Interference with cell cycle progression and induction of apoptosis by dideoxynucleoside analogs

The macrophage: a therapeutic target in HIV-1 infection

Human immunodeficiency virus (HIV) is still a serious global health concern responsible for more than 25 million deaths in last three decades. More than 34 million people are living with HIV infection. Macrophages and CD4+ T cells are the principal targets of HIV-1. The pathogenesis of HIV-1 takes different routes in macrophages and CD4+ T cells. Macrophages are resistant to the cytopathic effect of HIV-1 and produce virus for longer periods of time. In addition, macrophages being present in every organ system thus can disseminate virus to the different anatomical sites leading to the formation of viral sanctuaries. Complete cure of HIV-1 needs better understanding of viral pathogenesis in these reservoirs and implementation of knowledge into robust therapeutic products. In this review we will focus on the unique relationship between HIV-1 and macrophages. Furthermore, we will describe how successful antiretroviral therapy (ART) is in suppressing HIV and novel molecular and cellular strategies against HIV-1 in macrophages.

Cellular pharmacology and potency of HIV-1 nucleoside analogs in primary human macrophages

Understanding the cellular pharmacology of antiretroviral agents in macrophages and subsequent correlation with antiviral potency provides a sentinel foundation for definition of the dynamics between antiretroviral agents and viral reservoirs across multiple cell types, with the goal of eradication of HIV-1 from these cells. Various clinically relevant nucleoside antiviral agents, and the integrase inhibitor raltegravir, were selected for this study. The intracellular concentrations of the active metabolites of the nucleoside analogs were found to be 5- to 140-fold lower in macrophages than in lymphocytes, and their antiviral potency was significantly lower in macrophages constitutively activated with macrophage colony-stimulating factor (M-CSF) during acute infection than in resting macrophages (EC(50), 0.4 to 9.42 μM versus 0.03 to 0.4 μM, respectively). Although tenofovir-treated cells displayed significantly lower intracellular drug levels than cells treated with its prodrug, tenofovir disoproxil fumarate, the levels of tenofovir-diphosphate for tenofovir-treated cells were similar in lymphocytes and macrophages. Raltegravir also displayed significantly lower intracellular concentrations in macrophages than in lymphocytes, independent of the activation state, but had similar potencies in resting and activated macrophages. These data underscore the importance of delivering adequate levels of drug to macrophages to reduce and eradicate HIV-1 infection.

HIV RNA suppression and immune restoration: can we do better?

HAART has significantly changed the natural history of HIV infection: patients receiving antiretrovirals are usually able to control viremia, even though not all virological responders adequately recover their CD4+ count. The reasons for poor immune restoration are only partially known and they include genetic, demographic and immunologic factors. A crucial element affecting immune recovery is immune activation, related to residual viremia; indeed, a suboptimal virological control (i.e., low levels of plasma HIV RNA) has been related with higher levels of chronic inflammation and all-cause mortality. The sources of residual viremia are not yet completely known, even though the most important one is represented by latently infected cells. Several methods, including 2-LTR HIV DNA and unspliced HIV RNA measurement, have been developed to estimate residual viremia and predict the outcome of antiretroviral therapy. Considering that poor immunologic responders are exposed to a higher risk of both AIDS-related and non-AIDS-related diseases, there is a need of new therapeutic strategies, including immunomodulators and drugs targeting the latent viral reservoirs, in order to face residual viremia but also to “drive” the host immunologic responses.

Apoptosis: a clinically useful measure of antiretroviral drug toxicity?

Antiretroviral therapy (ART) has improved life expectancy with HIV infection, but long-term toxicities associated with these medications are now a major global disease burden. There is a clear need to develop useful methods for monitoring patients on antiretroviral drugs for early signs of toxicity. Assays with predictive utility -- allowing therapy to be changed before serious end organ damage occurs -- would be ideal. Attempts to develop biochemical methods of monitoring ART toxicity have concentrated on the mitochondrial toxicity of nucleoside analogue reverse transcriptase inhibitors and have not generally lead to assays with widespread clinical applications. For example, plasma lactate and peripheral blood measurements of mitochondrial DNA associate with exposure to potentially toxic nucleoside analogue reverse transcriptase inhibitors but have not reliably predicted clinical toxicity. Better assays are needed, including markers of toxicity from additional drug classes. Apoptosis may be a potential marker of ART toxicity. Increased apoptosis has been demonstrated both in vitro and in vivo in association with various antiretroviral drug classes and a range of clinical toxicities. However, quantifying apoptosis on biopsy specimens of tissue (such as adipose tissue) is impractical for patient monitoring. Novel assays have been described that can quantify apoptosis using minute tissue samples and initial results from clinical samples suggest peripheral blood may have utility in predicting ART toxicities. The limitations and potential of such techniques for monitoring patients for drug side effects will be discussed.

Centrosomal amplification and aneuploidy induced by the antiretroviral drug AZT in hamster and human cells

The centrosome directs chromosomal migration by a complex process of tubulin-chromatin binding. In this contribution centrosomal abnormalities, including centrosomal amplification, were explored in Chinese hamster ovary (CHO) and normal human mammary epithelial cells (NHMECs) exposed to the antiretroviral drug zidovudine (3'-azido-3'-deoxythymidine, AZT). Centrosomal amplification/fragmentation was observed in both cell types and kinetochore positive micronuclei were found in AZT-exposed CHO cells in correlation with dose. Normal human mammary epithelial cell (NMHEC) strain M99005, previously identified as a strain that incorporates high levels of AZT into DNA (high incorporator, HI), showed greater centrosomal amplification when compared with a second strain, NHMEC M98040, which did not incorporate AZT into DNA (low incorporator, LI). Additionally, an abnormal tubulin distribution was observed in AZT-exposed HI cells bearing multiple centrosomes. Immunofluorescent staining of human cells with Aurora A, a kinase involved in the maturation of the centrosome, confirmed the induction of centrosomal amplification and revealed multipolar mitotic figures. Flow cytometric studies revealed that cells bearing abnormal numbers of centrosomes and abnormal tubulin distribution had similar S-phase percentages suggesting that cells bearing unbalanced chromosomal segregation could divide. Therefore, AZT induces genomic instability and clastogenicity as well as alterations in proteins involved in centrosomal activation, all of which may contribute to the carcinogenic properties of this compound.

Effector caspase activation, in the absence of a conspicuous apoptosis induction, in mononuclear cells treated with azidothymidine

In the present study we focused our attention on the effect of AZT, at pharmacological and suprapharmacological concentrations, on some apoptosis-related key events and, particularly, on caspase activation in fresh human peripheral blood mononuclear cells (PBMCs). The main results can be summarized as follows: (i) AZT induced a strong, dose-dependent antiproliferative effect in mitogen-stimulated PBMCs, but low levels of cytotoxicity. in comparison with 5FU; (ii) low levels of cytotoxicity were coupled with a poor increase of apoptosis after AZT treatment in PBMCs; (iii) despite low levels of apoptosis, remarkable signs of both initiator and effector caspase enhanced expression with respect to control were detected by immunoblot analysis in AZT-treated PBMCs; (iv) enhanced caspase expression was associated with an increased expression of both anti-apoptotic Bcl-2 and pro-apoptotic Fas and p53 proteins, as detected by flow cytometry analysis; (v) combination treatment in vitro with AZT and anti-Fas significantly increased apoptosis in PBMCs with respect to single treatments. Overall, these results suggest that AZT treatment activates a complex, and apparently contrasting apoptosis-related signaling activity in PBMCs and that additional events are necessary to disrupt the balance induced by AZT towards apoptosis, on these cells.

Inhibition of cation channels and suicidal death of human erythrocytes by zidovudine

Zidovudine, a drug widely used in the treatment of AIDS, has been shown to influence cytosolic calcium activity in HIV-infected lymphocytes. Thus, zidovudine may modify the activity of Ca(2+)-permeable ion channels. In erythrocytes, activation of Ca(2+)-permeable cation channels stimulates eryptosis, the suicidal erythrocyte death. Eryptosis is characterized by cell shrinkage (apparent from a decrease of forward scatter) and phosphatidylserine (PS) exposure (apparent from annexin V-binding) at the erythrocyte surface. Triggers of eryptosis include isotonic cell shrinkage (Cl(-) replacement by gluconate), energy depletion (removal of glucose) or exposure to a variety of drugs including azathioprine. The present study explored, whether zidovudine influences the activity of erythrocytic Ca(2+)-permeable cation channels and eryptosis. Whole-cell patch-clamp recordings indeed revealed that zidovudine blocked the Ca(2+)-permeable cation channels activated by Cl(-) removal. In the presence of Cl(-) and glucose, the percentage of annexin V-binding cells was low and not significantly modified by the presence of zidovudine. Both, Cl(-) removal and glucose depletion increased annexin V-binding and decreased forward scatter, effects significantly blunted by zidovudine (2 microg/ml). According to Fluo3 fluorescence, zidovudine (2 microg/ml) did not significantly modify cytosolic Ca(2+) concentration under control conditions, but significantly blunted the increase in cytosolic Ca(2+) activity following glucose depletion. Furthermore, zidovudine significantly inhibited azathioprine-induced eryptosis. The present observations disclose a completely novel effect of zidovudine, i.e. its inhibitory influence on Ca(2+) entry and subsequent suicidal erythrocyte death during isotonic cell shrinkage or energy depletion.

Nucleoside reverse transcriptase inhibitors (NRTIs)-induced expression profile of mitochondria-related genes in the mouse liver

Mitochondrial dysfunction has been implicated in the adverse effects of nucleoside reverse transcriptase inhibitors (NRTIs) used to treat HIV-1 infections. To gain insight into the mechanism by which NRTIs alter mitochondrial function, the expression level of 542 genes associated with mitochondrial structure and functions was determined in the livers of p53 haplodeficient (+/-) C3B6F1 female mouse pups using mouse mitochondria-specific oligonucleotide microarray. The pups were transplacentally exposed to zidovudine (AZT) at 240 mg/kg bw/day or a combination of AZT and lamivudine (3TC) at 160 and 100mg/kg bw/day, respectively, from gestation day 12 through 18, followed by continuous treatment by oral administration from postnatal day 1-28. In addition, AZT/3TC effect was investigated in wild-type (+/+) C3B6F1 female mice. The genotype did not significantly affect the gene expression profile induced by AZT/3TC treatment. However, the transcriptional level of several genes associated with oxidative phosphorylation, mitochondrial tRNAs, fatty acid oxidation, steroid biosynthesis, and a few transport proteins were significantly altered in pups treated with AZT and AZT/3TC compared to their vehicle counterparts. Interestingly, AZT/3TC altered the expression level of 153 genes with false discovery rate of less than 0.05, in contrast to only 20 genes by AZT alone. These results suggest that NRTI-related effect on expression level of genes associated with mitochondrial functions was much greater in response to AZT/3TC combination treatment than AZT alone.

Decreasing CD4+ T-cell Count During Suppressed or Low-Level Viraemia in Patients with HIV Infection

Background

Suboptimal improvement in CD4+ T-cell count is not uncommon in HIV-infected patients with suppressed plasma HIV RNA levels, and a decrease in CD4+T-cell count in patients with suppressed or low-level viraemia has been observed.

Methods

Our objectives were to identify the prevalence of decreasing CD4+ T-cell counts during suppressed or low-level viraemia, to determine the frequency of clinical events during and immediately after such decreases, and to examine for associations with individual variables. A matched case-control study was undertaken using the Duke Infectious Diseases Clinic database ( n=3,949). Cases had at least two consecutive significant decreases in either CD4+ absolute count or CD4+ percentage, while also having plasma HIV RNA levels <1,000 copies/ml.

Results

The prevalence of decreasing CD4+ T-cell counts during suppressed or low-level viraemia was 1.22%. Only three HIV-associated clinical events occurred. The majority of cases had an increase in the CD4+ T-cell count immediately following the study period. The use of either zidovudine or stavudine was weakly associated with decreasing CD4+ T-cell counts in a multivariable analysis, but this association was not present in cases with only a decrease in CD4+ T-cell percentage.

Conclusions

Decreasing CD4+ T-cell counts during suppressed or low-level viraemia are rare, typically transient, and not associated with an increase in HIV-associated clinical events.

Genotoxicity assessed by the comet and GPA assays following in vitro exposure of human lymphoblastoid cells (H9) or perinatal exposure of mother-child pairs to AZT or AZT-3TC

The genotoxicity of zidovudine (AZT) based treatments was investigated in human H9 lymphoblastoid cells in an in vitro study and in red blood cells (RBCs) from perinatally exposed HIV-1-infected mothers and their infants in an observational cohort study. Exposure of H9 cells for 24 hr to AZT produced dose-dependent increases in Comet assay tail moment (TM) when electrophoresed at pH 13.0, but not at pH 12.1 or pH 8.0, suggesting that DNA damage was via alkali-labile lesions and not double-stranded DNA strand breaks. The TM dose response at pH 13.0 correlated directly with AZT-DNA incorporation determined by AZT-radioimmunoassay. Levels of DNA damage in utero, measured by Comet assay TM, were similar in cord blood mononuclear cells of nucleoside analog-exposed newborns (n = 43) and unexposed controls (n = 40). In contrast, the glycophorin A (GPA) somatic cell mutation assay (which screens for large-scale DNA damage in RBCs) showed clear evidence that GPA N/N variants, arising from chromosome loss and duplication, somatic recombination, and gene conversion, were significantly elevated in mother-child pairs receiving prepartum AZT plus lamivudine (3TC). Cord blood from newborns exposed to AZT-3TC had GPA N/N variant frequencies of 4.7 +/- 0.7 (mean +/- SE) x 10(-6) RBCs (n = 26 infants) compared with 2.2 +/- 0.3 x 10(-6) RBCs for unexposed controls (n = 30 infants; P < 0.001). Elevations in GPA N/N variants generally persisted through 1 year of age in nucleoside analog-exposed children. Overall, the mutagenic effects found in mother-child pairs receiving AZT-based treatments justify their surveillance for long-term genotoxic consequences.

Mechanisms of genotoxicity of nucleoside reverse transcriptase inhibitors

Nucleoside analogs were first approved by the U.S. Food and Drug Administration for use against HIV-AIDS in 1987. Since then, these agents, now commonly referred to as nucleoside reverse transcriptase inhibitors (NRTIs), have become essential components of the Highly Active Antiretroviral Therapy (HAART) drug combinations used for treatment of Human Immunodeficiency Virus-1 (HIV-1) infections. Their antiretroviral activity is likely two-fold: incorporation of the drug into viral DNA and inhibition of the viral reverse transcriptase. However, incorporation of the drug into host nuclear and mitochondrial DNA may be largely responsible for dose-limiting toxicities. Azidothymidine (AZT, 3'-azido-3'-deoxythymidine, zidovudine), the first NRTI approved for the therapy of HIV-1, is incorporated into DNA, causes mutations in the hypoxanthine-guanine phosphoribosyl-transferase (HPRT) and thymidine kinase (TK) genes, and induces micronuclei, chromosomal aberrations, sister chromatid exchange, shortened telomeres, and other genotoxic effects in cultured cells. Genomic instability would be predicted as a consequence of these events. Metabolic pathways that result in the phosphorylation of AZT play a crucial role in AZT-DNA incorporation, and may be altered after prolonged treatment. For example, thymidine kinase 1, the enzyme responsible for AZT mono-phosphorylation, is down-regulated during long-term exposure and appears to be associated with AZT-induced replication inhibition and the accumulation of cells in S-phase. Detailed information on the mechanisms underlying NRTI-associated antiretroviral efficacy, toxicity, and metabolic resistance were not available when AZT was first approved for use as an antiretroviral agent. Current insights, based on 15 years of research, may lead to intervention strategies to attenuate toxicity without altering drug efficacy.

The dissociation between virological and immunological responses to HAART

While HAART allows for the reconstitution of immune functions in most treated HIV patients, discrepant responses including failure to achieve a significant increase in circulating CD4+ T cells despite undetectable plasma viral loads (pVL), or a good immunological response while not reaching undetectable viremia, may occur. Thus, to evaluate the incidence of and risk factors for discrepant responses to HAART, we conducted a retrospective study of all 446 patients treated with HAART between 1 January 1998 and 31 August 2004 in our HIV unit. CD4+ T cell counts and pVL values at baseline and end of study were parameters of the type of response. Within a mean follow-up period of 33 months, discrepant immunological and virological responses occurred in even 50% patients. Of these, 174 (39%) did not have a rise in CD4+ T cells to above 400 per microl despite a good virological response (type 1 dissociation), while 49 (11.0%) had a rise in the CD4+ T cell count to at least 200 per microl but their pVL was not undetectable (type 2 dissociation). The risk factors for immunological failure despite an undetectable pVL were baseline CD4+ T cells below 100 per microl (OR 1.44, 95%CI 1.02-2.03) and HAART composed of three NRTIs (OR 1.92, 95%CI 1.35-2.73), while usage of two NRTIs in combination with PI(s) (OR 0.36, 95%CI 0.26-0.49), as well as simultaneous usage of all three drug classes (OR 0.37, 95%CI 0.26-0.53) were shown to be protective. The usage of PI-containing HAART regimens was protective against type 2 dissociation (OR=0.40, 95%CI 0.19-0.83). Importantly, there were no differences in the survival of HAART-treated patients irrespective of the type of response.

Short communication: HIV infection, antiretrovirals, and apoptosis: studies on skeletal muscle

Increased apoptosis in CD4+ T lymphocytes plays an important role in the pathogenesis of HIV infection and it has also invoked some HIV-related as well as antiretroviral-related adverse events. We assessed whether increased apoptosis is also present in the skeletal muscle of HIV-infected patients. We included 36 consecutive individuals, 18 without (group A) and 18 with HIV infection. The latter group consisted of five asymptomatic antiretroviral-naive HIV-infected individuals (group B), six asymptomatic HIV-infected individuals on highly active antiretroviral therapy (HAART, group C), and seven HIV-infected individuals on HAART with lipodystrophy (group D). Immunohistochemical reaction using deoxyribonucleotidyltransferase-mediated- dUTP-biotin nick-end labeling (TUNEL) was performed on skeletal muscle samples. None of the uninfected patients (group A) showed data of increased apoptosis, while 16 out of 18 infected patients did (p < 0.001). All subgroups of infected subjects (groups B-D) showed a significant increase of apoptosis in TUNEL with respect to uninfected individuals, but the comparison between the different subgroups of infected patients did not reveal significant differences. We conclude that skeletal muscle of HIV-infected patients exhibits increased apoptosis compared with that of uninfected patients, but the role of HAART in inducing apoptosis remains to be established.

Mitochondria are sensors for HIV drugs

Highly active anti-retroviral therapy (HAART) has drastically altered the course of HIV-1 infection, resulting in a major decrease in morbidity and mortality. However, adverse drug reactions and long-term toxicities associated with HAART are now a concern. A major toxicity that has been highlighted by the increased use of HAART is related to mitochondrial side-effects. At the same time, analysis of the biochemical pathways involved in programmed cell death has revealed that mitochondria are main sensors in this process. In this article, the regulation of mitochondrial damage following the use of nucleoside analogue reverse transcriptase inhibitors (NRTIs) and protease inhibitors is discussed, with a particular focus on the putative molecular mechanisms involved.

Synthesis, in vitro anticancer evaluation, and interference with cell cycle progression of N-phosphoamino acid esters of zidovudine and stavudine

A series of N-diisopropylphosphoryl (DIPP) L-amino acid ester prodrugs of zidovudine (AZT) (3a-3e) and stavudine (d4T) (4a-4e) has been prepared. The activity of these compounds against MCF-7 cells (human pleural effusion breast adenocarcinoma cell line) and K562 cells (human chronic myeloid leukemia (CML) cell line) was evaluated. In difference from that of AZT amino acid phosphoramidates, the alophatic amino acid esters of AZT were found to be more cytotoxic than the aromatic analogues toward MCF-7 cell. Two DIPP-L-amino acid esters of d4T 4b (CC50 = 83 microM) and 4c (CC50 = 182 microM) were found to be more cytotoxic than the parent drug toward K562 cells. MCF-7 and K562 cell cycle disturbance was investigated showing detectable blockade in the S phase when exposed to biologically active AZT, 3a, 3b, 3c, 4b and 4c, indicating that they inhibit cell growth by blocking cell cycle progression. Together with previous reports, present findings suggest that anti-breast cancer activity of AZT may be due to hamper DNA synthesis.

Zidovudine induces S-phase arrest and cell cycle gene expression changes in human cells

Antiretroviral therapy for the human immunodeficiency virus-1 (HIV-1) typically includes two nucleoside reverse transcriptase inhibitors (NRTIs). 3'-Azido-3'-deoxythymidine (AZT, Zidovudine) plus 2'-deoxy-3'-thiacytidine (3TC, Lamivudine) is a combination that is used frequently. The NRTIs are mutagenic nucleoside analogs that become incorporated into DNA and terminate replication. We therefore hypothesized that exposure to this class of drug may alter cell cycle parameters. We used flow cytometry to examine the cell cycle in human epithelioid carcinoma (HeLa) cells exposed to AZT and 3TC alone, as well as a series of AZT/3TC dose combinations: (A) 125.0 microM AZT/12.5 microM 3TC; (B) 250.0 microM AZT/25.0 microM 3TC; and (C) 500 microM AZT/50 microM 3TC. At 24 h, at all doses, there was a good cell viability (>/=68%), and incorporation of AZT into nuclear DNA. Using flow cytometry, a dose-related increase in the percentage of cells in S phase, from 9.5% with no drug, to 36.0% with dose C, was observed in cells exposed for 24 h (P = 0.001, ANOVA). A concomitant decrease in the percentage of cells in G(1) phase, from 82.6% with no drug to 58.5% with dose C, was observed in cells exposed for 24 h (P = 0.017, ANOVA). A similar S phase arrest was seen in cells exposed to 125, 250 and 500 microM AZT alone, but there was no S phase alteration with 50 microM 3TC alone, suggesting that AZT is responsible for the accumulation of cells in S phase. To elucidate the accumulation of cells in S phase and explore the cell cycle gene expression changes induced by AZT and 3TC, we used c-DNA microarray, Cell Cycle Super Array and real-time PCR. There was a strong upregulation of the DNA damage-inducible transcript 3 (DDIT3 or GADD153) in NRTI-exposed cells. In addition, AZT induced an upregulation of cyclin D1 accompanied by a downregulation of the cyclin D1-associated inhibitors P18 and P57, and the G(1)-S check point gene P21, the net effect of which would be to foster a cell progression into S phase. Cyclin A2 was down-regulated in cells exposed to AZT, suggesting a block in S-G(2)-M progression that would also be consistent with the accumulation of cells in S phase. Overall, the study demonstrates that AZT, but not 3TC, causes an arrest of cells in S phase with a consistent alteration in the expression of several cell cycle genes.

HIV Protease Inhibitors Prevent Mitochondrial Hyperpolarization and Redox Imbalance and Decrease Endogenous Uncoupler Protein-2 Expression in Gp120-Activated Human T Lymphocytes

It has been demonstrated that HIV protease inhibitors (PIs) are able to inhibit apoptosis of both infected and uninfected T cells. It was hypothesized that the mechanisms underlying this effect are associated with a specific activity of these drugs against mitochondrial modifications occurring in the execution phase of apoptosis. In this work, we investigated the activity of PIs towards the early changes occurring in mitochondrial membrane potential in freshly isolated uninfected human T lymphocytes sensitized to CD95/Fas-induced physiological apoptosis via pre-exposure to HIV envelope protein gp120. The results obtained clearly indicate that PIs are capable of hindering early morphogenetic changes bolstering T cell apoptosis, that is, cell polarization and mitochondrial hyperpolarization. The target effect on mitochondria appeared to be characterized by a specific activity of PIs in the maintenance of their homeostasis either in intact cells or in cell-free systems, that is, isolated mitochondria. PIs seem to act as boosters of mitochondrial defense mechanisms, including modulation of endogenous uncouplers. These results add new insights in the field of PI mitochondrial toxicity mechanisms and pharmacological perspectives for the use of these drugs in the control of immune system homeostasis.

Effect of indinavir used alone or in double or triple combination with AZT and ddC on human immune functions

Indinavir (IDV) is a potent and selective human immunodeficiency virus type 1 (HIV-1) protease inhibitor (PI) widely used in antiretroviral therapy, but its effects on the immune system are relatively unknown. In this study we have investigated the in vitro effect of IDV on normal human peripheral blood mononuclear cells (PBMC). We used the drug alone or in double and triple combination with AZT and ddC to assess whether IDV interferes with the previously observed immunomodulatory effects induced by AZT and ddC. We found that proliferative response, induction of immunoglobulins (Ig) production and cytokine production was not modulated by IDV. More importantly, IDV used in double or triple combination with AZT and ddC, does not further strenghten the inhibition of proliferative response induced by AZT and is able to abrogate the inhibitory effect induced by ddC on proliferative response. Similarly, IDV/AZT, IDV/ddC and IDV/AZT/ddC combinations does not strenghten the modulation of TNF-alpha, IFN-gamma and IL-4 induced by AZT, ddC and AZT/ddC. On the other hand, IDV neutralizes the up-regulating effects of AZT on IL-2 production while the up-regulating effects of ddC on IL-2 production is not affected. These data suggest that IDV used in combination with AZT and ddC did not add any further immunotoxicity.

Factors associated with a reduced CD4 lymphocyte count response to HAART despite full viral suppression in the EuroSIDA study

OBJECTIVES

To describe the prevalence and risk factors of poor CD4 count rise despite a good virological response on highly active antiretroviral treatment (HAART).

METHODS

The patients from the EuroSIDA study who started HAART with a baseline CD4 count of <350 cells/microL and where all viral load (pVL) measures remained below 500 HIV-1 RNA copies/mL between 6 and 12 months after the start of HAART were included. The risk factors for poor CD4 count rise were analyzed by multiple regression.

RESULTS

Seven hundred and eighty patients were included. A low CD4 count response was observed in 225 patients (29%). The risk factors for this condition were older age, lower CD4 count at baseline, higher increase from the nadir to baseline CD4 count and lower pVL at baseline. Patients taking > or =one drug from each of the three antiviral classes were more likely to have a good CD4 response but a minority of the study participants was taking this treatment regimen (3.1%) and the confidence interval was large.

CONCLUSIONS

A poor immune reconstitution despite a good virological control is frequent after initiation of HAART among patients with a baseline CD4 count of <350 cells/microL. The underlying mechanisms leading to this condition seems mainly driven by the age and the baseline immunological and virological status of the patients.

Mitochondrial membrane hyperpolarization hijacks activated T lymphocytes toward the apoptotic-prone phenotype: homeostatic mechanisms of HIV protease inhibitors

A decrease of mitochondrial membrane potential has been hypothesized to be a marker of apoptotic cells, including activated T lymphocytes. It was recently demonstrated that HIV protease inhibitors, independently from any viral infection, can hinder lymphocyte apoptosis by influencing mitochondrial homeostasis. To analyze the mechanisms underlying these effects, a specific study was undertaken in both resting and activated human PBL exposed to either receptor (e.g., anti-Fas)- or nonreceptor (e.g., radiation)-mediated apoptotic stimuli. T cell activation was found to be accompanied by a significant increase in mitochondrial membrane potential, or hyperpolarization, which was undetectable in resting cells. We also detected apoptotic hindering by HIV protease inhibitors only in activated T lymphocytes. This was apparently due to the ability of these drugs to block activation-associated mitochondria hyperpolarization, which, in turn, was paralleled by an impairment of cell cycle progression. Remarkably, protease inhibitors also prevented zidovudine-mediated mitochondrial toxicity. Finally, HIV-infected cells from naive patients behaved identically to activated T cells, displaying hyperpolarized mitochondria, while lymphocytes from patients under highly active antiretroviral therapy (which included HIV protease inhibitors) seemed to react as resting cells. Altogether these results clearly indicate that the hyperpolarization state of mitochondria may represent a prerequisite for the sensitization of lymphocytes to the so-called activation-induced cell death. They also suggest that HIV protease inhibitors, by interfering with induction of the mitochondrial hyperpolarization state, can result in cell survival even independent of any viral infection.

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.

Bench-to-bedside review: severe lactic acidosis in HIV patients treated with nucleoside analogue reverse transcriptase inhibitors

Nucleoside reverse transcriptase inhibitors (NRTIs) are effective antiretroviral therapy for the treatment of HIV-infected patients. NRTIs can induce mitochondrial impairment that leads to a number of adverse events, including symptomatic lactic acidosis. In the present review, we describe the underlying mechanism of NRTI-induced toxicity and the main clinical features of this infrequent, but severe, emerging complication. We also summarise experimental data and clinical observations that support the use of L-carnitine supplementation to reverse NRTI-induced mitochondrial impairment.

Pharmacological and biological aspects of basic research on nucleoside-based reverse transcriptase inhibitors

Antiretrovirals have progressively entered clinical practice since the discovery of the association between the acquired immunodeficiency syndrome (AIDS) and human immunodeficiency virus (HIV) infection. Among the classes of drugs which have shown efficacy against HIV, nucleoside-based reverse transcriptase inhibitors (NRTIs) have been extensively investigated in both their basic and therapeutic aspects. The basic mechanism of the effects of NRTIs relies on interaction with both viral and host cell functions. This implies that NRTIs could act not only by inhibiting viral genome replication, but also by interfering with some basic mechanism regulating cell growth and death. According to these characteristics, NRTIs might share several similarities with antineoplastic agents, including side effects. In this article, we have briefly reviewed the pharmacological activities of NRTIs in viral replication, neoplastic growth and cellular functions. These aspects might be involved both in the beneficial and adverse effects of NRTIs.

Immunomodulatory effect of zidovudine (ZDV) on cytotoxic T lymphocytes previously exposed to ZDV

In a previous study, zidovudine (ZDV) was shown to cause a concentration-dependent inhibition of antigen-specific cytotoxic T-lymphocyte (CTL) clonal expansion (S. Francke, C. G. Orosz, K. A. Hayes, and L. E. Mathes, Antimicrob. Agents Chemother. 44:1900-1905, 2000). However, this suppressive effect was lost if exposure to ZDV was delayed for 24 to 48 h during the antigen sensitization period, suggesting that antigen-primed CTL may be less susceptible than naive T lymphocytes to the suppressive effects of ZDV. The present study was undertaken to determine if naive T lymphocytes were more sensitive to the suppressive effects of ZDV than T lymphocytes previously exposed to antigen. The 50% inhibitory concentration (IC(50)) values of ZDV were determined on naive and antigen-primed T-cell responses in an alloantigen system. Lymphocyte cultures with continuous antigen exposure (double prime) were more resistant to ZDV suppression (IC(50) = 316 micro M) than were naive lymphocytes (IC(50) = 87.5 micro M). Interestingly, lymphocytes that were antigen primed but deprived of antigen during the final 7 days of culture (prime/hold) were exquisitely sensitive to ZDV suppression (IC(50) = 29.3 micro M). The addition of 80 micro M ZDV during the initial priming of the single-prime (prime/hold) and double-prime cultures did not select for a more drug-resistant cell population. The differences in ZDV sensitivities are likely a reflection of the physiological properties of the lymphocytes related to their activation state.

Induction of apoptosis by a nonnucleoside human immunodeficiency virus type 1 reverse transcriptase inhibitor

Inhibition of human immunodeficiency virus type 1 reverse transcriptase (RT) by both nucleoside and nonnucleoside RT inhibitors profoundly inhibits virus replication. Nucleoside RT inhibitors are known to be toxic, but there is little information regarding the toxicities of nonnucleoside RT inhibitors (NNRTI). We demonstrate that efavirenz (an NNRTI) induces caspase- and mitochondrion-dependent apoptosis of Jurkat T cells and human peripheral blood mononuclear cells. The clinical relevance of these observations is not yet clear.

Does melatonin induce apoptosis in MCF-7 human breast cancer cells in vitro?

Melatonin inhibits proliferation of the estrogen-responsive MCF-7 human breast cancer cells. The objective of this work was to assess whether melatonin not only regulates MCF-7 cell proliferation but also induces apoptosis. In this experiment we used 1,25-dihydroxycholecalciferol (D3) as a positive control because it inhibits MCF-7 cell proliferation and induces apoptosis. MCF-7 cells were cultured with either I nM melatonin, 100 nM D3 or its diluent to determine their effects on cell proliferation, cell viability, cell-cycle phase distribution, population of apoptotic cells, and expression of p53, p21WAF1, bcl-2, bcl-X(L) and bax proteins. After 24 or 48 hr of incubation, both melatonin and D3-treatment significantly decreased the number of viable cells in relation to the controls, although no differences in cell viability were observed between the treatments. The incidence of apoptosis, measured as the population of cells falling in the sub-G1 region of the DNA histogram, or by the TUNEL reaction, was similar in melatonin-treated and control cells whereas, as expected, apoptosis was higher among cells treated with D3 than in controls. The expression of p53 and p21WAF1 proteins significantly increased after 24 or 48 hr of incubation with either melatonin or D3. No significant changes in bcl-2, bcl-XL and bax mRNAs were detected after treatment with melatonin whereas in D3-treated cells, a significant drop in bcl-XL was observed. These data support the hypothesis that melatonin reduces MCF-7 cell proliferation by modulating cell-cycle length through the control of the p53-p21 pathway, but without clearly inducing apoptosis.

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.

Apoptosis and apoptosis-associated perturbations of peripheral blood lymphocytes during HIV infection: comparison between AIDS patients and asymptomatic long-term non-progressors

This study was designed to compare the degree of lymphocyte apoptosis and Fas-Fas ligand (FasL) expression in AIDS patients and long-term non-progressors (LTNPs) and correlate these parameters with apoptosis-associated perturbations in lymphocyte function. LTNPs had a lower frequency of apoptotic CD4+ and CD8+ T cells compared with subjects with AIDS. This correlated with a lower frequency of cells expressing Fas and FasL. The frequency of selected lymphocyte populations exhibiting a disrupted mitochondrial transmembrane potential (DeltaPsim) and increased superoxide generation was lower in LTNPs than in patients with AIDS; these abnormalities were associated with lower levels of caspase-1 activation in LTNPs. The results indicate a significantly reduced level of apoptosis and apoptosis-associated parameters in LTNPs than in patients developing AIDS. Based on these findings, a crucial role for mitochondria can be predicted in the process of lymphocyte apoptosis during the evolution of AIDS.

Effect of zidovudine on the primary cytolytic T-lymphocyte response and T-cell effector function

Azidothymidine (AZT) and other nucleoside analogues, used to treat AIDS, can cause severe clinical side effects and are suspected of suppressing immune cell proliferation and effector immune cell function. The purpose of the present study was to quantitatively measure the effects of AZT on cytotoxic T-lymphocyte (CTL) priming and to determine if the major histocompatibility complex-restricted CTL killing was affected by AZT exposure. For this purpose, we employed a murine alloantigen model and limiting-dilution analysis (LDA) to estimate cytotoxic effector cell frequencies of alloreactive splenocytes treated with drug during antigen sensitization. This noninfectious model was chosen to avoid analysis of a virus-compromised immune system. Exposure of splenocytes to therapeutic concentrations of AZT (2 to 10 microM) caused a two- to threefold dose-dependent reduction in CLT precursor frequency. This reduction was caused by decreased proliferation of alloantigen-specific CTLs rather than loss of function, because full cytolytic function could be restored by adjusting the AZT-treated effector/target cell ratios to that of untreated cells. In addition, when AZT was added to the assay system at various times during antigen sensitization there was a time-related loss of the suppressive effect on the generation of cytolytic effector function, suggesting that functional CTLs are not affected by even high doses of AZT. Taken together, the data indicate that the reduction of CTL function associated with AZT treatment is due to a quantitative decrease of effector cell precursor frequency rather than to direct drug cytotoxicity or interference with mediation of cytolysis. Furthermore, antigen-naive immune cells were most sensitive to this effect during the first few days following antigen encounter.

Protection by protein A of apoptotic cell death caused by anti-AIDS drug zidovudine

Zidovudine, the anti-AIDS drug, caused inhibition of mitogen-induced proliferation and perturbation of cell-cycle progression of cultured bone marrow cells of mice. There was significant hypoploidy observed in flow cytometric analysis of AZT-treated bone marrow cells. In apo-direct analysis, cells showed apoptosis in G0/G1 phase. In DNA gel analysis, characteristic laddering of apoptosis was observed in AZT-treated bone marrow cells. We demonstrated that, when the animals were pretreated with protein A (PA) of Staphylococcus aureus, the apoptotic changes could be prevented in bone marrow cells of AZT-treated animals. There is a significant (p < 0.05) increase in proliferation of bone marrow cells subjected to mitogen treatment in PA+AZT-treated animals, compared to only AZT-treated animals. However, cell-cycle phase distribution was not hampered and no laddering in DNA gel analysis was also observed in this group. In apo-direct analysis, PA treatment showed significant (p < 0.001) inhibition of AZT-induced apoptosis. These observations indicate that by using a suitable agent such as protein A the toxic side effects of AZT could be minimized.

Lack of immunotoxicity of saquinavir (Ro 31-8959) used alone or in double or triple combination with AZT and ddC

Saquinavir (Ro 31-8959; SQV) has been demonstrated to be a potent inhibitor of human immunodeficiency virus (HIV) proteinases and acts synergistically with dideoxynucleoside analogues. The aim of this study was to investigate the in vitro immunomodulatory effects of SQV on normal human peripheral blood mononuclear cells (PBMC) and on lamina propria mononuclear cells (LPMC). We used the drug either alone or in double and triple combination with AZT and ddC to assess whether SQV enhances the immunomodulatory effects induced by AZT and ddC that we previously observed. We demonstrated that SQV did not induce any modulation of the proliferative response either in PBMC or in LPMC. Similarly, NK cell-mediated cytotoxic activity and cytokine production were not modified by SQV. More importantly, SQV/AZT, SQV/ddC, and SQV/AZT/ddC combinations did not strengthen neither the inhibition of PBMC and LPMC proliferative response or the modulation of cytokine production induced by AZT, ddC, and AZT/ddC. On the other hand, the increased IL-2 production induced by AZT and ddC was not observed adding SQV to the dideoxynucleoside analogues. In conclusion, we demonstrated that SQV used in combination with AZT and ddC did not add any further immunotoxicity.