Studies with neuronal cells: From basic studies of mechanisms of neurotoxicity to the prediction of chemical toxicity

Neurotoxicology considers that chemicals perturb neurological functions by interfering with the structure or function of neural pathways, circuits and systems. Using in vitro methods for neurotoxicity studies should include evaluation of specific targets for the functionalism of the nervous system and general cellular targets. In this review we present the neuronal characteristics of primary cultures of cortical neurons and of cerebellar granule cells and their use in neurotoxicity studies. Primary cultures of cortical neurons are constituted by around 40% of GABAergic neurons, whereas primary cultures of cerebellar granule cells are mainly constituted by glutamatergic neurons. Both cultures express functional GABAA and ionotropic glutamate receptors. We present neurotoxicity studies performed in these cell cultures, where specific neural targets related to GABA and glutamate neurotransmission are evaluated. The effects of convulsant polychlorocycloalkane pesticides on the GABAA, glycine and NMDA receptors points to the GABAA receptor as the neural target that accounts for their in vivo acute toxicity, whereas NMDA disturbance might be relevant for long-term toxicity. Several compounds from a list of reference compounds, whose severe human poisoning result in convulsions, inhibited the GABAA receptor. We also present cell proteomic studies showing that the neurotoxic contaminant methylmercury affect mitochondrial proteins. We conclude that the in vitro assays that have been developed can be useful for their inclusion in an in vitro test battery to predict human toxicity.

Endoscopic treatment of postoperative fistulas resistant to conservative management using biological fibrin glue

BACKGROUND AND STUDY AIMS

Postoperative fistulae occur frequently in standard surgical practice, but there is no general agreement on how to treat them. We summarize here our experience with endoscopic treatment.

PATIENTS AND METHODS

Postoperative digestive fistulae resistant to conservative treatment, in 15 patients, are retrospectively reviewed. Our series included two internal fistulas: (one rectovesical, and one high-output pleuroesophagic), and 13 external fistulas (one low-output gastrocutaneous, two low-output esophagocutaneous, seven low-output enterocutaneous, and three high-output enterocutaneous). After failure of conservative treatment, the fistulas were endoscopically located and 2 - 4 ml of reconstituted fibrin glue, Tissucol 2.0 at 37 degrees C, was injected through a catheter.

RESULTS

The mean age of the patients was 61.2 years (38 - 86), and 60 % were men. Of the fistulas, 26.6 % were of the high-output type. The mean healing time was 16 days (5 - 40), and a mean of 2.5 sessions per patient were required (1 - 5). Complete sealing of fistulas was achieved in 86.6 % of cases; (87.5 % of the low-output and internal fistulas, and 55 % of the high-output fistulas). After follow-up ranging between 2 months and more than 3 years, only one of the sealed fistulas reopened. No complications were encountered. Overall mortality was 13.3 % (two out of 15), but in only one patient was this related to clinical deterioration because of the persistence of the fistula.

CONCLUSIONS

We think that conservative treatment should not be prolonged beyond 14 days and that endoscopic treatment should be performed at that stage. Endoscopic sealing treatment achieves a very high success rate, without complications and at a lower cost. It could probably reduce the hospital stay, and avoid some unnecessary surgical interventions. Appropriate multicenter randomized trials are needed to confirm these results.

Chromatographic removal combined with heat, acid and chaotropic inactivation of four model viruses

The virus removal of protein A affinity chromatography, inactivation capacity, acid pH and a combination of high temperature with a chaotropic agent was determined in this work. The model viruses studied were sendaivirus, human immunodeficency virus (HIV-IIIb), human poliovirus type-II, human herpesvirus I and canine parvovirus. The protein A affinity chromatography showed a maximum reduction factor of 8 logs in the case of viruses larger than 120 nm size, while for small viruses (18-30 nm) the maximum reduction factor was about 5 logs. Non viral inactivation was observed during the monoclonal antibody elution step. Low pH treatment showed a maximum inactivation factor of 7.1 logs for enveloped viruses. However, a weak inactivation factor (3.4 logs) was obtained for DNA nonenveloped viruses. The combination of high temperature with 3 M KSCN showed a high inactivation factor for all of the viruses studied. The total clearance factor was 23.1, 15.1, 13.6, 20.0 and 16.0 logs for sendaivirus, HIV-IIIb, human poliovirus type-II, human herpesvirus I and canine parvovirus, respectively.

[Polyps of the biliary tract: is their preoperative diagnosis possible?]

Bile duct polyps are a very uncommon cause of obstructive jaundice. We present our experience of three patients diagnosed in the last 10 years. Initial presentation usually takes the form of obstructive jaundice associated with abdominal pain, which simulates biliary lithiasis. The diagnosis is usually surgical. Although in some cases radiological studies and endoscopic retrograde cholangiopancreatography (ERCP) may sometimes detect bile duct polyps, exact diagnosis before surgery is very unusual. The radiological signs that suggest the existence of a bile duct polyp in the ERCP seem to be the presence of repletion defects, fixed unilaterally to the biliary conduit, without meniscus and without circumferential stenosis of the affected conduit. The most frequently found polyps are fibroinflammatory, and less frequently adenomatous.

[Esophageal perforation and postoperative fistulae of the upper digestive tract treated endoscopically with the application of Tissucol]

We present three patients with serious gastro-esophageal complications which were treated with Tissucol. The first patient developed a rare postoperative oesophago-pleural fistula. The second suffered a traumatic esophageal perforation (possibly iatrogenic) that was discovered at the end of the removal procedure of an alimentary bolus impacted in the distal esophagus. Attempts to close the high output oesophago-pleural fistula with standard treatment were unsuccessful. It was closed with Tissucol at the third attempt, in conjunction with oesophago-jejunal stenosis by means of endoscopic dilatation. In the second patient, early Tissucol application after detection of pneumomediastinum was an effective complementary treatment to the conservative approach and rapidly closed the perforation. The third patient developed a low debit postoperative gastro-cutaneous fistula that did not resolve with conservative treatment. It was closed with only one session of Tissucol sealing. We consider that the endoscopic application of fibrin glue should become the first step in the conservative treatment of small esophageal perforations or postoperative esophageal pleural fistulae, especially in cases of high output fistulae. The success of this technique depends on the localization and selective catheterization of the fistula and on brushing the fistular opening. Total resolution of any distal stenosis is necessary to prevent reopening of the fistula.

Formation of copper oxychloride and reactive oxygen species as causes of uterine injury during copper oxidation of Cu-IUD

The lining of the uterus and cervix might be injured by a variety of oxidation products of Cu in a Cu-IUD, including cuprous ions, dissolved and precipitated cupric ions, and reactive oxygen species such as superoxide radicals, hydrogen peroxide, and hydroxyl radicals. In this study, the human amnious WISH cell line was employed as a model of uterine cells in the presence of copper. The cell viability was decreased by elemental copper, which was alleviated up to 70% by the addition of catalase. The addition of copper oxychloride caused cell death in a dose-dependent manner. Hydroxyl radicals in the presence of copper were determined by the formation of malondialdehyde. Soluble cuprous chloride complexes are formed in the uterus by slowly entering oxygen. The complexes are partly oxidized to insoluble copper oxychloride. which damages the endometrium. Unoxidized cuprous ions migrate to the oxygen-rich cervix and are oxidized to copper oxychloride, causing cervix damage.

[High frequency ventilation strategies with neonatal conventional ventilator. Assessment of gas exchange, hemodynamic status and lung injury]

Experiments were performed to consider the use of conventional neonatal ventilators with assisted expiratory mechanism using ventilatory high frequency strategies. Gas exchange, hemodynamic state, and lung injury were also assessed. Twenty Albino Wistar rats, undergoing and acute lung lesion through physiological solution wash of the lungs were studied. Afterward, they were distributed into four groups according to the different ventilator strategies, based on the different pressure changes and the tidal volume, the baseline lung volume and the respiratory frequency. Group I, High Frequency Ventilation, with high baseline lung volumes (HFVh); group II, Conventional Mechanical Ventilation, with high baseline lung volume (CMVh), group III, High Frequency Ventilation, with low baseline lung volume (HFV1) and group IV Conventional Mechanical Ventilation, with low baseline lung volume (CMV1). Significant differences were found between group I (HFVh) and groups II (CMVh), III (HFV1) and IV (CMV1) as regards pO2, Artery/Alveolar relation to O2 (a/A), pCO2, arterial blood pressure and histopathologic lung lesion. The hypothesis concerning the decisive role of the baseline lung volume maintainence to minimize progressive damage caused by mechanical ventilation on a previously injured lung while attending ventilatory strategies that generate little pressure and volume cyclical changes was confirmed. We conclude that, high frequency mechanical ventilation is possible through conventional neonatal respirators with assisted expiratory mechanism.

[Phenotypic and molecular features of Vibrio cholerae isolated in Chile, Peru and Bolivia. Comparison with environmental reservoirs]

BACKGROUND

Since 1991, a massive cholera epidemic started in Peru and involved most Central and South American Countries. In Chile, 147 cases were registered, the last one in 1995.

AIM

To study the phenotypic and molecular features of Vibrio cholerae strains isolated from patients in Perú, Bolivia and Chile and from environmental reservoirs in Santiago, Chile.

MATERIALS AND METHODS

The phenotype, biotype and susceptibility to nine antimicrobials was determined for each isolated strain. Also, the genes of cholera and termolabile toxins were determined using DNA probes and a chromosomal restriction profile was done using HindIII, EcoRI and NotI enzymes.

RESULTS

Features studied were similar in the 53 strains isolated from patients. Those isolated from environmental reservoirs had different antimicrobial susceptibility, showing ampicillin resistance, and the GT gene was detected in one of 20 strains, compared to clinical samples were it was present in all. Strains isolated from patients and environment had similar chromosomal restriction profiles.

CONCLUSIONS

The chromosomal restriction profile gives an image of bacterial genome and it is a useful and reliable tool for the epidemiological surveillance of cholera.

Nicotine gum, 2 and 4 mg, for nicotine dependence. A double-blind placebo-controlled trial within a behavior modification support program

The effectiveness of nicotine gum in combination with a behavior modification program was studied. The nicotine dependence of participating smokers (N = 322) was assessed. One hundred sixty-eight smokers were labeled as high nicotine dependent and 154 as moderate to low dependent. In a randomized double-blind procedure, the high-dependent smokers were given gum containing 4 mg of nicotine (87) or 2 mg of nicotine (81) and the smokers with medium or low dependence were given gum containing 2 mg (76) or a placebo gum (78). The smokers were also randomized to familiarizing themselves with the medication a week before quit day (112) or to regular use, that is starting gum use on the quit day (122). In the high-dependent group, sustained and chemically verified nonsmoking rates at 6 weeks, 1 year, and 2 years were, respectively, 60%, 39%, and 34% in the subjects given the 4-mg dose compared with 41%, 16%, and 16% for those using the 2-mg dose. In the group with medium or low dependence, the success rates at the same time periods were 70%, 49%, and 39% for the subjects given the 2-mg dose and 38%, 22%, and 17% for those given placebo gum. The differences in success rates were significant at least at the p < 0.02% level for all comparisons. Familiarizing with the gum as compared with regular use gave fewer reports of side effects, 15% vs 34%, p < 0.001. A trend toward better success rates at 6 weeks, although not statistically significant, was observed for the familiarization group, 61% vs 52%. The study shows that high nicotine-dependent smokers need higher doses of nicotine replacement, in this case the 4-mg dose rather than the 2-mg dose, whereas 2 mg is superior to placebo among less dependent smokers. These results compare favorably with those reported from the more recent nicotine patch therapy.

[Comparative in vitro activity of new oral macrolides against Streptococcus pyogenes strains]

Some recently introduced macrolides have several clinical advantages over erythromycin. Azithrommcin, a prototype of these new macrolides could be a good alternative for the treatment of streptococcal pharyngitis, even over penicillin, whose failure rate can be as high as 30%. The aim of this study was to evaluate the in vitro susceptibility of 120 strains of S pyogenes isolated between 1990 and 1992 (40 per year), from diverse infections (specially tonsillitis). We determined Minimal Inhibitory Concentrations (MIC) of azithromycin, clarithromycin, roxithromycin, erythromycin and penicillin using the agar dilution method and the Minimal Bactericidal Concentration (MBC) by tube dilution for azythromycin and erythromycin. The MIC 90 for the new macrolides ranged from 0.03 to 0.12 microgram/ml, and was 0.03 microgram/ml for erythromycin and penicillin (not different). All strains were susceptible to all antibiotics and the date of isolation did not influence susceptibility. The MBC for azithromycin was 0.12 microgram/ml (identical to its MIC), which demonstrates the bactericidal effect of this antibiotic. It is concluded that this in vitro data supports the potential role of these new macrolides in the treatment of streptococcal infections.

[Pathogenic potential of vibrio cholerae 01 isolated from the Mapocho river and Aguada ditch]

The pathogenic potential of 20 strains of Vibrio Cholerae 01 isolated from the Mapocho river and Aguada ditch in Santiago, Chile was studied using a rabbit intestinal loop biological model. The presence of cholera toxin (CT) was previously found by the detection of CT gene, ELISA and passive reserve agglutination in only one of these strains. After 24 h of intestinal loop inoculation, the 20 strains showed enterotoxic activity. In four of these strains the secretory reaction was particularly intense. In these same four strains, the presence of cholera toxin was detected after the passage through the animal model. Thus, the number of cholera toxin producing strains increased after the inoculation in intestinal loops. These results suggest that the enterotoxic activity of strains that do not produce CT is given by the new cholera toxin (NCT). It is concluded that most of the strains of Vibrio Cholerae isolated from Mapocho river and its affluents are producers of NCT toxin, that some strains recover the capacity to produce CT after colonization of intestinal loops of living organisms and that the additive effects of CT and NCT may explain the intense enterotoxic activity of the strains that produce CT.

The World Health Organization and International Atomic Energy Agency second interlaboratory comparison study in 16 countries on quality performance of nuclear medicine imaging devices

Sixteen European countries participated in this WHO-IAEA intercomparison for which transmission CAP (College of American Pathologists) thyroid and IAEA-WHO liver phantoms were used. A total of 257 laboratories submitted 428 image evaluation reports. Overall results showed differences in performance between the various countries but similarities in performance for two gamma camera subgroups defined by year of manufacture, before and after 1980. A unique review of current European liver imaging practice is presented in terms of technical parameters, imaging conditions and evaluation procedures, and quality control procedures. The WHO-IAEA intercomparison demonstrated the need to establish new, or to improve the existing, quality control programmes in certain countries. However, the large number of participating laboratories, 257 compared with 70 in the previous WHO study, (Volodin et al. 1985), shows that these international studies are serving a useful purpose in promoting quality control in nuclear medicine imaging laboratories.

Effect of pentobarbital on the contraction and calcium movements in cat cerebral and peripheral arteries

Pentobarbital (PB) induced concentration-dependent vasodilation in cylindrical segments of cat cerebral and femoral arteries precontracted with 75 mM K+ or 10(-5) M serotonin (5-HT). PB (10(-4) or 10(-3) M, 10 min preincubations) caused concentration-dependent inhibition of the contraction produced by both agents. The exposure of the vessels to a Ca2+-free medium annulled the response elicited by K+ in both kinds of arteries. In this medium, the contraction induced by 5-HT in cerebral arteries was abolished, whereas in femoral ones it was significantly reduced. This residual response was abolished by PB. The intracellular 45Ca2+ uptake (La3+ method) elicited by K+ in both kinds of arteries and by 5-HT in cerebral ones was reduced in a concentration-dependent manner by PB (10(-4)-10(-3) M). The spontaneous 45Ca2+ efflux from these arteries and that induced by La3+ (10 mM) were unaffected by PB (10(-3) M). These results indicate that the vasodepressor effects induced by PB are essentially due to an interference of the barbiturate with the Ca2+ entry into the vascular smooth muscle cell in both kinds of arteries and with the intracellular Ca2+ movements in femoral ones. It does not seem to exist a clear selectivity of PB for brain or peripheral arteries for antagonizing the responses caused by K+ or 5-HT.