The effect of clofibrate on glucose tolerance, insulin secretion, triglycerides and fibrinogen in patients with coronary heart disease

Clofibrate inhibits the umami-savory taste of glutamate

In humans, umami taste can increase the palatability of foods rich in the amino acids glutamate and aspartate and the 5'-ribonucleotides IMP and GMP. Umami taste is transduced, in part, by T1R1-T1R3, a heteromeric G-protein coupled receptor. Umami perception is inhibited by sodium lactisole, which binds to the T1R3 subunit in vitro. Lactisole is structurally similar to the fibrate drugs. Clofibric acid, a lipid lowering drug, also binds the T1R3 subunit in vitro. The purpose of this study was to determine whether clofibric acid inhibits the umami taste of glutamate in human subjects. Ten participants rated the umami taste intensity elicited by 20 mM monosodium glutamate (MSG) mixed with varying concentrations of clofibric acid (0 to 16 mM). In addition, fourteen participants rated the effect of 1.4 mM clofibric acid on umami enhancement by 5' ribonucleotides. Participants were instructed to rate perceived intensity using a general Labeled Magnitude Scale (gLMS). Each participant was tested in triplicate. Clofibric acid inhibited umami taste intensity from 20 mM MSG in a dose dependent manner. Whereas MSG neat elicited "moderate" umami taste intensity, the addition of 16 mM clofibric acid elicited only "weak" umami intensity on average, and in some subjects no umami taste was elicited. We further show that 1.4 mM clofibric acid suppressed umami enhancement from GMP, but not from IMP. This study provides in vivo evidence that clofibric acid inhibits glutamate taste perception, presumably via T1R1-T1R3 inhibition, and lends further evidence that the T1R1-T1R3 receptor is the principal umami receptor in humans. T1R receptors are expressed extra-orally throughout the alimentary tract and in regulatory organs and are known to influence glucose and lipid metabolism. Whether clofibric acid as a lipid-lowering drug affects human metabolism, in part, through T1R inhibition warrants further examination.

Lipid-Lowering Pharmaceutical Clofibrate Inhibits Human Sweet Taste

T1R2-T1R3 is a heteromeric receptor that binds sugars, high potency sweeteners, and sweet taste blockers. In rodents, T1R2-T1R3 is largely responsible for transducing sweet taste perception. T1R2-T1R3 is also expressed in non-taste tissues, and a growing body of evidence suggests that it helps regulate glucose and lipid metabolism. It was previously shown that clofibric acid, a blood lipid-lowering drug, binds T1R2-T1R3 and inhibits its activity in vitro The purpose of this study was to determine whether clofibric acid inhibits sweetness perception in humans and is, therefore, a T1R2-T1R3 antagonist in vivo Fourteen participants rated the sweetness intensity of 4 sweeteners (sucrose, sucralose, Na cyclamate, acesulfame K) across a broad range of concentrations. Each sweetener was prepared in solution neat and in mixture with either clofibric acid or lactisole. Clofibric acid inhibited sweetness of every sweetener. Consistent with competitive binding, inhibition by clofibric acid was diminished with increasing sweetener concentration. This study provides in vivo evidence that the lipid-lowering drug clofibric acid inhibits sweetness perception and is, therefore, a T1R carbohydrate receptor inhibitor. Our results are consistent with previous in vitro findings. Given that T1R2-T1R3 may in part regulate glucose and lipid metabolism, future studies should investigate the metabolic effects of T1R inhibition.

Integrated physiology and systems biology of PPARα

The Peroxisome Proliferator Activated Receptor alpha (PPARα) is a transcription factor that plays a major role in metabolic regulation. This review addresses the functional role of PPARα in intermediary metabolism and provides a detailed overview of metabolic genes targeted by PPARα, with a focus on liver. A distinction is made between the impact of PPARα on metabolism upon physiological, pharmacological, and nutritional activation. Low and high throughput gene expression analyses have allowed the creation of a comprehensive map illustrating the role of PPARα as master regulator of lipid metabolism via regulation of numerous genes. The map puts PPARα at the center of a regulatory hub impacting fatty acid uptake, fatty acid activation, intracellular fatty acid binding, mitochondrial and peroxisomal fatty acid oxidation, ketogenesis, triglyceride turnover, lipid droplet biology, gluconeogenesis, and bile synthesis/secretion. In addition, PPARα governs the expression of several secreted proteins that exert local and endocrine functions.

Changes in triglyceride levels over time and risk of type 2 diabetes in young men

OBJECTIVE

The association between changes in triglyceride concentrations over time and diabetes is unknown. We assessed whether two triglyceride determinations obtained 5 years apart can predict incident type 2 diabetes.

RESEARCH DESIGN AND METHODS

Triglyceride levels at baseline (time 1) and 5 years later (time 2), followed by subsequent follow-up of 5.5 years, were measured in 13,953 apparently healthy men (age 26-45 years) with triglycerides <300 mg/dl (<3.39 mmol/l).

RESULTS

During 76,742 person-years, 322 cases of diabetes occurred. A multivariate model adjusted for age, BMI, total cholesterol-to-HDL cholesterol ratio, family history of diabetes, fasting glucose, blood pressure, physical activity, and smoking status revealed a continuous independent rise in incident diabetes with increasing time 1 triglyceride levels (P(trend) < 0.001). Men in the lowest tertile of time 1 triglyceride levels who progressed to the highest tertile over follow-up (low-high) exhibited a hazard ratio (HR) of 12.62 (95% CI 3.52-31.34) compared with those remaining in the lowest tertile at both time points (reference group: low-low). Whereas men who were at the top triglyceride level tertile throughout follow-up (high-high) had a HR for diabetes of 7.08 (2.52-14.45), those whose triglyceride level decreased to the lowest tertile (high-low) exhibited a HR of 1.97 (0.67-6.13). Alterations in triglyceride levels during follow-up were associated with changes in BMI, physical activity, and eating breakfast habit (P < 0.05), but remained an independent modifier of diabetes risk even after adjustment for such changes.

CONCLUSIONS

Two measurements of fasting triglyceride levels obtained 5 years apart can assist in identifying apparently healthy young men at increased risk for diabetes, independent of traditional risk factors and of associated changes in BMI and lifestyle parameters.

Fibrinogen, blood viscosity, and cerebral ischemia

This study examines the effect of fibrinogen and consequent blood viscosity reduction on cerebral blood flow and cellular injury following severe cerebral ischemia for 30 minutes in 78 Wistar rats. In half of these rats 10 to 15 cc's of blood was removed and replaced with a mixture of 5% albumin and autologous red blood cells maintaining a constant hematocrit but resulting in a 30% decrease in fibrinogen and corresponding reduction in viscosity. Fibrinogen reduction in a slight increase in baseline CBF and the elimination of post-ischemic hyperemia at 24 hours. Both study and control animals showed a similar decrease in CBF at 30 minutes and 2 hours. There was no significant difference in the severity of ischemic cellular change between the fibrinogen reduction group and controls, although there was a significant inverse relationship between the amount of viscosity change and severity of cellular injury within the treatment group. Fibrinogen reduction alone cannot significantly ameliorate ischemic injury in this model. Viscosity reduction therapy should include reduction of hematocrit and alteration of red cell deformability.

Clofibrate and diabetes control in patients treated with oral hypoglycaemic agents

1. Twenty-two maturity-onset type diabetics treated with oral hypoglycaemic agents entered a single-blind crossover study using placebo (periods A and C, 2 months each) and clofibrate (2 g/day; period B; 2 months). 2. In thirteen patients, under reasonably good control, clofibrate did not reduce fasting or post-prandial blood glucose, nor 24 h glycosuria; no improvement was noted in the M-value, an index of diabetes control. 3. In contrast, in nine patients, with poor diabetes control, clofibrate reduced 24 h glycosuria and significantly improved the M-value. 4. In all patients, clofibrate therapy was associated with a significant 19-23% reduction in plasma fibrinogen. 5. It is suggested that addition of clofibrate may be useful in maturity-onset diabetics not adequately controlled by diet combined with oral hypoglycaemic agents.

The effect of bezafibrate on the fibrinolytic enzyme system and the drug interaction with racemic phenprocoumon

The influence of a new hypolipidaemic agent, bezafibrate, on anticoagulant requirements and fibrinolysis was studied in 15 patients with hyperlipidaemia on long-term treatment with racemic phenprocoumon. Our results suggest a dose-dependent augmentation of the anticoagulant response to the coumarin drug. Treatment with bezafibrate at 450 and 600 mg daily required a reduction of the phenprocoumon dose by 18.5 and 33.5%, respectively. Correspondingly, the serum level of phenprocoumon decreased by 11.6 and 35.3%. No evidence for an altered drug elimination of racemic phenprocoumon could be found during treatment with bezafibrate. The results support the hypothesis that bezafibrate and analogous hypolipidaemic drugs enhance the response to oral anticoagulant drugs by increasing the affinity of the receptor site for coumarins or the rate of degradation of the vitamin-K-dependent clotting factors. The investigation of the fibrinolytic enzyme system demonstrated an increase of the fibrinolytic activity by enhancing the activity of the plasminogen activator. The lysis time for euglobulin clot was reduced significantly, plasma fibrinogen only moderately. The antiplasmin activity could not be altered substantially by a decrease of alpha1-antitrypsin and a slight increase of alpha2-macroglobulin. In contrast with the inhibition of platelet function the effect of bezafibrate on the fibrinolytic enzyme system showed no dose dependence.