Biomedical subjects

U Hofmann

Publications and source records attributed to U Hofmann.

At least 19 recordsLinked to original sources

PubMed1996

Prediction of CYP2D6-mediated polymorphic drug metabolism (sparteine type) based on in vitro investigations.

Discovery of genetic polymorphism in drug metabolism has contributed a great deal to understanding the variability in dose-concentration relationships introduced by genetic factors, thereby elucidating the mechanisms responsible for unexpected drug reactions. This knowledge should find its way into clinical practice in order to make therapy more efficient and safe. Moreover, genetic factors in drug metabolism should be taken into account during drug development. Therefore, in vitro methods for identifying the metabolic pattern of new compounds during early stages of drug development should be improved. This review summarizes in vitro methods available to identify genetic polymorphism in drug oxidation, in particular the CYP2D6-related polymorphism.

Animals↗

PubMed1996

Impact of quinidine on plasma and cerebrospinal fluid concentrations of codeine and morphine after codeine intake.

OBJECTIVE: The analgesic effect of codeine depends on its O-demethylation to morphine via sparteine oxygenase (CYP2D6) in the liver and presumably also via this enzyme in the CNS. We studied the ability of quinidine, which is a potent inhibitor of CYP2D6, to penetrate the blood brain barrier and its possible impact on codeine O-demethylation in CNS. METHODS: The study comprised 16 extensive and one poor metaboliser of sparteine, who underwent spinal anaesthesia for urinary tract surgery or examination. Eight patients were given an oral dose of 125 mg codeine and 9 patients (including the poor metaboliser) were given 200 mg quinidine 2 h before the same dose of codeine. Plasma and spinal fluid samples were collected 2 h after codeine intake. RESULTS: Free concentrations of quinidine were 11-times lower in cerebrospinal fluid than in plasma, and ranged from 9-15 nmol.l-1. Morphine concentrations were significantly lower in patients pre-treated with quinidine, both in plasma (median 1.45 nmol.l-1, range 0.74-1.95 nmol.l-1 vs 9.86 nmol.l-1, range 4.59-28.4 nmol.l-1) and in cerebrospinal fluid (0.23, 0.16-0.61 nmol.l-1 vs 3.63, 0.6-8.09 nmol.l-1). The morphine/codeine concentration ratio in plasma (3.07 x 10 (-3), 1.68-3.68 x 10 (-3) vs 19.87 x 10 (-3), 9.87-66.22 x 10 (-3) and in cerebrospinal fluid (0.83 d 10 (-3), 0.58-1.45 x 10 (-3) vs 7.19 x 10 (-3), 2.03-17.7 x 10 (-3) was also lower. The morphine/codeine concentration ratios were significantly lower in cerebrospinal fluid both without and with quinidine, but the difference between the plasma and spinal fluid ratio was significantly smaller with quinidine than without (p = 0.0002). CONCLUSION: Quinidine penetrates the blood brain barrier poorly, but quinidine pre-treatment leads to pronounced lowering of the cerebrospinal fluid concentration of morphine after codeine intake. However, the O-demethylation of codeine in CNS may not be totally blocked by quinidine.

Administration, Oral↗

PubMed1996

Antipyrine as a probe for human oxidative drug metabolism: identification of the cytochrome P450 enzymes catalyzing 4-hydroxyantipyrine, 3-hydroxymethylantipyrine, and norantipyrine formation.

BACKGROUND AND OBJECTIVE: Antipyrine has been widely used as a probe drug for human oxidative drug metabolism. To evaluate the role of antipyrine as a model drug, we have identified the cytochrome P450 enzymes involved in 4-hydroxyantipyrine, 3-hydroxymethylantipyrine, and norantipyrine formation. METHODS: We used the following methods for this study: (1) determination of enzyme kinetics for antipyrine metabolite formation in human liver microsomes, (2) inhibition studies with antibodies and inhibitors, and (3) formation of metabolites by stable expressed human P450 enzymes. RESULTS: Antipyrine biotransformation could be described by Michaelis-Menten kinetics: norantipyrine: maximum rate of metabolite formation (Vmax), 0.91 +/- 0.04 nmol . mg-1 . min-1; Michaelis-Menten constant (Km), 19.0 +/- 0.8 mmol/L; 4-hydroxyantipyrine: Vmax, 1.54 +/- 0.08 nmol . mg-1 . min-1;Km,39.6 +/- 2.5 mmol/L. Antibodies against CYP3A4 inhibited the formation of 4-hydroxyantipyrine by 25% to 65%. LKM-2 antibodies (anti-CYP2C) caused a 75% to 100% inhibition of norantipyrine and a 58% to 80% inhibition of 3-hydroxymethylantipyrine formation. Sulfaphenazole inhibited the formation of 3-hydroxymethylantipyrine and norantipyrine by about 50%. Furafylline and fluvoxamine inhibited norantipyrine, 4-hydroxyantipyrine, and 3-hydroxymethylantipyrine formation by about 30%, 30%, and 50%, respectively. Ketoconazole reduced formation of norantipyrine, 3-hydroxymethylantipyrine, and 4-hydroxyantipyrine by up to 80%. Formation in stable expressed enzymes indicated involvement of CYP1A2, CYP2B6, CYP2C, and CYP3A4 in metabolite formation. CONCLUSION: Antipyrine metabolites are formed by at least six hepatic cytochrome P450 enzymes (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C18, and CYP3A4). 4-Hydroxylation is mainly catalyzed by CYP3A4 and, to a lesser extent, by CYP1A2. The CYP2C subfamily contains the predominant enzymes for norantipyrine formation, and CYP1A2 is also involved. Formation of 3-hydroxymethylantipyrine is mediated by CYP1A2 and CYP2C9. Because several cytochrome P450 enzymes are involved in the formation of each metabolite, antipyrine is not well suited as a probe for distinct human cytochrome P450 enzymes.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1996

Disposition and first-pass metabolism of ethanol in humans: is it gastric or hepatic and does it depend on gender?

OBJECTIVE: To assess the extent and site of the first-pass metabolism of ethanol and to examine whether first-pass metabolism and disposition of ethanol are dependent on gender. METHODS: After a standardized lunch, healthy subjects (six women and six men) received on two separate occasions a 60-minute intravenous infusion of ethanol (0.3 gm/kg) and concomitantly an equimolar dose of d3-ethanol/kg either orally (over 20 minutes) or intraduodenally (infused over 30 minutes). Blood levels, urinary excretion of d0- and d3-ethanol, and sedative effects were monitored for 6 hours. Disposition and first-pass metabolism of ethanol were evaluated by applying an open two-compartment model with Michaelis-Menten elimination. RESULTS: Comparison of the corresponding intravenous/oral versus intravenous/intraduodenal data of each individual revealed that total first-pass metabolism (gastric plus hepatic) was not pronounced in either males (9.1% +/- 4.0%; mean +/- SD) or females (8.4% +/- 3.1%) and that this first-pass metabolism was partly of gastric origin. Dose-corrected values for area under blood concentration-time curve were on average 28% higher (p < 0.0001) in the women than in the men. Mean total blood ethanol disappearance rate was higher (p < 0.001) in women (3.92 +/- 0.40 mmol/L . hr) than in men (3.19 +/- 0.48 mmol/L . hr). Renal clearance was gender-independent and negligible. A linear relationship (p < 0.001) could be found between the blood levels of ethanol and sedation index. Because the slope was steeper in women (1.04) than in men (0.42) a higher central nervous system sensitivity to the sedative effects of ethanol in women can be assumed. CONCLUSIONS: Under realistic life conditions (social drinking of moderate doses of ethanol after a light lunch) only a minor, gender-independent first-pass metabolism is observed that is partly of gastric origin.

Administration, Oral↗

PubMed1996

Assessment of individual CYP2D6 activity in extensive metabolizers with renal failure: comparison of sparteine and dextromethorphan.

OBJECTIVES: To examine whether the variability of CYP2D6 activity in patients with chronic renal failure can be assessed, particularly among subjects with the extensive metabolizer phenotype, by use of standard in vivo indexes of CYP2D6 activity derived from oral administration of dextromethorphan and sparteine. METHODS: A single 100 mg oral dose of sparteine and a single 40 mg oral dose of dextromethorphan were administered on two occasions to 12 patients with chronic renal failure (creatinine clearance ranging from 20 to 70 ml/min) and 12 age- and sex-matched healthy subjects. Sparteine clearances, sparteine metabolic ratio, and urinary recovery of dextrorphan were calculated. Patients and healthy control subjects were not selected on the basis of their CYP2D6 phenotypes. RESULTS: Chronic renal failure was associated with a decrease in sparteine partial metabolic clearance to dehydrosparteine (median of 322 ml/min and range of 62 to 670 ml/min in patients with renal failure versus median of 635 ml/min and range of 77 to 1276 ml/min in normal subjects; p < 0.02). Sparteine apparent oral clearance (p < 0.03) and renal clearance (p < 0.001) decreased in patients with renal failure. However, sparteine metabolic ratio was not significantly altered in patients with renal failure and showed that all patients were extensive metabolizers of sparteine. Although fractional urinary excretion of dextrorphan decreased in patients with renal failure (median, 24.4%; range, 9.7% to 55.9%) compared with control (median, 47.5%; range, 24.1% to 72.1%) (p = 0.02), it also showed that all subjects were extensive metabolizers of dextromethorphan. The amount of dextromethorphan excreted in urine correlated with creatinine clearance independently from CYP2D6 activity measured as sparteine partial metabolic clearance. However, it did not correlate with sparteine metabolic ratio or with fractional urinary excretion of dehydrosparteine. CONCLUSION: Assessment of CYP2D6 activity by use of dextromethorphan and sparteine is possible in extensive metabolizer patients with chronic renal failure. However, in these subjects, dextromethorphan and sparteine do not reflect CYP2D6 activity in the same way.

Administration, Oral↗

PubMed1995

Direct gas chromatographic determination of dechloroethylcyclophosphamide following microsomal incubation of cyclophosphamide.

A method for the sensitive determination of dechloroethylcylclophosphamide (3-DCl) in microsomal incubation mixtures was developed. 3-DCl, a side-chain oxidation product of cyclophosphamide (CP), was isolated by extraction with acetic acid ethyl ester following solid-phase extraction on C8 cartridges. Quantification of the metabolite was performed by direct capillary gas chromatography with a nitrogen-phosphorus detector without prior derivatization. The method showed good sensitivity and reproducibility with a detection limit of 1 ng/ml and a limit of quantification of 5 ng/ml. The suitability of the method is shown for the quantification of 3-DCl following incubation of CP with human liver microsomes.

Animals↗

PubMed1995

Highly sensitive and specific gas chromatographic-tandem mass spectrometric method for the determination of trace amounts of antipyrine metabolites in biological material.

A highly sensitive and specific gas chromatographic-tandem mass spectrometric method was developed for the determination of the antipyrine (INN: phenazone) metabolites, norantipyrine, 4-hydroxyantipyrine and 3-hydroxy-methylantipyrine, in biological material. Deuterated analogues of the metabolites were used as internal standards. The method has a limit of quantitation of 5 ng per sample for the determination of norantipyrine, 4-hydroxy-antipyrine and 3-hyddroxymethylantipyrine with coefficients of variation of 19.4, 14.6 and 20.7%, respectively. Precision and accuracy are good over the whole range measured (5-500 ng/sample) with a coefficient of variation, respectively error of determination < or = 20%. Due to its high sensitivity the method can be used to study the formation of these metabolites in microsomal preparations containing only 100 micrograms of protein.

Animals↗

PubMed1995

Simultaneous determination of dihydrocodeine and dihydromorphine in serum by gas chromatography-tandem mass spectrometry.

A sensitive and specific method was developed for the determination of dihydrocodeine and its metabolite dihydromorphine in human serum using codeine and morphine as internal standards. Measurement is performed with GC-tandem MS after one simple extraction step and derivatization to the pentafluoropropionic esters. Sensitivity of the method is excellent and allows for the reproducible quantification of dihydrocodeine and dihydromorphine with limits of quantification of 2 ng/ml and 40 pg/ml serum, respectively. The method is therefore well suited for investigation of the pharmacokinetics and the metabolism of dihydrocodeine.

Codeine↗

PubMed1995

[Amelanotic nodular malignant melanoma of the vulva. Case report and review of the literature].

We describe a 55-year-old woman with an amelanotic nodular malignant melanoma of the vulva. The tumour had developed within 3 months. Physical examination showed a solid, erythematous, centrally depressed nodular tumour with a waxy appearance. It was 1.3 cm across and located on the right labium majus. The surface was eroded and showed teleangiectasias. Histopathological examination revealed a nodular malignant melanoma with predominantly spindle-shaped tumour cells, stage IV-V, and 7.2 mm thick. The primary tumour was excised but the patient died of generalized metastases 19 months later. There are very few reports on melanoma of the vulva in the dermatological literature. In addition to this case report we review the literature and discuss the clinical picture, histopathology and prognosis of this melanoma.

Female↗

PubMed1995

Dihydrocodeine: a new opioid substrate for the polymorphic CYP2D6 in humans.

BACKGROUND: The opioid dihydrocodeine (DHC) is frequently used as an analgesic and antitussive agent. However, until now there have been no detailed data on dihydrocodeine metabolism in humans. We therefore investigated pathways that contribute to elimination of dihydrocodeine, and we tested the hypothesis that dihydrocodeine O-demethylation to dihydromorphine (DHM) is catalyzed by the polymorphic CYP2D6. METHODS: A single oral dose of dihydrocodeine was administered to six extensive (metabolic ratio [MR] < or = 1), two intermediate (1 < MR < 20) and six poor metabolizers (MR > or = 20) of sparteine/debrisoquin. Serum concentrations of dihydrocodeine and dihydromorphine were measured up to 25 hours, and urinary excretion of conjugated and unconjugated dihydrocodeine, dihydromorphine, and nordihydrocodeine were determined. RESULTS: There were no differences in the pharmacokinetics of dihydrocodeine between extensive and poor metabolizers. However, the area under the serum concentration-time curve (AUC), partial metabolic clearance, and total urinary recovery of dihydromorphine were significantly lower in poor metabolizers (10.3 +/- 6.1 nmol.hr/L; 7.0 +/- 4.1 ml/min; 1.3% +/- 0.9% of dose) compared with extensive metabolizers (75.5 +/- 42.9 nmol.hr/L; 49.7 +/- 29.9 ml/min; 8.9% +/- 6.2%; p < 0.01). There was a strong correlation between the AUCDHC/AUCDHM ratio and the urinary metabolic ratio of sparteine (rS = 0.89, p = 0.001). No significant differences between extensive and poor metabolizers were detected in urine for conjugated dihydrocodeine (extensive metabolizers, 27.7% of dose; poor metabolizers, 31.5%), unconjugated dihydrocodeine (extensive metabolizers, 31.1%; poor metabolizers, 31.1%), conjugated nordihydrocodeine (extensive metabolizers, 6.3%; poor metabolizers, 5.4%), or unconjugated nordihydrocodeine (extensive metabolizers, 15.8%; poor metabolizers, 19.5%). CONCLUSIONS: Dihydrocodeine O-demethylation to dihydromorphine is impaired in poor metabolizers of sparteine. The main urinary metabolites after administration of dihydrocodeine are the parent compound and its conjugates in extensive and poor metabolizers.

Adult↗

PubMed1995

The effect of the timing and the administration of acarbose on postprandial hyperglycaemia.

To clarify the optimum timing for ingestion of acarbose, a 100 mg dose of this oral hypoglycaemic agent was administered 30 min before, at the beginning, and 15 min after ingestion of a test meal, and the effects of the drug on blood glucose rises were compared with increases observed after a control meal (no drug). Twenty-four patients with Type 2 diabetes were included in a randomized, open, cross-over study. The smallest increases in blood glucose (p < 0.001) occurred when acarbose was taken at the beginning and 15 min after starting the test meal (3.3 +/- 1.6 mmol l-1 and 3.3 +/- 1.4 mmol l-1). The increase in blood glucose levels when acarbose was taken 30 min before the test meal was significantly higher (4.2 +/- 1.8 mmol l-1) and it was at its maximum following the control meal (5.2 +/- 1.7 mmol l-1). Similar results were observed when the effects of acarbose on insulin and C-peptide levels were measured. It is recommended that patients should be instructed to take acarbose with their first mouthful of food.

Acarbose↗

PubMed1995

Identification of Actinobacillus actinomycetemcomitans in subgingival plaque by PCR.

The purpose of this study was to assess the sensitivity and specificity of the PCR in detecting Actinobacillus actinomycetemcomitans. The PCR's detection capability was compared with those of three other methods: culture-enhanced PCR (CE-PCR), colony hybridization (CH), and conventional culture with presumptive biochemical identification. A 285-bp stretch of the leukotoxin gene lktA of A. actinomycetemcomitans was amplified by PCR with primers TT-15 and TT-16. For CH, the PCR product was labeled with digoxigenin and used as a hybridization probe. Nucleotide sequence analysis of the PCR product of A. actinomycetemcomitans 1D4 and 1664 and three clinical isolates revealed complete homology among the tested strains, with only one base substitution (at position 1344) in comparison with the published sequence. With artificially infected subgingival plaque, the detection limit of PCR for A. actinomycetemcomitans was 10(3) CFU/ml of plaque suspension. Culturing subgingival plaque on tryptic soy-serum-bacitracin-vancomycin agar prior to PCR (CE-PCR) improved the limit of detection to 10(2) CFU/ml. Analysis of subgingival plaque samples from 35 patients with periodontal disease and 10 periodontally healthy subjects revealed that CE-PCR and CH had the highest overall rate of A. actinomycetemcomitans detection (both 58%), followed by PCR and culture (both 42%). With CH as the "gold standard", the sensitivities of CE-PCR, PCR, and culture were 88, 65, and 58%, respectively; the specificities were 84, 89, and 79%, respectively. The CE-PCR provided acceptable positive and negative predictive values (> or = 70%) when the prevalence of A. actinomycetemcomitans varied between 30 and 70%. PCR alone provided comparable predictive values over a narrower range of prevalence rates (30 to 50%), while culture did not afford acceptable predictive values at any prevalence rate. PCR and CE-PCR were found to be superior to culture with presumptive biochemical identification and should be the preferred methods for the detection of A. actinomycetemcomitans in subgingival plaque.

Aggregatibacter actinomycetemcomitans↗

PubMed1995

Immunoenzymometric assay of human glycogen phosphorylase isoenzyme BB in diagnosis of ischemic myocardial injury.

With a new immunoenzymometric assay we measured human glycogen phosphorylase isoenzyme BB (GPBB) in 116 healthy individuals, 14 patients with stable angina, 107 nontraumatic chest pain patients on admission to the emergency department [45 acute myocardial infarction (AMI), 49 unstable angina, 13 other diseases], and in serial samples from 41 AMI patients. GPBB was compared with creatine kinase (CK), CKMB mass, myoglobin, and cardiac troponin T. Receiver-operating characteristic plots demonstrated the significantly greater (P < or = 0.012) discriminatory power of GPBB to detect acute ischemic coronary syndromes compared with all other tested markers. GPBB was the most sensitive marker for detection of AMI during the first 4 h after onset of chest pain, and only GPBB was increased above the upper reference limit (7 micrograms/L) on admission in patients who had unstable angina at rest and reversible ST-T alterations. This and the high early sensitivity of GPBB are most likely explained by its function as a key enzyme of glycogenolysis.

Adult↗

PubMed1994

[Spinocellular cancer in lichen sclerosus et atrophicus of the vulva].

We report on a 78-year-old woman with a 47-year-history of lichen sclerosus et atrophicus of the vulva on which squamous cell carcinoma developed. The lesion started as a small nodule that increased gradually in size and became eroded. The tumour and the inguinal lymph nodes on both sides were excised. Physical examination, chest X-ray and sonography of the abdomen 15 months later showed no local recurrence or distant metastases. Lichen sclerosus et atrophicus of the vulva should be considered a possible precancerous condition.

Aged↗

PubMed1994

[Amelanotic polypoid malignant melanoma of the balloon cell type].

We describe a 59-year-old woman with amelanotic polypoid balloon cell melanoma. Physical examination showed exophytic erythematous tumour simulating a basal cell carcinoma or an adnexal tumour. Histopathology revealed a polypoid tumour that was composed mainly of balloon cells in sheets and nests. Examination 37 months after excision of the tumour with 3 cm safety margins disclosed no evidence of enlarged lymph nodes or cutaneous metastases. Metastases to internal organs could not be assessed because the patient repeatedly refused further examination for staging. To our knowledge our patient is the first case of amelanotic polypoid balloon cell melanoma to be reported in the German literature.

Antigens, Neoplasm↗

PubMed1994

Distribution and changing density of gamma-delta T cells in murine skin during the induced hair cycle.

Gamma-delta T cells (gdTC) are recognized as the predominant intraepidermal T-cell population in murine skin, although their physiological functions are still unclear. Little is known of the exact distribution of gdTC in the other epithelial skin compartments of normal mice. Using selective gdTC-receptor antibodies in immunohistology (alkaline phosphatase technique), the distribution and density of gdTC was analysed morphometrically in cryostat sections of full-thickness back skin of normal, adolescent C57 BL-6 mice in all the different stages of the depilation-induced hair cycle. We found that, during the entire hair cycle, V gamma 3-TCR-bearing lymphocytes are restricted to the epidermis, and to the epithelial hair bulb in, and distal to, the bulge area. No gdTC were seen in the sebaceous glands. During early anagen development, the number of pan-gdTC receptor-positive cells increased significantly (P < 0.005) in the interfollicular epidermis and the suprainfundibular portion of the hair bulb, whereas the number decreased in the infrainfundibular region (P < 0.005). As gdTC are thought to migrate into the skin only during embryogenesis, this finding suggests hair cycle-dependent, differential intraepithelial proliferation of gdTC in murine skin. We advocate employing only skin of defined hair cycle stages in immunological studies on murine skin, and discuss the value of the C57 BL-6 model for assessing the functions of gdTC in skin and hair biology.

Animals↗

PubMed1994

Expression of classical and non-classical MHC class I antigens in murine hair follicles.

Not all keratinocytes in human and rat hair follicles express MHC class I antigens (MHC I). In the present study, we report the first immunohistological profile of classical and non-classical MHC I expression in the skin of adolescent C57 BL-6 mice during the induced hair cycle. MHC I immunoreactivity (H-2b, H-2Db) is absent in the matrix and inner root sheath of growing (= anagen) hair follicles, and the dermal papillae are H-2b negative during catagen and telogen. This lack of normal MHC I expression may serve to sequester potentially damaging autoantigens from immune recognition. In addition, we present the first evidence of non-classical MHC class I antigen expression in normal mammalian skin: during the entire hair cycle, the distal hair follicle shows strong Qa-2 immunoreactivity, which appears to be restricted to an epithelial follicle compartment densely populated by gamma-delta T cells with which Qa-2 molecules may interact as part of a primitive antibacterial defense system of the follicle. The murine hair cycle is an attractive model for dissecting the functional roles of H-2b and Qa-2 molecules in hair biology and in related tissue-interaction systems.

Animals↗

PubMed1994

Alkaline phosphatase activity and localization during the murine hair cycle.

For unknown reasons, the pilosebaceous unit displays prominent alkaline phosphatase (AP) activity, and alterations in AP activity are seen in alopecia areata. The role of AP in hair biology and pathology has been obscured by contradictory reports on the localization and activity of AP during the hair cycle, and by a paucity of instructive models for studying AP functions. Using the C57 BL-6 mouse model for hair research, we have characterized endogenous AP with a simple histochemical developing solution routinely employed for AP immunohistology. This method was selective for AP, and revealed distinctive hair cycle-dependent changes in AP activity and localization. Although the dermal papilla displays unusually strong AP activity during the entire hair cycle, the outer root sheath is AP-positive only during late anagen and early catagen. Strong, rather homogeneous AP activity is seen in the sebaceous gland (SG) only during catagen and telogen. This AP staining pattern indicates hair cycle-dependent changes in SG functions, and differs to some extent from the previously reported AP activity during the hair cycle of various species. We propose a simple and effective technique for follicle classification based on the AP histochemistry of dermal papilla and sebaceous gland, and discuss uses of the C57 BL-6 mouse model for functional AP studies.

Alkaline Phosphatase↗