Approximately 10 percent of the general population take a proton pump inhibitor (PPI) drug to block stomach acid secretions and relieve symptoms of frequent heartburn, acid reflux and gastroesophageal reflux disease. That percentage can be as much as seven times higher for people with chronic liver disease. Researchers at University of California San Diego School of Medicine have discovered evidence in mice and humans that gastric acid suppression alters specific gut bacteria in a way that promotes liver injury and progression of three types of chronic liver disease.

The study was published October 10 in the journal Nature Communications.

“Our stomachs produce gastric acid to kill ingested microbes, and taking a medication to suppress gastric acid secretion can change the composition of the gut microbiome,” said senior author Bernd Schnabl, MD, associate professor of gastroenterology at UC San Diego School of Medicine. “Since we found previously that the gut microbiome — the communities of bacteria and other microbes living there — can influence liver disease risk, we wondered what effect gastric acid suppression might have on the progression of chronic liver disease. We found that the absence of gastric acid promotes growth of Enterococcus bacteria in the intestines and translocation to the liver, where they exacerbate inflammation and worsen chronic liver disease.”

PPIs, which include brand names such as Prilosec, Nexium and Prevacid, are among the most commonly prescribed medications in the world, particularly among people with chronic liver disease. They are also relatively inexpensive medications, retailing for approximately $7 for a recommended two-week course of generic, over-the-counter Prilosec (omeprazole). But the frequency of use adds up — one study estimates Americans spend $11 billion on PPIs each year.

To determine the effect of gastric acid suppression on the progression of chronic liver disease, Schnabl’s team looked at mouse models that mimic alcoholic liver disease, NAFLD and NASH in humans. In each, they blocked gastric acid production either by genetic engineering or with a PPI (omeprazole/Prilosec). They sequenced microbe-specific genes collected from the animals’ stool to determine the gut microbiome makeup of each mouse type, with or without blocked gastric acid production.

The researchers found that mice with gastric acid suppression developed alterations in their gut microbiomes. Specifically, they had more Enterococcus species of bacteria. These changes promoted liver inflammation and liver injury, increasing the progression of all three types of liver disease in the mice: alcohol-induced liver disease, NAFLD and NASH.

To confirm it was the increased Enterococcus that exacerbated chronic liver disease, Schnabl’s team also colonized mice with the common gut bacteria Enterococcus faecalis to mimic the overgrowth of intestinal enterococci they had observed following gastric acid suppression. They found that increased Enterococcus alone was sufficient to induce mild steatosis and increase alcohol-induced liver disease in mice.

The team also examined the link between PPI usage and alcoholic liver disease among people who abuse alcohol. They analyzed a cohort of 4,830 patients with a diagnosis of chronic alcohol abuse — 1,024 (21 percent) were active PPI users, 745 (15 percent) were previous users and 3061 (63 percent) had never used PPIs.

The researchers noted that PPI intake among these patients increased stool concentrations of Enterococcus. What’s more, the 10-year risk of a diagnosis of alcoholic liver disease was 20.7 percent for active users of PPIs, 16.1 percent for previous users and 12.4 percent for never users. In other words, the rate of liver disease in people who chronically abuse alcohol was 8.3 percent higher for those who actively use PPIs compared to those who never used the acid-blocking medications.

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