Shosaikoto as a potential antiatherosclerotic agent

Shosaikoto, a Kampo medicine used clinically to treat patients with chronic hepatitis or cirrhosis in Japan, displays immunoregulatory effects, especially on macrophage functions. Oral administration of shosaikoto influences the synthesis of humoral factors such as the interleukins, nitric oxide and prostaglandins in macrophages. In addition, phagocytic activity is enhanced by treatment with shosaikoto, resulting in an antigen that is effectively presented to T lymphocytes to produce more antibodies. The role of macrophages in the pathogenesis of atherosclerosis is well recognized, although a therapeutic agent targeted at macrophages has not yet been developed. When shosaikoto was administered to atherosclerotic rabbits, it did not exhibit antihyperlipidemic effects but did reduce the formation of atherosclerotic lesions. In addition, treatment with shosaikoto suppressed intimal hyperplasia in apoE-deficient mice fed a cholesterol-enriched diet for nine weeks. Biochemical studies demonstrated that the mechanism of the antiatherosclerotic effect was partly due to the increase of oxidized low-density lipoprotein (oxLDL) elimination by macrophages, resulting from stimulation of oxLDL uptake through scavenger receptors, activation of acyl-CoA:cholesterol acyltransferase and neutral cholesteryl ester hydrolase, and increase of cholesterol elimination by high-density lipoprotein. Furthermore, shosaikoto is able to reverse the depression of macrophage functions caused by hyperlipidemia. These results indicate the potential of this medicine as a new type of preventive or therapeutic agent for atherosclerosis.