Syzygium jambos and Solanum guaraniticum are both employed in Brazil as medicinal plants, even though their potential toxicity is not well established and they are frequently misused. The aim of this study was investigate the effect of the aqueous leaf extracts of both plants on δ-aminolevulinate dehydratase (δ-ALA-D) and acetylcholinesterase (AChE) activities and the antioxidant action against oxidative damage induced by sodium nitroprusside in rats, using in vitro assays. In addition, the presence of gallic, caffeic and chlorogenic acids, as well as rutin, quercetin and kaempferol as bioactive compounds in the extracts was identified by HPLC and their levels quantified. The antioxidant activities of both extracts were assessed by their capabilities to scavenge nitric oxide and to inhibit lipid peroxidation. Only Syzygium jambos presented thiol-peroxidase-like activity. Although OPEN ACCESSMolecules 2013, 18 9180 neither extract affected the AChE activity, the aqueous extract of Solanum guaraniticum inhibited brain δ-ALA-D activity, suggesting a possible impairment effect on the central nervous system. Our results showed that both extracts exhibited efficient free radical scavenger activity and are an interesting source of bioactive compounds, justifying their use in folk medicine, although Solanum guaraniticum extract could have neurotoxicity properties and we therefore suggest that its use should be restricted to ensure the health of the population.

Diabetes mellitus, a chronic metabolic disorder, has assumed epidemic proportions and its long-term complications can have devastating consequences. The oxidative stress in diabetes was greatly increased due to prolonged exposure to hyperglycemia and impairment of oxidant/antioxidant equilibrium. Syzygium cumini is being widely used to treat diabetes by the traditional practitioners over many centuries. Adenosine deaminase (ADA) and 5′-Nucleotidase (5′NT) are enzymes of purine nucleoside metabolism that play an important role in the regulation of adenosine (Ado) levels. In this study, we investigated the effect of Syzygium cumini aqueous leaves extract (ASc) on ADA and 5′NT activities and on parameters of oxidative stress under in vitro conditions, using platelets of patients with Type 2 diabetes mellitus. Platelet-Rich Plasma (PRP) was assayed by ADA, 5′NT, Catalase (CAT), Superoxide Dismutase (SOD) activities and Thiobarbituric acid reactive substances (TBARS) levels. We observed that ADA, 5′NT activities and TBARS levels were significantly higher when compared to the control group, and ASc (100 and 200 µg/mL) prevented these effects. Our study demonstrates that ASc was able to remove oxidant species generated in diabetic conditions and modulates in the Ado levels. Then, ASc may promote a compensatory response in platelet function, improving the susceptibility-induced by the diabetes mellitus.

Adenosine plays an important neuromodulatory role in the central nervous system, and adenosine deaminase is an important enzyme in the degradation of adenine nucleotides. Methylmercury is the most prevalent form of mercury found in the environment. Methylmercury neurotoxicity has been correlated to the production of reactive oxygen species. In this study, its potential pathogenic effects were investigated in vitro in cerebral cortex and hippocampus of rats. We first observed that adenosine deaminase activity was higher in young rat brains when compared to the 60-day-old rats and was higher in hippocampus when compared to the cortex. Methylmercury (0.1, 1.0, 20 μ M) inhibited adenosine deaminase activity in 7-and 60-day-old rats in a concentration-dependent manner. We have demonstrated that methylmercury-induced inhibition was antagonized by garlic alcoholic extract, but sodium selenate did not alter enzyme activity. In addition, glutathione and dithiothreitol restored the methylmercury-induced decrease of adenosine deaminase activity. These results demonstrated that there are age-related changes in adenosine deaminase activity and that thiol agents may contribute to the maintenance of adenosine deaminase activity and may be important in the neuromodulation of adenosine. Garlic alcoholic extract may be effective in reducing the effect of methylmercury-induced adenosine deaminase, which may be due to its sulphur-containing compounds.