FRIDAY, April 11 (HealthDay News) -- Severe hyperthyroidism is associated with a 40 percent drop in high-density lipoprotein cholesterol (HDL-C) levels in mice, according to study findings published online April 3 in Endocrinology.
Ivan Tancevski, M.D., from Innsbruck Medical University in Innsbruck, Austria, and colleagues examined the effect of severe hyperthyroidism on plasma HDL-C in mice. They note that a recent study had shown that triiodothyronine increased HDL-C clearance through upregulation of hepatic expression of scavenger receptor-BI.
The researchers found that severe hyperthyroidism reduced hepatic expression of ATP-binding cassette transporter 1 (ABCA1) and was associated with a 40 percent reduction in HDL-C, but had no effect on hepatic scavenger receptor-BI expression. There was a marked increase in the sterol content of bile, liver and feces, the report indicates. Plasma clearance of HDL-C was identical in control and hyperthyroid mice.
"From our results in mice we conclude that severe hyperthyroidism may reduce the formation of nascent HDL particles by a marked downregulation of hepatic ABCA1," Tancevski and colleagues write. "Our results suggest newly synthesized cholesterol to be retained in the liver and to be actively converted into bile salts for biliary excretion and/or directly transported into bile, thus increasing the sterol content in feces of hyperthyroid mice."
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