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Biomedical subjects

H Frank

Publications and source records attributed to H Frank.

At least 55 records · Page 3Linked to original sources
PubMed1998

Detoxification of optically active bay- and fjord-region polycyclic aromatic hydrocarbon dihydrodiol epoxides by human glutathione transferase P1-1 expressed in Chinese hamster V79 cells.

Dihydrodiol epoxides (DEs) are important carcinogenic metabolites of polycyclic aromatic hydrocarbons (PAHs). The metabolic formation of four stereoisomeric DEs (a pair of optically active diastereomers termed as syn- and anti-form) is possible. Glutathione tranferases (GSTs) have been demonstrated to catalyze the detoxification of DEs. Purified GSTs display remarkable differences in catalytic efficiencies towards bay- and fjord-region DEs along with a high degree of regio- and stereoselectivity. Here we determined to which extent heterologously expressed human GSTP1-1, a major GST isoform in lung, affects the mutagenicity of stereoisomeric bay-region DEs of benzo[a]pyrene in Chinese hamster V79 cells. To evaluate the influence of sterical crowding in the substrate on the activity of GSTP-1, the study was extended to the strongly mutagenic fjord-region (-)-anti-DEs of benzo[c]phenanthrene and dibenzo[a,l]pyrene. GSTP1-1,reduced preferentially the mutagenicity (studied at the hprt locus) of (+)-anti and (+)-syn-DEs of benzo[a]pyrene (by 66 and 67%) as compared with the corresponding (-)-anti- and (-)-syn-enantiomers (by 15 and 13%). These results are in line with previous studies on the enantioselectivity of purified GSTP1-1 towards the DE isomers of benzo[a]pyrene and benzo[c]phenanthrene showing that enantiomers with (R)-configuration at the benzylic oxiranyl carbon are better substrates than those with (S)-configuration. Interestingly, the (-)-anti-DEs of benzo[c]phenanthrene and dibenzo[a,l]pyrene were efficiently detoxified by GSTP-1-1 in the constructed cell line (reduction of mutagenicity by 66 and 64%). This study demonstrates that differences in the caalytic activity seen for purified GST towards individual mutagens do not necessarily reflect the detoxification of DEs by the same enzyme in a living cell and provides further evidence that specific human GSTs play a role in the detoxification of DEs of PAHs.

Animals↗
PubMed1998

Efficacy of thrombolytic therapy in pulmonary embolism determined by MION-enhanced MRA: an experimental study in rabbits.

RATIONALE AND OBJECTIVES: This study determined whether contrast-enhanced magnetic resonance angiography could be used as a noninvasive imaging technique to determine the therapeutic effect and endpoint in thrombolysis of acute pulmonary embolism in an animal model. METHODS: New Zealand white rabbits (n = 18) were anesthetized and mechanically ventilated. Single (n = 12 emboli) or dual (n = 12 emboli in 6 animals) pulmonary emboli were created by injecting autologous thrombi through a right internal jugular venous approach. Three-dimensional time of flight (TOF) magnetic resonance angiograms were obtained after intravenous administration of 2 mg Fe of a long circulating monocrystalline iron oxide. Animals then received 5000 IU heparin and 1.3 mg recombinant tissue plasminogen activator/kg intravenously, and magnetic resonance angiography was repeated 30 minutes and 60 minutes after initiation of thrombolytic therapy. RESULTS: MION-enhanced magnetic resonance angiography accurately detected pulmonary emboli in all rabbits. Thrombolysis during the observation period was successful in 8 of the 18 animals. In animals with a single embolus, the revascularization rate was 50% (6 of 12 emboli). The rate was 33% (4 of 12 emboli) in animals with multiple emboli. Magnetic resonance angiography allowed determination of thrombus resolution or thrombus persistence. CONCLUSIONS: It was feasible to diagnose pulmonary embolism accurately in this experimental study and to monitor thrombolysis of pulmonary emboli by MION-enhanced magnetic resonance angiography.

Acute Disease↗
PubMed1998

[Is combination therapy of chronic hepatitis C with interferon alpha and ribavirin in primary interferon nonresponders indicated?--An analysis of personal experiences and review of the literature].

Combination therapy of chronic hepatitis C with interferon alpha and ribavirin has been proven to be highly effective in naive and relapse patients with two to ten-fold increase of the response rate. However, combination therapy of primary non-responders to interferon alpha is discussed controversially. Therefore, to analyze the response rate to retreatment with a combination therapy with interferon alpha and ribavirin, we compared data of 555 patients described in 23 publications to the data of 16 non-responders treated in our center. The patients received interferon alpha (at least 3 MU tiw) and ribavirin in a dose of 1,000/1,200 mg per day. At the end of treatment 14% of our patients had normal ALT values and were HCV-RNA-negative compared to 34% of all patients described in the literature. In our patients the viral load decreased from 1,110 +/- 670 x 10(3) copies/ml prior to therapy to 300 +/- 480 x 10(3) copies/ml at the end of treatment (p = 0.002). After a follow-up period of six months quantitative RNA-levels rose again to 1,485 +/- 755 x 10(3) copies/ml. Whereas only 7.4% (24/325) of all patients described showed a response with normal ALT values and negative HCV-RNA at the end of follow-up, no sustained response was observed in our patients. In contrast to naive and relapse patients, the response rate of combination therapy in patients previously not responding to interferon alpha alone is only low. Thus, standard regime (IFN 3MU twi plus ribavirin for six months) as a regular therapy for non-responders is not recommended.

Adult↗
PubMed1997

Significance of morphological abnormalities detected by MRI in patients undergoing successful ablation of right ventricular outflow tract tachycardia.

BACKGROUND: MRI can demonstrate subtle morphological changes of the right ventricle in patients with idiopathic right ventricular outflow tract tachycardia (RVOT). The present study examines the incidence and significance of right ventricular (RV) abnormalities detected by MRI with respect to the site of successful radiofrequency catheter ablation of the clinical tachycardia. METHODS AND RESULTS: The study population comprised 20 patients (mean age, 40+/-12 years) undergoing elimination of recurrent RVOT by radiofrequency catheter ablation. MRI studies were performed before ablation to assess RV volumes and function, as well as structural abnormalities of the RV myocardium. Ten healthy age- and sex-matched subjects served as control subjects. The successful ablation sites, as documented by radiographs of the catheter position, were compared with MRI findings. Patients with RVOT showed no difference in respect to RV volumes and ejection fractions compared with control subjects. Whereas RV abnormalities were limited to prominent fatty deposits of the right atrioventricular groove extending into the inlet portion of the RV wall in 2 of 10 control subjects, MRI studies demonstrated morphological changes of the RV free wall in 13 (65%) of 20 patients with RVOT, including presence of fatty tissue (n=5), wall thinning (n=9), and dyskinetic wall segments (n=4). Eight of these patients had additional fat deposits, thinning, or a saccular aneurysm in the RV outflow tract, corresponding with the ablation site in 6 patients. CONCLUSIONS: In RVOT, structural abnormalities of the right ventricle can be detected in a substantial number of patients despite normal RV volumes and global function. MRI abnormalities within the RV outflow tract are significantly associated with the origin of tachycardia.

Adult↗
PubMed1997

Role of the Ha-ras gene in the malignant transformation of rat liver oval cells.

We have shown that the oval cell line OC/CDE 22 can be transformed by the highly carcinogenic fjord-region diol epoxides of benzo[c]phenanthrene. Mutational activation of the ras proto-oncogene family has been proposed to be a critical event in the formation of tumors induced by polycyclic aromatic hydrocarbons. Therefore, we investigated whether in the earlier transformed OC/CDE 22 cells any point mutations were detected in the ras proto-oncogene. The results indicate that the malignant transformation of OC/CDE 22 cells by the 4 stereoisomeric benzo[c]phenanthrene diol epoxides in vitro is independent of activation of the Ha-ras proto-oncogene. In addition, Northern and Western blot analyses revealed no overexpression of the Ha-ras protooncogene in the transformed OC/CDE 22 cell lines. However, transfection of the OC/CDE 22 cells with an activated Ha-ras oncogene malignantly transformed the OC/CDE 22 cells, and the transfected cells served as precursor cells of tumors with a cholangiocellular morphology and phenotype. Our latter finding reinforces the view that OC/CDE 22 cells are committed to the bile duct epithelial cell lineage.

Animals↗
PubMed1997

Visualization of a covalent intermediate between microsomal epoxide hydrolase, but not cholesterol epoxide hydrolase, and their substrates.

Mammalian soluble and microsomal epoxide hydrolases have been proposed to belong to the family of alpha/beta-hydrolase-fold enzymes. These enzymes hydrolyse their substrates by a catalytic triad, with the first step of the enzymatic reaction being the formation of a covalent enzyme-substrate ester. In the present paper, we describe the direct visualization of the ester formation between rat microsomal epoxide hydrolase and its substrate. Microsomal epoxide hydrolase was precipitated with acetone after brief incubation with [1-(14)C]epoxystearic acid. After denaturing SDS gel electrophoresis the protein-bound radioactivity was detected by fluorography. Pure epoxide hydrolase and crude microsomes showed a single radioactive signal of the expected molecular mass that could be suppressed by inclusion of the competitive inhibitor 1,1,1-trichloropropene oxide in the incubation mixture. In a similar manner, 4-fluorochalcone-oxide-sensitive binding of epoxystearic acid to rat soluble epoxide hydrolase could be demonstrated in rat liver cytosol. Under similar conditions, no covalent binding of [26-(14)C]cholesterol-5alpha,6alpha-epoxide to microsomal proteins or solubilized fractions tenfold enriched in cholesterol epoxide hydrolase activity could be observed. Our data provide definitive proof for the formation of an enzyme-substrate-ester intermediate formed in the course of epoxide hydrolysis by microsomal epoxide hydrolase, show no formation of a covalent intermediate between cholesterol epoxide hydrolase and its substrate under the same conditions as those under which an intermediate was shown for both microsomal and soluble epoxide hydrolases and therefore indicate that the cholesterol epoxide hydrolase apparently does not act by a similar mechanism and is probably not structurally related to microsomal and soluble epoxide hydrolases.

Amino Acid Sequence↗
PubMed1997

[Imaging methods in diagnosis of coronary heart disease].

Coronary heart disease is the leading cause of death and disability worldwide. Coronary angiography makes it possible to visualize coronary artery stenosis and can be used for angioplasty and stent implantation; however, it does not allow the assessment of changes in myocardial microcirculation. The severity of an angiographically evaluated coronary stenosis does not always correspond to the extent of myocardial ischemia. Noninvasive techniques are needed to re-examine our reliance on coronary angiography and to explore the clinical value of the physiological assessment of coronary artery stenoses. Such noninvasive techniques might become important tools in the future following an overall evaluation of coronary morphology, myocardial function and perfusion ascertained by all available methods.

Coronary Circulation↗
PubMed1997

[Aortic coarctation--long-term follow-up in adults].

Surgical repair of coarctation of the aorta has been performed since 1945. Although surgical techniques have improved, problems such as restenosis and aneurysm at the operation site or hypertensive cardiovascular disease, still remain. To evaluate the long-term results after surgical repair of coarctation, 41 patients, 25 male and 16 female patients (mean age: 28 +/- 11 years, range 14-57 years), were studied 16 +/- 8 years after surgery (range 3-44 years). Mean age at surgery was 12 +/- 9 years (range 0.5-35 years). In 24 patients resection and end-to-end anastomosis had been performed, patch graft aortoplasty in nine patients, tube interposition graft in seven patients and one patient had undergone the subclavian flap technique. All patients were assessed by exact physical examination, the resting arm-to-leg systolic pressure gradient was measured by Doppler sonography, a bicycle exercise test and an echocardiogram were performed. Twenty-one patients reported postoperative symptoms such as dizziness (n = 12), headache (n = 3), cold legs (n = 10) and/or dyspnea (n = 8). In two patients the resting arm-to-leg pressure gradient was greater than 30 mm Hg, in two patients it was greater than 20 mm Hg. Gradient calculated by Doppler echocardiography ranged from 0 to 80 mm Hg (21 +/- 17 mm Hg) and showed poor correlation with the arm-to-leg pressure difference. The mean functional capacity was 89 +/- 18% (range 42-110%). In 18 patients exercise-induced hypertension was found, while in only eight patients arterial hypertension had already been known. To evaluate the morphology of the aorta MRI was performed in 28 patients. No aneurysm was found. In five patients a minimal lumen diameter as small as 9-11 mm was measured. Patients were divided into two groups according to their age at operation, group I: < 9 years (n = 19) and group II: > 9 years (n = 22). Resting blood pressure was significantly higher in group II (135 +/- 27 mm Hg vs 114 +/- 20 mm Hg, p < 0.009), anti-hypertensive medication (43% vs 11%, p < 0.04) and symptoms were more frequent in these patients (15/22 vs 6/19, p < 0.04). However at time of follow-up examination the age of patients of group II was significantly higher (33 +/- 12 vs 22 +/- 5 years, p < 0.0005). Between these two groups there was no difference in follow-up time and results of echocardiography or stress test. In conclusion, despite good long-term results after surgical repair of coarctation of the aorta, patients should be followed on a regular basis primarily in order to recognize systemic hypertension as early as possible and to improve the long-term outcome in these patients by antihypertensive treatment.

Adolescent↗
PubMed1997

Time course of regression of left ventricular hypertrophy after successful parathyroidectomy.

BACKGROUND: We have shown that primary hyperparathyroidism may induce myocardial hypertrophy that is reversible after successful parathyroidectomy. The present study was designed to assess the time course of regression of left ventricular hypertrophy without further effects of drug treatment or disease states. METHODS: We performed echocardiographic studies in 16 patients with primary hyperparathyroidism and normal resting blood pressure, normal systolic left ventricular function, no evidence of valvular disease, and without any current medication before parathyroidectomy, as well as during intermediate and long-term follow-up after successful parathyroidectomy. RESULTS: Eleven patients (69%) had end-diastolic wall thickness of the interventicular septum and/or posterior wall greater than 11 mm on baseline echocardiogram. After surgical removal of the inciting disease and an average of 12.5 and 45.7 months of follow-up with normocalcemia and normal parathyroid hormone levels a prolonged regression of left ventricular hypertrophy was observed (interventricular septum, -0.68 mm at 12.5 months and -1.69 mm at 45.7 months; p = 0.02; posterior wall, -0.46 mm at 12.5 months and -2.24 mm at 45.7 months; p = 0.02). CONCLUSIONS: We conclude that the removal of the cause of myocardial hypertrophy by successful parathyroidectomy leads to a prolonged reversal of hypertrophy. The progressive reduction of left ventricular wall thickness is not completed within 12 months.

Aged↗
PubMed1997

Cardiac abnormalities in patients with primary hyperparathyroidism: implications for follow-up.

Patients with primary hyperparathyroidism (PHPT) show a high incidence of left ventricular hypertrophy, cardiac calcific deposits in the myocardium, and/or aortic and mitral valve calcification and thus may carry an increased risk of death from circulatory diseases. This prospective study was designed to assess an effect of parathyroidectomy on cardiac abnormalities of patients with PHPT. Echocardiography was used to evaluate the mechanical performance of the heart muscle, the thickness of the left ventricular wall, myocardial calcific deposits, and valvular calcifications within 12 and 41 months after parathyroidectomy. In a blinded fashion, aortic and mitral value calcifications were determined in 46% and 39% of patients with PHPT. Calcific deposits in the myocardium were found in 74% of patients. Follow-up studies after parathyroidectomy disclosed no evidence of progression of these calcifications. Before operation left ventricular hypertrophy was detected in 82%. After parathyroidectomy and 41 months of normocalcemia and normal PTH concentrations, a regression of hypertrophy of the interventricular septum and the posterior wall by -6% and -19% (P < 0.05) was observed. Subgroup analysis disclosed the most impressive long-term reduction of left ventricular hypertrophy in patients without a history of hypertension (-11% and -21%; P < 0.05 and P < 0.005); no changes were determined in 9 patients who developed secondary hyperparathyroidism after operation. The present data show a high incidence of left ventricular hypertrophy and aortic and/or mitral valve calcifications in patients with PHPT. Follow-up at 1 year and at 41 months after successful parathyroidectomy disclose regression of hypertrophy. Our results give evidence that parathyroid hormone per se plays an important role in the maintainance of myocardial hypertrophy. Post-surgical restoration of normocalcemia and normalization of parathyroid hormone valvular sclerosis persists without evidence of progression. We further conclude that patients with PHPT and parathyroidectomy are at low risk for the development of severe aortic and mitral valve stenosis within this period of time.

Aged↗
PubMed1997

Cell death of AKR-2B fibroblasts after serum removal: a process between apoptosis and necrosis.

AKR-2B cells disintegrate after serum removal. After a delay of approximately 90 minutes, cell death began and reached after six hours a plateau of 40-50% remaining living cells. We used time-lapse video microscopy to monitor dynamic structural changes and to measure the time span of individual cells to die. The first change was the rapid appearance of membrane blebs. Membrane vesicles were rapidly extruded and reintegrated by the cell. This highly dynamic process of an affected cell stopped after 80+/-20 minutes with its death. Conductivity measurements showed that at that time the membrane was electrically permeable. By using fluorescence double staining with propidium iodide and Hoechst 33258, we show that membrane leakage leading to disintegration is accompanied, and for some cells preceded, by nuclear condensation. The energy state of the intact cells was monitored by measuring the intracellular ATP content which remained high (6 mM) throughout the entire time of investigation. Mitochondrial potential was determined by rhodamine 123 fluorescence in parallel to the measurement of membrane permeability via uptake of propidium iodide and lead to the detection of a cell population that exhibits a high mitochondrial potential and an uptake of propidium iodide indicating a membrane disruption of cells which still have a high energy charge. It is shown by electron microscopy that mitochondria were swollen and damaged in parallel to nuclear condensation. There was no DNA fragmentation as shown by two independent methods. Addition of the ICE-like protease inhibitor tyr-val-ala-asp-chloromethylketone immediately after serum starvation lead to an almost complete survival of the cells up to 6 hours. A pronounced protection was still observed after 24 hours, suggesting an involvement of this type of protease in the onset of cell death after serum removal. Apparently, serum withdrawal activates a succession of initial events that are similar to those defined as 'apoptosis', i.e. nuclear condensation and membrane blebbing. These steps are, however, accompanied or rapidly followed by cell lysis and disruption of mitochondria, both of which are characteristic of necrosis.

Adenine Nucleotides↗
PubMed1997

The effect of anticoagulant therapy in primary and anorectic drug-induced pulmonary hypertension.

In a retrospective study, we tested the hypothesis that anticoagulant therapy with warfarin sodium (Coumadin) has a beneficial influence on the long-term prognosis in patients with primary pulmonary hypertension (PPH) and aminorex-induced plexogenic pulmonary hypertension. The study included a total of 173 patients from two European cities. One hundred four of these patients took the anorectic drug aminorex (Menocil), which was available in some European countries almost 30 years ago; 69 patients had pulmonary hypertension of unexplained etiology, ie, PPH. Fifty-six of the 104 aminorex-treated patients and 24 patients in the PPH group received warfarin after diagnosis was established. For analysis, patients were divided into four groups according to their history of aminorex intake and anticoagulant therapy. Survival time, changes in hemodynamics (pulmonary arterial pressure), and improvement in quality of life (scored by the New York Heart Association [NYHA] classification) were compared and analyzed. We found that aminorex-treated patients had a better long-term prognosis than those with PPH (7.5 vs 3.9 years; p < or = 0.001). The best mean survival time of 8.3 years was found in anticoagulated aminorex-treated patients, compared to 6.1 years in nonanticoagulated aminorex-treated patients. Moreover, aminorex-treated patients who received anticoagulant therapy soon after the onset of symptoms showed significantly better prognosis (10.9 years) than those who commenced treatment 2 years thereafter (5.9 years) (p < or = 0.05). In patients with PPH, systolic pulmonary pressure was shown to influence survival time significantly (p < or = 0.0005); however, this correlation was not found in aminorex-treated patients. An improvement of symptoms like dyspnea on exertion was seen in 44.8% of the anticoagulated aminorex-treated patients, while deterioration was evident in 72.2% of the nonanticoagulated aminorex-treated patients. In conclusion, our study has shown that anticoagulant therapy had a positive influence on long-term survival and a significant improvement in quality of life in patients with PPH, in particular in patients with a history of anorectic drug intake.

Adolescent↗
PubMed1996

Effect of medium conductivity and composition on the uptake of propidium iodide into electropermeabilized myeloma cells.

The effects of ionic composition and conductivity of the medium on electropermeabilization of the plasma membrane of mammalian cells were studied. Temporal and spatial uptake of propidium iodide (PI) into field-treated cells was measured by means of flow cytometry, spectrofluorimetry and confocal laser scanning microscopy. Murine myeloma cells were electropulsed in iso-osmolar solutions. These contained 10-100 micrograms ml-1 PI at different conductivities (0.8-14 mS cm-1) and ionic strengths, adjusted by varying concentrations of K+, Na+, Cl- and SO4(2-). Field-induced incorporation of PI into reversibly permeabilized cells was (almost) independent of ionic composition and strength (at a fixed medium conductivity), but increased dramatically with decreasing medium conductivity at a fixed field strength. The time-course of PI uptake (which apparently reflected the resealing process of the membrane) could be fitted by single-exponential curve (relaxation time about 2 min in the absence of Ca2+) and was independent of medium conductivity and composition. These and other data suggested that the expansion of the 'electroleaks' during the breakdown process is field-controlled and depends, therefore, on the (conductivity-dependent) discharging process of the permeabilized membrane. The threshold field strength for dye uptake increased with increasing K+ concentration (about 0.6 kV cm-1 in K(+)-free, NaCl-containing medium and about 0.9 kV cm-1 in 30 mM KCl-containing medium). Also, the spatial uptake pattern of PI shifted from an asymmetric permeation through the cell hemisphere facing the anode to a more symmetric uptake through both hemispheres. These results suggested that the generated potential is superimposed on the (K(+)-dependent) resting membrane potential. Taking this into account, the breakdown voltage of the membrane was estimated to be about 1 V.

Animals↗
PubMed1996

Suramin is a potent inhibitor of vascular endothelial growth factor. A contribution to the molecular basis of its antiangiogenic action.

Vascular Endothelial Growth Factor (VEGF) is a specific endothelial mitogen and an important angiogenic factor in vivo, capable of inducing therapeutic angiogenesis when administered to ischemic myocardium. Suramin, originally developed as an anti-trypanosomal agent, was recently shown to exert an antiangiogenic action. We have tested the hypothesis, whether the antiangiogenic effect of suramin may be mediated via inhibition of VEGF function. Using cultured endothelial cells and a [3H]thymidine incorporation assay we were able to show, that the action of VEGF upon mitogenicity is inhibited by suramin in a dose-dependent manner. The same was true for inhibition of VEGF-induced chemotaxis of endothelial cells. Suramin inhibited VEGF-inducible tyrosine phosphorylation of KDR as determined by in vitro kinase assay. Moreover, suramin was shown to inhibit VEGF-induced tyrosine phosphorylation of KDR in intact cells, indicating an interaction of suramin with the VEGF-receptor KDR as the cause of its inhibitory activity. The antiangiogenic effect of suramin may be mediated-at least in part-by inhibition of VEGF function. Given the feasibility of in vivo use, suramin may be a valuable tool for investigating the functional role of angiogenesis in the cardiovascular system.

Animals↗
PubMed1996

Glutathione S-transferase A1-1-catalysed conjugation of bay and fjord region diol epoxides or polycyclic aromatic hydrocarbons with glutathione.

Mammalian metabolism of polycyclic aromatic hydrocarbons results in the formation of vicinal diol epoxides (existing as enantiomeric pairs of two diastereomers) considered as important ultimate carcinogens if the oxirane ring is located in a bay or fjord region of the parent hydrocarbon. In the present study, individual stereoisomers of the bay region diol epoxides of chrysene, dibenz[a,h]-anthracene and benzo[a]pyrene, as well as of the fjord region diol epoxides of benzo[c]phenanthrene, benzo[c]chrysene and benzo[g]chrysene, have been incubated with glutathione (GSH) in the presence or absence of human glutathione S-transferase isoenzyme GST A1-1, a class Alpha enzyme. The formation of GSH conjugates was determined and quantified by HPLC. The results demonstrate that the GST A1-1 isoenzyme catalyzes the formation of GSH conjugates of all diol epoxides tested, although a marked variation in catalytic efficiency (>20-fold) was observed. With both bay and fjord region anti-diol epoxides a significant preference for conjugation of the enantiomer with the R configuration at the benzylic position of the oxirane ring was noted. Among the syn diastereomers of the fjord region diol epoxides a similar substrate enantioselectivity was noted, i.e. the enantiomer with the corresponding R configuration was again preferentially conjugated. In contrast, for the bay region syn-diol epoxides this substrate selectivity was reversed, resulting in a preference for the enantiomer with the S configuration. The chemically more reactive syn diastereomers were in general better substrates for GST A1-1 than the corresponding anti diastereomers. However, a comparison between different diol epoxide diastereomers revealed no obvious correlation between chemical reactivity of the compounds and catalytic efficiencies. Furthermore, no significant correlation between diol epoxide lipophilicity and catalytic efficiency was observed. It is suggested that stereochemical factors, including the size and the geometry of the aromatic ring system and the preferred conformation of the diol epoxide, are involved as the major determinant for the rate of catalysis by GST A1-1.

Chromatography, High Pressure Liquid↗
PubMed1995

Electropermeabilization and fluorescent tracer exchange: the role of whole-cell capacitance.

Transmembrane crossing of charged fluorescent tracers such as propidium iodide (PI) and carboxyfluorescein+ (CF) can be used to quantitate membrane permeabilization. Murine myeloma Sp2/0-Ag14 cells were loaded with CF (0.1 fmol/cell) before electropulsation (0.5-3.0 kV/cm, 40 microseconds) in medium containing 25-50 micrograms/ml PI at 21-23 degrees C. Cytograms of PI vs. CF fluorescence showed three readily distinguishable subpopulations: 1) intact living cells with CF but without PI (these form > 95% of the prepulsed population), 2) transiently electropermeabilized but resealed cells showing both CF and low-level PI fluorescence, and 3) permanently permeabilized cells without CF but with very high PI fluorescence. Despite the ready influx of PI, the efflux of CF from transiently permeabilized cells was negligible and was insensitive to pulse parameters; however, electrically killed cells (subpopulation 3) lost all CF fluorescence and probably lost their cytoplasm. This difference in transmembrane passage of the dyes is best explained by binding of intracellular CF to macromolecules (and/or organelles). In isotonic "pulse medium," the membranes resealed after electropulsing with a time constant (tau R) of about 2 min. In 150 mOsm medium, resealing was faster (typically tau R approximately 0.5 min). The population distribution of PI uptake [coefficient of variation (CV) > 40%] was very broad and could not be accounted for by the radius dependence of pulse-induced voltage (CVradius approximately 10%). The variability in PI uptake could be explained if the electrical energy of the charged membrane, which depends on the whole-cell capacitance (Cc), was taken into account. Evaluation of the Cc values with single-cell resolution was based on measurement of the electrical charging time constant of the plasma membrane by electrorotation.

Animals↗
PubMed1995

Fatal pulmonary toxicity following oral etoposide therapy.

Oral etoposide has considerable activity in small cell lung cancer and the low risk of toxicity has resulted in the frequent prescription of this agent in elderly or infirmed patients. We describe a case of fatal pulmonary toxicity following the administration of oral etoposide. This is the first report of biopsy-proven pulmonary toxicity associated with this agent.

Administration, Oral↗