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Biomedical subjects

G J Roth

Publications and source records attributed to G J Roth.

66 records · Page 4Linked to original sources
PubMed1977

Cyclic adenosine 3',5'-monophosphate inhibits the availability of arachidonate to prostaglandin synthetase in human platelet suspensions.

When thrombin is added to washed human platelets, one of its actions results in activation of a phospholipase that hydrolyzes arachidonic acid from phospholipids. The arachidonate is converted to the cyclic endoperoxides (prostaglandin G2 and prostaglandin H2) by fatty acid cyclo-oxygenase. These compounds are then converted to thromboxane A2, also called rabbit aorta-contracting substance, by thromboxane synthetase. These labile, pharmacologically active compounds then break down to inactive products including thromboxane B2 and malonaldehyde. Incubation of platelets with either dibutyryl cyclic adenosine 3',5'-monophosphate (dBcAMP) or prostaglandin E1 (PGE1) before thrombin addition blocks the subsequent formation of oxygenated products of arachidonic acid including thromboxane A2, thromboxane B2, and malonaldehyde. In contrast, when arachidonic acid is added directly to platelets, prior incubation with dBcAMP or PGE1 does not inhibit production of the prostaglandins or their metabolites. Thrombin treatment of platelets also blocks the acetylation of cyclo-oxygenase by aspirin since the hydrolyzed arachidonic acid competes with aspirin for the active site on cyclo-oxygenase. Prior treatment of platelets with dBcAMP or PGE1 reverses the thrombin inhibition of the acetylation of cyclo-oxygenase. We conclude that agents which elevate platelet cAMP levels inhibit the hydrolysis of arachidonic acid from platelet phospholipids. We also find that prostaglandin synthesis can be dissociated, in part, from platelet aggregation and release, and that cAMP has separate actions on these processes. Higher thrombin concentrations are required to stimulate prostaglandin synthesis (0.05-2 U/ml) than are required to induce [14C]serotonin release (0.02-0.1 U/ml). Furthermore, dBcAMP and PGE1 both inhibit platelet aggregation induced by either arachidonic acid or prostaglandin H2 without affecting the production of prostaglandin metabolites from these compounds.

Arachidonic Acids↗
PubMed1976

Aspirin as a quantitative acetylating reagent for the fatty acid oxygenase that forms prostaglandins.

A selective acetylation of the prostaglandin-forming fatty acid oxygenase (part of the prostaglandin "synthetase" system) occurs with 100 muM concentrations of aspirin (acetylsalicylic acid). The amount of acetylation, measured by counting the [3H]acetyl-protein formed, was proportional to the amount of active, functional oxygenase in a sample. When samples were aged to allow spontaneous inactivation of the oxygenase, the amount of acetylation was proportional to the remaining measurable activity rather than the initial amount of oxygenase protein in the sample. Diethyl dithiocarbamate inhibited the oxygenase activity, but did not interfere with the subsequent acetylation by aspirin. Indomethacin, on the other hand, appeared to inactivate the oxygenase in a manner that interfered only partially with the action of aspirin as an acetylating reagent. The amount of acetylation appeared to be dependent upon the amount of native, undenatured enzyme. The results suggest that the acetylation may be dependent upon an essential functional group or conformation of groups in the catalytic peptide chain(s) that can be destroyed during spontaneous inactivation of the oxygenase, and altered by indomethacin.

Acetylation↗
PubMed1975

Acetylation of prostaglandin synthase by aspirin.

When microsomes of sheep or bovine seminal vesicles are incubated with [acetyl-3H]aspirin (acetyl salicylic acid), 200 Ci/mol, we observe acetylation of a single protein, as measured by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The protein has a molecular weight of 85,000 and corresponds to a similar acetylated protein found in the particulate fraction of aspirin-treated human platelets. The aspirin-mediated acetylation reaction proceeds with the same time course and at the same concentration as does the inhibition of prostaglandin synthase (cyclo-oxygenase) (EC 1.14.99.1; 8,11,14-eicosatrienoate, hydrogen-donor:oxygen oxidoreductase) by the drug. At 100 muM aspirin, 50% inhibition of prostaglandin synthase and 50% of maximal acetylation are observed after 15 min at 37 degrees. Furthermore, the substrate for cyclo-oxygenase, arachidonic acid, inhibits protein acetylation by aspirin at concentrations (50% inhibition at 10-30 muM) which correlate with the Michaelis constant of arachidonic acid as a substrate for cyclooxygenase. Arachidonic acid analogues and indomethacin inhibit the acetylation reaction in proportion to their effectiveness as cyclo-oxygenase inhibitors. The results suggest that aspirin acts as an active-site acetylating agent for the enzyme cyclo-oxygenase. This action of aspirin may account for its anti-inflammatory and anti-platelet action.

Acetylation↗
PubMed1975

The mechanism of the effect of aspirin on human platelets. I. Acetylation of a particulate fraction protein.

Aspirin (acetylsalicylic acid) inhibits platelet prostaglandin synthesis and the ADP- and collagen-induced platelet release reaction. The mechanism of the inhibitory effect is unknown but may involve protein acetylation, since aspirin acetylates a variety of substrates, including platelet protein. We have examined the relationship between protein acetylation and aspirin's physiologic effect on platelets. Suspensions of washed human platelets were incubated at 37 degrees C with (3H)aspirin, and incorporation of radioactivity into protein was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Exposure to (acetyl-3H)aspirin but not (aromatic ring-3H)aspirin resulted in radioactive labeling of three platelet proteins, suggesting that the drug acetylates these three proteins. The acetylation of two of the proteins (located in the supernatant fraction) was not saturable, implying that these reactions may not be physiologically significant. Acetylation of the third protein, approximate mol wt 85,000 (located in the particulate fraction), saturated at an aspirin concentration of 30 muM and was complete within 20 min. Platelets prepared from aspirin-treated donors did not incorporate any (acetyl-3H)aspirin radioactivity into the particulate protein for 2 days after drug treatment and did not show full pretreatment uptake of radioactivity for 12 days thereafter. The course of increasing incorporation of (acetyl-3H)aspirin radioactivity parralleled that of platelet turnover. Therefore, in addition to its saturability, acetylation of the particulate fraction protein by aspirin was permanent. In two respects, the inhibition of platelet function by aspirin correlates well with the aspirin-mediated acetylation of the particulate fraction protein. Both persist for the life-span of the aspirin-treated platelet, and both occur at a similar saturating aspirin concentration. The evidence suggests that the physiologic effect of aspirin on human platelets is produced by acetylation of a single protein located in the particulate fraction. The acetylated protein may be related to cyclo-oxygenase, the prostaglandin G2 biosynthetic enzyme.

Acetates↗
PubMed1974

Naturally occurring immune-complex glomerulonephritis in monkeys (Macaca irus). I. Light, immunofluorescence and electron microscopic studies.

Light, immunofluorescence and electron microscopic studies were carried out on renal biopsies from 32 randomly selected adult monkeys (Macaca irus). Histopathology was limited to glomeruli and consisted of mild to moderate segmental increases in mesangial cells, mesangial matrix, and/or glomerular basement membrane (GBM) thickness in 41% of the animals. Granular deposits of IgM were present in the mesangial region and along the GBM in 72% of the monkeys, whereas IgG, C1q, C4 and C3 were detected in approximately 30%. Electrondense deposits were seen predominantly in epithelial foot processes adjacent to the GBM and, to a lesser extent, in the mesangium. Those monkeys with the heaviest IgM deposition were found to have decreased serum levels of C3, IgM and IgA. Follow-up biopsies over a period of 3 to 11 months revealed that the disease process was persistent yet nonprogressive. No correlation with age or sex was noted. All animals examined were clinically healthy and had normal renal function. This is the first documented occurrence of spontaneous immune-complex glomerulonephritis in a large monkey population. It appears to be a persistent disease which does not progress to renal insufficiency and which may serve as an investigative model for mild nonprogressive forms of human glomerulonephritis.

Animals↗
PubMedDate not supplied

Perforation of nasal septum in rheumatic diseases.

Perforation of the nasal septum was noted in 12 patients with rheumatic disease, including rheumatoid arthritis (RA), psoriatic arthritis (PsA), systemic lupus erythematosus (SLE), progressive systemic sclerosis (PSS), and mixed connective tissue disease (MCTD). Biopsies were taken from the rim of the perforation in 7 of the 12 and revealed no vasculitis, immunoglobulin deposition, or consistent abnormality. Nasal septal perforation is an occasional finding in rheumatic disease and the cause is unknown.

Adult↗
PubMedDate not supplied

The renal effect of intravenous adenine in humans.

The purine base, adenine, improves the posttransfusion viability of liquid stored blood. However, adenine in high doses may cause kidney damage becuase of the precipitation in renal tubules of its incoluble metabolite, 2,8-dioxyadenine. Adenine is not licensed for use in the United States because it may be nephrotoxic. In a controlled, randomized, double-blind study, eight human subjects received 10 mg/kg of adenine infused intravenously over one hour, four subjects received 5 mg/kg, and four subjects received no adenine. Renal function tests were performed on each subject before adenine infusion and one day and one week following the infusion. Tests included an assessment of glomerular function (serum creatinine, creatinine clearance, protein excretion), proximal tubular function (amino acid and glucose excretion), and distal tubular function (maximal acidifying and concentrating ability). Plasma and urine levels of adenine and 2,8-dioxyadenine were measured. Renal function tests showed no evidence of kidney damage secondary to adenine.

Adenine↗
PubMedDate not supplied

Clotting factors in supernatant plasma following cryoprecipitation.

The supernatant plasma which remains after cryoprecipitation is a useful component for transfusion therapy. However, from prior studies it was unclear how well plasma clotting factors were preserved following cryoprecipitation. Coagulation factor assays were performed on fresh plasma, supematant plasma after removal of cryoprecipitate, and the same supernatant plasma following refreezing and thawing. Factor VIII and fibrinogen levels fell considerably after removal of cryoprecipitate, but there was also a significant decline in factor V. Refreezing and thawing the supernatant plasma had little effect on clotting factors.

Adult↗