Bioactive Compounds and Biological Functions of Garlic (Allium sativum L.)

Abstract

Garlic (Allium sativum L.) is a widely consumed spice in the world. Garlic contains diverse bioactive compounds, such as allicin, alliin, diallyl sulfide, diallyl disulfide, diallyl trisulfide, ajoene, and S-allyl-cysteine. Substantial studies have shown that garlic and its bioactive constituents exhibit antioxidant, anti-inflammatory, antibacterial, antifungal, immunomodulatory, cardiovascular protective, anticancer, hepatoprotective, digestive system protective, anti-diabetic, anti-obesity, neuroprotective, and renal protective properties. In this review, the main bioactive compounds and important biological functions of garlic are summarized, highlighting and discussing the relevant mechanisms of actions. Overall, garlic is an excellent natural source of bioactive sulfur-containing compounds and has promising applications in the development of functional foods or nutraceuticals for the prevention and management of certain diseases.

Keywords: anticancer; antimicrobial; antioxidant; cardiovascular protection; garlic; health benefits; organic sulfides; phytochemicals.

Figure 1

The chemical structures of the main organosulfur compounds in garlic.

Figure 2

The mechanisms of the antihypertensive properties of garlic extract via increasing the production of nitric oxide (NO) in vascular smooth muscle cells. The l-arginine (L-Arg) in aged garlic extract (AGE) could be transformed into NO and L-citruline (L-Cit) mediated by nitric oxide synthase (NOS). Moreover, the nitrite in the fermented garlic extract (FGE) could be converted into NO in vivo by Bacillus subtilis. NO and atrial natriuretic peptide (ANP) activated particulate guanylyl cyclase (pGC) and soluble guanylyl cyclase (sGC), thus catalyzing the transform of guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP). The elevated cGMP activated PKG, and PKG decreased intracellular Ca²⁺ concentration by increasing intracytoplasmic Ca²⁺ transport into the sarcoplasmic reticulum through the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pathway, thereby preventing the release of Ca²⁺ from the sarcoplasmic reticulum to the cytoplasm, and stimulating the Ca²⁺-activated K⁺ (BK_Ca) channel on the cell membrane, as well as reducing the Ca²⁺ influx. As a result, the vascular smooth muscle relaxed, and the blood vessels dilated.

Figure 3

The mechanisms of garlic and its active compounds on the inhibition of the cell cycle in cancer cells. Garlic extract activated ataxia-telangiectasia mutated (ATM) and checkpoint kinase 2 (CHK2), and inhibited the phosphorylation of Cdc25C and Cdc2, which down-regulated cyclin B1 and up-regulating p21WAF1, thereby inhibiting the cell cycle in the G₂/M-phase. Aged garlic extract can down-regulate Cyclin B1 and Cyclin-dependent kinase 1 (CDK1) and block the cell cycle in the G₂/M-phase. Diallyl trisulfide and S-propargyl-l-cysteine can also block the cell cycle in the G₂/M-phase. Moreover, S-allyl-cysteine induced cell cycle arrest in the G₁/S-phase, and allicin induced cell cycle arrest during the S-phase.