The Psychopharmacological Effects of Blackcurrant Phytochemicals in Humans

Watson, Anthony (2014) The Psychopharmacological Effects of Blackcurrant Phytochemicals in Humans. Doctoral thesis, Northumbria University.

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Abstract

Self-medication of plant based foods and food extracts which have ostensible therapeutic benefits has considerably increased within non-clinical populations over the last two decades. The overarching reason for this rise in consumption is to improve health and cognitive performance. One such group of foods are flavonoid-rich berry fruits. In the literature, there has been a recent rise in evidence showing that the consumption of flavonoid-rich berries can modulate aspects of behaviour, especially memory, in animal models and in aged humans. Physiological parameters such as blood-flow and glucose levels; and biological mechanisms such as monoamine oxidase (MAO) activity and nitric oxide (NO) synthesis, which have the potential to impact human behaviour, are also shown to be manipulated by flavonoid compounds. The dark purple fruits of the blackcurrant (Ribes nigrum) are naturally high in flavonoids, however no literature assessing cognitive effects of their consumption is available. The main focus of this thesis was to assess the impact of standardised flavonoid-rich blackcurrant extracts upon cognitive performance and mood in healthy human participants. Two extracts were examined within the thesis, a freeze dried powder extract fortified to contain 30% anthocyanins (DelcyanTM) and a fresh from frozen cold pressed juice extract (Blackadder cultivar, Plant and Food Research Ltd). Utilising a series of randomised, between subjects, double bind studies, measures of memory, attention, executive function and psychomotor performance were implemented during the course of the thesis at various post-dose time points. Throughout the investigational chapters of the thesis, physiological parameters and potential mechanisms driving any behavioural changes were measured. Such measures included measures of central and peripheral haemodynamics, MAO inhibition, monoaminergic tone, prolactin secretion and post-prandial glucose profiles.

Single doses of each of the blackcurrant extracts used in this thesis yielded positive results with effects of post-harvest extraction technique evident. Although no clear pattern of behavioural modulation was found after consumption of the blackcurrant extracts, there was some evidence to show increases in attention processes during cognitively demanding paradigms in young participants. No positive effects were evident upon any other cognitive paradigm. Physiological effects of acute blackcurrant supplementation included a modulation of post-prandial glucose profile and hemispheric dependent modulations of cerebral blood flow. Most strikingly, a pharmaceutical level inhibition of both monoamine oxidase isoforms and reductions in blood plasma prolactin were found. The findings of this thesis may have implications for enhancement of cognitive performance, attenuation in natural cognitive decline over the lifespan, and potentially, clinical applications in the treatment of neurological diseases.

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