Influence of Insulin and Muscle Fiber Type in Nε-(Carboxymethyl)- Lysine Accumulation in Soleus Muscle of Rats with Streptozotocin-Induced Diabetes Mellitus

Background: Nε-(carboxymethyl)-lysine (CML) is an advanced glycation end product (AGE), the accumulation of which has been implicated in the etiology of diabetes complications. Skeletal muscle in diabetes demonstrates altered function, and increased accumulation of CML has been found in several fast-twitch muscles of diabetic animals. Objective: This study aims to explore the accumulation of CML in soleus (a slow muscle) in diabetic animals, with and without insulin therapy. Methods: Twenty-one rats were randomly divided into control and diabetes groups (DNI: diabetes without insulin; DI: diabetes with insulin; C: control). Diabetes was induced by intravenous administration of streptozotocin. At the end of the 12-week experimental period the soleus muscle was excised and snap frozen in liquid nitrogen. Muscle cross-sections were immunolabeled for CML. The number of CML-labeled muscle fibers was quantified; fibers were also evaluated for fiber types and cross-sectional areas. Results: The percentage of myofibers immunolabeling for CML was highest in the DNI group (13.8 ± 2.5%), lower in the DI group (5.4 ± 1.1%) and lowest in the C group (2.1 ± 0.6%). Statistical analysis revealed that AGE accumulation was significantly greater in the DNI group than in both C and DI groups (p = 0.0002). There was no significant difference between C and DI groups. In the DNI animals, AGE-positive myofibers showed a higher percentage of fast fiber types than did the AGE-negative fibers (49.5 ± 6.9 vs. 13.7 ± 1.5%, p = 0.002). No differences existed in cross-sectional areas between AGE-positive and AGE-negative fibers within any group. Conclusion: The greatest accumulation of AGE was in the soleus of the DNI group, and was significantly less in the DI group. These findings may be linked to disordered glucose metabolism, increased oxidative stress and/or fiber type transformation in these muscles.