Regulative Effect Of Aspartic Acid On Liver Injury And Muscle Protein Degradation Of Piglets After Lipopolysaccharide Challenge

These experiments were conducted to investigate the regulative role of aspartic acid (ASP) supplementation on liver injury and muscle protein degradation of piglets after lipopolysaccharide (LPS) challenge and its mechanisms.1. This experiment was conducted to investigate whether ASP could alleviate LPS-induced liver injury in piglets via modulation of toll-like receptor (TLR4) and nucleotide binding oligomerization domain protein (NOD) signaling pathways. Forty-eight weanling pigs were randomly assigned into4groups:(1) control (basal diet);(2) LPS (basal diet+LPS);(3)0.5%ASP (basal diet+0.5%ASP+LPS);(4)1.0%ASP (basal diet+1.0%ASP+LPS). On d20, the piglets in the LPS group,0.5%ASP group and1.0%ASP group were injected intraperitoneally with100μg/kg BW LPS, and the piglets in the control group were injected with the same dose of physiological saline. At4(early phase) and24h (late phase) following saline or LPS injection, blood and liver samples were obtained. The results showed that:(1)0.5%and1.0%ASP supplementation attenuated histological liver damage induced by LPS challenge at4or24h.(2)1.0%ASP attenuated the increase of serum alkaline phosphatise (AKP) and glutamyl transpeptidase activities induced by LPS challenge at4h.0.5%or1.0%ASP attenuated the increase of serum aspartate aminotransferase (AST) and AKP activities and the decrease of ALT/AST induced by LPS challenge at24h.(3)1.0%ASP attenuated the decrease of hepatic claudin-1protein expression induced by LPS challenge at24h.(4)0.5%and1.0%ASP attenuated the increase of mRNA expression of tumor necrosis factor-α (TNF-α), cyclooxygenase-2(COX-2) and heat shock protein70induced by LPS challenge at4h.1.0%ASP alleviated the decrease of mRNA expression of TNF-α and COX-2induced by LPS challenge at24h.(5)0.5%or1.0%ASP attenuated the increase of mRNA expression of liver TLR4, myeloid differentiation factor88, IL-1receptor-associated kinase1, TNF-a receptor-associated factor6, NOD1, N0D2, receptor-interacting serine/threonine-protein kinase2and nuclear factor-KB p65induced by LPS challenge at4h.0.5%or1.0%ASP attenuated the decrease of mRNA expression of TLR4, NOD1and NOD2induced by LPS challenge at24h. These results indicate that, at early and late phases of LPS challenge, ASP exerts opposite regulatory effects on hepatic pro-inflammatory cytokines via TLR4and NOD2signaling pathways, and improves liver integrity.2. This experiment was conducted to investigate whether ASP could alleviate LPS-induced muscle protein degradation in piglets via modulation of AMP-activated protein kinase (AMPK), Akt/forkhead box protein (FOXO), TLR4and NOD signaling pathways. Twenty-four weanling pigs were randomly assigned into4groups:(1) control (basal diet);(2) LPS (basal diet+LPS);(3)0.5%ASP (basal diet+0.5%ASP+LPS);(4)1.0%ASP (basal diet+1.0%ASP+LPS). On d19, the piglets in the LPS group,0.5%ASP group and1.0%ASP group were injected with100μg/kg BW LPS, and the piglets in the control group were injected with the same dose of physiological saline. At4h following saline or LPS injection, muscle samples were obtained. The results showed that:(1)0.5%ASP increased DNA and RNA concentrations in gastrocnemius muscles.1.0%ASP increased protein and RNA concentrations in gastrocnemius muscles, and increased RNA/DNA and protein/DNA in longissimus dorsi (LD) muscles (P<0.05).(2)1.0%ASP attenuated the increase of mRNA expression of muscle atrophy F-box and muscle RING fingle1(MuRF1) induced by LPS challenge in gastrocnemius muscles,0.5%and1.0%ASP attenuated the increase of mRNA expression of MuRFl induced by LPS challenge in LD muscles (P<0.05).(3)0.5%or1.0%ASP decreased pAMPKa/tAMPKa in gastrocnemius muscles, attenuated the decrease of pAkt/tAkt and pFOXO1/tFOXO1induced by LPS challenge in gastrocnemius or LD muscles, and decreased mRNA expression of FOXO4in LD muscles (P<0.05).(4) ASP did not attenuate the increase of mRNA expression of muscle TLR4signaling related genes induced by LPS challenge, and increased mRNA expression of cluster of differentiation14, MD2and LPS binding protein in LD muscles (P<0.05).(5)1.0%ASP increased mRNA expression of suppressor of cytokine signaling1(SOCS1) and toll interacting protein (Tollip) in gastrocnemius muscles, and RP105, SOCS1, Tollip and single Ig IL-1-related receptor in LD muscles (P<0.05). These results indicate ASP may suppress muscle protein degradation via regulation of AMPK and Akt/FOXO signalings.