Protective effect of metronidazole on uncoupling mitochondrial oxidative phosphorylation induced by NSAID: a new mechanism

Abstract

Background: The pathogenesis of non-steroidal anti-inflammatory drug (NSAID) enteropathy is complex. It involves uncoupling of mitochondrial oxidative phosphorylation which alters the intercellular junction and increases intestinal permeability with consequent intestinal damage. Metronidazole diminishes the inflammation induced by indomethacin but the mechanisms remain speculative. A direct effect on luminal bacteria has traditionally been thought to account for the protective effect of metronidazole. However, a protective effect of metronidazole on mitochondrial oxidative phosphorylation has never been tested.

Aims: To assess the protective effect of metronidazole on mitochondrial uncoupling induced by indomethacin and also on the increased intestinal permeability and macroscopic damage.

Material and methods: The protective effect of metronidazole was evaluated in rats given indomethacin; a macroscopic score was devised to quantify intestinal lesions, and intestinal permeability was measured by means of (51)Cr-ethylenediaminetetraacetic acid. The protective effect of metronidazole against mitochondrial uncoupling induced by indomethacin was assessed using isolated coupled rat liver mitochondria obtained from rats pretreated with metronidazole or saline.

Results: Metronidazole significantly reduced the macroscopic intestinal damage and increase in intestinal permeability induced by indomethacin; furthermore, at the mitochondrial level, it significantly reduced the increase in oxygen consumption in state 4 induced by indomethacin and caused less reduction of the respiratory control rate.

Conclusion: Our study confirmed the beneficial effects of metronidazole on intestinal damage and intestinal permeability, and demonstrated, for the first time, a direct protective effect of metronidazole on uncoupling of mitochondrial oxidative phosphorylation caused by NSAIDs.

Figure 1

Box and whisker plot showing median macroscopic score (horizontal line), 25th and 75th centiles (box), and range (whiskers) in the control (group 1, n=10), indomethacin (group 2, n=10), and indomethacin plus metronidazole (group 3, n=10) groups. Group 1 v group 2, p<0.0001; group 1 v group 3, NS; group 2 v group 3, p<0.001.

Figure 2

Box and whisker plot showing median intestinal permeability (horizontal line), 25th and 75th centiles (box), and range (whiskers) in the control (group 1, n=17), indomethacin (group 2, n=16), and indomethacin plus metronidazole (group 3, n=17) groups. Values are percentage of ⁵¹Cr-EDTA excreted in five hour urine. Group 1 v group 2, p<0.05; group 1 v group 3, NS; group 2 v group 3, p<0.05.

Figure 3

Regression analysis of the effects of metronidazole on oxygen consumption in the basal state (S4) (values are µmol of oxygen/mg of protein).

Figure 4

Regression analysis of the effects of metronidazole on respiratory control rate (RCR). Relation between consumption of oxygen with ADP (S3) and after it has been consumed (S4).