PARIS, 8 oct. (EUROPA PRESSE) –
A study from the Shibaura Institute of Technology (Japan) shed light on how an optimal intake of electrophilic compounds such as procyanidins is related to the hormesis of hemodynamic and metabolic responses.
B-type procyanidins, made up of catechin oligomers, are a class of polyphenols found abundantly in foods such as cocoa, apples, grape seeds, and red wine.
Several studies have established the benefits of these micronutrients in reducing the risk of cardiovascular disease and stroke.
B-type procyanidins also help control hypertension, dyslipidemia, and glucose intolerance. Studies show the physiological benefits of their consumption on the central nervous system (CNS), in particular the improvement of cognitive functions.
These physiological changes follow a pattern of hormesis, a phenomenon in which the maximum benefits of a substance are achieved at medium doses, gradually decreasing at lower and lower doses.
The dose-response relationship of most bioactive compounds follows a monotonic pattern, in which a higher dose results in a greater response. However, in rare cases, a U-shaped dose-response curve is observed.
This U-shaped curve signifies hormesis, an adaptive response in which a low dose of a generally harmful compound induces the organism’s resistance to its higher doses.
This means that exposure to low levels of a harmful trigger can induce the activation of stress-resistant pathways, resulting in increased capacity for repair and regeneration. In the case of type B procyanidins, several “in vitro” studies confirm their horticultural effects, but these results have not been demonstrated in vivo.
This study, published in the scientific journal “Frontiers of Nutrition”, reviewed data from intervention trials supporting horticultural responses to ingestion of procyanidin type B.
The team also conducted in vivo experiments to understand possible links between hormetic responses to procyanidin type B and activation of CNS neurotransmitter receptors.
Researchers observed that a single oral administration of an optimal dose of cocoa flavanol temporarily increased blood pressure and heart rate in rats. But the hemodynamics did not change with increasing or decreasing the dose. Administration of procyanidin type B monomer and various oligomers gave similar results.
According to Professor Naomi Osakabe, “These results are consistent with those from single-dose intervention studies of procyanidin type B-rich foods, and support the U-shaped dose-response theory, or hormesis, of polyphenols”.
To observe whether the sympathetic nervous system (SNS) is involved in hemodynamic changes induced by type B procyanidins, the team administered adrenaline blockers to laboratory rats. This reduced the temporary increase in heart rate induced by the optimal dose of cocoa flavanol.
Another type of blocker inhibited the transient increase in blood pressure. This suggests that the SNS, which controls the action of adrenaline blockers, is responsible for the hemodynamic and metabolic changes induced by a single oral dose of type B procyanidin.
The researchers then checked why optimal doses, and not high doses, are responsible for thermogenic and metabolic responses. They co-administered a high dose of cocoa flavanol and yohimbine (an A2 blocker) and observed a temporary but noticeable increase in blood pressure in the test animals. Similar observations have been made with the use of procyanidin oligomer type B and yohimbine.
“Since α2-blockers are associated with downregulation of the SNS, the reduction in metabolic and thermogenic outcomes with a high dose of B-type procyanidins observed in our study may have induced activation of α2 autoreceptors. Thus, SNS deactivation can be induced by a high dose of B-type procyanidins,” Osakabe assumes.