Deacetylation and further metabolism of the mercapturic acid of hexachloro-1,3-butadiene by rat kidney cytosol in vitro

Hexachloro-1,3-butadiene (HCBD) is more nephrotoxic to female than male rats. Metabolism of HCBD involves conjugation with glutathione followed by formation of the cysteine conjugate S-(pentachloro-1,3-butadienyl) cysteine (PCBD-CYS) and then the mercapturic acid N-acetyl-S-pentachloro-1,3-butadienyl-cysteine (PCBD-NAC). PCBD-NAC is also more nephrotoxic to female rats than male rats. The deacetylation of [¹⁴C]-PCBD-NAC to PCBD-CYS and the binding of radiolabelled metabolites to protein has been studied using renal cytosol preparations from male and female rats in vitro, since a sex-related difference in these reactions could explain the difference in nephrotoxicity found in vivo. PCBD-NAC was rapidly metabolised by renal cytosol. The rate of metabolism was similar with either male or female renal cytosol, and the major metabolite identified was PCBD-CYS. N-Acetylation of PCBD-CYS to PCBD-NAC was not detected in the presence of either male or female renal cytosol. Covalent binding of radioactivity from [¹⁴C]-PCBD-NAC to cytosolic protein could be detected after 5 min incubation, and although the extent of binding was similar for both male and female cytosol at early time periods, after 60 min incubation more binding was found in the presence of male cytosol. Covalent binding was largely prevented by aminooxyacetic acid, an inhibitor of cysteine conjugate -lyase, suggesting a role for this enzyme in the activation of HCBD. These results indicate that the sex differences in the nephrotoxicity of HCBD and PCBD-NAC in the rat are not attributable to differences in the rate of deacetylation of PCBD-NAC to give the proximate nephrotoxin PCBD-CYS.This work was supported by a fellowship from the European Science Foundation granted to I. S. P.     

Induction of light hydrocarbon nephropathy by p-dichlorobenzene

In order to clarify the etiology of a dose-related increase in the incidence of tubular cell adenocarcinomas of the kidney in male rats, the nephrotoxicity of p-dichlorobenzene (p-DCB) was investigated in a subchronic study. Groups of ten male and ten female Fischer 344 rats were dosed by gavage with 0 (controls), 75, 150, 300 or 600 mg p-DCB/kg/day in corn oil. Half of the animals were sacrificed after 4 weeks and the remainder after 13 weeks. Increased urinary LDH and epithelial cell excretion and exacerbation of hyaline droplet accumulation in the cytoplasm of renal cortical cells were observed in male rats over the entire dose range investigated. Tubular single cell necrosis, dilated tubules with granular cast formation in the outer zone of the medulla, were evident in male rats after 4 and 13 weeks of treatment with doses of 150–600 mg/kg/day. In female rats there was no indication of a nephrotoxic action of p-DCB. The effects on the kidney, both in their morphological characteristics and the fact that they occur exclusively in male animals, correspond to the light hydrocarbon nephropathy observed as a result of short-term treatment with a number of aliphatic and cyclic hydrocarbons. The development of cortical renal tumors seems to be associated with this kind of kidney damage which is unique to male rats. The literature on this subject generally regards these renal effects as not predictive for man.     

Thiol Reduction of 3′-Azidothymidine to 3′-Aminothymidine: Kinetics and Biomedical Implications

The ability of thiols to reduce 3-azidothymidine (AZT) to 3-aminothymidine has been investigated. Incubation with glutathione, dithiothreitol (DTT), or mercaptoethanol at pH 7.2 and 37°C leads to quantitative reduction of the azido moiety to an amine. The reaction is first order in AZT and first order in reducing agent (mono- or dithiol). The second-order rate constants are 2.77 × 10^–3, 6.55 × 10^–5, and 6.35 × 10^–6 M ^–l sec^–1 for the dithiothreitol, glutathione, and mercaptoethanol reductions, respectively. The thiol reduction of alkyl azide to amine under mild conditions is a synthetic method particularly suitable for water-soluble azido compounds that are sensitive to catalytic hydrogenation. The potential for the mono- or dithiol-mediated reduction of alkyl azides under biological conditions must be considered when conducting studies of azido drugs.     

Changes in ultrastructure of hepatocytes and liver test results before,during, and after treatment with interferon-β in patients with HBeAg-positive chronic active hepatitis

We studied the histological and ultrastructural changes in the liver and alterations in the liver test results before, during, and after treatment with human interferon- from five patients with hepatitis B e antigen-positive chronic active hepatitis. A daily dose of 3×10⁶ to 6×10⁶ units of interferon- was given intravenously for four weeks. The total index of periportal and portal inflammation, intralobular degeneration, and focal necrosis before treatment was decreased significantly six months after treatment (P<0.05). Ultrastructurally, the structure of endoplasmic reticulum was irregularly shaped or fragmentally decreased during treatment, but these disappeared six or 12 months after treatment. Glycogen particles diminished greatly during treatment. The alanine aminotransferase concentrations in these patients increased during treatment. Serum albumin and cholinesterase levels decreased significantly at the fourth week of treatment (P<0.01) and at the third day (P<0.01) to the second week (P<0.05) of treatment, respectively. These results suggest that interferon- injures endoplasmic reticulum and glycogen areas and damages the cholinesterase activity in the early stage of treatment and protein synthesis in patients with hepatitis B e antigen-positive chronic active hepatitis.     

Histochemical study of pituitary adenomas with Ki-67 and anti-DNA polymerase α monoclonal antibodies,bromodeoxyuridine labeling,and nucleolar organizer region counts

Summary The growth potential of 65 pituitary adenomas was determined by histochemical analysis with Ki-67 and anti-DNA polymerase monoclonal antibodies, bromodeoxyuridine (BrdUdR) labeling, and counts of argyrophilic nucleolar organizer regions (Ag-NORs). The mean proliferating cell indices (PCIs) determined by Ki-67 and anti-DNA polymerase and the BrdUdR labeling index (LI) were generally very low [1.0±0.2%, 1.1±0.2%, and 0.5±0.1% (±SE), respectively]. Apart from adrenocorticotropic hormone-positive adenomas, which had significantly higher indices, there were no statistically significant differences in the indices among the other subtypes of pituitary adenomas. Recurrent tumors had higher Ki-67 and DNA polymerase PCIs and BrdUdR LIs (3.6%, 4.2%, 1.4%) than primary tumors (0.8%, 0.8%, 0.3%; P<0.005). The number of Ag-NORs did not correlated significantly with any of the three indices. The mean number of Ag-NORs was higher in nonfunctioning adenomas than in functioning adenomas (2.04 vs 1.66, P<0.005); among prolactin-positive adenomas, those treated preoperatively with bromocriptine had more Ag-NORs than untreated tumors (1.75 vs 1.57, P<0.005). These results suggest that the Ki-67 and DNA polymerase PCIs and the BrdUdR LI predict the growth potential of individual pituitary adenomas, whereas the number of Ag-NORs appears to correlate with hormone production rather than with the proliferative potential.Supported by grants CA-13525 and CA-50210 from the National Cancer Institute, by a grant from the Phi Beta Psi Sorority, and by Grant-in-Aid A 63771083 from the Ministry of Education, Science, and Culture of Japan     

Regional brain kinetics of 6-fluoro-(β-11C)-L-dopa and (β-11C)-L-dopa following COMT inhibition. A study in vivo using positron emission tomography

Summary The regional brain kinetics of (-11C)-L-dopa and 6-fluoro-(-11C)-L-dopa was measured in six Rhesus monkeys using positron emission tomography (PET). Radioactivity accumulated specifically in the striatal region and the increase in L-dopa-derived radioactivity utilization with time was calculated using surrounding brain as a reference area, this being devoid of dopaminergic activity. The rate constant for selective striatal utilization i.e. grossly decarboxylation was 0.0110 ± 0.0007 (S.D) and 0.0057 ± 0.0006 min1 for (-11C)-L-dopa and 6-fluoro-(-11C)-L-dopa, respectively. After pre-treatment of the monkeys with the peripherally and centrally active catecholamine-O-methyl transferase (COMT) inhibitor Ro 40-7592 10 mg/kg, the decarboxylation rate remained unchanged (0.0112 ± 0.0015 min-1) for (11C)-L-dopa, whereas an increase in rate was measured for 6-fluoro-(-11C)L-dopa (0.0092 ± 0.0015 min–1). Differences in the distribution of radiolabelled metabolites i.e. the corresponding O-methyl-L-dopa in the reference area is most probably the reason for the difference in calculated decarboxylation rate seen between the radiotracers. The higher decarboxylation rate measured for 6-fluoro-(-11C)-L-dopa after blockade of COMT shows that the radiolabelled metabolites i.e. 6-fluoro-O-methyl-(-11C)-L-dopa significantly contributes to background radioactivity.     

Brain kinetics of 11 C-labelled L-tryptophan and 5-hydroxy-L-tryptophan in the Rhesus monkey

Summary 5-Hydroxy-L-tryptophan labelled with 11 C is introduced as a tracer for the in vivo assessment of brain serotonin synthesis in the Rhesus monkey using positron emission tomography, PET. Increasing radioactivities were seen in the striatal area in contrast to that seen in other brain regions. Following 11 C-labelled L-tryptophan an even spread of brain radioactivity was seen. This selective increase most probably results from the decarboxylation of tracer and retention of formed products since no striatal increase of radioactivity was seen when 5-hydroxy-L-tryptophan labelled with 11 C in the carboxy-position was administered. Furthermore, pretreatment of the monkey with a centrally active decarboxylase inhibitor (NSD 1015,10 mg/kg) did not lead to increased striatal radioactivities after the administration of 5-hydroxy-(-11C)-L-tryptophan. The selective utilization of the radiotracer in the striatal area increased with a rate constant calculated to be 0.0055 ± 0.0015 min^–1 (n = 5) using the surrounding brain as reference area. A non-significant influence of radiolabelled metabolites to the rate constants measured was shown after pretreatment of the monkeys with selective and non-selective monoamine oxidase inhibitors, respectively. These results may give a basis for the use of the new tracer 5-hydroxy-(-11 C)-L-tryptophan in PET-studies of brain serotonin metabolism in health and disease.     

Plasminogen activation in plasma of patients with systemic lupus erythematosus

Summary We measured ₂-plasmin inhibitor-plasmin complexes (PI-PC) in plasma of patients with systemic lupus erythematosus (SLE) to examine the plasminogen activation in SLE. The plasma PI-PC level in 23 patients with SLE was significantly higher than that in 18 normal subjects (P<0.001) and the SLE patients with nephrotic syndrome had higher plasma PI-PC levels than those without nephrotic syndrome (P<0.01). In addition, the plasma PI-PC level was significantly correlated with the level of plasma C3 breakdown products (iC3b/C3dg) in the patients with SLE (r=0.53, P<0.01). These results suggest that plasminogen is activated in plasma of patients with SLE and that the plasminogen activation may be associated with the activation of complement in SLE.     

The regional distribution of adenosine-regulating enzymes in the left and right ventricle walls of control and hypertrophic heart

Summary The transmural distribution of the adenosine-generating enzyme 5-nucleotidase (5N) and of the adenosine-degrading enzymes adenosine deaminase (ADA), AMP deaminase (AMP-D) and adenosine kinase (Ado-K) were determined across the walls of left and right ventricles of control and hypertrophic rat hearts.The enzyme distribution across the left ventricle wall (but not across the right wall) of normal hearts was not uniform: 5N activity shows its highest levels in the subepicardial and in the subendocardial regions, whereas all the other enzyme activities show their lowest levels. A similar pattern of transmural distribution was also detected in other mammalian species (ox and pig).In the experimental cardiac hypertrophy, caused by two different types of chronic cardiac overload, the levels and the profiles of transmural distribution of 5N and ADA enzyme activities may significantly change across the rat left ventricle wall.