Evaluation of mitochondrial DNA content and enzyme levels in tenofovir DF-treated rats, rhesus monkeys and woodchucks

Melatonin protects against tenofovir-induced nephrotoxicity in rats by targeting multiple cellular pathways

Nephrotoxicity is a dose-limiting side effect of long-term use of tenofovir, a reverse transcriptase inhibitor that is used for the treatment of HIV infection and chronic hepatitis B infection. Identifying an agent that prevents tenofovir disoproxil fumarate (TDF)-induced renal injury can lead to its better tolerance, and a more effective treatment can be achieved. The present study is aimed at investigating whether melatonin, a potent antioxidant and anti-inflammatory agent, protects against TDF nephrotoxicity in rats and to determine its cellular targets. Rats were divided into groups and treated as follows. Group I (control): Rats in this group (n = 6) received sterile water only by gavage for 35 days. Group II: Rats (n = 6) in this group received 600 mg/kg body weight TDF in sterile water by gavage for 35 days. Group III: Rats (n = 6) in this group received once daily 20 mg/kg bodyweight melatonin i.p. 2 h before the administration of 600 mg/kg body weight TDF in sterile water by gavage for 35 days. Group IV: Rats were pretreated daily with 20 mg/kg body weight melatonin i.p. 2 h before the administration of sterile water by gavage. All the rats were sacrificed on the 36th day, after overnight fast. Melatonin pretreatment protected the rats against TDF nephrotoxicity both histologically and biochemically. Biochemically, melatonin pretreatment attenuated TDF-induced, oxidative stress, nitrosative stress, mitochondrial pathway of apoptosis, PARP overactivation and preserved proximal tubular function (p < 0.01). This suggests that melatonin may be useful in ameliorating TDF nephrotoxicity.

Renal Dysfunction and Tubulopathy Induced by High-Dose Tenofovir Disoproxil Fumarate in C57BL/6 Mice

Tenofovir disoproxil fumarate (TDF) is the most preferred antiretroviral medicine in treating human immunodeficiency virus (HIV) and hepatitis B virus (HBV) infections. Recent clinical trials have reported conflicting results on renal toxicity and safety in TDF-treated patients, but reference animal studies, testing high-doses of TDF for renal toxicity, are scarce. In this preclinical study, we investigated whether daily oral TDF administration (200, 500, or 800 mg/kg/d, p.o.) for four weeks induces renal insufficiency in C57BL/6 mice, by evaluating changes in body weight, urine micro-total protein, urinary microalbumin, serum blood urea nitrogen (BUN), and creatinine levels, along with histological examination of kidney samples. In the G3 group (TDF 800 mg/kg/d, p.o.), three mice died on the 17th, 23rd and 26th days, and overall, significant increases in urinary and serum levels were observed after two weeks of TDF treatment. In addition, the proportion of pyknotic epithelial cells and acidophilic cytoplasm in renal tubules was also increased after two weeks, and congestion and hemorrhage were observed in renal tubules after three weeks. Taken together, high-dose TDF treatment of 800 mg/kg/d might lead to renal tubular damage and dysfunction, great enough to cause death in mice, even after a short period of one to two weeks.

Mitochondrial pathway of apoptosis and necrosis contribute to tenofovir disoproxil fumarate-induced renal damage in rats

Tenofovir disoproxil fumarate (TDF) is currently the only nucleotide analogue reverse-transcriptase inhibitor that is approved by the Food and Drug administration (FDA), USA, for the treatment of human immunodeficiency virus (HIV) infection. In recent days, renal toxicity is becoming common i HIV patients treated with TDF. However, the mechanism of tenofovir nephrotoxicity is not clear. We hypothesized that mitochondrial pathway of apoptosis, poly [ADP-ribose] polymerase (PARP) overactivation and neutrophil infiltration may contribute to tenofovir-induced renal damage. Renal damage was induced in adult male Wistar rats by the oral administration of 600 mg/kg body weight daily for five consecutive weeks. Kidneys were removed and used for histological and biochemical analyses. Apoptosis was detected by terminal deoxynucleotidyl transferase biotin-deoxyuridine triphosphate nick end-labelling (TUNEL) assay and caspase 3 activity and protein expression; mitochondrial pathway of apoptosis by cyt c release; and PARP activation by immunofluorescence, immunohistochemistry and Western blot techniques. Myeloperoxidase (MPO) activity was measured as a marker of neutrophil infiltration. TDF administration resulted in increased number of TUNEL-positive cells, activation of caspase 3 and release of cyt c from mitochondria into the cytosol in the kidneys. There was increased nuclear localization of PARP as well as increase in its protein level in the TDF-treated rat kidneys. In addition, renal MPO activity was increased ninefold as compared to controls. The results of the present study show that mitochondrial apoptotic pathway, PARP overactivation and neutrophil infiltration contribute to tenofovir-induced renal damage in rats.

Tenofovir disoproxil fumarate-associated renal tubular dysfunction: noninvasive assessment of mitochondrial injury

OBJECTIVE

To determine whether tenofovir disoproxil fumarate (TDF)-associated renal tubular dysfunction is associated with evidence of mitochondrial injury in urine.

DESIGN

Single-centre cross-sectional observational study of HIV-positive outpatients.

METHODS

Biochemistry was performed on paired serum and urine samples. Mitochondrial DNA (mtDNA) was studied by real-time PCR and long-range PCR on cellular fractions of urine.

RESULTS

In total, 48 study participants were enrolled of whom half were TDF treated. Mean age was 43 years. 58% had estimated glomerular filtration rate at least 90, with no differences between ART treatment groups. Urinary phosphate wasting was common and independently associated with TDF exposure (P = 0.02). No study participants had low molecular weight proteinuria. Cellular mtDNA content in urine was heavily influenced by the cellularity of the sample. The mtDNA 'common deletion' mutation was detectable significantly more commonly in the urine of TDF exposed study participants compared with unexposed (13/22 TDF study participants (59%), 4/21 TDF (19%), P = 0.01). Common deletion levels were not associated with age, estimated glomerular filtration rate, or urinary phosphate wasting. No mtDNA measures were associated with current or nadir CD4 lymphocyte counts, duration of disease or antiretroviral therapy, or historical exposure to nucleoside analogue reverse transcriptase inhibitors with systemic mitochondrial toxicity.

CONCLUSION

The presence of mtDNA mutations in the context of TDF exposure adds weight to the hypothesis that TDF-associated renal damage is at least in part mitochondrially mediated. The assessment of mtDNA markers in urine may be a feasible noninvasive investigation for TDF-treated patients.

Tenofovir disoproxil fumarate: toxicity, toxicokinetics, and toxicogenomics analysis after 13 weeks of oral administration in mice

Tenofovir disoproxil fumarate (TDF) is a prodrug of tenofovir that exhibits activity against HIV and hepatitis B. The goals of this study were to evaluate the molecular mechanism of TDF-induced toxicity in mice after 13 weeks of daily oral administration (50-1000 mg/kg) by correlating transcriptional changes with plasma drug levels and traditional toxicology end points. Plasma levels and systemic exposure of tenofovir increased less than dose proportionally and were similar on days 1 and 91. No overt toxicity was observed following the completion of TDF administration. The kidneys of TDF-treated mice were histopathologically normal. This result is consistent with the genomic microarray results, which showed no significant differences in kidney transcriptional levels between TDF-treated animals and controls. In liver, after 4 and 13 weeks, cytomegaly was observed in mice treated with 1000 mg/kg of TDF, but mice recovered from this effect following cessation of administration. Analysis of liver transcripts on day 91 reported elevated levels of Cdkn1a in TDF-treated animals compared with controls, which may have contributed to the inhibition of liver cell cycle progression.

Tenofovir-induced nephrotoxicity: incidence, mechanism, risk factors, prognosis and proposed agents for prevention

OBJECTIVE

In this study, data regarding epidemiology, risk factors, pathogenesis and outcome of tenofovir-induced nephrotoxicity will be reviewed, and current and future approaches for prevention will be discussed.

METHOD

The data were collected by searching Scopus, PubMed, Medline, Science direct, Clinical trials and Cochrane database systematic reviews. The keywords used as search terms were "Tenofovir", "TDF", "NRTI", "Nephrotoxicity", "Renal failure", "Kidney damage", "HIV" and "AIDS".

RESULTS AND CONCLUSION

Several predisposing factors including elevated baseline SCr, concomitant nephrotoxic medications, low body weight, advanced age, tenofovir disoproxil fumarate (TDF) dose and duration of treatment and lower CD4 cell count were identified as risk factors for development of TDF-induced nephrotoxicity. Cellular accumulation through increased entry from the human organic anion transporters and decreased efflux into tubular lumen is main mechanism of nucleotide analogue antiviral induced nephrotoxicity. Renal function assessment and monitoring at baseline and during TDF treatment are the main approach of prevention of TDF-induced nephrotoxicity. Rosiglitazone may be helpful in patients presenting with TDF-induced nephrotoxicity. Pretreatment with melatonin prevented all known histological changes in proximal tubular mitochondira induced by TDF. Use of antioxidants with mitochondria-targeted properties such as MitoQ or Mito-CP may prevent proximal tubular mitochondrial against TDF damage. Vitamin E, ebselen, lipoic acid, plastoquinone, nitroxides, SOD enzyme mimetics, Szeto-Schiller (SS) peptides, and quercetin are other potential agents for prevention of TDF-induced nephrotoxicity. However, data regarding effectiveness of nephroprotective agents against TDF-induced nephrotoxicity are not conclusive. Before extrapolation of the preclinical evidence to clinical practice, these evidence should be confirmed in future human studies.

Incomplete reversibility of estimated glomerular filtration rate decline following tenofovir disoproxil fumarate exposure

Background. Tenofovir disoproxil fumarate (TDF) has been linked to renal impairment, but the extent to which this impairment is reversible is unclear. We aimed to investigate the reversibility of renal decline during TDF therapy.

Methods. Cox proportional hazards models assessed factors associated with discontinuing TDF in those with an exposure duration of >6 months. In those who discontinued TDF therapy, linear piecewise regression models estimated glomerular filtration rate (eGFR) slopes before initiation of, during, and after discontinuation of TDF therapy. Factors associated with not achieving eGFR recovery 6 months after discontinuing TDF were assessed using multivariable logistic regression.

Results. We observed declines in the eGFR during TDF exposure (mean slopes, −15.7 mL/minute/1.73 m²/year [95% confidence interval {CI}, −20.5 to −10.9] during the first 3 months and −3.1 mL/minute/1.73 m²/year [95% CI, −4.6 to −1.7] thereafter) and evidence of eGFR increases following discontinuation of TDF therapy (mean slopes, 12.5 mL/minute/1.73 m²/year [95% CI, 8.9–16.1] during the first 3 months and 0.8 mL/minute/1.73 m²/year [95% CI, .1–1.5] thereafter). Following TDF discontinuation, 38.6% of patients with a decline in the eGFR did not experience recovery. A higher eGFR at baseline, a lower eGFR after discontinuation of TDF therapy, and more-prolonged exposure to TDF were associated with an increased risk of incomplete recovery 6 months after discontinuation of TDF therapy.

Conclusions. This study shows that a decline in the eGFR during TDF therapy was not fully reversible in one third of patients and suggests that prolonged TDF exposure at a low eGFR should be avoided.

Depletion of the cellular antioxidant system contributes to tenofovir disoproxil fumarate - induced mitochondrial damage and increased oxido-nitrosative stress in the kidney

BACKGROUND

Nephrotoxicity is a dose limiting side effect of tenofovir, a reverse transcriptase inhibitor that is used for the treatment of HIV infection. The mechanism of tenofovir nephrotoxicity is not clear. Tenofovir is specifically toxic to the proximal convoluted tubules and proximal tubular mitochondria are the targets of tenofovir cytotoxicity. Damaged mitochondria are major sources of reactive oxygen species and cellular damage is reported to occur after the antioxidants are depleted. The purpose of the study is to investigate the alterations in cellular antioxidant system in tenofovir induced renal damage using a rat model.

RESULTS

Chronic tenofovir administration to adult Wistar rats resulted in proximal tubular damage (as evidenced by light microscopy), proximal tubular dysfunction (as shown by Fanconi syndrome and tubular proteinuria), and extensive proximal tubular mitochondrial injury (as revealed by electron microscopy). A 50% increase in protein carbonyl content was observed in the kidneys of TDF treated rats as compared with the control. Reduced glutathione was decreased by 50%. The activity of superoxide dismutase was decreased by 57%, glutathione peroxidase by 45%, and glutathione reductase by 150% as compared with control. Carbonic Anhydrase activity was decreased by 45% in the TDF treated rat kidneys as compared with control. Succinate dehydrogenase activity, an indicator of mitochondrial activity was decreased by 29% in the TDF treated rat kidneys as compared with controls, suggesting mitochondrial dysfunction.

CONCLUSION

Tenofovir- induced mitochondrial damage and increased oxidative stress in the rat kidneys may be due to depletion of the antioxidant system particularly, the glutathione dependent system and MnSOD.

Update on tenofovir toxicity in the kidney

Tenofovir (TFV) is a widely used and effective treatment for HIV infection. Numerous studies have shown that TFV exposure is associated with small but significant declines in estimated glomerular filtration rate (eGFR). However, TFV toxicity is targeted mainly at the proximal tubule (PT), and in severe cases can cause the renal Fanconi syndrome or acute kidney injury. Severe toxicity occurs in a minority of patients, but milder PT dysfunction is more common; the long-term significance of this on kidney and bone health is uncertain. Recent work suggests that changes in eGFR on TFV therapy might be explained by inhibition of PT creatinine secretion rather than actual alterations in glomerular function. Risk factors for nephrotoxicity include pre-existing kidney disease, increased age, and low body mass. Mitochondria in the PT are the targets of TFV toxicity, but the exact mechanisms remain unclear. Substantial improvement of renal function occurs in many patients with TFV toxicity upon stopping therapy, but function does not always return to baseline. In recent years, TFV usage has been extended to new clinical spheres, including pediatrics, resource-poor settings and treatment of hepatitis B infection; theoretical reasons exist as to why some of these patients might be at higher or lower risk of TFV toxicity. Finally, strategies have been proposed to prevent TFV toxicity or enhance recovery.

Similar risk of renal events among patients treated with tenofovir or entecavir for chronic hepatitis B

BACKGROUND & AIMS

Tenofovir is a nucleotide reverse-transcriptase inhibitor approved for treatment of human immunodeficiency virus infection, as well as chronic hepatitis B (CHB). We evaluated nephrotoxicity among patients with CHB treated with tenofovir.

METHODS

We performed a community-based, retrospective cohort study of 80 patients with CHB who received tenofovir, alone or in a combination regimen; they were matched for age and sex with 80 CHB patients who received only entecavir. Incidences of serum creatinine (SCr) increase ≥0.2 mg/dL and new SCr levels of 1.5, 2.0, or 2.5 mg/dL were assessed. Patients with an estimated glomerular filtration rate (eGFR) <60 mL/min, calculated using the Modification of Diet in Renal Disease or Cockcroft-Gault formula, or who had ≥20% decrease in eGFR were also recorded.

RESULTS

More patients given entecavir had increases in SCr ≥2.5 mg/dL (1 vs 6; P = .053), whereas more patients given tenofovir had a new Cockcroft-Gault eGFR of <60 mL/min (15 vs 6; P = .022) and at least 1 dose adjustment (13 vs 4; P = .021). By multivariate analysis, the only significant factors associated with an increase in SCr were a history of organ transplantation (adjusted odds ratio, 6.740; 95% confidence interval, 1.799-28.250; P = .005) and pre-existing renal insufficiency (adjusted odds ratio, 10.960; 95% confidence interval, 2.419-48.850; P = .002). No factors, including therapy assignment, were associated with a new eGFR <60 mL/min.

CONCLUSIONS

Markers of renal function indicated that patients who received tenofovir were no more likely to have changes in renal function than patients treated with entecavir. History of transplant and pre-existing renal insufficiency were the only factors independently associated with increases in SCr.

IL-6 regulation on skeletal muscle mitochondrial remodeling during cancer cachexia in the ApcMin/+ mouse

BACKGROUND

Muscle protein turnover regulation during cancer cachexia is being rapidly defined, and skeletal muscle mitochondria function appears coupled to processes regulating muscle wasting. Skeletal muscle oxidative capacity and the expression of proteins regulating mitochondrial biogenesis and dynamics are disrupted in severely cachectic ApcMin/+ mice. It has not been determined if these changes occur at the onset of cachexia and are necessary for the progression of muscle wasting. Exercise and anti-cytokine therapies have proven effective in preventing cachexia development in tumor bearing mice, while their effect on mitochondrial content, biogenesis and dynamics is not well understood. The purposes of this study were to 1) determine IL-6 regulation on mitochondrial remodeling/dysfunction during the progression of cancer cachexia and 2) to determine if exercise training can attenuate mitochondrial dysfunction and the induction of proteolytic pathways during IL-6 induced cancer cachexia.

METHODS

ApcMin/+ mice were examined during the progression of cachexia, after systemic interleukin (IL)-6r antibody treatment, or after IL-6 over-expression with or without exercise. Direct effects of IL-6 on mitochondrial remodeling were examined in cultured C2C12 myoblasts.

RESULTS

Mitochondrial content was not reduced during the initial development of cachexia, while muscle PGC-1α and fusion (Mfn1, Mfn2) protein expression was repressed. With progressive weight loss mitochondrial content decreased, PGC-1α and fusion proteins were further suppressed, and fission protein (FIS1) was induced. IL-6 receptor antibody administration after the onset of cachexia improved mitochondrial content, PGC-1α, Mfn1/Mfn2 and FIS1 protein expression. IL-6 over-expression in pre-cachectic mice accelerated body weight loss and muscle wasting, without reducing mitochondrial content, while PGC-1α and Mfn1/Mfn2 protein expression was suppressed and FIS1 protein expression induced. Exercise normalized these IL-6 induced effects. C2C12 myotubes administered IL-6 had increased FIS1 protein expression, increased oxidative stress, and reduced PGC-1α gene expression without altered mitochondrial protein expression.

CONCLUSIONS

Altered expression of proteins regulating mitochondrial biogenesis and fusion are early events in the initiation of cachexia regulated by IL-6, which precede the loss of muscle mitochondrial content. Furthermore, IL-6 induced mitochondrial remodeling and proteolysis can be rescued with moderate exercise training even in the presence of high circulating IL-6 levels.

Safety of tenofovir use during pregnancy: early growth outcomes in HIV-exposed uninfected infants

OBJECTIVE

To evaluate the association of tenofovir disoproxil fumarate (TDF) use during pregnancy with early growth parameters in HIV-exposed, uninfected (HEU) infants.

DESIGN

US-based prospective cohort study of HEU children to examine potential adverse effects of prenatal TDF exposure.

METHODS

We evaluated the association of maternal TDF use during pregnancy with small for gestational age (SGA); low birth weight (LBW, <2.5 kg); weight-for-age z-scores (WAZ), length-for-age z-scores (LAZ), and head circumference-for-age (HCAZ) z-scores at newborn visit; and LAZ, HCAZ, and WAZ at age 1 year. Logistic regression models for LBW and SGA were fit, adjusting for maternal and sociodemographic factors. Adjusted linear regression models were used to evaluate LAZ, WAZ, and HCAZ by TDF exposure.

RESULTS

Of 2029 enrolled children with maternal antiretroviral information, TDF was used by 449 (21%) HIV-infected mothers, increasing from 14% in 2003 to 43% in 2010. There was no difference between those exposed to combination regimens with vs. without TDF for SGA, LBW, and newborn LAZ and HCAZ. However, at age 1 year, infants exposed to combination regimens with TDF had significantly lower adjusted mean LAZ and HCAZ than those without TDF (LAZ: -0.17 vs. -0.03, P=0.04; HCAZ: 0.17 vs. 0.42, P=0.02).

CONCLUSION

TDF use during pregnancy was not associated with increased risk for LBW or SGA. The slightly lower mean LAZ and HCAZ observed at age 1 year in TDF-exposed infants are of uncertain significance but underscore the need for additional studies of growth outcomes after TDF use during pregnancy.

Presteady state kinetic investigation of the incorporation of anti-hepatitis B nucleotide analogues catalyzed by noncanonical human DNA polymerases

Antiviral nucleoside analogues have been developed to inhibit the enzymatic activities of the hepatitis B virus (HBV) polymerase, thereby preventing the replication and production of HBV. However, the usage of these analogues can be limited by drug toxicity because the 5'-triphosphates of these nucleoside analogues (nucleotide analogues) are potential substrates for human DNA polymerases to incorporate into host DNA. Although they are poor substrates for human replicative DNA polymerases, it remains to be established whether these nucleotide analogues are substrates for the recently discovered human X- and Y-family DNA polymerases. Using presteady state kinetic techniques, we have measured the substrate specificity values for human DNA polymerases β, λ, η, ι, κ, and Rev1 incorporating the active forms of the following anti-HBV nucleoside analogues approved for clinical use: adefovir, tenofovir, lamivudine, telbivudine, and entecavir. Compared to the incorporation of a natural nucleotide, most of the nucleotide analogues were incorporated less efficiently (2 to >122,000) by the six human DNA polymerases. In addition, the potential for entecavir and telbivudine, two drugs which possess a 3'-hydroxyl, to become embedded into human DNA was examined by primer extension and DNA ligation assays. These results suggested that telbivudine functions as a chain terminator, while entecavir was efficiently extended by the six enzymes and was a substrate for human DNA ligase I. Our findings suggested that incorporation of anti-HBV nucleotide analogues catalyzed by human X- and Y-family polymerases may contribute to clinical toxicity.

Tenofovir-associated kidney toxicity in HIV-infected patients: a review of the evidence

Tenofovir (TDF) is an effective and widely used treatment for both human immunodeficiency virus (HIV) and hepatitis B virus infection. Although studies suggest that TDF has a low overall toxicity profile and only a modest effect on estimated glomerular filtration rate, numerous case reports have since appeared in the literature describing TDF-associated renal tubular dysfunction, and this is now a significant source of HIV-related referrals to nephrologists. The main target of toxicity appears to be the proximal tubule, and in severe cases, patients can develop renal Fanconi syndrome. We review findings from recent studies in this area performed by ourselves and others and discuss our direct experience as practicing nephrologists. In particular, we discuss: (1) the nature and extent of TDF-associated kidney toxicity in the HIV-infected population, (2) potential underlying mechanisms of toxicity in the proximal tubule, (3) risk factors for developing tubular dysfunction, and (4) suggested strategies to monitor patients on TDF therapy.

Evaluation of mitochondrial toxicity in Marmota himalayana treated with metacavir, a novel 2',3'-dideoxyguanosine prodrug for treatment of hepatitis B Virus

Metacavir (PNA) is a novel synthetic nucleoside analogue for the treatment of hepatitis B virus (HBV). Our recent studies showed that PNA, a prodrug of 2',3'-dideoxyguanosine (ddG), exhibited lower mitochondrial toxicity in long-term cultures of HepG2 cells. In the current study, we examined the long-term effects of PNA on mitochondrial toxicity in Marmota himalayana (Himalayan marmot). Himalayan marmots were treated daily with oral PNA (50 or 100 mg/kg), ziduvidine (AZT) (100 mg/kg), or water (control) for 90 days. PNA treatment did not alter the body weight or plasma lactate acid level. In livers from the animals treated with PNA at 100 mg/kg/day, histopathology showed mild steatosis or small focal liver cell necrosis. Electron microscopy also showed minor proliferation and partial mitochondrial swelling with crista reduction. Measurement of respiratory chain complex enzyme activity and mitochondrial DNA (mtDNA) content revealed no significant differences in skeletal muscle, liver, and kidney tissues between animals treated with PNA and controls. In contrast, in Himalayan marmots treated with AZT we observed delayed toxicity, including lactic acidosis, severe hepatic steatosis, obvious mitochondrial damage, and significant decreases in respiratory chain complex enzyme activity and mtDNA content. This is similar to the delayed toxicity syndrome observed previously in animals and humans. In summary, PNA treatment did not alter mitochondrial enzyme activity or mtDNA content. This suggests that PNA could pose a very low risk for adverse mitochondrion-related effects. However, long-term hepatotoxic effects of PNA were observed, and this indicates a need for continued monitoring of PNA-associated hepatotoxicity in clinical trials.

Muscle oxidative capacity during IL-6-dependent cancer cachexia

Many diseases are associated with catabolic conditions that induce skeletal muscle wasting. These various catabolic states may have similar and distinct mechanisms for inducing muscle protein loss. Mechanisms related to muscle wasting may also be related to muscle metabolism since glycolytic muscle fibers have greater wasting susceptibility with several diseases. The purpose of this study was to determine the relationship between muscle oxidative capacity and muscle mass loss in red and white hindlimb muscles during cancer cachexia development in the Apc(Min/+) mouse. Gastrocnemius and soleus muscles were excised from Apc(Min/+) mice at 20 wk of age. The gastrocnemius muscle was partitioned into red and white portions. Body mass (-20%), gastrocnemius muscle mass (-41%), soleus muscle mass (-34%), and epididymal fat pad (-100%) were significantly reduced in severely cachectic mice (n = 8) compared with mildly cachectic mice (n = 6). Circulating IL-6 was fivefold higher in severely cachectic mice. Cachexia significantly reduced the mitochondrial DNA-to-nuclear DNA ratio in both red and white portions of the gastrocnemius. Cytochrome c and cytochrome-c oxidase complex subunit IV (Cox IV) protein were reduced in all three muscles with severe cachexia. Changes in muscle oxidative capacity were not associated with altered myosin heavy chain expression. PGC-1α expression was suppressed by cachexia in the red and white gastrocnemius and soleus muscles. Cachexia reduced Mfn1 and Mfn2 mRNA expression and markers of oxidative stress, while Fis1 mRNA was increased by cachexia in all muscle types. Muscle oxidative capacity, mitochondria dynamics, and markers of oxidative stress are reduced in both oxidative and glycolytic muscle with severe wasting that is associated with increased circulating IL-6 levels.

Aging, human immunodeficiency virus, and bone health

Highly active antiretroviral therapy (HAART) has had a profound impact on improving the long-term prognosis for individuals infected with human immunodeficiency virus (HIV). HAART has been available for close to two decades, and now a significant number of patients with access to HAART are over the age of 50 years. Many clinical studies have indicated that HIV infection, as well as components of HAART, can increase the risk in these individuals to a variety of noninfectious complications, including a risk to bone health. There is a significant need for detailed mechanistic analysis of the aging, HIV-infected population regarding the risk of HIV infection and therapy in order to maintain bone health. Insights from basic mechanistic studies will help to shed light on the role of HIV infection and the components of HAART that impact bone health, and will help in identifying preventative countermeasures, particularly for individuals 50 years of age and older.

Clinical syndromes and consequences of antiretroviral-related hepatotoxicity

Highly active antiretroviral therapy (HAART)-related hepatotoxicity complicates the management of patients infected with human immunodeficiency virus (HIV), increases medical costs, alters the prescription patterns, and affects the guideline recommendations. Among the clinical consequences derived from HAART-related liver toxicity, hypersensitivity reactions and lactic acidosis are recognized as acute events with potential to evolve into fatal cases, whereas there seems to be other syndromes not as well characterized but of equal concern as possible long-term liver complications. Belonging to the latter category of syndrome, HAART-related nonalcoholic steatohepatitis, liver fibrosis, portal hypertension, and nodular regenerative hyperplasia are discussed in this review. Updated information on liver toxicity of current antiretroviral drugs, including the most recently licensed, is provided. Management and prevention of liver toxicity among HIV-infected patients treated with HAART are reviewed as well.

eNOS plays a major role in adiponectin synthesis in adipocytes

Nitric oxide (NO) stimulates mitochondrial biogenesis. We recently reported that adiponectin synthesis is regulated by mitochondrial function in adipocytes. This study was undertaken to test the hypothesis that endothelial NO synthase (eNOS) plays an important role in adiponectin synthesis by producing NO and enhancing mitochondrial function in adipocytes. We examined the effects of eNOS knockdown on adiponectin synthesis in 3T3-L1 adipocytes and also examined plasma adiponectin levels and the mitochondria in adipose tissue of eNOS knockout (eNOS(-/-)) mice with and without chronic administration of a NO donor. In cultured 3T3-L1 adipocytes, eNOS siRNA decreased rosiglitazone-induced adiponectin secretion, which was associated with decreases in mitochondrial proteins and biogenesis factors. Plasma adiponectin concentrations were reduced in adult eNOS(-/-) mice compared with age-matched wild-type mice. Mitochondrial contents in adipose tissue were reduced in eNOS(-/-) mice, and this was associated with decreased expression of mitochondrial biogenesis factors, increased levels of 8-hydroxyguanosine, a biomarker of oxidative stress, and morphological abnormalities in mitochondria. Rosiglitazone-induced increases in adiponectin expression and mitochondrial content were also reduced significantly in eNOS(-/-) mice. Chronic administration of a NO donor reversed mitochondrial abnormalities and increased adiponectin expression in adipose tissue of eNOS(-/-) mice. eNOS plays an important role in adiponectin synthesis in adipocytes by increasing mitochondrial biogenesis and enhancing mitochondrial function.

Efficacy and safety of tenofovir disoproxil fumarate in patients with chronic hepatitis B

Chronic hepatitis B (CHB) is prevalent worldwide. It may cause cirrhosis and hepatocellular carcinoma. Treatment for this condition may need to be lifelong, thus the drugs used must be both efficacious and safe. Clinical trials of tenofovir have demonstrated a good safety profile for this drug and it has potent antiviral properties. However, to better characterize the safety of this drug, the postmarketing surveillance must be taken into account. Clinicians need to be vigilant, as infrequent adverse events may be revealed during this phase. The current review presents a detailed exposé of preclinical and clinical data on tenofovir to increase awareness of possible adverse events and drug-drug interactions, based on the large experience of this drug in human immunodeficiency virus (HIV) treatment (and to date in patients with CHB). Several recommendations that may help the clinician to prevent the development of adverse events associated with tenofovir disoproxil fumarate (TDF) treatment are outlined, along with a suggested surveillance protocol for the timely and proper identification of possible renal and bone toxicity.

Nucleotide HIV reverse transcriptase inhibitors: tenofovir and beyond

PURPOSE OF REVIEW

This review describes the class of nucleotide HIV reverse transcriptase inhibitors and summarises recent findings related to tenofovir and its oral prodrug tenofovir disoproxil fumarate, currently the only nucleotide approved for the treatment of HIV infection. In addition, novel strategies in the design of anti-HIV nucleotides and their prodrugs are discussed.

RECENT FINDINGS

A number of studies have demonstrated a potent and durable clinical efficacy of tenofovir disoproxil fumarate in combination with other antiretrovirals, particularly lamivudine or emtricitabine and efavirenz. The prophylactic antiretroviral effect of tenofovir and tenofovir disoproxil fumarate has been characterized in various animal models and is currently being evaluated in controlled clinical studies. In addition, efficacy of tenofovir disoproxil fumarate against hepatitis B virus has been established and is currently being explored in phase III trials. The identification of GS-7340, an alternative prodrug of tenofovir has raised the possibility of using phosphonoamidates as novel prodrugs allowing for an effective intracellular delivery of nucleotides.

SUMMARY

The concept of nucleotides as a novel class of antiretroviral therapeutics has been successfully validated through tenofovir disoproxil fumarate, a nucleotide prodrug that exhibits potent and durable clinical efficacy and favourable safety profile both in treatment-naïve and experienced HIV-infected patients. Several novel nucleotide reverse transcriptase inhibitors such as GS-9148, PMDTA, and PMEO have recently emerged from continuing preclinical drug discovery efforts.

In vivo assessment of mitochondrial toxicity of metacavir in Rhesus monkeys after three months of intravenous administration

AIM

To explore the potential mitochondrial toxicities and their severities of intravenously administered metacavir, a nucleoside analog, in rhesus monkeys.

METHODS

Totally 21 rhesus monkeys were randomly divided into 4 groups: metacavir 120 mg/kg group, metacavir 40 mg/kg group, zidovudine(AZT) 50 mg/kg group, and blank control group. Animals were killed after the completion of dosing or further observed in a 4-week recovery phase. Changes of structure of mitochondria in liver, kidney, skeletal muscles, and cardiac muscles were observed under transmission electron microscope(TEM). Changes of the activities of mitochondrial respiratory chain complexes and mitochondrial DNA were also determined.

RESULTS

In metacavir 120 mg/kg group, some mitochondrial injuries were found in skeletal muscle, cardiac muscle, and liver, including that some cristae was broken and became sparse in density in the skeletal muscle, the morphology and size of mitochondria remained unchanged. Metacavir decreased the activities of respiratory chain complexes I and II and the mtDNA contents in three tissues in a dose-dependent manner; however, the extent of such decrease was lower than that in AZT 50 mg/kg group. The mitochondrial injuries in metacavir 40 mg/kg group were mild in each tissue and no obvious change in mitochondrial function was noted. On week 4 in the recovery phase, results showed that all these injuries were reversible after drug withdrawal.

CONCLUSION

These results suggest that metacavir has not a high risk for potential mitochondrial-related effects in rhesus monkeys.

Using ΦX174 DNA as an exogenous reference for measuring mitochondrial DNA copy number

Quantitative real-time PCR has become a popular method to analyze and quantify changes in the copy number of mitochondrial DNA (mtDNA), and nuclear DNA (nDNA) is often used as an endogenous reference for mtDNA abundance. In our experience, using nDNA as a reference is problematic, due to differences in the extraction efficiency of nDNA and mtDNA and variation in the ploidy of experimental samples. Here, we report that the ratio of mtDNA to nDNA varies in repeated DNA extractions but that ΦX174 DNA, added before DNA extraction, is extracted with a similar efficiency to mtDNA, making it a suitable alternative reference for quantifying mtDNA copy number.

CKS proteins protect mitochondrial genome integrity by interacting with mitochondrial single-stranded DNA-binding protein

Cyclin-dependent kinase subunit (CKS) proteins interact with cyclin-dependent kinases (CDKs) with high affinity. Mammalian CKS1 and CKS2 bind CDK1 and CDK2 and partake in the control of cell cycle progression. We identified CKS-interacting proteins by affinity purification followed by mass spectrometry in the human lymphocytic cell line Ramos. Apart from known interactors, such as CDKs, we identified a novel CDK-dependent interaction between CKS proteins and the mitochondrial single-stranded DNA-binding protein (mtSSB). mtSSB bound both CKS1 and CKS2 and underwent CDK-dependent phosphorylation. mtSSB is known to participate in replication of mitochondrial DNA. We demonstrated that mitochondrial morphology and DNA integrity were compromised in cells depleted of both CKS proteins or that had inhibited CDK activity. These features are consistent with the hypothesis of CKS-dependent regulation of mtSSB function and support a direct role of cell cycle proteins in controlling mitochondrial DNA replication.

Tenofovir disoproxil fumarate in pregnancy and prevention of mother-to-child transmission of HIV-1: is it time to move on from zidovudine?

OBJECTIVES

Zidovudine (ZDV) has been the cornerstone of antiretroviral (ARV) therapy for pregnant women infected with HIV-1 in the prevention of mother-to-child transmission (MTCT) and remains the only licensed ARV for use in pregnancy. We explored the current and future roles of tenofovir disoproxil fumarate (TDF) in the prevention of MTCT of HIV-1.

METHODS

We reviewed the published literature by conducting database searches of in vitro, animal and clinical studies, reported in journals and at conferences, using the search terms Tenofovir/gs4331/viread, pregnant/pregnancy, lactate, lactation, natal, reproduce/reproduction, placenta/placental, malformation, and teratogenicity/teratogenic.

RESULTS

In a macaque model, perinatal exposure to very high dose tenofovir resulted in bone toxicity in some offspring. However, perinatal use of TDF, both single dose and as part of highly active antiretroviral therapy in women, has been well tolerated in the short term by mothers and their infants. Further, the addition of single-dose TDF to single-dose nevirapine (SD-NVP) during delivery following maternal ZDV use during pregnancy significantly reduces the frequency of nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance.

CONCLUSIONS

The addition of TDF to SD-NVP reduces NNRTI resistance. The role of TDF in this setting and during pregnancy for reducing rates of MTCT requires investigation. While short-term toxicity data are encouraging, long-term follow-up of exposed mothers and infants is required.

Tenofovir-associated renal and bone toxicity

OBJECTIVES

The aims of the study were to describe the clinical presentation and renal and bone abnormalities in a case series of HIV-infected patients receiving treatment with tenofovir (TDF), and to recommend appropriate screening for toxicity related to TDF.

METHODS

Patients were identified from referrals to a specialist HIV renal clinic. Patients were included if treatment with TDF was assessed as the primary cause of the renal function impairment and clinical data were available prior to and following discontinuation of TDF treatment. Data were collected from case note review and clinic databases.

RESULTS

Twenty-two patients (1.6% of all those who received TDF) were identified with TDF-associated renal toxicity. All had normal serum creatinine prior to TDF therapy. All presented with proteinuria. On stopping TDF, renal function improved. Eight patients had confirmed Fanconi syndrome. Twelve patients presented with bone pain and osteomalacia was confirmed on an isotope bone scan in seven of these patients. The findings (in those patients tested) of tubular proteinuria, reduced tubular transport maximum of phosphate (TmP), and glycosuria were all consistent with the proximal tubule being the site of toxicity.

CONCLUSION

Renal toxicity remains a concern in patients treated with TDF. Clinical presentation may be with renal dysfunction, Fanconi syndrome or osteomalacia. Our investigations suggest proximal tubular toxicity as a common pathogenic mechanism.

An analysis of enzyme kinetics data for mitochondrial DNA strand termination by nucleoside reverse transcription inhibitors

Nucleoside analogs used in antiretroviral treatment have been associated with mitochondrial toxicity. The polymerase-γ hypothesis states that this toxicity stems from the analogs' inhibition of the mitochondrial DNA polymerase (polymerase-γ) leading to mitochondrial DNA (mtDNA) depletion. We have constructed a computational model of the interaction of polymerase-γ with activated nucleoside and nucleotide analog drugs, based on experimentally measured reaction rates and base excision rates, together with the mtDNA genome size, the human mtDNA sequence, and mitochondrial dNTP concentrations. The model predicts an approximately 1000-fold difference in the activated drug concentration required for a 50% probability of mtDNA strand termination between the activated di-deoxy analogs d4T, ddC, and ddI (activated to ddA) and the activated forms of the analogs 3TC, TDF, AZT, FTC, and ABC. These predictions are supported by experimental and clinical data showing significantly greater mtDNA depletion in cell culture and patient samples caused by the di-deoxy analog drugs. For zidovudine (AZT) we calculated a very low mtDNA replication termination probability, in contrast to its reported mitochondrial toxicity in vitro and clinically. Therefore AZT mitochondrial toxicity is likely due to a mechanism that does not involve strand termination of mtDNA replication.

While HIV/AIDS therapy is very successful at controlling HIV infection, the therapy must continue for the remainder of the patient's life. Approximately one-fourth of these patients suffer from serious drug toxicity problems. It is generally believed that the toxicity of these drugs is caused by damage to mitochondria, the “power plants” of every cell. But we do not know exactly how this damage occurs. The most common explanation is that these drugs damage mitochondria in the same way that they control the virus, by interfering with DNA replication. We tested that idea by analyzing data for the interaction of several AIDS drugs with the mitochondrial DNA polymerase, the protein responsible for copying mitochondrial DNA. By using a detailed simulation of the mitochondrial DNA polymerase, we show that some of these drugs do interact well enough with the mitochondrial DNA polymerase to lead to toxic effects. However, many of these drugs, including the commonly used drug AZT, had very little toxic effect in this simulation although AZT often causes toxicity in patients. This indicates that the toxicity of AZT occurs through some other process and not through the direct interruption of mitochondrial DNA replication.

Rosiglitazone reverses tenofovir-induced nephrotoxicity

Tenofovir disoproxil fumarate (TDF) is a first-line drug used in patients with highly active retroviral disease; however, it can cause renal failure associated with many tubular anomalies that may be due to down regulation of a variety of ion transporters. Because rosiglitazone, a peroxisome proliferator-activated receptor-gamma agonist induces the expression of many of these same transporters, we tested if the nephrotoxicity can be ameliorated by its use. High doses of TDF caused severe renal failure in rats accompanied by a reduction in endothelial nitric-oxide synthase and intense renal vasoconstriction; all of which were significantly improved by rosiglitazone treatment. Low-dose TDF did not alter glomerular filtration rate but produced significant phosphaturia, proximal tubular acidosis, polyuria and a reduced urinary concentrating ability. These alterations were caused by specific downregulation of the sodium-phosphorus cotransporter, sodium/hydrogen exchanger 3 and aquaporin 2. A Fanconi's-like syndrome was ruled out as there was no proteinuria or glycosuria. Rosiglitazone reversed TDF-induced tubular nephrotoxicity, normalized urinary biochemical parameters and membrane transporter protein expression. These studies suggest that rosiglitazone treatment might be useful in patients presenting with TFV-induced nephrotoxicity especially in those with hypophosphatemia or reduced glomerular filtration rate.

Tenofovir disoproxil fumarate for the treatment of HIV infection

Tenofovir disoproxil fumarate is a nucleotide analogue reverse transcriptase inhibitor approved by the FDA for the treatment of HIV infection. It is a potent agent with a long intracellular half-life that allows for once-daily dosing. It has been well tolerated in clinical trials, without evidence of the mitochondrial toxicity that has been associated with long-term treatment of some of the nucleoside analogue reverse transcriptase inhibitors. Because of its demonstrated efficacy and favourable safety profile, tenofovir disoproxil fumarate has quickly become a favoured nucleoside component of antiretroviral regimens for both treatment-naive and -experienced patients.

Tenofovir-induced kidney injury

Tenofovir disoproxil fumarate is a nucleotide reverse transcriptase inhibitor with activity against both HIV and the hepatitis B virus. It has had minimal nephrotoxic effects in early clinical trials, but as clinical use has widened, case reports describing tenofovir-induced renal tubular damage, Fanconi's syndrome and diabetes insipidus have been described. The authors review the pharmacokinetics, mechanism of action and clinical uses of tenofovir disoproxil fumarate. The large clinical trials, as well as the case reports of tenofovir-induced kidney injury, are also reviewed. The potential mechanism of renal damage is discussed and recommendations for evaluation and treatment of tenofovir-induced kidney injury are given.

From adefovir to Atripla™ via tenofovir, Viread™ and Truvada™

With the recent approvalof Atripla™ by the US FDA for the treatment of AIDS as the first triple-drug combination one-a-day pill, it would appear appropriate to review both the origin and development of this anti-HIV medicine. Atripla consists of three active ingredients, a nucleotide reverse transcriptase inhibitor (NtRTI), a nucleoside reverse transcriptase inhibitor (NRTI) and non-nucleoside reverse transcriptase inhibitor (NNRTI). The cornerstone in Atripla is the NtRTI tenofovir disoproxil fumarate (Viread™) complemented by the NRTI emtricitabine (Emtriva™) and the NNRTI efavirenz (Sustiva™). This triple-drug combination offers a number of advantages compared with the single-drug regimens, such as synergistic mechanism of action, decreased risk of drug-resistance development and reduction of toxic side effects of the individual drugs, while increasing drug compliance (based on once-daily dosing). Since the first NtRTI, adefovir, was described as an antiretroviral agent, it has taken exactly 20 years to successfully develop its combination with emtricitabine and efavirenz as the ‘combo’ pill Atripla for the treatment of AIDS.

Urinary beta2-microglobulin as a possible sensitive marker for renal injury caused by tenofovir disoproxil fumarate

Tenofovir disoproxil fumarate (TDF) is renally excreted by a combination of glomerular filtration and active tubular secretion, and its renal safety profiles have been reported based on a limited increase of serum creatinine (sCr) levels. However, renal tubular function has not previously been well monitored. We measured sCr and urinary beta2-microglobulin (U-beta2MG) levels cross-sectionally in 70 patients treated with TDF [TDF+] and 90 patients on other antiretroviral therapy who had never been exposed to TDF [TDF-]. The mean U-beta2MG was significantly higher in TDF+ patients than that in TDF- patients (p < 0.0001), though no statistical difference was detected in their creatinine clearance estimated by using the Cockcroft-Gault equation. Multivariate analysis showed that coadministration of boosted lopinavir (LPV) and patients' body weight were associated with U-beta 2MG levels in TDF+ patients. U-beta2MG levels were significantly higher in those who also received boosted LPV [TDF+LPV+] (p = 0.0007), and abnormally high levels were noted in 67.7% of them. Furthermore, in the TDF+LPV+ group, U-beta2MG levels showed significant negative correlation with patients' body weight (p = 0.0029) and abnormal U-beta2MG was observed in all six patients with body weight less than 55 kg. In four patients, a rapid fall in U-beta2MG occurred after cessation of TDF. Relative to sCr, U-beta2MG could be a more sensitive marker of renal tubular injury caused by TDF. Boosted LPV co-administration and low body weight may be risk factors for TDF-induced renal tubular dysfunction, probably because these factors are associated with an increase in TDF concentration.

Hepatic steatosis is associated with fibrosis, nucleoside analogue use, and hepatitis C virus genotype 3 infection in HIV-seropositive patients

BACKGROUND

We conducted a study to determine the prevalence and factors associated with hepatic steatosis in human immunodeficiency virus (HIV)-seropositive patients with hepatitis C and to investigate whether steatosis is associated with liver fibrosis.

METHODS

Retrospective chart reviews were conducted in 4 hospitals that serve community-based and incarcerated HIV-infected patients who had undergone a liver biopsy for evaluation of hepatitis C virus (HCV) infection during the period of 2000-2003. Demographic characteristics and medication and laboratory data were collected from the time of the biopsy. A pathologist blinded to all clinical data evaluated the specimens. The primary outcome was presence or absence of steatosis.

RESULTS

Of 260 HIV-HCV-coinfected patients, 183 met inclusion criteria and had a biopsy specimen adequate for review. Steatosis was present in 69% of patients (graded as minimal in 31%, mild in 27%, moderate in 18%, and severe in 1%). Factors associated with steatosis included use of dideoxynucleoside analogues, such as didanosine and stavudine (odds ratio [OR], 4.63; 95% confidence interval [CI], 1.55-13.82). There was a trend toward presence of steatosis and use of other nucleoside analogues or infection with HCV genotype 3 (OR, 2.65 [95% CI, 0.95-7.41] and 3.38 [95% CI, 0.86-13.28], respectively). The presence of steatosis was associated with fibrosis (OR, 1.37; 95% CI, 1.03-1.81).

CONCLUSIONS

In this multiracial population of HIV-HCV-coinfected patients, steatosis was prevalent and was associated with severity of liver fibrosis. Use of nucleoside analogues (particularly didanosine and stavudine) and HCV genotype 3 infection were associated with hepatic steatosis. The development of steatosis is multifactorial in nature and may play a contributory role in the progression of liver disease in HIV-infected patients.

Exploring Mitochondrial Nephrotoxicity as a Potential Mechanism of Kidney Dysfunction among HIV-Infected Patients on Highly Active Antiretroviral Therapy

Background

Tenofovir (TDF) exposure has been associated with renal dysfunction. Mitochondrial nephrotoxicity was investigated as an underlying mechanism. Given the interaction between TDF and didanosine (ddI), their concurrent use was also investigated.

Design

Relative kidney biopsy mitochondrial DNA (mtDNA) to nuclear DNA ratios were measured retrospectively. HIV+ individuals on TDF within 6 months preceeding the biopsy (HIV+/TDF+, n=21) were compared to HIV+ individuals who never received TDF (HIV+/TDF-, n=10) and to HIV uninfected controls (HIV–, n=22). Twelve of the HIV+/TDF+ individuals received concurrent ddI, 10 of those once at unadjusted ddI dosage. Tubular mitochondria morphology was also examined by electron microscopy. Statistical analyses were done on log-transformed mtDNA/nDNA, using non-parametric tests.

Results

Kidney mtDNA levels were different among the three groups ( P=0.046). mtDNA ratios were lower in HIV+/TDF+ subjects (7.5 [2.0–12.1]) than in HIV- ones (14.3 [6.0–16.5], P=0.014), but not lower than HIV+/TDF-controls (6.4 [2.8–11.9], P=0.82). Among HIV+ subjects, there was a difference between TDF-, TDF+/ddI- and TDF+/ddI+ ( P=0.005), with concurrent TDF/ddI use associated with lower mtDNA (2.1 [1.9–5.5], n=12) than TDF+/ddI- (13.8 [7.5–16.4], n=9, P=0.003). No TDF–/ddI+ biopsies were available. In regression analyses, only HIV infection ( P=0.03), and TDF/ddI use ( P=0.003) were associated with lower mtDNA. At the ultrastructural level, abnormal tubular mitochondria was more prevalent in HIV+/TDF+ biopsies than HIV+/TDF- and HIV- ones together ( P<0.001) but not more so in TDF+/ddI+ biopsies than TDF+/ddI- ones ( P=0.67).

Conclusions

Renal dysfunction in this population may be mediated through mitochondrial nephrotoxicity that involves more than one drug and/or pathogenesis. Kidney mtDNA depletion was associated with HIV infection and concurrent TDF/ddI therapy but not TDF use alone, while kidney ultrastructural mitochondrial abnormalities were seen with TDF use. The interaction between TDF and ddI may be relevant in the kidney where both drugs are cleared. The clinical relevance of our findings needs to be evaluated given the current recommendation for reduced doses of ddI when used in conjunction with TDF.

Longitudinal study on mitochondrial effects of didanosine-tenofovir combination

Tenofovir disoproxil fumarate (TDF) has been reported to be free of adverse effects on mitochondria. We evaluate the effects of the introduction of TDF in a didanosine (ddI)-based highly active antiretroviral therapy (HAART) on mitochondrial DNA (mtDNA) content, mitochondrial mass (MM), and cytochrome c oxidase (COX) activity of the oxidative phosphorylation (OXPHOS) system over a 12-month period. Forty-four asymptomatic HIV patients with undetectable viral load receiving a ddI-based HAART were recruited and switched to ddI plus TDF (ddI + TDF) and nevirapine (n = 22) or maintained with the same baseline ddIbased HAART scheme (n = 22). Peripheral blood mononuclear cells were obtained at 0, 6, and 12 months. COX activity and MM were determined by spectrophotometry and the mtDNA content by quantitative realtime PCR. The mtDNA content showed a progressive decrease over the 12-month period of the study for the two groups with respect to baseline, with such a decrease statistically significant only in the ddI + TDF group (55% decrease, p < 0.001). In addition, the decrease of mtDNA content over time was statistically different between both groups (p < 0.001). Consistently, MM and COX activity decreased significantly at 12 months with respect to baseline only in the ddI < TDF group (28% decrease for MM, p < 0.05; 47% decrease for COX activity, p < 0.001). We conclude that switching to a HAART regimen containing ddI + TDF is associated with evolutive mitochondrial damage expressed as mtDNA depletion, loss of MM, and decrease in COX efficiency. The particular relevance of either ddI, TDF, or any interaction between them in such a mitochondrial dysfunction remains to be established.

Protective effect of the acyclic nucleoside phosphonate tenofovir toward human T-cell leukemia/lymphotropic virus type 1 infection of human peripheral blood mononuclear cells in vitro

9-(R)-[(2-Phosphonomethoxy)propyls]adenine (tenofovir), is an acyclic nucleoside phosphonate known to inhibit HIV replication in vitro and to reduce viremia in HIV-infected patients. Here we have investigated whether tenofovir is able to protect peripheral blood mononuclear cells (PBMCs) from healthy donors against human T-cell leukemia/lymphotropic virus type 1 (HTLV-1) infection in vitro. PBMCs were pre-treated with tenofovir and infected by exposure to an irradiated cell line chronically harbouring HTLV-1. Measurements of viral DNA, as well as viral gene and protein expression, at 4 weeks after infection, revealed that tenofovir at concentrations of 1 microM and higher completely protected PBMCs against HTLV-1; lower concentrations did not fully prevent HTLV-1 infection of the cultures. Nevertheless, in the long term, cell growth of infected PBMCs was inhibited in vitro even by 0.1 microM tenofovir. In addition, tenofovir directly inhibited HTLV-1 reverse transcriptase activity, in a cell-free assay that utilizes a crude preparation from HTLV-1 viral particles as a source of the enzyme. The selectivity index of tenofovir for HTLV-1, was about four times higher than that of azidothymidine. Taken together our results strongly encourage further studies to investigate the real impact of tenofovir towards HTLV-1 infection.

Adefovir dipivoxil: review of a novel acyclic nucleoside analogue

Adefovir dipivoxil (ADF) is a novel acyclic nucleoside analogue that has recently been approved for the treatment of chronic hepatitis B virus (HBV). Adefovir was initially assessed at higher doses for the treatment of human immunodeficiency virus (HIV) infection. However, in these studies, nephrotoxicity proved a dose-limiting side effect. Large randomised controlled studies have recently shown that ADF results in histological, virological and biochemical improvement in both hepatitis B e antigen (HBeAg)-positive and HBeAg-negative chronic HBV. While the rate of HBeAg seroconversion at 1 year (12%) was lower than both lamivudine and interferon, this increases with prolonged treatment. The clinical improvements occurred without serious side effects or the development of resistance at the dose of 10 mg daily, in treatment trials of up to 2 years, although resistance has now been observed. In addition, the drug is efficacious in HBV/HIV co-infection and hepatitis B-infected liver transplant recipients, particularly in those who have developed lamivudine resistance. ADF can be added as a treatment option to existing treatment options (interferon-alpha and lamivudine) and assumes a role in the ongoing management of chronic HBV. The optimal use of ADF as either a monotherapy or as part of combination therapy requires further assessment.

Biological effects of short-term or prolonged administration of 9-[2-(phosphonomethoxy)propyl]adenine (tenofovir) to newborn and infant rhesus macaques

The reverse transcriptase inhibitor 9-[2-(phosphonomethoxy)propyl]adenine (PMPA; tenofovir) was previously found to offer strong prophylactic and therapeutic benefits in an infant macaque model of pediatric human immunodeficiency virus (HIV) infection. We now summarize the toxicity and safety of PMPA in these studies. When a range of PMPA doses (4 to 30 mg/kg of body weight administered subcutaneously once daily) was administered to 39 infant macaques for a short period of time (range, 1 day to 12 weeks), no adverse effects on their health or growth were observed; this included a subset of 12 animals which were monitored for more than 2 years. In contrast, daily administration of a high dose of PMPA (30 mg/kg subcutaneously) for prolonged periods of time (>8 to 21 months) to 13 animals resulted in a Fanconi-like syndrome (proximal renal tubular disorder) with glucosuria, aminoaciduria, hypophosphatemia, growth restriction, bone pathology (osteomalacia), and reduced clearance of PMPA. The adverse effects were reversible or were alleviated following either complete withdrawal of PMPA treatment or reduction of the daily regimen from 30 mg/kg to 2.5 to 10 mg/kg subcutaneously. Finally, to evaluate the safety of a prolonged low-dose treatment regimen, two newborn macaques were started on a 10-mg/kg/day subcutaneous regimen; these animals are healthy and have normal bone density and growth after 5 years of daily treatment. In conclusion, our findings suggest that chronic daily administration of a high dose of PMPA results in adverse effects on kidney and bone, while short-term administration of relatively high doses and prolonged low-dose administration are safe.

Mitochondrial toxicity of NRTI antiviral drugs: an integrated cellular perspective

Highly active antiretroviral therapy (HAART) regimes based on nucleoside reverse transcriptase inhibitors (NRTIs) have revolutionized the treatment of AIDS in recent years. Although HAART can successfully suppress viral replication in the long term, it is not without significant toxicity, which can seriously compromise treatment effectiveness. A major toxicity that has been recognized for more than a decade is NRTI-related mitochondrial toxicity, which manifests as serious side effects such as hepatic failure and lactic acidosis. However, a lack of understanding of the mechanisms underlying mitochondrial toxicity has hampered efforts to develop novel drugs with better side-effect profiles. This review characterizes the pharmacological mechanisms and pathways that are involved in mitochondrial dysfunction caused by NRTIs, and suggests opportunities for future pharmacological research.