Structural Design, Synthesis and Antioxidant, Antileishmania, Anti-Inflammatory and Anticancer Activities of a Novel Quercetin Acetylated Derivative

Quercetin as a Promising Antiprotozoan Phytochemical: Current Knowledge and Future Research Avenues

Despite tremendous advances in the prevention and treatment of infectious diseases, only few antiparasitic drugs have been developed to date. Protozoan infections such as malaria, leishmaniasis, and trypanosomiasis continue to exact an enormous toll on public health worldwide, underscoring the need to discover novel antiprotozoan drugs. Recently, there has been an explosion of research into the antiprotozoan properties of quercetin, one of the most abundant flavonoids in the human diet. In this review, we tried to consolidate the current knowledge on the antiprotozoal effects of quercetin and to provide the most fruitful avenues for future research. Quercetin exerts potent antiprotozoan activity against a broad spectrum of pathogens such as Leishmania spp., Trypanosoma spp., Plasmodium spp., Cryptosporidium spp., Trichomonas spp., and Toxoplasma gondii. In addition to its immunomodulatory roles, quercetin disrupts mitochondrial function, induces apoptotic/necrotic cell death, impairs iron uptake, inhibits multiple enzymes involved in fatty acid synthesis and the glycolytic pathways, suppresses the activity of DNA topoisomerases, and downregulates the expression of various heat shock proteins in these pathogens. In vivo studies also show that quercetin is effective in reducing parasitic loads, histopathological damage, and mortality in animals. Future research should focus on designing effective drug delivery systems to increase the oral bioavailability of quercetin. Incorporating quercetin into various nanocarrier systems would be a promising approach to manage localized cutaneous infections. Nevertheless, clinical trials are needed to validate the efficacy of quercetin in treating various protozoan infections.

Inactivation Mechanism of Algal Chlorophyll by Allelochemical Quercetin

Cyanobacteria harmful algal blooms (CyanoHABs) are a global concern. Application of allelochemicals is a promising solution for cyanobacteria control, due to its high efficiency, low cost and ecological safety. Flavonoids (natural polyphenols produced by aquatic plants) are reported capable of effectively inhibiting the growth of algae; however, the molecular mechanism of algae chlorophyll inactivation is still unclear. In this study, quercetin was used as a typical flavonoid, to investigate the inactivation effect of allelochemical on Microcystis aeruginosa chlorophyll a. The absorption and fluorescence spectra showed that chlorophyll reacted with quercetin to form pheophytin, and the formation rate of pheophytin increased with increasing quercetin concentration (1 × 10^-5-1 × 10^-2 M). FTIR spectra and DFT calculation showed that Mg²⁺ complexed with the 3-OH and 4-C = O groups in the quercetin ring C so that chlorophyll was inactivated due to the loss of Mg²⁺ ions. Overall, this study revealed that quercetin inactivated chlorophyll a of cyanobacteria by capturing Mg²⁺ ions, providing insights into the molecular mechanisms of algal bloom control by allelochemicals.

Hypoglycemic effect and toxicity of the dry extract of Eugenia biflora (L.) DC. leaves

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves of Eugenia biflora (Myrtaceae) are traditionally used by Amazonian populations for the control of diabetes. However, their chemical composition has not yet been described and pharmacological evidence has not been reported.

OBJECTIVE

This study aimed to identify the chemical constituents and evaluate the hypoglycemic and toxic effect of the dry extract of the E. biflora leaves (DEEB).

MATERIALS AND METHODS

DEEB, obtained by infusion, was analyzed using LC-HRMS and NMR, whose the catechin flavonoid was quantified using NMR. The antidiabetic effect of DEEB was evaluated according to its inhibition of the enzymes α-amylase and α-glucosidase, as well as the content of total phenols, free radical scavengingand antiglycation activities, and its in vitro cell viability. Oral maltose tolerance and chronic multiple dose tests (28 days) in streptozotocin-induced diabetic mice (STZ) were performed. The hypoglycemic effect and toxicity of this extract were evaluated in the multiple dose assay. Biochemical parameters, hemolysis, and levels of the thiobarbituric acid reactive species in the liver were investigated and histopathological analyses of the kidneys and liver were performed.

RESULTS

Eight phenolic compounds were identified, with catechin (15.5 ± 1.7 mg g-1) being the majority compound and a possible chemical marker of DEEB. The extract showed inhibition activity of the enzyme α-glucosidase. Chronic administration of DEEB (50 mg/kg of body weight) reduced glucose levels in diabetic animals, similar to acarbose; however, DEEB (100 and 200 mg/kg bw) caused premature death of mice by D22 of the treatment. Our data indicate that one of the mechanisms of toxicity in DEEB may be related to the aggravation of oxidative stress in the liver. This histopathological study indicated that DEEB failed to minimize the progression of the toxicity of diabetes caused by STZ.

CONCLUSIONS

This study demonstrated the hypoglycemic potential of E. biflora leaves. However, the prolonged use of this tea can be harmful to its users due to its considerable toxicity, which needs to be better investigated.