Dynamic headspace analysis of volatile metabolites from the reductive dehalogenation of trichloro- and tetrachloroethanes by hepatic microsomes

A dynamic headspace technique was developed to facilitate the identification and quantitation of low levels of volatile metabolites produced in vitro by subcellular preparations. The method is complementary to commonly used static headspace and solvent-extraction techniques, and involves purging the compounds from microsomal suspensions with an inert gas, trapping them on a short column of adsorbant resin, and transferring the metabolites to a gas chromatograph. An apparatus was designed to facilitate the incubations and isolations of volatile compounds. Recoveries of several chlorinated hydrocarbons with boiling points in the range 12 to 186 degrees C were 85% or higher, and the recovery of vinyl chloride (boiling point -13 degrees C) was 25%. The quantitative precision of the method was determined and calibration curves were established for each metabolite, demonstrating that no discrimination occurred over a wide range of concentrations. This technique was employed to investigate the reductive metabolism of 1,1,1-trichloroethane, 1,1,2-trichloroethane, and 1,1,2,2-tetrachloroethane by rat liver microsomes. The metabolites from these substrates were 1,1-dichloroethane, vinyl chloride, and 1,2-dichloroethylene, respectively. These conversions were NADPH-dependent, occurred only under anaerobic conditions, and indicate that chloroethanes with relatively low electron affinities can be reduced slowly by microsomal cytochrome P-450. The rates of formation of vinyl chloride, 1,1-dichloroethane, and 1,2-dichloroethylene with 1.0 mM substrate were 12.5 +/- 2.0, 122 +/- 14, and 147 +/- 12 pmol/min/mg of protein, respectively. The results show that there are distinct advantages of the purge/trap method over the static headspace method for studying volatile metabolites when high sensitivity is required.

Ultrasonic refraction by the rectus abdominis muscles: the double image artifact

Using a real-time mechanical sector scanner in a transverse plane of section, the authors noticed that a double image of an intrauterine gestational sac or an intrauterine contraceptive device can be obtained when the transducer is passed over the midline of the abdomen. It was suggested that this is caused by refraction of the sound passing through the medial edges of both rectus abdominis muscles. The authors were able to reproduce this artifact in vitro using isolated human cadaver rectus muscles and imaging a single object in a water bath.

Reductive metabolism of 1,1,1,2-tetrachloroethane and related chloroethanes by rat liver microsomes

The susceptibility of polychlorinated ethanes to reductive metabolism was evaluated by measuring the amount of each compound consumed during anaerobic incubations with rat live microsomes; 1,1,1,2-tetrachloroethane, pentachloroethane and hexachloroethane were metabolized extensively, 1,1,1,2-tetrachloroethane and the trichloroethanes were metabolized very slowly and the dichloroethanes were not metabolized at a detectable rate. The electron affinity of the chloroethanes was determined by measuring electrochemical half-wave reduction potentials. Chloroethanes with an E1/2 of - 1.35 V or less negative were reduced readily in microsomes while those with an E1/2 equal to or more negative than -1.90 V were not good substrates for enzymatic reduction. Metabolites produced from 1,1,1,2-tetrachloroethane in vitro were 1,1-dichloroethylene (DCE) and 1,1,2-trichloroethane (TCEA) and the ratio DCE/TCEA was about 25:1. These conversions were NADPH-dependent and were inhibited by air, CO and metyrapone. In the presence of SKF 525-A, DCE formation was inhibited by 47%. Microsomes from untreated or beta-naphthoflavone-treated rats were 70-90% less active than microsomes from phenobarbital-treated rats. The Km was 0.50 mM and the Vmax was 66 nmol min-1 mg-1 protein for DCE formation. The results are consistent with the proposal that 1,1,1,2-tetrachloroethane is reduced by hepatic cytochrome(s) P-450 to a free radical intermediate which, for the most part, remains closely associated with the enzyme, is reduced further and undergoes beta-elimination of a chloride ion to form DCE. The occurrence of this reductive pathway in vivo was demonstrated by the quantitation of DCE and TCEA in blood from rats treated with 1,1,1,2-tetrachloroethane.

Ultrasonography and computed tomography of hepatic candidiasis in immunosuppressed patients

The ultrasonic appearance of Candida infection in the livers of immunosuppressed patients is quite characteristic. Cystic, target-like lesions were found in three patients receiving chemotherapy for myeloproliferative diseases. The computed tomographic appearance is less characteristic. A possible explanation for the appearance of these lesions is presented.

Trapping of metabolically generated electrophilic species with cyanide ion: metabolism of methapyrilene

The popular antihistamine methapyrilene [N,N-dimethyl-N'-(2-pyridyl)-N'-(2-thienylmethyl)-1,2-ethanediamine] recently has been shown to be a potent hepatocarcinogen. Metabolic studies with rabbit liver 100000g microsomal preparations have resulted in the partial characterization of the in vitro metabolic profile of methapyrilene. Evidence for the formation of the N-oxide and the three possible carbinolamines resulting from the NADPH-dependent oxidation of the (dimethylamino)ethyl side chain nitrogen and carbon atoms of methapyrilene is presented. Attempts to trap iminium ion intermediates with electrophilic alkylating potential by coincubating methapyrilene with sodium cyanide have led to the isolation of N-(cyanomethyl)normethapyrilene. The possibility of characterizing the iminium ion intermediate that would result from the oxidative deamination of the dimethylamino moiety was precluded by the chemical instability of the corresponding alpha-cyano amine, which undergoes a spontaneous retro-Michael reaction and hydrolysis to the corresponding amide. The results are discussed in terms of the metabolic activation of methapyrilene to potential alkylating species.

Trapping of metabolically generated electrophilic species with cyanide ion: metabolism of 1-benzylpyrrolidine

Incubations of 1-benzylpyrrolidine (4) and specifically deuterium-labeled analogues of 4 with rabbit liver microsomal preparations in the presence of cyanide ion have led to the characterization of 1-benzyl-2-cyanopyrrolidine (13), cis- and trans-1-benzyl-2,5-dicyanopyrrolidine (14a and 14b, respectively), and 1-benzyl-5-cyano-2-pyrrolidinone (15). The cyano adducts of the amine are thought to result from nucleophilic attack by cyanide ion on metabolically generated iminium species. The cyanolactam may be produced by mixed function oxidation of the dicyano compounds. Incubations of tritium-labeled 1-benzylpyrrolidine with rabbit liver microsomal preparations led to the reduced nicotinamide adenine dinucleotide phosphate dependent incorporation of the label into the macromolecular fraction isolated from the postincubates. Although the level of incorporation was low compared to the amount of cyano adducts formed, it is comparable to that reported for other metabolically activated cytotoxic agents. Attempts to identify the possible arene oxide rearrangement product 1-(4-hydroxybenzyl)pyrrolidine (24) as a metabolite of 4 were unsuccessful. The results have prompted us to postulate that metabolically generated iminium ions are capable of alkylating nucleophilic functionalities present on microsomal macromolecules.

Amino acid residues of serum and CSF protein in multiple sclerosis. Clinical application of statistical discriminant analysis

Statistical discriminant analysis of the amino acid compostion of serum and cerebrospinal fluid (CSF) proteins provides an objective method for distinguishing between normal controls and patients with multiple sclerosis (MS). This method also results in a high degree of specificity in separating MS patients from those with other diseases of the nervous system. The CSF protein serine residue is highly correlated with the CSF IgG and holds promise for a more sensitive diagnostic test for MS than the currently used CSF IgG. Finally, the serum/CSF protein serine ratio seems to correlate best with clinically determined degree of activity for the disease, the most active cases having the lowest ratio. These results suggest that investigation of the amino acid composition of serum and CSF protein in multiple sclerosis and, possibly, in other diseases might lead to the development of clinically useful tests of diagnosis and degree of activity of MS.