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Biomedical subjects

B M Peskar

Publications and source records attributed to B M Peskar.

At least 73 records · Page 4Linked to original sources
PubMed1986

Radioimmunoassay for leukotriene E4. Use for determination of total sulfidopeptide-leukotriene release from rat gastric mucosa.

A conjugate of leukotriene (LT) E4 and bovine serum albumin (BSA) was prepared by covalently linking the free amino group of the hapten to the protein using dimethyl pimelindiimidate (DMP) as coupling reagent. Anti-LTE4 antibodies were raised in rabbits immunized with the conjugate. Binding of [3H]LTE4 to the antibodies is inhibited by 50% with 0.63 ng LTE4, while the relative cross-reaction of LTC4 and LTD4 is 46.3% and 12.6%, respectively. Using the radioimmunoassay release of sulfidopeptide-LT (SP-LT) from rat gastric mucosa incubated in vitro was determined after quantitative enzymatic conversion of SP-LT to LTE4. It could be demonstrated that this method is suitable for determination of SP-LT in biological material.

Amino Acids, Sulfur↗
PubMed1986

Leukotriene synthesis by human gastrointestinal tissues.

The prostaglandin and leukotriene synthesizing capacity of human gastrointestinal tissues obtained at surgery was investigated using radioimmunoassay for prostaglandin E2, leukotriene B4 and sulfidopeptide leukotrienes. The leukotriene immunoassay data were validated by high-pressure liquid chromatography (HPLC). During incubation at 37 degrees C, fragments of human gastric, jejuno-ileal and colonic mucosa released considerably larger amounts of prostaglandin E2 than of leukotriene B4 and sulfidopeptide leukotrienes. Gastrointestinal smooth muscle tissues released even larger amounts of prostaglandin E2, but smaller amounts of leukotrienes than the corresponding mucosal tissues. Adenocarcinoma tissue released larger amounts of leukotriene B4, sulfidopeptide leukotrienes and prostaglandin E2 than normal colonic mucosa. Ionophore A23187 (5 micrograms/ml) did not stimulate release of prostaglandin E2 from any of the tissues investigated, but enhanced release of leukotriene B4 and sulfidopeptide leukotrienes. HPLC analysis demonstrated that immunoreactive leukotriene B4 co-chromatographed almost exclusively with standard leukotriene B4, while immunoreactive sulfidopeptide leukotrienes consisted of a mixture of leukotrienes C4, D4 and E4. Leukotriene synthesis by human gastrointestinal tissues was inhibited by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the dual enzyme inhibitor BW755C (3-amino-1-(trifluoromethylphenyl)-2-pyrazoline hydrochloride). Synthesis of prostaglandin E2 was inhibited by the cyclooxygenase inhibitor indomethacin as well as by BW755C. Incubation of gastrointestinal tissues in the presence of glutathione decreased the amounts of leukotrienes D4 and E4, while release of leukotriene C4 was simultaneously increased. On the other hand, incubation of tritiated leukotriene C4 with incubation media from human gastric or colonic mucosa resulted in conversion of the substrate to [3H]leukotriene D4 and [3H]leukotriene E4. The results indicate the capacity of human gastrointestinal tissues to synthesize the 5-lipoxygenase-derived products of arachidonate metabolism, leukotriene B4 and sulfidopeptide leukotrienes, in addition to larger amounts of prostaglandin E2. Furthermore, considerable activities of the sulfidopeptide leukotriene-metabolizing enzymes gamma-glutamyl transpeptidase and dipeptidase were detected in human gastrointestinal tissues. These enzymes might play an important role in biological inactivation and/or change of biological profile of sulfidopeptide leukotrienes generated in the human gastrointestinal tract.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1986

[Leukotriene synthesis by gastrointestinal tissue and its pharmacologic modification].

Tissues of the gastrointestinal tract synthesize leukotriene (LT) B4 and the sulfidopeptide-leukotrienes LTC4, LTD4 and LTE4 from endogenous substrate. Formation of leukotrienes was demonstrated using radioimmunoassay, high pressure liquid chromatography (HPLC) and bioassay. Under basal conditions the gastrointestinal tissues released minor amounts of leukotrienes only. Formation of lipoxygenase-derived products of arachidonic acid metabolism was, however, significantly increased in the presence of various stimuli. Thus, significant amounts of LTB4 and of sulfidopeptide-leukotrienes were released from colonic and gastric mucosa of guinea-pigs sensitized against ovalbumin when incubations were carried out in the presence of antigen. Antigen-induced leukotriene formation was not found in the muscularis propria and subserosal of ovalbumin-sensitized guinea-pigs. Release of cyclooxygenase-derived metabolites of arachidonic acid, on the other hand, was most abundant in the subserosal layer of the guinea-pig colon and was not influenced by the immunological reaction. Inhibitors of cyclooxygenase, such as indomethacin, reduced gastrointestinal formation of prostaglandins, but not of leukotrienes. Inhibitors of 5-lipoxygenase, however, significantly decreased leukotriene formation. Synthesis of LTB4 and of sulfidopeptide-leukotrienes was also found in human colonic mucosal tissue, using the divalent cation-ionophore A23187 as stimulating agent. HPLC analysis demonstrated that the sulfidopeptide-leukotrienes released were composed of a mixture of LTC4, LTD4 and LTE4. In addition, human colonic mucosal tissue contained high activities of enzymes that rapidly convert LTC4 to LTE4. As in most biological systems LTE4 is less active than LTC4 and LTD4 degrading enzymes might represent a local inactivating mechanism. Mucosal tissue of patients with Crohn's disease synthesized considerably more LTB4 and sulfidopeptide-leukotrienes than non-inflamed mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Enhanced formation of sulfidopeptide-leukotrienes in ulcerative colitis and Crohn's disease: inhibition by sulfasalazine and 5-aminosalicylic acid.

Release of sulfidopeptide (SP)-leukotrienes (LT) in vitro from normal human colonic mucosa and from mucosal tissue obtained from patients with Crohn's disease (CD) and ulcerative colitis (UC) was investigated. It was found that inflamed mucosal tissue released significantly more SP-LT than normal colonic mucosa both under control conditions and after addition of calcium ionophore A23187. These results indicate the presence of endogenous stimuli as well as an increased responsiveness to an exogenous stimulus of LT formation in the inflamed mucosa. Sulfasalazine (SASP), a drug used in inflammatory bowel diseases, and its active metabolite 5-aminosalicylic acid (5-ASA) were found to inhibit colonic mucosal SP-LT formation, while only 5-ASA inhibited simultaneously synthesis of another arachidonic acid-derived inflammatory mediator, prostaglandin (PG) E2. The results suggest that SP-LT might be important mediators of inflammation in CD and UC.

Aminosalicylic Acids↗
PubMed1986

Ethanol stimulates formation of leukotriene C4 in rat gastric mucosa.

Ethanol-induced gastric mucosal damage is characterized by microcirculatory changes such as stasis and plasma leakage. Sluggish blood flow and stasis have also been observed after administration of exogenous leukotriene (LT) C4. The effect of ethanol on the release of LTC4 from rat gastric mucosa was therefore investigated. It was found that intragastric instillation of ethanol increases gastric mucosal release of LTC4 in a dose- and time-dependent manner parallel to the production of gastric lesions. The lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the anti-ulcer drug carbenoxolone (CX) inhibited mucosal release of LTC4 and simultaneously protected against gastric damage caused by ethanol. It is concluded that increased formation of LTC4 and/or other 5-lipoxygenase-derived products of arachidonate metabolism may be involved in ethanol-induced gastric damage. Furthermore, inhibition of the 5-lipoxygenase pathway may be an important mechanism of action of gastric protective drugs.

Animals↗
PubMed1986

Effect of anti-inflammatory and analgesic pyrazoles on arachidonic acid metabolism in isolated heart and gastric mucosa preparations.

The effects of acidic and nonacidic pyrazoles on the release of arachidonic acid-derived mediators from isolated perfused anaphylactic guinea pig hearts as well as rat and human gastric mucosa were investigated. High concentrations of the acidic drugs phenylbutazone and oxyphenbutazone as well as of the nonacidic metabolites of metamizol, i.e. 4-methylaminoantipyrine and 4-aminoantipyrine, inhibited the release of the cyclo-oxygenase products of arachidonic acid metabolism, TXB2 and 6-keto-PGF1 alpha, and simultaneously increased the release of LTC4-like immunoreactivity in hearts. By contrast, comparatively high concentrations of the metamizol metabolites 4-formylaminoantipyrine and 4-acetylaminoantipyrine were without effect. The comparable effects of acidic and nonacidic pyrazoles on eicosanoid release from anaphylactic hearts support the concept that hypersensitivity reactions to NSAIDs are related to their effect on arachidonic acid metabolism. The anti-inflammatory effects of phenylbutazone and oxyphenbutazone and of high concentrations of metamizol seem to be correlated with the inhibition of cyclo-oxygenase. On the other hand, lower concentrations of metamizol, which have analgesic and anti-pyretic effects, only marginally inhibit cardiac cyclo-oxygenase. It remains to be investigated whether the partial inhibition of the synthesis of PGI2, a major hyperalgesiccyclo-oxygenase product of arachidonic acid metabolism, at lower concentrations of the active metamizol metabolites contributes to the analgesic effect of metamizol. The acidic NSAID mofebutazone and its metabolite butyl malonic acid mono (1-phenylhydrazide) had no effect on the cardiac release of arachidonic acid-derived cyclo-oxygenase and lipoxygenase products. The anti-inflammatory effect of these compounds requires further investigation. In isolated gastric mucosa, the active metabolite of metamizol 4-methylaminoantipyrine was found to inhibit fatty acid cyclo-oxygenase dose-dependently. Pharmacokinetic differences due to the nonacidic structure of metamizol and its metabolites as compared to acidic NSAIDs may be responsible for the fact that metamizol is better tolerated than e.g. indomethacin. In rat experiments, phenylbutazone was found to inhibit gastric mucosal cyclo-oxygenase like indomethacin. On the other hand, mofebutazone and its metabolite butyl malonic acid mono (1-phenylhydrazide) did not affect gastric mucosal synthesis of 6-keto-PGF1 alpha. This lack of effect on gastric mucosal cyclo-oxygenase seems to be correlated with the considerably lower gastric toxicity of mofebutazone as compared to phenylbutazone.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

Gastrointestinal toxicity. Role of prostaglandins and leukotrienes.

Gastrointestinal tissues have a high synthesising capacity for prostaglandins. As exogenous prostaglandins protect the gastrointestinal mucosa against potentially noxious agents, it has been suggested that the generation of prostaglandins plays a crucial role in the maintenance of mucosal integrity. Analgesic and anti-inflammatory drugs with a potent inhibitory action on gastrointestinal cyclo-oxygenase, such as indomethacin, induce gastric and intestinal ulcerations in experimental animals and frequently lead to gastrointestinal side effects in man. However, drugs that do not reduce gastrointestinal prostaglandin formation, such as paracetamol (acetaminophen), are devoid of gastrointestinal toxicity. Various factors, e.g. tissue-specific differences in the sensitivity of cyclo-oxygenase against inhibition and pharmacokinetic properties, modify the inhibitory activity of analgesic and anti-inflammatory drugs on gastrointestinal prostaglandin formation. As leukotriene C4 is a potent gastric vasoconstrictor, increased metabolism of arachidonic acid via the 5-lipoxygenase pathway in the presence of inhibition of cyclo-oxygenase could possibly contribute to drug-induced gastrointestinal damage.

Animals↗
PubMed1984

[The prostaglandin and thromboxane system of the gastric mucosa as a target for protective and ulcerogenic drugs].

Human gastric mucosa synthesizes significant amounts of thromboxane, which has recently been found to be highly ulcerogenic, in addition to protective prostaglandins. The ratio of the various mucosal arachidonic acid metabolites formed may, therefore, exert a modifying influence on the resistance of the mucosa against noxious agents. This hypothesis is supported by the finding that carbenoxolone, a drug accelerating peptic ulcer healing by a mechanism which does not involve inhibition of acid secretion, stimulates gastric mucosal prostaglandin formation and, in parallel, inhibits mucosal thromboxane synthesis. Ulcerogenic non-steroidal anti-inflammatory drugs, on the other hand, usually reduce gastric prostaglandin formation. The inhibitory activity of the various compounds is dependent on their affinity to the gastric mucosal cyclooxygenase, as well as on pharmacokinetic properties. Since gastrointestinal side-effects frequently occur during anti-inflammatory-analgesic therapy, the elucidation of the underlying mechanisms seems of considerable clinical relevance.

Anti-Inflammatory Agents↗