A Specific Probe Substrate for Evaluation of CYP4A11 Activity in Human Tissue Microsomes and a Highly Selective CYP4A11 Inhibitor: Luciferin-4A and Epalrestat

Ionic Liquid 1-Octyl-3-Methylimidazolium (M8OI) Is Mono-Oxygenated by CYP3A4 and CYP3A5 in Adult Human Liver

Environmental sampling around a landfill site in the UK previously identified the methylimidazolium ionic liquid, 1-octyl-3-methylimidazolium (M8OI), in the soil. More recently, M8OI was shown to be detectable in sera from 5/20 PBC patients and 1/10 controls and to be oxidised on the alkyl chain in the human liver. The objective of this study was to examine the metabolism of M8OI in humans in more detail. In human hepatocytes, M8OI was mono-oxygenated to 1-(8-Hydroxyoctyl)-3-methyl-imidazolium (HO8IM) then further oxidised to 1-(7-carboxyheptyl)-3-methyl-1H-imidazol-3-ium (COOH7IM). The addition of ketoconazole-in contrast to a range of other cytochrome P450 inhibitors-blocked M8OI metabolism, suggesting primarily CYP3A-dependent mono-oxygenation of M8OI. Hepatocytes from one donor produced negligible and low levels of HO8IM and COOH7IM, respectively, on incubation with M8OI, when compared to hepatocytes from other donors. This donor had undetectable levels of CYP3A4 protein and low CYP3A enzyme activity. Transcript expression levels for other adult CYP3A isoforms-CYP3A5 and CYP3A43-suggest that a lack of CYP3A4 accounted primarily for this donor's low rate of M8OI oxidation. Insect cell (supersome) expression of various human CYPs identified CYP3A4 as the most active CYP mediating M8OI mono-oxygenation, followed by CYP3A5. HO8IM and COOH7IM were not toxic to human hepatocytes, in contrast to M8OI, and using a pooled preparation of human hepatocytes from five donors, ketoconazole potentiated M8OI toxicity. These data demonstrate that CYP3A initiates the mono-oxygenation and detoxification of M8OI in adult human livers and that CYP3A4 likely plays a major role in this process.

Effects of acidic non-steroidal anti-inflammatory drugs on human cytochrome P450 4A11 activity: Roles of carboxylic acid and a sulfur atom in potent inhibition by sulindac sulfide

Cytochrome P450 4A11 (CYP4A11) has many endogenous and exogenous compounds containing a carboxyl group in their structure as substrates. If drugs with this characteristic potently attenuate the catalytic function of CYP4A11, drug-drug interactions may occur. Acidic non-steroidal anti-inflammatory drugs (NSAIDs) possess a carboxylic acid in their structure. However, it remains unclear whether these drugs inhibit CYP4A11 activity. The present study examined the inhibitory effects of acidic NSAIDs on CYP4A11 activity using human liver microsomes (HLMs) and recombinant CYP4A11. Sulindac sulfide, ibuprofen, and flurbiprofen effectively decreased the luciferin-4A O-demethylase activity of HLMs and recombinant CYP4A11 (inhibition rates of 30-96% at an inhibitor concentration of 100 μM), while salicylic acid, aspirin, diclofenac, mefenamic acid, indomethacin, etodolac, ketoprofen, loxoprofen, S-naproxen, pranoprofen, zaltoprofen, and oxaprozin exhibited weaker inhibitory activity (inhibition rates up to 23%). Among the drugs tested, sulindac sulfide was the most potent inhibitor of CYP4A11 activity. A kinetic analysis of the inhibition of CYP4A11 by sulindac sulfide revealed mixed-type inhibition for HLMs (Ki = 3.38 μM) and recombinant CYP4A11 (Ki = 4.19 μM). Sulindac sulfide is a pharmacologically active metabolite of sulindac (sulfoxide form), which is also oxidized to sulindac sulfone. To elucidate the role of a sulfur atom of sulindac sulfide in the inhibition of CYP4A11, the inhibitory effects of sulindac sulfide and its oxidized forms on CYP4A11 activity were examined. The potency of inhibition against HLMs was greater in the order of sulindac sulfide, sulindac, and sulindac sulfone; IC50 values were 6.16, 52.7, and 71.6 μM, respectively. The present results indicate that sulindac sulfide is a potent inhibitor of CYP4A11. These results and the molecular modeling of CYP4A11 with sulindac sulfide and its oxidized forms suggest that a sulfur atom of sulindac sulfide as well as its carboxylic acid play important roles in the inhibition of CYP4A11.

Exploring human CYP4 enzymes: Physiological roles, function in diseases and focus on inhibitors

The cytochrome P450 (CYP)4 family of enzymes are monooxygenases responsible for the ω-oxidation of endogenous fatty acids and eicosanoids and play a crucial part in regulating numerous eicosanoid signaling pathways. Recently, CYP4 gained attention as a potential therapeutic target for several human diseases, including cancer, cardiovascular diseases and inflammation. Small-molecule inhibitors of CYP4 could provide promising treatments for these diseases. The aim of the present review is to highlight the advances in the field of CYP4, discussing the physiology and pathology of the CYP4 family and compiling CYP4 inhibitors into groups based on their chemical classes to provide clues for the future discovery of drug candidates targeting CYP4.

Branched and linear fatty acid esters of hydroxy fatty acids (FAHFA) relevant to human health

Fatty acid esters of hydroxy fatty acids (FAHFAs) represent a complex lipid class that contains both signaling mediators and structural components of lipid biofilms in humans. The majority of endogenous FAHFAs share a common chemical architecture, characterized by an estolide bond that links the hydroxy fatty acid (HFA) backbone and the fatty acid (FA). Two structurally and functionally distinct FAHFA superfamilies are recognized based on the position of the estolide bond: omega-FAHFAs and in-chain branched FAHFAs. The existing variety of possible HFAs and FAs combined with the position of the estolide bond generates a vast quantity of unique structures identified in FAHFA families. In this review, we discuss the anti-diabetic and anti-inflammatory effects of branched FAHFAs and the role of omega-FAHFA-derived lipids as surfactants in the tear film lipid layer and dry eye disease. To emphasize potential pharmacological targets, we recapitulate the biosynthesis of the HFA backbone within the superfamilies together with the degradation pathways and the FAHFA regioisomer distribution in human and mouse adipose tissue. We propose a theoretical involvement of cytochrome P450 enzymes in the generation and degradation of saturated HFA backbones and present an overview of small-molecule inhibitors used in FAHFA research. The FAHFA lipid class is huge and largely unexplored. Besides the unknown biological effects of individual FAHFAs, also the enigmatic enzymatic machinery behind their synthesis could provide new therapeutic approaches for inflammatory metabolic or eye diseases. Therefore, understanding the mechanisms of (FA)HFA synthesis at the molecular level should be the next step in FAHFA research.

Cytochrome P450-dependent biotransformation capacities in embryonic, juvenile and adult stages of zebrafish (Danio rerio)-a state-of-the-art review

Given the strong trend to implement zebrafish (Danio rerio) embryos as translational model not only in ecotoxicological, but also toxicological testing strategies, there is an increasing need for a better understanding of their capacity for xenobiotic biotransformation. With respect to the extrapolation of toxicological data from zebrafish embryos to other life stages or even other organisms, qualitative and quantitative differences in biotransformation pathways, above all in cytochrome P450-dependent (CYP) phase I biotransformation, may lead to over- or underestimation of the hazard and risk certain xenobiotic compounds may pose to later developmental stages or other species. This review provides a comprehensive state-of-the-art overview of the scientific knowledge on the development of the CYP1-4 families and corresponding phase I biotransformation and bioactivation capacities in zebrafish. A total of 68 publications dealing with spatiotemporal CYP mRNA expression patterns, activities towards mammalian CYP-probe substrates, bioactivation and detoxification activities, as well as metabolite profiling were analyzed and included in this review. The main results allow for the following conclusions: (1) Extensive work has been done to document mRNA expression of CYP isoforms from earliest embryonic stages of zebrafish, but juvenile and adult zebrafish have been largely neglected so far. (2) There is insufficient understanding of how sex- and developmental stage-related differences in expression levels of certain CYP isoforms may impact biotransformation and bioactivation capacities in the respective sexes and in different developmental stages of zebrafish. (3) Albeit qualitatively often identical, many studies revealed quantitative differences in metabolic activities of zebrafish embryos and later developmental stages. However, the actual relevance of age-related differences on the outcome of toxicological studies still needs to be clarified. (4) With respect to current remaining gaps, there is still an urgent need for further studies systematically assessing metabolic profiles and capacities of CYP isoforms in zebrafish. Given the increasing importance of Adverse Outcome Pathway (AOP) concepts, an improved understanding of CYP capacities appears essential for the interpretation and outcome of (eco)toxicological studies.

A broad-spectrum substrate for the human UDP-glucuronosyltransferases and its use for investigating glucuronidation inhibitors

Strong inhibition of the human UDP-glucuronosyltransferase enzymes (UGTs) may lead to undesirable effects, including hyperbilirubinaemia and drug/herb-drug interactions. Currently, there is no good way to examine the inhibitory effects and specificities of compounds toward all the important human UGTs, side-by-side and under identical conditions. Herein, we report a new, broad-spectrum substrate for human UGTs and its uses in screening and characterizing of UGT inhibitors. Following screening a variety of phenolic compound(s), we have found that methylophiopogonanone A (MOA) can be readily O-glucuronidated by all tested human UGTs, including the typical N-glucuronidating enzymes UGT1A4 and UGT2B10. MOA-O-glucuronidation yielded a single mono-O-glucuronide that was biosynthesized and purified for structural characterization and for constructing an LC-UV based MOA-O-glucuronidation activity assay, which was then used for investigating MOA-O-glucuronidation kinetics in recombinant human UGTs. The derived K_m values were crucial for selecting the most suitable assay conditions for assessing inhibitory potentials and specificity of test compound(s). Furthermore, the inhibitory effects and specificities of four known UGT inhibitors were reinvestigated by using MOA as the substrate for all tested UGTs. Collectively, MOA is a broad-spectrum substrate for the human UGTs, which offers a new and practical tool for assessing inhibitory effects and specificities of UGT inhibitors.

Metabolism of Benzalkonium Chlorides by Human Hepatic Cytochromes P450

Benzalkonium chlorides (BACs) are widely used as disinfectants in cleaning products, medical products, and the food processing industry. Despite a wide range of reported toxicities, limited studies have been conducted on the metabolism of these compounds in animal models and none in human-derived cells or tissues. In this work, we report on the metabolism of BACs in human liver microsomes (HLM) and by recombinant human hepatic cytochrome P450 (CYP) enzymes. BAC metabolism in HLM was NADPH-dependent and displayed apparent half-lives that increased with BAC alkyl chain length (C10 < C12 < C14 < C16), suggesting enhanced metabolic stability of the more lipophilic, longer chain BACs. Metabolites of d7-benzyl labeled BAC substrates retained all deuteriums and there was no evidence of N-dealkylation. Tandem mass spectrometry fragmentation of BAC metabolites confirmed that oxidation occurs on the alkyl chain region. Major metabolites of C10-BAC were identified as ω-hydroxy-, (ω-1)-hydroxy-, (ω, ω-1)-diol-, (ω-1)-ketone-, and ω-carboxylic acid-C10-BAC by liquid chromatography-mass spectrometry comparison with synthetic standards. In a screen of hepatic CYP isoforms, recombinant CYP2D6, CYP4F2, and CYP4F12 consumed substantial quantities of BAC substrates and produced the major microsomal metabolites. The use of potent pan-CYP4 inhibitor HET0016, the specific CYP2D6 inhibitor quinidine, or both confirmed major contributions of CYP4- and CYP2D6-mediated metabolism in the microsomal disappearance of BACs. Kinetic characterization of C10-BAC metabolite formation in HLM demonstrated robust Michaelis-Menten kinetic parameters for ω-hydroxylation (Vmax = 380 pmol/min/mg, Km = 0.69 μM) and (ω-1)-hydroxylation (Vmax = 126 pmol/min/mg, Km = 0.13 μM) reactions. This work illustrates important roles for CYP4-mediated ω-hydroxylation and CYP2D6/CYP4-mediated (ω-1)-hydroxylation during the hepatic elimination of BACs, an environmental contaminant of emerging concern. Furthermore, we demonstrate that CYP-mediated oxidation of C10-BAC mitigates the potent inhibition of cholesterol biosynthesis exhibited by this short-chain BAC.