Suppressed hepatocyte proliferation via a ROS-HNE-P21 pathway is associated with nicotine- and cotinine-enhanced alcoholic fatty liver in mice.

CYP2A5 is a major enzyme responsible for nicotine and cotinine metabolism in mice. Nicotine and cotinine enhance alcoholic fatty liver in wild type (WT) mice but not in CYP2A5 knockout (KO) mice, and reactive oxygen species (ROS) generated during the CYP2A5-mediated metabolism contributes to the enhancing effect. In combination with ethanol, nicotine and cotinine increased lipid peroxidation end product 4-hydroxynonenal (HNE) in WT mice but not in KO mice. In ethanol-fed KO mice, only 5 and 10 genes were regulated by nicotine and cotinine, respectively. However, in ethanol-fed WT mice, 59 and 104 genes were regulated by nicotine and cotinine, respectively, and 7 genes were up-regulated by both nicotine and cotinine. Plin 2 and Cdkn1a are among the 7 genes. Plin2 encodes adipose differentiation-related protein (ADRP), a lipid droplet-associated protein, which was confirmed to be increased by nicotine and cotinine in WT mice but not in KO mice. Cdkn1a encodes P21 and elevated P21 in nuclei was also confirmed. HNE can increase P21 and P21 inhibit cell proliferation. Consistently, hepatocyte proliferation markers proliferating cell nuclear antigen (PCNA) and Ki67 were decreased in WT mice but not in KO mice by nicotine/ethanol and cotinine/ethanol, respectively. These results suggest that inhibition of liver proliferation via a ROS-HNE-P21 pathway is involved in nicotine- and cotinine-enhanced alcoholic fatty liver.

Prediction of Hepatic Clearance of Stereoselective Metabolism of Carvedilol in Liver Microsomes and Hepatocytes of Sprague-Dawley and Cytochrome P450 2D-Deficient Dark Agouti Rats.

Hepatic clearance (CLh) of carvedilol (CAR), which is eliminated via stereoselective metabolism by the CYP2D subfamily of cytochromes P450 (CYPs), was predicted using liver microsomes and hepatocytes from Sprague-Dawley (SD) rats and CYP2D-deficient Dark Agouti (DA) rats to determine the usefulness of prediction method. Plasma concentrations of CAR following intravenous injection to DA rats were higher than those in SD rats. The volume of distribution at steady state and total clearance (CLtot) of S-CAR were approximately two times greater than those of R-CAR in both strains. CLh predicted from in vitro studies using DA rat liver microsomes was different from that obtained from in vivo studies. In contrast, in vitro CLh prediction using DA rat hepatocytes was nearly identical to the CLh observed in DA rats in vivo, and was lower than that in SD rats. The predicted CLh in vitro using hepatocytes correlated well with the observed CLtot in vivo, which is expected to be nearly the same as CLh. These results suggest that in vitro metabolic studies using hepatocytes are more relevant with regard to stereoselectively predicting CLh of CAR than those using liver microsomes.

Metabolism and Toxicity of Trichloroethylene and Tetrachloroethylene in Cytochrome P450 2E1 Knockout and Humanized Transgenic Mice.

Trichloroethylene (TCE) and tetrachloroethylene (PCE) are structurally similar olefins that can cause liver and kidney toxicity. Adverse effects of these chemicals are associated with metabolism to oxidative and glutathione conjugation moieties. It is thought that CYP2E1 is crucial to the oxidative metabolism of TCE and PCE, and may also play a role in formation of nephrotoxic metabolites; however, inter-species and inter-individual differences in contribution of CYP2E1 to metabolism and toxicity are not well understood. Therefore, the role of CYP2E1 in metabolism and toxic effects of TCE and PCE was investigated using male and female wild-type [129S1/SvlmJ], Cyp2e1(-/-), and humanized Cyp2e1 [hCYP2E1] mice. To fill in existing gaps in our knowledge, we conducted a toxicokinetic study of TCE (600 mg/kg, single dose, i.g.) and a subacute study of PCE (500 mg/kg/day, 5 days, i.g.) in 3 strains. Liver and kidney tissues were subject to profiling of oxidative and glutathione conjugation metabolites of TCE and PCE, as well as toxicity endpoints. The amounts of trichloroacetic acid formed in the liver was hCYP2E1≈ 129S1/SvlmJ > Cyp2e1(-/-) for both TCE and PCE; levels in males were about 2-fold higher than in females. Interestingly, 2- to 3-fold higher levels of conjugation metabolites were observed in TCE-treated Cyp2e1(-/-) mice. PCE induced lipid accumulation only in liver of 129S1/SvlmJ mice. In the kidney, PCE exposure resulted in acute proximal tubule injury in both sexes in all strains (hCYP2E1 ≈ 129S1/SvlmJ > Cyp2e1(-/-)). In conclusion, our results demonstrate that CYP2E1 is an important, but not exclusive actor in the oxidative metabolism and toxicity of TCE and PCE.

Vitamin D-Dependent Rickets Type 1B (25-Hydroxylase Deficiency): A Rare Condition or a Misdiagnosed Condition?

Vitamin D requires a two-step activation by hydroxylation: The first step is catalyzed by hepatic 25-hydroxylase (CYP2R1, 11p15.2) and the second one is catalyzed by renal 1α-hydroxylase (CYP27B1, 12q13.1), which produces the active hormonal form of 1,25-(OH)2 D. Mutations of CYP2R1 have been associated with vitamin D-dependent rickets type 1B (VDDR1B), a very rare condition that has only been reported to affect 4 families to date. We describe 7 patients from 2 unrelated families who presented with homozygous loss-of-function mutations of CYP2R1. Heterozygous mutations were present in their normal parents. We identified a new c.124_138delinsCGG (p.Gly42_Leu46delinsArg) variation and the previously published c.296T>C (p.Leu99Pro) mutation. Functional in vitro studies confirmed loss-of-function enzymatic activity in both cases. We discuss the difficulties in establishing the correct diagnosis and the specific biochemical pattern, namely, very low 25-OH-D suggestive of classical vitamin D deficiency, in the face of normal/high concentrations of 1,25-(OH)2 D. Siblings exhibited the three stages of rickets based on biochemical and radiographic findings. Interestingly, adult patients were able to maintain normal mineral metabolism without vitamin D supplementation. One index case presented with a partial improvement with 1alfa-hydroxyvitamin D3 or alfacalcidol (1α-OH-D3 ) treatment, and we observed a dramatic increase in the 1,25-(OH)2 D serum concentration, which indicated the role of accessory 25-hydroxylase enzymes. Lastly, in patients who received calcifediol (25-OH-D3 ), we documented normal 24-hydroxylase activity (CYP24A1). For the first time, and according to the concept of personalized medicine, we demonstrate dramatic improvements in patients who were given 25-OH-D therapy (clinical symptoms, biochemical data, and bone densitometry). In conclusion, the current study further expands the CYP2R1 mutation spectrum. We note that VDDR1B could be easily mistaken for classical vitamin D deficiency. © 2017 American Society for Bone and Mineral Research.

Cyp2c44 gene disruption is associated with increased hematopoietic stem cells: implication in chronic hypoxia-induced pulmonary hypertension.

We have recently demonstrated that disruption of the murine cytochrome P-450 2c44 gene (Cyp2c44) exacerbates chronic hypoxia-induced pulmonary artery remodeling and hypertension in mice. Subsequently, we serendipitously found that Cyp2c44 gene disruption also increases hematopoietic stem cell (HSC) numbers in bone marrow and blood. Therefore, the objective of the present study was to investigate whether CYP2C44-derived eicosanoids regulate HSC proliferation/cell growth and whether increased HSCs contribute to chronic hypoxia-induced remodeling of pulmonary arteries in Cyp2c44 knockout mice. Our findings demonstrated that lack of CYP2C44 epoxygenase, which catalyzed the oxidation of arachidonic acid to epoxyeicosatrienoic (EETs) and hydroxyeicosatetraenoic (HETE) acids, increases the numbers of 1) HSCs (CD34+, CD117+, and CD133+), 2) proangiogenic (CD34+CD133+ and CD34+CD117+CD133+) cells, and 3) immunogenic/inflammatory (CD34+CD11b+, CD133+CD11b+, F4/80+, CD11b+, and F4/80+CD11b+) macrophages in bone marrow and blood compared with wild-type mice. Among the various CYP2C44-derived arachidonic acids, only 15-HETE decreased CD117+ cell numbers when applied to bone marrow cell cultures. Interestingly, CD133+ and von Willebrand factor-positive cells, which are derived from proangiogenic stem cells, are increased in the bone marrow, blood, and lungs of mice exposed to chronic hypoxia and in remodeled and occluded pulmonary arteries of CYP2C44-deficient mice. In conclusion, our results demonstrate that CYP2C44-derived 15-HETE plays a critical role in downregulating HSC proliferation and growth, because disruption of the Cyp2c44 gene increased HSCs that potentially contribute to chronic hypoxia-induced pulmonary arterial remodeling and occlusion.NEW & NOTEWORTHY This study demonstrates that cytochrome P-450 2C44 plays a critical role in controlling the phenotype of hematopoietic stem cells and that when this enzyme is knocked out, stem cells are differentiated. These stem cells give rise to increased circulating monocytes and macrophages and contribute to the pathogenesis of chronic hypoxia-induced pulmonary artery remodeling and hypertension.

Role of Müller cell cytochrome P450 2c44 in murine retinal angiogenesis.

Polyunsaturated fatty acids (PUFA) and their cytochrome P450 (CYP450) metabolites have been linked to angiogenesis and vessel homeostasis. However, the role of individual CYP isoforms and their endogenous metabolites in those processes are not clear. Here, we focused on the role of Cyp2c44 in postnatal retinal angiogenesis and report that Cyp2c44 is highly expressed in Müller glial cells in the retina. The constitutive as well as inducible postnatal genetic deletion of Cyp2c44 resulted in an increased vessel network density without affecting vessel radial expansion during the first postnatal week. This phenotype was associated with an increased endothelial cell proliferation and attenuated Notch signaling. LC-MS/MS analyses revealed that levels of hydroxydocosahexaenoic acids (HDHA), i.e., 10-, 17- and 20-HDHA were significantly elevated in retinas from 5day old Cyp2c44-/- mice compared to their wild-type littermates. Enzymatic activity assays revealed that HDHAs were potential substrates for Cyp2c44 which could account for the increased levels of HDHAs in retinas from Cyp2c44-/- mice. These data indicate that Cyp2c44 is expressed in the murine retina and, like the soluble epoxide hydrolase, is expressed in Müller glia cells. The enhanced endothelial cell proliferation and Notch inhibition seen in retinas from Cyp2c44-deficient mice indicate a role for Cyp2c44-derived lipid mediators in physiological angiogenesis.