CROI 2018 Abstract eBook

Abstract eBook

Poster Abstracts

Background: Some HIV therapeutics in the nucleos(t)ide reverse transcriptase (N(t)RTI) inhibitor class (i.e. abacavir sulphate [ABC]) are reportedly associated with increased risk of cardiovascular events, such as myocardial infarction (MI). Increased MI risk is hypothesised to result from altered platelet reactivity in response to antiretroviral therapy. Thus, it is important to determine the impact of N(t)RTIs, including newly emerging therapeutics, such as tenofovir alafenamide (TAF), upon platelet aggregation as part of the process of determining their potential cardiovascular risk profile. Methods: In vitro : Platelets were isolated from healthy, HIV-negative, donors and aggregation assessed in vitro using a 96-well plate assay. Platelets were pre-incubated with plasma C max concentrations of N(t)RTIs and stimulated by platelet agonists (ADP, collagen, TRAP6 or thrombin). Platelet activation (granule release and integrin activation) was further assessed by multi-colour flow cytometry. In vivo : Collagen-evoked radiolabelled platelet aggregation was monitored in mice following i.p. administration of N(t)RTIs. Results: Platelet aggregation in response to ADP, collagen or TRAP6 was unaffected by incubation with ABC, TAF or TDF (tenofovir disoproxil fumarate). Equivalent plasma concentrations of tenofovir (TFV) or carbovir triphosphate (Cbv-TP) also did not lead to altered platelet aggregation in vitro. Treatment with Cbv-TP, but not TFV, led to a reversal of NO-mediated inhibition of platelet aggregation. ABC significantly enhanced expression of platelet activation markers whereas TAF and TDF had no effect (see Table 1). These increases demonstrate increased degranulation, indicating enhanced platelet activation and potentially a pro-thrombotic impact, in the presence of ABC. In vivo studies showed normal platelet aggregation responses in the presence of TAF or TDF, whereas ABC potentiated aggregation, again indicative of a pro-thrombotic effect. Conclusion: The reported increased MI risk in patients prescribed ABC may be driven by pharmacological modulation of the platelet activation response as well as interruption of NO-mediated inhibition of platelet aggregation, resulting in a greater propensity for agonist-induced platelet activation. Unlike earlier clinical studies, our observations are made in the absence of HIV infection, allowing assessment of direct pharmacological impacts of N(t)RIs on platelets.

672 EFFECTS OF ANTIRETROVIRAL THERAPY ON ALLELE-ASSOCIATED LIPOPROTEIN(A) LEVEL IN HIV Enkhmaa Byambaa 1 , Anuurad Erdembileg 1 , Chin-Shang Li 1 , Robert C. Kaplan 2 , Jason Lazar 3 , Daniel Merenstein 4 , Roksana Karim 5 , Bradley E. Aouizerat 6 , Mardge H. Cohen 7 , Kenneth R. Butler 8 , Savita Pahwa 9 , Igho Ofotokun 10 , Adaora Adimora 11 , Elizabeth T. Golub 12 , Lars Berglund 1 1 University of California Davis, Davis, CA, USA, 2 Albert Einstein College of Medicine, Bronx, NY, USA, 3 SUNY Downstate Medical Center, Brooklyn, NY, USA, 4 Georgetown University, Washington, DC, USA, 5 University of Southern California, Los Angeles, CA, USA, 6 New York University, New York City, NY, USA, 7 Cook County Health & Hospitals System, Chicago, IL, USA, 8 University of Mississippi, Jackson, MS, USA, 9 University of Miami, Miami, FL, USA, 10 Emory University, Atlanta, GA, USA, 11 University of North Carolina Chapel Hill, Chapel Hill, NC, USA, 12 Johns Hopkins Hospital, Baltimore, MD, USA Background: An elevated level of lipoprotein(a) [Lp(a)] is a causal risk factor for cardiovascular disease (CVD). Lp(a) levels are regulated by a size polymorphism in the apolipoprotein(a) [apo(a)] gene. In general, small apo(a) sizes are associated with a high Lp(a) level and an increased CVD risk. HIV infection and antiretroviral therapy (ART) have been shown to increase CVD risk. We demonstrated a significant positive association between Lp(a) level and subclinical atherosclerosis in HIV-seropositive women. Currently, the effects of ART initiation on Lp(a) level in relation to apo(a) size polymorphism remain unclear. Methods: The effects of ART initiation on Lp(a) levels and allele-specific apo(a) levels (ASL), the Lp(a) level associated with the larger or smaller apo(a) allele in each individual, were assessed in 126 HIV-seropositive women in the Women’s Interagency HIV Study. ART effects were tested by a mixed-effects model over three time points (the visit before ART initiation and the first and third visits after ART initiation). Data from 120 HIV-seronegative control women assessed at a single time point were used for comparison. Results: Mean age of the cohort was 38 ± 8 years; most were African-American (~70%). Pre-ART ASL associated with the larger (median: 4.6 mg/dL vs. 8.0 mg/ dL, p=0.024) or smaller (median: 13 mg/dL vs. 19 mg/dL, p=0.041) apo(a) sizes in the HIV-seropositive group were significantly lower compared to those in the HIV-seronegative group. Similarly, pre-ART prevalence of a high (≥30 mg/dL) Lp(a) level was lower in the HIV-seropositive vs. seronegative group (30% vs. 46%, p=0.013). However, post-ART both ASL or prevalence of a high Lp(a) level in the HIV-seropositive group did not differ significantly compared to those in the HIV-seronegative group. The median sizes for the larger or smaller apo(a) isoforms and frequency of a small size apo(a) (≤22 Kringle repeats) were similar across the HIV status. Notably, ART initiation significantly increased: 1) Lp(a) level [from pre-ART level of 18 mg/dL to post-ART level of 24 mg/dL, p<0.0001), and 2) ASL associated with the larger (5 mg/dL to 6 mg/dL, p=0.0003) or smaller (13 mg/dL to 16 mg/dL, p<0.0001) apo(a) sizes. Conclusion: ART initiation increased Lp(a) level and both ASL in HIV- seropositive women. Lp(a) level, regardless of its strong genetic regulation, can be modulated by HIV and its treatment. ART-induced increases in Lp(a) level could contribute to the higher CVD risk seen in HIV-seropositive individuals. 673 COMPARATIVE IMPACT OF ANTIRETROVIRALS ON HUMAN PLATELET ACTIVATION Kirk A. Taylor 1 , Francesca Rauzi 1 , Erica Smyth 1 , Mark Nelson 2 , Brian Gazzard 2 , Michael Emerson 1 1 Imperial College London, London, UK, 2 Imperial College Healthcare NHS Trust, London, UK

Poster Abstracts

674 LEUKOCYTES ARE KEY TO THE PRO-THROMBOTIC EFFECTS OF ABACAVIR Victor Collado-Diaz 1 , Ainhoa Sanchez-Lopez 1 , Samuel Orden 2 , Maria Amparo Blanch-Ruiz 1 , Maria Angeles Martinez-Cuesta 1 , Isabel Andujar 2 , Angeles Alvarez 1 , Juan V. Esplugues 1 1 University of Valencia, Valencia, Spain, 2 FISABIO, Valencia, Spain Background: Abacavir (ABC) shares a close structural similarity with endogenous purines like ATP and ADP, which are important signalling molecules in vascular physiopathology. ABC induces platelet-leukocyte-endothelial cell interactions and pro-thrombotic effects through a mechanism involving interference with the purinergic system, specifically ATP-P2X7 receptors. In previous in vitro experiments we have determined that the ATP-P2X7 receptors implicated in the actions of ABC are located primarily in leukocytes. Since the recruitment of leukocytes by platelets is an important phase in the formation of thrombi, the present study was performed to evaluate the role of white cells in the pro-thrombotic effects of ABC in an animal model of thrombosis. Methods: Male wild-type C57BL/6 mice were pre-treated with ABC (5–7.5 µg/ mL intrascrotally 4h) or rofecoxib (0.1 mg/kg, i.p. 2h). To generate leukopenia, some mice were treated with cyclophosphamide (150 mg/kg, i.p., 96h), which reduced the number of circulating leukocytes by almost 90%. Arterioles of the cremaster muscle were visualized with an intravascular microscope and blood flow was analyzed with a Doppler velocimeter. The endothelium-damaging agent ferric chloride was superfused at a concentration of 25 mM, a dose that

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