Hibiscus sabdari ff a 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 : 4

2.3. Hibiscus sabdari ff a L

Hibiscus sabdari ff a L. (Syn: Roselle, Rozelle, Indian sorrel, Sour tea and Karkade) has been used for several purposes in folk medicine. In India, Africa and Mexico, leaves or calyces are used to prepare infusions that are believed to exert choleretic, febrifugal, diuretic, and hypotensive effects (Da-Costa-Rocha et al., 2014).

The chemical composition of H. sabdari ff a extracts includes hibiscus acid, hibiscus acid glucosides, caffeoylquinic acids, flavonoids such as quercetin-3-rutinoside, kaempferol-3-O-rutinoside, myricetin, anthocyanins such as delphinidin-3-sambubioside and cyanidin-3-sambubioside ( Fig. 3 ) (Da-Costa-Rocha et al., 2014; Ramirez-Rodrigues et al., 2011).

H. sabdari ff a tea has been shown to be able to lower food intake, decrease lipogenesis, increase lipolysis, stimulate fatty acids β- oxidation and attenuate inflammatory responses and oxidative stress (Herranz-Lopez et al., 2017).

H. sabdari ff a extracts decrease BP in normotensive and hypertensive animals by several mechanisms (Mojiminiyi et al., 2007; Onyenekwe et al., 1999). A methanolic extract from H. sabdari ff a calyces reduces the rat aorta rings contractions induced by KCl and phenylephrine (Ajay et al., 2007), suggesting its ability to inhibit calcium influx. The relaxant effect of the hibiscus flower extract was also observed in guinea pig aorta and ileum, where it exerts a calcium antagonistic effect (Micucci et al., 2015). In addition, it was also demonstrated that the vasorelaxation was possibly mediated by the endothelium-derived nitric oxide-cGMP-relaxant pathway and by the inhibition of calciuminflux into vascular smooth muscle cells, as it was inhibited by removal of endothelium and by the presence of atropine, L-NAME or methylene blue (Ajay et al., 2007).

Another effect responsible for the hypotensive activity is ACE inhibition, which is due, at least in part, to delphinidin-3-sambubioside and cyanidin-3-O-sambubioside ( Fig. 3 ) (Ojeda et al., 2010).

In vivo experiments demonstrated that the oral administration of the water extract from H. sabdari ff a calyces to male albino Sprague–Dawley rats causes a diuretic effect (Alarcon-Alonso et al., 2012) probably related to quercetin. Polyphenol water extract, in fact, seems to inhibit ATPase activity (Mezesova et al., 2010) affecting the Na + /K + concentration gradient in nephron tubular segment epithelial cells. In addition, the diuretic- as well as natriuretic- and potassium sparing-effects of the extract seems to be due to H. sabdari ff a ability to downregulate aldosterone (Jimenez-Ferrer et al., 2012).

Interestingly, the hypotensive activity was observed also in humans (Nwachukwu et al., 2015). In particular, clinical studies demonstrated that the administration of H. sabdari ff a extracts to hypertensive patients reduces BP (Nwachukwu et al., 2015, 2017; Herrera-Arellano et al., 2004, 2007; McKay et al., 2010). In a double-blind placebo-controlled clinical trial, daily consumption of H. sabdari ff a L. calyx powder decreased systolic BP and serum triglycerides in metabolic syndrome patients (Asgary et al., 2016). In addition, the polyphenol content influences the course of obesity (Rodriguez-Perez et al., 2017). Moreover, Hibiscus sabdari ff a consumption was reported to improve renal function in a population study of Nigerians with mild to moderate hypertension (Nwachukwu et al., 2017).

The compounds contained in H. sabdari ff a extracts and individually studied for antihypertensive effects are caffeoylquinic acids, in particular the 5-caffeoyl regioisomer, and rutin previously mentioned as active constituents of M. alba leaves and leaf extracts. In addition, studies have been dedicated to hibiscus acid and garcinia acid, to the flavonoid myricetin and to the glucosides of the anthocyanins delphinidin and cyanidin ( Fig. 3 ). The two acids exert vasorelaxant action likely due to the inhibition of Ca 2+ influx via voltage-dependent Ca 2+ channels (Zheoat et al., 2019). Myricetin has been proved to significantly inhibit atherogenesis (Sasaki et al., 2018) and it could prevent the development of high blood pressure induced by a diet rich in fructose (Godse et al., 2010). Lastly, ACE inhibition and decreasing of its mRNA production have been demonstrated for the two antocyanins and quercetin (Ojeda et al., 2010; Parichatikanond et al., 2012).

Figures

Fig. 3. Chemical structure of the compounds contained in Hibiscus sabdariffa L. extracts whose vascular and blood pressure effects were investigated.