Research published in the current issue of the journal, Clinical Science, appears to have found a link between obstructive sleep apnoea and non-alcoholic steatohepatitis. Dr Anne-Christine Piguet and colleagues from the University of Bern, Switzerland, kept mice for a week in low-oxygen atmospheres and found that it led to increased levels of fat and inflammation in their livers.

Apnoea means "without breath" and occurs when the muscles in the airways behind the tongue relax in sleep, causing the person to snore and briefly, to stop breathing.

Nonalcoholic steatohepatitis (NASH) is a common, often "silent" liver disease occurring in around 40% of the population. It resembles alcoholic liver disease, but occurs in people who drink little or no alcohol. The major feature in NASH is fat in the liver, along with inflammation and damage. NASH can be severe and can lead to cirrhosis, in which the liver is permanently damaged and scarred and no longer able to work properly.

Obesity predisposes patients to both fatty liver diseases and obstructive sleep apnoea.

To mimic the effects of low oxygen levels caused by the repeated obstruction of the upper airways in sleep apnoea, the researchers kept mice in a low oxygen environment for seven days. After this time they were found to have more fat and inflammation in their livers compared to mice that had been kept in atmospheres with normal levels of oxygen. When the mice were exposed to low oxygen levels, the genes that controlled fat synthesis in the liver seemed to be more active while those that controlled fat breakdown demonstrated reduced activity.

In addition, the mice exposed to low levels of oxygen became less sensitive to insulin. This is the mechanism by which the body regulates blood sugar and is a cause of diabetes. Metabolic disorders such as diabetes and obesity can cause complications in patients with NASH.

Commenting on the finding, Dr Piguet said, "Hypoxia (lack of oxygen) may be the link leading to accumulation of fat in the liver and to the progression of non-alcoholic steatohepatitis. Our findings show that it is important both to screen obese patients for obstructive sleep apnoea to prevent it contributing to fatty liver disease and to treat those patients who already have NASH for hypoxia which may be making their condition worse".

Source: Biochemical Society

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