Type B procyanidins, made from oligomers of catechins, are a class of polyphenols found abundantly in foods such as cocoa, apples, grape seeds, and red wine. Several studies have demonstrated the benefits of this micronutrient in reducing the risk of cardiovascular disease and stroke.
Type B procyanidins are also successful in controlling hypertension, dyslipidemia, and glucose intolerance. Studies attest to the physiological benefits of its intake on the central nervous system (CNS), i.e. an improvement in cognitive functions. These physiological changes follow a hormonal pattern – a phenomenon in which the peak benefits of a substance are achieved at mid-range doses, and become progressively less at lower and higher doses.
The dose-response relationship for most bioactive 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 seen. This U-shaped curve indicates hormones – an adaptive response, where a low dose of a harmful compound normally causes the body to resist its higher doses.
This means that exposure to low levels of harmful stimuli can lead to activation of stress-resistant pathways, resulting in increased repair and regeneration capabilities. In the case of type B procyanidins, several in vitro studies support their hormonal effects, but these results have not been demonstrated in vivo.
To address this knowledge gap, researchers from the Shibura Institute of Technology (SIT) in Japan, led by Professor Naomi Osakabe from the Department of Biological Sciences and Engineering, reviewed data from intervention trials that support hormonal responses to ingestion of type B procyanidins.
The team, consisting of Taiki Fushimi and Yasuyuki Fujii from the Graduate School of Engineering and Science (SIT), also conducted in vivo experiments to understand the potential links between procyanidin-type B hormonal responses and CNS neurotransmitter receptor activation. Their article was published in Nutrition limits.
The researchers noted that oral administration of a single dose of cocoa flavanols temporarily increased blood pressure and heart rate in mice. But hemodynamics did not change when the dose was increased or decreased. Administration of procyanidin-type B monomer and different oligomers gave similar results. According to Professor Osakabe, “These findings are consistent with results from intervention studies that followed a single intake of a procyanidin-rich B-type food, and support the U-shaped, or hormonal, dose-response theory of polyphenols.”
To observe whether the sympathetic nervous system (SNS) was involved in the hemodynamic changes induced by type B procyanidins, the team administered epinephrine blockers to test mice. This succeeded in reducing the temporary increase in heart rate caused by the optimal dose of cocoa flavanols.
A different type of blocker – an A1 blocker – inhibits transient rise in blood pressure. This suggests that the SNS, which control the action of adrenaline blockers, are responsible for the hemodynamic and metabolic changes induced by a single oral dose of type B procyanidin.
Next, the researchers ascertained why optimum doses, not higher doses, were responsible for the thermogenic and metabolic responses. They co-administered high-dose cocoa flavanols and yohimbine (α2 blockers) and observed a temporary but distinct increase in blood pressure in test animals. Similar observations were made using type B procyanidin oligomer and yohimbine.
Prof. Osakabe states that “Because α2-blockers are associated with the down-regulation of SNS, the reduced metabolic and thermoregulatory metabolites with high dose of B-type procyanidins seen in our study induced activation of endogenous α2 receptors. Thus, SNS inactivation may occur by high dose of B-type procyanidins. Type B procyanidins.
Previous studies have demonstrated the role of the gut axis in controlling responses related to hormonal stress. Activation of the hypothalamic-pituitary-adrenal (HPA) axis by optimal stress has a powerful effect on memory, cognition and stress tolerance. This article highlights how HPA activation occurs after a single dose of type B procyanidin, suggesting that stimulation with an oral dose of type B procyanidin may be a stress factor in mammals and cause SNS activation.
Hormesis and its stimulating biochemical pathways provide protection against various pathological and aging processes, enhancing our overall health and making us resilient in the face of future stress. Although the exact relationship between type B procyanidins and the central nervous system needs further research, the health benefits of foods rich in type B procyanidins remain undisputed.
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Naomi Osakabe et al, The hormonal response to B-type procyanidin ingestion involves stress-related neuromodulation across the gut-brain axis: preclinical and clinical observations, Frontiers in Nutrition (2022). DOI: 10.3389 / fnut.2022.969823
Presented by Shibura Institute of Technology
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