PP171. Hospitalized preterm mild preeclamptics: Is there a difference in outcomes between isolated or superimposed disease?

INTRODUCTION: Currently the standard of care is to admit and monitor patients with preterm mild preeclampsia. This is particularly important if the disease is superimposed in patients with chpt or with isolated disease if proteinuria is over 500mg in 24hours. Despite the common nature of this disease process little is known about the outcomes of these two groups. OBJECTIVES: The objective of this project is to compare the maternal and neonatal outcomes of patients hospitalized with isolated mild preterm preeclampsia to those with preterm superimposed preeclampsia. METHODS: All patients admitted between 1/2008 and 12/2011 that were expectantly managed with either mild isolated preterm preeclampsia or chpt with mild superimposed preeclampsia at our tertiary center were evaluated for inclusion in this retrospective cohort study. This study was IRB approved. To be included in the study a patient must have singleton gestation, no overt diabetes, no major chronic medical conditions, no major obstetrical complications, no congenital anomaly, or planned delivery before 37weeks. Patients with the following maternal complications were excluded: lupus, renal disease, and cardiac disease. Patients with the following obstetrical complications were excluded: multiple gestations, preterm labor, placenta previa, and preterm PROM. Mild preeclampsia and chpt were diagnosed using ACOG criteria. Patients were not included if they had severe disease being treated expectantly. Patients that met inclusion criteria were divided into two groups based on the presence of chpt. All patients were admitted to labor and delivery, treated with corticosteroids if indicated and were managed as inpatients until delivery. All patients had an ultrasound on admission, frequent laboratory evaluations, and daily antepartum testing. Outcomes of interest included latency period in days, incidence of IUGR, incidence of abruption, indication for delivery, maternal complications as well as neonatal morbidity and mortality. RESULTS: To date, we have identified 115 patients that met inclusion criteria and were included in this ongoing study. Fifty nine had isolated mild preeclampsia and 56 patients had chronic hypertension with superimposed preeclampsia. The following table compares the results of the two groups. Differences between the groups included age (24 vs. 30yrs, p<0.01), race with more whites having preeclampsia and more blacks having superimposed disease, days in hospital were longer in the superimposed group (9 vs. 13days, p<0.01) despite there being no significant difference in the latency period (6 vs. 9days, p=0.35). More superimposed patients developed pulmonary edema, (0% vs. 7%, p=0.05). A trend for increased abruptions was seen in the isolated group (9% vs. 0%, p=0.06). Vaginal delivery was more common in the preeclamptic group and repeat section more common in the superimposed group. No differences in neonatal outcomes were seen. CONCLUSION: Patients with preeclampsia were more likely younger, white and delivered vaginally when compared to patients with superimposed disease. While the superimposed patients were more likely older, black, had more pulmonary edema, were more likely treated with antihypertensives both antenatally and postpartum and were delivered by repeat section than patients with isolated disease. Neonatal outcomes were similar between the groups.

Effect of progesterone on cervical shortening in women at risk for preterm birth: secondary analysis from a multinational, randomized, double-blind, placebo-controlled trial.

OBJECTIVES: To determine whether progesterone supplementation alters cervical shortening in women at increased risk for preterm birth. METHODS: We performed a planned secondary analysis from a large, multinational preterm birth prevention trial of daily intravaginal progesterone gel, 90 mg, compared with placebo in women with a history of spontaneous preterm birth or premature cervical shortening. Transvaginal cervical length measurements were obtained in all randomized patients at baseline (18 + 0 to 22 + 6 weeks' gestation) and at 28 weeks' gestation. For this secondary analysis, the difference in cervical length between these time points was compared for the study population with a history of spontaneous preterm birth and for a population with premature cervical shortening (< or = 30 mm) at randomization. Differences between groups in cervical length for the 28-week examination were analyzed using ANCOVA, including adjustment for relevant clinical parameters and maternal characteristics. RESULTS: Data were analyzed from 547 randomized patients with a history of preterm birth. The progesterone-treated patients had significantly less cervical shortening than the placebo group (difference 1.6 (95% CI, 0.3-3.0) mm; P = 0.02, ANCOVA). In the population of 104 subjects with premature cervical shortening at randomization, the cervical length also differed significantly on multivariable analysis, with the treatment group preserving more cervical length than the placebo group (difference 3.3 (95% CI, 0.3-6.2) mm; P = 0.03, ANCOVA), with adjustment for differences in cervical length at screening. A significant difference was also observed between groups for categorical outcomes including the frequency of cervical length progression to < or = 25 mm and a > or = 50% reduction in cervical length from baseline in this subpopulation. CONCLUSIONS: Intravaginal progesterone enhances preservation of cervical length in women at high risk for preterm birth.

Human P450s involved in drug metabolism and the use of structural modelling for understanding substrate selectivity and binding affinity.

The human cytochrome P450 enzymes and their substrates are reviewed, together with current knowledge on the three-dimensional structures of P450s obtained from X-ray crystallographic studies and from homology modelling based on mammalian P450 template crystal structures. There is a particular focus on human Phase 1 drug metabolism mediated by P450s, and a rationalization of their substrate selectivities and binding strengths in terms of lipophilicity and active site interactions. The combination of molecular modelling and quantitative structure-activity relationship (QSAR) studies facilitates understanding of the factors which determine substrate selectivity and binding to the human drug-metabolizing P450s.

Digibind attenuates cytokine TNFalpha-induced endothelial inflammatory response: potential benefit role of digibind in preeclampsia.

OBJECTIVE: Exaggerated inflammatory response occurs in preeclampsia. Preeclampsia is also associated with elevated endogenous digoxin-like factors (EDLFs). Clinical data suggest that Digibind (a polyclonal sheep digoxin binding Fab fragment) binds to EDLF and may have the potential to attenuate vasoconstriction and other clinical symptoms of preeclampsia. This study was undertaken to determine if Digibind could attenuate increased endothelial inflammatory response induced by tumor necrosis factor-alpha (TNFalpha). STUDY DESIGN: Confluent endothelial cells were treated with TNFalpha at different concentrations with or without Digibind in culture. Endothelial adhesion molecule ICAM, VCAM and E-selectin expressions were determined by an immunoassay directly detected on the endothelial surface. Effects of Digibind on TNFalpha-induced extracellular signal-regulated kinase and Na(+)/K(+)-ATPase expressions were also examined. RESULT: (1) TNFalpha induced dose-dependent increases in ICAM, VCAM and E-selectin expressions in endothelial cells; (2) Digibind could attenuate and reduce TNFalpha-induced upregulation of endothelial E-selectin, ICAM and VCAM expressions. The blocking effect was in a concentration dependent manner; (3) Digibind had no effects on TNFalpha-induced upregulation of extracellular signal-regulated kinase phosphorylation, but could block TNFalpha-induced downregulation of Na(+)/K(+)-ATPase beta1 expression. CONCLUSION: Digibind may exert beneficial effects by preserving cell membrane Na(+)/K(+)-ATPase function and consequently to offset increased inflammatory response in endothelial cells.

Hospitalized late preterm mild preeclamptic patients with mature lung testing: what are the risks of delivery?

OBJECTIVE: To evaluate the risk of elective delivery of hospitalized patients with isolated mild preeclampsia with mature fetal lung profile compared with a cohort of patients who had preeclampsia with indicated delivery matched for gestational age. STUDY DESIGN: Patients with mild preeclampsia requiring hospitalization between 34 and 37 weeks estimated gestational age were offered amniocentesis for assessment of fetal lung maturity. If fetal lung maturity was documented, patients were offered delivery. These cases were then compared with indicated or spontaneously delivered controls with preeclampsia matched for gestational age. RESULT: A total of 51 cases were identified and matched with 51 controls. Sixteen case neonates (31.4%) were admitted to neonatal intensive care unit compared with 21 controls (41.2%). Five cases (9.8%) in each group developed respiratory distress syndrome (RDS). CONCLUSION: Elective delivery of mild preeclampsia with mature lung profiles in the late preterm gestation is not without neonatal risks, including a 10% risk of RDS in this series.

Normoglycemic diabetic ketoacidosis in pregnancy.

The clinical presentation of diabetic ketoacidosis in pregnancy is usually the same as in nonpregnant women, although the blood glucose may not be as high as in the nongravid state. We report a case of a pregnant woman who developed diabetic ketoacidosis with a normal blood glucose and review the pertinent medical literature. A 29-year-old woman with type I diabetes developed diabetic ketoacidosis during induction of labor. She had a glucose level of 87 mg per 100 ml with ketonuria, a metabolic acidosis, and an anion gap of 20 mmol l(-1). Normoglycemic diabetic ketoacidosis during pregnancy is truly unusual but can occur with relatively low, or even normal, blood sugars and necessitates prompt recognition and treatment. In this case, the combination of an initial episode of hypoglycemia and subsequent blood glucose levels below 95 mg per 100 ml led to a prolonged delay in the initiation of a planned insulin infusion for insulin coverage during the induction of labor. A significant ketoacidosis consequently developed, despite the absence of even a single elevated blood glucose measurement. This case illustrated the importance of not withholding insulin in a patient with type I diabetes for more than a few hours even if the blood glucose is normal.

Predominant basal directional release of thromboxane, but not prostacyclin, by placental trophoblasts from normal and preeclamptic pregnancies.

OBJECTIVE: To investigate apical and basal releases of thromboxane (TX) and prostacyclin (PGI2) by trophoblasts (TCs) from normal and preeclamptic (PE) placentas. METHODS: TCs isolated from normal and PE placentas were incubated in cell culture inserts for 48h. Medium from the upper (apical) and the lower (basal) chambers were then collected separately and measured for TX and PGI2 by their stable metabolites of TXB2 and 6-keto PGF1alpha by ELISA. Apical and basal releases of TX and PGI were also examined with apical exposure of TCs to arachidonic acid (AA)+/-aspirin at different concentrations. Villous tissue expressions for PGI synthase, TX synthase and TX (TP) receptor were examined by immunohistochemistry. RESULTS: (1) TXB2, but not 6-keto PGF1alpha, concentrations were significantly higher in the lower than in the upper chambers with both normal and PE TCs (p<0.01); (2) apical exposure of TCs to AA resulted in a significant increase in TX release towards both the upper and the lower chambers in normal TCs (p<0.01), but only a significant increase in the upper chamber in PE TCs (p<0.01); (3) aspirin could attenuate AA-induced TX release both in the upper and the lower chambers in normal, but not in PE, TCs (p<0.01), respectively; (4) there were no differences in 6-keto PGF1alpha productions both in normal and PE TCs treated with AA+/-aspirin; (5) intense staining of TX synthase and TP receptor was seen in syncytiotrophoblast layer, villous core vessels and stromal cells in preeclamptic placental tissue sections. CONCLUSION: Predominant basal release of TX together with intense staining of TX synthase and TP receptor in trophoblasts, stromal cells and villous core vessels are found in placentas from PE. We speculate if predominant basal release of TX by TCs occurs in vivo as we found in our in vitro culture condition, basal released TX may play a significant role in increased placental vasoconstriction such as in PE.

Physiologically based modeling of the inhalation pharmacokinetics of ethylbenzene in B6C3F1 mice.

A physiologically based pharmacokinetic (PBPK) model was developed for inhaled ethylbenzene (EB) in B6C3F1 mice. The mouse physiological parameters were obtained from the literature, but the blood:air and tissue:air partition coefficients were determined by vial equilibration technique. The maximal velocity for hepatic metabolism (Vmax) obtained from a previously published rat study was increased by a factor of approximately 3 to account for enzyme induction during repeated exposures. The Michaelis affinity constant (Km) for hepatic metabolism of EB, obtained from a previously published rat PBPK modeling study, was kept unchanged during single and repeated exposure scenarios. Hepatic metabolism alone could not adequately describe the clearance of EB from mouse blood. Additional metabolism was assumed to be localized in the lung. The parameters for pulmonary metabolism were obtained by optimization of PBPK model fits to kinetic data collected following exposures to 75-1000 ppm. The PBPK model successfully predicted all available blood and tissue concentration data in mice exposed to 75 or 750 ppm EB. Overall, the results indicate that the rate of EB clearance is markedly higher in B6C3F1 mice than rats or humans and exceeds the hepatic metabolism capacity. Available biochemical evidence is consistent with a significant role for pulmonary metabolism; however, the extent to which the extrahepatic metabolism is localized in the lung is unclear. Overall, the PBPK model developed for the mouse adequately simulated the blood and tissue kinetics of EB by accounting for its high rate of clearance.

Vaginal progesterone is associated with a decrease in risk for early preterm birth and improved neonatal outcome in women with a short cervix: a secondary analysis from a randomized, double-blind, placebo-controlled trial.

OBJECTIVE: To investigate the efficacy of vaginal progesterone to prevent early preterm birth in women with sonographic evidence of a short cervical length in the midtrimester. METHODS: This was a planned, but modified, secondary analysis of our multinational, multicenter, randomized, placebo-controlled trial, in which women were randomized between 18 + 0 and 22 + 6 weeks of gestation to receive daily treatment with 90 mg of vaginal progesterone gel or placebo. Cervical length was measured with transvaginal ultrasound at enrollment and at 28 weeks of gestation. Treatment continued until either delivery, 37 weeks of gestation or development of preterm rupture of membranes. Maternal and neonatal outcomes were evaluated for the subset of all randomized women with cervical length < 28 mm at enrollment. The primary outcome was preterm birth at

Progesterone vaginal gel for the reduction of recurrent preterm birth: primary results from a randomized, double-blind, placebo-controlled trial.

OBJECTIVE: Preterm birth is the leading cause of perinatal morbidity and mortality worldwide. Treatment of preterm labor with tocolysis has not been successful in improving infant outcome. The administration of progesterone and related compounds has been proposed as a strategy to prevent preterm birth. The objective of this trial was to determine whether prophylactic administration of vaginal progesterone reduces the risk of preterm birth in women with a history of spontaneous preterm birth. METHODS: This randomized, double-blind, placebo- controlled, multinational trial enrolled and randomized 659 pregnant women with a history of spontaneous preterm birth. Between 18 + 0 and 22 + 6 weeks of gestation, patients were assigned randomly to once-daily treatment with either progesterone vaginal gel or placebo until either delivery, 37 weeks' gestation or development of preterm rupture of membranes. The primary outcome was preterm birth at

Increased chymotrypsin-like protease (chymase) expression and activity in placentas from women with preeclampsia.

Placenta-derived chymotrypsin-like protease (CLP/chymase) promotes endothelial P-selectin and E-selectin expression, which may be responsible for the increased neutrophil/endothelial interactions in preeclampsia (PE). However, little is known about this protease expression and production in human placenta. This study was undertaken to determine the distribution and gene expression of CLP in human placenta. Human placental tissues were obtained immediately after delivery from normal and PE pregnancies. We examined (1) CLP/chymase immunoactivity by immunohistochemical staining of villous tissue sections; (2) trophoblast mRNA and protein expression for chymase by RT-PCR and Western blot analysis; (3) chymase cDNA sequencing in isolated trophoblast cells (TCs); and (4) release of CLP by placental villous tissue cultured under 2% and 20% O(2). We found (1) CLP expression is mainly localized in the epithelial layer of syncytiotrophoblasts; (2) both mRNA and protein expression are significantly (p<0.05) upregulated in TCs isolated from PE vs. normal placentas; (3) TC chymase cDNA sequence and the deduced amino acid sequence are 100% identical to that reported for the human heart; and (4) villous tissue releases more chymotrypsin when cultured with 2% O(2). We conclude that (1) the DNA and protein sequence for chymase in placental trophoblast cells are the same as those reported in the human heart; (2) CLP/chymase expression is upregulated in TCs during PE; and (3) lowered oxygen condition promotes CLP release by placental TCs. Since chymase is a potent non-ACE angiotensin II producing enzyme, our data suggest that if placenta-derived CLP/chymase is released into the maternal circulation, it may contribute to the cardiovascular complications associated with PE.

Hypoxia-induced increase in soluble Flt-1 production correlates with enhanced oxidative stress in trophoblast cells from the human placenta.

OBJECTIVE: Placental trophoblast cells (TCs) produce soluble Flt-1 (sFlt-1). Hypoxia induces placental oxidative stress and modulates trophoblast function. The aim of this study was to investigate whether hypoxia mediates TC sFlt-1 production and whether increased sFlt-1 production correlates with increased oxidative stress in placental TCs. METHODS: Placentas were obtained immediately after delivery from normal pregnant women (n = 8). Placental TCs were isolated by Dispase digestion of villous tissue and purified by Percoll gradient centrifugation. Isolated TCs were cultured under normoxia (21% O2: 5% CO2/95% air) and hypoxia (2% O2/5% CO2/93% N2) conditions for 3 days in vitro. TC productions of sFlt-1, VEGF, and PlGF were measured by enzyme-linked immunosorbent assay (ELISA). Lipid peroxide production and superoxide dismutase (CuZn-SOD) levels were evaluated. Messenger RNA expressions of Flt-1, VEGF and PlGF were determined by RT-PCR. Messenger RNA expressions for superoxide dismutase (CuZn-SOD) and heme oxygenase-1 (HO-1) were also determined. Data are expressed as mean +/- SE. A p level less than 0.05 was considered statistically different. RESULTS: Our results show that sFlt-1 production was significantly increased by TCs cultured under hypoxia condition that correlates with increased lipid peroxide production. We also found that under hypoxia condition: (1) the ratio of PlGF/VEGF production was reversed; (2) the ratio of lipid peroxides to superoxide dismutase production was increased. The increased mRNA expressions for Flt-1 and VEGF and the decreased mRNA expression for PlGF in TCs were consistent with the protein productions under hypoxia condition. CONCLUSION: We concluded that upregulation of sFlt-1 and unbalanced PlGF/VEGF production associated with increased oxidative stress are consequences of hypoxia in placental TCs. Our results suggest that placental TCs are major sources of sFlt-1 and VEGF levels in the maternal circulation in women with preeclampsia.

Homology modelling of CYP3A4 from the CYP2C5 crystallographic template: analysis of typical CYP3A4 substrate interactions.

1. The results of homology modelling of cytochrome P4503A4 (CYP3A4), which is a human enzyme of major importance for the Phase 1 metabolism of drug substrates, from the CYP2C5 crystal structure is reported. 2. The overall homology between the two protein sequences was generally good (46%) with 24% of amino acid residues being identical and a 22% similarity between matched pairs in the CYP3A4 and CYP2C5 aligned sequences, thus indicating that CYP2C5 represents a viable template for modelling CYP3A4 by homology. 3. The CYP3A4 model appears to show consistency with the reported findings from the extensive site-directed mutagenesis studies already published. 4. Typical CYP3A4 substrates, such as midazolam, testosterone, nifedipine and verapamil, are shown to fit the putative active site of the enzyme structure in a manner consistent with their known positions of metabolism.

Protease chymotrypsin mediates the endothelial expression of P- and E-selectin, but not ICAM and VCAM, induced by placental trophoblasts from pre-eclamptic pregnancies.

OBJECTIVES: Soluble endothelial-cell adhesion molecules (ICAM, VCAM and PECAM) are markers of endothelial activation, and are elevated in the maternal circulation during pregnancy and even further increased in pregnancies complicated by pre-eclampsia (PE). To identify possible sources of endothelial activators during pregnancy, we addressed whether factors released from placental trophoblast cells (TCs) activate endothelial cells (ECs) to enhance adhesion molecule expression on ECs. We also examined whether proteases released by placental cells induce the endothelial cell surface molecule expression in PE. METHODS: Confluent ECs were co-cultured with placental TCs derived from normal (n=9) or PE (n=8) pregnancies or with placental conditioned media (CM) derived from PE placental cultures (n=7). ICAM, VCAM, P-selectin and E-selectin were quantified using an enzyme-linked immunosorbent assay (ELISA). The protease inhibitors alpha(2)-macroglobulin (alpha(2)M), thrombin inhibitor (TI) and chymotrypsin inhibitor (CI) were tested in the co-culture system. mRNAs for ICAM, VCAM, P-selectin and E-selectin were determined by RNase protection assay (RPA). NF-kappaB activity in ECs was also determined. RESULTS: (1) ICAM and VCAM expression was significantly increased on ECs co-cultured with both normal-TCs and PE-TCs, compared to control ECs (P<0.01). ICAM and VCAM expression in ECs co-cultured with normal-TCs did not differ from ECs co-cultured with PE-TCs. (2) E-selectin expression was increased on ECs co-cultured with normal-TCs (P<0.05) and further increased in ECs co-cultured with PE-TCs (P<0.01). (3) P-selectin expression was increased on ECs co-cultured with PE-TCs, but not ECs co-cultured with normal-TCs compared to control ECs (P<0.05). (4) alpha(2)M and TI did not alter the ICAM, VCAM, P-selectin and E-selectin expression on ECs induced by PE-CM. (5) CI blocked the upregulation of P-selectin and E-selectin (P<0.05), but not ICAM and VCAM expression, in ECs cultured with PE-CM. (6) Changes in mRNA for ICAM, VCAM, P-selectin and E-selectin paralleled the increases in protein expression on ECs cultured with PE-CM. (7) NF-kappaB activity was also increased in cells challenged with PE-CM. CONCLUSIONS: (1) Factor(s) released from both normal-TCs and PE-TCs promote ICAM and VCAM expression on ECs. (2) Factor(s) released from PE-TCs significantly increase EC P-selectin and E-selectin expression. (3) CI blocks the upregulation of P-selectin and E-selectin on ECs induced by factors released from PE placental cells, suggesting that chymotrypsin is responsible for the increased endothelial expression of P-selectin and E-selectin in pre-eclampsia.

Functional interaction of cytochrome P450 with its redox partners: a critical assessment and update of the topology of predicted contact regions.

The problem of donor-acceptor recognition has been the most important and intriguing one in the area of P450 research. The present review outlines the topological background of electron-transfer complex formation, showing that the progress in collaborative investigations, combining physical techniques with chemical-modification and immunolocalization studies as well as site-directed mutagenesis experiments, has increasingly enabled the substantiation of hypothetical work resulting from homology modelling of P450s. Circumstantial analysis reveals the contact regions for redox proteins to cluster on the proximal face of P450s, constituting parts of the highly conserved, heme-binding core fold. However, more variable structural components located in the periphery of the hemoprotein molecules also participate in donor docking. The cross-reactivity of electron carriers, purified from pro- and eukaryotic sources, with a diversity of P450 species points at a possible evolutionary conservation of common anchoring domains. While electrostatic mechanisms appear to dominate orientation toward each other of the redox partners to generate pre-collisional encounter complexes, hydrophobic forces are likely to foster electron transfer events by through-bonding or pi-stacking interactions. Moreover, electron-tunneling pathways seem to be operative as well. The availability of new P450 crystal structures together with improved validation strategies will undoubtedly permit the production of increasingly satisfactory three-dimensional donor-acceptor models serving to better understand the molecular principles governing functional association of the redox proteins.

Homology modelling of the nuclear receptors: human oestrogen receptorbeta (hERbeta), the human pregnane-X-receptor (PXR), the Ah receptor (AhR) and the constitutive androstane receptor (CAR) ligand binding domains from the human oestrogen receptor alpha (hERalpha) crystal structure, and the human peroxisome proliferator activated receptor alpha (PPARalpha) ligand binding domain from the human PPARgamma crystal structure.

We have generated by homology the three-dimensional structures of the ligand binding domain (LBD) of several interrelated human steroid hormone receptors (SHRs). These are the oestrogen receptor beta (hERbeta), the pregnane-X-receptor (PXR), the Ah receptor (AhR) and the constitutive androstane receptor (CAR). They were produced by homology modelling from the human oestrogen receptor alpha (hERalpha) crystallographic coordinates [Nature 389 (1997) 753] as a template together with the amino acid sequences for hERbeta [FEBS Lett. 392 (1996) 49], PXR [J. Clin. Invest. 102 (1998) 1016], AhR [Proc. Natl. Acad. Sci. U.S.A. 89 (1992) 815] and CAR [Nature 395 (1998) 612; Mol. Cell. Biol. 14 (1994) 1544], respectively. The selective endogenous ligand, in each case, was docked interactively within the putative ligand binding site using the position of oestradiol in hERalpha as a guide, and the total energy was calculated. In each receptor model a number of different ligands known to fit closely within the ligand binding site were interactively docked and binding interactions noted. Specific binding interactions included combinations of hydrogen bonding and hydrophobic contacts with key amino acid sidechains, which varied depending on the nature of the ligand and receptor concerned. We also produced the human peroxisome proliferator activated receptor alpha (PPARalpha) by homology modelling using the human PPARgamma (hPPARgamma) LBD crystallographic coordinates summarised in [Toxicol. In Vitro 12 (1998) 619] as a template together with the amino acid sequence for hPPARalpha [Toxicol. In Vitro 12 (1998) 619; Nature 395 (1998) 137]. The models will provide a useful tool in unravelling the complexity in the physiologic response to xenobiotics by examining the ligand binding interactions and differences between the steroid hormone receptors activation or inactivation by their ligands.

Homology modelling of human CYP1A2 based on the CYP2C5 crystallographic template structure.

1. The results of homology modelling of human cytochrome P4501A2 (CYP1A2) based on the CYP2C5 crystal structure are reported. It exhibits improved sequence homology relative to that of CYP102. 2. It was demonstrated that many selective substrates for CYP1A2 could fit within the putative active site of the enzyme, and in orientations which agree with documented evidence for CYP1A2-mediated metabolism. 3. Furthermore, a number of amino acid residues lining the haem pocket have been shown, via site-directed mutagenesis, to have an influence on substrate metabolism, and these experimental findings from the literature are consistent with the modelled interactions for selective substrates. 4. The binding affinities of several CYP1A2 substrates have also been calculated from the CYP1A2 active site interactions and they agree closely with experimental values.

Homology modelling of CYP2A6 based on the CYP2C5 crystallographic template: enzyme-substrate interactions and QSARs for binding affinity and inhibition.

The results of homology modelling of the human P450 enzyme CYP2A6, based on the CYP2C5 crystallographic template structure are reported. A substantial number of selective substrates of the CYP2A6 enzyme fit the putative active site in a manner that is consistent with their known metabolites. Moreover, the evidence from site-directed mutagenesis experiments is in accordance with the current model, particularly in relation to complementary amino acid contacts within the haem environment. The binding of substrates is rationalized in terms of QSAR analyses and from a consideration of the contributory factors affecting the binding affinity. The latter approach appears to represent a highly correlated (R=0.99) method for estimating the relative strength of enzyme-substrate binding within CYP2A6-selective compounds, albeit within a fairly limited dataset of substrates.

Homology modelling of human CYP2E1 based on the CYP2C5 crystal structure: investigation of enzyme-substrate and enzyme-inhibitor interactions.

The construction of a homology model of human cytochrome P450 2E1 (CYP2E1) is reported, based on the CYP2C5 crystallographic template. A relatively high degree of primary sequence homology (identity=59%), as expected for proteins of the same CYP family, ensured a straightforward generation of the 3-dimensional model due to relatively few deletions and insertions of amino acid residues with respect to the CYP2C5 crystal structure. Probing the CYP2E1 model with typical substrates of the enzyme showed a good agreement with experimental information in the form of positions of metabolism for substrates, and with site-directed mutagenesis data on certain residues. Furthermore, quantitative relationships between substrate binding affinity and various structural parameters associated with the substrate molecules facilitated the formulation of a procedure for estimating relative binding energy and, consequently, K(m) or K(D) values towards the CYP2E1 enzyme. This method has been based on a consideration of the active site interactions between substrates and key amino acid residues lining the haem pocket, together with compound lipophilicity data from partition coefficients.