Enhanced exercise-induced muscle damage and muscle protein degradation in streptozotocin-induced type 2 diabetic rats

Exercise ameliorates skeletal muscle insulin resistance by modulating GRK4-mediated D1R expression

Exercise has been recommended as a nonpharmaceutical therapy to treat insulin resistance (IR). Previous studies showed that dopamine D1-like receptor agonists, such as fenoldopam, could improve peripheral insulin sensitivity, while antipsychotics, which are dopamine receptor antagonists, increased susceptibility to Type 2 diabetes mellitus (T2DM). Meanwhile, exercise has been proved to stimulate dopamine receptors. However, whether the dopamine D1 receptor (D1R) is involved in exercise-mediated amelioration of IR remains unclear. We found that the D1-like receptor antagonist, SCH23390, reduced the effect of exercise on lowering blood glucose and insulin in insulin-resistant mice and inhibited the contraction-induced glucose uptake in C2C12 myotubes. Similarly, the opposite was true for the D1-like receptor agonist, fenoldopam. Furthermore, the expression of D1R was decreased in skeletal muscles from streptozotocin (STZ)- and high-fat intake-induced T2DM mice, accompanied by increased D1R phosphorylation, which was reversed by exercise. A screening study showed that G protein-coupled receptor kinase 4 (GRK4) may be the candidate kinase for the regulation of D1R function, because, in addition to the increased GRK4 expression in skeletal muscles of T2DM mice, GRK4 transgenic T2DM mice exhibited lower insulin sensitivity, accompanied by higher D1R phosphorylation than control mice, whereas the AAV9-shGRK4 mice were much more sensitive to insulin than AAV9-null mice. Mechanistically, the up-regulation of GRK4 expression caused by increased reactive oxygen species (ROS) in IR was ascribed to the enhanced expression of c-Myc, a transcriptional factor of GRK4. Taken together, the present study shows that exercise, via regulation of ROS/c-Myc/GRK4 pathway, ameliorates D1R dysfunction and improves insulin sensitivity.

Effects of streptozotocin-induced diabetes on leg muscle contractile properties and motor neuron morphology in rats

Skeletal muscle fiber subtypes are differentially sensitive to diabetes-related pathology; For example, fast-twitch muscles exhibit severe decreases in contraction force while slow-twitch muscles demonstrate prolonged half-relaxation time. However, such alterations have only been examined after a relatively short period following diabetes onset, with no information available regarding muscle damage caused by longer disease periods (>20 weeks). This study examined alterations in the contractile properties of the medial gastrocnemius (fast-twitch) and soleus (slow-twitch) muscles, as well as morphological changes in their motor neurons 12 and 22 weeks after diabetes onset. Adult male Wistar rats were divided into diabetic (12- or 22-week post-streptozotocin injection) and age-matched control groups. Electrically evoked maximum twitch and tetanic tension were recorded from leg muscles. Additionally, motor neuron number and cell body size were examined. At 12 weeks after diabetes onset, decreases in twitch force were observed predominantly in medial gastrocnemius muscles, while soleus muscles exhibited prolonged half-relaxation time. However, these differences became ambiguous at 22 weeks, with decreased twitch force and prolonged half-relaxation time observed in both muscles. On the other hand, reduction in soleus motor neurons was observed 12 weeks after diabetes onset, while medial gastrocnemius motor neurons were diminished at 22 weeks. These data indicate that experimental diabetes induces differential damage to medial gastrocnemius and soleus muscles as well as motor neurons. These diabetes-induced differences may partly underlie the differential deficits observed in gastrocnemius and soleus.

Exercise on Progenitor Cells in Healthy Subjects and Patients with Type 1 Diabetes

PURPOSE

To evaluate the acute effect of aerobic exercise (AE) and resistance exercise (RE) on the release of endothelial progenitor cell (EPCs, CD34+/KDR+/CD45 dim) and vascular function in type 1 diabetes (T1DM).

METHODS

Fourteen men with T1DM and 5 nondiabetic controls were randomly assigned to 40-min AE (60% VO 2peak) and RE sessions (60% 1-RM). The study had a crossover design, and interventions were 1 wk apart. Venous occlusion plethysmography (blood flow, reactive hyperemia, and vascular resistance) and blood collection (EPC levels, flow cytometry) were done immediately before and after exercise sessions.

RESULTS

Patients were 30.3 ± 1.6 yr-old, HbA1c 7.7% ± 0.2%; controls were 26.8 ± 2.3 yr-old. Groups did not differ in EPC levels at baseline or in relation to exercise. Over time, exercise did not induce changes in patients with T1DM, whereas, in controls, EPCs were decreased after AE (-10.7%, P = 0.017) and increased after RE (+12.2%, P = 0.004). Compared with baseline, blood flow increased and vascular resistance decreased after RE in both groups. Reactive hyperemia was increased 10 min after AE and RE sessions in patients with T1DM (36.5% and 42.0%, respectively) and in controls (35.4% and 74.3%), but no group differences were observed between groups in response to exercise.

CONCLUSIONS

Despite the increased vascular reactivity in both groups after both exercise sessions, EPCs were only influenced by exercise in controls. The unchanged number of EPCs in T1DM after exercise sessions might indicate a blunted endothelium regenerating capacity, revealing an early deterioration of the functional arterial characteristics not disclosed by only evaluating vascular functional variables.

Effects of chromium malate on glycometabolism, glycometabolism-related enzyme levels and lipid metabolism in type 2 diabetic rats: A dose-response and curative effects study

Aims/Introduction

The present study was designed to evaluate the effect of chromium malate on glycometabolism, glycometabolism-related enzyme levels and lipid metabolism in type 2 diabetic rats, and dose–response and curative effects.

Materials and Methods

The model of type 2 diabetes rats was developed, and daily treatment with chromium malate was given for 4 weeks. A rat enzyme-linked immunosorbent assay kit was used to assay glycometabolism, glycometabolism-related enzyme levels and lipid metabolism changes.

Results

The results showed that the antihyperglycemic activity increased with administration of chromium malate in a dose–dependent manner. The serum insulin level, insulin resistance index and C-peptide level of the chromium malate groups at a dose of 17.5, 20.0 and 20.8 μg chromium/kg bodyweight were significantly lower than that of the model, chromium trichloride and chromium picolinate groups. The hepatic glycogen, glucose-6-phosphate dehydrogenase and glucokinase levels of the chromium malate groups at a dose of 17.5, 20.0 and 20.8 μg chromium/kg bodyweight were significantly higher than that of the model, chromium trichloride and chromium picolinate groups. Chromium malate at a dose of 20.0 and 20.8 μg chromium/kg bodyweight significantly changed the total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglycerides levels compared with the chromium trichloride and chromium picolinate groups.

Conclusions

The results showed that chromium malate exhibits greater benefits in treating type 2 diabetes, and the curative effect of chromium malate is superior to chromium trichloride and chromium picolinate.