Similar Frequency and Inducibility of Intact Human Immunodeficiency Virus-1 Proviruses in Blood and Lymph Nodes

BACKGROUND

The human immunodeficiency virus (HIV)-1 latent reservoir (LR) in resting CD4+ T cells is a barrier to cure. LR measurements are commonly performed on blood samples and therefore may miss latently infected cells residing in tissues, including lymph nodes.

METHODS

We determined the frequency of intact HIV-1 proviruses and proviral inducibility in matched peripheral blood (PB) and lymph node (LN) samples from 10 HIV-1-infected patients on antiretroviral therapy (ART) using the intact proviral DNA assay and a novel quantitative viral induction assay. Prominent viral sequences from induced viral RNA were characterized using a next-generation sequencing assay.

RESULTS

The frequencies of CD4+ T cells with intact proviruses were not significantly different in PB versus LN (61/106 vs 104/106 CD4+ cells), and they were substantially lower than frequencies of CD4+ T cells with defective proviruses. The frequencies of CD4+ T cells induced to produce high levels of viral RNA were not significantly different in PB versus LN (4.3/106 vs 7.9/106), but they were 14-fold lower than the frequencies of cells with intact proviruses. Sequencing of HIV-1 RNA from induced proviruses revealed comparable sequences in paired PB and LN samples.

CONCLUSIONS

These results further support the use of PB as an appropriate proxy for the HIV-1 LR in secondary lymphoid organs.

Antiretroviral Adherence, Elevated Viral Load, and Drug Resistance Mutations in Human Immunodeficiency Virus-infected Women Initiating Treatment in Pregnancy: A Nested Case-control Study

BACKGROUND

Elevated viral load (VL) early after antiretroviral therapy (ART) initiation appears frequently in pregnant and postpartum women living with human immunodeficiency virus; however the relative contributions of pre-ART drug resistance mutations (DRMs) vs nonadherence in the etiology of elevated VL are unknown.

METHODS

Within a cohort of women initiating ART during pregnancy in Cape Town, South Africa, we compared women with elevated VL after initial suppression (cases, n = 80) incidence-density matched to women who maintained suppression over time (controls, n = 87). Groups were compared on pre-ART DRMs and detection of antiretrovirals in stored plasma.

RESULTS

The prevalence of pre-ART DRMs was 10% in cases and 5% in controls (adjusted odds ratio [aOR], 1.53 [95% confidence interval {CI}, .4-5.9]); all mutations were to nonnucleoside reverse transcriptase inhibitors. At the time of elevated VL, 19% of cases had antiretrovirals detected in plasma, compared with 87% of controls who were suppressed at a matched time point (aOR, 131.43 [95% CI, 32.8-527.4]). Based on these findings, we estimate that <10% of all elevated VL in the cohort may be attributable to pre-ART DRMs vs >90% attributable to ART nonadherence.

CONCLUSIONS

DRMs account for a small proportion of all elevated VL among women occurring in the 12 months after ART initiation during pregnancy in this setting, with nonadherence appearing to drive most episodes of elevated VL. Alongside the drive for access to more robust antiretroviral agents in resource-limited settings, there is an ongoing need for effective strategies to support ART adherence in this patient population.

A15 Archived ART resistance in the latent reservoir of virally suppressed Ugandans

The increased access of antiretroviral therapy (ART) has drastically improved the health of infected individuals. However, increased levels of ART resistance globally threaten ART effectiveness. Resistance monitoring is currently limited to viremic individuals or prior to ART initiation. The archival nature of the HIV latent reservoir (LR) of virally suppressed patients allows examination for the persistence of ART-resistant latent viral variants. Whole blood samples were collected longitudinally in Rakai, Uganda, from 70 virally suppressed HIV-1 infected individuals. The quantitative viral outgrowth assay was performed to measure the frequency of replication-competent latently infected resting-memory CD4 + (rCD4) T-cells. RNA was extracted from HIV p24-positive outgrowth supernatant, and the reverse transcriptase (RT) region was sequenced using a validated site-specific next-generation sequencing assay (Illumina, San Diego, CA). Consensus sequences containing >2.5 per cent of the total raw amplicons of each outgrowth well were analyzed for ART drug resistance mutations using the Stanford Database. The presence of clonal sequence is expressed as both percent clonality and Shannon Entropy. Replication-competent virus was cultured from 52/70 (74.3%) individuals, of which, RT-pol sequence data were obtained from 49/52 (94.3%) individuals. The presence of ART-resistant virus was found in the LR from one individual on second-line therapy that included a protease inhibitor. There were 20 and 44 total prominent consensus sequences from all wells at years 1 and 3 of follow-up, respectively. ART-resistant mutations for both RT-inhibitor drug classes were found in 30 per cent and 27.3 per cent of the total prominent consensus sequences of this one individual from years 1 and 3, respectively. The major ART resistance profile in this individual included: M184V, Y188L, K191E, and G190A. The percentage of total outgrowth that was clonal (percent clonality) increased from year 1 to year 3 (38.1–81.8%) and Shannon Entropy decreased (0.722–0.576). The presence of archived replication-competent ART-resistant virus in the LR was found in only one individual. There were two ART-resistant prominent consensus sequences isolated at year 3 that were not sampled 2 years earlier. The persistence of resistant, intact replication-competent proviral sequences in the LR of this individual seem to be supported by clonal expansion.

Quantitation of the latent HIV-1 reservoir from the sequence diversity in viral outgrowth assays

BACKGROUND

The ability of HIV-1 to integrate into the genomes of quiescent host immune cells, establishing a long-lived latent viral reservoir (LVR), is the primary obstacle to curing these infections. Quantitative viral outgrowth assays (QVOAs) are the gold standard for estimating the size of the replication-competent HIV-1 LVR, measured by the number of infectious units per million (IUPM) cells. QVOAs are time-consuming because they rely on culturing replicate wells to amplify the production of virus antigen or nucleic acid to reproducibly detectable levels. Sequence analysis can reduce the required number of culture wells because the virus genetic diversity within the LVR provides an internal replication and dilution series. Here we develop a Bayesian method to jointly estimate the IUPM and variant frequencies (a measure of clonality) from the sequence diversity of QVOAs.

RESULTS

Using simulation experiments, we find our Bayesian approach confers significantly greater accuracy over current methods to estimate the IUPM, particularly for reduced numbers of QVOA replicates and/or increasing actual IUPM. Furthermore, we determine that the improvement in accuracy is greater with increasing genetic diversity in the sample population. We contrast results of these different methods applied to new HIV-1 sequence data derived from QVOAs from two individuals with suppressed viral loads from the Rakai Health Sciences Program in Uganda.

CONCLUSIONS

Utilizing sequence variation has the additional benefit of providing information on the contribution of clonality of the LVR, where high clonality (the predominance of a single genetic variant) suggests a role for cell division in the long-term persistence of the reservoir. In addition, our Bayesian approach can be adapted to other limiting dilution assays where positive outcomes can be partitioned by their genetic heterogeneity, such as immune cell populations and other viruses.

The Effectiveness of a Family-Centered Childhood Obesity Intervention at the YMCA: A Pilot Study

Objective

Community-based, family-centered obesity prevention/treatment initiatives have been shown to be effective in reducing body mass index (BMI) and improving healthy habits in children if implemented with high intensity and sufficient duration. Let's Go! 5-2-1-0 Program (5-2-1-0) was incorporated into family-centered, monthly physical activity classes and cooking classes over six months delivered by Young Men's Christian Association (YMCA) staff. We hypothesized that implementation of this intervention would improve 5-2-1-0 knowledge attainment, increase healthy behavior (based on 5- 2-1-0 curriculum), and improve BMI and waist circumference measurements in children.

Methods

Children attending YMCA summer camps in Rochester, MN, during 2016 were recruited via study packets mailed to their families. Height, weight, and waist circumference measurements as well as the results of the Modified Healthy Habits Survey and the 5-2-1-0 Knowledge Acquisition Survey were recorded for each participating child at baseline and 6-month follow-up. The intervention group received monthly healthy habit reminder emails, and was invited to monthly evening cooking and physical activity classes for 7 sessions over a 6-month period.

Results

Fifteen families in the intervention group attended classes. Of those, 13 families regularly participated in (attended at least 5 out of 7) both the monthly physical activity and cooking classes. The children in the intervention group had a significant improvement in the number of Knowledge Acquisition Survey questions answered correctly (p<0.001), while there was no improvement in the control group. As compared to children in the control group, there was no significant change in BMI or waist circumference or healthy habits in the intervention group.

Conclusion

Our study findings indicate that our intervention resulted in improved knowledge about healthy habits, but did not significantly impact healthy habits or BMI. Potential reasons for this were the small sample size and the attenuated length and/or intensity of the intervention.

Short Communication: False Recent Ratio of the Limiting-Antigen Avidity Assay and Viral Load Testing Algorithm Among Cameroonians with Long-Term HIV Infection

Current serological assays that are used for cross-sectional HIV incidence estimation have been shown to misclassify individuals with chronic infection. Limited information exists on the performance of cross-sectional incidence assays in Central Africa. HIV-positive individuals from Cameroon who were infected for at least 1 or 2 years were evaluated to determine the false recent ratio (FRR) of a two-assay algorithm, which includes the Limiting Antigen Avidity (LAg-Avidity) assay (normalized optical density units, ODn <1.5) and HIV viral load (>1000 copies/ml). The subject-level FRR was 5.3% (95% confidence interval [CI], 2.1-10.5) for individuals infected for ≥1 year and 3.9% (95% CI, 0.8-11.0) for individuals infected for ≥2 years. These data suggest that the LAg-Avidity plus viral load incidence algorithm may overestimate HIV incidence rates in Central Africa.

Implementing Child-focused Activity Meter Utilization into the Elementary School Classroom Setting Using a Collaborative Community-based Approach

Introduction

The prevalence of pediatric obesity has increased over the past 3 decades and is a pressing public health program. New technology advancements that can encourage more physical in children are needed. The Zamzee program is an activity meter linked to a motivational website designed for children 8–14 years of age. The objective of the study was to use a collaborative approach between a medical center, the private sector and local school staff to assess the feasibility of using the Zamzee Program in the school-based setting to improve physical activity levels in children.

Methods

This was a pilot 8-week observational study offered to all children in one fifth grade classroom. Body mass index (BMI), the amount of physical activity by 3-day recall survey, and satisfaction with usability of the Zamzee Program were measured pre- and post-study.

Results

Out of 11 children who enrolled in the study, 7 completed all study activities. In those who completed the study, the median (interquartile range) total activity time by survey increased by 17 (1042) minutes and the BMI percentile change was 0 (8). Both children and their caregivers found the Zamzee Activity Meter (6/7) and website (6/7) “very easy” or “easy” to use.

Conclusion

The Zamzee Program was found to be usable but did not significantly improve physical activity levels or BMI. Collaborative obesity intervention projects involving medical centers, the private sector and local schools are feasible but the effectiveness needs to be evaluated in larger-scale studies.

Microfabricated silicon leak for sampling planetary atmospheres with a mass spectrometer

A microfabricated silicon mass spectrometer inlet leak has been designed, fabricated, and tested. This leak achieves a much lower conductance in a smaller volume than is possible with commonly available metal or glass capillary tubing. It will also be shown that it is possible to integrate significant additional functionality, such as inlet heaters and valves, into a silicon microleak with very little additional mass. The fabricated leak is compatible with high temperature (up to 500 degrees C) and high pressure (up to 100 bars) conditions, as would be encountered on a Venus atmospheric probe. These leaks behave in reasonable agreement with their theoretically calculated conductance, although this differs between devices and from the predicted value by as much as a factor of 2. This variation is believed to be the result of nonuniformity in the silicon etching process which is characterized in this work. Future versions of this device can compensate for characterized process variations in order to produce devices in closer agreement with designed conductance values. The integration of an inlet heater into the leak device has also been demonstrated in this work.

Effect of in vivo lymphocyte-depleting strategies on development of lymphoproliferative disorders in children post allogeneic bone marrow transplantation

T cell depletion (TCD) of marrow is a proven method of graft-versus-host disease (GVHD) prophylaxis in allogeneic bone marrow transplantation (BMT). Nonetheless, TCD is associated with an increased risk of developing post transplant lymphoproliferative disorder (PTLD). Between 1986 and 1998, 241 pediatric patients at the University of Iowa underwent BMT using ex vivo TCD of marrow from mismatched related or matched unrelated donors. Additional GVHD prophylaxis included antithymocyte globulin (ATG) or anti lymphocyte globulin (ALG) post transplant (in vivo TCD). A total of 30 cases of PTLD were identified based upon a combination of clinical, histological, and immunological features. Nearly all cases occurred within 3 months post BMT. A statistically significant increase in PTLD incidence was noted for patients treated with ATG vs ALG (33 vs 9%). While grade I-II acute GVHD was more common in patients receiving ATG vs ALG, no difference in grade III-IV GVHD or overall survival was noted between the two groups. Assessment of immune recovery at various times post BMT revealed significantly fewer T cells in the ATG-treated group, suggesting the deleterious effect of ATG may be due to excessive depletion of donor-derived Epstein-Barr virus-specific cytotoxic T cells. Thus, caution should be exercised in the use of anti-T-cell antibody therapy for additional GVHD prophylaxis in the setting of TCD BMT.

Expression and isolation of antimicrobial small molecules from soil DNA libraries

Natural products have been a critically important source of clinically relevant small molecule therapeutics. However, the discovery rate of novel structural classes of antimicrobial molecules has declined. Recently, increasing evidence has shown that the number of species cultivated from soil represents less than 1% of the total population, opening up the exciting possibility that these uncultured species may provide a large untapped pool from which novel natural products can be discovered. We have constructed and expressed in E. coli a BAC (bacterial artificial chromosome) library containing genomic fragments of DNA (5-120kb) isolated directly from soil organisms (S-DNA). Screening of the library resulted in the identification of several antimicrobial activities expressed by different recombinant clones. One clone (mg1.1) has been partially characterized and found to express several small molecules related to and including indirubin. These results show that genes involved in natural product synthesis can be cloned directly from S-DNA and expressed in a heterologous host, supporting the idea that this technology has the potential to provide novel natural products from the wealth of environmental microbial diversity and is a potentially important new tool for drug discovery.

Bone-targeted Src SH2 inhibitors block Src cellular activity and osteoclast-mediated resorption

Src, a nonreceptor tyrosine kinase, is an important regulator of osteoclast-mediated resorption. We have investigated whether compounds that bind to the Src SH2 domain inhibit Src activity in cells and decrease osteoclast-mediated resorption. Compounds were examined for binding to the Src SH2 domain in vitro using a fluorescence polarization binding assay. Experiments were carried out with compounds demonstrating in vitro binding activity (nmol/L range) to determine if they inhibit Src SH2 binding and Src function in cells, demonstrate blockade of Src signaling, and lack cellular toxicity. Cell-based assays included: (1) a mammalian two-hybrid assay; (2) morphological reversion and growth inhibition of cSrcY527F-transformed cells; and (3) inhibition of cortactin phosphorylation in csk-/- cells. The Src SH2 binding compounds inhibit Src activity in all three of these mechanism-based assays. The compounds described were synthesized to contain nonhydrolyzable phosphotyrosine mimics that bind to bone. These compounds were further tested and found to inhibit rabbit osteoclast-mediated resorption of dentine. These results indicate that compounds that bind to the Src SH2 domain can inhibit Src activity in cells and inhibit osteoclast-mediated resorption.

Structure-based design and solid-phase parallel synthesis of phosphorylated nonpeptides to explore hydrophobic binding at the Src SH2 domain

Using a novel, solid-phase parallel synthetic route and a computational docking program, a series of phosphorylated nonpeptides were generated to determine their structure-activity relationships (SAR) for binding at the SH2 domain of pp60src (Src). A functionalized benzoic acid intermediate was attached to solid support via Rink amide linkage, which upon acid cleavage generated the desired benzamide template-based nonpeptides in a facile manner. Compounds were synthesized using a combination of solid- and solution-phase techniques. Purification using reversed-phase, semipreparative HPLC allowed for quantitative SAR studies. Specifically, this work focused on functional group modifications, in a parallel fashion, designed to explore hydrophobic binding at the pY+3 pocket of the Src SH2 domain.

Cloning the soil metagenome: a strategy for accessing the genetic and functional diversity of uncultured microorganisms

Recent progress in molecular microbial ecology has revealed that traditional culturing methods fail to represent the scope of microbial diversity in nature, since only a small proportion of viable microorganisms in a sample are recovered by culturing techniques. To develop methods to investigate the full extent of microbial diversity, we used a bacterial artificial chromosome (BAC) vector to construct libraries of genomic DNA isolated directly from soil (termed metagenomic libraries). To date, we have constructed two such libraries, which contain more than 1 Gbp of DNA. Phylogenetic analysis of 16S rRNA gene sequences recovered from one of the libraries indicates that the BAC libraries contain DNA from a wide diversity of microbial phyla, including sequences from diverse taxa such as the low-G+C, gram-positive Acidobacterium, Cytophagales, and Proteobacteria. Initial screening of the libraries in Escherichia coli identified several clones that express heterologous genes from the inserts, confirming that the BAC vector can be used to maintain, express, and analyze environmental DNA. The phenotypes expressed by these clones include antibacterial, lipase, amylase, nuclease, and hemolytic activities. Metagenomic libraries are a powerful tool for exploring soil microbial diversity, providing access to the genetic information of uncultured soil microorganisms. Such libraries will be the basis of new initiatives to conduct genomic studies that link phylogenetic and functional information about the microbiota of environments dominated by microorganisms that are refractory to cultivation.

Simultaneous assay of Src SH3 and SH2 domain binding using different wavelength fluorescence polarization probes

pp60(c-src) is a prototypical nonreceptor tyrosine kinase and may play a role in diseases as diverse as cancer and osteoporosis. In Src, the SH3 domain (Src homology 3) binds proteins at specific, proline-rich sequences, while the SH2 domain (Src homology 2) binds phosphotyrosine-containing sequences. Inhibition of Src SH3 and SH2 domain function is of potential therapeutic value because of their importance in signaling pathways involved in disease states. We have developed dual-wavelength fluorescent peptide probes for both the Src SH3 and the Src SH2 domains, which allow the simultaneous measurement of compounds binding to each domain in assays based on the technique of fluorescence polarization. We demonstrate the utility of these probes in a dual-binding assay (suitable for high-throughput screening) to study the interactions of various peptides with these domains, including a sequence from the rat protein p130(CAS) which has been reported to bind simultaneously to both Src SH3 and SH2 domains. Utilizing this dual-binding assay, we confirm that sequences from p130(CAS) can simultaneously bind Src via both its SH3 and its SH2 domains. We also use the dual-binding assay as an internal control to identify substances which inhibit SH3 and SH2 binding via nonspecific mechanisms.

Discovery of potent and selective SH2 inhibitors of the tyrosine kinase ZAP-70

A series of 1,2,4-oxadiazole analogues has been shown to be potent and selective SH2 inhibitors of the tyrosine kinase ZAP-70, a potential therapeutic target for immune suppression. These compounds typically are 200-400-fold more potent than the native, monophosphorylated tetrapeptide sequences. When compared with the high-affinity zeta-1-ITAM peptide (Ac-NQL-pYNELNLGRREE-pYDVLD-NH(2), wherein pY refers to phosphotyrosine) some of the best 1,2, 4-oxadiazole analogues are approximately 1 order of magnitude less active. This series of compounds displays an unprecedented level of selectivity over the closely related tyrosine kinase Syk, as well as other SH2-containing proteins such as Src and Grb2. Gel shift studies using a protein construct consisting only of C-terminal ZAP-70 SH2 demonstrate that these compounds can effectively engage this particular SH2 domain.

Structure-activity relationships of a novel class of Src SH2 inhibitors

The structure-activity relationships (SAR) of a novel class of Src SH2 inhibitors are described. Variation at the pY+1 and pY+3 side chain positions using 2,4- and 2,5-substituted thiazoles and 1,2,4-oxadiazoles as scaffolds resulted in inhibitors that bound as well as the standard tetrapeptide Ac-pYEEI-NH2.

A fluorescence polarization based Src-SH2 binding assay

The tyrosine kinase pp60c.src has been implicated as being a potential therapeutic target in several human diseases including cancer and osteoporosis. An important region within this kinase is the SH2 domain (Src homology 2) which binds to phosphorylated tyrosine residues contained within specific peptide sequences. Homologous domains are found in a variety of cytoplasmic proteins and have been shown to be essential for controlling many important signaling pathways. Developing specific inhibitors of SH2 interactions would therefore be extremely useful for modulating a variety of signaling pathways and potentially be useful for the treatment of human disease. Current methodology for the development of organic molecules as drug leads requires the ability to test thousands of individual compounds or natural product extracts in biochemical assays. Such tests must be reproducible, simple, and versatile. This paper describes an assay based on fluorescence polarization for measuring the binding of compounds to the Src-SH2 domain. The assay is insensitive to changes in fluorescence intensity working even in solutions with moderate optical density and functions in the presence of up to 20% dimethyl sulfoxide. These features make it especially useful for high-throughput screening of both natural and synthetic compound libraries.

The fifth Datta Lecture. Structural similarities between the aspartate receptor of bacterial chemotaxis and the trp repressor of E. coli. Implications for transmembrane signaling

A high resolution structure of the N-terminal ligand-binding domain of the aspartate receptor which mediates aspartate chemotaxis in Salmonella typhimurium has recently been reported. A least-squares superposition of the alpha-amino nitrogen, alpha-carbon, beta-carbon, and alpha-carboxylate carbon of the aspartate bound to the aspartate receptor onto the equivalent atoms in the tryptophan bound to the trp repressor provides evidence for similarity between key parts of the active sites that bind to the alpha-amino and alpha-carboxylates of the respective ligands. Because the N-terminal domain of the aspartate receptor and the trp repressor also share other structural similarities, we hypothesize that the similarity between the aspartate receptor and the trp repressor derives from a similarity in ligand-induced conformational changes at the active sites of these proteins. This hypothesis also implies that an important signaling event in the aspartate receptor occurs through tertiary conformational changes within a single subunit.

Disulfide cross-linking studies of the transmembrane regions of the aspartate sensory receptor of Escherichia coli

The Escherichia coli aspartate receptor, a dimer of identical subunits, has two transmembrane regions (TM1, residues 7-30; TM2, residues 189-212) of 24 residues each. To study the relative placement and orientation of the regions, cysteine residues were introduced individually into the center of each: at positions 17, 18, and 19 in TM1; and at positions 198, 199, 200, and 201 in TM2. Based on the patterns of disulfide cross-linking observed between subunits in the mutant receptors, there appears to be close contact between the TM1 and TM1' regions at the dimer interface but no such direct interaction between the TM2 and TM2' regions. The cross-linking results are consistent with an alpha-helical structure extending across the transmembrane region up through at least residue 36, which lies on the periplasmic side of TM1. The ability of an 18-18' cross-linked dimer to transmit an aspartate-induced transmembrane signal is also supportive of such an extended helix. The changes in relative rates of disulfide cross-linking provide experimental evidence of a conformational change transmitted through the transmembrane domain during signaling. Once formed, disulfides between the transmembrane regions are unusually resistant to reduction by low molecular weight thiols in the presence of denaturants like SDS. These targeted disulfide cross-links can be used to reveal structural and dynamic aspects of protein function.

Effects of low protein diets or feed restriction on rat lung glutathione and oxygen toxicity

Male rats weighing 200-250 g were fed a 25% casein diet in restricted amounts or ad libitum or one of two low protein diets (3 and 0% casein) ad libitum. Decreased tolerance to hyperoxic stress was observed only in the rats fed low protein diets. These animals had a median death time of 49-50 h compared to 58-69 h for feed-restricted or normal control groups. Death was due to accelerated development of lung edema. Changes in total lung levels of glutathione reductase, glucose-6-phosphate dehydrogenase or catalase did not correlate with oxygen sensitivity. Lung glutathione levels were related to the amount of sulfur-containing amino acids in the diet and were depressed in the feed-restricted as well as the protein-restricted groups. However, feed restriction alone did not enhance oxygen toxicity. We conclude that a decrease in lung glutathione may be partially responsible for the increased oxygen sensitivity in the protein-deficient rats, but that other factors are necessary for explanation of the relative oxygen tolerance of the feed-restricted animals with reduced levels of glutathione in the lung.

Transient depletion of lung glutathione by diethylmaleate enhances oxygen toxicity

Diethylmaleate (DEM) decreases glutathione (GSH) levels in various organs by enzymatic conjugation with reduced GSH catalyzed by GSH transferase. We have examined levels of GSH, glutathione reductase (GR), and glucose-6-phosphate dehydrogenase (G6PD) in lungs of 200-250-g rats after intraperitoneal injection of 0.5 or 1 g DEM/kg body wt. The GSH levels are severely depressed at 2 and 4 h but have essentially recovered by 12 and 24 h after either dose of DEM. The GR and G6PD activities in the 1 g/kg group are depressed at 4 h to a lesser extent than the GSH levels and also return to normal by 12 and 24 h. These enzymes are not affected in the 0.5 g/kg group. To determine whether these transient decreases in GSH and related enzymes affected O2 tolerance, we exposed rats injected with DEM to greater than 98% O2 and found that halftime (t1/2) for survival was decreased in rats receiving both 0.5 and 1 g DEM/kg body wt when compared with untreated or saline-injected controls (t1/2 control, 74 h; 0.5 g DEM, 59 h; 1 g DEM, 53 h). No deaths occurred in air controls at 1 mg/kg DEM for up to 5 days. DEM, in itself, caused no morphological alteration of the lung. Thus a decrease in lung GSH and related enzymes, occurring by 4 h and reversed by 12 h, has a significant effect on the subsequent progression of lung pathology and indicates that early biochemical events occurring in lungs exposed to hyperoxia may be very important in determining the degree of longer-term damage to rat lungs.