Macrophage migration inhibitory factor inhibition is deleterious for high-fat diet-induced cardiac dysfunction

Impaired Myocardial MIF/AMPK Activation Aggravates Myocardial Ischemia Reperfusion Injury in High-Fat Diet-Induced Obesity

Background:

Obese patients are more sensitive to myocardial ischemia, which has been linked with high mortality rates. The following study investigates the effects of impaired macrophage Migration Inhibitory Factor (MIF)/AMP-Activated Protein Kinase (AMPK) activation on increased susceptibility to myocardial ischemia/reperfusion (I/R) in high-fat diet-induced obesity.

Methods:

Male C57BL/6J mice were fed with a normal diet (10% kcal as fat, lean group) or a high-fat diet (60kcal as fat, obese group) for 12 consecutive weeks. To detect the MIF expression and AMPK activation in response to I/R in isolated hearts from lean and obese mice, myocardial samples were collected from left ventricular areas at different time points. To determine whether MIF supplementation is protective against I/R injury, recombined MIF (10 ng/mL) was applied before ischemia. Myocardial infarct size was estimated by triphenyltetrazolium staining. Western blot was used to detect myocardial MIF expression, AMPK activation and membrane glucose transporter 4 (Glut4) expression.

Results:

The expression of MIF was remarkably higher in obese group compared to lean group. Ischemia increased myocardial MIF expression and phosphorylation of AMPK in lean mice, whereas it had no significant effect on obese mice. Furthermore, administration of recombinant MIF increased ischemic AMPK activation and membrane Glut4 expression in both lean and obese mice, while it reduced the infarct size in lean mice only.

Conclusion:

An impaired MIF/AMPK activation response and consequent reduced membrane Glut4 expression may play an important role in increasing myocardial susceptibility to I/R in obesity.

Advanced glycation end products receptor RAGE controls myocardial dysfunction and oxidative stress in high-fat fed mice by sustaining mitochondrial dynamics and autophagy-lysosome pathway

Oxidative stress and mitochondrial dysfunction are recognized as major contributors of cardiovascular damage in diabetes and high fat diet (HFD) fed mice. Blockade of receptor for advanced glycation end products (RAGE) attenuates vascular oxidative stress and development of atherosclerosis. We tested whether HFD-induced myocardial dysfunction would be reversed in RAGE deficiency mice, in association with changes in oxidative stress damage, mitochondrial respiration, mitochondrial fission and autophagy-lysosomal pathway. Cardiac antioxidant capacity was upregulated in RAGE^-/^- mice under normal diet as evidenced by increased superoxide dismutase and sirtuin mRNA expressions. Mitochondrial fragmentation and mitochondrial fission protein Drp1 and Fis1 expressions were increased in RAGE^-/^- mice. Autophagy-related protein expressions and cathepsin-L activity were increased in RAGE^-/^- mice suggesting sustained autophagy-lysosomal flux. HFD induced mitochondrial respiration defects, cardiac contractile dysfunction, disrupted mitochondrial dynamics and autophagy inhibition, which were partially prevented in RAGE^-/^- mice. Our results suggest that cardioprotection against HFD in RAGE^-/^- mice include reactivation of autophagy, as inhibition of autophagic flux by chloroquine fully abrogated beneficial myocardial effects and its stimulation by rapamycin improved myocardial function in HFD wild type mice. As mitochondrial fission is necessary to mitophagy, increased fragmentation of mitochondrial network in HFD RAGE^-/^- mice may have facilitated removal of damaged mitochondria leading to better mitochondrial quality control. In conclusion, modulation of RAGE pathway may improve mitochondrial damage and myocardial dysfunction in HFD mice. Attenuation of cardiac oxidative stress and maintenance of healthy mitochondria population ensuring adequate energy supply may be involved in myocardial protection against HFD.

Pathophysiology of cancer therapy-provoked atrial fibrillation

Atrial fibrillation (AF) occurs with increased frequency in cancer patients, especially in patients who undergo surgery or chemotherapy. AF disturbs the prognosis of cancer patients and challenges therapeutic outcomes of cancer treatment. Elucidating the mechanisms of cancer-induced AF would help identify specific strategies for preventing AF occurrence. In addition to concurrent risk factors of cancer and AF, cancer surgery, side effects of anticancer agents, and cancer-associated immune responses play critical roles in the genesis of AF. In this review, we provide succinct potential mechanisms of AF genesis in cancer patients.

Macrophage migration inhibitory factor (MIF) enzymatic activity and lung cancer

The cytokine macrophage migration inhibitory factor (MIF) possesses unique tautomerase enzymatic activity, which contributes to the biological functional activity of MIF. In this study, we investigated the effects of blocking the hydrophobic active site of the tautomerase activity of MIF in the pathogenesis of lung cancer. To address this, we initially established a Lewis lung carcinoma (LLC) murine model in Mif-KO and wild-type (WT) mice and compared tumor growth in a knock-in mouse model expressing a mutant MIF lacking enzymatic activity (Mif (P1G)). Primary tumor growth was significantly attenuated in both Mif-KO and Mif (P1G) mice compared with WT mice. We subsequently undertook a structure-based, virtual screen to identify putative small molecular weight inhibitors specific for the tautomerase enzymatic active site of MIF. From primary and secondary screens, the inhibitor SCD-19 was identified, which significantly attenuated the tautomerase enzymatic activity of MIF in vitro and in biological functional screens. In the LLC murine model, SCD-19, given intraperitoneally at the time of tumor inoculation, was found to significantly reduce primary tumor volume by 90% (p < 0.001) compared with the control treatment. To better replicate the human disease scenario, SCD-19 was given when the tumor was palpable (at d 7 after tumor inoculation) and, again, treatment was found to significantly reduce tumor volume by 81% (p < 0.001) compared with the control treatment. In this report, we identify a novel inhibitor that blocks the hydrophobic pocket of MIF, which houses its specific tautomerase enzymatic activity, and demonstrate that targeting this unique active site significantly attenuates lung cancer growth in in vitro and in vivo systems.