Howard Horng

Strong Correlation Between Concentrations of Tenofovir (TFV) Emtricitabine (FTC) in Hair and TFV Diphosphate and FTC Triphosphate in Dried Blood Spots in the iPrEx Open Label Extension: Implications for Pre-exposure Prophylaxis Adherence Monitoring

Self-reported adherence to pre-exposure prophylaxis (PrEP) has limitations, raising interest in pharmacologic monitoring. Drug concentrations in hair and dried blood spots (DBS) are used to assess long-term-exposure; hair shipment/storage occurs at room temperature. The iPrEx Open Label Extension collected DBS routinely, with opt-in hair collection; concentrations were measured with liquid chromatography/tandem mass spectrometry. In 806 hair-DBS pairs, tenofovir (TFV) hair levels and TFV diphosphate (DP) in DBS were strongly correlated (Spearman coefficient r = 0.734; P < .001), as were hair TFV/DBS emtricitabine (FTC) triphosphate (TP) (r = 0.781; P < .001); hair FTC/DBS TFV-DP (r = 0.74; P < .001); hair FTC/DBS FTC-TP (r = 0.587; P < .001). Drug detectability was generally concordant by matrix. Hair TFV/FTC concentrations correlate strongly with DBS levels, which are predictive of PrEP outcomes.

Hair Concentrations of Antiretrovirals Predict Viral Suppression in HIV-Infected Pregnant and Breastfeeding Ugandan Women

Objective:Hair concentrations are a noninvasive measure of cumulative antiretroviral exposure and the strongest predictor of viral suppression in large cohorts of nonpregnant patients. We examined hair concentrations of antiretrovirals in relation to virologic outcomes in pregnant and breastfeeding women for the first time. Design and methods:The Prevention of Malaria and HIV Disease in Tororo trial (NCT00993031) enrolled HIV-infected pregnant Ugandan women at 12–28 weeks gestation who were randomized to lopinavir or efavirenz-based antiretroviral therapy (ART). Small hair samples were collected at 30–34 weeks gestation and 10–25 weeks postpartum. Efavirenz and lopinavir hair concentrations were measured via liquid chromatography/tandem mass spectrometry. Multivariate logistic regression models examined predictors of viral suppression (HIV-1 RNA ⩽400 copies/ml) at delivery and 24 weeks postpartum. Results:Among 325 women, median CD4+ cell count was 366 cells/&mgr;l (interquartile range 270–488) at ART initiation. Mean self-reported 3-day adherence was greater than 97% in each arm. Viral suppression was achieved by 98.0% (efavirenz) and 87.4% (lopinavir) at delivery. At 24 weeks postpartum, 92.5% (efavirenz) and 90.6% (lopinavir) achieved viral suppression; 88% of women were breastfeeding. In multivariate models including self-reported adherence and pretreatment HIV-1 RNA, antiretroviral hair concentrations were the strongest predictor of viral suppression at delivery [efavirenz: adjusted odds ratio (aOR) 1.86 per doubling in concentration, 95% confidence interval (CI) 1.14–3.1, P = 0.013; lopinavir: aOR 1.90, 95% CI 1.33–2.7, P = 0.0004] and 24 weeks postpartum (efavirenz: aOR 1.81, 95% CI 1.22–2.7, P = 0.003; lopinavir: aOR 1.53, 95% CI 1.05–2.2, P = 0.026). Conclusion:Antiretroviral hair concentrations represent an innovative tool that strongly predicts viral suppression among HIV-infected childbearing women during the critical periods of delivery and breastfeeding.

Mechanistic Role of Acyl Glucuronides

Acyl glucuronides can be reactive metabolites capable of undergoing hydrolysis, intramolecular acyl migration, and covalent binding to proteins, both in vitro and in vivo. Glucuronidation occurs primarily in the liver and intestines, and is the major route of elimination for many xenobiotic and endogenous compounds containing a carboxylic acid function. Although glucuronidation is recognized as a detoxification process, acyl-linked glucuronides are considered chemically reactive electrophiles capable of covalent modification with nucleophilic sites on proteins. The extent of covalent binding with lysine amino groups of proteins correlates well with acyl glucuronide degradation rates (acyl migration and hydrolysis) and occurs either through a direct transacylation reaction or by a Schiff base mechanism via the open-chain aldehyde form of the acyl-migrated isomer. Subsequent formation of drug protein adducts has been proposed to elicit a direct toxicity or an immune-based reaction, both of which are consistent with the idiosyncratic toxicity commonly associated with carboxylic acid-containing drugs.

The nonenzymatic reactivity of the acyl-linked metabolites of mefenamic acid toward amino and thiol functional group bionucleophiles.

Mefenamic acid (MFA), a carboxylic acid–containing nonsteroidal anti-inflammatory drug, is metabolized into the chemically-reactive MFA-1-O-acyl-glucuronide (MFA-1-O-G), MFA-acyl-adenylate (MFA-AMP), and the MFA-S-acyl-coenzyme A (MFA-CoA), all of which are electrophilic and capable of acylating nucleophilic sites on biomolecules. In this study, we investigate the nonenzymatic ability of each MFA acyl-linked metabolite to transacylate amino and thiol functional groups on the acceptor biomolecules Gly, Tau, l-glutathione (GSH), and N-acetylcysteine (NAC). In vitro incubations with each of the MFA acyl-linked metabolites (1 μM) in buffer under physiologic conditions with Gly, Tau, GSH, or NAC (10 mM) revealed that MFA-CoA was 11.5- and 19.5-fold more reactive than MFA-AMP toward the acylation of cysteine-sulfhydryl groups of GSH and NAC, respectively. However, MFA-AMP was more reactive toward both Gly and Tau, 17.5-fold more reactive toward the N-acyl-amidation of taurine than its corresponding CoA thioester, while MFA-CoA displayed little reactivity toward glycine. Additionally, mefenamic acid-S-acyl-glutathione (MFA-GSH) was 5.6- and 108-fold more reactive toward NAC than MFA-CoA and MFA-AMP, respectively. In comparison with MFA-AMP and MFA-CoA, MFA-1-O-G was not significantly reactive toward all four bionucleophiles. MFA-AMP, MFA-CoA, MFA-1-O-G, MFA-GSH, and mefenamic acid-taurine were also detected in rat in vitro hepatocyte MFA (100 μM) incubations, while mefenamic acid-glycine was not. These results demonstrate that MFA-AMP selectively reacts with the amino functional groups of glycine and lysine nonenzymatically, MFA-CoA selectively reacts nonenzymatically with the thiol functional groups of GSH and NAC, and MFA-GSH reacts with the thiol functional group of GSH nonenzymatically, all of which may potentially elicit an idiosyncratic toxicity in vivo.

Hair Levels of Preexposure Prophylaxis Drugs Measure Adherence and Are Associated with Renal Decline Among Men/Transwomen.

Objective: The US preexposure prophylaxis (PrEP) Demonstration Project (U.S. Demo) evaluated MSM on PrEP postmarketing and found low seroconversion rates. The objective of this study is to examine hair levels as an adherence measure to PrEP. Design: Using an ‘opt-in’ design, participants of PrEP Demo were invited to enroll into a substudy where hair was collected quarterly. Methods: Tenofovir concentrations were measured in hair by liquid chromatography/tandem mass spectrometry. Hair levels consistent with ≥4 doses/week (protective in other studies) defined adequate adherence. Mixed effects multivariate logistic regression models examined factors associated with ≥4 doses/week. Separate mixed effects models evaluated the relationship between hair PrEP levels and changes in creatinine clearance (CrCl) over time. Results: Overall, 58% of U.S. Demo participants enrolled into this opt-in study; reasons for nonparticipation included insufficient hair (61%) and concerns about hairstyle (27%). Hair and dried blood spots levels consistent with ≥4 doses/week were highly concordant (84%). Hair levels showed adequate adherence in 87% of 875 person-visits (among 280 participants). Factors associated with adequate adherence in multivariate models were amphetamine use [adjusted odds ratio (aOR) 2.59 (0.97–6.9, P 0.06)], condomless receptive anal sex [aOR 2.28 (1.19–4.40, P 0.01)], and stable housing [aOR 2.63 (1.03–6.67), P 0.04]. Hair levels of tenofovir showed a monotonic relationship with decline in CrCl (P 0.01 for trend). Conclusion: In this substudy of the U.S. PrEP demonstration project, hair and dried blood spots levels were highly concordant and hair concentrations demonstrated adequate adherence 87% of the time, with stable housing and high-risk behavior associated with higher adherence. Daily PrEP drug taking is associated with modest declines in CrCl.

Characterization of the acyl-adenylate linked metabolite of mefenamic Acid.

Mefenamic acid, (MFA), a carboxylic acid-containing nonsteroidal anti-inflammatory drug (NSAID), is metabolized into the chemically reactive conjugates MFA-1-O-acyl-glucuronide (MFA-1-O-G) and MFA-S-acyl-CoA (MFA-CoA), which are both implicated in the formation of MFA-S-acyl-glutathione (MFA-GSH) conjugates, protein-adduct formation, and thus the potential toxicity of the drug. However, current studies suggest that an additional acyl-linked metabolite may be implicated in the formation of MFA-GSH. In the present study, we investigated the ability of MFA to become bioactivated into the acyl-linked metabolite, mefenamyl-adenylate (MFA-AMP). In vitro incubations in rat hepatocytes with MFA (100 μM), followed by LC-MS/MS analyses of extracts, led to the detection of MFA-AMP. In these incubations, the initial rate of MFA-AMP formation was rapid, leveling off at a maximum concentration of 90.1 nM (20 s), while MFA-GSH formation increased linearly, reaching a concentration of 1.7 μM after 60 min of incubation. In comparison, MFA-CoA was undetectable in incubation extracts until the 4 min time point, achieving a concentration of 45.6 nM at the 60 min time point, and MFA-1-O-G formation was linear, attaining a concentration of 42.2 μM after 60 min of incubation. In vitro incubation in buffer with the model nucleophile glutathione (GSH) under physiological conditions showed MFA-AMP to be reactive toward GSH, but 11-fold less reactive than MFA-CoA, while MFA-1-O-G exhibited little reactivity. However, in the presence of glutathione-S-transferase (GST), MFA-AMP mediated formation of MFA-GSH increased 6-fold, while MFA-CoA mediated formation of MFA-GSH only increased 1.4-fold. Collectively, in addition to the MFA-1-O-G, these results demonstrate that mefenamic acid does become bioactivated by acyl-CoA synthetase enzyme(s) in vitro in rat hepatocytes into the reactive transacylating derivatives MFA-AMP and MFA-CoA, both of which contribute to the transacylation of GSH and may be involved in the formation of protein adducts and potentially elicit an idiosyncratic toxicity.

Comparison of Measures of Adherence to Human Immunodeficiency Virus Preexposure Prophylaxis Among Adolescent and Young Men Who Have Sex With Men in the United States

Background Young men-who-have-sex-with-men (MSM) are disproportionately impacted by human immunodeficiency virus (HIV). Preexposure prophylaxis (PrEP) could reduce HIV acquisition among youth, but suboptimal adherence threatens effectiveness. Optimal metrics of PrEP adherence among adolescents have remain undefined. Methods The Adolescent Trials Network 110/113 studies provided daily oral PrEP with tenofovir (TFV) disoproxil fumarate/emtricitabine over 48 weeks to a diverse population of MSM (aged 15-22 years). Self-reported adherence was assessed and PrEP drug concentrations measured from hair and dried blood spot (DBS) samples; 23% of participants received Wisepill electronic monitoring devices. The average number of PrEP doses per week taken was estimated, and concordance between measures assessed. Results Among 243 participants, hair samples were collected at 1186/1238 (96%) person-visits. The concordance of TFV levels in hair and TFV-diphosphate in DBS around thresholds consistent with taking ≥4 and 7 PrEP doses/week was high (76% and 80%). Hair and DBS concentrations correlated poorly with self-report and Wisepill metrics. Through week 12, 40%-60% of participants (by hair and DBS), ≤31% (Wisepill), and >85% (self-report) were estimated to have taken ≥4 PrEP doses/week (a threshold associated with protection among MSM). For all measures except self-report, adherence declined over time, with half of participants taking <2 doses/week by week 48. Conclusions Among youth on PrEP, adherence waned over time. Self-report overestimated adherence, and use of Wisepill was limited. Hair collection was highly acceptable and provided similar interpretations to DBS. Incorporation of either metric in future PrEP studies among youth could identify suboptimal adherence and trigger interventions.

Brief Report: Lopinavir Hair Concentrations are the Strongest Predictor of Viremia in Hiv-infected Asian Children and Adolescents on Second-line Antiretroviral Therapy

Background: Children/adolescents display suboptimal antiretroviral therapy (ART) adherence and outcomes versus adults. Hair ART concentrations are objective adherence measures that predict viremia in adults but longitudinal data on hair levels in pediatric populations is limited. We assessed the predictive utility of hair lopinavir (LPV) levels on viremia among youth on second-line ART. Methods: We examined predictors of viremia (HIV-1 RNA >400 and >1000 copies/mL) at least 24 weeks after switch to LPV-based second-line ART in a cohort of HIV-infected Asian children followed between 2011 and 2014. Small hair samples, HIV-1 RNA, and self-reported adherence were collected biannually. Hair concentrations of LPV were measured through liquid chromatography/tandem mass spectrometry using validated methods. Time-to-first viremia was examined using discrete-time Cox models. Results: Overall, 244 children met the inclusion criteria for the present analysis. Approximately half (55%) were boys and the median age 10 years [interquartile range (IQR) 7–13]; 40% were older than 11 years. At switch to second-line ART, median CD4 count was 300 (IQR 146–547) cells/mm3 and median HIV-RNA level was 5.0 (IQR 4.3–5.6) log10/mL. Median time of study follow-up was 48 weeks and a median of 3 (range 1–5) hair samples were collected from each participant. Adjusting for age, sex, country, self-reported adherence, CD4, and HIV-RNA, higher LPV hair concentrations were the strongest predictor of lower odds of viremia (HIV-RNA >400 copies/mL adjusted odds ratio = 0.41 per doubling in hair concentration, 95% confidence interval: 0.29 to 0.58, P < 0.001; HIV-RNA >1000 copies/mL, adjusted odds ratio = 0.54, 95% confidence interval: 0.45 to 0.65, P < 0.001). Conclusions: Hair concentrations predict viremia among children with HIV on second-line ART and could guide clinical decisions for this population.

Fatal Taxus baccata ingestion with perimortem serum taxine B quantification

Abstract Introduction: Common yew (Taxus baccata) is a common decorative evergreen shrub with potentially fatal toxicity hallmarked by seizure, arrhythmia and cardiovascular collapse if ingested. Taxine B has been identified as one of the most cardiotoxic taxine alkaloids in Taxus spp, and another alkaloid, 3,5-dimethoxyphenol (3,5-DMP), is used as a marker of ingestion. We present a fatal case of ingestion of yew with perimortem serum and gastric taxine B, and 3,5-DMP concentrations. Case presentation: A 22-year-old woman was brought to the emergency department (ED) from a nearby botanical garden after she was found apneic and pulseless after a witnessed generalized tonic clonic seizure. The patient was found to have a wide complex rhythm with persistent cardiovascular collapse and expired despite maximal supportive care in the ED. A baggie of plant material was found on the patient, identified as Taxus baccata. Perimortem serum and gastric samples were analyzed to quantify serum and gastric taxine B and 3,5-DMP concentrations. Results: Perimortem serum showed a 3,5-DMP concentration of 86.9 ng/mL, and taxine B of 80.9 ug/mL. Conclusion: We report a perimortem serum and gastric taxine B and 3,5-DMP concentrations in a fatal case of T. baccata toxicity.

Cumulative Antiretroviral Exposure Measured in Hair Is Not Associated With Measures of HIV Persistence or Inflammation Among Individuals on Suppressive ART

Data on the relationship of antiretroviral exposure to measures of human immunodeficiency virus (HIV) persistence are limited. To address this gap, multiple viral, immunologic, and pharmacologic measures were analyzed from individuals with sustained virologic suppression on therapy (median 7 years) in the AIDS Clinical Trials Group A5321 cohort. Among 110 participants on tenofovir-(TFV)-disoproxil-fumarate (TDF)/emtricitabine (FTC)-containing regimens, we found no significant correlation between hair concentrations of individual antiretrovirals (ARVs) in the regimen and measures of HIV persistence (plasma HIV-1 RNA by single copy assay, cell-associated-DNA, cell-associated RNA) or soluble markers of inflammation. These findings suggest that higher systemic ARV exposure may not impact HIV persistence or inflammation.