We hypothesized that the mitochondrial-targeted antioxidant, mitoquinone (mitoQ), known to have mitochondrial uncoupling properties, might prevent the development of obesity and mitigate liver dysfunction by increasing energy expenditure, as opposed to reducing energy intake. We administered mitoQ or vehicle (ethanol) to obesity-prone C57BL/6 mice fed high-fat (HF) or normal-fat (NF) diets. MitoQ (500 mM) or vehicle (ethanol) was added to the drinking water for 28 weeks. MitoQ significantly reduced total body mass and fat mass in the HF-fed mice but had no effect on these parameters in NF mice. Food intake was reduced by mitoQ in the HF-fed but not in the NF-fed mice. Average daily water intake was reduced by mitoQ in both the NF-and HF-fed mice. Hypothalamic expression of neuropeptide Y, agouti-related peptide, and the long form of the leptin receptor were reduced in the HF but not in the NF mice. Hepatic total fat and triglyceride content did not differ between the mitoQ-treated and control HF-fed mice. However, mitoQ markedly reduced hepatic lipid hydroperoxides and reduced circulating alanine aminotransferase, a marker of liver function. MitoQ did not alter whole-body oxygen consumption or liver mitochondrial oxygen utilization, membrane potential, ATP production, or production of reactive oxygen species. In summary, mitoQ added to drinking water mitigated the development of obesity. Contrary to our hypothesis, the mechanism involved decreased energy intake likely mediated at the hypothalamic level. MitoQ also ameliorated HF-induced liver dysfunction by virtue of its antioxidant properties without altering liver fat or mitochondrial bioenergetics.

Mitochondrial dysfunction is an underlying pathology in numerous diseases. Delivery of diagnostic and therapeutic cargo directly into mitochondria is a powerful approach to study and treat these diseases. The triphenylphosphonium (TPP+) moiety is the most widely used mitochondriotropic carrier. However, studies have shown that TPP+ is not inert; TPP+ conjugates uncouple mitochondrial oxidative phosphorylation. To date, all efforts toward addressing this problem have focused on modifying lipophilicity of TPP+-linker-cargo conjugates to alter mitochondrial uptake, albeit with limited success. We show that structural modifications to the TPP+ phenyl rings that decrease electron density on the phosphorus atom can abrogate uncoupling activity as compared to the parent TPP+ moiety and prevent dissipation of mitochondrial membrane potential. These alterations of the TPP+ structure do not negatively affect the delivery of cargo to mitochondria. Results here identify the 4-CF3-phenyl TPP+ moiety as an inert mitochondria-targeting carrier to safely target pharmacophores and probes to mitochondria.

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Type 2 diabetes is associated with insulin resistance, impaired pancreatic β-cell insulin secretion, and nonalcoholic fatty liver disease. Tissue-specific SWELL1 ablation impairs insulin signaling in adipose, skeletal muscle, and endothelium, and impairs β-cell insulin secretion and glycemic control. Here, we show that ICl,SWELL and SWELL1 protein are reduced in adipose and β-cells in murine and human diabetes. Combining cryo-electron microscopy, molecular docking, medicinal chemistry, and functional studies, we define a structure activity relationship to rationally-design active derivatives of a SWELL1 channel inhibitor (DCPIB/SN-401), that bind the SWELL1 hexameric complex, restore SWELL1 protein, plasma membrane trafficking, signaling, glycemic control and islet insulin secretion via SWELL1-dependent mechanisms. In vivo, SN-401 restores glycemic control, reduces hepatic steatosis/injury, improves insulin-sensitivity and insulin secretion in murine diabetes. These findings demonstrate that SWELL1 channel modulators improve SWELL1-dependent systemic metabolism in Type 2 diabetes, representing a first-in-class therapeutic approach for diabetes and nonalcoholic fatty liver disease.

We recently reported that mitoquinone (mitoQ, 500 μmol/L) added to drinking water of C57BL/6J mice attenuated weight gain and reduced oxidative stress when administered to high‐fat (HF) fed mice. Here, we examined the effects of mitoQ administered to HF fed mice on pancreatic islet morphology, dynamics of insulin secretion, and islet mitochondrial metabolism. C57BL/6J mice were fed HF for 130 days while we administered vehicle (cyclodextrin [CD]) or mitoQ added to the drinking water at up to 500 μmol/L. MitoQ‐treated mice vs vehicle gained significantly less weight, expended significantly more energy as determined by indirect calorimetry, and trended to consume less (nonsignificant) food. As we and others reported before, mitoQ‐treated mice drank less water but showed no difference in percent body fluid by nuclear magnetic resonance. Circulating insulin and glucose‐stimulated insulin secretion by isolated islets were decreased in mitoQ‐treated mice while insulin sensitivity (plasma insulin x glucose) was greater. Islet respiration as basal oxygen consumption (OCR), OCR directed at ATP synthesis, and maximal uncoupled OCR were also reduced in mitoQ‐treated mice. Quantitative morphologic studies revealed that islet size was reduced in the mitoQ‐treated mice while visual inspection of histochemically stained sections suggested that mitoQ reduced islet lipid peroxides. MitoQ markedly improved liver function as determined by plasma alanine aminotransferase. In summary, mitoQ treatment reduced the demand for insulin and reduced islet size, likely consequent to the action of mitoQ to mitigate weight gain and improve liver function.

Generation of mitochondrial reactive oxygen species (ROS) is an important process in triggering cellular necrosis and tissue infarction during ischemia-reperfusion (IR) injury. Ischemia results in accumulation of the metabolite succinate. Rapid oxidation of this succinate by mitochondrial complex II (Cx-II) during reperfusion reduces the co-enzyme Q (Co-Q) pool, thereby driving electrons backward into complex-I (Cx-I), a process known as reverse electron transport (RET), which is thought to be a major source of ROS. During ischemia, enhanced glycolysis results in an acidic cellular pH at the onset of reperfusion. While the process of RsET within Cx-I is known to be enhanced by a high mitochondrial trans-membrane ΔpH, the impact of pH itself on the integrated process of Cx-II to Cx-I RET has not been fully studied. Using isolated mouse heart and liver mitochondria under conditions which mimic the onset of reperfusion (i.e., high [ADP]), we show that mitochondrial respiration (state 2 and state 3) as well as isolated Cx-II activity are impaired at acidic pH, whereas the overall generation of ROS by Cx-II to Cx-I RET was insensitive to pH. Together these data indicate that the acceleration of Cx-I RET ROS by ΔpH appears to be cancelled out by the impact of pH on the source of electrons, i.e. Cx-II. Implications for the role of Cx-II to Cx-I RET derived ROS in IR injury are discussed.

We recently reported that mitoquinone (mitoQ, 500 μmol/L) added to drinking water of C57BL/6J mice attenuated weight gain, decreased food intake, increased hypothalamic orexigenic gene expression, and mitigated oxidative stress when administered from the onset of high‐fat (HF) feeding. Here, we examined the effects of mitoQ on pre‐existing obesity in C57BL/6J mice first made obese by 107 days of HF feeding. In contrast to our preventative study, we found that already obese mice did not tolerate mitoQ at 500 μmol/L. Within 4 days of administration, obese mice markedly decreased food and water intake and lost substantial weight necessitating a dose reduction to 250 μmol/L. Food and water intake then improved. Over the next 4 weeks, body mass of the mitoQ‐treated mice increased faster than vehicle‐treated controls but did not catch up. Over the subsequent 10 weeks, weights of the mitoQ‐treated group remained significantly less than vehicle control, but percent fat and food intake did not differ. Although the mitoQ‐treated groups continued to drink less, there was no difference in percent body fluid and no laboratory evidence of dehydration at study end. At the time of killing, hypothalamic NPY gene expression was reduced in the mitoQ‐treated mice . Liver fat was markedly increased by HF feeding but did not differ between mitoQ and vehicle groups and, in contrast to our previous preventative study, there was no improvement in plasma alanine amino transferase or liver hydroperoxides. In summary, administration of mitoQ to already obese mice attenuated weight gain, but showed limited overall benefit.