Dietary phytic acid damages the intestinal mucus barrier and structural integrity in the grass carp (Ctenopharyngodon idella).

Phytic acid (PA) is a common anti-nutritional factor found in plant-based protein sources. Our previous research demonstrated that dietary PA negatively affected the growth of grass carp. Intestinal health plays a vital role in the growth, development, and disease resistance of fish. Therefore, in order to comprehensively reveal the impact of PA on the intestines of fish, we further used the grass carp to investigate the impact of PA on the intestines of fish. The 540 grass carp (120.56 ± 0.51 g) were separated into 6 groups and provided with diets that included varying levels of PA (0, 0.8, 1.6, 2.4, 3.2, and 4.0 %) over 60 days. The findings suggested that a higher level of PA in diet, particularly at 3.2 %-4.0 %, led to a decrease in the goblet cell number as well as a reduced expression of mucin 2 and mucin 3 in the intestine. Concurrently, there was an increase in 8-hydroxy-2'-deoxyguanosine, active oxygen species, protein carbonyl, and malondialdehyde. These changes were accompanied by lower anti-superoxide anion activity, total antioxidant capacity, and anti-hydroxyl radical activity, as well as lower activity and gene expression of antioxidant enzymes. The DNA fragmentation in the intestine increased. Additionally, the bcl-2-associated X protein, Fas-ligand, apoptotic protease activating factor-1, cysteine aspartate protease (caspase) 8, caspase 9, and caspase 3 gene expression was increased, while the expression of B-cell lymphoma 2, myeloid cell leukemia-1b, and inhibitor of apoptosis protein was decreased. The gene expression of tight junction-associated molecules (such as claudin-b, -3c, and -7b and zonula occludens-2b) was decreased, whereas the expression of claudin-15b and myosin light chain kinase was increased. These data suggested that dietary PA may compromise the intestinal mucus barrier and the structural integrity of grass carp by inducing a goblet cell number decrease, causing oxidative damage, promoting apoptosis, and disrupting tight junctions. These results indicated that we must consider the potential threat posed by PA to the intestine of grass carp when utilizing plant-based protein sources.