In Vitro Inhibition of Adult Rat Intestinal Heme Oxygenase by Metalloporphyrins

Abstract

ABSTRACT. We determined the inhibitory effects of concentrations of tin-and zinc protoporphyrin (1-100 pM) and mesoporphyrin (0.1-10 pM) on the in vitro heme oxygenase (HO) (E.C.1.14.99.3) activity in liver, spleen, and intestine 13, 000 % g tissue supernatants from fasted adult male Wistar rats through measurement of carbon monoxide by gas chromatography. All four metalloporphyrins inhibited intestinal HO, under the light-limited conditions of these experiments. The zinc porphyrins showed a clear concentration dependency over the entire range, reducing activity to near zero levels at their highest concentrations. The tin porphyrins reduced HO activity to 26% of initial levels, but the inhibition was not clearly concentration dependent. Liver and spleen supernatants exhibited concentration dependent inhibition by all four metalloporphyrins. We also assessed the effect of light on HO activity measurements. HO determinations in the light (8 pW/cmz/nm) yielded higher HO activity than for reactions performed in the dark. The presence of light and SnPP appeared to stimulate the H O activity of intestinal preparations thus overcoming the observed inhibition. Light and SnPP also decreased to a lesser degree the inhibition for the spleen preparation, but not for the liver. We conclude that heme oxygenase activity measurements via CO determination need to be conducted in the absence of light, in particular when photosensitizers are present. Furthermore, it appears that intestinal HO behaves in a quantitatively different way from other tissues, under varying conditions of metalloporphyrin inhibition and light exposure. (Pediatr Res 26:362-365,1989) Abbreviations HO, heme oxygenase ZnPP, zinc protoporphyrin ZnMP, zinc mesoporphyrin SnPP, tin protoporphyrin SnMP, tin mesoporphyrin Jaundice, a problem common to the human neonate, results from increased bilirubin production and immaturity of the bilirubin-conjugating mechanism in the liver. HO, the rate-limiting enzyme (E.C. 1.14.99.3) in the heme catabolic pathway, cleaves

In vitro Generation of Carbon Monoxide from Organic Molecules and Synthetic Metalloporphyrins Mediated by Light

“…However, the results of the present experiments lead us to believe that the CO was produced from organic mole cules, including NADPH, in the tissue prep arations under the influence of ambient light formed in the dark. This assay modification allowed us to explain the previously puzzling observation that rat intestinal HO appeared to be uninhibitable by SnPP at concentra tions which significantly inhibited spleen and liver HO [30], Comparison of results with assays performed in the dark versus those performed in the light showed that light exposure negated the SnPP-caused in hibition of intestinal HO observed in the dark [31]. These studies showed that intesti nal HO responds differently to SnPP than liver and spleen.…”

Zinc Mesoporphyrin Induces Rapid Proteasomal Degradation of Hepatitis C Nonstructural 5A Protein in Human Hepatoma Cells

“…ZnMP induces polyubiquitination of NS5A and display anti-viral activity, we found ZnMP an attractive choice, and we chose to use mainly ZnMP because of the profound effects on Bach117, because mesoporphyrin derivatives lack reactive vinyl groups and are therefore more chemically stable than protoporphyrin derivatives38, and because it is taken up by intact liver cells far better than other zinc derivatives such as bisglycol-deuteroporphyrin congener39. Zinc porphyrins, under some circumstances, may be toxic to hematopoietic cells in vitro40.…”

Metalloporphyrins – An Update

“…Because SnMP inhibits intestinal HO (Vreman et al, 1989) and decreases intestinal heme–iron absorption (Boni et al, 1993), this may account for the iron deficiency-like anemia that results after long-term SnMP exposure. Kappas et al (1993) reported that the deficiency was easily reversed by supplementation with iron.…”