Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is a novel coronavirus identified at the end of 2019. It is recognized as the causative agent of coronavirus disease 2019 (COVID-19). Flavonoids have been shown to exhibit therapeutical effect on complications related to COVID-19. The present study reviews possible therapeutic benefits of flavonoids on SARS-CoV-2. The Web of Science, PubMed, Scopus, and Google Scholar were searched using keywords: “COVID-19”, “SARS-CoV-2”, “Kaempferol” and “Quercetin” in the Title/Abstract. Relevant published articles in the English language until August 2020 were considered. Kaempferol and quercetin showed antiviral properties such as inhibition of protein kinase B and phosphorylation of protein kinase and blocking effects on a selective channel (3a channel) expressed in SARS-CoV infected cells. They also reduced the level of reactive oxygen species, expression of inducible nitric oxide synthase, pro-inflammatory mediators including TNF-α, IL-1α, IL-1β, IL-6, IL-10, and IL-12 p70, and chemokines. Kaempferol and quercetin might exert beneficial effects in the control or treatment of COVID-19 because of their antiviral, antioxidant, anti-inflammatory, and immunomodulatory effects.

Objective: To decipher the responsible compound present in the aqueous root extract of Vetiveria zizanioides which has tremendous immunomodulatory activity. Methods: Different fractions of the water extract were collected and analyzed for immunomodulatory activity by analyzing in vitro phagocytic activity and nitric oxide production. One fraction VF3 was selected and further analyzed for possible compounds by high performance liquid chromatography and gas chromatography coupled with a mass spectrometer. The in vitro immunomodulatory parameters such as phagocytic index, nitrite content, and tumor necrosis factor-α production in murine macrophages were analyzed. In vivo studies, sheep red blood cell induced haemagglutination titer, the number of antibody-producing cells, and sheep red blood cell induced delayed-type hypersensitivity were analyzed. Cytotoxic studies in L929 normal fibroblasts were also performed. Results: One of the fractions, VF3, was selected and confirmed the presence of an active compound valencene. The in vitro immunomodulatory parameters were significantly (P<0.05) increased by valencene treatment. In vivo studies in Swiss albino mice showed that valencene could significantly (P<0.05) increase haemagglutination titer, the number of antibody-producing cells, and delayed-type hypersensitivity. Cytotoxic studies also showed that valencene did not cause any morphological changes and DNA damage in normal fibroblasts. Conclusions: Valencene possesses immunomodulatory activities and can be commercially exploited for its immunostimulatory potentials.

Objective: To investigate the modulatory effects of bitter gourd extract on the insulin signaling pathway in the liver and skeletal muscle tissues of diabetic rats. Methods: The ethanolic extract of bitter gourd was prepared and its contents of total polyphenols and flavonoids were assayed. A neonatal streptozotocin-induced diabetic rat model was established and the diabetic rats were assigned into different groups and were treated with different doses of bitter gourd extract (100, 200, 400, or 600 mg/kg) or with glibenclamide (0.1 mg/kg) for 30 d. Fasting blood glucose, insulin, and lipid profile were evaluated and the insulin signaling pathway in the liver and skeletal muscle of rats was investigated. The correlations between homeostasis model assessment (HOMA) and the components of insulin signaling pathway were also evaluated. Results: Different doses of bitter gourd extract significantly ameliorated fasting blood glucose level and HOMA index for insulin resistance. Moreover, bitter gourd extract increased serum insulin and improved disrupted serum lipid profile. The levels of insulin receptor substrate-1 (IRS-1), p-insulin receptor β (p-IR-β), protein kinase C (PKC), GLUT2, and GLUT4 were improved by treatment with bitter gourd extract. The best results were obtained with 400 mg/kg dose of the extract, the effect of which was equivalent to that of glibenclamide. HOMA in the bitter gourd treated rats was negatively correlated with p-IR-β, IRS-1 and PKC in hepatic and skeletal muscle. HOMA was also negatively correlated with skeletal muscle GLUT4. Conclusions: Bitter gourd extract improves glucose homeostasis and lipid profile in diabetic rats via enhancement of insulin secretion and sensitivity. Therefore, bitter gourd can be used as a potential pharmacological agent for the treatment of type 2 diabetes mellitus.

Objective: To investigate the cytotoxic activity and molecular mechanism(s) of two Thai noni juice (TNJ) products ethanolic extracts against cholangiocarcinoma (CCA) cell lines and non-cancerous cells, and to explore phenolic acid compositions of TNJ products. Methods: Phenolic acid profiles of TNJ Chiangrai (TNJ-Cr) and TNJ Buasri (TNJ-Bs) ethanolic extracts were determined by HPLC. The cytotoxicity of TNJ ethanolic extracts on cancer and non-cancerous cells was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and trypan blue assays. Mechanism(s) underlying the anti-CCA activity of TNJ ethanolic extracts were determined by cell cycle, apoptosis, and reactive oxygen species (ROS) generation assays. The expression levels of proteins involved in apoptosis and ERK signaling were evaluated by Western blot analysis. Results: Phenolic acid profiles of both TNJ ethanolic extracts showed that the p-hydroxybenzoic, vanillic, and protocatechuic acids were the major phenolic acids in TNJ products. Cytotoxicity assays revealed that the TNJ-Cr and TNJ-Bs ethanolic extracts reduced viability of CCA cell lines through induction of apoptosis by up-regulation of p53 and Bax proapoptotic proteins. Both TNJ ethanolic extracts promoted ROS generation by activating the ERK1/2 signaling in well-differentiated CCA cells KKU-213B. Meanwhile, TNJ ethanolic extracts did not induce ROS production in poorly differentiated CCA cells KKU-100. Both TNJ ethanolic extracts showed no toxicity to human peripheral blood mononuclear cells. Conclusions: TNJ ethanolic extracts could inhibit CCA cell proliferation by inducing ROS generation and apoptosis and may be applicable for combination therapies in CCA treatment.

Objective: To compare the antioxidant and anti-genotoxic properties of Alpinia (A.) galanga, Curcuma (C.) amada, and C. caesia. Methods: Cytotoxicity of ethanolic extracts of A. galanga, C. amada, and C. caesia at selected doses was evaluated by trypan blue, MTT, and flow cytometry-based assays. Genotoxicity and anti-genotoxicity (against methyl methanesulfonate, 35 μM and H₂O₂, 250 μM) of these plants were studied by comet assay in human lymphocytes in vitro. Furthermore, DPPH, ABTS, FRAP, lipid peroxidation, and hydroxyl radical scavenging assays were performed to study the antioxidant potentials of the plants. Finally, anti-genotoxic potential of C. amada was validated in Swiss albino mice using comet assay. Phytochemical composition of C. amada was determined by GC/MS and HPLC. Results: The selected doses (2.5, 5, and 10 μg/mL) of A. galanga, C. amada, and C. caesia were non-toxic by cytotoxicity tests. All three ethanolic extracts of plant rhizomes demonstrated antioxidant and anti-genotoxic properties against methyl methanesulfonate-and H₂O₂-induced oxidative stress in human peripheral blood lymphocytes in vitro. Multivariate analysis revealed that various antioxidant properties of these extracts in DPPH, ABTS, and FRAP assays were strongly correlated with their total phenolic constituents. C. amada extract conferred protection against cyclophosphamide-induced DNA damage in the bone marrow cells of mice and DNA damage was significantly inhibited by 2.5 mg/kg C. amada extract. Conclusions: C. amada is rich in potentially bioactive molecules and exhibits potent antioxidant activities. Its anti-genotoxicity against cyclophosphamide-induced oxidative stress is also confirmed in this study.