Effects of apples on cardiovascular disease risk factors and gut microbiota

Evidence suggests that apples or their bioactive components (polyphenols and/or fiber) may have beneficial effects on lipid metabolism and other markers of cardiovascular disease (CVD). However, further adequately powered randomized controlled trials are necessary to confirm this evidence. Moreover, it has been shown that proanthocyanidins, the highest polyphenolic class in apples, reach the colon almost intact where together with fiber they interact with the gut microbiota. Recently, gut microbiota profiles and their metabolic output have also been suggested to influence CVD risk. This thesis investigated the potential interaction between modulation of the gut microbiota and cardiometabolic benefit in response to daily apple consumption. An in vitro batch culture fermentation identified that Renetta Canada variety significantly increased bifidobacteria, Faecalibacterium prausnitzii, and influenced microbial production of short chain fatty acids and phenolic microbial metabolites. Renetta Canada was therefore chosen for a randomized, controlled, crossover, dietary intervention study to determine the effects of apple intake on circulating lipids, vascular function, other CVD risk indicators and gut microbiota composition and activity in healthy mildly hypercholesterolemic subjects. Volunteers (23 women, 17 men), with a mean BMI 25.2 kg/m2 and age 51 years, consumed 2 apples/day, or a sugar matched control apple beverage for 8 weeks separated by a 4-week washout period in a random order. Blood lipids, bile acids, endothelial and inflammatory biomarkers and microvascular reactivity using laser Doppler imaging with Iontophoresis were measured. Fecal microbial profiles were monitored by 16S rRNA gene ilium ina MiSeq sequencing (V3-V4 region) and targeted groups of important gut bacteria quantified using Fluorescence in Situ Hybridization (FISH). Putative polyphenol metabolites of apple intake were identified in urine using LC-HRMS based metabolomics approach. Apple intake decreased serum total cholesterol (P=O.OOB) and LDL cholesterol (P=O.016) and vascular cell adhesion molecule-1 (P=O.037) compared with the control beverage. Apples had no effect on vascular function or other markers of CVD. No changes were observed in gut microbiota measured by 16S rRNA sequencing but apple intake significantly decreased Enterobacteriaceae enumerated by FISH compared with the control beverage. Valerolactones, valeric and phenolic acids were identified as microbial polyphenol metabolites among the 33 urine biomarkers related to the apple intake. These data suggest that the daily consumption of 2 Renetta Canada apples may result in beneficial effects on cardiovascular health and modifies both microbiota community structure and metabolic output