Lovastatin Lactone Inhibits Methane Production in Human Stool Homogenates

Abstract

Introduction: Research has linked an altered gut microbiome to symptoms of irritable bowel syndrome (IBS). In constipation-predominant IBS (IBS-C), methane production appears important as methane levels on breath are proportional to the degree of constipation, and antibiotic elimination of methane significantly improves constipation. The predominant methane-producing organism in humans is Methanobrevibacter smithii. Recent data suggests certain HMG-CoA reductase inhibitors (statins) may reduce methane production by inhibiting methanogenesis. This study examined the effects of various statins on methane production in fresh human stool homogenates. Methods: Five female subjects recruited based on high breath methane production (average=69.6ppm) provided a total of 8 fresh stool samples each. Samples were homogenized in 1XPBS (2g stool/3ml PBS) in an anaerobic chamber at 37°C and divided into 5 stoppered flasks. To assess statin effects, head gas withdrawn through a stopcock was collected at baseline, then every 30min for a total of 270min, and analyzed on a Quintron Model SC gas chromatograph for methane levels. Nine statins were initially assessed for methane inhibition at a concentration of 5mg/g stool: lovastatin lactone and hydroxyacid, pravastatin lactone and hydroxyacid, simvastatin lactone, mevastatin lactone, rosuvastatin lactone, and atorvastatin lactone and hydroxyacid. Once the ideal statin was determined, the effects of concentrations of 0.04, 0.12, 0.48, 1, 5, and 10mg/g stool were tested by sampling head gas every 90min after statin addition, up to 720min.Further assessments were then performed comparing three forms of lovastatin (lactone, diol and hydroxyacid). Results: Lovastatin lactone was identified as the only effective methane inhibitor (Figure 1), significantly inhibiting methane levels by -65% of the control stool. Lovastatin lactone at 5mg/g produced the maximum inhibiting effect resulting in an average methane level of 3% of the control over time (Figure 2). In a final validation comparison of 3 forms of lovastatin (5mg/g), both the lactone and diol forms proved to be effective. In all assessments, hydroxyacid forms were least able to inhibit methane production in fresh stool samples.Figure 1Figure 2Conclusion: Lovastatin lactone and lovastatin diol at concentrations of 5mg/g stool significantly reduce methane production in human stool homogenates. Future studies are needed to assess the effect of this statin on methane production and IBS-C symptoms in humans.