HIV Persistence in Adipose Tissue Reservoirs

PURPOSE OF REVIEW

The purpose of this review is to examine the evidence describing adipose tissue as a reservoir for HIV-1 and how this often expansive anatomic compartment contributes to HIV persistence.

RECENT FINDINGS

Memory CD4 T cells and macrophages, the major host cells for HIV, accumulate in adipose tissue during HIV/SIV infection of humans and rhesus macaques. Whereas HIV and SIV proviral DNA is detectable in CD4 T cells of multiple fat depots in virtually all infected humans and monkeys examined, viral RNA is less frequently detected, and infected macrophages may be less prevalent in adipose tissue. However, based on viral outgrowth assays, adipose-resident CD4 T cells are latently infected with virus that is replication-competent and infectious. Additionally, adipocytes interact with CD4 T cells and macrophages to promote immune cell activation and inflammation which may be supportive for HIV persistence. Antiviral effector cells, such as CD8 T cells and NK/NKT cells, are abundant in adipose tissue during HIV/SIV infection and typically exceed CD4 T cells, whereas B cells are largely absent from adipose tissue of humans and monkeys. Additionally, CD8 T cells in adipose tissue of HIV patients are activated and have a late differentiated phenotype, with unique TCR clonotypes of less diversity relative to blood CD8 T cells. With respect to the distribution of antiretroviral drugs in adipose tissue, data is limited, but there may be class-specific penetration of fat depots. The trafficking of infected immune cells within adipose tissues is a common event during HIV/SIV infection of humans and monkeys, but the virus may be mostly transcriptionally dormant. Viral replication may occur less in adipose tissue compared to other major reservoirs, such as lymphoid tissue, but replication competence and infectiousness of adipose latent virus are comparable to other tissues. Due to the ubiquitous nature of adipose tissue, inflammatory interactions among adipocytes and CD4 T cells and macrophages, and selective distribution of antiretroviral drugs, the sequestration of infected immune cells within fat depots likely represents a major challenge for cure efforts.

Telmisartan reverses antiretroviral-induced adipocyte toxicity and insulin resistance in vitro

BACKGROUND

Antiretroviral therapy in HIV-positive patients leads to insulin resistance which is central to the pathogenesis of various metabolic abnormalities and cardiovascular disease seen in this patient group. We have investigated the dose-response relationship of telmisartan, an antihypertensive, on adipocytes in vitro in order to determine whether it may have metabolic beneficial effects.

METHODS

Using in vitro chronic toxicity models (3T3-F442A murine and primary human adipocytes), we evaluated the effects of different concentrations of telmisartan on adipocyte differentiation and adipogenic gene expression using lipid accumulation assays and real-time polymerase chain reaction, respectively. Adipokine secretion and expression of insulin signalling mediators were evaluated using enzyme-linked immunosorbent assays.

RESULTS

Telmisartan partially reversed the deleterious effects of antiretrovirals on adipocyte lipid accumulation, expression of adipogenic regulators (peroxisome proliferator receptor-gamma and lipin 1), adipokine secretion and expression of the insulin signalling mediator pAkt_Ser473. The metabolic effects of telmisartan followed a non-monotonic response with the maximal effect observed at 5 µM in the primary human adipocyte model.

CONCLUSION

Telmisartan has beneficial metabolic effects in adipocytes in vitro, but its potential to reduce antiretroviral-induced cardiometabolic disease in HIV-infected individuals needs to be evaluated in a well-designed adequately powered clinical trial.

Adipocytes impair efficacy of antiretroviral therapy

Adequate distribution of antiretroviral drugs to infected cells in HIV patients is critical for viral suppression. In humans and primates, HIV- and SIV-infected CD4 T cells in adipose tissues have recently been identified as reservoirs for infectious virus. To better characterize adipose tissue as a pharmacological sanctuary for HIV-infected cells, in vitro experiments were conducted to assess antiretroviral drug efficacy in the presence of adipocytes, and drug penetration in adipose tissue cells (stromal-vascular-fraction cells and mature adipocytes) was examined in treated humans and monkeys. Co-culture experiments between HIV-1-infected CD4 T cells and primary human adipocytes showed that adipocytes consistently reduced the antiviral efficacy of the nucleotide reverse transcriptase inhibitor tenofovir and its prodrug forms tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF). In HIV-infected persons, LC-MS/MS analysis of intracellular lysates derived from adipose tissue stromal-vascular-fraction cells or mature adipocytes suggested that integrase inhibitors penetrate adipose tissue, whereas penetration of nucleoside/nucleotide reverse transcriptase inhibitors such as TDF, emtricitabine, abacavir, and lamivudine is restricted. The limited distribution and functions of key antiretroviral drugs within fat depots may contribute to viral persistence in adipose tissue.

Prevalence of insulin resistance and risk of diabetes mellitus in HIV-infected patients receiving current antiretroviral drugs

OBJECTIVE

HIV-infected patients had a higher prevalence of insulin resistance (IR) and risk of diabetes mellitus (DM) than that observed in healthy controls, but there are no data about the current prevalence considering the changes in HIV presentation and the use of newer antiretroviral drugs.

DESIGN

Longitudinal study which involved 265 HIV patients without DM, receiving first (n=71) and advanced lines of antiretroviral therapy (n=194).

METHODS

Prevalence of IR according to clinical and anthropometric variables, including dual X-ray absorptiometry (DXA) scan evaluation. IR was defined as homeostasis model assessment of IR≥3.8. Incident DM was assessed during the follow-up.

RESULTS

First-line patients had a short time of HIV infection, less hepatitis C virus coinfection, and received mainly an efavirenz-based regimen. Overall, the prevalence of IR was 21% (55 patients, 6% in first-line, 27% in pretreated). In a logistic regression analysis, significant associations were found between the waist/hip circumference ratio (RR 10; 95% CI 1.66-16; P<0.01, per unit), and central fat in percentage (RR 1.08; 95% CI 1.01-1.17; P=0.04, per unit) as evaluated by DXA, and IR. During 770.8 patient-years, DM was diagnosed in 8% (22 patients), mostly in pretreated patients (10 vs 4%; P=0.1). Thus, the overall rate of incident DM was 2.85 per 100 person-years, mostly in previous IR (10.39 vs 0.82/100 person-years; P=0.01).

CONCLUSIONS

A lower prevalence of IR is observed in the current HIV-infected patients with fewer risk factors and receiving newer antiretroviral drugs. IR continues to identify patients at high risk for developing DM in the short term.

Insulin resistance, glucose intolerance and diabetes mellitus in HIV-infected patients

An increased prevalence of insulin resistance, glucose intolerance and diabetes has been reported in HIV infection in the highly active antiretroviral therapy (HAART) era. This development might be clinically significant because of its association with cardiovascular morbidity and mortality as well as the therapeutic challenges of managing polypharmacy. The development of insulin resistance, glucose intolerance and diabetes could be related to the underlying HIV infection, the contribution of different antiretroviral agents, treatment-associated weight gain, immune restoration, as well as the non-HIV related factors. Dissecting these factors in clinical practice might be difficult. Clinical studies include short-term treatments in healthy, non-HIV-infected individuals; randomized, controlled trials; comparative studies of different HAART regimens; and randomized studies of switching regimens in patients with viral suppression and stable immune function. This article reviews the latest knowledge regarding the epidemiology, pathogenesis, prevention and treatment of insulin resistance, glucose intolerance and diabetes mellitus in HIV-infected individuals.

Relationship of Mitochondrial DNA Depletion and Respiratory Chain Activity in Preadipocytes treated with Nucleoside Reverse Transcriptase Inhibitors

Objective

To study the impact of adipocyte differentiation on nucleoside reverse transcriptase inhibitor (NRTI)-mediated mitochondrial DNA (mtDNA) depletion and to correlate mtDNA depletion with the activity of the respiratory chain complexes.

Methods

We studied adipocyte phenotype, viability, differentiation (CCAAT/enhancer-binding protein [C/EBP]-α and peroxisome proliferator-activated receptor [PPAR]-γ expression), adiponectin production, mtDNA content, activity of respiratory chain complexes and citrate synthase activity in 3T3–L1 adipocytes. Cells were exposed to zidovudine (6 μM or 180 μM), stavudine (3 μM or 90 μM), and zalcitabine (0.1 μM or 3 μM) at different developmental stages for up to 2 months.

Results

Zidovudine and stavudine impaired adiponectin production in vitro at therapeutic Cmax concentrations, but none of the tested NRTIs had a negative impact on adipocyte differentiation or led to mtDNA depletion at these concentrations. Susceptibility of preadipocytes to mtDNA depletion was dependent on cell proliferation and differentiation, and mtDNA depletion occurred only after exposure to high drug concentrations. Under these conditions, stavudine led to up to 80% mtDNA depletion in both dividing and differentiating preadipocytes, whereas zidovudine affected mtDNA only in the differentiating cells. Despite mtDNA depletion by NRTIs, activity of the respiratory chain complexes was found to be unimpaired.

Conclusions

We found mtDNA depletion in adipocytes but proliferation and/or differentiation of the cells seems to be a prerequisite for this phenomenon. Depletion of mtDNA up to 80%, however, was not associated with impaired respiratory chain activity in 3T3-L1 preadipocytes.

Nelfinavir Induces Adipocyte Insulin Resistance through the Induction of Oxidative Stress: Differential Protective Effect of Antioxidant Agents

Background

Antiretroviral therapy is frequently associated with adverse metabolic effects and lipodystrophy, but the role of HIV protease inhibitors and the mechanisms involved are poorly understood. The HIV protease inhibitor nelfinavir (NFV) impairs insulin signal propagation by inducing similar signalling defects to those induced by exposure to oxidative stress.

Aim

We set out to determine if oxidative stress is involved in NFV-induced insulin resistance in 3T3-L1 adipocytes, and whether antioxidant agents with unique modes of action can prevent this effect.

Results

Cells exposed to NFV exhibited the following markers of increased oxidative stress: a decrease in both total and low molecular weight reduced thiols, a 20-fold increase in haem oxygenase 1 (HO-1) mRNA, an increase in intracellular reactive oxygen species production (determined by 2′,7′-dichlorofluorescein fluorescence), and increased markers of apoptosis. Enhancing cellular thiols with N-acetylcystein prevented the NFV-induced drop in reduced thiols and partially protected against the induction in HO-1, but failed to prevent insulin resistance or cleavage of poly ADP ribose polymerase (PARP), a process indicative of activation of pro-apoptotic caspases. Conversely, the superoxide dismutase-mimetic antioxidant MnTBAP had no effect on cellular thiols in response to NFV, but protected against HO-1 induction and against the impairment in insulin-stimulated Akt/protein kinase B activation and PARP cleavage.

Conclusions

Induction of oxidative stress plays a role in adipocyte insulin resistance and apoptosis induced by NFV through a radical-dependent but thiol-independent mechanism(s). The results may suggest a new mechanism for the adverse effects of NFV on fat cells, and offer potential new intervention approaches.

In Combination, Nucleoside Reverse Transcriptase Inhibitors Have Significant Effects on 3T3–L1 Adipocyte Lipid Accumulation and Survival

The use of nucleoside reverse transcriptase inhibitors (NRTIs) for the treatment of HIV infection is clearly linked to the development of subcutaneous fat atrophy. Until recently, however, in vitro studies of adipocytes have shown no or only modest and inconsistent effects of these agents on adipocyte biology. This is in contrast to the protease inhibitors (PIs), which are also linked to the development of HIV lipodystrophy. These agents have relatively consistent inhibitory effects on the differentiation of cultured adipocytes, and have occasionally been found to have other effects on adipocyte biology as well. We aimed to explore more thoroughly the effects of NRTIs and combinations of antiretroviral agents commonly used in clinical practice on multiple aspects of adipocyte biology using the 3T3-L1 adipocyte cell line. We found that when used individually, NRTIs decrease cell survival but only lamivudine significantly alters lipid accumulation. However, NRTI and dual NRTI-PI combinations do significantly decrease lipid accumulation in 3T3-L1 adipocytes, have a much greater detrimental impact on cell survival and decrease adipocyte differentiation.

Reverse Transcriptase Inhibitors Alter Uncoupling Protein-1 and Mitochondrial Biogenesis in Brown Adipocytes

Objective

Human adipose depots contain remnant brown adipocytes interspersed among white adipocytes, and disturbances of brown with respect to white adipocyte biology have been implicated in highly active antiretroviral therapy (HAART)-induced lipo matosis. Brown adipocytes express the uncoupling protein-1 (UCP1) and contain a large number of mitochondria, potential targets of HAART toxicity. The aim of this study was to evaluate the effects of reverse transcriptase inhibitors (RTIs) on primary brown adipocytes differentiated in culture.

Design and methods

We analysed the effects of RTIs, nucleoside analogues (NRTIs: stavudine, zidovudine, didanosine and lamivudine) and non-nucleoside analogues (NNRTIs: nevirapine and efavirenz), on differentiation, mitochondrial biogenesis and gene expression in brown adipocytes.

Results

None of the NRTIs altered brown adipocyte differentiation whereas NNTRIs had differing effects. Efavirenz blocked lipid deposition and expression of adipose marker genes but nevirapine induced lipid accumulation and adipose gene expression, promoted mitochondrial biogenesis and increased UCP1. Stavudine, zidovudine and didanosine reduced mitochondrial DNA (mtDNA) content. However, mitochondrial genome expression was only impaired in didanosine-treated adipocytes. Stavudine, but not zidovudine, induced expression of the mitochondrial transcription factors and this may explain compensatory mechanisms for the depletion of mtDNA by up-regulating mtDNA transcription. Stavudine caused a specific induction of UCP1 gene expression through direct interaction with a retinoic acid-dependent pathway.

Conclusions

Specific disturbances in brown adipocytes in adipose depots may contribute to HAART-induced lipomatosis. Mitochondrial depletion does not appear to be the only mechanism explaining adverse effects in brown adipocytes because there is evidence of compensatory mechanisms that maintain mtDNA expression, and the expression of the UCP1 gene is specifically altered.

Altered Adipokine Response in Murine 3T3-F442A Adipocytes Treated with Protease Inhibitors and Nucleoside Reverse Transcriptase Inhibitors

Background

Abnormal levels of tumour necrosis factor (TNF)-α, interleukin (IL)-6 and adiponectin have been observed in HIV patients with lipodystrophy. However, because these patients have long drug and disease histories, it is unclear which drugs are responsible for these abnormalities. We have therefore investigated the effects of individual antiretrovirals on adipokine expression and adipogenesis using a murine cell line in vitro.

Methods

Differentiating murine 3T3-F442A adipocytes were incubated with 20 μM nucleoside reverse transcriptase inhibitors (NRTIs) zidovudine or stavudine, or protease inhibitors (PIs) indinavir, ritonavir, saquinavir or nelfinavir, in the presence and absence of rosiglitazone (10 μM). Adipogenesis was assessed using glycerol-3-phosphate dehydrogenase activity, while expression of TNF-α, IL-6 and adiponectin at protein and mRNA levels was assessed by ELISA and quantitative real-time PCR, respectively.

Results

Nelfinavir, ritonavir and saquinavir inhibited adipogenesis and up-regulated the expression of TNF-α and IL-6, but this effect was not seen with indinavir, zidovudine and stavudine. Adiponectin expression was significantly reduced in both NRTI- and PI-treated cells, although the most profound reductions were found with ritonavir and saquinavir. Co-incubation with rosiglitazone led to a partial attenuation of the change in TNF-α, IL-6 and adiponectin secretion.

Conclusions

Our data suggest that the PIs nelfinavir, ritonavir and saquinavir have potent effects in inhibiting adipocyte differentiation whilst up-regulating TNF-α and IL-6 mRNA levels and decreasing adiponectin levels. These changes were partially attenuated by rosiglitazone. Taken together, the data show that antiretrovirals have complex effects on adipocyte function, which may be mediated by an altered adipokine response.

Adipocytes Targets and Actors in the Pathogenesis of HIV-Associated Lipodystrophy and Metabolic Alterations

The recent clinical use of potent HIV-1 drugs, including nucleoside reverse transcriptase inhibitors (NRTIs) and non-peptidic viral protease inhibitors (PIs), and their combinations, termed highly active antiretroviral therapy (HAART), has dramatically reduced the infection-related mortality of AIDS patients, but it is associated with severe metabolic adverse events such as lipodystrophy syndrome, dyslipidaemia, insulin resistance and diabetes mellitus. The aetiology of this syndrome and metabolic alterations appear to be multifactorial, including HIV drug inhibitory effects on adipocyte differentiation, alteration of mitochondrial functions in adipocytes and altered leptin, adiponectin and cytokine expression in adipose tissue of patients. Adipose tissue may thus be a central regulator in disorganized lipid metabolism and insulin resistance associated with antiretroviral therapy, and we propose in this review to explore how adipose tissue may be a target, but also an actor, in the aetiopathogenesis of the lipodystrophy syndrome.