Isolation of Polyphenols from Soursop Annona muricata L Leaves Using Green Chemistry Techniques and their Anticancer Effect

HIGHLIGHTS Isolate, fractionate and characterize extracts obtained from soursop leaves. Use of emerging green technologies such as microwave-ultrasound hybridization. The extracts contain kaempferol, procyanidins, catechin, and quercetin. The total ethanolic extract demonstrates cytotoxic effect on HeLa cells.

Abstract Cervical cancer is classified as the fourth most common malignancy in women. Natural compounds are a therapeutic alternative in cancer therapy. The aim of the study is to isolate, fractionate, and characterize extracts obtained from soursop leaves (Annona muricata L.) and determine their cytotoxic effect against HeLa cervical cancer cells and non-carcinogenic fibroblast 3T3 cells. The phytochemicals of soursop leaves were extracted through emerging green technologies such as the novel use of microwave-ultrasound hybridization and the use of environmentally friendly solvents (water and ethanol), in addition to the purification of extracts enriched in polyphenols by liquid chromatography with Amberlite XAD-16. Total aqueous and ethanolic extract were purified, as well as the fraction one of each extract. The extracts recovered from soursop leaves contained kaempferol and its isomers, procyanidins, catechin, and quercetin. The viability of the cells was determined with the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. HeLa and 3T3 cells were exposed to concentrations of 25, 50, 75, 100, 150, 200, and 250 ppm of a solution of soursop leaf extract powder. The MTT assay showed that soursop leaf extracts were toxic to both cell lines in general, however, the ethanolic extract at 25 and 50 ppm demonstrated inhibition in cell viability against the HeLa cancer line and low cytotoxicity for 3T3 fibroblast cells. In conclusion, the novel microwave-ultrasound hybridization technology allows the extraction of polyphenols that may have a potential cytotoxic effect on cancer cells.

Mechanical-physicochemical properties and biocompatibility of catechin-incorporated adhesive resins

Abstract Several anti-proteolytic dentin therapies are being exhaustively studied in an attempt to reduce dentin bond degradation and improve clinical performance and longevity of adhesive restorations. Objectives This study assessed the effect of epigallocatechin-3-gallate (EGCG) on long-term bond strength when incorporated into adhesives. Material and Methods Adhesive systems were formulated with EGCG concentrations of 0 wt%: (no EGCG; control); 0.5 wt% EGCG; 1.0 wt% EGCG, and 1.5 wt% EGCG. Flexural strength (FS), modulus of elasticity (ME), modulus of resilience (MR), compressive strength (CS), degree of conversion (DC), polymerization shrinkage (PS), percentage of water sorption (%WS), percentage of water solubility (%WL) and cytotoxicity properties were tested. Dentin microtensile bond strength (µTBS) was evaluated after 24 h and again after 6 months of water storage. The adhesive interface was analyzed using scanning electron microscopy (SEM). Results No significant differences were found among the groups in terms of FS, ME, MR, CS and PS. EGCG-doped adhesives increased the DC relative to the control group. EGCG concentrations of 1.0 wt% and 0.5 wt% decreased the WS of adhesives. WL decreased in all cases in which EGCG was added to adhesives, regardless of the concentration. EGCG concentrations of 1.0 wt% and 0.5 wt% reduced cytotoxicity. EGCG concentrations of 1.0 wt% and 0.5 wt% preserved µTBS after 6 months of storage, while 1.5 wt% EGCG significantly decreased µTBS. SEM: the integrity of the hybrid layer was maintained in the 0.5 wt% and 1.0 wt% EGCG groups. Conclusion EGCG concentrations of 1.0 wt% and 0.5 wt% showed better biological and mechanical performance, preserved bond strength and adhesive interface, and reduced cytotoxicity.

Effect of (+)-catechin hydrate on oxidative stress induced by high sucrose and high fat diet in male Wistar rats.

Increased lipid peroxidation and reduced glutathione levels in liver of rats fed high sucrose high fat (HSHF) diet were normalized by concomitant administration of (+)-catechin hydrate. Plasma non-enzymatic antioxidants viz. α-tocopherol, ascorbic acid and total thiols decrease were also significantly less in rats administered with (+)-catechin hydrate concomitantly with HSHF diet. Thus the present results indicate that (+)-catechin hydrate has antioxidant activity and is effective in reducing oxidative stress. The study is of clinical importance as oxidative stress is known to be the cause of many clinical manifestations viz. cancer, Parkinson’s disease, atherosclerosis, heart failure, myocardial infarction and many other diseases.

Catechin-incorporated dental copolymers inhibit growth of Streptococcus mutans

Objective: To test the inhibitory growth activity of green tea catechin incorporated into dental resins compared to resins containing the broad-spectrum antimicrobial compound chlorhexidine against Streptococcus mutans in vitro. Material and Methods: The minimum inhibitory concentrations (MICs) of epigallocatechin-gallate (EGCg) and chlorhexidine (CHX) were determined according to the microdilution method. Resin discs (5 mm × 3 mm) were prepared from Bis-GMA/TEGDMA (R1) and Bis-GMA/CH3Bis-GMA (R2) comonomers (n=9) containing: a) no drug, b) EGCg, c) CHX. Two concentrations of each drug (0.5× MIC and 1× MIC) were incorporated into the resin discs. Samples were individually immersed in a bacterial culture and incubated for 24 h at 37°C under constant agitation. Cell viability was assessed by counting the number of colonies on replica agar plates. Statistical analysis was performed using one-way ANOVA, Tukey and Student t-tests (α=0.05). Results: Both resins containing EGCg and CHX showed a significant inhibition of bacterial growth at both concentrations tested (p<0.05). A significantly higher inhibition was observed in response to resins containing CHX at 0.5× MIC and 1× MIC, and EGCg at 1× MIC when compared to EGCg at 0.5× MIC. Also, EGCg at 0.5× MIC in R1 had a significantly higher growth inhibition than in R2. Conclusions: Both EGCg and CHX retained their antibacterial activity when incorporated into the resin matrix. EGCg at 1× MIC in R1 and R2 resins significantly reduced S. mutans survival at a level similar to CHX. The data generated from this study will provide advances in the field of bioactive dental materials with the potential of improving the lifespan of resin-based restorations.

Studies on interactions between plant secondary metabolites and glutathione transferase using fluorescence quenching method.

The interactions between plant secondary metabolites (tannic acid, rutin, cinnamic acid and catechin) and glutathione transferase (GST) were investigated by fluorescence and UV-Vis absorption spectroscopy. Intrinsic fluorescence of GST was measured by selectively exciting their tryptophan (Trp) residues and quenching constants were determined using the Stern-Volmer equation. The binding affinity was found to be strongest for tannic acid and ranked in the order tannic acid>rutin>cinnamic acid>catechin. The pH values in the range of 6.7-7.9, except for tannic acid, did not affect significantly the affinity of rutin, cinnamic acid and catechin with GST. Results showed that the fluorescence quenching of GST was a static_quenching. Fluorescence quenching and UV-Vis absorption spectroscopy suggested that only the tannic acid changed the microenvironment of the Trp residues. Furthermore, the number of binding sites and binding constants at different pH values showed that tannic acid had strongest affinity towards GST and hydrogen bonding played an important role in the affinity between GST and the metabolites.