Acute Impacts of Ionizing Radiation Exposure on the Gastrointestinal Tract and Gut Microbiome in Mice.

Radiation therapy for abdominopelvic malignancies often results in damage to the gastrointestinal tract (GIT) and permanent changes in bowel function. An overlooked component of the pathophysiology of radiation-induced bowel injury is the role of the gut microbiome. The goal of this research was to identify the impacts of acute radiation exposure on the GIT and gut microbiome. C57BL/6 mice exposed to whole-body X-rays (0.1-3 Gy) were assessed for histological and microbiome changes 48 h post-radiation exposure. Within the ileum, a dose of 3 Gy significantly decreased crypt depth as well as the number of goblet cells, but increased overall goblet cell size. Overall, radiation altered the microbial distribution within each of the main phyla in a dose- and tissue-dependent manner. Within the Firmicutes phylum, high dose irradiation resulted in significant alterations in bacteria from the class Bacilli within the small bowels, and from the class Clostridia in the large bowels. The 3 Gy radiation also significantly increased the abundance of bacterial families from the Bacteroidetes phylum in the colon and feces. Overall, we identified various alterations in microbiome composition following acute radiation exposure, which could potentially lead to novel biomarkers for tracking patient toxicities or could be used as targets for mitigation strategies against radiation damage.

The Effects of Oral Probiotics on Type 2 Diabetes Mellitus (T2DM): A Clinical Trial Systematic Literature Review.

Type 2 diabetes mellitus (T2DM) remains a global health concern. Emerging clinical trial (CT) evidence suggests that probiotic intervention may promote a healthy gut microbiome in individuals with T2DM, thereby improving management of the disease. This systematic literature review summarizes thirty-three CTs investigating the use of oral probiotics for the management of T2DM. Here, twenty-one studies (64%) demonstrated an improvement in at least one glycemic parameter, while fifteen studies (45%) showed an improvement in at least one lipid parameter. However, no article in this review was able to establish a uniform decrease in glycemic, lipid, or blood pressure profiles. The lack of consistency across the studies may be attributed to differences in probiotic composition, duration of probiotic consumption, and probiotic dose. An interesting finding of this literature review was the beneficial trend of metformin and probiotic co-administration. Here, patients with T2DM taking metformin demonstrated enhanced glycemic control via the co-administration of probiotics. Taken together, the overall positive findings reported across the studies in combination with minimal adverse effects constitute ground for further quality CTs. This review provides recommendations for future CTs that may address the shortcomings of the current studies and help to extract useful data from future investigations of the use of probiotics in T2DM management.

Molecular Mechanisms Associated with Antifungal Resistance in Pathogenic Candida Species.

Candidiasis is a highly pervasive infection posing major health risks, especially for immunocompromised populations. Pathogenic Candida species have evolved intrinsic and acquired resistance to a variety of antifungal medications. The primary goal of this literature review is to summarize the molecular mechanisms associated with antifungal resistance in Candida species. Resistance can be conferred via gain-of-function mutations in target pathway genes or their transcriptional regulators. Therefore, an overview of the known gene mutations is presented for the following antifungals: azoles (fluconazole, voriconazole, posaconazole and itraconazole), echinocandins (caspofungin, anidulafungin and micafungin), polyenes (amphotericin B and nystatin) and 5-fluorocytosine (5-FC). The following mutation hot spots were identified: (1) ergosterol biosynthesis pathway mutations (ERG11 and UPC2), resulting in azole resistance; (2) overexpression of the efflux pumps, promoting azole resistance (transcription factor genes: tac1 and mrr1; transporter genes: CDR1, CDR2, MDR1, PDR16 and SNQ2); (3) cell wall biosynthesis mutations (FKS1, FKS2 and PDR1), conferring resistance to echinocandins; (4) mutations of nucleic acid synthesis/repair genes (FCY1, FCY2 and FUR1), resulting in 5-FC resistance; and (5) biofilm production, promoting general antifungal resistance. This review also provides a summary of standardized inhibitory breakpoints obtained from international guidelines for prominent Candida species. Notably, N. glabrata, P. kudriavzevii and C. auris demonstrate fluconazole resistance.

The tricarboxylic acid (TCA) cycle: a malleable metabolic network to counter cellular stress.

The tricarboxylic acid (TCA) cycle is a primordial metabolic pathway that is conserved from bacteria to humans. Although this network is often viewed primarily as an energy producing engine fueling ATP synthesis via oxidative phosphorylation, mounting evidence reveals that this metabolic hub orchestrates a wide variety of pivotal biological processes. It plays an important part in combatting cellular stress by modulating NADH/NADPH homeostasis, scavenging ROS (reactive oxygen species), producing ATP by substrate-level phosphorylation, signaling and supplying metabolites to quell a range of cellular disruptions. This review elaborates on how the reprogramming of this network prompted by such abiotic stress as metal toxicity, oxidative tension, nutrient challenge and antibiotic insult is critical for countering these conditions in mostly microbial systems. The cross-talk between the stressors and the participants of TCA cycle that results in changes in metabolite and nucleotide concentrations aimed at combatting the abiotic challenge is presented. The fine-tuning of metabolites mediated by disparate enzymes associated with this metabolic hub is discussed. The modulation of enzymatic activities aimed at generating metabolic moieties dedicated to respond to the cellular perturbation is explained. This ancient metabolic network has to be recognized for its ability to execute a plethora of physiological functions beyond its well-established traditional roles.

Metabolic adaptation and ATP homeostasis in Pseudomonas fluorescens exposed to phosphate stress.

Phosphate (Pi) is essential for life as it is an integral part of the universal chemical energy adenosine triphosphate (ATP), and macromolecules such as, DNA, RNA proteins and lipids. Despite the core roles and the need of this nutrient in living cells, some bacteria can grow in environments that are poor in Pi. The metabolic mechanisms that enable bacteria to proliferate in a low phosphate environment are not fully understood. In this study, the soil microbe Pseudomonas (P.) fluorescens was cultured in a control and a low Pi (stress) medium in order to delineate how energy homeostasis is maintained. Although there was no significant variation in biomass yield in these cultures, metabolites like isocitrate, oxaloacetate, pyruvate and phosphoenolpyruvate (PEP) were markedly increased in the phosphate-starved condition. Components of the glycolytic, glyoxylate and tricarboxylic acid cycles operated in tandem to generate ATP by substrate level phosphorylation (SLP) as NADH-producing enzymes were impeded. The α-ketoglutarate (KG) produced when glutamine, the sole carbon nutrient was transformed into phosphoenol pyruvate (PEP) and succinyl-CoA (SC), two high energy moieties. The metabolic reprogramming orchestrated by isocitrate lyase (ICL), phosphoenolpyruvate synthase (PEPS), pyruvate phosphate dikinase (PPDK), and succinyl-CoA synthetase fulfilled the ATP budget. Cell free extract experiments confirmed ATP synthesis in the presence of such substrates as PEP, oxaloacetate and isocitrate respectively. Gene expression profiling revealed elevated transcripts associated with numerous enzymes including ICL, PEPS, and succinyl-CoA synthetase (SCS). This microbial adaptation will be critical in promoting biological activity in Pi-poor ecosystems.

A Metabolic Network Mediating the Cycling of Succinate, a Product of ROS Detoxification into α-Ketoglutarate, an Antioxidant.

Sulfur is an essential element for life. However, the soil microbe Pseudomonas (P.) fluorescens can survive in a low sulfur environment. When cultured in a sulfur-deficient medium, the bacterium reprograms its metabolic pathways to produce α-ketoglutarate (KG) and regenerate this keto-acid from succinate, a by-product of ROS detoxification. Succinate semialdehyde dehydrogenase (SSADH) and KG decarboxylase (KGDC) work in partnership to synthesize KG. This process is further aided by the increased activity of the enzymes glutamate decarboxylase (GDC) and γ-amino-butyrate transaminase (GABAT). The pool of succinate semialdehyde (SSA) generated is further channeled towards the formation of the antioxidant. Spectrophotometric analyses, HPLC experiments and electrophoretic studies with intact cells and cell-free extracts (CFE) pointed to the metabolites (succinate, SSA, GABA) and enzymes (SSADH, GDC, KGDC) contributing to this KG-forming metabolic machinery. Real-time polymerase chain reaction (RT-qPCR) revealed significant increase in transcripts of such enzymes as SSADH, GDC and KGDC. The findings of this study highlight a novel pathway involving keto-acids in ROS scavenging. The cycling of succinate into KG provides an efficient means of combatting an oxidative environment. Considering the central role of KG in biological processes, this metabolic network may be operative in other living systems.

Beyond mitochondria: Alternative energy-producing pathways from all strata of life.

It is well-established that mitochondria are the powerhouses of the cell, producing adenosine triphosphate (ATP), the universal energy currency. However, the most significant strengths of the electron transport chain (ETC), its intricacy and efficiency, are also its greatest downfalls. A reliance on metal complexes (FeS clusters, hemes), lipid moities such as cardiolipin, and cofactors including alpha-lipoic acid and quinones render oxidative phosphorylation vulnerable to environmental toxins, intracellular reactive oxygen species (ROS) and fluctuations in diet. To that effect, it is of interest to note that temporal disruptions in ETC activity in most organisms are rarely fatal, and often a redundant number of failsafes are in place to permit continued ATP production when needed. Here, we highlight the metabolic reconfigurations discovered in organisms ranging from parasitic Entamoeba to bacteria such as pseudomonads and then complex eukaryotic systems that allow these species to adapt to and occasionally thrive in harsh environments. The overarching aim of this review is to demonstrate the plasticity of metabolic networks and recognize that in times of duress, life finds a way.

Metabolic manipulation by Pseudomonas fluorescens: a powerful stratagem against oxidative and metal stress.

Metabolism is the foundation of all living organisms and is at the core of numerous if not all biological processes. The ability of an organism to modulate its metabolism is a central characteristic needed to proliferate, to be dormant and to survive any assault. Pseudomonas fluorescens is bestowed with a uniquely versatile metabolic framework that enables the microbe to adapt to a wide range of conditions including disparate nutrients and toxins. In this mini-review we elaborate on the various metabolic reconfigurations evoked by this microbial system to combat reactive oxygen/nitrogen species and metal stress. The fine-tuning of the NADH/NADPH homeostasis coupled with the production of α-keto-acids and ATP allows for the maintenance of a reductive intracellular milieu. The metabolic networks propelling the synthesis of metabolites like oxalate and aspartate are critical to keep toxic metals at bay. The biochemical processes resulting from these defensive mechanisms provide molecular clues to thwart infectious microbes and reveal elegant pathways to generate value-added products.

Metabolic adaptation and NADPH homeostasis evoked by a sulfur-deficient environment in Pseudomonas fluorescens.

Sulfur is essential for all living organisms due to its ability to mediate a variety of enzymatic reactions, signalling networks, and redox processes. The interplay between sulfhydryl group (SH) and disulfide bond (S-S) is central to the maintenance of intracellular oxidative balance. Although most aerobic organisms succumb to sulfur starvation, the nutritionally versatile soil microbe Pseudomonas fluorescens elaborates an intricate metabolic reprogramming in order to adapt to this challenge. When cultured in a sulfur-deficient medium with glutamine as the sole carbon and nitrogen source, the microbe reconfigures its metabolism aimed at the enhanced synthesis of NADPH, an antioxidant and the limited production of NADH, a pro-oxidant. While oxidative phosphorylation (OXPHOS) and tricarboxylic acid (TCA) cycle, metabolic modules known to generate reactive oxygen species are impeded, the activities NADPH-producing enzymes such as malic enzyme, and glutamate dehydrogenase (GDH) NADP-dependent are increased. The α-ketoglutarate (KG) generated from glutamine rapidly enters the TCA cycle via α-ketoglutarate dehydrogenase (KGDH), an enzyme that was prominent in the control cultures. In the S-deficient media, the severely impeded KGDH coupled with the increased activity of the reversible isocitrate dehydrogenase (ICDH) that fixes KG into isocitrate in the presence of NADH and HCO3- ensures a constant supply of this critical tricarboxylic acid. The up-regulation of ICDH-NADP dependent in the soluble fraction of the cells obtained from the S-deficient media results in enhanced NADPH synthesis, a reaction aided by the concomitant increase in NAD kinase activity. The latter converts NAD into NADP in the presence of ATP. Taken together, the data point to a metabolic network involving isocitrate, α-KG, and ICDH that converts NADH into NADPH in P. fluorescens subjected to a S-deprived environment.

Isocitrate Lyase and Succinate Semialdehyde Dehydrogenase Mediate the Synthesis of α-Ketoglutarate in Pseudomonas fluorescens.

Glycerol is an important by-product of the biodiesel industry and its transformation into value-added products like keto acids is being actively pursued in order to improve the efficacy of this renewable energy sector. Here, we report that the enhanced production of α-ketoglutarate (KG) effected by Pseudomonas fluorescens in a mineral medium supplemented with manganese (Mn) is propelled by the increased activities of succinate semialdehyde dehydrogenase (SSADH), γ-aminobutyric acid aminotransaminase (GABAT), and isocitrate lyase (ICL). The latter generates glyoxylate and succinate two key metabolites involved in this process. Fumarate reductase (FRD) also aids in augmenting the pool of succinate, a precursor of succinate semialdehyde (SSA). The latter is then carboxylated to KG with the assistance of α-ketoglutarate decarboxylase (KDC). These enzymes work in tandem to ensure copious secretion of the keto acid. When incubated with glycerol in the presence of bicarbonate ( H C O 3 - ), cell-free extracts readily produce KG with a metabolite fingerprint attributed to glutamate, γ-aminobutyric acid (GABA), succinate and succinate semialdehyde. Further targeted metabolomic and functional proteomic studies with high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and gel electrophoresis techniques provided molecular insights into this KG-generating machinery. Real-time quantitative polymerase chain reaction (RT-qPCR) analyses revealed the transcripts responsible for ICL and SSADH were elevated in the Mn-supplemented cultures. This hitherto unreported metabolic network where ICL and SSADH orchestrate the enhanced production of KG from glycerol, provides an elegant means of converting an industrial waste into a keto acid with wide-ranging application in the medical, cosmetic, and chemical sectors.

Reactive nitrogen species (RNS)-resistant microbes: adaptation and medical implications.

Nitrosative stress results from an increase in reactive nitrogen species (RNS) within the cell. Though the RNS - nitric oxide (·NO) and peroxynitrite (ONOO-) - play pivotal physiological roles, at elevated concentrations, these moieties can be poisonous to both prokaryotic and eukaryotic cells alike due to their capacity to disrupt a variety of essential biological processes. Numerous microbes are known to adapt to nitrosative stress by elaborating intricate strategies aimed at neutralizing RNS. In this review, we will discuss both the enzymatic systems dedicated to the elimination of RNS as well as the metabolic networks that are tailored to generate RNS-detoxifying metabolites - α-keto-acids. The latter has been demonstrated to nullify RNS via non-enzymatic decarboxylation resulting in the production of a carboxylic acid, many of which are potent signaling molecules. Furthermore, as aerobic energy production is severely impeded during nitrosative stress, alternative ATP-generating modules will be explored. To that end, a holistic understanding of the molecular adaptation to nitrosative stress, reinforces the notion that neutralization of toxicants necessitates significant metabolic reconfiguration to facilitate cell survival. As the alarming rise in antimicrobial resistant pathogens continues unabated, this review will also discuss the potential for developing therapies that target the alternative ATP-generating machinery of bacteria.

The role of glutamine synthetase in energy production and glutamine metabolism during oxidative stress.

Oxidative stress is known to severely impede aerobic adenosine triphosphate (ATP) synthesis. However, the metabolically-versatile Pseudomonas fluorescens survives this challenge by invoking alternative ATP-generating networks. When grown in a medium with glutamine as the sole organic nutrient in the presence of H2O2, the microbe utilizes glutamine synthetase (GS) to modulate its energy budget. The activity of this enzyme that mediates the release of energy stored in glutamine was sharply increased in the stressed cells compared to the controls. The enhanced activities of such enzymes as acetate kinase, adenylate kinase and nucleotide diphosphate kinase ensured the efficacy of this ATP producing-machine by transferring the high energy phosphate. The elevated amounts of phosphoenol pyruvate carboxylase and pyruvate orthophosphate dikinase recorded in the H2O2 exposed cells provided another route to ATP independent of the reduction of O2. This is the first demonstration of a metabolic pathway involving GS dedicated to ATP synthesis. The phospho-transfer network that is pivotal to the survival of the microorganism under oxidative stress may reveal therapeutic targets against infectious microbes reliant on glutamine for their proliferation.

Metabolic networks to generate pyruvate, PEP and ATP from glycerol in Pseudomonas fluorescens.

Glycerol is a major by-product of the biodiesel industry. In this study we report on the metabolic networks involved in its transformation into pyruvate, phosphoenolpyruvate (PEP) and ATP. When the nutritionally-versatile Pseudomonas fluorescens was exposed to hydrogen peroxide (H2O2) in a mineral medium with glycerol as the sole carbon source, the microbe reconfigured its metabolism to generate adenosine triphosphate (ATP) primarily via substrate-level phosphorylation (SLP). This alternative ATP-producing stratagem resulted in the synthesis of copious amounts of PEP and pyruvate. The production of these metabolites was mediated via the enhanced activities of such enzymes as pyruvate carboxylase (PC) and phosphoenolpyruvate carboxylase (PEPC). The high energy PEP was subsequently converted into ATP with the aid of pyruvate phosphate dikinase (PPDK), phosphoenolpyruvate synthase (PEPS) and pyruvate kinase (PK) with the concomitant formation of pyruvate. The participation of the phospho-transfer enzymes like adenylate kinase (AK) and acetate kinase (ACK) ensured the efficiency of this O2-independent energy-generating machinery. The increased activity of glycerol dehydrogenase (GDH) in the stressed bacteria provided the necessary precursors to fuel this process. This H2O2-induced anaerobic life-style fortuitously evokes metabolic networks to an effective pathway that can be harnessed into the synthesis of ATP, PEP and pyruvate. The bioconversion of glycerol to pyruvate will offer interesting economic benefit.

The role of formate in combatting oxidative stress.

The interaction of keto-acids with reactive oxygen species (ROS) is known to produce the corresponding carboxylic acid with the concomitant formation of CO2. Formate is liberated when the keto-acid glyoxylate neutralizes ROS. Here we report on how formate is involved in combating oxidative stress in the nutritionally-versatile Pseudomonas fluorescens. When the microbe was subjected to hydrogen peroxide (H2O2), the levels of formate were 8 and two-fold higher in the spent fluid and the soluble cell-free extracts obtained in the stressed cultures compared to the controls respectively. Formate was subsequently utilized as a reducing force to generate NADPH and succinate. The former is mediated by formate dehydrogenase (FDH-NADP), whose activity was enhanced in the stressed cells. Fumarate reductase that catalyzes the conversion of fumarate into succinate was also markedly increased in the stressed cells. These enzymes were modulated by H2O2. While the stressed whole cells produced copious amounts of formate in the presence of glycine, the cell-free extracts synthesized ATP and succinate from formate. Although the exact role of formate in anti-oxidative defence has to await further investigation, the data in this report suggest that this carboxylic acid may be a potent reductive force against oxidative stress.

Dysfunctional mitochondrial bioenergetics and the pathogenesis of hepatic disorders.

The liver is involved in a variety of critical biological functions including the homeostasis of glucose, fatty acids, amino acids, and the synthesis of proteins that are secreted in the blood. It is also at the forefront in the detoxification of noxious metabolites that would otherwise upset the functioning of the body. As such, this vital component of the mammalian system is exposed to a notable quantity of toxicants on a regular basis. It therefore comes as no surprise that there are over a hundred disparate hepatic disorders, encompassing such afflictions as fatty liver disease, hepatitis, and liver cancer. Most if not all of liver functions are dependent on energy, an ingredient that is primarily generated by the mitochondrion, the power house of all cells. This organelle is indispensable in providing adenosine triphosphate (ATP), a key effector of most biological processes. Dysfunctional mitochondria lead to a shortage in ATP, the leakage of deleterious reactive oxygen species (ROS), and the excessive storage of fats. Here we examine how incapacitated mitochondrial bioenergetics triggers the pathogenesis of various hepatic diseases. Exposure of liver cells to detrimental environmental hazards such as oxidative stress, metal toxicity, and various xenobiotics results in the inactivation of crucial mitochondrial enzymes and decreased ATP levels. The contribution of the latter to hepatic disorders and potential therapeutic cues to remedy these conditions are elaborated.

Metabolic reconfigurations aimed at the detoxification of a multi-metal stress in Pseudomonas fluorescens: implications for the bioremediation of metal pollutants.

Although the ability of microbial systems to adapt to the toxic challenge posed by numerous metal pollutants individually has been well documented, there is little detailed information on how bacteria survive in a multiple-metal environment. Here we describe the metabolic reconfiguration invoked by the soil microbe Pseudomonas fluorescens in a medium with millimolar amounts of aluminum (Al), iron (Fe), gallium (Ga), calcium (Ca), and zinc (Zn). While enzymes involved in the production of NADH were decreased, there was a marked increase in enzymatic activities dedicated to NADPH formation. A modified tricarboxylic acid (TCA) cycle coupled to an alternate glyoxylate shunt mediated the synthesis of adenosine triphosphate (ATP) with the concomitant generation of oxalate. This dicarboxylic acid was a key ingredient in the sequestration of the metals that were detoxified as a lipid complex. It appears that the microbe favors this strategy as opposed to a detoxification process aimed at each metal separately. These findings have interesting implications for bioremediation technologies.

Glycine metabolism and anti-oxidative defence mechanisms in Pseudomonas fluorescens.

The role of metabolism in anti-oxidative defence is only now beginning to emerge. Here, we show that the nutritionally-versatile microbe, Pseudomonas fluorescens, reconfigures its metabolism in an effort to generate NADPH, ATP and glyoxylate in order to fend off oxidative stress. Glyoxylate was produced predominantly via the enhanced activities of glycine dehydrogenase-NADP(+) (GDH), glycine transaminase (GTA) and isocitrate lyase (ICL) in a medium exposed to hydrogen peroxide (H2O2). This ketoacid was utilized to produce ATP by substrate-level phosphorylation and to neutralize reactive oxygen species with the concomitant formation of formate. The latter was also a source of NADPH, a process mediated by formate dehydrogenase-NADP(+) (FDH). The increased activities of phosphoenolpyruvate carboxylase (PEPC) and pyruvate orthophosphate dikinase (PPDK) worked in tandem to synthesize ATP in the H2O2-challenged cells that had markedly diminished capacity for oxidative phosphorylation. These metabolic networks provide an effective means of combating ROS and reveal therapeutic targets against microbes resistant to oxidative stress.

A novel ATP-generating machinery to counter nitrosative stress is mediated by substrate-level phosphorylation.

BACKGROUND: It is well-known that elevated amounts of nitric oxide and other reactive nitrogen species (RNS) impact negatively on the tricarboxylic acid (TCA) cycle and oxidative phosphorylation. These perturbations severely compromise O2-dependent energy production. While bacteria are known to adapt to RNS, a key tool employed by macrophages to combat infections, the exact mechanisms are unknown. METHODS: The bacterium was cultured in a defined mineral medium and cell-free extracts obtained at the same growth phase were utilized for various biochemical studies Blue native polyacrylamide gel electrophoresis followed by in-gel activity assays, high performance liquid chromatography and co-immunoprecipitaton are applied to investigate the effects of RNS on the model microbe Pseudomonas fluorescens. RESULTS: Citrate is channeled away from the tricarboxylic acid cycle using a novel metabolon consisting of citrate lyase (CL), phosphoenolpyruvate carboxylase (PEPC) and pyruvate phosphate dikinase (PPDK). This metabolic engine comprising three disparate enzymes appears to transiently assemble as a supercomplex aimed at ATP synthesis. The up-regulation in the activities of adenylate kinase (AK) and nucleoside diphosphate kinase (NDPK) ensured the efficacy of this ATP-making machine. CONCLUSION: Microbes may escape the effects of nitrosative stress by re-engineering metabolic networks in order to generate and store ATP anaerobically when the electron transport chain is defective. GENERAL SIGNIFICANCE: The molecular configuration described herein provides further understanding of how metabolism plays a key role in the adaptation to nitrosative stress and reveals novel targets that will inform the development of antimicrobial agents to counter RNS-resistant pathogens.

Nuclear lactate dehydrogenase modulates histone modification in human hepatocytes.

It is becoming increasingly apparent that the nucleus harbors metabolic enzymes that affect genetic transforming events. Here, we describe a nuclear isoform of lactate dehydrogenase (nLDH) and its ability to orchestrate histone deacetylation by controlling the availability of nicotinamide adenine dinucleotide (NAD(+)), a key ingredient of the sirtuin-1 (SIRT1) deacetylase system. There was an increase in the expression of nLDH concomitant with the presence of hydrogen peroxide (H2O2) in the culture medium. Under oxidative stress, the NAD(+) generated by nLDH resulted in the enhanced deacetylation of histones compared to the control hepatocytes despite no discernable change in the levels of SIRT1. There appeared to be an intimate association between nLDH and SIRT1 as these two enzymes co-immunoprecipitated. The ability of nLDH to regulate epigenetic modifications by manipulating NAD(+) reveals an intricate link between metabolism and the processing of genetic information.