Deep medicine … Navigating the intersection of technology, cognition and ethics in the digital age of medicine

The digital expansion in medicine and healthcare has been immense and extremely valuable. The biggest concern in the face of this inevitable growth is how we manage to keep contact with our patients and preserve the human touch so essential in healing. Digital healthcare should not be about technology replacing clinicians. Instead, it should be about augmenting and supplementing healthcare providers to improve the ways in which we deliver personalised healthcare. It is vital that we focus on how we can revitalise the patient-clinician relationship in this digital age.

An analysis of referrals to a level 3 intensive care unit in a resource-limited setting in South Africa

Background

With a shortage of intensive care unit (ICU) beds and rising healthcare costs in resource-limited settings, clinicians need to appropriately triage admissions into ICU to avoid wasteful expenditure and unnecessary bed utilisation.

Objectives

To assess the nature, appropriateness and outcome of referrals to a tertiary centre ICU.

Methods

A retrospective review of ICU consults from September 2016 to February 2017 at King Edward VIII Hospital was performed. The study was approved by the University of KwaZulu-Natal Biomedical Research Ethics Committee (BE291/17). Data pertaining to patients' demographics, referring doctor, diagnosis, comorbidities as well as biochemical and haemodynamic parameters were extracted. This information was then cross-referenced to the outcome of the ICU consultation. Data were descriptively analysed.

Results

Five hundred consultations were reviewed over a 6-month period; 52.2% of patients were male and the mean age was 44 years. Junior medical officers referred 164 (32.8%) of the consultations. Although specialist supervision was available in 459 cases, it was only utilised in 339 (73.9%) of these cases. Most referrals were from tertiary (46.8%) or regional (30.4%) hospitals; however, direct referrals from district hospitals and clinics accounted for 20.4% and 1.4% of consultations, respectively. The appropriate referral pathway was not followed in 81 (16.2%) consultations. Forty-five percent of consults were accepted; however, 9.3% of these patients died before arrival in ICU. A total of 151 (30.2%) patients were refused ICU admission, with the majority (57%) of these owing to futility. Patients were unstable at the time of consult in 53.2% of referrals and 34.4% of consults had missing data.

Conclusion

Critically ill patients are often referred by junior doctors without senior consultation, and directly from low-level healthcare facilities. A large proportion of ICU referrals are deemed futile and, of the patients accepted for admission, almost 1 in 10 dies prior to ICU admission. More emphasis needs to be placed on the training of doctors to appropriately triage and manage critically ill patients and ensure appropriate ICU referral and optimising of patient outcomes.

Contributions of the study

There is a paucity of information related to ICU referrals in South Africa. The nature, appropriateness and outcomes of referrals to a tertiary ICU is discussed in this study.

232 To Report A Rare Case of Fungal Necrotising Otitis Externa (NOE) Centred on The Left Temporomandibular Joint (TMJ)

Introduction

NOE is a rare life-threatening complication of otitis externa, affecting the skull base, mastoid and temporal bones. Pseudomonas aeruginosa account for 95% of cases, making fungal NOE unusual. Complications secondary to NOE include cranial neuropathies, meningitis and dural sinus thrombophlebitis.

Case-study

A 67-year-old man with stage-5 chronic kidney disease presented with left otalgia and otorrhea. He was treated with antipseudomonal topical antibiotics and microsuction for months as an outpatient. Aspergillus flavus was grown on an initial swab, but subsequent cultures were negative. Computerised Tomography scans revealed inflammatory changes in the left masticator space with mastoid bone involvement suggestive of left NOE. He received three months of intravenous anti-pseudomonal antibiotics, microsuction and topical aminoglycosides. Despite interventions symptoms persisted and magnetic resonance imaging scanning revealed disease progression into the left TMJ, prompting maxillofacial surgical opinion. Following washout of the TMJ, a tissue biopsy was positive for DNA on pan-fungal PCR, and the sequence identified as Aspergillus flavus group. The patient was successfully treated with oral posoconazole and topical amphotericin and discharged home.

Conclusions

Fungal NOE remains poorly treated as there is limited guidance on antifungal choice and duration of treatment. It should always be considered, particularly in immunocompromised patients with intractable cases of NOE

The Critical Care Society of Southern Africa guidelines on the allocation of scarce critical care resources during the COVID-19 public health emergency in South Africa

Letter by Gopalan et al. on article by Singh and Moodley (Singh JA, Moodley K. Critical care triaging in the shadow of COVID-19: Ethics considerations. S Afr Med J 2020;110(5):355-359. https://doi.org/10.7196/SAMJ.2020.v110i5.14778); and response by Singh and Moodley.

The Critical Care Society of Southern Africa Consensus Guideline on ICU Triage and Rationing (ConICTri)

Background

In South Africa (SA), administrators and intensive care practitioners are faced with the challenge of resource scarcity as well as an increasing demand for intensive care unit (ICU) services. ICU services are expensive, and practitioners in low- to middle-income countries experience the consequences of limited resources daily. Critically limited resources necessitate that rationing and triage (prioritisation) decisions are routinely necessary in SA, particularly in the publicly funded health sector.

Purpose

The purpose of this guideline is to utilise the relevant recommendations of the associated consensus meeting document and other internationally accepted principles to develop a guideline to inform frontline triage policy and ensure the best utilisation of adult intensive care in SA, while maintaining the fair distribution of available resources.

Recommendations

An overall conceptual framework for the triage process was developed. The components of the framework were developed on the basis that patients should be admitted preferentially when the likely incremental medical benefit derived from ICU admission justifies admission. An estimate of likely resource use should also form part of the triage decision, with those patients requiring relatively less resources to achieve substantial benefit receiving priority for admission. Thus, the triage system should maximise the benefits obtained from ICU resources available for the community. Where possible, practical examples of what the consensus group agreed would be considered appropriate practice under specified South African circumstances were provided, to assist clinicians with practical decision-making. It must be stressed that this guideline is not intended to be prescriptive for individual hospital or regional practice, and hospitals and regions are encouraged to develop specified local guidelines with locally relevant examples. The guideline should be reviewed and revised if appropriate within 5 years.

Conclusion

In recognition of the absolute need to limit patient access to ICU because of the lack of sufficient intensive care resources in public hospitals, this guideline has been developed to guide policy-making and assist frontline triage decision-making in SA. This document is not a complete plan for quality practice, but rather a template to support frontline clinicians, guide administrators and inform the public regarding appropriate triage decision-making.

The Critical Care Society of Southern Africa Consensus Statement on ICU Triage and Rationing (ConICTri)

Background

In South Africa (SA), intensive care is faced with the challenge of resource scarcity as well as an increasing demand for intensive care unit (ICU) services. ICU services are expensive, and practitioners in low- to middle-income countries experience daily the consequences of limited resources. Critically limited resources necessitate that rationing and triage (prioritisation) decisions are frequently necessary in SA, particularly in the publicly funded health sector.

Purpose

The purpose of this consensus statement is to examine key questions that arise when considering the status of ICU resources in SA, and more specifically ICU admission, rationing and triage decisions. The accompanying guideline in this issue is intended to guide frontline triage policy and ensure the best utilisation of intensive care in SA, while maintaining a fair distribution of available resources. Fair and efficient triage is important to ensure the ongoing provision of high-quality care to adult patients referred for intensive care.

Recommendations

In response to 14 key questions developed using a modified Delphi technique, 29 recommendations were formulated and graded using an adapted GRADE score. The 14 key questions addressed the status of the provision of ICU services in SA, the degree of resource restriction, the efficiency of resource management, the need for triage, and how triage could be most justly implemented. Important recommendations included the need to formally recognise and accurately quantify the provision of ICU services in SA by national audit; actively seek additional resources from governmental bodies; consider methods to maximise the efficiency of ICU care; evaluate lower level of care alternatives; develop a triage guideline to assist policy-makers and frontline practitioners to implement triage decisions in an efficient and fair way; measure and audit the consequence of triage; and promote research to improve the accuracy and consistency of triage decisions. The consensus document and guideline should be reviewed and revised appropriately within 5 years.

Conclusion

In recognition of the absolute need to limit patient access to ICU because of the lack of sufficient intensive care resources in public hospitals, recommendations and a guideline have been developed to guide policy-making and assist frontline triage decision-making in SA. These documents are not a complete plan for quality practice but rather the beginning of a long-term initiative to engage clinicians, the public and administrators in appropriate triage decision-making, and promote systems that will ultimately maximise the efficient and fair use of available ICU resources.

Defining fitness for purpose in South African anaesthesiologists using a Delphi technique to assess the CanMEDS framework

Background: Training of South African anaesthesiologists is based on the Canadian Medical Education Directives for Specialists (CanMEDS). However, the applicability of CanMEDS in this context has not been assessed. An expert panel participated in a Delphi process to create an appropriate expanded list of CanMEDS competencies that may be used in the future to assess fitness for purpose of local graduates. Methods: This descriptive study comprised a representative panel of 16 experts surveyed electronically over three rounds to assess the importance of the existing CanMEDS roles and enabling competencies and suggested additions deemed applicable locally. The primary outcome was the creation of a list of competencies applicable to South Africa. Results: There was a 100% response rate for all three rounds. Based on the existing seven CanMEDS meta-competencies (Medical Expert, Collaborator, Communicator, Leader, Scholar, Professional and Health Advocate), respondents scored the importance of 89 enabling competencies and 19 additional competencies. Seven CanMEDS enabling competencies did not achieve consensus and were excluded. Nineteen new enabling competencies and two new meta-competencies (Humaneness, Context Awareness) achieved consensus and were added. Median ratings of importance of meta-competencies showed highest scores for Medical Expert and Collaborator and lowest scores for Health Advocate. Weighting of meta-competencies revealed highest scores for Medical Expert and Professional with all others equally weighted. Conclusion: This study has formulated an adapted CanMEDS list of enabling competencies with the addition of the two new metacompetencies of Context Awareness and Humaneness for use in South African anaesthesiology. This provides a means with which future graduates may be assessed for fitness for purpose.

Psychosomatic Medicine for Non-Psychiatric Residents: Video Education and Incorporation of Technology

OBJECTIVES

Psychiatric education for non-psychiatric residents varies between training programs, and may affect resident comfort with psychiatric topics. This study's goals were to identify non-psychiatric residents' comfort with psychiatric topics and to test the effectiveness of a video intervention.

METHODS

Residents in various departments were given a survey. They were asked to rank their comfort level with multiple psychiatric topics, answer questions about medical decision making capacity (MDMC), watch a 15-min video about MDMC, and answer a post-test section.

RESULTS

In total, 91 Internal Medicine, General Surgery, and Obstetrics and Gynecology residents responded to the study. Of the 91 residents, 55 completed the pre- and post-test assessments. There was no significant difference in correct responses. Residents' comfort levels were assessed, and a significant improvement in comfort level with MDMC was found.

CONCLUSIONS

This study highlights potential opportunities for psychiatric education, and suggests brief video interventions can increase resident physicians' comfort with a psychiatric topic.

Optically modulated conduction in chromophore-functionalized single-wall carbon nanotubes

We demonstrate an optically active nanotube-hybrid material by functionalizing single-wall nanotubes with an azo-based chromophore. Upon UV illumination, the conjugated chromophore undergoes a cis-trans isomerization leading to a charge redistribution near the nanotube. This charge redistribution changes the local electrostatic environment, shifting the threshold voltage and increasing the conductivity of the nanotube transistor. For a approximately 1%-2% coverage, we measure a shift in the threshold voltage of up to 1.2 V. Further, the conductance change is reversible and repeatable over long periods of time, indicating that the chromophore-functionalized nanotubes are useful for integrated nanophotodetectors.

Predictive indicators for thyroid cartilage involvement in carcinoma of the larynx seen on spiral computed tomography scans

Objectives: Recent studies have shown that the spiral computed tomography (CT) scan is a sensitive imaging modality for predicting neoplastic invasion of thyroid cartilage. The objectives of our study were: to assess the accuracy of pre-operative spiral CT in predicting thyroid cartilage involvement in patients with carcinoma of the larynx; and to elucidate the factors that would accurately indicate cartilage involvement.

Material and methods: Medical records, including spiral CT scans and pathological reports, were reviewed for 27 patients who had undergone laryngectomy in two major hospitals in south Wales. A consultant radiologist with special interest in cross-sectional imaging re-evaluated the scans to assess neoplastic involvement of the thyroid cartilage, based on definite, objective criteria. These criteria included: soft tissue asymmetry; loss of medullary space; spiky or irregular surface; distortion of cartilage framework; and abnormal soft tissue on both sides of the cartilage. The radiological findings were then correlated with the histopathological evidence of cartilage invasion by the tumour.

Results: Out of the 27 cases, 15 had evidence of histological invasion of thyroid cartilage. The most specific criterion to predict thyroid cartilage involvement was the presence of tumour on both sides of the cartilage (specificity of 91 per cent, sensitivity of 66 per cent). Combining two criteria increased both the sensitivity and the specificity to 86 and 91 per cent, respectively.

A study of chorda tympani nerve injury and related symptoms following middle-ear surgery

This is a prospective study that looks into the prevalence of chorda tympani nerve (CTN) injury and related symptoms following varying degrees of trauma to the nerve during three common types of middle-ear operation: myringoplasty, tympanotomy and mastoidectomy. The number of patients with CTN-related symptoms varied widely between the three groups. Increased occurrence of the nerve related symptoms and a prolonged recovery time were observed in the tympanotomy group. Stretching of the nerve produced more symptomatic cases than cutting it in the myringoplasty and mastoidectomy groups. Recovery was complete in 92 percent of the symptomatic patients by 12 months. It is important to inform patients about the possibility of CTN injury during middle-ear operations, and it should also be emphasized that symptoms related to CTN injury can occur irrespective of the type of damage to the nerve.

Phaeochromocytoma and acute myocardial infarction

Phaeochromocytoma is uncommonly associated with myocardial infarction. We present a patient who, despite established alpha adrenoceptor blockade, sustained an acute myocardial infarction and was found to have coronary artery disease. Indications for coronary revascularization were not met, and adrenalectomy was successfully performed four weeks later. Factors contributing to the myocardial infarction, the role of beta adrenoceptor blockade, the timing of adrenalectomy and the place of coronary revascularization are discussed.

Effect of cricoid pressure on the success of endotracheal intubation with a lightwand

BACKGROUND

The lightwand may be useful as an alternative for tracheal intubation during a rapid-sequence induction of anesthesia in the presence of a full stomach. This study was undertaken to assess the effect of application of cricoid pressure on the success of lightwand intubation.

METHODS

Sixty adult female patients presenting for abdominal hysterectomy were randomly allocated to lightwand intubation with and without cricoid pressure. The time to successful intubation and number of attempts were recorded.

RESULTS

All 30 patients allocated to intubation without cricoid pressure were intubated successfully at the first attempt within a median time of 28 s (95% confidence interval, 18-77 s). Lightwand intubation with cricoid pressure was successful in 26 of 30 patients at the first attempt, but the median time to successful intubation was significantly longer at 48.5 s (95% confidence interval, 36-78 s; P = 0.001). Three patients required two attempts for successful intubation, and one could not be intubated with the lightwand while cricoid pressure was being applied.

CONCLUSIONS

The lightwand cannot be recommended for the first attempt at intubation where cricoid pressure is being applied because the time to successful intubation is significantly prolonged, and the failure rate for the first attempt at lightwand intubation is 13%.

Effect of Habit Modification on Optical and X-ray Structures of Sodium Halate Mixed Crystals: The Etiology of Anomalous Double Refraction

Structures of mixed crystals of the isomorphous salts NaClO3 and NaBrO3 (sodium chlorate and sodium bromate, respectively) were reinvestigated by X-ray diffraction. Contrary to previous reports, NaCl x Br1−x O3 is not cubic. Data from adjacent {100} growth sectors of crystals of varying composition were refined in the triclinic space group P1; halate ions occupy nominally symmetry-related sites nonstatistically. Optical measurements showed that six asymmetric sectors in cubes are disposed to give an object with approximate tetrahedral point symmetry. We address forgotten anomalies, first observed almost 150 years ago, which could have been a sufficient basis for earlier structural reinvestigations. The mixed-crystal structure speaks to the general non-applicability of the Law of Isomorphism to solid solutions. A link between optical anisotropy and nonstatistical guest site occupancy was achieved by annealing crystals between 523 and 533 K. Na2S2O3 and Na2S2O6 were used as habit-modifying impurities to produce NaCl x Brl−x O3 crystals with {111} and {\overline 1\overline 1\overline 1} habits, respectively. Diffraction data from {111} and {\overline 1\overline 1\overline 1} growth sectors were refined in the trigonal space group R3. In each case the pyramidal halate ion that was located on the special position was depleted in BrO3 −. Conoscopic optical investigations nevertheless showed that the crystals are biaxial with a small 2V (10–15°), in marked contrast to the 90° angle in {100} crystals. We failed to reconcile the optical and X-ray structures by calculating the optical indicatrix with bond polarizability sum models. This led us to estimate the magnitude of other factors which contribute to the optical properties, including strain associated with dislocations which may exert its influence through combined piezoelectric and linear electro-optic effects.

Peptides which bind to E-selectin and block neutrophil adhesion

E-selectin is an inducible cell adhesion molecule which mediates rolling of neutrophils on the endothelium, an early event in the development of an inflammatory response. Inhibition of selectin-mediated rolling is a possible means for controlling inflammation-induced diseases, and several classes of compounds have been tested for this use. We describe here the use of recombinant peptide library screening for identification and optimization of novel ligands which bind to E-selectin. Several of these peptides bind with Kd values in the low nanomolar range and block E-selectin-mediated adhesion of neutrophils in static and flow-cell assays. Administration of the peptide to mice undergoing an acute inflammatory response reduced the extent of neutrophil transmigration to the site of inflammation, demonstrating the utility of this compound as a potential therapeutic. The identification of a peptide ligand for E-selectin suggests that the complete natural ligand for this adhesion molecule may include protein as well as carbohydrate moieties.

Modulation of aflatoxin B1-induced glutathione S-transferase placental form positive hepatic foci by pretreatment of rats with phenobarbital and buthionine sulfoximine

Induction of glutathione S-transferase placental form (GST-P) positive hepatic foci has been examined by immunohistochemical analysis in young male Fischer rats 3 weeks after a single i.p. injection of aflatoxin B1 (AFB1). Pretreatment of rats with L-buthionine sulfoximine (BSO), a GSH depleter, at a dose of 4 mmol/kg body wt 4 and 2 h before 1.0 mg AFB1 treatment enhanced both the number of AFB1-induced hepatic foci and the area occupied by these foci by approximately 400 and 575% above their respective controls without affecting the mean diameter of these foci. Pretreatment of rats with 0.1% phenobarbital (PB) in their drinking water for 1 week before AFB1 (1 mg) treatment, inhibited AFB1-induced foci almost completely. However, the number of AFB1-induced foci in PB-pretreated rats was not significantly increased by BSO pretreatment.

Species and sex differences of aflatoxin B1-induced glutathione S-transferase placental form in single hepatocytes

Species and sex differences of aflatoxin B1 (AFB1)-induced glutathione S-transferase placental form (GST-P) positive single hepatocytes have been investigated 48 h after an intraperitoneal injection of AFB1 to young male and female Fischer rats (2 mg AFB1/kg body wt) and male Syrian golden hamsters (6 mg AFB1/kg body wt). The presence of GST-P positive hepatocytes was examined by the immunohistochemical method. Male rats formed three times as many AFB1-induced GST-P positive hepatocytes as females. Pretreatment of both male and female rats with an inhibitor of GSH synthesis, buthionine sulfoximine (BSO) (4 mmol/kg body wt), 2 h and 4 h before AFB1 injection increased AFB1-induced GST-P positive hepatocytes by about 120% above the controls. Male hamsters formed several-fold less AFB1-induced GST-P positive hepatocytes than male rats. Pretreatment with BSO did not increase AFB1-induced GST-P positive hepatocytes in hamsters even though it produced an increase in hepatic necrosis. It appears that GSH and GSH S-transferases play an important role in modulating hepatic AFB1-DNA binding and AFB1-induced GST-P positive hepatocytes in rats and hamsters.

Glutathione conjugation of microsome-mediated and synthetic aflatoxin B1-8,9-oxide by purified glutathione S-transferases from rats

Glutathione (GSH) conjugation of microsome-mediated and synthetic aflatoxin B1 (AFB1)-epoxide and styrene oxide has been investigated with purified GSH S-transferases (GSTs) from rats. Both styrene oxide and AFB1-epoxide were conjugated preferentially by millimicrons GSTs 3-3, 3-4 and 4-4 as compared to alpha GSTs 1-1, 1-2 and 2-2. The highest catalytic activity with styrene oxide conjugation was associated with GST 4-4. The highest catalytic activity with microsome-mediated AFB1-epoxide conjugation was observed with GST 3-3 whereas with the synthetic AFB1-epoxide conjugation was seen with GST 4-4. The catalytic activity of pi GST 7-7 was intermediate to millimicrons and alpha GSTs. It is suggested that GST 3-3 may play an important role in inactivation of AFB1-epoxide generated in vivo in the rat.

Effect of butylated hydroxyanisole pretreatment on aflatoxin B1-DNA binding and aflatoxin B1-glutathione conjugation in isolated hepatocytes from rats

The effect of 2(3)-tert-butyl-4-hydroxyanisole (BHA) pretreatment of rats on both aflatoxin B1 (AFB1)-DNA binding and AFB1-glutathione has been examined with isolated hepatocytes and in intact rats. Young male F344 rats were fed AIN-76A diet with or without 0.75% BHA for 2 weeks. Even though there were no significant differences in either cytochrome P-450 or reduced glutathione contents, there were marked differences in AFB1 metabolism in isolated hepatocytes from these two groups. Thus, at the 33 nM AFB1 level, AFB1-DNA binding was 3-fold higher in control compared to BHA-treated hepatocytes whereas AFB1-glutathione conjugation was 5-fold higher in treated compared to controls. Even at higher AFB1 concentrations (2 and 10 microM), DNA binding was 4-6-fold higher in controls whereas thiol conjugation was 5-9-fold higher in treated compared to control hepatocytes. Addition of 0.5-1.0 mM diethylmaleate did not have any significant effect in control hepatocytes whereas its presence produced about 70-100% increase in DNA binding with 65-80% inhibition of thiol conjugation in treated hepatocytes. Addition of 1 mM styrene oxide caused 75-100% and 4-8-fold increase in AFB1-DNA binding in control and treated hepatocytes, respectively, with corresponding decreases in thiol conjugation. In intact rats, BHA treatment reduced hepatic AFB1-DNA binding to 15% of controls with concomitant increase in biliary excretion of AFB1-reduced glutathione conjugate. It appears that the induced cytosolic GSH S-transferases after BHA treatment of rats play a significant role in inhibiting hepatic AFB1-DNA binding and AFB1 hepatocarcinogenesis presumably by inactivation of the reactive AFB1-epoxide.

A mechanism of inhibition of aflatoxin B1-DNA binding in the liver by phenobarbital pretreatment of rats

The effect of phenobarbital (PB) pretreatment of rats on both hepatic aflatoxin B1 (AFB1)-DNA binding and AFB1-glutathione (AFB1-SG) conjugation have been examined in studies in vivo and in vitro. Male Sprague-Dawley rats fed a commercial diet with 0.1% PB in their drinking water for 1 week had total wet liver weight and microsomal protein content about 27% and 38% higher, respectively, than controls. Hepatic cytochrome P-450 content, microsomal cytochrome P-450 mediated AFB1 binding to exogenous DNA and formation of hydroxy metabolites of AFB1 were also about threefold higher in PB-treated rats and cytosolic reduced glutathione S-transferase activities were about doubled. Microsome-mediated AFB1-DNA binding, when examined at 2 microM and 10 microM levels of AFB1, was inhibited two-to threefold more by cytosols of treated rats whereas AFB1-SG conjugation was two- to threefold higher by cytosols of treated rats. In reconstitution experiments with 2 microM AFB1, with intact nuclei serving as a source of endogenous DNA, addition of microsomes from either group generated a large amount of AFB1-DNA binding (68-105 pmol) and a smaller amount of AFB1-SG conjugate (12-21 pmol). The presence of cytosol from the controls reduced AFB1-DNA binding to a much lesser extent than the cytosol from the treated group whereas AFB1-SG conjugation was much higher with the cytosol from the treated group. These results are in agreement with the studies in vivo. In isolated hepatocytes at 33 nM, 2 microM and 10 microM AFB1 levels, AFB1-DNA binding was decreased 50 to 70% by prior PB-treatment whereas AFB1-SG conjugation was two- to threefold higher in treated compared to control hepatocytes. In hepatocytes, addition of 1 mM diethylmaleate increased DNA binding two- to threefold with a corresponding decrease in AFB1-SG conjugation. Addition of 1 mM styrene oxide caused 5- to 10-fold increases in AFB1-DNA binding at levels of AFB1 of 33 nM and 2 microM; but at 10 microM AFB1, increases in AFB1-DNA binding were two- to threefold. In intact rats, PB treatment reduced hepatic AFB1-DNA binding to 30% of controls with concomitant increase in biliary excretion of AFB1-SG conjugate. It appears that the induced cytosolic GSH S-transferases after PB treatment of rats plays a significant role in inhibiting hepatic AFB1-DNA binding and hepatocarcinogenesis presumably by inactivation of the reactive AFB1-epoxide.(ABSTRACT TRUNCATED AT 400 WORDS)

Thiol protease and cathepsin D activities in selected tissues and cultured cells from normal and dystrophic mice

Thiol protease and cathepsin D activities were studied in extracts from hindlimb muscle of 60-day-old normal and dystrophic mice, strain 129 ReJ, and from cultured normal and dystrophic cells. Total thiol protease activity in dystrophic muscle extracts was 3.5 times higher than in normal muscle extracts, while cathepsin D, activity was 2.2 times greater in dystrophic muscle compared with normal muscle. Activation (pH 4.5, 30 degrees C) of latent thiol protease activity in extracts of muscle occurred concomitant with the inactivation or dissociation of endogenous protease inhibitors. Thiol protease assays revealed a higher ratio of active to inactive protease activity in extracts from dystrophic muscle than from normal muscle. Cultured myoblasts (L69/1) were found to contain 30-fold more thiol protease(s) and 6-fold more cathepsin D activity than whole muscle. Cells established from dystrophic muscle and grown in culture for periods up to 6 months were more responsive to thiol protease activation conditions than similar cultures derived from normal muscle. From data on the rate and extent of thiol protease activation in extracts from dystrophic cells and hindlimb muscle compared with normal tissue, it appears that cells and tissues from dystrophic mice contain a lower level of protease inhibitors than cells and tissues from normal mice.

Evidence for a defective thiol protease inhibitor in skeletal muscle of mice with hereditary muscular dystrophy

The thiol protease inhibitor (TPI-d) from hind-limb skeletal muscle of dystrophic 60-day-old male mice (strain 129/ReJ/dy) has been purified to apparent homogeneity and compared with the thiol protease inhibitor (TPI-n) from hind-limb skeletal muscle of normal 60-day-old male littermates. While both TPI-d and TPI-n displayed identical properties on sodium dodecyl sulfate-polyacrylamide gels (14,800 relative mass), analytical isoelectric focusing gels (pI 4.5), and high performance liquid chromatography columns, TPI-d was unable to inhibit papain and cathepsin B after purification by isoelectric focusing. However, a component in the purified TPI-d preparation with an isoelectric point of 4.9 initially masked the functional state of TPI-d, using papain when assayed with the test proteases papain and cathepsins H and L. This inhibitory component was absent from TPI-n preparations. Pure TPI-d was also unable to inhibit in vitro myosin hydrolysis by cathepsin B, whereas TPI-n completely blocked cathepsin B catalyzed myosin hydrolysis. Given the central role of the thiol proteases, especially cathepsin B, in intracellular protein metabolism and the possibility that uncontrolled thiol protease activity in muscle leads to muscle protein breakdown and dystrophy, our data suggest that a modified (defective) thiol protease inhibitor (TPI-d) may be (one of) the end product(s) of the dystrophy gene in mice with the hereditary form of the disease.