Vit D3 versus L Carnitine Supplement in Alleviating Age-Related Insulin Resistance in A Naturally Aging Rat Model

Abstract
Background: Insulin Resistance (IR) has long been rec-ognized as a characteristic of aging. Many studies recorded beneficial roles of Vitamin D3 (VD3) and L-Carnitine (LC) in obesity and type 2 diabetes.
Aim of Study: To evaluate the role of VD3 versus LC in attenuating the age-related IR in a naturally aging rat model, clarifying their possible underlying mechanisms.
Material and methods: Rats were divided into 4 groups; Young Control (YC), aged group, VD3-treated aged group (VD3-aged) and LC-treated aged group (LC-aged). Experi-mental procedures included measurement of body weight, Body Mass Index (BMI) and Oral Glucose Tolerance Tests (OGTT). The Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) index was also calculated. Assays of fasting serum glucose and insulin levels as well as serum tumor necrosis factor-a (TNF-a), interleukin-6 (IL-6) and adiponectin levels were performed. Moreover, skeletal muscle Sirtuin-1 (SIRT-1), Triglycerides (TGs) and TNF-a levels alongside with the glucose transporter-4 (GLUt4) mRNA expression were assessed.
Results: Compared to YC rats, aged rats exhibited signif-icant increase in fasting serum insulin and HOMA-IR as well as an abnormal OGTT. Serum TNF-a and IL-6 levels were significantly increased, whereas serum adiponectin level was significantly decreased in old rats. Furthermore, the SIRT1 levels and GLUT 4 mRNA expression were significantly lower, whereas the TGs and TNF-a were significantly higher in skeletal muscle of aged rats compared to YC ones. On the other hand, these parameters, were equally and significantly attenuated in VD3 and LC supplemented rats compared to non-treated age matched group, except for the skeletal muscle SIRT-1 level which could be elevated only by VD3, while the anti-inflammatory and TGs lowering effects of LC were more prominent than VD3. Nevertheless, the overall effect of VD3 and LC on IR-related parameters were nearly equal.
Conclusion: Both VD3 or LC administrations were equally effective in alleviating the age-related IR, thus may provide a possible therapeutic intervention in the aging population.