Systemic inflammation and delirium during critical illness

PURPOSE

The purpose of this study was to determine associations between markers of inflammation and endogenous anticoagulant activity with delirium and coma during critical illness.

METHODS

In this prospective cohort study, we enrolled adults with respiratory failure and/or shock treated in medical or surgical intensive care units (ICUs) at 5 centers. Twice per day in the ICU, and daily thereafter, we assessed mental status using the Richmond Agitation Sedation Scale (RASS) and the Confusion Assessment Method-Intensive Care Unit (CAM-ICU). We collected blood samples on study days 1, 3, and 5, measuring levels of C-reactive protein (CRP), interferon gamma (IFN-γ), interleukin (IL)-1 beta (IL-1β), IL-6, IL-8, IL-10, IL-12, matrix metalloproteinase-9 (MMP-9), tumor necrosis factor-alpha (TNF-α), tumor necrosis factor receptor 1 (TNFR1), and protein C using validated protocols. We used multinomial logistic regression to analyze associations between biomarkers and the odds of delirium or coma versus normal mental status the following day, adjusting for age, sepsis, Sequential Organ Failure Assessment (SOFA), study day, corticosteroids, and sedatives.

RESULTS

Among 991 participants with a median age (interquartile range, IQR) of 62 [53-72] years and enrollment SOFA of 9 [7-11], higher concentrations of IL-6 (odds ratio [OR] [95% CI]: 1.8 [1.4-2.3]), IL-8 (1.3 [1.1-1.5]), IL-10 (1.5 [1.2-1.8]), TNF-α (1.2 [1.0-1.4]), and TNFR1 (1.3 [1.1-1.6]) and lower concentrations of protein C (0.7 [0.6-0.8])) were associated with delirium the following day. Higher concentrations of CRP (1.4 [1.1-1.7]), IFN-γ (1.3 [1.1-1.5]), IL-6 (2.3 [1.8-3.0]), IL-8 (1.8 [1.4-2.3]), and IL-10 (1.5 [1.2-2.0]) and lower concentrations of protein C (0.6 [0.5-0.8]) were associated with coma the following day. IL-1β, IL-12, and MMP-9 were not associated with mental status.

CONCLUSION

Markers of inflammation and possibly endogenous anticoagulant activity are associated with delirium and coma during critical illness.

Validation and utility of ARDS subphenotypes identified by machine-learning models using clinical data: an observational, multicohort, retrospective analysis

BACKGROUND

Two acute respiratory distress syndrome (ARDS) subphenotypes (hyperinflammatory and hypoinflammatory) with distinct clinical and biological features and differential treatment responses have been identified using latent class analysis (LCA) in seven individual cohorts. To facilitate bedside identification of subphenotypes, clinical classifier models using readily available clinical variables have been described in four randomised controlled trials. We aimed to assess the performance of these models in observational cohorts of ARDS.

METHODS

In this observational, multicohort, retrospective study, we validated two machine-learning clinical classifier models for assigning ARDS subphenotypes in two observational cohorts of patients with ARDS: Early Assessment of Renal and Lung Injury (EARLI; n=335) and Validating Acute Lung Injury Markers for Diagnosis (VALID; n=452), with LCA-derived subphenotypes as the gold standard. The primary model comprised only vital signs and laboratory variables, and the secondary model comprised all predictors in the primary model, with the addition of ventilatory variables and demographics. Model performance was assessed by calculating the area under the receiver operating characteristic curve (AUC) and calibration plots, and assigning subphenotypes using a probability cutoff value of 0·5 to determine sensitivity, specificity, and accuracy of the assignments. We also assessed the performance of the primary model in EARLI using data automatically extracted from an electronic health record (EHR; EHR-derived EARLI cohort). In Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure (LUNG SAFE; n=2813), a multinational, observational ARDS cohort, we applied a custom classifier model (with fewer variables than the primary model) to determine the prognostic value of the subphenotypes and tested their interaction with the positive end-expiratory pressure (PEEP) strategy, with 90-day mortality as the dependent variable.

FINDINGS

The primary clinical classifier model had an area under receiver operating characteristic curve (AUC) of 0·92 (95% CI 0·90-0·95) in EARLI and 0·88 (0·84-0·91) in VALID. Performance of the primary model was similar when using exclusively EHR-derived predictors compared with manually curated predictors (AUC=0·88 [95% CI 0·81-0·94] vs 0·92 [0·88-0·97]). In LUNG SAFE, 90-day mortality was higher in patients assigned the hyperinflammatory subphenotype than in those with the hypoinflammatory phenotype (414 [57%] of 725 vs 694 [33%] of 2088; p<0·0001). There was a significant treatment interaction with PEEP strategy and ARDS subphenotype (p=0·041), with lower 90-day mortality in the high PEEP group of patients with the hyperinflammatory subphenotype (hyperinflammatory subphenotype: 169 [54%] of 313 patients in the high PEEP group vs 127 [62%] of 205 patients in the low PEEP group; hypoinflammatory subphenotype: 231 [34%] of 675 patients in the high PEEP group vs 233 [32%] of 734 patients in the low PEEP group).

INTERPRETATION

Classifier models using clinical variables alone can accurately assign ARDS subphenotypes in observational cohorts. Application of these models can provide valuable prognostic information and could inform management strategies for personalised treatment, including application of PEEP, once prospectively validated.

FUNDING

US National Institutes of Health and European Society of Intensive Care Medicine.

Alveolar epithelial glycocalyx degradation mediates surfactant dysfunction and contributes to acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a common cause of respiratory failure yet has few pharmacologic therapies, reflecting the mechanistic heterogeneity of lung injury. We hypothesized that damage to the alveolar epithelial glycocalyx, a layer of glycosaminoglycans interposed between the epithelium and surfactant, contributes to lung injury in patients with ARDS. Using mass spectrometry of airspace fluid noninvasively collected from mechanically ventilated patients, we found that airspace glycosaminoglycan shedding (an index of glycocalyx degradation) occurred predominantly in patients with direct lung injury and was associated with duration of mechanical ventilation. Male patients had increased shedding, which correlated with airspace concentrations of matrix metalloproteinases. Selective epithelial glycocalyx degradation in mice was sufficient to induce surfactant dysfunction, a key characteristic of ARDS, leading to microatelectasis and decreased lung compliance. Rapid colorimetric quantification of airspace glycosaminoglycans was feasible and could provide point-of-care prognostic information to clinicians and/or be used for predictive enrichment in clinical trials.

Latent class analysis-derived subphenotypes are generalisable to observational cohorts of acute respiratory distress syndrome: a prospective study

RATIONALE

Using latent class analysis (LCA), two subphenotypes of acute respiratory distress syndrome (ARDS) have consistently been identified in five randomised controlled trials (RCTs), with distinct biological characteristics, divergent outcomes and differential treatment responses to randomised interventions. Their existence in unselected populations of ARDS remains unknown. We sought to identify subphenotypes in observational cohorts of ARDS using LCA.

METHODS

LCA was independently applied to patients with ARDS from two prospective observational cohorts of patients admitted to the intensive care unit, derived from the Validating Acute Lung Injury markers for Diagnosis (VALID) (n=624) and Early Assessment of Renal and Lung Injury (EARLI) (n=335) studies. Clinical and biological data were used as class-defining variables. To test for concordance with prior ARDS subphenotypes, the performance metrics of parsimonious classifier models (interleukin 8, bicarbonate, protein C and vasopressor-use), previously developed in RCTs, were evaluated in EARLI and VALID with LCA-derived subphenotypes as the gold-standard.

RESULTS

A 2-class model best fit the population in VALID (p=0.0010) and in EARLI (p<0.0001). Class 2 comprised 27% and 37% of the populations in VALID and EARLI, respectively. Consistent with the previously described 'hyperinflammatory' subphenotype, Class 2 was characterised by higher proinflammatory biomarkers, acidosis and increased shock and worse clinical outcomes. The similarities between these and prior RCT-derived subphenotypes were further substantiated by the performance of the parsimonious classifier models in both cohorts (area under the curves 0.92-0.94). The hyperinflammatory subphenotype was associated with increased prevalence of chronic liver disease and neutropenia and reduced incidence of chronic obstructive pulmonary disease. Measurement of novel biomarkers showed significantly higher levels of matrix metalloproteinase-8 and markers of endothelial injury in the hyperinflammatory subphenotype, whereas, matrix metalloproteinase-9 was significantly lower.

CONCLUSION

Previously described subphenotypes are generalisable to unselected populations of non-trauma ARDS.

Standardization of methods for sampling the distal airspace in mechanically ventilated patients using heat moisture exchange filter fluid

Noninvasive sampling of the distal airspace in patients with acute respiratory distress syndrome (ARDS) has long eluded clinical and translational researchers. We recently reported that fluid collected from heat moisture exchange (HME) filters closely mirrors fluid directly aspirated from the distal airspace. In the current study, we sought to determine fluid yield from different HME types, optimal HME circuit dwell time, and reliability of HME fluid in reflecting the distal airspace. We studied fluid yield from four different filter types by loading increasing volumes of saline and measuring volumes of fluid recovered. We collected filters after 1, 2, and 4 h of dwell time for measurement of fluid volume and total protein from 13 subjects. After identifying 4 h as the optimal dwell time, we measured total protein and IgM in HME fluid from 42 subjects with ARDS and nine with hydrostatic pulmonary edema (HYDRO). We found that the fluid yield varies greatly by filter type. With timed sample collection, fluid recovery increased with increasing circuit dwell time with a median volume of 2.0 mL [interquartile range (IQR) 1.2-2.7] after 4 h. Total protein was higher in the 42 subjects with ARDS compared with nine with HYDRO [median 708 µg/mL (IQR 244-2017) vs. 364 µg/mL (IQR 136-578), P = 0.047], confirming that total protein concentration in HME is higher in ARDS compared with hydrostatic edema. These studies establish a standardized HME fluid collection protocol and confirm that HME fluid analysis is a novel noninvasive tool for the study of the distal airspace in ARDS.

Inflammation and Coagulation during Critical Illness and Long-Term Cognitive Impairment and Disability

Rationale: The biological mechanisms of long-term cognitive impairment and disability after critical illness are unclear.Objectives: To test the hypothesis that markers of acute inflammation and coagulation are associated with subsequent long-term cognitive impairment and disability.Methods: We obtained plasma samples from adults with respiratory failure or shock on Study Days 1, 3, and 5 and measured concentrations of CRP (C-reactive protein), IFN-γ, IL-1β, IL-6, IL-8, IL-10, IL-12, MMP-9 (matrix metalloproteinase-9), TNF-α (tumor necrosis factor-α), soluble TNF receptor 1, and protein C. At 3 and 12 months after discharge, we assessed global cognition, executive function, and activities of daily living. We analyzed associations between markers and outcomes using multivariable regression, adjusting for age, sex, education, comorbidities, baseline cognition, doses of sedatives and opioids, stroke risk (in cognitive models), and baseline disability scores (in disability models).Measurements and Main Results: We included 548 participants who were a median (interquartile range) of 62 (53-72) years old, 88% of whom were mechanically ventilated, and who had an enrollment Sequential Organ Failure Assessment score of 9 (7-11). After adjusting for covariates, no markers were associated with long-term cognitive function. Two markers, CRP and MMP-9, were associated with greater disability in basic and instrumental activities of daily living at 3 and 12 months. No other markers were consistently associated with disability outcomes.Conclusions: Markers of systemic inflammation and coagulation measured early during critical illness are not associated with long-term cognitive outcomes and demonstrate inconsistent associations with disability outcomes. Future studies that pair longitudinal measurement of inflammation and related pathways throughout the course of critical illness and during recovery with long-term outcomes are needed.

Angiopoietin-2 outperforms other endothelial biomarkers associated with severe acute kidney injury in patients with severe sepsis and respiratory failure

BACKGROUND

Endothelial dysfunction and injury is a major pathophysiologic feature of sepsis. Sepsis is also the most frequent cause of acute kidney injury (AKI) in critically ill patients. Though most studies of AKI in sepsis have focused on tubular epithelial injury, the role of endothelial dysfunction and injury is less well studied. The goal of this study was first to investigate whether endothelial dysfunction and injury biomarkers were associated with severe AKI in sepsis patients. The second goal was to determine the best performing biomarker for severe AKI and whether this biomarker was associated with severe AKI across different etiologies of sepsis and clinical outcomes.

METHODS

We studied adults with severe sepsis and acute respiratory failure (ARF) enrolled in the prospective observational Validating Acute Lung Injury markers for Diagnosis (VALID) study. Plasma endothelial dysfunction and injury biomarkers, including angiopoietin-2, soluble vascular endothelial cadherin (sVE-cadherin), endocan and syndecan-1, were measured at study enrollment. Primary analysis focused on the association between endothelial biomarker levels with severe AKI (defined as Kidney Disease: Improving Global Outcomes [KDIGO] AKI stage 2 or 3), other organ dysfunctions (defined by Brussels organ failure scores), and comparison of pulmonary versus non-pulmonary sepsis.

RESULTS

Among 228 sepsis patients enrolled, 141 developed severe AKI. Plasma levels of angiopoietin-2, endocan, sVE-cadherin, and syndecan-1 were significantly higher in sepsis patients with severe AKI compared to those without severe AKI. Among four endothelial biomarkers, only angiopoietin-2 was independently associated with severe AKI (odds ratio 6.07 per log increase, 95% CI 2.34-15.78, p < 0.001). Plasma angiopoietin-2 levels by quartile were significantly higher in sepsis patients with hepatic, coagulation, and circulatory failure. Plasma angiopoietin-2 levels were also significantly higher in patients with non-pulmonary sepsis compared to subjects with pulmonary sepsis.

CONCLUSION

Among four biomarkers of endothelial dysfunction and injury, angiopoietin-2 had the most robust independent association with development of severe AKI in patients with severe sepsis and ARF. Plasma angiopoietin-2 levels were also associated with other organ dysfunctions, non-pulmonary sepsis, and death. These findings highlight the importance of early endothelial dysfunction and injury in the pathogenesis of sepsis-induced AKI.

Cell-free hemoglobin increases inflammation, lung apoptosis, and microvascular permeability in murine polymicrobial sepsis

Increased endothelial permeability is central to the pathogenesis of sepsis and leads to organ dysfunction and death but the endogenous mechanisms that drive increased endothelial permeability are not completely understood. We previously reported that cell-free hemoglobin (CFH), elevated in 80% of patients with sepsis, increases lung microvascular permeability in an ex vivo human lung model and cultured endothelial cells. In this study, we augmented a murine model of polymicrobial sepsis with elevated circulating CFH to test the hypothesis that CFH increases microvascular endothelial permeability by inducing endothelial apoptosis. Mice were treated with an intraperitoneal injection of cecal slurry with or without a single intravenous injection of CFH. Severity of illness, mortality, systemic and lung inflammation, endothelial injury and dysfunction and lung apoptosis were measured at selected time points. We found that CFH added to CS increased sepsis mortality, plasma inflammatory cytokines as well as lung apoptosis, edema and inflammation without affecting large vessel reactivity or vascular injury marker concentrations. These results suggest that CFH is an endogenous mediator of increased endothelial permeability and apoptosis in sepsis and may be a promising therapeutic target.

Plasma biomarkers of inflammation, coagulation, and brain injury as predictors of delirium duration in older hospitalized patients

Background

Delirium's pathophysiology is poorly understood. We sought to determine if plasma biomarkers of inflammation, coagulation, endothelial activation, and blood brain barrier (BBB) injury were associated with emergency department (ED) delirium duration.

Methods

We enrolled hospitalized patients who were 65 years or older from the ED. Plasma biomarkers of inflammation (interleukin-6 [IL-6], IL-8, soluble tumor necrosis factor receptor I [sTNFRI]), coagulation (Protein C), endothelial activation (plasminogen activating inhibitor-1 [PAI-1]), and BBB injury (S100B) at were measured using blood obtained at enrollment. The dependent variable was ED delirium duration which was determined by the Brief Confusion Assessment Method assessed in the ED and hospitalization. Proportional odds logistic regression analyses were performed adjusted for relevant confounders and allowing for interaction by baseline dementia status.

Results

A total of 156 patients were enrolled. IL-6 (POR = 1.59, 95%CI: 1.09–2.32) and PAI-1 (POR = 2.96, 95%CI: 1.48 to 6.85) were independently associated with more prominent ED delirium duration in subjects without dementia only. No significant associations between IL-8, Protein C, sTNRFI, and S100B and ED delirium duration were observed.

Conclusions

Plasma Biomarkers of systemic inflammation and endothelial activation are associated with ED delirium duration in older ED patients without dementia.

Association of neuronal repair biomarkers with delirium among survivors of critical illness

PURPOSE

Delirium is prevalent but with unclear pathogenesis. Neuronal injury repair pathways may be protective. We hypothesized that higher concentrations of neuronal repair biomarkers would be associated with decreased delirium in critically ill patients.

MATERIALS AND METHODS

We performed a nested study of hospital survivors within a prospective cohort that enrolled patients within 72 h of respiratory failure or shock. We measured plasma concentrations of ubiquitin carboxyl-terminal-esterase-L1 (UCHL1) and brain-derived neurotrophic factor (BDNF) from blood collected at enrollment. Delirium was assessed twice daily using the CAM-ICU. Multivariable regression was used to examine the associations between biomarkers and delirium prevalence/duration, adjusting for covariates and interactions with age and IL-6 plasma concentration.

RESULTS

We included 427 patients with a median age of 59 years (IQR 48-69) and APACHE II score of 25 (IQR 19-30). Higher plasma concentration of UCHL1 on admission was independently associated with lower prevalence of delirium (p = .04) but not associated with duration of delirium (p = .06). BDNF plasma concentration was not associated with prevalence (p = .26) or duration of delirium (p = .36).

CONCLUSIONS

During critical illness, higher UCHL1 plasma concentration is associated with lower prevalence of delirium; BDNF plasma concentration is not associated with delirium. Clinical trial number: NCT00392795; https://clinicaltrials.gov/ct2/show/NCT00392795.

Haptoglobin-2 variant increases susceptibility to acute respiratory distress syndrome during sepsis

Acute respiratory distress syndrome (ARDS) is an inflammatory lung disorder that frequently complicates critical illness and commonly occurs in sepsis. Although numerous clinical and environmental risk factors exist, not all patients with risk factors develop ARDS, raising the possibility of genetic underpinnings for ARDS susceptibility. We have previously reported that circulating cell-free hemoglobin (CFH) is elevated during sepsis, and higher levels predict worse outcomes. Excess CFH is rapidly scavenged by haptoglobin (Hp). A common HP genetic variant, HP2, is unique to humans and is common in many populations worldwide. HP2 haptoglobin has reduced ability to inhibit CFH-mediated inflammation and oxidative stress compared with the alternative HP1. We hypothesized that HP2 increases ARDS susceptibility during sepsis when plasma CFH levels are elevated. In a murine model of sepsis with elevated CFH, transgenic mice homozygous for Hp2 had increased lung inflammation, pulmonary vascular permeability, lung apoptosis, and mortality compared with wild-type mice. We then tested the clinical relevance of our findings in 496 septic critically ill adults, finding that HP2 increased ARDS susceptibility after controlling for clinical risk factors and plasma CFH. These observations identify HP2 as a potentially novel genetic ARDS risk factor during sepsis and may have important implications in the study and treatment of ARDS.

Novel Method for Noninvasive Sampling of the Distal Airspace in Acute Respiratory Distress Syndrome

RATIONALE

A major barrier to a more complete understanding of acute respiratory distress syndrome (ARDS) pathophysiology is the inability to sample the distal airspace of patients with ARDS. The heat moisture exchanger (HME) filter is an inline bacteriostatic sponge that collects exhaled moisture from the lungs of mechanically ventilated patients.

OBJECTIVES

To test the hypothesis that HME filter fluid (HMEF) represents the distal airspace fluid in patients with ARDS.

METHODS

Samples of HMEF were collected from 37 patients with acute pulmonary edema (either from ARDS or hydrostatic causes [HYDRO; control subjects]). Concurrent undiluted pulmonary edema fluid (EF) and HMEF were collected from six patients. HMEF from 11 patients (8 ARDS and 3 HYDRO) were analyzed by liquid chromatography-coupled tandem mass spectometry. Total protein (bicinchoninic acid assay), MMP-9 (matrix metalloproteinase-9), and MPO (myeloperoxidase) (ELISA) were measured in 29 subjects with ARDS and 5 subjects with HYDRO. SP-D (surfactant protein-D), RAGE (receptor for advanced glycation end-products) (ELISA), and cytokines (IL-1β, IL-6, IL-8, and tumor necrosis factor-α) (electrochemiluminescent assays) were measured in six concurrent HMEF and EF samples.

MEASUREMENTS AND MAIN RESULTS

Liquid chromatography-coupled tandem mass spectrometry on concurrent EF and HMEF samples from four patients revealed similar base peak intensities and m/z values indicating similar protein composition. There were 21 significantly elevated proteins in HMEF from patients with ARDS versus HYDRO. Eight proteins measured in concurrent EF and HMEF from six patients were highly correlated. In HMEF, total protein and MMP-9 were significantly higher in ARDS than in HYDRO.

CONCLUSIONS

These data suggest that HMEF is a novel, noninvasive method to accurately sample the distal airspace in patients with ARDS.

Vascular endothelial cadherin shedding is more severe in sepsis patients with severe acute kidney injury

BACKGROUND

Vascular endothelial cadherin (VE-cadherin) is a membrane protein that is the major component of adherens junctions between endothelial cells. It is crucial for regulating vascular integrity, endothelial permeability, and angiogenesis. During inflammatory processes, VE-cadherin is shed into circulation (sVE-cadherin). Plasma sVE-cadherin is elevated in sepsis, malignancy, autoimmune diseases, and coronary atherosclerosis. However, the relationship between specific organ failures, especially severe acute kidney injury (AKI) defined by requirement for renal replacement therapy (AKI-RRT), and plasma sVE-cadherin levels in severe sepsis has not been well studied.

METHODS

The present study is a prospective study of critically ill adults with sepsis and acute respiratory failure (age ≥ 18 years) enrolled in the Validating Acute Lung Injury markers for Diagnosis (VALID) study. Plasma sVE-cadherin was measured at study enrollment. Primary analysis focused on the association between sVE-cadherin levels and the development of AKI, AKI-RRT, other organ dysfunction as defined by Brussels organ failure scores, pulmonary versus non-pulmonary sepsis, acute respiratory distress syndrome (ARDS), and in-hospital mortality.

RESULTS

Of 228 severe sepsis patients included, 80 (35%) developed AKI-RRT. Plasma sVE-cadherin levels at enrollment were significantly higher in patients with AKI-RRT compared with patients without AKI-RRT (p = 0.003). Plasma sVE-cadherin levels by quartile were significantly higher in severe sepsis patients with acute kidney injury stage 3 (p = 0.044) as defined by Kidney Disease Improving Global Outcomes (KDIGO) criteria. Patients with greater than 2 organ failures had higher plasma sVE-cadherin levels than patients with 2 or fewer organ failures (p < 0.001). In a multivariable analysis, plasma sVE-cadherin was independently associated with AKI-RRT (odds ratio 6.44 per log increase in plasma sVE-cadherin, 95% CI 1.126-36.847, p = 0.036). Plasma sVE-cadherin levels were significantly higher in patients with non-pulmonary sepsis compared to pulmonary sepsis (p < 0.001).

CONCLUSION

Shedding of sVE-cadherin is associated with severe acute kidney injury and with more severe organ dysfunction in patients with sepsis, suggesting that breakdown of endothelial adherens junctions may contribute to the pathogenesis of organ dysfunction in sepsis. Further studies of sVE-cadherin as a biomarker of disease severity in clinical sepsis are needed to better elucidate the role of VE-cadherin shedding in sepsis-induced severe organ dysfunction.

Epithelial Heparan Sulfate Contributes to Alveolar Barrier Function and Is Shed during Lung Injury

The lung epithelial glycocalyx is a carbohydrate-enriched layer lining the pulmonary epithelial surface. Although epithelial glycocalyx visualization has been reported, its composition and function remain unknown. Using immunofluorescence and mass spectrometry, we identified heparan sulfate (HS) and chondroitin sulfate within the lung epithelial glycocalyx. In vivo selective enzymatic degradation of epithelial HS, but not chondroitin sulfate, increased lung permeability. Using mass spectrometry and gel electrophoresis approaches to determine the fate of epithelial HS during lung injury, we detected shedding of 20 saccharide-long or greater HS into BAL fluid in intratracheal LPS-treated mice. Furthermore, airspace HS in clinical samples from patients with acute respiratory distress syndrome correlated with indices of alveolar permeability, reflecting the clinical relevance of these findings. The length of HS shed during intratracheal LPS-induced injury (≥20 saccharides) suggests cleavage of the proteoglycan anchoring HS to the epithelial surface, rather than cleavage of HS itself. We used pharmacologic and transgenic animal approaches to determine that matrix metalloproteinases partially mediate HS shedding during intratracheal LPS-induced lung injury. Although there was a trend toward decreased alveolar permeability after treatment with the matrix metalloproteinase inhibitor, doxycycline, this did not reach statistical significance. These studies suggest that epithelial HS contributes to the lung epithelial barrier and its degradation is sufficient to increase lung permeability. The partial reduction of HS shedding achieved with doxycycline is not sufficient to rescue epithelial barrier function during intratracheal LPS-induced lung injury; however, whether complete attenuation of HS shedding is sufficient to rescue epithelial barrier function remains unknown.

Relationships between markers of neurologic and endothelial injury during critical illness and long-term cognitive impairment and disability

PURPOSE

Neurologic and endothelial injury biomarkers are associated with prolonged delirium during critical illness and may reflect injury pathways that lead to poor long-term outcomes. We hypothesized that blood-brain barrier (BBB), neuronal, and endothelial injury biomarkers measured during critical illness are associated with cognitive impairment and disability after discharge.

METHODS

We enrolled adults with respiratory failure and/or shock and measured plasma concentrations of BBB (S100B), neuronal (UCHL1, BDNF), and endothelial (E-selectin, PAI-1) injury markers within 72 h of ICU admission. At 3 and 12 months post-discharge, we assessed participants' global cognition, executive function, and activities of daily living (ADL). We used multivariable regression to determine whether biomarkers were associated with outcomes after adjusting for relevant demographic and acute illness covariates.

RESULTS

Our study included 419 survivors of critical illness with median age 59 years and APACHE II score 25. Higher S100B was associated with worse global cognition at 3 and 12 months (P = 0.008; P = 0.01). UCHL1 was nonlinearly associated with global cognition at 3 months (P = 0.02). Higher E-selectin was associated with worse global cognition (P = 0.006 at 3 months; P = 0.06 at 12 months). BDNF and PAI-1 were not associated with global cognition. No biomarkers were associated with executive function. Higher S100B (P = 0.05) and E-selectin (P = 0.02) were associated with increased disability in ADLs at 3 months.

CONCLUSIONS

S100B, a marker of BBB and/or astrocyte injury, and E-selectin, an adhesion molecule and marker of endothelial injury, are associated with long-term cognitive impairment after critical illness, findings that may reflect mechanisms of critical illness brain injury.

Cell-free hemoglobin promotes primary graft dysfunction through oxidative lung endothelial injury

Primary graft dysfunction (PGD) is acute lung injury within 72 hours of lung transplantation. We hypothesized that cell-free hemoglobin (CFH) contributes to PGD by increasing lung microvascular permeability and tested this in patients, ex vivo human lungs, and cultured human lung microvascular endothelial cells. In a nested case control study of 40 patients with severe PGD at 72 hours and 80 matched controls without PGD, elevated preoperative CFH was independently associated with increased PGD risk (odds ratio [OR] 2.75, 95%CI, 1.23-6.16, P = 0.014). The effect of CFH on PGD was magnified by reperfusion fraction of inspired oxygen (FiO2) ≥ 0.40 (OR 3.41, P = 0.031). Isolated perfused human lungs exposed to intravascular CFH (100 mg/dl) developed increased vascular permeability as measured by lung weight (CFH 14.4% vs. control 0.65%, P = 0.047) and extravasation of Evans blue-labeled albumin dye (EBD) into the airspace (P = 0.027). CFH (1 mg/dl) also increased paracellular permeability of human pulmonary microvascular endothelial cell monolayers (hPMVECs). Hyperoxia (FiO2 = 0.95) increased human lung and hPMVEC permeability compared with normoxia (FiO2 = 0.21). Treatment with acetaminophen (15 μg/ml), a specific hemoprotein reductant, prevented CFH-dependent permeability in human lungs (P = 0.046) and hPMVECs (P = 0.037). In summary, CFH may mediate PGD through oxidative effects on microvascular permeability, which are augmented by hyperoxia and abrogated by acetaminophen.

Oxygenation Saturation Index Predicts Clinical Outcomes in ARDS

BACKGROUND

Traditional measures of ARDS severity such as Pao₂/Fio₂ may not reliably predict clinical outcomes. The oxygenation index (OI [Fio₂ × mean airway pressure × 100)/Pao₂]) may more accurately reflect ARDS severity but requires arterial blood gas measurement. We hypothesized that the oxygenation saturation index (OSI [Fio₂ × mean airway pressure × 100)/oxygen saturation by pulse oximetry (Spo₂)]) is a reliable noninvasive surrogate for the OI that is associated with hospital mortality and ventilator-free days (VFDs) in patients with ARDS.

METHODS

Critically ill patients enrolled in a prospective cohort study were eligible if they developed ARDS (Berlin criteria) during the first 4 ICU days and had mean airway pressure, Spo₂/Fio₂, and Pao₂/Fio₂ values recorded on the first day of ARDS (N = 329). The highest mean airway pressure and lowest Spo₂/Fio₂ and Pao₂/Fio₂ values were used to calculate OI and OSI. The association between OI or OSI and hospital mortality or VFD was analyzed by using logistic regression and linear regression, respectively. The area under the receiver-operating characteristic curve (AUC) for mortality was compared among OI, OSI, Spo₂/Fio₂, Pao₂/Fio₂, and Acute Physiology and Chronic Health Evaluation II scores.

RESULTS

OI and OSI were strongly correlated (rho = 0.862; P < .001). OSI was independently associated with hospital mortality (OR per 5-point increase in OSI, 1.228 [95% CI, 1.056-1.429]; P = .008). OI and OSI were each associated with a reduction in VFD (OI, P = .023; OSI, P = .005). The AUC for mortality prediction was greatest for Acute Physiology and Chronic Health Evaluation II scores (AUC, 0.695; P < .005) and OSI (AUC, 0.602; P = .007). The AUC for OSI was substantially better in patients aged < 40 years (AUC, 0.779; P < .001).

CONCLUSIONS

In patients with ARDS, the OSI was correlated with the OI. The OSI on the day of ARDS diagnosis was significantly associated with increased mortality and fewer VFDs. The findings suggest that OSI is a reliable surrogate for OI that can noninvasively provide prognostic information and assessment of ARDS severity.

Endothelial glycocalyx degradation is more severe in patients with non-pulmonary sepsis compared to pulmonary sepsis and associates with risk of ARDS and other organ dysfunction

BACKGROUND

Disruption of the endothelial glycocalyx contributes to acute lung injury in experimental sepsis but has not been well studied in humans. To study glycocalyx degradation in sepsis-induced ARDS, we measured plasma levels of syndecan-1, a marker for glycocalyx degradation.

METHODS

The present study is a retrospective observational study of 262 ventilated medical ICU patients at risk of ARDS due to severe sepsis and APACHE II ≥ 25. Plasma syndecan-1 was measured at study enrollment. Primary analysis focused on the association between syndecan-1 levels and the development of ARDS, other organ dysfunction (Brussels criteria), or in-hospital mortality.

RESULTS

Overall, 135 (52%) patients developed ARDS. In patients with non-pulmonary sepsis, syndecan-1 levels were associated with ARDS (p = 0.05). Regardless of etiology of sepsis, higher syndecan-1 levels were associated with hepatic (p < 0.001), renal (p = 0.003), coagulation (p = 0.001), and circulatory (p = 0.02) failure as well as in-hospital mortality (p = 0.001), and there was a significant association between syndecan-1 levels and the number of vasopressors required in the first 24 h (p < 0.001). In addition, elevated syndecan levels were independently predictive of mortality in multivariable logistic regression adjusted for age and APACHE II score (odds ratio 1.85 per log increase in syndecan-1, 95% CI 1.056-3.241, p = 0.03).

CONCLUSION

The extent of endothelial glycocalyx degradation is associated with non-pulmonary organ dysfunction in subjects with sepsis and is associated with ARDS but only in the subgroup with non-pulmonary sepsis. Measurement of syndecan-1 levels in sepsis patients might be useful for identifying patients at high risk of organ dysfunction and mortality as well as those who could benefit from therapies targeted at protecting or restoring the glycocalyx.

Circulating microparticle levels are reduced in patients with ARDS

BACKGROUND

It is unclear how to identify which patients at risk for acute respiratory distress syndrome (ARDS) will develop this condition during critical illness. Elevated microparticle (MP) concentrations in the airspace during ARDS are associated with activation of coagulation and in vitro studies have demonstrated that MPs contribute to acute lung injury, but the significance of MPs in the circulation during ARDS has not been well studied. The goal of the present study was to test the hypothesis that elevated levels of circulating MPs could prospectively identify critically ill patients who will develop ARDS and that elevated circulating MPs are associated with poor clinical outcomes.

METHODS

A total of 280 patients with platelet-poor plasma samples from the prospective Validating Acute Lung Injury biomarkers for Diagnosis (VALID) cohort study were selected for this analysis. Demographics and clinical data were obtained by chart review. MP concentrations in plasma were measured at study enrollment on intensive care unit (ICU) day 2 and on ICU day 4 by MP capture assay. Activation of coagulation was measured by plasma recalcification (clot) times.

RESULTS

ARDS developed in 90 of 280 patients (32%) in the study. Elevated plasma MP concentrations were associated with reduced risk of developing ARDS (odds ratio (OR) 0.70 per 10 μM increase in MP concentration, 95% CI 0.50-0.98, p = 0.042), but had no significant effect on hospital mortality. MP concentration was greatest in patients with sepsis, pneumonia, or aspiration as compared with those with trauma or receiving multiple blood transfusions. MP levels did not significantly change over time. The inverse association of MP levels with ARDS development was most striking in patients with sepsis. After controlling for age, presence of sepsis, and severity of illness, higher MP concentrations were independently associated with a reduced risk of developing ARDS (OR 0.69, 95% CI 0.49-0.98, p = 0.038). MP concentration was associated with reduced plasma recalcification time.

CONCLUSIONS

Elevated levels of circulating MPs are independently associated with a reduced risk of ARDS in critically ill patients. Whether this is due to MP effects on systemic coagulation warrants further investigation.

Glycine metabolism in Candida albicans: characterization of the serine hydroxymethyltransferase (SHM1, SHM2) and threonine aldolase (GLY1) genes

Genes encoding the mitochondrial (SHM1) and cytosolic (SHM2) serine hydroxymethyltransferases, and the L-threonine aldolase gene (GLY1) from Candida albicans were cloned and sequenced. All three genes are involved in glycine metabolism. The C. albicans Shm1 protein is 82% identical to that from Saccharomyces cerevisiae and 56% identical to that from Homo sapiens. The corresponding identities for the Shm2 proteins are 68% and 53%. The Gly1 protein shares significant identity with the S. cerevisiae L-threonine aldolase (55%) and also with threonine aldolases from Aeromonas jandiae (36%) and Escherichia coli (36%). Genetic ablation experiments show that GLY1 is a non-essential gene in C. albicans and that L-threonine aldolase plays a lesser role in glycine metabolism than it does in S. cerevisiae. GenBank Accession Nos of the C. albicans SHM1 and SHM2 are AF009965 and AF009966, respectively. Accession No. for C. albicans GLY1 is AF009967.

Activated transcription independent of the RNA polymerase II holoenzyme in budding yeast

We investigated whether the multisubunit holoenzyme complex of RNA polymerase II (Pol II) and mediator is universally required for transcription in budding yeast. DeltaCTD Pol II lacking the carboxy-terminal domain of the large subunit cannot assemble with mediator but can still transcribe the CUP1 gene. CUP1 transcripts made by DeltaCTD Pol II initiated correctly and some extended past the normal poly(A) site yielding a novel dicistronic mRNA. Most CUP1 transcripts made by DeltaCTD Pol II were degraded but could be stabilized by deletion of the XRN1 gene. Unlike other genes, transcription of CUP1 and HSP82 also persisted after inactivation of the CTD kinase Kin28 or the mediator subunit Srb4. The upstream-activating sequence (UAS) of the CUP1 promoter was sufficient to drive Cu2+ inducible transcription without Srb4 and heat shock inducible transcription without the CTD. We conclude that the Pol II holoenzyme is not essential for all UAS-dependent activated transcription in yeast.

An unusual fibrillarin gene and protein: structure and functional implications

The diploid germinal nucleus of the ciliated protozoan Tetrahymena thermophila is unusual among eukaryotes in that it encodes a single copy of the gene for rRNA allowing identification of cis-acting mutations in rDNA affecting rRNA structure, function, and processing. The generally conserved nucleolar protein fibrillarin has been characterized from a number of systems and is involved in pre-rRNA processing. We have demonstrated that Tetrahymena has fibrillarin and have analyzed the cDNA and the genomic DNA encoding this protein. The derived amino acid sequence of the N-terminal region of Tetrahymena fibrillarin shows little similarity with the generally highly conserved glycine/arginine-rich N-terminal domain of other eukaryotic fibrillarins. The remainder of the amino acid sequence of the molecule is more conserved. Polyclonal antibodies generated against the full-length Tetrahymena fibrillarin expressed in bacteria recognize a protein of M(r) approximately 32,000 in whole-cell or nucleolar preparations. Immunocytochemistry localizes fibrillarin to nucleoli in the somatic macronuclei of vegetative cells. Transformation experiments demonstrate that fibrillarin is an essential protein in Tetrahymena. The Tetrahymena fibrillarin is expressed but does not complement a NOP1 null mutation when transformed into the yeast Saccharomyces cerevisiae, indicating less functional conservation among fibrillarins than previously suggested.

Identification of Saccharomyces cerevisiae GLY1 as a threonine aldolase: a key enzyme in glycine biosynthesis

Determination of enzyme-specific activities revealed that GLY1 encodes a threonine aldolase (TA) in Saccharomyces cerevisiae. A knock-out mutant auxotrophic for glycine lacked detectable activity. After transformation with YEp24GLY1 glycine prototrophy was restored and TA-specific activity was 16-fold higher than in the wild type. Growth experiments using glucose as the sole carbon source showed that GLY1 is more important for glycine biosynthesis than SHM1 and SHM2 encoding alternative serine hydroxymethyltransferases. On ethanol as carbon source simultaneous disruption of GLY1, SHM1 and SHM2 did not lead to glycine auxotrophy because glycine biosynthesis proceeds via alanine glyoxylate aminotransferase.

Cloning, and molecular characterization of the GCV1 gene encoding the glycine cleavage T-protein from Saccharomyces cerevisiae

We have isolated the gene encoding the glycine cleavage T-protein (GCV1) of the yeast Saccharomyces cerevisiae and shown through gene disruption and enzyme assays that inactivation of GCV1 destroys glycine cleavage function. A DNA fragment encoding the GCV1 gene was cloned by PCR amplification using degenerate oligodeoxyribonucleotides, and the cloned fragment was used as a probe to isolate the complete gene from a yeast genomic library. Growth with glycine stimulated expression of the GCV1 gene as determined by Northern analysis and increased the beta-galactosidase activity of a GCV1-lacZ fusion 30-fold. The URA3 gene was inserted into the coding sequence of GCV1 and the resulting construct was used to disrupt the chromosomal GCV1 gene in a diploid strain of yeast. gcv1::URA3 haploid derivatives grew normally or only slightly more slowly than the isogenic wild-type haploids. All gcv1 strains studied were unable to grow on glycine as a sole nitrogen source and lacked glycine cleavage enzyme activity. Growth of shm1 shm2 mutants was stimulated by glycine, whereas glycine could not supplement the growth of the isogenic gcv1 strain.

In vivo analysis of folate coenzymes and their compartmentation in Saccharomyces cerevisiae

In eukaryotes, enzymes responsible for the interconversion of one-carbon units exist in parallel in both mitochondria and the cytoplasm. Strains of Saccharomyces cerevisiae were constructed that possess combinations of gene disruptions at the SHM1 [mitochondrial serine hydroxymethyltransferase (SHMTm)], SHM2 [cytoplasmic SHMT (SHMTc)], MIS1 [mitochondrial C1-tetrahydrofolate synthase (C1-THFSm)], ADE3 [cytoplasmic C1-THF synthase (C1-THFSc)], GCV1 [glycine cleavage system (GCV) protein T], and the GLY1 (involved in glycine synthesis) loci. Analysis of the in vivo growth characteristics and phenotypes was used to determine the contribution to cytoplasmic nucleic acid and amino acid anabolism by the mitochondrial enzymes involved in the interconversion of folate coenzymes. The data indicate that mitochondria transport formate to the cytoplasmic compartment and mitochondrial synthesis of formate appears to rely primarily on SHMTm rather than the glycine cleavage system. The glycine cleavage system and SHMTm cooperate to specifically synthesize serine. With the inactivation of SHM1, however, the glycine cleavage system can make an observable contribution to the level of mitochondrial formate. Inactivation of SHM1, SHM2 and ADE3 is required to render yeast auxotrophic for TMP and methionine, suggesting that TMP synthesized in mitochondria may be available to the cytoplasmic compartment.

A simple in vivo footprinting method to examine DNA-protein interactions over the yeast PYK UAS element

In this report a modification to the in vivo footprinting assay is described. The method includes dimethyl sulfate treatment of whole yeast cells, followed by reiterative primer extension of the methylated genomic DNA using Taq DNA polymerase. Under appropriate reaction conditions chain extension terminates opposite a methylated purine when Taq DNA polymerase encounters a modified adenine or guanine. The procedure was used to examine, in vivo DNA-protein contacts over the upstream activation site (UAS) of the Saccharomyces cerevisiae PYK gene. In vivo analysis, using isogenic strains of yeast and Escherichia coli transformed with plasmid DNAs, confirmed the binding of both the trans-acting factor RAP1 and the transcriptional activator GCR1 to cis-acting recognition sites located within the PYK UAS element.

Cloning and molecular characterization of three genes, including two genes encoding serine hydroxymethyltransferases, whose inactivation is required to render yeast auxotrophic for glycine

The genes encoding both the cytosolic and mitochondrial serine hydroxymethyltransferases (SHM2 and SHM1, respectively) and a third unidentified gene of the yeast Saccharomyces cerevisiae have been isolated and their nucleotide sequences determined. Analysis of the predicted amino acid sequence of the amino-terminal regions, sequence comparison with other genes encoding SHMT enzymes, and subcellular fractionation studies all suggested that the SHM1 gene encodes the mitochondrial SHMT, while the SHM2 gene encodes the cytosolic enzyme. The SHM2 gene but not the SHM1 gene has putative GCN4 sites upstream of the putative TATA box, suggesting regulation of its transcription by the general amino acid control system. Yeast mutants with disruptions at each SHM gene and in both genes were constructed and all mutants had the same growth requirements as the parental strains. Mutagenesis of the double-disrupted, shm1 shm2 yeast yielded strains of a single complementation group that are auxotrophic for glycine. Complementation of the glycine auxotrophy using a yeast genomic library retrieved the SHM1 and SHM2 genes and a third gene designated GLY1. Gene disruption studies demonstrated that inactivation of SHM1, SHM2, and GLY1 is required to yield yeast that are completely auxotrophic for glycine.

The DNA-binding protein RAP1 is required for efficient transcriptional activation of the yeast PYK glycolytic gene

We show by deletion mutagenesis, followed by in vivo and in vitro analysis, that the binding of a protein factor to the upstream activation sequence (UAS) of the Saccharomyces cerevisiae glycolytic gene PYK, encoding pyruvate kinase, is required for efficient transcription of the corresponding coding region. In addition, gel electrophoretic mobility shift and DNase I protection studies, involving yeast gene products expressed in E. coli, suggest that this trans-acting DNA-binding protein is encoding by the RAP1 gene. The identification of RAP1 binding sites located within the UAS element of the yeast PYK, PGK (phosphoglycerate kinase) and ENO1 (enolase) genes, and in the 5'-upstream region of the ADHI (alcohol dehydrogenase) gene, suggests that a mechanism of coordinate gene expression involving several of the glycolytic genes may exist in yeast.

Functional characterization of a pyrimidine-rich element in the 5'-noncoding region of the yeast iso-1-cytochrome c gene

A predominantly pyrimidine-rich sequence (purine in the template strand, 32 of 37 bases) is located between a functional TATA element and the corresponding transcription start site region of the Saccharomyces cerevisiae iso-1-cytochrome c (CYC1) gene. By using linker deletions and gene fusion techniques, the functional characteristics of this pyrimidine sequence were examined. Results indicate that the function of this element is to limit the accumulation of full-length mRNAs with 5' ends which map upstream of the pyrimidine-rich sequence. Data suggest that the 5'-noncoding region of the CYC1 gene possesses signals for mRNA 3'-end processing.

Transcription initiation of the Saccharomyces cerevisiae iso-1-cytochrome c gene. Multiple, independent T-A-T-A sequences

The expression of the Saccharomyces cerevisiae CYC1 gene, which encodes iso-1-cytochrome c, produces a family of messenger RNAs whose 5' ends map in the region from position +7 to -93 relative to the first nucleotide at position +1 of the protein-coding DNA sequence. The mechanism of transcription initiation of the CYC1 gene has been examined by using linker-scanning deletions and gene fusions. The various CYC1 derivatives with mutations in the 5' non-coding region were constructed, reintroduced into yeast using a multicopy plasmid, and the mRNA starts mapped by primer extension. The results indicate that four, and possibly five T-A-T-A sequences are located within the 5' non-coding region of the CYC1 gene, and that each T-A-T-A is required for a specific subset of mRNA starts. This conclusion has been confirmed by oligonucleotide mutagenesis of a chromosomal CYC1 T-A-T-A sequence. A loose spatial relationship also exists between the T-A-T-A sequences and the mRNA start sites, and this distance relationship varies from 100 to 60 base-pairs (+/- 15 base-pairs).

Saccharomyces cerevisiae CYC1 mRNA 5'-end positioning: analysis by in vitro mutagenesis, using synthetic duplexes with random mismatch base pairs

Expression of the Saccharomyces cerevisiae CYC1 gene produces mRNA with more than 20 different 5' ends. A derivative of the CYC1 gene (CYC1-157) was constructed with a deletion of a portion of the CYC1 5'-noncoding region, which includes the sites at which many of the CYC1 mRNAs 5' ends map. A 54-mer double-stranded oligonucleotide homologous with the deleted sequence of CYC1-157 and which included a low level of random base pair mismatches (an average of two mismatches per duplex) was used to construct mutants of the CYC1 gene and examine the role of the DNA sequence at and immediately adjacent to the mRNA 5' ends in specifying their locations. The effect of these mutations on the site selection of mRNA 5' ends was examined by primer extension. Results indicate that there is a strong preference for 5' ends which align with an A residue (T in the template DNA strand) preceded by a short tract of pyrimidine residues.

Yeast/herpes simplex virus thymidine kinase gene fusions yield fusion proteins with thymidine kinase activity

Expression in Saccharomyces cerevisiae of the Herpes Simplex Virus type-1 (HSV-1) thymidine kinase gene was accomplished by the construction of a gene fusion between the TK and a yeast gene. The fusion of yeast DNA sequences (which include a promoter and DNA that codes for the amino terminus end of the yeast gene product) with the TK gene resulted in a protein fusion with thymidine kinase activity.

Efficient expression of the Escherichia coli leuB gene in yeast

Efficient expression of the Escherichia coli leuB (beta-isopropylmalate dehydrogenase) gene occurred in yeast after in vitro DNase digestion and religation of plasmid bound leuB and the yeast HIS3 DNA which placed the 5' end of the yeast HIS3 gene immediately adjacent to the coding region of the E. coli leuB gene. Two structurally distinct classes of gene fusions were constructed, each involved portions of the yeast HIS3 gene which contributed DNA sequences responsible for leuB expression in yeast. The first class involved fusion of the HIS3 coding region to bacterial DNA resulting in the production of a fusion protein with beta-isopropylmalate dehydrogenase activity. The second class consisted of bacterial DNA, including the leuB coding region, fused to the HIS3 promotor region with the absence of any portion of the HIS3 coding region. In both constructions the HIS3 promotor region is required for transcription, however, translation of the class two fusion is initiated at a bacterial DNA coded AUG, and the 5' end of the mRNA coded by the leuB gene mapped predominantly at bacterial DNA sequences. The DNA sequence responsible for the 5' end of the HIS3 mRNAs remain in the class two gene fusions but this did not preclude the initiation of transcription at bacterial DNA sequences. The pattern of mRNA initiation at bacterial DNA suggests that DNA sequences at, or adjacent to, the site of transcription initiation are involved in the determination of the sites of initiation, and perhaps the frequency at which initiation occurs.

Expression of the Herpes simplex virus thymidine kinase gene in Saccharomyces cerevisiae

Yeast plasmids have been constructed that carry the Herpes simplex Virus type 1 (HSV-1) thymidine kinase (TK) gene which is functionally expressed in Saccharomyces cerevisiae. The expression of the TK gene appears to be due to transcriptional read-through from a yeast promoter that lies on the 3' side of the HIS3 gene. The TK+ yeast possesses in vitro thymidine kinase activity which is absent in the original yeast strain. Yeast strains auxotrophic for thymidine monophosphate (dTMP) (tmp1) can grown on thymidine-containing medium after transformation with these plasmids. Tmp+, TK+ S. cerevisiae whose de novo synthesis of dTMP is inhibited with amethopterin plus sufanilamide is also capable of growth in thymidine. S. cerevisiae transformed with such plasmids is capable of incorporating thymidine and bromodeoxyuridine into DNA.

Chimeric plasmids for cloning of deoxyribonucleic acid sequences in Saccharomyces cerevisiae

Two sets of plasmids, each carrying a Saccharomyces cerevisiae gene and a portion or all of the yeast 2-micron circle linked to the Escherichia coli plasmid pBR322, have been constructed. One of these sets contains a BamHI fragment of S. cerevisiae deoxyribonucleic acid that includes the yeast his3 gene, whereas the other set contains a BamHI fragment of S. cerevisiae that includes the yeast leu2 gene. All plasmids transform S. cerevisiae and E. coli with a high frequency, possess unique restriction endonuclease sites, and are retrievable from both host organisms. Plasmids carrying the 2.4-megadalton EcoRI fragment of the 2-micron circle transform yeast with 2- to 10-fold greater frequency than those carrying the 1.5-megadalton EcoRI fragment of the 2-micron circle. Restriction endonuclease analysis of plasmics retrieved from S. cerevisiae transformed with plasmics carrying the 2.4-megadalton EcoRI fragment showed that in 13 of 96 cases the original plasmic has acquired an additional copy of the 2-mcron circle. These altered plasmids appear to have arisen by means of an interplasmid recombination event while in S. cerevisiae. A clone bank of S. cerevisiae genes based upon one of these composite plasmids has been constructed. By using this bank and selecting directly in S. cerevisiae, the ura3, tyr1, and met2 genes have been cloned.