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Our recent study showed different effects of glucose and fructose overconsumption on the development of obese phenotypes in Drosophila. Glucose induced glucose toxicity due to the increase in circulating glucose, whereas fructose was more prone to induce obesity promoting accumulation of reserve lipids and carbohydrates (Rovenko et al., Comp. Biochem. Physiol. A Mol. Integr. Physiol. 2015, 180, 75-85). Searching for mechanisms responsible for these phenotypes in this study, we analyzed mitochondrial activity, mitochondrial density, mtROS production, oxidative stress markers and antioxidant defense in fruit flies fed 0.25%, 4% and 10% glucose or fructose. It is shown that there is a complex interaction between dietary monosaccharide concentrations, mitochondrial activity and oxidative modifications to proteins and lipids. Glucose at high concentration (10%) reduced mitochondrial protein density and consequently respiration in flies, while fructose did not affect these parameters. The production of ROS by mitochondria did not reflect activities of mitochondrial complexes. Moreover, there was no clear connection between mtROS production and antioxidant defense or between antioxidant defense and developmental survival, shown in our previous study (Rovenko et al., Comp. Biochem. Physiol. A Mol. Integr. Physiol. 2015, 180, 75-85). Instead, mtROS and antioxidant machinery cooperated to maintain a redox state that determined survival rates, and paradoxically, pro-oxidant conditions facilitated larva survival independently of the type of carbohydrate. It seems that in this complex system glucose controls the amount of oxidative modification regulating mitochondrial activity, while fructose regulates steady-state mRNA levels of antioxidant enzymes., (Copyright © 2015. Published by Elsevier Inc.)

During the last 20 years, there has been a considerable scientific debate about the possible mechanisms of induction of metabolic disorders by reducing monosaccharides such as glucose or fructose. In this study, we report the metabolic rearrangement in response to consumption of these monosaccharides at concentrations ranging from 0.25% to 20% in a Drosophila model. Flies raised on high-glucose diet displayed delay in pupation and increased developmental mortality compared with fructose consumers. Both monosaccharides at high concentrations promoted an obese-like phenotype indicated by increased fly body mass, levels of uric acid, and circulating and stored carbohydrates and lipids; and decreased percentage of water in the body. However, flies raised on fructose showed lower levels of circulating glucose and higher concentrations of stored carbohydrates, lipids, and uric acid. The preferential induction of obesity caused by fructose in Drosophila was associated with increased food consumption and reduced mRNA levels of DILP2 and DILP5 in the brain of adult flies. Our data show that glucose and fructose differently affect carbohydrate and lipid metabolism in Drosophila in part by modulation of insulin/insulin-like growth factor signaling. Some reported similarities with effects observed in mammals make Drosophila as a useful model to study carbohydrate influence on metabolism and development of metabolic disorders., (Copyright © 2014 Elsevier Inc. All rights reserved.)

The influence of 6% sucrose and equimolar mixture of glucose and fructose in larva diet on the level of oxidized proteins and lipids as well as the activity of antioxidant and associated enzymes in adult fruit fly Drosophila melanogaster was investigated. Larva growing on the diet with sucrose led to the mild oxidative stress development in adult insects, which was differently expressed in both sexes. In males mainly molecules of proteins were subjected to oxidative damages, whereas in females--lipid molecules. This is evidenced by 77% increased content of protein carbonyl groups and decreased (by 40%) level of protein SH-groups in males fed on sucrose. In females fed on sucrose the content of lipid peroxides was by 44% higher, than in individuals, hold on the diet with equimolar mixture of glucose and fructose. The oxidative stress in females was accompanied with increased activity of catalase, superoxide dismutase and thiredoxin reductase by 30, 15 and 34%, respectively. The obtained results suggest that uptake mode of glucose and fructose affects free radical processes in fruit flies.

Activities of antioxidant and associated enzymes, and oxidative stress markers were assessed in newly enclosed adult fruit flies Drosophila melanogaster developed on diets with 4 and 10% glucose or fructose. In fly males, 10% fructose promoted higher content of protein carbonyls and catalase activity, but lower superoxide dismutase (SOD) activity than 4%, while in females-lower levels of high molecular mass thiols (H-SH). Females at all diets had virtually the same level of lipid peroxides, low-molecular-mass thiols, catalase, and superoxide dismutase activities. Fed with 4% fructose and glucose males demonstrated 24 and 26% lower H-SH level than females, respectively. On diets with 4% glucose, 10% glucose and fructose females had 32, 26 and 27% lower catalase activity than respective males, and 1.3-1.5-fold lower glucose-6-phosphate dehydrogenase activity on glucose-containing diets. Strong positive correlations between H-SH level and G6PD activity, as well as between catalase and G6PDH activity were found. These results suggest that type and concentration of dietary carbohydrate affect antioxidant defense in fruit flies. It also substantially depends on fly sex, comprising presumably levels of protein carbonyls and lipid peroxides, as well as catalase and SOD activities in males and G6PDH activity in females., (Copyright © 2011. Published by Elsevier Inc.)