Pharmacogenetics and drug metabolism: historical perspective and appraisal

Should secondary pharmacogenomic variants be actively screened and reported when diagnostic genome-wide sequencing is performed in a child?

This white paper was prepared by the Global Alliance for Genomics and Health Regulatory and Ethics Work Stream's Pediatric Task Team to review and provide perspective with respect to ethical, legal, and social issues regarding the return of secondary pharmacogenomic variants in children who have a serious disease or developmental disorder and are undergoing exome or genome sequencing to identify a genetic cause of their condition. We discuss actively searching for and reporting pharmacogenetic/genomic variants in pediatric patients, different methods of returning secondary pharmacogenomic findings to the patient/parents and/or treating clinicians, maintaining these data in the patient's health record over time, decision supports to assist using pharmacogenetic results in future treatment decisions, and sharing information in public databases to improve the clinical interpretation of pharmacogenetic variants identified in other children. We conclude by presenting a series of points to consider for clinicians and policymakers regarding whether, and under what circumstances, routine screening and return of pharmacogenomic variants unrelated to the indications for testing is appropriate in children who are undergoing genome-wide sequencing to assist in the diagnosis of a suspected genetic disease.

Intestines-erythrocytes-mediated bio-disposition deciphers the hypolipidemic effect of berberine from Rhizoma Coptidis: A neglected insight

ETHNOPHARMACOLOGICAL RELEVANCE

Rhizoma Coptidis (RC), the dried rhizome of Coptis Chinensis Franch., can dispel dampness and heat within the body and has been traditionally used for the treatment of cardiovascular disease (CVD)-associated problems including hyperlipidemia in China. Berberine (BBR) is the main active component of RC, which has been shown to possess significant therapeutic potential. However, only 0.14% of BBR is metabolized in the liver, and the extremely low bioavailability (<1%) and blood concentration of BBR in experimental and clinical settings is insufficient to achieve the effects as observed under in vitro conditions, which imposes challenges to explain its excellent pharmacological actions. Intense efforts are currently being devoted to defining its specific pharmacological molecular targets, while the exploration from the perspective of its pharmacokinetic disposition has rarely been reported to date, which could hardly make a comprehensive understanding of its hypolipidemic enigma.

AIM OF THE STUDY

This study made a pioneering endeavor to unveil the hypolipidemic mechanism of BBR from RC focusing on its unique intestines-erythrocytes-mediated bio-disposition.

MATERIALS AND METHODS

The fate of BBR in intestines and erythrocytes was probed by a rapid and sensitive LC/MS-IT-TOF method. To analyze the disposition of BBR, a reliable HPLC method was subsequently developed and validated for simultaneous determination of BBR and its key active metabolite oxyberberine (OBB) in whole blood, tissues, and excreta. Meanwhile, the enterohepatic circulation (BDC) of BBR and OBB was verified by bile duct catheterization rats. Finally, lipid overloading models of L02 and HepG2 cells were employed to probe the lipid-lowering activity of BBR and OBB at in vivo concentration.

RESULTS

The results showed that BBR underwent biotransformation in both intestines and erythrocytes, and converted into the major metabolite oxyberberine (OBB). The AUC_0-t ratio of total BBR to OBB was approximately 2:1 after oral administration. Besides, the AUC_0-t ratio of bound BBR to its unbound counterpart was 4.6:1, and this ratio of OBB was 2.5:1, indicative of abundant binding-type form in the blood. Liver dominated over other organs in tissue distribution. BBR was excreted in bile, while the excretion of OBB in feces was significantly higher than that in bile. Furthermore, the bimodal phenomenon of both BBR and OBB disappeared in BDC rats and the AUC_0-t was significantly lower than that in the sham-operated control rats. Interestingly, OBB significantly decreased triglycerides and cholesterol levels in lipid overloading models of L02 and HepG2 cells at in vivo-like concentration, which was superior to the prodrug BBR.

CONCLUSIONS

Cumulatively, BBR underwent unique extrahepatic metabolism and disposition into OBB by virtue of intestines and erythrocytes. BBR and OBB were mainly presented and transported in the protein-bound form within the circulating erythrocytes, potentially resulting in hepatocyte targeting accompanied by obvious enterohepatic circulation. The unique extrahepatic disposition of BBR via intestines and erythrocytes conceivably contributed enormously to its hypolipidemic effect. OBB was the important material basis for the hypolipidemic effect of BBR and RC.

Structure-Based Reactivity Profiles of Reactive Metabolites with Glutathione

Therapeutic agents can be transformed into reactive metabolites under the action of various metabolic enzymes in vivo and then covalently combine with biological macromolecules (such as protein or DNA), resulting in increasing toxicity. The screening of reactive metabolites in drug discovery and development stages and monitoring of biotransformation in post-market drugs has become an important research field. Generally, reactive metabolites are electrophilic and can be captured by small nucleophiles. Glutathione (GSH) is a small peptide composed of three amino acids (i.e., glutamic acid, cysteine, and glycine). It has a thiol group which can react with electrophilic groups of reactive metabolic intermediates (such as benzoquinone, N-acetyl-p-benzoquinoneimine, and Michael acceptor) to form a stable binding conjugate. This paper aims to provide a review on structure-based reactivity profiles of reactive metabolites with GSH. Furthermore, this review also reveals the relationship between drugs' molecular structures and reactive metabolic toxicity from the perspective of metabolism, giving a reference for drug design and development.