Centrally administered CYP2D inhibitors increase oral tramadol analgesia in rats

Brain Cytochrome P450: Navigating Neurological Health and Metabolic Regulation

Human cytochrome P450 (CYP) enzymes in the brain represent a crucial frontier in neuroscience, with far-reaching implications for drug detoxification, cellular metabolism, and the progression of neurodegenerative diseases. The brain's complex architecture, composed of interconnected cell types and receptors, drives unique neuronal signaling pathways, modulates enzyme functions, and leads to distinct CYP gene expression and regulation patterns compared to the liver. Despite their relatively low levels of expression, brain CYPs exert significant influence on drug responses, neurotoxin susceptibility, behavior, and neurological disease risk. These enzymes are essential for maintaining brain homeostasis, mediating cholesterol turnover, and synthesizing and metabolizing neurochemicals, neurosteroids, and neurotransmitters. Moreover, they are key participants in oxidative stress responses, neuroprotection, and the regulation of inflammation. In addition to their roles in metabolizing psychotropic drugs, substances of abuse, and endogenous compounds, brain CYPs impact drug efficacy, safety, and resistance, underscoring their importance beyond traditional drug metabolism. Their involvement in critical physiological processes also links them to neuroprotection, with significant implications for the onset and progression of neurodegenerative diseases. Understanding the roles of cerebral CYP enzymes is vital for advancing neuroprotective strategies, personalizing treatments for brain disorders, and developing CNS-targeting therapeutics. This review explores the emerging roles of CYP enzymes, particularly those within the CYP1-3 and CYP46 families, highlighting their functional diversity and the pathological consequences of their dysregulation on neurological health. It also examines the potential of cerebral CYP-based biomarkers to improve the diagnosis and treatment of neurodegenerative disorders, offering new avenues for therapeutic innovation.

Human CYP2D6 varies across the estrous cycle in brains of transgenic mice altering drug response

Cytochrome P450 (CYP) 2Ds are drug metabolizing enzymes found in brain and liver which metabolize numerous centrally acting drugs. Inhibition and induction of CYP2D-mediated metabolism in rodent brain alters brain drug and metabolite concentrations and resulting drug response. In female rats, brain CYP2D metabolism varies across the estrous cycle and with exogenous estrogen, changing brain drug concentrations and response. In this study harmine-induced hypothermia was lower in humanized CYP2D6 transgenic female mice during estrus compared to diestrus. Pretreatment into the cerebral ventricles with propranolol, a selective irreversible inhibitor of human CYP2D6 in brain, increased hypothermia in estrus but not in diestrus. In vivo enzyme activity was higher in brains of transgenic mice in estrus compared to diestrus and was lower after pretreatment with inhibitor in estrus, but not in diestrus. Hepatic activity and plasma harmine concentrations were unaffected by either estrous phase or inhibition of brain CYP2D6. In wild-type female mice, harmine-induced hypothermia was unaffected by either estrous phase or inhibitor pretreatment. Male mice were used as positive controls, where pretreatment with inhibitor increased harmine-induced hypothermia in transgenic but not wild-type, mice. This study provides evidence for female hormone cycle-based regulation of drug metabolism by human CYP2D6 in brain and resulting drug response. This suggests that brain CYP2D6 metabolism may vary, for example, during the menstrual cycle, pregnancy, or menopause, or while taking oral contraceptives or hormone therapy. This variation could contribute to individual differences in response to centrally acting CYP2D6-substrate drugs by altering local brain drug and/or metabolite concentrations.

CYP2D in the brain impacts oral hydrocodone analgesia in vivo

Cytochrome P450 2D (CYP2D) metabolises many centrally-acting substrates including opioids. Hydrocodone, an opioid and CYP2D substrate, is metabolised to hydromorphone, an active metabolite. CYP2D in the brain is active in vivo and can alter drug response however, it is unknown whether metabolism by CYP2D in the brain alters oral hydrocodone induced analgesia. Propranolol, a selective CYP2D mechanism-based inhibitor, or vehicle, was administered into the right cerebral ventricle of male rats, (HAN Wistars, Envigo), 24 h before testing for analgesia from oral hydrocodone (or hydromorphone, a non-CYP2D substrate). Hydrocodone and its CYP2D-mediated metabolites were simultaneously quantified using a novel LC-MS/MS assay. After propranolol vs vehicle pretreatment, there was significantly higher analgesia from oral hydrocodone, and a significantly lower brain CYP2D metabolic ratio (an in vivo phenotype of brain CYP2D activity that was derived from the molar sum of hydromorphone and its metabolites divided by hydrocodone). The brain CYP2D metabolic ratio correlated significantly with analgesia. There was no pretreatment effect on plasma hydrocodone concentrations, elimination rates, or metabolic ratio (an in vivo phenotype for hepatic CYP2D activity). The liver CYP2D metabolic ratio did not correlate with analgesia. Propranolol pretreatment had no impact on analgesia from oral hydromorphone. These data suggest that inhibited CYP2D activity in brain, causing reduced metabolism of brain hydrocodone, resulted in higher analgesia from oral hydrocodone, despite hydrocodone having a lower μ-opioid receptor affinity than hydromorphone. Thus, variation in CYP2D in the brain may be an important source of interindividual differences in response to CYP2D substrates, including oral hydrocodone.

Cytochrome P450 enzymes and metabolism of drugs and neurotoxins within the mammalian brain

Cytochrome P450 enzymes (CYPs) that metabolize xenobiotics are expressed and active in the brain. These CYPs contribute to the metabolism of many centrally acting compounds, including clinically used drugs, drugs of abuse, and neurotoxins. Although CYP levels are lower in the brain than in the liver, they may influence central substrate and metabolite concentrations, which could alter resulting centrally-mediated responses to these compounds. Additionally, xenobiotic metabolizing CYPs are highly variable due to genetic polymorphisms and regulation by endogenous and xenobiotic molecules. In the brain, these CYPs are sensitive to xenobiotic induction. As a result, CYPs in the brain vary widely, including among humans, and this CYP variation may influence central metabolism and resulting response to centrally acting compounds. It has been demonstrated, using experimental manipulation of CYP activity in vivo selectively within the brain, that CYP metabolism in the brain alters central substrate and metabolite concentrations, as well as drug response and neurotoxic effects. This suggests that variability in xenobiotic metabolizing CYPs in the human brain may meaningfully contribute to individual differences in response to, and effects of, centrally acting drugs and neurotoxins. This chapter will provide an overview of CYP expression in the brain, endogenous- and xenobiotic-mediated CYP regulation, and the functional impact of CYP-mediated metabolism of drugs and neurotoxins in the brain, with a focus on experimental approaches in mice, rats, and non-human primates, and a discussion regarding the potential role of xenobiotic metabolizing CYPs in the human brain.

Study on individualized analgesia guided by CYP3A4/5 polymorphisms in perioperative thoracoscopic surgery

OBJECTIVE

To explore the significance of CYP3A4 and CYP3A5 genetic polymorphisms in achieving personalized fentanyl application in patients undergoing thoracoscopic operation.

METHODS

This was a retrospective study. One hundred patients with lung cancer received thoracoscopic surgery operation under the conditions of general anesthesia. According to the results of individualized analgesia guided by CYP3A4/5 polymorphisms, the patients were assigned into three groups: group I (the wild-type homozygote, the induced dosage of fentanyl: 6 µg/kg, the background infusion rate of patient-controlled intravenous analgesia (PCIA): 2 mL/h), group II (the heterozygote, the induced dosage of fentanyl: 5 µg/kg, the background infusion rate of PCIA: 1.5 mL/h), and group III (the mutant homozygote, the induced dosage of fentanyl: 4 µg/kg, the background infusion rate of PCIA: 1 mL/h). The locking-time was 15 min. A visual analog scale (VAS) score less than 3 points suggested effective analgesia. The times of operation and recovery were examined. Surgical plethysmography index (SPI), blood glucose levels, VAS and bruggemann comfort scale (BCS) scores at different time points were recorded, respectively. Total consumption of fentanyl, the effective time of PCIA compression, and the incidence of adverse drug reactions were also recorded.

RESULTS

There were no statistical differences in SPI, blood glucose level, VAS, BCS scores and incidence of adverse reactions among the three groups. In term of intraoperative, postoperative fentanyl doses and the amount of effective PCA, significant differences were found among the groups (P < 0.05).

CONCLUSION

According to the genotype of CYP3A4/CYP3A5, an individualized application of fentanyl is feasible.

Alterations of Cytochrome P450s and UDP-Glucuronosyltransferases in Brain Under Diseases and Their Clinical Significances

Cytochrome P450s (CYPs) and UDP-glucuronosyltransferases (UGTs) are both greatly important metabolic enzymes in various tissues, including brain. Although expressions of brain CYPs and UGTs and their contributions to drug disposition are much less than liver, both CYPs and UGTs also mediate metabolism of endogenous substances including dopamine and serotonin as well as some drugs such as morphine in brain, demonstrating their important roles in maintenance of brain homeostasis or pharmacological activity of drugs. Some diseases such as epilepsy, Parkinson's disease and Alzheimer's disease are often associated with the alterations of CYPs and UGTs in brain, which may be involved in processes of these diseases via disturbing metabolism of endogenous substances or resisting drugs. This article reviewed the alterations of CYPs and UGTs in brain, the effects on endogenous substances and drugs and their clinical significances. Understanding the roles of CYPs and UGTs in brain provides some new strategies for the treatment of central nervous system diseases.