Allium sativum, L.

Micucci, M., Bolchi, C., Budriesi, R., Cevenini, M., Maroni, L., Capozza, S., Chiarini, A., Pallavicini, M. & Angeletti, A., 2020, Antihypertensive phytocomplexes of proven efficacy and well-established use: Mode of action and individual characterization of the active constituents, Phytochemistry (112222) 170, pp. 1-19 : 6-7

2.6. Allium sativum L

The use of Allium sativum L. (Garlic) is reported in several medical systems, including Egyptian, Greek and Indian traditions (Rivlin, 2001). Garlic-based preparations contain a large variety of phytochemicals including many organosulphides (alliin, allicin, S-allyl-cysteine, S-1- propenylcysteine, vinyldithianes and vinyldithiins, allixin, sulfides, such as diallyl-, methyl allyl-, and dipropyl mono-, di-, tri- and tetrasulfides), flavonoids, saponins and sapogenins, phenolic compounds, amides and proteins (Kopec et al., 2013; Lanzotti et al., 2014; Rekowska and Skupie ń, 2009). The hypotensive activity of garlic occurs, at least in part, through an endothelium-dependent mechanism, as it inhibits the hypertensive effect of N(ω)-nitro-L-arginine methyl ester (L-NAME) in normal and two kidney-one clip (2 K–1C) rats, and increases NO synthesis in in vivo and in vitro (Al-Qattan et al., 2006; Morihara et al., 2006). Fresh garlic extract exerts NO-dependent vasodilation (Ku et al., 2002) and fresh garlic homogenate inhibits angiotensin converting enzyme (ACE) and lowers BP in rats and guinea pigs (Asdaq and Inamdar, 2010). In addition, garlic and some related phytochemicals seem to modulate cellular sodium levels by inhibiting the activity of epithelial sodium channel (Krumm et al., 2012) and to augment sodium concentrations in urine in a kidney reperfusion injury model (Bagheri et al., 2011). It is also endowed of antihypertensive action in the 2 K–1C model of hypertension, which is partly mediated by the interaction between prostanoids and the Na + /H + exchanger isoforms 1 (Al-Qattan et al., 2003). Garlic extracts act also directly on vascular smooth muscle. Several garlic extracts and fractions, in fact, inhibit KCl and phenylephrine induced contractions in rats isolated aorta, suggesting calcium antagonistic and α- antagonistic properties (Ganado et al., 2004). A meta-analysis of randomized controlled trials showed that, respect to placebo, garlic is able significantly to decrease systolic and diastolic BP without any severe adverse effect (Xiong et al., 2015).

Allicin, S-allylcysteine, S-1-propenylcysteine, alliin, diallylsulfides and some dipeptides are the most studied garlic constituents ( Fig. 6 ). Allicin exerts NO-dependent vasodilation (Ku et al., 2002), shows the ability to suppress cholesterol biosynthesis and, by decomposition, it releases hydrogen sulphide, which lowers BP by relaxation of smoothmuscle cells (Borlinghaus et al., 2014). The above-mentioned inhibition of epithelial sodium channels by garlic has been imputed to allicin (Krumm et al., 2012). Allicin counteracts cardiovascular diseases in various ways and further efforts are necessary better to understand the molecular basis of its action. S-Allylcysteine was shown to exert ACE inhibitory activity and to lower BP in rats and guinea pigs (Asdaq and Inamdar, 2010). Recently, S-1-propenylcysteine, but not S-allylcysteine, was shown significantly to decrease systolic BP of spontaneously hypertensive rats (Ushijima et al., 2018). Garlic ingredients, such as alliin, allyl disulphide and diallyl trisulfide result in significant increase of human endothelial cell NO production (Mousa and Mousa, 2007). Lastly, seven dipeptides with ACE inhibitory properties were isolated from garlic aqueous extracts and tested for ACE inhibition, finding that Phe-Tyr was the most potent one (Suetsuna, 1998).

Figures

Fig. 6. The most studied garlic constituents.