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Inhibition of mitochondrial complex I (NADH dehydrogenase) is the primary mechanism of the antidiabetic drug metformin and various unrelated natural toxins. Complex I inhibition can also be induced by antidiabetic PPAR agonists, and it is elicited by methionine restriction, a nutritional intervention causing resistance to diabetes and obesity. Still, a comprehensible explanation to why complex I inhibition exerts antidiabetic properties and engenders metabolic inefficiency is missing. To evaluate this issue, we have systematically reanalyzed published transcriptomic datasets from MPP-treated neurons, metformin-treated hepatocytes, and methionine-restricted rats. We found that pathways leading to NADPH formation were widely induced, together with anabolic fatty acid biosynthesis, the latter appearing highly paradoxical in a state of mitochondrial impairment. However, concomitant induction of catabolic fatty acid oxidation indicated that complex I inhibition created a "futile" cycle of fatty acid synthesis and degradation, which was anatomically distributed between adipose tissue and liver in vivo. Cofactor balance analysis unveiled that such cycling would indeed be energetically futile (-3 ATP per acetyl-CoA), though it would not be redox-futile, as it would convert NADPH into respirable FADH2 without any net production of NADH. We conclude that inhibition of NADH dehydrogenase leads to a metabolic shift from glycolysis and the citric acid cycle (both generating NADH) towards the pentose phosphate pathway, whose product NADPH is translated 1:1 into FADH2 by fatty acid cycling. The diabetes-resistant phenotype following hepatic and intestinal complex I inhibition is attributed to FGF21- and GDF15-dependent fat hunger signaling, which remodels adipose tissue into a glucose-metabolizing organ. [ABSTRACT FROM AUTHOR]

To investigate the effects of dietary methionine restriction (MetR) and endurance exercise on bone quality under a condition of estrogen deficiency, female Sprague-Dawley rats (36-wk-old) were assigned to a sham surgery group or one of five ovariectomized groups subjected to interventions of no treatment (Ovx), endurance exercise (Exe), methionine restriction (MetR), methionine restriction plus endurance exercise (MetR + Exe), and estrogen treatment (Est). Rats in the exercise groups were subjected to a treadmill running regimen. MetR and control diets contained 0.172 and 0.86% methionine, respectively. After the 12-wk intervention, all animals were killed, and serum and bone tissues were collected for analyses. Compared with estrogen treatment, MetR diet and endurance exercise showed better or equivalent efficiency in reducing body weight gain caused by ovariectomy (P < 0.05). Whereas only the Est group showed evidence for reduced bone turnover compared with the Ovx group, MetR diet and/or endurance exercise demonstrated efficiencies in downregulating serum insulin, leptin, triglyceride, and thiobarbituric acid reactive substances (P < 0.05). Both the Exe and MetR groups showed higher femoral cortical and total volumetric bone mineral density (vBMD), but only the Exe and Est groups preserved cancellous bone volume and/or vBMD of distal femora (P < 0.05) compared with the Ovx group. After being normalized to body mass, femora of the MetR and MetR + Exe groups had relatively higher bending strength and dimension values followed by the Sham, Exe, and Est groups (P < 0.05). In conclusion, both MetR diet and endurance exercise improved cortical bone properties, but only endurance exercise preserved cancellous bone under estrogen deficiency. [ABSTRACT FROM AUTHOR]

Dietary methionine restriction (MR) has been suggested to be comparable to endurance exercise with respect to its beneficial effects on health. To further investigate the effects of MR and endurance exercise on growing bone, 7-wk-old male Sprague-Dawley rats were fed different L-methionine (Met)-containing diets with or without endurance exercise intervention (Ex; 0.86% Met, 0.52% Met, 0.17% Met, 0.86% Met-Ex, 0.52% Met-Ex, and 0.17% Met-Ex groups). After an 8-wk intervention period, exercise-trained rats had a 9.2% lower body weight (BW) than did sedentary rats (P < 0.05). Additionally, 0.17% Met-fed rats had 32% lower BW when compared with rats fed the other 2 diets (P < 0.05). Serum osteocalcin was lower in the 0.17% Met-Ex group compared with the other 2 exercise groups and the 0.17% Met group (P < 0.05) . Serum concentrations of C-terminal telopeptide of type 1 collagen were lower in exercise-trained and 0.17% Met-fed rats than in sedentary rats and rats fed the other 2 diets (P < 0.05 for both). Rats fed the 0.17% Met diet had lower trabecular bone volume, bone mineralization activities, and bone mineral content (BMC; e.g., total, cortical, and spongy BMC) and bone mineral density (BMD; e.g., total and spongy BMD) indices compared with rats fed the other 2 diets (P < 0.05). Exercise-trained rats also had lower bonemineralization activity, trabecular osteoclast density, total BMC, cortical BMC, and total BMD compared with sedentary rats (P < 0.05). In total BMD, only the 0.17% Met-Ex group had values lower than the other 2 exercise groups and the 0.17% Met group (P < 0.05). Compared with rats fed the other 2 diets and sedentary rats, the femora of 0.17% Met-fed and exercise-trained rats, respectively, had smaller size and/or lower extrinsic strength but enhanced intrinsic biomechanical properties (P < 0.05). The results indicate that MR and endurance exercise caused lower whole bone mass, size, and/or strength but might enhance intrinsic bone strength. [ABSTRACT FROM AUTHOR]