Combined exercise and calorie restriction therapies restore contractile and mitochondrial functions in skeletal muscle of obese-insulin resistant rats.

OBJECTIVES: A combined exercise training and calorie-restriction program is the mainstream treatment of obesity. However, the effect of the dual-action program on mitochondrial function in skeletal muscles has not yet been clarified. The aim of this study was to determine if the combined program, rather than a single program, restored both lost muscle activity and mitochondrial function in obesity. METHODS: The study included 30 female Wistar rats. Six rats fed a normal diet for 27 wk were used as the control group. The remaining 24 rats were fed a high-fat diet (HFD) for 27 wk. At week 20, the HFD rats were divided into the following four groups: sedentary lifestyle, endurance exercise five times per week, 60% of calorie restriction (CR) per day, and combined exercise training and CR. All conditions were maintained for 7 wk. RESULTS: We found that HFD-fed rats without therapy developed obese insulin resistance (IR) and impaired function of skeletal muscles. Skeletal muscles of the HFD-fed rats without therapy also exhibited early fatigability; impaired mitochondrial function, as indicated by increased reactive oxygen species production, membrane depolarization, and swelling; reduced mitochondrial dynamics as indicated by increased phosphorylation of DRP1 and decreased MFN2 expression; diminished mitochondrial biogenesis, as shown by decreased PGC1α and CPT1 expression; and increased apoptosis. Both exercise and CR in HFD-fed rats equally attenuated the impairment of muscle functions. However, combined therapies in HFD-fed rats restored functions of skeletal muscles. CONCLUSIONS: These findings reinforce the synergistic beneficial effects of combined exercise and CR on skeletal muscles of HFD-fed rats.

Combination of exercise and calorie restriction exerts greater efficacy on cardioprotection than monotherapy in obese-insulin resistant rats through the improvement of cardiac calcium regulation.

BACKGROUND: Long-term high-fat diet (HFD) consumption causes obese-insulin resistance which is known to be a major risk factor for cardiovascular diseases due to its impact on the impairment of left ventricular (LV) contractile function and cardiac mitochondrial function. Intracellular calcium [Ca2+]i regulation plays an important role in the maintenance of LV function. Although either caloric restriction (CR) or exercise (Ex) are shown to strongly affect metabolic status and LV function, the combined effects of exercise and calorie restriction on cardiometabolic status, cardiac mitochondrial dynamics and cardiac [Ca2+]i transient homeostasis under conditions of obese-insulin resistance have never been investigated. METHODS: Female rats were fed with either a high-fat diet (HFD: fat, 59.28%; protein, 26.45%; carbohydrate, 14.27%) or a normal diet (fat, 19.77%; protein, 28.24%; carbohydrate, 51.99%) for 13 weeks. HFD rats were then divided into 4 groups: 1) Vehicle (HFD + Veh); 2) Calorie restriction (HFD + CR); 3) Exercise (HFD + Ex) and 4) Combined therapy (HFD + CR + Ex). After 6-week intervention, the metabolic status, heart rate variability (HRV), LV function, cardiac mitochondrial dynamics, and [Ca2+]i transients were determined. RESULTS: Insulin resistance developed in HFD rats as indicated by increased plasma insulin and HOMA index. Although HFD + Veh rats had markedly impaired LV function, indicated by reduced %LVFS and impaired cardiac mitochondrial dynamics and [Ca2+]i transients, these impairments were attenuated in the HFD + CR, HFD + Ex and HFD + CR + Ex rats. However, the greatest improvement in cardiometabolic function was observed in HFD + CR + Ex rats. CONCLUSIONS: Our findings indicated that a combination of calorie restriction and exercise exerted greater cardioprotection than a monotherapy through the improvement of cardiometabolic status, cardiac mitochondrial dynamics and cardiac [Ca2+]i homeostasis in obese-insulin resistant rats.

Estrogen deprivation aggravates intracellular calcium dyshomeostasis in the heart of obese-insulin resistant rats.

The incidence of cardiovascular disease and metabolic syndrome increases after the onset of menopause, giving evidence for the vital role of estrogen. Intracellular calcium [Ca2+ ]i regulation plays an important role in the maintenance of left ventricular (LV) contractile function. Although either estrogen deprivation or obesity has been shown to strongly affect the metabolic status and LV function, the effects of estrogen deprivation on the cardiometabolic status and cardiac [Ca 2+ ]i regulation in the obese-insulin resistant condition have never been investigated. Our hypothesis was that estrogen deprivation aggravates LV dysfunction through the increased impairment of [Ca 2+ ]i homeostasis in obese-insulin resistant rats. Female rats were fed on either a high-fat (HFD, 59.28% fat) or normal (ND, 19.77% fat) diet for 13 weeks. Then, rats were divided into sham (HFS and NDS) operated or ovariectomized (HFO and NDO) groups. Six weeks after surgery, metabolic status, LV function and incidence of [Ca 2+ ]i transients were determined. NDO, HFS, and HFO rats had evidence of obese-insulin resistance indicated by increased body weight with hyperinsulinemia and euglycemia. Although NDO, HFS, and HFO rats had markedly reduced %LV fractional shortening, E/A ratio and decreased [Ca 2+ ]i transient amplitude and decay rate, HFO rats had the most severe impairments. These findings indicate that estrogen deprivation had a strong impact on abnormal LV function through [Ca 2+ ]i regulation. In addition, evidence was found that in obese-insulin resistant rats, estrogen deprivation severely aggravates LV dysfunction via increased impairment of [Ca 2+ ]i homeostasis.

Ovariectomy and obesity have equal impact in causing mitochondrial dysfunction and impaired skeletal muscle contraction in rats.

OBJECTIVE: Previous studies have demonstrated that either an obese-insulin resistance condition or a condition involving loss of estrogen impaired skeletal muscle function as indicated by a decrease in muscle contraction. The differing effects of combined estrogen deficiency over obese-insulin resistance on skeletal muscle function have, however, not yet been determined. Our hypothesis was that estrogen deficiency aggravates skeletal muscle dysfunction in obese-insulin resistant rats, via increased muscle oxidative stress and mitochondrial dysfunction. METHODS: Twenty-four female Wistar rats were divided into 2 groups and animals in each group were fed either a normal diet (ND) or a high-fat diet (HFD) for 24 weeks. At week 13, rats in each group were subdivided into 2 subgroups: sham-operated or ovariectomized (n = 6/subgroup). At the end of the experimental period the contraction of the gastrocnemius muscles was tested before the rats were sacrificed. Skeletal muscle was removed to assess oxidative stress and mitochondrial function. RESULTS: We found that an obese-insulin resistant condition was observed in sham-operated HFD-fed rats, ovariectomized ND-fed rats, and ovariectomized HFD-fed rats. Skeletal muscle contractile function (peak-force ratio [g/g]; 25.40 ±â€Š2.03 [ovariectomized ND-fed rats], 22.44 ±â€Š0.85 [sham-operated HFD-fed rats] and 25.06 ±â€Š0.61 [ovariectomized HFD-fed rats]), skeletal muscle mitochondrial function, and oxidative stress were equally significantly impaired in all 3 groups, when compared with those of sham-operated ND-fed rats (31.12 ±â€Š1.88 g/g [NDS]; P < 0.05). Surprisingly, loss of estrogen did not aggravate these dysfunctions of skeletal muscles in HFD-fed rats. CONCLUSIONS: These findings suggest that skeletal muscle dysfunction may occur due to increased muscle oxidative stress and mitochondrial dysfunction as a result of ovariectomy and obese-insulin resistance. Loss of estrogen, however, did not aggravate these impairments in the muscle of rats with obese-insulin resistant condition.

Both oophorectomy and obesity impaired solely hippocampal-dependent memory via increased hippocampal dysfunction.

Our previous study demonstrated that obesity aggravated peripheral insulin resistance and brain dysfunction in the ovariectomized condition. Conversely, the effect of obesity followed by oophorectomy on brain oxidative stress, brain apoptosis, synaptic function and cognitive function, particularly in hippocampal-dependent and hippocampal-independent memory, has not been investigated. Our hypothesis was that oophorectomy aggravated metabolic impairment, brain dysfunction and cognitive impairment in obese rats. Thirty-two female rats were fed with either a normal diet (ND, n = 16) or a high-fat diet (HFD, n = 16) for a total of 20 weeks. At week 13, rats in each group were subdivided into sham and ovariectomized subgroups (n = 8/subgroup). At week 20, all rats were tested for hippocampal-dependent and hippocampal-independent memory by using Morris water maze test (MWM) and Novel objective recognition (NOR) tests, respectively. We found that the obese-insulin resistant condition occurred in sham-HFD-fed rats (HFS), ovariectomized-ND-fed rats (NDO), and ovariectomized-HFD-fed rats (HFO). Increased hippocampal oxidative stress level, increased hippocampal apoptosis, increased hippocampal synaptic dysfunction, decreased hippocampal estrogen level and impaired hippocampal-dependent memory were observed in HFS, NDO, and HFO rats. However, the hippocampal-independent memory, cortical estrogen levels, cortical ROS production, and cortical apoptosis showed no significant difference between groups. These findings suggested that oophorectomy and obesity exclusively impaired hippocampal-dependent memory, possibly via increased hippocampal dysfunction. Nonetheless, oophorectomy did not aggravate these deleterious effects under conditions of obesity.

Estrogen deprivation aggravates cardiometabolic dysfunction in obese-insulin resistant rats through the impairment of cardiac mitochondrial dynamics.

The incidence of cardiovascular disease and metabolic syndrome increases after the onset of menopause, suggesting estrogen has a vital role in their prevention. Mitochondrial dynamics are known to play an important role in the maintenance of cardiac physiological function. However, the effects of estrogen deprivation on cardiometabolic status and cardiac mitochondrial dynamics under conditions of obese-insulin resistance have never been investigated. We hypothesized that estrogen deprivation aggravates cardiac dysfunction through increased cardiac mitochondrial fission in obese-insulin resistant rats. Female rats were fed on either a high fat (HFD, 57.60% fat) or normal (ND, 19.77% fat) diet for 13 weeks. The rats were then divided into 4 groups. Two sham groups (HFS and NDS) and 2 operated or ovariectomized (HFO and NDO) groups (n = 8/group). Six weeks after surgery, metabolic status, heart rate variability (HRV), left ventricular (LV) function, cardiac mitochondrial function and dynamics, and metabolic parameters were determined. Insulin resistance developed in NDO, HFS and HFO rats as indicated by increased plasma insulin and HOMA index. Although rats in both NDO and HFS groups had markedly impaired LV function indicated by reduced %LVFS and impaired cardiac mitochondrial function, rats in the HFO group had the most severe impairments. Moreover, the estrogen deprived rats (NDO and HFO) had increased cardiac mitochondrial fission through activation of phosphorylation of Drp-1 at serine 616. Our findings indicated that estrogen deprivation caused the worsening of LV dysfunction through increased cardiac mitochondrial fission in obese-insulin resistant rats.