Effect of metabolic inhibitors on arachidonic acid metabolism in the corneal epithelium: evidence for cytochrome P450-mediated reactions

The fatty acid omega hydroxylase genes (CYP4 family) in the progression of metabolic dysfunction-associated steatotic liver disease (MASLD): An RNA sequence database analysis and review

Fatty acid omega hydroxylase P450s consist of enzymes that hydroxylate various chain-length saturated and unsaturated fatty acids (FAs) and bioactive eicosanoid lipids. The human cytochrome P450 gene 4 family (CYP4) consists of 12 members that are associated with several human diseases. However, their role in the progression of metabolic dysfunction-associated fatty liver disease (MASLD) remains largely unknown. It has long been thought that the induction of CYP4 family P450 during fasting and starvation prevents FA-related lipotoxicity through FA metabolism to dicarboxylic acids that are chain-shortened in peroxisomes and then transported to the mitochondria for complete oxidation. Several studies have revealed that peroxisome succinate transported to the mitochondria is used for gluconeogenesis during fasting and starvation, and recent evidence suggests that peroxisome acetate can be utilized for lipogenesis and lipid droplet formation as well as epigenetic modification of gene transcription. In addition, omega hydroxylation of the bioactive eicosanoid arachidonic acid to 20-Hydroxyeicosatetraenoic acid (20-HETE) is essential for activating the GPR75 receptor, leading to vasoconstriction and cell proliferation. Several mouse models of diet-induced MASLD have revealed the induction of selective CYP4A members and the suppression of CYP4F during steatosis and steatohepatitis, suggesting a critical metabolic role in the progression of fatty liver disease. Thus, to further investigate the functional roles of CYP4 genes, we analyzed the differential gene expression of 12 members of CYP4 gene family in datasets from the Gene Expression Omnibus (GEO) from patients with steatosis, steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. We also observed the differential expression of various CYP4 genes in the progression of MASLD, indicating that different CYP4 members may have unique functional roles in the metabolism of specific FAs and eicosanoids at various stages of fatty liver disease. These results suggest that targeting selective members of the CYP4A family is a viable therapeutic approach for treating and managing MASLD.

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. Teaser: This review provides an updated view of the physiology and pathology of CYP4 enzymes. CYP4 inhibitors are compiled based on their skeletons to provide clues for the future discovery of drug candidates targeting CYP4.

Comparative Proteomics Analysis of the Postmitochondrial Supernatant Fraction of Human Lens-Free Whole Eye and Liver

The increasing incidence of ocular diseases has accelerated research into therapeutic interventions needed for the eye. Ocular enzymes play important roles in the metabolism of drugs and endobiotics. Various ocular drugs are designed as prodrugs that are activated by ocular enzymes. Moreover, ocular enzymes have been implicated in the bioactivation of drugs to their toxic metabolites. The key purpose of this study was to compare global proteomes of the pooled samples of the eye (n = 11) and the liver (n = 50) with a detailed analysis of the abundance of enzymes involved in the metabolism of xenobiotics and endobiotics. We used the postmitochondrial supernatant fraction (S9 fraction) of the lens-free whole eye homogenate as a model to allow accurate comparison with the liver S9 fraction. A total of 269 proteins (including 23 metabolic enzymes) were detected exclusively in the pooled eye S9 against 648 proteins in the liver S9 (including 174 metabolic enzymes), whereas 424 proteins (including 94 metabolic enzymes) were detected in both the organs. The major hepatic cytochrome P450 and UDP-glucuronosyltransferases enzymes were not detected, but aldehyde dehydrogenases and glutathione transferases were the predominant proteins in the eye. The comparative qualitative and quantitative proteomics data in the eye versus liver is expected to help in explaining differential metabolic and physiologic activities in the eye. SIGNIFICANCE STATEMENT: Information on the enzymes involved in xenobiotic and endobiotic metabolism in the human eye in relation to the liver is scarcely available. The study employed global proteomic analysis to compare the proteomes of the lens-free whole eye and the liver with a detailed analysis of the enzymes involved in xenobiotic and endobiotic metabolism. These data will help in better understanding of the ocular metabolism and activation of drugs and endobiotics.

Metabolic signatures of bacterial vaginosis

Bacterial vaginosis (BV) is characterized by shifts in the vaginal microbiota from Lactobacillus dominant to a microbiota with diverse anaerobic bacteria. Few studies have linked specific metabolites with bacteria found in the human vagina. Here, we report dramatic differences in metabolite compositions and concentrations associated with BV using a global metabolomics approach. We further validated important metabolites using samples from a second cohort of women and a different platform to measure metabolites. In the primary study, we compared metabolite profiles in cervicovaginal lavage fluid from 40 women with BV and 20 women without BV. Vaginal bacterial representation was determined using broad-range PCR with pyrosequencing and concentrations of bacteria by quantitative PCR. We detected 279 named biochemicals; levels of 62% of metabolites were significantly different in women with BV. Unsupervised clustering of metabolites separated women with and without BV. Women with BV have metabolite profiles marked by lower concentrations of amino acids and dipeptides, concomitant with higher levels of amino acid catabolites and polyamines. Higher levels of the signaling eicosanoid 12-hydroxyeicosatetraenoic acid (12-HETE), a biomarker for inflammation, were noted in BV. Lactobacillus crispatus and Lactobacillus jensenii exhibited similar metabolite correlation patterns, which were distinct from correlation patterns exhibited by BV-associated bacteria. Several metabolites were significantly associated with clinical signs and symptoms (Amsel criteria) used to diagnose BV, and no metabolite was associated with all four clinical criteria. BV has strong metabolic signatures across multiple metabolic pathways, and these signatures are associated with the presence and concentrations of particular bacteria.

Bacterial vaginosis (BV) is a common but highly enigmatic condition that is associated with adverse outcomes for women and their neonates. Small molecule metabolites in the vagina may influence host physiology, affect microbial community composition, and impact risk of adverse health outcomes, but few studies have comprehensively studied the metabolomics profile of BV. Here, we used mass spectrometry to link specific metabolites with particular bacteria detected in the human vagina by PCR. BV was associated with strong metabolic signatures across multiple pathways affecting amino acid, carbohydrate, and lipid metabolism, highlighting the profound metabolic changes in BV. These signatures were associated with the presence and concentrations of particular vaginal bacteria, including some bacteria yet to be cultivated, thereby providing clues as to the microbial origin of many metabolites. Insights from this study provide opportunities for developing new diagnostic markers of BV and novel approaches for treatment or prevention of BV.

Significance of arachidonic acid in ocular infections and inflammation

Innate immune responses in the cornea mainly play an important role to mobilize multiple interrelated pathways of corneal lipid, which involve in inflammatory corneal diseases. Signaling lipid mediators derived from arachidonic acid (AA) control cell proliferation, apoptosis, metabolism, and migration, are known as eicosanoids, phosphoinositides, sphingolipids, and fatty acids. Emerging evidences have highlighted the implication of lipid mediators in both injury and repair mechanisms in the cornea. Recently, the role of AA and its metabolites to induce proinflammatory mediators and inflammatory cell infiltration in the pathogen-infected cornea and to cause severe keratitis have been revealed. In this review, we focus on the novel roles of AA downstream signaling in the corneal inflammatory diseases and also the biological relevance of AA signaling in the therapeutic strategies for targeting sight-threatening diseases.

Ocular cytochrome P450s and transporters: roles in disease and endobiotic and xenobiotic disposition

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.

In vitro cell culture models to study the corneal drug absorption

INTRODUCTION

Many diseases of the anterior eye segment are treated using topically applied ophthalmic drugs. For these drugs, the cornea is the main barrier to reaching the interior of the eye. In vitro studies regarding transcorneal drug absorption are commonly performed using excised corneas from experimental animals. Due to several disadvantages and limitations of these animal experiments, establishing corneal cell culture models has been attempted as an alternative.

AREAS COVERED

This review summarizes the development of in vitro models based on corneal cell cultures for permeation studies during the last 20 years, starting with simple epithelial models and moving toward complex organotypical 3D corneal equivalents.

EXPERT OPINION

Current human 3D corneal cell culture models have the potential to replace excised animal corneas in drug absorption studies. However, for widespread use, the contemporary validation of existent systems is required.

Transfection of Cytochrome P4504B1 into the Cornea Increases Angiogenic Activity of the Limbal Vessels

Injury to the ocular surface induces the production of the corneal epithelial-derived 12-hydroxyeicosatetrienoic acid (12-HETrE), which exhibits stereospecific potent inflammatory and angiogenic properties and is formed by a cytochrome P450 (P450) enzyme, CYP4B1. We have cloned the rabbit corneal CYP4B1 into the expression plasmid pIRES2-enhanced green fluorescent protein (EGFP) and examined the effect of CYP4B1 overexpression on corneal inflammation in vivo and limbal vessel sprouting ex vivo. Cultured rabbit corneal epithelial cells transfected with pIRES2-EGFP-CYP4B1 metabolized arachidonic acid to 12-HETrE at a rate five times higher than that of pIRES2-EGFP-transfected cells (3.53 +/- 0.08 versus 0.62 +/- 0.10 nmol/h/10(6) cells; mean +/- S.E.M., n = 6, p < 0.05), indicating a functional expression of the CYP4B1. Injection of either plasmid into the rabbit cornea resulted in EGFP fluorescence in the corneal epithelium. However, corneal neovascularization, as measured by the length of penetrating blood vessels, was significantly greater in the corneas of eyes transfected with the pIRES2-CYP4B1 compared with pIRES2-EGFP. Corneal-limbal explants from eyes transfected with pIRES2-CYP4B1 showed a marked angiogenic activity (46 +/- 10 versus 12 +/- 3 mm capillary length, n = 6, p < 0.05), which correlated with increased levels of 12-HETrE, the CYP4B1-derived angiogenic 12-hydroxyeicosanoid (0.93 +/- 0.18 versus 0.15 +/- 0.02 pmol/explant, n = 6, p < 0.05), and was inhibited (76 +/- 5%) by the P450 inhibitor 17-octadecynoic acid. The results further implicate the corneal CYP4B1 as a component of the inflammatory and angiogenic cascade initiated by injury to the ocular surface and raise the possibility of a new therapeutic target for preventing corneal neovascularization, namely, the CYP4B1-12-HETrE system.

Effects of contact lens-induced hypoxia on the physiology of the corneal endothelium

Contact lens wear can cause a number of physiological changes in the cornea. Two areas of interest in my laboratory have been contact lens effects on the endothelium and, more recently, the role of metabolic activity in predicting corneal swelling. The first part of this review focuses on the function of the corneal endothelium, the nature of its fluid pump, and the effects of contact lens-induced hypoxia and corneal pH changes on corneal endothelial function. In the second part, the etiology of hypoxia-induced corneal swelling is reviewed in relation to new studies on the causes of intersubject corneal swelling variability. The results indicate that corneal swelling is influenced by both corneal metabolic activity and endothelial function.

Induction of rabbit lung CYP4A4 prostaglandin omega-hydroxylase by various steroid hormones

Cytochrome P4504A4 (CYP4A4) is expressed at low basal levels in adult rabbit lungs, but is significantly induced during pregnancy by an unknown mechanism. As the gradual rise in CYP4A4 levels appears to coincide with the progressive increase in several steroid hormones throughout pregnancy, we examined the induction of CYP4A4 after treatment with various steroid hormones by monitoring both the CYP4A4 mRNA level and the CYP4A4-specific prostaglandin E(1) (PGE(1)) omega-hydroxylation reaction in rabbit lung microsomes. Treatment with progesterone and/or a synthetic glucocorticoid (dexamethasone) resulted in a significant increase in PGE(1) omega-hydroxylase activity, whereas estradiol, aldosterone, dehydroepiandrosterone, and dehydroepiandrosterone sulfate did not. These studies indicated that dexamethasone was a more potent inducer of CYP4A4 than progesterone. Simultaneous injection of dexamethasone and glucocorticoid/progesterone antagonists (RU38486, RU40555, or RU43044) inhibited the increase in PGE(1) omega-hydroxylase activity as well as mRNA levels by approximately 50%. In addition, simultaneous treatment with both dexamethasone and progesterone did not result in an additive or synergistic effect on PGE(1) omega-hydroxylase activity. These data indicate that, while distinctive receptors for glucocorticoid and/or progesterone are involved, induction may also require common or interacting regulatory elements (yet to be determined) in the CYP4A4 gene. These findings implicate both of these steroid receptors (PR/GR) in the induction of CYP4A4 in rabbit lung.

Increased synthesis of specific eicosanoids in rejected corneal grafts

PURPOSE

Corneal injury stimulates the formation of both prostaglandins (PG) and 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), the major lipoxygenase metabolite. The purpose of this study was to investigate the metabolism of arachidonic acid (AA) in a model of corneal graft rejection.

METHODS

Corneal tissue from Dutch belted rabbits was transplanted to vascularized corneas of New Zealand white rabbits. Rejected corneas were removed at the endstage of allograft failure. The allograft, the host corneal rim, the contralateral control cornea rim of equal size and normal Dutch belted cornea from the same site as the allograft were incubated with 0.25 microCi [3H]AA and the released eicosanoids were analyzed by high-performance liquid chromatography.

RESULTS

The host corneal rims, adjacent to the failed allografts, produced up to five times as much 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) as contralateral control corneal rims. Additionally, prostaglandin E2 (PGE2) formation in the host rims increased 100% above controls, and 12(S)-HETE and PGE2 synthesis in the rejected corneal graft also increased. 12(R)-HETrE, an endogenous corneal angiogenic factor, was not detected in rejected corneas.

CONCLUSIONS

The results point to the importance of selective AA pathways as the source key inflammatory components found in rejected allografts.

Acidification of rabbit corneal endothelium during contact lens wear in vitro

Contact lens wear causes significant epithelial and stromal acidosis. In this study, we tested whether lens wear can cause endothelial acidosis as well. Rabbit corneas were isolated and perfused in vitro. The endothelial intracellular pH (pHi) was measured with a pH sensitive fluorescent probe (BCECF). Three conditions were examined: 1) Polymethylmethacrylate (PMMA) and rigid gas-permeable (RGP) contact lens wear using a range of oxygen transmissibility (Dk/L) from 0 to 121, 2) epithelial hypoxia produced by exposure to oligomycin/sodium azide solution or epithelial perfusion with 100% N2 equilibrated Ringer's solution, and 3) epithelial exposure to Ringer's equilibrated with 5% CO2, balance air. PMMA and RGP contact lens wear acidified endothelial cells by 0.23 +/- 0.01 (n = 23) and 0.11 +/- 0.01 pH units (n = 23), respectively, within twenty min of lens insertion. Epithelial hypoxia, induced by sodium azide and oligomycin, reversibly acidified the endothelium by 0.04 +/- 0.01 pH units (n = 4). However, epithelial hypoxia induced by perfusion with 100% N2 equilibrated Ringer's did not have a significant effect on endothelial pHi. Introduction of 5% CO2 to the epithelium, acidified the endothelium by 0.15 +/- 0.02 pH units (n = 7) within 10 min. We conclude that contact lens wear can significantly acidify corneal endothelial cells. The endothelial pHi change is caused almost exclusively by a build up of CO2 behind the lens; hypoxia having very little contribution. As expected, RGP contact lenses induced less endothelial acidosis than PMMA controls.