Amino acid homeostasis is a target of metformin therapy

OBJECTIVE

Unexplained changes in regulation of branched chain amino acids (BCAA) during diabetes therapy with metformin have been known for years. Here we have investigated mechanisms underlying this effect.

METHODS

We used cellular approaches, including single gene/protein measurements, as well as systems-level proteomics. Findings were then cross-validated with electronic health records and other data from human material.

RESULTS

In cell studies, we observed diminished uptake/incorporation of amino acids following metformin treatment of liver cells and cardiac myocytes. Supplementation of media with amino acids attenuated known effects of the drug, including on glucose production, providing a possible explanation for discrepancies between effective doses in vivo and in vitro observed in most studies. Data-Independent Acquisition proteomics identified that SNAT2, which mediates tertiary control of BCAA uptake, was the most strongly suppressed amino acid transporter in liver cells following metformin treatment. Other transporters were affected to a lesser extent. In humans, metformin attenuated increased risk of left ventricular hypertrophy due to the AA allele of KLF15, which is an inducer of BCAA catabolism. In plasma from a double-blind placebo-controlled trial in nondiabetic heart failure (trial registration: NCT00473876), metformin caused selective accumulation of plasma BCAA and glutamine, consistent with the effects in cells.

CONCLUSIONS

Metformin restricts tertiary control of BCAA cellular uptake. We conclude that modulation of amino acid homeostasis contributes to therapeutic actions of the drug.

8-Hydroxyquinoline-modified ruthenium(II) polypyridyl complexes for JMJD inhibition and photodynamic antitumor therapy

As an ideal scaffold for metal ion chelation, 8-hydroxyquinoline (8HQ) can chelate different metal ions, such as Fe²⁺, Cu²⁺, Zn²⁺, etc. Here, by integrating 8HQ with a ruthenium(II) polypyridyl moiety, two Ru(II)-8HQ complexes (Ru1 and Ru2), [Ru(N-N)₂L](PF₆)₂ (L = 2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)quinolin-8-ol; N-N: 2,2'-bipyridine (bpy, in Ru1), 1,10-phenanthroline (phen, in Ru2)) were designed and synthesized. In both complexes, ligand L is an 8HQ derivative designed to chelate the cofactor Fe²⁺ of jumonji C domain-containing demethylase (JMJD). As expected, Ru1 and Ru2 could inhibit the activity of JMJD by chelating the key cofactor Fe²⁺ of JMJD, resulting in the upregulation of histone-methylation levels in human lung cancer (A549) cells, and the upregulation was more pronounced under light conditions. In addition, MTT data showed that Ru1 and Ru2 exhibited lower dark toxicity, and light irradiation could significantly enhance their antitumor activity. The marked photodynamic activities of Ru1 and Ru2 could induce the elevation of reactive oxygen species (ROS), depolarization of mitochondrial membrane potential (MMP), and activation of caspases. These mechanistic studies indicated that Ru1 and Ru2 could induce apoptosis through the combination of JMJD inhibitory and PDT activities, thereby achieving dual antitumor effects.

Waterborne zinc bioaccumulation influences glucose metabolism in orange-spotted grouper embryos

Fish embryos, as an endogenous system, strictly regulate an energy metabolism that is particularly sensitive to environmental pressure. This study used orange-spotted grouper embryos and stable isotope ⁶⁷Zn to test the hypothesis that waterborne Zn exposure had a significant effect on energy metabolism in embryos. The fish embryos were exposed to a gradient level of waterborne ⁶⁷Zn, and then sampled to quantify ⁶⁷Zn bioaccumulation and mRNA expressions of key genes involved glucose metabolism. The results indicated that the bioaccumulated ⁶⁷Zn generally increased with increasing waterborne ⁶⁷Zn concentrations, while it tended to be saturated at waterborne ⁶⁷Zn > 0.7 mg L^-1. As we hypothesized, the expression of PK and PFK gene involved glycolysis pathway was significantly up-regulated under waterborne ⁶⁷Zn exposure >4 mg L^-1. Waterborne ⁶⁷Zn exposure >2 mg L^-1 significantly suppressed PCK and G6PC gene expression involved gluconeogenesis pathway, and also inhibited the AKT2, GSK-3beta and GLUT4 genes involved Akt signaling pathway. Our findings first characterized developmental stage-dependent Zn uptake and genotoxicity in fish embryos. We suggest fish embryos, as a small-scale modeling biosystem, have a large potential and wide applicability for determining cytotoxicity/genotoxicity of waterborne metal in aquatic ecosystem.

Metformin selectively targets redox control of complex I energy transduction

Many guanide-containing drugs are antihyperglycaemic but most exhibit toxicity, to the extent that only the biguanide metformin has enjoyed sustained clinical use. Here, we have isolated unique mitochondrial redox control properties of metformin that are likely to account for this difference. In primary hepatocytes and H4IIE hepatoma cells we found that antihyperglycaemic diguanides DG5-DG10 and the biguanide phenformin were up to 1000-fold more potent than metformin on cell signalling responses, gluconeogenic promoter expression and hepatocyte glucose production. Each drug inhibited cellular oxygen consumption similarly but there were marked differences in other respects. All diguanides and phenformin but not metformin inhibited NADH oxidation in submitochondrial particles, indicative of complex I inhibition, which also corresponded closely with dehydrogenase activity in living cells measured by WST-1. Consistent with these findings, in isolated mitochondria, DG8 but not metformin caused the NADH/NAD+ couple to become more reduced over time and mitochondrial deterioration ensued, suggesting direct inhibition of complex I and mitochondrial toxicity of DG8. In contrast, metformin exerted a selective oxidation of the mitochondrial NADH/NAD+ couple, without triggering mitochondrial deterioration. Together, our results suggest that metformin suppresses energy transduction by selectively inducing a state in complex I where redox and proton transfer domains are no longer efficiently coupled.

Histomonosis in poultry: previous and current strategies for prevention and therapy

Histomonosis is a parasitic disease of poultry with worldwide prevalence. The disease can cause morbidity and mortality in chicken and turkey flocks entailing severe economic losses. In the first half of the last century, there was a high demand to control histomonosis as the turkey industry was severely affected by the disease. Consequently, numerous chemical compounds were tested for their efficacy against Histomonas meleagridis with varying outcomes, that are summarized and specified in this review. At the same time, preliminary attempts to protect birds with cultured histomonads indicated the possibility of vaccination. Several years ago antihistomonal drugs were banned in countries with tight regulations on pharmaceuticals in order to comply with the demand of consumer protection. As a consequence, outbreaks of histomonosis in poultry flocks increased and the disease became endemic again. New approaches to prevent and treat histomonosis are, therefore, needed and recently performed studies focused on various areas to combat the disease, from alternative chemotherapeutic substances to plant-derived compounds until vaccination, altogether reviewed here. Considering existing regulations and the overall outcome of experimental studies, it can be concluded that vaccination is very promising, despite the fact that various challenges need to be addressed until the first ever developed vaccine based upon live flagellates in human or bird medicine can be marketed.

In vitro studies on the pleotropic antidiabetic effects of zinc oxide nanoparticles

Aim: Our earlier study demonstrated antidiabetic activity of zinc oxide nanoparticles (ZON) in diabetic rats. The present study was performed to elucidate its mechanism of antidiabetic action. Methods: Protein tyrosine phosphatase 1B, protein kinase B and hormone sensitive lipase phosphorylation; glucose transporter 4 translocation and glucose uptake; glucose 6 phosphatase, phosphoenol pyruvate carboxykinase and glucokinase expression; and pancreatic beta cell proliferation were evaluated after ZON treatment to cells. Result: ZON treatment resulted in PKB activation, protein tyrosine phosphatase 1B inactivation, increased glucose transporter 4 translocation and enhanced glucose uptake, decreased glucose 6 phosphatase and phosphoenol pyruvate carboxykinase expression, hormone sensitive lipase inactivation and pancreatic beta cell proliferation. Conclusion: To the best of our knowledge, we report for the first time, pleiotropic antidiabetic effects of ZON viz. improved insulin signaling, enhanced glucose uptake, decreased hepatic glucose output, decreased lipolysis and enhanced pancreatic beta cell mass.

Investigation of salicylate hepatic responses in comparison with chemical analogues of the drug

Anti-hyperglycaemic effects of the hydroxybenzoic acid salicylate might stem from effects of the drug on mitochondrial uncoupling, activation of AMP-activated protein kinase, and inhibition of NF-κB signalling. Here, we have gauged the contribution of these effects to control of hepatocyte glucose production, comparing salicylate with inactive hydroxybenzoic acid analogues of the drug. In rat H4IIE hepatoma cells, salicylate was the only drug tested that activated AMPK. Salicylate also reduced mTOR signalling, but this property was observed widely among the analogues. In a sub-panel of analogues, salicylate alone reduced promoter activity of the key gluconeogenic enzyme glucose 6-phosphatase and suppressed basal glucose production in mouse primary hepatocytes. Both salicylate and 2,6 dihydroxybenzoic acid suppressed TNFα-induced IκB degradation, and in genetic knockout experiments, we found that the effect of salicylate on IκB degradation was AMPK-independent. Previous data also identified AMPK-independent regulation of glucose but we found that direct inhibition of neither NF-κB nor mTOR signalling suppressed glucose production, suggesting that other factors besides these cell signalling pathways may need to be considered to account for this response to salicylate. We found, for example, that H4IIE cells were exquisitely sensitive to uncoupling with modest doses of salicylate, which occurred on a similar time course to another anti-hyperglycaemic uncoupling agent 2,4-dinitrophenol, while there was no discernible effect at all of two salicylate analogues which are not anti-hyperglycaemic. This finding supports much earlier literature suggesting that salicylates exert anti-hyperglycaemic effects at least in part through uncoupling.

8-Hydroxyquinolines: a review of their metal chelating properties and medicinal applications

Metal ions play an important role in biological processes and in metal homeostasis. Metal imbalance is the leading cause for many neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis. 8-Hydroxyquinoline (8HQ) is a small planar molecule with a lipophilic effect and a metal chelating ability. As a result, 8HQ and its derivatives hold medicinal properties such as antineurodegenerative, anticancer, antioxidant, antimicrobial, anti-inflammatory, and antidiabetic activities. Herein, diverse bioactivities of 8HQ and newly synthesized 8HQ-based compounds are discussed together with their mechanisms of actions and structure–activity relationships.