Metabolism of 1-fluoro-1,1,2-trichloroethane, 1,2-dichloro-1,1-difluoroethane, and 1,1,1-trifluoro-2-chloroethane

1-Fluoro-1,1,2-trichloroethane (HCFC-131a), 1,2-dichloro-1,1-difluoroethane (HCFC-132b), and 1,1,1-trifluoro-2-chloroethane (HCFC-133a) were chosen as models for comparative metabolism studies on 1,1,1,2-tetrahaloethanes, which are under consideration as replacements for ozone-depleting chlorofluorocarbons (CFCs). Male Fischer 344 rats were given 10 mmol/kg ip HCFC-131a or HCFC-132b or exposed by inhalation to 1% HCFC-133a for 2 h. Urine collected in the first 24 h after exposure was analyzed by 19F NMR and GC/MS and with a fluoride-selective ion electrode for the formation of fluorine-containing metabolites. Metabolites of HCFC-131a included 2,2-dichloro-2-fluoroethyl glucuronide, 2,2-dichloro-2-fluoroethyl sulfate, dichlorofluoroacetic acid, and inorganic fluoride. Metabolites of HCFC-132b were characterized as 2-chloro-2,2-difluoroethyl glucuronide, 2-chloro-2,2-difluoroethyl sulfate, chlorodifluoroacetic acid, chlorodifluoroacetaldehyde hydrate, chlorodifluoroacetaldehyde-urea adduct, and inorganic fluoride. HCFC-133a was metabolized to 2,2,2-trifluoroethyl glucuronide, trifluoroacetic acid, trifluoroacetaldehyde hydrate, trifluoroacetaldehyde-urea adduct, inorganic fluoride, and a minor, unidentified metabolite. With HCFC-131a and HCFC-132b, glucuronide conjugates of 2,2,2-trihaloethanols were the major urinary metabolites, whereas with HCFC-133a, a trifluoroacetaldehyde-urea adduct was the major urinary metabolite. Analysis of metabolite distribution in vivo indicated that aldehydic metabolites increased as fluorine substitution increased in the order HCFC-131a < HCFC-132b < HCFC-133a. With NADPH-fortified rat liver microsomes, HCFC-133a and HCFC-132b were biotransformed to trifluoroacetaldehyde and chlorodifluoroacetaldehyde, respectively, whereas HCFC-131a was converted to dichlorofluoroacetic acid. No covalently bound metabolites were detected by 19F NMR spectroscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation time determination by high-resolution unipolar and bipolar extracellular electrograms in the canine heart

INTRODUCTION

To identify the optimal criteria for activation time (AT) determination of bipolar electrograms from normal hearts, a high-resolution cross electrode array comprising 128 unipolar electrodes of 500-microns spacing was used to record extracellular potentials from the left ventricular epicardium of 12 dog hearts.

METHODS AND RESULTS

Recordings were made during broad wavefront propagation (B wave) and local elliptical wavefront propagation (E wave). Characteristics of 863 bipolar electrograms (1-mm spacing) were constructed from unipolar data standardized for differences in polarity, then classified morphologically. Features for bipolar AT determination were compared to the time of the negative peak of the first temporal derivative of a unipolar electrogram situated mid-way between the bipoles. During B wave, three distinct morphologies were observed: uniphasic (61%), biphasic (23%), and triphasic (16%). Peak voltage of uniphasic and triphasic signals was the best predictor of AT (error: 0.6 +/- 0.6 msec and 0.6 +/- 0.8 msec, respectively). During E wave, parallel orientation of the bipoles with respect to the direction of impulse propagation wavefront resulted in uniphasic signals (> 99%), while for perpendicular orientation of the bipoles, electrogram morphology was variable. For parallel orientation of the bipoles, peak negative voltage was the best predictor of AT for both longitudinal and transverse propagation, while for perpendicular bipole orientation, peak negative voltage was a less reliable predictor for propagation along both fiber axes. Increasing interpolar distance resulted in a degradation in AT accuracy for B wave (from 0.6 +/- 0.6 msec at 1 mm to 1.1 +/- 1.2 msec at 7 mm) and for E wave (from 0.4 +/- 0.3 msec at 1 mm to 3.1 +/- 2.9 msec at 7 mm).

CONCLUSIONS

(1) The accuracy of bipolar electrograms is sensitive to wavefront direction, bipole orientation, and interpolar distance; (2) peak negative voltage of uniphasic and triphasic signals is a reliable predictor of AT, but only for B wave; (3) a maximum interpolar distance of 2 mm and bipole orientation parallel to the direction of the impulse wavefront are minimally required for accurate determination of AT during impulse propagation initiated near the recording electrodes; and (4) for impulses initiated near the recording site in normal tissue, a biphasic or triphasic morphology almost certainly indicates that the bipolar electrode is oriented perpendicular to the wavefront direction, irrespective of fiber orientation.

[Determination of ursodeoxycholic acid and chenodeoxycholic acid in Chinese medicinal compound preparations by TLC-densitometry]

The contents of ursodeoxycholic acid (UDCA) and chenodeoxycholic acid (CDCA) in Chinese medicinal compound preparations have been determined by TLC-densitometry. The determination wavelength was 375nm and reference wavelength was 700nm. For UDCA the linear range was 3.0-15.0 micrograms and recovery was 97.2% (RSD = 1.2%), and for CDCA the linear range was 4.0-20.0 micrograms and recovery was 99.3% (RSD = 2.1%).

Reentrant arrhythmias in the subacute infarction period. The proarrhythmic effect of flecainide acetate on functional reentrant circuits

BACKGROUND

The Cardiac Arrhythmia Suppression Trial has shown that flecainide was associated with an increased incidence of sudden cardiac death in postinfarction patients. The exact mechanism(s) of the proarrhythmic effects of flecainide remain unclear. We performed a detailed analysis of the electrophysiological and proarrhythmic effects of flecainide in a well-characterized model of reentrant arrhythmias in the subacute phase of myocardial infarction.

METHODS AND RESULTS

Sixteen dogs were studied 4 days after ligation of the left anterior descending coronary artery. Isochronal mapping of ventricular activation showed that flecainide facilitated both the induction and sustenance of ventricular tachycardia, especially at shorter basic cycle lengths. Flecainide had negligible effect on the length of the arc of functional conduction block but markedly depressed conduction of the common reentrant wave front that was usually oriented parallel to fiber axis. Whole heart mapping was analyzed in combination with basic measurements of the effects of flecainide on conduction and refractory properties of both normal and ischemic myocardia using a high-resolution cross electrode consisting of four orthogonal arms, each comprised of 16 poles with an interelectrode spacing of 500 microns. The electrode was especially designed to study the effects of the drug on anisotropic conduction as determined by a linear regression of activation time and distance in each direction. Flecainide resulted preferentially in more marked rate-dependent depression of conduction in ischemic compared with normal myocardium. On the other hand, the effect of flecainide on refractoriness in both normal and ischemic myocardia was negligible.

CONCLUSIONS

Because flecainide caused no significant change in refractoriness in both normal and ischemic myocardia, there was no difference in the dimension of the potential reentrant pathway, that is, the continuous line of functional conduction block, around which the reentrant wave fronts circulate. Yet, flecainide resulted in significant rate-dependent slowing of conduction preferentially in ischemic myocardium. The additional slowing of conduction of the common reentrant wave front coupled with minimal changes in the length of the reentrant pathway allowed additional time for the wave front to reexcite normal myocardium on the proximal side of the arc of block. After flecainide, reentry could be induced in hearts in which reentry could not be induced during control. The same proarrhythmic mechanism explains the propensity of nonsustained figure-8 reentrant tachycardias to become sustained after flecainide.

The efficacy of Japanese encephalitis vaccine in Henan, China: a case-control study

A population based case-control study to evaluate Japanese encephalitis (JE) vaccine efficacy was carried out in Gusi County, Henan Province, China from June to September in 1991. This study showed that the JE vaccine had a strong protective effect. The estimate of the vaccine efficacy was 78% (95% CI = 16-94%). An unimmunized child was at 4.54 times greater risk of developing JE than were fully immunized children during the study period. The present study may have underestimated the vaccine efficacy due to evaluation based on routine vaccination which might have been affected by vaccination management and the local cold chain system.

Tethered particle motion method for studying transcript elongation by a single RNA polymerase molecule

Schafer et al. (Nature 352:444-448 (1991)) devised the tethered particle motion (TPM) method to detect directly the movement of single, isolated molecules of a processive nucleic acid polymerase along a template DNA molecule. In TPM studies, the polymerase molecule is immobilized on a glass surface, and a particle (e.g., a 0.23 microns diameter polystyrene bead) is attached to one end of the enzyme-bound DNA molecule. Time-resolved measurements of the DNA contour length between the particle and the immobilized enzyme (the "tether length") are made by determining the magnitude of the Brownian motion of the DNA-tethered particle using light microscopy and digital image processing. We report here improved sample preparation methods that permit TPM data collection on transcript elongation by the Escherichia coli RNA polymerase at rates (approximately 10(2)-fold higher than those previously obtained) sufficient for practical use of microscopic kinetics techniques to analyze polymerase reaction mechanisms. In earlier TPM experiments, calculation of tether length from the observed Brownian motion was based on an untested numerical simulation of tethered bead Brownian motion. Using the improved methods, we have now empirically validated the TPM technique for tether lengths of 308-1915 base pairs (bp) using calibration specimens containing particles tethered by individual DNA molecules of known lengths. TPM analysis of such specimens yielded a linear calibration curve relating observed Brownian motion to tether length and allowed determination of the accuracy of the technique and measurement of how temporal bandwidth, tether length, and other experimental variables affect measurement precision. Under a standard set of experimental conditions (0.23 microns diameter bead, 0.23 Hz bandwidth, 23 degrees), accuracy is 108 and 258 bp r.m.s. at tether lengths of 308 and 1915 bp, respectively. Precision improves linearly with decreasing tether length to an extrapolated instrumentation limit of 10 bp r.m.s. and improves proportionally to the inverse square root of measurement bandwidth (1.9 x 10(2) bp Hz-1/2 for 1090-bp tethers). Measurements on large numbers of individual polymerase molecules reveal that time-averaged single-molecule elongation rates are more variable than is predicted from the random error in TPM measurements, demonstrating that the surface-immobilized RNA polymerase molecules are kinetically heterogeneous.

[Effects of chrysotile on the conformation of membrane protein and the antagonistic action of aluminum citrate]

Effects of Mangai and Laiyuan chrysotile on the conformation of membrane protein and the antagonistic action of aluminum citrate to them were studied with circular dichroism. Results showed that these two kinds of chrysotile could significantly reduce the amount of alpha-helix in membrane protein of human erythrocytes in 20 minutes with a dose-dependent manner. Effect of Mangai chrysotile was stronger than that of Laiyuan one. It suggested the changes in the conformation of membrane protein were the key link in chrysotile-caused hemolysis. After treatment with aluminum citrate, these effects weakened. It provided important information for elucidating the mechanism of aluminum citrate in antagonism to cytotoxicity of chrysotile.

Second-order conditioning and Pavlovian conditioned inhibition: operational similarities and differences

Procedures for establishing second-order excitation (conditioned stimulus [CS] 1-unconditioned stimulus [US] trials followed by CS2-CS1 trials) are highly similar to those for Pavlovian conditioned inhibition (CS1-US trials interspersed with CS2-CS1 trials). Conditioned suppression in rats was used to identify the critical operational differences that result in second-order excitation as opposed to Pavlovian inhibition. No, few, or many CS2-CS1 trials were either interspersed with or given after CS1-US trials. CS2 proved excitatory only after few CS2-CS1 trials, either interspersed or sequential (Experiment 1). In contrast, CS2 proved inhibitory on both summation (Experiment 2) and retardation (Experiment 3) tests only after many CS2-CS1 trials, and then only when the excitatory status of CS1 was preserved. Apparently, the critical difference for establishing second-order excitation or Pavlovian inhibition is the number of CS2-CS1 pairings.

[Studies on generation and inhibition of active oxygen in alveolar macrophage by chrysolite and aluminum citrate]

Chrysolite-induced generation and aluminum citrate-induced inhibition of active oxygen in alveolar macrophage were studied with ESR spin-trapping technique, cytochrome C reduction and phenol red oxidation assays. Results showed, under certain conditions, Mangya and Laiyuan chrysolite fiber could stimulate macrophage to generate OH., O2-. and H2O2 in a dose-dependent manner. But such an induced-generation of active oxygen would be inhibited by the treatment of chrysolite with aluminum citrate solution at room temperature for one hour.

Detection of human papillomavirus DNA in esophageal squamous cell carcinomas by the polymerase chain reaction using general consensus primers

We studied 40 formalin-fixed, paraffin-embedded esophageal squamous cell carcinomas from a high risk region for this tumor for the presence of human papillomavirus (HPV) DNA by the polymerase chain reaction (PCR). We used two general consensus primers from a highly conserved E1 region of HPV types 6, 11, 16, and 18. Human papillomavirus DNA was detected in 60% (24 of 40) of the cases without relation to the tumor grade. Two lymph node metastases had the same HPV types as the primary tumor. Human papillomavirus types were determined in the 24 HPV-positive cases by Southern blot analysis of amplified DNA. Human papillomavirus type 6 was detected in 50% (12 of 24) of the cases, HPV type 16 in 8% (two of 24), and HPV types 6 and 16 in 17% (four of 24); in 25% (six of 24) of the cases the type was unknown. Human papillomavirus types 11 and 18 were not detected. Esophageal mucosa adjacent to the tumor was studied for morphological changes of HPV effect in 27 cases. Adjacent esophageal mucosa in 16 HPV-positive tumors showed statistically significant (P < .05) koilocytosis in six cases. Papillomatosis was the next most frequent finding in four cases. This study supports the role of HPV in the causation of esophageal squamous cell carcinomas, especially in high risk regions for this tumor.

Trial spacing and trial distribution effects in Pavlovian conditioning: contributions of a comparator mechanism

A potential basis for trial spacing and trial distribution effects was investigated in rats. In Experiment 1, a conditioned stimulus (e.g., CS A) was trained with either massed (e.g., A---->A---->A) or spaced (e.g., A-->A-->A) trials. When trials were massed, brief exposure to the training context (a condition typical of massed training) impaired responding, whereas more extensive exposure to the context during or after training reduced this apparent massed trials deficit. In Experiment 2, different CSs were trained in either a massed (e.g., A-->A-->A--> B-->B-->B-->C-->C-->C) or a distributed (e.g., A-->B-->C-->A-->B-->C, etc.) manner. Trials massed in this sense resulted in impaired responding to the CS, and this impairment was attenuated by posttraining extinction of the context cues. Thus, trial distribution and apparent trial spacing effects are at least in part reversible deficits in performance rather than failures of learning.

Autoimmune sera react with multiple epitopes on recombinant 52 and 60 kDa Ro(SSA) proteins

OBJECTIVE

To determine the reactivity of recombinant 52 and 60 kDa Ro(SSA) (Ro) proteins with sera from 3 subsets of patients with Ro autoantibody associated disease.

METHODS

Complementary DNA (cDNA) clones that encode the human 52 and 60 kDa Ro autoantigens were isolated by the polymerase chain reaction and utilized to express recombinant glutathione S-transferase (GST) fusion proteins. Double immunodiffusion (ID) defined Ro positive autoimmune sera from 12 patients with neonatal lupus erythematosus (NLE), 16 with subacute cutaneous lupus erythematosus (SCLE) and 12 with primary Sjögren's syndrome (SS) were tested by enzyme linked immunosorbent assay (ELISA) against the recombinant 52 and 60 kDa Ro fusion proteins.

RESULTS

Seventy-five percent of NLE, 56% of SCLE and 83% of SS sera reacted with the 52 kDa fusion protein. Seventy-five percent of NLE, 63% of SCLE and 83% of SS sera reacted with the 60 kDa fusion protein. Seventeen percent of NLE sera, 25% of SCLE sera and 8% of SS sera were nonreactive to both full length fusion proteins. Eight (57%) of 14 ID defined Ro negative NLE, SCLE and SS sera were reactive with both Ro fusion proteins by ELISA: ELISA studies with recombinant 52 and 60 kDa Ro protein fragments revealed at least 2 major epitopes on each Ro protein. A fragment of the 52 kDa Ro protein that contains a putative leucine zipper motif reacted with 100% of ID defined Ro positive SS sera.

CONCLUSION

Our data demonstrate that the ID assay and the recombinant Ro ELISA together are more sensitive in detecting Ro antibodies than either assay alone, and that multiple epitopes are present on both Ro proteins.

Complete cDNA sequence of a human dioxin-inducible mRNA identifies a new gene subfamily of cytochrome P450 that maps to chromosome 2

Previously, levels of a novel human mRNA, detected by a recombinant cDNA designated clone 1, were shown to be increased 50-fold in response to treatment of a keratinocyte cell line with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in part as a function of increased rates of gene transcription (Sutter, T.R., Guzman, K., Dold, K.M., and Greenlee, W.F. (1991) Science 254, 415-418). Here we report the complete corresponding 5.1-kilobase cDNA sequence. A single open reading frame that predicts a protein of 543 amino acid residues was determined by computer-assisted analysis of the cDNA sequence. This predicted protein identifies a new gene subfamily of cytochrome P450, cytochrome P4501B1 (CYP1B1), that maps to human chromosome 2. Southern blot analysis of genomic DNA indicates that the human CYP1B subfamily is likely to contain only this single gene. Northern blot analysis of RNA isolated from primary cultures of normal human epidermal keratinocytes showed approximately 100-fold increased levels of the CYP1B1 mRNA after treatment with 10 nM TCDD for 24 h. Low levels of constitutive CYP1B1 mRNA were detected in 15 different human tissue samples. These results indicate that CYP1B1 is expressed in many normal human tissues and advance our understanding of the complexity of a gene family of cytochromes P450 whose expression is altered by TCDD.

Trial spacing and trial distribution effects in Pavlovian conditioning: contributions of a comparator mechanism

A potential basis for trial spacing and trial distribution effects was investigated in rats. In Experiment 1, a conditioned stimulus (e.g., CS A) was trained with either massed (e.g., A---->A---->A) or spaced (e.g., A-->A-->A) trials. When trials were massed, brief exposure to the training context (a condition typical of massed training) impaired responding, whereas more extensive exposure to the context during or after training reduced this apparent massed trials deficit. In Experiment 2, different CSs were trained in either a massed (e.g., A-->A-->A--> B-->B-->B-->C-->C-->C) or a distributed (e.g., A-->B-->C-->A-->B-->C, etc.) manner. Trials massed in this sense resulted in impaired responding to the CS, and this impairment was attenuated by posttraining extinction of the context cues. Thus, trial distribution and apparent trial spacing effects are at least in part reversible deficits in performance rather than failures of learning.

[Risk factors of prostate cancer--a matched case-control study]

A 1:2 matched case-control study was used to determine the risk factors of prostate cancer. Twenty-seven cases of prostate cancer were matched with an equal number of other malignant tumor cases (non-urological tumor) and other urological cases (non-malignant tumor). Both study and control groups were the same in age, sex, race, and day of admission. All of these patients were treated in the First Affiliated Hospital of West China University of Medical Sciences. The questionnaire was used to survey the both groups of patients. Such data as diet, lifestyle, marital status and past history of other prostate diseases were obtained. Single factor analysis and multiple conditional logistic regression analysis were used to estimate the relative risk (RR), 95% confidence interval (95% CI) and P values. Statistical analysis was performed using the Egret, Epilog soft ware. The results were as follows: 1. Increasing dietary vitamin A was associated with a significant decrease in the risk of prostate cancer (RR = 0.948, 95% CI = 0.9309-0.9947, P = 0.029). This factor also showed dose response gradients. The relative risk was decreasing with exposure dose increasing. 2. The positive previous prostate history, such as prostatitis and benign prostate hyperplasia, increased the risk of prostate cancer (RR = 6.385, 95% CI = 1.046-38.97, P = 0.045). 3. Another finding in the widower, divorce and remarried men (RR = 4.312, 95% CI = 1.367-13.6, P = 0.013). And 4. There was no relationship between the risk of prostate cancer and dietary fat intake, vasectomy, socioeconomic status, familial malignant tumor history, smoking and alcohol consumption.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of Leontopodium leontopodioides (Willd.) Beauv. on inflammation induced by animal reversed passive arthus (RPA)]

The extract from Leontopodium leontopodioides 50-100mg/kg ip has been proved able to suppress the swelling of normal or adrenalectomised rat hind paws induced by RPA, and strongly inhibit the cutaneous hemorrhage of animals induced by RPA, lysosome or lysosome of broken membrane. It has also been shown that the extract 100 mg/kg ip can markedly inhibit the migration of leukocytes. These suggest that the anti-inflammatory properties of the extract are not dependent on the pituitary-adrenal system or membrane of lysosome.

Fibronectin in the tendon-synovial complex: quantitation in vivo and in vitro by ELISA and relative mRNA levels by polymerase chain reaction and northern blot

An enzyme-linked immunosorbent assay was used to quantitate fibronectin (Fn) levels in the outer synovia (epitenon) and internal fibrous portion (endotenon) of chicken flexor tendon and sheath. Primary cell cultures from these tissues and their secretions also were assayed for Fn levels. The polymerase chain reaction (PCR) was used to determine relative steady-state levels of Fn mRNA in primary cultures of synovial and internal fibroblasts from chicken tendon, and Northern blot analysis was performed to verify relative levels of the Fn message. The epitenon contained 3.8-fold more Fn than did the endotenon, and the sheath synovium contained 21-fold more Fn than did the internal fibrous portion of sheath. Cells cultured from the epitenon produced 9.3 and 13-fold more cell-associated and secreted Fn, respectively, than did cultured endotenon fibroblasts. Sheath synovial cells produced 17 and 3.2-fold more cell-associated and secreted Fn, respectively, than did sheath internal fibroblasts. Levels of Fn mRNA, as measured by PCR and Northern blot, were 1.6 and 1.8-fold greater, respectively, in tendon synovial cells compared with tendon internal fibroblasts. The biologic reason for increased Fn in tendon synovium is not known. We theorize that Fn may stabilize tendon synovium to shear stress and may play a role in the modulation of synovial rheology in the normal tendon. In the injured tendon, Fn may be involved in the organization of collagen deposition or may act through association with growth factors to aid healing.

Exposure of workers to a mixture of toluene and xylenes. II. Effects

The health effects of exposure to a mixture of toluene and xylene isomers was studied on the fourth or fifth days of a working week in factories in China. The study population comprised 233 subjects (122 men and 111 women), who were exposed to the time weighted geometric mean (maximum) concentrations of toluene (3 (203) ppm) and xylenes (4 (103) ppm). For comparison, 241 non-exposed controls (116 men and 125 women) were recruited from the same regions. The prevalence of some subjective symptoms significantly increased in the exposed population, and the symptom profiles were similar to those found after exposure to toluene or xylenes alone. Haematology and serum biochemistry did not show notable changes. It seems reasonable to conclude that the effects of the toxicities of toluene and xylenes in combination are additive.

Mechanistic studies of uridine diphosphate glucuronosyltransferase

Bisubstrate reaction kinetics and product inhibition studies were used to characterize the kinetic mechanism of a partially purified uridine diphosphate glucuronosyltransferase (UDPGT). These studies indicate that the reaction most likely occurs via a random order sequential mechanism. The effect of electron withdrawing and donating groups on the rate of reaction was also determined. It was found that electron donating groups increased the rate of glucuronide conjugation. This result is consistent with nucleophilic attack of the C-1 carbon of the UDP-glucuronic acid (UDPGA) by an SN2 mechanism. This is the first direct evidence for a SN2 mechanism in UDPGT catalysis.

Ethanol-inducible cytochrome P4502E1: genetic polymorphism, regulation, and possible role in the etiology of alcohol-induced liver disease

In the Tsukamoto-French model, ethanol causes an important 10-20-fold induction of ethanol-inducible cytochrome P4502E1 (CYP2E1), mediated through enzyme stabilization and increased rate of gene transcription. The CYP2E1 induction results in a pronounced increase in the rate of NADPH-dependent microsomal lipid peroxidation, an elevation which is not seen after simultaneous administration of the CYP2E1 inhibitor diallylsulfide. Increased amounts of lipid peroxides are seen in plasma and red blood cells of both rats and humans during high ethanol intake. A mechanism for ethanol-dependent liver damage is proposed which involves the CYP2E1-dependent lipid peroxide formation, either directly by its capability to induce NADPH-dependent peroxidation in the microsomal membranes or indirectly by a hypoxia-mediated transformation of xanthine dehydrogenase to xanthine oxidase, in activation of Ito cells and Kupffer cells to yield cytokine and collagen production. The CYP2E1 gene is polymorphic among Caucasians. Four different unrelated or partially linked polymorphisms have been observed. One polymorphism in the 5'-flanking region has been described to be associated with altered enzyme expression in vitro, and the rare allele was found to be less frequent among Swedish patients having lung cancer when compared to two different control groups. Another polymorphism, detectable with Dra I restriction endonuclease fragment length polymorphism (RFLP), was localized to intron 6, and the rare allele was less common among Italian alcoholics with clinical signs of liver cirrhosis, as compared to controls. Several other mutations in the CYP2E1 gene were found to be associated with this allele. However, further research is needed to relate the CYP2E1 gene polymorphism with incidence of liver cirrhosis.

Slow-binding inhibition of carboxylesterase and other serine hydrolases by chlorodifluoroacetaldehyde

The chlorofluorocarbon substitute 1,2-dichloro-1,1-difluoroethane (HCFC-132b) undergoes oxidative metabolism in rats to give a range of metabolites, including chlorodifluoroacetaldehyde [Harris and Anders (1991) Chem. Res. Toxicol. 4, 180]. The present experiments were undertaken after studies to characterize an unidentified metabolite of HCFC-132b revealed that chlorodifluoroacetaldehyde was toxic in vivo: rats given chlorodifluoroacetaldehyde died showing signs of cholinergic stimulation. Because some fluoroketones are known inhibitors of hydrolases, including acetylcholinesterase, the inhibitory effects of chlorodifluoroacetaldehyde on acetylcholinesterase (electric eel and human erythrocyte), on pseudocholinesterase (horse serum), on carboxylesterase (pig liver), and on alpha-chymotrypsin (bovine pancreas) were studied. In aqueous solution, the ratio chlorodifluoroacetaldehyde:chlorodifluroacetaldehyde hydrate, as determined by 1H nuclear magnetic resonance spectroscopy, was 1:157. Chlorodifluoroacetaldehyde was a slow-binding inhibitor of both acetylcholinesterases, of pseudocholinesterase, and of carboxylesterase; the Ki values, corrected for the aldehyde:hydrate ratio, were 150 nM, 1.7 nM, 3.7 nM, and 23 pM, respectively, as determined by final velocity of the progress curves; the kon values were 9.1 x 10(4), 1.1 x 10(5), 3.2 x 10(4), and 9.2 x 10(5) M-1 min-1, respectively. Chlorodifluoroacetaldehyde did not inhibit alpha-chymotrypsin. Acetaldehyde and trichloroacetaldehyde were classical competitive inhibitors of acetylcholinesterase. These results show that hydrochlorofluorocarbon metabolites may exert significant biological effects.

Dose-dependent increase in subjective symptoms among toluene-exposed workers

A factory survey on dose-response relationship in toluene toxicity was conducted in 1985-1989 in four cities in China. The examination items consisted of personal diffusive sampling for TWA exposure measurement, questionnaires on subjective symptoms, hematology and serum biochemistry, and clinical examination including simple neurology tests. Hippuric acid was also determined in urine samples collected at the end of the shift. With selection criteria that (1) complete results were available on all study items and (2) valid toluene exposure data (i.e., toluene shared 90% or more of the exposure) were obtained for the exposed, 452 toluene-exposed workers (206 men and 246 women; toluene exposure at 24.7 ppm as GM) and 517 nonexposed controls (246 men and 271 women) were selected. The subjective symptoms increased in close association with the intensity of exposure to toluene; the threshold concentration appeared to exist at 100 ppm in the case of symptoms during work, and it might be at 50-100 ppm when symptoms off work were evaluated. During the work with exposure at higher concentrations, various symptoms possibly related to CNS or local effects (e.g., eyes, nose, and throat) were complained, and dizziness and floating sensations were identified as typical symptoms with significant dose-response relationship. Several symptoms persisted off work, most of which were apparently related but not necessarily limited to CNS effects. Hematology and serum biochemistry were essentially negative.