High-altitude hemorrhagic shock induces myocardial immunosuppression and metabolic disorder in rats: integrative proteo-metabolomic analysis reveals the limitations in resuscitation with lactated Ringer's solution

To characterize the myocardial proteomic and metabolomic alterations induced by high-altitude exposure and hemorrhagic shock (HS) under hypobaric hypoxic conditions, and to evaluate the regulatory effects of early lactated Ringer's (LR) resuscitation on related molecular abnormalities, providing evidence for elucidating the mechanisms of myocardial injury in high-altitude HS and optimizing resuscitation strategies in such conditions.

Forty SPF-grade male SD rats (10 to 12 weeks old, weighing 180 to 220 g) were randomly divided into a normoxic control group (NC), a high-altitude sham group (Sham), a high-altitude uncontrolled HS (UHS) and a high-altitude HS with LR resuscitation group (LR1h), with 10 animals in each group. Hypobaric hypoxic condition was induced by rats placed in a hypobaric chamber to simulate an altitude of 5000 m for 48 h. After chamber exit, the rats received an injection of oleic acid via the tail vein for 0.5 h, followed by splenic artery transection to induce uncontrolled hemorrhage until the mean arterial pressure (MAP) decreased to 40 mmHg. Thus, a high-altitude HS model was established. After successful modeling, the UHS group received no resuscitation with continuous monitoring only, while the LR1h group received an infusion of LR solution via the femoral vein for 1 h resuscitation under hypobaric condition. At designated time points, heart tissues were collected for 4D-FastDIA quantitative proteomics (n=4) and untargeted metabolomics analysis (n=6). Principal component analysis (PCA), differential protein/metabolite screening, and gene ontology (GO) and kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses were performed to characterize myocardial molecular expression profiles under different treatment conditions.

High-altitude exposure effect (Sham vs NC): totally 229 differentially expressed proteins (DEPs) were identified (154 up-regulated and 75 down-regulated, P<0.05). Enrichment analyses showed up-regulation of immune and inflammatory response-related processes, and downregulation of cardiac contraction, mitochondrial gene expression, and protein synthesis. There were 633 differential metabolites identified (509 up-regulated and 124 down-regulated, VIP≥1, P<0.05), primarily enriched in fundamental metabolic pathways, such as lipid, terpenoid/polyketide, and amino acid metabolic pathways. HS shock effect (UHS vs Sham): A total of 193 DEPs were identified (42 up-regulated and 151 down-regulated, P<0.05), characterized by enhanced cholesterol and lipid metabolism, whereas global down-regulation of complement-coagulation cascades, lysosomal function, immune and inflammatory regulation, and multiple infection-related pathways. Among the 1100 identified differential metabolites, there were 267 up-regulated and 833 down-regulated (VIP≥1, P<0.05). The types of enriched pathways were generally consistent, but the overall number of enriched compounds was decreased, with more pronounced reductions in key metabolic axes, including lipid metabolism (from 31 to 20), terpenoid/polyketide metabolism (from 20 to 14), and amino acid metabolism (from 11 to 6). LR resuscitation effect (LR1h vs UHS): A total of 108 DEPs were identified (39 up-regulated and 69 down-regulated, P<0.05). Vesicular transport, autophagy, and renin-angiotensin system pathways were up-regulated, but complement-coagulation cascade, humoral immunity, inflammatory response, and multiple infection-and metabolism-related pathways remained down-regulated, along with suppression of oxygen transport processes. Totally 494 differential metabolites were identified (456 up-regulated and 38 down-regulated, VIP≥1, P<0.05). Enriched pathways remained concentrated in the above main metabolic routes, but the number of enriched compounds in these pathways further decreased compared with the shock state, including lipid metabolism (from 20 to 10), terpenoid/polyketide metabolism (from 14 to 12), and amino acid metabolism (from 6 to 0).

Under high-altitude hypobaric hypoxia, HS induces myocardial immune/coagulation suppression and metabolic disorder. Early resuscitation with LR solution fails to reverse these molecular alterations, indicating that simple crystalloid volume resuscitation is insufficient to protect the myocardium in high-altitude hemorrhagic shock.