Taurine ameliorates hyperglycemia and dyslipidemia by reducing insulin resistance and leptin level in Otsuka Long-Evans Tokushima fatty (OLETF) rats with long-term diabetes

Abstract

This study aimed to determine whether taurine supplementation improves metabolic disturbances and diabetic complications in an animal model for type 2 diabetes. We investigated whether taurine has therapeutic effects on glucose metabolism, lipid metabolism, and diabetic complications in Otsuka Long- Evans Tokushima fatty (OLETF) rats with long-term duration of diabetes. Fourteen 50-week-old OLETF rats with chronic diabetes were fed a diet supplemented with taurine (2%) or a non-supplemented control diet for 12 weeks. Taurine reduced blood glucose levels over 12 weeks, and improved OGTT outcomes at 6 weeks after taurine supplementation, in OLETF rats. Taurine significantly reduced insulin resistance but did not improve β-cell function or islet mass. After 12 weeks, taurine significantly decreased serum levels of lipids such as triglyceride, cholesterol, high density lipoprotein cholesterol, and low density lipoprotein cholesterol. Taurine significantly reduced serum leptin, but not adiponectin levels. However, taurine had no therapeutic effect on damaged tissues. Taurine ameliorated hyperglycemia and dyslipidemia, at least in part, by improving insulin sensitivity and leptin modulation in OLETF rats with long-term diabetes. Additional study is needed to investigate whether taurine has the same beneficial effects in human diabetic patients.

Figure 1

The effect of taurine supplementation on glucose metabolism in OLETF rats with long-term diabetes. A taurine (2%)-supplemented diet was fed to OLETF rats for 12 weeks, beginning at 50 weeks of age. (A) Blood glucose levels during the 12-weeks supplementation period. (B) Comparison of food intake between taurine and control groups. Data are expressed as mean ± standard error of the mean (SEM). Between-group differences were compared using the Mann-Whitney U test. Differences were considered statistically significant at P < 0.05. ^*P < 0.05; ^**P < 0.01; NS, not significant.

Figure 2

The effects of taurine supplementation on oral glucose tolerance tests (OGTTs) and glycated haemoglobin (HbA1c) in OLETF rats. (A) OGTTs were conducted at 0, 6, and 12 weeks after beginning the taurine-supplemented diet. (B) HbA1c levels. Data are expressed as the mean ± standard error of the mean (SEM). Between-group differences were compared using the Mann-Whitney U test. Differences were considered statistically significant at P < 0.05. ^*P < 0.05; NS, not significant.

Figure 3

The effects of taurine supplementation on insulin resistance (HOMA-IR) and beta cell function (HOMA-β) in OLETF rats. (A) Levels of glucose and insulin 0, 6, and 12 weeks after beginning the taurine-supplemented diet. (B) Comparison of HOMA-IR and HOMA-β between taurine and the control groups. (C) Comparison of Insulin Tolerance Test (ITT) between two groups. Between-group differences were compared using the Mann-Whitney U test. Differences were considered statistically significant at P < 0.05. ^*P < 0.05; NS, not significant.

Figure 4

The effects of taurine supplementation on tissue targets of insulin secretion and action in OLETF rats. (A) Pancreatic tissue was stained by H&E (upper panel) and anti-insulin antibody (lower panel) (Magnification: H&E stain, 40×; Immunostaining, 10×). (B) Fat, liver, and muscle tissues were stained by H&E after adhering to a taurine diet for 12 weeks (H&E stain, 100 × magnification).

Figure 5

The effects of taurine supplementation on serum lipid and serum adipokine levels in OLETF rats. (A) Levels of triglycerides (TG), cholesterol, high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C). (B) Serum adiponectin and leptin levels in OLETF rats after adhering to a taurine diet for 12 weeks. Between-group differences were compared using the Mann-Whitney U test. Differences were considered statistically significant at P < 0.05. ^*P < 0.05; ^**P < 0.01; NS, not significant.

Figure 6

The effects of taurine supplementation on various tissues that have been negatively affected by diabetes. Heart, aorta, and kidney tissues were H&E stained, and the degree of tissue damage was compared between LETO and OLETF rats after adhering to a taurine diet for 12 weeks (H&E stain; Magnification: 200× for kidney, 100× for heart and aorta).