Uridine supplementation antagonizes zalcitabine-induced microvesicular steatohepatitis in mice

Biological Functions and Potential Therapeutic Significance of O-GlcNAcylation in Hepatic Cellular Stress and Liver Diseases

O-linked-β-D-N-acetylglucosamine (O-GlcNAc) glycosylation (O-GlcNAcylation), which is dynamically regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), is a post-translational modification involved in multiple cellular processes. O-GlcNAcylation of proteins can regulate their biological functions via crosstalk with other post-translational modifications, such as phosphorylation, ubiquitination, acetylation, and methylation. Liver diseases are a major cause of death worldwide; yet, key pathological features of the disease, such as inflammation, fibrosis, steatosis, and tumorigenesis, are not fully understood. The dysregulation of O-GlcNAcylation has been shown to be involved in some severe hepatic cellular stress, viral hepatitis, liver fibrosis, nonalcoholic fatty acid liver disease (NAFLD), malignant progression, and drug resistance of hepatocellular carcinoma (HCC) through multiple molecular signaling pathways. Here, we summarize the emerging link between O-GlcNAcylation and hepatic pathological processes and provide information about the development of therapeutic strategies for liver diseases.

Uridine and its role in metabolic diseases, tumors, and neurodegenerative diseases

Uridine is a pyrimidine nucleoside found in plasma and cerebrospinal fluid with a concentration higher than the other nucleosides. As a simple metabolite, uridine plays a pivotal role in various biological processes. In addition to nucleic acid synthesis, uridine is critical to glycogen synthesis through the formation of uridine diphosphate glucose in which promotes the production of UDP-GlcNAc in the hexosamine biosynthetic pathway and supplies UDP-GlcNAc for O-GlcNAcylation. This process can regulate protein modification and affect its function. Moreover, Uridine has an effect on body temperature and circadian rhythms, which can regulate the metabolic rate and the expression of metabolic genes. Abnormal levels of blood uridine have been found in people with diabetes and obesity, suggesting a link of uridine dysregulation and metabolic disorders. At present, the role of uridine in glucose metabolism and lipid metabolism is controversial, and the mechanism is not clear, but it shows the trend of long-term damage and short-term benefit. Therefore, maintaining uridine homeostasis is essential for maintaining basic functions and normal metabolism. This article summarizes the latest findings about the metabolic effects of uridine and the potential of uridine metabolism as therapeutic target in treatment of metabolic disorders.

Effects of the Long-Term Administration of Uridine on the Functioning of Rat Liver Mitochondria in Hyperthyroidism

The effect of uridine (30 mg/kg for 7 days; intraperitoneally) on the functions of liver mitochondria in rats with experimentally induced hyperthyroidism (HT) (200 µg/100 g for 7 days, intraperitoneally) is studied in this paper. An excess of thyroid hormones (THs) led to an intensification of energy metabolism, the development of oxidative stress, a significant increase in the biogenesis, and changes in the content of proteins responsible for the fusion and fission of mitochondria. The injection of uridine did not change the concentration of THs in the blood of hyperthyroid rats (HRs) but normalized their body weight. The exposure to uridine improved the parameters of oxidative phosphorylation and corrected the activity of some complexes of the electron transport chain (ETC) in the liver mitochondria of HRs. The analysis of ETC complexes showed that the level of CI-CV did not change by the action of uridine in rats with the condition of HT. The application of uridine caused a significant increase in the activity of superoxide dismutase and lowered the rate of hydrogen peroxide production. It was found that uridine affected mitochondrial biogenesis by increasing the expression of the genes Ppargc1a and NRF1 and diminishing the expression of the Parkin gene responsible for mitophagy compared with the control animals. In addition, the mRNA level of the OPA1 gene was restored, which may indicate an improvement in the ETC activity and oxidative phosphorylation in the mitochondria of HR. As a whole, the results obtained demonstrate that uridine has a protective effect against HT-mediated functional disorders in the metabolism of rat liver mitochondria.

Mechanistic insights into phenanthrene-triggered oxidative stress-associated neurotoxicity, genotoxicity, and behavioral disturbances toward the brandling worm (Eisenia fetida) brain: The need for an ecotoxicological evaluation

In this study, earthworm (Eisenia fetida) brain was chosen as targeted receptors to probe the mechanisms of oxidative stress-related neurotoxicity, genotoxicity, and behavioral disturbances triggered by PHE. Results showed that PHE stress can initiate significant amounts of ROS, thus triggering oxidative stress in E. fetida brain. These effects were accompanied by a significant increase of damage to macromolecules DNA and lipids, resulting in severe oxidative effects. PHE exposure can induce AChE inhibition by ROS-induced injury and the accumulation of excess ACh at the nicotinic post-synaptic membrane, thus inducing aggravated neurological dysfunction and neurotoxicity of E. fetida through an oxidative stress pathway. Moreover, the burrowing behavior of earthworms was disturbed by oxidative stress-induced neurotoxicity after exposure to PHE. Furthermore, the abnormal mRNA expression profiles of oxidative stress- and neurotoxicity-related genes in worm brain were induced by PHE stress. The IBR results suggested that E. fetida brain was suffered more serious damage caused by PHE under higher doses and long-term exposure. Taken together, PHE exposure can trigger oxidative stress-mediated neurotoxicity and genotoxicity in worm brain and behavioral disorder through ROS-induced damage. This study is of great significance to evaluate the harmful effects of PHE and its mechanisms on soil ecological health.

Ecotoxicological evaluation of oxidative stress-mediated neurotoxic effects, genetic toxicity, behavioral disorders, and the corresponding mechanisms induced by fluorene-contaminated soil targeted to earthworm (Eisenia fetida) brain

Fluorene is a commonly identified PAH pollutant in soil and exhibits various worrisome hazardous effects to soil organisms. Currently, the toxicity profiles of fluorene on earthworm brain are rare, and the mechanisms and their corresponding pathways involved in fluorene-triggered neurotoxicity, genotoxicity, and behavior changes have not been reported hitherto. Herein, earthworm (Eisenia fetida) brain was chosen as targeted receptor to explore the neurotoxic effects, genetic toxicity, behavioral disorders, and related mechanisms caused by fluorene-induced oxidative stress pathways. The results showed excess fluorene initiated the release of excessive quantities of ROS in earthworm brain, which have caused oxidative stress and accompanied by serious oxidative effects, including LPO (lipid peroxidation) and DNA injury. To minimize the damage effects, the antioxidant defense mechanisms (antioxidant enzymes and non-enzymatic antioxidants) were activated, and entailed a decrease of the antioxidant capacity in E. fetida brain, which, in turn, causes further ROS-induced ROS release. Exposure of fluorene induced the abnormal mRNA expression of genes relevant to oxidative stress (e.g., GST, SOD, CAT, GPx, MT, and Hsp70) and neurotoxicity (e.g., H02, C04, D06, and E08) in E. fetida brain. Specifically, fluorene can bind directly to AChE, destroying the conformation of this protein, and even affecting its physiological functions. This occurrence caused the inhibition of AChE activity and excess ACh accumulation at the nicotinic post-synaptic membrane, finally triggering neurotoxicity by activation of pathways related to oxidative stress. Moreover, the avoidance responses and burrowing behavior were obviously disturbed by oxidative stress-induced neurotoxicity after exposure to fluorene. The results form IBR suggested more severe poisoning effects to E. fetida brain initiated by high-dose and long-term exposure of fluorene. Among, oxidative stress injury and genotoxic potential are more sensitive endpoint than others. Collectively, fluorene stress can provoke potential neurotoxicity, genotoxicity, and behavioral disturbances targeted to E. fetida brain through the ROS-mediated pathways involving oxidative stress. These findings are of great significance to estimate the detrimental effects of fluorene and the corresponding mechanisms on soil eco-safety.

Nucleotide metabolism: a pan-cancer metabolic dependency

Metabolic alterations are a key hallmark of cancer cells, and the augmented synthesis and use of nucleotide triphosphates is a critical and universal metabolic dependency of cancer cells across different cancer types and genetic backgrounds. Many of the aggressive behaviours of cancer cells, including uncontrolled proliferation, chemotherapy resistance, immune evasion and metastasis, rely heavily on augmented nucleotide metabolism. Furthermore, most of the known oncogenic drivers upregulate nucleotide biosynthetic capacity, suggesting that this phenotype is a prerequisite for cancer initiation and progression. Despite the wealth of data demonstrating the efficacy of nucleotide synthesis inhibitors in preclinical cancer models and the well-established clinical use of these drugs in certain cancer settings, the full potential of these agents remains unrealized. In this Review, we discuss recent studies that have generated mechanistic insights into the diverse biological roles of hyperactive cancer cell nucleotide metabolism. We explore opportunities for combination therapies that are highlighted by these recent advances and detail key questions that remain to be answered, with the goal of informing urgently warranted future studies.

Moschus exerted protective activity against H2O2-induced cell injury in PC12 cells through regulating Nrf-2/ARE signaling pathways

The pivotal characteristics of Alzheimer's disease (AD) are irreversible memory loss and progressive cognitive decline, eventually causing death from brain failure. In the various proposed hypotheses of AD, oxidative stress is also regarded as a symbolic pathophysiologic cascade contributing to brain diseases. Using Chinese herbal medicine may be beneficial for treating and preventing AD. As a rare and valuable animal medicine, Moschus possesses antioxidant and antiapoptotic efficacy and is extensively applied for treating unconsciousness, stroke, coma, and cerebrovascular diseases. We aim to evaluate whether Moschus protects PC12 cells from hydrogen peroxide (H₂O₂)-induced cellular injury. The chemical constituents of Moschus are analyzed by GC-MS assay. The cell viability, reactive oxygen species (ROS) levels, mitochondrial membrane potential (MMP) levels, oxidative stress-related indicators, and apoptotic proteins are determined. Through GC-MS analysis, nineteen active contents were identified. The cell viability loss, lactate dehydrogenase releases, MMP levels, ROS productions, and Malondialdehyde (MDA) activities decreased, and BAX, Caspase-3, and Kelch-like ECH-associated protein 1 expression also significantly down-regulated and heme oxygenase 1, nuclear factor erythroid-2-related factor 2 (Nrf-2), and quinine oxidoreductase 1 expression upregulated after pretreatment of Moschus. The result indicated Moschus has neuroprotective activity in relieving H₂O₂-induced cellular damage, and the potential mechanism might be associated with regulating the Nrf-2/ARE signaling pathway. A more in-depth and comprehensive understanding of Moschus in the pathogenesis of AD will provide a fundamental basis for in vivo AD animal model research, which may be able to provide further insights and new targets for AD therapy.

Effect of Chronic Treatment with Uridine on Cardiac Mitochondrial Dysfunction in the C57BL/6 Mouse Model of High-Fat Diet-Streptozotocin-Induced Diabetes

Long-term hyperglycemia in diabetes mellitus is associated with complex damage to cardiomyocytes and the development of mitochondrial dysfunction in the myocardium. Uridine, a pyrimidine nucleoside, plays an important role in cellular metabolism and is used to improve cardiac function. Herein, the antidiabetic potential of uridine (30 mg/kg/day for 21 days, i.p.) and its effect on mitochondrial homeostasis in the heart tissue were examined in a high-fat diet-streptozotocin-induced model of diabetes in C57BL/6 mice. We found that chronic administration of uridine to diabetic mice normalized plasma glucose and triglyceride levels and the heart weight/body weight ratio and increased the rate of glucose utilization during the intraperitoneal glucose tolerance test. Analysis of TEM revealed that uridine prevented diabetes-induced ultrastructural abnormalities in mitochondria and sarcomeres in ventricular cardiomyocytes. In diabetic heart tissue, the mRNA level of Ppargc1a decreased and Drp1 and Parkin gene expression increased, suggesting the disturbances of mitochondrial biogenesis, fission, and mitophagy, respectively. Uridine treatment of diabetic mice restored the mRNA level of Ppargc1a and enhanced Pink1 gene expression, which may indicate an increase in the intensity of mitochondrial biogenesis and mitophagy, and as a consequence, mitochondrial turnover. Uridine also reduced oxidative phosphorylation dysfunction and suppressed lipid peroxidation, but it had no significant effect on the impaired calcium retention capacity and potassium transport in the heart mitochondria of diabetic mice. Altogether, these findings suggest that, along with its hypoglycemic effect, uridine has a protective action against diabetes-mediated functional and structural damage to cardiac mitochondria and disruption of mitochondrial quality-control systems in the diabetic heart.

Uncovering the roles of dihydropyrimidine dehydrogenase in fatty-acid induced steatosis using human cellular models

Pyrimidine catabolism is implicated in hepatic steatosis. Dihydropyrimidine dehydrogenase (DPYD) is an enzyme responsible for uracil and thymine catabolism, and DPYD human genetic variability affects clinically observed toxicity following 5-Fluorouracil administration. In an in vitro model of fatty acid-induced steatosis, the pharmacologic inhibition of DPYD resulted in protection from lipid accumulation. Additionally, a gain-of-function mutation of DPYD, created through clustered regularly interspaced short palindromic repeats associated protein 9 (CRISPR-Cas9) engineering, led to an increased lipid burden, which was associated with altered mitochondrial functionality in a hepatocarcionma cell line. The studies presented herein describe a novel role for DPYD in hepatocyte metabolic regulation as a modulator of hepatic steatosis.

Uridine attenuates obesity, ameliorates hepatic lipid accumulation and modifies the gut microbiota composition in mice fed with a high-fat diet

Uridine (UR) is a pyrimidine nucleoside that plays an important role in regulating glucose and lipid metabolism. The aim of this study was to investigate the effect of UR on obesity, fat accumulation in liver, and gut microbiota composition in high-fat diet (HFD)-fed mice. ICR mice were, respectively, divided into 3 groups for 8 weeks, that is, control (CON, n = 12), high fat diet (HFD, n = 16), and HFD + UR groups (0.4 mg mL-1 in drinking water, n = 16). UR supplementation significantly reduced the body weight and suppressed the accumulation of subcutaneous, epididymal, and mesenteric WAT in HFD-fed mice (P < 0.05). Meanwhile, UR also decreased the lipid droplet accumulation in the liver and liver organoids (P < 0.05). In addition, UR supplementation increased bacterial diversity and Bacteroidetes abundance, and decreased the Firmicutes-to-Bacteroidetes ratio in HFD-fed mice significantly (P < 0.05). UR promoted the growth of butyrate-producing bacteria of Odoribacter, unidentified-Ruminococcaceae, Intestinimonas, Ruminiclostridium, and unidentified-Lachnospiraceae. A close correlation between several specific bacterial phyla or genera and the levels of WAT weight, hepatic TC, or hepatic TG genera was revealed through Spearman's correlation analysis. These results demonstrated that UR supplementation could be beneficial by attenuating HFD-induced obesity and nonalcoholic fatty liver disease.

Uridine Metabolism and Its Role in Glucose, Lipid, and Amino Acid Homeostasis

Pyrimidine nucleoside uridine plays a critical role in maintaining cellular function and energy metabolism. In addition to its role in nucleoside synthesis, uridine and its derivatives contribute to reduction of cytotoxicity and suppression of drug-induced hepatic steatosis. Uridine is mostly present in blood and cerebrospinal fluid, where it contributes to the maintenance of basic cellular functions affected by UPase enzyme activity, feeding habits, and ATP depletion. Uridine metabolism depends on three stages: de novo synthesis, salvage synthesis pathway and catabolism, and homeostasis, which is tightly relating to glucose homeostasis and lipid and amino acid metabolism. This review is devoted to uridine metabolism and its role in glucose, lipid, and amino acid homeostasis.

MUC1 oncoprotein mitigates ER stress via CDA-mediated reprogramming of pyrimidine metabolism

The Mucin 1 (MUC1) protein is overexpressed in various cancers and mediates chemotherapy resistance. However, the mechanism is not fully understood. Given that most chemotherapeutic drugs disrupt ER homeostasis as part of their toxicity, and MUC1 expression is regulated by proteins involved in ER homeostasis, we investigated the link between MUC1 and ER homeostasis. MUC1 knockdown in pancreatic cancer cells enhanced unfolded protein response (UPR) signaling and cell death upon ER stress induction. Transcriptomic analysis revealed alterations in the pyrimidine metabolic pathway and cytidine deaminase (CDA). ChIP and CDA activity assays showed that MUC1 occupied CDA gene promoter upon ER stress induction correlating with increased CDA expression and activity in MUC1-expressing cells as compared to MUC1 knockdown cells. Inhibition of either the CDA or pyrimidine metabolic pathway diminished survival in MUC1-expressing cancer cells upon ER stress induction. Metabolomic analysis demonstrated that MUC1-mediated CDA activity corresponded to deoxycytidine to deoxyuridine metabolic reprogramming upon ER stress induction. The resulting increase in deoxyuridine mitigated ER stress-induced cytotoxicity. Additionally, given 1) the established roles of MUC1 in protecting cells against reactive oxygen species (ROS) insults, 2) ER stress-generated ROS further promote ER stress and 3) the emerging anti-oxidant property of deoxyuridine, we further investigated if MUC1 regulated ER stress by a deoxyuridine-mediated modulation of ROS levels. We observed that deoxyuridine could abrogate ROS-induced ER stress to promote cancer cell survival. Taken together, our findings demonstrate a novel MUC1-CDA axis of the adaptive UPR that provides survival advantage upon ER stress induction.

Nucleoside reverse transcriptase inhibitors induced hepatocellular mitochondrial DNA lesions and compensatory enhancement of mitochondrial function and DNA repair

Nucleoside reverse transcriptase inhibitors (NRTIs) are the backbone of combined antiretroviral therapy (cART) and are widely used in anti-human immunodeficiency virus (HIV) therapy. Long-term administration of NRTIs can result in mitochondrial dysfunction in certain HIV-1-infected patients. However, NRTI-associated liver mitochondrial toxicity is not well known. Herein, the liver autopsy of acquired immune deficiency syndrome (AIDS) patients and the liver tissues of mice with 12 months of NRTI exposure were used to identify NRTI-associated liver toxicity with immunofluorescence, quantitative real-time polymerase chain reaction (qPCR), Amplex red and horseradish peroxidase, and cloning and sequencing. Laser capture microdissection was used to capture hepatocytes from liver tissues. We observed DNA oxidative damage and mitochondrial DNA (mtDNA) loss in the livers of AIDS patients, and cART patients had higher DNA oxidative damage and lower DNA repair function in liver tissues than non-cART patients. We also observed liver oxidative damage, increased DNA repair and mtDNA loss in mice with exposure to four different NRTIs for 12 months, and hepatocytes had no more mtDNA loss than liver tissues. Although NRTIs could induce mitochondrial hydrogen peroxide production, increased mitochondrial oxygen consumption was found with a Clark-type electrode. The captured hepatocytes had greater diversity in their mtDNA D-loop, dehydrogenase subunit1 (ND1) and ND4 than the controls. Long-term NRTI exposure induced single nucleotide variation in hepatocellular mtDNA D-loop, ND1 and ND4. Our findings indicate that NRTIs can induce liver mtDNA lesions, but simultaneously enhance mitochondrial function and mtDNA repair.

Role of nonalcoholic fatty liver disease as risk factor for drug-induced hepatotoxicity

BACKGROUND

Obesity is often associated with nonalcoholic fatty liver disease (NAFLD), which refers to a large spectrum of hepatic lesions including fatty liver, nonalcoholic steatohepatitis (NASH) and cirrhosis. Different investigations showed or suggested that obesity and NAFLD are able to increase the risk of hepatotoxicity of different drugs. Some of these drugs could induce more frequently an acute hepatitis in obese individuals whereas others could worsen pre-existing NAFLD.

AIM

The main objective of the present review was to collect the available information regarding the role of NAFLD as risk factor for drug-induced hepatotoxicity. For this purpose, we performed a data-mining analysis using different queries including drug-induced liver injury (or DILI), drug-induced hepatotoxicity, fatty liver, nonalcoholic fatty liver disease (or NAFLD), steatosis and obesity. The main data from the collected articles are reported in this review and when available, some pathophysiological hypotheses are put forward.

RELEVANCE FOR PATIENTS

Drugs that could pose a potential risk in obese patients include compounds belonging to different pharmacological classes such as acetaminophen, halothane, methotrexate, rosiglitazone, stavudine and tamoxifen. For some of these drugs, experimental investigations in obese rodents confirmed the clinical observations and unveiled different pathophysiological mechanisms which could explain why these pharmaceuticals are particularly hepatotoxic in obesity and NAFLD. Other drugs such as pentoxifylline, phenobarbital and omeprazole might also pose a risk but more investigations are required to determine whether this risk is significant or not. Because obese people often take several drugs for the treatment of different obesity-related diseases such as type 2 diabetes, hyperlipidemia and coronary heart disease, it is urgent to identify the main pharmaceuticals that can cause acute hepatitis on a fatty liver background or induce NAFLD worsening.

Chronic Uridine Administration Induces Fatty Liver and Pre-Diabetic Conditions in Mice

Uridine is a pyrimidine nucleoside that exerts restorative functions in tissues under stress. Short-term co-administration of uridine with multiple unrelated drugs prevents drug-induced liver lipid accumulation. Uridine has the ability to modulate liver metabolism; however, the precise mechanism has not been delineated. In this study, long-term effects of uridine on liver metabolism were examined in both HepG2 cell cultures and C57BL/6J mice. We report that uridine administration was associated with O-GlcNAc modification of FOXO1, increased gluconeogenesis, reduced insulin signaling activity, and reduced expression of a liver-specific fatty acid binding protein FABP1. Long-term uridine feeding induced systemic glucose intolerance and severe liver lipid accumulation in mice. Our findings suggest that the therapeutic potentials of uridine should be designed for short-term acute administration.

Uridine affects liver protein glycosylation, insulin signaling, and heme biosynthesis

Purines and pyrimidines are complementary bases of the genetic code. The roles of purines and their derivatives in cellular signal transduction and energy metabolism are well-known. In contrast, the roles of pyrimidines and their derivatives in cellular function remain poorly understood. In this study, the roles of uridine, a pyrimidine nucleoside, in liver metabolism are examined in mice. We report that short-term uridine administration in C57BL/6J mice increases liver protein glycosylation profiles, reduces phosphorylation level of insulin signaling proteins, and activates the HRI-eIF-2α-ATF4 heme-deficiency stress response pathway. Short-term uridine administration is also associated with reduced liver hemin level and reduced ability for insulin-stimulated blood glucose removal during an insulin tolerance test. Some of the short-term effects of exogenous uridine in C57BL/6J mice are conserved in transgenic UPase1^−/− mice with long-term elevation of endogenous uridine level. UPase1^−/− mice exhibit activation of the liver HRI-eIF-2α-ATF4 heme-deficiency stress response pathway. UPase1^−/− mice also exhibit impaired ability for insulin-stimulated blood glucose removal. However, other short-term effects of exogenous uridine in C57BL/6J mice are not conserved in UPase1^−/− mice. UPase1^−/− mice exhibit normal phosphorylation level of liver insulin signaling proteins and increased liver hemin concentration compared to untreated control C57BL/6J mice. Contrasting short-term and long-term consequences of uridine on liver metabolism suggest that uridine exerts transient effects and elicits adaptive responses. Taken together, our data support potential roles of pyrimidines and their derivatives in the regulation of liver metabolism.

Uridine prevents tamoxifen-induced liver lipid droplet accumulation

BACKGROUND

Tamoxifen, an agonist of estrogen receptor, is widely prescribed for the prevention and long-term treatment of breast cancer. A side effect of tamoxifen is fatty liver, which increases the risk for non-alcoholic fatty liver disease. Prevention of tamoxifen-induced fatty liver has the potential to improve the safety of long-term tamoxifen usage.

METHODS

Uridine, a pyrimidine nucleoside with reported protective effects against drug-induced fatty liver, was co-administered with tamoxifen in C57BL/6J mice. Liver lipid levels were evaluated with lipid visualization using coherent anti-Stokes Raman scatting (CARS) microscopy, biochemical assay measurement of triacylglyceride (TAG), and liquid chromatography coupled with mass spectrometry (LC-MS) measurement of membrane phospholipid. Blood TAG and cholesterol levels were measured. Mitochondrial respiration of primary hepatocytes in the presence of tamoxifen and/or uridine was evaluated by measuring oxygen consumption rate with an extracellular flux analyzer. Liver protein lysine acetylation profiles were evaluated with 1D and 2D Western blots. In addition, the relationship between endogenous uridine levels, fatty liver, and tamoxifen administration was evaluated in transgenic mice UPase1-/-and UPase1-TG.

RESULTS

Uridine co-administration prevented tamoxifen-induced liver lipid droplet accumulation in mice. The most prominent effect of uridine co-administration with tamoxifen was the stimulation of liver membrane phospholipid biosynthesis. Uridine had no protective effect against tamoxifen-induced impairment to mitochondrial respiration of primary hepatocytes or liver TAG and cholesterol export. Uridine had no effect on tamoxifen-induced changes to liver protein acetylation profile. Transgenic mice UPase1-/-with increased pyrimidine salvage activity were protected against tamoxifen-induced liver lipid droplet accumulation. In contrast, UPase1-TG mice with increased pyrimidine catabolism activity had intrinsic liver lipid droplet accumulation, which was aggravated following tamoxifen administration.

CONCLUSION

Uridine co-administration was effective at preventing tamoxifen-induced liver lipid droplet accumulation. The ability of uridine to prevent tamoxifen-induced fatty liver appeared to depend on the pyrimidine salvage pathway, which promotes biosynthesis of membrane phospholipid.

Uridine prevents fenofibrate-induced fatty liver

Uridine, a pyrimidine nucleoside, can modulate liver lipid metabolism although its specific acting targets have not been identified. Using mice with fenofibrate-induced fatty liver as a model system, the effects of uridine on liver lipid metabolism are examined. At a daily dosage of 400 mg/kg, fenofibrate treatment causes reduction of liver NAD(+)/NADH ratio, induces hyper-acetylation of peroxisomal bifunctional enzyme (ECHD) and acyl-CoA oxidase 1 (ACOX1), and induces excessive accumulation of long chain fatty acids (LCFA) and very long chain fatty acids (VLCFA). Uridine co-administration at a daily dosage of 400 mg/kg raises NAD(+)/NADH ratio, inhibits fenofibrate-induced hyper-acetylation of ECHD, ACOX1, and reduces accumulation of LCFA and VLCFA. Our data indicates a therapeutic potential for uridine co-administration to prevent fenofibrate-induced fatty liver.

Muscle-fiber transdifferentiation in an experimental model of respiratory chain myopathy

Introduction

Skeletal muscle fiber composition and muscle energetics are not static and change in muscle disease. This study was performed to determine whether a mitochondrial myopathy is associated with adjustments in skeletal muscle fiber-type composition.

Methods

Ten rats were treated with zidovudine, an antiretroviral nucleoside reverse transcriptase inhibitor that induces a myopathy by interfering with mitochondrial functions. Soleus muscles were examined after 21 weeks of treatment. Ten untreated rats served as controls.

Results

Zidovudine induced a myopathy with mitochondrial DNA depletion, abnormalities in mitochondrial ultrastructure, and reduced cytochrome c oxidase activity. Mitochondrial DNA was disproportionally more diminished in type I compared with type II fibers, whereas atrophy predominated in type II fibers. Compared with those of controls, zidovudine-exposed soleus muscles contained an increased proportion (256%) of type II fibers, whereas neonatal myosin heavy chains remained repressed, indicating fiber-type transformation in the absence of regeneration. Microarray gene-expression analysis confirmed enhanced fast-fiber isoforms, repressed slow-fiber transcripts, and reduced neonatal fiber transcripts in the mitochondrial myopathy. Respiratory chain transcripts were diminished, whereas the enzymes of glycolysis and glycogenolysis were enhanced, indicating a metabolic adjustment from oxidative to glycolytic capacities. A coordinated regulation was found of transcription factors known to orchestrate type II fiber formation (upregulation of MyoD, Six1, Six2, Eya1, and Sox6, and downregulation of myogenin and ERRγ).

Conclusions

The type I to type II fiber transformation in mitochondrial myopathy implicates mitochondrial function as a new regulator of skeletal muscle fiber type.

Antiretroviral nucleoside analogues suppress antibody synthesis in human B-lymphocytes

BACKGROUND

Some antiretroviral nucleoside reverse transcriptase inhibitors (NRTI) impair mitochondrial polymerase-γ and T-cell proliferation, possibly by pyrimidine depletion. We aimed to analyse NRTI effects on the content of mitochondrial DNA (mtDNA) and B-cells, and on their proliferation and antibody synthesis.

METHODS

Peripheral blood B-lymphocytes from six healthy individuals were stimulated in vitro with interleukin-4 and Staphylococcus aureus superantigen in the presence or absence of NRTI in concentrations equivalent to, or fivefold exceeding, human peak plasma levels. We also tested the effects of uridine, a pyrimidine precursor, which has antagonized NRTI toxicities in other models.

RESULTS

During 9 days of culture, B-lymphocyte proliferation and vitality were not affected by NRTI. Didanosine and stavudine, but not zidovudine, dose-dependently induced mtDNA depletion. All three NRTI significantly and dose-dependently impaired the synthesis of all immunoglobulin classes. The lymphocytotoxic effects of the thymidine analogues zidovudine and stavudine on B-lymphocytes were antagonized by the addition of uridine.

CONCLUSIONS

Didanosine, stavudine and zidovudine induce mitochondrial toxicity in human B-lymphocytes and impair the immunoglobulin synthesis in vitro, warranting further studies on their in vivo effects.

High-dose clevudine impairs mitochondrial function and glucose-stimulated insulin secretion in INS-1E cells

Background

Clevudine is a nucleoside analog reverse transcriptase inhibitor that exhibits potent antiviral activity against hepatitis B virus (HBV) without serious side effects. However, mitochondrial myopathy has been observed in patients with chronic HBV infection taking clevudine. Moreover, the development of diabetes was recently reported in patients receiving long-term treatment with clevudine. In this study, we investigated the effects of clevudine on mitochondrial function and insulin release in a rat clonal β-cell line, INS-1E.

Methods

The mitochondrial DNA (mtDNA) copy number and the mRNA levels were measured by using quantitative PCR. MTT analysis, ATP/lactate measurements, and insulin assay were performed.

Results

Both INS-1E cells and HepG2 cells, which originated from human hepatoma, showed dose-dependent decreases in mtDNA copy number and cytochrome c oxidase-1 (Cox-1) mRNA level following culture with clevudine (10 μM-1 mM) for 4 weeks. INS-1E cells treated with clevudine had reduced total mitochondrial activities, lower cytosolic ATP contents, enhanced lactate production, and more lipid accumulation. Insulin release in response to glucose application was markedly decreased in clevudine-treated INS-1E cells, which might be a consequence of mitochondrial dysfunction.

Conclusions

Our data suggest that high-dose treatment with clevudine induces mitochondrial defects associated with mtDNA depletion and impairs glucose-stimulated insulin secretion in insulin-releasing cells. These findings partly explain the development of diabetes in patients receiving clevudine who might have a high susceptibility to mitochondrial toxicity.

Role of pyrimidine depletion in the mitochondrial cardiotoxicity of nucleoside analogue reverse transcriptase inhibitors

OBJECTIVE

Long-term antiretroviral treatment with nucleoside analogue reverse transcriptase inhibitors (NRTI) may result in a cardiomyopathy due to mitochondrial DNA (mtDNA) depletion. An intact mitochondrial function is required for the synthesis of intramyocardial pyrimidine nucleotides, which in turn are building blocks of mtDNA. We investigated if NRTI-related cardiomyopathy can be prevented with pyrimidine precursors.

METHODS

Mice were fed with zidovudine or zalcitabine with or without simultaneous Mitocnol, a dietary supplement with high uridine bioavailability. Myocardia were examined after 9 weeks.

RESULTS

Both NRTI induced a cardiomyopathy with mitochondrial enlargement, a disrupted cristal architecture on electron microscopy and diminished myocardial mtDNA copy numbers. The myocardial mtDNA-encoded cytochrome c-oxidase I subunit was impaired more profoundly than the nucleus-encoded cytochrome c-oxidase IV subunit. The myocardial formation of reactive oxygen species and mtDNA mutations was enhanced in zidovudine and zalcitabine treated animals. Mitocnol attenuated or normalized all myocardial pathology when given with both NRTI, but by itself had no intrinsic effects and no apparent adverse effects.

CONCLUSIONS

Zidovudine and zalcitabine induce a mitochondrial cardiomyopathy, which is antagonized with uridine supplementation, implicating pyrimidine pool depletion in its pathogenesis. Pyrimidine pool replenishment may be exploited clinically because uridine is well tolerated.

Mitochondrial function, inflammation, fat and bone in HIV lipoatrophy: randomized study of uridine supplementation or switch to tenofovir

BACKGROUND

Lipoatrophy modestly improves when the thymidine analogue nucleoside reverse transcriptase inhibitor (tNRTI) is removed. In vitro, uridine (NucleomaxX(®); Pharma Nord, Vojens, Denmark) reversed tNRTI mitochondrial toxicity.

METHODS

All patients had lipoatrophy on a tNRTI-containing regimen with HIV RNA<400 copies/ml. A randomized 48-week study switched patients from tNRTI to tenofovir (TDF) or added uridine (continuing tNRTI). End points were changes in limb fat (DEXA), subcutaneous abdominal fat mitochondrial DNA (mtDNA) and mitochondrial RNA (mtRNA), inflammation markers (soluble tumour necrosis factor receptors, high-sensitivity C reactive protein [hsCRP], interleukin-6 [IL-6], soluble vascular cell adhesion molecule 1), bone mineral density (BMD) of the hip and spine, HIV-1 RNA, CD4(+) T-cells and fasting metabolic parameters.

RESULTS

Fifty patients were enrolled (n=24 TDF switch; n=26 uridine); median age 48 years; 54% white; 86% male; limb fat 4,494 g. Baseline characteristics were similar between groups. In the NucleomaxX(®) arm, mtRNA increased (all P<0.001), hsCRP and IL-6 increased (both P=0.02), whereas fat mtDNA decreased without changes in limb fat. In the TDF-switch arm, fat mtDNA and inflammation markers did not change; however, significant increases in mtRNAs (P<0.001), limb fat (409 g; IQR -59-1,155) and CD4(+) T-cell count (P=0.03), and decreases in total and hip BMD (median -3.3%; IQR -5.1-0; P=0.005) were observed. Between-group changes were significant for fat mtDNA, hsCRP, IL-6, limb fat and hip BMD. No correlation was found between changes in limb fat and those of fat mtRNA, inflammation markers or protease inhibitor duration.

CONCLUSIONS

In HIV lipoatrophy, NucleomaxX(®) improved mtRNA, but worsened inflammation markers and fat mtDNA without changes in limb fat. Switching from a tNRTI to TDF for 48 weeks increased limb fat and fat mtRNA. Large decreases in total and hip BMD were seen after TDF switch.
ClinicalTrials.gov identifier: NCT00119379.

Central role of mitochondria in drug-induced liver injury

A frequent mechanism for drug-induced liver injury (DILI) is the formation of reactive metabolites that trigger hepatitis through direct toxicity or immune reactions. Both events cause mitochondrial membrane disruption. Genetic or acquired factors predispose to metabolite-mediated hepatitis by increasing the formation of the reactive metabolite, decreasing its detoxification, or by the presence of critical human leukocyte antigen molecule(s). In other instances, the parent drug itself triggers mitochondrial membrane disruption or inhibits mitochondrial function through different mechanisms. Drugs can sequester coenzyme A or can inhibit mitochondrial β-oxidation enzymes, the transfer of electrons along the respiratory chain, or adenosine triphosphate (ATP) synthase. Drugs can also destroy mitochondrial DNA, inhibit its replication, decrease mitochondrial transcripts, or hamper mitochondrial protein synthesis. Quite often, a single drug has many different effects on mitochondrial function. A severe impairment of oxidative phosphorylation decreases hepatic ATP, leading to cell dysfunction or necrosis; it can also secondarily inhibit ß-oxidation, thus causing steatosis, and can also inhibit pyruvate catabolism, leading to lactic acidosis. A severe impairment of β-oxidation can cause a fatty liver; further, decreased gluconeogenesis and increased utilization of glucose to compensate for the inability to oxidize fatty acids, together with the mitochondrial toxicity of accumulated free fatty acids and lipid peroxidation products, may impair energy production, possibly leading to coma and death. Susceptibility to parent drug-mediated mitochondrial dysfunction can be increased by factors impairing the removal of the toxic parent compound or by the presence of other medical condition(s) impairing mitochondrial function. New drug molecules should be screened for possible mitochondrial effects.

Uridine supplementation in the treatment of HIV lipoatrophy: results of ACTG 5229

BACKGROUND

Lipoatrophy is prevalent on thymidine nucleoside reverse transcriptase inhibitors (tNRTIs). A pilot trial showed that uridine (NucleomaxX) increased limb fat.

METHODS

A5229 was a multicenter trial in which HIV-infected individuals with lipoatrophy on tNRTI regimens were randomized to NucleomaxX or placebo. Primary endpoint was change in limb fat from baseline to week 48. The study was powered to detect 400-g difference between arms at week 48. A stratified Wilcoxon rank-sum test was used to assess between-arm differences.

RESULTS

The 165 participants were 91% men, 62% white; median age 49 years, CD4 cell count 506 cells/μl, and limb fat 3037 g; 81% had HIV-1 RNA 50 copies/ml or less; 76% were on zidovudine (ZDV). Baseline characteristics were similar between groups. Only 59% completed 48 weeks of treatment; however, only three participants (one on uridine) discontinued due to toxicity (diarrhea). In intent to treat, there was no difference for changes in limb fat between treatments at week 24 or week 48. On as-treated analysis, uridine resulted in an increase in %limb fat vs. placebo (3.4 vs. -0.8%, P = 0.01) at week 24 but not at week 48 (1.8 vs. 3.8%, P = 0.93). Similar results were seen when limiting the analysis to patients with at least 80% adherence. The results were not related to severity of lipoatrophy or type of tNRTI. No changes were found in facial anthropometrics, fasting lipids, trunk fat, CD4 cell count, or HIV RNA.

CONCLUSIONS

We found a modest transient improvement in limb fat after 24 weeks of uridine. The lack of sustained efficacy at week 48 was not due to changes in adherence or reduction in sample size. Uridine was well tolerated and did not impair virologic control.

Oral uridine supplementation antagonizes the peripheral neuropathy and encephalopathy induced by antiretroviral nucleoside analogues

OBJECTIVE

Peripheral neuropathy and central nervous system neurodegeneration may result from the mitochondrial toxicity of some antiretroviral nucleoside analogues. We investigated whether this neuropathology may be antagonized by uridine supplementation in vivo.

DESIGN

Because of the obvious difficulties in obtaining human neural tissues, the mitochondrial neurotoxicity of the nucleoside analogues was studied in mice.

METHODS

BALB/C mice (7 weeks of age) were fed for 9 weeks with zalcitabine (13 mg/kg per day) or zidovudine (100 mg/kg per day) with or without mitocnol (340 mg/kg per day), a dietary supplement with high uridine bioavailability. Hippocampal and sciatic nerve mitochondria were analyzed.

RESULTS

Zalcitabine and to a lesser extent zidovudine induced a significant peripheral neuropathy and encephalopathy with disrupted mitochondrial ultrastructure, depleted mitochondrial DNA, reduced levels of cytochrome c oxidase activity and diminished expression of mitochondrial DNA-encoded cytochrome c oxidase subunit I. Mitocnol had no intrinsic effects but attenuated or fully normalized all measured disorder of the peripheral and central nervous system.

CONCLUSION

Zidovudine and zalcitabine induce a mitochondrial disorder in the peripheral and central nervous system, both of which are antagonized by uridine supplementation.

Antiretroviral therapy-induced liver alterations

PURPOSE OF REVIEW

Antiretroviral drugs are associated with hepatotoxicity. Progress in our knowledge on the prevalence, contributory factors and mechanisms is reviewed.

RECENT FINDINGS

Liver toxicity is highly prevalent and a major cause of hospitalization among HIV-infected individuals. Liver steatosis is probably more frequent in the setting of hepatitis C virus coinfection but is also seen in noncoinfected patients. Among the individual drugs, severe liver toxicity is more strongly associated with nevirapine, and the mitochondrial toxicity of some nucleoside analogues. Mitochondrial toxicity can also induce or contribute to steatohepatitis, with dietary uridine supplementation as a possible strategy of prevention. Atazanavir inhibits UDP-glucuronosyltransferase, which in Gilberts' syndrome has been associated with breast cancer. A UDP-glucuronosyltransferase gene promoter variant predisposes to hyperbilirubinemia. Tipranavir induces elevated transaminases more frequently than boosted comparator protease inhibitors. CCR5 inhibitors may predispose to hepatotoxic events by causing an imbalance in the cytokine response.

SUMMARY

Hepatotoxicity is associated with all classes of antiretroviral agents and continues to contribute to hospitalization.

Mechanisms of antiretroviral therapy-induced mitochondrial dysfunction

PURPOSE OF REVIEW

To discuss novel developments related to the mechanisms of antiretroviral therapy-related mitochondrial toxicity, describe some apparent paradoxes in the current understanding of this field, and present questions that should be addressed by future research.

RECENT FINDINGS

The early polymerase gamma hypothesis states that nucleoside reverse transcriptase inhibitors can inhibit mitochondrial DNA replication and cause mitochondrial toxicity through mtDNA depletion. This mechanism is supported by a large body of evidence. Clinical manifestations of mitochondrial dysfunction are not always associated with mtDNA depletion. Increased mtDNA levels after nucleoside reverse transcriptase inhibitor exposure, as well as seemingly severe mtDNA depletion in individuals who show no clinical toxicity, have been reported. These and other observations suggest that additional mechanisms are involved in antiretroviral therapy toxicity, a notion supported by recent studies. Individuals given the same antiretroviral regimen can differ vastly with respect to the development of mitochondrial toxicity symptoms, reflecting interindividual variability. Some factors that may modulate this variability will be discussed.

SUMMARY

Mitochondrial toxicity induced by nucleoside reverse transcriptase inhibitors and their metabolic intermediates is probably mediated through many direct and indirect mechanisms. Depending on the mechanisms at play, the long-term health consequences of this toxicity may vary.

Mitochondrial DNA depletion in rat liver induced by fosalvudine tidoxil, a novel nucleoside reverse transcriptase inhibitor prodrug

Fosalvudine tidoxil is a prodrug derived from the nucleoside reverse transcriptase inhibitor 3-deoxy-3-fluorothymidine (FLT; alovudine). FLT effectively inhibits resistant human immunodeficiency virus type 1, but its clinical development was stopped due to bone marrow and liver toxicity. In this study, we examined the long-term in vivo effects of fosalvudine tidoxil on the mitochondrial DNA (mtDNA) contents in rats. Sprague-Dawley rats received fosalvudine tidoxil (15, 40, or 100 mg/kg of body weight/day) by oral gavage during a period of 8 weeks. Didanosine (100 mg/kg/day) was used as a positive control for mitochondrial toxicity. mtDNA levels in liver, gastrocnemius muscle, sciatic nerve, and inguinal fat pad tissues were quantified by real-time PCR. In hepatic mitochondria, fosalvudine tidoxil induced significant mtDNA depletion. At doses of 15, 40, and 100 mg/kg, the mean hepatic mtDNA values were 62, 64, and 47% of control values, respectively. Rats exposed to 100 mg/kg of fosalvudine tidoxil, unlike all other groups, had slightly elevated levels of glutamate pyruvate transaminase in sera. Didanosine induced a loss of mtDNA (to 48% of the control level) similar to that induced by fosalvudine tidoxil. mtDNA levels in skeletal, neural, and adipose tissues in the negative control and treatment groups were similar. Our results suggest that fosalvudine tidoxil induces mitochondrial hepatotoxicity and that this effect warrants scrutiny in clinical trials.

Mitochondrial toxicity in HIV type-1-exposed pregnancies in the era of highly active antiretroviral therapy

Background

The aim of this study was to determine the effects of HIV type-1 (HIV-1) infection and antiretroviral therapy (ART) on placental mitochondria.

Methods

HIV-1-infected pregnant women and HIV-1 -uninfected controls were enrolled prospectively. Placental mitochondrial DNA (mtDNA) copy numbers were determined by quantitative PCR, subunits II and IV of cytochrome c oxidase (COX) were quantified by western blot and mitochondrial ultrastructure was evaluated by electron microscopy. Venous blood lactate was measured in newborns.

Results

In total, 45 HIV-1-infected pregnant women on ART and 32 controls were included. Mean ±sd mtDNA copy numbers were significantly reduced in ART and HIV-1-exposed placentas (240 ±118 copies/ cell) in comparison with controls (686 ±842 copies/cell; P<0.001). The mean COX II/IV ratio was 48% lower in the investigational group compared with controls ( P<0.001). There was no evidence of severe ultrastructural damage within mitochondria of HIV-1-infected ART-exposed placentas. Although lactate levels between newborns did not differ, they were negatively correlated with placental mtDNA levels. There was no clear association between mitochondrial parameters and a particular nucleoside reverse transcriptase inhibitor (NRTI), the number of NRTIs or time of NRTI exposure.

Conclusions

Placental tissue of HIV-1-infected ART-exposed pregnancies shows evidence of mtDNA depletion with secondary respiratory chain compromise. The clinical effects of this finding warrant further investigation.

Drug-induced liver injury through mitochondrial dysfunction: mechanisms and detection during preclinical safety studies

Mitochondrial dysfunction is a major mechanism whereby drugs can induce liver injury and other serious side effects such as lactic acidosis and rhabdomyolysis in some patients. By severely altering mitochondrial function in the liver, drugs can induce microvesicular steatosis, a potentially severe lesion that can be associated with profound hypoglycaemia and encephalopathy. They can also trigger hepatic necrosis and/or apoptosis, causing cytolytic hepatitis, which can evolve into liver failure. Milder mitochondrial dysfunction, sometimes combined with an inhibition of triglyceride egress from the liver, can induce macrovacuolar steatosis, a benign lesion in the short term. However, in the long term this lesion can evolve in some individuals towards steatohepatitis, which itself can progress to extensive fibrosis and cirrhosis. As liver injury caused by mitochondrial dysfunction can induce the premature end of clinical trials, or drug withdrawal after marketing, it should be detected during the preclinical safety studies. Several in vitro and in vivo investigations can be performed to determine if newly developed drugs disturb mitochondrial fatty acid oxidation (FAO) and the oxidative phosphorylation (OXPHOS) process, deplete hepatic mitochondrial DNA (mtDNA), or trigger the opening of the mitochondrial permeability transition (MPT) pore. As drugs can be deleterious for hepatic mitochondria in some individuals but not in others, it may also be important to use novel animal models with underlying mitochondrial and/or metabolic abnormalities. This could help us to better predict idiosyncratic liver injury caused by drug-induced mitochondrial dysfunction.

Uridine supplementation antagonizes zidovudine-induced mitochondrial myopathy and hyperlactatemia in mice

OBJECTIVE

Zidovudine is an antiretroviral nucleoside analog reverse transcriptase inhibitor that induces mitochondrial myopathy by interfering with the replication of mitochondrial DNA (mtDNA). Because zidovudine inhibits thymidine kinases, the mechanism of mtDNA depletion may be related to an impairment of the de novo synthesis of pyrimidine nucleotides, which are required building blocks of mtDNA. This study was undertaken to determine whether mitochondrial myopathy is a class effect of antiretroviral nucleoside analogs, and whether the muscle disease can be prevented by treatment with uridine as a pyrimidine nucleotide precursor.

METHODS

BALB/c mice were treated with zidovudine or zalcitabine. Some of the mice were cotreated with mitocnol, a dietary supplement with high uridine bioavailability. Mice hind limb muscles were examined after 10 weeks.

RESULTS

Zidovudine induced muscle fiber thinning, myocellular fat deposition, and abnormalities of mitochondrial ultrastructure. In mice treated with zidovudine, organelles contained low mtDNA copy numbers and reduced cytochrome c oxidase activity. The expression of the mtDNA-encoded cytochrome c oxidase I subunit, but not of nucleus-encoded mitochondrial proteins, was impaired. Zidovudine also increased the levels of myocellular reactive oxygen species and blood lactate. Uridine supplementation attenuated or normalized all pathologic abnormalities and had no intrinsic effects. Zalcitabine did not elicit muscle toxicity.

CONCLUSION

Our findings indicate that zidovudine, but not zalcitabine, induces mitochondrial myopathy, which is substantially antagonized by uridine supplementation. These results provide proof of the importance of pyrimidine pools in the pathogenesis of zidovudine myopathy. Since uridine supplementation is tolerated well by humans, this treatment strategy should be investigated in clinical trials.

Pyrimidine nucleoside depletion sensitizes to the mitochondrial hepatotoxicity of the reverse transcriptase inhibitor stavudine

Stavudine is a hepatotoxic antiretroviral nucleoside analogue that also inhibits the replication of mitochondrial DNA (mtDNA). To elucidate the mechanism and consequences of mtDNA depletion, we treated HepG2 cells with stavudine and either redoxal, an inhibitor of de novo pyrimidine synthesis, or uridine, from which pyrimidine pools are salvaged. Compared with treatment with stavudine alone, co-treatment with redoxal accelerated mtDNA depletion, impaired cell division, and activated caspase 3. These adverse effects were completely abrogated by uridine. Intracellular ATP levels were unaffected. Transcriptosome profiling demonstrated that redoxal and stavudine acted synergistically to induce CDKN2A and p21, indicating cell cycle arrest in G1, as well as genes involved in intrinsic and extrinsic apoptosis. Moreover, redoxal and stavudine showed synergistic interaction in the up-regulation of transcripts encoded by mtDNA and the induction of nuclear transcripts participating in energy metabolism, mitochondrial biogenesis, oxidative stress, and DNA repair. Genes involved in nucleotide metabolism were also synergistically up-regulated by both agents; this effect was completely antagonized by uridine. Thus, pyrimidine depletion sensitizes cells to stavudine-mediated mtDNA depletion and enhances secondary cell toxicity. Our results indicate that drugs that diminish pyrimidine pools should be avoided in stavudine-treated human immunodeficiency virus patients. Uridine supplementation reverses this toxicity and, because of its good tolerability, has potential clinical value for the treatment of side effects associated with pyrimidine depletion.

Uridine Supplementation for the treatment of Antiretroviral Therapy-Associated Lipoatrophy: A Randomized, Double-Blind, Placebo-Controlled Trial

Background

Highly active antiretroviral therapy (HAART) is associated with loss of subcutaneous fat (lipoatrophy) presumably due to mitochondrial toxicity of nucleoside reverse transcriptase inhibitors. In vitro, uridine abrogates thymidine analogue-induced toxicity in adipocytes.

Methods

A total of 20 patients with HAART-associated lipoatrophy were randomized to receive either a dietary uridine supplement (36 g three times a day for 10 consecutive days/month) or placebo, for 3 months. Body composition was measured using dual energy X-ray absorptiometry, magnetic resonance imaging and proton spectroscopy. Data are mean ± standard error of mean.

Results

The mean increases in limb fat (880 ±140 versus 230 ±270 g; P<0.05), intra-abdominal fat (210 ±80 versus -80 ±70 cm3; P<0.05) and total body fat (1,920 ±240 versus 240 ±520 g; P<0.01) were significantly greater in the uridine than in the placebo group. Within the uridine group, the changes from baseline to 3 months were statistically significant in total limb fat ( P<0.001), intra-abdominal fat ( P<0.05) and total body fat ( P<0.001). The proportion of limb fat to total fat increased from 18% to 25% ( P<0.05) in the uridine group. Liver fat content and lean body mass remained unchanged in both groups. High-density lipoprotein-cholesterol concentrations decreased in the uridine and increased in the placebo group, whereas fasting serum insulin concentrations did not change. Uridine supplementation was well tolerated and the virological effect of HAART was not affected.

Conclusion

Uridine supplementation significantly and predominantly increased subcutaneous fat mass in lipoatrophic HIV-infected patients during unchanged HAART.