Hyperlactatemia syndromes in people with HIV infection

Exploring the relationship between hyperlactatemia and anemia

Hyperlactatemia and anemia commonly coexist and their crosstalk is a longstanding mystery with elusive mechanisms involved in physical activities, infections, cancers, and genetic disorders. For instance, hyperlactatemia leads to iron restriction by upregulating hepatic hepcidin expression. Increasing evidence also points to lactate as a crucial signaling molecule rather than merely a metabolic byproduct. Here, we discuss the mutual influence between anemia and hyperlactatemia. This opinion calls for a reconsideration of the multifaceted roles of lactate and lactylation in anemia and emphasizes the need to fill knowledge gaps, including the dose dependence of lactate's effects, its sources, and its subcellular localization.

The utility of bandemia in prognostication and prediction of mortality in sepsis

Background: Bandemia, defined as a band count >10%, is indicative of underlying infection and is increasingly being used for early detection of sepsis. While an absolute band level has been linked to worse outcomes, its trend has not been extensively studied as a prognostic marker. In this study, we assessed patients admitted to the ICU with sepsis or septic shock and evaluated the correlation between bandemia trends and clinical trajectory among these patients. Methods: This study was a retrospective chart review. Band counts, serum lactate levels, and SOFA scores at 0 and 72 h after admission to the ICU were collected. Patients were risk stratified into groups depending on their SOFA trends, and corresponding band trends and serum lactate levels were compared. Results: 134 patients were included for analysis. There was a statistically significant decrease in bandemia trends for patients with a reduction in SOFA scores [median (IQR)-4.5 (-11, 0); p < 0.0001], and a statistically significant increase in bandemia trends for patients with worsening SOFA scores [median (IQR) 4 (0, 8); p = 0.0007]. Conclusion: Early trends of serum band levels in patients with sepsis or septic shock may help to predict a clinical trajectory and overall prognosis. More investigation is warranted as to whether incorporating bandemia trends, when used in conjunction with other known markers such as lactate levels, may help to guide bedside clinical decisions such as risk stratification, tailored therapies, and ultimately improve outcomes.

DNA polymerase-γ hypothesis in nucleoside reverse transcriptase-induced mitochondrial toxicity revisited: A potentially protective role for citrus fruit-derived naringenin?

Nucleoside reverse transcriptase inhibitors (NRTIs) form the backbone in combination antiretroviral therapy (cARVs). They halt chain elongation of the viral cDNA by acting as false substrates in counterfeit incorporation mechanism to viral RNA-dependent DNA polymerase. In the process genomic DNA polymerase as well as mitochondrial DNA (mtDNA) polymerase-γ (which has a much higher affinity for these drugs at therapeutic doses) are also impaired. This leads to mitochondrial toxicity that manifests clinically as mitochondrial myopathy, peripheral neuropathy, hyperlactatemia or lactic acidosis and lipoatrophy. This has led to the revision of clinical guidelines by World Health Organization to remove stavudine from first-line listing in the treatment of HIV infections. Recent reports have implicated oxidative stress besides mtDNA polymerase-γ hypothesis in NRTI-induced metabolic complications. Reduced plasma antioxidant concentrations have been reported in HIV positive patients on cARVs but clinical intervention with antioxidant supplements have not been successful either due to low efficacy or poor experimental designs. Citrus fruit-derived naringenin has previously been demonstrated to possess antioxidant and free radical scavenging properties which could prevent mitochondrial toxicity associated with these drugs. This review revisits the controversy surrounding mtDNA polymerase-γ hypothesis and evaluates the potential benefits of naringenin as a potent anti-oxidant and free radical scavenger which as a nutritional supplement or therapeutic adjunct could mitigate the development of mitochondrial toxicity associated with these drugs.

Ombitasvir-Paritaprevir-Ritonavir-Dasabuvir (Viekira Pak)-Induced Lactic Acidosis

OBJECTIVE

To report a case series of three patients with hepatitis C virus infection who all presented with severe type B lactic acidosis shortly after starting treatment with ombitasvir-paritaprevir-ritonavir-dasabuvir.

DESIGN

Case series.

SETTING

ICU.

PATIENTS

Three patients, all who had HCV cirrhosis with mild hepatic impairment (Child-Pugh A) and had started taking ombitasvir-paritaprevir-ritonavir-dasabuvir within the preceding 2 weeks, presented with similar nonspecific symptoms of lethargy, fatigue, and nausea. All had elevated lactate levels at admission without evidence of hypovolemia, cardiogenic failure, or vasodilatory shock.

INTERVENTIONS

All patients were given appropriate supportive intensive care for what was initially suspected to be sepsis, including a minimum of 30 mL/kg of IV fluids, infectious workup including blood cultures, broad-spectrum antibiotics, and mechanical ventilatory support. The first patient received continuous veno-venous hemofiltration. The second patient received hemodialysis. The third patient was initially started on hemodialysis despite high norepinephrine requirements and ultimately transitioned to continuous veno-venous hemofiltration.

MEASUREMENTS AND MAIN RESULTS

The first patient died despite maximal intensive care. The second patient improved immediately upon starting hemodialysis and was extubated within 48 hours and discharged home. The third patient eventually became hypotensive and was treated with repeated sessions of renal replacement therapy. He ultimately was extubated and discharged home. The infectious workup was negative for all three patients, and antibiotics were discontinued after 2 days in the second and third patients.

CONCLUSIONS

Ombitasvir-paritaprevir-ritonavir-dasabuvir may cause type B lactic acidosis. Further study is warranted to identify risk factors and elucidate the mechanisms of excessive lactate production.

Mild to Moderate Symptoms Do Not Correlate with Lactate Levels in HIV-Positive Patients on Nucleoside Reverse Transcriptase Inhibitors

PURPOSE

Nucleoside reverse transcriptase inhibitors (NRTIs) are associated with mitochondrial toxicities ranging from asymptomatic hyperlactatemia to fatal lactic acidosis. It is uncertain whether mild clinical symptoms predict hyperlactatemia and the need to consider changes in antiretroviral therapy. This cross-sectional study evaluated whether an association exists between mild symptoms and lactate levels.

METHOD

HIV-positive patients on NRTIs attending routine clinic visits were surveyed about symptoms associated with hyperlactatemia. Symptom severity was quantified using Likert scales, and the sum was converted into a symptom score ranging from 0 to 30. Tourniquet-free blood specimens were collected simultaneously to measure serum lactate. Symptom scores were compared between patients with normal and elevated lactates.

RESULTS

284 individuals were included. The most common NRTIs used included lamivudine (79%), zidovudine (50%), abacavir (39%), and stavudine (24%). Twenty-two patients (8%) had increased lactates (mean = 2.7 mmol/L; range, 2.1-4.5 mmol/L), while 262 patients (92%) had normal lactates (mean = 1.2 mmol/L, range, 0.1-2.0 mmol/L). Median symptom scores were similar between groups (3 vs. 2, p = .23). Spearman's correlation coefficient for lactate and symptom score was 0.07 (p = .22).

CONCLUSIONS

Mild symptoms did not correlate with lactate levels, and symptoms alone should not trigger clinicians to measure serum lactates and stop NRTIs if the levels are elevated.

Blood lactate in HIV-infected children on antiretroviral therapy in rural South Africa

We studied blood lactate levels in 253 South African children on antiretroviral therapy. The prevalence of hyperlactatemia was 68% and severity was mild in most cases (69%). There was no association of symptoms and/or signs with hyperlactatemia. Independent predictors were lipo-dystrophy, time on antiretroviral therapy and baseline CD4 count. Increased awareness of hyperlactatemia in African children on antiretroviral therapy is warranted.

Fatal toxicity from symptomatic hyperlactataemia: a retrospective cohort study of factors implicated with long-term nucleoside reverse transcriptase inhibitor use in a South African hospital

BACKGROUND

In many Sub-Saharan African countries, first-line therapy for HIV may include a nucleoside reverse transcriptase inhibitor (NRTI). Long-term NRTI use is associated with symptomatic hyperlactataemia due to inhibition of mitochondrial DNA polymerase γ, a potentially fatal complication.

OBJECTIVE

The purpose of the study was to evaluate the factors associated with inhospital fatality for HIV inpatients prescribed NRTIs long term who presented with symptomatic hyperlactataemia.

METHODS

We performed a retrospective cohort study at a 900-bed university hospital in South Africa over 4 years (2005-2008). We included HIV inpatients prescribed NRTIs long term who presented with symptomatic hyperlactataemia (long-term NRTI use; lactate >4.0 mmol/L; absence of infectious source; symptoms requiring admission). Data included demographics, medical history, NRTI duration, blood pressure, symptom duration and relevant laboratory data.

RESULTS

Of 79 patients who met inclusion criteria (mean age 38.2 ± 10.5 years, 97% female) there were 46 fatalities (58%). Factors significantly associated with fatality were presence of diabetes mellitus (p = 0.04), lactate ≥10 mmol/L (p = 0.003), pH <7.2 (p = 0.002), creatinine ≥200 μmol/L (p = 0.03) and altered mental status (p = 0.03).

CONCLUSIONS

In this study, NRTI-related symptomatic hyperlactataemia occurred predominantly in females. Mortality was associated with severely elevated lactate (≥10 mmol/L), the degree of acidosis, elevated creatinine, history of diabetes and altered mental status on presentation.

Risk factors for fatality in HIV-infected patients with dideoxynucleoside-induced severe hyperlactataemia or lactic acidosis

BACKGROUND

Lactic acidosis (LA) and severe hyperlactataemia (HL) are infrequent but serious complications of antiretroviral therapy that have been associated with a high fatality rate.

METHODS

In a multinational retrospective cohort study, LA was defined as arterial blood pH<7.35, bicarbonate <20 mmol/l and lactate above normal, and HL as confirmed blood lactate >5 mmol/l. Logistic regression was used to identify factors associated with fatality. Sensitivity and specificity of different case definitions as predictors of death were compared.

RESULTS

The overall case-fatality rate was 19/110 (17.3%), but among acidotic patients it was 33% (16/49 cases). There were 10 asymptomatic patients and none of them died as a consequence of the event. The median lactate for fatal, non-fatal and all patients was 8.3 mmol/l (IQR 7.2-13.1), 6.4 mmol/l (IQR 5.4-7.8) and 6.7 mmol/l (IQR 5.5-8.1), respectively. After adjusting for age and current CD4(+) T-cell count, lactate >7 mmol/l (OR 6.27, 95% CI 1.13-34.93), blood bicarbonate <12 mmol/l (OR 10.02 relative to >18 mmol/l, 95% CI 1.33-75.65) and concurrent opportunistic infections (OR 8.69, 95% CI 1.45-52.22) were independently associated with case fatality. Blood lactate >7 mmol/l showed a sensitivity of 84% for fatality with a specificity of 60%, whereas bicarbonate <12 mmol/l showed a better specificity (85%) but a poorer sensitivity (42%). Bicarbonate <18 mmol/l appears to be as good as lactate <7 mmol/l at predicting death (sensitivity 90% and specificity 54%).

CONCLUSIONS

Our data suggest that blood lactate >7 mmol/l and blood bicarbonate <18 mmol/l appear to predict death and might help clinicians in selecting patients who may benefit from more intense monitoring.

Antiretroviral medications: adverse effects on the kidney

The widespread introduction of highly active antiretroviral therapy (HAART) in the mid-1990s dramatically altered the course of human immunodeficiency virus (HIV) infection, with improvements in survival and reductions in the incidence of AIDS-defining illnesses. Although antiretroviral therapy has been shown to reduce the incidence of both AIDS-defining and non-AIDS conditions, long-term exposure to HAART may also be associated with significant toxicity. This article reviews the potential nephrotoxicity of specific antiretroviral agents and the impact of antiretroviral therapy on related metabolic disorders. The antiretroviral agents most strongly associated with direct nephrotoxicity include the nucleotide reverse transcriptase inhibitor, tenofovir, and the protease inhibitor indinavir, although other agents have been implicated less frequently. Tenofovir and related nucleotide analogs have primarily been associated with proximal tubular dysfunction and acute kidney injury, whereas indinavir is known to cause nephrolithiasis, obstructive nephropathy, and interstitial nephritis. Kidney damage related to antiretroviral therapy is typically reversible with early recognition and timely discontinuation of the offending agent, and nephrologists should be familiar with the potential toxicity of these agents to avoid delays in diagnosis.

Risk factors for mortality in symptomatic hyperlactatemia among HIV-infected patients receiving antiretroviral therapy in a resource-limited setting

OBJECTIVES

To determine the mortality rate and risk factors after experiencing symptomatic hyperlactatemia in HIV-infected patients receiving antiretroviral therapy (ART).

METHODS

A retrospective cohort study was conducted among patients who were diagnosed with symptomatic hyperlactatemia (lactate >2.5mmol/l) between January 2004 and April 2006. All patients were followed until 3 months after the diagnosis.

RESULTS

One hundred and twenty-five patients were included in the study. The mean+/-standard deviation (SD) age was 39.9+/-10.1 years and body weight was 58.2+/-16.9kg; 60.8% were male. Symptomatic hyperlactatemia in 114 (91.2%) was associated with receiving d4T, in five (4.0%) with d4T+ddI, in four (3.2%) with ZDV+ddI, and in two (1.6%) with ddI (d4T, stavudine; ddI, didanosine; ZDV, zidovudine). The median duration of ART was 13 months. Nine (7.2%) patients died. Patients who died had a higher mean lactate level (8.0 vs. 5.1mmol/l) and mean alanine aminotransferase (ALT; 164 vs. 48U/l) at the time of diagnosis when compared to those who survived (p<0.05). Patients who died had a lower mean weight than those who survived (48 vs. 59kg, p=0.008). By logistic regression, mortality was associated with patients whose body weight was <45kg (p=0.014, odds ratio (OR) 9.090, 95% confidence interval (CI) 1.575-52.632) and whose serum lactate was >10mmol/l (p=0.004, OR 20.372, 95% CI 2.610-159.001).

CONCLUSIONS

The mortality rate of symptomatic hyperlactatemia among HIV-infected patients receiving ART is substantial. Almost all patients received d4T. Patients who have a low body weight and high serum lactate level are at a higher risk of mortality.

Reverse iontophoresis of L‐lactate: In vitro and in vivo studies

This work investigates the reverse iontophoretic extraction of lactate, a widely used marker of tissue distress in critically ill patients and of sports performance. In vitro experiments were performed to establish the relationship between subdermal lactate levels and lactate iontophoretic extraction fluxes. Subsequently, the iontophoretic extraction of lactate was performed in vivo in healthy volunteers. Lactate was quickly and easily extracted by iontophoresis both in vitro and in vivo. During a short initial phase, iontophoresis extracts the lactate present in the skin reservoir, providing information of relevance, perhaps, for dermatological and cosmetic applications. In a second step, lactate is extracted from the interstitial subdermal fluid allowing local lactate kinetics to be followed in a completely non-invasive way. The simultaneous in vivo extraction of chloride, and its possible role as an internal standard to calibrate lactate reverse iontophoretic fluxes, was also demonstrated. Despite these positive findings, however, considerably more research is necessary to eliminate potential artefacts and to facilitate interpretation of the data.

Adverse effects of highly active antiretroviral therapy in developing countries

Recent increases in access to highly active antiretroviral therapy (HAART) have made the management of drug toxicities an increasingly crucial component of human immunodeficiency virus (HIV) care in developing countries. The spectrum of adverse effects related to HAART in developing countries may differ from that in developed countries because of the high prevalence of conditions such as anemia, malnutrition, and tuberculosis and frequent initial presentation with advanced HIV disease. The severity of adverse effects may vary as a result of host genetics and diagnostic delays attributable to inadequate laboratory monitoring. This article reviews current knowledge about toxicities related to HAART in resource-limited regions, which are in the process of rapid treatment scale-up. We conclude that initiating HAART before advanced immunosuppression, titrating doses in single-pill drug combinations to differences in patients' body weights, providing more intensive laboratory monitoring during the initial months of therapy, and providing access to less-toxic nucleoside reverse-transcriptase inhibitors may decrease the incidence of toxicities related to HAART in resource-limited regions.

A High Incidence of Lactic Acidosis and Symptomatic Hyperlactatemia in Women Receiving Highly Active Antiretroviral Therapy in Soweto, South Africa

BACKGROUND

Lactic acidosis and symptomatic hyperlactatemia may complicate nucleoside reverse-transcriptase inhibitor use. Females may be at increased risk for such complications. Our study evaluated the incidence of lactic acidosis and symptomatic hyperlactatemia by sex, analyzed clinical features, and described the safety of reintroducing highly active antiretroviral therapy (HAART) with zidovudine replacing stavudine.

METHODS

A retrospective cohort analysis was performed for 1735 adults (63% of whom were female) who initiated HAART from April 2004 through August 2005 in Soweto, South Africa, with follow-up until February 2006. Patients with lactate levels > or =4.5 mmol/L and no potential cause of elevated lactic acidosis other than receipt of HAART were included in the study.

RESULTS

A total of 23 patients (22 of whom were female) experienced lactic acidosis. The overall incidence was 10.6 cases per 1000 patient-years; the incidence was 16.1 cases per 1000 patient-years in female patients and 1.2 cases per 1000 patient-years in male patients. Seven (30.4%) of the patients died. Eight (34.8%) of the patients were obese (body mass index [calculated as weight in kilograms divided by the square of height in meters], >30) at HAART initiation. Forty-four patients (37 of whom were female) had symptomatic hyperlactatemia. The overall incidence was 20.2 cases per 1000 patient-years, with an incidence of 27.0 cases per 1000 patient-years in female patients and 8.7 cases per 1000 patient-years in male patients. None of the patients died. Nine (20.4%) of the patients were obese at HAART initiation. Sixty-six of 67 patients were receiving stavudine, and 5 patients were receiving didanosine. Among 56 patients who restarted HAART with zidovudine for a cumulative nucleoside reverse-transcriptase inhibitor reexposure of 44.6 patient-years--including 41 patients who received treatment for > or =9 months--there were no relapses.

CONCLUSION

Women in Soweto, South Africa, have a higher frequency of symptomatic hyperlactatemia and lactic acidosis than has been reported for patients in other study groups. In cases associated with stavudine use, restarting HAART with zidovudine seemed to be safe and effective for patients with limited nucleoside reverse-transcriptase inhibitor alternatives.

Adverse effects of antiretroviral drugs on HIV-1-infected and -uninfected human monocyte-derived macrophages

Antiretroviral drugs approved for treatment of HIV-1 infection include nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs). Use of these drugs in combinations (highly active antiretroviral therapy) has delayed disease progression. However, long-term therapy is associated with potentially serious adverse effects. NRTIs are thought to contribute to these adverse effects via depletion of mtDNA. Inasmuch as macrophages (major targets for HIV-1) are highly metabolically active with large numbers of mitochondria, we investigated the effects of NRTIs (didanosine, stavudine, lamivudine, and zidovudine) on the viability and function of HIV-1-infected and -uninfected human monocyte-derived macrophages (MDMs). We demonstrate that the combinations didanosine/stavudine and lamivudine/zidovudine decrease mtDNA content in MDMs, with HIV-1-infected MDMs displaying a greater reduction than uninfected cells. This decrease correlated with decreased complement-mediated phagocytosis (C'MP) by MDMs, a process dependent on mitochondrial function. Inasmuch as PIs have previously been reported to interact with cellular proteases and given that cellular proteases are involved in the phagocytic process, we investigated the effects of the PI indinavir on C'MP. We demonstrate that indinavir augments C'MP by uninfected MDMs, but not HIV-1-infected MDMs. This study provides additional understanding on the effects of commonly used antiretroviral drugs on cellular immune function.

Mitochondrial toxicity of nucleoside analogues: mechanism, monitoring and management

Nucleoside analogues (NRTIs) are potent antiretroviral medications and are central to effective highly active antiretroviral therapy (HAART). Their intended action is to inhibit HIV reverse transcriptase. Nucleoside analogues also inhibit replication of mitochondrial DNA, and the pathogenesis of many of the toxicities associated with HAART is thought to be NRTI-induced mitochondrial dysfunction. Individuals with HIV infection may be particularly susceptible to clinically significant mitochondrial toxicity due to possible effects of HIV itself on mitochondria. At present there is no reliable method of detecting subclinical mitochondrial toxicity in patients exposed to NRTIs. Clinical awareness of this problem is therefore important to ensure the early detection of significant side effects and to allow timely consideration of changing therapy in those affected. There is no proven, effective therapy for NRTI-associated mitochondrial toxicity other than ceasing the implicated agent, and even with this strategy, resolution of symptoms may be incomplete. Similarly, there are no established methods for preventing mitochondrial toxicity in those on therapy including NRTIs. Micronutrients may have a role, but further study is needed to clarify optimal prevention as well as monitoring strategies.

Mitochondrial dysfunction: patient monitoring and toxicity management

Mitochondrial toxicity has been implicated in the development of a variety of nucleoside reverse transcriptase inhibitor-associated syndromes. Mitochondrial damage and decreases in mitochondrial DNA levels have been demonstrated in various tissues of patients treated with NRTIs, especially in conjunction with exposure to stavudine. Clinical syndromes that may be mediated by mitochondrial toxicity include hyperlactatemia and lactic acidosis, hepatic steatosis, lipoatrophy, peripheral neuropathy, HIV-associated neuromuscular weakness syndrome, pancreatitis, skeletal myopathies, and cardiomyopathy. Early recognition of these syndromes in their mild forms involves close monitoring and a high index of suspicion. This may allow prompt discontinuation of the causative agent(s) and initiation of appropriate therapeutic measures, thereby increasing the chances of reversibility of the syndrome.

Risk Factors for and Outcome of Hyperlactatemia in HIV-Infected Persons: Is There a Need for Routine Lactate Monitoring?

BACKGROUND

Lactic acidosis is a rare but life-threatening complication of combination antiretroviral therapy (CART). Asymptomatic or mildly symptomatic episodes of hyperlactatemia are more frequent, but their clinical relevance is unknown.

METHODS

The incidences of, risk factors for, and courses of hyperlactatemia and lactic acidosis were prospectively assessed in the following 3 groups at the Zurich center of the Swiss HIV Cohort Study: persons already receiving CART at baseline, treatment-naive persons who initiated CART during the observation period, and persons who received no CART before or during the observation period.

RESULTS

During 4788 person-years of follow-up, a total of 22,678 lactate assessments were performed for 1566 persons; 662 (42.3%) had at least 1 lactate level measurement of > 2.4 mmol/L, and 49 (3.1%) had severe hyperlactatemia (lactate level of > 5.0 mmol/L). The incidence of hyperlactatemia was 227 cases (95% confidence interval [CI], 210-245) and 59 cases (95% CI, 38-93) per 1000 person-years of follow-up among persons with and persons without CART, respectively. During the observation period, the incidence decreased from 459 cases (95% CI, 415-508) to 85 cases (95% CI, 76-107) per 1000 person-years of follow-up, respectively, because of changing CART prescription patterns. Severe hyperlactatemia occurred in treated persons only. In multivariable Cox proportional hazards models, significant risk factors for severe hyperlactatemia were regimens containing stavudine and didanosine (hazard ratio [HR], 6.65; 95% CI, 2.70-16.3) and regimens containing efavirenz (HR, 2.85; 95% CI, 1.31-6.21). Lactic acidosis was diagnosed in 4 of 1566 persons, all of whom were receiving stavudine and didanosine.

CONCLUSIONS

Hyperlactatemia was frequently observed in all 3 groups, but severe hyperlactatemia and lactic acidosis were rarely observed among persons who received CART. Lactate monitoring appears to be indicated primarily for persons receiving stavudine and didanosine and for persons who are symptomatic. Long-term follow-up is needed to investigate the risk of novel treatment regimens for hyperlactatemia.

Kinetics of lactate metabolism after submaximal ergometric exercise in HIV-infected patients

OBJECTIVES

It is unknown whether high levels of lactate result from enhanced production or decreased degradation. We therefore investigated differences in the kinetics of plasma lactic acid in HIV-infected patients receiving or not receiving highly active antiretroviral therapy (HAART) and in uninfected controls after submaximal ergometric exercise.

METHODS

Ten healthy controls, 11 HIV-infected therapy-naïve patients, 15 HIV-infected patients on HAART with normal baseline lactate levels, and nine HIV-infected patients on HAART with elevated baseline lactate levels >2 mmol/L performed 10 min of ergometric exercise, with a heart rate of 200 beats/min minus age. Lactate levels were measured at baseline, at the end of exercise and 15, 30, 45, 60 and 120 min thereafter.

RESULTS

Mean baseline lactate levels were 1.4, 1.5, 1.5 and 2.8 mmol/L in the controls, the therapy-naïve patients, the patients on HAART with normal lactate levels and the patients on HAART with elevated lactate levels, respectively. Maximum lactate levels after exercise were similar in all groups (9.7, 9.4, 9.0 and 10.1 mmol/L, respectively). Significant differences were found in the slope of lactate decline between controls and untreated individuals (P=0.038) and between patients on HAART with normal baseline lactate and patients on HAART with elevated baseline lactate (P=0.028).

CONCLUSIONS

Differences in lactate metabolism do exist between healthy controls and HIV-infected therapy-naïve individuals. Thus, HIV infection in itself may influence lactate levels. Elevated baseline lactate levels are associated with a delayed decline of lactate after exercise. These results could be explained by impaired lactate clearance. Lactate production upon exercise does not seem to be affected by baseline lactate levels.

Complications Associated with Nrti Therapy: Update on Clinical Features and Possible Pathogenic Mechanisms

The availability of durable, effective antiretroviral therapy for HIV-infected patients has fundamentally altered the prognosis of this disease and has also increased awareness that long-term drug toxicities have the potential to cause significant morbidity and even mortality in this patient population. The long-term use of nucleoside analogue reverse transcriptase inhibitor (NRTI) drugs has been associated with a number of clinically relevant toxicities including hyperlactataemia and lactic acidosis, neuropathy, pancreatitis and, more recently, a syndrome of pathological loss of subcutaneous fat tissue (lipoatrophy). Importantly, the toxicity profile of each NRTI drug within this class is unique in terms of the overall risk of long-term complications, as well as the tissue specificity of its toxic effects. In this review, the clinical manifestations, risk factors and pathological basis for NRTI-associated toxicity syndromes are explored, with an emphasis on clinical assessment and management.

Lack of Recurrence of Hyperlactatemia in HIV-Infected Patients Switched From Stavudine to Abacavir or Zidovudine

Stavudine (d4T) has been observed in clinical trials and cohort studies to be more often implicated in cases of hyperlactatemia than other nucleoside reverse transcriptase inhibitors, possibly because of its relatively greater propensity to induce mitochondrial toxicity. The ESS40010 study was a 48-week, open-label, switch study that assessed changes in serum lactate levels and signs/symptoms of hyperlactatemia after substitution of abacavir (n = 86) or zidovudine (n = 32) for d4T in 118 virologically suppressed HIV-infected patients (HIV-1 RNA <400 copies/mL) who had developed serum lactate concentrations > or =2.2 mmol/L (n = 16) or had remained normolactatemic (n = 102) after receiving > or =6 months of d4T-based treatment. Median serum lactate decreased significantly below baseline at week 24 (-0.15 mmol/L, P = 0.0002) and week 48 (-0.15 mmol/L, P = 0.0015). In 10 hyperlactatemic patients in whom d4T was discontinued, serum HIV-1 RNA levels rebounded over the ensuing 31 days, but virologic suppression (HIV-1 RNA <400 copies/mL) was regained when treatment using abacavir or zidovudine was subsequently instituted. In the group with elevated lactate at baseline, symptoms of hyperlactatemia improved in 8% to 23% of patients, did not change in 69%, and worsened in 8%. Serum transaminases, which had been elevated while patients received d4T, normalized after d4T discontinuation and remained in the normal range after the switch to abacavir or zidovudine. Overall, in patients with d4T-associated hyperlactatemia, stopping d4T results in normalization of lactate and a rebound in viral load; restarting treatment using abacavir or zidovudine subsequently maintains normal lactate levels and rapidly leads to a return of virologic suppression.

Nucleoside-related mitochondrial toxicity among HIV-infected patients receiving antiretroviral therapy: insights from the evaluation of venous lactic acid and peripheral blood mitochondrial DNA

Nucleoside analogues inhibit human DNA polymerase gamma. As a result, they can produce mitochondrial toxicity. We evaluated the possible role of random venous lactic-acid determinations as a screening tool for mitochondrial toxicity among patients receiving nucleoside therapy. More recently, we have developed an assay that can detect changes in mitochondrial DNA (mtDNA) levels in peripheral blood cells. Using this assay, we have characterized changes in mtDNA relative to nuclear DNA (nDNA) in peripheral blood cells from patients with symptomatic nucleoside-induced hyperlactatemia. Our results demonstrated that symptomatic hyperlactatemia was associated with markedly low mtDNA : nDNA ratios. A statistically significant increase in the mtDNA : nDNA ratio was observed after the discontinuation of antiretroviral therapy. Full validation of monitoring the mtDNA : nDNA ratio is currently under way.

Primer on clinical acid-base problem solving

Acid-base problem solving has been an integral part of medical practice in recent generations. Diseases discovered in the last 30-plus years, for example, Bartter syndrome and Gitelman syndrome, D-lactic acidosis, and bulimia nervosa, can be diagnosed according to characteristic acid-base findings. Accuracy in acid-base problem solving is a direct result of a reproducible, systematic approach to arterial pH, partial pressure of carbon dioxide, bicarbonate concentration, and electrolytes. The 'Rules of Five' is one tool that enables clinicians to determine the cause of simple and complex disorders, even triple acid-base disturbances, with consistency. In addition, other electrolyte abnormalities that accompany acid-base disorders, such as hypokalemia, can be incorporated into algorithms that complement the Rules and contribute to efficient problem solving in a wide variety of diseases. Recently urine electrolytes have also assisted clinicians in further characterizing select disturbances. Acid-base patterns, in many ways, can serve as a 'common diagnostic pathway' shared by all subspecialties in medicine. From infectious disease (eg, lactic acidemia with highly active antiviral therapy therapy) through endocrinology (eg, Conn's syndrome, high urine chloride alkalemia) to the interface between primary care and psychiatry (eg, bulimia nervosa with multiple potential acid-base disturbances), acid-base problem solving is the key to unlocking otherwise unrelated diagnoses. Inasmuch as the Rules are clinical tools, they are applied throughout this monograph to diverse pathologic conditions typical in contemporary practice.

The cellular pharmacology of nucleoside- and nucleotide-analogue reverse-transcriptase inhibitors and its relationship to clinical toxicities

Nucleoside- and nucleotide-analogue reverse-transcriptase inhibitors (NRTIs) require intracellular phosphorylation for anti-human immunodeficiency virus (HIV) activity and toxicity. Long-term toxicities associated with NRTIs may be related to overactivation of this process. In vitro experiments have shown increased rates of NRTI and endogenous nucleoside phosphorylation to be associated with cellular activation. Patients with advanced HIV disease often have overexpression of cytokines, which corresponds to an elevated cellular activation state. These patients also have higher rates of NRTI phosphorylation and NRTI toxicity, suggesting an interaction between a proinflammatory biological state, NRTI phosphorylation, and toxicity. Studies suggest that women may have higher rates of NRTI phosphorylation than do men, as well as increased risk for NRTI-induced toxicity. Future research is needed to understand the NRTI activation process and improve the long-term toxicity profile of NRTIs. Such research should include comparisons of NRTI phosphorylation according to sex and cellular activation state (i.e., elevated vs. low).

Depletion of mitochondrial DNA in liver under antiretroviral therapy with didanosine, stavudine, or zalcitabine

The "D drug" HIV reverse-transcriptase inhibitors zalcitabine, didanosine, and stavudine are relatively strong inhibitors of polymerase-gamma compared with the "non-D drugs" zidovudine, lamivudine, and abacavir. D drugs deplete mitochondrial DNA (mtDNA) in cultured hepatocytes. This mtDNA depletion is associated with an increased in vitro production of lactate. To investigate the origin of hyperlactatemia in HIV-infected patients and the effects of antiretroviral therapy on liver mtDNA, we biopsied liver tissue from 94 individuals with chronic hepatitis C virus (HCV) infection. Eighty subjects were coinfected with HIV. Serum lactate was measured at the time of biopsy. Hepatic mtDNA and liver histology were centrally assessed. Liver mtDNA content of HIV-infected patients receiving D drugs at the time of biopsy (n = 34) was decreased by 47% (P<.0001) compared with those without D drugs (n = 35). Aside from a possible association between HCV genotype I status and mtDNA depletion in multivariate analysis, there were no other virologic, immunologic, histologic, demographic or treatment-related variables that could explain the mtDNA depletion. Lactate was above the upper limit of normal in only three patients, all of whom were treated with D drugs. The mtDNA in each of them was lower than in any non-D drug patient and significantly (P =.017) depleted compared with D drug patients with normal lactate. In conclusion, D drug treatment is associated with decreased hepatic mtDNA in HIV-infected patients with chronic HCV infection. Moderate mtDNA depletion in liver does not necessarily lead to hyperlactatemia, but more pronounced decreases in hepatic mtDNA may be an important contributor to lactate elevation.

Dose-ranging, randomized, clinical trial of atazanavir with lamivudine and stavudine in antiretroviral-naive subjects: 48-week results

OBJECTIVE

To compare the efficiency and safety of atazanavir and nelfinavir in antiretroviral-naive patients.

DESIGN

Randomization to atazanavir 400 mg or 600 mg once daily; nelfinavir 1250 mg twice a day, plus lamivudine and stavudine.

METHODS

A blinded (to the atazanavir dose), 48-week trial in patients with HIV-1 RNA > or = 2000 copies/ml, CD4 cell count > or = 100 x 10(6) cells/l. Primary end-point: change in HIV-1 RNA from baseline at 48 weeks. Secondary end-point: subjects with HIV-1 RNA < 400, and < 50 copies/ml, CD4 cell count changes, adverse events.

RESULTS

The 467 randomized subjects had comparable baseline characteristics across treatments. With atazanavir 400 mg, 600 mg and nelfinavir, respectively, mean changes in HIV-1 RNA (log10 copies/ml) from baseline to 48 weeks were -2.51, -2.58, -2.31; HIV-1 RNA < 400 copies/ml [intent-to-treat population (ITT), non-completion = failure (NC = F)], 64%, 67%, 53%; HIV-1 RNA < 50 copies/ml (ITT NC = F), 35%, 36%, 34%; mean CD4 cell count increased comparably at 48 weeks (234 x 10(6), 243 x 10(6), 211 x 10(6) cells/l). Adverse events were similar across treatments with the exception of diarrhea (more frequent with nelfinavir) and jaundice (more frequent with atazanavir). Mean changes from baseline to 48 weeks were: fasting low density lipoprotein cholesterol, +5.2%, +7.1% and +23.2% (at 56 weeks) and fasting triglycerides (48 weeks), +7.2%, +7.6% and +49.5%, in the atazanavir 400 mg, 600 mg, and nelfinavir groups, respectively (P < 0.01, atazanavir versus nelfinavir).

CONCLUSIONS

Atazanavir is a potent, safe, well tolerated, and effective once-daily protease inhibitor with low pill burden (two capsules/day). Lipid changes with atazanavir were significantly less than with nelfinavir, however, clinical significance of these finding in terms of decreased cardiovascular risk is unknown.

Critical issues in nephrology

Renal and electrolyte problems are common in patients in the ICU. Several advances that occurred in the recent past have been incorporated in the diagnosis and management of these disorders and were reviewed in this article. Unfortunately, many important questions remain unanswered, especially in the area of ARF, where new therapies are anxiously awaited to make the transition from bench to bedside. Better studies are sorely needed to define the best approach to dialysis in patients who have ARF.

Factors associated with mitochondrial dysfunction in circulating peripheral blood lymphocytes from HIV-infected people

Nucleoside analogue reverse transcriptase inhibitor (NRTI)-associated mitochondrial toxicity is an important issue in the clinical management of HIV infection. The aim of this study was the detection of mitochondrial dysfunction by flow cytometry in lymphocytes from HIV-infected individuals and its association with blood lactate levels, clinical and virologic status, and the different NRTI-based therapies. Lower peripheral blood lymphocytes with mitochondrial dysfunction (PBLmd) percentages were observed in healthy controls (1.2, interquartile range [IQR] = 0.4-1.9) than in patients (2.2, IQR = 0.9-3.7; P < 0.01). Stavudine-containing therapy showed higher PBLmd percentages (3.0, IQR = 1.1-4.5) than no treatment (2.1, IQR = 0.8-2.8; P < 0.05) or zidovudine-based therapy (0.9, IQR = 0.3-1.4; P < 0.01). A significant inverse correlation was found between PBLmd and CD4 T-cell percentage and absolute count. Patients with an AIDS diagnosis had higher PBLmd percentage (2.7, IQR = 1.1-4.4) than HIV-positive non-AIDS patients (1.4, IQR = 0.6-3.0; P = 0.012). In multivariate analysis, use of stavudine (odds ratio [OR] = 5.86, 95% CI = 1.81-19.01, P = 0.003) and CD4 T-cell counts <200/microL (OR = 4.51, 95% CI = 1.38-14.70, P = 0.012) were independent predictors of high PBLmd percentage. This cross-sectional study shows that antiretroviral drugs can impair the in vivo mitochondrial function of PBLs.

Mitochondrial Toxicity in the Era of HAART: Evaluating Venous Lactate and Peripheral Blood Mitochondrial DNA in HIV-Infected Patients Taking Antiretroviral Therapy

Nucleoside analogs can induce mitochondrial toxicity by inhibiting the human DNA polymerase gamma. This can lead to a wide range of clinical toxicities, from asymptomatic hyperlactatemia to death. Despite their technical and physiological variability, we propose that random venous lactate measurements can be useful to monitor the development of nucleoside-related mitochondrial toxicity. Recently, we have developed an assay that can measure changes in mitochondrial DNA levels in peripheral blood cells. Using this assay we have characterized changes in mitochondrial DNA (mtDNA) relative to nuclear DNA (nDNA) in peripheral blood cells of patients with symptomatic nucleoside-induced hyperlactatemia. Our results demonstrate that symptomatic hyperlactatemia was associated with markedly low mtDNA/nDNA ratios, which were on average 69% lower than HIV-uninfected controls and 45% lower than HIV-infected asymptomatic/antiretroviral naive controls. A statistically significant (p = .016) increase in mtDNA/nDNA ratio was observed following discontinuation of antiretroviral therapy. The mtDNA/nDNA ratio remained stable among selected patients who reintroduced antiretroviral therapy with stavudine (d4T)-sparing regimens. Of note, the decline in mtDNA preceded the increase in venous lactate levels. More recently we have evaluated changes in the mtDNA/nDNA ratio in relation to selected antiretroviral drug regimens in a cross-sectional study on a non-random sample of participants within the British Columbia Centre for Excellence in HIV/AIDS Drug Treatment Program. Eligible patients had continuously received saquinavir plus ritonavir with either nevirapine (n = 20), lamivudine (n = 15), d4T (n = 53) or lamivudine + d4T (n = 69), for 4 to 30 months. d4T-sparing regimens were associated with a higher median mtDNA/nDNA ratio than d4T-containing regimens (p = .016), despite the fact that study patients had received d4T-containing regimens for a shorter median time than patients taking d4T-sparing regimens (13 versus 25 months, p = .002). In summary, mtDNA levels are significantly decreased among patients who develop symptomatic, nucleoside-related hyperlactatemia, an effect reversed upon therapy discontinuation. Furthermore, mtDNA/nDNA ratios were statistically significantly lower in patients taking d4T-containing regimens than in those taking selected d4T-sparing regimens in a population setting. These results suggest that measurement of this parameter should be investigated as a potential clinical management tool.

Mitochondrion-mediated apoptosis in HIV-1 infection

Acquired immunodeficiency syndrome (AIDS), which is caused by human immunodeficiency virus (HIV-1), involves the apoptotic destruction of lymphocytes and, in the context of AIDS-associated pathologies, of neurons and myocytes. Several proteins encoded by HIV-1 trigger apoptosis by inducing permeabilization of the mitochondrial membrane. Several nucleoside analogs used clinically in the treatment of HIV-1 inhibit the replication of mitochondrial DNA (mtDNA) and/or increase the frequency of mtDNA mutations. These cause severe mitochondriopathy and might contribute to lipodystrophy, the complication associated with HIV-1 therapy. HIV-1 protease inhibitors can inhibit apoptosis at the mitochondrial level, which might help to alleviate lymphopenia. Thus, it appears that the pathogenesis of AIDS, and the pharmacological interventions and complications associated with this disease, affect the mitochondrial regulation of apoptosis, which, therefore, largely determines the outcome of HIV-1 infection.

Hyperlactataemia syndromes associated with HIV therapy

Hyperlactataemia is seen in 8-18.3% of HIV-infected patients taking nucleoside-analogue reverse transcriptase inhibitors (NRTIs). Recent epidemiological studies suggest that most episodes are transient and subclinical. However, symptomatic and occasionally life-threatening cases accompanied by metabolic acidosis and hepatic steatosis (ie, lactic acidosis syndrome) have also been described. Though yet to be fully elucidated, the proposed mechanism is NRTI-induced inhibition of mitochondrial DNA polymerase culminating in derangements in oxidative phosphorylation and lactate homeostasis. Signs and symptoms range from mild hyperlactataemia accompanied by nausea, abdominal discomfort, and weight loss to severe, intractable lactic acidosis complicated by coma and multi-organ failure. Significant progress has recently been made with regard to the natural history of NRTI-related hyperlactataemia. However, other important aspects of the disorder, such as its pathogenesis, predisposing conditions, and management, remain poorly understood. This article reviews the current published work on these issues, identifies areas of controversy, and addresses directions for future research.

Antiretroviral-associated liver injury

ART-related hepatotoxicity can manifest in a variety of ways. Although benign, asymptomatic LEEs predominate, liver injury occurring in the context of either hypersensitivity or hyperlactatemia, represents a medical emergency and mandates immediate cessation of ART. Underpinning this broad spectrum of presentations are several, as yet poorly understood, mechanisms of liver damage that reflect contributions by constituents of HAART and host factors. Thus far, the most significant predisposing condition to emerge from clinical studies is chronic viral hepatitis. A more precise understanding, however, of the processes and factors that underlie ART-related hepatotoxicity is critical not only to the management of liver injury from current antiretroviral drugs but also to the design of safer drugs in the future.

Tests for mitochondrial function and DNA: potentials and pitfalls

PURPOSE OF REVIEW

In the past few years, mitochondria have been carefully studied to ascertain whether and how in patients affected by HIV antiretroviral therapy is able to alter their functionality and exert a toxic effect on immune cells, as well as on cells present in other districts.

RECENT FINDINGS

A variety of in-vivo and ex-vivo models have been developed to investigate the functionality of mitochondria and DNA during a variety of physiopathological situations, including HIV infection and its treatment. Numerous technologies are available to study at the single-cell or at the single-organelle level a variety of parameters, such as membrane potential, the activity of respiratory chain enzymes, and DNA content or its sequence. As far as in-vitro studies are concerned, a substantial homogeneity of data exists, and several changes in different mitochondrial parameters have been described that depend upon the drug used, the cell model and the parameter investigated. On the other hand, different results have been reported on biological material collected from HIV-positive patients and immediately analysed. Ex-vivo studies showed that changes in mitochondrial DNA content or in the functionality of the organelle exist in some tissues or cells, but not in others.

SUMMARY

One of the possible causes of the discrepancies is the technologies used to investigate mitochondria, and this paper summarizes some of the pros and cons of the main methods used to study mitochondrial function or DNA.

Results of a phase 2 clinical trial at 48 weeks (AI424-007): a dose-ranging, safety, and efficacy comparative trial of atazanavir at three doses in combination with didanosine and stavudine in antiretroviral-naive subjects

Three dose levels of the protease inhibitor (PI) atazanavir (200, 400, and 500 mg once daily) were compared with nelfinavir (750 mg three times daily) when given both as monotherapy and in combination with didanosine and stavudine in 420 antiretroviral-naive subjects infected with HIV-1. Subjects received monotherapy for 2 weeks, followed by combination therapy for 46 weeks. After 48 weeks, mean change from baseline in HIV RNA (-2.57 to -2.33 log 10 copies/mL), the proportion of subjects with HIV RNA <400 copies/mL (56%-64%) and <50 copies/mL (28%-42%), and mean increases in CD4 cell count (185-221 cells/mm 3) were comparable across treatment groups. Diarrhea was two to three times more common in the nelfinavir group (61% of subjects) than in the atazanavir groups (23%-30% of subjects, <.0001 versus nelfinavir), and jaundice occurred only in atazanavir-treated subjects (6%, 6%, and 12% in the 200-, 400-, and 500-mg groups, respectively) ( <.03 for all atazanavir regimens vs. nelfinavir). Mean percent change from baseline in fasting low-density lipoprotein (LDL) cholesterol was significantly less in the atazanavir groups (-7% to 4%) than in the nelfinavir group (31%) ( <.0001). In conclusion, once-daily atazanavir is a potent, safe, and well tolerated PI that rapidly and durably suppresses HIV RNA and durably increases CD4 cell count in antiretroviral-naive subjects. Through 48 weeks, atazanavir was not associated with clinically relevant increases in total cholesterol, fasting LDL cholesterol, or fasting triglycerides. In comparison, nelfinavir was associated with prompt, marked, and sustained elevations in these parameters of a magnitude that suggests they are clinically relevant.