Gut health and integrity has been associated to an effective nutrient uptake and is involved in the modulation of fish immune system and antioxidant status. A disruption in the fish intestinal permeability and homeostasis may result in reduced growth and feed efficiency, lower resistance to stressors and diseases, and overall poorer health status.
Soy saponin (SAP) has been shown to provoke mild to severe intestinal inflammatory processes in fish. This study aimed to assess this compound as a potential disruptor of intestinal permeability and homeostasis in gilthead seabream juveniles by evaluating the intestinal response to different doses of SAP at 48 and 72 h after intake. The expression of genes coding for antioxidant response (catalase – cat and glutathione peroxidase – gpx), paracellular permeability (occludin – ocl, claudin 12 – cldn12 and tight junction protein 2 – tjp2), and immune response (cyclooxygenase 2 – cox2 and immunoglobulin M – IgM) was evaluated to identify molecular markers linked to homeostatic disruption in the gut.
Gilthead seabream juveniles (body weight ± 152 g) were fed gelatine capsules by the “assisted-feeding” technique. Fish were fed either empty (CTRL) or capsules containing soy saponin at 125 mg (SAP1), 350 mg (SAP2) and 700 mg (SAP3). Eighteen fish per treatment were transferred to two 100 L cylindric-conical tanks and maintained at optimal conditions.
At 48 h, the intestine of three fish per treatment were sampled to evaluate histopathology parameters. Also, 48 and 72 h after intake, intestine from six fish per treatment were sampled for gene expression.
After 48 h, histology and gene expression analyses were not significantly different among treatments. However, 72 h after ingestion, fish from the SAP3 treatment presented a differential response revealed by principal component analysis (PCA), being the differential expression of gpx, tjp2 and cox2 the main loadings responsible for clustering SAP3 observations.
These results suggest that the oral administration of 700 mg of SAP may provoke a mild disruption of intestinal homeostasis in gilthead seabream after 72 h. Nevertheless, the administration of a higher dose of dietary SAP for a longer period is being evaluated to provoke an acute gut inflammatory reaction. This method will allow to assess the potential of functional feeds in fish intestinal recovery and health.
This work was funded through Project FICA, co-financed by COMPETE 2020, CRESC Algarve 2020, Portugal 2020 and the European Union through ERDF under reference ALG-01-0247-FEDER-047175. This study received Portuguese national funds from FCT – Foundation for Science and Technology through projects UIDB/04326/2020, UIDP/04326/2020 and LA/P/0101/2020 to CCMAR