Allium Flavonols: Health Benefits, Molecular Targets, and Bioavailability

Abstract

Allium species are revered worldwide as vegetables, condiments, and spices as well as the therapeutic agents in traditional medicine. The bioactive compounds in alliums mainly include organosulfur compounds, polyphenols, dietary fibers, and saponins. Flavonoids, particularly flavonols from alliums, have been demonstrated to have the antioxidant, anticancer, hypolipidemic, anti-diabetic, cardioprotective, neuroprotective, and antimicrobial activities. However, flavonols are mostly characterized from onions and have not been comprehensively reviewed across different species. This article therefore focuses on flavonol profiles from different Allium species, their health effects, underlying molecular mechanisms, and bioavailability. Intriguingly, the functional health effects of flavonols were mainly ascribed to their antioxidant and anti-inflammatory activities involving a cascade of multiple signaling pathways. Although the Allium-derived flavonols offer tremendous potential in preventing chronic disease risks, in-depth studies are needed to translate their clinical application.

Keywords: Allium; antioxidant effects; bioavailability; flavonols; health benefits; molecular targets.

Figure 1

Polyphenolic compounds in the genus Allium.

Figure 2

Chemical structure of the major representatives of flavonol aglycones in Allium spp.

Figure 3

Examples of some molecular targets of Allium-derived flavonols during a chronic disease condition. Blue line indicates activation; red line indicates inhibiton; black line indicates pathways. AMPK, AMP-activated protein kinase; AP-1, Activator protein-1; ERK, extracellular signal-regulated kinase; JNK, jun N-terminal kinase MAPK, mitogen-activated protein kinase; PI3, phosphatidylinositol 3-kinase; Akt, protein kinase B; ROS, reactive oxygen species; NF-κB, nuclear factor kappa-light-chain-enhancer of activated B cells; Nrf2, nuclear factor erythroid 2-related factor 2.

Figure 4

A simplified schematic representation of oral bioavailability of flavonols in humans. LPH, phlorizin lactase; COMT, catechol-O-methyl-transferases; SULT, sulfotransferases; UGT, uridine 5’-diphospho-glucuronosyl transferases.