Biomedical subjects

J Aubrecht

Publications and source records attributed to J Aubrecht.

15 recordsLinked to original sources

PubMed2002

Noninvasive evaluation of portal-systemic shunting by glyceryl trinitrate.

Portal-systemic shunting is an important circulatory abnormality in patients with liver cirrhosis. Glyceryl trinitrate (GTN) that is normally subject to first pass elimination, may exhibit higher bioavailability in these patients. This study compares the pharmacodynamic effects of GTN after peroral and sublingual administration for noninvasive assessment of shunting. Six control subjects and 15 patients with cirrhosis were studied after oral and sublingual application of 0.5 mg of GTN. Liver cirrhosis was complicated by portal hypertension in 7 of the patients and 4 patients had surgically implanted portocaval anastomosis. Digital plethysmography, which is highly sensitive and is essentially noninvasive in nature, was used to assess and compare the pharmacodynamic effects of GTN. The following values of the ratio of areas under the pharmacodynamic effects/time curve were obtained: 0.08 +/- 0.06 in healthy subjects, 0.52 +/- 0.21 in patients with uncomplicated cirrhosis, 0.99 +/- 0.34 in patients with portal hypertension and 1.24 +/- 0.43 in patients with portal-systemic shunts. We conclude that increased bioavailability of GTN reflects portal-systemic shunting and might be used providing that the pharmacodynamic data reflect both pharmacokinetic variability and the pharmacokinetic-pharmacodynamic interrelations.

Administration, Oral↗

PubMed2001

Restriction enzymes increase efficiencies of illegitimate DNA integration but decrease homologous integration in mammalian cells.

Mammalian cells repair DNA double-strand breaks by illegitimate end-joining or by homologous recombination. We investigated the effects of restriction enzymes on illegitimate and homologous DNA integration in mammalian cells. A plasmid containing the neo(R) expression cassette, which confers G418 resistance, was used to select for illegitimate integration events in CHO wild-type and xrcc5 mutant cells. Co-transfection with the restriction enzymes BamHI, BglII, EcoRI and KpnI increased the efficiency of linearized plasmid integration up to 5-fold in CHO cells. In contrast, the restriction enzymes did not increase the integration efficiency in xrcc5 mutant cells. Effects of restriction enzymes on illegitimate and homologous integration were also studied in mouse embryonic stem (ES) cells using a plasmid containing the neo(R) gene flanked by exon 3 of HPRT: The enzymes BamHI, BglII and EcoRI increased the illegitimate integration efficiency of transforming DNA several-fold, similar to the results for CHO cells. However, all three enzymes decreased the absolute frequency of homologous integration approximately 2-fold, and the percentage of homologous integration decreased >10-fold. This suggests that random DNA breaks attract illegitimate recombination (IR) events that compete with homology search.

Animals↗

PubMed1999

Molecular genotoxicity profiles of apoptosis-inducing vanadocene complexes.

Metallocene complexes containing vanadium induce apoptosis in human cancer cells by an as yet unknown mechanism and may therefore be useful as a new class of cytotoxic anticancer drugs. Ultrastructural studies showing the formation of metallocene-DNA complexes prompted the hypothesis that their mechanism of action may resemble the DNA damage induced by cisplatin. Molecular genotoxicity testing provides insights into the mechanisms of action of new chemotherapeutic agents. Therefore, we determined the effects of three cytotoxic vanadocene complexes, vanadocene dichloride, vanadocene dithiocyanate, and vanadocene dioxycyanate, on genomic stability using the yeast DEL recombination assay and transcriptional activation of genotoxic stress-specific promoters in human HepG2 cells using the CAT-Tox(L) assay. Cisplatin caused an 11-fold increase of recombination frequency in yeast and induced transcriptional activation of the DNA damage-associated promoters such as the minimum promoter containing p53 response elements and the GADD45 promoter in addition to activating the promoters for c-fos, heat shock protein 70, metallothionine IIa, and the minimum promoter containing nuclear factor kappa(kappa)B response elements. In contrast to cisplatin, vanadocene complexes did not increase the DEL recombination frequency in yeast nor did they activate any of the DNA damage-associated promoters in HepG2 cells. Vanadocene complexes triggered activation of the c-fos promoter without affecting the minimum promoter containing p53 response elements or the GADD45 promoter. These results indicate that the apoptotic signal of vanadocene complexes is not triggered by primary DNA damage and it does not require p53 induction, thereby disproving the hypothesis that it mechanistically resembles the cytotoxic action of cisplatin.

Antineoplastic Agents↗

PubMed1999

Involvement of p53 in X-ray induced intrachromosomal recombination in mice.

The tumor suppressor gene Trp53 (also known as p53) is the most frequently mutated gene in human cancers. p53 is induced in response to DNA damage and effects a G(1) cell cycle arrest. It is believed that p53 plays a key role in maintaining genomic integrity following exposure to DNA-damaging agents. We determined the frequency of spontaneous and DNA damage-induced homologous intrachromosomal recombination in p53-deficient mouse embryos. Homologous intrachromosomal recombination events resulting in deletions at the pink eyed unstable (p(un)) locus result in reversion to the p gene. Reversions occurring in embryonic premelanocytes give rise to black spots on the gray fur of the offspring. Pregnant C57BL/6J p(un)/p(un) p53(+/-) mice were exposed to X-rays (1 Gy) or administered benzo¿apyrene (B¿aP; 30 or 150 mg/kg i.p.) 10 days after conception. Frequencies of spontaneous p(un) reversions in p53(-/-) and p53(+/-) animals were not significantly different compared with their wild-type littermates. X-ray treatment increased the recombination frequency in wild-type and p53(+/-), but surprisingly not in p53(-/-) offspring. In contrast, B¿aP treatment caused a dose-dependent increase in p(un) reversion frequencies in all three genotypes. Western blot analysis of embryos indicated that p53 protein levels increased approximately 3-fold following X-ray treatment, while B¿aP had no effect on p53 expression. These results are in agreement with the proposal that p53 is involved in the DNA damage response following X-ray exposure and suggest that X-ray-induced double-strand breaks are processed differently in p53(-/-) animals.

Animals↗

PubMed1997

Polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin induce intrachromosomal recombination in vitro and in vivo.

Polychlorinated aromatic hydrocarbons such as polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are extremely stable and widely distributed environmental pollutants. These chemicals are animal carcinogens and probable human carcinogens, and TCDD is possibly one of the most potent toxins ever evaluated by the United States Environmental Protection Agency. Polychlorinated aromatic hydrocarbons score negatively in most genotoxicity assays, including the Ames (Salmonella) assay. Although their mechanism of toxicity is not well understood, they induce aryl hydrocarbon (AH) hydroxylases and bind to the AH receptor, which is believed to mediate toxicity. Here, we determine effects of polychlorinated aromatic hydrocarbons in genotoxicity assays that score for DNA deletions by intrachromosomal recombination in vivo and in vitro. In this study, TCDD, Aroclor 1221, and Aroclor 1260 induced deletions in vivo in the mouse embryo; Aroclor 1221 and Aroclor 1260 induced deletions in yeast. We also show that the induced deletion events did not correlate with induction of AH hydroxylase. None of the tested compounds induced CYP1A-associated ethoxyresorufin-O-deethylase activity in mouse embryos or in vitro. These results clearly demonstrate a genotoxic activity of polychlorinated aromatic hydrocarbons in vitro and in vivo, which is independent of induction of cytochrome P450 activity. Because genetic instability and deletions may be mechanistically involved in carcinogenesis, these results may encourage further research to determine whether such genotoxic mechanisms may be useful for cancer risk assessment of polychlorinated aromatic hydrocarbons.

Animals↗

PubMed1997

Carcinogens induce reversion of the mouse pink-eyed unstable mutation.

Deletions and other genome rearrangements are associated with carcinogenesis and inheritable diseases. The pink-eyed unstable (pun) mutation in the mouse is caused by duplication of a 70-kb internal fragment of the p gene. Spontaneous reversion events in homozygous pun/pun mice occur through deletion of a duplicated sequence. Reversion events in premelanocytes in the mouse embryo detected as black spots on the gray fur of the offspring were inducible by the carcinogen x-rays, ethyl methanesulfonate, methyl methanesulfonate, ethyl nitrosourea, benzo[a]pyrene, trichloroethylene, benzene, and sodium arsenate. The latter three carcinogens are not detectable with several in vitro or in vivo mutagenesis assays. We studied the molecular mechanism of the carcinogen-induced reversion events by cDNA analysis using reverse transcriptase-PCR method and identified the induced reversion events as deletions. DNA deletion assays may be sensitive indicators for carcinogen exposure.

Animals↗

PubMed1997

Expression of hygR in transgenic mice causes resistance to toxic effects of hygromycin B in vivo.

Aminoglycoside antibiotics are indispensable for treatment of serious bacterial infections, and despite careful attention to dosage regimens, nephrotoxicity and ototoxicity still cause concern. In the present study, we tested whether side effects of aminoglycoside therapy could be limited by expression of prokaryotic genes of antibiotic resistance in vivo. We characterized the acute and tissue-specific toxicity of hygromycin B in transgenic mice bearing the hygromycin B phosphotransferase (hygR) gene under control of a constitutive promoter. We characterized the tissue-specific expression of hygR mRNA and also investigated the acute toxicity of hygromycin B in hygR and wild-type mice. The hygR mRNA reached its highest levels in brain and reached intermediate levels in spleen, muscle, kidney, liver and testis. The lowest levels were detected in heart and lungs. The hygR expression in transgenic animals caused an 89-fold increase in the approximate lethal dose of hygromycin B compared with wild-type mice. Serum biochemical analysis of hygR and wild-type mice treated with lethal doses of hygromycin B indicated liver and kidney damage measured as ALT, AST and BUN. On the morphological level, these changes led to acute tubular nephrosis in wild-type mice and acute liver damage in hygR mice. Our results show that constitutive expression of the bacterial hygR gene in transgenic mice in vivo confers resistance to hygromycin B.

Animals↗

PubMed1997

Tissue specific toxicities of the anticancer drug 6-thioguanine is dependent on the Hprt status in transgenic mice.

6-Thioguanine (6TG) a cytostatic antimetabolite is currently used to treat patients with cancer, in particular leukemias. However, one drawback of such use is the development of 6TG resistance. Hypoxanthine-guanine phosphoribosyl transferase (Hprt) plays a crucial role in the bioactivation of 6TG. Loss of Hprt has been associated with the resistance of leukemias to 6TG chemotherapy, however, nothing has been known about the effect of Hprt status on tissue specific toxicity of 6TG in vivo. We determined the effect of Hprt status on the tissue-specific toxicity of 6TG in vivo in transgenic Hprt-deficient mice. The approximate lethal dose for Hprt-deficient mice was 23-fold higher than for the wild-type. Serum biochemical analyses of 6TG-treated wild-type mice showed elevated serum enzyme levels characteristic of liver damage whereas the levels in Hprt-deficient 6TG-treated mice were within normal physiological limits. Histopathological examination of tissues from wild-type and from Hprt-deficient mice showed contrasting spectrums of microscopic lesions. Wild-type mice had loss of hematopoietic cells from bone marrow starting at the lowest dose of 25 mg/kg 6TG whereas Hprt-deficient mice had normal bone marrow and spleen even at doses of 720 mg/kg 6TG. Wild-type mice also experienced severe loss of epithelial cells from the gastrointestinal tract starting at 50 mg/kg; however, the gastrointestinal tract of Hprt -/- mice remained unaffected. Wild-type livers revealed atrophy and necrosis at doses of 25 mg/kg 6TG although Hprt -/- livers displayed no effect until 507 mg/kg. In this study we show that Hprt-deficient mice had 6TG-resistant bone marrow and there are several other factors contributing to 6TG resistance in patients. Because variations among people exist in terms of their 6TG sensitivity, determining 6TG sensitivity of lymphocytes prior to 6TG chemotherapy and restricting treatment to 6TG-sensitive patients may improve the efficacy.

Adenine↗

PubMed1996

Controlled gene expression in mammalian cells via a regulatory cascade involving the tetracycline transactivator and lac repressor.

Regulatory cascades or regulons control pathways at multiple points or multiple genes by one initial signal. In this paper, we describe the construction of an artificial regulatory cascade in CHO cells, which responded to various concentrations of tetracycline (Tc) and/or IPTG. The system consists of the constitutively produced transactivator (TTA) of the Tc operon (tet), which induced the expression of a lacI gene controlled by tet operator (tetO) and upstream CMV promoter (p*CMV) sequences. LacI repressed the activity of a cat gene by binding to lacO sites in its upstream RSV promoter (pRSV) region. However, this repression could be alleviated by exposure to Tc or IPTG, which inhibited the binding activities of TTA and LacI, respectively. Hence, treatment with either Tc or IPTG led to a tenfold increase in CAT activity. After the withdrawal of the inducer, cat expression reverted to basal levels. Regulation by Tc showed a phenotypic lag, and full induction was reached after 192 h, whereas IPTG addition led to full induction within 24 h. When cells were treated with both Tc and IPTG, full induction of cat was reached in 24 h and maintained thereafter while in the presence of Tc alone. This suggests that regulation by Tc is fast and that the phenotypic lag may be due to slow turnover of the LacI repressor. This TTA/lacI regulatory system may serve as an example in which cat expression was used as a reporter. The data indicate that regulatory cascades regulated at multiple points can be constructed with any cloned gene in mammalian cells.

Animals↗

PubMed1996

Differential induction of mRNA expression of cytochromes P450 (CYP2B1 and CYP1A1/2) by metyrapone in primary rat hepatocyte cultures.

The mRNA expression of members of two cytochrome P450 (CYP) gene subfamilies involved in carcinogen activation, the CYP1A1/2 and CYP2B1 forms, was determined in primary rat hepatocyte cultures in response to metyrapone and to the inducer phenobarbital or 5,6-benzoflavone (BNF), respectively. Incubation of cells with 0.5 mM metyrapone resulted in accumulation of CYP1A1 and CYP1A2 mRNA and in a marked increase in CYP1A-associated enzymatic activity as determined by deethylation of ethoxyresorufin. Metyrapone and phenobarbital in combination acted synergistically in elevation of ethoxyresorufin O-deethylase activity. In hepatocytes treated with metyrapone or with phenobarbital, accumulation of CYP2B1 mRNA levels preceded an increase in CYP2B-associated, pentoxyresorufin O-depentylase activity. However, CYP2B1 mRNA levels were first detectable after 24 hours of treatment with phenobarbital, whereas metyrapone elicited a substantial increase in mRNA levels within 14 hours, suggesting differing mechanisms leading to accumulation of CYP2B1 mRNA under the two inducers.

Animals↗

PubMed1995

Induction of cytochrome P-4502B1-related mouse cytochrome P-450 and regulation of its expression by epidermal growth factor/transforming growth factor alpha in primary hepatocyte culture.

Phenobarbital-dependent induction of mouse cytochrome P-450 (Cyp) orthologous to rat CYP2B1 and its modulation by hepatotrophic growth factors were examined in primary hepatocyte cultures. Compared to rat hepatocytes, induction in mouse hepatocytes was more rapid and effective. Ligands of the EGF receptor, epidermal growth factor, and transforming growth factor alpha inhibited induction on the basis of protein expression and CYP2B-associated 7-pentoxyresorufin-O-depentylase activity. Furthermore, EGF led to repression of accumulation of corresponding mRNA under phenobarbital, an effect not blocked by inhibition of protein synthesis under cycloheximide. Ligands of the EGF receptor may contribute towards the decrease in hepatic CYP expression observed during (pre)neoplastic development and regeneration.

Animals↗

PubMed1995

Carcinogens induce intrachromosomal recombination in human cells.

A major portion of new cases of cancer may be linked to environmental carcinogens. The Ames (Salmonella) test is currently the most widely used short-term test to predict carcinogenic properties of compounds. However, approximately 50% of all carcinogens have been sufficiently tested in long-term animal bioassays do not induce mutations in the Salmonella assay, and many of these carcinogens are also not detectable by other short-term assays. In the work described here we determined the effect of carcinogen exposure on intrachromosomal recombination in a human cell line. The recombination events caused the deletion of one copy of a duplication of exons 2 and 3 of the hprt gene. We found that these deletion events were induced by exposure to the Salmonella assay positive carcinogens UV, gamma-rays and methyl methanesulfonate, as well as the Salmonella assay negative carcinogens Aroclor 1221, benzene and thiourea. These data may further support the accumulating evidence that recombination and deletions may be important in carcinogenesis.

Carcinogens↗

PubMed1993

Regulation of fibronectin mRNA expression in primary hepatocytes in response to EGF and phenobarbital.

Adult rat hepatocytes were cultured in serum free chemically defined MX-83 medium. Fibronectin mRNA expression accumulated to high levels in primary cultures of hepatocytes and transcripts were detectable even after 2 hrs. However, the presence of phenobarbital (PB) in the culture medium led to a dose-dependent decrease in fibronectin mRNA levels concomitant to an increase of cytochrome P450-2B1 (CYP2B1) mRNA, whereas the coaddition of EGF reversed the suppressive effect of PB in a similar dose-dependent manner. Culturing hepatocytes on a fibronectin matrix partially inhibited the accumulation of cytochrome CYP2B-dependent pentoxyresorufin-O-depentylase (PROD) activities in the presence of the inductor PB.

Animals↗

PubMed1990

[The effect of the method of detecting indocyanine green (HPLC, spectrophotometry) on the determination of pharmacokinetic parameters].

The method of determination of indocyanine green (ICG) in plasma by means of high-performance liquid chromatography (HPLC) is compared with the method of spectrophotometry. A sample for HPLC is purified by deproteination with acetonitrile and the supernatant is directly spread on the column. The internal standard is diazepam. The mobile phase consists of 50% of phosphate buffer pH 6 prepared according to PhBs 4, 47% of acetonitrile and 3% of methanol. Detection takes place at 260 nm. Spectrophotometric analysis consists in the measurement of plasma absorbance at 805 nm. Correlation of both methods is linear r = 0.989, n = 20, p less than 0.05. From the curves of elimination of the dye from the blood bed the principal pharmacokinetic parameters were calculated by means of a one-compartmental model after single intravascular administration. In spectrophotometric examination, elimination of ICG seems to be slower as compared with HPLC.

Chromatography, High Pressure Liquid↗

PubMedDate not supplied

Increased cotinine elimination and cotinine-N-oxide formation by phenobarbital induction in rat and mouse.

The metabolic fate of cotinine, the major metabolite of nicotine, was studied in phenobarbital-induced and non-induced isolated perfused rat lung and liver and in isolated hepatocytes of rats and mice. The non-induced lung tissue showed low cotinine metabolizing capacity while the perfused liver was approximately four times more active. After phenobarbital pretreatment the metabolism of cotinine was increased eight-fold in the intact liver. A substantial increase in cotinine metabolism was also found in isolated hepatocytes from PB-induced rats and in cultured mouse hepatocytes grown in a medium supplemented with PB. This was paralleled by an increased formation of cotinine-N-oxide which could be inhibited by 100 microM metyrapone. In contrast, the pulmonary elimination of cotinine was not affected by PB. A dominant role of primary N-oxidation of nicotine compared to C-oxidation was apparent in non-induced rat liver. After PB treatment the rate of nicotine-N'-oxide formation dropped markedly while the cotinine related pathways were increased causing an inversion of the N- to C-oxidation ratio. In the lung, cotinine formation was the preferred metabolic pathway of nicotine already in non-induced organs. The pattern of nicotine metabolites was not altered by PB induction. In conscious PB-induced rats receiving nicotine orally or intravenously, 3'-hydroxycotinine was found as the main urinary metabolite of nicotine while only a small fraction was excreted as cotinine-N-oxide. This discrepancy between the profile of nicotine metabolites in perfused liver and lung and in the urine in vivo indicates that extrahepatic organs other than the lung may be important sites of cotinine metabolism.

Animals↗