Derivation of a Unique, Algorithm-Based Approach to Cancer Patient Navigator Workload Management

PURPOSE

Cancer patient navigators (CPNs) can decrease the time from diagnosis to treatment, but workloads vary widely, which may lead to burnout and less optimal navigation. Current practice for patient distribution among CPNs at our institution approximates random distribution. A literature search did not uncover previous reports of an automated algorithm to distribute patients to CPNs. We sought to develop an automated algorithm to fairly distribute new patients among CPNs specializing in the same cancer type(s) and assess its performance through simulation on a retrospective data set.

METHODS

Using a 3-year data set, a proxy for CPN work was identified and multiple models were developed to predict the upcoming week's workload for each patient. An XGBoost-based predictor was retained on the basis of its superior performance. A distribution model was developed to fairly distribute new patients among CPNs within a specialty on the basis of predicted work needed. The predicted work included the week's predicted workload from a CPN's existing patients plus that of newly distributed patients to the CPN. Resulting workload unfairness was compared between predictor-informed and random distribution.

RESULTS

Predictor-informed distribution significantly outperformed random distribution for equalizing weekly workloads across CPNs within a specialty.

CONCLUSION

This derivation work demonstrates the feasibility of an automated model to distribute new patients more fairly than random assignment (with unfairness assessed using a workload proxy). Improved workload management may help reduce CPN burnout and improve navigation assistance for patients with cancer.

Novel Techniques to Assess Predictive Systems and Reduce Their Alarm Burden

Machine prediction algorithms (e.g., binary classifiers) often are adopted on the basis of claimed performance using classic metrics such as precision and recall. However, classifier performance depends heavily upon the context (workflow) in which the classifier operates. Classic metrics do not reflect the realized performance of a predictor unless certain implicit assumptions are met, and these assumptions cannot be met in many common clinical scenarios. This often results in suboptimal implementations and in disappointment when expected outcomes are not achieved. One common failure mode for classic metrics arises when multiple predictions can be made for the same event, particularly when redundant true positive predictions produce little additional value. This describes many clinical alerting systems. We explain why classic metrics cannot correctly represent predictor performance in such contexts, and introduce an improved performance assessment technique using utility functions to score predictions based on their utility in a specific workflow context. The resulting utility metrics (u-metrics) explicitly account for the effects of temporal relationships on prediction utility. Compared to traditional measures, u-metrics more accurately reflect the real-world costs and benefits of a predictor operating in a realized context. The improvement can be significant. We also describe a formal approach to snoozing, a mitigation strategy in which some predictions are suppressed to improve predictor performance by reducing false positives while retaining event capture. Snoozing is especially useful for predictors that generate interruptive alarms. U-metrics correctly measure and predict the performance benefits of snoozing, whereas traditional metrics do not.

Closing the Gap: A Comparison of Engagement Interventions to Achieve Equitable Breast Cancer Screening in Rural Illinois

Mammography screening rates are typically lower in those with less economic advantage (EA). This study, conducted at an integrated health care system covering a mixed rurality population, assessed the ability of interventions (text messages linking to a Web microsite, digital health care workers, and a community health fair) to affect mammography screening rates and disparity in those rates among different EA populations. Payor type served as a proxy for greater (commercially insured) versus lower (Medicaid insured) EA. 4,342 subjects were included across the preintervention ("Pre") and postintervention ("Post") periods. Interventions were prospectively applied to all Medicaid subjects and randomly selected commercial subjects. Applying interventions only to lower EA subjects reversed the screening rate disparity (2.6% Pre vs. -3.7% Post, odds ratio [OR] 2.4 P < 0.01). When intervention arms ("Least," "More," "Most") were equally applied, screening rates in both EA groups significantly increased in the More arm (Medicaid OR = 2.04 P = 0.04, Commercial OR = 3.08 P < 0.01) and Most arm (Medicaid OR 2.57 P < 0.01, Commercial OR 2.33 P < 0.01), but not in the Least (text-only) arm (Medicaid OR 1.83 P = 0.11, Commercial OR 1.72 P = 0.09), although this text-only arm was inadequately powered to detect a difference. In summary, targeting interventions to those with lower EA reversed screening rate disparities, text messaging combined with other interventions improved screening rates in both groups, and future research is needed to determine whether interventions can simultaneously improve screening rates for all without worsening the disparity.

Delphi consensus on the feasibility of translating the ACEP clinical policies into computerized clinical decision support

Clinical practice guidelines are developed to reduce variations in clinical practice, with the goal of improving health care quality and cost. However, evidence-based practice guidelines face barriers to dissemination, implementation, usability, integration into practice, and use. The American College of Emergency Physicians (ACEP) clinical policies have been shown to be safe and effective and are even cited by other specialties. In spite of the benefits of the ACEP clinical policies, implementation of these clinical practice guidelines into physician practice continues to be a challenge. Translation of the ACEP clinical policies into real-time computerized clinical decision support systems could help address these barriers and improve clinician decision making at the point of care. The investigators convened an emergency medicine informatics expert panel and used a Delphi consensus process to assess the feasibility of translating the current ACEP clinical policies into clinical decision support content. This resulting consensus document will serve to identify limitations to implementation of the existing ACEP Clinical Policies so that future clinical practice guideline development will consider implementation into clinical decision support at all stages of guideline development.

Indistinguishable from magic: health and wellness in a future of sufficiently advanced technology

We describe a future in which health and wellness are transformed by (1) the availability of definitive and unambiguous tests to prove or disprove each diagnosis, (2) new methods based in systems biology to help unravel the web of messages transmitted across cellular and subcellular networks, and (3) universal access to data that has been freed from data silos to produce true data liquidity for a constellation of purposes ranging from personal health management to population health research. We believe the resulting "connected health" environment will have a profound impact on every aspect of modern life.

Cancer-associated neutropenic fever: clinical outcome and economic costs of emergency department care

Purpose. Febrile neutropenia (FN) is a common, costly, and potentially fatal complication in oncology. While FN in the inpatient setting has been extensively studied, only one study has evaluated emergency department (ED) care for FN cancer patients. That study found that 96% of patients survived the complication. We evaluated clinical and economic outcomes for cancer patients with chemotherapy-associated FN treated in an ED. Methods. ED records for consecutive oncology patients with FN were reviewed for information on death, intensive care unit (ICU) use, blood cultures, and costs. Results. Forty-eight patients (n = 57 visits) were evaluated. Six patients died from FN (12%) and four received ICU care within 2 weeks and survived (8%). Blood cultures were positive for 37% of the ED visits. The median ED time was 3.3 hours. In 91% of visits, i.v. antibiotics were administered in the ED, ordered at a median of 1.7 hours from triage (interquartile range [IQR], 1.2-2.8 hours). All patients with death or ICU in 2 weeks and all but one patient with positive blood cultures received antibiotics. The median per patient ED costs were $1,455 (IQR, $1,300-$1,579)-42.4% for hospital/nursing, 23.5% for radiology, 20.8% for physician services, 10.9% for diagnostic tests, and 2.4% for antibiotics. Conclusions. Cancer patients with FN in this sample presenting to the ED frequently had no identified source of infection. One third of the patients had positive ED blood cultures and one fifth died or required ICU care within 2 weeks. Costs of ED care were similar to the cost of a single day of inpatient care. Disclosure of potential conflicts of interest is found at the end of this article.

Metrics in the Science of Surge

Metrics are the driver to positive change toward better patient care. However, the research into the metrics of the science of surge is incomplete, research funding is inadequate, and we lack a criterion standard metric for identifying and quantifying surge capacity. Therefore, a consensus working group was formed through a "viral invitation" process. With a combination of online discussion through a group e-mail list and in-person discussion at a breakout session of the Academic Emergency Medicine 2006 Consensus Conference, "The Science of Surge," seven consensus statements were generated. These statements emphasize the importance of funded research in the area of surge capacity metrics; the utility of an emergency medicine research registry; the need to make the data available to clinicians, administrators, public health officials, and internal and external systems; the importance of real-time data, data standards, and electronic transmission; seamless integration of data capture into the care process; the value of having data available from a single point of access through which data mining, forecasting, and modeling can be performed; and the basic necessity of a criterion standard metric for quantifying surge capacity. Further consensus work is needed to select a criterion standard metric for quantifying surge capacity. These consensus statements cover the future research needs, the infrastructure needs, and the data that are needed for a state-of-the-art approach to surge and surge capacity.

Computerized physician order entry and online decision support

Computerized physician order entry (CPOE) and decision support systems (DSS) can reduce certain types of error but often slow clinicians and may increase other types of error. The net effect of these systems on an emergency department (ED) is unknown. The consensus participants combined published evidence with expert opinion to outline recommendations for success. These include seamless integration of CPOE and DSS into systems and workflow; ensuring access to Internet-based and other online support material in the clinical arena; designing systems specifically for the ED and measuring their impact to ensure an overall benefit; ensuring that CPOE systems provide error and interaction checking and facilitate weight- and physiology-based dosing; using interruptive alerts only for the highest-severity events; providing a simple, vendor-independent interface for institutional customization of CPOE alert thresholds; maximizing the use of automated systems and passive data capture; and ensuring the widespread availability of CPOE and DSS using secure wireless and portable technologies where appropriate. Decisions regarding CPOE and DSS in the ED should be guided by the ED chair or designee. Much of what is believed to be true regarding CPOE and DSS has not been adequately studied. Additional CPOE and DSS research is needed quickly, and this research should receive funding priority. DSS and CPOE hold great promise to improve patient care, but not all systems are equal. Evidence must guide these efforts, and the measured outcomes must consider the many factors of quality care.

Clinical information systems: instant ubiquitous clinical data for error reduction and improved clinical outcomes

Immediate access to existing clinical information is inadequate in current medical practice; lack of existing information causes or contributes to many classes of medical error, including diagnostic and treatment error. A review of the literature finds ample evidence to support a description of the problems caused by data that are missing or unavailable but little evidence to support one proposed solution over another. A primary recommendation of the Consensus Committee is that hospitals and departments should adopt systems that provide fast, ubiquitous, and unified access to all types of existing data. Additional recommendations cover a variety of related functions and operational concepts, from backups and biosurveillance to speed, training, and usability.

Keynote address: medical informatics and emergency medicine

A personal look at some of the developments in practical clinical informatics over the past two decades, with discussion of several successful projects, including the National Center for Emergency Medicine Informatics, the Azyxxi system, Federal Project ER One, the Institutes for Innovation in Medicine, the Medical MediaLab, Project Sentinel, and others. Lessons learned, and hints and suggestions for future developers and informaticists.

Clinical predictors of bioterrorism-related inhalational anthrax

Limitation of a bioterrorist anthrax attack will require rapid and accurate recognition of the earliest victims. To identify clinical characteristics of inhalational anthrax, we compared 47 historical cases (including 11 cases of bioterrorism-related anthrax) with 376 controls with community-acquired pneumonia or influenza-like illness. Nausea, vomiting, pallor or cyanosis, diaphoresis, altered mental status, and raised haematocrit were more frequently recorded in the inhalational anthrax cases than in either the community-acquired pneumonia or influenza-like illness controls. The most accurate predictor of anthrax was mediastinal widening or pleural effusion on a chest radiograph. This finding was 100% sensitive (95% CI 84.6-100.0) for inhalational anthrax, 71.8% specific (64.8-78.1) compared with community-acquired pneumonia, and 95.6% specific (90.0-98.5) compared with influenza-like illness. Our findings represent preliminary efforts toward identifying clinical predictors of inhalational anthrax.

False-positive urine beta-HCG in a woman with a tubo-ovarian abscess

Modern urine beta-human chorionic gonadotropin (HCG) assays that use enzyme-linked immunosorbent assay (ELISA) technology are sensitive and specific for diagnosing pregnancy, both intrauterine and ectopic, and have become indispensable to the practice of Emergency Medicine. A urine HCG test is often relied on by the Emergency Physician as a critical component in the diagnostic regimen of a patient with a possible ectopic pregnancy. We report a case of a false-positive urine beta-HCG test in a patient with a ruptured tubo-ovarian abscess. Though false-positive pregnancy tests with tubo-ovarian abscesses have previously been reported with older methods of HCG detection, we believe that this is the first case where the pregnancy test was the modern ELISA type. The mechanism for the false-positive reaction in this case is unknown, but time may show that the ELISA test kit, like its predecessors, may occasionally give a false-positive reaction in this class of patients.

Defining, identifying, and measuring error in emergency medicine

The findings of a consensus committee created to address the definition, measurement, and identification of error in emergency medicine (EM) are presented. The literature of error measurement in medicine is also reviewed and analyzed. The consensus committee recommended adopting a standard set of terms found in the medical error literature. Issues surrounding error identification are discussed. The pros and cons of mandatory reporting, voluntary reporting, and surveillance systems are addressed, as is error reporting at the clinician, hospital, and oversight group levels. Committee recommendations are made regarding the initial steps EM should take to address error. The establishment of patient safety boards at each institution is also recommended.

Emergency medicine can play a leadership role in enterprise-wide clinical information systems

At many institutions, the department of emergency medicine is uniquely suited to a leadership role in the deployment of new clinical decision support systems (computer systems that support clinical practice). Many factors favor such a leadership role, including institutional politics, organizational structure, extent of local control, clinician solidarity, openness to change, departmental size and scale, and willingness to take risks. Such a role should be undertaken in partnership with the institution's information services (IS) department, and a clear understanding of goals and responsibilities will facilitate such a partnership. A leadership position with respect to new information systems entails a certain risk, but the potential benefit to an emergency department in today's competitive environment is substantial. The authors' experience with one such collaborative development project is presented.

Computers and connectivity in Illinois emergency departments

Although the Internet has been described as "ubiquitous," little is known about the extent to which physicians have access to the Internet while providing clinical care.

OBJECTIVE

To assess the extent of Internet connectivity within the clinical area of every ED within the state of Illinois.

METHODS

This was a prospective observational study. Each Illinois ED listed in a published directory was called by telephone, and a responsible party was identified to provide information regarding the type and size of the ED, patient demographics, the types of personal computers (PCs) available in the ED (if any), the types of operating systems used, the availability of access to the World Wide Web (Web), and the highest speed at which an Internet connection could be established. Responses regarding the presence and types of PCs and the types of operating systems used were assessed using one-factor chi-square. Univariate and multivariate predictors of the type of PC used, the presence or absence of Web access, and the highest speed of Internet access were evaluated using optimal discriminant analysis and nonlinear classification tree analysis, respectively.

RESULTS

One hundred ninety-eight of the 199 EDs in the state of Illinois (99.5%) completed the survey. Of the responding EDs, 50.5% had PCs, but only 17.6% had Web access. When Web access was available, it was most often available through a high-speed Internet connection that was faster than a dial-up modem. Most departments (68.1%) with PCs used the Windows 95 or Windows 98 operating systems. A majority (62.5%) used the Netscape browser exclusively. Larger EDs (more than six ED beds) in rural or suburban areas were more likely to have a PC compared with smaller EDs (six or fewer beds). Large EDs (more than 12 ED beds) in private tertiary care or academic hospitals were most likely to have Web access.

CONCLUSIONS

Although half of Illinois EDs have PCs, only one in six has access to the Internet; thus, most emergency physicians do not have ready access to the Web from the site where they deliver clinical care.

Selective inhibition of phospholipases by atiprimod, a macrophage targeting antiarthritic compound

Azaspiranes are cationic amphiphilic compounds that are active in a number of models of autoimmune disease and transplantation. Repeated administration of cationic amphiphiles induces phospholipid accumulation in a variety of species. The present study was conducted to explore the mechanism of phospholipid accumulation in rats caused by treatment with the novel azaspirane, SK&F 106615 (atiprimod). Atiprimod inhibited the activities of partially purified phospholipases A(2) and C, but not D, in a noncompetitive manner in vitro. Treatment of rats for 28 days with 10 mg/kg/day of atiprimod increased the contents of arachidonate-containing molecular species within plasmalogen subclasses of hepatic phosphatidylcholine and phosphatidylethanolamine. In contrast, diacyl-linked species were not affected, indicating a selective effect upon an hepatic plasmalogen-selective phospholipase A(2). Taken together, the data suggest that the beneficial effects of atiprimod in autoimmune diseases may involve inhibition of phospholipase A(2) and C activities. Further, the data suggest that atiprimod is a selective inhibitor of plasmalogen-selective phospholipase A(2) in vivo.

Atiprimod (SK&F 106615), a novel macrophage targeting agent, enhances alveolar macrophage candidacidal activity and is not immunosuppressive in Candida-infected mice

Azaspiranes are novel macrophage-targeting agents with activity in preclinical animal models of autoimmune disease and transplantation. The purpose of this work was to determine the effects of atiprimod (SK&F 106615), an azaspirane being developed for the treatment of rheumatoid arthritis, on rat pulmonary alveolar macrophage (AM) function and immunocompetance in Candida-infected mice. AM from rats treated with 20 mg/kg/day of atiprimod for 15 days demonstrated enhanced killing of Candida albicans ex vivo. Concentration-dependent increases in candidacidal activity were also observed as early as one hour after exposure in vitro in AM from untreated normal rats. Treatment of AM with atiprimod in vitro did not increase particulate-stimulated superoxide production or phagocytosis of Candida but decreased their ability to concentrate acridine orange, indicating an increase in lysosomal pH. Increased candidacidal activity was inhibited by superoxide dismutase and catalase, suggesting a role for reactive oxygen intermediates (ROI). Atiprimod also increased free radical-mediated killing of Candida in the presence of H2O2, iron and iodide in a cell-free system. These findings indicated that treatment with atiprimod increased the candidacidal activity of rat AM in a free radical-dependent manner. The data also suggested that atiprimod did not increase ROI production by AM, but rather increased the efficiency of radical-mediated killing. This increase may be caused by cyclization of atiprimod, facilitating electron transfer and peroxidation of lipid membranes. In vivo studies in Candida-infected CBA mice showed that atiprimod (10 mg/kg/day), did not compromise immune function in the infected mice and could be differentiated from prototypical immunosuppressive compounds used for treatment of autoimmune diseases.

Effect of aging on mixed-function oxidation and conjugation by isolated perfused rat livers

Aging is known to decrease hepatic cytochrome P450 content in rats. However, limited information is available on the effects of aging on mixed-function oxidation and conjugation in intact liver. The purpose of these studies was to determine the effects of aging on oxidation and conjugation of p-nitrophenol (pNP) in perfused livers from male Sprague-Dawley rats. Livers from senescent (22-24 months) or young adult (3-6 months) rats were perfused in a nonrecirculating hemoglobin-free system and supplemented with pNP (60 microM). Glucuronide and sulfate conjugates of the oxidation product, 4-nitrocatechol, in effluent perfusate were cleaved enzymatically and 4-nitrocatechol was determined colorimetrically. Rates of 4-nitrocatechol production were decreased in senescent compared with young adult rats (0.67 +/- 0.14 vs 0.92 +/- 0.15 micromol/g/hr). However, the rates of oxidation of pNP in microsomes from senescent rats were similar to those in young adult rats. Hepatic malate content was decreased approximately 50% in livers from senescent compared with young adult rats in the presence and absence of pNP, suggesting that movement of reducing equivalents from the mitochondria to the cytosol, and thus cytosolic NADPH supply, may have been diminished by senescence. The rates of conjugation of 60 microM pNP in perfused livers from senescent rats were similar to those in young adult rats, but Km and Vmax values of microsomal 4-nitrocatechol glucuronyltransferase were about 2.5- and 1.6-fold higher, respectively, in livers from senescent compared with young adult rats. Hepatic glycogen content was about 50% lower in livers from senescent compared with young adult rats, but the contents of UDP-glucose and UDP glucuronic acid were similar between the two groups. Taken together, the data are consistent with the hypothesis that rates of mixed-function oxidation are decreased in intact livers from senescent compared with young adult rats, due possibly to age-related changes in cofactor supplies. Glucuronidation of low, but not high, concentrations of substrates may be affected by age-related changes in Km and Vmax values of microsomal glucuronyltransferase.

Toxic psychosis: an unusual presentation of propranolol intoxication

Timely diagnosis of acute propranolol intoxication requires a high index of suspicion and a knowledge of the multiple ways in which these patients may present to the emergency department. We report a case of severe propranolol intoxication that presented as an acute psychotic episode preceding cardiovascular decompensation and seizures by several hours. Though acute reversible psychosis has been appreciated after initiating or increasing propranolol dosage therapeutically, this association has not been reported in the literature regarding beta blocker overdose or intoxication. Propranolol psychosis and several other pertinent aspects of this case are discussed.

General ophthalmologic examination

Caring for patients with eye emergencies will always challenge even the most experienced emergency clinician. The threat of loss of sight is anxiety provoking for patients and requires the physician to act in an organized and expeditious manner. By avoiding these pitfalls and examining each patient in a systematic and comprehensive fashion, the physician can ensure the best possible outcome. The ensuing articles describe the approach to diagnosing and treating significant eye emergencies in greater detail.

Acute pulmonary embolism. Aggressive therapy with anticoagulants and thrombolytics

Patients with acute pulmonary embolism are at risk for early death or chronic morbidity. Appropriate therapy can dramatically reduce the incidence of both. Oxygen and heparin therapy should be started as soon as the diagnosis is suspected. The condition of a hypotensive patient with right ventricular overload from acute pulmonary embolism usually is made worse by a fluid challenge; hypotension may be relieved by preload reduction or even by gentle diuresis. Norepinephrine (Levophed), isoproterenol hydrochloride (Isuprel), and epinephrine are the pressor agents of choice. Immediate thrombolysis is the standard of care for any patient with significant hypoxemia or hypotension due to proven pulmonary embolism. Beyond this, the potential benefit of using thrombolytic agents should be considered routinely for every patient with proven pulmonary embolism. Surgical embolectomy is useful for unstable pulmonary embolism when there are absolute contraindications to thrombolysis or when thrombolytic therapy fails. Empirical use of thrombolysis may be considered as a last-ditch effort for a critically ill patient when there is a high clinical suspicion of pulmonary embolism. Standard closed-chest cardiopulmonary resuscitation is ineffective when the pulmonary circulation is obstructed by thrombus. Emergency thoracotomy or femorofemoral cardiopulmonary bypass is appropriately used in patients with full cardiac arrest from pulmonary embolism.

Chronic pulmonary embolism. Often misdiagnosed, difficult to treat

Chronic thromboembolic pulmonary hypertension with cor pulmonale is an extremely debilitating disease that (1) is more common than generally recognized, (2) is often misdiagnosed, and (3) is difficult to treat. When a patient has persistent exertional dyspnea with no obvious cause, a ventilation-perfusion scan, echocardiography, and (if indicated) pulmonary angiography should be done. Prevention is especially important because by the time a patient is symptomatic, the disease is already far advanced and hemodynamic reserves are greatly reduced. Prevention of recurrence mandates lifetime anticoagulation and placement of a vena cava filter. The only effective treatment is pulmonary endarterectomy, which is being performed at an increasing number of specialty centers across the United States.

Hepatobiliary function in senescent male Sprague-Dawley rats

The purpose of these studies was to investigate intrahepatic changes underlying age-related decreases in bile flow by evaluating the effects of aging on bile acid-dependent and -independent flow, canalicular versus ductular flow and hepatic tight junction permeability. The isolated perfused liver was used to assess age-related changes in intrinsic hepatobiliary function without the complications of extrahepatic factors such as circulating hormones or hemodynamics. Livers from young adults (3 to 6 mo old) or senescent (22 to 26 mo old) male Sprague-Dawley rats were isolated and perfused in a nonrecirculating, hemoglobin-free system to assess oxygen uptake, bile acid-dependent and -independent bile flow, bile acid uptake, carbon 14-labeled erythritol clearance as a measure of canalicular flow, tight junction permeability and transcellular transport into bile. Rates of oxygen uptake by livers from senescent rats were significantly lower than those of young adults (75 +/- 8 mumol/gm/hr vs. 121 +/- 5 mumol/gm/hr). Age-related decreases in total bile flow were observed and were associated with similar reductions in 14C-erythritol clearance suggestive of decreased canalicular bile flow. Bile acid-dependent and -independent flow was decreased by 50% and 60%, respectively, in isolated perfused livers from senescent rats. Hepatocellular uptake of taurocholate and rates of bile acid excretion also were about 50% lower in senescent than in young adult rats. Tight junction permeability and transcellular transport were assessed by monitoring appearance of tritiated inulin and horseradish peroxidase in bile after bolus injections of these compounds through the portal vein. Tritiated inulin appearance in bile was decreased slightly in senescent compared with young rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of hepatobiliary function in vivo and ex vivo in the rat

Many xenobiotics cause hepatobiliary toxicity and cholestasis in the rat. Initial assessment of hepatobiliary damage in rats can be accomplished by measuring serum concentrations of bile acids and bilirubin, serum activities of liver-associated enzymes such as 5'-nucleotidase, alkaline phosphatase, gamma-glutamyltranspeptidase, and plasma clearances of dyes [e.g., bromosulfophthalein (BSP)] excreted primarily through the bile. More detailed evaluation of hepatobiliary disturbances involves cannulation of the bile duct of anesthetized rats and subsequent measurement of rates of bile flow, bile acid excretion, and bile composition. Canalicular bile flow can be estimated from clearances of nonmetabolized sugars (i.e., erythritol) which enter bile via paracellular transport. Tight junction permeability also can be assessed by either biliary excretion of such a marker as horseradish peroxidase or sucrose following portal vein infusion or via retrograde biliary infusion. Subsequent morphologic evaluation of the liver provides information on damage to cells which may contribute to hepatobiliary dysfunction (i.e., bile duct obstruction). Isolated perfused livers offer the ability to measure all of the above mentioned parameters as well as to make a more accurate determination of the effects of xenobiotics on bile acid-dependent and -independent bile flow. A good example of the advantage of combining techniques as well as following complete time courses of changes in hepatobiliary function is provided by using studies of alpha-naphthylisothiocyanate-induced hepatotoxicity.

Cholestatic potentials of alpha-naphthylisothiocyanate (ANIT) and beta-naphthylisothiocyanate (BNIT) in the isolated perfused rat liver

Previous studies in rats have shown that a single oral dose of alpha-naphthylisothiocyanate (ANIT), but not the regioisomer beta-naphthylisothiocyanate (BNIT), results in intrahepatic cholestasis. The present studies were designed to evaluate the intrinsic cholestatic potential of ANIT and BNIT in the isolated perfused rat liver. Livers from male Sprague-Dawley rats (300-450 g) were isolated and perfused with Krebs-Henseleit buffer supplemented with 50 microM taurocholate and ANIT or BNIT (0, 5, 15 or 50 microM). Rates of bile flow, bile acid uptake and bile acid excretion were monitored for up to 70 min. Permeability of tight junctions also was evaluated. At concentrations of 5 microM, neither ANIT nor BNIT altered hepatobiliary function or tight junction permeability. In contrast, perfusion with 50 microM ANIT or BNIT for 35 min resulted in decreases in bile flow rates of 19 +/- 8 and 13 +/- 4%, respectively. After 70 min of perfusion with ANIT or BNIT, rates of bile flow were decreased by 78 +/- 5 and 71 +/- 4%, respectively. Bile acid excretion also was decreased following perfusion with 50 microM ANIT or BNIT. Perfusion with 50 microM ANIT or BNIT decreased bile acid uptake by 51 +/- 13 and 46 +/- 6%, respectively, at 60 min. Bile/plasma (B/P) ratios of [3H]sucrose were not affected by ANIT or BNIT at any time during perfusion, indicating that changes in bile flow and bile acid excretion in the isolated perfused liver were not associated with increased hepatocyte tight junction permeability. These data demonstrate that the direct portal infusion of a 50 microM concentration of either ANIT or BNIT produced marked decreases in bile flow, indicating that these isomers have a comparable intrinsic cholestatic potential in the isolated perfused liver.

Evidence that catalase is a major pathway of ethanol oxidation in vivo: dose-response studies in deer mice using methanol as a selective substrate

Recently, it was demonstrated that 4-methylpyrazole was not only an inhibitor of alcohol dehydrogenase but also caused competitive inhibition of fatty acyl-CoA synthetase, the enzyme which activates fatty acids (B. U. Bradford, D. T. Forman, and R. G. Thurman, 1993, Mol. Pharmacol. 43, 115-119). Rates of catalase-dependent alcohol metabolism were decreased in alcohol dehydrogenase-negative (ADH-) deer mice because the H2O2 supply for catalase via peroxisomal fatty acid oxidation was inhibited due to substrate limitation. In light of these findings it became necessary to reevaluate the role of catalase and alcohol dehydrogenase in alcohol metabolism. In this study, methanol, a selective substrate for catalase in rodents, was compared with ethanol. Rates of ethanol and methanol metabolism were studied in vivo at blood alcohol levels ranging from 50 to 500 mg/dl. In the ADH- deer mouse, rates of methanol and ethanol metabolism increased when alcohol was elevated from 0 to 100 mg/dl and were maximal at values around 6-8 mmol/kg/h (half-maximal rates were observed at blood alcohol levels around 50 mg/dl). In the ADH+ deer mouse, rates of ethanol metabolism increased to values around 9 mmol/kg/h at 100 mg/dl and remained constant at blood levels up to 500 mg/dl. In contrast, rates of methanol metabolism increased to values of only 5 mmol/kg/h at levels of 100 mg/dl (the half-maximal rate was about 2.5 mmol/kg/h at 50 mg/dl) followed by a steady increase to 9 mmol/kg/h as the blood level was increased from 100 to 500 mg/dl (the half-maximal rate for this second component was around 6 mmol/kg/h at 300 mg/dl). Rates of methanol uptake were 50 +/- 4 nmol/min/mg protein in 10,000g pellets from ADH- deer mouse livers; however, methanol was not metabolized by isolated microsomes. The catalase inhibitor aminotriazole decreased ethanol and methanol metabolism 75% in ADH- deer mice. Further, olive oil, which is rich in oleate, increased methanol metabolism from 7 to 11.5 mmol/kg/h. This stimulation was blocked by fructose, which diminishes ATP and decreases H2O2 supply. In the ADH+ deer mouse, fructose (2 g/kg) stimulated ethanol metabolism as expected; however, inhibition of both ethanol and methanol metabolism was observed with higher doses of fructose (10 g/kg). Taken together, these data support the hypothesis that catalase is the predominant pathway for alcohol metabolism in the ADH- deer mouse. The contribution of catalase was about 50% in the ADH+ mutant at low doses of ethanol and approached 100% as the alcohol concentration was elevated.

Temporal relationship of changes in hepatobiliary function and morphology in rats following alpha-naphthylisothiocyanate (ANIT) administration

These studies were designed to evaluate ANIT-induced changes in both hepatobiliary function and morphology during the onset, progression, and recovery of ANIT-induced cholestasis. A single oral dose of 150 mg/kg of ANIT or vehicle was administered by gavage to male Sprague-Dawley rats and hepatobiliary structure and function were evaluated 16, 24, 48, 72, and 168 hr later. Increased hepatocellular tight junction permeability, increased serum bile acids, and decreased bile acid excretion were observed 16 hr after ANIT administration. At 24 hr, bile flow was decreased in ANIT-treated rats, an effect accompanied by increased tight junction permeability, decreased bile acid excretion, and decreased erythritol clearance (estimate of canalicular flow). In addition, scattered small loci of hepatocellular necrosis accompanied by an inflammatory cell response were observed in ANIT-treated rats at this time, with no microscopic evidence of bile duct obstruction (BDO). These data suggest that the onset of ANIT-induced cholestasis was associated with hepatocanalicular changes and not BDO. In contrast, at 48 and 72 hr after ANIT treatment, cholestasis was more profound and was accompanied by mild hepatocellular necrosis and widespread BDO. Hepatocyte tight junction permeability in ANIT-treated rats was not different from controls at 72 hr. These data suggest that the pathogenesis of ANIT-induced cholestasis is biphasic; the onset of cholestasis appears to be associated with changes in hepatocanalicular function and increased tight junction permeability whereas the later and more profound phase of cholestasis appears to be related to a combination of BDO and hepatocellular dysfunction. The time course of biochemical and morphologic changes following ANIT treatment further suggests that the pathophysiologic changes during the onset or initiation phase of cholestasis differ from those involved in the later and more profound phase of ANIT-induced cholestasis.

Chronic ethanol treatment induces H2O2 production selectively in pericentral regions of the liver lobule

Chronic treatment with ethanol damages pericentral regions of the liver selectively, and reactive oxygen species such as H2O2 may be involved in the mechanism of hepatotoxicity. To test this idea, the effect of chronic treatment with ethanol on rates of H2O2 production was measured in tissue cylinders isolated from periportal and pericentral regions of livers from ethanol-treated rats. Rates of hydrogen peroxide production, assessed from the oxidation of methanol to formaldehyde by catalase-H2O2, were similar in tissue cylinders isolated from periportal regions in control and ethanol-treated rats. In contrast, rates of H2O2 production were over 4-fold higher in tissue isolated from pericentral regions of livers from ethanol-treated than control animals (1.7 +/- 0.5 vs. 0.4 +/- 0.3 nmol/min/mg protein, respectively). Rates of H2O2-generating acyl CoA oxidase activity were equivalent in tissue cylinders from periportal regions of livers from both groups (approximately 2 nmol/min/mg protein), but were over 2-fold higher in tissue cylinders from pericentral regions of livers from ethanol-treated rats than from controls. In contrast, catalase activity was increased nearly 2-fold in homogenates from both periportal and pericentral regions by ethanol treatment while glutathione peroxidase activity was decreased significantly in both regions. These data demonstrate that ethanol increases H2O2 generation in pericentral regions of the liver lobule in part by elevating rates of peroxisomal beta-oxidation of acyl CoA compounds and are consistent with the hypothesis that local increases in H2O2 production may be involved in the mechanism of ethanol-induced hepatotoxicity.

Transient activation of hepatic glycogenolysis by thrombin in perfused rat livers

Thrombin, a peptide with native protease activity, caused a rapid (less than 1 min) increase in glycogenolysis of about 30%, assessed from rates of production of glucose+lactate+pyruvate, and in oxygen uptake in perfused rat liver. These increases were followed by a rapid return to basal values within 5 min. The effect of thrombin on glycogenolysis was dose-dependent and was maximal at perfusate concentrations around 1 U/ml. Interestingly, the effect of thrombin on glycogenolysis could be elicited only once in any given liver. The activation of glycogenolysis by thrombin was diminished nearly 50% by prior infusion of the protease inhibitor, diisopropyl fluorophosphate (10 microM), and over 90% when thrombin was treated with diisopropyl fluorophosphate prior to infusion. The stimulation of glycogenolysis by thrombin could be detected in isolated hepatocytes or in livers stored for 24 h in cold Euro-Collins solution, a treatment which destroys endothelial cells. Further, thrombin stimulated production of prostaglandin D2 from arachidonic acid in cultured hepatic endothelial but not Kupffer cells. The effect of thrombin on carbohydrate output was also blocked by a phospholipase A2 inhibitor (quinacrine, 50 microM) and by an inhibitor of the cyclooxygenase (indomethacin, 20 microM), suggesting the involvement of cyclooxygenase in the mechanism of action of thrombin. In support of this idea, the transient kinetics of stimulation of glycogenolysis by thrombin and arachidonic acid was nearly identical to release of thromboxane B2 (80-420 pg/ml) and prostaglandin D2 (300-900 pg/ml) from the perfused liver. Further, a second addition of thrombin failed to increase thromboxane and prostaglandin D2 release as well as carbohydrate production, supporting a causal link between these phenomena. Taken together, these data support the hypothesis that thrombin interacts with receptors in the liver, possibly on endothelial cells, leading to activation of phospholipase A2 and subsequent transient production of prostaglandins and thromboxanes. These mediators subsequently interact with receptors on parenchymal cells, leading to a transient stimulation of glycogenolysis.

Oxidoreduction of butanol in deermice (Peromyscus maniculatus) lacking hepatic cytosolic alcohol dehydrogenase

In view of conflicting information in the literature regarding enzyme systems responsible for alcohol oxidation in deermice previously reported to lack hepatic alcohol dehydrogenase (ADH) activity, the reversibility of butanol oxidation was studied in vivo and in liver-perfusion systems. Mixtures of [1,1-2H2]ethanol and butanol were given intraperitoneally to deermice lacking (ADH-) or possessing (ADH+) ADH activity, followed by analysis of alcohols in blood by GC/MS. 2H exchange between the two alcohols was seen in all experiments. In ADH- deermice, the 2H excess of butanol increased steadily and reached 18 +/- 5% after 2.5 h. In ADH+ deermice, butanol was rapidly eliminated and the 2H excess was about 7% after 0.5 h. In similar experiments with rats, the 2H excess was about 40% for 2 h. Perfusions of livers from ADH- deermice with mixtures of unlabelled and 1-[2H]butanol showed significant but slow intermolecular hydrogen transfer at C1, indicating oxidoreduction catalyzed by a dehydrogenase. Slow reduction of butanal was observed in mitochondria from ADH- deermice. ADH activity with a pH optimum of 10 and Km for ethanol of 6 mM was detected in the inner mitochondrial membranes from rats and deermice. However, low rates of oxidation observed in experiments carried out with perfused livers and in vitro suggest that this enzyme system does not contribute significantly to alcohol oxidation in vivo. Thus, perfused liver from ADH- deermice appears to be a useful system for studies of ADH-independent oxidation of alcohols. The 2H exchange between the alcohols seen in vivo indicates that both ethanol and butanol are substrates for a common extrahepatic dehydrogenase in ADH- deermice.

Induction of peroxisomes by treatment with perfluorooctanoate does not increase rates of H2O2 production in intact liver

Increases in acyl coenzyme A (CoA) oxidase activity due to peroxisome proliferation are postulated to cause oxidative stress via elevated production of H2O2, leading to DNA damage. These changes are suspected to be responsible for tumor formation caused by non-genotoxic carcinogens which do not bind to DNA but cause proliferation of peroxisomes. However, the activity of the peroxisomal enzyme acyl CoA oxidase assayed in vitro in the presence of excess fatty acyl CoA substrate may not reflect rates of H2O2 generation in intact liver where fatty acid supply is carefully controlled in part by delivery of substrate. The purpose of this work was to determine if rates of hepatic H2O2 generation were altered in perfused liver and in vivo following induction of H2O2-generating acyl CoA oxidase activity. Injection of the potent peroxisome proliferating agent perfluorooctanoate into rats 5 days prior to sacrifice caused an expected 4-fold increase of H2O2-generating acyl CoA oxidase activity measured in hepatic homogenates. In contrast, rates of H2O2 generation in perfused liver measured spectrophotometrically (660-640 nm) through a lobe of the liver were not altered by perfluorooctanoate treatment (7.3 +/- 1.5 vs. 7.8 +/- 0.5 mumol/g/h in livers from untreated control rats). Similar treatment with perfluorooctanoate also increased in vitro acyl CoA oxidase activity 9-fold in livers from deermice; however, rates of elimination of methanol, a selective substrate for catalase in rodents whose oxidation is limited by the supply of H2O2, were not altered significantly in vivo (control, 110 +/- 11 mumol/g/h vs. perfluorooctanoate, 112 +/- 32 mumol/g/h). Taken together, these data demonstrate that elevation of H2O2 formation by acyl CoA oxidase activity measured in vitro is not necessarily associated with increases in rates of H2O2 generation in intact perfused liver or in vivo, most likely due to rate-limitation in intact cells by fatty acid supply. These data do not support the hypothesis that the induction of peroxisomes leads to excessive H2O2 production and oxidative stress. It follows that alternative hypotheses to explain carcinogenesis caused by peroxisome-proliferating agents need to be considered.

Inhibition of ethanol metabolism by fructose in alcohol dehydrogenase-deficient deer mice in vivo

The purpose of this work was to compare the roles of a newly described mitochondrial dehydrogenase and catalase in ethanol elimination in deer mice deficient in alcohol dehydrogenase (ADH-). Fructose was used because of its well-known ability to stimulate dehydrogenase-dependent ethanol metabolism. Rates of ethanol metabolism in vivo were decreased significantly by about 60% in a dose-dependent manner by fructose in deer mice fed an ethanol-containing or a corn oil control diet. In addition, rates of metabolism of methanol, a selective substrate for catalase in rodents, were similar to rates of ethanol elimination and were decreased from 6.9 +/- 1.0 to 1.7 +/- 0.5 mmol/kg/h by fructose, supporting the hypothesis that catalase and not a mitochondrial dehydrogenase predominates in ethanol oxidation in ADH-deer mice. Glycolate, a substrate for peroxisomal H2O2 generation, reversed the inhibition of alcohol metabolism by fructose completely, indicating that fructose did not inhibit catalase directly. As expected, the ATP/ADP ratio was decreased by fructose significantly from 4.2 +/- 0.4 to 2.4 +/- 0.4 in deer mouse livers. These data are consistent with the hypothesis that fructose decreases catalase-dependent ethanol metabolism in vivo by inhibiting hepatic H2O2 generation.

Studies on the reduction of endogenously generated prostaglandin G2 by prostaglandin H synthase

Prostaglandin H synthase oxidizes arachidonic acid to prostaglandin G2 (PGG2) via its cyclooxygenase activity and reduces PGG2 to prostaglandin H2 by its peroxidase activity. The purpose of this study was to determine if endogenously generated PGG2 is the preferred substrate for the peroxidase compared with exogenous PGG2. Arachidonic acid and varying concentrations of exogenous PGG2 were incubated with ram seminal vesicle microsomes or purified prostaglandin H synthase in the presence of the reducing cosubstrate, aminopyrine. The formation of the aminopyrine cation free radical (AP.+) served as an index of peroxide reduction. The simultaneous addition of PGG2 with arachidonic acid did not alter cyclooxygenase activity of ram seminal vesicle microsomes or the formation of the AP.+. This suggests that the formation of AP.+, catalyzed by the peroxidase, was supported by endogenous endoperoxide formed from arachidonic acid oxidation rather than by the reduction of exogenous PGG2. In addition to the AP.+ assay, the reduction of exogenous versus endogenous PGG2 was studied by using [5,6,8,9,11,12,14,15-2H]arachidonic acid and unlabeled PGG2 as substrates, with gas chromatography-mass spectrometry techniques to measure the amount of reduction of endogenous versus exogenous PGG2. Two distinct results were observed. With ram seminal vesicle microsomes, little reduction of exogenous PGG2 was observed even under conditions in which all of the endogenous PGG2 was reduced. In contrast, studies with purified prostaglandin H synthase showed complete reduction of both exogenous and endogenous PGG2 using similar experimental conditions. Our findings indicate that PGG2 formed by the oxidation of arachidonic acid by prostaglandin H synthase in microsomal membranes is reduced preferentially by prostaglandin H synthase.

Acute and chronic ethanol treatment in vivo increases malate-aspartate shuttle capacity in perfused rat liver

The effects of acute and chronic treatment with ethanol on transport of reducing equivalents into mitochondria via the malate-aspartate shuttle were studied in perfused rat liver. The shuttle capacity was estimated from the decrease in rates of glucose production from the reduced substrate sorbitol caused by an increase in the NADH/NAD+ ratio in the cytosol due to metabolism of ethanol. The greater the capacity of the malate-aspartate shuttle, the smaller the inhibition of glucose synthesis by ethanol. Glucose synthesis was decreased about 2-fold less in livers from fasted rats treated acutely 2.5 h earlier with ethanol than in untreated controls. Chronic treatment with ethanol for 3-5 weeks prevented completely the decrease in glucose synthesis from sorbitol due to ethanol oxidation. Rates of ethanol uptake were elevated significantly from 69 +/- 7 mumols/g/h in livers from control rats up to 92 +/- 7 mumols/g/h in livers from SIAM rats. Similarly, rates of ethanol uptake were stimulated by chronic ethanol treatment from 71 +/- 6 to 222 +/- 15 mumols/g/h; this increase was largely sensitive to aminooxyacetate. Taken together, these data indicate that flux of reducing equivalents over the malate-aspartate shuttle is increased by both acute and chronic treatment with ethanol and that movement of reducing equivalents from the cytosol into the mitochondria via the malate-aspartate shuttle is an important rate determinant in hepatic ethanol oxidation.

Mitogenic signaling by epidermal growth factor (EGF), but not platelet-derived growth factor, requires arachidonic acid metabolism in BALB/c 3T3 cells. Modulation of EGF-dependent c-myc expression by prostaglandins

Previously, we have shown that prostaglandins are necessary, but not sufficient, for the stimulation of mitogenesis in BALB/c 3T3 fibroblasts by epidermal growth factor (EGF) (Nolan, R. D., Danilowicz, R. M., and Eling, T. E. (1988) Mol. Pharmacol. 33, 650-656). The purpose of this work was to extend these findings to another potent mitogen, platelet-derived growth factor (PDGF), and to determine if metabolism of arachidonic acid to prostaglandins is necessary for stimulation of expression of the protooncogene c-myc by EGF, which is an early event in the mitogenic cascade. In BALB/c 3T3 cells grown to about 70% confluence and deprived of serum for 16-24 h, PDGF stimulated [3H]thymidine uptake into DNA significantly in a concentration-dependent manner, but did not increase production of prostaglandin E2 (PGE2). The addition of indomethacin, a prostaglandin H synthase inhibitor, or nordihydroguaiaretic acid, a lipoxygenase inhibitor, did not affect PDGF-stimulated thymidine uptake into DNA. In addition, PGE2 enhanced EGF-dependent, but not PDGF-dependent, mitogenesis. Taken together, the data support the hypothesis that prostaglandins are not involved in PDGF-dependent mitogenesis. In contrast, indomethacin (10(-6) M) and nordihydroguaiaretic acid (10(-6) M) inhibited EGF-stimulated thymidine uptake and c-myc expression by approximately 50%. Addition of PGG2 (10(-7) to 10(-5) M) in the presence of indomethacin and EGF restored the ability of EGF to elevate c-myc RNA levels and DNA synthesis. When PGF2 alpha (10(-8) to 10(-5) M) was added in the presence of EGF, c-myc RNA levels and thymidine incorporation were elevated up to 5-6-fold above levels observed with EGF alone. These data support the hypothesis that metabolism of arachidonic acid to prostaglandins is necessary for stimulation of c-myc expression by EGF in BALB/c 3T3 cells.

Interactions between plasticizers and fatty acid metabolism in the perfused rat liver and in vivo. Inhibition of ketogenesis by 2-ethylhexanol

Rates of ketone body (beta-hydroxybutyrate plus acetoacetate) production by perfused livers from starved rats were decreased about 60% from 39 +/- 2 to 17 +/- 3 mumol/g/hr by 2-ethylhexanol (200 microM), a primary metabolite of the plasticizer diethylhexyl phthalate. Inhibition of ketogenesis by ethylhexanol was dose dependent (half-maximal inhibition occurred with 25 microM) in the presence or absence of 4-methylpyrazole, an inhibitor of alcohol dehydrogenase. Concentrations of beta-hydroxybutyrate relative to acetoacetate (B/A) increased in a step-wise manner from 0.32 to 0.75 in the effluent perfusate when ethylhexanol was infused. In contrast, the B/A ratio decreased in parallel with inhibition of ketone body production when alcohol dehydrogenase was inhibited. Pretreatment of rats with phenobarbital, an inducer of omega and omega-1 hydroxylases, diminished inhibition of ketone body production by low (less than 50 microM) of ethylhexanol. Thus, ethylhexanol is oxidized via phenobarbital-inducible pathways to metabolites which do not inhibit ketogenesis. Studies were conducted to determine the site of inhibition of fatty acid oxidation by ethylhexanol. Rates of ketone body production in the presence of oleate (250 microM), which requires transport of the corresponding CoA compound into mitochondria, were reduced from 80 +/- 6 to 58 +/- 8 mumol/g/hr by ethylhexanol. In contrast, ketone body production from hexanoate, which is activated in the mitochondria, was not affected by ethylhexanol. Basal and oleate-stimulated rates of H2O2 production were not affected by ethylhexanol, indicating that peroxisomal beta-oxidation was not altered by the compound. Based on these data it is concluded that 2-ethylhexanol inhibits beta-oxidation of fatty acids in mitochondria but not in peroxisomes. Treatment of rats with ethylhexanol (0.32 g/kg, i.p.) decreased plasma ketone bodies from 1.6 to 0.8 mM, increased hepatic triglycerides and increased lipid predominantly in periportal regions of the liver lobule. These data indicate that alterations in hepatic fatty acid metabolism in periportal regions of the liver lobule may be early events in peroxisome proliferation.

Redox interactions between catalase and alcohol dehydrogenase pathways of ethanol metabolism in the perfused rat liver

Alcohol metabolism via alcohol dehydrogenase (ADH) and catalase was studied in perfused rat livers by measuring the oxidation of methanol and butanol, selective substrates for catalase and ADH, respectively. In livers from fasted rats, basal rates of methanol uptake of 15 +/- 1 mumol/g/h were decreased significantly to 8 +/- 2 mumol/g/h by addition of butanol. Concomitantly, pyridine nucleotide fluorescence detected from the liver surface was increased by butanol but not methanol. Both effects of butanol were blocked by an inhibitor of ADH, 4-methylpyrazole, consistent with the hypothesis that elevation of the NADH redox state by butanol inhibited H2O2 production via NAD+-requiring peroxisomal beta-oxidation, leading indirectly to diminished rates of catalase-dependent methanol uptake. In support of this idea, both butanol and butyraldehyde inhibited H2O2 generation. The NADH redox state was also elevated by xylitol, causing a 75% decrease in rates of methanol uptake by livers from fasted rats. This effect was not observed in livers from fed rats unless malate-aspartate shuttle activity was reduced by infusion of the transaminase inhibitor aminooxyacetate. Taken together, these data indicate that generation of reducing equivalents from ADH in the cytosol inhibits H2O2 generation leading to significantly diminished rates of peroxidation of alcohols via catalase. This phenomenon may represent an important physiological mechanism of regulation of ethanol oxidation in intact cells.

Dehydrogenase-dependent ethanol metabolism in deer mice (Peromyscus maniculatus) lacking cytosolic alcohol dehydrogenase. Reversibility and isotope effects in vivo and in subcellular fractions

Elimination of [2H]ethanol in vivo as studied by gas chromatography/mass spectrometry occurred at about half the rate in deer mice reported to lack alcohol dehydrogenase (ADH-) compared with ADH+ deer mice and exhibited kinetic isotope effects on Vmax and Km (D(V/K] of 2.2 +/- 0.1 and 3.2 +/- 0.8 in the two strains, respectively. To an equal extent in both strains, ethanol elimination was accompanied by an ethanol-acetaldehyde exchange with an intermolecular transfer of hydrogen atoms, indicating the occurrence of dehydrogenase activity. This exchange was also observed in perfused deer mouse livers. Based on calculations it was estimated that at least 50% of ethanol elimination in ADH- deer mice was caused by the action of dehydrogenase systems. NADPH-supported cytochrome P-450-dependent ethanol oxidation in liver microsomes from ADH+ and ADH- deer mice was not stereoselective and occurred with a D(V/K) of 3.6. The D(V/K) value of catalase-dependent oxidation was 1.8, whereas a kinetic isotope effect of cytosolic ADH in the ADH+ strain was 3.2. Mitochondria from both ADH+ and ADH- deer mice catalyzed NAD+-dependent ethanol oxidation and NADH-dependent acetaldehyde reduction. The kinetic isotope effects of NAD+-dependent ethanol oxidation in the mitochondrial fraction from ADH+ and ADH- deer mice were 2.0 +/- 0.1 and 2.3 +/- 0.3, respectively. The results indicate only a minor contribution by cytochrome P-450 to ethanol elimination, whereas the isotope effects are consistent with ethanol oxidation by the catalase-H2O2 system in ADH- deer mice in addition to the dehydrogenase systems.

New perspectives in catalase-dependent ethanol metabolism

The notion that catalase is a minor pathway of ethanol oxidation must be reexamined in view of recent work. Studies with aminotriazole demonstrate clearly that catalase can be the predominant pathway of ethanol metabolism. In addition, these studies illustrate that caution must be used in interpretation of work with aminotriazole unless the extent of inhibition of catalase is controlled carefully. Studies of rates of oxidation of butanol, a specific substrate for alcohol dehydrogenase, and methanol, a substrate for catalase, indicate that peroxidation via catalase supported by H2O2 formed by the peroxisomal beta-oxidation of fatty acids is the predominant pathway of alcohol oxidation in the fasted state.

Hepatic ethanol metabolism is mediated predominantly by catalase-H2O2 in the fasted state

Methanol and butanol were employed as selective substrates for catalase-H2O2 and alcohol dehydrogenase (ADH), respectively, in the perfused rat liver. As expected, rates of butanol metabolism accounted for over 85% of overall rates of alcohol oxidation indicating that ADH was the predominant pathway of alcohol metabolism in both the fed or fasted state in the absence of added substrate. In the fasted state, however, addition of oleate (1 mM) diminished butanol oxidation 20-25% yet increased rates of methanol oxidation over 4-fold. Under these conditions, methanol uptake accounted for nearly two-thirds of overall rates of alcohol oxidation. These data demonstrate that catalase-H2O2 is the predominant pathway of alcohol oxidation in the fasted state in the presence of fatty acids. Accordingly, it is concluded that diet and nutritional state play important roles in the contribution of the ADH and catalase pathways to alcohol oxidation.

Catalase-dependent ethanol oxidation in perfused rat liver. Requirement for fatty-acid-stimulated H2O2 production by peroxisomes

The purpose of this study was to measure rates of catalase-dependent ethanol uptake and rates of H2O2 generation in perfused rat livers in the presence of fatty acids of varying chain length. Rates of ethanol uptake in livers from fasted rats, perfused in a recirculating system, of about 80 mumol g-1 h-1 were decreased to about 10 mumol g-1 h-1 by the addition of an inhibitor of alcohol dehydrogenase (ADH), 4-methylpyrazole. The medium-chain-length fatty acid, laurate (12:0; 1 mM), increased rates of 4-methylpyrazole-insensitive ethanol uptake maximally to 80-85 mumol g-1 h-1. Rates of ethanol uptake diminished as the chain length of fatty acid was decreased [hexanoate (6:0) = 23 mumol g-1 h-1; octanoate (8:0) = 55 mumol g-1 h-1; decanoate (10:0) = 65 mumol g-1 h-1] or increased [myristate (14:0) = 77 mumol g-1 h-1; palmitate (16:0) = 80 mumol g-1 h-1; stearate (18:0) = 29 mumol g-1 h-1; oleate (18:1) = 60 mumol g-1 h-1; erucate (22:3) = 22 mumol g-1 h-1] from 12:0. Oleate did not increase rates of hydroxylation of p-nitrophenol, a substrate for the ethanol-inducible form of cytochrome P-450, indicating that the stimulation of ethanol uptake by fatty acids was not due to increased mixed-function oxidation. The increase of ethanol uptake was also not due to displacement of 4-methylpyrazole from ADH by fatty acids, since oleate stimulated ethanol uptake by about 50% in perfused livers from deermice genetically deficient in ADH. The increase in 4-methylpyrazole-insensitive ethanol uptake by fatty acids was blocked by the catalase inhibitor, aminotriazole, indicating the involvement of catalase. Rates of H2O2 generation by livers perfused in a non-recirculating system with 1.7% albumin were increased from 6 +/- 1 to 23 +/- 5 mumol g-1 h-1 by oleate (1 mM). Because of the discrepancy between rates of ethanol metabolism and H2O2 production, methods were developed to measure H2O2 production in a recirculating perfusion system. H2O2 generation was determined from the time necessary for steady-state level of catalase-H2O2, measured spectrophotometrically (660-640 nm) through a lobe of the liver, to return to basal values after the addition of a known quantity of methanol, which is not metabolized by ADH in the rat.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of P-450ALC in microsomes from alcohol dehydrogenase-deficient deermice: contribution to ethanol elimination in vivo

Isozyme 3a of rabbit hepatic cytochrome P-450, also termed P-450ALC, was previously isolated and characterized and was shown to be induced 3- to 5-fold by exposure to ethanol. In the present study, antibody against rabbit P-450ALC was used to identify a homologous protein in alcohol dehydrogenase-negative (ADH-) and -positive (ADH+) deermice, Peromyscus maniculatus. The antibody reacts with a single protein having an apparent molecular weight of 52,000 on immunoblots of hepatic microsomes from untreated and ethanol-treated deermice from both strains. The level of the homologous protein was about 2-fold greater in microsomes from naive ADH- than from naive ADH+ animals. Ethanol treatment induced the protein about 3-fold in the ADH+ strain and about 4-fold in the ADH- strain. The antibody to rabbit P-450ALC inhibited the microsomal metabolism of ethanol and aniline. The homologous protein, termed deermouse P-450ALC, catalyzed from 70 to 80% of the oxidation of ethanol and about 90% of the hydroxylation of aniline by microsomes from both strains after ethanol treatment. The antibody-inhibited portion of the microsomal activities, which are attributable to the P-450ALC homolog, increased about 3-fold upon ethanol treatment in the ADH+ strain and about 4-fold in the ADH- strain, in excellent agreement with the results from immunoblots. The total microsomal P-450 content and the rate of ethanol oxidation were induced 1.4-fold and 2.2-fold, respectively, by ethanol in the ADH+ strain and 1.9-fold and 3.3-fold, respectively, in the ADH- strain. Thus, the total microsomal P-450 content and ethanol oxidation underestimate the induction of the P-450ALC homolog in both strains. A comparison of the rates of microsomal ethanol oxidation in vitro with rates of ethanol elimination in vivo indicates that deermouse P-450ALC could account optimally for 3 and 8% of total ethanol elimination in naive ADH+ and ADH- strains, respectively. After chronic ethanol treatment, P-450ALC could account maximally for 8% of the total ethanol elimination in the ADH+ strain and 22% in the ADH- strain. Further, cytochrome P-450ALC appears to be responsible for about one-half of the increase in the rate of ethanol elimination in vivo after chronic treatment with ethanol. These results indicate that the contribution of P-450ALC to ethanol oxidation in the deermouse is relatively small. Desferrioxamine had no effect on rates of ethanol uptake by perfused livers from ADH-negative deermice, indicating that ethanol oxidation by a hydroxyl radical-mediated mechanism was not involved in ethanol metabolism in this mutant.(ABSTRACT TRUNCATED AT 400 WORDS)