The Changes Of IGF-1 System Function And Regulation Of High-Nitrogen Enteral Nutrition In A Rat Model Of Trauma-Hemorrhagic Shock Resuscitation

Background/Objective:Clinical observation demonstrates that when under severe stress, patients often appear the growth hormone resistance syndrome, the feature of which is the increased levels of serum growth hormone (GH) while accompanying with the decreased levels of insulin-like growth factor-1 (IGF-1). The derangement of GH-IGF-1 axis function indicates the damaged body protein anabolism, which may be a leading cause of severe muscle wasting in critical illness. The aim of this study was to establish a rat model of trauma-hemorrhagic shock resuscitation (T-HS) to simulate the clinical severe stress, and further to investigate the changes of IGF-1 system function and the impact on the muscle protein metabolism in T-HS injured rats.Methods:Male Sprague-Dawley rats were randomized into 2 groups:shame (n=9) and T-HS (n=11). Rats were underwent midline laparotomies (5 cm), and were bled to a target mean arterial pressure of 30-35 mmHg within 20 minutes and maintained for 45 minutes following resuscitation. Samples were collected to determine the serum levels of free IGF-1, insulin-like growth factor binding protein-3 (IGFBP-3), and IGFBP-1 by ELISA. Phosphorylations of mammalian target of rapamycin (mTOR) related protein anabolic signaling pathway and muscle 3-methylhistidine (3-MH) levels were also detected by western blot and HPLC respectively.Results:Rats serum levels of free IGF-1 and IGFBP-3 dramatically decreased after T-HS, accompanying with the significant increase of IGFBP-1. Phosphorylations of several downstream signaling molecules including protein kinase B (PKB/Akt), mTOR, and ribosomal protein S6 kinase 1 (S6K1) in T-HS group were significantly inhibited compared with shame group, indicating that the protein translation initiation after T-HS was suppressed. Muscle 3-MH levels in T-HS rats were also significantly higher than that observed in shame group, which demonstrated the aggravated protein catabolism.Conclusion:The disorder of skeletal muscle protein metabolism caused by IGF-1 system dysfunction may be an important factor leading to the muscle wasting following severe trauma.Background/Objective:The sustained decrease of circulating IGF-1 levels can be against the lean body mass maintenance in critical illness. Studies found that sufficient protein and energy intake were essential for the normal expression of IGF-1, and the amino acid composition in food also played a role in this process. The historical approach would have been to provide equivalent amounts of protein or amino acids in nutrition support, attempting to counteract the dramatic nitrogen loss in critically ill patients. We aimed to investigate whether the essential amino acid (EAA) enriched high-nitrogen enteral nutrition (EN) modulated the IGF-1 system and activated the mTOR anabolic signaling pathway in a T-HS rat model.Methods:Male Sprague-Dawley rats (n=90) were randomly assigned to 5 groups:(1) normal control (NC), (2) pair-fed (PF), (3) T-HS Control (T-HS/Ctr), (4) T-HS and standard EN (T-HS/SE), and (5) T-HS and EAA enriched high-nitrogen EN (T-HS/EAA). Six animals from each group were harvested on days 2,4, and 6 for serum, gastrocnemius, soleus, and extensor digitorum longus (EDL) samples collection. Body weight and muscle mass were recorded. We detected the serum levels of free IGF-1, IGFBP-1, IGFBP-3, insulin, and corticosterone by ELISA. Phosphorylations of Akt, mTOR, and S6K1 in gastrocnemius at day 6 were determined by western blot. The serum EAA and muscle 3-MH levels at day6 were detected using HPLC.Results:T-HS induced significant reductions in gastrocnemius and EDL masses. Gastrocnemius masses in T-HS/SE and T-HS/EAA groups were significantly higher than T-HS/Ctr group by day 2. By day 4, a significant increase in gastrocnemius mass was also observed in T-HS/EAA group compared with T-HS/SE group. For soleus, T-HS/EAA group exhibited a significant increase compared with T-HS/SE, T-HS/Ctr, and PF groups by day 6. The serum levels of IGF-1 and IGFBP-3 were dramatically decreased after T-HS, while the IGFBP-1 levels were markedly increased. Compared with T-HS/Ctr group, T-HS/SE and T-HS/EAA groups had a significant reduction of IGFBP-1 levels by day 2 and increase of free IGF-1 and IGFBP-3 levels by day 4. These changes were consistent with the concomitant elevation in serum insulin and reduction in corticosterone levels. Meanwhile,T-HS/EAA group presented 18% higher serum free IGF-1 levels following 3 days of nutrition support and 22% higher after 5 days compared with T-HS/SE group. The serum levels of IGFBP-3 in T-HS/EAA group also exhibited a 170% and 140% increase compared with T-HS/SE group by days 4 and 6 respectively. For mTOR signal pathway activation in gastrocnemius at day 6, phosphorylations of Akt, mTOR, and S6K1 were greatly suppressed in T-HS/Ctr group. Phospho-Akt,-mTOR, and-S6K1 levels in T-HS/EAA group, rather than T-HS/SE group, were significant higher than T-HS/Ctr group. In addition, the phosphorylations of mTOR and S6K1 in T-HS/EAA group were also higher than T-HS/SE group. Furthermore, pronounced increase of branched chain amino acid (BCAA) levels was detected in T-HS/EAA group compared with T-HS/Ctr group. And the serum levels of leucine and valine in T-HS/EAA group were even higher than T-HS/SE group. Muscle 3-MH concentrations in T-HS/EAA group were also reduced remarkably compared with T-HS/Ctr group.Conclusion:Our study demonstrated that EAA enriched high-nitrogen EN was in favor of the early recovery of IGF-1 system function and effectively activated the downstream anabolic signaling transduction in T-HS injured rats. This was beneficial for the muscle mass maintenance in severe stress state. These results provide valuable insight into the metabolic regulation stimulated by high-nitrogen nutrition support during the stress response to critical illness.