Avaliação das propriedades biológicas de extratos e compostos de duas espécies de plantas medicinais.

Abstract

Medicinal plants have been employed in the prevention of diseases since the beginning of human civilization, and their therapeutic properties are related with the chemical composition of their crude extracts. Cymbopogon citratus (C. citratus), popularly known as lemongrass, is worldwide consume due to its action on the central nervous system. However, despite the therapeutic effects of medicinal plants to humans, it has already proven that some extracts can be exhibit some toxicity. In this way, it is important to evaluate the toxicity of its extracts and related compounds. In this study, the toxicity of C. citratus extracts and fractions obtained from different extraction procedures, as well for essential oil and its main chemical compounds, citral and geraniol, was evaluated in Artemia salina, and in human blood cells (leukocytes and erythrocytes). The ethyl acetate fractions obtained in acidic and basic conditions after essential oil removal from plant leaves, reduced the cell viability of leukocytes. Furthermore, the essential oil, citral and geraniol were also cytotoxic to these cells at the highest concentration analyzed. These samples also increased the osmotic fragility of erythrocytes, and field emission scanning electron microscopy (FESEM) analyzes revealed changes in the erythrocytes morphology. In this work, the anxiolytic and anticonvulsant effects of C. citratus hydroalcoholic extract and essential oil, citral and geraniol (isolated and in association) were evaluated in zebrafish. The light/dark test demonstrated that pretreatment with the samples increased the time spent by the animals in the light side of the tank and increased the latency time for the first seizure induced by pentylenetetrazole (PTZ), indicating anxiolytic and anticonvulsant effects, respectively. The mixture between citral and geraniol at the lowest concentrations employed in each test also showed a significant effect. These effects were antagonized when animals were previous exposed to flumazenil (FMZ) solution, which revealed the involvement of GABAA receptors in the effects. Moreover, pretreatment with samples restored malondialdehyde (MDA), catalase (CAT), nitric oxide (NO) and glutathione (GSH) levels in zebrafish brain homogenates after PTZ exposure. In this study, the antioxidant activity of Cannabis sativa (C. sativa), a medicinal plant used for recreational and medicinal purposes in some countries, and its major constituents, cannabidiol (CBD) and tetrahydrocannabinol (THC) (isolated and in association) was also investigated. Therefore, spectrophotometric (reducing power ability, 2,2-diphenil-1-picryl-hydrazyl (DPPH), 2,2- azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and hypochlorous acid (HOCl) scavenger assays), and electrochemical assays (cyclic voltammetry and differential pulse voltammetry) were employed. All samples exhibited a significant antioxidant effect in the assays used in this study. Furthermore, a synergistic effect between these cannabinoids in the antioxidant activity was verified. Pearson’s correlation analysis showed a good correlation between the results obtained by spectrophotometric and electrochemical assays, which indicated that these techniques can be employed in the evaluation of samples containing cannabinoids. Thus, the results obtained in the present thesis evidenced the importance of medicinal plants in the discovery of new drugs and their therapeutic properties.