Endoplasmic reticulum stress and insulin resistance post-trauma: similarities to type 2 diabetes

Farnesysltransferase Inhibitor Prevents Burn Injury-Induced Metabolome Changes in Muscle

Burn injury remains a significant public health issue worldwide. Metabolic derangements are a major complication of burn injury and negatively affect the clinical outcomes of severely burned patients. These metabolic aberrations include muscle wasting, hypermetabolism, hyperglycemia, hyperlactatemia, insulin resistance, and mitochondrial dysfunction. However, little is known about the impact of burn injury on the metabolome profile in skeletal muscle. We have previously shown that farnesyltransferase inhibitor (FTI) reverses burn injury-induced insulin resistance, mitochondrial dysfunction, and the Warburg effect in mouse skeletal muscle. To evaluate metabolome composition, targeted quantitative analysis was performed using capillary electrophoresis mass spectrometry in mouse skeletal muscle. Principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), and hierarchical cluster analysis demonstrated that burn injury induced a global change in metabolome composition. FTI treatment almost completely prevented burn injury-induced alterations in metabolite levels. Pathway analysis revealed that the pathways most affected by burn injury were purine, glutathione, β-alanine, glycine, serine, and threonine metabolism. Burn injury induced a suppressed oxidized to reduced nicotinamide adenine dinucleotide (NAD⁺/NADH) ratio as well as oxidative stress and adenosine triphosphate (ATP) depletion, all of which were reversed by FTI. Moreover, our data raise the possibility that burn injury may lead to increased glutaminolysis and reductive carboxylation in mouse skeletal muscle.

Role of stilbenes against insulin resistance: A review

Insulin resistance (IR) is a state characterized by the inability of tissues to utilize blood glucose particularly liver, muscle, and adipose tissues resulting in hyperglycemia and hyperinsulinemia. A close relationship exists between IR and the development of type 2 diabetes (T2D). Therefore, therapeutic approaches to treat IR also improve T2D simultaneously. Scientific evidence has highlighted the major role of inflammatory cytokines, reactive oxygen species (ROS), environmental & genetic factors, and auto-immune disorders in the pathophysiology of IR. Among therapeutic remedies, nutraceuticals like polyphenols are being used widely to ameliorate IR due to their safer nature compared to pharmaceutics. Stilbenes are considered important metabolically active polyphenols currently under the limelight of research to cope with IR. In this review, efforts are made to elucidate cellular and subcellular mechanisms influenced by stilbenes including modulating insulin signaling cascade, correcting glucose transport pathways, lowering postprandial glucose levels, and protecting β-cell damage and its effects on the hyperactive immune system and proinflammatory cytokines to attenuate IR. Furthermore, future directions to further the research in stilbenes as a strong candidate against IR are included so that concrete recommendation for their use in humans is made.

Activation of ER stress signalling increases mortality after a major trauma

The endoplasmic reticulum (ER) adapts to stress by activating a signalling cascade known as the ER stress response. While ER stress signalling is a central component of the cellular defence against environmental insult, persistent activation is thought to contribute to the progression of various metabolic complications via loss of protein function and cell death. Despite its importance however, whether and how ER stress impacts morbidity and mortality in conditions of hypermetabolism remain unclear. In this study, we discovered that chronic ER stress response plays a role in mediating adverse outcomes that occur after major trauma. Using a murine model of thermal injury, we show that induction of ER stress with Tunicamycin not only increased mortality but also resulted in hepatic damage and hepatic steatosis. Importantly, post‐burn treatment with chaperone ER stress inhibitors attenuated hepatic ER stress and improved organ function following injury. Our study identifies ER stress as a potential hub of the signalling network affecting multiple aspects of metabolism after major trauma and as a novel potential molecular target to improve the clinical outcomes of severely burned patients.

Flavonoids and type 2 diabetes: Evidence of efficacy in clinical and animal studies and delivery strategies to enhance their therapeutic efficacy

Diabetes mellitus type 2 (T2DM) is a metabolic disorder develops due to the overproduction of free radicals where oxidative stress could contribute it. Possible factors are defective insulin signals, glucose oxidation, and degradation of glycated proteins as well as alteration in glutathione metabolism which induced hyperglycemia. Previous studies revealed a link between T2DM with oxidative stress, inflammation and insulin resistance which are assumed to be regulated by numerous cellular networks such as NF-κB, PI3K/Akt, MAPK, GSK3 and PPARγ. Flavonoids are ubiquitously present in the nature and classified according to their chemical structures for example, flavonols, flavones, flavan-3-ols, anthocyanidins, flavanones, and isoflavones. Flavonoids indicate poor bioavailability which could be improved by employing various nano-delivery systems against the occurrences of T2DM. These bioactive compounds exert versatile anti-diabetic activities via modulating targeted cellular signaling networks, thereby, improving glucose metabolism, α -glycosidase, and glucose transport or aldose reductase by carbohydrate metabolic pathway in pancreatic β-cells, hepatocytes, adipocytes and skeletal myofibres. Moreover, anti-diabetic properties of flavonoids also encounter diabetic related complications. This review article has designed to shed light on the anti-diabetic potential of flavonoids, contribution of oxidative stress, evidence of efficacy in clinical, cellular and animal studies and nano-delivery approaches to enhance their therapeutic efficacy. This article might give some new insights for therapeutic intervention against T2DM in near future.

Increased proliferation of hepatic periportal ductal progenitor cells contributes to persistent hypermetabolism after trauma

Prolonged and persistent hypermetabolism and excessive inflammatory response after severe trauma is detrimental and associated with poor outcome. The predisposing pathology or signals mediating this complex response are essentially unknown. As the liver is the central organ mediating the systemic metabolic responses and considering that adult hepatic stem cells are on top of the hierarchy of cell differentiation and may pass epigenetic information to their progeny, we asked whether liver progenitor cells are activated, signal hypermetabolism upon post-traumatic cellular stress responses, and pass this to differentiated progeny. We generated Sox9CreERT2 : ROSA26 EYFP mice to lineage-trace the periportal ductal progenitor cells (PDPCs) and verify the fate of these cells post-burn. We observed increased proliferation of PDPCs and their progeny peaking around two weeks post-burn, concomitant with the hepatomegaly and the cellular stress responses. We then sorted out PDPCs, PDPC-derived hepatocytes and mature hepatocytes, compared their transcriptome and showed that PDPCs and their progeny present a significant up-regulation in signalling pathways associated with inflammation and metabolic activation, contributing to persistent hypermetabolic and hyper-inflammatory state. Furthermore, concomitant down-regulation of LXR signalling in PDPCs and their progeny implicates the therapeutic potential of early and short-term administration of LXR agonists in ameliorating such persistent hypermetabolism.

Obesity, Insulin Resistance, and Type 2 Diabetes: Associations and Therapeutic Implications

Obesity is a triggering factor for diabetes associated with insulin resistance. In individuals who are obese, higher amounts of non-esterified fatty acids, glycerol, hormones, and pro-inflammatory cytokines that could participate in the development of insulin resistance are released by adipose tissue. Besides, endoplasmic reticulum stress, adipose tissue hypoxia, oxidative stress, lipodystrophy, and genetic background have a role in insulin resistance. However, no effective drug therapy was developed for type 2 diabetes mellitus targeting these physiological factors. This is might be due to a lack of agreement on the comprehensive mechanism of insulin resistance. Therefore, this review assesses the cellular components of each physiologic and pathophysiologic factors that are involved in obesity associated insulin resistance, and may encourage further drug development in this field.

Aggregated and Hyperstable Damage-Associated Molecular Patterns Are Released During ER Stress to Modulate Immune Function

Chronic ER stress occurs when protein misfolding in the Endoplasmic reticulum (ER) lumen remains unresolved despite activation of the unfolded protein response. We have shown that traumatic injury such as a severe burn leads to chronic ER stress in vivo leading to systemic inflammation which can last for more than a year. The mechanisms linking chronic ER stress to systemic inflammatory responses are not clear. Here we show that induction of chronic ER stress leads to the release of known and novel damage-associated molecular patterns (DAMPs). The secreted DAMPs are aggregated and markedly protease resistant. ER stress-derived DAMPs activate dendritic cells (DCs) which are then capable of polarizing naïve T cells. Our findings indicate that induction of chronic ER stress may lead to the release of hyperstable DAMPs into the circulation resulting in persistent systemic inflammation and adverse outcomes.

Hepatic steatosis associated with decreased β-oxidation and mitochondrial function contributes to cell damage in obese mice after thermal injury

Severely burned patients who are morbidly obese have poor clinical outcomes with aggravated metabolic consequences, a higher incidence of multiple organ dysfunction/failure, and significantly increased morbidity and mortality. The underlying mechanisms of these adverse outcomes are essentially unknown. Since the liver is one of the central metabolic organs, we hypothesized that thermal injury in obese patients leads to substantially increased lipolysis, hepatic fat infiltration, resulting in profound hepatic cellular and organellar alterations, consequently causing liver damage and severely augmented metabolic dysfunction. We tested this hypothesis using an obese mouse model subjected to a 20% total body surface area burn injury. C57BL/6 mice were randomly divided into low-fat diet (LFD) and high-fat diet (HFD) sham and burn groups (n = 6 per group) and fed for 16 weeks. 7 days after the thermal injury portal and cardiac blood were taken separately and liver tissue was collected for western blotting and immunohistochemical analysis. Gross examination of the liver showed apparent lipid infiltration in HFD fed and burned mice. We confirmed that augmented ER stress and inhibition of Akt-mTOR signaling dysregulated calcium homeostasis, contributed to the decrease of ER–mitochondria contact, and reduced mitochondrial β-oxidation in HFD fed and burned mice, leading to profound hepatic fat infiltration and substantial liver damage, hence increased morbidity and mortality. We conclude that obesity contributes to hepatic fat infiltration by suppressing β-oxidation, inducing cell damage and subsequent organ dysfunction after injury.

Natural products for the treatment of type 2 diabetes mellitus: Pharmacology and mechanisms

Epidemiological studies have implied that diabetes mellitus (DM) will become an epidemic accompany with metabolic and endocrine disorders worldwide. Most of DM patients are affected by type 2 diabetes mellitus (T2DM) with insulin resistance and insulin secretion defect. Generally, the strategies to treat T2DM are diet control, moderate exercise, hypoglycemic and lipid-lowing agents. Despite the therapeutic benefits for the treatment of T2DM, most of the drugs can produce some undesirable side effects. Considering the pathogenesis of T2DM, natural products (NPs) have become the important resources of bioactive agents for anti-T2DM drug discovery. Recently, more and more natural components have been elucidated to possess anti-T2DM properties, and many efforts have been carried out to elucidate the possible mechanisms. The aim of this paper was to overview the activities and underlying mechanisms of NPs against T2DM. Developments of anti-T2DM agents will be greatly promoted with the increasing comprehensions of NPs for their multiple regulating effects on various targets and signal pathways.

The bioenergetics of inflammation: insights into obesity and type 2 diabetes

Diabetes mellitus is one of the most common chronic metabolic disorders worldwide, and its incidence in Asian countries is alarmingly high. Type 2 diabetes (T2DM) is closely associated with obesity, and the staggering rise in obesity is one of the primary factors related to the increased frequency of T2DM. Low-grade chronic inflammation is also accepted as an integral metabolic adaption in obesity and T2DM, and is believed to be a major player in the onset of insulin resistance. However, the exact mechanism(s) that cause a persistent chronic low-grade infiltration of leukocytes into insulin-target tissues such as adipose, skeletal muscle and liver are not entirely known. Recent developments in the understanding of leukocyte metabolism have revealed that the inflammatory polarization of immune cells, and consequently their immunological function, are strongly connected to their metabolic profile. Therefore, it is hypothesized that dysfunctional immune cell metabolism is a central cellular mechanism that prevents the resolution of inflammation in chronic metabolic conditions such as that observed in obesity and T2DM. The purpose of this review is to explore the metabolic demands of different immune cell types, and identify the molecular switches that control immune cell metabolism and ultimately function. Understanding of these concepts may allow the development of interventions that can correct immune function and may possibly decrease chronic low-grade inflammation in humans suffering from obesity and T2DM. We also review the latest clinical techniques used to measure metabolic flux in primary leukocytes isolated from obese and T2DM patients.

Maternal high-fat diet intensifies the metabolic response to stress in male rat offspring

BACKGROUND

The mother's consumption of high-fat food can affect glucose metabolism and the hypothalamic-pituitary-adrenal axis responsiveness in the offspring and potentially affect the metabolic responses to stress as well. This study examines the effect of maternal high-fat diet on the expression of pancreatic glucose transporter 2 and the secretion of insulin in response to stress in offspring.

METHODS

Female rats were randomly divided into normal and high-fat diet groups and were fed in accordance with their given diets from pre-pregnancy to the end of lactation. The offspring were divided into control (NC and HFC) and stress (NS and HFS) groups based on their mothers' diet and exposure to stress in adulthood. After the two-week stress induction period was over, an intraperitoneal glucose tolerance test (IPGTT) was performed and plasma glucose and insulin levels were assessed. The pancreas was then removed for measuring insulin secretion from the isolated islets as well as glucose transporter 2 mRNA expression and protein levels.

RESULTS

According to the results obtained, plasma corticosterone concentrations increased significantly on days 1 and 14 of the stress induction period and were lower on the last day compared to on the first day. In both the NS and HFS groups, stress reduced plasma insulin concentration in the IPGTT without changing the plasma glucose concentration, suggesting an increased insulin sensitivity in the NS and HFS groups, although more markedly in the latter. Stress reduced insulin secretion (at high glucose concentrations) and increased glucose transporter 2 mRNA and protein expression, especially in the HFS group.

CONCLUSION

Mothers' high-fat diet appears to intensify the stress response by changing the programming of the neuroendocrine system in the offspring.

Burned Adults Develop Profound Glucose Intolerance

OBJECTIVES

Metabolic alterations after burn injury have been well described in children; however, in adult patients, glucose metabolism and insulin sensitivity are essentially unknown. We sought to characterize metabolic alterations and insulin resistance after burn injury and determine their magnitude and persistence at discharge.

DESIGN

Prospective, cohort study.

SETTING

Tertiary burn centre.

PATIENTS

Nondiabetic adults with an acute burn involving greater than or equal to 20% total body surface area.

INTERVENTIONS

An oral glucose tolerance test was administered at discharge.

MEASUREMENTS AND MAIN RESULTS

Glucose, insulin, and C-peptide levels were measured to derive surrogate measures of insulin resistance and β-cell function, including quantitative insulin sensitivity check index, homeostasis model assessment of β-cell function, homeostasis model assessment of insulin sensitivity, homeostasis model assessment of insulin resistance, and the composite whole-body insulin sensitivity index. Patients were grouped according to the degree of glucose tolerance: normal glucose tolerance, impaired fasting glucose/impaired glucose tolerance, or diabetes. Forty-five adults, 44 ± 15 years old and with 38% ± 14% total body surface area burned, underwent an oral glucose tolerance test at discharge. Median quantitative insulin sensitivity check index (0.348 [0.332-0.375]) and median homeostasis model assessment of insulin resistance (1.13 [0.69-1.45]) were abnormal, indicating insulin resistance and impaired insulin production at discharge. Two-thirds of patients (n = 28) met criteria for impaired fasting glucose/impaired glucose tolerance or diabetes.

CONCLUSIONS

We have demonstrated that burn-injured adults remain hyperglycemic, are insulin resistant, and express defects in insulin secretion at discharge. Patients with lower burn severity (total body surface area, 20-30%) express similar metabolic alterations as patients with larger burns (total body surface area, ≥ 30%). Glucose tolerance testing at discharge offers an opportunity for early identification of burn patients who may be at high risk of prediabetes and diabetes. Our findings demonstrated that two-thirds of burn patients had some degree of glucose intolerance. With this in mind, surveillance of glucose intolerance post discharge should be considered. As hyperglycemia and insulin resistance are associated with poor outcomes, studies should focus on how long these profound alterations persist.

Alternative Mechanism for White Adipose Tissue Lipolysis after Thermal Injury

Extensively burned patients often suffer from sepsis, a complication that enhances postburn hypermetabolism and contributes to increased incidence of multiple organ failure, morbidity and mortality. Despite the clinical importance of burn sepsis, the molecular and cellular mechanisms of such infection-related metabolic derangements and organ dysfunction are still largely unknown. We recently found that upon endoplasmic reticulum (ER) stress, the white adipose tissue (WAT) interacts with the liver via inflammatory and metabolic signals leading to profound hepatic alterations, including hepatocyte apoptosis and hepatic fatty infiltration. We therefore hypothesized that burn plus infection causes an increase in lipolysis of WAT after major burn, partially through induction of ER stress, contributing to hyperlipidemia and profound hepatic lipid infiltration. We used a two-hit rat model of 60% total body surface area scald burn, followed by intraperitoneal (IP) injection of Pseudomonas Aeruginosa-derived lipopolysaccharide (LPS) 3 d postburn. One day later, animals were euthanized and liver and epididymal WAT (EWAT) samples were collected for gene expression, protein analysis and histological study of inflammasome activation, ER stress, apoptosis and lipid metabolism. Our results showed that burn plus LPS profoundly increased lipolysis in WAT associated with significantly increased hepatic lipid infiltration. Burn plus LPS augmented ER stress by upregulating CHOP and activating ATF6, inducing NLRP3 inflammasome activation and leading to increased apoptosis and lipolysis in WAT with a distinct enzymatic mechanism related to inhibition of AMPK signaling. In conclusion, burn sepsis causes profound alterations in WAT and liver that are associated with changes in organ function and structure.

Leukocyte infiltration and activation of the NLRP3 inflammasome in white adipose tissue following thermal injury

OBJECTIVES

Severe thermal injury is associated with extreme and prolonged inflammatory and hypermetabolic responses, resulting in significant catabolism that delays recovery or even leads to multiple organ failure and death. Burned patients exhibit many symptoms of stress-induced diabetes, including hyperglycemia, hyperinsulinemia, and hyperlipidemia. Recently, the nucleotide-binding domain, leucine-rich family (NLR), pyrin-containing 3 (NLRP3) inflammasome has received much attention as the sensor of endogenous "danger signals" and mediator of "sterile inflammation" in type II diabetes. Therefore, we investigated whether the NLRP3 inflammasome is activated in the adipose tissue of burned patients, as we hypothesize that, similar to the scenario observed in chronic diabetes, the cytokines produced by the inflammasome mediate insulin resistance and metabolic dysfunction.

DESIGN

Prospective cohort study.

SETTING

Ross Tilley Burn Centre & Sunnybrook Research Institute.

PATIENTS

We enrolled 76 patients with burn sizes ranging from 1% to 70% total body surface area. All severely burned patients exhibited burn-induced insulin resistance and hyperglycemia.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We examined the adipose tissue of control and burned patients and found, via flow cytometry and gene expression studies, increased infiltration of leukocytes-especially macrophages-and evidence of inflammasome priming and activation. Furthermore, we observed increased levels of interleukin-1β in the plasma of burned patients when compared to controls.

CONCLUSIONS

In summary, our study is the first to show activation of the inflammasome in burned humans, and our results provide impetus for further investigation of the role of the inflammasome in burn-induced hypermetabolism and, potentially, developing novel therapies targeting this protein complex for the treatment of stress-induced diabetes.

Endoplasmic Reticulum Stress and Related Pathological Processes

The endoplasmic reticulum (ER) plays a pivotal role in lipid and protein biosynthesis as well as calcium store regulation, which determines its essential role in cell function. Hypoxia, nutrient deprivation, perturbation of redox status and aberrant calcium regulation can all trigger the ER stress response, which is mediated through three main sensors, namely inositol requiring element-1 (IRE-1), protein kinase-like ER kinase (PERK) and activating transcription factor 6 (ATF6). This review explores the interaction of ER stress and ER stress-associated pathological processes, including inflammation, apoptosis, aberrant autophagy, mitochondrial dysfunction and hypoxic responses. In addition, the correlation of ER stress with lipid and calcium homeostasis and dysregulation, and its role in disease development is also presented. Improved understanding of ER stress and its cofactors in pathological processes may provide new perspective on disease development and control.

Clinical review: Glucose control in severely burned patients - current best practice

Tight glucose control changed the way many burn centers practice burn ICU care. However, after the initial impressive data, various clinical trials followed that showed mixed results. The objective of the present review is to discuss recent studies in the area of burn and critical care, and to identify the current best practice for current burn care providers. We reviewed relevant publications from PubMed and selected high-impact publications on tight glycemic control in various patient populations with a focus on burn patients. We conclude that in burns there seems to be a signal that insulin administration to a target range of 130 to 150 mg/dl is beneficial in terms of morbidity and mortality without the risk of hypoglycemia.

Fenofibrate does not affect burn-induced hepatic endoplasmic reticulum stress

BACKGROUND

Burn injury causes major metabolic derangements such as hypermetabolism, hyperlipidemia, and insulin resistance and is associated with liver damage, hepatomegaly, and hepatic endoplasmic reticulum (ER) stress. Although the physiological consequences of such derangements have been delineated, the underlying molecular mechanisms remain unknown. Previously, it was shown that fenofibrate improves patient outcome by attenuating postburn stress responses.

METHODS

Fenofibrate, a peroxisome proliferator-activated receptor alpha agonist, regulates liver lipid metabolism and has been used to treat hypertriglyceridemia and hypercholesterolemia for many years. The aim of the present study is to determine the effects of fenofibrate on burn-induced hepatic morphologic and metabolic changes. We randomized rats to sham, burn injury, and burn injury plus fenofibrate. Animals were sacrificed and livers were assessed at 24 or 48 h post burn.

RESULTS

Burn injury decreased albumin and increased alanine transaminase (P = 0.1 versus sham), indicating liver injury. Fenofibrate administration did not restore albumin or decrease alanine transaminase. In addition, ER stress was significantly increased after burn injury both with and without fenofibrate (P < 0.05 versus sham). Burn injury increased fatty acid metabolism gene expression (P < 0.05 versus sham), downstream of peroxisome proliferator-activated receptor alpha. Fenofibrate treatment increased fatty acid metabolism further, which reduced postburn hepatic steatosis (burn versus sham P < 0.05, burn + fenofibrate versus sham not significant).

CONCLUSIONS

Fenofibrate did not alleviate thermal injury-induced hepatic ER stress and dysfunction, but it reduced hepatic steatosis by modulating hepatic genes related to fat metabolism.

Endoplasmic reticulum stress and Parkinson's disease: the role of HRD1 in averting apoptosis in neurodegenerative disease

Endoplasmic reticulum (ER) stress has been known to be involved in the pathogenesis of various diseases, particularly neurodegenerative disorders such as Parkinson's disease (PD). We previously identified the human ubiquitin ligase HRD1 that is associated with protection against ER stress and its associated apoptosis. HRD1 promotes the ubiquitination and degradation of Parkin-associated endothelin receptor-like receptor (Pael-R), an ER stress inducer and causative factor of familial PD, thereby preventing Pael-R-induced neuronal cell death. Moreover, upregulation of HRD1 by the antiepileptic drug zonisamide suppresses 6-hydroxydopamine-induced neuronal cell death. We review recent progress in the studies on the mechanism of ER stress-induced neuronal death related to PD, particularly focusing on the involvement of HRD1 in the prevention of neuronal death as well as a potential therapeutic approach for PD based on the upregulation of HRD1.

Effects of glucocorticoids and exercise on pancreatic β-cell function and diabetes development

Peripheral insulin resistance and pancreatic β-cell dysfunction are hallmark characteristics of type 2 diabetes mellitus (T2DM). Several contributing factors have been proposed to promote these two defects in individuals with T2DM, including physical inactivity and chronic exposure to various psychosocial factors that increase the body's exposure to glucocorticoids, the main stress hormones in humans. Initially, β-cells have been shown to adapt to these stimuli, a phenomenon known as β-cell 'compensation'. However, long-term exposure to these physiologic and psychological stressors induces islet failure. Interestingly, glucocorticoids stimulate β-cell mass growth in parallel with promoting severe insulin resistance, the former being an important adaptive response to the latter. The direct relationship between glucocorticoids and β-cell dysfunction remains a controversial area of research. Elevations in circulating and/or tissue specific glucocorticoids have been associated with the development of obesity and T2DM in human and rodent models; however, the progression from insulin resistance to overt T2DM is highly disputed with respect to the in vivo and in vitro effects of glucocorticoids. Paradoxically, both intermittent physical stress and regular exercise alleviate insulin resistance and help to preserve β-cell mass, potentially by lowering glucocorticoid levels. Recent studies have begun to examine the mechanisms of intermittent and chronic glucocorticoid exposure and regular exercise in altering β-cell function. This review highlights recent discoveries on the physiological regulation of β-cells and diabetes development in conditions of elevated glucocorticoids, regular exercise and intermittent stress.