Dietary supplementation with Aloe vera induces hepatic steatosis and oxidative stress together with a disruption of cellular signaling pathways and lipid metabolism related genes' expression in gilthead sea bream (Sparus aurata)

Abstract

This study aimed to assess the effects of dietary increasing concentrations of Aloe vera (AV) powder of 0.5%, 2.5% and 5% on the growth performance, hepatic oxidative status, histology, and lipid metabolism and cellular signaling pathways-related genes' expression in gilthead sea bream (Sparus aurata). The preliminary phytochemical analysis revealed the richness of the dried AV extract on total phenol content, total flavonoid content, and condensed tannins when compared to the lyophilized sample. The dried extract showed a good DPPH-radical scavenging activity and its profiling by HPLC-DAD-ESI-MS revealed the presence of anthraquinones namely aloin A, aloin B and their hydroxyl (7-hydroxyaloin A and 7-hydroxyaloin B) and methyl-hydroxy (8-O-methyl-7-hydroxyaloin A and 8-O-methyl-7-hydroxyaloin B) derivatives as well as aloeresin A and B. The AV supplementation in fish diet did not affect growth performance (WG, WGR, and SGR) and feed utilization (FI, FCR, FER), and HSI indexes. However, the hepatic insulin-like growth factors (IGF-I and II) levels were significantly enhanced. Genes' expression levels of enzymes or transcription factors involved in lipolysis (lpl, hsl, and atgl), beta-oxidation (pparα, hadh), fatty acid transporters (cd36, fabp11) and lxrα were significantly down-regulated by the two high concentrations of AV powder. In contrast, fatty acid synthase (fas), a key gene of lipogenesis was significantly up regulated by dietary AV 5% powder supplementation. The induction of fas together with the down-regulation of peroxisome proliferator-activated receptor (pparα) and hydroxyacyl-coenzyme A dehydrogenase (hadh) could explain the lipid accumulation resulting in hepatic steatosis, which was confirmed by histological analysis, since the diets at the two higher concentrations (AV 2.5% and AV 5%) induced a significant increase in the number and diameter of hepatic lipid vacuoles in a dose dependent manner. Moreover, the mRNA levels of protein kinase B named (akt), mammalian target of rapamycin (mtor) and extracellular regulated kinase (erk1/2) involved in cell survival and proliferation were decreased by all AV powder supplemented diets. AV 5% increased catalase and glutathione S transferase activities suggesting a cellular strategy to fight against reactive oxygen species (ROS) accumulation. In conclusion, dietary supplementation with AV 0.5% is recommended for gilthead sea bream feed formulation, as it stimulates the igf-i expression. However, higher levels of AV should be avoided as they might cause lipid metabolism disruption, oxidative stress and liver steatosis.