In-vivo and ex-vivo tests for culprit drugs identification in severe cutaneous adverse drugs reactions

Drug causality assessment in severe cutaneous adverse reactions (SCARs) remains challenging. We investigated the usefulness of in-vivo drug patch tests (PT), ex-vivo interferon (IFN)-γ enzyme-linked immunospot (ELISpot) assay, and lymphocyte transformation test (LTT) in 30 SCARs patients within the past 36 months. Drug PT yielded a 20% positivity rate (n = 6), while IFN-γ ELISpot and LTT showed positive rates of 56.67% (n = 17) and 41.38% (n = 12), respectively. Combining the three tests resulted in an overall positive rate of 66.67% (n = 20) of cases. IFN-γ ELISpot offered additional positivity, especially with oxypurinol. Employing a combined diagnostic approach may enhance the chances of obtaining a positive result.

Monocyte-to-lymphocyte ratio as a predictor of TB among people living with HIV

BACKGROUND: Diagnostic tools to identify incipient or subclinical TB stages will be helpful for preventive intervention. A simple biomarker to predict TB may be the monocytes to lymphocytes ratio (ML ratio) in peripheral blood.METHODS: We assessed the relationship between multiple time-updated ML ratio measurements and incidence of TB in people living with HIV (PLWH) after antiretroviral therapy (ART) was initiated. The ML ratio was updated at least every 6 months. TB incidence with corresponding 95% confidence intervals stratified according to time-updated ML ratio was calculated using ML ratio in quartiles.RESULTS: A total of 1305 PLWH were included in the analyses: 46 had incident TB and 1259 remained TB-free. The TB incidence rate was 10.3 (95% CI 7.1-14.9) cases/1000 patient-years (PYR) among participants with ML ratio ≥0.25 compared with 1.1/1000 PYR (95% CI 0.4-2.9) among those with ML ratio <0.15. At cut-point 0.23, the ML ratio provided a diagnostic area under the receiver operating characteristics curve (AROC) of 0.849 (95% CI 0.784-0.914) and a sensitivity of 85% and specificity of 71%.CONCLUSION: Increased ML ratio was predictive of incident TB among PLWH on or after ART. The ML ratio can be a simple tool to stratify the risk of TB in PLWH.

Tunable stiffness enables fast and efficient swimming in fish-like robots

Fish maintain high swimming efficiencies over a wide range of speeds. A key to this achievement is their flexibility, yet even flexible robotic fish trail real fish in terms of performance. Here, we explore how fish leverage tunable flexibility by using their muscles to modulate the stiffness of their tails to achieve efficient swimming. We derived a model that explains how and why tuning stiffness affects performance. We show that to maximize efficiency, muscle tension should scale with swimming speed squared, offering a simple tuning strategy for fish-like robots. Tuning stiffness can double swimming efficiency at tuna-like frequencies and speeds (0 to 6 hertz; 0 to 2 body lengths per second). Energy savings increase with frequency, suggesting that high-frequency fish-like robots have the most to gain from tuning stiffness.

Predictive factors for identifying macrolide responder in treating chronic rhinosinusitis

BACKGROUND

Low-dose macrolides (LDM) are anti-inflammatory agents with antineutrophilic activity, but patient selection for LDM therapy in treating chronic rhinosinusitis (CRS) is controversial. This study aimed to assess factors which predict LDM responders.

METHODOLOGY

A prospective cohort study was performed. Patients with CRS received roxithromycin (150 mg) once daily for 12 weeks. Nasal secretions and serology were collected. Nine predictors for LDM response were assessed: nasal secretion IgE, nasal secretion IL-5, serum IgE, serum eosinophils, serum neutrophils, nasal polyps, asthma, allergy, and aspirin hypersensitivity, using receiver-operating curve analysis and multivariable logistic regression. Macrolide responders were those with sino-nasal outcome test-22 improvement, symptoms visual analogue scale decreased to ≤ ≤ ≤5, and no rescue medication.

RESULTS

One hundred CRS patients (mean age 47.4 +- 14.1 years, 45% male) were enrolled. Univariable logistic regression showed local total IgE less than 5.21; and serum eosinophils less than 2.2% associated with macrolide response. Multivariate models showed local total IgE maintained an independent association with macrolide response, with an ability to discriminate between responders and non-responders of 63%. Serum total IgE, nasal secretion IL-5, serum neutrophil, nasal polyp, asthma, allergy, and aspirin hypersensitivity showed no association with LDM response.

CONCLUSIONS

Low total IgE level in the nasal secretion but not in the serum, predict LDM response.

Performance characteristics and optimal cut-off value of triple adenylate nucleotides test versus adenosine triphosphate test as point-of-care testing for predicting inadequacy of duodenoscope reprocessing

BACKGROUND

Adenosine triphosphate (ATP) test based on one nucleotide has been applied as point-of-care testing (POCT) for bacterial contamination in the medical and food industries. Hypothetically, testing three adenylate nucleotides (A3) may provide better detection of duodenoscope bacterial contamination than ATP test.

AIM

To evaluate performance characteristics and optimal cut-off value of A3 and ATP tests in predicting bacterial contamination of duodenoscopes.

METHODS

Four hundred duodenoscope samples obtained after 100 endoscopic retrograde cholangiopancreatography procedures were randomized into group A (A3 test) or B (ATP test). Samples were collected from the elevator at the four-step cleaning process of duodenoscope. We defined the new cut-off value of the test for reaching 100% negative predictive value (NPV) from our receiver operating characteristic (ROC).

FINDINGS

Using the cultures from the four-step cleaning process as the reference, the areas under ROC (AUROC) were 0.83 and 0.84 for group A (N = 200) and group B (N = 200), respectively. Using the cultures from post-high-level disinfection (HLD) as the reference, the AUROC were 0.35 and 0.74 for group A (N = 50) and group B (N = 50), respectively. We investigated ATP as a POCT after HLD with a new cut-off value of 40 RLU. However, this threshold did not allow detection of low numbers of bacteria.

CONCLUSION

A3 and ATP tests provide good performances in predicting bacterial contamination of duodenoscopes for the four-step cleaning process. The ATP <40 RLU is helpful as a POCT after HLD; however, the limitation of this cut-off value is its inability to detect low numbers of bacteria.

Life expectancy of HIV-positive people after starting combination antiretroviral therapy: a meta-analysis

OBJECTIVES

Life expectancy is an important indicator informing decision making in policies relating to HIV-infected people. Studies estimating life expectancy after starting combination antiretroviral therapy (cART) have noted differences between income regions. The objective of our study was to perform a meta-analysis to assess life expectancy of HIV-positive people after starting cART, and to quantify differences between low/middle- and high-income countries.

METHODS

Eight cohort studies estimating life expectancy in HIV-positive people initiating cART aged ≥ 14 years using the abridged life table method were identified. Random effects meta-analysis was used to pool estimated outcomes, overall and by income region. Heterogeneity between studies was assessed with the I² statistic. We estimated additional years of life expected after starting cART at ages 20 and 35 years.

RESULTS

Overall life expectancy in high-income countries was an additional 43.3 years [95% confidence interval (CI) 42.5-44.2 years] and 32.2 years (95% CI 30.9-33.5 years) at ages 20 and 35 years, respectively, and 28.3 (95% CI 23.3-33.3) and 25.6 (95% CI 22.1-29.2) additional years, respectively, in low/middle-income countries. In low/middle-income countries, life expectancy after starting cART at age 20 years was an additional 22.9 years (95% CI 18.4-27.5 years) for men and 33.0 years (95% CI 30.4-35.6 years) for women, but was similar in the two sexes in high-income countries. In all income regions, life expectancy after starting cART increased over calendar time.

CONCLUSIONS

Our results suggest that the life expectancy of HIV-positive people after starting cART has improved over time. Monitoring life expectancy into the future is important to assess how changes to cART guidelines will affect patient long-term outcomes.

Cervical cytological abnormalities and HPV infection in perinatally HIV-infected adolescents

BACKGROUND

Behaviourally HIV-infected adolescent females are at higher risk for abnormal cervical cytology and HPV infection compared to those who are uninfected, but data on perinatally HIV-infected adolescent females are lacking.

METHODS

Cervical cytology, HPV infection and E6/E7 mRNA were assessed in sexually active 12-24-year-old adolescent females: perinatally HIV-infected (group 1, n = 40), behaviourally HIV-infected (group 2, n = 10), and HIV-uninfected (group 3, n = 10).

RESULTS

Median age was lower in group 1 (18 years) than in groups 2 (24 years) and 3 (20.5 years) (P < 0.001), and median time since sexual debut was shorter: 2 vs 5 vs 4 years (P < 0.001). More trial participants in group 1 than group 2 were on antiretrovirals (90% vs 70%; P <0.001). Abnormal cervical cytology (atypical squamous cells of undetermined significance and higher) was observed in 30% (group 1), 40% (group 2) and 30% (group 3) (P = 0.92), whereas high-risk HPV infection was observed in 45%, 45% and 40%, respectively (P = 1.00). Positive E6/E7 mRNA was found in 28% of group 1, but not in other groups. High-risk HPV infection predicted abnormal cytology in all groups [OR 6.77, 95% confidence interval (CI) 1.99-23.0; P = 0.001). Additionally, plasma HIV RNA ≥50 copies/mL (OR 13.3, 95% CI 1.16-153.06; P = 0.04) predicted abnormal cytology in HIV-infected adolescent females.

CONCLUSIONS

Despite the younger age and shorter time since sexual debut, cervical cytological abnormalities and HPV infection were as common in perinatally HIV-infected as in behaviourally infected and uninfected adolescents. HPV vaccination, pre-cancer screening and antiretroviral treatment in HIV-infected female adolescents should be implemented to minimise the risk of cervical cancer.

Assessing adherence in Thai patients taking combination antiretroviral therapy

In settings where medications and viral load (VL) monitoring are limited by cost, clinicians need reliable ways to assess patient adherence to therapy. We assessed sensitivity and specificity of two self-reported adherence tools (a visual analogue scale [VAS] and the CASE [Center for Adherence Support Evaluation] adherence index), against a standard of detectable VL, with 288 patients from three sites in Thailand. We also assessed predictors of non-adherence. The sensitivity and specificity of the VAS <95% and CASE adherence index ≤11 against a VL >50 copies/mL were 26% and 90%, 19% and 95%, respectively. Against a VL ≥1000 copies/mL sensitivities increased to 55% and 36%, respectively, and specificities were unchanged. Attending a clinic not staffed by HIV specialists (odds ratio [OR] 3.14; 95% confidence interval [CI] 1.19-8.34) and being educated to primary school level or less (OR 2.24; 95% CI 1.01-4.94) were associated with self-reported adherence <95% on the VAS in multivariate analysis. Adherence assessed by the VAS was a more accurate predictor of detectable VL. Policy-makers in resource-limited settings should ensure that treatment centres are staffed with well-trained personnel aware of the importance of good patient adherence.

Dynamics of cognitive change in HIV-infected individuals commencing three different initial antiretroviral regimens: a randomized, controlled study

BACKGROUND

Improvements in neurocognitive (NC) function have been associated with commencing antiretroviral therapy in HIV-infected subjects. However, the dynamics of such improvements are poorly understood.

METHODS

We assessed changes in NC function via a validated computerized battery (CogState™, Melbourne, Victoria, Australia) at baseline and after 24 and 48 weeks in a subset of therapy-naïve neuro-asymptomatic HIV-infected subjects, randomized to commence three different antiretroviral regimens.

RESULTS

Of 28 subjects enrolled in the study, nine, eight and 11 were randomly allocated to commence tenofovir/emtricitabine with efavirenz (arm 1), atazanavir/ritonavir (arm 2) and zidovudine/abacavir (arm 3), respectively. Overall improvements in NC function were observed at week 24 and function continued to improve at week 48 (changes in z-score for overall cognitive global score of 0.16 and 0.18 at weeks 24 and 48, respectively). Within the NC speed domains, generally greater improvements were observed in arms 2 and 3, compared with arm 1 (changes in z-score for composite speed scores at weeks 24/48 of 0.16/0.16, -0.29/-0.24 and -0.15/-0.31 in arms 1, 2 and 3, respectively; P = 0.04 for change at week 48 in arm 3 versus arm 1). Finally, improvements in executive function occurred later (only observed at week 48) and were driven by improvements in arm 3 (z-score changes of 0.23, 0.06 and -0.78 in arms 1, 2 and 3, respectively; P = 0.02 for change in arm 3 versus arm 1).

CONCLUSION

Improvements in NC function continue over the first year after initiating antiretroviral therapy in neuro-asymptomatic HIV-infected subjects.

Genital shedding of HIV after scheduled treatment interruption

This study assessed genital shedding of HIV in patients on intermittent combination antiretroviral therapy (cART) and assessed predictors of having detectable genital HIV RNA in 156 Thai patients with CD4 > 350 cells/μL and HIV RNA ≤50 copies/mL who were randomized to continuous therapy (CT, n = 65) or CD4-guided cART (n = 91). There were 383 matched genital and plasma HIV RNA samples (CT: 158, CD4 guided: 225). In 14 samples collected within eight weeks of treatment interruption, detectable HIV RNA was present in 29% of genital samples and 71% of plasma samples. In 55 samples collected after eight weeks of treatment interruption, detectable HIV RNA was present in 60% of genital samples and 98% of plasma samples. In 110 samples collected up to 96 weeks after treatment re-initiation, detectable genital HIV RNA was found in 8% of samples and all of these were within the first 17 weeks. Independent predictors of detectable genital HIV RNA were increasing age and increasing concentrations of HIV RNA in plasma. These findings support the role of cART in maintaining undetectable HIV RNA in genital secretions.

Concurrent quantification of quinolinic, picolinic, and nicotinic acids using electron-capture negative-ion gas chromatography-mass spectrometry

Quinolinic, picolinic, and nicotinic acids and nicotinamide are end products of the kynurenine pathway from l-tryptophan and are intermediates in the biosynthesis of nicotinamide adenine dinucleotide. These compounds are involved in complex interrelationships with inflammatory and apoptotic responses associated with neuronal cell damage and death in the central nervous system. To facilitate the study of these compounds, we have utilized gas chromatography-mass spectrometry in electron capture negative ionization mode for their concurrent trace quantification in a single sample. Deuterium-labeled quinolinic, picolinic, and nicotinic acids were used as internal standards and the compounds were converted to their hexafluoroisopropyl esters prior to chromatography. Nicotinamide was readily quantified after conversion to nicotinic acid using gas-phase hydrolysis-a process which did not affect the deuterated internal standards. The on-column limit of quantification was less than 1 fmol for each of the analytes and calibration curves were linear. A packed column liner was used in the gas chromatograph inlet to effectively eliminate sample interference effects in the analysis of trace (femtomolar) levels of quinolinic acid. The method enables rapid and specific concurrent quantification of quinolinic, picolinic, and nicotinic acids in tissue extracts and physiological and culture media.

IFN-beta1b induces kynurenine pathway metabolism in human macrophages: potential implications for multiple sclerosis treatment

Interferon-beta(1b) (IFN-beta(1b)) has limited efficacy in the treatment of relapsing-remitting multiple sclerosis (RRMS). The kynurenine pathway (KP) is chiefly activated by IFN-gamma and IFN-alpha, leading to the production of a variety of neurotoxins. We sought to determine whether IFN-beta(1b) induces the KP in human monocyte-derived macrophages, as one explanation for its limited efficacy. Serial dilutions of IFN-beta(1b) (at concentrations comparable to those found in the sera of IFN-beta(1b)-treated patients) were added to human macrophage cultures. Supernatants were collected at various time points and assayed for the KP end product, quinolinic acid (QUIN). The effect of IFN-beta(1b) on the KP enzymes indoleamine 2,3-dioxygenase (IDO), 3-hydroxyanthranilate dioxygenase (3HAO), and quinolinate phosphoribosyltransferase (QPRTase) mRNA expression was assessed by semiquantitative RT-PCR. IFN-beta(1b) (> or =10 IU/ml) led to increased mRNA expression of both IDO and QUIN production (7901 +/- 715 nM) after 72 h at 50 IU/ml IFN-beta(1b) (p < 0.0001). This study demonstrates that IFN-beta(1b), in pharmacologically relevant concentrations, induces KP metabolism in human macrophages and may be a limiting factor in its efficacy in the treatment of MS. Inhibitors of the KP may be able to augment the efficacy of IFN-beta in MS.

Kynurenine pathway metabolism in human astrocytes: a paradox for neuronal protection

There is good evidence that the kynurenine pathway (KP) and one of its products, quinolinic acid (QUIN), play a role in the pathogenesis of neurological diseases, in particular AIDS dementia complex. Although QUIN has been shown to be produced in neurotoxic concentrations by macrophages and microglia, the role of astrocytes in QUIN production is controversial. Using cytokine-stimulated cultures of human astrocytes, we assayed key enzymes and products of the KP. We found that human astrocytes lack kynurenine hydroxylase so that large amounts of kynurenine and the QUIN antagonist kynurenic acid were produced. However, the amounts of QUIN that were synthesized were subsequently completely degraded. We then showed that kynurenine in concentrations comparable with those produced by astrocytes led to significant production of QUIN by macrophages. These results suggest that astrocytes alone are neuroprotective by minimizing QUIN production and maximizing synthesis of kynurenic acid. However, it is likely that, in the presence of macrophages and/or microglia, astrocytes become indirectly neurotoxic by the production of large concentrations of kynurenine that can be secondarily metabolized by neighbouring or infiltrating monocytic cells to form the neurotoxin QUIN.

Characterisation of kynurenine pathway metabolism in human astrocytes and implications in neuropathogenesis

The role of astrocytes in the production of the neurotoxin quinolinic acid (QUIN) and other products of the kynurenine pathway (KP) is controversial. Using cytokine-stimulated human astrocytes, we assayed key enzymes and products of the KP. We found that astrocytes lack kynurenine-hydroxylase so that large amounts of kynurenine (KYN) and kynurenic acid (KYNA) were produced, while minor amounts of QUIN were synthesised that were completely degraded. We then showed that kynurenine added to macrophages led to significant production of QUIN. These results suggest that astrocytes alone are neuroprotective by minimising QUIN production and maximising synthesis of KYNA. However, it is likely that, in the presence of macrophages and/or microglia, astrocytes are neurotoxic by producing large concentrations of KYN that can be metabolised by neighbouring monocytic cells to QUIN.

Kynurenine pathway metabolism in human astrocytes

The involvement of astrocytes in Kynurenine pathway (KP) metabolism is still poorly understood. In the present study, we investigated the ability of human fetal astrocytes in vitro to produce quinolinic and picolinic acids using mass spectrometry. In parallel, we estimated the level of expression of five major KP enzymes using RT-PCR. The results demonstrated that astrocytes express most KP enzymes, except for kynurenine-hydroxylase. This in vitro study provides novel informations regarding the ability of human fetal astrocytes to degrade L-tryptophan along the KP.

Chronic exposure of human neurons to quinolinic acid results in neuronal changes consistent with AIDS dementia complex

OBJECTIVE

Concentrations of quinolinic acid, an N-methyl-D-aspartate agonist, are often elevated for long periods of time in the cerebrospinal fluid (CSF) and brain tissue of patients with AIDS dementia complex (ADC). This study was designed to test the hypothesis that chronic exposure of human neurons to quinolinic acid levels equivalent to those in the CSF of ADC patients is neurotoxic.

DESIGN AND METHODS

Human fetal brain 14-16 weeks post-menses was cultured in medium with no detectable levels of quinolinic acid. After 4 weeks, 350 or 1200 nmol/l quinolinic acid was added to the feeding medium for a further 5 weeks. Neurotoxicity was evaluated using immunohistochemistry, transmission and scanning electron microscopy, and image analysis.

RESULTS

A total of 1200 nmol/l quinolinic acid caused altered cell associations, a decrease in cell density and decreased microtubule-associated protein (MAP)-2 immunoreactivity compared with cultures exposed to 350 nmol/l quinolinic acid or controls. Image analysis of neurons in randomly selected fields revealed significantly swollen cells (P < 0.0001) compared with those treated with 350 nmol/l quinolinic acid or controls. Dendritic varicosities and discontinuous microtubular arrays were present in neurons exposed to both quinolinic acid concentrations, but not in control cultures.

CONCLUSIONS

This study is the first to assess quinolinic acid levels in the experimental medium, and demonstrates that chronic exposure of human neurons to concentrations of quinolinic acid equivalent to those in the CSF of patients with ADC leads to alterations in dendritic ultrastructure and MAP-2 immunoreactivity, which is consistent with ADC pathology.

Kynurenine pathway inhibition reduces neurotoxicity of HIV-1-infected macrophages

The AIDS dementia complex (ADC) is a consequence of excessive immune activation driven at least in part by systemic HIV infection and probably brain infection. Quinolinic acid (QUIN) is a neurotoxic tryptophan metabolite produced by macrophages in response to stimulation with cytokines or infection with HIV-1. Consequently it has been implicated in ADC pathogenesis. However, macrophages infected with HIV-1 synthesize numerous neurotoxic substances. Therefore we conducted experiments using human fetal brain tissue to determine the relative importance of QUIN as a neurotoxin in ADC. Human macrophages were infected with HIV-1 in vitro using a viral isolate from a demented patient. 6-Chloro-D-tryptophan, an inhibitor of QUIN biosynthesis, was added to half the macrophage cultures to block formation of QUIN. Supernatants containing QUIN (SQpos) or in which QUIN biosynthesis had been inhibited (SQneg) were then added to human fetal brain aggregate cultures. Toxicity was evaluated using lactate dehydrogenase efflux, trypan blue exclusion, immunohistochemistry, image analysis, and electron microscopy. Each technique showed a reduction of toxicity in SQneg-treated cultures. These studies confirm the significance of QUIN as a neurotoxin in ADC and suggest that neuroprotective strategies may have a place in the treatment of this disease.

Quinolinic acid production by macrophages stimulated with IFN-gamma, TNF-alpha, and IFN-alpha

Quinolinic acid (QUIN) has been associated with several inflammatory neurologic disorders, including AIDS dementia complex (ADC). Recent studies suggest that activation of macrophages with either HIV-1 or interferon-gamma (IFN-gamma) can lead to QUIN production. However, the importance of other cytokines, especially those related to the macrophage and that are especially important in ADC pathogenesis, remains unclear. We, therefore, sought to determine the role of tumor necrosis factor-alpha (TNF-alpha) and IFN-alpha in the production of QUIN. Primary human macrophages were stimulated with two different concentrations of these cytokines alone, in combination with each other, and with IFN-gamma. QUIN concentrations in the supernatants were then measured by mass spectrometry at 24, 48, and 72 hs. Results at 72 h showed significant increases in QUIN production in the cells stimulated with IFN-gamma (10297 +/- 170 nmol/L) and also in those stimulated with IFN-alpha (3600 +/- 113 nmol/L), whereas TNF-alpha-stimulated macrophages produced low levels of QUIN (1108 +/- 23 nmol/L). Macrophages stimulated with the cytokine combinations TNF-alpha and IFN-gamma, IFN-alpha, and IFN-gamma, and TNF-alpha and IFN-alpha also resulted in increases in QUIN production (11471 +/- 77.6 nmol/L, 16656 +/- 184 nmol/L, and 3369 +/- 120.5 nmol/L, respectively). The increases in QUIN production in all of the cytokine treatments approached or exceeded in vivo concentrations of QUIN that have been shown to be neurotoxic. These data further support a role for QUIN in cytokine-mediated neuronal death in inflammatory disorders of the brain, especially ADC.

Extracorporeal support for intractable cardiorespiratory failure due to meningococcal disease

BACKGROUND

Meningococcal disease is still associated with considerable mortality, despite the use of early antibiotics and management in specialised intensive care units, due principally to early refractory myocardial depression and hypotension as well as severe acute respiratory distress syndrome. Extracorporeal membrane oxygenation (ECMO) is a complex technology that uses a modified "heart-lung" machine to provide temporary cardiac and respiratory support. We reviewed the UK and Australian experience of the use of ECMO in patients with refractory cardiorespiratory failure due to meningococcal disease.

METHODS

The records from all 12 known patients supported with ECMO for meningococcal disease in the UK and Australia since 1989 were reviewed.

FINDINGS

12 patients (aged 4 months to 18 years, median 26 months) with meningococcal disease received ECMO over 8 years. In seven patients, ECMO was required early for cardiac support for intractable shock within 36 h of admission to intensive care. In the other five patients, ECMO was indicated for respiratory failure due to severe adult respiratory distress syndrome, which tended to occur later in the disease. The paediatric risk of mortality score ranged from 13 to 40 (median 29, median predicted risk of mortality 72%). Six of the 12 patients required cardiopulmonary resuscitation before ECMO and the other six were deteriorating despite maximal conventional therapy. Overall, eight of the 12 patients survived, with six leading functionally normal lives at a median of 1 year (range 4 months to 4 years) of follow-up.

INTERPRETATION

ECMO might be considered to support patients with intractable cardiorespiratory failure due to meningococcal disease who are not responding to conventional treatment.

Neurocytotoxity of quinolinic acid in human brain cultures

Quinolinic acid (QUIN) is a tryptophan metabolite which has been found to be an excitotoxin in rats, although its toxicity in humans is unknown. QUIN has been implicated in the pathogenesis of AIDS dementia complex. This study examined the effect of QUIN on human fetal brain tissue in vitro. After at least 14 days in vitro, QUIN was added to the cultures in the feeding medium, and lactate dehydrogenase (LDH) efflux at 20 h and neuronal morphology were used as a measure of neuronal injury. LDH levels in media from cultures exposed to QUIN concentrations of 5 and 10 mM were consistently elevated compared to controls. Overall, LDH levels in media from cultures exposed to lower QUIN concentrations did not differ significantly from controls. These data are comparable to animal in vitro studies, and support the hypothesis that QUIN is toxic to human central nervous system neurons and further strengthen its potential role in the pathogenesis of AIDS dementia complex.

Role of ECMO in the treatment of respiratory syncytial virus bronchiolitis: a collaborative report

AIM

To report the collaborative experience of extracorporeal membrane oxygenation (ECMO) in the treatment of respiratory syncytial virus (RSV) bronchiolitis between April 1989 and January 1995.

METHODS

The medical records of patients with confirmed RSV bronchiolitis referred to three centres (Leicester, Glasgow, and Great Ormond Street) were reviewed.

RESULTS

Twenty four infants were identified. Seventeen had been born prematurely (gestational range 23-40 weeks, median 30 weeks). Thirteen infants had been mechanically ventilated after birth and seven of these had evidence of bronchopulmonary dysplasia (BPD). The age of onset of RSV infection varied from three to 64 weeks (mean 17.4 weeks, median 12 weeks). Ventilation before ECMO ranged from one to 16 days and oxygenation indices at the time of referral ranged from 21-73 (mean 39). Ribavirin was used in eight of the 24 patients. Sixteen patients received venoarterial and eight veno-venous ECMO. ECMO hours ranged from 32-647 (median 196 hours). One infant died (survival rate 96%). Cranial ultrasound abnormalities were detected in three patients. However, at follow up only one of the 23 survivors had evidence of developmental delay.

CONCLUSION

A group of paediatric patients in whom ECMO can be of benefit has been identified. The use of ECMO should be considered when other means of support prove unsuccessful.

Elevated levels of eukaryotic translation initiation factor eIF-4E, mRNA in a broad spectrum of transformed cell lines

Translation initiation factor eIF-4E, which binds to the 5' cap structure of eukaryotic mRNAs, is believed to play an important role in the control of cell growth. Over-expression of eIF-4E in fibroblasts results in their malignant transformation. However, no information on eIF-4E expression in established transformed cell lines has been available. We report here that a variety of tumor cell lines, chemically, virally and oncogenically transformed, exhibit elevated levels of eIF-4E mRNA expression as compared to their normal counterparts. Overexpression of eIF-4E, which is normally rate-limiting in protein synthesis, may stimulate the translation of regulatory and oncogenic proteins involved in transformation.

Methylated oxypurines and induction of differentiation of murine erythroleukemia cells

Murine erythroleukemia cell lines derived from Friend virus infected mice can be induced to differentiate in vitro by numerous agents. Among these compounds are certain naturally occurring purines such as hypoxanthine or 1-methylhypoxanthine. We have extended these studies to other modified oxypurines and have identified some areas of cell regulation with which they may be interacting. Monomethylated derivatives of guanine, hypoxanthine or xanthine are active as inducers of differentiation. Excluding hypoxanthine, the parent oxypurines guanine and xanthine are ineffective in inducing differentiation. The dimethyl- and trimethylxanthine derivatives are also inactive as inducers. The methylated oxypurines are not metabolized to nucleotides by the cell and, therefore, probably do not interact with nucleic acid synthesis directly. We have investigated one cellular process of possible regulatory significance with which they do interact. ADP-ribosylation has been implicated in control of gene expression and differentiation. The methylated oxypurines inhibit this reaction, as measured in permeabilized cells, in the same concentration range at which they are effective as inducers of differentiation. Additionally, 1-methylguanine and 7-methylguanine decrease incorporation of mannose and glucosamine into glycoprotein and into dolichol-oligosaccharide precursors. These effects may be related to cell surface alterations observed during differentiation.

Different immunological sensitizing regimens and airway responsiveness in vitro to contractile agonists in guinea-pigs

Groups of guinea-pigs were sensitized to ovalbumin, using different regimens to induce either IgG-like antibodies or IgE-like and IgG-like antibodies and the responsiveness to histamine and carbachol in vitro of tracheal and lung parenchymal strips was determined. EC50 values for histamine and carbachol in both tracheal and lung parenchymal strips were not significantly different for either group of sensitized guinea-pigs or their respective controls. The maximal tension developed in parenchymal strips was not significantly different for either sensitized or control groups. For tracheal strips, maximal tension was not significantly different in each group except in animals with IgG-like antibodies, which developed less maximal tension with histamine than controls. The absence of any increase in maximal tension or any change in EC50 to histamine or to carbachol in tracheal or parenchymal strips from immunized guinea-pigs indicates that immunological sensitization does not increase the responsiveness of smooth muscle to these contractile agonists.

Ribavirin induced differentiation of murine erythroleukemia cells

The synthetic nucleoside, ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide), a broad spectrum antiviral agent currently being tested in clinical studies with AIDS patients; and mycophenolic acid, a non-nucleoside inhibitor of inosinate (IMP) dehydrogenase, are effective inducers of terminal differentiation of Friend virus transformed murine erythroleukemia cells. The inhibition of cell division and the induced maturation produced by these agents appears to be a consequence of inhibition of IMP dehydrogenase, since growth inhibition is reversed and differentiation is prevented by the simultaneous exposure of cells treated with the agents to exogenous guanine or guanosine, which circumvents the effects of blockage of IMP dehydrogenase. However, while the effects mycophenolic acid, a pure IMP dehydrogenase inhibitor with no other biochemical effects, were completely reversed by guanine salvage supplies, cells exposed to ribavirin responded in a different manner. At levels of guanine salvage supplies below 50 microM, growth inhibition and cell differentiation were partially reversed. At salvage supply concentrations greater than 50 microM, while differentiation was completely blocked, the toxicity of ribavirin was increased and cell division was greatly diminished. These results indicate additional biochemical effects for ribavirin unrelated to the inhibition of IMP dehydrogenase, which may be related to its antiviral properties.

Mutant allele frequencies in the cat population of Omaha, Nebraska

The phenotypes of 256 cats seen in Omaha, Nebraska, during the summer of 1983 were recorded and compared to those of other midcontinental USA cat populations. When cats that were "pure-bred," or derived from pure breeds, were excluded, random breeding at the O locus was confirmed and mutant allele frequencies were: O = 0.352, a = 0.813, tb = 0.354, d = 0.525, I = 0.369, S = 0.197, and W = 0.039. Siamese and Himalayan cats constituted 10.9 percent of the total sample (cs = 0.342), but analysis suggests that they are not randomly mating with the general population. Mutant allele frequencies of Omaha cats are more similar to those of cats in Champaign, Illinois, than to those of St. Louis, suggesting that an overland route was more important than a river route in founding the Omaha cat population.

1-Methylguanine and 7-methylguanine increase cell agglutinability

1-Methylguanine and 7-methylguanine, both metabolic products of tRNA degradation, are known to induce transformation of Chinese hamster fibroblasts in culture. The effects of these compounds on the cell membrane have been studied by the method of Concanavalin A-mediated hemadsorption. 1-Methylguanine or 7-methylguanine induced a 50% increase of Con A-mediated hemadsorption within 20 hours of exposure of the cells to the agent at a concentration of 10(-5) M. This alteration was reversed within 13 days when the cells were grown in the control medium. Prolonged treatment with 1-methylguanine or 7-methylguanine resulted in changes which were only slowly reversed during growth of the cells in the control medium. The effect of the methylated purines on the cell membrane could be completely inhibited by simultaneous addition of dibutyryl-cAMP at a concentration of 10(-5) M. The possible mechanism of cell membrane alteration by methylated purines and its relevance to transformation in vitro are discussed.

Long term parenteral infusion in the rat: a new technique

We developed an improved method for continuous parenteral infusion of rats with minimal animals restraint. This method is reliable, relatively inexpensive, and imposes less stress upon the animal than other methods of infusion previously described.

An improved rapid assay for S-adenosyl-L-homocysteine hydrolase

A coupled enzyme system was devised to assay S-adenosyl-L-homocysteine hydrolase activity spectrophotometrically and to stain the hydrolase selectively in polyacrylamide gels. The assay procedure monitors the formation of uric acid derived from the catabolism of the adenosine moiety of S-adenosylhomocysteine. The staining procedure allows the determination of the molecular weight of the hydrolase when extracts are electrophoresed on polyacrylamide gradient gels and compared to standard of known molecular weight. The specificity of the enzyme for the homocysteine moiety was also investigated by testing modified compounds as substrates. All the analogs tested were inactive as substrates for hydrolysis, indicating a strict specificity.

The nucleus as the site of tRNA methylation

Mouse L-cells were enucleated by exposure to cytochalasin B followed by centrifugation. The resulting karyoplasts, nuclei surrounded by a thin shell of cytoplasm and an outer cell membrane, and cytoplasts, the enucleated cell cytoplasm, were assayed for tRNA methyltransferase activity. The bulk of the enzyme activity was found to be localized in the nuclei. Analysis of the methylated nucleosides produced by the enzyme from the two sources showed that all the base-specific enzyme activities which are found in whole cell extracts were present in the nuclear extracts. The cytoplast extracts retained a low but detectable enzyme activity, which was composed predominantly of only two base-specific activities. This may represent tRNA methyltransferases of the mitochondria or may be cytoplasmic enzymes for late modification reactions.

Karyotype and tumorigenicity of 1-methylguanine-transformed Chinese hamster cells

Chinese hamster embryo cells transformed with the tRNA catabolite 1-methylguanine were characterized by Giemsa-banded karyotyping and by their tumorigenic potency in athymic nude mice. All seven 1-methylguanine-transformed cell lines were hyperdiploid with a modal chromosome number of 23. Three of these lines had an additional marker chromosome derived from the long (q) arm of chromosome no. 4, and they had alterations of chromosome no. 5 as well. Two of these three cell lines were tumorigenic. Nonrandom chromosome changes were observed in the other four 1-methylguanine-transformed cell lines, which included the addition of all or a portion of chromosome no. 6. One of these cell lines was also tumorigenic in nude mice, Specific cytogenetic changes were observed in most 1-methylguanine-transformed populations in contrast to the karyotypic heterogeneity of a benzo[a]pyrene-transformed cell line.

Selective changes in tRNA methyltransferase activity in confluent monolayers of WI-38 cells stimulated to proliferate

In quiescent confluent monolayers of WI-38 cells, the specific activity of the tRNA methyltransferases falls to 20% of the level found in log phase cells. When the resting cells are stimulated to proliferate by a change to fresh medium, the enzyme show a rapid rise in specific activity which correlates with early increases in the rate of tRNA synthesis. The specific activity of the enzymes continues to rise throughout the period of DNA synthesis, at the end of which it is somewhat higher than that of log phase cells. The increases in enzyme activity could be blocked by exposure of the stimulated cells to Actinomycin D (2 microgram/ml). The increases in activity were not equivalent for the different base-specific enzymes. The contribution of the N2-methylguanine specific enzyme remained relatively constant, while that of the N2,N2-dimethyl-guanine specific and 1-methyladenine specific enzymes doubled and tripled, respectively, by late S phase. The contributions of the 1-methylguanine and the 7-methylguanine specific enzymes fell to a few percent of the total by late S phase. This indicates non-coordinate variations in the expression of the different base-specific enzymes after stimulation of resting cells and may be related to altered isoaccepting tRNA profiles observed in resting and growing cells.

Altered growth properties of Chinese hamster cells exposed to 1-methylguanine and 7-methylguanine

Primary Chinese hamster embryo cell cultures generally yield cell lines with a finite lifetime in culture. However, if early-passage cells are exposed chronically to either of two normal degradation products of transfer RNA, 1-methylguanine or 7-methylguanine, they are converted to continuous lines with altered growth characteristics and morphology. The continuous cell lines have saturation densities 2- to 10-fold higher than did finite control cultures, and some have the ability to grow in soft agar. Certain cultures have the general appearance of fibroblasts while others are more epithelial-like. Quantitative and qualitative alterations in the transfer RNA methyltransferases are early markers for neoplastic transformation in vivo and in vitro. Transfer RNA methyltransferase activity in the continuous lines is elevated compared to that of finite Chinese hamster cells. Neoplastic transformation has been demonstrated for a 1-methylguanine-derived line, and both 1-methylguanine- and 7-methylguanine-treated cell lines exhibit characteristics similar to those of Chinese hamster cells transformed with the carcinogen 3,4-benzopyrene or the DNA tumor virus SV40.