Biomedical subjects

J M Roberts

Publications and source records attributed to J M Roberts.

At least 145 records · Page 8Linked to original sources

PubMed1996

Evidence of endothelial activation and endothelial activators in cord blood of infants of preeclamptic women.

OBJECTIVE: In preeclampsia markers of endothelial activation (e.g., increased cellular fibronectin and activities that alter in vitro endothelial function (e.g., stimulation of nitric oxide and prostacyclin generation) are increased in the maternal circulation. We tested preeclamptic infant blood for these markers and activities and correlated these findings with fetal growth. STUDY DESIGN: Plasma was obtained from 17 term nulliparcus preeclamptic and normal pregnant women and their infants and from 8 additional preeclamptic mother-baby pairs from earlier gestations. Plasma cellular fibronectin and production of nitric oxide and prostacyclin by cultured endothelial cells exposed to 2% plasma were measured. RESULTS: Cellular fibronectin was higher in maternal plasma of preeclamptic than nonpregnant women (6.1 +/- 0.29 vs 4.2 +/- 0.27 microgram/ml, p < 0.01), as were stimulated endothelial nitric oxide and prostacyclin production (nitric oxide 42.5 +/- 3.9 vs 26.9 +/- 2.3 nmol nitrite/microgram protein/24 hours, p < 0.05; prostacyclin 261.7 +/- 31.2 vs 151.9 +/- 18.7 pg prostaglandin F1 alpha/microgram protein/24 hours, p < 0.05). In the preeclamptic infants cellular fibronectin was also greater (3.3 +/- 0.15 vs 2.6 +/- 0.14 microgram/ml, p < 0.01), as was endothelial nitric oxide production in response to the plasma (24.4 +/- 1.1 vs 21.4 +/- 0.09 mumol/L nmol nitrite/microgram protein/24 hours, p < 0.05). Prostacyclin production was not significantly different. In preeclamptic infants across a wide gestational age there was no correlation of endothelial activation and fetal growth. CONCLUSIONS: Infants of women with preeclampsia may be affected by endothelial dysfunction, as well as reduced uteroplacental perfusion.

Adult↗

PubMed1996

Heterogeneous causes constituting the single syndrome of preeclampsia: a hypothesis and its implications.

The cause of preeclampsia remains elusive in spite of many attempts to understand its biologic characteristics and to characterize its predictors. We suggest that there are distinct origins of preeclampsia, each with its own pathologic characteristics and natural history. One genesis is the result of reduced placental perfusion, which we will call placental, and another results from maternal disorders preexisting (but sometimes not evident before) pregnancy. These preexisting maternal disorders comprise predisposing factors for cardiovascular disease such as hypertension, renal disease, overweight, and diabetes. A critical review of the epidemiologic and pathologic literature is presented, which supports the hypothesis that preeclampsia is the result of heterogeneous causes. The implications of this hypothesis are discussed, particularly its impact on the development of rules to predict the occurrence of preeclampsia.

Female↗

PubMed1996

Nitric oxide synthase activity in the gravid rat uterus decreases a day before the onset of parturition.

OBJECTIVE: Our purpose was to determine the timing, tissue location, and isoform of the uterine nitric oxide synthase activity decrease at term in gravid rat uteri. STUDY DESIGN: Nitric oxide synthase specific activity was assayed in rat uteri 11 through 22 days' gestation by the difference in radiolabeled arginine to citrulline conversion with and without the cofactor reduced nicotinamide adenine dinucleotide phosphate. Nitric oxide synthase isoform was assessed by calcium sensitivity and subcellular location. RESULTS: Rat uterine nitric oxide synthase activity decreased between days 15 and 21 of gestation but did not decrease further at term (day 22), before and after the onset of labor. Decidual nitric oxide synthase activity exceeded the myometrial activity at 15 days' gestation, but then the two were equal at 18 through 22 days' gestation. The nitric oxide synthase activity was calcium insensitive except for half the decidual cytosolic activity on day 15. CONCLUSION: The decrease in pregnant rat uterine nitric oxide synthase activity coincides with the preparation of the uterus for parturition rather than the final activation of labor.

Animals↗

PubMed1996

Fasting serum triglycerides, free fatty acids, and malondialdehyde are increased in preeclampsia, are positively correlated, and decrease within 48 hours post partum.

OBJECTIVE: We tested the hypothesis that serum free (nonesterified) fatty acid and triglyceride concentrations are increased in nulliparous women with preeclampsia relative to women with uncomplicated pregnancies and that these lipids decrease post partum, consistent with the known resolution of clinical symptoms. The relationships between serum concentrations of these lipids and the lipid peroxidation metabolite malondialdehyde were also examined. STUDY DESIGN: Predelivery and 24 to 48 hour postpartum venous blood samples were collected from eight women with preeclampsia and nine women with uncomplicated pregnancies after an 8- to 10-hour fast. Sera were analyzed for concentrations of triglycerides, free fatty acids, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and malondialdehyde. RESULTS: Antepartum serum triglyceride and free fatty acid concentrations were increased approximately twofold in women with preeclampsia relative to uncomplicated pregnancies (p <0.02 and 0.004, respectively). Total, high-density lipoprotein, and low-density lipoprotein cholesterol concentrations did not differ between groups. Concentrations of all lipids decreased significantly in both groups within 48 hours post partum. However, triglyceride and free fatty acid concentrations remained higher in women with preeclampsia (p<0.006, both variables). Triglyceride and free fatty acid concentrations correlated positively, both ante partum (R2 0.42, p<0.01) and post partum (R2 0.39, p<0.02). Antepartum concentrations of malondialdehyde were 50% higher in women with preeclampsia (p<0.01) and decreased post partum (p <0.02) but did not decrease in controls (p = 0.07). Antepartum serum triglycerides and free fatty acids correlated positively with malondialdehyde concentrations (R2 0.38, p <0.02, both cases). CONCLUSION: Triglycerides and free fatty acids, but not cholesterol, are increased in preeclampsia and correlate with the lipid peroxidation metabolite malondialdehyde. We speculate that these interactions may contribute to endothelial cell dysfunction in preeclampsia.

Adult↗

PubMed1996

Urine but not plasma nitric oxide metabolites are decreased in women with preeclampsia.

OBJECTIVE: Nitric oxide is a potent vasorelaxant produced by endothelial cells. We tested the hypothesis that urinary and perhaps plasma nitric oxide metabolites would be reduced in women with preeclampsia. STUDY DESIGN: Plasma and urine from 14 women meeting strict clinical criteria for the diagnosis of preeclampsia and 20 normal nulliparous women were assayed for the stable metabolites of nitric oxide, nitrate and nitrite. RESULT: There was no significant difference of plasma concentrations of nitrate and nitrite between women with preeclampsia and women with normal pregnancies (32.7 +/- 3.1 vs 25.8 +/- 2.4 micromol/L). Plasma creatinine levels were elevated in women with preeclampsia (0.85 +/- 0.09 vs 0.66 +/- 0.02 mg/dl, p<0.01), indicating a reduced glomerular filtration rate. Urine concentrations of nitrate and nitrite normalized by creatinine excretion were significantly lower in women with preeclampsia compared with normal pregnant women (0.37 +/- 0.06 vs 0.69 +/- 0.11 micromol of nitrite per milligram creatinine, p. <0.05). CONCLUSIONS: Our study using concomitant measurement of plasma and urine nitrate and nitrite suggests a reduced production of nitric oxide in women with preeclampsia compared with normal pregnant women.

Adult↗

PubMed1996

Hyperuricemia and xanthine oxidase in preeclampsia, revisited.

Hyperuricemia is associated with the severity of preeclampsia and with fetal outcome. Traditionally the high uric acid concentration in preeclampsia has been attributed soley to renal dysfunction. Preeclampsia is also characterized by increased free radical formation and elevated oxidative stress. Xanthine dehydrogenase/oxidase produces uric acid. Xanthine dehydrogenase/oxidase is present as two isoforms in vivo. Uric acid production is coupled with formation of reactive oxygen species when the enzyme is in the oxidase form. Several factors can increase the holoenzyme activity and the conversion of xanthine dehydrogenase/oxidase to its oxidase form. These factors include hypoxia-reperfusion, cytokines, and increased substrate availability (xanthine and hypoxanthine). Preeclampsia is characterized by hyperuricemia and signs of increased formation of reactive oxygen species and decreased levels of antioxidants. Preeclampsia is also characterized by shallow implantation, producing a relatively hypoxic maternal-fetal interface, and increased turnover of trophoblast tissue, which can result in higher xanthine and hypoxanthine concentrations and higher levels of circulating cytokines. These mechanisms can lead to increased production of uric acid and free radicals and contribute to the hyperuricemia and increased oxidative stress present in preeclampsia.

Female↗

PubMed1996

Mechanical stress eliminates the effects of plasma from patients with preeclampsia on endothelial cells.

OBJECTIVE: Our purpose was to determine whether mechanical deformation alters in vitro effects of plasma from patients with preeclampsia on endothelial cell function to produce a paradigm similar to the in vivo disease state. STUDY DESIGN: The effects of 2% plasma from 12 patients with preeclampsia and 12 normal pregnant women on prostacyclin, nitric oxide, and endothelin production by cultured endothelial cells were measured in the presence or absence of cyclic stretch and laminar shear stress. RESULTS: In the absence of mechanical stress plasma from patients with preeclampsia resulted in greater prostacyclin and nitric oxide production (but no change in endothelin production) compared with plasma from normal pregnant women. Cyclic stretch did not affect prostacyclin or endothelin production but produced similar increases in nitric oxide production in cells exposed to plasma from the two groups. Shear stress markedly increased prostacyclin and nitric oxide production (but did not alter endothelin production). In the presence of shear stress there were no differences in production rates of nitric oxide or prostacyclin between cells exposed to plasma from the two groups. CONCLUSION: Shear stress alters the effects of plasma on endothelial cells. This is an important caveat in the interpretation of previous static in vitro culture studies and may partially explain the dichotomy between in vitro studies and in vivo findings in preeclampsia.

Adult↗

PubMed1996

End of the line: proteolytic degradation of cyclin-dependent kinase inhibitors.

Cyclin-dependent kinase inhibitors (CKIs) are crucial regulators of cell-cycle progression. The CKI Sic1 controls the timing of DNA replication by inhibiting Clb-Cdc28 kinase. Phosphorylation of Sic1 by CIn-Cdc28 kinase alleviates this inhibition by targeting Sic1 for degradation through the ubiquitin-mediated proteolytic pathway.

Cell Cycle↗

PubMed1996

Changes in cell-cycle protein expression during experimental mesangial proliferative glomerulonephritis.

A characteristic response to mesangial cell injury is proliferation, which is closely linked to mesangial matrix accumulation and the progression of glomerular disease. Cell proliferation in non-renal cells in vitro is regulated at the level of the cell-cycle by specific cyclins and their catalytic partners, cyclin dependent kinases (CDK). Cyclin kinase inhibitors (CKI) prevent proliferation by inhibiting cell-cycle progression. However, the expression of cell-cycle regulatory proteins in the kidney and in renal disease is unknown. To determine this we studied the expression of cell-cycle proteins in vivo in normal rats and rats with experimental mesangial proliferative glomerulonephritis (Thy1 model). Normal quiescent rat glomeruli have a differential expression for CKI's, where p27Kip1 is highly expressed, and the levels for p21 (Cip1, Waf1, Sdi1, Cap20) (p21) are low. The onset of mesangial cell proliferation in Thy1 glomerulonephritis is associated with a reduction in p27Kip1 levels when mesangial cell proliferation is maximal. Mesangial cell proliferation in vivo is also associated with an increase in glomerular expression of cyclin A, and an increase in expression and activity for CDK2. The resolution of mesangial cell proliferation was associated with a return to baseline levels for p27Kip1, while the expression for p21 increased substantially. Furthermore, mesangial cell p21 expression was maintained following the resolution of proliferation. These results provide evidence for a complex interplay of cell-cycle regulatory proteins during the glomerular response to injury in vivo. The marked increase in CDK2 expression during mesangial cell proliferation and the sustained increase in p21 expression following the resolution of mesangial cell proliferation suggests that the in vivo expression of certain cell-cycle proteins may differ from that described in non-renal cells in vitro.

Animals↗

PubMed1996

Decreased transferrin and increased transferrin saturation in sera of women with preeclampsia: implications for oxidative stress.

OBJECTIVE: The concerted iron-binding antioxidant activity of transferrin and ceruloplasmin decreases with increasing transferrin saturation by iron. We examined interactions between serum iron and iron-binding capacity and concentrations of the lipid peroxidation metabolite malondialdehyde in normal and preeclamptic pregnancies. We also asked if the release of iron from free hemoglobin by lipid hydroperoxides is a potential mechanism to increase transferrin saturation in preeclampsia. STUDY DESIGN: Predelivery and 24 to 48 hour postpartum venous blood was collected from 19 women with uncomplicated pregnancies and 17 with preeclampsia. Serum iron, iron binding capacity, and malondialdehyde were measured. In a subset of predelivery samples electron paramagnetic resonance spectroscopy was used to determine diferric transferrin, total transferrin, and ceruloplasmin concentrations and to examine interactions of an organic hydroperoxide with hemoglobin and transferrin. RESULTS: Antepartum serum iron concentrations were 46% greater, percent saturation of iron binding capacity was 98% greater, and malondialdehyde 50% greater, whereas total iron-binding capacity was 14% lower, in women with preeclampsia. By 48 hours post partum group differences between these variables other than total iron-binding capacity were not observed. Electron paramagnetic resonance spectroscopy confirmed antepartum differences and that total iron-binding capacity and percent saturation were equivalent to total transferrin and the ratio diferric transferrin/total transferrin, respectively. Antepartum concentrations of ceruloplasmin were not different. Antepartum malondialdehyde concentrations correlated positively with percent transferrin saturation and negatively with unsaturated iron-binding capacity (apotransferrin). Electron paramagnetic resonance spectroscopy demonstrated that the release of iron from free hemoglobin by lipid hydroperoxides in serum is a potential mechanism to increase transferrin saturation. CONCLUSION: Increased transferrin saturation and decreased unsaturated iron-binding capacity in preeclampsia may occur consequent to oxidative stress and then further promote oxidative stress by decreasing serum antioxidant buffering against redox-active iron.

Adult↗

PubMed1996

Adhesion-dependent cell cycle progression linked to the expression of cyclin D1, activation of cyclin E-cdk2, and phosphorylation of the retinoblastoma protein.

Growth factors and cell anchorage jointly regulate transit through G1 in almost all cell types, but the cell cycle basis for this combined requirement remains largely uncharacterized. We show here that cell adhesion and growth factors jointly regulate the cyclin D1- and E-dependent kinases. Adhesion to substratum regulates both the induction and translation of cyclin D1 mRNA. Nonadherent cells fail to phosphorylate the retinoblastoma protein (Rb), and enforced expression of cyclin D1 rescues Rb phosphorylation and entry into S phase when G1 cells are cultured in the absence of substratum. Nonadherent cells also fail to activate the cyclin E-associated kinase, and this effect can be linked to an increased association of the cdk inhibitors, p21 and p27. These data describe a striking convergence in the cell cycle controls used by the two major signal transduction systems responsible for normal and abnormal cell growth. Taken together with our previous studies showing adhesion-dependent expression of cyclin A, they also establish the cell cycle basis for explaining the combined requirement for growth factors and the extracellular matrix in transit through the Rb checkpoint, entry into S phase, and anchorage-dependent growth.

3T3 Cells↗

PubMed1996

Deregulation of cell cycle control in hematologic malignancies.

Cell cycle progression is governed by a complex network of positive and negative regulatory molecules. Mutations in cell cycle regulatory proteins occur frequently in tumor cells and defective cell cycle control is a common and perhaps universal feature of malignant transformation. This review outlines current models of normal cell cycle progression, focusing on the G1 phase of the cell cycle, and describes specific mutations that have been discovered in leukemias and lymphomas.

Cell Cycle↗

PubMed1996

Long-term use of permethrin-impregnated nets does not increase Anopheles gambiae permethrin tolerance.

Previous use of permethrin-impregnated bednets (mosquito nets) and curtains in four Kenyan villages for one year, 1990-91, raised the permethrin LT50 of Anopheles gambiae to 2.4-fold above its baseline value, designated permethrin tolerance (PT), as measured by exposure to 0.25% permethrin-impregnated papers in W.H.O. test-kits. During 1992-93, with ongoing use of permethrin-impregnated nets and curtains, PT regressed slightly compared with the contemporary susceptibility level of An.gambiae from non-intervention villages, to 1.8-fold in 1992 and only 1.6-fold in 1993. Thus the selection pressure of impregnated nets for PT in An.gambiae appears to be minimal in our study villages, although the impact of permethrin was demonstrated by a significantly lower parous-rate of An.gambiae females in the intervention (63-66%) than in non-intervention (79%) villages, and by reduced malaria transmission (reported elsewhere). In a selected stock of An.gambiae from the study area, PT did not affect the susceptibility to deltamethrin, fenitrothion, propoxur or DDT. Bioassays described herein provide easy procedures for field-monitoring of mosquito susceptibility/tolerance/resistance to insecticides used for net impregnation in operational programmes.

Animals↗

PubMed1996

Natural immune response to the C-terminal 19-kilodalton domain of Plasmodium falciparum merozoite surface protein 1.

We have characterized the natural immune responses to the 19-kDa domain of merozoite surface protein 1 in individuals from an area of western Kenya in which malaria is holoendemic. We used the three known natural variant forms of the yeast-expressed recombinant 19-kDa fragment that are referred to as the E-KNG, Q-KNG, and E-TSR antigens. T-cell proliferative responses in individuals older than 15 years and the profile of immunoglobulin G (IgG) antibody isotypes in individuals from 2 to 74 years old were determined. Positive proliferative responses to the Q-KNG antigen were observed for 54% of the individuals, and 37 and 35% of the individuals responded to the E-KNG and E-TSR constructs, respectively. Considerable heterogeneity in the T-cell proliferative responses to these three variant antigens was observed in different individuals, suggesting that the 19-kDa antigen may contain variant-specific T epitopes. Among responses of the different isotypes of the IgG antibody, IgG1 and IgG3 isotype responses were predominant, and the prevalence and levels of the responses increased with age. We also found that a higher level of IgG1 antibody response correlated with lower parasite density among young age groups, suggesting that IgG1 antibody response may play a role in protection against malaria. However, there was no correlation between the IgG3 antibody level and protection. Furthermore, we observed that although the natural antibodies cross-reacted with all three variant 19-kDa antigens, IgG3 antibodies in 12 plasma samples recognized only the E-KNG and Q-KNG constructs and not the E-TSR antigen. This result suggests that the fine specificity of IgG3 antibodies differentiates among variant-specific natural B-cell determinants in the second epidermal growth factor domain (KNG and TSR) of the antigen.

Adolescent↗

PubMed1996

Mutations in the homologous ZDS1 and ZDS2 genes affect cell cycle progression.

The Saccharomyces cerevisiae ZDS1 and ZDS2 genes were identified as multicopy suppressors in distinct genetic screens but were found to encode highly similar proteins. We show that at semipermissive temperatures, a yeast strain with a cdc28-1N allele was uniquely deficient in plasmid maintenance in comparison with strains harboring other cdc28 thermolabile alleles. Quantitative analysis of plasmid loss rates in cdc28-1N strains carrying plasmids with multiple replication origins suggests that a defect in initiating DNA replication probably causes this plasmid loss phenotype. The ZDS1 gene was isolated as a multicopy suppressor of the cdc28-1N plasmid loss defect. A zds1 deletion exhibits genetic interactions with cdc28-1N but not with other cdc28 alleles. SIN4 encodes a protein which is part of the RNA polymerase II holoenzyme-mediator complex, and a sin4 null mutation has pleiotropic effects suggesting roles in transcriptional regulation and chromatin structure. The ZDS2 gene was isolated as a multicopy suppressor of the temperature-sensitive growth defect caused by the sin4 null mutation. Disruption of either ZDS1 or ZDS2 causes only modest phenotypes. However, a strain with both ZDS1 and ZDS2 disrupted is extremely slowly growing, has marked defects in bud morphology, and shows defects in completing S phase or entering mitosis.

Adaptor Proteins, Signal Transducing↗

PubMed1996

Plasma of preeclamptic women stimulates and then inhibits endothelial prostacyclin.

We propose that the dichotomy between the in vivo reduction in intravascular prostacyclin production that occurs in preeclampsia and the in vitro stimulatory effect of plasma from preeclamptic patients on endothelial cell prostacyclin production is due to differential effects of chronic versus acute exposure to the plasma. We studied the acute versus chronic effects of 2% plasma from healthy pregnant and preeclamptic subjects by measuring endothelial prostacyclin production at different time periods after exposure to plasma. To determine whether such effects were specific to prostacyclin, we also measured prostaglandin E2 production. To determine whether chronic changes in prostacyclin production resulted from altered cellular responsiveness, we stimulated cells that had been exposed to plasma for 72 hours with arachidonic acid and measured prostaglandin production. Preliminary characterization of the plasma factor or factors responsible for alterations in prostaglandin production was performed. After 24 hours cells exposed to plasma from preeclamptic women produced more prostacyclin and prostaglandin E2 than cells exposed to plasma from healthy pregnant women. In contrast, after 72 hours exposure to plasma from preeclamptic women resulted in less endothelial cell prostacyclin production than exposure to plasma from healthy pregnant women, but there were no such differences in prostaglandin E2 production. Cells that had been exposed to plasma from preeclamptic women for 72 hours produced less prostacyclin but the same quantity of prostaglandin E2 after stimulation with arachidonic acid than cells exposed to plasma from healthy pregnant women. The plasma factor or factors responsible for altered prostacyclin production were sensitive to heat, acid, and proteases. In contrast to acute exposure, chronic exposure to plasma from preeclamptic women alters endothelial cells to result in decreased prostacyclin production, an observation consistent with in vivo findings.

Adult↗

PubMed1996

Distinct factors in plasma of preeclamptic women increase endothelial nitric oxide or prostacyclin.

The pathogenesis of preeclampsia is proposed to be due to uncharacterized circulating factors that activate endothelial cells. Support for this hypothesis is provided by in vitro activation of endothelial cells by plasma from preeclamptic women, eg, increased nitric oxide and prostacyclin generation. We performed molecular sizing, lipid extraction, and lipoprotein fractionation of plasma from normal pregnant and preeclamptic women and determined the ability of these plasma fractions to increase nitric oxide or prostacyclin generation by endothelial cells. Fractions from plasma of preeclamptic women were consistently more active than fractions from normal pregnant women, although characterization was qualitatively similar. The factors stimulating nitric oxide and prostacyclin were different. The factor (or factors) stimulating nitric oxide generation was extractable by charcoal and present in lipid extracts and lipoprotein isolates with a molecular weight greater that 1.5 million daltons, which is characteristic of a lipoprotein or lipoprotein aggregate. By contrast, activity to stimulate prostacyclin persisted after charcoal stripping or lipoprotein removal, partitioned to the aqueous fraction, and had a molecular weight of approximately 50,000 D. Two distinct factors in the blood of preeclamptic women alter endothelial function in vitro. This information should guide the search for circulating factors contributing to the pathophysiology of preeclampsia.

6-Ketoprostaglandin F1 alpha↗

PubMed1996

The Santa Lucia strain of Plasmodium falciparum as a model for vaccine studies. I. Development in Aotus lemurinus griseimembra monkeys.

The Santa Lucia strain of Plasmodium falciparum and the Aotus lemurinus griseimembra monkey are proposed as models for the testing of sporozoite vaccines and transmission-blocking vaccines. Approximately 85% of splenectomized monkeys were infected when fed upon by 10 or more heavily infected Anopheles freeborni mosquitoes. Sporozoite-induced infections in monkeys with or without previous infection with P. vivax readily infected mosquitoes, thus making them candidates for testing transmission-blocking vaccines.

Animals↗