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Abstract Background Breast cancer (BC) is one of the malignant diseases threatening the life and health of women worldwide. The CYP4B1 gene was abnormally expressed in BC and was associated with the prognosis of BC patients. This study aimed to explore the relationship between CYP4B1 single nucleotide polymorphisms (SNPs) and BC risk in Chinese women. Methods A case-control study of 1,143 women (571 patients and 572 healthy individuals) was conducted. Rs2297813 G/T, rs12142787 G/A, and rs3766197 C/T in CYP4B1 were selected and genotyped by MassARRAY system. The relationships between these SNPs and the risk of BC were assessed by logistic regression analysis. In addition, multi-factor dimensionality reduction (MDR) was used to analyze SNP-SNP interactions. Results CYP4B1 rs2297813 had a risk-increasing effect on BC in women with body mass index (BMI) ≤ 24 kg/m2 (OR = 1.72, p = 0.026). CYP4B1 rs12142787 was associated with an increased BC risk in smokers (AA: OR = 1.32, p = 0.045). Among non-drinkers, rs2297813 (OR = 1.69, p = 0.009) and rs12142787 (OR = 1.51, p = 0.020) were related to an increased incidence of BC. CYP4B1 rs3766197 (OR = 1.61p = 0.031) was associated with a higher risk of advanced stages (III/IV stage) of BC. Besides, the contributions of CYP4B1 rs2297813 (OR = 1.55, p = 0.021) and rs12142787 (OR = 1.53, p = 0.033) to BC risk might be associated with more than one birth in patients with BC. The three-locus model consisting of rs2297813, rs12142787, and rs3766197 was regarded as the best predictive model for BC risk. Conclusion CYP4B1 SNPs were associated with BC risk in Chinese women, especially in patients with BMI ≤ 24 kg/m2, smokers, non-drinkers, patients in advanced stages (III/IV stage), and patients who reproduced once. These findings shed light on the relationship between CYP4B1 SNPs and BC risk in Chinese women.

Abstract Introduction Understanding the etiology and risk factors of lung cancer (LC) is the key to developing scientific and effective prevention and control strategies for LC. CYP4B1 genetic polymorphism has been reported to be associated with susceptibility to various diseases. We aimed to explore the association between CYP4B1 genetic variants and LC susceptibility. Methods One thousand three hundred thirty-nine participants were recruited to perform an association analysis through SNPStats online software. Statistical analysis of this study was mainly completed by SPSS 22.0 software. False-positive report probability analysis (FPRP) to detect whether the positive findings were noteworthy. Finally, the interaction of SNP-SNP in LC risk was evaluated by multi-factor dimensionality reduction. Results We found evidence that missense variants in CYP4B1 (rs2297810, rs4646491, and rs2297809) are associated with LC susceptibility. In particular, genotype GA of CYP4B1-rs2297810 was significantly associated with an increased risk of LC in both overall and stratified analyses (genotype GA: OR (95% CI) = 1.35 (1.08-1.69), p = 0.010). CYP4B1-rs4646491 (overdominant: OR (95% CI) = 1.30 (1.04-1.62), p = 0.023) and CYP4B1-rs2297809 (genotype CT: OR (95% CI) = 1.26 (1.01-1.59), p = 0.046) are also associated with an increased risk of LC. FPRP analysis showed that all positive results in this study are noteworthy findings Conclusion Three missense variants in CYP4B1 (rs2297810, rs4646491, and rs2297809) are associated with increasing risk of LC.

Background: Breast cancer (BC) is one of the malignant diseases threatening the life and health of women worldwide. The CYP4B1 gene was abnormally expressed in BC and was associated with the prognosis of BC patients. This study aimed to explore the relationship between CYP4B1 single nucleotide polymorphisms (SNPs) and BC risk in Chinese women. Methods: A case-control study of 1,143 women (571 patients and 572 healthy individuals) was conducted. Rs2297813 G/T, rs12142787 G/A, and rs3766197 C/T in CYP4B1 were selected and genotyped by MassARRAY system. The relationships between these SNPs and the risk of BC were assessed by logistic regression analysis. In addition, multi-factor dimensionality reduction (MDR) was used to analyze SNP-SNP interactions. Results: CYP4B1 rs2297813 had a risk-increasing effect on BC in women with body mass index (BMI) ≤ 24 kg/m2 (OR = 1.72, p = 0.026). CYP4B1 rs12142787 was associated with an increased BC risk in smokers (AA: OR = 1.32, p = 0.045). Among non-drinkers, rs2297813 (OR = 1.69, p = 0.009) and rs12142787 (OR = 1.51, p = 0.020) were related to an increased incidence of BC. CYP4B1 rs3766197 (OR = 1.61p = 0.031) was associated with a higher risk of advanced stages (III/IV stage) of BC. Besides, the contributions of CYP4B1 rs2297813 (OR = 1.55, p = 0.021) and rs12142787 (OR = 1.53, p = 0.033) to BC risk might be associated with more than one birth in patients with BC. The three-locus model consisting of rs2297813, rs12142787, and rs3766197 was regarded as the best predictive model for BC risk. Conclusion: CYP4B1 SNPs were associated with BC risk in Chinese women, especially in patients with BMI ≤ 24 kg/m2, smokers, non-drinkers, patients in advanced stages (III/IV stage), and patients who reproduced once. These findings shed light on the relationship between CYP4B1 SNPs and BC risk in Chinese women. [ABSTRACT FROM AUTHOR]

Introduction: Understanding the etiology and risk factors of lung cancer (LC) is the key to developing scientific and effective prevention and control strategies for LC. CYP4B1 genetic polymorphism has been reported to be associated with susceptibility to various diseases. We aimed to explore the association between CYP4B1 genetic variants and LC susceptibility. Methods: One thousand three hundred thirty-nine participants were recruited to perform an association analysis through SNPStats online software. Statistical analysis of this study was mainly completed by SPSS 22.0 software. False-positive report probability analysis (FPRP) to detect whether the positive findings were noteworthy. Finally, the interaction of SNP-SNP in LC risk was evaluated by multi-factor dimensionality reduction. Results: We found evidence that missense variants in CYP4B1 (rs2297810, rs4646491, and rs2297809) are associated with LC susceptibility. In particular, genotype GA of CYP4B1-rs2297810 was significantly associated with an increased risk of LC in both overall and stratified analyses (genotype GA: OR (95% CI) = 1.35 (1.08-1.69), p = 0.010). CYP4B1-rs4646491 (overdominant: OR (95% CI) = 1.30 (1.04-1.62), p = 0.023) and CYP4B1-rs2297809 (genotype CT: OR (95% CI) = 1.26 (1.01-1.59), p = 0.046) are also associated with an increased risk of LC. FPRP analysis showed that all positive results in this study are noteworthy findings Conclusion: Three missense variants in CYP4B1 (rs2297810, rs4646491, and rs2297809) are associated with increasing risk of LC. [ABSTRACT FROM AUTHOR]

The mammalian cytochrome P450 monooxygenase CYP4B1 can bioactivate a wide range of xenobiotics, such as its defining/hallmark substrate 4-ipomeanol leading to tissue-specific toxicities. Similar to other members of the CYP4 family, CYP4B1 has the ability to hydroxylate fatty acids and fatty alcohols. Structural insights into the enigmatic role of CYP4B1 with functions in both, xenobiotic and endobiotic metabolism, as well as its unusual heme-binding characteristics are now possible by the recently solved crystal structures of native rabbit CYP4B1 and the p.E310A variant. Importantly, CYP4B1 does not play a major role in hepatic P450-catalyzed phase I drug metabolism due to its predominant extra-hepatic expression, mainly in the lung. In addition, no catalytic activity of human CYP4B1 has been observed owing to a unique substitution of an evolutionary strongly conserved proline 427 to serine. Nevertheless, association of CYP4B1 expression patterns with various cancers and potential roles in cancer development have been reported for the human enzyme. This review will summarize the current status of CYP4B1 research with a spotlight on its roles in the metabolism of endogenous and exogenous compounds, structural properties, and cancer association, as well as its potential application in suicide gene approaches for targeted cancer therapy. [ABSTRACT FROM AUTHOR]

The mammalian cytochrome P450 monooxygenase CYP4B1 can bioactivate a wide range of xenobiotics, such as its defining/hallmark substrate 4-ipomeanol leading to tissue-specific toxicities. Similar to other members of the CYP4 family, CYP4B1 has the ability to hydroxylate fatty acids and fatty alcohols. Structural insights into the enigmatic role of CYP4B1 with functions in both, xenobiotic and endobiotic metabolism, as well as its unusual heme-binding characteristics are now possible by the recently solved crystal structures of native rabbit CYP4B1 and the p.E310A variant. Importantly, CYP4B1 does not play a major role in hepatic P450-catalyzed phase I drug metabolism due to its predominant extra-hepatic expression, mainly in the lung. In addition, no catalytic activity of human CYP4B1 has been observed owing to a unique substitution of an evolutionary strongly conserved proline 427 to serine. Nevertheless, association of CYP4B1 expression patterns with various cancers and potential roles in cancer development have been reported for the human enzyme. This review will summarize the current status of CYP4B1 research with a spotlight on its roles in the metabolism of endogenous and exogenous compounds, structural properties, and cancer association, as well as its potential application in suicide gene approaches for targeted cancer therapy.

Background Context: Ossification of the posterior longitudinal ligament (OPLL) in the cervical spine is known as a rare, complex genetic disease, its complexity being partly because OPLL is diagnosed by radiological findings regardless of clinical or genetic evaluations. Although many genes associated with susceptibility have been reported, the exact causative genes are still unknown.Purpose: We performed an analysis using next-generation sequencing and including only patients with a clear involved phenotype.Study Design/setting: This was a case control study.Patient Sample: A total of 74 patients with severe OPLL and 26 healthy controls were included.Outcome Measures: Causal single-nucleotide variant (SNV), gene-wise variant burden (GVB), and related pathway METHOD: We consecutively included the severe OPLL patients with continuous-/mixed-type and an occupying ratio of ≥ 40%, and performed whole-exome sequencing (WES) and bioinformatic analysis. Then, a validation test was performed for candidate variations. Participants were divided into 4 groups (rapidly-growing OPLL, growing rate ≥ 2.5%/y; slow-growing, < 2.5%/y; uncertain; and control).Results: WES was performed on samples from 74 patients with OPLL (rapidly-growing, 33 patients; slow-growing, 37; and uncertain, 4) with 26 healthy controls. Analysis of 100 participants identified a newly implicated SNV and 4candidate genes based on GVB. The GVB of CYP4B1 showed a more deleterious score in the OPLL than the control group. Comparison between the rapidly growing OPLL and control groups revealed seven newly identified SNVs. We found significant association for 2 rare missense variants; rs121502220 (odds ratio [OR] = infinite; minor allele frequency [MAF] = 0.034) in NLRP1 and rs13980628 (OR= infinite; MAF = 0.032) in SSH2. The 3 genes are associated with inflammation control and arthritis, and SSH2 and NLRP1 are also related to vitamin D modulation.Conclusions: Identification of unique variants in novel genes such as CYP4B1 gene may induce the development of OPLL. In subgroup analysis, NLRP1 and SSH2 genes coding inflammation molecules may related with rapidly-growing OPLL. [ABSTRACT FROM AUTHOR]

Cytochrome P450 4B1 (CYP4B1) plays crucial roles in biotransforming of xenobiotics. Its predominant extrahepatic expression has been associated with certain tissue-specific toxicities. However, the expressions of CYP4B1 in various cancers and hence their potential roles in cancer development were inclusive. In this work, existing knowledge on expression and regulation of CYP4B1 gene and protein, catalysis of CYP4B1, association of CYP4B1 with cancers, contradicting findings about human CYP4B1 activities as well as the employing CYP4B1 in suicide gene approach for cancer treatment were reviewed. To date, it appears that there is a wide spectrum of tissue distribution of CYP4B1 with lungs as the predominant sites. Several nuclear receptors are possibly responsible for regulating its gene expression. The involvement of CYP4B1 in cancer was considered via activation of procarcinogens and neovascularization. However, human CYP4B1 was found to be inactive due to a substitution of proline with serine at position 427. Suicide gene approach combining reengineered CYP4B1 and prodrug 4-ipomeanol (4-IPO) has shown a promising potential for targeted cancer therapy. Further studies should focus on the verification of human CYP4B1 catalytic activities. More compounds with similar structure as 4-IPO should be tested to identify more alternative agents for the suicide gene approach in cancer treatment. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the expression level of cytochrome P450 4B1 (CYP4B1) protein and its clinical significance in specimens from patients with urothelial carcinomas (UC) including upper tract urothelial carcinoma (UTUC, n = 340) and urinary bladder urothelial carcinoma (UBUC, n = 295). Data mining on public domains identified five potential candidate transcripts which were downregulated in advanced UBUCs, indicating that it might implicate in UC progression. Immunohistochemistry was performed to analyze the CYP4B1 protein levels on 635 tissues from UC patients retrospectively. Immunoexpression of CYP4B1 was further estimated using the H‐score method. Correlations between CYP4B1 H‐score and important clinicopathological factors, as well as the significance of CYP4B1 expression level for disease‐specific and metastasis‐free survivals were evaluated. In UTUCs and UBUCs, 118 (34.7%) and 92 (31.2%) patients, respectively, were identified to be of CYP4B1 downregulation. The CYP4B1 expression level was found to be associated with several clinicopathological factors and patient survivals. Downregulation of CYP4B1 protein was correlated to advanced primary tumor (p < 0.001), nodal metastasis (p < 0.001), high histological grade (p = 0.001), vascular invasion (p < 0.001), perineural invasion (p = 0.017) and mitotic rate (p = 0.036) in UTUCs and/or UBUCs. Low CYP4B1 protein level independently predicted inferior disease‐specific (p = 0.009; p < 0.001) and metastasis‐free (p = 0.035; p < 0.001) survivals in UTUC and UBUC patients. Our findings showed that downregulation of CYP4B1 protein level is an independent unfavorable prognosticator. Loss of the CYP4B1 gene expression may play an important role in UC progression. [ABSTRACT FROM AUTHOR]

Human CYP4B1, a cytochrome P450 monooxygenase predominantly expressed in the lung, inefficiently metabolizes classical CYP4B1 substrates, such as the naturally occurring furan pro-toxin 4-ipomeanol (4-IPO). Highly active animal forms of the enzyme convert 4-IPO to reactive alkylating metabolite(s) that bind(s) to cellular macromolecules. By substitution of 13 amino acids, we restored the enzymatic activity of human CYP4B1 toward 4-IPO and this modified cDNA is potentially valuable as a suicide gene for adoptive T-cell therapies. In order to find novel pro-toxins, we tested numerous furan analogs in in vitro cell culture cytotoxicity assays by expressing the wildtype rabbit and variants of human CYP4B1 in human liver-derived HepG2 cells. To evaluate the CYP4B1 substrate specificities and furan analog catalysis, we optimized the N-terminal sequence of the CYP4B1 variants by modification/truncation and established their heterologous expression in Escherichia coli (yielding 70 and 800 nmol·l-1 of recombinant human and rabbit enzyme, respectively). Finally, spectral binding affinities and oxidative metabolism of the furan analogs by the purified recombinant CYP4B1 variants were analyzed: the naturally occurring perilla ketone was found to be the tightest binder to CYP4B1, but also the analog that was most extensively metabolized by oxidative processes to numerous non-reactive reaction products. [ABSTRACT FROM AUTHOR]

Background: Lymph node metastasis is one of the important factors affecting the prognosis of lung adenocarcinoma (LUAD) patients. The key molecules in lymph node metastasis have not yet been fully revealed. Therefore, we aimed to construct a prognostic model based on lymph node metastasis-related genes to evaluate the prognosis of LUAD patients., Methods: The differentially expressed genes (DEGs) in the process of LUAD metastasis were identified in The Cancer Genome Atlas (TCGA) database, and the biological roles of the DEGs were depicted using Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and a protein-protein interaction (PPI) network. Survival analysis and Cox regression analysis were used to identify the genes related to the prognosis of patients with LUAD, and a nomogram and a prognostic model were constructed. The potential prognostic value, immune escape, and regulatory mechanisms of the prognostic model in LUAD progression were explored through survival analysis and gene set enrichment analysis (GSEA)., Results: A total of 75 genes were upregulated, and 138 genes were downregulated in tissues of lymph node metastasis. The expression levels of STC1 , CYP17A1 , RHOV , GUCA2B , TM4SF20 , DEFB1 , CRHR2 , ABCC2 , CYP4B1 , KRT16 , and NTS were revealed as risk factors for a poor prognosis in LUAD patients. High-risk LUAD patients had a poor prognosis in the prognostic model based on RHOV , ABCC2 , and CYP4B1 . The clinical stage and the risk score were found to be independent risk factors for a poor prognosis in LUAD patients, and the risk score was associated with the tumor purity, T cell, natural killer (NK) cell, and other immune cells. The prognostic model might affect the progression of LUAD using DNA replication, the cell cycle, P53, and other signaling pathways., Conclusions: Lymph node metastasis-related genes RHOV , ABCC2 , and CYP4B1 are associated with a poor prognosis in LUAD. A prognostic model based on RHOV , ABCC2 , and CYP4B1 might predict the prognosis of LUAD patients and be associated with immune infiltration., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-23-265/coif). The authors have no conflicts of interest to declare., (2023 Journal of Thoracic Disease. All rights reserved.)

Drug metabolism and transport processes in the liver, intestine and kidney that affect the pharmacokinetics and pharmacodynamics of therapeutic agents have been studied extensively. In contrast, comparatively little research has been conducted on these topics as they pertain to the eye. Recently, however, catalytic functions of ocular cytochrome P450 enzymes have gained increasing attention, in large part due to the roles of CYP1B1 and CYP4V2 variants in primary congenital glaucoma and Bietti's corneoretinal crystalline dystrophy, respectively. In this review, we discuss challenges to ophthalmic drug delivery, including Phase I drug metabolism and transport in the eye, and the role of three specific P450s, CYP4B1, CYP1B1 and CYP4V2 in ocular inflammation and genetically determined ocular disease. [ABSTRACT FROM AUTHOR]

We report the development of a 18F-labeled 4-ipomeanol (4-IM), which is metabolized by the CYP4B1 enzyme, to image tumors and monitor enzyme-activating anticancer prodrugs. The fluorine-substituted derivative, 1-(3-furyl)-4-hydroxy-5-fluoro-1-pentanone (F-4-IM, 1), was synthesized from 3-furaldehyde. [18F]F-4-IM ([18F] 1) was prepared in 20%-35% radiochemical yield by a fluorine-18 displacement reaction, followed by reduction and deprotection of the ketal group, and was shown to be stable (>96% at 2 hours) in human serum at 37°C. The biodistribution of [18F]F-4-IM in normal rats was high in the lung, where CYP4B1 gene is preferentially expressed. We transduced C6-glioma cells with a retrovirus-expressing CYP4B1 (C6-CYP4B1). Evaluation of CYP4B1 expression was confirmed by reverse transcription polymerase chain reaction and MTT assay. Cell assays were carried out using C6 and C6-CYP4B, and the uptake of [18F]F-4-IM in these cells was compared with that in parental controls. The uptake ratio of [18F]F-4-IM was 2.8-fold higher in C6-CYP4B1 compared with that in parental cells at 1 hour, whereas [3H]4-IM was taken up at similar rates in both cell lines after 6 hours. These results suggest that [18F]F-4-IM could be a promising PET imaging agent with potential to be used for imaging of CYP4B1-transfected tumor cells, as well as for monitoring CYP4B1 enzyme/prodrug interactions. [ABSTRACT FROM AUTHOR]

Abstract: Cytochromes P450 (CYPs) are critically important in the oxidative metabolism of a diverse array of xenobiotics and endogenous substrates. We have previously reported the cloning and characterisation of the koala CYP4A15, the first reported member of the CYP4 family from marsupials, and have demonstrated important species differences in CYP4A activity and tissue expression. In the present study, the cloning of CYP4B1 in the wallaby (Macropus eugenii) and their expression across marsupials is described. Rabbit anti-mouse CYP4B1 antibody detected immunoreactive proteins in lung and liver microsomes from all test marsupials, with relative weak signal detected from the koala, suggesting a species-specific expression. Microsomal 2-aminofluorene bio-activation (a CYP4B1 marker) in wallaby lung was comparable to that of rabbit, with significant higher activities detected in wallaby liver and kidneys compared to rabbit. A 1548bp wallaby lung CYP4B complete cDNA, designated CYP4B1, which encodes a protein of 510 amino acids and shares 72% nucleotide and 69% amino acid sequence identity to human CYP4B1, was cloned by polymerase chain reaction approaches. The results demonstrate the presence of wallaby CYP4B1 that shares several common features with other published CYP4Bs; however the wallaby CYP4B1 cDNA contains four extra amino acid residues at the NH2-terminal, a fundamentally conserved transmembrane anchor of all eukaryote CYPs. [ABSTRACT FROM AUTHOR]

Objective To investgate the metabolism of terephthalic acid (TPA) in rats and its mechanism. Methods Metabolism was evaluated by incubating sodium terephthalate (NaTPA) with rat normal liver microsomes, or with microsomes pretreated by phenobarbital sodium, or with 3-methycholanthrene, or with diet control following a NADPH-generating system. The determination was performed by high performance liquid chromatography (HPLC), and the mutagenic activation was analyzed by umu tester strain Salmonella typhimurium NM2009. Expression of CYP4B 1 mRNA was detected by RT-PCR. Results The amount of NaTPA (12.5–200 μmo1·L-1 detected by HPLC did not decrease in microsomes induced by NADPH-generating system. Incubation of TPA (0.025–0.1 mmol·L-1) with induced or noninduced liver microsomes in an NM2009 umu response system did not show any mutagenic activation. TPA exposure increased the expression of CYP4B1 mRNA in rat liver, kidney, and bladder. Conclusion Lack of metabolism of TPA in liver and negative genotoxic data from NM2009 study are consistent with other previous short-term tests, suggesting that the carcinogenesis in TPA feeding animals is not directly interfered with TPA itself and/or its metabolites. [ABSTRACT FROM AUTHOR]

Expression of cytochromes P450 CYP1A1, CYP1B1, CYP2E1 and CYP4B1 was analysed on the transcript level in human urothelial cells obtained by various methods. As a source of urothelial cells, exfoliated cells in urine samples were used. Their expression profiles were determined either immediately after centrifugal enrichment ( n=4) or after their cultivation and propagation ( n=8). Another source of urothelial cells were ureter specimens from surgical subjects ( n=4). Generally, expression was most prominent for CYP1B1 and CYP4B1 among the CYP transcripts analysed. CYP1B1 mRNA was detected in all samples investigated except for one ureter specimen. CYP4B1 mRNA was present in cell cultures from three out of eight healthy subjects, in three out of four directly investigated urinary sediments and in the cells of all five ureter specimens of four donors investigated after resection and subsequent cell culture. In most cases, CYP2E1 transcript levels were lower than those of CYP1B1 and CYP4B1. CYP2E1 mRNA was detected in cell cultures of six out of eight healthy subjects, in one out of four urinary sediments and in three out of five ureter specimens. CYP1A1 mRNA was clearly observed only in cells from resected ureters. In cell cultures the relative mRNA expression levels varied with subjects interindividually, intraindividually and also during the time of cell culture. The study demonstrates constitutive mRNA expressions of xenobiotic metabolising CYP enzymes in human urothelial cells obtained by different methods. In particular, transcripts of CYP1B1 and CYP4B1 are present, coding for enzymes which are active in the metabolism of polycyclic aromatic hydrocarbons and arylamines, respectively. [ABSTRACT FROM AUTHOR]

Modifications at the N-terminus of the rabbit CYP4B1 gene resulted in expression levels in Escherichia coli of up to 660 nmol/L. Solubilization of the enzyme from bacterial membranes led to substantial conversion to cytochrome P420 unless α-naphthoflavone was added as a stabilizing ligand. Mass spectrometry analysis and Edman sequencing of purified enzyme preparations revealed differential N-terminal post-translational processing of the various constructs expressed. Notably, bacterial expression of CYP4B1 produced a holoenzyme with >98.5% of its heme prosthetic group covalently linked to the protein backbone. The near fully covalently linked hemoproteins exhibited similar rates and regioselectivities of lauric acid hydroxylation to that observed previously for the partially heme processed enzyme expressed in insect cells. These studies shed new light on the consequences of covalent heme processing in CYP4B1 and provide a facile system for future mechanistic and structural studies with the enzyme. [Copyright &y& Elsevier]

CYP4B1 is an enigmatic mammalian cytochrome P450 monooxygenase acting at the interface between xenobiotic and endobiotic metabolism. A prominent CYP4B1 substrate is the furan pro-toxin 4-ipomeanol (IPO). Our recent investigation on metabolism of IPO related compounds that maintain the furan functionality of IPO while replacing its alcohol group with alkyl chains of varying structure and length revealed that, in addition to cytotoxic reactive metabolite formation (resulting from furan activation) non-cytotoxic ω-hydroxylation at the alkyl chain can also occur. We hypothesized that substrate reorientations may happen in the active site of CYP4B1. These findings prompted us to re-investigate oxidation of unsaturated fatty acids and fatty alcohols with C9–C16 carbon chain length by CYP4B1. Strikingly, we found that besides the previously reported ω- and ω-1-hydroxylations, CYP4B1 is also capable of α-, β-, γ-, and δ-fatty acid hydroxylation. In contrast, fatty alcohols of the same chain length are exclusively hydroxylated at ω, ω-1, and ω-2 positions. Docking results for the corresponding CYP4B1-substrate complexes revealed that fatty acids can adopt U-shaped bonding conformations, such that carbon atoms in both arms may approach the heme-iron. Quantum chemical estimates of activation energies of the hydrogen radical abstraction by the reactive compound 1 as well as electron densities of the substrate orbitals led to the conclusion that fatty acid and fatty alcohol oxidations by CYP4B1 are kinetically controlled reactions. • CYP4B1 fatty acid hydroxylation patterns are more diverse than previously reported. • The presence of cytochrome b 5 reduces uncoupling and increases CYP4B1 activity. • Computational docking allows interpretation of the observed hydroxylation patterns. • Activation energy calculations imply that the reactions are kinetically controlled. [ABSTRACT FROM AUTHOR]

Cytochrome P450 4B1 (4B1) functions in both xenobiotic and endobiotic metabolism. An ester linkage between Glu-310 in 4B1 and the 5-methyl group of heme facilitates preferential hydroxylation of terminal (ω) methyl groups of hydrocarbons (HCs) and fatty acids compared with ω-1 sites bearing weaker C-H bonds. This preference is retained albeit diminished 4-fold for the E310A mutant, but the reason for this is unclear. Here, a crystal structure of the E310A-octane complex disclosed that noncovalent interactions maintain heme deformation in the absence of the ester linkage. Consistent with the lower symmetry of the heme, resonance Raman (RR) spectroscopy revealed large enhancements of RR peaks for high-spin HC complexes of 4B1 and the E310A mutant relative to P450 3A4. Whereas these enhancements were diminished in RR spectra of a low-spin 4B1- N -hydroxy- N '-(4-butyl-2-methylphenyl)formamidine complex, a crystal structure indicated that this inhibitor does not alter heme ruffling. RR spectra of Fe 2+ -CO HC complexes revealed larger effects of HC length in E310A than in 4B1, suggesting that reduced rigidity probably underlies increased E310A-catalyzed (ω-1)-hydroxylation. Diminished effects of the HC on the position of the Fe-CO stretching mode in 4B1 suggested that the ester linkage limits substrate access to the CO. Heme ruffling probably facilitates autocatalytic ester formation by reducing inhibitory coordination of Glu-310 with the heme iron. This also positions the 5-methyl for a reaction with the proposed glutamyl radical intermediate and potentially enhances oxo-ferryl intermediate reactivity for generation of the glutamyl radical to initiate ester bond formation and ω-hydroxylation., (© 2018 Jennings et al.)