STUDIES ON THE ABSORPTION, MECHANISM OF ACTION, AND EXCRETION OF TOLBUTAMIDE IN THE RAT

Lead Optimization Resources in Drug Discovery for Diabetes

BACKGROUND

Diabetes, defined as a chronic metabolic syndrome, exhibits global prevalence and phenomenal rise worldwide. The rising incidence accounts for a global health crisis, demonstrating a profound effect on low and middle-income countries, particularly people with limited healthcare facilities.

METHODS

Highlighting the prevalence of diabetes and its socio-economic implications on the population across the globe, the article aimed to address the emerging significance of computational biology in drug designing and development, pertaining to identification and validation of lead molecules for diabetes treatment.

RESULTS

The drug discovery programs have shifted the focus on in silico prediction strategies minimizing prolonged clinical trials and expenses. Despite technological advances and effective drug therapies, the fight against life-threatening, disabling disease has witnessed multiple challenges. The lead optimization resources in computational biology have transformed the research on the identification and optimization of anti-diabetic lead molecules in drug discovery studies. The QSAR approaches and ADMET/Toxicity parameters provide significant evaluation of prospective "drug-like" molecules from natural sources.

CONCLUSION

The science of computational biology has facilitated the drug discovery and development studies and the available data may be utilized in a rational construction of a drug 'blueprint' for a particular individual based on the genetic organization. The identification of natural products possessing bioactive properties as well as their scientific validation is an emerging prospective approach in antidiabetic drug discovery.

Changes in the dissolution of tolbutamide by a traditional Chinese medicine, Sho-saiko-to (Xiao Chaihu Tang)

Dissolution rate is considered an important factor affecting absorption and efficacy after the oral administration of tolbutamide. Since in many cases traditional Chinese medicines, including Sho-saiko-to (TJ-9, Xiao Chaihu Tang), are taken with other drugs, it is likely that the dissolution and absorption of concomitant drugs in the gastrointestinal tract are influenced by the presence of traditional Chinese medicines. In this study, the effects of TJ-9 on the in vitro dissolution of tolbutamide were examined. We carried out the dissolution test of tolbutamide in the absence or presence of traditional Chinese medicines (Kakkon-to, TJ-1; Hachimi-jio-gan, TJ-7; Chorei-to, TJ-40; Shakuyaku-kanzo-to, TJ-68; TJ-9; Glycyrrhizae Radix, GR; glycyrrhizin, GL) by using a pH 1.2 dissolution medium. Tolbutamide was determined by HPLC assay. The moment parameters, ie., mean dissolution time (MDT), and the dissolution rate constant up to 20 min (kd) were estimated from the dissolution profiles on the basis of the first-order kinetics. Preparations containing GR, namely TJ-1, TJ-9 and TJ-68, significantly reduced the kd and increased the MDT of tolbutamide, while TJ-7 and TJ-40 had no effect on the early dissolution profile of tolbutamide. The extent of decrease in the kd in the presence of TJ-1, TJ-9 and TJ-68 was dependent on their GR contents. Similar inhibitory effects on the dissolution rate of tolbutamide were observed when GR alone was added to the test medium. In addition, GL, a major constituent of GR, induced a 50% increase in MDT and a 30% decrease in kd. The above results indicate that Chinese traditional preparations containing GR have an inhibitory effect on the in vitro dissolution of tolbutamide, which is derived from GL in the preparations.

Effects of sho-saiko-to (xiao chai hu tang), a Chinese traditional medicine, on the gastric function and absorption of tolbutamide in rats

This study was carried out to investigate the effects of Sho-saiko-to (Xiao Chai Hu Tang), a Chinese traditional medicine, on the gastric function including the gastric emptying rate (GER) and intragastric pH in rats. Additionally, the effects of the GER and intragastric pH on tolbutamide absorption after oral administration were examined. The GER measured at 40 min after dosing was reduced to about 70% by the pretreatment of Sho-saiko-to (500 mg/kg). The plasma tolbutamide concentration in the rats treated with a 250 mg/kg dose of Sho-saiko-to was significantly lower than that in the control group. Plasma tolbutamide concentrations increased along with the GER in the group co-administered Sho-saiko-to, and there were significant correlations between the GERs and plasma levels in both time points at 20 and 40 min after administration. In the study using pylorus-ligated rats, Sho-saiko-to significantly elevated the intragastric pH, but induced no change in the concentrations of tolbutamide dissolved in the gastric content. Additionally, Sho-saiko-to did not change the area under the plasma concentration-time curve (AUC) of tolbutamide up to 60 min after administration into the stomach loop, and gastric absorption has been considered to minimally contribute to whole absorption of tolbutamide in the gastrointestinal tract. These results indicate that Sho-saiko-to has an inhibitory effect on the function of gastric emptying in rats. The reduced gastric emptying could affect gastrointestinal absorption, resulting in the lower plasma concentration of tolbutamide after oral administration. Furthermore, it is suggested that Sho-saiko-to can raise the intragastric pH but affect neither the intragastric dissolution nor the gastric absorption of tolbutamide.

A Chinese traditional medicine, sho-saiko-to (xiao-chaihu-tang), reduces the bioavailability of tolbutamide after oral administration in rats

The effects of Sho-saiko-to on the pharmacokinetics of tolbutamide were investigated in rats. After intravenous administration of tolbutamide (5 mg/kg), no significant change in the pharmacokinetics of tolbutamide was observed in both groups of single and multiple (7 days) pre-administration of Sho-saiko-to (500 mg/kg). In the study of single oral administration of tolbutamide (50 mg/kg), co-administration of Sho-saiko-to tended to accelerate the initial absorption rate of tolbutamide. The area under the plasma concentration-time curve of tolbutamide after oral administration was significantly reduced by Sho-saiko-to. Subsequently, a significant decrease was observed in the oral bioavailability of this drug when Sho-saiko-to was given concomitantly. These findings suggest that Sho-saiko-to reduces the bioavailability of tolbutamide after oral administration in rats, and that this change is not related to hepatic metabolism.

JTT-608 restores impaired early insulin secretion in diabetic Goto-Kakizaki rats

1. We investigated the pharmacological effects of a new antidiabetic agent, JTT-608, in comparison with the sulphonylurea tolbutamide, in Goto-Kakizaki (GK) rats, a genetic model of non-obese insulin-dependent diabetes mellitus (NIDDM). 2. In isolated perfused pancreas from GK rats, JTT-608 (200 microM) enhanced 11.1 mM glucose-stimulated insulin secretion in the first and second phases, but had little effect on insulin secretion at 2.8 mM glucose. In contrast, tolbutamide (100 microM) markedly stimulated insulin secretion at 2.8 mM glucose and enhanced the second phase of insulin secretion but not the first phase at 11.1 mM glucose. 3. In vivo JTT-608 also enhanced early insulin secretion only with glucose-loading. In contrast, tolbutamide enhanced insulin secretion both with and without glucose-loading. 4. JTT-608 (10-100 mg kg(-1)) improved oral glucose tolerance with enhanced insulin secretion in a meal tolerance test (MTT). In comparison with tolbutamide, JTT-608 improved glucose tolerance more efficiently in GK rats than in Wistar rats. 5. We conclude that in diabetic GK rats JTT-608 suppressed postprandial glucose excursions with enhanced glucose-stimulated insulin secretion, especially the first phase of insulin secretion.

Simultaneous determinations of tolbutamide and its hydroxy and carboxy metabolites in serum and urine: application to pharmacokinetic studies of tolbutamide in the rat

Methods of analysis of tolbutamide (1) and its hydroxylated (2) and carboxylated (3) metabolites in serum and urine based on high-performance liquid chromatography were developed. The separation was performed on a Apex ODS column in the isocratic mode using a mobile phase composed of 22.5% acetonitrile, 77.5% Sorensen phosphate buffer (pH 7.0), and 0.30 mL of tetrabutylammonium phosphate reagent (Pic A). The compounds were detected at 254 mm. The retention times of 3, 2, 1, and the internal standard chlorpropamide were 3.1, 4.1, 14.8, and 10.0 min, respectively. These conditions were suitable for the simultaneous quantitation of 1, 2, and 3 in serum or plasma samples, but not for the determination of metabolites 2 and 3 in urine. For the analysis of 2 and 3 in urine, the mobile phase was modified to 18% acetonitrile, 82% Sorensen phosphate buffer (pH 7.0), and 0.35 mL of Pic A. Under these conditions, the retention times of the carboxy and hydroxylated metabolites and the internal standard salicylic acid were 4.6, 6.7, and 8.1 min, respectively. These methods were applied to study the pharmacokinetics of 1 administered intravenously and intraperitoneally to the rat. Tolbutamide was almost completely recovered as metabolites 2 and 3 in the urine within 24 h.