Carbonylation of adipose proteins in obesity and insulin resistance: identification of adipocyte fatty acid-binding protein as a cellular target of 4-hydroxynonenal

Unresolved questions in the regulation of skeletal muscle insulin action by reactive oxygen species

Reactive oxygen species (ROS) are well-established signaling molecules implicated in a wide range of cellular processes, including both oxidative stress and intracellular redox signaling. In the context of insulin action within its target tissues, ROS have been reported to exert both positive and negative regulatory effects. However, the precise molecular mechanisms underlying this duality remain unclear. This Review examines the complex role of ROS in insulin action, with a particular focus on skeletal muscle. We aim to address three critical aspects: (a) the proposed intracellular pro-oxidative redox shift elicited by insulin, (b) the evidence supporting that redox-sensitive cysteine modifications impact insulin signaling and action, and (c) cellular mechanisms underlying how ROS can paradoxically act as both enhancers and inhibitors of insulin action. This Review underscores the urgent need for more systematic research to identify specific reactive species, redox targets, and the physiological significance of redox signaling in maintaining insulin action and metabolic health, with a particular emphasis on human skeletal muscle.

Lipid Peroxidation-Related Redox Signaling in Osteosarcoma

Oxidative stress and lipid peroxidation play important roles in numerous physiological and pathological processes, while the bioactive products of lipid peroxidation, lipid hydroperoxides and reactive aldehydes, act as important mediators of redox signaling in normal and malignant cells. Many types of cancer, including osteosarcoma, express altered redox signaling pathways. Such redox signaling pathways protect cancer cells from the cytotoxic effects of oxidative stress, thus supporting malignant transformation, and eventually from cytotoxic anticancer therapies associated with oxidative stress. In this review, we aim to explore the status of lipid peroxidation in osteosarcoma and highlight the involvement of lipid peroxidation products in redox signaling pathways, including the involvement of lipid peroxidation in osteosarcoma therapies.

Composition of fatty acids in a high-fat diet affects adipose tissue inflammation by inducing calreticulin on adipocytes and activating group 1 innate lymphoid cells

Obesity-induced adipose tissue inflammation plays a critical role in the development of metabolic diseases. For example, NK1.1+ group 1 innate lymphoid cells (G1-ILCs) in adipose tissues are activated in the early stages of inflammation in response to a high-fat diet (HFD). In this study, we examined whether the composition of fatty acids affected adipose inflammatory responses induced by an HFD. Mice were fed a stearic acid (C18:0)-rich HFD (HFD-S) or a linoleic acid (C18:2)-rich HFD (HFD-L). HFD-L-fed mice showed significant obesity compared with HFD-S-fed mice. Visceral and subcutaneous fat pads were enlarged and contained more NK1.1+KLRG1+ cells, indicating that G1-ILCs were activated in HFD-L-fed mice. We examined early changes in adipose tissues during the first week of HFD intake, and found that mice fed HFD-L showed increased levels of NK1.1+CD11b+KLRG1+ cells in adipose tissues. In adipose tissue culture, addition of 4-hydroxynonenal, the most frequent product of lipid peroxidation derived from unsaturated fatty acids, induced NK1.1+CD11b+CD27- cells. We found that calreticulin, a ligand for the NK activating receptor, was induced on the surface of adipocytes after exposure to 4-hydroxynonenal or a 1-week feeding with HFD-L. Thus, excess fatty acid intake and the activation of G1-ILCs initiate and/or modify adipose inflammation.

The Role of Glutathione and Its Precursors in Type 2 Diabetes

Type 2 diabetes (T2D) is a major worldwide health crisis affecting about 6.2% of the world's population. Alarmingly, about one in five children in the USA have prediabetes. Glutathione (GSH) and its precursors play a promising role in the prevention and management of type T2D. Oxidative stress (OxS) is a probable factor in both T2D initiation and progression. GSH is the major cytosolic water-soluble chemical antioxidant and emerging evidence supports its role in improving T2D outcomes. Dietary supplementation with N-acetyl-cysteine (NAC) and/or glycine (GLY), which are GSH precursors, has also been studied for possible beneficial effects on T2D. This review will focus on the underlying pathophysiological and molecular mechanisms linking GSH and its precursors with T2D and OxS. In addition to their traditional antioxidant roles, the in vivo effects of GSH/NAC/GLY supplements will be evaluated for their potential abilities to modulate the complex pro-oxidant pathophysiological factors (e.g., hyperglycemia) driving T2D progression. Positive feedback loops that amplify OxS over long time intervals are likely to result in irreversible T2D micro- and macro-vascular damage. Most clinical studies with GSH/NAC/GLY have focused on adults or the elderly. Future research with pediatric populations should be a high priority since early intervention is critical.

Metabolic Syndrome: A Narrative Review from the Oxidative Stress to the Management of Related Diseases

Metabolic syndrome (MS) is a growing disorder affecting thousands of people worldwide, especially in industrialised countries, increasing mortality. Oxidative stress, hyperglycaemia, insulin resistance, inflammation, dysbiosis, abdominal obesity, atherogenic dyslipidaemia and hypertension are important factors linked to MS clusters of different pathologies, such as diabesity, cardiovascular diseases and neurological disorders. All biochemical changes observed in MS, such as dysregulation in the glucose and lipid metabolism, immune response, endothelial cell function and intestinal microbiota, promote pathological bridges between metabolic syndrome, diabesity and cardiovascular and neurodegenerative disorders. This review aims to summarise metabolic syndrome's involvement in diabesity and highlight the link between MS and cardiovascular and neurological diseases. A better understanding of MS could promote a novel strategic approach to reduce MS comorbidities.

Carnosine supplementation and retinal oxidative parameters in a high-calorie diet rat model

BACKGROUND

To assess oxidative effects induced by a high-calorie diet on the retina of Wistar rats and test the antioxidative effects of carnosine supplementation.

METHODS

Wistar rats were randomly divided into the following groups: standard diet (SD), high-calorie diet (HcD), standard diet + carnosine (SD + Car), and high-calorie diet + carnosine (HcD + Car). The body weight, adiposity index, plasma glucose, total lipids, high-density lipoprotein (HDL), low-density lipoprotein (LDL), uric acid, creatinine, and triglycerides of the animals were evaluated. The retinas were analyzed for markers of oxidative stress. Hydrogen peroxide production was assessed by 2',7'-dichlorodihydrofluorescein diacetate (DCF) oxidation. The total glutathione (tGSH), total antioxidant capacity (TAC), protein carbonyl, and sulfhydryl groups of the antioxidant system were analyzed.

RESULTS

TAC levels increased in the retinas of the SD + Car group compared to the SD group (p < 0.05) and in the HcD + Car group compared to the HcD group (p < 0.05). The levels of GSH and the GSSH:GSSG ratio were increased in the HcD + Car group compared to the SD + Car group (p < 0.05). An increase in the retinal carbonyl content was observed in the HcD group compared to the SD group (p < 0.05) and in the HcD + Car group compared to the SD + Car group (p < 0.05). A high-calorie diet (HcD) was also associated with a decrease in retinal sulfhydryl-type levels compared to the SD group (p < 0.05).

CONCLUSION

The results suggest that feeding a high-calorie diet to rats can promote an increase in carbonyl content and a reduction in sulfhydryl groups in their retinas. The administration of carnosine was not effective in attenuating these oxidative markers.

TRIAL REGISTRATION

Animal Ethics Committee of Botucatu Medical School - Certificate number 1292/2019.

Overexpression of Glutathione S-Transferases in Human Diseases: Drug Targets and Therapeutic Implications

Glutathione S-transferases (GSTs) are a major class of phase II metabolic enzymes. Besides their essential role in detoxification, GSTs also exert diverse biological activities in the occurrence and development of various diseases. In the past few decades, much research interest has been paid to exploring the mechanisms of GST overexpression in tumor drug resistance. Correspondingly, many GST inhibitors have been developed and applied, solely or in combination with chemotherapeutic drugs, for the treatment of multi-drug resistant tumors. Moreover, novel roles of GSTs in other diseases, such as pulmonary fibrosis and neurodegenerative diseases, have been recognized in recent years, although the exact regulatory mechanisms remain to be elucidated. This review, firstly summarizes the roles of GSTs and their overexpression in the above-mentioned diseases with emphasis on the modulation of cell signaling pathways and protein functions. Secondly, specific GST inhibitors currently in pre-clinical development and in clinical stages are inventoried. Lastly, applications of GST inhibitors in targeting cell signaling pathways and intracellular biological processes are discussed, and the potential for disease treatment is prospected. Taken together, this review is expected to provide new insights into the interconnection between GST overexpression and human diseases, which may assist future drug discovery targeting GSTs.

Efficient scavenging of reactive carbonyl species in chloroplasts is required for light acclimation and fitness of plants

Reactive carbonyl species (RCS) derived from lipid peroxides can act as critical damage or signaling mediators downstream of reactive oxygen species by modifying target proteins. However, their biological effects and underlying mechanisms remain largely unknown in plants. Here, we have uncovered the mechanism by which the RCS 4-hydroxy-(E)-2-nonenal (HNE) participates in photosystem II (PSII) repair cycle of chloroplasts, a crucial process for maintaining PSII activity under high and changing light conditions. High Light Sensitive 1 (HLT1) is a potential NADPH-dependent reductase in chloroplasts. Deficiency of HLT1 had no impact on the growth of Arabidopsis plants under normal light conditions but increased sensitivity to high light, which resulted from a defective PSII repair cycle. In hlt1 plants, the accumulation of HNE-modified D1 subunit of PSII was observed, which did not affect D1 degradation but hampered the dimerization of repaired PSII monomers and reassembly of PSII supercomplexes on grana stacks. HLT1 is conserved in all photosynthetic organisms and has functions in overall growth and plant fitness in both Arabidopsis and rice under naturally challenging field conditions. Our work provides the mechanistic basis underlying RCS scavenging in light acclimation and suggests a potential strategy to improve plant productivity by manipulating RCS signaling in chloroplasts.

Fitness correlates of blubber oxidative stress and cellular defences in grey seals (Halichoerus grypus): support for the life-history-oxidative stress theory from an animal model of simultaneous lactation and fasting

Life-history-oxidative stress theory predicts that elevated energy costs during reproduction reduce allocation to defences and increase cellular stress, with fitness consequences, particularly when resources are limited. As capital breeders, grey seals are a natural system in which to test this theory. We investigated oxidative damage (malondialdehyde (MDA) concentration) and cellular defences (relative mRNA abundance of heat shock proteins (Hsps) and redox enzymes (REs)) in blubber of wild female grey seals during the lactation fast (n = 17) and summer foraging (n = 13). Transcript abundance of Hsc70 increased, and Nox4, a pro-oxidant enzyme, decreased throughout lactation. Foraging females had higher mRNA abundance of some Hsps and lower RE transcript abundance and MDA concentrations, suggesting they experienced lower oxidative stress than lactating mothers, which diverted resources into pup rearing at the expense of blubber tissue damage. Lactation duration and maternal mass loss rate were both positively related to pup weaning mass. Pups whose mothers had higher blubber glutathione-S-transferase (GST) expression at early lactation gained mass more slowly. Higher glutathione peroxidase (GPx) and lower catalase (CAT) were associated with longer lactation but reduced maternal transfer efficiency and lower pup weaning mass. Cellular stress, and the ability to mount effective cellular defences, could proscribe lactation strategy in grey seal mothers and thus affect pup survival probability. These data support the life-history-oxidative stress hypothesis in a capital breeding mammal and suggest lactation is a period of heightened vulnerability to environmental factors that exacerbate cellular stress. Fitness consequences of stress may thus be accentuated during periods of rapid environmental change.

The 4-Hydroxynonenal–Protein Adducts and Their Biological Relevance: Are Some Proteins Preferred Targets?

It is well known that oxidative stress and lipid peroxidation (LPO) play a role in physiology and pathology. The most studied LPO product with pleiotropic capabilities is 4-hydroxynonenal (4-HNE). It is considered as an important mediator of cellular signaling processes and a second messenger of reactive oxygen species. The effects of 4-HNE are mainly attributed to its adduction with proteins. Whereas the Michael adducts thus formed are preferred in an order of potency of cysteine > histidine > lysine over Schiff base formation, it is not known which proteins are the preferred targets for 4-HNE under what physiological or pathological conditions. In this review, we briefly discuss the methods used to identify 4-HNE–protein adducts, the progress of mass spectrometry in deciphering the specific protein targets, and their biological relevance, focusing on the role of 4-HNE protein adducts in the adaptive response through modulation of the NRF2/KEAP1 pathway and ferroptosis.

Transcriptome profile of skeletal muscle using different sources of dietary fatty acids in male pigs

Pork is of great importance in world trade and represents the largest source of fatty acids in the human diet. Lipid sources such as soybean oil (SOY), canola (CO), and fish oil (FO) are used in pig diets and influence blood parameters and the ratio of deposited fatty acids. In this study, the main objective was to evaluate changes in gene expression in porcine skeletal muscle tissue resulting from the dietary oil sources and to identify metabolic pathways and biological process networks through RNA-Seq. The addition of FO in the diet of pigs led to intramuscular lipid with a higher FA profile composition of C20:5 n-3, C22:6 n-3, and SFA (C16:0 and C18:0). Blood parameters for the FO group showed lower cholesterol and HDL content compared with CO and SOY groups. Skeletal muscle transcriptome analyses revealed 65 differentially expressed genes (DEG, FDR 10%) between CO vs SOY, and 32 DEG for CO vs FO, and 531 DEG for SOY vs FO comparison. Several genes, including AZGP1, PDE3B, APOE, PLIN1, and LIPS, were found to be down-regulated in the diet of the SOY group compared to the FO group. The enrichment analysis revealed DEG involved in lipid metabolism, metabolic diseases, and inflammation between the oil groups, with specific gene functions in each group and altered blood parameters. The results provide mechanisms to help us understand the behavior of genes according to fatty acids.

Hsp70.1 carbonylation induces lysosomal cell death for lifestyle-related diseases

Alzheimer's disease, type 2 diabetes, and non-alcoholic steatohepatitis (NASH) constitute increasingly prevalent disorders. Individuals with type 2 diabetes are well-known to be susceptible to Alzheimer's disease. Although the pathogenesis of each disorder is multifactorial and the causal relation remains poorly understood, reactive oxygen species (ROS)-induced lipid and protein oxidation conceivably plays a common role. Lipid peroxidation product was recently reported to be a key factor also for non-alcoholic steatohepatitis, because of inducing hepatocyte degeneration/death. Here, we focus on implication of the representative lipid-peroxidation product 'hydroxynonenal' for the cell degeneration/death of brain, pancreas, and liver. Since Hsp70.1 has dual roles as a chaperone and lysosomal membrane stabilizer, hydroxynonenal-mediated oxidative injury (carbonylation) of Hsp70.1 was highlighted. After intake of high-fat diets, oxidation of free fatty acids in mitochondria generates ROS which enhance oxidation of ω-6 polyunsaturated fatty acids (PUFA) involved within biomembranes and generate hydroxynonenal. In addition, hydroxynonenal is generated during cooking deep-fried foods with vegetable oils especially containing linoleic acids. These intrinsic and exogenous hydroxynonenal synergically causes an increase in its serum and organ levels to induce Hsp70.1 oxidation. As it is amphiphilic; being water-soluble but displays strong lipophilic characteristics, hydroxynonenal can diffuse within the cells and react with targets like senile and/or atheromatous plaques outside the cells. Hydroxynonenal can deepen and expand lysosomal injuries by facilitating 'calpain-mediated cleavage of the carbonylated Hsp70.1'. Despite the unique anatomical, physiological, and biochemical characteristics of each organ for its specific disease, there should be a common cascade of the cell degeneration/death which is caused by hydroxynonenal. This review aims to implicate hydroxynonenal-mediated Hsp70.1 carbonylation for lysosomal membrane permeabilization/rupture and the resultant cathepsin leakage for inducing cell degeneration/death. Given the tremendous number of worldwide people suffering various lifestyle-related diseases, it is valuable to consider how ω-6 PUFA-rich vegetable oils is implicated for the organ disorder.

Influence of Protein Carbonylation on Human Adipose Tissue Dysfunction in Obesity and Insulin Resistance

BACKGROUND

Obesity is characterized by adipose tissue dysregulation and predisposes individuals to insulin resistance and type 2 diabetes. At the molecular level, adipocyte dysfunction has been linked to obesity-triggered oxidative stress and protein carbonylation, considering protein carbonylation as a link between oxidative stress and metabolic dysfunction. The identification of specific carbonylated proteins in adipose tissue could provide novel biomarkers of oxidative damage related to metabolic status (i.e prediabetes). Thus, we aimed at characterizing the subcutaneous and omental human adipose tissue carbonylome in obesity-associated insulin resistance.

METHODS

2D-PAGE was used to identify carbonylated proteins, and clinical correlations studies and molecular biology approaches including intracellular trafficking, reactive oxygen species assay, and iron content were performed using in vitro models of insulin resistance.

RESULTS

The carbonylome of human adipose tissue included common (serotransferrin, vimentin, actin, and annexin A2) and depot-specific (carbonic anhydrase and α-crystallin B in the subcutaneous depot; and α-1-antitrypsin and tubulin in the omental depot) differences that point out the complexity of oxidative stress at the metabolic level, highlighting changes in carbonylated transferrin expression. Posterior studies using in vitro prediabetic model evidence alteration in transferrin receptor translocation, linked to the prediabetic environment. Finally, ligand-receptor molecular docking studies showed a reduced affinity for carbonylated transferrin binding to its receptor compared to wild-type transferrin, emphasizing the role of transferrin carbonylation in the link between oxidative stress and metabolic dysfunction.

CONCLUSIONS

The adipose tissue carbonylome contributes to understanding the molecular mechanism driving adipocyte dysfunction and identifies possible adipose tissue carbonylated targets in obesity-associated insulin resistance.

Protocol to detect smooth muscle actin-alpha and measure oxidative damage in neonatal mouse intestine

This protocol describes how to characterize α-Smooth muscle actin (αSMA) spatiotemporal expression during mouse small intestinal development. Specific tissue fixation preserves αSMA arrangement in low αSMA expressing cells that are conventionally undetectable under αSMA immunofluorescent stain due to inappropriate fixative-caused artificial actin depolymerization. Parallel analysis of αSMA carbonylation allows estimation of oxidative damage in gut muscular lineage. This approach improves the molecular specificity offered by commercialized kits that estimate total protein carbonyl level in cell lysates without protein specificity.

For complete details on the use and execution of this protocol, please refer to Hu et al. (2021).

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Optimal fixative improves αSMA immunofluorescent staining in the mouse intestine

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Improved cellular resolution of αSMA protein in whole mount immunofluorescent staining

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Semiquantitative measurement of oxidative damage on specific tissue proteins in vivo

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This protocol identifies the size distribution of total protein carbonyl in animal tissue

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Lipid Peroxidation in Obesity: Can Bariatric Surgery Help?

Obesity and chronic oxidative stress, often being associated with each other in a vicious circle, are important factors of chronic diseases. Although it was usually considered to accompany aging and wealth, global trends show the increase in obesity among children even in Third World countries. Being manifested by an imbalance between energy consumption and food intake, obesity is characterized by an excessive or abnormal fat accumulation, impaired redox homeostasis and metabolic changes often associated with the self-catalyzed lipid peroxidation generating 4-hydroxynonenal, pluripotent bioactive peroxidation product of polyunsaturated fatty acids. Conservative methods targeting obesity produced only modest and transient results in the treatment of morbid obesity. Therefore, in recent years, surgery, primarily bariatric, became an attractive treatment for morbid obesity. Since adipose tissue is well known as a stress organ with pronounced endocrine functions, surgery results in redox balance and metabolic improvement of the entire organism. The source of bioactive lipids and lipid-soluble antioxidants, and the complex pathophysiology of lipid peroxidation should thus be considered from the aspects of personalized and integrative biomedicine to treat obesity in an appropriate way.

Adipose Tissue Plasticity in Response to Pathophysiological Cues: A Connecting Link between Obesity and Its Associated Comorbidities

Adipose tissue (AT) is a remarkably plastic and active organ with functional pleiotropism and high remodeling capacity. Although the expansion of fat mass, by definition, represents the hallmark of obesity, the dysregulation of the adipose organ emerges as the forefront of the link between adiposity and its associated metabolic and cardiovascular complications. The dysfunctional fat displays distinct biological signatures, which include enlarged fat cells, low-grade inflammation, impaired redox homeostasis, and cellular senescence. While these events are orchestrated in a cell-type, context-dependent and temporal manner, the failure of the adipose precursor cells to form new adipocytes appears to be the main instigator of the adipose dysregulation, which, ultimately, poses a deleterious milieu either by promoting ectopic lipid overspill in non-adipose targets (i.e., lipotoxicity) or by inducing an altered secretion of different adipose-derived hormones (i.e., adipokines and lipokines). This “adipocentric view” extends the previous “expandability hypothesis”, which implies a reduced plasticity of the adipose organ at the nexus between unhealthy fat expansion and the development of obesity-associated comorbidities. In this review, we will briefly summarize the potential mechanisms by which adaptive changes to variations of energy balance may impair adipose plasticity and promote fat organ dysfunction. We will also highlight the conundrum with the perturbation of the adipose microenvironment and the development of cardio-metabolic complications by focusing on adipose lipoxidation, inflammation and cellular senescence as a novel triad orchestrating the conspiracy to adipose dysfunction. Finally, we discuss the scientific rationale for proposing adipose organ plasticity as a target to curb/prevent adiposity-linked cardio-metabolic complications.

Obesity Hinders the Protective Effect of Selenite Supplementation on Insulin Signaling

The intake of high-fat diets (HFDs) containing large amounts of saturated long-chain fatty acids leads to obesity, oxidative stress, inflammation, and insulin resistance. The trace element selenium, as a crucial part of antioxidative selenoproteins, can protect against the development of diet-induced insulin resistance in white adipose tissue (WAT) by increasing glutathione peroxidase 3 (GPx3) and insulin receptor (IR) expression. Whether selenite (Se) can attenuate insulin resistance in established lipotoxic and obese conditions is unclear. We confirm that GPX3 mRNA expression in adipose tissue correlates with BMI in humans. Cultivating 3T3-L1 pre-adipocytes in palmitate-containing medium followed by Se treatment attenuates insulin resistance with enhanced GPx3 and IR expression and adipocyte differentiation. However, feeding obese mice a selenium-enriched high-fat diet (SRHFD) only resulted in a modest increase in overall selenoprotein gene expression in WAT in mice with unaltered body weight development, glucose tolerance, and insulin resistance. While Se supplementation improved adipocyte morphology, it did not alter WAT insulin sensitivity. However, mice fed a SRHFD exhibited increased insulin content in the pancreas. Overall, while selenite protects against palmitate-induced insulin resistance in vitro, obesity impedes the effect of selenite on insulin action and adipose tissue metabolism in vivo.

Chemistry and Biochemistry Aspects of the 4-Hydroxy-2,3-trans-nonenal

4-hydroxy-2,3-trans-nonenal (C₉H₁₆O₂), also known as 4-hydroxy-2E-nonenal (C₉H₁₆O₂; HNE) is an α,β-unsaturated hydroxyalkenal. HNE is a major aldehyde, formed in the peroxidation process of ω-6 polyunsaturated fatty acids (ω-6 PUFAs), such as linoleic and arachidonic acid. HNE is not only harmful but also beneficial. In the 1980s, the HNE was regarded as a “toxic product of lipid peroxidation” and the “second toxic messenger of free radicals”. However, already at the beginning of the 21st century, HNE was perceived as a reliable marker of oxidative stress, growth modulating factor and signaling molecule. Many literature data also indicate that an elevated level of HNE in blood plasma and cells of the animal and human body is observed in the course of many diseases, including cancer. On the other hand, it is currently proven that cancer cells divert to apoptosis if they are exposed to supraphysiological levels of HNE in the cancer microenvironment. In this review, we briefly summarize the current knowledge about the biological properties of HNE.

The asymmetric Pitx2 gene regulates gut muscular-lacteal development and protects against fatty liver disease

Intestinal lacteals are essential lymphatic channels for absorption and transport of dietary lipids and drive the pathogenesis of debilitating metabolic diseases. However, organ-specific mechanisms linking lymphatic dysfunction to disease etiology remain largely unknown. In this study, we uncover an intestinal lymphatic program that is linked to the left-right (LR) asymmetric transcription factor Pitx2. We show that deletion of the asymmetric Pitx2 enhancer ASE alters normal lacteal development through the lacteal-associated contractile smooth muscle lineage. ASE deletion leads to abnormal muscle morphogenesis induced by oxidative stress, resulting in impaired lacteal extension and defective lymphatic system-dependent lipid transport. Surprisingly, activation of lymphatic system-independent trafficking directs dietary lipids from the gut directly to the liver, causing diet-induced fatty liver disease. Our study reveals the molecular mechanism linking gut lymphatic function to the earliest symmetry-breaking Pitx2 and highlights the important relationship between intestinal lymphangiogenesis and the gut-liver axis.

Branched chain amino acids-friend or foe in the control of energy substrate turnover and insulin sensitivity?

Branched chain amino acids (BCAA) and their derivatives are bioactive molecules with pleiotropic functions in the human body. Elevated fasting blood BCAA concentrations are considered as a metabolic hallmark of obesity, insulin resistance, dyslipidaemia, nonalcoholic fatty liver disease, type 2 diabetes and cardiovascular disease. However, since increased BCAA amount is observed both in metabolically healthy and obese subjects, a question whether BCAA are mechanistic drivers of insulin resistance and its morbidities or only markers of metabolic dysregulation, still remains open. The beneficial effects of BCAA on body weight and composition, aerobic capacity, insulin secretion and sensitivity demand high catabolic potential toward amino acids and/or adequate BCAA intake. On the opposite, BCAA-related inhibition of lipogenesis and lipolysis enhancement may preclude impairment in insulin sensitivity. Thereby, the following review addresses various strategies pertaining to the modulation of BCAA catabolism and the possible roles of BCAA in energy homeostasis. We also aim to elucidate mechanisms behind the heterogeneity of ramifications associated with BCAA modulation.

GSTM1 Gene, Diet, and Kidney Disease: Implication for Precision Medicine?: Recent Advances in Hypertension

In the United States, the prevalence of chronic kidney disease in adults is ≈14%. The mainstay of therapy for chronic kidney disease is angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, but many patients with chronic kidney disease still progress to end-stage kidney disease. Increased oxidative stress is a major molecular underpinning of chronic kidney disease progression. In humans, a common deletion variant of the glutathione-S-transferase μ-1 (GSTM1) gene, the GSTM1 null allele (GSTM1(0)), results in decreased GSTM1 enzymatic activity and is associated with higher levels of oxidative stress. GSTM1 belongs to the superfamily of GSTs that are phase II antioxidant enzymes and are regulated by Nrf2 (nuclear factor erythroid 2-related factor 2). Cruciferous vegetables in general, and broccoli in particular, are rich in glucoraphanin, a precursor of sulforaphane that has been shown to have protective effects against oxidative damage through the activation of Nrf2. This review will highlight recent human and animal studies implicating the role of GSTM1 deficiency in hypertension and kidney disease, and its impact on the effects of cruciferous vegetables on kidney injury and disease progression, illustrating the significance of gene and environment interaction and a potential for targeted precision medicine in the treatment of kidney disease.

4-Hydroxy-2-nonenal, a lipid peroxidation product, as a biomarker in diabetes and its complications: challenges and opportunities

Over 30 million Americans are diagnosed with diabetes and this number is only expected to increase. There are various causes that induce complications with diabetes, including oxidative stress. In oxidative stress, lipid peroxidation-derived reactive carbonyl species such as 4-hydroxy-2-nonenal (4-HNE) is shown to cause damage in organs that leads to diabetic complications. We provided evidence to show that 4-HNE or/and 4-HNE-protein adducts are elevated in various organ systems of diabetic patients and animal models. We then discussed the advantages and disadvantages of different methodologies used for the detection of 4-HNE in diabetic tissues. We also discussed how novel approaches such as electrochemistry and nanotechnology can be used for monitoring 4-HNE levels in biological systems in real-time. Thus, this review enlightens the involvement of 4-HNE in the pathogenesis of diabetes and its complications and efficient methods to identify it. Furthermore, the article presents that 4-HNE can be developed as a biomarker for end-organ damage in diabetes such as diabetic cardiac complications.

Histone Carbonylation Is a Redox-Regulated Epigenomic Mark That Accumulates with Obesity and Aging

Oxidative stress is a hallmark of metabolic disease, though the mechanisms that define this link are not fully understood. Irreversible modification of proteins by reactive lipid aldehydes (protein carbonylation) is a major consequence of oxidative stress in adipose tissue and the substrates and specificity of this modification are largely unexplored. Here we show that histones are avidly modified by 4-hydroxynonenal (4-HNE) in vitro and in vivo. Carbonylation of histones by 4-HNE increased with age in male flies and visceral fat depots of mice and was potentiated in genetic (ob/ob) and high-fat feeding models of obesity. Proteomic evaluation of in vitro 4-HNE- modified histones led to the identification of both Michael and Schiff base adducts. In contrast, mapping of sites in vivo from obese mice exclusively revealed Michael adducts. In total, we identified 11 sites of 4-hydroxy hexenal (4-HHE) and 10 sites of 4-HNE histone modification in visceral adipose tissue. In summary, these results characterize adipose histone carbonylation as a redox-linked epigenomic mark associated with metabolic disease and aging.

High-dose Nandrolone Decanoate induces oxidative stress and inflammation in retroperitoneal adipose tissue of male rats

The non-therapeutic use of the androgenic anabolic steroid Nandrolone Decanoate is popular due to its effects on physical performance and body composition, especially for its lipolytic and anabolic effects associated. However, high doses of such drugs are often associated with a series of pathologies related to unbalanced redox homeostasis, which, in turn, can be linked to inflammation. The oxidative stress onset could deregulate the secretion of cytokines, evidencing a dysfunctional adipocyte. Thus, the aim of this study was to investigate the effect of supraphysiological doses of Nandrolone Decanoate on redox homeostasis of retroperitoneal fatpad of male rats and its relationship with cytokines-based inflammatory signaling. Hydrogen peroxide production was assessed in the retroperitoneal fat pad of adult male rats which received either 10 mg kg of Nandrolone Decanoate or only a vehicle. Also, catalase, superoxide dismutase and glutathione peroxidase activities were measured, together with total reduced thiols and protein carbonylation, as well as IL-1β, TNF-α, and IL-6 local levels. High doses of Nandrolone Decanoate caused an increase in the hydrogen peroxide production, together with lower activities of the antioxidant enzymes and lower levels of total reduced thiol. There were also higher protein carbonylation and greater levels of IL-1β, TNF-α, and IL-6 in the treated group compared to control group. Therefore, it was possible to verify that high doses of Nandrolone Decanoate cause oxidative stress and induce higher inflammatory signaling in retroperitoneal fat pad of male rats.

The Role of microRNAs in Metabolic Syndrome-Related Oxidative Stress

Oxidative stress (OxS) is the cause and the consequence of metabolic syndrome (MetS), the incidence and economic burden of which is increasing each year. OxS triggers the dysregulation of signaling pathways associated with metabolism and epigenetics, including microRNAs, which are biomarkers of metabolic disorders. In this review, we aimed to summarize the current knowledge regarding the interplay between microRNAs and OxS in MetS and its components. We searched PubMed and Google Scholar to summarize the most relevant studies. Collected data suggested that different sources of OxS (e.g., hyperglycemia, insulin resistance (IR), hyperlipidemia, obesity, proinflammatory cytokines) change the expression of numerous microRNAs in organs involved in the regulation of glucose and lipid metabolism and endothelium. Dysregulated microRNAs either directly or indirectly affect the expression and/or activity of molecules of antioxidative signaling pathways (SIRT1, FOXOs, Keap1/Nrf2) along with effector enzymes (e.g., GPx-1, SOD1/2, HO-1), ROS producers (e.g., NOX4/5), as well as genes of numerous signaling pathways connected with inflammation, insulin sensitivity, and lipid metabolism, thus promoting the progression of metabolic imbalance. MicroRNAs appear to be important epigenetic modifiers in managing the delicate redox balance, mediating either pro- or antioxidant biological impacts. Summarizing, microRNAs may be promising therapeutic targets in ameliorating the repercussions of OxS in MetS.

Oxidatively Modified Proteins: Cause and Control of Diseases

Proteins succumb to numerous post-translational modifications (PTMs). These relate to enzymatic or non-enzymatic reactions taking place in either the intracellular or extracellular compartment. While intracellular oxidative changes are mainly due to redox stress, extracellular PTMs may be induced in an inflammatory micro milieu that is rich in reactive species. The increasing recognition of oxidative modifications as a causing agent or side-effect of pathophysiological states and diseases puts oxidative PTMS (oxPTMs) into the spotlight of inflammation research. Pathological hyper-modification of proteins can lead to accumulation, aggregation, cell stress, altered antigenic peptides, and damage-associated molecular pattern (DAMP)-like recognition by host immunity. Such processes are linked to cardiovascular disease and autoinflammation. At the same time, a detailed understanding of the mechanisms governing inflammatory responses to oxPTMs may capitalize on new therapeutic routes for enhancing adaptive immune responses as needed, for instance, in oncology. We here summarize some of the latest developments of oxPTMs in disease diagnosis and therapy. Potential target proteins and upcoming technologies, such as gas plasmas, are outlined for future research that may aid in identifying the molecular basis of immunogenic vs. tolerogenic oxPTMs.

The relevance of pathophysiological alterations in redox signaling of 4-hydroxynonenal for pharmacological therapies of major stress-associated diseases

Modern analytical methods combined with the modern concepts of redox signaling revealed 4-hydroxy-2-nonenal (4-HNE) as particular growth regulating factor involved in redox signaling under physiological and pathophysiological circumstances. In this review current knowledge of the relevance of 4-HNE as "the second messenger of reactive oxygen species" (ROS) in redox signaling of representative major stress-associated diseases is briefly summarized. The findings presented allow for 4-HNE to be considered not only as second messenger of ROS, but also as one of fundamental factors of the stress- and age-associated diseases. While standard, even modern concepts of molecular medicine and respective therapies in majority of these diseases target mostly the disease-specific symptoms. 4-HNE, especially its protein adducts, might appear to be the bioactive markers that would allow better monitoring of specific pathophysiological processes reflecting their complexity. Eventually that could help development of advanced integrative medicine approach for patients and the diseases they suffer from on the personalized basis implementing biomedical remedies that would optimize beneficial effects of ROS and 4-HNE to prevent the onset and progression of the illness, perhaps even providing the real cure.

Obesity ‑ a risk factor for increased COVID‑19 prevalence, severity and lethality (Review)

Coronaviruses (CoVs), enveloped positive-sense RNA viruses, are a group of viruses that cause infections in the human respiratory tract, which can be characterized clinically from mild to fatal. The severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is the virus responsible. The global spread of COVID‑19 can be described as the worst pandemic in humanity in the last century. To date, COVID‑19 has infected more than 3,000,000 people worldwide and killed more than 200,000 people. All age groups can be infected from the virus, but more serious symptoms that can possibly result in death are observed in older people and those with underlying medical conditions such as cardiovascular and pulmonary disease. Novel data report more severe symptoms and even a negative prognosis for the obese patients. A growing body of evidence connects obesity with COVID‑19 and a number of mechanisms from immune system activity attenuation to chronic inflammation are implicated. Lipid peroxidation creates reactive lipid aldehydes which in a patient with metabolic disorder and COVID‑19 will affect its prognosis. Finally, pregnancy‑associated obesity needs to be studied further in connection to COVID‑19 as this infection could pose high risk both to pregnant women and the fetus.

TL1A regulates adipose-resident innate lymphoid immune responses and enables diet-induced obesity in mice

BACKGROUND/OBJECTIVES

TL1A is a pro-inflammatory cytokine that is homologous to TNFα and connected with the development of several chronic inflammatory disorders. The preliminary results of this study indicated reduced fat accumulation in 9-month-old TL1A-deficient mice at steady state. Thus, the objective was to investigate whether TL1A-deficient mice are resistant to the development of high-fat (HF) diet-induced obesity and to investigate the impact on lymphocyte infiltration in adipose tissue.

METHODS

TL1A-deficient and TL1A-sufficient male BALB/cJ littermate mice were fed a 60% HF diet or a 10% low-fat control diet for 22 weeks. Mouse body composition and weight were monitored, and tissues were processed and evaluated by flow cytometry, qPCR, and histology.

RESULTS

In this study, the TL1A-deficient HF-diet-fed mice had reduced whole-body weight gain, which was directly explained by a corresponding fat mass reduction (average 37.2%), compared with that of their TL1A-sufficient littermates. Despite previous data showing marked changes in the gut microbial community, TL1A-deficient GF mice also displayed reduced adiposity. Furthermore, the TL1A-deficient mice were resistant to hepatic steatosis and were shown to have improved glucose tolerance, as determined by oral glucose tolerance test (OGTT), and greater insulin sensitivity. In the epididymal white adipose tissue (eWAT), TL1A deficiency in HF-diet-fed mice resulted in a reduced abundance of IL-18Ra⁺ type-1 ILCs and γδT cells as well as markedly reduced expression of the mitochondria-regulating genes Ucp1, Ucp2, Ucp3, and Prdm16. Finally, to investigate the link of TL1A to obesity in humans, we identified a noncoding polymorphism (rs4979453) close to the TL1A locus that is associated with waist circumference in men (p = 0.00096, n = 60586).

CONCLUSIONS

These findings indicate that TL1A plays an important role in regulating adipose tissue mass and that this role is independent of the gut microbiota. Furthermore, we show that TL1A regulates adipose-resident innate lymphocytes and mitochondria-mediated oxidative stress in eWAT.

The Impact of Oxidative Stress on Adipose Tissue Energy Balance

Overnutrition and sedentary activity reinforce the growing trend of worldwide obesity, insulin resistance, and type 2 diabetes. However, we have limited insight into how food intake generates sophisticated metabolic perturbations associated with obesity. Accumulation of mitochondrial oxidative stress contributes to the metabolic changes in obesity, but the mechanisms and significance are unclear. In white adipose tissue (WAT), mitochondrial oxidative stress, and the generation of reactive oxygen species (ROS) impact the endocrine and metabolic function of fat cells. The central role of mitochondria in nutrient handling suggests pharmacological targeting of pathological oxidative stress likely improves the metabolic profile of obesity. This review will summarize the critical pathogenic mechanisms of obesity-driven oxidative stress in WAT.

A new class of protein biomarkers based on subcellular distribution: application to a mouse liver cancer model

To-date, most proteomic studies aimed at discovering tissue-based cancer biomarkers have compared the quantity of selected proteins between case and control groups. However, proteins generally function in association with other proteins to form modules localized in particular subcellular compartments in specialized cell types and tissues. Sub-cellular mislocalization of proteins has in fact been detected as a key feature in a variety of cancer cells. Here, we describe a strategy for tissue-biomarker detection based on a mitochondrial fold enrichment (mtFE) score, which is sensitive to protein abundance changes as well as changes in subcellular distribution between mitochondria and cytosol. The mtFE score integrates protein abundance data from total cellular lysates and mitochondria-enriched fractions, and provides novel information for the classification of cancer samples that is not necessarily apparent from conventional abundance measurements alone. We apply this new strategy to a panel of wild-type and mutant mice with a liver-specific gene deletion of Liver receptor homolog 1 (Lrh-1^hep−/−), with both lines containing control individuals as well as individuals with liver cancer induced by diethylnitrosamine (DEN). Lrh-1 gene deletion attenuates cancer cell metabolism in hepatocytes through mitochondrial glutamine processing. We show that proteome changes based on mtFE scores outperform protein abundance measurements in discriminating DEN-induced liver cancer from healthy liver tissue, and are uniquely robust against genetic perturbation. We validate the capacity of selected proteins with informative mtFE scores to indicate hepatic malignant changes in two independent mouse models of hepatocellular carcinoma (HCC), thus demonstrating the robustness of this new approach to biomarker research. Overall, the method provides a novel, sensitive approach to cancer biomarker discovery that considers contextual information of tested proteins.

Lipoxidation in cardiovascular diseases

Lipids can go through lipid peroxidation, an endogenous chain reaction that consists in the oxidative degradation of lipids leading to the generation of a wide variety of highly reactive carbonyl species (RCS), such as short-chain carbonyl derivatives and oxidized truncated phospholipids. RCS exert a wide range of biological effects due to their ability to interact and covalently bind to nucleophilic groups on other macromolecules, such as nucleic acids, phospholipids, and proteins, forming reversible and/or irreversible modifications and generating the so-called advanced lipoxidation end-products (ALEs). Lipoxidation plays a relevant role in the onset of cardiovascular diseases (CVD), mainly in the atherosclerosis-based diseases in which oxidized lipids and their adducts have been extensively characterized and associated with several processes responsible for the onset and development of atherosclerosis, such as endothelial dysfunction and inflammation. Herein we will review the current knowledge on the sources of lipids that undergo oxidation in the context of cardiovascular diseases, both from the bloodstream and tissues, and the methods for detection, characterization, and quantitation of their oxidative products and protein adducts. Moreover, lipoxidation and ALEs have been associated with many oxidative-based diseases, including CVD, not only as potential biomarkers but also as therapeutic targets. Indeed, several therapeutic strategies, acting at different levels of the ALEs cascade, have been proposed, essentially blocking ALEs formation, but also their catabolism or the resulting biological responses they induce. However, a deeper understanding of the mechanisms of formation and targets of ALEs could expand the available therapeutic strategies.

A carnosine analog mitigates metabolic disorders of obesity by reducing carbonyl stress

Sugar- and lipid-derived aldehydes are reactive carbonyl species (RCS) frequently used as surrogate markers of oxidative stress in obesity. A pathogenic role for RCS in metabolic diseases of obesity remains controversial, however, partly because of their highly diffuse and broad reactivity and the lack of specific RCS-scavenging therapies. Naturally occurring histidine dipeptides (e.g., anserine and carnosine) show RCS reactivity, but their therapeutic potential in humans is limited by serum carnosinases. Here, we present the rational design, characterization, and pharmacological evaluation of carnosinol, i.e., (2S)-2-(3-amino propanoylamino)-3-(1H-imidazol-5-yl)propanol, a derivative of carnosine with high oral bioavailability that is resistant to carnosinases. Carnosinol displayed a suitable ADMET (absorption, distribution, metabolism, excretion, and toxicity) profile and was determined to have the greatest potency and selectivity toward α,β-unsaturated aldehydes (e.g., 4-hydroxynonenal, HNE, ACR) among all others reported thus far. In rodent models of diet-induced obesity and metabolic syndrome, carnosinol dose-dependently attenuated HNE adduct formation in liver and skeletal muscle, while simultaneously mitigating inflammation, dyslipidemia, insulin resistance, and steatohepatitis. These improvements in metabolic parameters with carnosinol were not due to changes in energy expenditure, physical activity, adiposity, or body weight. Collectively, our findings illustrate a pathogenic role for RCS in obesity-related metabolic disorders and provide validation for a promising new class of carbonyl-scavenging therapeutic compounds rationally derived from carnosine.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Comparative Proteomic Analysis of Two Differently Extracted Coptis chinensis in the Treatment of Type 2 Diabetic Rats

Coptis chinensis (CC) is widely used to treat diabetes in traditional Chinese medicine due to its significant hypoglycemic and hypolipidemic effects. It was reported that CC powders are more effective than CC decoctions. In this study, a rat model of type 2 diabetes was established and treated with supercritical-extracted CC and gastric juice extracted CC, respectively. Body weight, fasting plasma insulin, insulin resistance index, and lipid profiles were measured along with oral glucose tolerance tests (OGTTs). In addition, the levels of plasma proteins were compared between type 2 diabetic rats and CC-treated rats using an iTRAQ-based quantitative proteomic analysis. The results showed that the plasma levels of triglyceride (TC), total cholesterol (TG), and low-density lipoprotein (LDL) in rats of both CC-treated groups were significantly decreased. In addition, the proteomic analysis identified 929 proteins, while 15 proteins were selected from these 929 proteins based on their expression levels and bioinformatic results. Among these 15 proteins, 9 proteins (IGF-1, Igfbp4, Igfbp-6, Igfals, C2, C4, Cfi, Prdx-2, and Prdx-3) were upregulated in the two CC-treated groups, while 6 proteins (Pla2g7, Pcyox1, ApoC-1, ApoC-3, ApoB-100, and ApoE) were downregulated. The functions of these proteins are associated with glucose metabolism, insulin action, immunity, inflammation, lipid metabolism, oxidation, and antioxidation. The two differently extracted CC did not show significant differences in terms of their treatment efficacy. This research expanded our understanding on the therapeutic effects and mechanisms of CC in the treatment of type 2 diabetes.

Obesity-induced protein carbonylation in murine adipose tissue regulates the DNA-binding domain of nuclear zinc finger proteins

In obesity-linked insulin resistance, oxidative stress in adipocytes leads to lipid peroxidation and subsequent carbonylation of proteins by diffusible lipid electrophiles. Reduction in oxidative stress attenuates protein carbonylation and insulin resistance, suggesting that lipid modification of proteins may play a role in metabolic disease, but the mechanisms remain incompletely understood. Herein, we show that in vivo, diet-induced obesity in mice surprisingly results in preferential carbonylation of nuclear proteins by 4-hydroxy-trans-2,3-nonenal (4-HNE) or 4-hydroxy-trans-2,3-hexenal (4-HHE). Proteomic and structural analyses revealed that residues in or around the sites of zinc coordination of zinc finger proteins, such as those containing the C2H2 or MATRIN, RING, C3H1, or N4-type DNA-binding domains, are particularly susceptible to carbonylation by lipid aldehydes. These observations strongly suggest that carbonylation functionally disrupts protein secondary structure supported by metal coordination. Analysis of one such target, the nuclear protein estrogen-related receptor γ (ERR-γ), showed that ERR-γ is modified by 4-HHE in the obese state. In vitro carbonylation decreased the DNA-binding capacity of ERR-γ and correlated with the obesity-linked down-regulation of many key genes promoting mitochondrial bioenergetics. Taken together, these findings reveal a novel mechanistic connection between oxidative stress and metabolic dysfunction arising from carbonylation of nuclear zinc finger proteins, such as the transcriptional regulator ERR-γ.

Prevention of 4-hydroxynonenal-induced lipolytic activation by carnosic acid is related to the induction of glutathione S-transferase in 3T3-L1 adipocytes

Induction of 4-hydroxynonenal (4-HNE), a major lipid peroxidation aldehyde, is observed in patients with obesity and type 2 diabetes mellitus. The lipolytic response by 4-HNE has been linked to insulin resistance. In this study, we investigated the effects of carnosic acid (CA) on 4-HNE-induced lipolysis and the inhibition of β-oxidation in 3T3-L1 adipocytes. The results indicated that cells pretreated with CA reduced 4-HNE-mediated free fatty acid (FFA) release. Furthermore, CA reversed the inhibition of phosphorylation of Tyr⁶³² of insulin receptor substrate-1 (IRS-1) and Akt and the phosphorylation of Ser³⁰⁷ of IRS-1. CA inhibited 4-HNE-induced phosphorylation of protein kinase A (PKA) and hormone-sensitive lipase (HSL), and reversed the suppression by 4-HNE of phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (p < 0.05). Pretreatment of cells with forskolin (a cAMP agonist) and compound C (an AMPK inhibitor) reversed these effects, respectively (p < 0.05). In human subcutaneous adipocytes, CA also attenuated 4-HNE-induced FFA release and the phosphorylation of PKA and HSL (p < 0.05). Moreover, CA increased the protein expression of glutathione S-transferase (GST) A and M. Pretreatment with ethacrynic acid, a GST inhibitor, prevented the 4-HNE-conjugated proteins suppression, the PKA and HSL phosphorylation reduction, and the FFA release inhibition by CA (p < 0.05).

CONCLUSION

The attenuation by CA of the lipolytic response by 4-HNE is likely related to the induction of GST, which in turn reduced 4-HNE-conjugated proteins and decreased the activation of the PKA/HSL pathway. The observed effects may explain how CA improves 4-HNE-induced insulin resistance.

(-)-Epicatechin and its metabolites prevent palmitate-induced NADPH oxidase upregulation, oxidative stress and insulin resistance in HepG2 cells

While diets rich in fruit and vegetables can decrease the risk for type 2 diabetes (T2D), diets rich in fat and carbohydrates can increase it. The flavanol-3-ol (-)-epicatechin (EC) can improve insulin sensitivity both in humans and animal models of T2D. NADPH oxidases and oxidative stress can contribute to the development of insulin resistance. This study investigated the capacity of EC and EC metabolites (ECM) to downregulate NADPH oxidases and oxidative stress, and its association to an improvement of insulin sensitivity. This was studied in in vivo (high fat-fed mice) and in vitro (HepG2 cells) conditions of hepatic lipid overload. EC decreased NOX3/NOX4 liver expression and mitigated oxidative stress in high fat-fed mice. In HepG2 cells, incubation with palmitate increased: i) lipid deposition, ii) NOX3/NOX4 expression, iii) NADPH oxidase activity, and iv) oxidative stress; promoting v) the activation of redox-sensitive kinases (JNK and IKK), and vi) impaired insulin responses. Physiological concentrations of EC and ECM, and NADPH oxidase inhibitors (apocynin, VAS2870) prevented all those deleterious effects of palmitate. The obtained results points to NADPH oxidases as an important target in the capacity of EC to improve insulin sensitivity in conditions of liver lipid overload, as those associated with Western-style diets.

Nutrients and Oxidative Stress: Friend or Foe?

There are different types of nutritionally mediated oxidative stress sources that trigger inflammation. Much information indicates that high intakes of macronutrients can promote oxidative stress and subsequently contribute to inflammation via nuclear factor-kappa B- (NF-κB-) mediated cell signaling pathways. Dietary carbohydrates, animal-based proteins, and fats are important to highlight here because they may contribute to the long-term consequences of nutritionally mediated inflammation. Oxidative stress is a central player of metabolic ailments associated with high-carbohydrate and animal-based protein diets and excessive fat consumption. Obesity has become an epidemic and represents the major risk factor for several chronic diseases, including diabetes, cardiovascular disease (CVD), and cancer. However, the molecular mechanisms of nutritionally mediated oxidative stress are complex and poorly understood. Therefore, this review aimed to explore how dietary choices exacerbate or dampen the oxidative stress and inflammation. We also discussed the implications of oxidative stress in the adipocyte and glucose metabolism and obesity-associated noncommunicable diseases (NCDs). Taken together, a better understanding of the role of oxidative stress in obesity and the development of obesity-related NCDs would provide a useful approach. This is because oxidative stress can be mediated by both extrinsic and intrinsic factors, hence providing a plausible means for the prevention of metabolic disorders.

Deletion of estrogen receptor α in skeletal muscle results in impaired contractility in female mice

Estradiol deficiency in females can result in skeletal muscle strength loss, and treatment with estradiol mitigates the loss. There are three primary estrogen receptors (ERs), and estradiol elicits effects through these receptors in various tissues. Ubiquitous ERα-knockout mice exhibit numerous biological disorders, but little is known regarding the specific role of ERα in skeletal muscle contractile function. The purpose of this study was to determine the impact of skeletal muscle-specific ERα deletion on contractile function, hypothesizing that ERα is a main receptor through which estradiol affects muscle strength in females. Deletion of ERα specifically in skeletal muscle (skmERαKO) did not affect body mass compared with wild-type littermates (skmERαWT) until 26 wk of age, at which time body mass of skmERαKO mice began to increase disproportionally. Overall, skmERαKO mice had low strength demonstrated in multiple muscles and by several contractile parameters. Isolated extensor digitorum longus muscles from skmERαKO mice produced 16% less eccentric and 16-26% less submaximal and maximal isometric force, and isolated soleus muscles were more fatigable, with impaired force recovery relative to skmERαWT mice. In vivo maximal torque productions by plantarflexors and dorsiflexors were 16% and 12% lower in skmERαKO than skmERαWT mice, and skmERαKO muscles had low phosphorylation of myosin regulatory light chain. Plantarflexors also generated 21-32% less power, submaximal isometric and peak concentric torques. Data support the hypothesis that ablation of ERα in skeletal muscle results in muscle weakness, suggesting that the beneficial effects of estradiol on muscle strength are receptor mediated through ERα. NEW & NOTEWORTHY We comprehensively measured in vitro and in vivo skeletal muscle contractility in female estrogen receptor α (ERα) skeletal muscle-specific knockout mice and report that force generation is impaired across multiple parameters. These results support the hypothesis that a primary mechanism through which estradiol elicits its effects on strength is mediated by ERα. Evidence is presented that estradiol signaling through ERα appears to modulate force at the molecular level via posttranslational modifications of myosin regulatory light chain.

Role of protein carbonylation in diabetes

Diabetes mellitus is a metabolic disease characterized by, among others, elevated blood glucose levels. Hyperglycaemia as well as enhanced levels of glucose-derived reactive metabolites contribute to the development of diabetic complications partly via increased generation of reactive oxygen species (ROS). ROS are not only part of signaling pathways themselves but also lead to carbonylation of particular amino acid side chains by direct metal-catalyzed oxidation. In addition, carbonyl groups can be introduced into proteins indirectly by non-oxidative covalent adduction of reactive carbonyl species generated by the oxidation of lipids or carbohydrates. Both direct and indirect carbonylation mechanisms may affect protein conformation, activity, and function. Herein we introduce the different mechanisms of the carbonylation reaction, discuss degradation mechanisms, and the fate of proteins modified this way and how the overall degree of carbonylation affects protein homeostasis and function differently. The role of protein carbonylation in metabolic control systems and cell signaling are also summarized. Finally, current diagnostic and antioxidant therapeutic options in diabetes are discussed.

Down regulation of Peroxiredoxin-3 in 3T3-L1 adipocytes leads to oxidation of Rictor in the mammalian-target of rapamycin complex 2 (mTORC2)

Mitochondrially-derived oxidative stress has been implicated in the development of obesity-induced insulin resistance and is correlated with down regulation of Peroxiredoxin-3 (Prdx3). Prdx3 knockout mice exhibit whole-body insulin resistance, while Prdx3 transgenic animals remain insulin sensitive when placed on a high fat diet. To define the molecular events linking mitochondrial oxidative stress to insulin action, Prdx3 was silenced in 3T3-L1 adipocytes (Prdx3 KD) and the resultant cells evaluated for mitochondrial function, endoplasmic reticulum stress (ER stress), mitochondrial unfolded protein response (mtUPR) and insulin signaling. Prdx3 KD cells exhibit a two-fold increase in H₂O₂, reduced insulin-stimulated glucose transport and attenuated S⁴⁷³ phosphorylation of the mTORC2 substrate, Akt. Importantly, the decrease in glucose uptake can be rescued by pre-treatment with the antioxidant N-acetyl-cysteine (NAC). The changes in insulin sensitivity occur independently from activation of the ER stress or mtUPR pathways. Analysis of mTORC2, the complex responsible for phosphorylating Akt at S⁴⁷³, reveals increased cysteine oxidation of Rictor in Prdx3 KD cells that can be rescued with NAC. Taken together, these data suggest mitochondrial dysfunction in adipocytes may attenuate insulin signaling via oxidation of the mammalian-target of rapamycin complex 2 (mTORC2).

4-Hydroxynonenal (HNE) modified proteins in metabolic diseases

4-Hydroxynonenal (HNE) is one of the quantitatively most important products of lipid peroxidation. Due to its high toxicity it is quickly metabolized, however, a small share of HNE avoids enzymatic detoxification and reacts with biomolecules including proteins. The formation of HNE-protein-adducts is one of the accompanying processes in oxidative stress or redox disbalance. The modification of proteins might occur at several amino acids side chains, leading to a variety of products and having effects on the protein function and fate. This review summarizes current knowledge on the formation of HNE-modified proteins, their fate in mammalian cells and their potential role as a damaging agents during oxidative stress. Furthermore, the potential of HNE-modified proteins as biomarkers for several diseases are highlighted.

Adipose tissue inflammation: a cause or consequence of obesity-related insulin resistance?

The worldwide obesity epidemic has become a major health concern, because it contributes to higher mortality due to an increased risk for noncommunicable diseases including cardiovascular diseases, type 2 diabetes, musculoskeletal disorders and some cancers. Insulin resistance may link accumulation of adipose tissue in obesity to metabolic diseases, although the underlying mechanisms are not completely understood. In the past decades, data from human studies and transgenic animal models strongly suggested correlative, but also causative associations between activation of proinflammatory pathways and insulin resistance. Particularly chronic inflammation in adipose tissue seems to play an important role in the development of obesity-related insulin resistance. On the other hand, adipose tissue inflammation has been shown to be essential for healthy adipose tissue expansion and remodelling. However, whether adipose tissue inflammation represents a consequence or a cause of impaired insulin sensitivity remains an open question. A better understanding of the molecular pathways linking excess adipose tissue storage to chronic inflammation and insulin resistance may provide the basis for the future development of anti-inflammatory treatment strategies to improve adverse metabolic consequences of obesity. In this review, potential mechanisms of adipose tissue inflammation and how adipose tissue inflammation may cause insulin resistance are discussed.

Targeting the NO/superoxide ratio in adipose tissue: relevance to obesity and diabetes management

Insulin sensitivity and metabolic homeostasis depend on the capacity of adipose tissue to take up and utilize excess glucose and fatty acids. The key aspects that determine the fuel-buffering capacity of adipose tissue depend on the physiological levels of the small redox molecule, nitric oxide (NO). In addition to impairment of NO synthesis, excessive formation of the superoxide anion (О2•- ) in adipose tissue may be an important interfering factor diverting the signalling of NO and other reactive oxygen and nitrogen species in obesity, resulting in metabolic dysfunction of adipose tissue over time. Besides its role in relief from superoxide burst, enhanced NO signalling may be responsible for the therapeutic benefits of different superoxide dismutase mimetics, in obesity and experimental diabetes models. This review summarizes the role of NO in adipose tissue and highlights the effects of NO/О2•- ratio 'teetering' as a promising pharmacological target in the metabolic syndrome.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Effect of under- and overfeeding on sheep and goat milk and plasma enzymes activities related to oxidation

Twenty-four dairy sheep and goats, respectively, were assigned each to three homogenous subgroups per animal species and fed the same diet in quantities which met 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements. The results showed that the underfed sheep in comparison with the control had significantly lower glutathione reductase (GR), superoxide dismutase (SOD), catalase and glutathione peroxidase (GPX) activities and total antioxidant capacity (measured with Ferric Reducing Ability of Plasma [FRAP] assay) in their blood plasma. A significant increase in the glutathione transferase (GST) and GPX activities, malondialdehyde content and total antioxidant capacity (measured with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) [ABTS] assay) in the blood plasma of underfed goats compared with controls was observed, while the opposite happened for the GR and SOD activities. The underfeeding in both animal species caused a significant increase in the protein carbonyls (PC) content of their blood plasma. The overfeeding, compared with the control, caused a significant decline in the GPX activity and total antioxidant capacity (measured with FRAP) in the blood plasma of sheep while the opposite happened for the GPX and GST activities in the case of goats. The overfed animals, of both species, compared with the respective controls, had higher PC content in their blood plasma. The feeding level had no noticeable impact on the antioxidants' enzymes activities of milk in both animal species. Moreover, the underfeeding in the blood plasma and the overfeeding in milk of both animal species resulted into a significant increase in the PC content. Finally, only in sheep milk, the underfeeding, compared with the respective control, and overfeeding reduced significantly the total antioxidant capacity (measured with ABTS). The feeding level caused oxidative stress in both organism and milk but the response was different in animal species and needs further investigation.

Combined metformin and insulin treatment reverses metabolically impaired omental adipogenesis and accumulation of 4-hydroxynonenal in obese diabetic patients

Objective

Obesity-associated impaired fat accumulation in the visceral adipose tissue can lead to ectopic fat deposition and increased risk of insulin resistance and type 2 diabetes mellitus (T2DM). This study investigated whether impaired adipogenesis of omental (OM) adipose tissues and elevated 4-hydroxynonenal (4-HNE) accumulation contribute to this process, and if combined metformin and insulin treatment in T2DM patients could rescue this phenotype.

Methods

OM adipose tissues were obtained from forty clinically well characterized obese individuals during weight reduction surgery. Levels of 4-HNE protein adducts, adipocyte size and number of macrophages were determined within these tissues by immunohistochemistry. Adipogenic capacity and gene expression profiles were assessed in preadipocytes derived from these tissues in relation to insulin resistance and in response to 4-HNE, metformin or combined metformin and insulin treatment.

Results

Preadipocytes isolated from insulin resistant (IR) and T2DM individuals exhibited lower adipogenesis, marked by upregulation of anti-adipogenic genes, compared to preadipocytes derived from insulin sensitive (IS) individuals. Impaired adipogenesis was also associated with increased 4-HNE levels, smaller adipocytes and greater macrophage presence in the adipose tissues. Within the T2DM group, preadipocytes from combined metformin and insulin treated subset showed better in vitro adipogenesis compared to metformin alone, which was associated with less presence of macrophages and 4-HNE in the adipose tissues. Treatment of preadipocytes in vitro with 4-HNE reduced their adipogenesis and increased proliferation, even in the presence of metformin, which was partially rescued by the presence of insulin.

Conclusion

This study reveals involvement of 4-HNE in the impaired OM adipogenesis-associated with insulin resistance and T2DM and provides a proof of concept that this impairment can be reversed by the synergistic action of insulin and metformin. Further studies are needed to evaluate involvement of 4-HNE in metabolically impaired abdominal adipogenesis and to confirm benefits of combined metformin-insulin therapy in T2DM patients.