The development of drug metabolism research as expressed in the publications of ASPET: Part 3, 1984-2008

The Evolution of Drug Metabolism and Disposition: A Perspective From the Editors

This article was solicited to commemorate the 50th anniversary of Drug Metabolism and Disposition (DMD) and features perspectives from five former editors spanning the years 1994 to 2020. During that time frame the journal underwent significant changes in manuscript submission and processing as well as multiple generational changes in the composition of the editorial board and associate editors. A constant, however, has been the commitment to be the premier journal for publications of articles in the areas of drug metabolism, absorption, distribution, excretion, and pharmacokinetics. Advances in some of those areas during the past 3 decades have been monumental. Two cases in point involve cytochromes P450 and drug transporters. In 1994 rigorous characterization of human cytochrome P450 enzymes was in its infancy, there were no proven selective inhibitors, and the idea of solving a human P450 X-ray crystal structure was just a fantasy. Likewise, little was known about individual drug transporters. Today, detailed knowledge of individual human P450 enzymes and drug transporters is integral in drug design and drug discovery and in avoiding drug interactions. In the face of these huge advances in knowledge, each editor has been charged with maintaining the caliber and significance of the journal and its financial solvency while serving the needs of individual authors. We present 5 individual perspectives on the challenges and rewards of serving as DMD editor and hope that, by humanizing the job, we will encourage others to assume positions of responsibility in publication of society journals. SIGNIFICANCE STATEMENT: The 5 most recent former editors of DMD describe their experiences and perspectives on the position in the context of constantly changing scientific emphases, technology, and publishing practices. The article offers subscribers, authors, and future editors and editorial board members valuable insights into the inner workings of the journal.

New insights on the consequences of biotransformation processes on the distribution and pharmacodynamic profiles of some neuropsychotropic drugs

The metabolic processes frequently trigger highly complex pharmacokinetic (PK) and pharmacodynamic (PD) characteristics for the coexisting entities, parent drug and its active or inactive metabolites. The interpretation of both individual and cumulative profiles, frequently used in the therapeutic drug monitoring procedures, must take into consideration the biological coherence of the changes of the molecular descriptors characterizing the metabolites versus the parent drugs, and further qualitative and quantitative consequences on permeability processes across highly specialized biological barriers (e.g. blood-brain barrier [BBB]). This paper analyzes the correlation of molecular descriptor differences and the PK/PD consequences for three representative psychotropic drugs (risperidone, clozapine and tramadol) and their active metabolites, underlying the safety and efficacy concerns of using the products of metabolic processes as potential new drugs. The minimal structural changes are correlated with the predicted or experimental penetrability across the biological membranes, with a special emphasis on BBB penetration, as the limiting phase for the effect at central nervous system level. The PD characteristics related to the active metabolites are compared to the ones reported for the parent drugs, concerning mainly the affinity for cerebral receptors and the type of activity at a specific level. For the neuropsychotropic substances, with BBB penetrability as a sine qua non condition, the comparative analysis of PK/PD properties for the parent drug and its metabolites generates a complete and highly complex image of the consequences of their coexistence, since these entities must be conceived and analyzed not separately, but by inclusion of usually complementary properties generating a unique therapeutic profile.

Bioactivities of berberine metabolites after transformation through CYP450 isoenzymes

Background

Berberine (BBR) is a drug with multiple effects on cellular energy metabolism. The present study explored answers to the question of which CYP450 (Cytochrome P450) isoenzymes execute the phase-I transformation for BBR, and what are the bioactivities of its metabolites on energy pathways.

Methods

BBR metabolites were detected using LC-MS/MS. Computer-assistant docking technology as well as bioassays with recombinant CYP450s were employed to identify CYP450 isoenzymes responsible for BBR phase-I transformation. Bioactivities of BBR metabolites in liver cells were examined with real time RT-PCR and kinase phosphorylation assay.

Results

In rat experiments, 4 major metabolites of BBR, berberrubine (M1), thalifendine (M2), demethyleneberberine (M3) and jatrorrhizine (M4) were identified in rat's livers using LC-MS/MS (liquid chromatography-tandem mass spectrometry). In the cell-free transformation reactions, M2 and M3 were detectable after incubating BBR with rCYP450s or human liver microsomes; however, M1 and M4 were below detective level. CYP2D6 and CYP1A2 played a major role in transforming BBR into M2; CYP2D6, CYP1A2 and CYP3A4 were for M3 production. The hepatocyte culture showed that BBR was active in enhancing the expression of insulin receptor (InsR) and low-density-lipoprotein receptor (LDLR) mRNA, as well as in activating AMP-activated protein kinase (AMPK). BBR's metabolites, M1-M4, remained to be active in up-regulating InsR expression with a potency reduced by 50-70%; LDLR mRNA was increased only by M1 or M2 (but not M3 and M4) with an activity level 35% or 26% of that of BBR, respectively. Similarly, AMPK-α phosphorylation was enhanced by M1 and M2 only, with a degree less than that of BBR.

Conclusions

Four major BBR metabolites (M1-M4) were identified after phase-I transformation in rat liver. Cell-free reactions showed that CYP2D6, CYP1A2 and CYP3A4 seemed to be the dominant CYP450 isoenzymes transforming BBR into its metabolites M2 and M3. BBR's metabolites remained to be active on BBR's targets (InsR, LDLR, and AMPK) but with reduced potency.