Biomedical subjects

R Herber

Publications and source records attributed to R Herber.

At least 19 recordsLinked to original sources

PubMed2000

Microseismological evidence for a changing wave climate in the northeast Atlantic Ocean.

One possible consequence of a change in climate over the past several decades is an increase in wave heights, potentially threatening coastal areas as well as the marine industry. But the difficulties in observing wave heights exacerbates a general problem of climate-change detection: inhomogeneities in long-term observational records owing to changes in the instruments or techniques used, which may cause artificial trends. Ground movements with periods of 4-16 seconds, known as microseisms, are associated with ocean waves and coastal surf, and have been recorded continuously since the early days of seismology. Here we use such a 40-year record of wintertime microseisms from Hamburg, Germany, to reconstruct the wave climate in the northeast Atlantic Ocean. For the period 1954-77, we detect an average of seven days per month with strong microseismic activity, without a significant trend. This number increases significantly in the second half of the record, reaching approximately 14 days of strong microseisms per month. The implied increase in northeast Atlantic wave height over the past 20 years parallels increased surface air temperatures and storminess in this region, suggesting a common forcing.

Journal Article↗

PubMed2000

Differential oxidation of apolipoprotein E isoforms and interaction with phospholipids.

Accumulation of oxidized proteins has been demonstrated in the brain of patients suffering from Alzheimer's disease (AD). Among the proteins found in cerebral amyloid deposits, apolipoprotein (apo) E is a polymorphic protein which one specific isoform, apo E4, has been widely associated with AD. Apo E may be linked with AD by its isoform-specific interaction with lipids or other proteins in amyloid plaques. Using the myeloperoxidase oxidative system, we report that oxidation of the three recombinant apo E isoforms is differential (as estimated using immunoblot and high-performance liquid chromatography analysis), with apo E4 being more susceptible than apo E3, which in turn is much more susceptible than apo E2. In addition, susceptibility to thrombin proteolysis is reduced when apo E is oxidized, and oxidation of apo E decreases its incorporation into phospholipid discs by approximately 50%. Oxidation of apo E may contribute to inefficient lipid recycling in the brain, particularly regarding apo E4 and E3. Our results link and strengthen both the E4 allele linkage with AD and the role of protein oxidation in AD. The cerebral mechanisms underlying apo E oxidation and/or myeloperoxidase functions in vivo remain to be assessed.

Alleles↗

PubMed1999

Characterization of the UDP-glucuronosyltransferases involved in the glucuronidation of an antithrombotic thioxyloside in rat and humans.

To investigate the glucuronidation on the hydroxyl group of carbohydrate-containing drugs, the in vitro formation of glucuronides on the thioxyloside ring of the antithrombotic drug, LF 4.0212, was followed in rat and human liver microsomes and with recombinant UDP-glucuronosyltransferases (UGT). The reaction revealed a marked regioselectivity in rat and humans. Human liver microsomes glucuronidated the compound mainly on the 2-hydroxyl position of the thioxyloside ring, whereas rat was able to form glucuronide on either the 2-, 3-, or 4- hydroxyl group of the molecule, although to a lower extent. LF 4.0212 was a much better substrate of human UGT than the rat enzyme (Vmax/Km 30.0 and 0.06 microl/min/mg, respectively). Phenobarbital, 3-methylcholanthrene, and clofibrate enhanced the glucuronidation of LF 4.0212 on positions 2, 3, and 4 of the thioxyloside ring, thus indicating that several UGT isoforms were involved in this process. The biosynthesis of the 2-O-glucuronide isomer was catalyzed by the human UGT1A9 and 2B4, but not by UGT1A6 and 2B11. By contrast, the rat liver recombinant UGT1A6 and 2B1 failed to form the 2-O-glucuronide isomers. From all the recombinant UGTs tested, none catalyzed the formation of the 3-O-glucuronide isomer. Interestingly, glucuronidation on the 4-position was found in all the metabolic competent V79 cell lines considered, including the nontransfected V79 cells, suggesting the presence of an endogenous UGT in fibroblasts able to actively glucuronidate the drug. This activity, which was nonsensitive to the inhibitory effect of 7,7,7-triphenylheptanoic acid, a potent UGT inhibitor, could reflect the existence of a different enzyme.

Animals↗

PubMed1998

Species-dependent enantioselective glucuronidation of carprofen.

1. The stereoselective glucuronidation of carprofen, a non-steroidal anti-inflammatory drug, was investigated in vitro using microsomes prepared from liver of different species (rat, dog, horse, sheep and man) or UGT2B1 expressed in fibroblasts. 2. The Km towards the drug was very similar among these species and for the two enantiomers, whereas the Vmax varied substantially according to the animal used. The rat exhibited a high stereoselective glucuronidation whereas other species, including man, presented a low stereoselectivity. The R-enantiomer was glucuronidated at a more efficient rate than its enantiomorph, and was a better substrate (in terms of Vmax/Km). 3. To explain the enantioselective disposition of carprofen in man and in the different species, the ratio of the enzymatic efficacies (Vmax/Km) were compared with the ratio of the pharmacokinetic parameters AUCs. The basic hypothesis that the intrinsic clearance reflect the enantioselective behaviour of carprofen seemed substantiated when we focused on man and rat glucuronidation, but the in vivo-in-vitro correlation was not possible in other species. 4. In conclusion, the chiral pharmacokinetics of carprofen is less dependent on the stereoselective glucuronidation than other stereoselective processes such as protein binding of carprofen, enzymatic hydrolysis, or renal elimination of glucuronides.

Animals↗

PubMed1998

Effect of cigarette smoke on UDP-glucuronosyltransferase activity and cytochrome P450 content in liver, lung and kidney microsomes in mice.

The effect of cigarette smoke on the expression of several cytochromes P450 (CYP) and UDP-glucuronosyl-transferases (UGT) was studied in mice. The animals were exposed to cigarette smoke for 4 to 30 days. Enzymatic activities supported by CYP1A1, 1A2, 2B, 2E1 and the glucuronidation activity toward phenols were measured in lung, liver and kidney microsomes. Cigarette smoke induced several CYPs, especially in lung. CYP2E1 was more induced than CYP1A1 in this organ. The expression of CYP2E1 was also increased in kidney (5.6 times after 30 days). The glucuronidation in kidney was non-sensitive to the treatment whatever substrate used. In contrast, this activity was enhanced in liver and particularly in lung, in which the glucuronidation of 1-naphthol and 2-hydroxybiphenyl was increased by 122 and 180%, respectively. Interestingly, the times of induction differed according to the substrate used, thus suggesting the presence of different UGTs active toward phenols that were differentially affected by cigarette smoke. The UGT activities toward phenols were low in lung, when compared with those measured in liver or kidney. In conclusion, cigarette smoke greatly affected both glucuronidation activity and the hydroxylation reactions supported by CYPs in mouse liver and lung.

Animals↗

PubMed1996

Squamous epithelial hyperplasia and carcinoma in mice transgenic for the human papillomavirus type 16 E7 oncogene.

The human papillomavirus type 16 (HPV-16) genome is commonly present in human cervical carcinoma, in which a subset of the viral genes, E6 and E7, are expressed. The HPV-16 E6 and E7 gene products can associated with and inactivate the tumor suppressor proteins p53 and Rb (the retinoblastoma susceptibility gene product), and in tissue culture cells, these viral genes display oncogenic properties. These findings have led to the hypothesis that E6 and E7 contribute to cervical carcinogenesis. This hypothesis has recently been tested by using transgenic mice as an animal model. HPV-16 E6 and E7 together were found to induce cancers in multiple tissues in which they were expressed, including squamous cell carcinoma, the cancer type most commonly associated with HPV-16 in the human cervix. We have extended these studies to investigate the in vivo activities of HPV-16 E7 when expressed in squamous epithelia of transgenic mice. Grossly, E7 transgenic mice had multiple phenotypes, including wrinkled skin that was apparent prior to the appearance of hair on neonates, thickened ears, and loss of hair in adults. In lines of mice expressing higher levels of E7, we observed stunted growth and mortality at an early age, potentially caused by an incapacity to feed. Histological analysis demonstrated that E7 causes epidermal hyperplasia in multiple transgenic lineages with high penetrance. This epithelial hyperplasia was characterized by an expansion of the proliferating compartment and an expansion of the keratin 10-positive layer of cells and was associated with hyperkeratosis. Hyperplasia was found at multiple sites in the animals in addition to the skin, including the mouth palate, esophagus, forestomach, and exocervix. In multiple transgenic lineages, adult animals developed skin tumors late in life with low penetrance. These tumors arose from the squamous epithelia and from sebaceous glands and were characterized histologically to be highly differentiated, locally invasive, and aggressive in their growth properties. On the basis of these phenotypes, we conclude that HPV-16 E7 can alter epithelial cell growth parameters sufficiently to potentiate tumorigenesis in mice.

Animals↗

PubMed1995

Reduction and glucuronidation of naftazone by human and rat liver microsomes.

Reduction and glucuronidation of the vasoprotectant drug, naftazone, by human and rat liver microsomes and by recombinant UDP-glucuronosyltransferases (UGT) stably expressed in V79 cells were studied. The oxo group was first reduced in the presence of NADPH or NADH, and was subsequently readily glucuronidated on the phenolic moiety leading to a 1 beta-O-glucuronide, as revealed from MS and by proton and 13C-NMR. Glucuronide extracted from the urine of rats treated with the drug presented the same structure. In all enzyme systems tested, NADH was the most efficient electron donor, when compared with NADPH. The reaction was strongly inhibited by quercitrin, a specific inhibitor of carbonyl reductase. Attempts to isolate the reduced intermediate were unsuccessful because of its marked instability. In humans, a large interindividual variation for the formation of glucuronide was observed with microsomes of seven different liver samples (3.98 +/- 3.22 nmol/min.mg). In rat, glucuronidation of reduced naftazone was strongly induced (12-fold) by 3-methylcholanthrene and, to a lesser extent (2.6-fold) by phenobarbital, but was not affected by clofibrate. In addition, liver microsomes from Gunn rats, which present a genetic defect in bilirubin and phenol UGTs could not form glucuronide of reduced naftazone. The drug, after addition of NADH, was a substrate of the human liver recombinant UGT1*6 that presents a strict specificity toward planar phenolic substances, but not that of UGT2B4 and UGT2B1 expressed in V79 fibroblasts. The reducing step by the endogenous V79 cellular reductase was rate-limiting. In conclusion, the powerful inducing effect exerted by 3-methylcholanthrene, the lack of glucuronidation in the Gunn rat and the ability of UGT1*6 encoded by the UGT1 gene to glucuronidate reduced naftazone suggest that, in humans and in the rat, the compound is metabolized by a UGT isoform (UGT1*6 and the rat orthologous form) belonging to family 1, with a restricted specificity toward the drug.

Adult↗

PubMed1994

The chemical modification of human liver UDP-glucuronosyltransferase UGT1*6 reveals the involvement of a carboxyl group in catalysis.

The treatment of UDP-glucuronosyltransferase UGT1*6 stably expressed in V79 cells with three carboxyl-specific reagents, dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and N-ethyl-5-phenylisoxazolium-3'-sulfonate (Woodward's reagent K), resulted in a fast, dose-dependent decrease of the 4-methylumbelliferone glucuronidation. The inactivation reactions followed pseudo-first order kinetics. The pKa of the modified residue was close to 5.0. A partial protection against inactivation by Woodward's reagent was observed at pH 7.4 in the presence of UDP-glucuronic acid, UDP, and, to a lesser extent, in the presence of 4-methylumbelliferone. Dicyclohexylcarbodiimide significantly decreased the Vmax, without affecting the apparent Km towards UDP-glucuronic acid and 4-methylumbelliferone. The results support the involvement of a carboxyl group in the catalytic process.

Catalysis↗

PubMed1993

Differential effects of human recombinant interleukin-1 beta and dexamethasone on hepatic drug-metabolizing enzymes in male and female rats.

Interleukin-1 beta (IL-1) is one of the major inflammation mediators, commonly reported to be an inhibitor of hepatic drug metabolism. We studied the effect of IL-1 treatment on various drug-metabolizing enzymes in male and female rats. IL-1 induced both cytochrome P450 (P450) 3A1 activity and protein in females, but in males, IL-1 repressed P450 3A2 activity, without decreasing the protein. P450 1A1 was impaired in males, but was retained after dexamethasone pretreatment. IL-1 did not change P450 2B1/2 activity and protein, but counteracted their induction by dexamethasone. Uridine diphospho-glucuronosyltransferase (UGT) 1A2 (bilirubin) activity and its induction by dexamethasone were not affected by IL-1 treatment. Both P450 2C11 and epoxide hydrolase activities were repressed by IL-1 treatment, and both activities were impaired after dexamethasone treatment. These results clearly demonstrate that IL-1 acts at different steps of protein synthesis and gene expression. The effect of IL-1 on P450 was isoform-dependent, indicating that IL-1 can act on pretranscriptional events. The discrepancy between the variations of the activities and the protein of P450 3A2 suggests a post-translational regulation. For P450 2C11, 3A1, and for microsomal epoxide hydrolase, but not for P450 1A1 and 2B1/2, IL-1 mimics the glucocorticoid effects. These differential effects can affect the kinetics and the bioavailability of drugs used in pathologies in which IL-1 is increased.

Animals↗

PubMed1993

Tumorigenicity by human papillomavirus type 16 E6 and E7 in transgenic mice correlates with alterations in epithelial cell growth and differentiation.

The human papillomavirus type 16 (HPV-16) E6 and E7 oncogenes are thought to play a role in the development of most human cervical cancers. These E6 and E7 oncoproteins affect cell growth control at least in part through their association with and inactivation of the cellular tumor suppressor gene products, p53 and Rb. To study the biological activities of the HPV-16 E6 and E7 genes in epithelial cells in vivo, transgenic mice were generated in which expression of E6 and E7 was targeted to the ocular lens. Expression of the transgenes correlated with bilateral microphthalmia and cataracts (100% penetrance) resulting from an efficient impairment of lens fiber cell differentiation and coincident induction of cell proliferation. Lens tumors formed in 40% of adult mice from the mouse lineage with the highest level of E6 and E7 expression. Additionally, when lens cells from neonatal transgenic animals were placed in tissue culture, immortalized cell populations grew out and acquired a tumorigenic phenotype with continuous passage. These observations indicate that genetic changes in addition to the transgenes are likely necessary for tumor formation. These transgenic mice and cell lines provide the basis for further studies into the mechanism of action of E6 and E7 in eliciting the observed pathology and into the genetic alterations required for HPV-16-associated tumor progression.

Animals↗

PubMed1993

International project for producing reference values for concentrations of trace elements in human blood and urine--TRACY.

In assessing the concentrations of toxic metals, such as cadmium, chromium, and mercury, in human blood and urine samples to determine whether they are abnormal or not, reliable reference values are needed from populations of nonoccupationally exposed subjects. Numerous publications present concentrations claimed to be typical for the study populations, but they can differ by up to an order of magnitude for a particular element. This is the consequence of general problems that are related to the definition of the reference groups, and the sampling and analytical procedures used, and that make it difficult to define typical and unbiased values. An international group of experts now establishes criteria and procedures to evaluate publications containing information on the concentrations of metals in tissues and body fluids for reference populations. These evaluations have been compiled in a data base (TRACY).

Hazardous Substances↗

PubMed1993

Interleukin-1 beta differentially represses drug-metabolizing enzymes in arthritic female rats.

Experimental arthritis and inflammation have been reported to reduce liver cytochrome P-450-dependent mono-oxygenase activities with subsequent impairment of drug metabolism. Interleukin-1 beta (IL-1) is among the proven mediators of both inflammation and P-450 decrease, although some paradoxical effects were sometimes reported in experimental models of arthritis. The aim of the present study was to evaluate the main liver drug-metabolizing isoenzymes during established collagen-induced arthritis in rats, and to investigate whether a systemic IL-1 treatment was able to mimic or sometimes to reverse the influence of the inflammatory process on these enzymes. Arthritis was induced on day 0 by type II collagen and a low dose (0.2 mg) of N-acetylmuramyl-L-alanyl-D-isoglutamine, and human recombinant IL-1 was administered s.c. at the daily dose of 0.02, 0.2 or 2.0 micrograms per arthritic rat, from day 21 to 25 and on day 28. Ethoxyresorufin-O-deethylation was depressed 6-fold in arthritic rat liver microsomes and the highest dosage of IL-1 potentiated this depression. Pentoxyresorufin-O-deethylation decreased by 50% in arthritic rat, a dose-dependent decrease being observed after IL-1 treatment. Progesterone 6 beta-hydroxylation and P-450 IIIA protein increased by 2-fold in both untreated arthritic rat liver microsomes and those treated by the lowest dose of IL-1. The two higher doses decreased this activity, vs. the dose, to reach the naive level. Lauric acid hydroxylation increased 2-fold in arthritic rat and was further potentiated by IL-1. UDP glucuronosyl transferase IA2 activity was increased 2-fold in arthritic rats, with subsequent decrease after 2.0 micrograms of IL-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylmuramyl-Alanyl-Isoglutamine↗

PubMed1992

Glucuronidation of 3'-azido-3'-deoxythymidine in human liver microsomes: enzyme inhibition by drugs and steroid hormones.

The molecular form of UDP-glucuronosyltransferase involved in the catalysis of 3'-azido-3'-deoxythymidine (AZT)-5'-O-glucuronide was characterized in human liver microsomes. The specific activity (1.3 nmol/min per mg protein) in transplantable liver was more than 2-times higher than in post-mortem fragments. Liver microsomes from patients suffering Crigler-Najjar syndrome, who are genetically deficient in bilirubin UDP-glucuronosyltransferase, could also glucuronidate AZT to a similar extent, thus indicating that this protein was not involved in that process. A genetically engineered V79 cell line stably expressing a cDNA which encodes a human isozyme active towards 1-naphthol was unable to glucuronidate AZT. Clinically used drugs, most of them being glucuronidated, were tested as potential inhibitors of the glucuronidation of AZT in human liver microsomes. The drugs chemically related to 2-phenylpropionic acid, naproxen and flurbiprofen, and the steroid compounds testosterone, estrone and ethynylestradiol strongly inhibited AZT glucuronidation. Codeine and morphine also decreased the reaction rate although to a lower extent. Except estrone which elicited a partial competitive inhibition, ethynylestradiol, flurbiprofen naproxen and testosterone could competitively inhibit AZT glucuronidation with an apparent Ki of 38, 50, 172 and 250 microM, respectively. The results suggest that these drugs were substrates of the same isozyme(s) involved in AZT glucuronidation. Probenecid was a weak inhibitor of the reaction (Ki 900 microM), only when non-disrupted microsomes were used. This drug may compete with the anion carrier system involved in the microsomal uptake of UDP-glucuronic acid.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1992

Induction of a mucosal barrier to bovine herpesvirus 1 replication in cattle.

Current vaccines for human and animal herpesviruses engender an immunity that may ameliorate disease but generally fails to prevent infection, latency, reactivation from latency, or spread through a population. By administering intranasally to cattle bovine herpesvirus type 1 virion envelope proteins combined with the potent mucosal immune system adjuvant, cholera toxin B subunit, we engendered a local antibody response that acted as a barrier to infection of mucosal epithelial cells and thereby prevented viral replication, consequently precluding disease, latency, and spread.

Animals↗

PubMed1992

In vitro N-glucuronidation of a novel antiepileptic drug, lamotrigine, by human liver microsomes.

The metabolism of the antiepileptic drug lamotrigine was characterized in human liver microsomes. For that purpose a high performance liquid chromatography method allowing the separation of lamotrigine glucuronide from the parent compound, and the quantitation of the glucuronide, was developed. The drug undergoes glucuronidation on the 2-nitrogen atom of the triazine ring, leading to a quaternary ammonium-linked glucuronide. This metabolite was positively identified from its hydrolysis by beta-glucuronidase and its associated radioactivity when UDP-[U-14C] glucuronic acid was used as the cosubstrate. Structural confirmation of the glucuronide was finally obtained by high performance liquid chromatography-mass spectrometry, by using a thermospray interface. The reaction proceeded with an apparent Vmax of 0.65 nmol/min/mg and Km of 2.56 mM. The average value of lamotrigine glucuronidation in four human samples of transplantable liver was 0.43 +/- 0.14 nmol/min/mg, thus indicating a large interindividual variation. An interspecies comparison of hepatic lamotrigine glucuronidation (human, rabbit, rat, monkey) revealed that the rate of glucuronidation was low. Of all the species considered, humans glucuronidated the drug to the greatest extent, with a specific activity 2-fold higher than that observed in rabbit liver microsomes. In contrast, the activity was greater than 20 times lower in monkey (0.019 nmol/min/mg) and at the limit of detection in rat liver microsomes. However, in this species, phenobarbital treatment enhanced lamotrigine glucuronidation slightly (0.017 nmol/min/mg). Among the drugs that undergo quaternary ammonium-linked glucuronidation, chlorpromazine, but not imipramine, amitriptyline and cyproheptadine, inhibited the glucuronidation of lamotrigine in vitro (IC50 of 5.0 x 10(-4) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Effects of RP 52028 and phenobarbital on mRNA levels of inducible and constitutive sex-specific cytochrome P450 isozymes in rat liver.

Sex-related differences in basal levels of mRNA coding for various cytochrome P450 isozymes and their inducibility by 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3- isoquinoline carboxamide (RP 52028) in comparison to phenobarbital (PB) were investigated in Sprague-Dawley rats. We observed that the inducible isozymes, namely cytochromes P450IIB1/2 and P450IIIA1/2 were barely detectable in non-induced animal livers. On the contrary, mRNAs coding for two constitutive forms of cytochrome, P450IIC7 and IIC11, were expressed at a high level in untreated rats in a sex-dependent manner. Cytochrome P450IIC11 mRNA was present in male rats only whereas P450IIC7 was expressed in both sexes but at a higher level in female rats. RP 52028 had a dose-dependent inducing effect on the P450IIB1/2 and IIIA1/2 isoforms in both sexes. After administration of a high dose (500 mg/kg), this molecule exhibited a pattern of induction similar to that of PB. Increases in the accumulation of these IIB1/2 and IIIA1/2 messengers were correlated with protein data, suggesting that RP 52028, like PB, induces these isozymes mainly through a pretranslational regulatory mechanism. On the other hand, PB and RP 52028 caused only a slight increase, less pronounced than in Wistar rats, in the mRNA level of the constitutive female-predominant P450IIC7, indicating a strain-related difference in inducibility of this isozyme. RP 52028 had no effect on P450IIC11 mRNA level in male rat liver, in contrast to the decreasing effect obtained with PB. Furthermore, the non-correlated changes in P450IIC11 mRNA level and microsomal testosterone 2 alpha-hydroxylase activity after treatment with RP suggests that this molecule modulates the expression of P450IIC11 at a posttranscriptional level only.

Animals↗

PubMed1991

Identification of novel phencyclidine metabolites formed in vitro by rabbit microsomal metabolism.

1. Phencyclidine (PCP) was incubated with rabbit liver and brain microsomal fractions, and the structures of metabolites formed by oxidation determined by g.l.c.-mass spectrometry. 2. The formation of several known mono- and di-hydroxylated metabolites, as well as two new metabolites, was seen in the liver preparations. 3. Hydroxylated PCP metabolites were also formed after incubation of PCP with brain microsomes, indicating that PCP biotransformation may occur in the brain itself.

Animals↗

PubMed1987

Influence of occupational low-level lead exposure on renal parameters.

The influence of lead exposure on renal function was examined. In 155 lead workers and 126 control workers, lead in blood (PbB) and zinc protoporphyrin in blood (ZPP) were measured as indicators of exposure to lead; various proteins in urine were measured as parameters of renal functions. Regression and matched-pair analyses suggest that tubular parameters may be more influenced by lead exposure than glomerular parameters. Changes in renal function parameters may already occur at PbB levels below 3 mumol/liter (600 micrograms/liter). The excretion of N-acetyl-beta-D-glucosaminidase appears to be the most consistent and sensitive parameter of an early effect on the tubular function.

Adult↗