Ethanol Induced Alteration of Microsomal Membrane Bound Enzymes of Rat Liver in Vitro

Abstract: Ethanol appeared to inhibit more readily the 0-demethylation of p-nitroanisole than the activity of arylhydrocarbon hydroxylase. Arylhydrocarbon hydroxylase was more sensitive to the inhibition by ethanol in control or phenobarbital pretreated rats than in rats administered 3,4-benzpyrene. Ethanol was shown to activate the glucuronidation of p-nitrophenol at 2.45 mol/l, which was followed by inhibition at higher ethanol concentrations. A similar activation could also be demonstrated in rats pretreated with phenobarbital or 3,4-benzpyrene. This activation was not seen in microsomes pretreated in vitro with detergents like digitonin and cetylpyridinium chloride. Glucose 6-phosphatase was not clearly inhibited until the ethanol concentration was as high as 4 mol/l. Digitonin and trypsin treatments of the microsomal membrane in vitro appeared to activate the measurable glucose 6-phosphatase activity.     

Exposure of gasoline road-tanker drivers to methyl tert-butyl ether and methyl tert-amyl ether

Organic oxygenates, namely, methyl tert-butyl ether (MTBE) and methyl tert-amyl ether (MTAE), are added to gasoline to reduce carbon monoxide in exhausts and to enhance the octane number. The aim of this study was to investigate road-tanker drivers' exposure to oxygenate vapors during road-tanker loading and unloading as well as to evaluate the measurements of these ethers and their metabolites in the urine as a means of assessing the uptake of the ethers. A total of 11 drivers in different parts of Finland were trained to monitor their exposure with personal samplers, to report their working conditions, and to collect their whole-day urine samples. Charcoal tubes of the air samples were analyzed for MTBE, MTAE, benzene, toluene, and aliphatic hydrocarbons. For biological monitoring purposes the two main oxygenates, tertiary ethers MTBE and MTAE, as well as their main metabolites, tertiary alcohols tert-butanol (TBA) and tert-amyl alcohol (TAA), were determined in urine specimens. On average the drivers were exposed to vapors for short periods (21 ± 14 min) three times during a work shift. The mean concentrations of MTBE and MTAE (mean ± SD) were 8.1 ± 8.4 and 0.3 ± 0.4 mg/m³. The total MTBE uptake during the shift was calculated to be an average of 106 ± 65 μmol. The mean concentrations of MTBE, TBA, MTAE and TAA detected in the first urine after the work shift were 113 ± 76, 461 ± 337, 16 ± 21, and 40 ± 38 nmol/l, and those found the next morning, 16 h later, were 18 ± 12, 322 ± 213, 9 ± 10, and 20 ± 27 nmol/l. The good relationship (r = 0.84) found between MTBE exposure and postshift excretion suggests that urinary MTBE can be used for biological monitoring of exposure, but at the present low level of exposure the corresponding metabolite TBA is not equally reliable. The determination of MTAE and its metabolite TAA in urine is sensitive enough to detect the low degree of exposure to MTAE, but in this study the data were too scarce to allow calculation of the correlations due to very low levels of MTAE exposure. Received: 10 February 1997 / Accepted: 2 July 1997     

Hand dermatitis and allergic patch test reactions caused by nickel in electroplaters

A worksite survey was conducted in all 38 Finnish electroplating plants. All workers ( n =163) who worked with nickel plating (bath workers, hangers and solution makers) were interviewed with a questionnaire about symptoms of nickel dermatitis, hand dermatitis, and about protective measures, atopy, etc. Patch testing with nickel sulfate was done with the TRUE Test^TM method. All the workers, 94 men and 69 women, answered the questionnaire. The mean age of women was 41.1 years, and of men 43.1 years, respectively. Men had longer occupational exposure to nickel (14 years) than women (10 years). Most workers used protective gloves. 35% of women and 30% of men reported present or past hand dermatosis. 19% reported a history of atopic dermatitis. 15% of women ( n = 8) and 4% ( n = 2) of men had an allergic patch test reaction to nickel sulfate. 70% of those with an allergic patch test reaction to nickel reported past or present hand eczema. The prevalence of nickel allergy among the electroplaters was similar to that of patients in patch test clinics in Finland. An allergic patch test reaction to nickel sulfate does not necessarily oblige an electroplater to change jobs.     

Hassallidins,antifungal glycolipopeptides,are widespread among cyanobacteria and are the end-product of a nonribosomal pathway

Cyanobacteria produce a wide variety of cyclic peptides, including the widespread hepatotoxins microcystins and nodularins. Another class of peptides, cyclic glycosylated lipopeptides called hassallidins, show antifungal activity. Previously, two hassallidins (A and B) were reported from an epilithic cyanobacterium Hassallia sp. and found to be active against opportunistic human pathogenic fungi. Bioinformatic analysis of the Anabaena sp. 90 genome identified a 59-kb cryptic inactive nonribosomal peptide synthetase gene cluster proposed to be responsible for hassallidin biosynthesis. Here we describe the hassallidin biosynthetic pathway from Anabaena sp. SYKE748A, as well as the large chemical variation and common occurrence of hassallidins in filamentous cyanobacteria. Analysis demonstrated that 20 strains of the genus Anabaena carry hassallidin synthetase genes and produce a multitude of hassallidin variants that exhibit activity against Candida albicans. The compounds discovered here were distinct from previously reported hassallidins A and B. The IC₅₀ of hassallidin D was 0.29–1.0 µM against Candida strains. A large variation in amino acids, sugars, their degree of acetylation, and fatty acid side chain length was detected. In addition, hassallidins were detected in other cyanobacteria including Aphanizomenon, Cylindrospermopsis raciborskii, Nostoc, and Tolypothrix. These compounds may protect some of the most important bloom-forming and globally distributed cyanobacteria against attacks by parasitic fungi.Cyanobacteria are known for their propensity to form toxic blooms that have caused the deaths of wild and domestic animals all over the world (1). However, they are also a rich source of natural products that exhibit antimicrobial, anticancer, and immunosuppressive activities that can be exploited in drug development (2, 3). These secondary metabolites have versatile and often highly complex chemical structures with diverse biosynthetic origins. The majority of bioactive compounds reported from cyanobacteria are cyclic or linear peptides that can be heavily modified, including derivatization such as epimerization, glycosylation, acylation, formylation, methylation, halogenation, or sulphation (4). Many of these peptides are made nonribosomally with peptide cores consisting of an array of proteinogenic or nonproteinogenic amino acids as well as components of polyketide origin. They are assembled on large enzyme complexes by a thiotemplate mechanism in which the nonribosomal peptide synthetases (NRPSs) act simultaneously as template and biosynthetic machinery (5, 6). NRPSs are organized into modules, each of which is responsible for one amino acid activation and peptide bond formation (5, 7–9). The selectivity of NRPS adenylation domains combined with NRPS catalytic domain organization that generally follows the colinearity principle (7, 10) offers a means to predict the amino acid building blocks and thus the putative peptide structure.Microbial genomes are replete with NRPS gene clusters (11, 12). However, the majority of these gene clusters are cryptic and their products are unknown (4, 12). The mining of microbial genomes provides a useful approach for natural product discovery. The initial genome annotation of the toxic bloom-forming cyanobacterium Anabaena sp. 90 identified gene clusters for anabaenopeptins, anabaenopeptilides, and microcystins (13–15). Surprisingly, a fourth cryptic inactive gene cluster was found and proposed to be responsible for the biosynthesis of hassallidins (16). In the present study, we report the detailed characterization of the gene cluster from the genome of Anabaena sp. SYKE748A and show that it is responsible for the production of numerous novel glycosylated lipopeptides. These compounds resemble antifungal hassallidins A and B, which were isolated from an epilithic cyanobacterium Hassallia sp. (17, 18). A large number of new hassallidin variants was detected, showing that the ability to produce these compounds is widespread in heterocyst-forming cyanobacteria.     

Kinetics of 2,4,6-trichlorophenol in different organs of the rat

The concentration of 2,4,6-trichlorophenol was measured in the blood and various other tissues of the rat after IP administration of the compound at 25 mg per kg body weight. The highest concentration, 329±117 nmol·g^–1, was found in the kidney. Half-times were between 1.4 and 1.8 h in the blood, brain, fat, kidney, liver and muscle. The extent of conjugation of 2,4,6-trichlorophenol was also investigated by measuring total and free chlorophenol in the blood.     

Cigarette smoke: inducer of glucuronide synthesis in the isolated perfused rat lung.

Exposure of rats to the smoke of one filter cigarette daily for 10 consecutive days enhanced the glucuronide conjugation rate of 4-methylumbelliferone in the isolated perfused lung preparation. The glucuronide formation rate was 90 nmol/hr/lung for smoke-exposed and 55 nmol/hr/lung for control rats, when the lungs were perfused for 3 hr. The pulmonary microsomal UDP glucuronosyltransferase activities were 200 and 150 nmol/hr/lung in smoke-exposed and control rats, respectively. The glucuronide conjugation rates in the perfused lungs are about half of those expected from the values of microsomal enzyme assays.     

Recognition of tandem PxxP motifs as a unique Src homology 3-binding mode triggers pathogen-driven actin assembly

Src homology 3 (SH3) domains are globular protein interaction modules that regulate cell behavior. The classic SH3 ligand-binding site accommodates a hydrophobic PxxP motif and a positively charged specificity-determining residue. We have determined the NMR structure of insulin receptor tyrosine kinase substrate (IRTKS) SH3 domain in complex with a repeat from Escherichia coli-secreted protein F-like protein encoded on prophage U (EspF(U)), a translocated effector of enterohemorrhagic E. coli that commandeers the mammalian actin assembly machinery. EspF(U)-IRTKS interaction is among the highest affinity natural SH3 ligands. Our complex structure reveals a unique type of SH3 interaction based on recognition of tandem PxxP motifs in the ligand. Strikingly, the specificity pocket of IRTKS SH3 has evolved to accommodate a polyproline type II helical peptide analogously to docking of the canonical PxxP by the conserved IRTKS SH3 proline-binding pockets. This cooperative binding explains the high-affinity SH3 interaction and is required for EspF(U)-IRTKS interaction in mammalian cells as well as the formation of localized actin "pedestals" beneath bound bacteria. Importantly, tandem PxxP motifs are also found in mammalian ligands and have been shown to contribute to IRTKS SH3 recognition similarly.     

N-acetylcysteine -- passe-partout or much ado about nothing?

In experimental studies, the old mucolytic agent N-acetylcysteine (NAC) has had beneficial effects in disorders supposedly linked to oxidative stress. Numerous, mainly small clinical trials with variable doses have yielded inconsistent results in a wide variety of diseases. NAC added to the conventional therapy of human immunodeficiency virus infection might be of benefit; in respect of chronic obstructive pulmonary disease, systematic reviews and meta-analyses suggested that prolonged treatment with NAC is efficacious, but a recent multicentre study has questioned this. In a large intervention trial on cancer recurrence, NAC was ineffective. NAC infusions have been widely used in acute hepatic failure but convincing evidence of its benefits is lacking. A preliminary study reported that NAC is effective in preventing radiocontrast-induced nephropathy but thereafter highly mixed results have been published, and even meta-analyses disagree on its efficacy. In intensive care NAC has mostly been a disappointment but recently it has 'given promises' in surgery with cardiopulmonary bypass. NAC therapy is routine only in paracetamol intoxication.