Thymosin Beta 4 (TB-500)

Insulin resistance is a key feature of type 2 diabetes mellitus and is also associated with an increased risk of cardiovascular disease (CVD) [1-3]. There are lots of drugs in the market which aim to improve insulin resistance. However, besides metformin, other drugs have had serious adverse effects and have either been withdrawn from the market or subjected to serious warnings. For instance, rosiglitazone, an insulin sensitizer which acts by binding to the PPAR receptors in fat cells and making the cells more responsive to insulin, has been found to be associated with an increased risk of heart attack [4]. Thus, it is very necessary to explore novel potential insulin sensitizers which could not only improve the insulin resistance but also decrease the risk of cardiovascular disease.

Thymosin Beta 4 (Tβ4) is a major intracellular G-actin-sequestering peptide. Previous studies have showed that Tβ4 levels decreased significantly in corneas of diabetic patients compared with healthy subjects [5], and exogenous Tβ4 administration would promote wound healing in diabetic and nondiabetic corneas [6,7]. Therefore, this study was designed to determine the role of Tβ4 on glucose tolerance and hyperinsulinaemia in a KK Cg – Ay/J (KK) mouse model of type 2 diabetes mellitus.

All KK mice were purchased from the Jackson Laboratory and C57BL mice were obtained from the Animal Resources Centre, NUS. In this study, non-diabetic C57BL mice were used as normal control. KK mice were divided into the following groups: KK control group with saline treatment; KK Tβ4 group with daily Tβ4 100 ng/10 g body weight intraperitoneal injection for 12 weeks. The phosphorylated AKT and total AKT protein levels of skeletal muscle from all groups were determined. OGTT, Tβ4, plasma insulin, HbA1c, serum adiponectin, cholesterol, and triglyceride were measured before and after Tβ4 treatment.

 

The plasma Tβ4 concentrations increased slightly to 6.00 ± 0.45 μg/ml in C57BL Tβ4 group and 2.94 ± 0.23 μg/ml in KK Tβ4 group. However, the statistical difference between concentration at baseline and that after 12 weeks treatment both in C57BL and KK mice was not significant.

 

As shown in Figure 2.A, KK mice developed hyperglycemia and glucose intolerance at 12-14 weeks old, and glucose concentrations of two KK groups were significantly higher than those in the C57BL groups. In Figure 2.B & C, KK control group remained hyperglycemic and glucose intolerant at 6 weeks after saline treatment, and still had severe hyperglycemia and glucose intolerance at 12 weeks after saline treatment. As shown in Figure 2.D, KK mice developed hyperinsulinaemia at 12-14 weeks of age, and remained it at 6 weeks after Tβ4 treatment. Plasma insulin concentrations of KK groups were significantly higher than those in the C57BL groups. At 12 weeks after saline or Tβ4 treatment, KK control group mice remained severely hyperinsulinaemia.

 

Table 1 show that results of the fasting plasma metabolites. Fasting insulin and triglyceride in the two KK groups were significantly higher than those of C57BL groups at 12 to 14 weeks old. AT 6 weeks after Tβ4 treatment, they were still higher in the two KK groups than those of C57BL groups. At 12 weeks after saline treatment, the fasting insulin levels of KK control mice have increased, while KK Tβ4 group remained unchanged.

 

As the data shown in figure 3, Tβ4 treatment increased AKT activity in response to glucose challenge, which might lead to increased uptake of glucose by skeletal muscles.

 

The blood glucose level in KK Tβ4 group was lower than that in KK control group. The average insulin level of KK Tβ4 group was lower than the counterpart of KK control group. However, the difference between them did not reach statistical significance.

In conclusion, the preliminary data indicates that Tβ4 could improve glucose intolerance and ameliorated insulin resistance in KK mouse. Moreover, Tβ4 may be a potential alternative insulin sensitizer for the treatment of type 2 diabetes mellitus.