The Effect of Burn Trauma on Lipid and Glucose Metabolism: Implications for Insulin Sensitivity

Blood glucose control in the burn intensive care unit: A narrative review of literature

Burn survivors undergoing complex glycemic derangements in the acute period after burn are at significantly increased risk of worse outcomes. Although most critical care investigations recommend intensive glycemic control to prevent morbidity and mortality, conflicting recommendations exist. To date, no literature review has studied outcomes associated with intensive glucose control in the burn intensive care unit (ICU) population. This review addresses this gap to improve practice guidelines and support further research regarding glycemic control. This is a narrative review of literature utilizing PubMed for articles published at any time. Inclusion criteria were English studies describing glucose management in ICU adult burn patients. Studies involving pediatric patients, non-human subjects, care non-ICU care, case reports, editorials, and position pieces were excluded. Our literature search identified 2154 articles. Full text review of 61 articles identified eight meeting inclusion criteria. Two studies reported mortality benefit of intensive glucose control ( mg/dL) compared to controls ( mg/dL), while two studies showed no mortality differences. Three studies reported reduced infectious complications such as pneumonia, urinary tract infection, sepsis, and bacteremia. A majority of the studies (6/8) reported higher risk for hypoglycemia with tight glucose control, but few reported instances of adverse sequela associated with hypoglycemia. Intensive glucose control may provide benefit to burn patients, but complications associated with hypoglycemia must be considered. This review recommends an individualized patient-centered approach factoring comorbidities, burn injury characteristics, and risk factors when determining whether to employ intensive glucose control.

Modulation of Burn Hypermetabolism in Preclinical Models

Severe burns elicit a state of physiological stress and increased metabolism to help the body compensate for the changes associated with the traumatic injury. However, this hypermetabolic state is associated with increased insulin resistance, cardiovascular dysfunction, skeletal muscle catabolism, impaired wound healing, and delayed recovery. Several interventions were attempted to modulate burn hypermetabolism, including nutritional support, early excision and grafting, and growth hormone application. However, burn hypermetabolism still imposes significant morbidity and mortality in burn patients. Due to the limitations of in vitro models, animal models are indispensable in burn research. Animal models provide researchers with invaluable tools to test the safety and efficacy of novel treatments or advance our knowledge of previously utilized agents. Several animal studies evaluated novel therapies to modulate burn hypermetabolism in the last few years, including recombinant human growth hormone, erythropoietin, acipimox, apelin, anti-interleukin-6 monoclonal antibody, and ghrelin therapies. Results from these studies are promising and may be effectively translated into human studies. In addition, other studies revisited drugs previously used in clinical practice, such as insulin and metformin, to further investigate their underlying mechanisms as modulators of burn hypermetabolism. This review aims to update burn experts with the novel therapies under investigation in burn hypermetabolism with a focus on applicability and translation. Furthermore, we aim to guide researchers in selecting the correct animal model for their experiments by providing a summary of the methodology and the rationale of the latest studies.

Associations of Traumatic Injury with Abnormal Glucose Metabolism: A Population-Based Prospective Cohort Study

Purpose

Empirical data on the association between traumatic injury and abnormal glucose metabolism risk is limited. This study aimed to investigate the association between traumatic injury and abnormal glucose metabolism.

Patients and Methods

This study included 153,162 participants in the Kailuan Study from 2006 to 2013. Participants with abnormal glucose metabolism at baseline were excluded. All participants were monitored every two years until December 31, 2019. During follow-up, 1915 subjects with a first traumatic injury (defined as a physical injury caused by an external force) were identified. For each subject with traumatic injury, one control subject was randomly selected and matched for age (± 3 years) and sex. A total of 3830 subjects were included in the final analysis. Cox proportional hazards models were used to examine the association between traumatic injury and the subsequent risk of abnormal glucose metabolism.

Results

During a median follow-up of 6.91 (3.57-9.41) years, 990 abnormal glucose metabolism events occurred. After adjustment for demographics, lifestyle behaviors, and traditional risk factors, those who had traumatic injury compared to controls were 32% more likely to develop any abnormal glucose metabolism (hazard ratio [HR] 1.32; 95% confidence interval [CI]1.16-1.49), including impaired fasting glucose (IFG) (HR 1.29; 95% CI 1.12-1.48) and diabetes (HR 1.37; 95% CI 1.10-1.70). The risks for abnormal glucose metabolism, IFG, and diabetes in subjects with moderate-severe injury were higher than in subjects with mild injury for the 1-year follow-up period, while the association was not significantly different by injury severity for the whole follow-up period.

Conclusion

Traumatic injury was associated with an increased risk of abnormal glucose metabolism. However, the risks of outcome events decreased as the follow-up period extended. Improved short- and long-term prevention and management strategies for controlling glucose are needed for individuals with traumatic injury.

Spinal Irisin Gene Delivery Attenuates Burn Injury-Induced Muscle Atrophy by Promoting Axonal Myelination and Innervation of Neuromuscular Junctions

Muscle loss and weakness after a burn injury are typically the consequences of neuronal dysregulation and metabolic change. Hypermetabolism has been noted to cause muscle atrophy. However, the mechanism underlying the development of burn-induced motor neuropathy and its contribution to muscle atrophy warrant elucidation. Current therapeutic interventions for burn-induced motor neuropathy demonstrate moderate efficacy and have side effects, which limit their usage. We previously used a third-degree burn injury rodent model and found that irisin-an exercise-induced myokine-exerts a protective effect against burn injury-induced sensory and motor neuropathy by attenuating neuronal damage in the spinal cord. In the current study, spinal irisin gene delivery was noted to attenuate burn injury-induced sciatic nerve demyelination and reduction of neuromuscular junction innervation. Spinal overexpression of irisin leads to myelination rehabilitation and muscular innervation through the modulation of brain-derived neurotrophic factor and glial-cell-line-derived neurotrophic factor expression along the sciatic nerve to the muscle tissues and thereby modulates the Akt/mTOR pathway and metabolic derangement and prevents muscle atrophy.

Effects of Different Ratios of Carbohydrate-Fat in Enteral Nutrition on Metabolic Pattern and Organ Damage in Burned Rats

(1) Background: Nutritional support is one of the most important cornerstones in the management of patients with severe burns, but the carbohydrate-to-fat ratios in burn nutrition therapy remain highly controversial. In this study, we aimed to discuss the effects of different ratios of carbohydrate–fat through enteral nutrition on the metabolic changes and organ damage in burned rats. (2) Methods: Twenty-four burned rats were randomly divided into 5%, 10%, 20% and 30% fat nutritional groups. REE and body weight were measured individually for each rat daily. Then, 75% of REE was given in the first week after burns, and the full dose was given in the second week. Glucose tolerance of the rats was measured on days 1, 3, 7, 10 and 14. Blood biochemistry analysis and organ damage analysis were performed after 7 and 14 days of nutritional therapy, and nuclear magnetic resonance (NMR) and insulin content analysis were performed after 14 days. (3) Results: NMR spectra showed significant differences of glucose, lipid and amino acid metabolic pathways. The energy expenditure increased, and body weight decreased significantly after burn injury, with larger change in the 20%, 5% and 30% fat groups, and minimal change in the 10% fat group. The obvious changes in the level of plasma protein, glucose, lipids and insulin, as well as the organ damage, were in the 30%, 20% and 5% fat groups. In relative terms, the 10% fat group showed the least variation and was closest to normal group. (4) Conclusion: Lower fat intake is beneficial to maintaining metabolic stability and lessening organ damage after burns, but percentage of fat supply should not be less than 10% in burned rats.

Integrated analysis of dysregulated microRNA and mRNA expression in intestinal epithelial cells following ethanol intoxication and burn injury

Gut barrier dysfunction is often implicated in pathology following alcohol intoxication and burn injury. MicroRNAs (miRNAs) are negative regulators of gene expression that play a central role in gut homeostasis, although their role after alcohol and burn injury is poorly understood. We performed an integrated analysis of miRNA and RNA sequencing data to identify a network of interactions within small intestinal epithelial cells (IECs) which could promote gut barrier disruption. Mice were gavaged with ~ 2.9 g/kg ethanol and four hours later given a ~ 12.5% TBSA full thickness scald injury. One day later, IECs were harvested and total RNA extracted for RNA-seq and miRNA-seq. RNA sequencing showed 712 differentially expressed genes (DEGs) (padj < 0.05) in IECs following alcohol and burn injury. Furthermore, miRNA sequencing revealed 17 differentially expressed miRNAs (DEMs) (padj < 0.1). Utilizing the miRNet, miRDB and TargetScan databases, we identified both validated and predicted miRNA gene targets. Integration of small RNA sequencing data with mRNA sequencing results identified correlated changes in miRNA and target expression. Upregulated miRNAs were associated with decreased proliferation (miR-98-3p and miR-381-3p) and cellular adhesion (miR-29a-3p, miR-429-3p and miR3535), while downregulated miRNAs were connected to upregulation of apoptosis (Let-7d-5p and miR-130b-5p) and metabolism (miR-674-3p and miR-185-5p). Overall, these findings suggest that alcohol and burn injury significantly alters the mRNA and miRNA expression profile of IECs and reveals numerous miRNA–mRNA interactions that regulate critical pathways for gut barrier function after alcohol and burn injury.