A Novel Antibacterial Component and the Mechanisms of an Amaranthus tricolor Leaf Ethyl Acetate Extract against Acidovorax avenae subsp. citrulli

The aim of the present investigation was to determine the active ingredients in Amaranthus tricolor L. leaves and develop a biological pesticide. Organic solvent extraction, column chromatography, liquid chromatography, ODS-C18 reverse elution, Sephadex LH-20 gel filtration, H spectrum, and C spectrum were used to isolate the pure product for an assessment of the agricultural activity and bacteriostatic mechanisms. The results showed that the activity of the crude extract following carbon powder filtration was 1.63-fold that of the non-filtered extract. Further isolation was performed to obtain two pure products, namely, hydroxybenzoic acid (HBA) and benzo[b]furan-2-carboxaldehyde (BFC), and their molecular formulas and molecular weights were C7H6O3 and 138.12, and C9H6O2 and 146.12, respectively. Our study is the first to determine that HBA has bacteriostatic activity (MIC 125 μg/mL) and is also the first to isolate BFC from A. tricolor. The ultrastructure observation results showed that HBA caused the bacteria to become shriveled, distorted, and deformed, as well as exhibit uneven surfaces. After HBA treatment, 70 differentially expressed metabolites were detected in the bacteria, of which 9 were downregulated and 61 were upregulated. The differentially expressed metabolites were mainly strigolactones, organic acids and derivatives, fatty acids, benzene and substituted benzene derivatives, amino acids and associated metabolites, and alcohols and amines. Among all of the downregulated differentially expressed metabolites, MEDP1280 was the most critical, as it participates in many physiological and biochemical processes. The enrichment analysis showed that the differentially expressed metabolites mainly participate in tyrosine metabolism, biosynthesis of amino acids, cysteine and methionine metabolism, and arginine and proline metabolism. Additionally, HBA was found to disrupt cell membrane permeability and integrity, causing the leakage of substances and apoptosis. The physiological and biochemical test results showed that HBA could increase the pyruvate levels in bacteria but could decrease the activities of respiratory enzymes (malate dehydrogenase (MDH) and NADH oxidase) and antioxidant enzymes (superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX)). Inverse molecular docking was used to study the binding between HBA and respiratory and antioxidant enzymes. The results showed that HBA could bind to MDH, NADH oxidase, SOD, and GSH-PX, suggesting that these enzymes may be the effector targets of HBA. Conclusion: The optimal active ingredient in A. tricolor that can inhibit Acidovorax avenae subsp. citrulli was identified as HBA. HBA mainly disrupts the cell membrane, damages the metabolic system, and inhibits respiration and antioxidant enzyme activity to control bacterial growth. These results provide a reference for the further development of biological pesticides.

Comparative hypoglycemic potentials and phytochemical profiles of 12 common leafy culinary vegetables consumed in Nsukka, Southeastern Nigeria

Background Metabolic disease like diabetes mellitus is on the increase in developing countries due to lack of access to orthodox medicine owing to its high cost. Health benefits of culinary vegetables cannot be overemphasized. This study therefore aims to profile the hypoglycaemic potentials of 12 common leafy vegetables consumed in Nsukka, Southeastern Nigeria and advise diabetic patients accordingly. Methods A total of 75 albino Wistar rats assigned to 15 groups of five rats per group were used for the study. Diabetes was induced in groups 1-14 rats by intraperitoneal injection of alloxan monohydrate (160 mg/kg), and rats in group 15 were not made diabetic. Groups 1-12 rats were treated with aqueous extracts of the vegetables (200 mg/kg), and group 13 rats received glibenclamide at 2 mg/kg and served as standard control. Rats in groups 14 and 15 received distilled water (10 mL/kg) to serve as negative and normal controls, respectively. The fasting blood glucose (FBG) values of the rats were determined 3, 6 and 24 h post-treatment. Phytochemical studies on the vegetables were also carried out. Results Results revealed that the hypoglycaemic activities of Gongronema latifolium, Pterocarpus santalinoides, Ocimum gratissimum, Pterocarpus mildbraedii and Vernonia amygdalina were comparable (p>0.05) to that obtained for glibenclamide (standard anti-diabetic drug) while Gnetum africanum and Piper guineense did not show significant hypoglycaemic activities. Phytochemicals such as flavonoids, alkaloids, tannins, saponins, glycosides, and terpenes were present in the vegetables. Conclusions It was concluded that the vegetables possess hypoglycaemic activities at different capacities with G. latifolium being the most potent.