Alzheimer's and Parkinson's diseases are considered the most common neurodegenerative disorders, representing a major focus of neuroscience research to understanding the cellular alterations and pathophysiological mechanisms involved. Several natural products, including flavonoids, are considered able to cross the blood-brain barrier and are known for their central nervous system-related activity. Therefore, studies are being conducted with these chemical constituents to analyze their activities in slowing down the progression of neurodegenerative diseases. The present systematic review summarizes the pharmacological effects of flavonoids in animal models for Alzheimer's and Parkinson's diseases. A PRISMA model for systematic review was utilized for this search. The research was conducted in the following databases: PubMed, Web of Science, BIREME, and Science Direct. Based on the inclusion criteria, 31 articles were selected and discussed in this review. The studies listed revealed that the main targets of action for Alzheimer's disease therapy were reduction of reactive oxygen species and amyloid beta-protein production, while for Parkinson's disease reduction of the cellular oxidative potential and the activation of mechanisms of neuronal death. Results showed that a variety of flavonoids is being studied and can be promising for the development of new drugs to treat neurodegenerative diseases. Moreover, it was possible to verify that there is a lack of translational research and clinical evidence of these promising compounds.

Syzygium aromaticum, a medicinal plant commonly known as clove, is used to treat toothache, respiratory disorders, inflammation, and gastrointestinal disorders. From the flower buds of S. aromaticum, it is possible to obtain an essential oil comprised of a mixture of aliphatic and cyclic volatile terpenes and phenylpropanoids, being eugenol as the main component. The aims of this study were: (1) to extract the essential oil of the flower buds of S. aromaticum, (2) to identify and quantify the main component of the essential oil, and (3) to evaluate its antiulcer activity using different animal models. Assays were performed using the following protocols in rats: indomethacin-induced and ethanol/HCl-induced ulcer model. Both essential oils from S. aromaticum and eugenol displayed antiulcer activities in the rat models of indomethacin- and ethanol-induced ulcer. Studies focusing on the possible mechanisms of gastroprotection were also undertaken using the following experiments: evaluation of gastric secretion by the pylorus-ligated model, determination of mucus in gastric content, participation of nitric oxide (NO) and endogenous sulfhydryl in gastric protection. The results show that there was no significant effect on the volume of gastric juice and total acidity. However, the quantification of free gastric mucus showed that the clove oil and eugenol were capable of significantly enhancing mucus production. With regard to the NO and endogenous sulfhydryls, the results demonstrated that the gastroprotection induced by clove oil and eugenol are not related to the activities of the nitric oxide and endogenous sulfhydryls. No sign of toxicity was observed in the acute toxicity study. In conclusion, the results of this study show that essential oil of S. aromaticum, as well as its main component (eugenol), possesses antiulcer activity. The data suggest that the effectiveness of the essential oil and eugenol is based on its ability to stimulate the synthesis of mucus, an important gastroprotective factor. However, further pharmacological and toxicological investigations are required to enable its use for the treatment of gastric ulcer.

Inflammatory diseases result from the body's response to tissue damage, and if the resolution is not adequate or the stimulus persists, there will be progression from acute inflammation to chronic inflammation, leading to the development of cancer and neurodegenerative and autoimmune diseases. Due to the complexity of events that occur in inflammation associated with the adverse effects of drugs used in clinical practice, it is necessary to search for new biologically active compounds with anti-inflammatory activity. Among natural products, essential oils (EOs) present promising results in preclinical studies, with action in the main mechanisms involved in the pathology of inflammation. The present systematic review summarizes the pharmacological effects of EOs and their compounds in in vitro and in vivo models for inflammation. The research was conducted in the following databases: PubMed, Scopus, BIREME, Scielo, Open Grey, and Science Direct. Based on the inclusion criteria, 30 articles were selected and discussed in this review. The studies listed revealed a potential activity of EOs and their compounds for the treatment of inflammatory diseases, especially in chronic inflammatory conditions, with the main mechanism involving reduction of reactive oxygen and nitrogen species associated with an elevation of antioxidant enzymes as well as the reduction of the nuclear factor kappa B (NF-κB), reducing the expression of proinflammatory cytokines. Thus, this review suggests that EOs and their major compounds are promising tools for the treatment of chronic inflammation.