Retinoids, particularly all-trans-retinoic acid (RA), are potent regulators of cell differentiation, cell proliferation, and apoptosis. The role of all-trans-RA during development and in the maintenance of adult tissues has been well established. The control of all-trans-RA levels in cells and tissues is regulated by the balance between its biosynthesis and its catabolism to inactive metabolites. The cytochrome P450 enzyme P450RAI (herein renamed P450RAI-1) is partially responsible for this inactivation of all-trans-RA. In this report, we describe the identification, molecular cloning, and characterization of a second related enzyme, P450RAI-2, which is also involved in the specific inactivation of all-trans-RA. Transiently transfected P450RAI-2 can convert all-trans-RA to more polar metabolites including 4-oxo-, 4-OH-, and 18-OH-all-trans-RA. Competition experiments with other retinoids suggest that all-trans-RA is the preferred substrate. The high level of expression of P450RAI-2, particularly in the cerebellum and pons of human adult brain, suggests a unique role for this enzyme in the protection of specific tissues from exposure to retinoids.

Retinoids are potent regulators of cell proliferation, cell differentiation, and morphogenesis and are important therapeutic agents in oncology and dermatology. The gene regulatory activity of endogenous retinoids is effected primarily by retinoic acid isomers (all-trans and 9-cis) that are synthesized from retinaldehyde precursors in a broad range of tissues and act as ligands for nuclear retinoic acid receptors. The catabolism of alltrans-retinoic acid (atRA) is an important mechanism of controlling RA levels in cell and tissues. We have previously identified two cytochrome P450s, P450RAI-1 and P450RAI-2 (herein named CYP26A1 and CYP26B1), which were shown to be responsible for catabolism of atRA both in the embryo and the adult. In this report, we describe the identification, molecular cloning, and substrate characterization of a third member of the CYP26 family, named CYP26C1. Transiently transfected cells expressing CYP26C1 convert atRA to polar water-soluble metabolites similar to those generated by CYP26A1 and -B1. Competition studies with all-trans, 13-cis, and 9-cis isomers of retinoic acid demonstrated that atRA was the preferred substrate for CYP26C1. Although CYP26C1 shares extensive sequence similarity with CYP26A1 and CYP26B1, its catalytic activity appears distinct from those of other CYP26 family members. Specifically, CYP26C1 can also recognize and metabolize 9-cis-RA and is much less sensitive than the other CYP26 family members to the inhibitory effects of ketoconazole. CYP26C1 is not widely expressed in the adult but is inducible by RA in HPK1a, transformed human keratinocyte cell lines. This third CYP26 member may play a specific role in catabolizing both all-trans and 9-cis isomers of RA.

Long chain fatty acids have recently emerged as critical signaling molecules in neuronal, cardiovascular, and renal processes, yet little is presently known about the precise mechanisms controlling their tissue distribution and bioactivation. We have identified a novel cytochrome P450, CYP2U1, which may play an important role in modulating the arachidonic acid signaling pathway. Northern blot and real-time PCR analysis demonstrated that CYP2U1 transcripts were most abundant in the thymus and the brain (cerebellum), indicating a specific physiological role for CYP2U1 in these tissues. Recombinant human CYP2U1 protein, expressed in baculovirus-infected Sf9 insect cells, was found to metabolize arachidonic acid exclusively to two region-specific products as determined by liquid chromatography-mass spectrometry. These metabolites were identified as 19-and 20-hydroxy-modified arachidonic acids by liquid chromatography-tandem mass spectrometry analysis. In addition to /-1 hydroxylation of arachidonic acid, CYP2U1 protein also catalyzed the hydroxylation of structurally related long chain fatty acid (docosahexaenoic acid) but not fatty acids such as lauric acid or linoleic acid. This is the first report of the cloning and functional expression of a new human member of P450 family 2, CYP2U1, which metabolizes long chain fatty acids. Based on the ability of CYP2U1 to generate bioactive eicosanoid derivatives, we postulate that CYP2U1 plays an important physiological role in fatty acid signaling processes in both cerebellum and thymus.

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P reeclampsia in a first pregnancy is reportedly the strongest risk factor for having preeclampsia in subsequent pregnancies, with the odds for recurrence increasing with earlier gestational age at prior delivery. There is no information, however, on the absolute recurrence risk across the spectrum of gestational ages in prior deliveries. In this population-based study, the authors aimed to establish guides for recurrence risk based on gestational age at the first pregnancy complicated by preeclampsia and to determine whether demographic and clinical factors modify the risk.Taking data from a state-wide program in Missouri that links maternal birth and neonatal death certificates, the study population consisted of women who delivered their first two singleton births from 1989 through 1997 (n = 103,860). These were divided into two groups: those with preeclampsia (n = 6157) vs. those without (n = 97,703) during the first births. Covariates evaluated included maternal age, race, medical history, interbirth interval, change in paternity, smoking during pregnancy, body mass index (BMI), previous fetal death or stillbirth, small-for-gestational-age (SGA) newborns, and gestational age in the first delivery. The risk of preeclampsia was computed as the percentage of women in each group who developed preeclampsia during the second pregnancy. Regression models for both groups determined the adjusted risk ratios for known confounders between primary exposure and preeclampsia during the second pregnancy and adjusted for risk ratios for known confounders.In second pregnancies, 14.7% of women who had preeclampsia in the first pregnancy had a recurrence vs. recurrence in1.8% of those who did not (risk ratio, 8.4; 95% confidence interval, 7.8-9.1). Earlier gestational age at first delivery was a significant predictor of subsequent preeclampsia in both groups, although the association was markedly increased in those with prior preeclampsia and preterm birth. In women with prior preeclampsia, the risk of recurrence in those who delivered at term in the first pregnancy was approximately 12%, versus nearly 40% for those who delivered at <28 weeks' gestation. Increasing BMI also progressively increased risk in both groups at all gestational ages, while the length of the interbirth interval and paternity change had no impact.These findings suggest that the primary markers for recurrent preeclampsia in a second pregnancy are earlier gestational age in the first pregnancy and higher prepregnancy BMI (a modifiable risk). The same risk factors apply to women who did not have preeclampsia in a previous preg-nancy, although the magnitude of risk is much lower than in those who did. The authors suggest that these results could form the basis for counseling women with prior preeclampsia on the risk of recurrence in subsequent pregnancies. P arturients with preeclampsia (PE) are known to be at increased risk of hypertension, ischemic heart disease, and premature cardiovascular death, compared with normotensive women. It is not clear whether c...

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Type 1 Diabetes Mellitus (T1DM) is characterized by an augmented pro-inflammatory immune state. This contributes to the increased risk for gestational complications observed in T1DM mothers. In normal pregnancies, critical immunological changes occur, including the massive recruitment of lymphocytes, particularly CD56bright NK cells, into early decidua basalis and a 2nd trimester shift towards Type 2 immunity. Decidual CD56bright NK cells arise at least partly from circulating progenitors expressing adhesion molecules SELL and ITGA4 and the chemokine receptors CXCR3 and CXCR4. In vitro studies show that T1DM reduces interactions between blood CD56+ NK cells and decidual endothelial cells by reducing SELL and ITGA4-based interactions. To address the mechanisms by which specific lymphocyte subsets may be recruited from the circulation during pregnancy and whether these mechanisms are altered in T1DM, flow cytometry was used to examine eight peripheral blood lymphocyte subsets (Type 1 (IL18R1+) and Type 2 (IL1RL1+) CD56bright NK, CD56dim NK, NKT and T cells) from control and T1DM women. Blood was collected serially over pregnancy and postpartum, and lymphocytes were compared for expression of homing receptors SELL, ITGA4, CXCR3, and CXCR4. The decline of Type 1/Type 2 immune cells in normal pregnancy was driven by an increase in Type 2 cells that did not occur in T1DM. CD56bright NK cells from control women had the highest expression of all four receptors with greatest expression in 2nd trimester. At this time, these receptors were expressed at very low levels by CD56bright NK cells from TIDM patients. Type 1/Type 2 NKT cell ratios were not influenced by either pregnancy or TIDM. Our results suggest that T1DM alters immunological balances during pregnancy with its greatest impact on CD56bright NK cells. This implicates CD56bright NK cells in diabetic pregnancy complications.