Adverse effects of reverse transcriptase inhibitors: mitochondrial toxicity as common pathway

Toxicity of antiretroviral nucleoside and nucleotide analogues: is mitochondrial toxicity the only mechanism?

Nucleoside analogues represent the cornerstones of antiretroviral regimens. A range of drug- or tissue-specific toxicities, such as peripheral neuropathy, myopathy, pancreatitis and lactic acidosis with hepatic steatosis, has been documented with these agents. The fat atrophy seen on long term antiretroviral therapy may also be related to nucleoside analogues. The mechanisms by which nucleoside analogues cause toxicity are not clearly established. In vitro, the triphosphates of these agents are weak to modest substrates for human DNA polymerases, showing the greatest affinity for mitochondrial DNA polymerase gamma. Short term exposure in vitro to some nucleoside analogues has been demonstrated to cause increased lactate production or falls in mitochondrial DNA suggestive of mitochondrial toxicity. However, stavudine and to a lesser extent zidovudine are poor substrates for mitochondrial thymidine kinase type 2, the predominant form in cells that are not actively mitotic such as neurons, myocytes and adipocytes. These are the cell types where the proposed mitochondrial toxicities neuropathy, myopathy and lipoatrophy are observed. Thus, active concentrations of phosphorylated products of stavudine and zidovudine may not be present in mitochondria. The familial mitochondrial diseases do not have identical presentations to nucleoside analogue toxicities. These disorders most commonly involve the CNS, typically with seizures or dementia, and occasionally the kidneys. Although nucleoside analogues are known to penetrate the CNS and are commonly renally excreted unchanged, mitochondrial toxicities at these sites have not been documented. Furthermore, toxicity caused by nucleoside or nucleotide analogues does not always appear to arise through the mitochondrial route. Cidofovir appears to cause renal tubular dysfunction via a toxic intracellular metabolite, and zidovudine-related anaemia appears to be related to decreased globin RNA synthesis. In vitro or animal models suggest that zidovudine myopathy, stavudine-related (but not zalcitabine- or didanosine-related) neuropathy and didanosine-related pancreatitis may all be not related, or not exclusively related, to mitochondrial dysfunction. The integration of nucleoside analogues into nuclear DNA, best documented with zidovudine but likely to occur with other agents, represents an alternative but potentially delayed pathway to cytotoxicity and cell apoptosis. This is the mechanism of cell death during therapy with antineoplastic nucleoside analogues, and may have contributed to the multisystem toxicities observed with the anti-hepatitis B drug fialuridine. New research evaluating the effects of long term exposure of cell lines is required to address the possibility that nuclear genotoxicity plays a role in long term nucleoside analogue toxicity.

Technical report: perinatal human immunodeficiency virus testing and prevention of transmission. Committee on Pediatric Aids

In 1994, the US Public Health Service published guidelines for the use of zidovudine to decrease the risk of perinatal transmission of human immunodeficiency virus (HIV). In 1995, the American Academy of Pediatrics and the US Public Health Service recommended documented, routine HIV education and testing with consent for all pregnant women in the United States. Widespread incorporation of these guidelines into clinical practice has resulted in a dramatic decrease in the rate of perinatal HIV transmission and has contributed to more than a 75% decrease in reported cases of pediatric acquired immunodeficiency syndrome (AIDS) since 1992. Substantial advances have been made in the treatment and monitoring of HIV infection; combination antiretroviral regimens that maximally suppress virus replication are now available. These regimens are recommended for pregnant and nonpregnant individuals who require treatment. Risk factors associated with perinatal HIV transmission are now better understood, and recent results from trials to decrease the rate of mother-to-child HIV transmission have contributed new strategies with established efficacy. However, perinatal HIV transmission still occurs; the Centers for Disease Control and Prevention estimates that 300 to 400 infected infants are born annually. Full implementation of recommendations for universal, routine prenatal HIV testing and evaluation of missed prevention opportunities will be critical to further decrease the incidence of pediatric HIV infection in the United States. This technical report summarizes recent advances in the prevention of perinatal transmission of HIV relevant to screening of pregnant women and their infants.

Symptomatic hyperlactataemia: an emerging complication of antiretroviral therapy

BACKGROUND

Fatal lactic acidosis is a serious complication of therapy with nucleoside analogues.

OBJECTIVE

To examine symptomatic hyperlactataemia in HIV-infected adults treated with antiretroviral drugs.

METHODS

In this prospective study, arterial blood lactate levels were measured in patients presenting with unexplained clinical symptoms. When these levels were high, functional respiratory tests (FRT) were carried out. Liver or muscle biopsies were further proposed. Incidences were calculated by comparison with the entire cohort of patients treated in the department.

RESULTS

Fourteen HIV-infected adults treated with antiretroviral drugs were identified with symptomatic hyperlactataemia during a 2-year period follow-up study. The incidence of hyperlactataemia was 0.8% per year but reached 1.2% if only patients treated with a regimen including stavudine were considered. Clinical symptoms included abnormal fatigue, tachycardia, abdominal pain, weight loss, peripheral neuropathy, and more specifically exercise-induced dyspnoea occurring despite effective antiretroviral treatment. FRT showed a metabolic deviation towards anaerobiosis with a high lactate/pyruvate ratio. Ultrastructural mitochondrial abnormalities were seen in all four patients for whom this was examined. There was a marked decrease in complex IV activity in muscle biopsies from four of five patients, consistent with a mitochondrial dysfunction. Evolution was favourable in 13 patients, probably because of an early diagnosis.

CONCLUSIONS

Potentially fatal adverse events occurring during antiretroviral treatment may be avoided by close monitoring of clinical signs and blood lactate levels. If other studies confirm that the cumulative long-term toxicity of antiretroviral drugs results from mitochondrial dysfunction, the incidence of hyperlactataemia and its clinical consequences may become more important.

The management of the clinical complications of antiretroviral therapy

In clinical practice, combination antiretroviral therapy is frequently complicated by adverse reactions and drug-related toxicities. The incidence, presentation, differential diagnosis, and management of the most frequent and severe of these complications are discussed. The recently described spectrum of metabolic complications, including hyperlipidemia, fat redistribution, and lactic acidosis, are covered in detail. The management of nephrotoxicity, pancreatitis, bone marrow suppression, peripheral neuropathy, and hypersensitivity reactions related to antiretroviral therapy is also discussed.

Significant Toxicities Associated with Antiretroviral Therapy

Use of at least three potent antiretroviral agents has become the standard of care in the management of HIV infection. The potential toxicities associated with highly active antiretroviral therapy (HAART) however, may limit a patient’s ability to adhere to and tolerate these agents. Although a comprehensive discussion of all toxicities associated with HAART is beyond the scope of this article, selected short-term and long-term significant toxicities will be reviewed. Short-term toxicities that will be discussed include abacavir-induced hypersensitivity reactions, efavirenz-associated central nervous system side effects and rash associated with the non-nucleoside reverse transcriptase inhibitors (NNRTIs) and the protease inhibitor (PI) amprenavir. Several long-term toxicities associated with the nucleoside reverse transcriptase inhibitors (NRTIs) are hypothesized to be due to mitochondrial toxicity. These toxicities include myositis and lactic acidosis with hepatic steatosis, pancreatitis and peripheral neuropathy. Some experts also hypothesize that mitochondrial toxicity is responsible for the lipodystrophy syndrome, which includes hyperglycemia, abnormal fat redistribution and dyslipidemia. Finally, indinavir-associated nephrolithiasis, which may present with either short term or long term use will be discussed. This article will provide the practicing pharmacist with a review of these significant toxicities, the implicated agents, incidence, usual clinical presentation, and recommendations for management.

Lipodystrophy syndrome in HIV infection: what is it, what causes it and how can it be managed?

Since the introduction of HIV-1 protease inhibitors as components of antiretroviral drug combination regimens, the clinical course of HIV disease and opportunistic infections has changed dramatically. Besides the favourable virological, immunological and clinical impact of highly active antiretroviral therapy (HAART), several adverse drug reactions have been observed in patients with HIV receiving therapy. Particularly, peripheral lipodystrophy, central adiposity, dyslipidaemia and insulin resistance have been described with a prevalence of up to 80% in patients infected with HIV, and attributed to almost all components of HAART. Hyperlipidaemia is characterised by an increase of low and very low density lipoprotein-cholesterol as well as apolipoproteins B and E. Several studies strongly suggest that there are either multiple syndromes or a variety of factors inducing different changes that influence the ultimate phenotype. Similarities between HIV-associated fat redistribution and metabolic abnormalities with both inherited lipodystrophies and benign symmetric lipomatosis suggest the pathophysiological involvement of, for example, nuclear factors like lamin A/C and drug-induced mitochondrial dysfunction. Moreover, there is some evidence that cytokines and hormones impair fat and glucose homeostasis in patients with HIV receiving HAART. Three years after the first description of HIV therapy-associated abnormal fat redistribution, there is still an ongoing discussion about the case definition, diagnostic procedure and treatment options for both body shape changes and metabolic disturbances. Regarding therapy, there is a major concern about possible complex pharmacological interactions and overlapping adverse effects between HAART and, for example, lipid-lowering therapy. In addition, the likely contribution of both nucleoside analogue reverse transcriptase inhibitors and protease inhibitors to the development of abnormal fat redistribution in patients with HIV limits options of changing to alternative effective antiretroviral drug combinations. Thus, the occurrence of hyperlipidaemia, maturity onset diabetes mellitus, and marked changes in body habitus resulted in important social and clinical consequences such as an increased risk of atherosclerosis. It also sheds new light on the use of protease inhibitors regarding risk factors for the initial treatment decision. In this article, we discuss the features, pathogenesis and treatment options for body fat redistribution and metabolic disturbances associated with HAART in HIV-1 infection.

Lack of evidence of mitochondrial dysfunction in the offspring of HIV-infected women. Retrospective review of perinatal exposure to antiretroviral drugs in the Perinatal AIDS Collaborative Transmission Study

A recent report suggesting mitochondrial dysfunction among eight HIV-exposed but uninfected children exposed perinatally to nucleoside reverse transcriptase inhibitors (NRTIs) prompted a review within the Perinatal AIDS Collaborative Transmission Study (PACTS). A standardized retrospective review was conducted of 118 deaths at < 5 years. Deaths were classified as unrelated to mitochondrial dysfunction (Class 1), unlikely related (Class 2), possibly related (Class 3), or likely related or proven (Class 4). Among 35 deaths recorded in HIV-uninfected or indeterminate children, none were classified in either Class 2, 3, or 4. We also reviewed signs or symptoms consistent with possible mitochondrial dysfunction among 1,954 living uninfected children. Only one child was in Class 3 and two siblings were in Class 2; none had perinatal antiretroviral drug exposure. We found no evidence indicating that uninfected infants exposed to perinatal NRTIs died of mitochondrial disorders or that living exposed children had symptoms of mitochondrial dysfunction.

Effects of prenatal AZT+3TC treatment on open field behavior and responsiveness to scopolamine in adult mice

Treatment of pregnant seropositive women and their neonates with the nucleoside analogs (reverse transcriptase inhibitors) zidovudine (AZT), lamivudine (3TC) and their combination has become a standard of care in industrialized countries to prevent transmission of the HIV-1 virus. Animal studies indicated limited but significant behavioral changes in AZT or 3TC-prenatally exposed offspring, whereas data on the potential neurobehavioral outcomes of AZT+3TC combination are still lacking. The aim of the present study was to assess in mice prenatally exposed to AZT+3TC the functional state of cholinergic muscarinic neuroregulation at adulthood. Pregnant CD-1 mice received per orem twice daily AZT+3TC (160 and 500 mg/kg, respectively) or vehicle solution (NaCl 0.9%) from gestational day (GD) 10 to delivery (GD 19). Locomotor activity, exploratory behavior and responsiveness to the muscarinic cholinergic blocker scopolamine (2 mg/kg) were analyzed at adulthood (PND 70) in offspring of both sexes in an open field test. Results indicated that prenatal AZT+3TC exposure does not influence responsiveness to the muscarinic cholinergic antagonist as measured by analysis of the drug's effects on locomotor and exploratory activity and different behavioral items. However, AZT+3TC-treated mice displayed higher frequency of rearing, and lower frequency and duration of self-grooming behavior, consistent with an effect on dopaminergic neurotransmission. However, this would need confirmatory experiments.

Adverse effects of antiretroviral therapy

Antiretroviral toxicity is an increasingly important issue in the management of HIV-infected patients. With the sustained major declines in opportunistic complications, HIV infection is a more chronic disease, and so more drugs are being used in more patients for longer periods. This review focuses on the pathogenesis, clinical features, and management of the principal toxicities of the 15 licensed antiretroviral drugs, including mitochondrial toxicity, hypersensitivity, and lipodystrophy, as well as more drug-specific adverse effects and special clinical settings.

Nevirapine: a review of its use in the prevention and treatment of paediatric HIV infection

Nevirapine is a highly specific inhibitor of HIV-1 reverse transcriptase (RT), an important therapeutic target for the treatment of HIV infection. It was the first non-nucleoside RT inhibitor (NNRTI) to be approved for use in HIV-infected individuals, including children. Nevirapine inhibits replication of multiple HIV-1 strains and clinical isolates in cultured human T cells, but has no activity against other retroviral RTs (including HIV-2 RT) or endogenous human DNA polymerases. Monotherapy with nevirapine rapidly selects for high level drug resistance conferred by a single amino acid substitution in the HIV RT gene. The pattern of resistance mutations selected by nevirapine overlaps with those of other NNRTIs, but is distinct from those of nucleoside analogue RT inhibitors and protease inhibitors. The pharmacokinetics of nevirapine are characterised by rapid and nearly complete oral absorption, an apparently even distribution throughout all organs and tissues in the body, and a long elimination half-life. Nevirapine is both metabolised by and induces the activity of cytochrome P450 isoenzymes. Caution is required when coadministering nevirapine with other drugs metabolised by this system, including HIV protease inhibitors. As a single dose therapy given to pregnant women in labour and to neonates shortly after birth, nevirapine reduced the rate of perinatal HIV transmission by 47% compared with a short course of intrapartum and neonatal zidovudine in a randomised trial in breastfeeding women in Uganda. Nevirapine was more cost effective than zidovudine-based regimens for the prevention of perinatal HIV transmission in a cost-effectiveness model in sub-Saharan Africa. Nevirapine has shown antiretroviral efficacy as part of combination therapy with zidovudine and either didanosine or lamivudine in small numbers of paediatric patients in phase I/II trials. Triple therapy of nevirapine, zidovudine and didanosine was moderately effective in a randomised, nonblind trial in patients with advanced disease. The most frequent adverse event associated with nevirapine is rash, which occasionally develops into severe rash or Stevens-Johnson syndrome. Elevations in liver enzyme levels can occasionally lead to severe complications in patients receiving multiple dose nevirapine.

CONCLUSION

Single dose nevirapine appears to be the most cost-effective of available options for the prevention of perinatal HIV transmission suitable for use in developing countries. In addition, preliminary clinical trial data suggest that nevirapine adds to the efficacy of combination therapy for the treatment of HIV infection in infants and children, and is reasonably well tolerated.

Cardiomyopathy in AIDS: a pathophysiological perspective

This report addresses issues of pathogenesis, pathophysiology, and epidemiology of an increasingly prevalent cardiomyopathy in acquired immunodeficiency syndrome (AIDS). As patient survival increases with more effective antiretroviral therapy, cardiomyopathy in AIDS will become more apparent. The interactions of cellular and organism factors in AIDS and their relationships to the development of cardiomyopathy are reviewed herein. Amongst the factors addressed in this review are: (1) comorbid conditions found with AIDS, (2) the role of inflammatory heart disease and cytokines in the development of AIDS cardiomyopathy, (3) the pathogenetic role of vascular cells and myocardial cells in the development of cardiomyopathy, (4) the role of myocardial retroviral infection in AIDS, and (5) the impact of toxicity from antiretroviral therapy on the development of cardiomyopathy. Because it is possible that more than 1 of these factors is present in a given patient inflicted with AIDS, a multifactorial pathogenesis in AIDS cardiomyopathy must be considered.

Clinical manifestations and management of antiretroviral nucleoside analog-related mitochondrial toxicity

OBJECTIVES

This article reviews the clinical manifestations of mitochondrial toxicity associated with the use of nucleoside analog reverse transcriptase inhibitors (NRTIs) and outlines strategies to manage these sequelae.

BACKGROUND

NRTIs are the key components of the antiretroviral combinations used in the management of patients infected with HIV. The available NRTIs differ in their convenience of administration, frequency of dosing, resistance profiles, and side-effect profiles. NRTIs act as competitive inhibitors of the RNA/DNA polymerase reverse transcriptase of HIV and cause chain termination in the growing viral DNA chain. Many of the important and treatment-limiting side effects of NRTIs may be related to the effect of these agents on human DNA polymerases, in particular, mitochondrial DNA polymerase gamma. Depletion of mitochondrial DNA during chronic NRTI therapy may lead to cellular respiratory dysfunction and generalized and tissue- and drug-specific toxicities, including myopathy, peripheral neuropathy, and lactic acidosis. Recently, it has been proposed that the fat redistribution syndrome, or lipodystrophy, reported during chronic antiretroviral therapy is a manifestation of the differential impact of at least some NRTIs on peripheral and visceral adipocytes. Management of potential mitochondrial toxicity during NRTI therapy remains a challenge. A range of nutritional supplements, both as treatments and prophylaxes, have been proposed, and some have been investigated in vitro; no in vivo studies have yet been conducted.

METHODS

The information in this review was compiled using MEDLINE and AIDSLINE searches of the literature, including conference abstracts.

CONCLUSIONS

At present, interruption of NRTI therapy or substitution of the probable causative agent with alternative NRTIs that appear to be better tolerated represents the mainstay of management for mitochondrial toxicity and its clinical manifestations.

HIV protease inhibitors block adipogenesis and increase lipolysis in vitro

AIDS therapies employing HIV protease inhibitors (PIs) are associated with changes in fat metabolism. However, the cellular mechanisms affected by PIs are not clear. Thus, the affects of PIs on adipocyte differentiation were examined in vitro using C3H10T1/2 stem cells. In these cells the PIs, nelfinavir, saquinavir, and ritonavir, reduced triglyceride accumulation, lipogenesis, and expression of the adipose markers, aP2 and LPL. Histological analysis revealed nelfinavir, saquinavir and ritonavir treatment decreased oil red O-staining of cytoplasmic fat droplets. Inhibition occurred in the presence of the RXR agonist LGD1069, indicating the inhibitory effects were not due to an absence of RXR ligand. Moreover, these three PIs increased acute lipolysis in adipocytes. In contrast, two HIV PIs, amprenavir and indinavir, had little effect on lipolysis, lipogenesis, or expression of aP2 and LPL. Although, saquinavir, inhibited ligand-binding to PPARgamma with an IC(50) of 12.7+/-3.2 microM, none of the other PIs bound to the nuclear receptors RXRalpha or PPARgamma, (IC(50)s>20 microM), suggesting that inhibition of adipogenesis is not due to antagonism of ligand binding to RXRalpha or PPARgamma. Taken together, the results suggest that some, but not all, PIs block adipogenesis and stimulate fat catabolism in vitro and this may contribute to the effects of PIs on metabolism in the clinic.

Contribution of nucleoside analogue reverse transcriptase inhibitors to subcutaneous fat wasting in patients with HIV infection

BACKGROUND

Progressive subcutaneous fat wasting, fat accumulation, dyslipidaemia and insulin resistance in HIV-infected patients on antiretroviral therapy has been attributed to the long-term toxicity of HIV protease inhibitors (PI). More recently, fat wasting has been observed in patients who have never taken a PI, implicating an independent effect of nucleoside analogue reverse transcriptase inhibitor (NRTI) therapy.

OBJECTIVES

To determine the relative contribution of NRTI and PI, as well as any other factors, to fat wasting in HIV-infected patients.

DESIGN

Longitudinal cohort study involving 277 participants of the Western Australian HIV Cohort Study.

METHODS

The time to onset of clinically apparent fat wasting in patients receiving different antiretroviral regimens was compared using standardized clinical criteria. Regional fat measured by dual energy X-ray absorptiometry (DEXA) in 161 patients was also compared. The average rate of percentage fat reduction was estimated in 70 patients who had consecutive DEXA scans at approximately 6-monthly intervals. Multiple confounding factors were considered in the analyses.

RESULTS

Progressive subcutaneous fat wasting, indistinguishable from that described in PI-treated patients, does occur in PI-naive, NRTI-treated patients. In patients taking triple combination antiretroviral therapy, age (relative risk = 1.052 per year; P < 0.0001), white race (relative risk = 3.9; P = 0.023), longer duration of dual NRTI therapy prior to addition of PI (relative risk = 1.021 per month; P = 0.0046) and increased cumulative time on stavudine-containing regimens compared with time on zidovudine-containing regimens (relative risk = 1.085 per month; P < 0.0001) are associated with increased risk of fat wasting. Stavudine increases the risk of fat wasting by 265% per year compared with zidovudine. However PI therapy is associated with faster progression to clinically apparent wasting compared with dual NRTI therapy without PI. The results of DEXA scanning supports these clinical data and suggest a non-linear decline in fat over time.

CONCLUSIONS

NRTIs do have an independent contribution to fat wasting, but PI are the predominant influence and may act synergistically with NRTIs. NRTIs appear to predispose individuals to slowly progressive fat loss, which is markedly accelerated when a PI and NRTIs are combined. Of the NRTIs, stavudine leads to an earlier onset of clinically apparent fat wasting compared with zidovudine. Fat wasting associated with NRTI use may be a manifestation of mitochondrial toxicity, which may be exacerbated by PI use.

Therapeutic interventions in HIV infection - a critical view

The introduction of highly effective combination regimens of antiretroviral drugs has led in recent years to substantial improvements in morbidity and mortality. As yet immune-based therapies have had little if any impact. However it is clear that eradication of HIV is not achievable with existing anti-HIV drugs and in spite of the major advances there remain many challenges in the clinical management of HIV-infected individuals. These benefits are unlikely to be extended to resource poor countries in the foreseeable future. The barriers are primarily but not only the costs. In resource-rich countries there are concerns about long term toxicities and many people have already exhausted all of the current therapeutic options. There is an urgent need for new drugs, ideally attacking new targets or with no cross resistance to existing drugs, and which are well tolerated and safe, easy to take and cheap. Many important questions still remain unanswered, in particular when to start antiretroviral therapy.

Lipodystrophy syndrome in HIV infection: what is it, what causes it and how can it be managed?

Since the introduction of HIV-1 protease inhibitors as components of antiretroviral drug combination regimens, the clinical course of HIV disease and opportunistic infections has changed dramatically. Besides the favourable virological, immunological and clinical impact of highly active antiretroviral therapy (HAART), several adverse drug reactions have been observed in patients with HIV receiving therapy. Particularly, peripheral lipodystrophy, central adiposity, dyslipidaemia and insulin resistance have been described with a prevalence of up to 80% in patients infected with HIV, and attributed to almost all components of HAART. Hyperlipidaemia is characterised by an increase of low and very low density lipoprotein-cholesterol as well as apolipoproteins B and E. Several studies strongly suggest that there are either multiple syndromes or a variety of factors inducing different changes that influence the ultimate phenotype. Similarities between HIV-associated fat redistribution and metabolic abnormalities with both inherited lipodystrophies and benign symmetric lipomatosis suggest the pathophysiological involvement of, for example, nuclear factors like lamin A/C and drug-induced mitochondrial dysfunction. Moreover, there is some evidence that cytokines and hormones impair fat and glucose homeostasis in patients with HIV receiving HAART. Three years after the first description of HIV therapy-associated abnormal fat redistribution, there is still an ongoing discussion about the case definition, diagnostic procedure and treatment options for both body shape changes and metabolic disturbances. Regarding therapy, there is a major concern about possible complex pharmacological interactions and overlapping adverse effects between HAART and, for example, lipid-lowering therapy. In addition, the likely contribution of both nucleoside analogue reverse transcriptase inhibitors and protease inhibitors to the development of abnormal fat redistribution in patients with HIV limits options of changing to alternative effective antiretroviral drug combinations. Thus, the occurrence of hyperlipidaemia, maturity onset diabetes mellitus, and marked changes in body habitus resulted in important social and clinical consequences such as an increased risk of atherosclerosis. It also sheds new light on the use of protease inhibitors regarding risk factors for the initial treatment decision. In this article, we discuss the features, pathogenesis and treatment options for body fat redistribution and metabolic disturbances associated with HAART in HIV-1 infection.

Hyperlactatemia and hepatic abnormalities in 10 human immunodeficiency virus-infected patients receiving nucleoside analogue combination regimens

During a 6-and-a-half month period, we identified 10 human immunodeficiency virus (HIV)-infected men who were receiving antiretroviral regimens, including nucleoside analogues, and who developed unexplained reproducible hyperlactatemia in association with either abdominal symptoms or an unaccounted-for elevated alanine aminotransferase level, or both. After careful consideration of the possible etiologies, antiretrovirals were discontinued; lactate levels normalized in all patients. The estimated incidence of this phenomenon in our clinic was 20.9 cases per 1000 person-years of nucleoside analogue treatment. These observations extend the spectrum of the nucleoside analogue-induced lactic acidosis/hepatic steatosis syndrome by the identification of a subtle and perhaps earlier form, which has characteristic symptoms and laboratory abnormalities, and a favorable prognosis on discontinuation of antiretroviral therapy.

Advances and research directions in the prevention of mother-to-child HIV-1 transmission

Although substantial progress has been made in preventing mother-to-child HIV-1 transmission in the past decade, critical research questions remain. Two perinatal epidemics now exist. In more-developed countries, integration of prenatal HIV-1 counselling and testing programmes into an existing antenatal infrastructure, availability of effective antiretroviral prophylaxis, and access to infant formula have resulted in new perinatal infections becoming rare. However, identification of missed prevention opportunities, the causes of prophylaxis failure, and the potential effects of in-utero antiretroviral exposure have become a priority. In less-developed countries, antenatal care is limited, testing programmes are almost non-existent, effective interventions remain unimplemented, and prevention of postnatal transmission through breastmilk while maintaining adequate infant nutrition is a major dilemma. The challenge for the next decade is to simultaneously address questions relevant to both epidemics while bridging the gap in prevention of perinatal transmission between more-developed and less-developed countries.

Pharmacology of nucleoside and nucleotide reverse transcriptase inhibitor-induced mitochondrial toxicity

OBJECTIVE

This paper reviews the function of the mitochondria and the mechanisms by which nucleoside and nucleotide reverse transcriptase inhibitors (NRTIs) cause mitochondrial toxicity.

BACKGROUND

Highly active antiretroviral therapy (HAART) reduces rates of morbidity and mortality due to HIV disease. However, long-term treatment with these drugs may be associated with adverse effects. Nucleoside and nucleotide analogues are potent inhibitors of HIV reverse transcriptase and have become the cornerstone of HAART. Unfortunately, these drugs have also been shown to inhibit cellular polymerases, most notably mitochondrial DNA polymerase gamma.

RESULTS

Studies of the NRTIs in enzyme assays and cell cultures demonstrate the following hierarchy of mitochondrial DNA polymerase gamma inhibition: zalcitabine > didanosine > stavudine > lamivudine > zidovudine > abacavir. In vitro investigations have also documented impairment of the mitochondrial enzymes adenylate kinase and the adenosine diphosphate/adenosine triphosphate translocator. Inhibition of DNA polymerase gamma and other mitochondrial enzymes can gradually lead to mitochondrial dysfunction and cellular toxicity. The clinical manifestations of NRTI-induced mitochondrial toxicity resemble those of inherited mitochondrial diseases (ie, hepatic steatosis, lactic acidosis, myopathy, nephrotoxicity, peripheral neuropathy, and pancreatitis). Fat redistribution syndrome, or HIV-associated lipodystrophy, is another side effect attributed in part to NRTI therapy. The morphologic and metabolic complications of this syndrome are similar to those of the mitochondrial disorder known as multiple symmetric lipomatosis: suggesting that this too may be related to mitochondrial toxicity. The pathophysiology of less common adverse effects of nucleoside analogue therapy, such as diabetes, ototoxicity, and retinal lesions, may be related to mitochondrial dysfunction but have not been adequately studied.

CONCLUSION

NRTls can block both HIV reverse transcriptase and mitochondrial DNA polymerase gamma. Inhibition of the latter enzyme is the most likely cause of the adverse effects associated with these drugs.

Management of the adverse effects of antiretroviral therapy and medication adherence

A commonly cited cause of poor adherence to highly active antiretroviral therapy (HAART) is adverse drug reactions. Short-term adverse effects are potential threats to successful introduction and maintenance of HAART. The long-term toxicities of HAART are still emerging and being defined, as evidenced by the recently described metabolic disorders (i.e., the syndrome of maldistribution, hyperlipemia, glucose intolerance and insulin resistance). With 14 licensed agents in 2000, other agents in common use, and numerous combinations of >/=3 drugs, awareness and recognition of adverse effects are increasingly important for clinicians and patients. The common adverse drug reactions encountered with HAART, including new agents and their impact on patient adherence, are reviewed. Current strategies to anticipate and mitigate adverse effects are summarized.

Preventing mother-to-child transmission of HIV-1 in Africa in the year 2000

OBJECTIVES

Various approaches to preventing mother-to-child transmission (MTCT) of HIV have recently been, or are being, evaluated in developing countries, especially in Africa. New findings from these trials are now becoming available, the implications of which, for population-based intervention programmes, need urgent consideration.

METHOD

A critical review of 18 randomized trials and other relevant studies from developing and industrialized countries.

RESULTS

Most African results relate to trials of antiretroviral agents (ARV). They demonstrate efficacy in reducing transmission in the first 6 months of life with short regimens of zidovudine (ZDV), with or without lamivudine (3TC), and nevirapine (NVP) alone. Preliminary results suggest the long-term efficacy of zidovudine. Antiseptic and nutritional interventions have been shown to reduce maternal and infant mortality and morbidity but not MTCT of HIV. HIV confidential voluntary counselling and testing for pregnant women, a short regimen of peripartum ARV with alternatives to breastfeeding such as early weaning or breast milk substitutes from birth currently represent the best option to reduce MTCTof HIV in Africa. However, the prevention of postnatal transmission requires further research, particularly in view of the consequences of different feeding options and the possibility of post-perinatal exposure prophylaxis of newborns with ARV. Issues relating to the implementation of currently validated strategies are discussed.

An Introduction to Nucleoside and Nucleotide Analogues

The introduction of newer and more potent agents has diverted attention away from the importance of nucleoside analogue reverse transcriptase inhibitors (NRTIs) in modern antiretroviral drug regimens. As a class, these proviral chain terminators lack the virological potency of either non-nucleoside reverse transcriptase inhibitor (NNRTI) or protease inhibitor (PI) drugs, due largely to their competitive mode of inhibition and requirement for metabolic activation. However, neither NNRTIs nor PIs alone can maintain the complete suppression of HIV replication required for extended therapy, and both suffer from serious class cross-resistance on therapeutic failure. Thus, the NRTIs will remain essential components of highly active antiretroviral therapy (HAART) for the foreseeable future, both for their contribution to a regimen's virological potency and the subsequent preservation of the more potent drug classes used with them. However, it has become apparent in recent years that the current NRTIs exhibit duration-dependent adverse events as a class, which may limit the length of time for which they can be safely used. An independent contribution to peripheral fat wasting in lipodystrophy syndrome has been established for the use of NRTI drugs. Of greater clinical concern is their established association with potentially fatal lactic acidaemia and hepatic steatosis. Both these class events, as well as several individual drug events, such as peripheral neuropathy, can be linked to progressive mitochondrial destruction with a greater or lesser degree of confidence. Mitochondrial toxicity, due in large part to the high affinity of several NRTI agents for uptake by mitochondrial DNA polymerase γ, has been demonstrated both in vitro and in vivo. New chain-terminating agents are urgently needed that address issues of improved virological potency, greater efficacy in NRTI-experienced individuals, and greater long-term safety. The nucleotide class of reverse transcriptase inhibitor (NtRTI), currently under clinical development, addresses improved potency by abbreviating the intracellular activation pathway to allow a more rapid and complete conversion to the active agent. These nucleoside monophosphate analogues are taken as masked prodrugs bearing labile lipophilic groups to facilitate penetration of target cell membranes. Subsequent unmasking by endogenous chemolytic enzymes releases a partially activated nucleoside analogue metabolite. The NtRTI furthest along the developmental process is tenofovir disoproxil fumarate (TDF), an orally available acyclic adenine phosphonate analogue, currently in Phase III clinical trials. This agent has shown high potency and an unusually durable response in trials of single-agent therapy intensification in highly treatment-experienced individuals, and its active metabolite, tenofovir diphosphate, exhibits a long intracellular half-life in both resting and activated peripheral blood mononuclear cells that permits once daily dosing. Tenofovir diphosphate also exhibits a very low affinity for DNA polymerase γ in vitro, suggesting a low degree of in vivo mitochondrial toxicity may be observed on long-term follow-up, although clinical data to support this inference are not yet available. The introduction of TDF and other NtRTIs as ‘second-generation’ nucleoside analogues carefully evaluated for potential long-term toxicity, can be expected to significantly improve the therapeutic options for both those currently on HAART and those yet to begin.

The implications of HIV for the anaesthetist and the intensivist

The acquired immune deficiency syndrome has reached pandemic proportions. Anaesthetists should be aware of the implications of dealing with increasing numbers of both diagnosed and undiagnosed, symptomatic and asymptomatic, human immunodeficiency virus-infected patients in the fields of intensive therapy, operating theatre anaesthesia, obstetrics and pain management. With recent advances, important insights have been gained into the pathogenesis of human immunodeficiency virus. Molecular techniques allow quantification of viral burden, and together with CD4 T-lymphocyte count, prognosis and response to therapy can be evaluated. New drugs and therapeutic regimens have improved prognosis for those who are infected with the virus and vertical transmission of infection from mother to infant can be minimised. Should accidental occupational exposure to the virus occur, a prophylactic regimen of antiretroviral drugs can be administered in an attempt to prevent subsequent human immunodeficiency virus infection.

Accelerated bone mineral loss in HIV-infected patients receiving potent antiretroviral therapy

BACKGROUND

The use of highly active antiretroviral therapy (HAART) has been associated with multiple metabolic complications whose pathogenesis is poorly understood at the present time.

METHODS

We performed a cross-sectional analysis of whole-body, lumbar spine (L1-L4) and proximal femur bone mineral density in 112 male subjects (HIV-infected patients on HAART that included a protease inhibitor, HIV-infected patients not receiving a protease inhibitor and healthy seronegative adults) using dual energy x-ray absorptiometry.

RESULTS

Men receiving protease inhibitors had a higher incidence of osteopenia and osteoporosis according to World Health Organization definitions: relative risk = 2.19 (95% confidence interval 1.13-4.23) (P = 0.02). Subjects receiving protease inhibitors had greater central: appendicular adipose tissue ratios than the other two groups (P < 0.0001). There was no relationship between the central: appendicular fat ratio and the lumbar spine or proximal femur bone mineral density t- or z- scores, suggesting that osteoporosis and body fat redistribution are independent side effects of HAART.

CONCLUSIONS

Osteopenia and osteoporosis are unique metabolic complications associated with protease inhibitor-containing potent antiretroviral regimens, that appear to be independent of adipose tissue maldistribution.

A syndrome of lipoatrophy, lactic acidaemia and liver dysfunction associated with HIV nucleoside analogue therapy: contribution to protease inhibitor-related lipodystrophy syndrome

BACKGROUND

Lipodystrophy (LD; peripheral lipoatrophy, central adiposity) hyperlipidaemia and insulin resistance often complicate protease inhibitor-containing antiretroviral therapy. Lipoatrophy and abdominal distension were observed in protease inhibitor-naive nucleoside analogue reverse transcriptase inhibitor (NRTI) recipients with lactic acidaemia and hepatic impairment, which are known NRTI-induced mitochondrial toxicities.

DESIGN AND SETTING

Case-control study in a university-based outpatient clinic.

PATIENTS AND METHODS

The patients studied included 14 NRTI recipients with lipoatrophy, 32 antiretroviral-naive patients without LD, 28 NRTI recipients without LD, 44 combined NRTI-protease inhibitor recipients without LD, and 102 NRTI-protease inhibitor recipients with LD. Data was obtained on body composition (questionnaire, physical examination, dual-energy x-ray absorptiometry and abdominal computerized tomography), with biochemical, lipid and glycaemic parameters.

RESULTS

The NRTI-LD syndrome was characterized by recent onset fatigue and nausea, peripheral lipoatrophy (6 kg loss over 4 months), abdominal distension (ascites +/- hepatomegaly) and elevated lactate (4.6, 1.1, 1.2, 1.4 and 1.7 mmol/l, respectively; P< 0.0001) and liver enzymes. Cases without hepatic involvement also had lower body fat and greater lactate than unaffected controls. Metabolic disturbances and weight improved after cessation. The NRTI-LD syndrome differed from protease inhibitor-related LD syndrome by the presence of recent onset symptoms and weight loss, higher lactate and alanine aminotransferase, and lower albumin, cholesterol, triglycerides, glucose and insulin. In treated controls, current stavudine therapy, protease inhibitor duration, and lactic acidaemia were independently associated with both lipoatrophy and abdominal obesity; total NRTI duration was also associated with lipoatrophy, and lamivudine and protease inhibitor duration with buffalo hump.

CONCLUSIONS

A syndrome of lipoatrophy, constitutional illness, lactic acidaemia and hepatic dysfunction can complicate NRTI therapy. Both protease inhibitor and NRTI therapies, particularly if associated with lactic acidaemia, contribute to LD syndrome, but have some distinguishable clinical and metabolic effects.

The case for more cautious, patient-focused antiretroviral therapy

Many clinicians who care for patients with HIV infection are dissatisfied with the existing recommendations on antiretroviral therapy. Current practice focuses on the early suppression of viremia, yet the outcome of that approach may not be in the best interest of individual patients or populations. The major goal of HIV therapy is to maintain the long-term health of the patient while avoiding drug-related toxicity and preserving viable future treatment options. Recent studies have challenged the principles on which recommendations for early, aggressive treatment were based. Key studies that lead to licensure of antiretroviral medications usually involve short-term results in treatment-naive patients; it is difficult to apply these results to long-term management of therapy-experienced patients. Early, aggressive therapy often prematurely exposes patients to risks for medication-related side effects and resistance. A more cautious, patient-focused, long-term approach to therapy would help foster studies of alternate strategies, such as delayed initiation of therapy, protease-sparing therapy, class-sparing therapy, planned drug interruptions, switches in therapy, and immune-based therapy. It is time for clinicians to rethink their approach to the treatment of HIV infection.

Mitochondrial toxicity of nucleoside analogue reverse transcriptase inhibitors: a looming obstacle for long-term antiretroviral therapy?

Nucleoside reverse transcriptase inhibitors suppress HIV replication by blocking reverse transcriptase, an RNA-dependent DNA polymerase. These drugs can also affect cellular and mitochondrial DNA polymerases. Mitochondrial DNA polymerase gamma is particularly sensitive to nucleoside reverse transcriptase inhibitors, and the majority of adverse effects caused by nucleoside reverse transcriptase inhibitors are most likely caused by mitochondrial dysfunction. This article reviews the recent clinical implications of nucleoside reverse transcriptase inhibitor-induced mitochondrial toxicity and discusses options for management.

Beneficial effects of protease inhibitors on body composition and energy expenditure: a comparison between HIV-infected and AIDS patients

OBJECTIVES

(i) To investigate whether protease inhibitor (PI) (nelfinavir)-containing highly active antiretroviral therapy (HAART) affects body composition differently in HIV-infected and AIDS patients without wasting syndrome. (ii) To delineate the changes in resting energy expenditure (REE) under PI therapy, and to determine whether sustained reductions in HIV RNA would decrease REE.

DESIGN

Prospective longitudinal cohort study with individually matched healthy controls.

SETTING

Tertiary care centre at a University Hospital.

METHODS

HIV-seropositive (n = 20) and AIDS patients (n = 17) with a plasma viral load of at least 10000 copies/ml and 37 healthy volunteers were enrolled. All participants were weight stable, free of acute opportunistic infections, and naive to PI therapy. Patients underwent testing of bioelectrical impedance analysis (BIA), indirect calorimetry and food intake, shortly before the initiation of HAART and 24 weeks thereafter.

RESULTS

Both patient groups gained weight, body mass index (BMI), and fat-free mass (FFM) (P < 0.05 versus baseline), whereas only AIDS patients gained fat mass. Increases were more pronounced in the AIDS group. REE was elevated compared with corresponding controls at baseline, and decreased similarly in HIV and in AIDS patients during PI therapy (P < 0.05). The reduction in the viral burden preceded the decrease in REE by several weeks.

CONCLUSION

Body composition and metabolic parameters improved during PI therapy in HIV-infected and AIDS patients without wasting. Although an early reduction in viral load as a result of HAART does not seem to influence REE directly, sustained viral load suppression may promote a decrease in energy expenditure.

Immuno-activation with anti-CD3 and recombinant human IL-2 in HIV-1-infected patients on potent antiretroviral therapy

BACKGROUND

A stable reservoir of latently infected, resting CD4 T cells has been demonstrated in HIV-1-infected patients despite prolonged antiretroviral treatment. This is a major barrier for the eradication of HIV by antiretroviral agents alone. Activation of these cells in the presence of antiretroviral therapy might be a strategy to increase the turnover rate of this reservoir.

METHODS

Three HIV-1-positive patients on potent antiretroviral therapy, in whom plasma viremia had been suppressed to below 5 copies/ml for at least 26 weeks, were treated with a combination of OKT3 (days 1-5) and recombinant human IL-2 (days 2 6).

RESULTS

The side-effects were fever, headache, nausea, diarrhea, and in one of the patients transient renal failure and seizures. The regimen resulted in profound T cell activation. In one patient plasma HIV-1 RNA transiently increased with a peak at 1500 copies/ml. In the other two patients plasma HIV-1 RNA levels remained below the detection limit, but HIV-1 RNA levels in the lymph nodes increased two- to threefold. All patients developed antibodies against OKT3.

CONCLUSION

OKT3/IL-2 resulted in T cell activation and proliferation, and could stimulate HIV replication in patients having achieved prolonged suppression of plasma viremia. OKT3/IL-2 therapy was toxic and rapidly induced antibodies against OKT3.

AIDS dementia complex

Human immunodeficiency virus (HIV) infection is often complicated by the development of AIDS dementia complex (ADC). This article examines the typical and atypical presentations of ADC, along with aspects of the prevalence and natural history of the disorder. Salient aspects of the neuropathology, neurovirology, neuroimmunology, and pathogenesis are also considered. The intricacies of management of ADC, especially in the era of highly active antiretroviral therapy, are fully evaluated. Finally, this information is synthesized into an approach to the diagnosis of ADC in a particular patient.

Mitochondrial toxicity induced by nucleoside-analogue reverse-transcriptase inhibitors is a key factor in the pathogenesis of antiretroviral-therapy-related lipodystrophy

Highly active antiretroviral therapy (HAART) can induce a characteristic lipodystrophy syndrome of peripheral fat wasting and central adiposity. HIV-1 protease inhibitors are generally believed to be the causal agents, although the syndrome has also been observed with protease-inhibitor-sparing regimens. Here, we postulate that the mitochondrial toxicity of the nucleoside-analogue reverse-transcriptase inhibitors plays an essential part in the development of this lipodystrophy, similar to the role of mitochondrial defects in the development of multiple symmetrical lipomatosis.

Persistent mitochondrial dysfunction and perinatal exposure to antiretroviral nucleoside analogues

BACKGROUND

Zidovudine is commonly administered during pregnancy to prevent mother-to-child HIV-1 transmission. We investigated mitochondrial toxic effects in children exposed to zidovudine in utero and after birth.

METHODS

We analysed observations of a trial of tolerance of combined zidovudine and lamivudine and preliminary results of a continuing retrospective analysis of clinical and biological symptoms of mitochondrial dysfunction in children born to HIV-1-infected women in France. Mitochondrial dysfunction was studied by spectrophotometry and polarography of respiratory-chain complexes in various tissues.

FINDINGS

Eight children had mitochondrial dysfunction. Five, of whom two died, presented with delayed neurological symptoms and three were symptom-free but had severe biological or neurological abnormalities. Four of these children had been exposed to combined zidovudine and lamivudine, and four to zidovudine alone. No child was infected with HIV-1. All children had abnormally low absolute or relative activities of respiratory-chain complexes I, IV, or both months or years after the end of antiretroviral treatment. No mutation currently associated with constitutional disease was detected in any patient.

INTERPRETATION

Our findings support the hypothesis of a link between mitochondrial dysfunction and the perinatal administration of prophylactic nucleoside analogues. Current recommendations for zidovudine monotherapy should however be maintained. Further assessment of the toxic effects of these drugs is required.

Indinavir-based treatment of HIV-1 infected patients: efficacy in the central nervous system

OBJECTIVE

To study the pharmacokinetic properties and clinical efficacy of the HIV-1 protease inhibitor (PI) indinavir in the central nervous system (CNS).

DESIGN

Twenty-five consecutive HIV-1 infected patients on combination therapy that included indinavir, had cerebrospinal fluid (CSF) and plasma samples taken on 32 different occasions, at different times after indinavir administration. CSF and viral load data obtained from these treated patients were compared with those from 36 untreated HIV-1 infected patients of similar immunological and demographic pre-treatment status.

METHODS

Concentrations of indinavir were measured in CSF and plasma by high-pressure liquid chromatography with ultraviolet light detection and the data were used in pharmacokinetic modelling.

RESULTS

The concentration of indinavir in plasma varied with time over a dose interval by about two orders of magnitude, whereas the concentration in CSF was relatively stable. The median concentration of indinavir in CSF was 210 nmol/l, which is above the 95% inhibitory concentration in vitro. Findings from the pharmacokinetic modelling indicate that indinavir is actively transported out of the CSF (P <0.001 compared with a passive transport-only model). In the PI-treated group there was a reduction in viral load to below 50 copies/ml in most subjects and a normalization of the CSF cell content and IgG-index.

CONCLUSIONS

This study has shown that one PI, indinavir, is present in the CSF at therapeutic concentrations, and is likely to contribute to the antiretroviral activities observed within the CNS.

Time course of cerebrospinal fluid responses to antiretroviral therapy: evidence for variable compartmentalization of infection

OBJECTIVES

To compare the kinetics and magnitude of HIV-1 RNA responses to antiretroviral therapy (ART) in the cerebrospinal fluid (CSF) and plasma.

DESIGN

Repeated lumbar punctures (LPs) were performed after the initiation or change in ART in 15 HIV-1-infected subjects, with the focus on two phases of response: an acute phase within the first 11 days, for which crude estimates of viral RNA half-lives and decay rates were derived and CSF:plasma relative decay ratios quantitatively analysed; and a longer-term phase beyond 4 weeks that was descriptively assessed.

RESULTS

In 13 subjects studied during the acute phase, the crude HIV-1 RNA half-life was longer (median 2.0 compared with 1.9 days), the decay rate slower (median 0.13 compared with 0.16 log10 copies/day) and, most notably, the variability greater (intraquartile range of half-life 1.8-4.3 compared with 1.7-2.1 days) in the CSF than in the plasma. A slower decay in the CSF correlated with lower initial blood CD4 T lymphocyte counts (P = 0.001). Seven of 11 subjects studied at 4 weeks or later, including some with slower acute-phase CSF responses, showed greater or more durable viral suppression in the CSF.

CONCLUSION

Divergent acute-phase viral kinetics in the CSF and plasma, and proportionally greater long-term decrements in CSF HIV-1 RNA in slow early-responders or poor overall plasma responders indicate variable compartmentalization of CSF infection, consistent with a model of two prototypes of CSF infection: short-lived, transitory infection that predominates in early HIV-1 infection and longer-lived, more autonomous CSF infection predominating in late HIV-1 infection. Additional studies will be needed to define more precisely the acute and longer-term CSF kinetics in different clinical settings and to assess this model.