investigation was to optimize antilipid therapy by utilizing the combined activity of two lipid-lowering agents, niacin and bezafibrate, and improve their efficacy by targeting them to their presumed presystemic site(s) of action. Thus, continuous duodenal (IGI) administration of the drug combination should augment their efficacy in comparison with intermittent oral treatment. Three hyperlipidemic rat models were studied: Models A and B were based on cholesterol-enriched diets and Model C was based on on acute hyperlipidemia induced by triton injection. Continuous IGI administration of the drug combination [bezafibrate, 30mg/kg/day, and niacin, 40 mg/kg/day for 3 days (Models A and B) or for 18 h (Model C)] produced significantly greater lowering of total cholesterol and triglycerides and elevation of high-density lipoprotein (HDL) cholesterol in comparison with intermittent oral administration of the same doses either given individually or in combination (Models A and B). Similar results were found in Model C for the IGI administration of the drug combination in contrast to oral and also to intravenous infusions. The results indicate that the combination of bezafibrate and niacin produces a significant hypolipidemic response, with major site(s) of action located presystemically. Because a slow-release matrix tablet of the drug combination resulted in a similar magnitude of effect as the IGI administration, the present study provides a pharmacodynamic rationale for the use of a slow-release low-dose niacin-bezafibrate combination.