Brain segmentation and the generation of cortical surfaces

This paper describes methods for white matter segmentation in brain images and the generation of cortical surfaces from the segmentations. We have developed a system that allows a user to start with a brain volume, obtained by modalities such as MRI or cryosection, and constructs a complete digital representation of the cortical surface. The methodology consists of three basic components: local parametric modeling and Bayesian segmentation; surface generation and local quadratic coordinate fitting; and surface editing. Segmentations are computed by parametrically fitting known density functions to the histogram of the image using the expectation maximization algorithm [DLR77]. The parametric fits are obtained locally rather than globally over the whole volume to overcome local variations in gray levels. To represent the boundary of the gray and white matter we use triangulated meshes generated using isosurface generation algorithms [GH95]. A complete system of local parametric quadratic charts [JWM+95] is superimposed on the triangulated graph to facilitate smoothing and geodesic curve tracking. Algorithms for surface editing include extraction of the largest closed surface. Results for several macaque brains are presented comparing automated and hand surface generation.

Not all reading disabilities are alike

In this article, reading disability is defined broadly to refer to below-average achievement in reading comprehension as assessed by a standardized test. With our research we tried to answer the question of whether all children with reading disability share a common etiology of deficient phonology, or constitute heterogeneous groups. The answer to this question was sought in four studies that examined reading disabilities from the perspective of componential skills of reading. In Part 1, the results of the first study are reported. A principal-components analysis of the performance of 139 children from Grades 3, 4, and 6 on reading-related tasks yielded two factors: decoding and comprehension. However, factor analyses conducted for each grade separately indicated that orthographic skill and processing speed could possibly constitute a third component. The orthography-speed factor emerged as a factor only in the 6th grade. Part 2 of this article reports the findings of three studies that analyzed the componential skills profiles of poor readers. It was found that the poor readers constituted heterogeneous groups and that four different types of poor readers could be identified with deficiency in any one of the following skills: (a) decoding only, (b) comprehension only, (c) a combination of decoding and comprehension, and (d) a combination of orthographic processing and reading speed. It was also found that the criteria used in selecting poor readers influenced the distribution of the ratio of the four types of poor readers within any given group.

Piperacillin/tazobactam plus tobramycin versus ceftazidime plus tobramycin for the treatment of patients with nosocomial lower respiratory tract infection. Piperacillin/tazobactam Nosocomial Pneumonia Study Group

An open-label, randomized, comparative, multi-centre study was conducted at 25 centres in the USA and Canada to compare the safety and efficacy of piperacillin/tazobactam plus tobramycin with ceftazidime plus tobramycin in patients with lower respiratory tract infections. Piperacillin/tazobactam (3 g/375 mg) every 4 h or ceftazidime (2 g) every 8 h were administered i.v. for a minimum of 5 days. Tobramycin (5 mg/kg/day) given in divided doses every 8 h was administered to all patients. Patients with Pseudomonas aeruginosa isolated from respiratory secretions at baseline were to continue tobramycin for the duration of the study. Tobramycin could be discontinued in other patients after the baseline culture results were known. A total of 300 patients was randomized, 155 into the piperacillin/tazobactam group and 145 into the ceftazidime group. Of these, 136 patients (78 in the piperacillin/tazobactam group and 58 in the ceftazidime group) were considered clinically evaluable. Both groups were comparable for age, sex, duration of treatment and other demographic features. The clinical success rate in evaluable patients was significantly greater (P = 0.006) in the piperacillin/tazobactam treatment group (58/78; 74%) than in the ceftazidime group (29/58; 50%). Eradication of the baseline pathogen was significantly greater (P = 0.003) in the piperacillin/tazobactam group (66%) than in the ceftazidime group (38%). The clinical and bacteriological responses of those patients with nosocomial pneumonia were similar to the overall results. Twelve (7.7%) piperacillin/tazobactam-treated patients and 24 (17%) ceftazidime-treated patients died during the study (P = 0.03). Seven of the 24 deaths in the ceftazidime treatment group but only one of the 12 deaths in the piperacillin/tazobactam treatment group were directly related to failure to control infection. The majority of adverse events were thought by the investigator to be attributable to the patients' underlying disease and not drug related. In this study, piperacillin/tazobactam plus tobramycin was shown to be more effective and as safe as ceftazidime plus tobramycin in the treatment of patients with nosocomial LRTI.

Heat-induced changes in the photochemical centres and the protein secondary structures of photosystem II studied by variable fluorescence and difference FT-IR spectroscopy

Variable fluorescence (Fv), i.e., Fv = Fm-Fo where Fo is the minimal fluorescence and Fm the maximum fluorescence, and difference Fourier transform infrared (FT-IR) spectroscopy were used to study the effect of heat stress in the 25-55 degrees C range on photosystem II (PSII) structure and function. First, the Fv intensity reflects accurately the changes in the number of open photochemical centers in PSII. Secondly, the use of Fv in combination with FT-IR spectroscopy can disclose structure-function correlations in the heat inactivation of the PSII complex. Analysis of the midpoint temperatures of thermal denaturation, i.e., 50% inactivation, reported so far in investigations of the thylakoid membrane components has revealed that most of the thermal transitions attributed to PSII are in the 39-46 degrees C range. In this work, it is shown specifically that the midpoint temperature of PSII inactivation is at about 40 degrees C. Moreover, it was clearly demonstrated that the heat-induced changes above 40 degrees C are the result of a marked decrease in the number of open photochemical centers in PSII. It was also seen that above this same temperature the loss of photochemical centers has its structural counterpart in overall modifications of the secondary structures of the PSII proteins resulting from the decrease in the alpha-helix content concomitant with the increase in extended chain (beta-strand) conformations. In brief, a novel finding reported here is that the number of open photochemical centers in PSII is dependent on a dynamic equilibrium between the contents of the PSII proteins in alpha-helix and extended chains (beta-strands), but not in beta-sheets and beta-turn structures except for the antiparallel-beta-sheet conformations. This therefore associates the thermal inactivation of the photochemical centers in photosystem II with distinct conformational changes in the proteins of the PSII supramolecular complex. In the particular context of the present study, these findings constitute a significant contribution to the investigation of structure-function correlations in the photosynthetic membrane. In a broader context, this information might be essential for the comprehension of the molecular arrangements or local structure order that are involved directly or indirectly in biological catalysis.

Hemoglobin biosynthesis in Vitreoscilla stercoraria DW: cloning, expression, and characterization of a new homolog of a bacterial globin gene

In the strictly aerobic, gram-negative bacterium Vitreoscilla strain C1, oxygen-limited growth conditions create a more than 50-fold increase in the expression of a homodimeric heme protein which was recognized as the first bacterial hemoglobin (Hb). The recently determined crystal structure of Vitreoscilla Hb has indicated that the heme pocket of microbial globins differs from that of eukaryotic Hbs. In an attempt to understand the diverse functions of Hb-like proteins in prokaryotes, we have cloned and characterized the gene (vgb) encoding an Hb-like protein from another strain of Vitreoscilla, V. stercoraria DW. Several silent changes were observed within the coding region of the V. stercoraria vgb gene. Apart from that, V. stercoraria Hb exhibited interesting differences between the A and E helices. Compared to its Hb counterpart from Vitreoscilla strain C1, the purified preparation of V. stercoraria Hb displays a slower autooxidation rate. The differences between Vitreoscilla Hb and V. stercoraria Hb were mapped onto the three-dimensional structure of Vitreoscilla Hb, which indicated that the four changes, namely, Ile7Val, Ile9Thr, Ile10Ser, and Leu62Val, present within the V. stercoraria Hb fall in the region where the A and E helices contact each other. Therefore, alteration in the relative orientation of the A and E helices and the corresponding conformational change in the heme binding pocket of V. stercoraria Hb can be correlated to its slower autooxidation rate. In sharp contrast to the oxygen-regulated biosynthesis of Hb in Vitreoscilla strain C1, production of Hb in V. stercoraria has been found to be low and independent of oxygen control, which is supported by the absence of a fumarate and nitrate reductase regulator box within the V. stercoraria vgb promoter region. Thus, the regulation mechanisms of the Hb-encoding gene appear to be quite different in the two closely related species of Vitreoscilla. The relatively slower autooxidation rate of V. stercoraria Hb, lack of oxygen sensitivity, and constitutive production of Hb suggest that it may have some other function(s) in the cellular physiology of V. stercoraria DW, together with facilitated oxygen transport, predicted for earlier reported Vitreoscilla Hb.

The diagnostic and therapeutic approach to lower respiratory tract infections in the neutropenic patient

In the neutropenic host, the impaired inflammatory response diminishes the signs and symptoms of pulmonary infection, making diagnosis difficult. A practical approach to diagnosis and treatment in this population is to assess the radiographic appearance of infiltrates as localized (occurring as early, refractory or late phase), or diffuse; this approach is reviewed here.

Effect of prophylactic administration of recombinant human granulocyte colony-stimulating factor (filgrastim) on the frequency of nosocomial infections in patients with acute traumatic brain injury or cerebral hemorrhage. The Filgrastim Study Group

OBJECTIVE

To determine whether the use of prophylactic recombinant human granulocyte colony-stimulating factor (filgrastim) reduces the frequency of nosocomial infections in patients with either acute traumatic brain injury or cerebral hemorrhage.

DESIGN

Randomized, placebo-controlled, double-blind, multicenter phase II study.

SETTING

Intensive care units of seven medical centers.

PATIENTS

Patients with either acute traumatic brain injury or cerebral hemorrhage who were intubated within 6 hrs of admission and who were expected to be ventilated for >72 hrs.

INTERVENTIONS

Patients were randomized to receive daily subcutaneous injections of placebo (n = 21) or one of two doses of filgrastim (75 microg [n = 20] or 300 microg [n = 20]) for 10 days or until the absolute neutrophil count was >75,000 cells/mm3 or until extubation.

MEASUREMENTS AND MAIN RESULTS

End points included increase in absolute neutrophil count, safety of filgrastim, and frequency of nosocomial infections (pneumonia, bacteremia, and urinary tract infection). Filgrastim caused a dose-dependent increase in absolute neutrophil count. There were no differences in the frequency of pneumonia or urinary tract infection; however, there was a dose-dependent decrease in the frequency of bacteremias (p < .05). Adverse events were similar among the three groups. There was one case of acute respiratory distress syndrome in the placebo group.

CONCLUSION

In this patient population, use of filgrastim was safe and the agent appeared to reduce the risk of primary bacteremias but had no beneficial effects on mortality, length of stay, or other nosocomial infections.

Implications of Calreticulin Function in Parasite Biology

Calreticulin (CR) is a Ca(2+)-binding, multifunctional protein. The amazing array of CR-associated functions range from intracellular activities in secondary messenger release, protein folding and the modulation of gene expression to potential interactions with host receptors and signaling machinery and recognition by the host immune system. The multifunctional nature of CR may impact upon the ability of cells to recognize extracellular stimuli and coordinate appropriate responses. Identification of CR isolated from parasites and the conservation of its functions suggests that investigations into the contributions of CR to various aspects of parasite biology should be undertaken because it may reveal information regarding parasite interaction with the host and how the parasite may modulate its response to the host.

Reductions in hospital use from self management training for chronic asthmatics

The purpose of this study was to assess the impact of asthma Self Management Training on the health status and resource use of patients with chronic asthma. The study consisted of a randomized control design of chronic asthmatic patients in a tertiary care center in India. The intervention group (153 patients) received four training sessions in addition to the regular care provided to the control group (150 patients). Health status and resource use were measured at baseline and over a one year follow-up period. The intervention group had significantly better health status (measured by breathing ability), fewer productive days lost, and lower resource use (hospitalizations and emergency room visits) than the control group. Total annual costs (direct and indirect) were also lower, though physician costs were not included in the assessment. Therefore, incorporation of asthma Self Management Training as part of clinical management of asthma can result in improvements in health status and reductions in hospital use.

The structure of the upper atmosphere of mars: In situ accelerometer measurements from mars global surveyor

The Mars Global Surveyor (MGS) z-axis accelerometer has obtained over 200 vertical structures of thermospheric density, temperature, and pressure, ranging from 110 to 170 kilometers, compared to only three previous such vertical structures. In November 1997, a regional dust storm in the Southern Hemisphere triggered an unexpectedly large thermospheric response at mid-northern latitudes, increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm. Throughout the MGS mission, thermospheric density bulges have been detected on opposite sides of the planet near 90 degreesE and 90 degreesW, in the vicinity of maximum terrain heights. This wave 2 pattern may be caused by topographically-forced planetary waves propagating up from the lower atmosphere.

Improving the quality of the NCQA (National Committee for Quality Assurance) Annual Member Health Care Survey Version 1.0

The National Committee for Quality Assurance (NCQA) developed a standardized survey instrument in 1995 designed to measure enrollee satisfaction with the care and services received from health plans across the United States. After the survey was administered for a large number of health plans and thousands of responses were received, some areas for survey improvement have emerged. The objective of this research was to evaluate the NCQA Annual Member Health Care Survey Version 1.0 (the standard form) relative to an alternate survey form created in cooperation with the HMO Group, Maritz Marketing Research, Inc., and Healthcare Research Systems, Ltd. The alternate form of the NCQA survey was constructed to test several theories of measurement improvement via rewording of items, reordering of items, deletion of items, and addition of items. The most important findings of the research project are reported herein. Ten geographically dispersed member health maintenance organizations (HMOs) of The HMO Group took part in the project. A split-half design was used to test the standard and alternate survey forms concurrently. Surveys were administered by using the NCQA-recommended mail methodology of survey and cover letter, reminder card, and second survey. Assuming a 50% response rate, a target of 400 responses (200 for each survey form) per HMO was planned. The window for responding was allowed to remain open 4 weeks beyond the mailing of the second survey to achieve the desired response rate. A total of 4,056 responses were collected (2,022 for the standard form and 2,034 for the alternate form). It was found that the addition of "No Experience" and "No Opinion" response options to the majority of satisfaction items reduced the random error associated with informed responses and produced statistically significant higher correlations with the global satisfaction items relative to the standard form items. Only four of the eight Short Form 12 summary scales, General Health, Reported Health Transition, Mental Health, and Social Functioning, were useful for adjusting data (covariation). The entire set of comorbidities (chronic disease checklist) could be eliminated without losing significant data adjustment capability. The multiple linear regression models generated by using the global satisfaction items on the alternate form had higher adjusted R2 values than the standard-form models. The alternate-form item Overall Value correlated highly with cost items and general satisfaction item, making it a useful global satisfaction variable for predictive modeling.

Osteonecrosis following meningococcemia and disseminated intravascular coagulation in an adult: case report and review

Meningococcemia and disseminated intravascular coagulation (DIC) have a known association, and they have been identified as a rare cause of osteonecrosis in children. To our knowledge, we report only the second case of an adult with DIC and Neisseria meningitidis infection whose condition was subsequently diagnosed as osteonecrosis. We also review the world medical literature that pertains to osteonecrosis as a sequelae of meningococcal infection associated with DIC.

The importance of L-arginine metabolism in melanoma: an hypothesis for the role of nitric oxide and polyamines in tumor angiogenesis

There is a worldwide increase in the incidence of melanoma. Without treatment, melanomas can progress to metastatic disease and result in death. It is now accepted that for a tumor to grow, non-tumorous host tissue must form blood vessels in and around the tumor. Tumor cells and blood vessels must form a highly regulated system whereby endothelial cells can be switched from a resting state to one of rapid growth. Tumor cells have been shown to produce diffusible angiogenic regulatory molecules. Nitric oxide [NO] and polyamines [PA] have been implicated in the angiogenic process. This paper hypothesizes that NO and PA regulate melanoma angiogenesis differently. During early stages of malignant melanoma an increase in PA synthesis is expected to promote endothelial cell proliferation and therefore angiogenesis. NO is expected to be maintained at low levels. During the vascular stage of malignant melanoma, NO synthesis is hypothesized to be elevated which will decrease endothelial cell proliferation and maintain a vasodilator tone in and around the tumor. PA concentrations are expected to be lower. A regulatory link between NO and PA may be involved in the maintenance of tumor homeostasis. The regulation of L-arginine metabolism in tumor angiogenesis requires investigation as it may lead to novel selective therapeutic interventions in cancer therapy.

Isolation and characterization of Leishmania donovani calreticulin gene and its conservation of the RNA binding activity

Calreticulin has been implicated in multiple cell functions. Recently, we have shown that both human and simian calreticulin are RNA binding proteins and that their binding activity is due to phosphorylation. To demonstrate that the RNA binding property of calreticulin is an intrinsic part of this multi-functional molecule and is evolutionarily conserved, we isolated and characterized the calreticulin gene from the unicellular parasite, Leishmania donovani. Amino acid sequence homology between human and Leishmania calreticulin (L. d. cal) is limited, but like the human homologue, L. d. cal binds Ca+2, can be phosphorylated in vitro and binds certain RNA sequences in a phosphorylation-dependent manner. Unlike human calreticulin, L. d. cal is glycosylated and its binding to endogenous Leishmania RNA is phosphorylation-independent. The binding of L. d. cal to Leishmania RNA suggests that the RNA binding activity of calreticulin has remained evolutionarily conserved.

Conservation of low-copy gene loci in Old World leishmanias identifies mechanisms of parasite evolution and diagnostic markers

Genome plasticity has been hypothesized to be a driving force behind parasite speciation. We have evaluated divergence in single and low-copy genes in terms of locus organization, chromosomal localization and gene expression in Leishmania infantum, L. major, L. tropica and three widely divergent geographic isolates of L. donovani. Seventeen genes of low to moderate copy number (1-4 copies/haploid genome) were analyzed to identify restriction fragment length polymorphisms (RFLPs) providing heritable markers distinguishing Old World (OW) leishmanias. These RFLP markers were conserved in parasite isolates from primary infections demonstrating their utility as diagnostic tools. The species designations established by RFLP analysis of field isolates was confirmed by use of monoclonal antibodies. All 17 genes were present in each OW leishmania analyzed except LSIP (A45), which was absent from L. infantum. The 17 genes were found to be distributed among 9 distinct chromosomes. However, in spite of variations in chromosome karyotypes among the various OW leishmanias, individual gene probes localized to a similar sized chromosome from each isolate. These observations coupled with a molecular tree derived from RFLP data suggest that the OW leishmanias comprise a monophyletic lineage, with species associated with cutaneous disease exhibiting the greatest level of divergence. Data from this study supports previous observations that species causing cutaneous and visceral disease have diverged primarily by nucleotide substitutions. Such nucleotide divergence may not only lead to changes in protein function and antigenicity, but may also alter gene regulation programs as exemplified by the finding that the LdI-9-5 and LdE-6-1 genes were expressed only in visceralizing leishmanias.

Role of the accident and emergency department in the non-heart-beating donor programme in Leicester

OBJECTIVE

To describe the development of a non-heart-beating donor (NHBD) programme in an accident and emergency (A&E) department over a three year period.

BACKGROUND AND METHODS

The A&E department at the Leicester Royal Infirmary at present deals with approximately 200 prehospital cardiopulmonary arrests per year. A programme of kidney retrieval from non-heart-beating donors was started in April 1992. Strict criteria for admission to the programme, appropriate consent procedures, facilities, lines of communication, and feedback were developed to enhance its success.

RESULTS

Of 66 patients referred to the NHBD programme over a three year period from 1 April 1992, 51 sets of relatives were available to be asked for possible organ donation, and 34 sets (66%) gave their consent. Twenty five patients had successful in situ perfusion of the kidneys. Forty seven organs were retrieved and 34 went on to be transplanted. To date, 27 kidneys are still working. As a result, 23.8% of kidneys transplanted in Leicester over this time period have been from the NHBD programme.

CONCLUSIONS

The NHBD programme in Leicester has proved very successful, requiring organisation of resources and personnel both from the transplant service and the A&E department. The programme has provided such a significant boost to the renal transplant rate in Leicester that other hospitals with large A&E departments should consider setting up similar programmes.

Nitric oxide synthase activity is up-regulated in melanoma cell lines: a potential mechanism for metastases formation

Nitric oxide (NO) may be an important mediator of tumour angiogenesis and metastasis formation. Tumour cell derived NO may be important in the regulation of angiogenesis and vasodilatation of the blood vessels surrounding a tumour. The aims of the present study were, firstly, to determine whether malignant melanoma cells and normal melanocytes had nitric oxide synthase (NOS) activity (measured by the conversion of L-arginine to L-citrulline) and, secondly, to determine whether there was a difference in NOS activity between malignant and normal cell types. This paper assays NOS activity directly in lysates from normal human melanocyte and malignant melanoma cell lines. The enzyme activity was not inducible with bacterial lipopolysaccharide and could be heat denatured. The activity of NOS was demonstrated to be both NADPH- and calcium-dependent and it was inhibitable in a dose-dependent manner by the NOS inhibitor Nw-nitro-L-arginine methyl ester. We conclude that melanoma and melanocyte cells express a constitutive form of NOS. Finally, nitric oxide synthase activity in melanoma cell lines was found to be significantly greater than in normal melanocytes. These findings suggest that NO synthesis is elevated in malignant melanoma. An elevated NO concentration in melanoma is expected to promote metastases by maintaining a vasodilator tone in the blood vessels in and around the melanoma.

Mitral dilatation with the Multi-Track system: an alternative approach

We developed a simple and versatile new technique (Multi-Track) for percutaneous mitral valvotomy using two two separate balloon catheters positioned on a single guidewire. The first catheter, with only a distal guidewire lumen and a proximal balloon, is introduced over the guidewire into the vein and then advanced into the mitral valve orifice. Subsequently, a normal balloon catheter running on the same guidewire is inserted and lined up with the first catheter so the two are positioned side by side. The balloons are then inflated simultaneously. The technique was applied in 12 patients between 10 and 44 years of age (mean, 27.1) and weighing 24-80 kg (mean, 50.3). Valve area increased from 0.66 cm2 (range, 0.3-0.9 cm2) to 1.97 cm2 (range, 1.3-3.1 cm2) and mean left atrial pressure dropped from 31 mmHg (range, 18-52 mmHg) to 12 mmHg (range, 5-22 mmHg). Mitral dilatation with the Multi-Track system gives results comparable to those with previously described techniques and uses simpler and less costly catheters.

Molecular cloning and characterization of a Leishmania donovani alpha-tubulin gene

We have isolated a cDNA for an alpha-tubulin mRNA from L. donovani promastigotes and determined its complete nucleotide sequence. Both nucleotide and deduced amino acid sequence analysis of this cDNA showed significant similarity with a previously reported, partial sequence of an L. enriettii alpha-tubulin and the complete sequence of human alpha-tubulin. Further, the in vitro translated L. donovani alpha-tubulin gene product was specifically immunoprecipitated with a monoclonal antibody against human alpha-tubulin. Northern blot analysis revealed that there was little change in the expression of the L. donovani alpha-tubulin RNA during parasite differentiation from promastigote to the in vitro grown "amastigote" form. Southern blot analysis revealed a simple genomic organization for the L. donovani alpha-tubulin gene with more than one copy of the alpha-tubulin gene in the parasite genome. To our knowledge, this is the first complete sequence of an alpha-tubulin for Leishmania to be reported in the literature.

Investigation of the role of reactive oxygen species in bilirubin metabolism in the Gunn rat

It has been previously established that the attenuation of hepatic lipid peroxidation by a fat-free diet is accompanied by a marked rise in plasma bilirubin in Gunn rats. Present in vitro studies confirmed that microsomal lipid peroxidation caused the concurrent degradation of added bilirubin but failed to show that microsomal superoxide, hydroxyl radical or hydrogen peroxide would degrade bilirubin. Moreover, although injection of vitamin E completely inhibited microsomal lipid peroxidation and bilirubin degradation it had no effect on plasma bilirubin. No evidence has therefore been obtained that in Gunn rats, in the absence of bilirubin glucuronidation, that reactive oxygen species provide a significant physiological pathway of bilirubin disposal.

Proteolysis in cultured liver epithelial cells during oxidative stress. Role of the multicatalytic proteinase complex, proteasome

Exposure to various forms of mild oxidative stress significantly increased the intracellular degradation of both "short-lived" and "long-lived," metabolically radiolabeled, cell proteins in cultures of Clone 9 liver cells (normal liver epithelia). The oxidative stresses employed were bolus H2O2 addition; continuous H2O2 flux; the redox cycling quinones, menadione and paraquat; and the aldehydic products of lipid peroxidation, 4-hydroxynonenal, malonyldialdehyde, and hexenal. In general, exposure to more severe oxidative stress produced a concentration-dependent decline in intracellular proteolysis, in some cases to below baseline levels. Oxidatively modified "foreign" proteins (superoxide dismutase and hemoglobin) were also selectively degraded, in comparison with untreated foreign proteins, when added to lysates of Clone 9 liver cells. As with intracellular proteolysis, the degradation of foreign proteins added to cell lysates was greatly increased by mild oxidative modification, but depressed by more severe oxidative modification. The proteinase activity was recovered in > 300-kDa cell fractions, and inhibitor profiles and immunoprecipitation studies indicated that the multicatalytic proteinase complex, proteasome, was responsible for most of the selective degradation observed with mild oxidative stress; up to approximately 95% for intracellular proteolysis and 65-80% for degradation of foreign modified proteins. Seven days of daily treatment with an antisense oligodeoxynucleotide, directed against the initiation codon region of the proteasome C2 subunit gene, severely depressed the intracellular levels of several proteasome subunit polypeptides (by Western blot analysis), and also depressed the H2O2 induced increase in intracellular proteolysis by approximately 95%, without significantly affecting baseline proteolytic rates. Extensive studies revealed only small or no increases in the overall capacity of oxidatively stressed cells to degrade oxidatively modified protein substrates; a finding supported by both Western blot and Northern blot analyses which revealed no significant increase in the levels of proteasome subunit polypeptides or mRNA transcripts. We conclude that mild oxidative stress increases intracellular proteolysis by modifying cellular proteins, thus increasing their proteolytic susceptibility. In contrast, severe oxidative stress diminishes intracellular proteolysis, probably by generating severely damaged cell proteins that cannot be easily degraded (e.g. cross-linked/aggregated proteins), and by damaging proteolytic enzymes. We further conclude that the multicatalytic proteinase complex proteasome is responsible for most of the recognition and selective degradation of oxidatively modified proteins in Clone 9 liver cells.

Monocyte procoagulant activity: development of a microtitre plate chromogenic assay

A monocyte procoagulant assay was developed based on the original method of Surprenant and Zuckerman, which quantitates a factor Xa-specific chromogenic substrate (at 405 nm) activated via the extrinsic coagulation pathway. Normal tissue factor initiation of the pathway is replaced by tissue factor generated from monocytes, stimulated by various agents including bacterial lipopolysaccharide, and antibody/antigen complexes. Hydrolysis of the chromogenic substrate is therefore directly proportional to the degree of monocyte activation. Using a chromogenic substrate as an end-point the assay was performed in a standard microtitre plate.