The proposed study will investigate how short-term supplementation with GP-SPI may modify the gut microbial community in healthy participants while monitoring liver and kidney function/health.
Significance:
Biochemical properties of the GP-SPI food ingredient are well-documented and GP-SPI and SPI supplements have been tested extensively in mice. The proposed study is a logical follow up to animal studies, which showed that compared to control mice fed a high-fat diet (HFD) supplemented with SPI alone, mice fed an isocaloric HFD supplemented with GP-SPI exhibited greater resistance to weight gain, adiposity, and glucose intolerance. These effects were accompanied by changes in murine gut microbiota composition, including increased abundance of the microbe Akkermansia muciniphila, associated with metabolic resilience. Similar gut microbiota changes were observed in lean mice fed low-fat diet (LFD) supplemented with GP-SPI.
The B-type proanthocyanidin (PAC) class of polyphenols contained in grape berries, especially skins and seeds, have been associated with health benefits; however, PACs are poorly absorbed and reach high concentration only in the colon raising questions about mechanism(s) of action. Prior studies showed that dietary PACs from grape and cranberry alter the gut microbiota in association with metabolic resilience. PACs are also biotransformed by gut bacteria to yield microbial metabolites (MMs) that may contribute to health benefits.
Research Design and Methods
Prospective participants will be recruited through flyers posted locally on Rutgers University campuses and sent to university email lists. Interested persons will be screened according to inclusion and exclusion criteria.
Enrolled subjects will begin the 17-day study.
Study Procedures
- Thirty subjects will be enrolled.
- Food List: Participants will maintain their usual diet except for a provided list of PAC-rich foods that they will be asked to abstain from for a 5-day wash-out period and during the 10-day intervention. The Food List is provided below. The goal is to have GP-SPI as the main/only source of PAC in the diet for the study period.
- Wash-out and SPI (Day -5 through -1): On day -5 (pre-baseline) before any supplementation, each subject will collect their fecal and urine sample. Each subject will then consume SPI twice a day (provided as pre-weighed packets of 20 g) during a 5-day wash-out period (days -5, -4, -3, -2, and -1). Subjects will be instructed to mix each packet of SPI in 250 mL of water or in a smoothie (recipe example below will be provided) using allowed foods as detailed in instructions and consume once in the morning before breakfast and once in the evening before dinner.
- Day 0: On the following day each subject will collect their baseline (day 0) stool and urine samples. They will have a blood sample drawn by a study nurse. Blood will be used for CMP test and prepared serum will be aliquoted and stored at -80 °C until processing for marker analysis and metabolomics. Analysis of day 0 samples should help isolate any effects due to SPI alone from subsequent samples collected during GP-SPI intervention. On day 0 subjects will drop off urine and stool samples at IFNH and collect GP-SPI packets. On Day 0 participants will also take a break from consuming SPI and will start GP-SPI supplementation on morning of Day 1.
- GP-SPI (Day 1 - 10): Each subject will receive twenty pre-weighed 20 g packets of GP-SPI. On day 1 subjects will be instructed to mix each packet of GP-SPI in 250 mL of water or in smoothie (recipe example will be provided, please see below) using allowed foods as detailed in instructions and consume the GP-SPI mix once in the morning before breakfast and once in the evening before dinner for 10 consecutive days.
- Subjects will be provided with a personal blender for smoothie preparation (value ~ $25) that they can keep.
- Digital food diary: Participants will be asked to take photos of all their food and drink (except water) including the study supplements with their personal mobile computing device (e.g. smart phone, iPad, or similar). Participants will be required to download the free mobile app WhatsApp to send photos with a brief description of the food items. Photos and food description may also be sent to an email address created for this study (food4microbes@sebs.rutgers.edu). The food diary must be kept over the 5-day SPI and wash-out period, day 0 (break day), the 10-day GP-SPI intervention period, and up until the final blood draw on day 11 (17 days total).
- Stool samples: Subjects will be provided with tubes containing 95% ethanol and/or tubes containing 50% glycerol (50% water) along with paper toilet accessories for easy self-collection of fecal samples; each participant will be instructed on use of stool collection materials. Fecal samples will be aliquoted and stored at -80 °C until extraction. Collection of fecal samples in 50% glycerol and immediate freezing will allow culturing of gut bacteria for in vitro experiments.
- Bristol stool scale form: Subjects will be provided with the Bristol stool scale (BSS) form and asked to complete it for stool samples they collect on days -5, 0, 2, 4, 6, 8, and 10 of the study. Stool consistency has been shown to strongly correlate with gut microbiota richness and composition, enterotypes, and bacterial growth rates. Subjects that report at least one bowel movement per day will be recruited for ease of compliance with study protocol. In addition, the BSS form contains an extra column to capture information about menstruation during time of sample collections as this variable could impact metabolite or bacteria profiles .
- Urine samples: Subjects will be provided with sterile collection containers for collection of urine samples on days 2, 4, 6, 8, 10 and asked to keep samples in 4 °C fridge until transport to the laboratory to maintain metabolite stability. Subjects will be asked to bring their samples to the laboratory as soon as possible, within 2-3 days of collection, for processing. Urine samples will be aliquoted and stored at -80 °C until processing for metabolomics studies.
- Blood sample: On day 11 subjects will have a final blood sample drawn. Blood will be used for CMP test and prepared serum will be aliquoted and stored at -80 °C until processing for marker analysis and metabolomics.
Samples will be used for a longitudinal, microbiome-wide association study (MWAS) to identify gut bacteria species/strains that are positively or negatively associated with GP-SPI supplementation. Metabolomics analysis will be performed on collected urine, fecal, and blood samples to identify/quantify known and unknown metabolites. Shotgun metagenomic sequencing will be performed on fecal samples to generate high quality draft genomes for species/strain level identification. These dynamic data sets will serve as input for the MWAS to correlate increasing/decreasing levels of gut bacterial species/strains to increasing/decreasing metabolites. These bacteria-metabolite associations will then be used to infer cause-effect relationships that can be further tested in vitro and in mouse models. We expect that successful completion of these studies will contribute to mechanistic explanations for how dietary polyphenols such as grape PACs alter the gut microbiota and resulting MM to promote metabolic health.