Biomedical subjects

J Y Shim

Publications and source records attributed to J Y Shim.

At least 19 recordsLinked to original sources

PubMed2006

An orally active cathepsin K inhibitor, furan-2-carboxylic acid, 1-{1-[4-fluoro-2-(2-oxo-pyrrolidin-1-yl)-phenyl]-3-oxo-piperidin-4-ylcarbamoyl}-cyclohexyl)-amide (OST-4077), inhibits osteoclast activity in vitro and bone loss in ovariectomized rats.

Human cathepsin K, a cysteine proteinase of the papain family, has been recognized as a potential drug target for the treatment of osteoporosis. The predominant expression of cathepsin K in osteoclasts has rendered the enzyme into a major target for the development of novel antiresorptive drugs. Now, we report the pharmacological properties of OST-4077 [furan-2-carboxylic acid (1-{1-[4-fluoro-2-(2-oxo-pyrrolidin-1-yl)-phenyl]-3-oxo-piperidin-4-ylcarbamoyl}-cyclohexyl)-amide] as a novel selective cathepsin K inhibitor. Human and rat cathepsin K were inhibited in vitro by OST-4077 with the IC50 values of 11 and 427 nM, respectively. OST-4077 suppressed bone resorption induced by rabbit osteoclasts (IC50, 37 nM) but did not affect bone mineralization or cellular alkaline phosphatase activity in MC3T3-E1 cells. Parathyroid hormone-induced bone resorption was inhibited in a dose-dependent manner in thyroparathyroidectomized rats gavaged with a single dose of OST-4077 (ED50, 69 mg/kg). When given orally twice daily for 4 weeks to 3-month-old ovariectomized (OVX) rats, OST-4077 dose-dependently prevented bone loss, as monitored by bone densitometry, ash content, and urinary excretion of deoxypyridinoline. No change in serum osteocalcin in the OVX rats by OST-4077 suggested that bone formation might not be affected by the agent. In summary, OST-4077 selectively inhibited bone resorbing activities of osteoclasts and prevented bone loss induced by estrogen deficiency but did not affect bone formation. OST-4077, an orally active selective human cathepsin K inhibitor, may have the therapeutic potential for the treatment of diseases characterized by excessive bone loss including osteoporosis.

Alkaline Phosphatase↗

PubMed2005

Successful vesicoamniotic shunting of posterior urethral valves in the first trimester of pregnancy.

Prenatal ultrasonography early in gestation allows diagnosis of posterior urethral valves. We report on a fetus with posterior urethral valves treated using vesicoamniotic shunting at 13 + 5 weeks' gestation. A double-basket catheter was used for shunting. A 2582-g male neonate was delivered at 33 weeks' gestation, and the infant continued to show normal renal function at 3 years of age. To the best of our knowledge this is the first report of successful vesicoamniotic shunt placement using a double-basket catheter in the first trimester of pregnancy.

Adult↗

PubMed2004

Self-reported prevalence and risk factors of asthma among Korean adolescents: 5-year follow-up study, 1995-2000.

OBJECTIVES: The International Study of Asthma and Allergies in Childhood (ISAAC) questionnaires have shown that the prevalence of childhood asthma is increasing worldwide. Although Asian countries used to have lower prevalence rates of allergic disease than Western countries, this prevalence is increasing in several Asian countries. To determine whether the prevalence of childhood asthma is changing in Korean adolescents, we compared findings from nationwide cross-sectional surveys in 1995 and 2000 on populations of middle-school children using the Korean version of the ISAAC questionnaire. METHODS: We developed Korean versions of the ISAAC written (WQ) and video (AVQ) questionnaires for allergic diseases. In 1995, the enrolled population consisted of 15,481 children, ages 12-15, and encompassing all three grades in middle school, selected from 34 schools across the nation; the response rate was 97.3%. In 2000, 15,894 children were selected from 31 of the same schools, and the response rate was 96.4%. The SAS system version 8.0 was utilized for all statistical analyses. RESULTS: The WQ showed that the lifetime and 12-month prevalence of wheeze did not change from 1995 to 2000. While the 12-month prevalence rates of sleep disturbed by wheezing and night cough increased, the rates of severe attack of wheezing and exercise-induced wheeze did not change, over this period of time. The lifetime prevalence of asthma diagnosis, however, increased significantly, from 2.7% in 1995 to 5.3% in 2000, as did the 12-month prevalence of asthma treatment, from 1.0% in 1995 to 1.9% in 2000. The AVQ also showed increases in the lifetime and 12-month prevalence rates of wheeze at rest, exercise-induced wheeze, nocturnal wheeze, nocturnal cough, and severe wheeze over this period of time. These were especially because of significant increases in the Provincial cities of Korea. Interestingly, the 12-month prevalence of wheeze was consistently high in Cheju with low air pollution indices, whereas this rate was low in Ulsan and Ansan with very high air pollution indices. Risk factor analysis showed that body mass index (BMI), passive smoking, and living with a dog or cat, but not air pollution, were associated with higher risk of wheeze. CONCLUSIONS: In the 5-year period from 1995 to 2000, the prevalence of asthma symptoms has increased in Korean adolescents, much of it because of increases in Provincial Centers. BMI, passive smoking, and living with a dog or cat are important risk factors. Environmental factors other than air pollution may be associated with increases in asthma, especially in Provincial Centers.

Adolescent↗

PubMed2003

New sonographic finding for the prenatal diagnosis of bladder exstrophy: a case report.

Bladder exstrophy is a very rare congenital malformation in which the anterior wall of the bladder is absent, and the posterior wall is exposed externally. Although sonographic findings of bladder exstrophy have been documented, we report a case presenting with a solid mass in the lower fetal abdomen with umbilical arteries running alongside the mass. The relationship between umbilical arteries and bladder exstrophy is a new sonographic finding which may be helpful in the prenatal diagnosis of this condition.

Abnormalities, Multiple↗

PubMed2003

C-reactive protein in umbilical cord blood: a simple and widely available clinical method to assess the risk of amniotic fluid infection and funisitis.

OBJECTIVE: The purpose of this study was to determine whether concentrations of C-reactive protein (CRP) in umbilical cord plasma at birth were elevated in neonates with sepsis, an inflammatory lesion of the umbilical cord (funisitis) or who were born to mothers with microbial invasion of the amniotic cavity. METHODS: Umbilical cord plasma was collected at birth from 313 singleton preterm neonates (20-35 weeks of gestation). The results of amniotic fluid culture performed within 5 days of birth, the occurrence of congenital neonatal sepsis and the presence of funisitis were assessed. Amniocentesis was performed in 152 patients within 5 days of birth. Amniotic fluid was cultured for aerobic and anaerobic bacteria and for mycoplasmas. The CRP concentration was measured with a highly sensitive immunoassay. RESULTS: The median cord plasma CRP concentration was significantly higher in neonates with a positive amniotic fluid culture than in those with negative culture (median 245.9 (range 11.6-4885.5) ng/ml vs. median 44.3 (range 2.3-7401.8) ng/ml; p < 0.001), in those with congenital proven sepsis than in those without this complication (median 789.5 (range 20.4-2584.3) ng/ml vs. median 41.5 (range 1.3-7401.8) ng/ml; p < 0.005) and in neonates with funisitis than in those without funisitis (median 403.8 (range 4.9-10897.4) ng/ml vs. median 31.0 (range 1.3-7401.8) ng/ml; p < 0.001). The sensitivity of CRP in the identification of amniotic fluid infection, neonatal sepsis and funisitis was similar to that of interleukin-6 (> 17.5 pg/ml). However, the specificity of CRP in the identification of neonatal sepsis and funisitis was significantly higher than that of interleukin-6 (74% vs. 69%, p < 0.05; 83% vs. 76%, p < 0.01). CONCLUSION: Umbilical cord plasma CRP concentrations were elevated in patients with amniotic fluid infection, congenital neonatal sepsis and funisitis.

Adult↗

PubMed2001

Effects of 6-arylamino-5,8-quinolinediones and 6-chloro-7-arylamino-5,8-isoquinolinediones on NAD(P)H: quinone oxidoreductase (NQO1) activity and their cytotoxic potential.

Synthesized 6-arylamino-5,8-quinolinediones 4a-4j and 6-chloro-7-arylamino-5,8-isoquinolinediones 5a-5g were evaluated for effects on NAD(P)H: quinone oxidoreductase (NQO1) activity with the cytosolic fractions derived from cultured human lung cancer cells and their cytotoxicity in cultured several human solid cancer cell lines. The 5,8-quinolinediones 4 and 5,8-isoquinolinediones 5 affected the reduction potential by NQO1 activity and showed a potent cytotoxic activity against human cancer cell lines. The tested compounds 4a, 5c, 5f, and 5g were considered as more potent cytotoxic agents. The compounds 4d, 5b, 5c, 5e and 5g were comparable modulators of NQO1 activity.

Antineoplastic Agents↗

PubMed2001

Epidural naloxone reduces intestinal hypomotility but not analgesia of epidural morphine.

PURPOSE: Epidural morphine is associated with decreased bowel motility and increased transit time. Low doses of intravenous naloxone reduce morphine-induced pruritus without reversing analgesia, but the effect of epidural naloxone on bowel motility has not been studied. Therefore we evaluated bowel motility and analgesia when naloxone was co-administered with morphine into the epidural space. METHODS: Forty-three patients having combined thoracic epidural and general anesthesia for subtotal gastrectomy were randomly assigned to one of two study groups. All received a bolus dose of 3 mg epidural morphine at the beginning of surgery, followed by a continuous epidural infusion containing 3 mg morphine in 100 ml bupivacaine 0.125% with either no naloxone (control group, n = 18) or a calculated dose of 0.208 microg x kg(-1) x hr(-1) of naloxone (experimental group, n = 25) for 48 hr. We measured the time to the first postoperative passage of flatus and feces to evaluate the restoration of bowel function, and visual analog scales (VAS) for pain during rest and movement. Scores were assessed at 2, 4, 8, 16, 24, 36 and 48 hr postoperatively. RESULTS: The experimental group had a shorter time to the first postoperative passage of flatus (5 1.9 +/- 1 6.6 hr vs 87.0 +/- 19.5 hr, P < 0.001 ) and feces (95.3 +/- 25.0 hr vs 132.9 +/- 29.4 hr, P < 0.001). No differences were found in either resting or active VAS between the two groups. CONCLUSION: Epidural naloxone reduces epidural morphine-induced intestinal hypomotility without reversing its analgesic effects.

Analgesia, Epidural↗

PubMed2001

Meningeal solitary fibrous tumor as an unusual cause of expohthalmos: case report and review of the literature.

OBJECTIVE AND IMPORTANCE: We report an extremely rare case of a patient with meningeal solitary fibrous tumor with orbital involvement presenting as unilateral exophthalmos. This rare tumor should be considered in the differential diagnosis for aggressive dural-based lesions. CLINICAL PRESENTATION: A 54-year-old man presented with a protruded eyeball on the right side and left hemiparesis. Computed tomography and magnetic resonance imaging demonstrated a huge mass, markedly enhanced in and around the right anterior clinoid process, which extended to the orbit and middle cranial fossa. Cerebral angiography revealed a richly vascular tumor fed by branches of both the right external and internal carotid arteries. A presumptive diagnosis of meningioma or hemangiopericytoma was considered. INTERVENTION: The tumor was exposed through an orbitozygomatic approach. At surgery, the tumor was grossly firm to hard and had destroyed the dura, orbital roof, anterior clinoid process, temporal bone, and muscle. Histological analysis revealed that the tumor was composed of spindle-cell proliferation in a collagen-rich background, but it exhibited regional variations. The vascular network demonstrated irregular vascular lumina with a "hemangiopericytoma-like" pattern. Histological features included high cellularity and a high degree of pleomorphism. Immunohistochemical analysis of the tumor demonstrated diffuse positive staining for CD34 and vimentin. The tumor displayed no positive staining for cytokeratin, epithelial membrane antigen, glial fibrillary antigenic protein, S-100 protein, and factor XIII. CONCLUSION: Meningeal solitary fibrous tumor is considered a unique pathological entity. Wider use of immunohistochemical screening should enable analysis of the real incidence of these tumors; larger series and longer follow-up duration will allow conclusions to be drawn regarding treatment and prognosis. Differential diagnosis is discussed and the literature is reviewed.

Angiography, Digital Subtraction↗

PubMed2000

A second photochromic bacteriophytochrome from Synechocystis sp. PCC 6803: spectral analysis and down-regulation by light.

It now appears that photosynthetic prokaryotes and lower eukaryotes possess higher plant phytochrome-like proteins. In this work, a second phytochrome-like gene was isolated, in addition to the recently identified Cph1 phytochrome, from the Synechocystis sp. PCC 6803, and its gene product was characterized photochemically. The open reading frame sll0821 (designated cph2 in this work) has structural characteristics similar to those of the plant phytochromes and the Synechocystis Cph1 with high amino acid sequence homology in the N-terminal chromophore binding domain. The predicted Cph2 protein consists of 1276 amino acids with a calculated molecular mass of 145 kDa. Interestingly, the Cph2 protein has two putative chromophore binding domains, one around Cys-129 and the other around Cys-1022. The Cph2 was overexpressed in E. coli as an Intein/CBD (chitin binding domain) fusion and in vitro reconstituted with phycocyanobilin (PCB) or phytochromobilin (PPhiB). Both the Cph2-PCB and Cph2-PPhiB adducts showed the typical photochromic reversibility with the difference spectral maxima at 643/690 and 655/701 nm, respectively. The Cys-129 was confirmed to be the chromophore binding residue by in vitro mutagenesis and Zn(2+) fluorescence. The microenvironment of the chromophore in Cph2 seems to be similar to that in plant phytochromes. The cph2 gene expression was dark-induced and down-regulated to a basal level by light, like the cph1 gene. These observations suggest that Synechocystis species have multiple photosensory proteins, probably with distinct roles, as in higher plants.

Amino Acid Sequence↗

PubMed2000

Chromophore-apoprotein interactions in Synechocystis sp. PCC6803 phytochrome Cph1.

The secondary, tertiary, and quaternary structures of the Synechocystis Cph1 phytochrome were investigated by absorption and circular dichroism spectroscopy, size exclusion chromatography, and limited proteolysis. The Cph1 protein was coexpressed with a bacterial thioredoxin in Escherichia coli, reconstituted in vitro with tetrapyrrole chromophores, and purified by chitin affinity chromatography. The resultant Cph1 holoproteins were essentially pure and had the specific absorbance ratio (SAR) of 0.8-0.9. Circular dichroism spectroscopy and limited proteolysis showed that the chromophore binding induced marked conformational changes in the Cph1 protein. The alpha-helical content increased to 42-44% in the holoproteins from 37% in the apoprotein. However, no significant difference in the secondary structure was detected between the Pr and Pfr forms. The tertiary structure of the Cph1 apoprotein appeared to be relatively flexible but became more compact and resistant to tryptic digestion upon chromophore binding. Interestingly, a small chromopeptide of about 30 kDa was still predominant even after longer tryptic digestion. The N-terminal location of this chromopeptide was confirmed by expression in E. coli and in vitro reconstitution with chromophores of the 32.5 kDa N-terminal fragment of the Cph1 protein. This chromopeptide was fully photoreversible with the spectral characteristic similar to that of the full-size Cph1 protein. The Cph1 protein forms dimers through the C-terminal region. These results suggest that the prokaryotic Cph1 phytochrome shares the structural and conformational characteristics of plant phytochromes, such as the two-domain structure consisting of the relatively compact N-terminal and the relatively flexible C-terminal regions, in addition to the chromophore-induced conformational changes.

Apoproteins↗

PubMed2000

A case of primary cutaneous actinomycosis.

Primary cutaneous actinomycosis is very uncommon because of the exclusively endogenous habitat of the organism. We report a case of primary cutaneous actinomycosis characterized by histopathological "sulfur granules". The patient had a well-defined subcutaneous nodule on the left thigh without any other lesion and was treated with surgical excision and subsequent oral ampicillin for six weeks. There has been no recurrence during a 1-year period of follow-up.

Actinomycosis↗

PubMed2000

Development of a novel class of monocyclic and bicyclic alkyl amides that exhibit CB1 and CB2 cannabinoid receptor affinity and receptor activation.

CB1 and CB2 cannabinoid receptors can be activated by several different classes of agonists, including cannabinoids such as delta9-tetrahydrocannabinol and 9-nor-9beta-hydroxyhexahydrocannabinol, and eicosanoids such as arachidonylethanolamide. Structure-activity relationship studies have identified potential pharmacophoric elements for binding to cannabinoid receptors by both cannabinoids and eicosanoids. Molecular models have hypothesized conformational, spatial, and pharmacophoric distance requirements based upon radioligand binding data whereby overlap of pharmacophoric elements of the two classes disclose a low energy conformation of arachidonylethanolamide that can occupy the same receptor space as cannabinoid ligands. To test this model, we have developed a novel class of monocyclic and bicyclic alkyl amide cannabinoid receptor ligands. Further, we predicted a spatial conformation for these compounds in a molecular model based on the pharmacophoric and structural requirements for binding to the CB1 cannabinoid receptor.

Adenylyl Cyclase Inhibitors↗

PubMed1999

Signal transduction of eicosanoid CB1 receptor ligands.

The eicosanoid ligand, arachidonylethanolamide (anandamide), interacts with the CB1 cannabinoid receptor in the brain to signal its response. Pharmacophoric points of interaction between this agonist and the receptor have been proposed based upon structure-activity relationship studies of ligand binding to the receptor. Three dimensional quantitative structure-activity relationship (3D-QSAR) models have been constructed based upon the corresponding pharmacophoric points predicted for cannabinoid ligands delta9-tetrahydrocannabinol and 9-nor-9beta-hydroxyhexa-hydrocannabinol. A novel data set has been used to test the statistical validity of these models. Once the ligand interacts with the CB1 receptor, signal transduction occurs via G-proteins of the Gi/o family which are shown to be associated with the receptor. Evidence suggests that the juxtamembrane region of the C-terminal of the CB1 receptor is critical for activation of these G-proteins.

Animals↗

PubMed1999

Theoretical study of the SNV reaction of trichloroethylene (TCE) and CH3S- as a model for glutathione conjugation of TCE.

Trichloroethylene (TCE), a major environmental pollutant, is activated to mutagenic and nephrotoxic intermediates through a glutathione (GSH) conjugation pathway. Three product isomers of GSH-TCE conjugation, having potentially different toxicities, are theoretically possible: cis- or trans-S-(1, 2-dichlorovinyl)glutathione (cis- or trans-1,2-DCVG, respectively) or 2,2-DCVG. This study involved application of ab initio molecular orbital theory to computing potential energy profiles (PEPs) and predicting product outcome of the reaction of CH3S- with TCE as a model for GSH-TCE conjugation in biological systems. A goal of this study was to determine the extent to which a body of chemical knowledge pertaining to nucleophilic vinylic substitution (SNV) reactions, of which the GSH-TCE conjugation is a representative example, is relevant to this biological conjugation problem. PEPs were computed for all studied species at the HF/6-31+G level of theory; electron correlation effects were estimated at the MP2/6-31+G and MP4/6-31+G levels, and the influence of solvation was estimated using the PS-GVB solvation model. Multiple proposed reaction pathways were considered, including conjugation at the C1 or C2 site on TCE, by in-plane (sigma) or out-of-plane (pi) approach of the nucleophile. Some aspects of the MP2 and HF PEPs were found to differ significantly. However, on the basis of comparison of activation barriers, calculations at all levels of theory predict preference for C2 conjugation over C1 conjugation and formation of the trans-1,2-DCVM product over the cis-1,2-DCVM product. These predictions are consistent with GSH-TCE conjugation results from in vivo experiments. In contrast, relative product energies appear to be a poor indicator of the product outcome for this system. Hence, theoretical consideration of the reaction chemistry in the vicinity of the site of nucleophilic addition appears to be necessary and sufficient to predict the outcome of the enzyme-mediated GSH-TCE conjugation.

Environmental Pollutants↗

PubMed1999

Isothermal age-hardening behaviour in a Au-1.6 wt% Ti alloy.

This study describes research with a view to developing a new age-hardenable, high-carat dental gold alloy with better biocompatibility by addition of a small quantity of titanium to gold. The relationship between isothermal age-hardening and phase transformation of the Au-1.6 wt% Ti alloy was investigated by means of hardness testing, X-ray diffraction study, scanning electron microscopic observation and energy dispersive spectroscopy. The hardening in the initial stage of ageing seemed to be attributable to the continuous precipitation of the Au4Ti ordered phase in the supersaturated alpha solid solution matrix. The overaging with softening was attributed mainly to the formation of precipitates at the grain boundaries, which grew to bright lamellae and seemed to be composed of the Au4Ti phase.

Crystallization↗

PubMed1998

Three-dimensional quantitative structure-activity relationship study of the cannabimimetic (aminoalkyl)indoles using comparative molecular field analysis.

The present study describes the implementation of comparative molecular field analysis (CoMFA) to develop two 3D-QSAR (quantitative structure-activity relationship) models (CoMFA models 1 and 2) of the cannabimimetic (aminoalkyl)indoles (AAIs) for CB1 cannabinoid receptor binding affinity, based on pKi values measured using radioligand binding assays that displace two different agonist ligands, [3H]CP-55940 and [3H]WIN-55212-2. Both models exhibited a strong correlation between the calculated steric-electrostatic fields and the observed biological activity for the respective training set compounds. In light of the basicity of the morpholine nitrogen in the AAIs, separate CoMFA models were built for the AAIs as unprotonated and protonated species. Comparison of the statistical parameters resulting from these CoMFA models failed to provide unequivocal evidence as to whether the AAIs are protonated or neutral as receptor-bound species. Although the training sets of CoMFA model 1 and CoMFA model 2 differed with respect to composition and to the choice of displacement radioligand in each biological assay, their CoMFA StDevCoeff contour plots reveal similarities in terms of identifying those regions around the AAIs that are important for CB1 cannabinoid receptor binding such as the sterically favored region around the C3 aroyl group and the sterically forbidden region around the indole ring. When the experimental pKi values for the training set compounds to displace the AAI radioligand [3H]WIN-55212-2 were plotted against the pKi values as predicted for the same compounds to displace the cannabinoid radioligand [3H]CP-55940, the correlation was moderately strong (r = 0.73). However, the degree of correlation may have been lowered by the structural differences in the compounds comprising the training sets for CoMFA model 1 and CoMFA model 2. Taken together, the results of this study suggest that the binding site region within the CB1 cannabinoid receptor can accommodate a wide range of structurally diverse cannabimimetic analogues including the AAIs.

Animals↗

PubMed1997

Theoretical evaluation of two plausible routes for bioactivation of S-(1,1-difluoro-2,2-dihaloethyl)-L-cysteine conjugates: thiirane vs thionoacyl fluoride pathway.

The selective nephrotoxicity of halogenated alkenes has been attributed to a glutathione (GSH) S-conjugate pathway involving enzymatic hydrolysis to the cysteine S-conjugate and beta-lyase bioactivation to thiolates, which are presumed to give rise to the ultimate mutagenic or cytotoxic reactive species. Studies have shown that the brominated S-(2,2-dihalo-1,1-difluoroethyl)-L-cysteine conjugates are mutagenic in the Ames test, whereas the nonbrominated analogues are nonmutagenic. While careful experimentation has contributed much to current understanding, the ultimate reactive species responsible for the differing mutagenic effects remain unknown. Computational methods were applied to the investigation of two proposed metabolic pathways leading from the thiolate to either a thiirane or thionoacyl fluoride intermediate, both electrophilic species presumed capable of binding to proteins or DNA. Studied were six F-, Cl-, and Br-substituted 2,2-dihalo-1,1-difluoroethane-1-thiolates (2,2-dihalo-DFETs). Pathway preference was determined for each thiolate by comparison of reaction energy profiles and activation energies. At all but the lowest level of ab initio theory, a thionoacyl fluoride pathway was predicted for 2,2-difluoro-DFET, while a thiirane pathway was energetically preferred for the brominated 2,2-dihalo-DFETs. These results offer a clear mechanism-based rationale for distinguishing 2,2-difluoro-DFET from the brominated 2,2-dihalo-DFETs, while the results are less clear for the 2,2-dichloro and 2-chloro-2-fluoro-DFETs, which at the highest level of ab initio treatment had a relatively small energy preference (2.4 kcal/mol) for the thiirane pathway. The predicted clear preference for a thiirane pathway for the brominated 2,2-dihalo-DFETs is not consistent with a recently proposed pathway involving alpha-thiolactone formation through a thionoacyl fluoride intermediate [Finkelstein, M. B., et al. (1995) J. Am. Chem. Soc. 117, 9590-9591], but is supported by results of a recent study providing experimental evidence for thiirane formation from the brominated 2,2-dihalo-DFETs [Finkelstein, M. B., et al. (1996) Chem. Res. Toxicol. 9, 227-231].

Biotransformation↗

PubMed1997

Glutathione S-transferase-mediated induction of GC-->AT transitions by halomethanes in Salmonella.

Halomethanes are among the most common mutagenic and carcinogenic disinfection by-products present in the volatile/semivolatile fraction of chlorinated drinking water. Recent studies have demonstrated that the mutagenicity of dichloromethane (CH2Cl2) and bromodichloromethane (BrCHCl2) can be mediated by a theta-class glutathione S-transferase (GSTT1-1). These studies used strain RSJ100 of Salmonella, which is a derivative of the base-substitution strain TA1535 (hisG46, rfa, delta uvrB), into which has been cloned the GSTT1-1 gene from rat. In the present report, we have extended these studies by demonstrating that the mutagenicity of two additional brominated trihalomethanes, bromoform (CHBr3) and chlorodibromomethane (CICHBr2), are also mediated by GSTT1-1 in RSJ100. Using a Tedlar bag vaporization technique, the mutagenic potencies (revertants/ppm) for these two compounds as well as the compounds tested previously rank as follows: CHBr3 approximately CICHBr2 > BrCHCl2 approximately CH2Cl2. To explore the mutational mechanism, we determined the mutation spectra of all four halomethanes at the hisG46 allele by performing colony probe hybridizations of approximately 100 revertants induced by each compound. The majority (96-100%) of the mutations were GC-->AT transitions, and 87-100% of these were at the second position of the CCC/GGG target. In contrast, only 15% of mutants induced by CH2Cl2 were GC-->AT transitions in the absence of the GSTT1-1 gene in strain TA100 (a homologue of TA1535 containing the plasmid pKM101). The ability of GSTT1-1 to mediate the mutagenicity of these di- and trihalomethanes and the induction of almost exclusively GC-->AT transitions by these compounds suggest that these halomethanes are activated by similar pathways in RSJ100, possibly through similar reactive intermediates. The implications of these findings are discussed in relation to previous experimental work on the GST-mediated bioactivation of dihalomethanes, which includes the possible formation of GSH intermediates and/or GSH-DNA adducts.

DNA↗