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F F Hsu

Publications and source records attributed to F F Hsu.

67 records · Page 4Linked to original sources
PubMed1993

Confirmation of a dopamine metabolite in parkinsonian brain tissue by gas chromatography-mass spectrometry.

Gas chromatography-mass spectrometry was used to identify a dopamine metabolite isolated from the substantia nigra of parkinsonian brain tissue. Incubation of dopamine with monoamine oxidase B gave the same product which was identified as 3,4-dihydroxyphenylacetaldehyde. The structure of the compound was established by chemical synthesis, metastable ion measurement and high-resolution mass spectrometry.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

N-acetylbenzidine-N'-glucuronidation by human, dog and rat liver.

While N-glucuronidation is an important pathway for metabolism of aromatic amines, it has not been demonstrated for N-acetylbenzidine. A glucuronide of N-acetylbenzidine was synthesized and identified by mass spectrometry as N-acetylbenzidine-N'-glucuronide. This N'-glucuronide is acid labile with a t1/2 of 4 min at pH 5.3. A similar acid lability was also observed with benzidine-N-glucuronide. The formation of N-acetylbenzidine-N'-glucuronide was assessed with liver slices and microsomes prepared from human, dog and rat. When 0.014 mM [3H]N-acetylbenzidine was incubated with human liver slices a significant amount of N-acetylbendizine-N'-glucuronide was produced (8-26% of the total radioactivity recovered). With higher concentrations of [3H]N-acetylbenzidine (1 mM) rat slices also produced N-acetylbenzidine-N'-glucuronide. However, N'-glucuronide formation was not detected with dog liver slices incubated with either 0.014 or 1 mM [3H]N-acetylbenzidine. N-Acetylbenzidine-N'-glucuronide formation was observed with microsomes prepared from human, dog and rat. To assess maximum activity four detergents were used at two concentrations. With or without detergent activation the relative amount of glucuronidation was human > > dog > rat. The rate of benzidine N-glucuronide formation was 4.3- and 1.6-fold greater than N-acetylbenzidine-N'-glucuronide in dog and rat respectively, while in human both rates were similar (1.1-fold). With or without detergent activation the relative amount of benzidine-N-glucuronide formation was human > dog > > rat. N-Glucuronidation of [3H]N,N'-diacetylbenzidine was not observed. Thus N-actylbenzidine-N'-glucuronide formation appears to be an important pathway for metabolism of N-acetylbenzidine, especially in humans. Due to their acid lability, formation of the N-glucuronides of N-acetylbenzidine and benzidine provides a mechanism for hepatic detoxification and accumulation of these carcinogens in the bladder. A new model is described illustrating the effect of N-glucuronidation and the influence of N-acetylation on arylmono- and aryldiamine-induced bladder carcinogenesis.

Animals↗
PubMed1992

Water as a useful calibrant for thermospray mass spectrometry.

The present report demonstrates that thermospray liquid chromotography/mass spectrometry (LC/MS) calibration can be easily achieved by the observation of water cluster ions in filament-on or discharge ionization modes. Cluster ions of sizes ranging from 1 to 44 water molecules are readily observed and thus are useful over the mass range from 17 to 792 Da.

Calibration↗
PubMed1992

Role of N-glucuronidation in benzidine-induced bladder cancer in dog.

The mechanism by which benzidine induces bladder cancer in dog was evaluated by assessing metabolism of [3H]benzidine by dog liver slices and microsomes. Slices incubated with 0.05 mM [3H]benzidine exhibited a 32.5 min incubated with 0.05 mM [3H]benzidine exhibited a 32.5 min peak, which was also produced when microsomal incubations were supplemented with UDP-glucuronic acid. In contrast to microsomes, very little of the 32.5 min peak was produced with the 100,000 g supernatant fraction. Microsomal metabolism was increased 5-fold by pretreatment with Triton X-100. Very little activity was observed with rat microsomes in either the presence or absence of Triton X-100. This metabolite was also generated by incubating benzidine with glucuronic acid at 4 degrees C for 3 days. Thermospray MS identified this metabolite as benzidine N-glucuronide. At 37 degrees C, the t1/2 stability of purified N-glucuronide was 99, 25 and 3 min in dog urine adjusted to pH 7.3, 6.3 and 5.3 respectively. The N-glucuronide was quite stable at pH 9.3, in dog plasma, and in aprotic solvents for 4 h at 37 degrees C. Relative to benzidine, its N-glucuronide is weakly bound to plasma proteins but not more reactive with DNA. Thus, detoxification by liver provides a mechanism for accumulation of benzidine in acidic urine, uptake of benzidine into bladder epithelium, and activation of benzidine in bladder. The liver and N-glucuronidation play a potentially important role in the species specificity of benzidine carcinogenesis.

Animals↗
PubMed1991

Metabolism and disposition of bladder carcinogens in rat and guinea pig: possible mechanism of guinea pig resistance to bladder cancer.

The metabolism and disposition of N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) and 2-amino-4-(5-nitro-2-furyl)thiazole (ANFT) were studied in rat and guinea pig. Rat is susceptible whereas guinea pig is resistant to FANFT-induced bladder cancer. Rats and guinea pigs were p.o. administered either 2-[14C]ANFT or 2-[14C]FANFT (100 mg/kg), and 18-h urine and feces were collected. Tissue distribution of radiolabel was determined. In both species, the highest concentrations of radioactivity expressed as nmol/g tissue were observed in the urine and intestines. Urinary metabolites were separated by high-performance liquid chromatography and radioactivity determined by radioanalytical detection. FANFT was not detected in urine from either species under any experimental condition. More ANFT was observed in urine following FANFT than ANFT administration. This deformylation-dependent excretion of FANFT was demonstrated in both species and has been previously described as renal metabolic/excretory coupling. Less ANFT, the carcinogen more proximate than FANFT, is excreted in guinea pigs compared with rats. A unique ANFT metabolite was identified in guinea pig but not rat urine. This metabolite represented 80 and 18% of radioactivity recovered in guinea pig urine following ANFT and FANFT administration, respectively. A metabolite produced by guinea pig liver and kidney microsomes in the presence of uridine-5'-diphosphoglucuronic acid coeluted with this unique metabolite. The urinary metabolite was characterized using hydrolytic enzymes, acid hydrolysis, and mass spectrometry and identified as an ANFT-N-glucuronide. A unique UDP-glucuronosyl-transferase appears to be responsible, at least in part, for the reduced amount of free ANFT excreted by guinea pigs compared with rats. Reduced levels of urinary ANFT observed in guinea pigs may partially explain the resistance of this species to FANFT-induced bladder cancer.

Animals↗
PubMed1991

Readily synthesized calibration compounds for quadrupole and magnetic instruments for use over the mass range to 2000 daltons.

Volatile mass calibration standards have been prepared by esterifying beta-cellobiose (4-beta-D-glucopyranosyl-D-glucose) with a mixture of heptafluorobutyric (HFB) anhydride and pentafluoropropionic (PFP) anhydride. The mixed esters produce spectra that are useful for mass spectrometer calibration with positive or negative ion methane chemical ionization and electron impact over the mass range 300-2000. The spectra contain prominent ions spaced at m/z 20 and m/z 50 intervals. Using the mixed ester with direct insertion probe introduction gives intense spectra that persist for tens of minutes. All signals above m/z 194 derived from these substances disappear rapidly upon withdrawal of the probe. The composition and exact masses are given for the positive and negative ion spectra of a mixed HFB/PFP ester of beta-cellobiose. Two other calibrants are described: one made from beta-cellobiose using a mixture of HFB, PFP and trifluoroacetic anhydrides, and another the HFB/PFP mixed ester of perseitol. These are examples of the flexibility of this approach with respect to mass range and ion composition.

Calibration↗
PubMed1990

Studies on the permethylation/dephosphorylation of inositol polyphosphates: an approach to a more sensitive assay.

Methods for the permethylation of inositol phosphates (i.e. the formation of the completely substituted C-O-methyl/P-O-methyl derivatives) have been studied as a precursor to preparing C-O-methyl inositols where the remaining inositol hydroxyl groups are at the positions originally occupied by the phosphomonoesters. Classical sodium-driven methylations, diazomethane methylations and methylation with methyl trifluoromethanesulfonate were studied and only the latter was found to produce completely alkylated inositol phosphates. Treatment of the permethylated substrates with methanolic HCl removed the dimethylphosphate groups to produce C-O-methyl inositols which are candidates for negative ion chemical ionization gas chromatographic/mass spectrometric analysis as heptafluorobutyryl C-O-methyl inositols. As an example, gas chromatographic/mass spectrometric analysis of myo-inositol 1,2,6-trisphosphate was carried out by methylation, dephosphorylation and conversion to the tris(heptafluorobutyryl) derivative. Detection at the low-femtomole level was achieved by this means. A limitation of the method may be that the methylation procedure appears to produce a variable degree of phosphate positional isomerization, with resulting loss of specificity. If stable isotope internal standards were available for the inositol polyphosphates of interest, this limitation could be compensated for.

Gas Chromatography-Mass Spectrometry↗
PubMed1990

Thermospray liquid chromatographic/mass spectrometric studies with inositol phosphates.

Thermospray mass spectrometry of inositol mono- and polyphosphates, separated by ion-exchange chromatography, was evaluated for its potential as a general method for quantitative analysis of these substances. The only ions of significant abundance that are produced by the thermospray ionization process result from the total loss of phosphate from inositol. Thus inositol mono-, tris- and hexakisphosphate each gave mass spectra consisting solely of [MH]+ and [MNH4]+ of inositol. When the chromatographic eluates are passed through a heated reactor prior to the thermospray source maximal yields of these ions are obtained. The sensitivity of the technique falls short of that needed for a general method for biological applications, because the lower limit of detection is about 100 pmol microliter-1. Inositol phosphates peracetylated on C-hydroxyls were also studied, with separation by ion-exchange chromatography. Again, thermospray ionization produces totally dephosphorylated species, with the highest-mass ions retaining all of the acetyl groups, even when using the thermal reactor. Losses of acetate were also observed. Sensitivity with the acetyl derivative was comparable to that with the underivatized inositol phosphates.

Gas Chromatography-Mass Spectrometry↗
PubMed1990

Thermospray high performance liquid chromatography/mass spectrometric identification of a bladder carcinogen metabolite isolated from guinea pig urine.

An in vivo urinary metabolite of the bladder carcinogen 2-amino-4-(5-nitro-2-furyl) thiazole was isolated from guinea pig urine and was identified by direct analysis using thermospray mass spectrometry/high-performance liquid chromatography as 1-(2-amino-4-(5-nitro-2-furyl)-2-thiazolyl)-1-deoxy-beta-D-glucopyran uronic acid. The structure of this metabolite was also established by chemical synthesis. Both positive and negative ion thermospray mass spectrometry of the conjugate showed fragment ions resulting from cleavage across the pyran ring of the glucuronic acid comprising of aglycone moiety. These characteristic fragment ions may be diagnostic for identification of N-glucuronides from O-glucuronides.

Animals↗
PubMedDate not supplied

The role of acetylation in benzidine metabolism and DNA adduct formation in dog and rat liver.

To determine whether benzidine is acetylated in dog, like rat, the metabolism of benzidine was assessed with dog and rat liver slices. Slices were incubated with 0.05 mM [3M]benzidine for 4 h. Media and cellular DNA were analyzed for acetylated benzidine metabolites and adducts. In rat, benzidine was rapidly converted to acetylated metabolites. At 1 h, benzidine, N-acetylbenzidine, and N,N'-diacetylbenzidine represented 5%, 23%, and 54%, respectively, of the total radioactivity in media. Within 2 h, 75% of the radioactivity was N,N'-diacetylbenzidine. In dog, 45% of the radioactivity was present in metabolites more polar than benzidine by 4 h. No N-acetylated metabolites were observed in dog liver slice media. To identify acetylated benzidine DNA adducts, N-(deoxyguanosin-8-yl)-N,N'-diacetylbenzidine was prepared and identified by FAB MS. This nucleoside adduct was used to synthesize N-(deoxyguanosin-8-yl)-N-acetylbenzidine and N'-(deoxyguanosin-8-yl)-N-acetylbenzidine. Nucleoside adducts from slices incubated with [3H]benzidine were analyzed by HPLC. With this method of analysis, the 3H-material did not correlate with the synthetic adduct standards. To improve sensitivity and identify liver adducts, a 32P-postlabeling method was developed. 2'-Deoxyguanosine 3'-monophosphate adduct standards of acetylated benzidine were prepared. 32P-Postlabeling analysis demonstrated that rat liver contained only N'-(3'-monophosphodeoxyguanosine-8-yl)-N-acetylbenzidine after a 1- or 4-h exposure to benzidine. In contrast, no acetylated adducts were detected in dog. Results indicate that dog is a nonacetylator with respect to benzidine. The availability of acetylated benzidine nucleotide standards allowed unambiguous identification of N'-(3'-monophosphodeoxyguanosin-8-yl)-N-acetylbenzidine as the adduct present in rat liver slices. These nucleotide adduct standards will be useful in subsequent studies in animals and human.

Acetylation↗