Antidepressant Exposure and DNA Methylation: Insights from a Methylome-Wide Association Study

Importance

Understanding antidepressant mechanisms could help design more effective and tolerated treatments.

Objective

Identify DNA methylation (DNAm) changes associated with antidepressant exposure.

Design

Case-control methylome-wide association studies (MWAS) of antidepressant exposure were performed from blood samples collected between 2006-2011 in Generation Scotland (GS). The summary statistics were tested for enrichment in specific tissues, gene ontologies and an independent MWAS in the Netherlands Study of Depression and Anxiety (NESDA). A methylation profile score (MPS) was derived and tested for its association with antidepressant exposure in eight independent cohorts, alongside prospective data from GS.

Setting

Cohorts; GS, NESDA, FTC, SHIP-Trend, FOR2107, LBC1936, MARS-UniDep, ALSPAC, E-Risk, and NTR.

Participants

Participants with DNAm data and self-report/prescription derived antidepressant exposure.

Main Outcomes and Measures

Whole-blood DNAm levels were assayed by the EPIC/450K Illumina array (9 studies, N exposed = 661, N unexposed = 9,575) alongside MBD-Seq in NESDA (N exposed = 398, N unexposed = 414). Antidepressant exposure was measured by self- report and/or antidepressant prescriptions.

Results

The self-report MWAS (N = 16,536, N exposed = 1,508, mean age = 48, 59% female) and the prescription-derived MWAS (N = 7,951, N exposed = 861, mean age = 47, 59% female), found hypermethylation at seven and four DNAm sites (p < 9.42x10 -8 ), respectively. The top locus was cg26277237 ( KANK1, p self-report = 9.3x10 -13 , p prescription = 6.1x10 -3 ). The self-report MWAS found a differentially methylated region, mapping to DGUOK-AS1 ( p adj = 5.0x10 -3 ) alongside significant enrichment for genes expressed in the amygdala, the "synaptic vesicle membrane" gene ontology and the top 1% of CpGs from the NESDA MWAS (OR = 1.39, p < 0.042). The MPS was associated with antidepressant exposure in meta-analysed data from external cohorts (N studies = 9, N = 10,236, N exposed = 661, f3 = 0.196, p < 1x10 -4 ).

Conclusions and Relevance

Antidepressant exposure is associated with changes in DNAm across different cohorts. Further investigation into these changes could inform on new targets for antidepressant treatments.

3 Key Points

Question: Is antidepressant exposure associated with differential whole blood DNA methylation?Findings: In this methylome-wide association study of 16,536 adults across Scotland, antidepressant exposure was significantly associated with hypermethylation at CpGs mapping to KANK1 and DGUOK-AS1. A methylation profile score trained on this sample was significantly associated with antidepressant exposure (pooled f3 [95%CI]=0.196 [0.105, 0.288], p < 1x10 -4 ) in a meta-analysis of external datasets. Meaning: Antidepressant exposure is associated with hypermethylation at KANK1 and DGUOK-AS1 , which have roles in mitochondrial metabolism and neurite outgrowth. If replicated in future studies, targeting these genes could inform the design of more effective and better tolerated treatments for depression.

Dose Escalation in Esophageal Cancer: Comparing Pre-Accrual and On-Trial Target Volume Delineation in the UK SCOPE2 Trial

PURPOSE/OBJECTIVE(S)

The ongoing UK SCOPE2 trial evaluates radiotherapy (RT) dose escalation and PET-guided systemic therapy in esophageal cancer, and has an accompanying RT trials quality assurance (RTTQA) program, evolved through the preceding SCOPE trials. We compare pre-accrual with on-trial individual case review (ICR) target volume delineation (TVD).

MATERIALS/METHODS

Prior to recruitment, centers were required to undertake TVD exercises using 3D/4D DICOM datasets with relevant clinical details and a RT planning guidance document (RPGD) provided. Contours were then compared against the RTTQA team-defined gold standard. Exceptions were those who had satisfied QA requirements for a previous esophageal RT trial (NeoSCOPE). For ICRs, prospective reviews (prior RT start, PRs) were undertaken for each center's first submission, plus high-dose cases submitted pending formal safety review. Additional PRs were undertaken at the RTTQA team's discretion. Timely retrospective reviews (within 2 weeks of RT start, TRR) were also undertaken for a random 10% sample. TVDs were assessed for compliance using predefined criteria and the RPGD. Resubmission was requested at reviewer's discretion, usually due to unacceptable variation (UV) from protocol. Clarification was sought before contour approval/resubmission request if appropriate. Review outcomes were then evaluated. PTV6000 was new to SCOPE2, along with a greater emphasis on use of 4DCT than in prior SCOPE trials.

RESULTS

A total of 85 pre-accrual cases from 33 UK centers were reviewed, of which 20 (24%) were resubmissions, and 50 (59%) were accepted. 99 TVD UVs were observed in 49 cases, most commonly in CTVB (42/99, 42%), which included editing for normal structures and elective lymph node regions, followed by ITV (4D cases only, 14/52, 27%) and PTV6000 (13/99, 13%). 121 ICRs from 31 UK centers were available for review. 87 (72%) were PRs and 34 (28%) TRRs. 43 (36%) completed the relevant SCOPE2 exercise. 19 (16%) were resubmissions, and 82 (68%) were accepted. 72 UVs were observed in 45 ICRs; again, most commonly in CTVB (34/72, 48%), PTV6000 (high dose arm only, 11/46, 24%) and ITV (4D only, 5/26, 19%). Of the 45 cases where a UV was recorded, 16 (36%) had completed the relevant SCOPE2 pre-accrual. Comparing area of UV on SCOPE2 pre-accrual cases and ICRs, 3 (19%) contours contained the same (2 = CTVB, 1 = PTV6000), 5 (31%) contained different and 8 (50%) had no UVs at pre-accrual. The rate of UV was significantly lower for ICR than for pre-accrual submissions (0.60 and 1.16 respectively, p = 0.001).

CONCLUSION

Significantly fewer UVs in ICR compared with pre-accrual supports a robust, educational RTTQA program through national collaboration and evolving trial series. CTVB, along with newer volumes of ITV and PTV6000, were recurring UV domains and should inform RPGD development and RTTQA for ongoing recruitment and future trials.

Observation versus intervention for incidental common bile duct stones at intraoperative cholangiogram: a systematic review

BACKGROUND

The natural history of incidental common bile duct stones (CBDS) is poorly understood. Current evidence is conflicting, with several studies suggesting the majority may pass spontaneously. Despite this, guidelines recommend routine removal even if asymptomatic. This study aimed to systematically review the outcomes of expectant management for CBDS detected on operative cholangiography during cholecystectomy.

METHODS

MEDLINE, Embase and CINAHL databases were systematically searched. Participants were adult patients with CBDS identified by intraoperative cholangiography. Intervention was regarded as any perioperative effort to remove common bile duct stones, including endoscopic retrograde cholangiopancreatography (ERCP), laparoscopic and open bile duct exploration. This was compared to observation. Outcomes of interest included rates of spontaneous stone passage, success of duct clearance and complications. Risk of bias was assessed using the ROBINS-I tool.

RESULTS

Eight studies were included. All studies were non-randomized, heterogeneous and at serious risk of bias. In patients observed after a positive IOC, 20.9% went on to have symptomatic retained stones. In patients directed to ERCP for positive IOC, persistent CBDS were found in 50.6%. Spontaneous passage was not associated with stone size. Meta-analysis is dominated by the results from one large database, which recommends intervention for incidental stones, despite low rates of persistent stones seen at postoperative ERCP.

CONCLUSIONS

Further evidence is required before a definitive recommendation on observation can be made. There is some evidence that asymptomatic stones may be safely observed. In clinical scenarios where the risks of biliary intervention are considered high, a conservative strategy could be more widely considered.

Spring and latch dynamics can act as control pathways in ultrafast systems

Ultrafast movements propelled by springs and released by latches are thought limited to energetic adjustments prior to movement, and seemingly cannot adjust once movement begins. Even so, across the tree of life, ultrafast organisms navigate dynamic environments and generate a range of movements, suggesting unrecognized capabilities for control. We develop a framework of control pathways leveraging the non-linear dynamics of spring-propelled, latch-released systems. We analytically model spring dynamics and develop reduced-parameter models of latch dynamics to quantify how they can be tuned internally or through changing external environments. Using Lagrangian mechanics, we test feedforward and feedback control implementation via spring and latch dynamics. We establish through empirically-informed modeling that ultrafast movement can be controllably varied during latch release and spring propulsion. A deeper understanding of the interconnection between multiple control pathways, and the tunability of each control pathway, in ultrafast biomechanical systems presented here has the potential to expand the capabilities of synthetic ultra-fast systems and provides a new framework to understand the behaviors of fast organisms subject to perturbations and environmental non-idealities.

Temperature-related chest pain presentations and future projections with climate change

Background

Climate change has led to increased interest in studying adverse health effects relating to ambient temperatures. It is unclear whether incident chest pain is associated with non-optimal temperatures and how chest pain presentation rates might be affected by climate change.

Methods

The study included ambulance data of chest pain presentations in Melbourne, Australia from 1/1/2015 to 30/6/2019 with linkage to hospital and emergency discharge diagnosis data. A time series quasi-Poisson regression with a distributed lag nonlinear model was fitted to assess the temperature-chest pain presentation associations, after adjusting for season, day of the week and long-term trend. Future excess chest pain presentations associated with cold and heat were projected under six general circulation models under medium and high emission scenarios.

Results

In 206,789 chest pain presentations, mean (SD) age was 61.2 (18.9) years and 50.3% were female. Significant heat- and cold-related increased risk of chest pain presentations were observed for mean air temperatures above and below 20.8°C, respectively (Figure 1). Excess chest pain presentations related to heat were observed in all subgroups, but appeared to be attenuated for older patients (≥70 years) and patients of higher socioeconomic status (SES). We projected no significant change in net temperature-related chest pain presentations with climate change under medium- and high-emission scenarios, with increases in heat-related chest pain presentations offset by decreases in chest pain presentations related to cold temperatures.

Conclusions

Heat- and cold-exposure appear to increase risk of chest pain presentations, especially among younger patients and patients of lower SES. In Melbourne, Australia, chest pain presentations overall were not projected to increase with climate change, but increases in heat-related chest pain presentations highlight the importance of risk mitigation strategies to minimise adverse health impacts on hotter days.

Funding Acknowledgement

Type of funding sources: Public hospital(s). Main funding source(s): Alfred Health.

Impact of ambulance off-load delays on mortality in patients with chest pain

Background

Ambulance off-load delays in transferring patient care to emergency departments (EDs) are increasingly common, but it is unclear whether clinical outcomes are impacted.

Methods

Population-based cohort study of ambulance attendances for non-traumatic chest pain transported to ED in Victoria, Australia (1/1/2015–30/6/2019) excluding patients transported to hospital with “lights and sirens” or triaged as ED category 1. Multivariable models were used to assess the relationship between ambulance off-load times and 30-day mortality and ambulance re-attendance for chest pain.

Results

The study included 213,544 ambulance attendances for chest pain (mean age 62 [SD 18] years; 51% female). Median ambulance off-load times increased across the study period from 21 minutes (interquartile range [IQR] 15–30) in 2015 to 24 minutes (IQR 17–37) in 2019. Patients were divided into tertiles according to off-load times with 69,247 patients included in tertile 1 (0–17 minutes), 73,109 patients in tertile 2 (18–28 minutes), and 71,188 patients in tertile 3 (&gt;28 minutes). In multivariable models, ambulance off-load delays were associated with higher unadjusted and adjusted rates of 30-day mortality (1.57% tertile 3 vs. 1.29% tertile 1, adjusted risk difference 0.28% [95% CI 0.16% - 0.42%], p&lt;0.001) and ambulance re-attendance for chest pain (9.89% tertile 3 vs. 8.59% tertile 1, adjusted risk difference 1.30% [95% CI 1.00% - 1.61%], p&lt;0.001). Similarly, in analysis using off-load times as a continuous variable with restricted cubic splines, a non-linear increase in adjusted odds ratio for mortality was observed (Figure 1).

Conclusions

Delays in ambulance off-load times appear to be associated with increased mortality and ambulance re-attendance risk among chest pain cohorts. This study has important policy implications given the increasing frequency of off-load delays in many healthcare settings.

Funding Acknowledgement

Type of funding sources: Public hospital(s). Main funding source(s): Alfred health

Variation in health-care quality and outcomes according to time of chest pain presentation: a state-wide prospective cohort study

Background

Previous studies examining temporal variation in cardiovascular care have largely been limited to assessing weekend and after-hours effects whereby those presenting on the weekend or after-hours have a poorer outcome. However, emerging evidence suggests more complex patterns in patterns and outcomes may exist.

Purpose

We aimed to determine patterns of temporal variation in chest pain presentations and subsequent health-care quality and outcomes.

Methods

This was an observational, prospective-cohort study of adult patients aged 18 and over who were attended by emergency medical services for non-traumatic chest pain between 1 January 2015 and 30 June 2019 in Victoria, Australia. Major exclusion criteria included pre-hospital diagnosis of ST elevation myocardial infarction or an out of hospital cardiac arrest. The exposure variable was time of day and day of week stratified into 168 hourly time periods. The primary outcome measure was 30-day mortality.

Results

The study cohort comprised 196,365 ambulance attendances for acute non-traumatic chest pain; mean age 62.4 years (SD 18.3) and 99,497 (50.7%) females. Three temporal patterns were observed for chest pain presentations (Figure 1): (1) a diurnal pattern with a sharp increase in presentations from 8 am, peaking around midday, before decreasing into late evening with a nadir between 3–4 am, (2) a weekend effect where Saturday and Sunday had a relatively lower rate of presentations compared to during the week, and (3) a Monday – Sunday gradient where more presentations were likely earlier in the week, than later. Six patterns were identified across pre-hospital and hospital key performance indicators (KPI) (diurnal, in/after-hours, weekend effect, Monday – Sunday gradient, a peak period and morning vs afternoon/evening effect. Risk of 30-day mortality was associated with weekend presentation (OR 1.15, 95% CI 1.06–1.24, p=0.001) and morning presentation between midnight and midday (OR 1.17, 95% CI 1.09–1.25, p&lt;0.001) (Figure 2).

Conclusion

Chest pain presentations, care quality and outcomes demonstrate complex temporal variation beyond the already established weekend and after-hours effect. Such relationships should be considered during resource allocation and quality improvement programs in order to improve treatment quality across all days and times of the week.

Funding Acknowledgement

Type of funding sources: None.

Does tamsulosin decrease postoperative urinary retention in spine surgery? A double-blind, randomized controlled trial

OBJECTIVE

The authors' objective was to determine whether preoperative administration of tamsulosin decreases postoperative urinary retention after spine surgery.

METHODS

In this randomized, double-blind, placebo-controlled clinical trial performed at a single institution between 2016 and 2019, eligible males aged 50 to 85 years were administered tamsulosin or placebo for 5 days prior to elective spine surgery. Patients were excluded if they were taking alpha adrenergic blocking drugs; were allergic to tamsulosin, lactose, or sulfa drugs; had a preexisting indwelling urinary catheter, orthostatic hypotension, history of urological surgery, or renal failure; or were scheduled for cataract surgery within 2 weeks. Screening identified 1051 eligible patients (140 declined participation, 150 did not meet the inclusion criteria, and 151 did not enroll for other reasons). A total of 610 patients were randomly assigned to receive 0.4 mg oral tamsulosin or an identical placebo capsule for 5 days preoperatively and 2 days postoperatively.

RESULTS

A total of 497 patients were included in the final statistical analysis. The overall rate of postoperative urinary retention was 9.7%, and tamsulosin had no observed effect on reducing the rate of postoperative urinary retention as compared with placebo (9.4% vs 9.9%, p = 0.96). There were no significant differences in the reported adverse events between groups. Multivariate logistic regression was performed to model the effects of patient, surgical, and anesthetic factors on postoperative urinary retention, and the study drug remained an insignificant factor.

CONCLUSIONS

This study did not detect an effect of perioperative tamsulosin on reducing the rate of postoperative urinary retention in male patients aged 50 to 85 years who underwent elective spine surgery. This study does not support the routine use of tamsulosin to reduce postoperative urinary retention in patients without a previous prescription. It is unknown if subpopulations exist for which prophylactic tamsulosin may reduce postoperative urinary retention.

Capacity Building for a New Multicenter Network Within the ECHO IDeA States Pediatric Clinical Trials Network

Introduction: Research capacity building is a critical component of professional development for pediatrician scientists, yet this process has been elusive in the literature. The ECHO IDeA States Pediatric Clinical Trials Network (ISPCTN) seeks to implement pediatric trials across medically underserved and rural populations. A key component of achieving this objective is building pediatric research capacity, including enhancement of infrastructure and faculty development. This article presents findings from a site assessment inventory completed during the initial year of the ISPCTN. Methods: An assessment inventory was developed for surveying ISPCTN sites. The inventory captured site-level activities designed to increase clinical trial research capacity for pediatrician scientists and team members. The inventory findings were utilized by the ISPCTN Data Coordinating and Operations Center to construct training modules covering 3 broad domains: Faculty/coordinator development; Infrastructure; Trials/Research concept development. Results: Key lessons learned reveal substantial participation in the training modules, the importance of an inventory to guide the development of trainings, and recognizing local barriers to clinical trials research. Conclusions: Research networks that seek to implement successfully completed trials need to build capacity across and within the sites engaged. Our findings indicate that building research capacity is a multi-faceted endeavor, but likely necessary for sustainability of a unique network addressing high impact pediatric health problems. The ISPCTN emphasis on building and enhancing site capacity, including pediatrician scientists and team members, is critical to successful trial implementation/completion and the production of findings that enhance the lives of children and families.

Team Science Process Builds Research Coordinators' Voices in a National Pediatric Clinical Trials Network

Geographically-dispersed teams have become the norm in clinical research collaborations. The Institutional Development Awards (IDeA) Program, first authorized by Congress in 1993 and managed by the National Institute of General Medical Sciences, has been developed for the purpose of broadening the geographic distribution of National Institutes of Health (NIH) funding for biomedical and behavioral research by enhancing the competitiveness for research funding of institutions located in states in which the aggregate success rate for grant applications to the NIH has historically been low. The IDeA States are composed of the Commonwealth of Puerto Rico and the following 23 states: Alaska, Arkansas, Delaware, Hawaii, Idaho, Kansas, Kentucky, Louisiana, Maine, Mississippi, Montana, Nebraska, Nevada, New Hampshire, New Mexico, North Dakota, Oklahoma, Rhode Island, South Carolina, South Dakota, Vermont, West Virginia, Wyoming. The Environmental influences on Child Health Outcomes (ECHO) research program's IDeA States Pediatric Clinical Trials Network (ISPCTN) was formed in 2016 with 24 sites within the IDeA states to provide clinical trial access to children in rural and underserved communities while building research capacity and infrastructure. In order to become effective, the network research coordinators used many methods to become more cohesive and productive. One of those methods was the use of Team Science.

Training as an Intervention to Decrease Medical Record Abstraction Errors Multicenter Studies

Studies often rely on medical record abstraction as a major source of data. However, data quality from medical record abstraction has long been questioned. Electronic Health Records (EHRs) potentially add variability to the abstraction process due to the complexity of navigating and locating study data within these systems. We report training for and initial quality assessment of medical record abstraction for a clinical study conducted by the IDeA States Pediatric Clinical Trials Network (ISPCTN) and the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Neonatal Research Network (NRN) using medical record abstraction as the primary data source. As part of overall quality assurance, study-specific training for medical record abstractors was developed and deployed during study start-up. The training consisted of a didactic session with an example case abstraction and an independent abstraction of two standardized cases. Sixty-nine site abstractors from thirty sites were trained. The training was designed to achieve an error rate for each abstractor of no greater than 4.93% with a mean of 2.53%, at study initiation. Twenty-three percent of the trainees exceeded the acceptance limit on one or both of the training test cases, supporting the need for such training. We describe lessons learned in the design and operationalization of the study-specific, medical record abstraction training program.

Mitral paravalvular leak closure by antegrade percutaneous approach using amplatzer PFO closure device

Percutaneous closure of paravalvular leaks is becoming a more widely practiced technique. We describe the technique we used to deploy an Amplatzer PFO closure device to treat a prosthetic mitral paravalvular leak. The procedure was performed under real time 3D trans-oesophageal echo and fluoroscopic guidance requiring a trans-septal puncture and utilising an 035″ Safari wire which was developed for TAVR implantation. An excellent result was achieved acutely and at 4 month follow-up. © 2016 Wiley Periodicals, Inc.

Evaluation of chlorine dioxide based product as a hatchery sanitizer

Formaldehyde is commonly used to overcome contaminants introduced by hatching eggs or water supply in the hatcher cabinets. However, health risks associated with its use make economical alternatives important. This project evaluated a chlorine dioxide based product (CDBP) (0.3% concentrate) as a hatchery sanitizer in decontaminating microbial populations on the shell surface of hatching eggs (>18 d old), as well as its impact on hatchability and chick performance. Hatchers (0.20 m2) designed to hold approximately 50 eggs and equipped with circulation fans, heaters, and thermostats were used for the evaluation. For each of the 2 trials conducted, 450 hatching eggs were obtained and incubated in a common setter. Eggs used in trial 1 were floor eggs whereas in trial 2 nest eggs were used. On d 18 of incubation, eggs were removed from the setter, and viable eggs were randomly allocated to 9 hatchers. Pre-treatment egg rinse samples (10 eggs per hatcher) were collected for initial microbial analysis. Three hatchers were treated with CDBP and 3 hatchers with a formaldehyde based product (FBP). Three untreated hatchers served as control (C). Prior to hatch, 10 eggs/incubator, not previously rinsed, were used for post treatment microbial counts. The hatched chicks were reared until d 21 in floor pens with a common starter diet. For the CDBP treated eggs, hatchability and chick performance (weight gains, mortality, and FCR on d 7 and d 21) were similar to the other treatments. The application rate of CDBP evaluated in this study was not an effective antimicrobial alternative to formaldehyde for sanitizing hatching eggs in hatcher cabinets prior to hatch.

Use of information and communication technology amongst New Zealand dental students

Although international studies have shown an increasing use of information and communication technology (ICT) amongst dental students, there are no published studies specific to New Zealand (NZ). The aim of this research was to identify device ownership and academic utilisation patterns amongst New Zealand dental students, including preferences and perceptions, and barriers to use. All currently enrolled dental students (322) were invited to complete a 15-item questionnaire. Data were statistically analysed in SPSS version 20.0. Qualitative data were analysed using a general inductive technique. The participation rate was 78.6% (N = 253 of 322). The majority of respondents personally owned laptop computers (98%) and smartphones (80.2%). A total of 10.8% of participants used a desktop computer everyday for academic purposes, whilst 78.7% used a laptop computer daily, and 54.7% a smartphone. New Zealand dental students demonstrated a high usage of ICT for their coursework with varied use of different online resources. The most frequently used online resources were search engines, social networking sites and lecture slides provided on Blackboard(®) . A high perceived value was placed on both audio podcasts and video podcasts despite the high value also placed on the traditional lectures. Although most participants (84.5%) felt that their ICT knowledge was adequate to meet academic requirements, a small number (1.6%) did not agree.

Role of nutritional status and intervention in oesophageal cancer treated with definitive chemoradiotherapy: outcomes from SCOPE1

BACKGROUND

Malnutrition is common in oesophageal cancer. We aimed to identify nutritional prognostic factors and survival outcomes associated with nutritional intervention in the SCOPE1 (Study of Chemoradiotherapy in OesoPhageal Cancer with or without Erbitux) trial.

METHODS

Two hundred and fifty eight patients were randomly allocated to definitive chemoradiotherapy (dCRT) +/- cetuximab. Nutritional Risk Index (NRI) scores were calculated; NRI<100 identified patients at risk of malnutrition. Nutritional intervention included dietary advice, oral supplementation or major intervention (enteral feeding/tube placement). Univariable and multivariable analyses using Cox proportional hazard modelling were conducted.

RESULTS

At baseline NRI<100 strongly predicted for reduced overall survival (hazard ratio (HR) 12.45, 95% CI 5.24-29.57; P<0.001). Nutritional intervention improved survival if provided at baseline (dietary advice (HR 0.12, P=0.004), oral supplementation (HR 0.13, P<0.001) or major intervention (HR 0.13, P=0.003)), but not if provided later in the treatment course. Cetuximab patients receiving major nutritional intervention had worse outcomes compared with controls (13 vs 28 months, P=0.003).

CONCLUSIONS

Pre-treatment assessment and correction of malnutrition may improve survival outcomes in oesophageal cancer patients treated with dCRT. Nutritional Risk Index is a simple and objective screening tool to identify patients at risk of malnutrition.

Comparison of the Mechanism of Toxicity of 3′-Azido-3′-Deoxythymidine and 3′-Fluoro-3′-Deoxythymidine in Human Lymphocytes

The thymidine analogue 3′-azido-3′-deoxythymidine (AZT), whilst a useful drug for the treatment of acquired immunodeficiency syndrome, produces toxic side-effects which can be severe and can interfere with therapy. The toxic mechanism of AZT is unknown. We have investigated the relationship between the phosphorylation and effect on natural dNTP pools of 3′-azido-3′-deoxythymidine and the closely related 3′-fluoro-3′-deoxythymidine and their toxicity in human lymphocytes. We attempted to reduce the toxicity by co-administration of natural nucleosides.

The toxicity of 3′-fluoro-3′-deoxythymidine could be reduced with thymidine or deoxyuridine five- and 10-fold, respectively. The toxicity of 3′-azido-3′-deoxythymidine could be reduced twofold with cytidine or uridine but was increased by all other nucleosides, including thymidine. Neither analogue caused significant changes in the dNTP pools at cytotoxic concentrations; the effect of the nucleosides in reducing toxicity was not owing to replacement of a depleted dNTP. Thymidine reduced the phosphorylation of 3′-azido-3′-deoxythymidine and 3′-fluoro-3′-deoxythymidine 6 and 17 times, respectively.

3′-azido-3′-deoxythymidine and 3′-fluoro-3′-deoxythymidine appear to have different mechanisms of toxicity. The toxic mechanism of 3′-fluoro-3′-deoxythymidine is probably inhibition of cellular DNA synthesis by the triphosphate. The toxicity of 3′-azido-3′-deoxythymidine in lymphocytes does not appear to be directly related to the amounts of the phosphorylated forms. The mechanism may be interference with RNA metabolism or precursors, perhaps by the nucleoside.

Intracellular Metabolism of 3′-Azido-3′-Deoxythymidine in the Presence of Ganciclovir or Foscarnet

Comparisons were made between the intracellular phosphorylation of 3′-Azido-3′-deoxythymidine (AZT) alone and in combination with ganciclovir (GCV) or foscarnet (PFA) in lymphocytes, uninfected fibroblasts and CMV-infected fibroblasts. The effects of AZT and the combinations of AZT with GCV or PFA on cellular dNTP pools were also examined. The phosphorylation of AZT was not altered by the presence of GCV or PFA in lymphocytes, and neither AZT nor the combinations of AZT with GCV or PFA changed the levels of cellular dNTP pools in these cells. AZT was phosphorylated to a greater extent in lymphocytes when compared to fibroblasts, but the proportion of AZT di- and triphosphates was greater in fibroblasts. The infection of fibroblasts with CMV enhanced AZT phosphorylation and increased the levels of cellular dNTP pools. GCV caused a specific reduction in AZT phosphorylation in CMV-infected fibroblasts, with a seven-fold drop in AZT triphosphate compared to AZT alone. GCV did not affect AZT phosphorylation in uninfected fibroblasts, nor did GCV reduce the dTTP pool compared to AZT alone. The effects of GCV upon AZT phosphorylation in CMV-infected cells may shed light on the antagonistic effects of GCV upon the anti-HIV activity of AZT, and are of importance for the development of effective combination therapies for the treatment of AIDS patients infected with CMV.

Studies on the Reversal of Azidothymidine Toxicity in Human Lymphocytes by Cytidine and Uridine

The toxicity of 3′-azidothymidine (AZT) in human lymphocytes has been shown previously to be reversed by co-incubation with the ribonucleosides cytidine or uridine. In the present paper, the effects of 3′-azidothymidine and cytidine/uridine, both alone and in combination, were studied upon key processes in lymphocytes in order to discover more about the mechanism of toxicity reversal.

In these experiments 3′-azidothymidine had only minor effects on the ribonucleoside triphosphate pools. Cytidine increased the CTP pool, and uridine the UTP pool. Co-incubation with AZT caused similar changes to incubation with cytidine or uridine alone. Toxicity reversal was not linked to replacement of deficient ribonucleoside triphosphate pools.

3′-Azidothymidine caused the excretion of thymidine from lymphocytes. Incubation with cytidine and uridine increased the intracellular cytidine and uridine pools, respectively. Co-incubation with 3′-azidothymidine increased still further the intracellular cytidine and uridine pools. Cytidine and uridine did not affect the intracellular 3′-azidothymidine pool.

The toxicity of 3′-azidothymidine was increased by co-incubation with the bases adenine, guanine, hypoxanthine, and uracil, but not by dihydrouracil, thymine, or xanthine.