Biological mechanisms
In vitro and in vivo studies focused on mechanism of action
have determined several potential mechanisms of the HS
extracts that may explain the hypotensive activity, including
(1) vasodilation mediated through endothelium-derived relaxant
pathways and inhibition of calciuminflux [9,57], (2) ACE
inhibition [9] by the stimulation of new vessel formation and a
reduction of myocardial mass [52] or anthocyanins competing
with the substrate for the active site [58], (3) decrease in blood
viscosity through cyclooxygenase inhibitory activity [44], and
(4) inhibition of adipocyte differentiation through the modulation
of PI3-K/Akt and ERK pathway [59].
Other potential mechanisms have been tested to explain
the positive impact of HS extract on cholesterol metabolism.
For example, cholesterol biosynthesis may be reduced by
inhibiting HMG-CoA reductase [42,60]. Decreases in LDL-C
may be the result of the inhibition of triacylglycerol synthesis
by hibiscus acid racemization [43]. The positive effects of the
extract in diabetic animal models may be partially the result
of the reduction in the expression of CTGF and RAGE [30].
Additionally, although not directly related to the reduction
in cholesterol but beneficial for improving cardiovascular
risk factors, HS may hinder atherosclerosis and improve
vasoreactivity through (1) impediment of the formation of
macrophage-derived foam cells [61] and/or (2) inhibition of
LDL-C oxidation due to antioxidant effects of the extract