Dietary L-arginine accelerates pupation and promotes high protein levels but induces oxidative stress and reduces fecundity and life span in Drosophila melanogaster.

L-Arginine, a precursor of many amino acids and of nitric oxide, plays multiple important roles in nutrient metabolism and regulation of physiological functions. In this study, the effects of L-arginine-enriched diets on selected physiological responses and metabolic processes were assessed in Drosophila melanogaster. Dietary L-arginine at concentrations 5-20 mM accelerated larval development and increased body mass, and total protein concentrations in third instar larvae, but did not affect these parameters when diets contained 100 mM arginine. Young (2 days old) adult flies of both sexes reared on food supplemented with 20 and 100 mM L-arginine possessed higher total protein concentrations and lower glucose and triacylglycerol concentrations than controls. Additionally, flies fed 20 mM L-arginine had higher proline and uric acid concentrations. L-Arginine concentration in the diet also affected oxidative stress intensity in adult flies. Food with 20 mM L-arginine promoted lower protein thiol concentrations and higher catalase activity in flies of both sexes and higher concentrations of low molecular mass thiols in males. When flies were fed on a diet with 100 mM L-arginine, lower catalase activities and concentrations of protein thiols were found in both sexes as well as lower low molecular mass thiols in females. L-Arginine-fed males demonstrated higher climbing activity, whereas females showed higher cold tolerance and lower fecundity, compared with controls. Food containing 20 mM L-arginine shortened life span in both males and females. The results suggest that dietary L-arginine shows certain beneficial effects at the larval stage and in young adults. However, the long-term consumption of L-arginine-enriched food had unfavorable effects on D. melanogaster due to decreasing fecundity and life span.

Dietary alpha-ketoglutarate promotes higher protein and lower triacylglyceride levels and induces oxidative stress in larvae and young adults but not in middle-aged Drosophila melanogaster.

Alpha-ketoglutarate (AKG) is involved in multiple metabolic and regulatory pathways. In this work, the effects of AKG-supplemented diets on selected physiological responses and metabolic processes, including metabolism of reactive oxygen species, was assessed in larvae and adult (both 2 and 24days old) Drosophila melanogaster. Dietary supplementation with AKG resulted in dose-dependent effects on larval development, body composition and antioxidant status of third instar larvae. Larvae and young (2days post-eclosion) adult females fed on AKG shared similar metabolic changes such as higher total protein levels, lower triacylglyceride levels and higher values for oxidative stress indices, namely lipid peroxides and low molecular mass thiols. The latter indicated the development of oxidative stress which, in turn, may induce adaptive responses that can explain the higher resistance of AKG-fed young females to heat shock and hydrogen peroxide exposure. In contrast to young flies, middle-aged females (24days) on AKG-containing diet possessed higher total protein, glucose and triacylglyceride levels, whereas oxidative stress parameters were virtually the same as compared with control females of the same age. In parallel, females fed an AKG-supplemented diet showed lower fecundity, higher heat shock resistance but no change in oxidative stress resistance at middle age which in combination with levels of protein, glucose, and triacylglycerides can be considered as potentially beneficial AKG effects for aging organisms. To our best knowledge, this is the first study on age-matched AKG influence on animals' organism which shows that Drosophila may be used as a model for previous quick study in cost-efficient manner age-related AKG effects in mammals and humans.

Alpha-ketoglutarate attenuates toxic effects of sodium nitroprusside and hydrogen peroxide in Drosophila melanogaster.

The protective effects of dietary alpha-ketoglutarate (AKG) are described that aid fruit flies, Drosophila melanogaster, to resist sodium nitroprusside (SNP) and hydrogen peroxide toxicity. Food supplementation with 10mM AKG alleviated toxic effects of 1mM SNP added to food and improved fly development. Dietary AKG also prevented the increase in levels of oxidative stress markers seen in SNP-reared adult flies. In vitro AKG did not affect the rate of SNP decomposition and did not bind iron and nitrite ions released in this process. Alpha-ketoglutarate also displayed high H2O2-scavenging activity in vitro and efficiently protected adult flies against this compound in combined treatments. Based on the observed antioxidant activity of AKG, it may be suggested that the antioxidant mode of AKG action (apart from its cyanide-binding capability) may be used to prevent the toxic effects of SNP and improve general physiological state of D. melanogaster and other animals and humans.

Sodium chromate demonstrates some insulin-mimetic properties in the fruit fly Drosophila melanogaster.

The effects of food supplementation with sodium chromate at concentrations of 1-500 µM on development of Drosophila melanogaster larvae and food intake, carbohydrate and lipid pools in adult fruit flies were investigated. Food supplementation with hexavalent chromium (Na2CrO4) at high concentrations delayed larval development and decreased the percentage of larvae that pupated which indicated a relatively low toxicity. The supplement decreased glucose levels in fly hemolymph, but at concentrations of 5-25 µM increased fly carbohydrate reserves: hemolymph trehalose and whole body trehalose and glycogen. The data on parameters of carbohydrate metabolism show that chromate possesses some insulin-mimetic properties. The changes in metabolism of carbohydrates under chromate exposure were also accompanied by an increase in total lipid levels and in the portion of triacylglycerides among all lipids. Chromate addition to fly food did not affect male or female body mass, but reduced food consumption by females at all concentrations used, whereas in males only 500 µM chromate decreased food consumption. The data show that: (1) Cr(6+) has many of the same effects as Cr(3+) suggesting that it might be just as effective to treat diabetic states, likely as a result of intracellular reduction of Cr(6+) ions, and (2) the Drosophila model can be used to develop new approaches to investigate the molecular mechanisms of chromium as an insulin-mimetic. Although it is usually believed that hexavalent chromium possesses higher toxicity than the trivalent ion, due to its easier penetration into the cell, application of hexavalent chromium may substantially decrease the chromium doses needed to get the desired effects.

Molybdate partly mimics insulin-promoted metabolic effects in Drosophila melanogaster.

Molybdenum-containing salts have been found to attenuate diabetes complications in mammals by affecting processes normally regulated by insulin and thus were believed to mimic insulin activity. In this study, we used a fruit fly model to test sodium molybdate, Na2MoO4, action in relation to insulin-promoted processes and toxicity. We studied how larval food supplementation with sodium molybdate affected levels of body carbohydrates and lipids in two-day old adult Drosophila melanogaster. Molybdate salt, in the concentrations used (0.025, 0.05, 0.5, 5, and 10mM), showed low toxicity to fly larvae and slightly influenced development and the percentage of pupated animals. Additionally, sodium molybdate decreased the level of hemolymph glucose in males by 30%, and increased the level of hemolymph trehalose in flies of both sexes. These changes were accompanied by an increase in whole body trehalose and glycogen of about 30-90%. Although total lipid levels in flies of both sexes were depleted by 25%, an increased amount of triacylglycerides among total lipids was observed. These effects were not related to changes in food intake. Taken together, the present data let us suggest that sodium molybdate may at least partly mimic insulin-related effects in Drosophila.

The mitochondrial uncoupler 2,4-dinitrophenol attenuates sodium nitroprusside-induced toxicity in Drosophila melanogaster: potential involvement of free radicals.

The toxicity of sodium nitroprusside (SNP) (an inducer of oxidative/nitrosative stress) and the attenuation of SNP effects by 2,4-dinitrophenol (DNP) (that induces mild uncoupling of respiration) were evaluated in the Drosophila melanogaster model system. Fly larvae were raised on food supplemented with 1.0 mM SNP, 0.5 or 1.25 mM DNP, or with mixtures 1.0 mM SNP plus 0.5 or 1.25 mM DNP. Food supplementation with SNP decreased larval viability and pupation height whereas supplementation with DNP substantially reversed these changes. Biochemical analyses of oxidative stress markers and activities of antioxidant and associated enzymes were carried out on 2-day-old flies emerged from control larvae and larvae fed on food supplemented with SNP, DNP, or SNP/DNP mixtures. Larval exposure to SNP lowered activities of aconitase, while the presence of DNP reduced the negative impact of SNP by raising aconitase activity back to near control levels. Larval treatment with SNP also elevated the contents of carbonyl protein, uric acid and low molecular mass thiols and produced higher activities of superoxide dismutase, glutathione S-transferase, glucose-6-phosphate dehydrogenase and thioredoxin reductase in adult flies. However, the presence of DNP in the food mixtures prevented SNP-induced changes in thioredoxin reductase and glucose-6-phosphate dehydrogenase activities, as well as uric acid and low-molecular-mass thiol content. The potential mechanisms by which DNP exerts protective effects against SNP toxicity are discussed.

S-nitrosoglutathione-induced toxicity in Drosophila melanogaster: Delayed pupation and induced mild oxidative/nitrosative stress in eclosed flies.

The toxicity of the nitric oxide donor S-nitrosoglutathione (GSNO) was tested on the Drosophila melanogaster model system. Fly larvae were raised on food supplemented with GSNO at concentrations of 1.0, 1.5 or 4.0mM. Food supplementation with GSNO caused a developmental delay in the flies. Biochemical analyses of oxidative stress markers and activities of antioxidant and associated enzymes were carried out on 2-day-old flies that emerged from control larvae and larvae fed on food supplemented with GSNO. Larval exposure to GSNO resulted in lower activities of aconitase in both sexes and also lower activities of catalase and isocitrate dehydrogenase in adult males relative to the control cohort. Larval treatment with GSNO resulted in higher carbonyl protein content and higher activities of glucose-6-phosphate dehydrogenase in males and higher activities of superoxide dismutase and glutathione-S-transferase in both sexes. Among the parameters tested, aconitase activity and developmental end points may be useful early indicators of toxicity caused by GSNO.

Sodium nitroprusside toxicity in Drosophila melanogaster: delayed pupation, reduced adult emergence, and induced oxidative/nitrosative stress in eclosed flies.

The toxicity of sodium nitroprusside (SNP) was tested on the Drosophila melanogaster model system. Fly larvae were raised on food supplemented with SNP at concentrations of 0.01-1.5 mM. Food supplementation with SNP caused a developmental delay in flies and reduced adult eclosion. Biochemical analyses such as levels of oxidative stress markers and activities of antioxidant and associated enzymes were carried out on 2-day-old flies emerged from control and SNP-fed larvae. Larval exposure to SNP resulted in lower activities of aconitase and catalase in adult flies relative to the control cohort. However, larval treatment with SNP led to higher carbonyl protein content and higher activities of superoxide dismutase, glucose-6-phosphate dehydrogenase, thioredoxin reductase, and glutathione-S-transferase in flies. Among the parameters tested, aconitase activity and developmental end points may be useful early indicators of toxicity caused by SNP. The study also suggests that the toxicity of SNP may arise not just from its direct effects, but also from its decomposition products such as nitric oxide and iron ions.