Department of Cardiovascular Medicine and Center for Metabolic Regulation of Healthy Aging, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Chuo-ku, Kumamoto, 860-8556, Japan. Department of Cardiovascular Medicine and Center for Metabolic Regulation of Healthy Aging, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Chuo-ku, Kumamoto, 860-8556, Japan. kaikitak@kumamoto-u.ac.jp. Diabetes Center, Jinnouchi Hospital, 6-2-3 Kuhonji, Chuo-ku, Kumamoto, 862-0976, Japan.