Expression of beta-carotene 15,15'-monooxygenase gene and retinol status in type 2 diabetic Goto-Kakizaki rats.
The vitamin A status has been studied in type 2 diabetes and it is known that plasma retinol levels of patients with type 2 diabetes are elevated. However, the details of vitamin A metabolism in type 2 diabetes are unclear. beta-Carotene exhibits biological activity as provitamin A and beta-carotene 15,15'-monooxygenase (BCM) cleaves beta-carotene to form retinal. We studied BCM gene expression in type 2 diabetic Goto-Kakizaki (GK) rats. BCM gene expression was analyzed in the liver, intestine, and testis of 8- and 13-week-old GK rats and Wistar rats (control). The plasma and liver retinol levels were measured, and plasma retinol-binding protein (RBP) was detected. BCM gene expression in the liver, intestine and testis of GK rats was increased compared with that in controls. Plasma retinol levels and RBP levels were increased in GK rats, but hepatic retinol levels did not differ between GK rats and controls. BCM gene expression in the liver and intestine might affect retinol levels in type 2 diabetes. Conversion of beta-carotene to retinal might be accelerated in the presence of insulin resistance status, so that plasma retinol levels are increased in type 2 diabetes.