High-fat diet-induced changes in liver thioredoxin and thioredoxin reductase as a novel feature of insulin resistance

Discovery of novel organoarsenicals as robust thioredoxin reductase inhibitors for oxidative stress mediated cancer therapy

Targeting overexpressed thioredoxin reductase (TrxR) in cancer cells to induce oxidative stress has been proved to be an effective strategy for cancer therapy. However, the treatment was hindered by the low efficiency and frequent administration of TrxR inhibitors, and hence more potent TrxR inhibitors were urgently needed. Herein, we designed and synthesized a series of TrxR inhibitors based on arsenicals. Among these, compound 1d inhibited the proliferation of a variety of cancer cells at low micromolar concentrations and exhibited low toxicity to normal cells. Importantly, compound 1d induced the accumulation of reactive oxygen species (ROS) by inhibiting the TrxR activity, further causing the collapse of the redox system, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and DNA damage, followed by oxidative stress-induced cell apoptosis. In vivo data showed that, compared with the clinical TrxR inhibitor auranofin (AUR), compound 1d could more effectively eliminate tumors by 90 % at a dose of 1.5 mg/kg without any obvious side effects. These results indicated that compound 1d was a potent TrxR inhibitor against cancer.

Extracting functionally accurate context-specific models of Atlantic salmon metabolism

Constraint-based models (CBMs) are used to study metabolic network structure and function in organisms ranging from microbes to multicellular eukaryotes. Published CBMs are usually generic rather than context-specific, meaning that they do not capture differences in reaction activities, which, in turn, determine metabolic capabilities, between cell types, tissues, environments, or other conditions. Only a subset of a CBM's metabolic reactions and capabilities are likely to be active in any given context, and several methods have therefore been developed to extract context-specific models from generic CBMs through integration of omics data. We tested the ability of six model extraction methods (MEMs) to create functionally accurate context-specific models of Atlantic salmon using a generic CBM (SALARECON) and liver transcriptomics data from contexts differing in water salinity (life stage) and dietary lipids. Three MEMs (iMAT, INIT, and GIMME) outperformed the others in terms of functional accuracy, which we defined as the extracted models' ability to perform context-specific metabolic tasks inferred directly from the data, and one MEM (GIMME) was faster than the others. Context-specific versions of SALARECON consistently outperformed the generic version, showing that context-specific modeling better captures salmon metabolism. Thus, we demonstrate that results from human studies also hold for a non-mammalian animal and major livestock species.

Pathways Linking Nicotinamide Adenine Dinucleotide Phosphate Production to Endoplasmic Reticulum Protein Oxidation and Stress

The endoplasmic reticulum (ER) lumen is highly oxidizing compared to other subcellular compartments, and maintaining the appropriate levels of oxidizing and reducing equivalents is essential to ER function. Both protein oxidation itself and other essential ER processes, such as the degradation of misfolded proteins and the sequestration of cellular calcium, are tuned to the ER redox state. Simultaneously, nutrients are oxidized in the cytosol and mitochondria to power ATP generation, reductive biosynthesis, and defense against reactive oxygen species. These parallel needs for protein oxidation in the ER and nutrient oxidation in the cytosol and mitochondria raise the possibility that the two processes compete for electron acceptors, even though they occur in separate cellular compartments. A key molecule central to both processes is NADPH, which is produced by reduction of NADP+ during nutrient catabolism and which in turn drives the reduction of components such as glutathione and thioredoxin that influence the redox potential in the ER lumen. For this reason, NADPH might serve as a mediator linking metabolic activity to ER homeostasis and stress, and represent a novel form of mitochondria-to-ER communication. In this review, we discuss oxidative protein folding in the ER, NADPH generation by the major pathways that mediate it, and ER-localized systems that can link the two processes to connect ER function to metabolic activity.

Lipid-induced S-palmitoylation as a Vital Regulator of Cell Signaling and Disease Development

Lipid metabolites are emerging as pivotal regulators of protein function and cell signaling. The availability of intracellular fatty acid is tightly regulated by glycolipid metabolism and may affect human body through many biological mechanisms. Recent studies have demonstrated palmitate, either from exogenous fatty acid uptake or de novo fatty acid synthesis, may serve as the substrate for protein palmitoylation and regulate protein function via palmitoylation. Palmitoylation, the most-studied protein lipidation, encompasses the reversible covalent attachment of palmitate moieties to protein cysteine residues. It controls various cellular physiological processes and alters protein stability, conformation, localization, membrane association and interaction with other effectors. Dysregulation of palmitoylation has been implicated in a plethora of diseases, such as metabolic syndrome, cancers, neurological disorders and infections. Accordingly, it could be one of the molecular mechanisms underlying the impact of palmitate metabolite on cellular homeostasis and human diseases. Herein, we explore the relationship between lipid metabolites and the regulation of protein function through palmitoylation. We review the current progress made on the putative role of palmitate in altering the palmitoylation of key proteins and thus contributing to the pathogenesis of various diseases, among which we focus on metabolic disorders, cancers, inflammation and infections, neurodegenerative diseases. We also highlight the opportunities and new therapeutics to target palmitoylation in disease development.

Selenium as a Bioactive Micronutrient in the Human Diet and Its Cancer Chemopreventive Activity

This review answers the question of why selenium is such an important trace element in the human diet. Daily dietary intake of selenium and its content in various food products is discussed in this paper, as well as the effects of its deficiency and excess in the body. Moreover, the biological activity of selenium, which it performs mainly through selenoproteins, is discussed. These specific proteins are responsible for thyroid hormone management, fertility, the aging process, and immunity, but their key role is to maintain a redox balance in cells. Furthermore, taking into account world news and the current SARS-CoV-2 virus pandemic, the impact of selenium on the course of COVID-19 is also discussed. Another worldwide problem is the number of new cancer cases and cancer-related mortality. Thus, the last part of the article discusses the impact of selenium on cancer risk based on clinical trials (including NPC and SELECT), systematic reviews, and meta-analyses. Additionally, this review discusses the possible mechanisms of selenium action that prevent cancer development.

Improvement of the hepatic lipid status in intrauterine growth retarded pigs by resveratrol is related to the inhibition of mitochondrial dysfunction, oxidative stress and inflammation

Mitochondrial dysfunction, oxidative stress and inflammation are crucial contributors to liver damage and nonalcoholic fatty liver disease (NAFLD) in adulthood in offspring affected by intrauterine growth retardation (IUGR). Resveratrol (RSV) has been reported to treat and/or prevent hepatic diseases under various pathological conditions. However, the therapeutic and/or preventive effects of RSV on hepatic abnormality in IUGR adults have not been investigated until now. The effects of IUGR and RSV on the hepatic metabolic status, mitochondrial function, redox homeostasis and inflammation in pigs in adulthood were investigated. A total of 36 pairs of IUGR and normal birth weight piglets were orally fed with 80 mg RSV per kg body weight per d or vehicle (0.5% carboxymethylcellulose) for 7-21 d after birth. And then the offspring were fed with a basal diet supplemented with 300 mg RSV per kg feed or a basal diet from weaning to slaughter at 150 d. The plasma and liver samples were collected for subsequent analysis. RSV exerted beneficial effects on hepatic injury and metabolic alterations in IUGR pigs, which may be due to improved mitochondrial function and fatty acid oxidation by intensified mitochondrial biogenesis, enhanced antioxidant levels such as glutathione reductase and total superoxide dismutase activities, increased interleukin 10 gene expression and repolarization of macrophages. RSV alleviated hepatic lipid accumulation in IUGR pigs by improving mitochondrial function, redox status and inflammation, implying that it is a potential candidate for further development as an effective clinical treatment for NAFLD associated with IUGR.

New insights into serum/extracellular thioredoxin in regulating hepatic insulin receptor activation

BACKGROUND

Serum thioredoxin of type-2 diabetic patients is significantly higher than that of healthy people. Pathophysiological significance is unclear.

METHODS

Effects of serum/extracellular thioredoxin on phosphorylation (activation) of hepatic insulin receptor (IR) were investigated by using methods in biochemistry, cell/molecular biology and mass spectrometry.

RESULTS

In human serum, thioredoxin and insulin may interact. Their mixture contains a mixed disulfide between insulin B-chain and thioredoxin-Cys73, which limits their activities. In contrast, free form of serum/extracellular thioredoxin is active, and can regulate phosphorylation of insulin receptor β-subunits (IRβ) via direct/indirect mechanisms. The direct mechanism associates with positive regulation. Serum/extracellular thioredoxin increases insulin binding to IR, facilitating insulin-induced phosphorylation of IRβ and downstream AKT. The indirect mechanism is involved in negative regulation. Entry of extracellular thioredoxin into hepatic cells via IR enhances the expression and activity of cellular protein-tyrosine phosphatase 1B (PTP1B), which negatively regulates IRβ phosphorylation. After coordination between these two mechanisms, the positive impact of serum/extracellular thioredoxin overwhelms its negative impact on IRβ phosphorylation, which subsequently accelerates hepatic glucose uptake. In hepatic cells with thioredoxin deficiency, insulin-induced IRβ phosphorylation is decreased, which could be restored by extracellular thioredoxin entry. Moreover, the results from assaying 475 serum samples demonstrate a discriminating value of serum thioredoxin activity in diagnosing type-2 diabetes.

CONCLUSION

Serum/extracellular thioredoxin plays a critical role in regulating hepatic IRβ phosphorylation.

GENERAL SIGNIFICANCE

In case of insulin resistance/type-2 diabetes, hepatic IRβ is at low phosphorylation level, thereby the improvement effect of serum/extracellular thioredoxin on insulin-induced IRβ phosphorylation seems particularly important.

The Role of Mitochondria in Sex-Dependent Differences in Hepatic Steatosis and Oxidative Stress in Response to Cafeteria Diet-Induced Obesity in Mice

Female mice fed a cafeteria diet (FCaf) develop higher liver steatosis and oxidative stress than males (MCaf) as a consequence of unresolved ER stress. Here, we investigated whether mitochondria play a role in this sex difference. The isolated mitochondria from FCaf showed more signs of oxidative stress than those of MCaf, correlated with a reduced content of GSH, increased amount of reactive oxygen species (ROS), and lower activities of enzymes involved in ROS neutralisation. Mitochondria from FCaf and MCaf livers exhibited lower rates of succinate-driven state III respiration and reduced ATPase activity in intact coupled mitochondria compared to their controls fed a standard diet (FC and MC), with no differences between the sexes. Fatty acid oxidation in mitochondria and peroxisomes was higher in MCaf and FCaf compared to their respective controls. In the intact perfused liver, there was no difference between sex or diet regarding the fatty acid oxidation rate. These results indicated that cafeteria diet did not affect mitochondrial energy metabolism, even in FCaf livers, which have higher steatosis and cellular oxidative stress. Nevertheless, the increase in mitochondrial ROS generation associated with a decrease in the antioxidant defence capacity, probably contributes to inducing or reinforcing the ER stress in FCaf livers.

Role and mechanism of homocysteine in affecting hepatic protein-tyrosine phosphatase 1B

BACKGROUND

Elevated homocysteine is epidemiologically related to insulin resistance. Protein-tyrosine phosphatase 1B (PTP1B) is a negative regulator of insulin signaling. However, the effect of homocysteine on PTP1B remains unclear.

METHODS

S-homocysteinylated PTP1B was identified by LC-ESI-MS/MS. The ability of thioredoxin system to recover active PTP1B from S-homocysteinylated PTP1B was confirmed by RNA interference. To address the mechanism for homocysteine to affect PTP1B activity, we performed 5-IAF insertion, activity assays, Western blotting, co-immunoprecipitation and glucose uptake experiments.

RESULTS

The thiol-containing form of homocysteine (HcySH) suppressed phosphorylation of insulin receptor-β subunit, but enhanced PTP1B activity. This phenomenon was partially related to the fact that HcySH promoted PTP1B expression. Although the disulfide-bonded form of homocysteine (HSSH) modified PTP1B to form an inactive S-homocysteinylated PTP1B, HcySH-induced increase in the activities of cellular thioredoxin and thioredoxin reductase, components of thioredoxin system, could recover active PTP1B from S-homocysteinylated PTP1B. Thioredoxin system transferred electrons from NADPH to S-homocysteinylated PTP1B, regenerating active PTP1B in vitro and in hepatocytes. The actions of HcySH were also related with decrease in hepatic glucose uptake.

CONCLUSIONS

The effect of HcySH/HSSH on PTP1B activity depends, at least partially, on the ratio of active PTP1B and S-homocysteinylated PTP1B. High HcySH-induced an increase in thioredoxin system activity is beneficial to de-S-homocysteinylation and is good for PTP1B activity.

GENERAL SIGNIFICANCE

Our data provide a novel insight into post-translational regulation of PTP1B, and expand the biological functions of thioredoxin system.

Dyslipidemia in Ischemia/Reperfusion Injury

Ischemic heart disease is the main cause of morbidity and mortality in the developed world. Although reperfusion therapies are currently the best treatment for this entity, the restoration of blood flow leads, under certain circumstances, to a form of myocardial damage called reperfusion injury. Several studies have shown that age, sex, smoking, diabetes and dyslipidemia are risk factors for cardiovascular diseases. Among these risk factors, dyslipidemias are present in 40% of patients with ischemic heart disease and represent the clinical factor with the greatest impact on the prognosis of patients with cardiovascular diseases. It is known that during reperfusion the increase of the oxidative stress is perhaps one of the most important mechanisms implicated in cell damage. That is why several researchers have studied protective mechanisms against reperfusion injury, such as the ischemic pre- and post- conditioning, making emphasis mainly on the reduction of oxidative stress. However, few of these efforts have been successfully translated into the clinical setting. The controversial results in regards to the relation between cardioprotective mechanisms and dyslipidemia/hypercholesterolemia are mainly due to the difference among quality, composition and the time of administration of hypercholesterolemic diets, as well as the difference in the species used in each of the studies. Therefore, in order to compare results, it is crucial that all variables that could modify the obtained results are taken into consideration.

The role of the thioredoxin/thioredoxin reductase system in the metabolic syndrome: towards a possible prognostic marker?

Mammalian thioredoxin reductase (TrxR) is a selenoprotein with three existing isoenzymes (TrxR1, TrxR2, and TrxR3), which is found primarily intracellularly but also in extracellular fluids. The main substrate thioredoxin (Trx) is similarly found (as Trx1 and Trx2) in various intracellular compartments, in blood plasma, and is the cell's major disulfide reductase. Thioredoxin reductase is necessary as a NADPH-dependent reducing agent in biochemical reactions involving Trx. Genetic and environmental factors like selenium status influence the activity of TrxR. Research shows that the Trx/TrxR system plays a significant role in the physiology of the adipose tissue, in carbohydrate metabolism, insulin production and sensitivity, blood pressure regulation, inflammation, chemotactic activity of macrophages, and atherogenesis. Based on recent research, it has been reported that the modulation of the Trx/TrxR system may be considered as a new target in the management of the metabolic syndrome, insulin resistance, and type 2 diabetes, as well as in the treatment of hypertension and atherosclerosis. In this review evidence about a possible role of this system as a marker of the metabolic syndrome is reported.

Antioxidants and HNE in redox homeostasis

Under physiological conditions, cells are in a stable state known as redox homeostasis, which is maintained by the balance between continuous ROS/RNS generation and several mechanisms involved in antioxidant activity. ROS overproduction results in alterations in the redox homeostasis that promote oxidative damage to major components of the cell, including the biomembrane phospholipids. Lipid peroxidation subsequently generates a diverse set of products, including α,β-unsaturated aldehydes. Of these products, 4-hydroxy-2-nonenal (HNE) is the most studied aldehyde on the basis of its involvement in cellular physiology and pathology. This review summarizes the current knowledge in the field of HNE generation, metabolism, and detoxification, as well as its interactions with various cellular macromolecules (protein, phospholipid, and nucleic acid). The formation of HNE-protein adducts enables HNE to participate in multi-step regulation of cellular metabolic pathways that include signaling and transcription of antioxidant enzymes, pro-inflammatory factors, and anti-apoptotic proteins. The most widely described roles for HNE in the signaling pathways are associated with its activation of kinases, as well as transcription factors that are responsible for redox homeostasis (Ref-1, Nrf2, p53, NFκB, and Hsf1). Depending on its level, HNE exerts harmful or protective effects associated with the induction of antioxidant defense mechanisms. These effects make HNE a key player in maintaining redox homeostasis, as well as producing imbalances in this system that participate in aging and the development of pathological conditions.

Selenium deficiency-induced thioredoxin suppression and thioredoxin knock down disbalanced insulin responsiveness in chicken cardiomyocytes through PI3K/Akt pathway inhibition

Thioredoxin (Txn) system is the most crucial antioxidant defense mechanism in cell consisting of Txn, thioredoxin reductase (TR) and Nicotinamide Adenine Dinucleotide Phosphate (NADPH). Perturbations in Txn system may compromise cell survival through oxidative stress induction. Metabolic activity of insulin plays important roles in fulfilling the stable and persistent demands of heart through glucose metabolism. However, the roles of Txn and Txn system in insulin modulated cardiac energy metabolism have been less reported. Therefore, to investigate the role of Txn in myocardial metabolism, we developed a Se-deficient chicken model (0.033mg/kg) for in-vivo and Txn knock down cardiomyocytes culture model (siRNA) for in-vitro studies. Quantitative real time PCR and western blotting was performed. Se deficiency suppressed Txn and TR in cardiac tissues. Significant increases in ROS (P<0.05) levels signify the onset of oxidative stress and in both models. Se deficiency-induced Txn suppression model and Txn knock down cardiomyocytes models significantly decreased (P<0.05), the mRNA and protein levels of insulin-like growth factors (IGF1, IGF2), IGF-binding proteins (IGFBP2, IGFBP4), insulin receptor (IR), insulin receptor substrates (IRS1, IRS2), and glucose transporters (GLUT1, GLUT3, GLUT8), however, IGFBP3 expression increased in Txn knock down cardiomyocytes. In addition, in contrast to their respective controls, Se deficiency-induced Txn depleted tissues and Txn deleted cardiomyocytes showed suppression in mRNA and protein levels of PI3K, AKT, P-PI3K, and repression in FOX, P-FOX JNK genes. Combing the in vitro and in vivo experiments, we demonstrate that Txn gene suppression can cause dysfunction of insulin-modulated cardiac energy metabolism and increase insulin resistance through PI3K-Akt pathway inhibition. Herein, we conclude that inactivation of Txn system can alter cellular insulin response through IRS/PI3K/Akt pathway repression and JNK and FOX expression. These findings point out that Txn system can redox regulate the insulin dependent glucose metabolism in heart and is essential for cell vitality. Moreover, the increased expression of IGFBP3 indicates that it can be a potential negative modulator of metabolic activity of insulin in Txn deficient cells.

Inhibition of Src homology 2 domain-containing phosphatase 1 increases insulin sensitivity in high-fat diet-induced insulin-resistant mice

Insulin resistance plays a crucial role in the development of type 2 diabetes. Insulin receptor signalling is antagonized and tightly controlled by protein tyrosine phosphatases (PTPs). However, the precise role of the PTP src homology 2 domain‐containing phosphatase 1 (SHP‐1) in insulin resistance has not been explored. Male C57BL/6J mice were fed a high‐fat diet (HFD, 60% kcal from fat), to induce insulin resistance, or a low‐fat diet (LFD, 10% kcal from fat) for 10 weeks. Afterwards, HFD‐fed mice were pharmacologically treated with the SHP‐1 (Ptpn6) inhibitor sodium stibogluconate and the broad spectrum pan‐PTP inhibitor bis(maltolato)oxovanadium(IV) (BMOV). Both inhibitors ameliorated the metabolic phenotype, as evidenced by reduced body weight, improved insulin sensitivity and glucose tolerance, which was not due to altered PTP gene expression. In parallel, phosphorylation of the insulin receptor and of the insulin signalling key intermediate Akt was enhanced, and both PTP inhibitors and siRNA‐mediated SHP‐1 downregulation resulted in an increased glucose uptake in vitro. Finally, recombinant SHP‐1 was capable of dephosphorylating the ligand‐induced tyrosine‐phosphorylated insulin receptor. These results indicate a central role of SHP‐1 in insulin signalling during obesity, and SHP‐1 inhibition as a potential therapeutic approach in metabolic diseases.

Curation of the Mammalian Palmitoylome Indicates a Pivotal Role for Palmitoylation in Diseases and Disorders of the Nervous System and Cancers

Palmitoylation involves the reversible posttranslational addition of palmitate to cysteines and promotes membrane binding and subcellular localization. Recent advancements in the detection and identification of palmitoylated proteins have led to multiple palmitoylation proteomics studies but these datasets are contained within large supplemental tables, making downstream analysis and data mining time-consuming and difficult. Consequently, we curated the data from 15 palmitoylation proteomics studies into one compendium containing 1,838 genes encoding palmitoylated proteins; representing approximately 10% of the genome. Enrichment analysis revealed highly significant enrichments for Gene Ontology biological processes, pathway maps, and process networks related to the nervous system. Strikingly, 41% of synaptic genes encode a palmitoylated protein in the compendium. The top disease associations included cancers and diseases and disorders of the nervous system, with Schizophrenia, HD, and pancreatic ductal carcinoma among the top five, suggesting that aberrant palmitoylation may play a pivotal role in the balance of cell death and survival. This compendium provides a much-needed resource for cell biologists and the palmitoylation field, providing new perspectives for cancer and neurodegeneration.

Protein localization is essential for mediating protein function within the cellular context. Mislocalization of proteins can offset cellular balance, influencing whether a cell lives or dies. Many proteins are directed to cellular membranes through the addition of fats, or lipidation. In particular, palmitoylation involves the reversible addition of the fatty acid palmitate to cysteines. Its reversibility makes it a unique form of lipidation allowing its dynamic regulation. Recent advancements in fast, sensitive, non-radioactive methods to detect palmitoylation have led to an explosion in the identification of palmitoylated proteins through proteomics studies. However, the data is hidden in large supplemental tables in various formats. Thus, we curated a list of palmitoylated proteins revealing that approximately 10 percent of the human genome encodes for a proteoform that is palmitoylated. Computational analysis confirmed that palmitoylation is involved in protein localization and indicated a new role in metabolism. Importantly, we found that palmitoylation was enriched at neuronal synapses and in disorders of the nervous system, including Schizophrenia and Huntington disease. Interestingly, palmitoylation was equally enriched in cancers. Consequently, we suggest that palmitoylation plays a critical role in cell fate and our compendium provides a plethora of targets for neurodegeneration and cancer.

New insights into the posttranslational regulation of human cytosolic thioredoxin by S-palmitoylation

High level of palmitate is associated with metabolic disorders. We recently showed that enhanced level of S-palmitoylated cytosolic thioredoxin (Trx1) in mouse liver was new characteristic feature of insulin resistance. However, our understanding of the effect of S-palmitoylation on Trx1 is limited, and the tissue specificity of Trx1 S-palmitoylation is unclear. Here we show that S-palmitoylation also occurs at Cys73 of Trx1 in living endothelial cells, and the level of S-palmitoylated Trx1 undergoes regulation by insulin signaling. Trx1 prefers thiol-thioester exchange with palmitoyl-CoA to acetyl-CoA. S-palmitoylation alters conformation or secondary structure of Trx1, as well as decreases the ability of Trx1 to transfer electrons from thioredoxin reductase to S-nitrosylated protein-tyrosine phosphatase 1B and S-nitroso-glutathione. Our results demonstrate that S-palmitoylation is an important post-translational modification of human Trx1.

Mechanistic insights into the inhibitory effects of palmitoylation on cytosolic thioredoxin reductase and thioredoxin

Overnutrition can lead to oxidative stress, but its underlying mechanism remains unclear. In this study, we report that human liver-derived HepG2 cells utilize cytosolic thioredoxin reductase (TrxR1) and thioredoxin (hTrx1) to defend against the high glucose/palmitate-mediated increase in reactive oxygen species. However, enhanced TrxR1/hTrx1 palmitoylation occurs in parallel with a decrease in their activities under the conditions studied here. An autoacylation process appears to be the major mechanism for generating palmitoylated TrxR1/Trx1 in HepG2 cells. A novel feature of this post-translational modification is the covalent inhibition of TrxR1/hTrx1 by palmitoyl-CoA, an activated form of palmitate. The palmitoyl-CoA/TrxR1 reaction is NADPH-dependent and produces palmitoylated TrxR1 at an active site selenocysteine residue. Conversely, S-palmitoylation occurs at the structural Cys62/Cys69/Cys72 residues but not the active site Cys32/Cys35 residues of hTrx1. Palmitoyl-CoA concentration and the period of incubation with TrxR1/hTrx1 are important factors that influence the inhibitory efficacy of palmitoyl-CoA on TrxR1/hTrx1. Thus, an increase in TrxR1/hTrx1 palmitoylation could be a potential consequence of high glucose/palmitate. The time-dependent inactivation of the NADPH-TrxR1-Trx1 system by palmitoyl-CoA occurs in a biphasic manner - a fast phase followed by a slow phase. Kinetic analysis suggests that the fast phase is consistent with a fast and reversible association between TrxR1/hTrx1 and palmitoyl-CoA. The slow phase is correlated with a slow and irreversible inactivation, in which selenolate/thiolate groups nucleophilically attack the α-carbon of bound palmitoyl-CoA, leading to the formation of thioester/selenoester bonds. hTrx1 can enhance rate of fast phase but limits the rate of slow phase when it is present in a preincubation mixture containing NADPH, TrxR1 and palmitoyl-CoA. Therefore, hTrx1 may provide palmitoylation sites or partially protect the TrxR1 active site selenol/thiol group(s) from palmitoylation. Our data suggest that Se/S-palmitoylation acts as an important modulator of TrxR1/hTrx1 activities, representing a novel potential mechanism that underlies overnutrition-induced events.