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Biomedical subjects

D F Lewis

Publications and source records attributed to D F Lewis.

At least 55 records · Page 3Linked to original sources
PubMed1999

Splenic rupture associated with severe preeclampsia. A case report.

BACKGROUND: Splenic rupture is a very rare event complicating pregnancy. Approximately 5% of cases reported have involved the postpartum period. Unrecognized, this complication is universally fatal. CASE: Preeclampsia and pulmonary edema complicated a 42-year-old woman's intrapartum care. After cesarean delivery she was supported with mechanical ventilation, blood products and invasive monitoring. Shortly thereafter, she became hypotensive and developed disseminated intravascular coagulation. During exploratory laparotomy a splenic capsular rupture was identified. Splenectomy and continued intensive care support ultimately reversed the severe end-organ consequences. CONCLUSION: It is extremely important that this condition be maintained in the diagnostic differential of post-operative hemodynamic instability. Failure to identify it is invariably fatal. Awareness and intervention are essential to ensure a good outcome.

Adult↗
PubMed1998

Structural determinants of cytochrome P450 substrate specificity, binding affinity and catalytic rate.

The structural characteristics of cytochrome P450 substrates are summarised, showing that molecular descriptors can discriminate between chemicals of differing P450 isozyme specificity. Procedures for the estimation of P450 substrate binding interaction energies and rates of metabolism are described, providing specific examples in both individual compounds binding to P450s, including those of known crystal structure, and within series of structurally related chemicals. It is demonstrated that binding energy components are primarily hydrophobic/desolvation and electrostatic/hydrogen-bonded in nature, whereas electronic factors are of importance in determining variations in reaction rates. It is thus shown that the prediction of P450 substrate binding affinities and catalytic rates may be feasible, provided that sufficient structural information is available for the relevant enzyme-substrate complex.

Animals↗
PubMed1998

Cationic and anionic polymeric additives for wall deactivation and selectivity control in the capillary electrophoretic separation of proteins in food samples.

Both cationic and anionic polymeric additives were used for the capillary electrophoretic separation of proteins in food samples. The cationic polyelectrolyte polydiallyldimethylammonium chloride was more effective in minimizing protein-wall interactions at pH 3 than at pH 7, presumably due to greater repulsion between the adsorbed polymer and proteins. Improved resolution was observed in the presence of the co-additive sodium octanesulphonate, presumably due to ion-pairing interactions with protein sample components. The anionic polymer dextran sulfate produced relatively high efficiencies, 120,000-180,000 theoretical plates, for protein separation, presumably because the polymer adsorbed to the capillary wall, rendering the surface more hydrophilic. In addition to reduced protein-wall interactions, improved resolution was observed, presumably due to analyte-polymer ion-exchange/ion-pairing interactions. When poly(vinyl sulphonic acid) was used instead of dextran sulfate, broader profiles were obtained and fewer components were resolved, presumably due to reduced wall deactivation that is related to the lower hydrophilicity of poly(vinyl sulphonic acid).

Animals↗
PubMed1998

Molecular modelling and quantitative structure-activity relationship studies on the interaction of omeprazole with cytochrome P450 isozymes.

Molecular modelling of the anti-ulcerative agent, omeprazole, with the putative active sites of cytochromes P4503A4 and P4502C19, enzymes which are the major catalysts of omeprazole metabolism in man, are reported. Interactive docking of omeprazole in both CYP3A4 and CYP2C19 gives rise to binding orientations which are consistent with both the known sites of metabolism reported for these isoforms and with evidence from site-directed mutagenesis experiments on CYP2C19, a P450 associated with genetic polymorphism in human drug metabolism. The potential P450 enzymic interactions, inhibition and induction of omeprazole are discussed in the light of molecular modelling and QSAR (quantitative structure-activity relationship) studies on related compounds.

Anti-Ulcer Agents↗
PubMed1998

Further evaluation of COMPACT, the molecular orbital approach for the prospective safety evaluation of chemicals.

The molecular dimensions and electronic structures of the first group of 100 US NCI/NTP miscellaneous chemicals, evaluated for potential carcinogenicity by computer-optimized molecular parametric analysis for chemical toxicity (COMPACT) have been re-determined. Using improved criteria for cytochrome P450 (CYP) substrate specificity, re-defined for CYP1 as having a COMPACT radius [square root of (deltaE - 9.5)2 + (a/d(2) - 7.8)2] of < 6.5, and for CYP2E as having a collision diameter of 6.5 angstroms or less and deltaE < 15.5, the likely substrates of CYP1 and CYP2E, which are regarded as potential carcinogens, have been identified. In addition, log P values have been taken into account; those chemicals with log P < 0 are non-lipophilic substrates unlikely to reach the activating cytochrome enzymes, and have been regarded as non-carcinogens. The second group of 100 US NCI/NTP chemicals have also now been categorized by COMPACT into CYP1 and CYP2E substrates, and their potential carcinogenicities evaluated. Of the 203 chemicals in the 2 groups, those positive in the rodent two-species life-span carcinogenicity study (rodent assay) were 53%, those positive in the Ames test (mutagenicity) were 48%, and those positive in the COMPACT programme (carcinogenicity, mutagenicity, cytotoxicity) were 54%. Concordance between the COMPACT prediction of carcinogenicity/cytotoxicity and rodent two species life-span carcinogenicity data for the 203 chemicals is 69%, and correlation of COMPACT with Ames test data is 61%. The sensitivity of COMPACT for predicting rodent carcinogenicity is 72%, whereas the sensitivity of the Ames test for predicting carcinogenicity for the 203 chemicals was only 57%. The degree (severity) of rodent carcinogenicity also showed correlation with the COMPACT predictive evaluations of the chemicals.

Animals↗
PubMed1998

Oral or vaginal misoprostol administration for induction of labor: a randomized, double-blind trial.

OBJECTIVE: To compare the efficacy and vaginal birth intervals after intravaginal or oral misoprostol for labor induction. METHODS: One hundred seventy-eight women were randomized to one of two double-blind groups: 1) oral misoprostol 200 microg and one-half tablet placebo intravaginal or 2) oral placebo tablet and one-half tablet of a 100-microg misoprostol intravaginal (dose 50 microg). Doses were repeated every 6 hours until labor was established (maximum of three doses). RESULTS: Ninety-three subjects were assigned to oral misoprostol and 85 to intravaginal administration. Oral administration was accompanied by significantly shorter intervals to the onset of uterine contractility (133+/-78 minutes versus 168+/-93, P < .01) but a higher incidence of abnormal uterine contractile activity (tachysystole 38.7% versus 20.0%, P < .01; hyperstimulation syndrome 44.1% versus 21.2%, P < .01). No adverse maternal or neonatal outcomes were noted, nor were there differences in cesarean delivery rates or total lengths of labor. CONCLUSION: Oral administration of 200 microg misoprostol has similar efficacy to intravaginal administration of 50 microg but is associated with more frequent abnormal uterine contractility.

Administration, Intravaginal↗
PubMed1998

Molecular modelling of steroidogenic cytochromes P450 from families CYP11, CYP17, CYP19 and CYP21 based on the CYP102 crystal structure.

The results of homology modelling of mammalian steroidogenic cytochromes P450 (CYP) from families CYP11, CYP17, CYP19 and CYP21 are reported, based on a novel protein sequence alignment with CYP102, a bacterial P450 of known crystal structure. The molecular models generated from the CYP102 crystal structure template are consistent with experimental information from site-directed mutagenesis studies, steroidal substrate specificity and active site inhibitor studies. Interactive docking studies with both substrates and inhibitors of these enzymes indicate key residue interactions with the putative active site regions of each isoform investigated, which point to potential determinants of substrate specificity within these related enzymes.

Amino Acid Sequence↗
PubMed1998

Evolution of the cytochrome P450 superfamily: sequence alignments and pharmacogenetics.

The evolution of the cytochrome P450 (CYP) superfamily is described, with particular reference to major events in the development of biological forms during geological time. It is noted that the currently accepted timescale for the elaboration of the P450 phylogenetic tree exhibits close parallels with the evolution of terrestrial biota. Indeed, the present human P450 complement of xenobiotic-metabolizing enzymes may have originated from coevolutionary 'warfare' between plants and animals during the Devonian period about 400 million years ago. A number of key correspondences between the evolution of P450 system and the course of biological development over time, point to a mechanistic molecular biology of evolution which is consistent with a steady increase in atmospheric oxygenation beginning over 2000 million years ago, whereas dietary changes during more recent geological time may provide one possible explanation for certain species differences in metabolism. Alignment between P450 protein sequences within the same family or subfamily, together with across-family comparisons, aid the rationalization of drug metabolism specificities for different P450 isoforms, and can assist in an understanding of genetic polymorphisms in P450-mediated oxidations at the molecular level. Moreover, the variation in P450 regulatory mechanisms and inducibilities between different mammalian species are likely to have important implications for current procedures of chemical safety evaluation, which rely on pure genetic strains of laboratory bred rodents for the testing of compounds destined for human exposure.

Amino Acid Sequence↗
PubMed1998

The CYP2 family: models, mutants and interactions.

1. The construction of three-dimensional models of mammalian cytochromes P450 from the CYP2 family is reported based on protein sequence alignment with CYP102, a bacterial P450 of known crystal structure. 2. The homology models of CYP2 family enzymes appear to show self-consistency with the currently accumulated information from site-directed mutagenesis and chemical modification of amino acid residues known to affect redox partner interactions. 3. The generation of these models from the recently reported crystal structure of substrate-bound CYP102 enables the exploration of likely active site contacts with specific substrates of CYP2 family isozymes.

Amino Acid Sequence↗
PubMed1998

Molecular modelling of human CYP2C subfamily enzymes CYP2C9 and CYP2C19: rationalization of substrate specificity and site-directed mutagenesis experiments in the CYP2C subfamily.

1. The results of molecular modelling of human CYP2C isozymes, CYP2C9 and CYP2C19, are reported based on an alignment with a bacterial form of the enzyme, CYP102. 2. The three-dimensional structures of the CYP2C enzymes are consistent with known experimental evidence from site-directed mutagenesis, antibody recognition and regiospecificity of substrate metabolism. 3. The variations in substrate specificity between CYP2C9 and CYP2C19 can be rationalized in terms of single amino acid residue changes within the putative active site region, of which I99H appears to be the most significant.

Amino Acid Sequence↗
PubMed1998

Amino acid residue 250 has a functional role in the assembly of rabbit liver microsomal cytochrome P450 2B4.

Cytochrome P450 2B4 lacking amino acids 2-27, CYP2B4 (delta2-27), was mutated at position 250 and expressed in E. coli fused to glutathione S-transferase. Expression of the E250S variant (holo- plus apoenzyme) proceeded to an extent comparable with that of CYP2B4 (delta2-27), while the protein level of the E250P mutant averaged 42% that of the control pigment. Comparison of these data with the corresponding reduced CO difference spectra of the various CYP2B4 (delta2-27) forms revealed that, in the control and E250S preparations, about 90% and 44%, respectively, of the total amount of hemoprotein present existed in the form of holoenzyme, whereas the E250P derivative failed to produce a reduced carbonyl complex. Thus, replacement of the negatively charged E250 with an uncharged, polar serine residue substantially hampered assembly of CYP2B4 (delta2-27); introduction of an alpha-helix-disrupting proline completely blocked the formation of holoenzyme. These phenomena suggested that the negative charge of E250, residing in the putative G helix, underwent pairing with some positively charged group, possibly H285 located in the I helix. Deletion of the negative charge obviously perturbed the active-site geometry such as to affect both the incorporation and/or retention of the heme ligand and the spectral binding of substrates such as hexobarbital.

Animals↗
PubMed1998

Influence of mutation of the amino-terminal signal anchor sequence of cytochrome P450 2B4 on the enzyme structure and electron transfer processes.

The role of the NH2-terminal hydrophobic patch of cytochrome P4502B4 (CYP2B4) in interactions with NADPH-cytochrome P450 reductase (P450R) and cytochrome b5 (b5) was assessed using a variant lacking the signal anchor sequence (Delta2-27). CD, second-derivative, and fluorescence emission spectra indicated that the structure of the deletion mutant slightly differed from that of the native CYP2B4. Fitting of the initial-velocity patterns for P450R- and b5-directed electron transfer to the ferric CYP2B4 forms to Michaelis-Menten kinetics revealed an approximately 2.3-fold decrease in the affinity of the two electron donors for the engineered enzyme, while the reductive efficiency remained unaffected. Circumstantial analysis suggested that impaired association of the redox proteins with P4502B4(Delta2-27) accounted for this phenomenon. Interestingly, spectral docking of P450R to the truncated pigment was not hampered, while the binding of b5 was blocked. The rates of substrate-triggered aerobic NADPH consumption in systems containing CYP2B4(Delta2-27) and P450R were 16 to 56% those obtained with the unchanged hemoprotein. Decelerated cofactor oxidation did not arise on defective substrate binding or perturbed utilization of the substrate-bound oxy complex. Experiments with b5 as the ultimate electron donor hinted at some damage to second-electron transfer to the truncated enzyme. The results are consistent with the proposal that the NH2-terminal hydrophobic region of CYP2B4 might be of importance in preservation of the catalytic competence of the enzyme.

Amino Acid Sequence↗
PubMed1998

Obstructive sleep apnea during pregnancy resulting in pulmonary hypertension.

Obesity is known to increase maternal morbidity and mortality. We describe a case of obstructive sleep apnea due to obesity and discuss our treatment of the resulting pulmonary hypertension. A patient was transferred to our hospital at 29 weeks' gestation with severe anasarca and more than a 100-pound weight gain during pregnancy. Pulmonary hypertension due to obstructive sleep apnea was diagnosed. The patient was treated with nasal continuous positive airway pressure (CPAP) during sleep and remained in the hospital the remainder of her pregnancy. She had a massive spontaneous diuresis during her hospital stay and lost more than 100 pounds. She was delivered at term via cesarean section because of transverse lie. Preoperative hemodynamic monitoring confirmed the diagnosis of pulmonary hypertension. This represents the first case in the literature of obstructive sleep apnea leading to pulmonary hypertension in pregnancy. This patient responded well to nasal CPAP as evident by the massive diuresis and good maternal outcome.

Adult↗
PubMed1998

A combined COMPACT and HazardExpert study of 40 chemicals for which information on mutagenicity and carcinogenicity is known, including the results of human epidemiological studies.

The COMPACT approach for defining structural criteria for substrates and inducers of cytochrome P450 (CYP) enzymes which mediate the formation of reactive intermediates is discussed in the context of prediction of potential carcinogenicity. This is broadened to encompass structural studies on mammalian P450s, including those relevant to genetic polymorphism in man. The use of the COMPACT system, in parallel with the structure alert program HazardExpert (now incorporated into the Pallas system), for evaluating human carcinogenicity data is reported, as an example of the possible employment of a battery of short-term test procedures for safety evaluation. In particular, the importance of using the log P value (as a measure of compound lipophilicity) to assess the likelihood of a potentially toxic compound reaching the site of activation, is emphasized by the finding that most procarcinogens requiring metabolic activation by P450s are lipophilic in nature.

Animals↗
PubMed1998

Cytochromes P450 and species differences in xenobiotic metabolism and activation of carcinogen.

The importance of cytochrome P450 isoforms to species differences in the metabolism of foreign compounds and activation of procarcinogens has been identified. The possible range of P450 isozymes in significant variations in toxicity exhibited by experimental rodent species may have a relevance to chemical risk assessment, especially as human P450s are likely to show changes in the way they metabolize xenobiotics. Consequently, in the safety evaluation of chemicals, we should be cautious in extrapolating results from experimental animal models to humans. This paper focuses on examples in which species differences in P450s lead to significant alterations in carcinogenic response, and includes a discussion of the current procedures for toxicity screening, with an emphasis on short-term tests.

Animals↗
PubMed1998

Can shoulder dystocia be predicted? Preconceptive and prenatal factors.

OBJECTIVE: To evaluate the predictability of shoulder dystocia using preconceptive and prenatal risk factors. STUDY DESIGN: Data from 1,622 term patients with prenatal care prior to 20 weeks who delivered single, vertex fetuses during a consecutive 12-month period were analyzed. Two groups were chosen. The first group was patients whose fetuses experienced shoulder dystocia during delivery (cases). The second group (controls) consisted of the remaining patients, whose fetuses had not experienced shoulder dystocia. The two groups were compared with regard to demographics and pregnancy characteristics. RESULTS: Factors not significantly different between the two groups included were obesity, multiparity, history of diabetes, short maternal stature, postdatism and advanced maternal age. The incidence of macrosomia was significantly higher (P < .001) in cases (35.4%) than in controls (4.8%). Other factors associated with shoulder dystocia were previous shoulder dystocia, concurrent diabetes, prior delivery of a fetus > 4,000 g and excessive weight gain during pregnancy. Many factors previously associated with shoulder dystocia were found to be nonsignificant in our study. CONCLUSION: Macrosomia appears to be the single important factor associated with shoulder dystocia which, even in the presence of significant risk factors, remains largely unpredictable.

Adolescent↗