Leukotriene synthesis by human gastrointestinal tissues

Area of Science:

• Biochemistry
• Gastroenterology
• Pharmacology

Background:

• Prostaglandins and leukotrienes are key eicosanoids involved in gastrointestinal physiology and pathology.
• Understanding the synthesis and metabolism of these mediators in human tissues is crucial for therapeutic development.

Purpose of the Study:

• To investigate the capacity of human gastrointestinal tissues to synthesize prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and sulfidopeptide leukotrienes (sLTs).
• To characterize the enzymatic activities involved in sLT metabolism within these tissues.

Main Methods:

• Radioimmunoassay (RIA) was used to quantify PGE2, LTB4, and sLTs released from human gastric, jejuno-ileal, colonic mucosa, smooth muscle, and adenocarcinoma tissues.
• High-pressure liquid chromatography (HPLC) validated leukotriene immunoassay data.
• Enzyme activity assays were performed to detect gamma-glutamyl transpeptidase and dipeptidase.

Main Results:

• Human gastrointestinal tissues, particularly smooth muscle and mucosa, released significantly more PGE2 than LTB4 and sLTs.
• Adenocarcinoma tissue showed increased release of LTB4, sLTs, and PGE2 compared to normal colonic mucosa.
• Ionophore A23187 stimulated LTB4 and sLT release but not PGE2. Lipoxygenase and cyclooxygenase inhibitors, as well as glutathione, modulated eicosanoid synthesis and metabolism.
• HPLC confirmed LTB4 identity and identified sLTs as LTC4, LTD4, and LTE4.
• Enzymes involved in sLT metabolism were detected in gastrointestinal tissues.

Conclusions:

• Human gastrointestinal tissues possess the enzymatic machinery to synthesize LTB4, sLTs, and PGE2.
• The balance of synthesis and metabolism of these eicosanoids may be altered in conditions like adenocarcinoma.
• Detected sulfidopeptide leukotriene-metabolizing enzymes suggest a role in regulating local inflammatory responses and potentially influencing the biological activity of sLTs in the gastrointestinal tract.