The consumption of functional drinks, containing vitamins, taurine, caffeine, and herbal extracts is increasing, as demonstrated by their large market growth.1) Although the ingredients of functional drinks are being investigated in various studies on behavior or lifespan, few studies have investigated the relationship between behavior, lifespan, and the antioxidant activity of vitamin and energy drinks. Therefore, we aimed to investigate the effects of functional drinks, as well as their major ingredients, on behavior patterns, survival, and antioxidant activity using the well-characterized study model species D. melanogaster.
In the present study, we utilized commercial drinks to investigate significant difference in locomotor activity during subjective nighttime and daytime (Fig. 1). Taurine, which is present in energy drinks, significantly decreased the subjective nighttime and daytime activity compared with the normal and ascorbic acid. In contrast, caffeine significantly increased subjective nighttime activity as compared to that in the normal, ascorbic acid, and taurine groups. The active ingredients in vitamin drinks, such as ascorbic acid are essential for collagen and carnitine and acts as co-factor for the enzyme dopamine-β-hydroxylase.16) Furthermore, ascorbic acid inhibits T-cells apoptosis and maintains T-cell proliferation to enhance immune responses.17) Also, Lin et al. reported the interaction of caffeine and/or taurine on locomotion and sleep of Drosophila, and addressed the potential impact of energy drink consumption.10) Taurine is the second most abundant amino acid in the mammalian brain and is also present in mushroom bodies (MBs) in Drosophila.18) It GABAA receptor agonists (GABAA-Rs or Rdl) and associated activation of glycine receptors (Gly-Rs), result in cellular membrane stability and modulation of intracellular calcium levels.19) Caffeine in energy drinks inhibits adenosine receptors and also increases levels of epinephrine, which can positively affect physical and mental performance.20)
We also demonstrated the dose-dependent effects of drink ingredients on locomotor activity in fruit flies, and showing that high levels of taurine and caffeine altered locomotor activity during both the subjective nighttime and daytime of the circadian rhythm (Fig. 2). In addition, we assessed the dose-dependent effects of ascorbic acid, taurine, and caffeine on climbing ability (Fig. 3). The climbing ability of fruit flies induced by taurine and caffeine supplementation might be associated with the mitigation and arousal effect. These results are consistent with those of a previous report showing that taurine reduces locomotor activity in a dose-dependent manner while caffeine increases locomotor activity.10) It is well known that circadian rhythms are fundamental biological phenomena resulting from molecular genetic mechanisms known as circadian clocks, our results indicated that taurine and caffeine might exert biological effects on the circadian rhythm.
We studied the dose-dependent effects of ascorbic acid, taurine, and caffeine on the lifespan of fruit flies (Fig. 4). We also found that the administration of 1.6% taurine, and 0.025 and 0.05% caffeine was associated with decreased survival flies (Fig. 5). Although mean lifespan of flies was found to be similar to controls for concentrations of 0.1 and 10 mM ascorbic acid, higher concentrations of ascorbic acid (10 and 50 mM) enhanced the toxic effects of iron, with the iron pool significantly increased in adult whole-body extracts.21) Also, a concentration of 10 and 50 mM ascorbic acid diminished lifespan of male flies by 6.9 and 12.8%, compared to the normal group and 1 mM ascorbic acid treatment.22) Taken together, these results show that administration of ascorbic acid did not affect the lifespan of fruit flies. However, taurine and caffeine at relatively high doses and concentrations compared with those present in commercial drinks reduced the lifespan of flies. Nikitin et al. reported a negative dosage-dependent effect of caffeine on longevity and other life history parameters.23)
To better understand the effect of drink ingredients on dose-dependent changes in locomotor activity, lifespan and survival, we utilized qRT-PCR and analyzed enzyme activities to compare the effects of antioxidant activity on these parameters (Figs. 6, 7). In Drosophila, caffeine modulates the cAMP- protein kinase A (PKA) pathway, resulting in increased the cAMP-levels and fragmented sleep.24) Also, Dop1R1 levels have been shown to mediate caffeine-induced arousal and higher-order brain functions such as motor control, learning and memory. Furthermore, GABA exerts its effects through ionotropic GABAA, to produce fast synaptic inhibition, and metabotropic GABAB receptors, to produce slow, prolonged inhibitory neurotransmission. GABAB receptor agonists are involved in inhibiting dopamine release and regulating glutamatergic systems of dopamine.25) The sleep–wake cycle disturbance associated with behavioral and biological processes can be partially explained through alteration in neuronal signaling. There are indications that neuronal signals generated by taurine or caffeine administration at synapses could interact with various receptors, cause receptor desensitization and alteration of neuromodulator homeostasis, and lead to neurological disorders. Administration of ascorbic acid is significantly related to the adverse effect of reactive oxygen and nitrogen species, which can cause oxidative damage to DNA, proteins, and lipids and reduces superoxide anions via the modulation of antioxidant enzymes activity (SOD, glutathione peroxidase (GPx)).26,27) Nonaka et al. reported that taurine reduces endoplasmic reticulum (ER) stress induced by homocysteine and affects the expression and secretion of extracellular SOD (EC-SOD).28) In addition, chronic caffeine ingestion modulated lipid peroxidation and the concentration of reduced-GSH, which similarly increased the activities of SOD and GSH reductase (GR).29) Our results indicate a relationship among lifespan, antioxidants and behavior induced by ascorbic acid, taurine and caffeine, which are major active ingredients in vitamin and energy drinks. Ascorbic acid has an enhancing effect that maintains the stability of the body rhythm and increases anti-oxidative activity. In contrast, taurine and caffeine are neuromodulators that induce behavioral inhibition and arousal. These behavioral changes following taurine and caffeine supplementation are thought to affect the antioxidant activity and lifespan of flies. Growing evidence suggests that several functional beverages are associated with antioxidant activity, lifespan and locomotor activity. The results of the present study might represent fundamental data on the industrial application of the functional drink market.