Homology modelling of human cytochromes P450 involved in xenobiotic metabolism and rationalization of substrate selectivity

Molecular modelling of human cytochrome P450 (CYP) isoforms is described, based on amino acid sequence homology with a unique bacterial P450 (CYP102) of known crystal structure. It is found that for the human hepatic P450s involved in the metabolism of xenobiotics, ie. CYPIA2, CYP 1A6, CYP2B6, CYP2C9, CYP2C 19, CYP2D6, CYP2E1 and CYP3A4, there is a satisfactory agreement between specific substrate characteristics and topographical features of the putative active sites, including complementarity with key amino acid residues in the P450 haem environments. A combination of homology model interactions with substrates and certain molecular properties of the compounds themselves provides a methodology for the evaluation of potential P450 selectivity in new chemical entities (NCEs).

Increased neutrophil-endothelial adhesion induced by placental factors is mediated by platelet-activating factor in preeclampsia

OBJECTIVE

Endothelial cell activation or dysfunction and neutrophil-endothelial cell adhesion have been suggested to be important in the pathophysiology of preeclampsia. However, the mechanisms that underlie the alteration of endothelial cell function in preeclampsia are unknown. Placenta from preeclamptic pregnancies produces mediators and autacoids, which may be released into the maternal circulation and modulate endothelial function. In this study, the effect of placental factor(s) on neutrophil-endothelial adhesion and the possible role of platelet-activating factor (PAF) in mediating the response have been examined.

METHODS

Endothelial cells were isolated from human umbilical veins (HUVECs) from normal pregnancies. Confluent primary passage HUVECs were exposed to conditioned medium derived from normal and preeclamptic placental tissue cultures, with unconditioned medium as a control. Placental-conditioned medium was prepared by incubation of placental whole villous tissue in Dulbecco's Modified Eagle's Medium (DMEM) for 48 hours. Neutrophil-endothelial adhesion assays were performed to evaluate placental factors in mediating neutrophil-endothelial adhesion, and a PAF-3H scintillation proximity assay (SPA) system was used to determine endothelial PAF production. The PAF-receptor antagonist WEB 2086 was used to block placental factor-mediated increased neutrophil-endothelial adhesion induced by conditioned medium derived from preeclamptic placenta.

RESULTS

Neutrophils were significantly more adherent to HUVECs treated with conditioned medium from preeclamptic placentas (28.44 +/- 2.47%) than to HUVECs treated with conditioned medium from normal placentas (18.95 +/- 1.57%) or with unconditioned medium (14.60 +/- 1.29%, P < .01). Also, HUVECs exposed to preeclamptic placental-conditioned medium produced more PAF than the cells exposed to normal conditioned medium and unconditioned medium, 416.18 +/- 17.14 pg/1 x 10(7) cells versus 330.90 +/- 35.70 and 296.43 +/- 44.40 pg/1 x 10(7) cells, P < .05, respectively. The PAF receptor antagonist WEB 2086 completely blocked increased neutrophil-endothelial adhesion induced by preeclamptic placental-conditioned medium (13.24 +/- 0.81% versus 31.31 +/- 4.75%, P < .01).

CONCLUSION

In preeclampsia, the placenta releases one or more factors promoting neutrophil-endothelial adhesion. The increased neutrophil-endothelial adhesion thereby induced is a PAF-mediated event. It is suggested that if preeclamptic placentas release toxic factors into the maternal circulation in vivo, these factors may contribute to the altered vascular endothelial cell function in preeclampsia.

Molecular modelling of CYP2B6, the human CYP2B isoform, by homology with the substrate-bound CYP102 crystal structure: evaluation of CYP2B6 substrate characteristics, the cytochrome b5 binding site and comparisons with CYP2B1 and CYP2B4

1. Molecular modelling studies of CYP2B isoforms from rat (CYP2B1), rabbit (CYP2B4) and man (CYP2B6) are reported, with particular emphasis on substrate interactions with the human CYP2B isoform, CYP2B6. 2. The findings represent an advance on our previous study that focused primarily on the rat CYP2B isoform, CYP2B1, and involved homology modelling with substrate-free CYP102. 3. The current work utilizes the recently published substrate-bound CYP102 crystal structure as a template for construction of the CYP2B subfamily isoforms and shows, in particular, that known CYP2B6 substrate specificity and regioselectivity can be rationalized by putative active site interactions.

Molecular modelling of the human cytochrome P450 isoform CYP2A6 and investigations of CYP2A substrate selectivity

(1) The generation of a homology model of CYP2A6, the major catalyst of human hepatic coumarin 7-hydroxylase activity, involves the use of the recently published substrate-bound CYP102 crystal structure as a template. (2) A substantial number of structurally diverse CYP2A6 substrates are found to dock satisfactorily within the putative active site of the enzyme, leading to the formulation of a structural template (or pharmacophore) for CYP2A6 specificity/selectivity. (3) The CYP2A6 model is consistent with available evidence from site-directed mutagenesis studies carried out on CYP2A subfamily isoforms, and enables some explanation of species differences in CYP2A-mediated metabolism of certain substrates. (4) Quantitative structure-activity relationship (QSAR) analysis of CYP2A5 (the mouse orthologue) mutants yields statistically significant correlations between various properties of amino acid residues and coumarin 7-hydroxylase activity.

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.

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.

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.

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.

Activation of endothelial cells in preeclampsia: increased neutrophil-endothelial adhesion correlates with up-regulation of adhesion molecule P-selectin in human umbilical vein endothelial cells isolated from preeclampsia

OBJECTIVE

Increased endothelial activation has been suggested to be important in the pathophysiology for preeclampsia. Our objective was to examine whether in preeclampsia neutrophil adherence to endothelial cells is increased and whether endothelial cell-surface adhesion molecule expression is up-regulated.

METHODS

Endothelial cells were isolated from normal (n = 10) and preeclamptic (n = 9) human umbilical veins (HUVECs). Neutrophils were isolated from normal, healthy, nonpregnant female volunteers. Freshly isolated neutrophils were labeled with 51Cr, and labeled neutrophils were coincubated with confluent normal and preeclamptic endothelial monolayers. Adhesion assays were then performed. To determine whether in preeclampsia endothelial cellular-surface adhesion molecules are responsible for increased neutrophil-endothelial adhesion, cellular adhesion molecule expression of P-selectin, intercellular adhesion molecule-1 (ICAM-1), vascular cellular adhesion molecule-1 (VCAM-1), and E-selectin were examined by an enzyme-linked binding assay. Furthermore, adhesion assays were also performed on HUVECs pretreated with antibodies against P-selectin, ICAM-1, VCAM-1, and E-selectin.

RESULTS

Neutrophil adhesion to the HUVECs from preeclamptic pregnancies was significantly increased compared with neutrophil adhesion to the HUVECs from normal pregnancies (P < .01). Expression of cellular-surface adhesion molecule of P-selectin was significantly higher (P < .01) and ICAM-1 was significantly lower (P < .05) in HUVECs isolated from preeclampsia than from normal controls, whereas there was no difference for VCAM-1 and E-selectin expression between HUVECs from normal and preeclamptic pregnancies. No differences were found for neutrophil-endothelial adhesion on normal HUVECs pretreated with anti-P-selectin, anti-ICAM-1, anti-VCAM-1, and anti-E-selectin compared with the untreated cells. However, pretreatment of preeclampsia HUVECs with anti-P-selectin, anti-ICAM-1, anti-VCAM-1, and anti-E-selectin completely or partially blocked the neutrophil-endothelial adhesion compared to the untreated cells.

CONCLUSION

There is a significant increase in neutrophil adhesion to HUVECs that are isolated from preeclamptic pregnancies compared with normal controls. This increase appears to be a result of up-regulation of the cell-surface adhesion molecule P-selectin. Elevated P-selectin expression may play a significant role in neutrophil-endothelial hyperadhesiveness and contribute to vascular complications associated with preeclampsia.

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).

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.

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.

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.

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.

Expression of platelet-derived growth factor-A mRNA in human placenta: effect of magnesium infusion in pre-eclampsia

The expression of platelet-derived growth factor-A (PDGF-A) mRNA was examined in the cotyledons of normal human placentae and those from patients with pre-eclampsia. These patients exhibited pre-delivery blood pressure of 154+/-4/99+/-4 mmHg (mean+/-SEM) and met the criteria established for pre-eclampsia. During labour they received MgSO4 infusion for various time intervals (4-25 h). The PDGF-A message was quantitated to beta-actin by the solution hybridization nuclease protection assay. Since the two groups differed in two parameters (pre-eclampsia and MgSO4 treatment), the direct comparison was not feasible. An analysis of covariance revealed a significant difference in the message between the pre-eclamptic and control groups (P<0.01); the gestational age was not a significant covariate for either group but the time on MgSO4 in pre-eclampsia group was significant (P<0.002). A linear regression analysis of PDGF-A mRNA values for the pre-eclamptic group showed a time-dependent downregulation of the message by MgSO4 (P<0.01, r=- 0.796). These results show a uniform expression of PDGF-A mRNA in cotyledons of normal human placenta between 35 and 40 weeks of gestation. Furthermore, MgSO4 has an inhibitory effect on the expression of this message which may have aside from its anticonvulsive action beneficial effect on the function of pre-eclamptic placenta.

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.

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 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.

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.

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.

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.

Successful tocolysis: does cervical change affect time to delivery?

Generally, it is preferable to tocolyze patients with idiopathic preterm labor (PTL). Little information is available about ultimate outcomes after successful tocolysis. Our objective is to evaluate the relationship between cervical change after the initiation of tocolysis and the delay in time to delivery in patients with preterm labor. A historical analysis of all patients with successful tocolysis after PTL between January 1992 and December 1993 was undertaken. The patients were then placed in one of three categories (regression, unchanged, or progression) based on cervical change after the initiation of tocolysis. Various demographic pregnancy characteristics and pregnancy outcome data were analyzed. One hundred and twenty-six patients had successful tocolysis and met the admission criteria. Patients who had cervical progression had shorter delay to delivery, delivered at an earlier gestational age (31.7 weeks compared to 34.0 and 34.1 weeks, respectively, p < 0.05), and were more likely to deliver before 35 weeks (88% compared to 50.0 and 55.0%, respectively, p < 0.05). Also, neonates remained in the hospital longer and were more likely to have respiratory distress syndrome when compared to the other two groups. Patients who had cervical progression after the initiation of tocolysis are more likely to deliver prematurely, had a shorter delay to delivery, and delivered lower birth weight infants than did patients whose cervix regressed or remained unchanged. In our population, patients who had successful tocolysis had a preterm delivery rate of 59.5% before the 35th week of gestation.