Allium cepa: A Treasure of Bioactive Phytochemicals with Prospective Health Benefits

Table 1

An overview of recent in vivo and in vitro studies of Allium cepa based on its therapeutic efficacy.

Field of Study	Subject	Dosage	Outcome	Mechanism of Action	References
Antimicrobial effect (in vivo)	Broiler chicks	1.5–2.5 g	Population of E. coli in ileum was decreased at a rate of 2.5 g/kg feed, while the amount of Lactobacillus was increased	Onion may alter a microflora intestinal, which improves digestion and absorption of nutrients in the intestines	[56]
Antimicrobial effect (in vitro)	Escherichia coli bacterial strains	Powdered bulb onion	The strain tested had MIC = 93.8 ± 44.2 µg/mL and MBC = 312.5 ± 265 µg/mL showing that A. cepa had antibacterial effect to a certain extent	Destroys bacteria by using their most active extract forms, or combining them to achieve latent synergistic effects	[158]
	Food-borne bacterial strains	15.6–1000 μg/mL	All bacteria projected inhibition zone, but a greater inhibitory effect was observed for S. aureus (IZD = 6.90 ± 1.26)	n.m.	[58]
	Gram-positive and Gram-negative bacteria	n.m.	Methanolic extract of onion inhibits E. coli and S. aureus.	Flavonoids, phenolic compounds, quercetin inhibited the growth of Gram positive and Gram-negative bacteria	[45]
	Gastrointestinal tract pathogens	n.m.	100% aqueous extracts of green onion bulbs displayed maximum bacterial kill, and its kill rate is slightly higher than the kill rate by positive control for E. aerogenes	Flavonoids and phenolic compounds of green onion bulb destroy bacterial membrane and shows antibacterial activity	[60]
Antiplatelet activity (in vivo)	Sprague Dawley rats	6 µg/mL	Significant inhibition of aggregation of platelets	Flavones such as apigenin, chrysin, and phloretin inhibited aggregation of platelets	[87]
	Rats	5 μg/mL	Platelet aggregation was inhibited	Inhibition of aggregation-inducing molecules, thromboxane A2 (TXA2), and intracellular Ca^2+ by blocking TXA2 synthase (TXAS) and cyclooxygenase-1 (COX-1) activities	[159]
Antiplatelet activity (in vitro)	Two healthy nonsmoker donors	n.m.	The dose-response curves developed using different dosages of allium juice vs. the percentage of inhibition of aggregation are calculated for juice levels needed to reduce platelet aggregation by 50% (IC50)	Aglycone part did not take part in inhibiting platelet aggregation. The flavone part of flavonoids of A. cepa played the major role	[160]
Gallstone treatment (in vivo)	Sprague Dawley rats	7% (w/w) onion powder	Lowered ballooning, hepatic steatosis, and lobular inflammation	Quercetin decreases the levels of hepatic enzymes, serum lipids, steatosis, and inflammation through regulating the expressions of NF-kB, p65, Sirt1, and iNOS	[134]
Antiparasitic activity (in vitro)	Leishmania tarentolae and Trypanosoma brucei brucei	3–5 µg/mL	Zwiebelane in the onion extract killed both types of parasites efficiently	The forming of disulfide bonds between SH classes of essential redox compounds and secondary metabolites containing sulfur are inhibiting trypanothion reductases	[137]
Antidepressant activity (in vivo)	Albino Wistar mice	200 mg/kg/day	Immobilization stress substantially reduced	Reduce stress by its potential antioxidant mechanism	[144]
Anti-inflammatory (in vivo)	Wistar rats	35–140 mg/kg/day	Reduced the pulmonary inflammatory cells, such as eosinophil, neutrophil, and monocyte and overall WBC	Inhibited NF-κB cells which induce inflammation	[156]
	BV-2 microglial cells	50–500 mg/mL	Attenuated neuroinflammation	Onion increases iNOS expression at the protein levels and mRNA in LPS-stimulated BV-2 microglial cells, thus reducing proinflammatory cytokines IL-1-b, TNF-a, and IL-6	[155]
	Wistar rats	150 and 300 mg/kg	Reduced lymphocyte and eosinophil count in the blood and bronchoalveolar lavage fluid (BALF)	n.m.	[154]
Inflammatory responses (in vitro)	RAW 264.7 cells	100 mg/mL	LPS-induced inflammation	Dose-dependent reduction in IL-6, TNF-a, and IL-1-b secretion, as well as NO production	[4]
Neuroprotective activity (In vivo)	Swiss albino male mice	200 mg/kg/day	Reduced lipid peroxidation and nitrate/nitrite ratios, as well as increased GSH and catalase activities. The amount of AChE in the body was also decreased.	Quercetin, kaempferol, cycloartenol, phytosterols like lophenol, 24-ethyl cycloartenol, and 24-methyl lophenol have been found to inhibit transcription of genes like FAS, S14, transferrin, apolipoprotein CIII	[161]
	Mice	300 mg/kg	Protects mice from neuronal harm in I/R induced retinal injury.	Changes the expression of neurotrophic factor	[162]
Ashthma (in vivo)	Blomia tropicalis (a type of mite)	100–1000 mg/kg	Induced asthma	Reduced IL-4, IL-5, IL-13, and IgE levels	[163]
Inhibitory and stimulatory activity (in vivo)	Mice	10–200 g	Inhibitory effect on Th2 activity and stimulatory effect on Th1	Th2 cytokines, IL-4, IL-5, and IL-13, as well as IgE, were inhibited at 1000 µg/mL	[164]
Osteoclastogenesis (in vitro)	RAW264.7 cells	100–1000 μg/mL	Induced inflammatory conditions	Cepa inhibited the development of IL-6 and IL-1a while increasing the production of IL-3 and IL-4 and inhibiting the NF- κB pathway	[165]
In breast cancer (in vivo)	Female BALB/c mice	0.1 mL/100 g bw	Stimulatory effects on Th1 but inhibitory effects on Th2 activity	Induced decreases in IL-4 and rises in IFN-c levels and IFN-c/IL4 ratio (Th1/Th2 balance)	[166]
Allergic rhinitis (In vivo)	BALB/c mice	20–40 mL	Decreased allergic symptoms, Reduced eosinophil penetration of nasal turbinate mucosa, and OVA-specific IgE levels	Levels of IL-4, IL-5, IL-10, IL-13, and IFN-c decreased in groups treated with onion extract	[167]
Immunomodulatory property (in vitro)	BALB/c mice	3.5–15 μg/mL	Showed immunomodulatory properties	Inhibited the development of Th2 cytokines such as IL-4, IL-5, IL-13, and IgE	[164]
Immunoprotective effects (in vivo)	Wistar rats	1–100 intraperitoneal	Natural and cyclophosphamide-induced immunosuppression	TNF-a, IL-10, COX-2, IgG and IgA levels in serum were increased by and immune parameters such as myeloid cells (RBC, WBC, and hb), body weight, splenic index, and thymic index in the spleen and thymus were enhanced	[168]
Lung disorder (in vivo)	Wistar rats	0.175–0.7 mg/mL	WBC count were improved, but their lymphocytes were reduced ( to ).	A significant decrease in tracheal tolerance, neutrophil and eosinophil counts, but a significant increase in lymphocyte count ( to )	[169]
Hepatoprotective (in vivo)	Adult male albino rats	200–450 mg/kg	Decreased alanine aminotransferase and overall serum bilirubin levels in a dose-dependent way	Decrease in alanine levels. Paracetamol hepatotoxic rats’ aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and complete serum bilirubin (TSB).	[23]
Anti-cancer effect (in vitro)	Murine ovarian cancer model	20 mg/kg	Blocks tumor cell growth	Blocks the activation of M2 macrophages	[95]
Antidiabetic effect (in vivo)	Diabetic rats	Aqueous extract of onions (25 mg/kg) for 21 days	Reduced blood glucose level	Increased glucose uptake into soleus muscle	[101]
	Rats	200 mg/kg	Decrease in blood glucose level	Stimulate the formation of pancreatic β cells	[102]
	Rats	3 mL/100 g	Decrease in blood glucose level	n.m.	[100]
Antihypercholesterolemic effect (in vivo)	Sprague Dawley rats	4.5 g/kg body weight	Inhibited the formation of atherosclerosis	n.m.	[106]
	Mice	2% raw or heat processed onions with high cholesterol diet	Reduced the risk of CGS	Decrease cholesterol secretion in bile and increase bile acid excretion	[107]
Antioxidant effects (in vivo)	Broiler chicken	3 g/kg diet	Increased antioxidant enzyme activities	n.m.	[122]
Antiobesity effects (in vivo)	Rats	92.6 mg/kg bw/days	Weight gain reduced significantly compared to the rats who were only fed high fat diet	n.m.	[130]

MIC = minimum inhibitory concentration, MBC = minimum bactericidal concentration, IZD = inhibition zone diameter, n.m. = not mentioned, HDL = high density lipoprotein, LDL = low density lipoprotein, ACA = Allium cepa agglutinin, PROE = phenol-rich onion extract, CGS = cholesterol gallstone.