The greater frequency and aggressiveness of hepatocellular carcinoma (HCC) in men than in women might be attributable to greater synthesis and accumulation of serotonin in males, according to a report published online in Cellular and Molecular Gastroenterology and Hepatology (2017 May. doi: org/10.1016/j.jcmgh.2017.01.002 ).

HCC is nearly five times more common in men than in women, and several molecular studies “have shown a more robust and active HCC tumor microenvironment” in men as well. For example, the density of infiltrating, tumor-associated macrophages is higher among males in a mouse model of the cancer, and human men have substantially higher amounts of intratumoral cluster-of-differentiation cells and neutrophils that indicate a poor prognosis, said Qiqi Yang, PhD , of the department of biological sciences at the National University of Singapore, and her associates.

The investigators developed several zebrafish models of HCC in which the cancer could be induced by transgenic expression of an oncogene in the animals’ hepatocytes. These models “allow the oncogene to be activated at a given and controlled timing in both sexes, providing an excellent platform to study the sex disparity in HCC initiation and progression,” they noted.

They also confirmed the zebrafish findings in human lab studies by analyzing tissue samples from 5 normal livers, 7 inflamed livers, 16 cirrhotic livers, and 30 livers affected with HCC.

The investigators found an increased level of serotonin production in male, compared with female, livers. They demonstrated that serotonin was necessary for the survival of hepatic stellate cells, which also are more abundant in males than in females and have recently been shown to promote tumorigenesis. Serotonin also was crucial for activating hepatic stellate cells during HCC carcinogenesis.

In addition, serotonin levels were significantly elevated in inflamed, cirrhotic, and cancerous livers, compared with normal livers, among men but not among women. “This is in line with the prevailing knowledge that men have a significantly higher rate of serotonin synthesis than do women,” Dr. Yang and her associates said.


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