Dimethyl malonate preserves renal and mitochondrial functions following ischemia-reperfusion via inhibition of succinate dehydrogenase

BACKGROUND

Acute kidney injury (AKI), often experienced at the intensive care units, is associated with high morbidity/mortality where ischemia-reperfusion injury is a main causative factor. Succinate accumulation during ischemia contributes to the excessive generation of reactive oxygen species at reperfusion. Inhibition of succinate dehydrogenase has been associated with protective outcome in cardiac ischemia-reperfusion after 24h, but the effects on kidney and mitochondrial functions are less well studied.

AIM

To investigate the therapeutic potential of succinate dehydrogenase inhibition, by using dimethyl malonate (DMM), on kidney and mitochondria functions in a mouse model of AKI.

METHODS

Male C57BL/6J mice were pre-treated with DMM or placebo, i.p. 30min prior to bilateral renal ischemia (20min). After 3-days of reperfusion, glomerular filtration rate (GFR) was calculated from plasma clearance of FITC-inulin. Kidney mitochondria was isolated and mass specific and intrinsic mitochondrial function were evaluated by high resolution respirometry. Kidney sections were stained (i.e., hematoxylin-eosin and TUNEL) and analyzed for histopathological evaluation of injuries and apotosis, respectively. NADPH oxidase activity in kidney and human proximal tubular cell-line (HK2) were measured luminometrically.

RESULTS

DMM treatment improved GFR (p < 0.05) and reduced levels of blood urea nitrogen (p < 0.01) compared to untreated animals, which was associated with lower degree of ischemia-reperfusion-induced tubular injuries (P < 0.001) and apoptosis (P < 0.01). These therapeutic renal effects were linked with improved mitochondrial function, both mass-specific and intrinsic. Finally, DMM treatment prevented ischemia-reperfusion-induced NADPH oxidase activity in the kidney (p < 0.001), which was showed also in HK2 cells exposed to hypoxia and reoxygenation (P < 0.01).

CONCLUSION

Inhibition of succinate dehydrogenase with DMM, in conjunction with the ischemia-reperfusion phase, significantly improved both renal and mitochondrial functions. These findings may have clinical implications for future therapeutic strategies to prevent development of AKI and associated adverse complications, especially in high risk hospitalized patients.

Metabolic reprogramming in inflammatory microglia indicates a potential way of targeting inflammation in Alzheimer's disease

Microglia activation drives the pro-inflammatory activity in the early stages of Alzheimer's disease (AD). However, the mechanistic basis is elusive, and the hypothesis of targeting microglia to prevent AD onset is little explored. Here, we demonstrated that upon LPS exposure, microglia shift towards an energetic phenotype characterised by high glycolysis and high mitochondrial respiration with dysfunction. Although the activity of electron transport chain (ETC) complexes is boosted by LPS, this is mostly devoted to the generation of reactive oxygen species. We showed that by inhibiting succinate dehydrogenase (SDH) with dimethyl malonate (DMM), it is possible to modulate the LPS-induced metabolic rewiring, facilitating an anti-inflammatory phenotype. DMM improves mitochondrial function in a direct way and by reducing LPS-induced mitochondrial biogenesis. Moreover, the block of SDH with DMM inhibits the recruitment of hypoxia inducible-factor 1 α (HIF-1α), which mediates the induction of glycolysis and cytokine expression. Similar bioenergetic alterations were observed in the microglia isolated from AD mice (3xTg-AD), which present high levels of circulating LPS and brain toll-like receptor4 (TLR4). Moreover, this well-established model of AD was used to show a potential effect of SDH inhibition in vivo as DMM administration abrogated brain inflammation and modulated the microglia metabolic alterations of 3xTg-AD mice. The RNA-sequencing analysis from a public dataset confirmed the consistent transcription of genes encoding for ETC subunits in the microglia of AD mice (5xFAD). In conclusion, TLR4 activation promotes metabolic changes and the pro-inflammatory activity in microglia, and SDH might represent a promising therapeutic target to prevent AD development.

Succinate level is increased and succinate dehydrogenase exerts forward and reverse catalytic activities in lipopolysaccharides-stimulated cardiac tissue: The protective role of dimethyl malonate

This study aimed to investigate the alterations of myocardial succinate and fumarate levels with or without succinate dehydrogenase (SDH) inhibitor dimethyl malonate during 24 h of lipopolysaccharides (LPS) challenge, as well as the effects of dimethyl malonate on the impaired cardiac tissue. Myocardial succinate and fumarate levels were increased in the initial 9 h of LPS challenge. During this time, dimethyl malonate increased the succinate level, decreased the fumarate level, aggravated the cardiac dysfunction, reduced the oxidative stress, had little effect on interleukin-1β production, promoted interleukin-10 production and bothered the ATP production. Co-treatment with exogenous succinate significantly increased interleukin-1β production in this period. After 12 h of LPS challenge, myocardial the succinate level increased sharply, while the fumarate level gradually decreased. During 12-24 h of LPS challenge, dimethyl malonate effectively reduced the succinate level, increased the fumarate level, improved cardiac dysfunction, inhibited interleukin-1β production, and had little effect on oxidative stress, interleukin-10 production, and ATP production. LPS challenge also significantly increased the myocardial succinate receptor 1 expression and circulating succinate level. Inhibition of succinate receptor 1 significantly reduced the mRNA expression of interleukin-1β. In conclusion, the current study suggests that myocardial succinate accumulates during LPS challenge, and that SDH activity may be transformed (from forward to reversed) and involved in a line of stress response. Dimethyl malonate inhibits SDH and, depending on the time of treatment, reduces LPS-induced cardiac impairment. Furthermore, accumulated succinate exerts pro-inflammatory effects partly via succinate receptor 1 signaling.

Succinate dehydrogenase inhibitor dimethyl malonate alleviates LPS/d-galactosamine-induced acute hepatic damage in mice

In addition to its energy-supplying function, increasing evidence suggests that mitochondria also play crucial roles in the regulation of inflammation. Succinate dehydrogenase is also known as mitochondrial complex II, and inhibition of succinate dehydrogenase by dimethyl malonate has been reported to suppress the production of pro-inflammatory cytokines. In the present study, the potential anti-inflammatory benefits of dimethyl malonate were investigated in a mouse model with LPS/d-galactosamine-induced acute hepatic damage. Male BALB/c mice were injected i.p. with LPS and d-galactosamine to cause liver injury. The degree of liver injury, inflammatory response and oxidative stress and the survival of the experimental animals were determined. The results indicated dimethyl malonate decreased the level of aminotransferases in plasma, alleviated histological abnormalities in liver, inhibited the induction of TNF-α and IL-6 in plasma, suppressed hepatocyte apoptosis and improved the survival of LPS/d-galactosamine-exposed mice. Therefore, inhibition of succinate dehydrogenase by dimethyl malonate significantly alleviated LPS/d-galactosamine-induced hepatic damage, which suggests that succinate dehydrogenase might become a novel target for the intervention of inflammation-based hepatic disorders.

Protection against cardiac ischemia-reperfusion injury by hypothermia and by inhibition of succinate accumulation and oxidation is additive

Hypothermia induced at the onset of ischemia is a potent experimental cardioprotective strategy for myocardial infarction. The aim of our study was to determine whether the beneficial effects of hypothermia may be due to decreasing mitochondria-mediated mechanisms of damage that contribute to the pathophysiology of ischemia/reperfusion injury. New Zealand male rabbits were submitted to 30 min of myocardial ischemia with hypothermia (32 °C) induced by total liquid ventilation (TLV). Hypothermia was applied during ischemia alone (TLV group), during ischemia and reperfusion (TLV-IR group) and normothermia (Control group). In all the cases, ischemia was performed by surgical ligation of the left anterior descending coronary artery and was followed by 3 h of reperfusion before assessment of infarct size. In a parallel study, male C57BL6/J mice underwent 30 min myocardial ischemia followed by reperfusion under either normothermia (37 °C) or conventionally induced hypothermia (32 °C). In both the models, the levels of the citric acid cycle intermediate succinate, mitochondrial complex I activity were assessed at various times. The benefit of hypothermia during ischemia on infarct size was compared to inhibition of succinate accumulation and oxidation by the complex II inhibitor malonate, applied as the pro-drug dimethyl malonate under either normothermic or hypothermic conditions. Hypothermia during ischemia was cardioprotective, even when followed by normothermic reperfusion. Hypothermia during ischemia only, or during both, ischemia and reperfusion, significantly reduced infarct size (2.8 ± 0.6%, 24.2 ± 3.0% and 49.6 ± 2.6% of the area at risk, for TLV-IR, TLV and Control groups, respectively). The significant reduction of infarct size by hypothermia was neither associated with a decrease in ischemic myocardial succinate accumulation, nor with a change in its rate of oxidation at reperfusion. Similarly, dimethyl malonate infusion and hypothermia during ischemia additively reduced infarct size (4.8 ± 2.2% of risk zone) as compared to either strategy alone. Hypothermic cardioprotection is neither dependent on the inhibition of succinate accumulation during ischemia, nor of its rapid oxidation at reperfusion. The additive effect of hypothermia and dimethyl malonate on infarct size shows that they are protective by distinct mechanisms and also suggests that combining these different therapeutic approaches could further protect against ischemia/reperfusion injury during acute myocardial infarction.