Therapeutic Uses and Pharmacological Properties of Shallot (Allium ascalonicum): A Systematic Review

Abstract

Background: Shallot (Allium ascalonicum L.) is a traditional plant species used throughout the world both for culinary purposes and as a folk remedy. To date (i.e., April 2022), there is no report on the main pharmacological activities exerted by shallot preparations and/or extracts.

Scope and approach: The aim of this study was to comprehensively review the pharmacological activities exerted by shallot, with rigorous inclusion and exclusion criteria based on the scientific rigor of studies. Prisma guidelines were followed to perform the literature search.

Key findings and conclusions: The literature search yielded 2,410 articles of which 116 passed the required rigorous criteria for inclusion in this review. The extracts exert a potent antioxidant activity both in vitro and in vivo, as well as a strong inhibitory capacity on various pathogens with relevant implications for public health. Moreover, shallot can be used as adjuvant therapy in cardiovascular diseases, diabetes, cancer prevention, and other non-communicable diseases associated with inflammatory and oxidative pathways. Future studies investigating the chemical composition of this species, as well as the molecular mechanisms involved in the empirically observed pharmacological actions are required.

Keywords: Allium ascalonicum; Allium cepa var. aggregatum; pharmacological activity; shallot; therapeutic use.

Figure 1

(A) Representation of inclusion and exclusion criteria, with corresponding results from the literature search used. (B) Venn Diagram of type and number of studies included in this review. The overlapping zones and the associated numbers correspond to number of articles which describe two or more pharmacological actions.

Figure 2

Antimicrobial effects of shallot. (a) Antimycobacterial activity of partially purified extract of Allium ascalonicum. (b) Anti-fungal activity of ascalin against B. cinerea. (A) Control, (B) Ascalin (75 μg), and (C) Ascalin (15 μg). Shallot extract effect on (c) Penicillium sp., (d) Candida albicans, (e) Allium ascalonicum aqueous extracts inhibited the growth of Candida albicans. (f) Biofilm formation observed after 24 h with shallot extract (A) without treatment (B) 0.25 MIC, (C) 0.5 MIC, (D) 1 MIC and (E) 2 MIC at 40× magnification. A reduction of activity was observed with increasing concentration of treatment. Inhibitory effect of adding shallot at various times pre-infection or post-infection of adenovirus [ADV-41 (g); ADV-3 (h)] to A549 cells. Different concentrations of shallot [120 mg/L (open triangles), 240 mg/L (filled triangle), 480 mg/L (open circles), 960 mg/L (filled circles)], were added at various times pre-infection (~1 h), co-infection (0 h) or post-infection (1–24 h) of adenovirus (ADV-41; ADV-3) to A549 cells at 37°C. The x-axis indicates the time course of adding shallot (42). (i) Adult and larvae maize weevil fumigant toxicity experiment: (A) application of essential oil on filter paper (B) filter paper in jar lid; (C) maize weevil adults; (D) fumigant toxicity effects observed in the jar; (E) jars maintained at rearing temperature and humidity; (F) application of essential oil on filter paper; (G) filter paper in jar lid; (H) maize weevil larvae; (I) fumigant toxicity effects observed in the jar; (J) jars maintained at rearing temperature and humidity (29, 34, 36, 40, 45). (j) The growth-inhibitory effect of shallot juice extract in EA.hy926 cells. (k) Apparent changes occurred in round scad during ice storage. Shallot extract, the round scad was immersed in shallot extract; Garlic extract, the round scad was immersed in garlic extract; Control, the round scad was immersed in distilled water (19, 46). (l) Anti-angiogenic effect of ethyl acetate fraction on CAM model of angiogenesis (arrows show neovascular forming in the chicken chorioallantoic membrane); (A) control, (B) treatment with EA fraction at 3 ng/egg, (C) treatment with ethyl acetate fraction at 10 ng/egg (47).

Figure 3

Chemical structure of (A) quercetin (3,5,7,3′,4′-pentahydroxyflavone); (B) the quercetin-derived benzofuranone [2-(3,4-dihydroxybenzoyl)-2,4,6-tri-hydroxy-3(2H)-benzofuranone]. (C) Aminoethyl cysteine ketimine decarboxylated dimer (AECK–DD); (D) Cepa2; (E) binding mode of isorhamnetin-3-glucoside with xanthine oxidase. (F) High-resolution α-glucosidase inhibition profile of the ethyl acetate extract of the peel of A. ascalonicum with overlaid HPLC chromatogram at 254 nm. Peaks numbered 1–4 (corresponding to compounds 1–4) correlated with α-glucosidase inhibition and were analyzed by HPLC-HRMS-SPE-NMR. (G) Chemical structures of compounds 1–10 isolated from shallot screened for anoctamin inhibitory capacity. Compounds 2 and 9 exerted the highest anoctamin inhibitory potential (–83).

Figure 4

Protective effects of shallot extracts on liver. (A) Histological changes in the liver of representative rats of each group (H and E, ×100). (a) Normal control group; (b) hyperuricemic control group; (c) hyperuricemic + 5 mg/kg/day allopurinol; (d) hyperuricemic + 3.5 g/kg/day shallot juice; (e) hyperuricemic + 7.0 g/kg/day shallot juice: (f) hyperuricemic + 10.5 g/kg/day onion juice (110). (B) Effect of aqueous crude extract of A. ascalonicum bulbs on ethanol-induced liver injury in mice. Groups of mice were administered with 50% (v/v) ethanol for 14 consecutive days followed by treatment with silymarin (10 mg/kg), and extracts (50, 100, and 200 mg/kg), by oral gavage once a day for 7 consecutive days. Liver enzyme activities namely AST, ALT, GGT, and ALP were measured. Normal mice were given only DW and acted as healthy control (125). (C) Histopathology of liver cell degeneration in rat K-treated. (1) Normal liver cells. (2) The degenerated liver cells are seen to have swollen so that the cavity looks wider (97). (D) Kidney sections from vehicle (A) and shallot extract (B) treated groups, showing essentially normal tubules. CsA treated group (C) showing severe vascular and hydropic degenerative changes. Intracytoplasmic vacuoles (arrow) are present in most of the affected proximal tubular cells. Pyknotic nuclei (arrowhead) and coagulative necrotic cells (asterisk) are evident. Necrotic tubules with dystrophic calcification (double arrow) are observed mainly on the cortico-medullary transitional zone. CsA plus shallot extract treated group (D) showing only multiple small intracytoplasmic vacuoles (111). (E) The melanin inhibitory effect of AA 20-4-40 on B16F10 cells. After treatment with AA 20-4-40 (0–10 mg/ml) for 48 h, melanin content and cell viability were measured. The percentage of melanin content was calculated relative to the control group. Arbutin was used as the positive control (109). (F) Microscopic view of excision wound healing and epidermal/dermal re-modeling in the pure petroleum gel (Group I), 10% Allium ascalonicum extract (Group II), 20% Allium ascalonicum extract (Group III), and Terramycin (Group IV) administered animals on days 8 and 14 (20).