Mutual information: Measuring nonlinear dependence in longitudinal epidemiological data

Given a large clinical database of longitudinal patient information including many covariates, it is computationally prohibitive to consider all types of interdependence between patient variables of interest. This challenge motivates the use of mutual information (MI), a statistical summary of data interdependence with appealing properties that make it a suitable alternative or addition to correlation for identifying relationships in data. MI: (i) captures all types of dependence, both linear and nonlinear, (ii) is zero only when random variables are independent, (iii) serves as a measure of relationship strength (similar to but more general than R2), and (iv) is interpreted the same way for numerical and categorical data. Unfortunately, MI typically receives little to no attention in introductory statistics courses and is more difficult than correlation to estimate from data. In this article, we motivate the use of MI in the analyses of epidemiologic data, while providing a general introduction to estimation and interpretation. We illustrate its utility through a retrospective study relating intraoperative heart rate (HR) and mean arterial pressure (MAP). We: (i) show postoperative mortality is associated with decreased MI between HR and MAP and (ii) improve existing postoperative mortality risk assessment by including MI and additional hemodynamic statistics.

Adaptation or Revolution: Telemental Health and Advanced Practice Psychiatric Nursing During COVID-19

OBJECTIVE

This article will describe the current COVID-19 crisis and the evolving mental health concerns associated with it, discuss how mental health practice has changed, and ways in which psychiatric mental health nurse practitioners (PMHNPs) can adapt and prepare for the future.

METHOD

A search of current literature on the COVID-19 crisis, and topics relevant to the mental health components associated with the pandemic are reviewed. Telemental health (TMH) and PMHNP practice are discussed as they relate to the unfolding picture of the viral pandemic.

RESULTS

The COVID-19 crisis is having far-reaching implications for mental health treatment and in particular for PMHNPs in practice settings. There have been widespread consequences of the containment measures used for the protection and mitigation of the disease. One such result has been the inability of patients to have face-to-face contact with their providers. The role of TMH has become increasingly important as an adaptation in professional practice.

CONCLUSION

Technology has rapidly transformed traditional practice due to the COVID-19 crisis and there is strong evidence that it is well accepted by patients and providers. It is incumbent on PMHNPs to embrace TMH and become educated on best practices and TMH services.

Extrema-weighted feature extraction for functional data

Motivation

Although there is a rich literature on methods for assessing the impact of functional predictors, the focus has been on approaches for dimension reduction that do not suit certain applications. Examples of standard approaches include functional linear models, functional principal components regression and cluster-based approaches, such as latent trajectory analysis. This article is motivated by applications in which the dynamics in a predictor, across times when the value is relatively extreme, are particularly informative about the response. For example, physicians are interested in relating the dynamics of blood pressure changes during surgery to post-surgery adverse outcomes, and it is thought that the dynamics are more important when blood pressure is significantly elevated or lowered.

Results

We propose a novel class of extrema-weighted feature (XWF) extraction models. Key components in defining XWFs include the marginal density of the predictor, a function up-weighting values at extreme quantiles of this marginal, and functionals characterizing local dynamics. Algorithms are proposed for fitting of XWF-based regression and classification models, and are compared with current methods for functional predictors in simulations and a blood pressure during surgery application. XWFs find features of intraoperative blood pressure trajectories that are predictive of postoperative mortality. By their nature, most of these features cannot be found by previous methods.

Availability and implementation

The R package 'xwf' is available at the CRAN repository: https://cran.r-project.org/package=xwf.

Supplementary information

Supplementary data are available at Bioinformatics online.

Unique Practice, Unique Place: Exploring Two Assertive Community Treatment Teams in Maine

Assertive Community Treatment (ACT) is a model of care that provides comprehensive community-based psychiatric care for persons with serious mental illness. This model has been widely documented and has shown to be an evidence-based model of care for reducing hospitalizations for this targeted population. Critical ingredients of the ACT model are the holistic nature of their services, a team based approach to treatment and nurses who assist with illness management, medication monitoring, and provider collaboration. Although the model remains strong there are clear differences between urban and rural teams. This article describes present day practice in two disparate ACT programs in urban and rural Maine. It offers a new perspective on the evolving and innovative program of services that treat those with serious mental illness along with a review of literature pertinent to the ACT model and future recommendations for nursing practice. The success and longevity of these two ACT programs are testament to the quality of care and commitment of staff that work with seriously mentally ill consumers. Integrative care models such as these community-based treatment teams and nursing driven interventions are prime elements of this successful model.

Effect of A1C and Glucose on Postoperative Mortality in Noncardiac and Cardiac Surgeries

OBJECTIVE

Hemoglobin A_1c (A1C) is used in assessment of patients for elective surgeries because hyperglycemia increases risk of adverse events. However, the interplay of A1C, glucose, and surgical outcomes remains unclarified, with often only two of these three factors considered simultaneously. We assessed the association of preoperative A1C with perioperative glucose control and their relationship with 30-day mortality.

RESEARCH DESIGN AND METHODS

Retrospective analysis on 431,480 surgeries within the Duke University Health System determined the association of preoperative A1C with perioperative glucose (averaged over the first 3 postoperative days) and 30-day mortality among 6,684 noncardiac and 6,393 cardiac surgeries with A1C and glucose measurements. A generalized additive model was used, enabling nonlinear relationships.

RESULTS

A1C and glucose were strongly associated. Glucose and mortality were positively associated for noncardiac cases: 1.0% mortality at mean glucose of 100 mg/dL and 1.6% at mean glucose of 200 mg/dL. For cardiac procedures, there was a striking U-shaped relationship between glucose and mortality, ranging from 4.5% at 100 mg/dL to a nadir of 1.5% at 140 mg/dL and rising again to 6.9% at 200 mg/dL. A1C and 30-day mortality were not associated when controlling for glucose in noncardiac or cardiac procedures.

CONCLUSIONS

Although A1C is positively associated with perioperative glucose, it is not associated with increased 30-day mortality after controlling for glucose. Perioperative glucose predicts 30-day mortality, linearly in noncardiac and nonlinearly in cardiac procedures. This confirms that perioperative glucose control is related to surgical outcomes but that A1C, reflecting antecedent glycemia, is a less useful predictor.

Can we make postoperative patient handovers safer? A systematic review of the literature

Postoperative patient handovers are fraught with technical and communication errors and may negatively impact patient safety. We systematically reviewed the literature on handover of care from the operating room to postanesthesia or intensive care units and summarized process and communication recommendations based on these findings. From >500 papers, we identified 31 dealing with postoperative handovers. Twenty-four included recommendations for structuring the handover process or information transfer. Several recommendations were broadly supported, including (1) standardize processes (e.g., through the use of checklists and protocols); (2) complete urgent clinical tasks before the information transfer; (3) allow only patient-specific discussions during verbal handovers; (4) require that all relevant team members be present; and (5) provide training in team skills and communication. Only 4 of the studies developed an intervention and formally assessed its impact on different process measures. All 4 interventions improved metrics of effectiveness, efficiency, and perceived teamwork. Most of the papers were cross-sectional studies that identified barriers to safe, effective postoperative handovers including the incomplete transfer of information and other communication issues, inconsistent or incomplete teams, absent or inefficient execution of clinical tasks, and poor standardization. An association between poor-quality handovers and adverse events was also demonstrated. More innovative research is needed to define optimal patient handovers and to determine the effect of handover quality on patient outcomes.

Glacial-postglacial temperature difference deduced from aspartic Acid racemization in fossil bones

The magnitude of the temperature increase that occurred in continental regions following the termination of the last glaciation has been determined from the degree of racemization of aspartic acid in fossil bones of known age. The results indicate an increase of 4 degrees C for the Mediterranean coast and 5 degrees to 6 degrees C for East Africa. These estimates are believed to be reliable within 1 degrees C.

"Ghost" publications among applicants to a general surgery residency program

OBJECTIVE

To determine the incidence of potentially fraudulent (or "ghost") publications in applications to a general surgery residency program.

METHODS

Electronic Residency Application Services applications submitted in 2005 to the general surgery residency program were reviewed in an IRB-approved study. No identifiers were collected. Publications were checked against Medline, PubMed, ISI Web of Science, and Google. Nonverifiable publications were then submitted to the medical librarian for verification. Ghost publications were defined as journals, books, or meetings that cannot be verified; verified journals without the listed publication; or verified publications without an applicant author. Data analyses were performed using univariate and multivariate regression analysis for nonparametric data. A p value < 0.05 was considered significant.

RESULTS

Four hundred ninety-three applications were received. Thirty-one percent (150 of 493) of applicants listed a total of 596 publications, including 30 abstracts, 359 journal articles, and 207 chapters. Thirty-three percent (196 of 596) of the publications could not be verified: 7 abstracts, 177 journal articles, and 12 chapters. The distribution of ghost publications was skewed toward the journals subgroup (p < 0.001). Positive predictors of ghost publications were age and foreign medical school. The sole negative predictor was enrollment in a top-10 US research medical school.

CONCLUSION

A disturbingly substantial fraction of publications listed on Electronic Residency Application Services applications cannot be verified. This might indicate a need for greater mentorship and oversight for medical school applicants. It is unknown whether this behavior predicts lack of integrity in other professional settings.

Predictive indices of morbidity and mortality after liver resection

OBJECTIVE

To determine if use of Model for End-Stage Liver Disease (MELD) scores to elective resections accurately predicts short-term morbidity or mortality.

SUMMARY BACKGROUND DATA

MELD scores have been validated in the setting of end-stage liver disease for patients awaiting transplantation or undergoing transvenous intrahepatic portosystemic shunt procedures. Its use in predicting outcomes after elective hepatic resection has not been evaluated.

METHODS

Records of 587 patients who underwent elective hepatic resection and were included in the National Surgical Quality Improvement Program Database were reviewed. MELD score, CTP score, Charlson Index of Comorbidity, American Society of Anesthesiology classification, and age were evaluated for their ability to predict short-term morbidity and mortality. Morbidity was defined as the development of one or more of the following complications: pulmonary edema or embolism, myocardial infarction, stroke, renal failure or insufficiency, pneumonia, deep venous thrombosis, bleeding, deep wound infection, reoperation, or hyperbilirubinemia. The analysis was repeated with patients divided according to their procedure and their primary diagnosis. Parametric or nonparametric analyses were performed as appropriate. Also, a new index was developed by dividing the patients into a development and a validation cohort, to predict morbidity and mortality in patients undergoing elective hepatic resection. ROC curves were also constructed for each of the primary indices.

RESULTS

CTP and ASA scores were superior in predicting outcome. Also, patients undergoing resection of primary malignancies had a higher rate of mortality but no difference in morbidity.

CONCLUSION

MELD scores should not be used to predict outcomes in the setting of elective hepatic resection.

Is the Valve OK or Not? Immediate Evaluation of a Replaced Aortic Valve

Transesophageal echocardiography is a crucial tool in intraoperative evaluation of newly implanted/repaired heart valves because suspected valvular malfunction needs to be identified and sometimes surgically corrected. Although color Doppler is often adequate in evaluating the expected regurgitant jets, as well as excluding pathologic paravalvular leaks, spectral Doppler techniques are the most commonly used methods for estimating transvalvular gradients in the operating room. However, these methods are subject to a variety of confounding factors, including subvalvular gradients and pressure recovery. Other methods of valve area estimation should also be used when evaluating a prostethic aortic valve, including the continuity equation and the left ventricular outflow tract/aortic valve velocity ratio.

Intraoperative fluid management during orthotopic liver transplantation

OBJECTIVE

To assess clinical safety of a low central venous pressure (CVP) fluid management strategy in patients undergoing liver transplantation.

DESIGN

Retrospective record review comparing 2 transplant centers, one using the low CVP method and the other using the normal CVP method.

SETTING

University-based, academic, tertiary care centers.

PARTICIPANTS

Patients undergoing orthotopic cadaveric liver transplantation.

INTERVENTIONS

Each center practiced according to its own standard of care. Center 1 maintained an intraoperative CVP <5 mmHg using fluid restriction, nitroglycerin, forced diuresis, and morphine. If pressors were required to maintain systolic arterial pressure >90 mmHg, phenylephrine or norepinephrine was used. At center 2, CVP was kept 7 to 10 mmHg and mean arterial pressure >75 mmHg with minimal use of vasoactive drugs.

MEASUREMENTS AND MAIN RESULTS

Data collected included United Network for Organ Sharing status, surgical technique, intraoperative transfusion rate, preoperative and peak postoperative creatinine, time spent in intensive care unit and hospital, incidence of death, and postoperative need for hemodialysis. Principal findings include an increased rate of transfusion in the normal CVP group but increased rates of postoperative renal failure (elevated creatinine and more frequent need for dialysis) and 30-day mortality in the low CVP group.

CONCLUSIONS

Despite success in lowering blood transfusion requirements in liver resection patients, a low CVP should be avoided in patients undergoing liver transplantation.

Determining benchmarks for evaluation and management coding in an academic division of general surgery1 1No competing interests declared

BACKGROUND

Academic divisions of general surgery are facing ever-increasing financial pressures. Cost-cutting is a common approach to maintaining profitability, but strategies to increase revenue should not be ignored. One specific avenue for enhanced revenue generation in general surgery is that of coding for evaluation and management (E&M). Although this is the financial life-blood for many of the consultative services in departments of medicine, E&M coding is an often neglected and misunderstood component of surgical care.

STUDY DESIGN

The financial records for the Division of General Surgery were reviewed for the period of January 2001 to June 2003. Specifically, charges and receipts for inpatient procedures and hospital visits (CPT codes 99231, 99232, and 99233) were determined. The analysis was limited to surgeons with a primary clinical focus based at the University hospital rather than the neighboring community or Veteran's Affairs hospitals. In addition, ICD-9 and All Patient Refined Diagnosis Related Groups (APR-DRG) data were analyzed to determine the surgeon-specific number of inpatients and inpatient-days with more than one ICD-9 code or secondary ICD-9 codes, or both, or an APR-DRG severity of illness score of 2, 3, or 4. These categories were defined to determine the number of inpatient-days for which E&M coding could be billed for management of secondary medical diagnoses.

RESULTS

Analysis demonstrates that actual E&M charges were 40% to 47% of predicted minimums for E&M charges for the period under study. In theory, this result translates into an annual gain in receipts of 400,000 dollars to 600,000 dollars.

CONCLUSIONS

We conclude that the ICD-9 and APR-DRG models may serve as benchmarks to determine the limits for E&M revenue stream, and E&M coding may represent an underutilized source of revenue among academic departments of surgery.

Optimization of operating room allocation using linear programming techniques

BACKGROUND

New and innovative approaches must be used to rationally allocate scarce resources such as operating room time while simultaneously optimizing the associated financial return. In this article we use the technique of linear programming to optimize allocation of OR time among a group of surgeons based on professional fee generation.

STUDY DESIGN

For the period of December 1, 2000, to July 31, 2002, the following individualized data were obtained for the Division of General Surgery at Duke University Medical Center: allocated OR time (hours), case mix as determined by CPT codes, total OR time used, and normalized professional charges and receipts. Inpatient, outpatient, and emergency cases were included. The Solver linear programming routine in Microsoft Excel (Microsoft Corp.) was used to determine the optimal mix of surgical OR time allocation to maximize professional receipts.

RESULTS

Our model of optimized OR allocation would maximize weekly professional revenues at 237,523 US dollars, a potential increase of 15% over the historical value of 207,700 US dollars or an annualized increase of approximately 1.5 million US dollars.

CONCLUSIONS

Our results suggest that mathematical modeling techniques used in operations research, management science, or decision science may rationally optimize OR allocation to maximize revenue or to minimize costs. These techniques may optimize allocation of scarce resources in the context of the goals specific to individual academic departments of surgery.

Tolerance and the "Holy Grail" of transplantation

Advances in transplantation biology have greatly improved patient outcomes following transplant surgery. However, generalized immunosuppression remains the Achilles heel of modern transplantation surgery with its associated infectious and neoplastic morbidities. Tolerance remains the ultimate goal for the entire field. Although recent advances in transplant immunology suggest that tolerance may be achievable in the near future, the complex and redundant nature of the human immune system may not allow us to circumvent such a basic function as the recognition of nonself. In this paper, advances in transplant immunology are reviewed and their potential relevance to achieving the "Holy Grail" of transplantation are discussed.

Emergencies after liver transplantation

Liver transplantation has become the procedure of choice for a wide variety of patients with end-stage liver disease. Perioperative morbidity and mortality have decreased dramatically over the past two decades, and superior graft and patient survival rates are now routine. Despite these advances, however, there remain several potentially lethal possibilities that may complicate the immediate postoperative period. Failure of the graft to regain any useful metabolic activity is known as primary nonfunction, and almost uniformly requires retransplantation for any hope of survival. Lesser degrees of immediate dysfunction require experienced clinical judgment as to the probability of sustaining long-term patient viability. Another potentially catastrophic development is thrombosis of the grafted hepatic artery. This is sometimes successfully managed by surgical reconstruction. It may develop immediately, or present insidiously much later. Thrombosis of the portal vein, while not usually fatal, can significantly complicate the immediate course, carrying with it a significant risk of sepsis. Close monitoring of patients in the period following liver transplantation is crucial, as prompt diagnosis and early intervention directly affects the patient's chances of survival.

Nitric oxide is necessary for CC-class chemokine expression in endotoxin-stimulated ANA-1 murine macrophages

The production of nitric oxide (NO) in response to endotoxin (LPS)-stimulation is associated with a myriad of NO-dependent regulatory functions. The study of NO-dependent genetic programs in the setting of endotoxin stimulation can be aided by determination of genes whose transcription is upregulated in the presence of NO and LPS. Using subtractive suppression hybridization analysis, we demonstrate that ANA-1 murine macrophages produce the CC class chemokines, monocyte chemoattractant protein-1 (JE/MCP-1) and macrophage inflammatory protein-related protein-1 (C10/MRP-1), in response to LPS-mediated nitric oxide (NO) production. MCP-1 and MRP-1 gene transcription and protein synthesis are upregulated in the setting of LPS-induced NO synthesis. NO alone is necessary but insufficient for induction of chemokine protein expression; an additional LPS-dependent signaling pathway is also required. This study suggests a novel mechanism by which NO induces chemokine expression and regulates the host inflammatory response to endotoxin.

Nature and chlorine reactivity of organic constituents from reclaimed water in groundwater, Los Angeles County, California

The nature and chlorine reactivity of organic constituents in reclaimed water (tertiary-treated municipal wastewater) before, during, and after recharge into groundwater at the Montebello Forebay in Los Angeles County, CA, was the focus of this study. Dissolved organic matter (DOM) in reclaimed water from this site is primarily a mixture of aromatic sulfonates from anionic surfactant degradation, N-acetyl amino sugars and proteins from bacterial activity, and natural fulvic acid, whereas DOM from native groundwaters in the aquifer to which reclaimed water was recharged consists of natural fulvic acids. The hydrophilic neutral N-acetyl amino sugars that constitute 40% of the DOM in reclaimed water are removed during the first 3 m of vertical infiltration in the recharge basin. Groundwater age dating with 3H and 3He isotopes, and determinations of organic and inorganic C isotopes, enabled clear differentiation of recent recharged water from older native groundwater. Phenol structures in natural fulvic acids in DOM isolated from groundwater produced significant trihalomethanes (THM) and total organic halogen (TOX) yields upon chlorination, and these structures also were responsible for the enhanced SUVA and specific fluorescence characteristics relative to DOM in reclaimed water. Aromatic sulfonates and fulvic acids in reclaimed water DOM produced minimal THM and TOX yields.

Osteopontin is a negative feedback regulator of nitric oxide synthesis in murine macrophages

In a system of endotoxin (LPS)-mediated NO production in ANA-1 murine macrophages, suppression subtractive hybridization was used to identify genes up-regulated by NO. Osteopontin (OPN), a secreted acidic phosphoprotein that binds to a cell surface RGD integrin-binding motif, was found to be differentially expressed in the presence of NO. OPN has been demonstrated to inhibit NO production in a variety of cell types. Northern blot and nuclear run-on analyses demonstrated that OPN mRNA levels and gene transcription were significantly increased in the presence of LPS-induced NO synthesis. Transient transfection of an OPN promoter-luciferase reporter plasmid construct showed that promoter activity is increased in the presence of LPS and NO. Immunoblot analysis showed that OPN protein is secreted into the extracellular fluid. Similar results were noted with an alternative cell system, RAW 264.7 macrophages, and alternative inducers of NO synthesis, IFN-gamma and IL-1beta. In the presence of GRGDSP, a hexapeptide that blocks binding of RGD-containing proteins to cell surface integrins, NO production is significantly increased in the presence of LPS stimulation. These data suggest a unique trans-regulatory mechanism in which LPS-induced NO synthesis feedback regulates itself through up-regulation of OPN promoter activity and gene transcription.

Pulmonary expression of iNOS and HO-1 protein is upregulated in a rat model of prehepatic portal hypertension

Portal hypertension is associated with a wide range of pulmonary pathophysiologies, ranging from portopulmonary hypertension to hepatopulmonary syndrome. Although the clinical and pathological features of pulmonary dysfunction in this setting have been extensively characterized, the underlying biology is not well understood. Specifically, the role of mediators that regulate mesenteric vascular hemodynamics in portal hypertension, such as nitric oxide and endothelin, have not been studied in the lung. Using a rat model of prehepatic portal hypertension with preserved hepatic function, we examined pulmonary elaboration of endothelial nitric oxide synthase (NOS), inducible NOS, heme oxygenase- 1 (HO-1), heme oxygenase-2 (HO-2), endothelin-1 mRNA, and protein. In comparison to sham controls, portal hypertensive animals exhibited significantly increased pulmonary iNOS and HO-1 mRNA and protein. Cyclic GMP was significantly increased in portal hypertensive lung tissue, suggesting activation of guanylyl cyclase by the endproducts of iNOS and/or HO-1 activity. Using immunohistochemical analysis, iNOS expression was localized to the vascular endothelium, while HO-1 localized to bronchiolar epithelium and macrophages. These results suggest that production of nitric oxide and carbon monoxide may contribute to the pulmonary pathology associated with portal hypertension.

Nitric oxide-dependent ribosomal RNA cleavage is associated with inhibition of ribosomal peptidyl transferase activity in ANA-1 murine macrophages

NO can regulate specific cellular functions by altering transcriptional programs and protein reactivity. With respect to global cellular processes, NO has also been demonstrated to inhibit total protein synthesis and cell proliferation. The underlying mechanisms are unknown. In a system of ANA-1 murine macrophages, iNOS expression and NO production were induced by exposure to endotoxin (LPS). In selected instances, cells were exposed to an exogenous NO donor, S-nitroso-N-acetylpenicillamine or a substrate inhibitor of NO synthesis. Cellular exposure to NO, from both endogenous and exogenous sources, was associated with a significant time-dependent decrease in total protein synthesis and cell proliferation. Gene transcription was unaltered. In parallel with decreased protein synthesis, cells exhibited a distinctive cleavage pattern of 28S and 18S rRNA that were the result of two distinct cuts in both 28S and 18S rRNA. Total levels of intact 28S rRNA, 18S rRNA, and the composite 60S ribosome were significantly decreased in the setting of cell exposure to NO. Finally, 60S ribosome-associated peptidyl transferase activity, a key enzyme for peptide chain elongation, was also significantly decreased. Our data suggest that NO-mediated cleavage of 28S and 18S rRNA results in decreased 60S ribosome associated peptidyl transferase activity and inhibition of total protein synthesis.

Use of aerosolized inhaled epoprostenol in the treatment of portopulmonary hypertension

BACKGROUND

Portopulmonary hypertension is a known complication in the liver transplant candidate. Intravenous epoprostenol has been demonstrated to decrease pulmonary artery pressures and possibly remodel right ventricle geometry.

METHODS

In this report, we document the efficacy of inhaled aerosolized epoprostenol in a patient with portopulmonary hypertension. The effect was of rapid onset and offset.

RESULTS

After 10 min of delivery, mean pulmonary artery pressure decreased 26%; cardiac output increased by 22%; pulmonary vascular resistance decreased by 42%; and the transpulmonary gradient decreased by 29%. There were no untoward side effects.

CONCLUSION

The inhaled route of delivery of epoprostenol is potential alternative for the acute therapy of portpulmonary hypertension.

Intraoperative use of inhaled PGI(2) for acute pulmonary hypertension and right ventricular failure

Inhaled prostacyclin (PGI(2)) can be used as an effective pulmonary vasodilator intraoperatively to treat pulmonary hypertension and impending right ventricular failure.

Superoxide enhances interleukin 1beta-mediated transcription of the hepatocyte-inducible nitric oxide synthase gene

BACKGROUND & AIMS

Exposure to oxidative stress, as in states of shock, ischemia-reperfusion injury, or sepsis, commonly initiates a complex cellular cascade of interlocking redox modulatory systems that detoxify electrophiles. In interleukin 1beta (IL-1beta)-treated rat hepatocytes, we have previously demonstrated that inducible nitric oxide synthase (iNOS) protein expression, steady-state iNOS messenger RNA (mRNA) levels, and NO synthesis are increased by oxidative stress induced by superoxide. The effect of hepatocellular redox state upon iNOS gene transcription has not been previously studied.

METHODS

Using rat hepatocytes in primary culture, iNOS gene transcription was induced by IL-1beta. Oxidative stress was mediated by 1,2,3-benzenetriol (BZT), an autocatalytic source of superoxide. Nuclear run-on assays and transient transfection assays using the rat hepatocyte iNOS full-length promoter and deletion constructs were designed to isolate a cis-acting regulatory element. Specificity was confirmed by site-directed mutagenesis. Gel shift analysis determined the presence of a corresponding trans-acting regulatory factor.

RESULTS

In IL-1beta-treated cells, BZT increased iNOS gene transcription without altering mRNA half-life. An antioxidant-responsive element (ARE) was found in the iNOS promoter at base pair -1347, which conferred redox sensitivity. Gel shift analysis identified a corresponding nuclear protein capable of binding to ARE in IL-1beta- and BZT-treated rat hepatocytes.

CONCLUSIONS

An ARE in the rat hepatocyte iNOS promoter confers redox sensitivity and augments IL-1beta-mediated iNOS gene and protein expression in the setting of superoxide treatment.

Endotoxin-mediated nitric oxide synthesis inhibits IL-1beta gene transcription in ANA-1 murine macrophages

On the basis of previous work demonstrating nitric oxide (NO)-mediated inhibition of nuclear factor-kappaB (NF-kappaB) DNA binding, we hypothesized that NO downregulates NF-kappaB-dependent interleukin-1beta (IL-1beta) production in an ANA-1 macrophage model of lipopolysaccharide (LPS) stimulation. In the presence of LPS (100 ng/ml), levels of IL-1beta protein and mRNA were significantly upregulated with NO synthase inhibition. Using nuclear run-on analysis and transient transfection studies, IL-1beta gene transcription and IL-1beta promoter activity were also found to be increased with inhibition of NO production. Parallel transfection studies using an NF-kappaB long terminal repeat-reporter plasmid exhibited similar findings, suggesting an NO-mediated effect on NF-kappaB activity. Gel shift studies showed that LPS-associated NF-kappaB DNA binding was increased, both in the setting of NO synthase inhibition and in a reducing environment. Repletion of NO by addition of an S-nitrosothiol restored IL-1beta protein synthesis, mRNA levels, gene transcription, promoter activity, and NF-kappaB DNA binding to levels noted in the presence of LPS alone. Our studies indicate that NO may regulate LPS-associated inflammation by downregulating IL-1beta gene transcription through S-nitrosation of NF-kappaB.

Redox regulation of the rat hepatocyte iNOS promoter

BACKGROUND

The purpose of this study was to define the redox sensitive cis-acting transcriptional mechanisms that regulate inducible nitric oxide synthase (iNOS) promoter function in the hepatocyte.

METHODS

Clonal deletion constructs of the rat hepatocyte iNOS promoter (Genbank X95629; 1845 base pair)-reporter plasmid were transiently transfected into HepG2 cells treated with IL-1 beta and IL-1 beta + hydrogen peroxide.

RESULTS

A segment of the promoter upstream from nucleotide -1126 was associated with redox-sensitive augmentation of promoter activity. Site-directed mutagenesis of 2 antioxidant response elements (AREs) was combined with transfection analysis to demonstrate that mutation of the ARE at nt-1347 ablated oxidant stress-mediated activation of the iNOS promoter.

CONCLUSIONS

This ARE conveys the redox-sensitive response of the rat iNOS promoter. Hepatocyte iNOS expression is a novel and, as yet, poorly described antioxidant mechanism that is cytokine and redox sensitive and that plays a pleuripotent regulatory role in hepatocellular function in the face of sepsis and shock.

Portopulmonary hypertension and the liver transplant candidate

The management of the liver transplant (OLT) candidate with portopulmonary hypertension (PPHTN) has dramatically changed in the past 3 years. Careful preoperative evaluation with functional characterization of right ventricular function plays a critical role. The pulmonary vascular response to epoprostenol infusion serves as a deciding factor for OLT candidacy. Careful perioperative attention to avoid right ventricular failure from acutely elevated pulmonary artery pressures or sudden increases in right ventricular preload is a key physiologic tenet of management. With increased surgical expertise, anesthetic sophistication, and availability of epoprostenol, PPHTN is no longer considered an absolute contraindication for OLT.

Endotoxin-mediated S-nitrosylation of p50 alters NF-kappa B-dependent gene transcription in ANA-1 murine macrophages

Nitric oxide (NO) regulates cellular function, in part, by S-nitrosylating active site thiol groups of proteins. Ex vivo S-nitrosylation of NF-kappa B p50 significantly decreases its capacity for DNA binding. To determine the cellular relevance of this observation, we utilized the ANA-l murine macrophage model of endotoxin (LPS)-mediated NO synthesis. In selected instances, the NO synthase inhibitor, L-arginine methyl ester (L-NAME; 100 microM), or the NO donor, S-nitroso-N-acetylcysteine (SNAC; 100 microM), was added. In contrast to that of LPS cells, nuclear extracts from LPS + L-NAME cells demonstrated increased NF-kappa B DNA binding on gel shift analysis. Addition of SNAC to LPS + L-NAME cells restored binding to a level equivalent to that of LPS cells. Spectrophotometric analysis of NF-kappa B p50 immunoprecipitates demonstrated S-NO bonds exclusively in LPS cells; these p50 protein isolates retained the same DNA binding characteristics as that of the nuclear extracts. Transfection assays utilizing NF-kappa B-dependent promoter-reporter constructs demonstrated increased activity in LPS + L-NAME cells compared with LPS cells; nuclear run-on assays confirmed increased transcription of the corresponding genes. These results suggest that LPS-mediated NO synthesis is associated with S-nitrosylation of NF-kappa B p50 and inhibition of NF-kappa B-dependent DNA binding, promoter activity, and gene transcription. We conclude that NO can regulate gene transcription by S-nitrosylation of NF-kappa B.

Endotoxin-Mediated S-Nitrosylation of p50 Alters NF-κB-Dependent Gene Transcription in ANA-1 Murine Macrophages

Nitric oxide (NO) regulates cellular function, in part, by S-nitrosylating active site thiol groups of proteins. Ex vivo S-nitrosylation of NF-κB p50 significantly decreases its capacity for DNA binding. To determine the cellular relevance of this observation, we utilized the ANA-l murine macrophage model of endotoxin (LPS)-mediated NO synthesis. In selected instances, the NO synthase inhibitor, l-arginine methyl ester (L-NAME; 100 μM), or the NO donor, S-nitroso-N-acetylcysteine (SNAC; 100 μM), was added. In contrast to that of LPS cells, nuclear extracts from LPS + L-NAME cells demonstrated increased NF-κB DNA binding on gel shift analysis. Addition of SNAC to LPS + L-NAME cells restored binding to a level equivalent to that of LPS cells. Spectrophotometric analysis of NF-κB p50 immunoprecipitates demonstrated S-NO bonds exclusively in LPS cells; these p50 protein isolates retained the same DNA binding characteristics as that of the nuclear extracts. Transfection assays utilizing NF-κB-dependent promoter-reporter constructs demonstrated increased activity in LPS + L-NAME cells compared with LPS cells; nuclear run-on assays confirmed increased transcription of the corresponding genes. These results suggest that LPS-mediated NO synthesis is associated with S-nitrosylation of NF-κB p50 and inhibition of NF-κB-dependent DNA binding, promoter activity, and gene transcription. We conclude that NO can regulate gene transcription by S-nitrosylation of NF-κB.

Differential effects of nitric oxide-mediated S-nitrosylation on p50 and c-jun DNA binding

BACKGROUND

Nitric oxide (NO) regulates a variety of cellular functions. One mechanism by which NO may exert its influence is through formation of S-nitrosothiols at critical thiol residues in protein-active sites, including those of nuclear protein transcription factors.

METHODS

NF-kappa B p50 and AP-1 c-jun were S-nitrosylated in the presence of acidic NaNO2. Wild-type protein and protein subjected to nitrosylating conditions in the absence of NaNO2 served as controls. Confirmatory evidence for S-nitrosothiol bond formation was obtained by ultraviolet-visible spectrophotometry with the absorption maximum for S-NO bonds at approximately 320 to 360 nm. With consensus oligonucleotide probes, gel-shift analysis was used to examine DNA binding characteristics.

RESULTS

In the case of NF-kappa B p50, S-nitrosylation resulted in significantly decreased DNA binding. In contrast, S-nitrosylation did not alter c-jun DNA binding. The S-nitrosylating conditions themselves did not alter p50 or c-jun DNA binding. Quantitative analysis was performed according to the Scatchard plot technique to generate the respective dissociation constants. S-nitrosylated p50 was associated with a fourfold greater dissociation constant than that of the wild-type p50.

CONCLUSIONS

S-nitrosylation of transcription factors may be one mechanism by which NO may selectively regulate gene transcription.

Interleukin 1beta-stimulated production of nitric oxide in rat hepatocytes is mediated through endogenous synthesis of interferon gamma

The multiple interlocking regulatory mechanisms that underlie induction of hepatocyte inducible nitric oxide synthase (iNOS) expression are largely unknown. Although previous work has indicated the requirement for multiple proinflammatory cytokines to induce hepatocyte NO production, investigators have recently shown that interleukin-1beta (IL-1beta) alone can initiate iNOS expression. In contrast, interferon gamma (IFN-gamma) serves as the sole initiating factor in other cell systems. On the basis of the known ability of IL-1beta to induce transcription and translation of the IFN family of genes, we hypothesized that IL-1beta-mediated hepatocyte expression of iNOS is dependent on endogenous IFN-gamma synthesis. In a system of rat hepatocytes in primary culture, IL-1beta induced production of both NO and IFN-gamma. Using in situ hybridization and immunoblot analysis, IFN-gamma messenger RNA (mRNA) and protein were detected in hepatocytes exposed to IL-1beta. Inhibition of NO synthesis using the competitive substrate inhibitor N-monomethyl-L-arginine (100 micromol/L) did not alter the extent of IL-1beta-mediated IFN-gamma synthesis. In contrast, anti-IFN-gamma antibody or inhibition of IFN-gamma mRNA translation by addition of antisense IFN-gamma oligodeoxynucleotide probes resulted in undetectable levels of NO metabolites and iNOS protein. Repletion of IFN-gamma to the system restored NO production to levels noted in the presence of IL-1beta alone. Transient transfection analysis using a rat hepatocyte iNOS promoter-reporter gene plasmid construct showed that IL-1beta-induced promoter activation was abolished in the presence of anti-IFN-gamma or antisense IFN-gamma. Again, addition of IFN-gamma to the system restored activity of the iNOS promoter. Parallel experiments examining IL-1beta-mediated endogenous hepatocyte IL-1beta and TNF-alpha synthesis indicated no role for these cytokines in the induction of iNOS expression by IL-1beta. It is concluded that IL-1beta-mediated hepatocyte synthesis of NO is dependent on the simultaneous endogenous synthesis of IFN-gamma.

Testicular toxicity assessment of Andrographis paniculata dried extract in rats

The possible testicular toxicity of Andrographis paniculata, Nees (Acanthaceae) standardized dried extract was evaluated in male Sprague Dawley rats for 60 days. No testicular toxicity was found with the treatment of 20, 200 and 1000 mg/kg during 60 days as evaluated by reproductive organ weight, testicular histology, ultrastructural analysis of Leydig cells and testosterone levels after 60 days of treatment. It is concluded that Andrographis paniculata dried extract did not produce subchronic testicular toxicity effect in male rats.

Alteration of NF-kappa B p50 DNA binding kinetics by S-nitrosylation

Nitric oxide (NO) regulates a wide variety of cellular functions, in part, by formation of S-NO bonds at critical active site thiol groups within proteins, including transcription factors. Previous studies have qualitatively demonstrated that S-nitrosothiol formation can alter transcription factor binding to the DNA recognition site. To more precisely define the effect of S-nitrosylation on transcription factor binding, the equilibrium binding constant was derived for S-nitrosylated NF-kappa B p50 (S-NO-p50) in a cell free system utilizing gel shift assays. Binding of NF-kappa B p50 subjected to the nitrosylation conditions in the absence of NaNO2 (C-p50-2) was not different from that of wild type NF-kappa B (C-p50-1). The extent of S-NO-p50 binding to its DNA target sequence was significantly decreased in comparison to that noted with C-p50-1 and C-p50-2. The binding constant was derived for each of the NF-kappa B variants: C-p50-1 = 1.01 x 10(10) M(-1); C-p50-2 = 0.92 x 10(10) M(-1); and S-NO-p50 = 0.28 x 10(10) M(-1). These data indicate that S-nitrosylation of p50 decreases its affinity for the target DNA sequence by four-fold.

CD14-dependent mechanism for endotoxin-mediated nitric oxide synthesis in murine macrophages

Endotoxin-mediated macrophage synthesis of nitric oxide (NO) is associated with immune effector function, intercellular communication, leukocyte adhesion, vascular integrity, and neurotransmission. However, little is known of the cellular receptor and signal transduction pathway by which endotoxin induces NO production. With the use of a model of ANA-1 murine macrophages, we stimulated NO production by incubation with increasing concentrations of endotoxin and 5% fetal calf serum. In selected instances, the anti-CD14 antibody, ED9, was added. Endotoxin-mediated NO synthesis was dependent on CD14 function and the presence of an additional serum factor. Endotoxin treatment increased plasma membrane GTPase activity and 35S-labeled guanosine 5'-O-(3-thiotriphosphate) ([35S]GTP gamma S) binding. Conversely, coincubation of cells with endotoxin and the heterotrimeric G protein inhibitors, suramin and guanosine 5'-O-(2-thiodiphosphate) trilithium salt, was associated with decreased NO synthesis, plasma membrane GTPase activity, and [35S]GTP gamma S binding. Blockade of CD14 or G protein function was associated with ablation of endotoxin-mediated inducible NO synthase (iNOS) protein expression, iNOS mRNA levels, and iNOS gene transcription, as determined by immunoblot, reverse transcriptase-polymerase chain reaction, and nuclear run-on analyses, respectively. These results indicate that endotoxin-mediated NO synthesis is a CD14-heterotrimeric G protein-dependent process.

Nitric oxide and acetaminophen-mediated oxidative injury: modulation of interleukin-1-induced nitric oxide synthesis in cultured rat hepatocytes

The role of endogenous hepatocyte synthesis of nitric oxide (NO) in states of oxidative stress is largely unknown. In a model of rat hepatocytes in primary culture, NO production was induced by exposure to interleukin-1beta (IL-1beta, 50 ng/ml). Acetaminophen-mediated oxidative injury was analyzed in unstimulated and stimulated hepatocytes in the presence and absence of N-methyl-L-arginine, a substrate inhibitor of NO synthesis (100 microM). Inhibition of NO synthesis was associated with exacerbation of acetaminophen-mediated oxidative injury. This effect was independent of guanylyl cyclase and cytochrome P450 activity. In addition, oxidative stress was associated with augmentation of interleukin-1beta-induced NO synthesis. Elevated NO synthesis occurred in parallel with increased inducible NO synthase (iNOS) enzyme activity and mass, steady-state levels of iNOS mRNA, increased transcription of the iNOS gene, and increased iNOS promoter activity. These effects were abrogated in the presence of antioxidants, suggesting that oxidative stress augments NO synthesis through a promoter-specific transcriptional regulatory mechanism. Thus, in conditions where oxidative injury may be a component of the overall proinflammatory state, induction of iNOS with subsequent elaboration of NO and augmentation of NO production may serve as an hepatoprotective mechanism against oxidative injury.

Endotoxin-mediated synthesis of nitric oxide is dependent on Gq protein signal transduction

BACKGROUND

Nitric oxide (NO) is a ubiquitous multifunctional free radical produced during sepsis, shock, reperfusion injury, and allograft rejection. Many studies are presently evaluating the functional roles of NO production in these settings. However, the signal transduction mechanisms underlying initiation of NO production are largely unknown. This study defines the cell surface receptor proteins that mediate endotoxin-induced NO synthesis in ANA-1 murine macrophages.

METHODS

Endotoxin (LPS, 10 micrograms/ml) was added to ANA-1 macrophages to induce NO synthesis. In selected instances guanosine 5'-O-(2-thiodiphosphate)-trilithium salt (GOTP), pertussis toxin, cholera toxin, or suramin were added as inhibitors of specific subclasses of heterotrimeric G proteins. Calphostin was added as a protein kinase C inhibitor, and ET-OCH3 was added as a phospholipase C-beta inhibitor. NO release was quantified by measurement of the NO metabolite, nitrite. Membrane guanosine triphosphatase (GTPase) activity was also analyzed. Steady-state levels of inducible nitric oxide synthase (iNOS) mRNA were determined by using reverse transcription-polymerase chain reaction analysis.

RESULTS

Inhibition of G protein function by suramin or GOTP significantly decreased synthesis of NO and expression of iNOS mRNA. Pertussis and cholera toxin did not alter NO synthesis, suggesting that the Gi and Gs classes are not involved. Inhibition of protein kinase C or upstream phospholipase C-beta activity decreased NO synthesis, implicating the Gq class of heterotrimeric G proteins.

CONCLUSIONS

In ANA-1 macrophages, endotoxin-mediated NO synthesis is dependent on heterotrimeric Gq protein-phospholipase C-beta-protein kinase C signal transduction.

Oxidative stress increases hepatocyte iNOS gene transcription and promoter activity

Hepatocyte expression of inducible nitric oxide synthase (iNOS) is initiated by the presence of pro-inflammatory cytokines, such as interleukin-1beta (IL-1). In the presence of oxidative stress, IL-1beta mediated hepatocyte iNOS expression and NO synthesis are significantly increased. To determine the underlying molecular mechanism responsible for oxidative stress augmentation of hepatocyte iNOS expression, rat hepatocytes in primary culture were stimulated with IL-1beta (250 U/mL) in the presence and absence of benzenetriol (BZT, 0-100 microM), an autocatalytic source of superoxide at physiologic pH. Nuclear runon analysis demonstrated that BZT was associated with increased iNOS gene transcription in the setting of IL-1 stimulation. Transient transfection of a plasmid construct composed of the rat hepatocyte iNOS promoter and a chloramphenicol transferase reporter gene demonstrated that the combination of BZT and IL-1 significantly increased iNOS promoter activity in comparison to that of IL-1beta alone. These data indicate that BZT-mediated oxidative stress increases IL-1beta induced iNOS gene transcription and iNOS promoter activity.

Volume-mediated pulmonary responses in liver transplant candidates

Pulmonary hypertension, defined as mean pulmonary artery pressure (mPAP) greater than or equal to 25 mmHg, is a recognized complication of hepatic dysfunction with portal hypertension and is considered a relative contraindication to liver transplantation. To characterize pulmonary hemodynamic responses in OLT candidates without pre-existing primary pulmonary hypertension, 22 consecutive patients referred for OLT at the Stanford University Hospital underwent prospective right heart catheterization with pressure determinations at baseline and following infusion of 11 crystalloid over 10 min. In addition, EKG, chest X-ray and transthoracic echocardiograms were performed as a part of the routine evaluation. Eleven non-cirrhotic patients served as controls. At baseline, 1/22 (4.5%) OLT patients had pulmonary hypertension while 9/22 (41%) developed pulmonary hypertension following volume infusion (p < 0.0001). In contrast, 0/11 controls manifested elevated pulmonary pressures at baseline or following volume challenge. OLT candidates were found to have significant increases in mean pulmonary pressure and capillary wedge pressure (PCWP) compared to controls, suggesting intravascular volume overload or left ventricular dysfunction as potential causes. OLT candidates who manifested volume-dependent pulmonary hypertension (a) had a 2-fold higher baseline PCWP, (b) currently smoked, and (c) had previously undergone portosystemic shunts. Aggregate analysis of EKG, echo and CXR for determination of volume-mediated pulmonary hypertension revealed a sensitivity of 25%, specificity of 75% and a positive predictive value of 40%. Preoperative identification of patients with a predisposition to manifesting elevated pulmonary pressures in the context of rapid volume infusion offers the potential for improved risk stratification and optimized clinical management.

Interleukin-1-induced nitric oxide production modulates glutathione synthesis in cultured rat hepatocytes

In cultured rat hepatocytes, we have previously demonstrated that inhibition of interleukin-1 (IL-1)-mediated nitric oxide (NO) synthesis is associated with depletion of intracellular reduced glutathione (GSH) in toxin-mediated oxidative injury. To further examine NO's effects on GSH metabolism in rat hepatocytes, IL-1-mediated NO synthesis was examined in the context of 1) cysteine, cystine, and methionine uptake; 2) gene transcription and enzyme activities for gamma-glutamylcysteine synthetase, the rate-limiting enzyme in GSH synthesis, glutathione reductase, and glutathione peroxidase; and 3) GSH and oxidized glutathione (GSSG) levels. Inhibition of NO synthesis decreased the GSH content and GSH/GSSG ratio in a guanylyl cyclase-independent fashion. Enzyme activity and steady-state levels of mRNA for gamma-glutamylcysteine synthetase were also depressed. Nuclear run-on analysis demonstrated ablation of gamma-glutamylcysteine synthetase gene transcription. Hepatocellular uptake of cysteine, cystine, and methionine was not altered. Activity and steady-state mRNA levels for glutathione reductase and glutathione peroxidase were not affected. These results indicate that IL-1-mediated NO synthesis regulates hepatocyte GSH synthesis through a mechanism that is dependent on transcriptional regulation of the rate-limiting enzyme in GSH synthesis. In the setting of oxidative stress and IL-1 exposure, hepatocyte synthesis of NO may be protective through regulation of GSH synthesis.

The emerging multifaceted roles of nitric oxide

Nitric oxide (NO) is a highly reactive free radical with a multitude of organ specific regulatory functions. Since 1985, NO has been the subject of numerous research efforts and as a result, has been found to play a major role in the cardiovascular, pulmonary, gastrointestinal, immune, and central nervous systems. In addition, deranged NO synthesis is the basis for a number of pathophysiologic states, such as atherosclerosis, pulmonary hypertension, pyloric stenosis, and the hypertension associated with renal failure. Traditional NO donors such as sodium nitroprusside and new pharmacologic NO adducts such as S-nitrosothiols may serve as exogenous sources of NO for the treatment of NO-deficient pathologic states. This review is an attempt to acquaint the surgical community with the fundamentals of NO biochemistry and physiology. Increased knowledge of its functions in normal homeostasis and pathologic states will enable physicians to better understand these disease processes and utilize new pharmacologic therapies.

A safe approach to the treatment of iliac artery aneurysms. Aortobifemoral bypass grafting with exclusion of the aneurysm

Aneurysms of the iliac arterial system are often difficult to approach surgically. Aortobifemoral (ABF) bypass grafting with exclusion of the aneurysms can be used as an alternative to the usually recommended approach of endoaneurysmorrhaphy. Fourteen patients with iliac artery aneurysms treated by ABF are compared to 16 patients treated by direct repair to compare the incidence of complications related to decreased pelvic blood flow or to the presence of the excluded iliac artery aneurysm. There were no differences between the two groups. Therefore, it is concluded that ABF is a reasonable alternative in the treatment of iliac artery aneurysms.

Coronary revascularization rather than cardiac transplantation for chronic ischemic cardiomyopathy

Patients with very poor ventricular function have been thought to be highly vulnerable to elective myocardial revascularization. Ischemic cardiomyopathy is now the major indication for cardiac transplantation. The 2-year survival of medically treated patients with ejection fractions less than 20%, but who are not sufficiently symptomatic for cardiac transplantation, is less than 25%. At our institution we have taken an aggressive approach by using myocardial revascularization for chronic ischemic cardiomyopathy. Between 1983 and 1988, 39 patients with preoperative ejection fractions less than 20% underwent coronary artery bypass. Patients were excluded if they had valvular heart disease other than mild to moderate mitral regurgitation, required resection of a left ventricular aneurysm, or required emergency operation for acute coronary occlusion. Mean age was 63.3 years (range, 43 to 80 years) and 31 were men. Mean preoperative ejection fraction was 18.3% (range, 10% to 20%) and the mean preoperative left ventricular end diastolic pressure was 22 mm Hg (range, 8 mm Hg to 38 mm Hg). There was one operative death (2.6%). Mean follow-up was 21 months (range, 3 to 60 months) with eight late deaths (a total mortality rate of 21%). Seven deaths were due to arrhythmias. Three patients continued to have severe heart failure, one of whom underwent successful cardiac transplantation. By life table analysis, there was a 3-year survival rate of 83%. With the present shortage of cardiac transplant donors, myocardial revascularization for ischemic cardiomyopathy is a reasonably effective means for preserving residual ventricular function.