Subject(s)
Amphotericin B/therapeutic use , Antifungal Agents/therapeutic use , Gastrointestinal Hemorrhage/microbiology , Mucormycosis/diagnosis , Mucormycosis/drug therapy , Nitriles/therapeutic use , Pyridines/therapeutic use , Triazoles/therapeutic use , Urinary Bladder Diseases/drug therapy , Urinary Bladder Diseases/microbiology , Biopsy , Diagnosis, Differential , Endoscopy, Digestive System , Humans , Male , Middle AgedSubject(s)
Capsule Endoscopy , Duodenal Neoplasms/diagnosis , Esophageal Neoplasms/diagnosis , HIV Seropositivity/diagnosis , Jejunal Neoplasms/diagnosis , Neoplasms, Multiple Primary/diagnosis , Sarcoma, Kaposi/diagnosis , Stomach Neoplasms/diagnosis , Biopsy , Duodenal Neoplasms/pathology , Endoscopy, Gastrointestinal , Esophageal Neoplasms/pathology , HIV Seropositivity/pathology , Herpesvirus 8, Human , Humans , Intestinal Mucosa/pathology , Jejunal Neoplasms/pathology , Male , Middle Aged , Neoplasms, Multiple Primary/pathology , Sarcoma, Kaposi/pathology , Stomach Neoplasms/pathologyABSTRACT
Catechol-O-methyltransferase (COMT) exists as two isoenzymes, a membrane-bound form (MB-COMT) and a soluble form (S-COMT), with different roles in the metabolism of catecholamines and other catechol compounds. This report documents an HPLC assay for separate estimation of S-COMT and MB-COMT activity and examines activities of the two isoenzymes among different rat tissues and in human and rat erythrocytes. Activities of MB-COMT and S-COMT varied widely among tissues. There were higher activities of S-COMT than MB-COMT in all tissues except the adrenal medulla where MB-COMT was the predominant isoenzyme, consistent with the importance of this tissue and MB-COMT for the O-methylation of catecholamines. MB-COMT and S-COMT in rat and human erythrocytes showed divergent levels and patterns of activity. The assay represents a rapid and accurate method for quantifying MB-COMT and S-COMT in various tissues and examining the relative roles of COMT isoenzymes in the metabolism of catechol compounds in health and disease.
Subject(s)
Catechol O-Methyltransferase/metabolism , Erythrocyte Membrane/enzymology , Animals , Catechol O-Methyltransferase/blood , Humans , Male , Rats , Rats, Sprague-Dawley , Reproducibility of Results , SolubilityABSTRACT
This study examined whether the high sensitivity of plasma free metanephrines for diagnosis of pheochromocytoma may result from production of free metanephrines within tumors. Presence in pheochromocytomas of catechol-O-methyltransferase (COMT), the enzyme responsible for conversion of catecholamines to metanephrines, was confirmed by Western blot analysis, enzyme assay, and immunohistochemistry. Western blot analysis and enzyme assay indicated that membrane-bound and not soluble COMT was the predominant form of the enzyme in pheochromocytoma. Immunohistochemistry revealed colocalization of COMT in the same chromaffin cells where catecholamines are translocated into storage vesicles by the vesicular monoamine transporter. Levels of free metanephrines in pheochromocytoma over 10,000 times higher than plasma concentrations in the same patients before removal of tumors indicated production of metanephrines within tumors. Comparisons of the production of metanephrines in patients with pheochromocytoma with production from catecholamines released or infused into the circulation indicated that more than 93% of the consistently elevated levels of circulating free metanephrines in patients with pheochromocytoma are derived from metabolism before and not after release of catecholamines into the circulation. The data indicate that the elevated plasma levels of free metanephrines in patients with pheochromocytoma are derived from catecholamines produced and metabolized within tumors. Some tumors do not secrete catecholamines, but all appear to metabolize catecholamines to free metanephrines, thus explaining the better sensitivity of plasma free metanephrines over other tests for diagnosis of pheochromocytoma.
