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Biomedical subjects

D J Meyer

Publications and source records attributed to D J Meyer.

At least 55 records · Page 3Linked to original sources
PubMed1995

Activation of acute phase response factor (APRF)/Stat3 transcription factor by growth hormone.

The mechanism by which the binding of growth hormone (GH) to its cell surface receptor elicits changes in gene transcription are largely unknown. The transcription factor Stat1/p91 has been shown to be activated by GH. Here we show that acute phase response factor or Stat3 f1p4an antigenically related protein), is also activated by GH. Stat3 has been implicated in the interleukin-6-dependent induction of acute phase response genes. GH promotes in 3T3-F442A fibroblasts the tyrosyl phosphorylation of a protein immunoprecipitated by antibodies to Stat3. This protein co-migrates with a tyrosyl phosphorylated protein from cells treated with leukemia inhibitory factor, a cytokine known to activate Stat3. Tyrosyl phosphorylated Stat3 is also observed in response to interferon-gamma. Stat3 is present in GH-inducible DNA-binding complexes that bind the sis-inducible element in the c-fos promoter and the acute phase response element in the alpha 2-macroglobulin promoter. The ability of GH to activate both Stat1 and Stat3 (i.e. increase their tyrosyl phosphorylation and ability to bind to DNA) suggests that gene regulation by GH involves multiple Stat proteins. Shared transcription factors among hormones and cytokines that activate JAK kinases provide an explanation for shared responses, while the ability of the different ligands to differentially recruit various Stat family members suggests mechanisms by which specificity in gene regulation could be achieved.

3T3 Cells↗
PubMed1995

Interpretation of liver biopsies.

Liver biopsies help define the disease process and can assist the clinician in forming a prognosis. The small size of liver biopsy specimens and limited responses of the liver to a wide spectrum of injuries often do not allow for a specific etiologic diagnosis. Determination of the distribution and morphology of the lesion often provides useful diagnostic and prognostic information. Maximum value can be attained from liver biopsies when the histologic findings are correlated with the results of other diagnostic tests and there is good communication between the clinician and pathologist.

Animals↗
PubMed1995

Bile acids in the diagnosis, pathology, and therapy of hepatobiliary diseases.

Bile acids are normally confined in the enterohepatic circulation in which they play an important role in bile formation, biliary lipid excretion, and intestinal lipid absorption. In hepatobiliary diseases, bile acids escape the confinement of the enterohepatic circulation, allowing the measurement of the serum total bile acid concentration as a diagnostic indicator. Accumulation of certain bile acids within the hepatocyte, amplified as a consequence of cholestatic hepatobiliary disease, probably enhances cytotoxicity and leads to secondary pathology. Ursodeoxycholate, a bile acid with atypical physiological effects, may be useful in the treatment of various long-term cholestatic hepatobiliary diseases. Presently, most of the information on the toxicity and therapeutic usefulness of bile acids are based on studies in humans and experimental animals. Further studies, both basic and clinical, are needed to determine the pathologic as well as the therapeutic effects of bile acids in domestic animals.

Animals↗
PubMed1995

Automated and accurate assessment of the distribution, magnitude, and direction of pincushion distortion in angiographic images.

RATIONALE AND OBJECTIVES: Pincushion distortion continues to be a potential problem for the accurate assessment of arterial and catheter dimensions from x-ray angiograms. The authors investigate whether the distortion of state-of-the-art intensifiers is yet small enough to be neglected, and whether the rotation/angulation of the x-ray system plays a significant role. METHODS: The location and degree of distortion from x-ray images of a centimeter grid, which is positioned against the input screen of the image intensifier, are assessed automatically using image processing techniques. A value for the maximum amount of change in the distortion vector field is derived that allows the estimation of the maximum relative error associated with a diameter measurement uncorrected for pincushion distortion. RESULTS: The accuracy of the algorithm itself was assessed by rotating and translating the centimeter grid under the image intensifier at anteroposterior position. For the distortion vector length, the standard deviation in the measurement of the distortion areas was found to be 3.7 cm2 (1.3% of the total area). For the gradient values, the standard deviation was 2.2 cm2 or 0.75% of the total image intensifier area. In the second evaluation study, the centimeter grid was fixed onto the input screen of the image intensifier, and the gantry was rotated to span all possible positions of the system. In this case, the changes in measured areas were often much larger (up to 51.25 cm2 for a 9-inch image intensifier, equivalent to 15.6% of the total image intensifier area) than the standard deviations that had been found in the first evaluation study. CONCLUSIONS: The distortion is highly dependent upon the actual spatial position of the image intensifier, and correcting for pincushion distortion may therefore introduce larger errors than leaving the measurements uncorrected.

Algorithms↗
PubMed1995

Copper chelation-induced reduction of the biological activity of S-nitrosothiols.

1. The effect of copper on the activity of the S-nitrosothiol compounds S-nitrosocysteine (cysNO) and S-nitrosoglutathione (GSNO) was investigated, using the specific copper chelator bathocuproine sulphonate (BCS), and human washed platelets as target cells. 2. Chelation of trace copper with BCS (10 microM) in washed platelet suspensions reduced the inhibition of thrombin-induced platelet aggregation by GSNO; however, BCS had no significant effect on the anti-aggregatory action of cysNO. BCS inhibited cyclic GMP generation in response to both cysNO and GSNO. 3. The effect of BCS was rapid (within 30 s), and could be abolished by increasing the platelet concentration to 500 x 10(9) l-1. 4. In BCS-treated platelet suspensions, the addition of Cu2+ ions (0.37-2.37 microM) led to a restoration of both guanylate cyclase activation and platelet aggregation inhibition by GSNO. 5. The anti-aggregatory activity of GSNO was reduced in a concentration-dependent manner by the copper (I)-specific chelators BCS and neocuproine, and to a smaller extent by desferal. No effect was observed with the copper (II) specific chelator, cuprizone, the iron-specific chelator, bathophenanthroline sulphonate, or the broader-specificity copper chelator, D-penicillamine. 6. In both BCS-treated and -untreated platelet suspensions, cys NO was more potent than GSNO as a stimulator of guanylate cyclase. In BCS-treated platelet suspensions there was no significant difference between the anti-aggregatory potency of cysNO and GSNO; however, in untreated suspensions, GSNO was significantly more potent than cysNO. Thus, when copper was available, GSNO produced a greater inhibition of aggregation than cysNO, despite being a less potent activator of guanylate cyclase. 7. The breakdown of cysNO and GSNO was measured spectrophotometrically by decrease in absorbance at 334 nm. In Tyrode buffer, cysNO (10 microM) broke down at a rate of 3.3 microM min-1. BCS (10 microM)reduced this to 0.5 microM min-1. GSNO, however, was stable, showing no fall in absorbance over a period of 7 min even in the absence of BCS.8. We conclude that copper is required for the activity of both cysNO and GSNO, although its influence on anti-aggregatory activity is only evident with GSNO. The stimulatory effect of copper is unlikely to be explained solely by catalysis of S-nitrosothiol breakdown. The enhancement by copper of the anti-aggregatory activity of GSNO, relative to cysNO, suggests that copper may be required for biological activity of GSNO which is independent of guanylate cyclase stimulation.

Blood Platelets↗
PubMed1994

Effects of human and rat glutathione S-transferases on the covalent DNA binding of the N-acetoxy derivatives of heterocyclic amine carcinogens in vitro: a possible mechanism of organ specificity in their carcinogenesis.

The effects of glutathione (GSH) and of purified human and rat GSH S-transferases (GSTs) on the covalent DNA binding of 3 putative ultimate food-borne carcinogens, the N-acetoxy derivatives of 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), 2-amino-3-methylimidazo(4,5-f)quinoline (IQ), and 2-amino-3,8-dimethylimidazo(4,5-f)quinoxaline (MeIQx), were studied in vitro. GSH (5 mM) alone slightly inhibited (10%) the DNA binding of N-acetoxy-PhIP (100 microM) at pH 7.5, but the binding could be strongly inhibited in the presence of both GSH and GSTs. Among human GSTs, the isozyme A1-1 (alpha-class) was most effective (90% inhibition) followed by A1-2 (40% inhibition); the effect of adding A2-2 was negligible, suggesting that the activity exists in subunit A1. In addition, human GST P1-1 (pi-class) also had some inhibitory effect (30%). Among the rat GSTs tested, GST 1-2 and GST 12-12 (theta-class), which are the equivalent of human A1-2 and T2-2, respectively, were able to inhibit DNA binding of N-acetoxy-PhIP (75 and 40%, respectively). This activity toward N-acetoxy-PhIP was dependent on enzyme concentration and was subject to inactivation by triethyltin bromide, a known GST inhibitor. In contrast, the binding of N-acetoxy-IQ or N-acetoxy-MeIQx to DNA was unaffected by addition of the human or rat GSTs; however, GSH alone significantly inhibited (40%) their binding to DNA. High-performance liquid chromatographic analyses of incubation mixtures containing N-acetoxy-PhIP, GSH, and GST A1-1 failed to detect GSH conjugates of PhIP. Only oxidized glutathione and the parent amine, PhIP, were detected as reaction products, suggesting a redox mechanism. GST activity in human hepatic and colon mucosal cytosols was subsequently examined using the synthetic or O-acetyltransferase-generated N-acetoxy derivatives of PhIP, IQ, and MeIQx as substrates. GST activity toward N-acetoxy-PhIP was expressed in all 8 livers but not in 6 colons. No activity toward N-acetoxy-IQ or N-acetoxy-MeIQx was detected in human liver cytosols. This study indicates that a GST-dependent detoxification pathway may be an important determinant for the organ specificity of the heterocyclic amine carcinogens. Moreover, the high specificity of the reaction for GST A1-1, which is known to be inducible by cruciferous and yellow-green vegetable consumption, is consistent with the protective effects of such diets against human colorectal cancer.

Animals↗
PubMed1994

Human glutathione transferase catalysis of the formation of S-nitrosoglutathione from organic nitrites plus glutathione.

The kinetics of spontaneous and human glutathione transferase catalysed formation of S-nitrosoglutathione (GSNO) from glutathione (GSH) and n-butyl- or amyl nitrite have been studied. At physiological pH and temperature, k2 values of 22.3 and 21.0 M-1.min-1 were obtained for n-butyl- and amyl nitrites, respectively. Rate enhancements, (kcat/Km x k2) x 10(-4), due to purified human GSH transferases A1-1, A2-2 and M1a-1a were, respectively, 7.00, 2.94 and 10.6 for n-butyl nitrite and 121, 3.92 and 34.5 for amyl nitrite. GSH transferase P1-1 showed no detectable catalysis of the formation of GSNO. The data suggest that the presence of GSTs A1-1, A2-2 or M1-1 contribute substantially to intracellular metabolism of alkyl nitrites to GSNO. The results may be significant with regard to the immunotoxicity of alkyl nitrites.

Catalysis↗
PubMed1994

Kinetics and equilibria of S-nitrosothiol-thiol exchange between glutathione, cysteine, penicillamines and serum albumin.

The kinetics and equilibria of S-nitrosothiol-thiol (SNO-SH) exchange reactions were determined using differential optical absorption. At pH 7.4 and 37 degrees C, k2 values ranged from 0.9 M-1.s-1 for the reaction between S-nitroso-glutathione (GSNO) and N-acetyl-penicillamine, and up to 279 M-1.s-1 for the exchange between S-nitroso-penicillamine (penSNO) and GSH. SNO-SH exchange involving GSH/GSNO and cysteine/cySNO was relatively rapid, k2 approx. 80 M-1.s-1 with an equilibrium constant slightly in favour of GSNO. GSNO was strongly favoured in equilibrium with penSNO, keq 0.0039. In the case of SNO-SH exchange between S-nitroso human serum albumin (albSNO) and GSH or cysteine k2 values were 3.2 and 9.1 M-1.s-1, respectively. The results show that the initial rate of SNO-SH exchange between physiological albSNO (7 microM) and venous plasma levels of GSH and cysteine is very slow, < 1%/min. On the other hand, if a nitrosothiol such as cySNO were to enter a cell, it would be rapidly converted to GSNO (43%/s).

Cysteine↗
PubMed1994

Human glutathione S-transferase theta (GSTT1): cDNA cloning and the characterization of a genetic polymorphism.

In humans, glutathione-dependent conjugation of halomethanes is polymorphic, with 60% of the population classed as conjugators and 40% as non-conjugators. We report the characterization of the genetic polymorphism causing the phenotypic difference. We have isolated a cDNA that encodes a human class Theta GST (GSTT1) and which shares 82% sequence identity with rat class Theta GST5-5. From PCR and Southern blot analyses, it is shown that the GSTT1 gene is absent from 38% of the population. The presence or absence of the GSTT1 gene is coincident with the conjugator (GSST1+) and non-conjugator (GSTT1-) phenotypes respectively. The GSTT1+ phenotype can catalyse the glutathione conjugation of dichloromethane, a metabolic pathway which has been shown to be mutagenic in Salmonella typhimurium mutagenicity tester strains and is believed to be responsible for carcinogenicity of dichloromethane in the mouse. In humans, the enzyme is found in the erythrocyte and this may act as a detoxification sink. Characterization of the GSTT1 polymorphism will thus enable a more accurate assessment of human health risk from synthetic halomethanes and other industrial chemicals.

Amino Acid Sequence↗
PubMed1994

Growth hormone induces a DNA binding factor related to the interferon-stimulated 91-kDa transcription factor.

Signaling mechanisms leading to regulation of gene transcription by growth hormone (GH) and other molecules that signal via the cytokine receptor family have been elusive. Based upon recent findings that GH and interferons activate JAK family tyrosine kinases, we have identified a novel signaling pathway leading from the GH receptor to the nucleus. We report that in 3T3-F442A fibroblasts, GH stimulates tyrosyl phosphorylation of a protein recognized by antibody to p91, a component of DNA-binding complexes that are activated by tyrosyl phosphorylation in response to interferons alpha and gamma. In addition, a GH-inducible DNA binding factor (GHIF) is identified that binds to the c-sis-inducible element of the c-fos promoter. GHIF contains a protein antigenically related to p91 and is tyrosyl-phosphorylated. These findings indicate that in signaling between their receptors and the nucleus, GH and interferons utilize related or identical components, including JAK family tyrosine kinases and proteins in the p91 family. When combined with recent findings that many members of the cytokine receptor family activate JAK kinases, including some cytokines that activate p91-related proteins, these findings suggest that signaling pathways involving JAK kinases and p91 family members may be broadly distributed.

3T3 Cells↗
PubMed1994

Echinocytosis associated with rattlesnake envenomation in dogs.

A retrospective study of 28 cases of rattlesnake bites in dogs indicated an association of envenomation with echinocytosis; 25/28 dogs (89%) had echinocytosis within 24 hours of a rattlesnake bite being reported. Eighteen of the 28 dogs had marked type III echinocytosis (95-100% of mature erythrocytes affected), and seven dogs had moderate echinocytosis (15-30% of mature erythrocytes affected). The echinocytosis was transient, resolving within 48 hours of envenomation in those for which subsequent blood films were available (13/25). Hypokalemia was noted in 14 of 18 dogs for which biochemical data were available. The hypokalemia was not consistently associated with echinocytosis. The observation of echinocytosis in dogs supports a clinical diagnosis of rattlesnake envenomation.

Animals↗
PubMed1994

A full-coordinate model of the polymerase domain of HIV-1 reverse transcriptase and its interaction with a nucleic acid substrate.

We present a full-coordinate model of residues 1-319 of the polymerase domain of HIV-I reverse transcriptase. This model was constructed from the x-ray crystallographic structure of Jacobo-Molina et al. (Jacobo-Molina et al., P.N.A.S. USA 90, 6320-6324 (1993)) which is currently available to the degree of C-coordinates. The backbone and side-chain atoms were constructed using the MAXSPROUT suite of programs (L. Holm and C. Sander, J. Mol. Biol. 218, 183-194 (1991)) and refined through molecular modeling. A seven base pair A-form dsDNA was positioned in the nucleic acid binding cleft to represent the template-primer complex. The orientation of the template-primer complex in the nucleic acid binding cleft was guided by the positions of phosphorus atoms in the crystal structure.

Amino Acid Sequence↗
PubMed1994

Evaluation of total serum bile acids concentration and bile acid profiles in healthy cats after oral administration of ursodeoxycholic acid.

Ursodeoxycholic acid (UDCA; 10 mg/kg of body weight) was administered orally to 5 healthy cats for 3 months. Signs of illness were not apparent in any cat during treatment with UDCA. Results of monthly CBC, serum biochemical analysis, and urinalysis were unchanged during drug administration. There was a decrease in serum cholesterol concentration in 4 cats. Total postprandial serum bile acids (PPSBA) concentration was significantly (P = 0.0003) increased over total preprandial serum bile acids (PRSBA) concentration at all sample collection periods. The PRSBA and PPSBA concentrations were significantly (P < 0.05) increased at all sample collection periods after administration of UDCA, compared with baseline values. Ursodeoxycholic and tauroursodeoxycholic acids were not detected in serum prior to initiating administration of UDCA. Both bile acids were detected in the serum of all cats 1 and 2 months after UDCA administration and were detected in the serum of 2 cats 3 months after initiating UCDA administration. Hepatic ultrasonographic findings were normal before and after completion of UDCA administration. A mild, focal lymphocytic infiltrate was observed in 3 cats 3 months after initiating UDCA administration. Results of the study indicate that UDCA is absorbed into the systemic circulation of cats after oral administration, undergoes hepatic conjugation, and appears to be safe.

Administration, Oral↗
PubMed1993

Unusual reactivity of Tyr-7 of GSH transferase P1-1.

Reaction of human GSH transferase P1-1 (GSTP1-1) with diethylpyrocarbonate (DEPC) at pH 7.0 and 4 degrees C resulted in covalent modification of an equivalent of one histidine and one tyrosine residue per subunit, with loss of activity. Sequence analysis showed that His-71 and Tyr-7 were modified. Reference to the three-dimensional structure of GSTP1-1 [Reinemer, Dirr, Ladenstein, Huber, Lo Bello, Frederici and Parker (1992) J. Mol. Biol. 227, 214-226] shows that the modification of Tyr-7 is most likely to affect enzyme activity. Kinetic analysis of the DEPC modification of Tyr-7 in GSTP1-1 gave a k2 approx. 150 times that of a peptide comprising residues 1-11 of GSTP1-1. The reaction of Tyr-7 of GSTP1-1 with DEPC was poorly inhibited by 1 mM GSH (14%) or 10 microM S-hexylglutathione (18%). DEPC treatment of the enzyme altered the absorbance at 290 nm in second-derivative spectra, suggesting that a significant amount of tyrosinate ion occurs in the enzyme. GSH, however, did not significantly alter the A290. The data provide the first evidence of unusual chemical reactivity of Tyr-7 and are consistent with its proposed role as a proton acceptor during catalysis.

Diethyl Pyrocarbonate↗
PubMed1993

Chemical modification of GSH transferase P1-1 confirms the presence of Arg-13, Lys-44 and one carboxylate group in the GSH-binding domain of the active site.

GSH transferase P1-1 (GSTP1-1) was modified with group-specific reagents. Kinetic experiments demonstrated that inactivation of GSTP1-1 occurred upon reaction of one arginine residue per subunit with diacetyl, one lysine residue per subunit with 2,4,6-trinitrobenzene sulphonate, or one carboxylate group per subunit with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. All three inactivation reactions were inhibited by compounds known to bind at the GSH site of the enzyme but were unaffected by the electrophile 1-chloro-2,4-dinitrobenzene. N-terminal sequence analysis showed that Arg-13 was modified by diacetyl and that this modification was inhibited by GSH. Arg-11 was not modified. The lysine residue modified by 2,4,6-trinitrobenzene sulphonate and protected by S-octylglutathione was identified as Lys-44 by sequencing of tryptic peptides. The findings are in agreement with the involvement of Arg-13 and Lys-44 in binding of GSH, as determined from the crystal structure [Reinemer, Dirr, Ladenstein, Huber, Lo Bello, Frederici and Parker (1992) J. Mol. Biol. 227, 214-226]. The present data also implicate a single carboxylate in GSH binding, consistent with the involvement of Asp-98 of subunit B determined from the crystallographic study. The GSH-binding determinants of GSTP1-1 are compared using sequence similarity with those of GSTs of Alpha, Mu and Theta classes.

Amino Acid Sequence↗
PubMed1993

The serum response element can mediate induction of c-fos by growth hormone.

The c-fos protooncogene is transcriptionally activated by a wide variety of agents including serum, growth factors, and phorbol esters. This induction is rapid and transient and is mediated through a number of identified promoter elements. Growth hormone (GH) is also known to induce transcription of c-fos in a variety of cell types including NIH 3T3 fibroblasts and 3T3-F442A preadipocytes. To identify DNA sequences in the c-fos gene regulated by GH, this study sought to determine whether induction of c-fos by GH involves previously identified c-fos promoter elements. A plasmid containing a growth factor-sensitive fragment of the upstream region of the c-fos promoter from -361 to -264 bp was tested for GH sensitivity. The fragment was cloned upstream of a human c-fos reporter [designated FOS by Human Gene Mapping 11 (1991)], which included basal promoter elements. In transiently transfected mouse NIH 3T3 fibroblasts, the promoter fragment conferred GH sensitivity on the human c-fos reporter. To identify a specific GH-sensitive DNA sequence in this promoter, a serum response element (SRE)-reporter plasmid was tested and found to be stimulated by GH. GH was effective in inducing expression through the SRE over a range of physiological GH concentrations. Since GH was recently found to synergize with serum factors in inducing c-fos transcription, the effect of GH and serum on SRE function was examined for insight into the mechanism for such synergism. The combined effect of GH and serum to induce reporter expression through the SRE was greater than the added effects of GH and serum, indicating that the synergism between GH and serum in inducing c-fos involves the SRE sequence. These studies identify the SRE as one specific DNA sequence in the c-fos promoter functionally regulated by GH. It is notable that GH is effective at physiological concentrations. Furthermore, synergism in c-fos induction between GH and serum factors is evident through the SRE.

3T3 Cells↗