A rinse or a drink? An exploration of blackcurrant juice-mediated MAO-B inhibition

This is a double-blind, placebo-controlled, cross-over design intervention study which aims to characterise temporal platelet monoamine oxidase-B (MAO-B) activity immediately following blackcurrant juice ingestion and oral rinsing. Furthermore, subjective changes in mood, blood glucose, and cognitive performance will be assessed following blackcurrant ingestion and oral rinse, and putative metabolites associated with MAO-B inhibition identified. Prospective participants who have passed the study’s inclusion/exclusion criteria will be asked to attend a familiarisation session where they will meet with the study’s trial coordinator. During this session, the study’s trial coordinator and the principal investigator will explain the logistics of the trial to them and introduce them to the visual analogue scales for mood and mental fatigue that they will be asked to complete to during their test sessions. Participants will also be instructed on how to complete the five cognitive tasks that will make up the cognitive battery that they will undergo during their test sessions. These tasks are word recall, digit vigilance, Stroop, rapid visual information processing and logical reasoning. This familiarisation session will last approximately 30 minutes. Participants will be given a list of foods (e.g. berry-derived foods, anthocyanin-rich foods) to abstain from consuming 24 hours before each trial day. Participants will be randomly allocated into one of the two intervention groups: oral rinse or ingested drink, at a ratio of 1:1. The participants will be randomly assigned the order in which they will receive the two treatments: blackcurrant and placebo, 1:1. The oral rinse treatment will be: (1) 225 mL water followed by mouth-rinsing with 25 mL blackcurrant solution for 1 minute and (2) 225 mL of water followed by mouth-rinsing with 25 mL placebo solution for 1 minute. The ingestion group will be: (1) 25 mL of blackcurrant solution followed by 225 mL of water and (2) 25 mL of placebo solution followed by 225 mL of water. On the first day of the allocated trial arm, participants will arrive at the research facility to complete a test session to assess the effects of their allocated intervention on their MAO-B activity, mood and cognitive function. A person trained in cannulation and venepuncture will insert a venous cannula into a peripheral vein of the arm of the participant to collect blood samples across multiple times points. Before each blood sample, the participant's mood, stress, anxiety and mental fatigue will be assessed using Bond-Lader and visual analogue scales (VAS). Approximately fifteen minutes after the first blood sample, participants will receive their allocated intervention. The intervention will be served in a small opaque white vessel. Seven blood samples will be collected (~10mL each) beginning on arrival and 2, 5, 10, 20, 60, 120-140 min post-intervention. Research staff will be present throughout the study period to ensure adherence to protocol. After the 60 min blood sample, participants will undergo the cognitive battery. After this battery, there will be a final mood assessment and a blood sample will be collected. Participants will be provided with snacks and allowed to leave the facility. Approximately one week after this first visit, participants will be scheduled to come into the research facility and complete the same trial as above, consuming the other intervention they did not consume in the first session.