Biomedical subjects

Yadhu N Singh

Publications and source records attributed to Yadhu N Singh.

5 recordsLinked to original sources

PubMed2005

Potential for interaction of kava and St. John's wort with drugs.

The present interest and widespread use of herbal remedies has created the possibility of interaction between them and pharmaceutical drugs if they are used simultaneously. Before the recent reports of apparent hepatotoxicity associated with its use, kava (Piper methysticum Forst. F.), was one of the top 10 selling herbal remedies in Europe and North America. This adverse effect was not previously encountered with the traditional beverage which was prepared as a water infusion in contrast to the commercial products which are extracted with organic solvents. Kavalactones, the active principles in kava, are potent inhibitors of several of the CYP 450 enzymes, suggesting a high potential for causing pharmacokinetic interactions with drugs and other herbs which are metabolized by the same CYP 450 enzymes. Furthermore, some kavalactones have been shown to possess pharmacological effects, such as blockade of GABA receptors and sodium and calcium ion channels, which may lead to pharmacodynamic interactions with other substances which possess similar pharmacological proprieties. St. John's wort (Hypericum perforatum L.), used extensively for the treatment of mild to moderate clinical depression, has long been considered safer than the conventional pharmaceutical agents. However, its ability, through its active constituents hypericin, pseudohypericin and hyperforin, to induce intestinal P-glycoprotein/MRD1 and both intestinal and hepatic CYP3A4 enzyme, could markedly reduce the distribution and disposition of their co-substrates. In addition, St. John's wort is a potent uptake inhibitor of the neurotransmitters serotonin, norepinephrine and dopamine all of which have a role in mood control. Consequently, the very real potential for a pharmacodynamic interaction between the herb and pharmaceutical drugs which share this mechanism of action and, like St. John's wort, are used for mood elevation. However, presently there is very little evidence to substantiate actual pharmacokinetic and/or pharmacodynamic interaction between drugs and kava or St. John's wort. This review provides a brief overview of the existing data on interactions of kava and St. John's wort with pharmaceutical agents and as a result reveals the urgent need for detailed investigations to identify clinically significant interactions for these herbal remedies that have the potential to cause adverse effects.

Herb-Drug Interactions↗

PubMed2004

Consequences of thyroxine treatment on diaphragm and EDL of normal and dystrophic hamsters.

Previously administration of thyroxine (T4) to dystrophic hamsters improved ventilation and slowed the progression of the disease. We hypothesized that the normalization of ventilation in these animals was due to T4 improving structural and functional characteristics of the diaphragm. In the present study, contractile characteristics of the diaphragm and the extensor digitorum longus (EDL) from normal and dystrophic hamsters were evaluated after two months of T4 treatment. Compared to their placebo-treated counterparts, diaphragms and EDLs of T4-treated normal hamsters showed increased optimal muscle lengths and twitch tension, decreased contraction times and increased fatigability. T4-treatment in dystrophic hamsters showed only an increase in diaphragmatic twitch tension development. Force-frequency curves before treatment were generally higher for the normal compared to dystrophic diaphragms and EDLs. T4 administration only increased the force in normal diaphragms at the lower frequencies and in the EDLs at the higher frequencies. Although T4 serum levels were increased in both T4-treated groups, triiodothyronine (T3) was much lower in the dystrophic compared to normal hamsters, suggesting that conversion of T4 to T3 was reduced in dystrophic hamsters. We conclude that the limited functional changes in the diaphragms of T4-treated dystrophic hamsters cannot account for the marked improvement in ventilation previously reported.

Animals↗

PubMed2004

5'-Deiodinase type 1 activity in liver and brain of the thyroxine-treated dystrophic hamster.

Dystrophic hamsters (DH), as well as dystrophic patients, exhibit alveolar hypoventilation (AH) and low plasma thyroid hormone levels. Thyroxine (T4) treatment of young DH retards AH development, and improves respiratory function and contractility of skeletal muscles. However, the mechanism responsible for the hypothyroidism in DH is not known. One possible cause of the hypothyroidism is reduced activity of the 5'-deiodinase enzyme system, which converts T4 to the more active triiodothyronine (T3). This study tested the above hypothesis by measuring the serum T3 and T4 levels and the activity of the enzyme type 1 5'-deiodinase (D1) in the liver and brain of normal and dystrophic hamsters before, and 8 weeks after, placebo or T4 treatment. There was no significant difference in T4 level between normal and dystrophic hamsters before or after treatment. However, the T4 level was lower in DH before treatment and 8 weeks after placebo and T4 treatment. Both in the liver and brain, D1 activity in DH was depressed compared with normal hamsters. In the liver, T4 supplementation restored enzyme activity to normal level, while in the brain there was no significant difference. The data indicate that the hypothyroidism in DH may be, in part, due to reduced activity of D1 enzyme, which could be partially reversed by T4 treatment.

Animals↗

PubMed2003

Aqueous kava extracts do not affect liver function tests in rats.

Kava ( Piper methysticum Forst. f., Piperaceae), prepared as the traditional aqueous infusion, was tested in the rat for possible effects on liver function tests. Extracts were administered in daily dosages of 200 or 500 mg of the active kavalactones/kg for two or four weeks. Sera were assayed for four enzymes that are markers of liver toxicity and liver homogenates for malondialdehyde formation that indicates changes in lipid peroxidation. The data showed that none of the enzymes, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and lactate dehydrogenase, nor malondialdehyde were elevated, in fact in some cases they were significantly reduced, suggesting the lack of a toxic effect by kava on the liver.

Alanine Transaminase↗

PubMed2002

Therapeutic potential of kava in the treatment of anxiety disorders.

Anxiety disorders are among the most common psychiatric disorders that affect all age groups of the general population. Currently, the preferred treatment is with pharmacological drugs that have antidepressant or anti-anxiety properties. However, these agents have numerous and often serious adverse effects, including sedation, impaired cognition, ataxia, aggression, sexual dysfunction, tolerance and dependence. Withdrawal reactions on termination after long-term administration are also a major limiting factor in the use of these agents. Herbal remedies, including kava (Piper methysticum), have been shown to be effective as alternative treatments, at least in mild to moderate cases of anxiety. Kava is a social and ceremonial herb from the South Pacific. It is available in the west as an over-the-counter preparation. Its biological effects, due to a mixture of compounds called kavalactones, are reported to include sedative, anxiolytic, antistress, analgesic, local anaesthetic, anticonvulsant and neuroprotective properties. The pharmacological properties of kava are postulated to include blockade of voltage-gated sodium ion channels, enhanced ligand binding to gamma-aminobutyric acid (GABA) type A receptors, diminished excitatory neurotransmitter release due to calcium ion channel blockade, reduced neuronal reuptake of noradrenaline (norepinephrine), reversible inhibition of monoamine oxidase B and suppression of the synthesis of the eicosanoid thromboxane A(2), which antagonises GABA(A) receptor function. Clinical studies have shown that kava and kavalactones are effective in the treatment of anxiety at subclinical and clinical levels, anxiety associated with menopause and anxiety due to various medical conditions. Until recently, the adverse effects attributed to kava use were considered mild or negligible, except for the occurrence of a skin lesion. This disorder, called kava dermopathy, occurs only with prolonged use of large amounts of kava and is reversible on reduced intake or cessation. Rare cases of interactions have occurred with pharmaceutical drugs that share one or more mechanisms of action with the kavalactones. In the past few years, about 35 cases of severe liver toxicity associated with kava intake have been reported in Europe and the US. However, a direct causal relationship with kava use has been difficult to establish in the majority of the cases, and there is insufficient evidence to implicate kava as the responsible agent. Nevertheless, until further research clarifies any causality, kava should be used with caution.

Animals↗