Many health benefits from foods rich in B-type procyanidin, such as chocolate and apples, when consumed in the right amounts

B-type procyanidins, which are composed of catechin oligomers, are a class of polyphenols that are abundant in foods such as cocoa, apples, grape seeds, and red wine. Several studies have shown the benefits of these micronutrients in reducing the risk of cardiovascular disease and stroke.

B-type procyanidins also successfully control hypertension, dyslipidemia, and glucose intolerance. Studies confirm the physiological benefits of their intake on the central nervous system (CNS), namely the improvement of cognitive functions. These physiological changes occur according to the pattern of hormesis, a phenomenon in which the peak benefits of a substance are achieved at medium doses and become smaller at lower and higher doses.

The dose-response relationship of most biologically active compounds follows a monotonic pattern, with a higher dose showing a greater response. However, in some exceptional cases, a U-shaped dose-response curve is observed. This U-shaped curve represents hormesis—an adaptive response in which a low dose of a normally harmful compound causes the body to resist higher doses of it.

This means that exposure to low levels of a noxious trigger can cause the activation of stress-resistant pathways, leading to a greater capacity for repair and regeneration. In the case of B-type procyanidins, several in vitro studies support their hormetic effects, but these results have not been demonstrated in vivo.

To solve this knowledge gapresearchers at Shibaura Institute of Technology (SIT), Japan, led by Professor Naomi Osakabe of the Department of Biological Sciences and Engineering, reviewed data from interventional trials supporting hormetic responses to B-type procyanidin.

The team, which includes Taiki Fushimi and Yasuyuki Fuji from the Graduate School of Engineering and Science (SIT), also performed in vivo experiments to understand possible links between hormetic responses to B-type procyanidin and activation of CNS neurotransmitter receptors. Their article is published in Nutritional limits.

The researchers noted that a single oral administration of an optimal dose of cocoa flavanol transiently increased blood pressure and heart rate in rats. But hemodynamics did not change when the dose was increased or decreased. Administration of B-type procyanidin monomer and various oligomers gave similar results. According to Professor Osakabe, “these results are consistent with those of interventional studies following a single meal rich in B-type procyanidin and support the U-shaped dose-response theory, or polyphenol hormesis.”

To observe whether the sympathetic nervous system (SNS) is involved in the hemodynamic changes caused by B-type procyanidins, the team administered epinephrine blockers to experimental rats. It successfully reduced the transient increase in heart rate induced by the optimal dose of cocoa flavonol.

Another type of blockers, a1-blockers, inhibited the temporary increase in blood pressure. This suggests that the SNS, which controls the effects of epinephrine blockers, is responsible for the hemodynamic and metabolic changes induced by a single oral dose of B-type procyanidin.

The researchers then determined why optimal doses, rather than high doses, were responsible for the thermogenic and metabolic responses. They simultaneously administered a high dose of cocoa flavonol and yohimbine (an α2 blocker) and noted a temporary but significant increase in blood pressure in test animals. Similar observations were made using the B-type procyanidin oligomer and yohimbine.

Professor Osakabe says that “because α2-blockers are associated with down-regulation of the SNS, the reduction in metabolic and thermogenic outcomes at high doses of B-type procyanidins observed in our study may have been caused by activation of α2 autoreceptors. Thus, SNS deactivation can be induced by high-dose B-type procyanidins.”

Previous studies have demonstrated a role for the gut-brain axis in controlling stress-related hormetic responses. Activation of the hypothalamic-pituitary-adrenal (HPA) axis by optimal stress has strong effects on memory, cognition, and stress resilience. This article highlights how HPA activation occurs after a single dose of B-type procyanidin, suggesting that stimulation with an oral dose of B-type procyanidin may be stressful to mammals and cause SNS activation.

Hormesis and its triggering biochemical pathways provide protection against various pathological and aging processes by enhancing our general health and makes us resilient to future stresses. Although the exact relationship between B-type procyanidins and the CNS requires more research, the health benefits of foods rich in B-type procyanidins remain indisputable.

Courtesy of Shibaura Institute of Technology