Effect of methamphetamine on the pharmacokinetics of dextromethorphan and midazolam in rats

Effect of methamphetamine on clock genes and drug-metabolizing enzyme expression

This study examined the association between clock gene expression and the effect of methamphetamine (MA) on drug-metabolizing enzymes from the perspective of drug metabolism. The relationship between expression of the clock genes BMAL1 and PER2 and the drug-metabolizing enzymes CYP3A4 and CYP2D6 was investigated using livers from autopsy cases of MA-intoxication deaths. Additionally, the effect of MA exposure on various genes was examined in HepG2 human hepatocellular carcinoma cells. Comparisons of the expression of various genes in MA users according to blood MA concentration revealed that CYP3A4 expression was similar to that of PER2, and CYP2D6 expression was similar to that of BMAL1. In cultured cell experiments, BMAL1 and CYP2D6 expression decreased depending on the time elapsed after MA addition, and PER2 and CYP3A4 expression increased slightly in a concentration-dependent manner. These results were consistent with the findings of autopsy examinations. Expression of CYP3A4 and CYP2D6 under BMAL1 and PER2 suppression, but not CYP2D6 under PER2 suppression alone, was upregulated in response to MA. These results suggest that CYPs are regulated via the clock genes BMAL1 and PER2 during MA metabolism.

Methamphetamine deaths: Changing trends and diagnostic issues

The term 'amphetamine' refers to a class of synthetic drugs which includes methamphetamine. The latter is a globally popular drug of abuse which induces euphoria, affecting cognitive/psychomotor performance and sleep. It also provokes risk taking and violent behaviour. The central effects of methamphetamine are due to the overproduction of neurotransmitters, resulting in high levels of dopamine. In recent years, there have been significant increases in cases of methamphetamine abuse in North and South America, Australia and Asia due to its ready availability and low cost. The following review examines changing trends in methamphetamine use and problems that arise diagnostically in medico-legal cases in determining the significance of post-mortem blood levels, the relationship of these to ante-mortem levels, the possible effects on physical and psychological behaviours and the possible contribution of the drug to a lethal episode.

Methamphetamine administration increases hepatic CYP1A2 but not CYP3A activity in female guinea pigs

Methamphetamine use has increased over the past decade and the first use of methamphetamine is most often when women are of reproductive age. Methamphetamine accumulates in the liver; however, little is known about the effect of methamphetamine use on hepatic drug metabolism. Methamphetamine was administered on 3 occassions to female Dunkin Hartley guinea pigs of reproductive age, mimicking recreational drug use. Low doses of test drugs caffeine and midazolam were administered after the third dose of methamphetamine to assess the functional activity of cytochrome P450 1A2 and 3A, respectively. Real-time quantitative polymerase chain reaction was used to quantify the mRNA expression of factors involved in glucocorticoid signalling, inflammation, oxidative stress and drug transporters. This study showed that methamphetamine administration decreased hepatic CYP1A2 mRNA expression, but increased CYP1A2 enzyme activity. Methamphetamine had no effect on CYP3A enzyme activity. In addition, we found that methamphetamine may also result in changes in glucocorticoid bioavailability, as we found a decrease in 11β-hydroxysteroid dehydrogenase 1 mRNA expression, which converts inactive cortisone into active cortisol. This study has shown that methamphetamine administration has the potential to alter drug metabolism via the CYP1A2 metabolic pathway in female guinea pigs. This may have clinical implications for drug dosing in female methamphetamine users of reproductive age.

Concentration-dependent inhibitory effects of baicalin on the metabolism of dextromethorphan, a dual probe of CYP2D and CYP3A, in rats

Baicalin has been shown to possess many pharmacological effects, including antiviral, antioxidant, anti-cancer and anti-inflammatory properties. In the current study, we reveal the inhibitory effects of baicalin on the metabolism of dextromethorphan (DXM), a dual probe substrate of CYP2D and CYP3A, in rats. Lineweaver-Burk plots demonstrated that baicalin inhibited the activities of CYP2D and CYP3A in a non-competitive manner in rat liver microsomes (RLMs). Concomitant administration of baicalin (0.90 g/kg, i.v.) and DXM (10 mg/kg, i.v.) increased the maximum drug concentration (C(max)) (37%) and the area under concentration-time curve (AUC) (42%) and decreased the clearance (CL) (27%) of DXM in a randomised, crossover study in rats (P < 0.01). The change in the AUC of DXM was significantly correlated with the C(max) and AUC of baicalin (P < 0.05). The inhibitory effects of multiple doses of baicalin (0.90 g/kg, i.v., 12 days) on the metabolism of DXM were similar to those observed following a single dose in rats. The activity of CYP3A in excised liver samples from rats following multiple baicalin treatment was significantly decreased compared to that of the control group (P < 0.05), whereas multiple doses of baicalin had no obvious effect on the activity of CYP2D. Taken together, these data demonstrate that baicalin inhibits the metabolism of DXM in a concentration-dependent manner in rats, possibly through inhibiting hepatic CYP2D and CYP3A activities.