Pharmacokinetics of sildenafil and its metabolite, N-desmethylsildenafil, in rats with liver cirrhosis and diabetes mellitus, alone and in combination

Influence of lauric acid on the relaxation of corpus cavernosum in streptozotocin-induced diabetic male Wistar rats

Background

Diabetes mellitus is a global health challenge and has been recognised as a risk factor for erectile dysfunction. Dissatisfaction with standard medications has been reported by some patients, hence therapeutic plants are being considered as a viable alternative therapy, with their active components being investigated to create a standard regimen. Lauric acid is the most abundant constituent of coconut oil and is proposed to be responsible for its therapeutic properties. The corpus cavernosum plays an important role in erectile function with its relaxation favouring erection. This study thus sought to investigate the possible relaxant action and mechanism of lauric acid on the corpus cavernosum of diabetic male Wistar rats. Diabetes was induced by intraperitoneal injection of streptozotocin after which graded doses of lauric acid were administered orally to three groups of diabetic rats, once daily for 4 weeks. At the end of the experiment, the corpus cavernosal tissues of the rat penis were extracted. Following phenylephrine or potassium chloride (KCl)—induced contraction, relaxation response to acetylcholine and sodium nitroprusside was used to evaluate endothelium-dependent and nitric oxide-mediated relaxation, respectively.

Results

Relaxation response to acetylcholine, following pre-contraction with phenylephrine, was significantly decreased in the cavernosal tissues of diabetic untreated rats and was not significantly improved in lauric acid treated diabetic groups. Relaxation response to acetylcholine, following pre-contraction with KCl, was significantly decreased in the diabetic untreated group but was significantly improved in lauric acid treated diabetic groups at the lowest dose. Decreased relaxation response to sodium nitroprusside, following pre-contraction with phenylephrine in tissues of diabetic untreated rats, was significantly improved in lauric acid-treated diabetic groups at lower doses. Decreased relaxation response to sodium nitroprusside, following pre-contraction with KCl, was significantly improved in lauric acid-treated diabetic groups at all doses.

Conclusion

Lauric acid improved relaxation of corpus cavernosum muscle in diabetic male rats by enhancing nitric oxide-mediated relaxing action of sodium nitroprusside and possibly inhibiting KCl-induced contraction.

Structure elucidation of a PDE5 inhibitor detected as an illegal adulteration in a libido-boosting dietary supplement

A compound with potent inhibitory activity for phosphodiesterase type 5 (PDE5) was identified as an illegal adulteration in a libido-boosting dietary supplement being sold at a store in Tokyo. This compound was identified as 5,6-diethyl-2-{5-[(4-methylpiperazin-1-yl)sulphonyl]-2-propoxyphenyl}pyrimidin-4(3H)-one using liquid chromatography-diode array detector (LC-DAD), liquid chromatography-tandem mass spectrometer (LC-MS), LC-HRMS, nuclear magnetic resonance (NMR), and X-ray crystallography. The IC₅₀ value of the inhibitory activity for PDE5A1 (one of the PDE5 isoforms) was 2.0 nM (sildenafil IC₅₀ value was 4.5 nM). This compound was previously synthesised as a PDE5 inhibitor by Shanghai Institute of Materia Medica. The dietary supplement contained 85 mg of this compound in a capsule, which was about 26% of the capsule content (320 mg).

Investigation of the Presence of Sildenafil in Herbal Dietary Supplements by Validated HPLC Method

Objectives

As the first FDA-approved phosphodiesterase type 5 inhibitor, sildenafil (SDF) is widely used in the treatment of erectile dysfunction due to its strong pharmacodynamic activity. Since many food supplements are now involved in illegal adulteration, the presence of SDF in food supplements is very important because of their toxicological risks. In this study a simple fast, reliable high-performance liquid chromatography method with ultraviolet (UV) detector has been developed and validated for SDF analysis in herbal dietary supplements (HDSs).

Materials and Methods

10 mM phosphate buffer containing 0.1% triethylamine (pH 3.5) and acetonitrile (65:35, v/v), as mobile phase was applied isocratically to a reverse phase C₁₈ analytical (4.6×250 mm, 5 μm) column. Chromatographic separation was achieved by a C₁₈ reverse-phase analytical column 4.6×250 mm, 5 μm particle size, using acetonitrile, with 10 mM phosphate buffer containing 0.1% triethylamine (65:35, v/v, pH 3.5) as a mobile phase. The mobile phase flow rate was 1 mL min^-1 and the column temperature was 35°C. The UV detector was set at 293 nm. The liquid-liquid extraction method used in the study provided a simple and practical method for the recovery of SDF in HDSs and their obtained values ranged from 87.6 to 111.7%.

Results

The method showed linearity with an excellent correlation coefficient (r²>0.999). Moreover, it was specific and sensitive with the limit of quantification, 6.5 ng mL^-1. Intraday and interday method precision was ≤8.2 (relative standard deviation %). Intraday and interday method accuracy was between -4.0 and 7.1 (RE%). The method was strong according to the robustness test results obtained from UV detection, mobile phase buffer pH, column temperature, and flow rate changes. The described procedure was simple, fast, precise, and feasible for routine adulteration analysis of SDF, especially in food control or toxicology laboratories. This method was successfully applied to 50 individual solid and liquid form HDSs.

Conclusion

The results showed that 37 out of 50 samples of HDSs (represented 74.0%) examined contained SDF between 0.01 and 465.47 mg/g, 150.87±127.48 (mean ± standard deviation), which could lead to serious health problems and might even be fatal for consumers. The described procedure was found to be simple, rapid, precise and feasible for routine adulteration analysis of SDF, especially in food control or toxicology laboratories.

Pharmacokinetic changes of drugs in a rat model of liver cirrhosis induced by dimethylnitrosamine, alone and in combination with diabetes mellitus induced by streptozotocin

Rats with liver cirrhosis induced by N-dimethylnitrosamine (LC) and rats with LC with diabetes mellitus induced by streptozotocin (LCD) have been developed as animal models for human liver cirrhosis and liver cirrhosis with diabetes mellitus, respectively. Changes in the pharmacokinetics of drugs (mainly non-renal clearance, CLNR) in LC and LCD rats reported in the literature compared with respective control rats were reviewed. This review mainly explains the changes in the CLNRs of drugs (which are mainly metabolized via hepatic microsomal cytochrome P450s, CYPs) in LC and LCD rats, in terms of the changes in in vitro hepatic intrinsic clearance (CLint; mainly due to the changes in CYPs in the disease state), free (unbound) fraction of a drug in the plasma (fp) and hepatic blood flow rate (QH) depending on the hepatic excretion ratio of the drug. Generally, changes in the CLNRs of drugs in LC and LCD rats could be well explained by the above-mentioned three factors. The mechanism of urinary excretion of drugs (such as glomerular filtration or renal active secretion or reabsorption) in LC and LCD rats is also discussed. The pharmacokinetics of the drugs reported in the LC and LCD rats were scarce in humans. Thus, the present rat data should be extrapolated carefully to humans.

Combined contributions of impaired hepatic CYP2C11 and intestinal breast cancer resistance protein activities and expression to increased oral glibenclamide exposure in rats with streptozotocin-induced diabetes mellitus

The purpose of this study was to evaluate the contributions of impaired cytochrome P450 and breast cancer resistance protein (BCRP) activity and expression to drug pharmacokinetics under diabetic conditions. Diabetes was induced in rats with the intraperitoneal administration of streptozocin. Glibenclamide (GLB), a substrate of BCRP, served as a model drug. The pharmacokinetics of orally administered GLB (10 mg/kg) were studied. The results showed that diabetes mellitus significantly increased exposure (area under the curve and peak concentration) to GLB after oral administration. Data from hepatic microsomes suggested impairment of GLB metabolism in diabetic rats. GLB metabolism in hepatic microsomes was significantly inhibited by a selective inhibitor (sulfaphenazole) of CYP2C11 and an anti-CYP2C11 antibody. Western blotting further indicated the contribution of impaired CYP2C11 expression to the impairment of GLB metabolism. Excretion data showed that ∼72% of the orally administered dose was excreted in the feces of normal rats, which indicates an important role for intestinal BCRP. Diabetes significantly decreased the recovery from feces, which was only 40% of the orally administered dose. Results from in situ, single-pass, intestinal perfusion experiments revealed that diabetes significantly increased the apparent effective permeability and decreased the efflux of GLB through the intestine; this suggests impairment of intestinal BCRP function, which may play a role in the increased exposure to orally administered GLB in diabetic rats. Insulin treatment partly or completely reversed the changes in diabetic rats. All results yielded the conclusion that impaired hepatic CYP2C11 and intestinal BCRP expression and activity induced by diabetes contributed to the increased exposure of orally administered GLB.

Development of sildenafil-loaded orally disintegrating tablet with new lactate salt

To develop a sildenafil lactate-loaded orally disintegrating tablet with a faster drug effect onset and immediate action of erection, the orally disintegrating tablets were prepared with various amounts of menthol and colloidal silica using the direct compression technique followed by vacuum drying. Their tablet properties such as friability, hardness, wetting time and disintegration time were investigated. The oral bioavailability of sildenafil in the orally disintegrating tablet was then compared with the sildenafil citrate-loaded commercial tablet (Viagra(®)) in rabbits. Sildenafil lactate was a new salt form with more improved solubility and alleviated bitterness compared with commercial salt, sildenafil citrate. As the amount of menthol in the orally disintegrating tablet increased, the friability increased and hardness decreased, resulting in a shorter wetting time and disintegration time. Colloidal silica did the opposite. The sildenafil lactate-loaded orally disintegrating tablet prepared with 45 mg/tab of menthol and 1.5 mg/tab of colloidal silica gave a hardness of 3-4 KP, friability less than 0.5% and disintegration time less than 30 s, suggesting that it was a practical and commercial product with good tablet property and excellent efficacy. Furthermore, it gave higher AUC and C(max), and shorter T(max) values than did the commercial tablet, indicating that it improved the oral bioavailability of sildenafil in rabbits compared with the commercial tablet. Thus, the sildenafil lactate-loaded orally disintegrating tablet might induce a fast onset of action and immediate erection compared with the sildenafil citrate-loaded commercial tablet.