Dried Plums Modify Fecal Short Chain Fatty Acid Concentrations and Gene Expression in a Rat Model of Colon Carcinogenesis
Authors: Seidel Derek V , Hicks Kristen K , Taddeo Stella S , Azcarate‐Peril M Andrea , Carroll Raymond J , Turner Nancy D 
Published: November 2023

Diet is known to alter metabolism and composition of colon microbiota, which has considerable implications for disease prevention and treatment. We have previously shown that rats consuming a plum diet (PD) have significantly different abundances of major bacterial phyla throughout the colon, but most notably in the distal colon, compared to rats consuming a control diet (CD). Furthermore, PD rats had significantly reduced numbers of precancerous lesions (i.e. aberrant crypt foci) of colon cancer. Based on these observations, we hypothesized that consumption of PD would affect the levels of fecal short chain fatty acids (SCFA), and the expression of genes involved in host‐microbe interaction and cancer development. Male Sprague‐Dawley rats were provided either CD (n=25) or PD (5% of calories, n=26) for 3 wk before being given two injections of AOM (15 mg/kg BW) or saline, and sacrificed 8 wk later. The expression of toll‐like receptors 2 (TLR2) and 4 (TLR4) was greater in the distal colon of all rats versus proximal (all groups p<0.05). CD rats receiving AOM (CA) had greater proximal TLR2 expression versus PD+AOM (PA) rats (p=0.016); however, expression did not differ between either diet group in saline rats (CD+Saline, CS, and PD+Saline, PS). Expression of SLC5A8 (Na+ coupled) and SLC16A1 (H+ coupled) SCFA transporters was greater in the distal versus proximal colon of all groups (p<0.05), except for CA animals where the distal expression of SLC16A1 was not greater than proximal expression (p=0.644). Expression of inducible nitric oxide synthase (iNOS) was generally increased in the distal colon and in response to AOM treatment; however, PD reduced overall iNOS expression (main effect p‐value=0.0139). At baseline, following 3 weeks of experimental diet acclimation, there was no difference in total fecal SCFA between the CD and PD rats (p=0.1048); however, rats consuming the PD had lower fecal concentrations of isobutyrate (p<0.0001), isovalerate (p<0.0001), and valerate (p=0.0002) and tended to have lower acetate concentrations (p=0.1047). After the second AOM injection, fecal acetate in CA rats was greater than all other treatment groups (each comparison p<0.05) with PA rats maintaining comparable levels to CS and PS rats. Levels of butyrate remained comparable between all groups throughout the study (p>0.05); however, the proportion of butyrate, as a function of total SCFA, tended to be greater in PD rats throughout the study with significance being achieved at the 3 week post‐diet start and 48 h post‐AOM #2 time points (p=0.0476 and 0.014, respectively). These data demonstrate the efficacy of dried plums to affect expression of genes involved in host‐microbiota interactions and potentially the production and/or absorption of SCFA from the intestinal lumen, which may be part of the mechanisms whereby the plum diet reduced early colon cancer lesions.Support or Funding InformationSupported by California Dried Plum Board PN 12–20.