Structural characterization of human cholesterol 7α-hydroxylase

Cloning and Characterization of Cyp7a1 and Cyp27a1 Genes from the Non-Parasitic Japanese Lamprey Lethenteron reissneri

Two cytochrome P450 genes homologous to human CYP7A1 and CYP27A1 were cloned from the non-parasitic Japanese lamprey Lethenteron reissneri. Lamprey cyp7a1 mRNA had varied expression levels among individuals: about four orders of magnitude differences in larval liver and nearly three orders of magnitude differences in male adult liver. Overexpressed Cyp7a1 protein tagged with green fluorescent protein (GFP) was localized to the endoplasmic reticulum. Lamprey cyp27a1 mRNA had relatively constant expression levels: within two orders of magnitude differences in larvae and adult liver and intestine. GFP-tagged Cyp27a1 protein was localized to mitochondria. The expression profiles of lamprey cyp7a1 and cyp27a1 genes and the cellular localizations of their products were in good agreement with their counterparts in mammals, where these two P450s catalyze initial hydroxylation reactions of cholesterol in classical and alternative pathways of bile acid synthesis, respectively. The cyp7a1 mRNA levels in adult male liver showed significant negative correlations to both body weight and total length of the animal, implying the involvement of the gene in the production of female-attractive pheromones in sexually matured male livers. The lamprey Cyp7a1 contains a long extension of 116 amino acids between helices D and E of the protein. Possible roles of this extension in regulating the enzymatic activity of lamprey Cyp7a1 are discussed.

Discovery of highly potent proapoptotic antiestrogens in a series of androst-5,16-dienes D-modified with imidazole-annulated pendants

Heterocyclic derivatives of steroid hormones are potent anticancer agents, which are used in the chemotherapy of breast and prostate cancers. Here, we describe a novel series of androstenes, D-modified with imidazole-annulated pendants, with significant anticancer activity. Novel C17-linked imidazole-annulated heterocyclic derivatives of dehydropregnenolone acetate were synthesized by the cyclocondensation with amidines using 3β-acetoxy-21-bromopregna-5,16-dien-20-one as the substrate. The antiproliferative potency of all the synthesized compounds was evaluated against human prostate (22Rv1) and human breast (MCF7) cancer cell lines and cytochromes P450. The lead compound, imidazo[1,2-a]pyridine derivative 3h, was revealed to be a promising candidate for future anticancer drug design, particularly against ERα-positive breast cancer. Lead compound 3h was found to be selective against MCF7 cells with IC₅₀ of 0.1μM and to act as both a potent selective agent blocking estrogen receptor α, which is involved in the stimulation of breast cancer growth, and an effective apoptosis inducer. The potential ability of compound 3h to bind to ERα was studded using molecular docking and molecular dynamics simulation. The selectivity analysis showed that lead steroid 3h produces no effects on cytochromes P450 CYP17A1, CYP7A1, and CYP21A2.

X-ray structure analysis of the cholesterol 25- and 20-hydroperoxides, the elusive primary sidechain autoxidation products of cholesterol

The systematic X-ray structure analyses of the primary cholesterol sidechain autoxidation products cholesterol 25- and 20β(S)-hydroperoxide are presented and compared to cholesterol and 25-hydroxycholesterol. Intermolecular interactions in crystal structures of the molecules are revealed through Hirshfeld surface analysis and fingerprint plots. The magnitude of energy frameworks is presented by combining efficient calculations of intermolecular interaction energies with novel graphical representation.

Hepatic cholesterol transport and its role in non-alcoholic fatty liver disease and atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) is a quickly emerging global health problem representing the most common chronic liver disease in the world. Atherosclerotic cardiovascular disease represents the leading cause of mortality in NAFLD patients. Cholesterol metabolism has a crucial role in the pathogenesis of both NAFLD and atherosclerosis. The liver is the major organ for cholesterol metabolism. Abnormal hepatic cholesterol metabolism not only leads to NAFLD but also drives the development of atherosclerotic dyslipidemia. The cholesterol level in hepatocytes reflects the dynamic balance between endogenous synthesis, uptake, esterification, and export, a process in which cholesterol is converted to neutral cholesteryl esters either for storage in cytosolic lipid droplets or for secretion as a major constituent of plasma lipoproteins, including very-low-density lipoproteins, chylomicrons, high-density lipoproteins, and low-density lipoproteins. In this review, we describe decades of research aimed at identifying key molecules and cellular players involved in each main aspect of hepatic cholesterol metabolism. Furthermore, we summarize the recent advances regarding the biological processes of hepatic cholesterol transport and its role in NAFLD and atherosclerosis.

Novel alkylaminoethyl derivatives of androstane 3-oximes as anticancer candidates: synthesis and evaluation of cytotoxic effects

Steroid anticancer drugs are the focus of numerous scientific research efforts. Due to their high cytotoxic effects against tumor cells, some natural or synthetic steroid compounds seem to be promising for the treatment of different classes of cancer. In the present study, fourteen novel O-alkylated oxyimino androst-4-ene derivatives were synthesized from isomerically pure 3E-oximes, using different alkylaminoethyl chlorides. Their in vitro cytotoxic activity was evaluated against eight human cancer cell lines, as well as against normal fetal lung (MRC-5) and human foreskin (BJ) fibroblasts, to test the efficiency and selectivity of the compounds. Most derivatives displayed strong activity against malignant melanoma (G-361), lung adenocarcinoma (A549) and colon adenocarcinoma (HT-29) cell lines. Angiogenesis was assessed in vitro using migration scratch and tube formation assays on HUVEC cells, where partial inhibition of endothelial cell migration was observed for the 17α-(pyridin-2-yl)methyl 2-(morpholin-4-yl)ethyl derivative. Among the compounds that most impaired the growth of lung cancer A549 cells, the (17E)-(pyridin-2-yl)methylidene derivative bearing a 2-(pyrrolidin-1-yl)ethyl substituent induced significant apoptosis in these cells. In combination with low cytotoxicity toward normal MRC-5 cells, this molecule stands out as a good candidate for further anticancer studies. In addition, in vitro investigations against cytochrome P450 enzymes revealed that certain compounds can bind selectively in the active sites of human steroid hydroxylases CYP7, CYP17A1, CYP19A1 or CYP21A2, which could be important for the development of novel activity modulators of these enzymes and identification of possible side effects.

Novel steroid O-alkylated 3-oxyimino derivatives were synthesized and evaluated in vitro for their antitumor properties. The obtained data indicate the potential of these functionalities for the development of new candidates for tumor treatment.

Unique Variant of Cerebrotendinous Xanthomatosis Presenting With Eyelid Involvement Due to Heterozygous CYP7A1 and SLC10A1 Gene Mutations

ABSTRACT

We report a case of a novel phenotypic variant of cerebrotendinous xanthomatosis (CTX) with an adult onset, caused by 2 coexisting mutations involving the CYP7A1 and SLC10A1 genes. A 49-year-old male patient presented with eyelid xanthomatosis associated with dermatochalasis, nystagmus, right-sided paresis with hyperreflexia and atypical parkinsonism. Bilateral xanthomatous plaques involving both Achilles tendons were subsequently detected. Histopathology of the eyelids demonstrated marked diffuse stromal infiltrates of prominent foamy histiocytes. His lipid profile showed only a slightly elevated non-high density lipoprotein cholesterol level but with normal cholesterol and cholestanol levels. By contrast, classic CTX characteristically demonstrates a markedly elevated cholestanol and a mutation involving the CYP27A1 gene for enzyme cholesterol 27-hydroxylase. Unexpectedly, molecular studies on this patient revealed a heterozygous mutation involving 2 different genes, namely, CYP7A1 and SLC10A1 genes. The CYP7A1 gene encodes for the enzyme cholesterol 7α-hydroxylase, which is a rate-limiting enzyme in the cholesterol degradation. The SLC10A1 Na+/taurocholate cotransporter gene is involved in the enterohepatic circulation of bile acids and for the hepatocyte uptake of cholesterol. We are the first to report an unusual case of an adult-onset CTX manifesting with eyelid xanthomas associated with an uncharacteristic lipid profile and a detection of novel heterozygous mutations of CYP7A1 and SLC10A1 genes in this neurocutaneous syndrome.

Fe(iii)-Catalyzed synthesis of steroidal imidazoheterocycles as potent antiproliferative agents

An efficient and practical method has been developed for the synthesis of steroidal imidazoheterocycles via cost-effective and environmentally benign FeCl₃-catalyzed oxidative amination. A library of steroidal imidazo[1,2-a]pyridines was directly synthesized from readily available 2-aminopyridines and steroidal ketones in aerobic conditions. The synthesized compounds were screened for activity on human microsomal cytochrome P450s CYP7, CYP17 and CYP21. Antiproliferative activity of two lead compounds 3ia and 3la was additionally evaluated against the human MCF-7 (breast cancer), SKOV3 (ovarian cancer), and 22Rv1 (prostate cancer) cell lines. Steroidal imidazo[1,2-a]pyridine 3la which is a substrate molecule for CYP17A1 with IC₅₀ = 1.7 μM (MCF-7), 3.0 (SKOV3), and 6.0 μM (22Rv1) has proved to be more active than reference drug cisplatin.

Pruritus secondary to primary biliary cholangitis: a review of the pathophysiology and management with phototherapy

BACKGROUND

Primary biliary cholangitis (PBC) is an autoimmune hepatobiliary disorder characterized by destruction of liver bile ducts leading to intrahepatic cholestasis. It causes intractable pruritus for which ultraviolet (UV)B phototherapy is an experimental treatment when alternative therapies fail. The pathophysiology of cholestatic itch and the mechanism of action of narrowband UVB in this condition remains poorly understood.

OBJECTIVES

To summarize the current literature and propose testable hypotheses for the mechanism of action of phototherapy in attenuating itch.

METHODS

A focused PubMed search for articles relating to the pathogenesis of itch in cholestatic disease was performed. A total of 3855 articles were screened and 50 were found suitable for literature review. Evidence from this literature review was combined with author expertise in the area.

RESULTS

Formulated hypotheses focus on the role of bile salts, autotaxin and specific receptors including G-protein-coupled bile acid receptor, Gpbar1 (also known as TGR5) and the nuclear transcription factor farnesoid X receptor.

CONCLUSIONS

Several testable mechanisms through which phototherapy may exert its effects are discussed in this review. The next steps are to carry out an objective assessment of the efficacy of phototherapy in cholestatic pruritus, gain further knowledge on the underlying pathways, and subsequently trial its use against current licensed therapies. Such studies could lead to increased mechanistic understanding, identification of novel therapeutic targets and the potential to refine phototherapy protocols, leading to improved control of itch and quality of life in patients with PBC. What's already known about this topic? Primary biliary cholangitis (PBC) is frequently associated with intractable pruritus for which current treatment options are often unsuccessful. Phototherapy is used as an experimental treatment for PBC-associated pruritus when alternative better-studied treatments fail. What does this study add? This study reviews the current literature on the pathophysiology and management of cholestatic pruritus, an area which remains poorly understood. We propose testable hypotheses of the mechanisms behind the attenuation of cholestatic pruritus with phototherapy.

Ligand-binding properties and catalytic activity of the purified human 24-hydroxycholesterol 7α-hydroxylase, CYP39A1

Oxysterols are derivatives of cholesterol and biologically active molecules that are involved in a number of functions, including cholesterol homeostasis, immune response, embryogenic development and pathophysiology of neurodegenerative diseases. Enzymes catalyzing their synthesis and metabolism are of particular interest as potential or evaluated drug targets. Here we report for the first time biochemical analysis of purified human oxysterol 7α-hydroxylase selective for 24-hydroxycholesterol. Binding analyses indicated a tight binding of the oxysterols and estrone. Ligand screening revealed that CYP39A1 binds with high affinity antifungal drugs and prostate cancer drug galeterone (TOK-001). Site-directed mutagenesis of conserved Asn residue in the active site revealed its crucial role for protein folding and heme incorporation. Developed protocol for expression and purification enables further investigation of this hepatic enzyme as off-target in development of specific drugs targeting cytochrome P450 enzymes.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Mammalian Cells Engineered To Produce New Steroids

Steroids can be difficult to modify through traditional organic synthesis methods, but many enzymes regio- and stereoselectively process a wide variety of steroid substrates. We tested whether steroid-modifying enzymes could make novel steroids from non-native substrates. Numerous genes encoding steroid-modifying enzymes, including some bacterial enzymes, were expressed in mammalian cells by transient transfection and found to be active. We made three unusual steroids by stable expression, in HEK293 cells, of the 7α-hydroxylase CYP7B1, which was selected because of its high native product yield. These cells made 7α,17α-dihydroxypregnenolone and 7β,17α-dihydroxypregnenolone from 17α-hydroxypregnenolone and produced 11α,16α-dihydroxyprogesterone from 16α-hydroxyprogesterone. The last two products were the result of CYP7B1-catalyzed hydroxylation at previously unobserved sites. A Rosetta docking model of CYP7B1 suggested that these substrates' D-ring hydroxy groups might prevent them from binding in the same way as the native substrates, bringing different carbon atoms close to the active ferryl oxygen atom. This new approach could potentially use other enzymes and substrates to produce many novel steroids for drug candidate testing.

Oxysterols: Old Tale, New Twists

Oxysterols have long been known for their important role in cholesterol homeostasis, where they are involved in both transcriptional and posttranscriptional mechanisms for controlling cholesterol levels. However, they are increasingly associated with a wide variety of other, sometimes surprising cell functions. They are activators of the Hedgehog pathway (important in embryogenesis), and they act as ligands for a growing list of receptors, including some that are of importance to the immune system. Oxysterols have also been implicated in several diseases such as neurodegenerative diseases and atherosclerosis. Here, we explore the latest research into the roles oxy-sterols play in different areas, and we evaluate the current evidence for these roles. In addition, we outline critical concepts to consider when investigating the roles of oxysterols in various situations, which includes ensuring that the concentration and form of the oxysterol are relevant in that context--a caveat with which many studies have struggled.

Recent Structural Insights into Cytochrome P450 Function

Cytochrome P450 (P450) enzymes are important in the metabolism of drugs, steroids, fat-soluble vitamins, carcinogens, pesticides, and many other types of chemicals. Their catalytic activities are important issues in areas such as drug-drug interactions and endocrine function. During the past 30 years, structures of P450s have been very helpful in understanding function, particularly the mammalian P450 structures available in the past 15 years. We review recent activity in this area, focusing on the past 2 years (2014-2015). Structural work with microbial P450s includes studies related to the biosynthesis of natural products and the use of parasitic and fungal P450 structures as targets for drug discovery. Studies on mammalian P450s include the utilization of information about 'drug-metabolizing' P450s to improve drug development and also to understand the molecular bases of endocrine dysfunction.

The use of isomeric testosterone dimers to explore allosteric effects in substrate binding to cytochrome P450 CYP3A4

Cytochrome P450 CYP3A4 is the main drug-metabolizing enzyme in the human liver, being responsible for oxidation of 50% of all pharmaceuticals metabolized by human P450 enzymes. Possessing a large substrate binding pocket, it can simultaneously bind several substrate molecules and often exhibits a complex pattern of drug-drug interactions. In order to better understand structural and functional aspects of binding of multiple substrate molecules to CYP3A4 we used resonance Raman and UV-VIS spectroscopy to document the effects of binding of synthetic testosterone dimers of different configurations, cis-TST2 and trans-TST2. We directly demonstrate that the binding of two steroid molecules, which can assume multiple possible configurations inside the substrate binding pocket of monomeric CYP3A4, can lead to active site structural changes that affect functional properties. Using resonance Raman spectroscopy, we have documented perturbations in the ferric and Fe-CO states by these substrates, and compared these results with effects caused by binding of monomeric TST. While the binding of trans-TST2 yields results similar to those obtained with monomeric TST, the binding of cis-TST2 is much tighter and results in significantly more pronounced conformational changes of the porphyrin side chains and Fe-CO unit. In addition, binding of an additional monomeric TST molecule in the remote allosteric site significantly improves binding affinity and the overall spin shift for CYP3A4 with trans-TST2 dimer bound inside the substrate binding pocket. This result provides the first direct evidence for an allosteric effect of the peripheral binding site at the protein-membrane interface on the functional properties of CYP3A4.

Cholesterol hydroperoxides as substrates for cholesterol-metabolizing cytochrome P450 enzymes and alternative sources of 25-hydroxycholesterol and other oxysterols

The interaction of the primary autoxidation products of cholesterol, namely 25- and 20ξ-hydroperoxides, with the four principal cholesterol-metabolizing cytochrome P450 enzymes is reported. Addition of cholesterol 25-hydroperoxide to the enzymes CYP27A1 and CYP11A1 induced well-defined spectral changes while generating 25-hydroxycholesterol as the major product. The 20ξ-hydroperoxides induced spectral shifts in CYP27A1 and CYP11A1 but glycol metabolites were detected only with CYP11A1. CYP7A1 and CYP46A1 failed to give metabolites with any of the hydroperoxides. A P450 hydroperoxide-shunt reaction is proposed, where the hydroperoxides serve as both donor for reduced oxygen and substrate. CYP27A1 was shown to mediate the reduction of cholesterol 25-hydroperoxide to 25-hydroxycholesterol, a role of potential significance for cholesterol-rich tissues with high oxidative stress. CYP27A1 may participate in the removal of harmful autoxidation products in these tissues, while providing a complementary source of 25-hydroxycholesterol, a modulator of immune cell function and mediator of viral cell entry.

The efficient and selective biocatalytic oxidation of norisoprenoid and aromatic substrates by CYP101B1 from Novosphingobium aromaticivorans DSM12444

CYP101B1 fromNovosphingobium aromaticivoransoxidises ionone derivatives and phenylcyclohexane with high activity and regioselectivity.