The mechanism of microsomal and mitochondrial nitroreductase. Electron spin resonance evidence for nitroaromatic free radical intermediates

Electron spin resonance spectra are observed during the enzymatic reduction of many nitrophenyl derivatives by rat hepatic microsomes or mitochondria. The spectra indicate that nitroaromatic anion radicals are present and are freely rotating in aqueous solution at a steady-state concentration of 0.1-6 muM. The rate of formation of p-nitrobenzoate (NBZO) dianion radical in microsomal incubates is consistent with the radical being an obligate intermediate in the reduction of NBZO to p-aminobenzoic acid. A model system consisting of NBZO, NADPH, and FMN, but no heme-containing compounds, also reduced NBZO to the NBZO dianion free radical. The steady-state concentration of the anion radicals in microsomal systems is not altered by CO. This observation, together with the results from the model system, suggests that the formation of nitroaromatic anion radicals is mediated through a flavine and not cytochrome P-450. The oxidation of the anion radical intermediate by O2 to the parent nitro compound is proposed to account for the well-known O2 inhibition of microsomal nitroreductase.

The distribution of the components of mixed-function oxidase between the rough and the smooth endoplasmic reticulum of liver cells

Mixed-function oxidase activity, when measured by the N-demethylation of ethylmorphine or the hydroxylation of aniline, is significantly higher in the smooth hepatic endoplasmic reticulum than in the rough. In the rabbit the smooth membrane/rough membrane activity ratios are significantly greater than 1 whether the activities are expressed per g. of liver (ratio 5), per mg. of protein (ratio 3-5), per mug. of phospholipid phosphorus (ratio 2), per unit of cytochrome P-450 (ratio 1.7) or per unit of NADPH-cytochrome c reductase activity (ratio 2). On the other hand, if the activities are normalized to the NADPH-cytochrome P-450 reductase, there is no significant difference between the rough and smooth membranes. These results suggest that, in the rabbit, the rate-limiting step is the reduction of cytochrome P-450. In contrast, in the rat the difference in activities can be explained by differences in the concentration of cytochrome P-450.

Tau activation of microglial cGAS-IFN reduces MEF2C-mediated cognitive resilience

Pathological hallmarks of Alzheimer's disease (AD) precede clinical symptoms by years, indicating a period of cognitive resilience before the onset of dementia. Here, we report that activation of cyclic GMP-AMP synthase (cGAS) diminishes cognitive resilience by decreasing the neuronal transcriptional network of myocyte enhancer factor 2c (MEF2C) through type I interferon (IFN-I) signaling. Pathogenic tau activates cGAS and IFN-I responses in microglia, in part mediated by cytosolic leakage of mitochondrial DNA. Genetic ablation of Cgas in mice with tauopathy diminished the microglial IFN-I response, preserved synapse integrity and plasticity and protected against cognitive impairment without affecting the pathogenic tau load. cGAS ablation increased, while activation of IFN-I decreased, the neuronal MEF2C expression network linked to cognitive resilience in AD. Pharmacological inhibition of cGAS in mice with tauopathy enhanced the neuronal MEF2C transcriptional network and restored synaptic integrity, plasticity and memory, supporting the therapeutic potential of targeting the cGAS-IFN-MEF2C axis to improve resilience against AD-related pathological insults.

Reliability and intraoperative validity of preoperative assessment of standardized plain radiographs in predicting bone loss at revision hip surgery

BACKGROUND

The most challenging aspect of revision hip surgery is the management of bone loss. A reliable and valid measure of bone loss is important since it will aid in future studies of hip revisions and in preoperative planning. We developed a measure of femoral and acetabular bone loss associated with failed total hip arthroplasty. The purpose of the present study was to measure the reliability and the intraoperative validity of this measure and to determine how it may be useful in preoperative planning.

METHODS

From July 1997 to December 1998, forty-five consecutive patients with a failed hip prosthesis in need of revision surgery were prospectively followed. Three general orthopaedic surgeons were taught the radiographic classification system, and two of them classified standardized preoperative anteroposterior and lateral hip radiographs with use of the system. Interobserver testing was carried out in a blinded fashion. These results were then compared with the intraoperative findings of the third surgeon, who was blinded to the preoperative ratings. Kappa statistics (unweighted and weighted) were used to assess correlation. Interobserver reliability was assessed by examining the agreement between the two preoperative raters. Prognostic validity was assessed by examining the agreement between the assessment by either Rater 1 or Rater 2 and the intraoperative assessment (reference standard).

RESULTS

With regard to the assessments of both the femur and the acetabulum, there was significant agreement (p < 0.0001) between the preoperative raters (reliability), with weighted kappa values of >0.75. There was also significant agreement (p < 0.0001) between each rater's assessment and the intraoperative assessment (validity) of both the femur and the acetabulum, with weighted kappa values of >0.75.

CONCLUSIONS

With use of the newly developed classification system, preoperative radiographs are reliable and valid for assessment of the severity of bone loss that will be found intraoperatively.

Development, test reliability and validation of a classification for revision hip arthroplasty

The objective of the study was to develop a valid and reliable classification system for failed hip arthroplasties. The study uses research principals derived from multi-attribute utility theory and consensus group techniques. The development of the severity measure was done in two phases. Phase I of the study included: (a) questionnaire development, (b) submission of the questionnaire to the respondents, (c) data synthesis of the responses and item reduction, and (d) classification development and inter-observer reliability testing. Phase II included: (a) resubmission of the instrument to the respondents for suggestions/feedback, (b) instrument revision by the co-investigators based on the respondents' second feedback, and (c) inter-observer reliability testing and intraoperative validity testing of the instrument. The questionnaires sought to capture expert opinion as to what clinical determinants obtained preoperatively (during patient interview, physical exam and review of plain radiographs - AP pelvis and hip lateral) that would in their clinical experience reveal intraoperative severity. There was an 80% (16/20) response rate from the outside experts invited to participate in the study. Based on item reduction and test retest analysis, a five-grade radiographic classification for the acetabulum as well as the femur was developed. This system was then reviewed by 13 of the initial outside experts (16, 80%) who participated in the first round. Inter-rater reliability testing of the final format of the classification revealed a weighted kappa statistic value of 0.88 between the two-blinded raters (inter-rater reliability) and 0.87 between the blinded raters and the reference standard (intraoperative validity). We conclude that the study developed a reliable and valid radiographic classification system for failed hip arthroplasty.

Physiologic concentrations of homocysteine inhibit the human plasma GSH peroxidase that reduces organic hydroperoxides

The plasma reduced glutathione (GSH) selenoperoxidase is a highly conserved enzyme. Furthermore, a small clinical study reported that patients with severe atherosclerosis had low peroxidase activities. Together these observations suggest that the peroxidase is important in preventing atherosclerosis. Yet others have reported that when the assay was run in Tris buffer, it was inactive with the concentrations of GSH found in the plasma. Second, it is known that hyperhomocysteinemia increases the rate of atherogenesis. Because there is some homology between homocysteine and the cysteine in GSH, the question is whether the hyperhomocysteinemia effect may be due to inhibition of the peroxidase. We purified the peroxidase from human plasma and determined its activity by a coupled spectrophotometric assay and a substrate disappearance chemiluminescence assay. When the peroxidase activity was determined in phosphate-buffered saline solution (PBS), there was significant activity with the reported plasma GSH concentrations (5 to 20 micromol/L). The peroxidase was exclusively in the HDL fraction. There was no correlation between the peroxidase activity and the HDL or LDL cholesterol concentrations. Finally, at physiologic concentrations of GSH (9 micromol/L), the peroxidase was inhibited by physiologic, free homocysteine concentrations (1 to 5 micromol/L). These data suggest that the peroxidase is active in vivo and may be important in protecting the endothelium from atherosclerosis by preventing oxidant injury. The homocysteine inhibition of the peroxidase suggests a possible biochemical basis for the observed association between hyperhomocysteinemia and cardiovascular disease. Our studies imply that low concentrations of this peroxidase may be an independent risk factor for atherosclerosis.

Interaction of flecainide with digoxin and propranolol

The effect of flecainide, 200 mg twice daily for 5 days, on steady-state plasma digoxin levels was determined in 15 healthy male subjects who received 0.25 mg of digoxin per day. The predose mean plasma digoxin level before flecainide administration on days 9 and 10 was 0.46 ng/ml, compared with 0.57 ng/ml on day 13 (p less than 0.05) and 0.49 ng/ml on day 15 (difference not significant [NS]) when flecainide was given concurrently with digoxin. The 6-hour postdose mean level for days 9 and 10 was 0.58 ng/ml, compared with mean levels of 0.62 ng/ml on day 13 (NS) and 0.65 ng/ml on day 15 (p less than 0.05). On average, predose and 6-hour postdose digoxin levels increased by 24 +/- 35% and 13 +/- 19%, respectively, during co-administration. A significant prolongation of the electrocardiographic PR interval in 6 of 15 subjects was noted on the combined drug dosage. This reverted to normal after cessation of drug administration. Vital signs showed no significant clinical change during the course of the study. Ten other healthy male subjects were given propranolol, 80 mg 3 times daily, or flecainide, 200 mg twice daily, alone or in combination. Effects on vital signs, exercise heart rate, electrocardiographic interval, M-mode indexes of ventricular function and plasma drug levels were monitored to determine effects of the study drugs when given separately or concurrently. Both drugs caused a decrease in blood pressure, with the systolic pressure affected more than the diastolic; the effects of propranolol and flecainide were additive.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of cytochrome CYPIA1 and formation of toxic metabolites of benzo[a]pyrene by rat aorta: a possible role in atherogenesis

Cigarette smoking is a leading risk factor for atherosclerosis. Endothelial injury may be the initial event in this process. The carcinogenic metabolites of the polycyclic aromatic hydrocarbons found in cigarette smoke tars could cause this injury. We tested this model by examining the effect of 3-methylcholanthrene administration on aortic polycyclic aromatic hydrocarbon metabolism. Immunoblotting with a monoclonal antibody (mAb 1-7-1) specific for cytochromes CYPIA1 and CYPIA2 showed that aortic microsomes from treated, but not from control, animals contained CYPIA1; the CYPIA1 was primarily in the endothelium. Aortic microsomes from induced animals metabolized benzo[a]pyrene (BaP) to the 7R,8S,9,10-tetrahydrotetrol-, 7,8-dihydrodiol-, 1,6 quinone-, 3,6 quinone-, 6,12 quinone-, 3-hydroxy-, and 9-hydroxy-BaP. mAb 1-7-1 inhibited the formation of the tetrahydrotetrol, the dihydrodiol-BaP, and the 3-hydroxy-BaP but did not inhibit the quinones or the 9-hydroxy-BaP. Arachidonic acid did not affect metabolism. These data suggest that the aortas of induced animals metabolize the BaP in cigarette smoke to carcinogenic and toxic products and that this metabolism may initiate vessel injury and lead to the accelerated atherosclerosis seen in cigarette smokers.

Causes of increasing mortality in a nursing home population

OBJECTIVE

To examine the roles played by changes in case-mix, quality of care, and aggressiveness of care in explaining the 42% increase in mortality of the Medicaid nursing home population of Hennepin County, Minnesota, between 1984 and 1988.

DESIGN

Retrospective chart review.

SETTING

All nursing homes in Hennepin County, MN, that care for Medicaid patients.

PATIENTS

A random sample of 1605 Medicaid nursing home residents from 1984 and 1988 stratified by year and by whether the resident died in that year. Sampling was disproportionate to allow approximately 400 individuals per stratum. A total of 1405 charts (87%) were reviewed; the remainder were either lost or destroyed.

MAIN OUTCOME MEASURES

Measures included case-mix (Charlson index, functional status, implicit reviewer assigned severity [range 1-4]), aggressiveness of care (orders limiting care), quality of care (process of care for tracer conditions [range 1-5], falls), and resident death.

RESULTS

Implicitly rated severity of illness worsened between 1984 and 1988 (2.77 vs 2.91; P = .009), but other measures of case-mix were unchanged. A greater percentage of residents had a DNR order in 1988 (12% in 1984 vs 37% in 1988; P < .001), and more received less aggressive care (31% vs 40%; P = .006). Overall process of care improved between 1984 and 1988 (2.88 vs 3.01; P < .05). With adjustment of the mortality rates and with logistic regression controlling for age and gender, changes in quality of care alone accounted for less than 5% of the mortality rate change between 1984 and 1988, case-mix alone accounted for 49%, and aggressiveness of care alone accounted for nearly 100%.

CONCLUSIONS

The nursing home population became sicker between 1984 and 1988, but process of care improved. These changes had a modest effect on the mortality rate. The increase in less aggressive care between 1984 and 1988 accounts for nearly all of the increase in mortality.

Long-term functional status and quality of life after lower extremity revascularization

OBJECTIVE

The objective of this study was to assess the longer term (up to 7 years) functional status and quality of life outcomes from lower extremity revascularization.

METHODS

This study was designed as a cross-sectional telephone survey and chart review at the University of Minnesota Hospital. The subjects were patients who underwent their first lower extremity revascularization procedure or a primary amputation for vascular disease between January 1, 1989, and January 31, 1995, who had granted consent or had died. The main outcome measures were ability to walk, SF-36 physical function, SF-12, subsequent amputation, and death.

RESULTS

The medical records for all 329 subjects were reviewed after the qualifying procedures for details of the primary procedure (62.6% arterial bypass graft, 36.8% angioplasty, 0.6% atherectomy), comorbidities (64% diabetics), severity of disease, and other vascular risk factors. All 166 patients who were living were surveyed by telephone between June and August 1996. At 7 years after the qualifying procedure, 73% of the patients who were alive still had the qualifying limb, although 63% of the patients had died. Overall, at the time of the follow-up examination (1 to 7.5 years after the qualifying procedure), 65% of the patients who were living were able to walk independently and 43% had little or no limitation in walking several blocks. In a multiple regression model, patients with diabetes and patients who were older were less likely to be able to walk at follow-up examination and had a worse functional status on the SF-36 and a lower physical health on the SF-12. Number of years since the procedure was not a predictor in any of the analyses.

CONCLUSION

Although the long-term mortality rate is high in the population that undergoes lower limb revascularization, the survivors are likely to retain their limb over time and have good functional status.

Optical diagnostics in the oral cavity: an overview

As the emphasis shifts from damage mitigation to disease prevention or reversal of early disease in the oral cavity, the need for sensitive and accurate detection and diagnostic tools become more important. Many novel and emergent optical diagnostic modalities for the oral cavity are becoming available to clinicians with a variety of desirable attributes including: (i) non-invasiveness, (ii) absence of ionizing radiation, (iii) patient-friendliness, (iv) real-time information (v) repeatability, and (vi) high-resolution surface and subsurface images. In this article, the principles behind optical diagnostic approaches, their feasibility and applicability for imaging soft and hard tissues, and their potential usefulness as a tool in the diagnosis of oral mucosal lesions, dental pathologies, and other dental applications will be reviewed. The clinical applications of light-based imaging technologies in the oral cavity and of their derivative devices will be discussed to provide the reader with a comprehensive understanding of emergent diagnostic modalities.

The covalent binding of [14C]acetaminophen to mouse hepatic microsomal proteins: the specific binding to calreticulin and the two forms of the thiol:protein disulfide oxidoreductases

Numerous in vitro studies have indicated that acetaminophen is activated by mouse hepatic microsomal cytochrome P450 to form N-acetylbenzoquinone imine. This in turn covalently binds through a Michael addition to protein sulfhydryl and amino groups. Although acetaminophen adducts of several cytosolic proteins have been purified after its administration in vivo, no adducts of specific microsomal proteins have been reported. We find that, after the in vitro incubation of mouse hepatic microsomes with [ring-14C] acetaminophen in the presence of an NADPH generating system, 95% of the bound radioactivity was associated with adducts to three intraluminal microsomal proteins: calreticulin and the two forms of thiol:protein disulfide oxidoreductase, Q2 and Q5. The acetaminophen bound to 0.35, 1.32, and 0.25 mol/mol of the three proteins, respectively. Sequencing of the 14C-labeled tryptic peptides indicated that the acetaminophen bound to lysine 103 of Q2, lysines 202, 209 or 210 and 354 of Q5 and lysines 233 or 239 of calreticulin. No adducts of cysteine residues were observed. Our data might suggest that acetaminophen hepatotoxicity results from the formation of the reactive metabolite within the endoplasmic reticulum. This then binds to these essential proteins and blocks the posttranslational modification of secretory and membrane proteins. This inhibition could then lead to cellular injury and death.

The reported cDNA sequence for phospholipase C alpha encodes protein disulfide isomerase, isozyme Q-2 and not phospholipase-C

We have previously shown that the cDNA sequence published for the rat gene encoding phosphatidylinositol specific phospholipase C alpha (1) may be identical to the sequence of a new isoform of protein disulfide isomerase, Isozyme Q2 (2). To determine whether the presumed phospholipase C alpha gene encodes phospholipase C or protein disulfide isomerase, we have now expressed the cDNA in Escherichia coli and find that the 55.5 kDa protein that it synthesized contains no phospholipase C activity. Moreover, an extract of Escherichia coli containing the expressed protein shows a concentration dependent increase in protein disulfide isomerase activity. The expressed protein is identical to protein disulfide isomerase, Isozyme Q2 on SDS-PAGE and by Western blot analysis. These current studies confirm that the published sequence of phospholipase C alpha is, in fact, the sequence of protein disulfide isomerase, Isozyme Q2.

Changes in orders limiting care and the use of less aggressive care in a nursing home population

OBJECTIVE

To examine changes in the aggressiveness of care of the nursing home population and to determine the factors that predict whether care is limited.

DESIGN

Retrospective chart review.

SETTING

All nursing homes in Hennepin County, Minnesota that care for Medicaid patients.

PATIENTS

A random sample of 1605 residents of Hennepin County, MN nursing homes from 1984 and 1988 who were also Medicaid beneficiaries. The sample was stratified by year and by whether the resident died in that year. The residents were sampled disproportionately to allow approximately 400 individuals in each stratum. A total of 1405 charts (87%) was reviewed; the remainder had either been lost or destroyed.

MAIN OUTCOME MEASURE

Orders limiting care (do not resuscitate, supportive care only, etc.), care that was less aggressive than care usually given to a person of that age (eg, not using antibiotics for a clear infection or not sending a resident to the hospital for an illness for which someone would "usually" be sent to the hospital), determined implicitly through chart review.

RESULTS

The demographic characteristics of the nursing home population did not change between 1984 and 1988, but the population had significantly greater severity of illness in 1988. The percentage of residents with 'do not resuscitate' orders (DNR) increased from 12% to 37% (P < 0.0001), and the use of other orders to limit care (do not hospitalize, supportive care only, etc.) increased from 12% to 17% (P < 0.05). The use of CPR did not change between the two years but the percentage of residents who were found to receive less aggressive care through implicit chart review increased from 31% to 40% (P < 0.01). The year the resident was in the nursing home, the severity of illness, functional status, and dementia were significant predictors of DNR status. Factors that predict receipt of less aggressive care were similar except that age was also a significant predictor.

CONCLUSIONS

The nursing home population received less aggressive care in 1988 than in 1984. Further, there was a discrepancy between what was ordered and what was delivered in the nursing home in that residents with DNR orders had care limited beyond the withholding of CPR.

The effects of clinical pathways for renal transplant on patient outcomes and length of stay

OBJECTIVES

Clinical pathways have been implemented nationwide but little is understood about their effects on efficiency of care and patient outcomes. The present study examined the effects of both development and implementation of two renal transplant pathways.

METHODS

Cohorts of patients at a university hospital were compared before, during, and after the development and implementation of two renal transplant clinical pathways: isolated renal transplant from cadaveric donors (n = 170) or from living donors (n = 178). Clinical pathways for cadaveric and living related donor renal transplants were developed and implemented. Hospital length of stay and complications and infections after renal transplant were determined.

RESULTS

Mean length of hospital stay decreased after development and implementation of the cadaveric donor pathway (11.8 days after implementation versus 17.5 days before development). Cadaveric kidney recipients also had statistically fewer complications and infections after both guideline development and guideline implementation (57.1% before, 24.5% during, 18.5% after), but the greatest effect occurred during development. All of these findings persisted after control for demographic and comorbid factors. There were no changes in hospital stay, complications, or infections in the patients who received kidneys from living donors.

CONCLUSIONS

The development and use of a clinical pathway for cadaveric donor renal transplant patients was associated with a significant decline in length of stay, complications, and infections, but much of the effect was seen during development rather than during implementation, and a closely related pathway for living related donor patients had no effect. Further understanding of what factors predict an effective pathway and what elements (ie, development or implementation) have an effect should be undertaken.

Effect of influenza vaccine on warfarin anticoagulation

Recent studies have indicated that viral infections, influenza vaccination, or drugs that increase interferon synthesis all decrease hepatic drug metabolism. We report a case in which influenza vaccination was temporally related to an increased anticoagulant effect of warfarin. A prospective study evaluating the effect of influenza vaccination on the prothrombin time of eight patients anticoagulated over the long term showed that there was prolongation of prothrombin time of 40%. In a second study, the effect of influenza vaccination on warfarin t1/2 was determined in healthy subjects. No significant effect on warfarin metabolism was observed after vaccination. We conclude that influenza vaccination is associated with increased anticoagulant response in some patients receiving anticoagulants over a long term. This effect appears to be related to some step in the coagulation pathway and not to decreased warfarin metabolism and a subsequent rise in serum concentration.