Zinc status, pregnancy complications, and labor abnormalities

Maternal plasma zinc levels, red blood cell levels, and serum alkaline phosphatase activity were used as indices of zinc status in 279 pregnant women at delivery and were compared with the incidence of complications during the antenatal period and major dysfunctional labor patterns. The median values for plasma zinc, red blood cell zinc, and alkaline phosphatase were used as cutoff points to subdivide the patient population into "low" and "high" groups. Low levels of maternal plasma zinc were associated with more complications in the antenatal or intrapartum periods than maternal levels of either alkaline phosphatase or red blood cell zinc. Plasma zinc levels less than the median value were more commonly associated with mild toxemia (p = 0.02), vaginitis (p = 0.01), and postdates (p = 0.01) in the antenatal period. During the intrapartum period, low plasma zinc levels were associated with a prolonged latent phase (p = 0.05), a protracted active phase (p = 0.04), labor greater than 20 hours (p = 0.03), second stage greater than 2.5 hours (p = 0.01), and cervical and vaginal lacerations (p = 0.02). Low levels of maternal alkaline phosphatase were strongly associated with a history of previous stillbirth (p = 0.0005). A low maternal red blood cell zinc level was not associated with complications during either period. Since a low plasma zinc level is a valid predictor of pregnancy complications and abnormal labor, the results suggest that plasma zinc screening, as part of the patient's antenatal workup should be evaluated.

Inhibition of hydroxymethylglutaryl-coenzyme A synthase by L-659,699

A beta-lactone isolated from Fusarium sp. has been shown to be a potent specific inhibitor of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase [(S)-3-hydroxy-3-methylglutaryl-CoA acetoacetyl-CoA-lyase (CoA-acetylating), EC, 4.1.3.5] from rat liver. The structure of this beta-lactone, termed L-659,699, is (E,E)-11-[3-(hydroxy-methyl)-4-oxo-2-oxytanyl]-3,5,7-trimethyl-2,4 - undecadienenoic acid. A partially purified preparation of cytoplasmic HMG-CoA synthase from rat liver was inhibited by L-659,699 with an IC50 of 0.12 microM. The enzyme HMG-CoA reductase, beta-ketoacyl-CoA thiolase, acetoacetyl-CoA synthetase, and fatty acid synthase were not inhibited to any extent by this compound. In cultured Hep G2 cells, the compound inhibited the incorporation of [14C]acetate into sterols with an IC50 of 6 microM, while incorporation of [3H]mevalonate into sterols in these cells was not affected. The activity of HMG-CoA reductase in the cultured Hep G2 cells was induced in a dose-dependent manner by incubation with L-659,699. A 37-fold increase in reductase was observed after a 24-hr incubation with 62 microM L-659,699. The effect of a number of analogs of L-659,699 on HMG-CoA synthase is also discussed.

Decreased levels of hepatic epidermal growth factor receptors in obese hyperglycemic rodents

Stimulation of epidermal growth factor (EGF) receptor autophosphorylation by EGF and phosphorylation of a Mr 52,000 protein endogenous to the membrane extracts were decreased 6-12-fold in liver membrane extracts from mice homozygous for either the ob/ob or db/db mutation when compared to controls. Liver membranes from the mutant mice bound 4-5-fold less 125I-EGF/unit of protein than did their normal littermates, but exhibited normal EGF binding affinity. Similar decreases in EGF binding were noted in liver membranes from homozygous fa/fa Zucker rats, another obese, hyperinsulinemic animal model, when compared to values from control animals. We also immunoprecipitated hepatic EGF receptors from mice injected with [35S]methionine, and found that livers from db/db mice contained approximately 35% of the labeled EGF receptors found in control animals. Both ob/ob and db/db mice had serum immunoreactive EGF levels similar to or lower than those found in unaffected littermates, suggesting that ligand-mediated down-regulation of receptors was not the cause of the decreased EGF binding. In one mutant, db/db, the decreased binding was associated with a 6-fold decrease in the levels of liver EGF receptor mRNA transcripts; in the ob/ob mice, at most a 2-fold decrease in the level of liver EGF receptor transcripts was observed. EGF binding to cultured peritoneal fibroblasts derived from db/db mice was normal, suggesting that the abnormality in the mutant mice might result from altered environmental or tissue-specific factors rather than an abnormal receptor gene. This was supported by Southern blot analysis of DNA from these animals, which showed identical restriction fragment patterns for the EGF receptor gene in both control and mutant animals. These data indicate that three distinct strains of obese hyperglycemic rodents have decreased levels of hepatic EGF receptors, and suggest that this decrease may result from altered environmental stimuli or tissue-specific factors rather than a primary defect in the EGF receptor gene.

Characterization of a Drosophila protein that binds both epidermal growth factor and insulin-related growth factors

The identification of a novel protein from Drosophila melanogaster that binds both mammalian epidermal growth factor (EGF) and insulin has been reported (Thompson, K. L., S. J. Decker, and M. R. Rosner, 1985, Proc. Natl. Acad. Sci. USA., 82:8443-8447). This 100-kD protein (designated dp100) is also recognized by an antiserum against the human EGF receptor. To further characterize the properties of this protein, we have determined the binding spectrum, glycosylation state, and cellular distribution of dp100. Our results indicate that dp100 binds to other insulin-like and EGF-like growth factors with dissociation constants ranging from 10(-6) to 10(-9) M, and these ligands compete with each other for binding to dp100. All other ligands tested, including platelet-derived growth factor, transforming growth factor-beta, nerve growth factor, and glucagon, either did not bind or bound with a Kd greater than 10(-6) M. Unlike the Drosophila insulin receptor, dp100 does not bind to wheat germ agglutinin and is present in a cytoplasmic as well as a membrane-bound form that cannot be differentiated by two-dimensional PAGE. Further, dp100 is the sole transforming growth factor-alpha-binding protein detected by affinity labeling in Drosophila Kc cells. These results indicate that dp100 shares properties in common with, but distinct from, the Drosophila homologues of the insulin and EGF receptors.

Characterization of rodent epidermal growth factor receptor transcripts using a mouse genomic probe

Two genomic DNA clones encoding part of the mouse epidermal growth factor (EGF) receptor were isolated: an 8.0 kb insert that hybridized with the human EGF receptor kinase domain; and a 2.4 kb insert that mapped between the kinase and 3' autophosphorylation domains of the human EGF receptor gene. The 2.4 kb insert was further digested to a 2.0 kb fragment and a 0.4 kb fragment containing 49 residues that were almost identical to the corresponding human EGF receptor sequence. Ribonuclease protection studies with mouse RNA identified three exons of 170 kb, 105 kb, and 50 kb in the 2.0 kb probe that were less homologous to the corresponding human or rat mRNAs. Northern blot hybridizations identified two EGF receptor transcripts of 10 kb and 6 kb in normal, but not EGF-nonresponsive, mouse cell lines, and a single 9.5 kb transcript in rat cells. An additional 6.5 kb transcript from rat NRK cells was identified that is related to but not transcribed from the EGF receptor gene.

Identification of a novel receptor in Drosophila for both epidermal growth factor and insulin

The notable amino acid homology among mammalian growth factor receptors with tyrosine-specific protein kinase activity has led to speculation that these receptors derived from a common evolutionary precursor. We report the identification of a novel growth factor receptor from Drosophila cell cultures that has dual binding specificity for both insulin and epidermal growth factor (EGF). This 100-kDa protein is also related antigenically to the mammalian receptors for EGF and possibly insulin but may not correspond to the mammalian counterpart of either receptor in Drosophila. The Drosophila protein is recognized by antisera directed against the mammalian receptor for EGF in immunoblot hybridizations. It can be affinity labeled with either 125I-labeled insulin or 125I-labeled EGF after immunoprecipitation with anti-EGF receptor antiserum. Excess unlabeled EGF or insulin will block the affinity labeling with either growth factor, suggesting that both EGF and insulin share a common binding site on the 100-kDa Drosophila receptor. This Drosophila protein, therefore, may be closely related to an evolutionary precursor of the mammalian receptors for insulin and EGF.