Biomedical subjects

R Honchel

Publications and source records attributed to R Honchel.

At least 19 recordsLinked to original sources

PubMed2001

Loss of critical palindromic transgene promoter sequence in chemically induced Tg.AC mouse skin papillomas expressing transgene-derived mRNA.

The Tg.AC transgenic mouse carries a v-Ha-ras transgene. Skin papillomas develop in Tg.AC mice upon repeated dermal application of tumor promoters and carcinogens. The transgene is inserted at a single site on chromosome 11 in a multiple-copy array. Although most of the >or= 40 copies are arranged in a direct-repeat orientation, two copies of the transgene are inserted in a palindromic, inverted-repeat orientation. Deletion of the palindromic transgene promoter sequence is associated strongly with and diagnostic of loss of phenotypic responsiveness to Tg.AC papillomagens, such as 12-O-tetradecanoylphorbol-13-acetate (TPA). Unexpectedly, a loss of palindromic transgene sequence, in the absence of an observable reduction in copy number of the direct-repeat-oriented transgene sequence, is seen in DNA from papillomas when compared to genomic DNA from tail clips or skin samples away from the application site. Transgene-derived transcripts were detectable in all Tg.AC papillomas sampled. The transgene locus was hypomethylated in papillomas but not in samples from tail clips from the same animal or from skin samples away from the application site in responder Tg.AC mice, as shown by loss of resistance to digestion by HpaII. A cell line derived from a Tg.AC squamous cell carcinoma showed complete loss of the palindromic transgene sequence, hypomethylation of the transgene locus, and strong expression of v-Ha-ras mRNA. These data indicate that the palindromic transgene sequence, which appears to be necessary for initial responsiveness to tumorigens, may be susceptible to deletion during rapid cellular proliferation and is not required for transgene expression in later phases of papilloma growth.

Animals↗

PubMed2001

Loss of palindromic symmetry in Tg.AC mice with a nonresponder phenotype.

The Tg.AC transgenic mouse carries the v-Ha-ras oncogene under the control of the zeta-globin promoter and is currently being used in a short-term carcinogenesis assay for safety testing of pharmaceuticals. A subset of hemizygous Tg.AC mice was found to be nonresponsive to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate, which characteristically induces skin papillomas in these mice with repeated dermal applications. We previously showed that responder and nonresponder hemizygous Tg.AC mice carry about 40 copies of transgene but that the nonresponders had lost a 2-kb BamHI fragment containing the zeta-globin promoter sequence. The present restriction enzyme and S1 nuclease digestion experiments strongly suggested that the 2-kb BamHI fragment resulted from the orientation of two transgenes in an inverted repeat formation. Two subsets of nonresponder Tg.AC mice were identified. Restriction enzyme and S1 nuclease digestion experiments suggested that one nonresponder genotype was produced by a large deletion of one or more near complete copies of transgene sequence and the other genotype was produced by a small deletion near the apex of the "head-to-head" juncture of the inverted repeat. Polymerase chain reaction amplification, cloning, and sequencing results confirmed the palindromic orientation of transgene in Tg.AC mice. Our results indicated that, despite the presence of multiple copies of transgene in a direct repeat orientation, loss of symmetry in the palindromic array of transgene sequence results in the loss of the responder phenotype in Tg.AC mice. Mol. Carcinog. 30:99-110, 2001. Published 2001 Wiley-Liss, Inc.

Animals↗

PubMed1999

Hereditary desmoid disease in a family with a germline Alu I repeat mutation of the APC gene.

Two families with autosomal dominantly inherited desmoid tumors have recently been shown to have germline mutations at the 3' end of the APC gene. We subsequently identified an Amish family with autosomal dominantly inherited desmoid tumors. Genetic analysis performed on one family member, a 47-year-old man with multiple desmoid tumors and no colon polyps, revealed a protein truncating mutation in the middle of the APC gene. The truncating mutation is the result of a 337-bp insertion of an Alu I sequence into codon 1526 of the APC gene. The presence of a poly(A) tail at the 3' end of the insertion suggests that the Alu I sequence was inserted by a retrotranspositional event. Germline insertions of Alu I sequences have occasionally been reported to cause other genetic diseases including type I neurofibromatosis, hereditary site-specific breast cancer (BRCA2), and hemophilia B. However, this is the first report of a germline mutation of the APC gene resulting from an Alu I insertion.

Adenomatous Polyposis Coli↗

PubMed1996

Altered expression of hMSH2 and hMLH1 in tumors with microsatellite instability and genetic alterations in mismatch repair genes.

To date, at least four genes involved in DNA mismatch repair (MMR) have been demonstrated to be altered in the germline of patients with hereditary nonpolyposis colon cancer: hMSH2, hMLH1, hPMS1, and hPMS2. Additionally, loss of MMR function has been demonstrated to lead to the phenomenon of microsatellite instability (MIN) in tumors from these patients. In this study, we have examined the protein expression pattern of hMSH2 and hMLH1 by immunohistochemistry in paraffin-embedded tumors from 7 patients with MIN+ sporadic cancer, 13 patients with familial colorectal cancer, and 12 patients meeting the strict Amsterdam criteria for hereditary nonpolyposis colon cancer. The relationship between the expression of these two gene products, the presence of germline or somatic mutations, and the presence of tumor MIN was examined. Nineteen of the 28 tumors studied demonstrated MIN, whereas mutations in hMLH1 and hMSH2 were detected in 6 and 2 patients, respectively. Of the eight MIN+/mutation+ cases, the absence of protein expression was observed for the corresponding gene product in all but one case (missense mutation in hMLH1). However, seven MIN+/mutation- cases also showed no expression of either hMLH1 (n = 5), hMSH2 (n = 1), or both (n = 1), whereas four MIN+/mutation- cases demonstrated normal expression for both. None of the MIN-/mutation- cases (n = 9) demonstrated an altered expression pattern for either protein. These data suggest that examination of protein expression by immunohistochemistry may be a rapid method for prescreening tumors for mutations in the MMR genes.

Adaptor Proteins, Signal Transducing↗

PubMed1996

Tumor necrosis factor-alpha allelic frequency and chromosome 6 allelic imbalance in patients with colorectal cancer.

The human tumor necrosis factor (TNF) locus is located on chromosome 6p21.3 and contains at least five polymorphic microsatellites. In this study, we compared the allelic frequencies derived from 50 normal controls to 64 patients with colorectal cancer at one of these loci, TNF alpha. No differences in allelic frequencies were observed between these two groups (P = 0.47). However, sequencing of the TNF alpha PCR product revealed two populations of TNF alpha alleles; alleles with the expected DNA sequence (i.e., the expected number of AC/GT repeats) and alleles that contained 8-bp deletions adjacent to the microsatellite repeat. In addition, we also examined paired normal and tumor DNA from the colorectal cancer group for microsatellite alterations at the TNF alpha locus, including allelic loss of heterozygosity and microsatellite instability. Of the 64 tumors examined, 13 (20%) demonstrated microsatellite instability, and 14 (42%) of 33 informative cases demonstrated allelic imbalance. Analysis of 10 additional chromosome 6 loci for allelic loss showed that 23 (47%) of 49 informative cases exhibited allelic imbalance with at least one chromosome 6p marker, 23 (47%) of 49 with at least one 6q marker, and 29 (59%) of 49 with at least one marker on chromosome 6. Examination of tumors for the minimal region of deletion overlap suggests the presence of tumor suppressor genes on both 6p and 6q.

Alleles↗

PubMed1996

Microsatellite instability and mutation analysis of hMSH2 and hMLH1 in patients with sporadic, familial and hereditary colorectal cancer.

To date, at least four genes involved in DNA mismatch repair, hMSH2, hMLH1, hPMS1 and hPMS2, have been demonstrated to be altered in the germline of patients with hereditary nonpolyposis colorectal cancer (HNPCC). Additionally, defective mismatch repair is thought to account for the observation of microsatellite instability (MIN) in tumors from these patients. The genetic defect responsible for the MIN+ phenotype in sporadic colorectal cancer, however, has yet to be clearly delineated. In order to better understand the role of somatic and germline alterations within hMSH2 and hMLH1 in the process of colorectal tumorigenesis, we examined the entire coding regions of both of these genes in seven patients with MIN+ sporadic colorectal cancer, 19 patients with familial colorectal cancer, and 20 patients meeting the strict Amsterdam criteria for HNPCC. Thirteen germline, two somatic, and four neutral alterations were identified. The two somatic mutations occurred in patients having familial cancer, while the germline mutations were distributed among one sporadic (14%), three familial (16%), and nine HNPCC (45%) cases. All patients with identified mutations in the mismatch repair genes, whose tumors were available for analysis, demonstrated MIN. On the other hand, we could not identify mutations in the subset of clinically defined HNPCC patients with MIN negative tumors nor in the majority (6/7) of MIN+ sporadic tumors.

Adaptor Proteins, Signal Transducing↗

PubMed1995

Microsatellite instability in keratoacanthoma.

BACKGROUND: Tumors from patients with hereditary nonpolyposis colorectal cancer (HNPCC) and from a subset of patients with the related Muir-Torre syndrome (MTS) exhibit a novel type of genomic instability known as microsatellite instability (MIN). In general, this form of genomic instability results from mutations that inactivate DNA mismatch repair genes. The detection of MIN in a keratoacanthoma (KA) from a patient with MTS suggested that defective mismatch repair may play a role in the pathogenesis of these neoplasms. METHODS: Randomly selected paraffin embedded KA from 53 patients and paraffin embedded tumors from an additional 12 patients diagnosed with KA and colorectal carcinoma were examined for MIN at six loci. In addition, several KA were examined for mutations within the hMSH2 gene. RESULTS: Six of the 53 randomly selected KAs had MIN at two or more loci. One of these six patients had HNPCC, whereas another had MTS. Two patients with KAs lacking MIN had colon tumors that exhibited widespread MIN, and one of these patients had MTS. Three of the 12 additional patients diagnosed with a KA and a colorectal carcinoma had at least one tumor that had MIN at two or more loci, and one of these patients had HNPCC: A 2-base pair somatic deletion in exon 3 of the hMSH2 gene was identified in one of the MIN+ KAs. CONCLUSIONS: Defective mismatch repair appears to play a role in the process of tumorigenesis in some KAs. Microsatellite instability in a KA or the cooccurrence of a colorectal carcinoma and a KA in a patient suggests that the patient may have either HNPCC or its phenotypic variant MTS.

Aged↗

PubMed1995

Genomic instability in neoplasia.

Recent studies have demonstrated novel alterations of microsatellite DNA in tumor tissue. The alterations, termed microsatellite instability or replication error phenotype, have now been observed in tumors from patients with hereditary nonpolyposis colorectal cancer (HNPCC), the Muir-Torre syndrome (MTS) and in an increasing number of sporadic tumors. These observations, along with the use of genetic linkage analysis, have led to the identification of at least four genetic susceptibility loci for HNPCC, hMSH2, hMLH1, hPMS1 and hPMS2, each of which are involved in DNA mismatch repair. For those tumors demonstrating microsatellite instability, several different phenotypes may exist, the significance of which is currently unknown. Defective DNA mismatch repair may have important implications for the mechanism of tumorigenesis and the clinical behavior of tumors.

Colorectal Neoplasms↗

PubMed1995

Familial medullary thyroid cancer and prominent corneal nerves: clinical and genetic analysis.

A unique kindred manifesting medullary thyroid carcinoma and corneal nerve thickening without other aspects of the multiple endocrine neoplasia syndrome (MEN) was analyzed by linkage analysis using four highly polymorphic (CA)n repeat markers (sTCL-1, D10S141, ZNF22, and sJRH-1). Additionally, the RET protooncogene was examined for specific mutations by DNA sequence analyses in all affected family members. Screening of 11 family members spanning 4 generations revealed 7 subjects with corneal nerve thickening; of these subjects, 3 had abnormal pentagastrin-stimulated calcitonin studies, and these 3 subjects were each found to have C-cell hyperplasia or medullary thyroid carcinoma at surgery. Linkage analysis showed cosegregation of alleles (as defined by the above markers), with the presence of both corneal nerve thickening and medullary thyroid carcinoma/C-cell hyperplasia (maximum LOD score, 2.69; consistent with, but not proving linkage). DNA sequence analysis showed that none of the affected individuals had mutations in either exon 10 or 11, or in exon 16 of the RET protooncogene, regions where mutations have been described for MEN type 2A (MEN-2A) and MEN-2B families, respectively. Thus, compared to the defined syndromes of MEN-2A and MEN-2B, this kindred appears to represent a true clinical overlap syndrome whose genetic basis may be distinct from these two syndromes.

Aged↗

PubMed1995

Mutations in the RET protooncogene in sporadic pheochromocytomas.

Mutations in the RET protooncogene have recently been demonstrated in families with multiple endocrine neoplasia (MEN) types 2A and 2B. We have studied pheochromocytomas from 29 individuals who had no clinical evidence of MEN-2A or -2B to determine the frequency of germline and/or somatic mutations in exons 10, 11, and 16 of the RET protooncogene. Of the 29 tumors examined, 3 (10%) were found to have a mutation in 1 of the 3 exons. These mutations were not found in the DNA from the peripheral blood from these individuals, indicating that the mutations in the tumors were somatic in origin. Although we cannot exclude the possibility of mutations in other regions of the RET protooncogene, our data suggest that 1) individuals presenting with apparently sporadic pheochromocytomas are not likely to have undiagnosed MEN-2A or -2B; and 2) somatic mutations in exons 10, 11, and 16 in the RET protooncogene contribute to the process of tumorigenesis in a small percentage of sporadic pheochromocytomas.

Adrenal Gland Neoplasms↗

PubMed1995

Thiopurine methyltransferase pharmacogenetics. Cloning of human liver cDNA and a processed pseudogene on human chromosome 18q21.1.

Thiopurine methyltransferase (TPMT) is a genetically polymorphic enzyme that catalyzes the S-methylation of thiopurine drugs such as 6-mercaptopurine. This genetic polymorphism is an important factor responsible for individual variation in thiopurine drug response. A cDNA for TPMT has been cloned from T84 human colon carcinoma cells. Northern blot analysis of multiple human tissues was performed with the T84 human colon carcinoma TPMT cDNA open reading frame (ORF) as a probe as one step toward understanding the molecular basis for the TPMT genetic polymorphism. Three mRNA species (approximately 1.4, 2.0, and 3.6 kb in length) were present in all tissues studied, including liver. However, none of these mRNAs matched the length of the 2.7 kb T84 TPMT cDNA. Therefore, it was important to clone a TPMT cDNA from a human drug-metabolizing organ such as the liver to determine whether its sequence matched that of the cDNA cloned from the T84 cell line. A human liver cDNA library was screened with the T84 TPMT cDNA ORF as a probe, and a 1.8 kb cDNA was isolated with a coding region sequence identical to that of the T84 TPMT cDNA. The TPMT cDNA ORF was then used to screen a human lymphocytes genomic DNA library in an attempt to clone the TPMT gene(s) in humans. Three intronless clones were isolated with identical ORF sequences that were 96% identical to that of the TPMT cDNA, but which contained multiple nucleotide substitutions and one deletion. The 3'- and 5'-flanking regions of one of the genomic DNA clones were sequenced.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗

PubMed1994

Microsatellite instability in Muir-Torre syndrome.

Muir-Torre syndrome (MTS) is characterized by the presence of at least one sebaceous tumor and at least one visceral malignancy. Although a wide range of internal malignancies have been reported, the most frequently observed internal neoplasm is colorectal carcinoma. MTS and hereditary nonpolyposis colorectal carcinoma (HNPCC) share many clinical and pathological characteristics and thus may share similar genetic mechanisms of tumorigenesis. Recently, microsatellite instability (MIN) has been reported in tumor tissue from patients with HNPCC. In order to determine if tumors from MTS patients might also show MIN, we examined DNA extracted from paraffin-embedded tissues for the presence of MIN at (CA)n repeats on chromosomes 5q, 15q, 17p, and 18q. Data was obtained on 13 patients, 9 of which had at least one colorectal tumor. Of these, six demonstrated widespread MIN in all sebaceous and colorectal tumors examined, as well as in a transitional cell carcinoma of the renal pelvis, a prostatic adenocarcinoma and a keratoacanthoma. Overall, patients with MIN differed from patients without MIN in several respects, the most important of which include: (a) uniform presence and early onset of colorectal cancer (average age, 40 versus 70 years); (b) prolonged survival following diagnosis of visceral malignancy (median survival, 32 versus 11 years); and (c) a greater number of visceral and skin tumors. These data suggests that patients with MTS may be composed of at least two subgroups, each demonstrating different genetic, pathological and clinical features. Furthermore, the subgroup demonstrating MIN may share similar genetic mechanisms of tumorigenesis with patients having HNPCC, supporting the notion that these syndromes are allelic.

Adult↗

PubMed1994

Human histamine N-methyltransferase pharmacogenetics: cloning and expression of kidney cDNA.

Histamine N-methyltransferase (HNMT) catalyzes the NT-methylation of histamine. The level of HNMT activity in human red blood cells is controlled by a common genetic polymorphism. We set out to clone and express a cDNA for HNMT from human tissue as a first step toward a determination of the molecular basis for this genetic polymorphism. The cloning strategy was based on possible sequence homology between rat and human kidney HNMT. Human kidney cDNA libraries were screened with the 885-nucleotide open reading frame of rat kidney HNMT cDNA. A 1.4-kilobase cDNA clone was isolated that contained two potential translation initiation codons, both in the same reading frame. The longest open reading frame of the human kidney cDNA clone contained 876 nucleotides and encoded a protein 292 amino acids in length. The amino acid sequence of this protein was 84% identical to that of rat kidney HNMT. The human kidney cDNA clone was transcribed in vitro and translated in a rabbit reticulocyte lystate system to yield a protein with an apparent molecular mass of 33 kDa, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The human kidney cDNA was also subcloned into the eukaryotic expression vector p91023(B). Partially purified HNMT isolated from the cytosol of GOS-1 cells transfected with this expression construct had biochemical properties similar to those of human kidney HNMT. Human renal cortical HNMT, partially purified human renal cortical HNMT, and partially purified transfected COS-1 cell HNMT had Km values for histamine and S-adenosyl-L-methionine, the two cosubstrates for the enzyme reaction, of 20, 13, and 14 microM and 2.0, 3.0, and 6.2 microM, respectively. IC50 values for the HNMT inhibitor amodiaquine were 0.50, 0.48, and 0.40 microM, respectively, for enzyme from these same three sources. Northern blot analyses performed with poly(A)+ RNA from a series of human tissues including kidney demonstrated three transcripts, approximately 1.3, 3.8, and 4.0 kilobases in length. Cloning of a cDNA for HNMT may now make it possible to determine the molecular basis for the HNMT genetic polymorphism in humans.

Amino Acid Sequence↗

PubMed1993

Human thiopurine methyltransferase: molecular cloning and expression of T84 colon carcinoma cell cDNA.

Thiopurine methyltransferase (TPMT) catalyzes the S-methylation of thiopurine drugs such as 6-mercaptopurine. Levels of TPMT activity in human tissue are controlled by a common genetic polymorphism that is an important factor responsible for individual variation in thiopurine drug toxicity and therapeutic efficacy. Our goal was to purify, to obtain a partial amino acid sequence for, and to clone and express cDNA for human TPMT as a first step in determining the molecular basis for this genetic polymorphism. Human kidney TPMT was purified, the protein was subjected to limited proteolysis, and amino acid sequence information was obtained from the resultant peptide fragments. Primers based on the amino acid sequence information were used to amplify a unique sequence from human liver cDNA by use of the polymerase chain reaction. Because TPMT has been reported to be present in the colon, T84 human colon carcinoma cells were studied and were found to express TPMT activity with biochemical properties similar to those of the human kidney and liver enzymes. Oligonucleotide probes based on the human kidney TPMT amino acid sequence were then used to screen a T84 human colon carcinoma cell cDNA library. A 2.7-kilobase cDNA clone was isolated that contained an open reading frame of 735 nucleotides, which encoded a protein of 245 amino acids. The deduced amino acid sequence of the encoded protein included one 24- and two separate 12-amino acid sequences identical to those obtained by sequencing proteolytic fragments of purified human kidney TPMT. Transcripts were made in vitro from the open reading frame of the cDNA clone. These transcripts were translated in a rabbit reticulocyte lysate system, and the resulting translation product comigrated with human kidney TPMT in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The T84 cell cDNA clone, truncated within the 3' untranslated region at an Sstl restriction site, was then used to create an expression construct with the eukaryotic expression vector P91023(B), and this construct was used to transfect COS-1 cells. The transfected cells expressed a high level of TPMT enzymatic activity, and this activity displayed a pattern of inhibition by TPMT inhibitors identical to that of human kidney and T84 human colon carcinoma cell TPMT. Cloning of cDNA for this important drug-metabolizing enzyme may make it possible to define the molecular basis of the TPMT genetic polymorphism in humans.

Amino Acid Sequence↗

PubMed1992

Tumor necrosis factor in alcohol enhanced endotoxin liver injury.

Endotoxin administration causes liver injury. Patients with alcoholic liver disease frequently have portal vein and systemic endotoxemia, and some investigators have suggested that endotoxin plays an etiologic role in alcoholic liver injury. Many of the metabolic effects of endotoxin are mediated by the cytokine tumor necrosis factor (TNF). It was the purpose of this study to determine whether TNF plays a role in ethanol-enhanced endotoxin liver injury. Rats were fed either a diet in which 36% of the calories were from ethanol or an isocaloric control diet. After 6 weeks, groups of 10 rats were intravenously injected with either saline, 1 mg/kg endotoxin, or 30 micrograms/kg of a prostaglandin E1 (PGE1) analogue + 1 mg/kg endotoxin 24 hr prior to sacrifice. Ethanol/endotoxin-treated rats had significantly higher liver enzyme levels (ALT: 1064 +/- 355 IU/liter, AST: 2024 +/- 515 IU/liter) compared with isocaloric/endotoxin controls (ALT: 237 +/- 54 IU/liter, AST: 602 +/- 80 IU/liter). Ethanol/endotoxin rats also had significantly higher peak serum TNF concentrations (992 +/- 200 units/ml) compared with isocaloric/endotoxin controls (344 +/- 96 units/ml). Pretreatment of ethanol/endotoxin rats with PGE1 caused significant attenuation of liver injury (ALT: 267 +/- 64 IU/liter, AST: 612 +/- 77 IU/liter) and a diminished serum TNF response. In contrast to chronic ethanol administration, acute gavage with 2 mg/kg ethanol (30% w/v) followed by intravenous injection of 2 mg/kg endotoxin produced significantly lower peak serum TNF concentrations (401 +/- 76 units/ml) than gavage with distilled water (1152 +/- 208 units/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Alprostadil↗

PubMed1992

Human liver thiopurine methyltransferase pharmacogenetics: biochemical properties, liver-erythrocyte correlation and presence of isozymes.

Thiopurine methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs such as 6-mercaptopurine (6-MP). TPMT activity in the human red blood cell (RBC) is controlled by a common genetic polymorphism. Gene frequencies for this polymorphism are such that approximately one in 300 subjects is homozygous for the allele for low activity and lacks RBC TPMT activity, 11% of subjects are heterozygous and have intermediate levels of enzyme activity and 89% are homozygous for the allele for high activity. Our experiments were performed to determine whether the properties of TPMT in an important human drug metabolizing organ, the liver, were similar to those of RBC TPMT and to test the hypothesis that the genetic polymorphism which controls TPMT activity in the human RBC might also regulate the level of this enzyme activity in hepatic tissue. Human liver TPMT is a cytoplasmic enzyme and the Km values for 6-MP and S-adenosyl-L-methionine, cosubstrates for the reaction, were 580 microM and 2.7 microM, respectively. These properties, as well as the sensitivity of human liver TPMT to a panel of methyltransferase inhibitors, were similar to those of RBC TPMT. The enzyme activity was then measured in 119 surgical biopsy samples of hepatic tissue. Average hepatic TPMT activity was 13.6% higher in samples from male than in those from female patients. Frequency distribution histograms demonstrated the presence of a subgroup with intermediate enzyme activity that included 8.4% of samples. In addition, when TPMT activity was measured in both RBCs and hepatic tissue for 35 patients, those with inherited intermediate levels of RBC TPMT activity also had intermediate hepatic enzyme activity. Finally, ion exchange chromatography demonstrated the presence of two isozymes of TPMT in human hepatic tissue, but the isozymes did not appear to explain the molecular mechanism responsible for the genetic polymorphism. These results were compatible with the conclusion that the genetic polymorphism which controls TPMT activity in the RBC also controls levels of this important enzyme activity in a major human drug metabolizing organ, the liver.

Adult↗

PubMed1991

3,3',4,4'-Tetrabromobiphenyl sensitizes rats to the hepatotoxic effects of endotoxin by a mechanism that involves more than tumor necrosis factor.

To determine whether the cytokine tumor necrosis factor/cachectin might be a mediator of hepatotoxicity seen after exposure to polyhalogenated aromatic hydrocarbons, rats treated with a single dose of 3,3',4,4'-tetrabromobiphenyl (150 mumol/kg intraperitoneally) or corn oil vehicle were studied. The 3,3',4,4'-tetrabromobiphenyl caused the expected anorexia, alterations in organ weights and changes in cytochromes P-450 over 21 days. Although tumor necrosis factor could not be detected in the serum of rats at any time after 3,3',4,4'-tetrabromobiphenyl treatment alone (from 90 min to 21 days), 3,3',4,4'-tetrabromobiphenyl treatment significantly increased peak serum tumor necrosis factor concentrations after intravenous bacterial endotoxin (lipopolysaccharide, 1 mg/kg). This effect was seen with lipopolysaccharide given 24 hr, 48 hr, and 20 days after 3,3',4,4'-tetrabromobiphenyl treatment and increases in peak serum tumor necrosis factor levels ranged from threefold to eightfold over controls in various experiments with no significant differences between the three time points. However, a synergistic increase in hepatic damage (assessed by serum enzymes and liver histological findings 24 hr after lipopolysaccharide injection) was seen in rats given lipopolysaccharide 24 hr and 48 hr after 3,3',4,4'-tetrabromobiphenyl administration, with 75% and 25% lethality, respectively. There was no lethality with lipopolysaccharide given 20 days after 3,3',4,4'-tetrabromobiphenyl administration or with simultaneous administration. A lower dose of lipopolysaccharide (0.1 mg/kg) given 24 hr after 3,3',4,4'-tetrabromobiphenyl also enhanced hepatotoxicity and serum tumor necrosis factor but without lethality. Lipopolysaccharide decreased cytochromes P-450 concentrations and activities to similar extents at all time points tested in both control and 3,3'4,4'-tetrabromobiphenyl-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Lead enhances lipopolysaccharide and tumor necrosis factor liver injury.

Lead markedly augments the lethality of endotoxin lipopolysaccharide (LPS) in rats. In this model of LPS toxicity, the liver is severely injured. Much of the tissue injury produced by LPS is thought to be mediated by the cytokine tumor necrosis factor (TNF). Tumor necrosis factor recently has been speculated to be a mediator of several models of liver injury such as that produced by galactosamine. To investigate the possible role of TNF in the lead-enhanced LPS toxicity model, we administered doses of lead acetate (15 mg/kg), LPS (100 micrograms/kg), or TNF (6.25 x 10(6) U/kg) that produced minimal changes in liver enzymes. However, when lead was administered simultaneously with either LPS or TNF, serum aspartate transaminase, alanine transaminase, alkaline phosphatase, glutamyl transpeptidase, and plasma triglyceride levels were markedly increased. Lead + LPS treatment increased both peak serum TNF concentrations and TNF "area under the curve" as compared with LPS alone. We conclude that lead not only enhances LPS lethality but also LPS liver injury. Furthermore, lead enhances TNF liver injury and increases LPS-stimulated serum TNF levels. These data suggest that the lead-enhanced LPS model offers a system for studying TNF-induced liver injury.

Alanine Transaminase↗