Site specific alterations of adipose tissue mitochondria in 3′-azido-3′-deoxythymidine (AZT)-treated rats: An early stage in lipodystrophy?

Inflammation in HIV and Its Impact on Atherosclerotic Cardiovascular Disease

People living with HIV have a 1.5- to 2-fold increased risk of developing cardiovascular disease. Despite treatment with highly effective antiretroviral therapy, people living with HIV have chronic inflammation that makes them susceptible to multiple comorbidities. Several factors, including the HIV reservoir, coinfections, clonal hematopoiesis of indeterminate potential (CHIP), microbial translocation, and antiretroviral therapy, may contribute to the chronic state of inflammation. Within the innate immune system, macrophages harbor latent HIV and are among the prominent immune cells present in atheroma during the progression of atherosclerosis. They secrete inflammatory cytokines such as IL (interleukin)-6 and tumor necrosis-α that stimulate the expression of adhesion molecules on the endothelium. This leads to the recruitment of other immune cells, including cluster of differentiation (CD)8+ and CD4+ T cells, also present in early and late atheroma. As such, cells of the innate and adaptive immune systems contribute to both systemic inflammation and vascular inflammation. On a molecular level, HIV-1 primes the NLRP3 (NLR family pyrin domain containing 3) inflammasome, leading to an increased expression of IL-1β, which is important for cardiovascular outcomes. Moreover, activation of TLRs (toll-like receptors) by HIV, gut microbes, and substance abuse further activates the NLRP3 inflammasome pathway. Finally, HIV proteins such as Nef (negative regulatory factor) can inhibit cholesterol efflux in monocytes and macrophages through direct action on the cholesterol transporter ABCA1 (ATP-binding cassette transporter A1), which promotes the formation of foam cells and the progression of atherosclerotic plaque. Here, we summarize the stages of atherosclerosis in the context of HIV, highlighting the effects of HIV, coinfections, and antiretroviral therapy on cells of the innate and adaptive immune system and describe current and future interventions to reduce residual inflammation and improve cardiovascular outcomes among people living with HIV.

Prior exposure to thymidine analogs and didanosine is associated with long-lasting alterations in adipose tissue distribution and cardiovascular risk factors

BACKGROUND

Thymidine analogs and didanosine (ddI) have been associated with redistribution of body fat from subcutaneous adipose tissue (SAT) to visceral adipose tissue (VAT), which, in turn, is a risk factor for cardiovascular disease. We explored differences in adipose tissue distribution between people living with HIV (PLWH) with prior exposure to thymidine analogs and/or ddI, without exposure, and uninfected controls and the association with cardiovascular disease risk factors.

METHODS

In all, 761 PLWH from the Copenhagen Comorbidity in HIV Infection study, and 2283 age and sex-matched uninfected controls from the Copenhagen General Population Study were included. PLWH were stratified according to prior exposure to thymidine analogs and/or ddI. VAT and SAT were determined by abdominal computed tomography scan. Hypotheses were tested using regression analyses.

RESULTS

Exposure to thymidine analogs and/or ddI was associated with 21.6 cm larger VAT (13.8-29.3) compared to HIV infection without exposure. HIV-negative status was associated with similar VAT compared to HIV infection without exposure. Cumulative exposure to thymidine analogs and/or ddI [3.7 cm per year (2.3-5.1)], but not time since discontinuation [-1.1 cm per year (-3.4 to 1.1)], was associated with VAT. Prior exposure to thymidine analogs and/or ddI was associated with excess risk of hypertension [adjusted odds ratio (aOR) 1.62 (1.13-2.31)], hypercholesterolemia [aOR 1.49 (1.06-2.11)], and low high-density lipoprotein [aOR 1.40 (0.99-1.99)].

CONCLUSIONS

This study suggests a potentially irreversible and harmful association of thymidine analogs and ddI with VAT accumulation, which appears be involved in the increased risk of hypertension, hypercholesterolemia, and low high-density lipoprotein found in PLWH with prior exposure to thymidine analogs and/or ddI, even years after treatment discontinuation.

Zidovudine induces visceral mitochondrial toxicity and intra-abdominal fat gain in a rodent model of lipodystrophy

BACKGROUND

The use of zidovudine is associated with a loss of subcutaneous adipose tissue (SAT). We assessed if zidovudine treatment also affects visceral adipose tissue (VAT) and if uridine supplementation abrogates the adverse effects of zidovudine on VAT.

METHODS

Rats were fed zidovudine for 21 weeks with or without simultaneous uridine supplementation. Control animals did not receive zidovudine, or were treated with uridine alone. Changes in SAT and VAT were monitored by magnetic resonance imaging. Adipose tissue was examined for structural and molecular signs of mitochondrial toxicity.

RESULTS

Zidovudine induced lipoatrophy in SAT and fat hypertrophy in VAT. Compared with controls zidovudine-exposed VAT adipocytes had increased diameters, microvesicular steatosis and enlarged mitochondria with disrupted crystal architecture on electron microscopy. VAT adipocyte mitochondrial DNA (mtDNA) copy numbers were diminished, as were mtDNA-encoded respiratory chain proteins. The 'common' mtDNA deletion was detected in high frequencies in zidovudine treated animals, but not in the controls. Although mtDNA depletion was more profound in SAT compared with VAT, the 'common' deletion tended to be more frequent in the VAT than in the SAT. Uridine coadministration abrogated all effects of zidovudine on VAT and SAT pathology.

CONCLUSIONS

Zidovudine induces a gain of intra-abdominal fat in association with quantitative and qualitative alterations of the mitochondrial genome and impaired expression of mtDNA-encoded respiratory chain components, indicating that zidovudine may contribute to abdominal fat hypertrophy in HIV-infected patients. In this rodent model, uridine supplementation abrogates both SAT and VAT pathology induced by zidovudine.

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.

Curcumin-loaded apotransferrin nanoparticles provide efficient cellular uptake and effectively inhibit HIV-1 replication in vitro

BACKGROUND

Curcumin (diferuloylmethane) shows significant activity across a wide spectrum of conditions, but its usefulness is rather limited because of its low bioavailability. Use of nanoparticle formulations to enhance curcumin bioavailability is an emerging area of research.

METHODOLOGY/PRINCIPAL FINDINGS

In the present study, curcumin-loaded apotransferrin nanoparticles (nano-curcumin) prepared by sol-oil chemistry and were characterized by electron and atomic force microscopy. Confocal studies and fluorimetric analysis revealed that these particles enter T cells through transferrin-mediated endocytosis. Nano-curcumin releases significant quantities of drug gradually over a fairly long period, ∼50% of curcumin still remaining at 6 h of time. In contrast, intracellular soluble curcumin (sol-curcumin) reaches a maximum at 2 h followed by its complete elimination by 4 h. While sol-curcumin (GI(50) = 15.6 µM) is twice more toxic than nano-curcumin (GI(50) = 32.5 µM), nano-curcumin (IC(50)<1.75 µM) shows a higher anti-HIV activity compared to sol-curcumin (IC(50) = 5.1 µM). Studies in vitro showed that nano-curcumin prominently inhibited the HIV-1 induced expression of Topo II α, IL-1β and COX-2, an effect not seen with sol-curcumin. Nano-curcumin did not affect the expression of Topoisomerase II β and TNF α. This point out that nano-curcumin affects the HIV-1 induced inflammatory responses through pathways downstream or independent of TNF α. Furthermore, nano-curcumin completely blocks the synthesis of viral cDNA in the gag region suggesting that the nano-curcumin mediated inhibition of HIV-1 replication is targeted to viral cDNA synthesis.

CONCLUSION

Curcumin-loaded apotransferrin nanoparticles are highly efficacious inhibitors of HIV-1 replication in vitro and promise a high potential for clinical usefulness.

Adipose tissue biology and HIV-infection

HIV-1/highly active antiretroviral therapy-associated lipodystrophy syndrome (HALS) is an adipose tissue redistribution disorder characterized by subcutaneous adipose tissue lipoatrophy, sometimes including visceral adipose tissue hypertrophy and accumulation of dorsocervical fat ('buffalo hump'). The pathophysiology of HALS appears to be multifactorial and several key pathophysiological factors associated with HALS have been identified. These include mitochondrial dysfunction, adipocyte differentiation disturbances, high adipocyte lipolysis, and adipocyte apoptosis. These alterations in adipose tissue biology expand to involve systemic metabolism through alterations in endocrine functions of adipose tissue (via disturbed adipokine release), enhanced production of pro-inflammatory cytokines and excessive free fatty-acid release due to lipolysis. The deleterious action of some antiretroviral drugs is an important factor in eliciting these alterations in adipose tissue. However, HIV-1 infection-related events and HIV-1-encoded proteins also contribute directly to the complex development of HALS through effects on adipocyte biology, or indirectly through the promotion of local inflammation in adipose tissue.

Disorders of fat partitioning in treated HIV-infection

HIV-associated lipodystrophy is clinically characterized by body fat changes including subcutaneous fat loss (lipoatrophy) with or without truncal fat accumulation (lipohypertrophy). Thymidine nucleoside reverse transcriptase inhibitors, stavudine and to a lesser extent zidovudine, are major contributors for lipoatrophy. Drug factors are not clear for lipohypertrophy. Restoration to health with effective viral suppression and weight gain may be factors playing significant roles in lipohypertrophy. Mitochondrial dysfunction and inflammation in subcutaneous adipose tissue are key factors in the pathogenesis of HIV-associated lipoatrophy. The pathogenesis of lipohypertrophy is less well understood. Switching from thymidine nucleoside reverse transcriptase inhibitors restores subcutaneous fat in patients with HIV-associated lipoatrophy, but improvement is slow and limited. Surgical filling cosmetically improves facial lipoatrophy. Exercise and diet may reduce increased visceral adipose tissue. Liposuction may be useful to remove superficial, localized fat accumuli.

Balancing mitochondrial redox signaling: a key point in metabolic regulation

Mitochondrial reactive oxygen species (mROS) have emerged as signaling molecules in physiology primarily as a result of studies of uncoupling mechanisms in mitochondrial respiration. The discovery that this mechanism negatively regulates mROS generation in many cell types has drawn the attention of the scientific community to the pathological consequences of excess mROS production. From reports of the energetic fluxes in cells grown under normal conditions, the hypothesis that mROS are an integrated physiological signal of the metabolic status of the cell has emerged. Here, we consider recent studies that support this point of view in two key nutrient sensors of the body, beta cells and the hypothalamus, which are the main coordinators of endocrine and nervous controls of energy metabolism and adipose tissue, which is of paramount importance in controlling body weight and, therefore, the development of obesity and type 2 diabetes. In this context, finely balanced mROS production may be at the core of proper metabolic maintenance, and unbalanced mROS production, which is largely documented, might be an important trigger of metabolic disorders.

Glyceroneogenesis is inhibited through HIV protease inhibitor-induced inflammation in human subcutaneous but not visceral adipose tissue

Glyceroneogenesis, a metabolic pathway that participates during lipolysis in the recycling of free fatty acids to triglycerides into adipocytes, contributes to the lipid-buffering function of adipose tissue. We investigated whether glyceroneogenesis could be affected by human immunodeficiency virus (HIV) protease inhibitors (PIs) responsible or not for dyslipidemia in HIV-infected patients. We treated explants obtained from subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) depots from lean individuals. We observed that the dyslipidemic PIs nelfinavir, lopinavir and ritonavir, but not the lipid-neutral PI atazanavir, increased lipolysis and decreased glyceroneogenesis, leading to an increased release of fatty acids from SAT but not from VAT. At the same time, dyslipidemic PIs decreased the amount of perilipin and increased interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) secretion in SAT but not in VAT. Parthenolide, an inhibitor of the NFκB pathway, counteracted PI-induced increased inflammation and decreased glyceroneogenesis. IL-6 (100 ng) inhibited the activity of phosphoenolpyruvate carboxykinase, the key enzyme of glyceroneogenesis, in SAT but not in VAT. Our data show that dyslipidemic but not lipid-neutral PIs decreased glyceroneogenesis as a consequence of PI-induced increased inflammation in SAT that could have an affect on adipocytes and/or macrophages. These results add a new link between fat inflammation and increased fatty acids release and suggest a greater sensitivity of SAT than VAT to PI-induced inflammation.

Effects of zidovudine and stavudine on mitochondrial DNA of differentiating 3T3-F442a cells are not associated with imbalanced deoxynucleotide pools

To test whether zidovudine (3'-azido-3'-deoxythymidine) (AZT) inhibition of thymidine phosphorylation causes depletion of the TTP pool resulting in mitochondrial DNA depletion, 3T3-F442a cells were differentiated in the presence of AZT and analyzed to determine mitochondrial DNA content and deoxynucleotide levels. These results suggest that AZT toxicity may not be related to deoxynucleotide pool alterations.

Drug-specific effect of nelfinavir and stavudine on primary culture of human preadipocytes

Lipodystrophic syndrome is a major side effect of antiviral therapy leading to profound disturbances in adipose tissue. Human preadipocyte primary culture represents a model to understand mechanisms by which antiretroviral drugs alter adipocyte biology. The aim of this study was to evaluate the effects of various protease and nucleoside reverse transcriptase inhibitors in this model. We tested the effect of drugs on triglyceride accumulation and expression of specific genes by real-time polymerase chain reaction. To determine differential mechanisms by which the efficient drugs operate, we studied mitochondrial effects by evaluating oxygen consumption rates and nuclear lamina alteration by immunocytology. Only stavudine and nelfinavir, both at 10 microM, altered human adipose cell differentiation, as shown by reduced triglyceride accumulation. Our studies revealed that stavudine increased expression of genes such as PGC1 and LPL and affected mitochondrial respiration. Cells treated with nelfinavir had a lower expression of PPARgamma, LPL, and ap2 and presented disorganization of lamin A/C. Our data suggest for the first time in a model of human adipocytes differentiated in vitro that stavudine and nelfinavir interfere with the process of differentiation by 2 distinct mechanisms. This may be particularly relevant in understanding the physiopathologic mechanisms underlying the lipodystrophic syndrome.

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.

Lipodystrophy in HIV 1-infected patients: lessons for obesity research

Lipodystrophy is a common alteration in HIV 1-infected patients under anti-retroviral treatment. This syndrome is usually associated with peripheral lipoatrophy, central adiposity and, in some cases, lipomatosis, as well as systemic insulin resistance and hyperlipidemia. Research on the ethiopathogenesis of the disease revealed novel aspects of adipose tissue biology highly relevant to obesity research: the pivotal role of mitochondria in white adipose tissue function, the role that interference with master transcription factors of adipogenesis may have in human adipose tissue, the capacity of human white adipose tissue to acquire brown fat-like features, as well as the importance of apoptosis and the potential impact of viral infections in adipose tissue. The dramatic difference between subcutaneous adipose depots, prone to lipoatrophy, and the visceral adipose depots, prone to enlargement, has been further evidenced in the study of the lipodystrophy syndrome. The recognition of a local pro-inflammatory environment in lipoatrophic adipose tissue from affected patients, including macrophage infiltration and enhanced expression of chemokines and cytokines, points to events paradoxically similar to those in the hypertrophied adipose tissue in obesity. However, this also potentially provides an explanation for the existence of systemic alterations common to lipodystrophy and obese patients and reminiscent of the metabolic syndrome.

High Doses of Stavudine Induce Fat Wasting and Mild Liver Damage without Impairing Mitochondrial Respiration in Mice

Objective

Stavudine (d4T), a nucleoside reverse-transcriptase inhibitor (NRTI), can induce lipoatrophy, fatty liver, hyperlactataemia and abnormal liver tests. NRTI toxicity is usually ascribed to mitochondrial DNA (mtDNA) depletion and impaired mitochondrial respiration. However, NRTIs could have effects unrelated to mtDNA. Recently, we reported that 100 mg/kg/day of d4T stimulated fatty acid oxidation (FAO) in mouse liver, and reduced body fatness without depleting white adipose tissue (WAT) mtDNA. We hypothesized that higher d4T doses could further reduce adiposity, while inhibiting hepatic FAO.

Methods

Mice were treated for 2 weeks with d4T (500 mg/kg/day), L-carnitine (200 mg/kg/day) or both drugs concomitantly. Body fatness was assessed by dual energy X-ray absorptiometry, and investigations were performed in plasma, liver, muscle and WAT.

Results

D4T reduced the gain of body adiposity, WAT leptin, whole body FAO and plasma ketone bodies, and increased liver triglycerides and plasma aminotransferases with mild ultrastructural abnormalities in hepatocytes. Plasma lactate and respiratory chain activities in tissues were unchanged. Stearoyl-CoA desaturase (SCD-1), an enzyme negatively regulated by leptin, was overexpressed in liver. High doses of β-aminoisobutyric acid (BAIBA), a d4T catabolite, increased plasma ketone bodies. Although L-carnitine did not correct body adiposity, it prevented d4T-induced impairment of FAO and liver abnormalities.

Conclusions

D4T overdosage triggers fat wasting, leptin insufficiency and mild liver damage, without causing respiratory chain dysfunction. Overexpression of SCD-1 reduces fatty acid oxidation and overcomes the stimulating effect of BAIBA on hepatic FAO. L-carnitine does not correct leptin insufficiency but prevents d4T-induced impairment of FAO and liver damage.

Zidovudine inhibits thymidine phosphorylation in the isolated perfused rat heart

Zidovudine (AZT; 3'-azido-3'-deoxythymidine), a thymidine analog, has been a staple of highly active antiretroviral therapy. It is phosphorylated in the host to the triphosphate and functions by inhibiting the viral reverse transcriptase. However, long-term use of AZT is linked to various tissue toxicities, including cardiomyopathy. These toxicities are associated with mitochondrial DNA depletion, which is hypothesized to be caused by AZT triphosphate inhibition of mitochondrial DNA polymerase gamma. In previous work with isolated heart mitochondria, we demonstrated that AZT phosphorylation beyond the monophosphate was not detected and that AZT itself was a potent inhibitor of thymidine phosphorylation. This suggests an alternative hypothesis in which depletion of the TTP pool may limit mitochondrial DNA replication. The present work extends these studies to the whole cell by investigating the metabolism of thymidine and AZT in the intact isolated perfused rat heart. [3H]thymidine is converted to [3H]TTP in a time- and concentration-dependent manner. The level of [3H]TMP is low, suggesting that the reaction catalyzed by thymidine kinase is the rate-limiting step in phosphorylation. [3H]AZT is converted in a time- and concentration-dependent manner to AZT monophosphate, the only phosphorylated product detected after 3 h of perfusion. Both compounds display negative cooperativity, similar to the observations with cloned and purified mitochondrial thymidine kinase 2. The presence of AZT in the perfusate inhibits the phosphorylation of [3H]thymidine with a 50% inhibitory concentration of 24+/-4 microM. These data support the hypothesis that AZT-induced mitochondrial cardiotoxicity may be caused by a limiting pool of TTP that lowers mitochondrial DNA replication.

Site-specific reduction of oxidative and lipid metabolism in adipose tissue of 3'-azido-3'-deoxythymidine-treated rats

Although it is well accepted that treatment with some nucleoside reverse transcriptase inhibitors modifies both fat metabolism and fat distribution in humans, the mechanisms underlying these modifications are not yet known. The present investigation examined whether a decrease in oxidative capacity, induced by a chronic oral administration of 3'-azido-3'-deoxythymidine (AZT) in rats, could be associated with an alteration of the lipogenic capacity of white adipose tissues. The impact of obesity as a factor was then evaluated. Results showed that AZT treatment induced differential effects depending on anatomical localization. Indeed, in the inguinal adipose tissue, the specific activities of cytochrome c oxidase and fatty acid synthase, two rate-controlling enzymes in energy and lipogenic metabolisms, respectively, both decreased under AZT treatment, thus leading to a lowered cell lipid accumulation. Moreover, the AMP-activated protein kinase phosphorylation level tended to increase, thus implying that AZT causes an energy imbalance. Furthermore, the inguinal tissue of obese rats presented a sensitivity to AZT treatment that was higher than that of lean rats. In contrast, for epididymal tissue, no significant change in all these parameters could be detected under AZT treatment, regardless of the nutritional status of the animals. Taken together, these data demonstrate differential effects of AZT on subcutaneous adipose tissue and visceral white adipose tissue. It could be considered that the chronic decreases in energy and lipogenic metabolism of inguinal adipocyte, consecutive to AZT treatment, may lead, in the long term, to adipose tissue atrophy.

Adipose Tissue Proadipogenic Redox Changes in Obesity

The role of inflammation and oxidative stress in the development of obesity and associated metabolic disorders is under debate. We investigated the redox metabolism in a non-diabetic obesity model, i.e. 11-week-old obese Zucker rats. Antioxidant enzyme activities, lipophilic antioxidant (alpha-tocopherol, coenzymes Q) and hydrophilic antioxidant (glutathione, vitamin C) contents and their redox state (% oxidized form), were studied in inguinal white fat and compared with blood and liver. The adipose tissues of obese animals showed a specific higher content of hydrophilic molecules in a lower redox state than those of lean animals, which were associated with lower lipophilic molecule content and lipid peroxidation. Conversely and as expected, glutathione content decreased and its redox state increased in adipose tissues of rats subjected to lipopolysaccharide-induced systemic oxidative stress. In these in vivo models, oxidative stress and obesity thus had opposite effects on adipose tissue redox state. Moreover, the increase in glutathione content and the decrease of its redox state by antioxidant treatment promoted in vitro the accumulation of triglycerides in preadipocytes. Taken together and contrary to the emergent view, our results suggest that obesity is associated with an intracellular reduced redox state that promotes on its own the development of a deleterious proadipogenic process.

3'-Azido-3'-deoxythymidine (AZT) is a competitive inhibitor of thymidine phosphorylation in isolated rat heart and liver mitochondria

Long-term use of 3'-azido-3'-deoxythymidine (AZT) is associated with various tissue toxicities, including hepatotoxicity and cardiomyopathy, and with mitochondrial DNA depletion. AZT-5'-triphosphate (AZTTP) is a known inhibitor of the mitochondrial DNA polymerase gamma and has been targeted as the source of the mitochondrial DNA depletion. However, in previous work from this laboratory with isolated rat heart and liver mitochondria, AZT itself was shown to be a more potent inhibitor of thymidine phosphorylation (IC50 of 7.0+/-1.0 microM AZT in heart mitochondria and of 14.4+/-2.6 microM AZT in liver mitochondria) than AZTTP is of polymerase gamma (IC50 of >100 microM AZTTP), suggesting that depletion of mitochondrial stores of TTP may limit replication and could be the cause of the mitochondrial DNA depletion observed in tissues affected by AZT toxicity. The purpose of this work is to characterize the nature of AZT inhibition of thymidine phosphorylation in isolated rat heart and rat liver mitochondria. In both of these tissues, AZT was found to be a competitive inhibitor of the phosphorylation of thymidine to TMP, catalyzed by thymidine kinase 2. The inhibition constant (Ki) for heart mitochondria is 10.6+/-4.5 microM AZT, and for liver mitochondria Ki is 14.0+/-2.5 microM AZT. Since AZT is functioning as a competitive inhibitor, increasing thymidine concentrations may be one mechanism to overcome the inhibition and decrease AZT-related toxicity in these tissues.

3'-Azido-3'-deoxythymidine (AZT) inhibits thymidine phosphorylation in isolated rat liver mitochondria: a possible mechanism of AZT hepatotoxicity

3'-azido-3'-deoxythymidine (AZT) is a staple of highly active antiretroviral therapy (HAART). Prior to HAART, long-term use of high-dosage AZT caused myopathy, cardiomyopathy, and hepatotoxicity, associated with mitochondrial DNA depletion. As a component of HARRT, AZT causes cytopenias and lipodystrophy. AZT-5'-triphosphate (AZTTP) is a known inhibitor of the mitochondrial polymerase gamma and has been targeted as the source of the mitochondrial DNA depletion. However, in previous work from this laboratory with isolated rat heart mitochondria, AZT phosphorylation beyond AZT-5'-monophosphate (AZTMP) was not detected. Rather, AZT was shown to be a more potent inhibitor of thymidine phosphorylation (50% inhibitory concentration (IC50) of 7.0+/-1.0 microM) than AZTTP is of polymerase gamma (IC50 of >100 microM), suggesting that depletion of mitochondrial stores of TTP may limit replication. This work has investigated whether an identical mechanism might account for the hepatotoxicity seen with long-term use of AZT. Isolated rat liver mitochondria were incubated with labeled thymidine or AZT, and the rate and extent of phosphorylation were determined by HPLC analysis of acid-soluble extracts of the incubated mitochondria. The results showed that in the phosphorylation of thymidine to TMP, liver mitochondria exhibit a higher Vmax and Km than heart mitochondria, but otherwise heart and liver mitochondria display similar kinetics. AZT is phosphorylated to AZTMP, but no further phosphorylated forms were detected. In addition, AZT inhibited the production of TTP, with an IC50 of 14.4+/-2.6 microM AZT. This is higher, but comparable to, the results seen in isolated rat heart mitochondria.

Low interleukin-10 production is associated with diabetes in HIV-infected patients undergoing antiviral therapy

Reduced interleukin-10 (IL-10) production is associated with type 2 diabetes in elderly individuals. Antiviral therapy (ARV)-induced immune modulation results in diminished IL-10 production, and diabetes can be observed in ARV-treated human immunodeficiency virus (HIV)-infected individuals. We analyzed, in a cross-sectional pilot study, HIV-antigen-stimulated IL-10 and tumor necrosis factor alpha (TNFalpha) production, and intracellular concentration (ICC), as well as B7-H1 expression, a marker preferentially presented by IL-10-producing cells, in 20 ARV-treated individuals in whom diabetes did (n=10; diabetes mellitus, DM) or did not (n=10; controls) develop. Pre-ARV glucose, cholesterol, and triglycerides levels, duration of HIV infection and of therapy, exposure to protease inhibitors (PI), HIV plasma viremia, CD4 counts, and nadir were similar in DM and control patients. Results showed that: (1) IL-10 production was lower; (2) IL-10 ICC was reduced; (3) B7-H1-expressing CD19(+) cells were diminished; and (4) TNFalpha production and ICC by CD4(+) T cells was augmented in DM patients. Development of diabetes in HIV infected, ARV-treated individuals could be a response to therapy. Similar to what is observed in elderly individuals, low IL-10 production is associated with diabetes in antiviral-treated HIV infection. Further studies will be necessary to clarify whether low IL-10 is a risk factor for, or a consequence of, diabetes.