Researchers have found that tobacco smoke exposure from secondhand smoking can result in nonalcoholic fatty liver disease (NAFLD), a common disease and cause of chronic liver injury in which fat accumulates in the liver of people who drink little or no alcohol.
Secondhand smoke is the combination of smoke exhaled by a smoker and smoke given off by the burning end of a tobacco product. Lingering in the air long after tobacco products have been extinguished, it is involuntarily inhaled by nonsmokers in the vicinity. Exposure to secondhand smoke is also called involuntary smoking or passive smoking. Of the more than 4,000 chemicals that have been identified from secondhand smoking, at least 250 are known to be harmful, and 50 of these are known to cause cancer.
The researchers found fat accumulated in liver cells of mice exposed to second-hand cigarette smoke for a year in the lab. Such fat buildup is a sign of NAFLD, leading eventually to liver dysfunction.
The study focused on two key regulators of lipid (fat) metabolism that are found in many human cells as well: SREBP (sterol regulatory element-binding protein) that stimulates synthesis of fatty acids in the liver, and AMPK (adenosine monophosphate kinase) that turns SREBP on and off.
It was found that secondhand smoke exposure inhibits AMPK activity, which, in turn, causes an increase in activity of SREBP. When SREBP is more active, more fatty acids get synthesized. The result is NAFLD induced by second-hand smoking.
“Our study provides compelling experimental evidence in support of tobacco smoke exposure playing a major role in NAFLD development,” said Manuela Martins-Green, who led the study.
The study emphasizes that discouraging cigarette smoking helps prevent not only cardiovascular disease, pulmonary disease and cancer, but now also liver disease.
Second-hand smoke is a major toxicant that affects children, the elderly and nonsmokers living in the household of adults who smoke. Many state and local governments have passed laws prohibiting smoking in public facilities. Diseases associated with second-hand smoking include cancer, heart disease, atherosclerosis, pneumonia, bronchitis and severe asthma.
Despite the large body of scientific evidence documenting the effects of passive or active smoking on the heart and lungs, reports investigating how smoking causes liver injury are scant.
“Until our study, second-hand smoking had not been linked to NAFLD development,” Martins-Green said.
References:
1. Manuela Martins-Green, et al. Second-hand smoke stimulates lipid accumulation in the liver by modulating AMPK and SREBP-1. Journal of Hepatology, Volume 51, Issue 3, September 2009, Pages 535-547.
2. National Cancer Institute.
