HIV-1 induces in vivo platelet activation by enhancing platelet NOX2 activity

Role of inflammatory signaling pathways involving the CD40-CD40L-TRAF cascade in diabetes and hypertension-insights from animal and human studies

CD40L-CD40-TRAF signaling plays a role in atherosclerosis progression and affects the pathogenesis of coronary heart disease (CHD). We tested the hypothesis that CD40L-CD40-TRAF signaling is a potential therapeutic target in hyperlipidemia, diabetes, and hypertension. In mouse models of hyperlipidemia plus diabetes (db/db mice) or hypertension (1 mg/kg/d angiotensin-II for 7 days), TRAF6 inhibitor treatment (2.5 mg/kg/d for 7 or 14 days) normalized markers of oxidative stress and inflammation. As diabetes and hypertension are important comorbidities aggravating CHD, we explored whether the CD40L-CD40-TRAF signaling cascade and their associated inflammatory pathways are expressed in CHD patients suffering from comorbidities. Therefore, we analyzed vascular bypass material (aorta or internal mammary artery) and plasma from patients with CHD with diabetes and/or hypertension. Our Olink targeted plasma proteomic analysis using the IMMUNO-ONCOLOGY panel revealed a pattern of step-wise increase for 13/92 markers of low-grade inflammation with significant changes. CD40L or CD40 significantly correlated with 38 or 56 other inflammatory targets. In addition, specific gene clusters that correlate with the comorbidities were identified in isolated aortic mRNA of CHD patients through RNA-sequencing. These signaling clusters comprised CD40L-CD40-TRAF, immune system, hemostasis, muscle contraction, metabolism of lipids, developmental biology, and apoptosis. Finally, immunological analysis revealed key markers correlated with comorbidities in CHD patients, such as CD40L, NOX2, CD68, and 3-nitrotyrosine. These data indicate that comorbidities increase inflammatory pathways in CHD, and targeting these pathways will be beneficial in reducing cardiovascular events in CHD patients with comorbidities.

Challenges in Platelet Functions in HIV/AIDS Management

The interest in platelet functions in HIV/AIDS is due to the high incidence of microvascular thrombosis in these individuals. A lot of laboratory data have been generated regarding platelet functions in this population. The tests demonstrate platelet hyperactivity but decreased aggregation, though results are inconsistent depending on the study design. Antiretroviral treatments currently in use display complex interactions. Many studies on platelet functions in these patients have been for research purposes, but none have found utility in guiding drug treatment of thrombosis.

Platelets as Key Factors in Inflammation: Focus on CD40L/CD40

Platelets are anucleate cytoplasmic fragments derived from the fragmentation of medullary megakaryocytes. Activated platelets adhere to the damaged endothelium by means of glycoproteins on their surface, forming the platelet plug. Activated platelets can also secrete the contents of their granules, notably the growth factors contained in the α-granules, which are involved in platelet aggregation and maintain endothelial activation, but also contribute to vascular repair and angiogenesis. Platelets also have a major inflammatory and immune function in antibacterial defence, essentially through their Toll-like Receptors (TLRs) and Sialic acid-binding immunoglobulin-type lectin (SIGLEC). Platelet activation also contributes to the extensive release of anti- or pro-inflammatory mediators such as IL-1β, RANTES (Regulated on Activation, Normal T Expressed and Secreted) or CD154, also known as the CD40-ligand. Platelets are involved in the direct activation of immune cells, polynuclear neutrophils (PNNs) and dendritic cells via the CD40L/CD40 complex. As a general rule, all of the studies presented in this review show that platelets are capable of covering most of the stages of inflammation, primarily through the CD40L/CD40 interaction, thus confirming their own role in this pathophysiological condition.

Platelet-HIV: interactions and their implications

While it is clear that platelets interact with viruses, the ramifications and mechanisms of those interactions are still being defined for each type of viral infection. HIV/AIDS⁺ represents a potentially unique example of how viremia affects platelets since the increasing efficacy of antiretroviral therapeutics (ART) has made it a chronic disease that increases the risk of cardiovascular disease. In this opinion article, we discuss some of the open questions about how platelets interact with HIV. What happens to a virion once it binds a platelet? What is the nature of virus-induced platelet activation? Are platelets a normal part of the immune response to viremia that has been co-opted to increase the spread of HIV? The answers to these and similar questions will help define how platelet-directed therapeutics might be used in treating HIV/AIDS⁺ patients.

Platelets in HIV: A Guardian of Host Defence or Transient Reservoir of the Virus?

The immune and inflammatory responses of platelets to human immunodeficiency virus 1 (HIV-1) and its envelope proteins are of great significance to both the treatment of the infection, and to the comorbidities related to systemic inflammation. Platelets can interact with the HIV-1 virus itself, or with viral membrane proteins, or with dysregulated inflammatory molecules in circulation, ensuing from HIV-1 infection. Platelets can facilitate the inhibition of HIV-1 infection via endogenously-produced inhibitors of HIV-1 replication, or the virus can temporarily hide from the immune system inside platelets, whereby platelets act as HIV-1 reservoirs. Platelets are therefore both guardians of the host defence system, and transient reservoirs of the virus. Such reservoirs may be of particular significance during combination antiretroviral therapy (cART) interruption, as it may drive viral persistence, and result in significant implications for treatment. Both HIV-1 envelope proteins and circulating inflammatory molecules can also initiate platelet complex formation with immune cells and erythrocytes. Complex formation cause platelet hypercoagulation and may lead to an increased thrombotic risk. Ultimately, HIV-1 infection can initiate platelet depletion and thrombocytopenia. Because of their relatively short lifespan, platelets are important signalling entities, and could be targeted more directly during HIV-1 infection and cART.

Platelet Function in Viral Immunity and SARS-CoV-2 Infection

Platelets, as nonnucleated blood components, are classically recognized for their pivotal role in hemostasis. In recent years, however, accumulating evidence points to a nonhemostatic role for platelets, as active participants in the inflammatory and immune responses to microbial organisms in infectious diseases. This stems from the ability of activated platelets to secrete a plethora of immunomodulatory cytokines and chemokines, as well as directly interplaying with viral receptors. While much attention has been given to the role of the cytokine storm in the severity of the coronavirus disease 2019 (COVID-19), less is known about the contribution of platelets to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Here, we give a brief overview on the platelet contribution to antiviral immunity and response during SARS-CoV-2 infection.

Interactions of HIV and Antiretroviral Therapy With Neutrophils and Platelets

Neutrophils are important components of the innate immune system that mediate pathogen defense by multiple processes including phagocytosis, release of proteolytic enzymes, production of reactive oxygen species, and neutrophil extracellular trap formation. Abnormalities of neutrophil count and function have been described in the setting of HIV infection, with the majority of antiretroviral agents (ARVs), excluding zidovudine, having been reported to correct neutropenia. Questions still remain, however, about their impact on neutrophil function, particularly the possibility of persistent neutrophil activation, which could predispose people living with HIV to chronic inflammatory disorders, even in the presence of virally-suppressive treatment. In this context, the effects of protease inhibitors and integrase strand transfer inhibitors, in particular, on neutrophil function remain poorly understood and deserve further study. Besides mediating hemostatic functions, platelets are increasingly recognized as critical role players in the immune response against infection. In the setting of HIV, these cells have been found to harbor the virus, even in the presence of antiretroviral therapy (ART) potentially promoting viral dissemination. While HIV-infected individuals often present with thrombocytopenia, they have also been reported to have increased platelet activation, as measured by an upregulation of expression of CD62P (P-selectin), CD40 ligand, glycoprotein IV, and RANTES. Despite ART-mediated viral suppression, HIV-infected individuals reportedly have sustained platelet activation and dysfunction. This, in turn, contributes to persistent immune activation and an inflammatory vascular environment, seemingly involving neutrophil-platelet-endothelium interactions that increase the risk for development of comorbidities such as cardiovascular disease (CVD) that has become the leading cause of morbidity and mortality in HIV-infected individuals on treatment, clearly underscoring the importance of unraveling the possible etiologic roles of ARVs. In this context, abacavir and ritonavir-boosted lopinavir and darunavir have all been linked to an increased risk of CVD. This narrative review is therefore focused primarily on the role of neutrophils and platelets in HIV transmission and disease, as well as on the effect of HIV and the most common ARVs on the numbers and functions of these cells, including neutrophil-platelet-endothelial interactions.

Thrombocytopenia in Virus Infections

Thrombocytopenia, which signifies a low platelet count usually below 150 × 10⁹/L, is a common finding following or during many viral infections. In clinical medicine, mild thrombocytopenia, combined with lymphopenia in a patient with signs and symptoms of an infectious disease, raises the suspicion of a viral infection. This phenomenon is classically attributed to platelet consumption due to inflammation-induced coagulation, sequestration from the circulation by phagocytosis and hypersplenism, and impaired platelet production due to defective megakaryopoiesis or cytokine-induced myelosuppression. All these mechanisms, while plausible and supported by substantial evidence, regard platelets as passive bystanders during viral infection. However, platelets are increasingly recognized as active players in the (antiviral) immune response and have been shown to interact with cells of the innate and adaptive immune system as well as directly with viruses. These findings can be of interest both for understanding the pathogenesis of viral infectious diseases and predicting outcome. In this review, we will summarize and discuss the literature currently available on various mechanisms within the relationship between thrombocytopenia and virus infections.

Lipopolysaccharide induces platelet activation in HIV patients: the role of different viral load patterns

OBJECTIVES

This study aimed to assess whether gut-derived lipopolysaccharide (LPS) could affect platelet function in HIV-1 patients with residual viral load.

METHODS

In 23 HIV-1 patients on effective antiretroviral treatment, 10 treatment-naïve HIV-1 subjects and 20 healthy subjects (HS), LPS, zonulin, markers of platelet activation and oxidative stress were evaluated. In vitro, platelets from HS were exposed to plasma from HIV-1-infected treated and untreated patients.

RESULTS

Compared with HS, LPS was higher in treated and treatment-naïve subjects with HIV-1 (7.7 ± 2.9, 80.9 ± 13.7 and 75.3 ± 22.6 pg/mL, P < 0.001 vs. HS) as well as serum zonulin (1.3 ± 0.5, 6.1 ± 1.5 and 5.3 ± 1.7 ng/mL, P < 0.001 vs. HS). LPS and zonulin were correlated in HIV patients (Spearman correlation coefficient (rS) = 0.73, P < 0.0001). Levels of soluble CD40 ligand (sCD40L), soluble P-selectin (sP-selectin) and thromboxane B₂ (TxB₂ ) were higher in HIV-1-treated and treatment-naïve subjects compared with HS as well as NADPH oxidase 2 (NOX2) activation and hydrogen peroxide (H₂ O₂ ) production. In vitro, sCD40L, sP-selectin and TxB₂ production, NOX2 activation and p47^phox phosphorylation were higher in platelets exposed to plasma from HIV-1 patients with different viral load compared with the exposure to plasma from HS. This effect was blunted in platelets pre-treated with TLR4 or TLR7 inhibitors.

CONCLUSIONS

Low-grade endotoxaemia and persistent viraemia increase platelet function with a mechanism mediated by NOX2 in patients with HIV-1 infection.

Platelet activation in adult HIV-infected patients on antiretroviral therapy: a systematic review and meta-analysis

BACKGROUND

Antiretroviral therapy (ART) alters platelet reactivity, and as a consequence, patients living with HIV may be at an increased risk of cardiovascular disease (CVD). The current evidence on platelet activation levels in patients with HIV remains inconclusive. We therefore aimed to systematically synthesise evidence on the association of platelet activation in HIV-infected patients on successful treatment.

METHODS

Electronic databases were searched from inception until November 2019. Studies were included if the primary or secondary outcome of the study was to assess platelet activation in HIV-infected patients on ART. The primary outcome of this review included the levels of platelet activation. The pooled effect estimates were calculated using a random-effects meta-analysis model.

RESULTS

We identified 30 studies comprising of 2325 participants. The pooled estimates showed elevated levels of platelet activation in treatment-naïve HIV-infected patients compared to uninfected controls (Hedges' g 2.00 [95%CI 1.05, 2.94]; z = 4.12, p < 0.0001). These remained elevated despite successful ART (Hedges' g 2.05 [95%CI 0.58, 3.52]; z = 2.71, p = 0.0067).

CONCLUSION

The levels of platelet activation are elevated in treatment-naïve HIV-infected patients, and these persist during successful ART. Further studies should assess the clinical relevance of monitoring the levels of platelet activation in HIV-infected patients on ART.

Soluble E-cadherin is associated with oxidative stress in patients with chronic HBV infection

Mounting evidence indicates that serum soluble E-cadherin (sE-cadherin) serves as an important player in various physiological and pathological processes. However, the crosstalk between serum sE-cadherin and oxidative stress in chronic hepatitis B (CHB) remains to be illustrated. The main purpose of this study is to explore the molecular mechanisms underlying the function of sE-cadherin in CHB virus infection. Levels of serum sE-cadherin, total antioxidant capacity (TAC), glutathione (GSH), superoxide dismutase (SOD), total oxidant activity (TOA), NADPH oxidase 2 (NOX2), and malondialdehyde (MDA), from 51 patients with hepatitis B envelope antigen (HBeAg)-negative CHB, 54 patients with HBeAg-positive CHB, and 109 healthy individuals were detected by enzyme-linked immunosorbent assay. In our study, patients with CHB showed significantly higher serum sE-cadherin levels than healthy individuals (P < .01). Furthermore, we also found that the serum sE-cadherin levels were significantly negatively correlated with TAC, antioxidant enzymes (GSH and SOD) in patients with CHB, and that serum sE-cadherin concentrations were significantly positively correlated with liver enzyme markers (alanine transaminase and aspartate aminotransferase) and oxidative markers (TOA, NOX2, and MDA) in patients with CHB. Therefore, serum sE-cadherin may act as a new candidate biomarker for reflecting inflammation and oxidative stress status in the development and progression of hepatitis B virus infection.

Atrial fibrillation and human immunodeficiency virus type-1 infection: a systematic review. Implications for anticoagulant and antiarrhythmic therapy

The prevalence and incidence of atrial fibrillation/flutter (AF/AFL) in patients with human immunodeficiency virus type-1 (HIV-1) infection have been poorly investigated. We performed a systematic review using PubMed and Cochrane Database of Systematic Reviews, and screening of references, searching for clinical studies reporting on the association between HIV-1 infection and AF/AFL. We also summarized the main interactions of antiretroviral agents with antithrombotic and antiarrhythmic drugs. We found a prevalence of AF/AFL ranging from 2.0% to 5.13% in patients with HIV-1, with an incidence rate of 3.6/1000 person-years. Low CD4+ count (<200-250 cells ml^-1 ) and high viral load were predictors of AF/AFL. Regarding drugs interactions, nucleoside reverse transcriptase inhibitors, integrase inhibitor and maraviroc have the lowest interactions with oral anticoagulants. Among anticoagulants, dabigatran presents the most favourable profile. Most of antiarrhythmic drugs interact with protease inhibitors, with beta blockers and diltiazem having fewer interactions. The few studies available suggest a non-negligible prevalence of AF/AFL in patients with HIV-1 infection. Awareness of potential interactions with anticoagulation and antiarrhythmic drugs is needed to offer optimal management in this population.

Short-term in vivo modifications of platelet NADPH oxidase 2 (NOX2) and prostaglandin F2α in HIV-1 patients on abacavir-based therapies

OBJECTIVES

The aim of the study was to investigate the in vivo effect of abacavir (ABC) on platelet oxidative stress.

METHODS

We performed a randomized pilot study including 39 HIV-1-infected patients, 17 on zidovudine/lamivudine (ZDV/3TC) and 22 on tenofovir/emtricitabine (TDF/FTC). Ten patients on ZDV/3TC and eight patients on TDF/FTC were randomly allocated to switching the nucleoside backbone to ABC/3TC. At baseline and after 6 months, platelet oxidative stress was assessed by platelet NADPH oxidase 2 (NOX2)-derived peptide (sNOX2-dp), a marker of NOX2 activation, and platelet prostaglandin F_2α (8-iso-PGF_2α ). Platelet activation was measured by soluble CD40L (sCD40L).

RESULTS

At baseline, no differences between ZDV/3TC or TDF/FTC recipients were found. After 6 months, patients switching from ZDV/3TC showed a decrease of sNOX2-dp (from 20.9±5.7 to 12.5±3.8 pg/ml, p=0.002) and 8-iso-PGF_2α (from 154.3±41.9 to 122.9±28.0 pmol/l, p=0.025). No effects on platelet oxidative stress biomarkers were observed in subjects from TDF/FTC, who showed a significant increase in blood glucose (p=0.043) and total cholesterol (p=0.027). ABC showed no effect on sCD40L levels in both groups.

CONCLUSIONS

ABC reduced platelet sNOX2-dp and 8-iso-PGF_2α in HIV-1 subjects switching from ZDV/3TC but not in those from TDF/FTC after 6 months. No changes in platelet activation were found in both groups.

HIV-1 transcriptional activity during frequent longitudinal sampling in aviremic patients on antiretroviral therapy

BACKGROUND

HIV-1 transcription during suppressive antiretroviral therapy (ART) is not well understood. This is problematic as latency-reactivating agent-based HIV-1 eradication trials utilize changes in viral transcription as an efficacy biomarker.

METHODS

We conducted an observational cohort study enrolling aviremic, HIV-1-infected adults on long-term ART. Cell-associated unspliced (CA-US) HIV-1 RNA and total HIV-1 DNA were quantified in unfractionated CD4 T cells monthly for a total of six consecutive visits. Random-effects models were used to determine the following: (i) proportion of variation attributable to intra-individual versus inter-individual changes; (ii) range estimate for random samples from any participant or cohort-matched individual (95% prediction interval); and (iii) range estimate for random samples from the same person (95% variation intervals expressed as fold change).

RESULTS

Among our cohort of 26 HIV-1 patients, 10.4% of variation in CA-US HIV-1 RNA was attributable to intra-individual fluctuations. Similarly, intra-individual changes also accounted for minor proportions of the variation in total HIV-1 DNA (5.1%) and RNA/DNA (28.3%). The 95% prediction interval (per 10 CD4 T cells) for CA-US HIV-1 RNA and HIV-1 DNA were each approximately 2 log10. Finally, model-derived 95% variation intervals indicate that spontaneous changes above 2.11-fold in CA-US HIV-1 RNA would occur in less than 5% of repeated measurements in an individual on long-term ART.

CONCLUSION

The individual CA-US HIV-1 RNA levels are remarkably stable during ART. Importantly, the observed variations were less than the reported changes for latency-reactivating agent trials. These data will serve as a foundation for planning and interpreting future eradication trials.