Background: Hydrogen sulfide (H2S) and methanthiol (CH3SH) have been implicated as bacterially derived toxins which may be damaging to the gut mucosa. The addition of nitrate and metals that bind sulfide could potentially reduce the concentrations of these toxic gases. In this study, the effects of iron, zinc, bismuth and nitrate on free H2S concentrations in fecal batch cultures were investigated.
Methods: Stool samples were collected from six healthy subjects. Ten percent fecal slurries was made up with phosphate buffer. One milliliter of fecal slurry and 1 ml of metal solution were added to 28 ml anaerobic broth in a 30-ml vial giving final metal concentrations of 0.1, 0.5 and 1.0 mmol/l. For a control, the metal iron solution was replaced by 1 ml of water. After 24 h of incubation at 37 degrees C, 1 ml of the supernatant from the broth was distilled by microdistillation and sulfide determined by HPLC using amperometric detection.
Results: A significant reduction in H2S (P<0.05) of 57% was seen with 1.0 mmol/l zinc, but not with 0 and 0.5 mmol/l zinc treatments. Iron at 0.1, 0.5 and 1.0 mmol/l significantly reduced H2S concentrations (P<0.05) by 36%, 44% and 58%, respectively. Bismuth, the most effective metal, reduced H2S concentrations by more than 90% for all treatments. Both magnesium citrate and magnesium acetate did not affect sulfide concentrations, while 41% and 68% reductions were seen from the addition of 0.5 and 1.0 mmol/l magnesium nitrate, respectively (P<0.05).
Conclusions: Bismuth, iron, zinc and nitrate are effective at reducing free H2S concentrations in batch cultures. Side effects of these metals may limit their use in vivo. Nitrate is considered toxic because of its contribution to the formation of the carcinogenic nitrite and nitrosamine, though results presented here may indicate a beneficial effect in the large intestine.