Nephrotic syndrome due to minimal-change disease superimposed on anti-glomerular basement membrane antibody positive glomerulonephritis; a case report

Background

The prognosis for renal function in anti-GBM glomerulonephritis (anti-GBM GN) is extremely poor, and when renal impairment progresses severely, it is difficult to expect improvement. In addition, it is also known that once the disease activity can be controlled by aggressive treatment, its recurrence is rare. We experienced an anti-GBM GN that improved from severe renal dysfunction and relapsed. A possible cause was the superimpose of nephrotic syndrome due to minimal change disease (MCD).

Case presentation

A 30-year-old man was admitted to our hospital because of general malaise, fever, oliguria and renal dysfunction. The patient’s laboratory data showed serum creatinine as high as 6.6 mg/dl, and severe inflammation (C-reactive protein 20.6 mg/dl). Anti-glomerular basement membrane antibody (anti-GBM Ab) was detected in his serum, which led to the diagnosis of anti-GBM GN. Treatment was initiated with high-dose glucocorticoid (GC) and plasma exchange therapy (PE), and the patient’s renal function and oliguria improved rapidly and he was discharged 40 days after admission. Renal biopsy findings showed cellular crescents associated with linear IgG depositions along the glomerular tufts compatible with anti-GBM GN, but only about one-third of the glomeruli was involved, suggesting that it still remains an early stage of the disease. However, 2 months after discharge, he had a relapse and was readmitted due to severe proteinuria with positive anti-GBM Ab. On the second admission, after high-dose GC and PE combined with intravenous cyclophosphamide, and remission was achieved. Despite the relatively minor renal biopsy findings, the patient showed rapid renal dysfunction and relatively rapid improvement with our treatment. Electron microscopy of the renal biopsy tissue showed significant foot process effacement on podocytes in the apparently normal glomeruli, without electron dense deposits.

Conclusion

On the basis of clinical course and renal pathology, it is suggested that the present case was a rare complication of an early stage of anti-GBM GN and minimal change nephrotic syndrome. Although the simultaneous development of anti-GBM GN and MCD with anti-GBM antibody is unclear, it might have been precipitated by influenza infection or some unknown factor.

Effect of arylthiolated 2,3-dimethoxy-1,4-benzoquinones on respiratory activity and lipid peroxidation in bovine heart mitochondria

A series of arylthiolated 2,3-dimethoxy-1,4-benzoquinones was synthesized and tested for the effect on the respiratory system and the lipid peroxidation in bovine heart mitochondria (BHM). These quinones showed intense inhibitory activities on the respiratory system in BHM. Their inhibitory activity in the succinate oxidase system was greater than that in the NADH oxidase system. No difference between the difference spectra, with and without these quinones, of the reduced minus oxidized forms of cytochromes (cyt.) suggested that these quinones inhibit at the site after cyt. a+a3 in the respiratory chain. Moreover, these quinones were as efficient as exogenous ubiquinone-10 (UQ-10) for the inhibition of lipid peroxidation. 5- And 5,6-di-arylthio groups on the quinone ring were found to be favorable for inhibition of the respiratory system and lipid peroxidation. Our results suggest that arylthiolated 2,3-dimethoxy-1,4-benzoquinones act as antioxidants by increasing the amount of endogenous reduced UQ-10 in BHM.

ESR study of membrane perturbation and the lysis of liposomes induced by chlorpromazine

The mechanism of interaction between chlorpromazine (CPZ) and artificial lipid membranes, negatively or positively charged liposomes was studied by an electron spin resonance (ESR) technique. Analysis by a 5-doxyl stearic acid (DS) spin probe indicated that regardless of the electric charge of liposomes, CPZ disordered the hydrophobic region near the surface of lipid membranes at CPZ/lipid > 1. In the same CPZ/lipid range, the lysis of liposomes was observed, and it was considered that the formation of the CPZ/lipid mixed micelles as a consequence of this collapse of liposomes would probably lead to the disordering of the 5-DS reporting region. As to the middle portion of the fatty acyl chains reported by the 12-DS spin probe, the membrane disordering action of CPZ was only detected with the negatively charged liposomes at a ratio of CPZ/lipid < 1, but no membrane alteration was observed with the positively charged liposomes, regardless of the concentration range of CPZ used. In comparing these two opposite results, it is conceivable that the disordering at the 12-DS reporting region was probably induced by the cationized CPZ which would enter into the hydrocarbon-polar interface, leading to an expansion of the space between the hydrocarbon chains at this area. Also, a strong influence of CPZ on the innermost portion of the lipid bilayers was observed with both the negatively and positively charged liposomes, as reported by the 16-DS probe. This perturbing action presumably occurred when undissociated CPZ molecules penetrated into the center of the bilayers (lipid core), which could have resulted in a reduction of hydrophobic interactions of the lipid molecules.

Distribution of ubiquinone and ubiquinol homologues in rat tissues and subcellular fractions

The oxidized (UQox) and reduced (UQred) forms of ubiquinone (UQ) homologues in rat tissues and subcellular fractions were analyzed to elucidate their distribution and physiological role. UQ-9 and UQ-10 were detected in all tissues studied, and UQ-9 was the predominant homologue. The total amount of UQox-10 and UQred-10 was 20-50% that of UQox-9 and UQred-9. The levels of these homologues were highest in heart with lesser amounts occurring in kidney, liver and other organs. In liver and blood plasma, the UQred homologue amounted to 70-80% of the total UQ (UQox + UQred = t-UQ). UQred was less than 30% of t-UQ in other tissues and blood cells. t-UQ was much higher in leukocytes and platelets in blood than in erythrocytes. In erythrocytes, t-UQ was exclusively located in the cell membranes. UQox and UQred were also found in all subcellular fractions isolated from liver and kidney in about the same ratio as UQred/t-UQ was present in the whole organ. The levels of UQox and UQred per mg protein in subcellular fractions from liver were highest in mitochondria, with lesser amounts present in plasma membranes, lysosomes, Golgi complex, nuclei, microsomes and cytosol. In the mitochondria, the outer membranes were richer in t-UQ than the inner membranes. In the Golgi complex, the light and intermediate fractions were rich in t-UQ when compared to the heavy fraction. The possible physiological role of UQox and UQred in tissues and subcellular fractions is discussed.

Hydrogen peroxide-dependent oxidation metabolism of 1-methyl-2-mercaptoimidazole (methimazole) catalysed by myeloperoxidase

1. Myeloperoxidase catalysed the H2O2-supported oxidation of 1-methyl-2-mercaptoimidazole (MMI) in the presence of Cl-. The rate of MMI oxidation was determined by monitoring a decrease in the absorbance at 251 nm. The pH optimum of the oxidation was around 4.5. The rate of MMI oxidation showed typical Michaelis-Menten saturation kinetics with respect to H2O2. Inhibition by excess H2O2 was not seen. 2. When the H2O2/MMI ratio was 0.5, MMI was oxidized by hyochlorous acid produced by the myeloperoxidase-H2O2-Cl- system giving bis-(1-methyl-2-imidazolyl)disulphide (MMI-disulphide) as an initial product, which gradually underwent disproportionation and subsequent hydrolysis giving 1-methylimidazole and MMI as the final products stoichiometrically. 3. When the H2O2/MMI ratio was one or above, hypochlorous acid produced in excess reacted with MMI-disulphide to give unidentified compounds. The sum of the amounts of 1-methylimidazole formed and of MMI reformed was less than 81% of the MMI added.

The mechanism of myeloperoxidase-catalysed oxidation of aminopyrine

1. Myeloperoxidase catalysed the H2O2-supported oxidation of aminopyrine in the presence of Cl-, generating the aminopyrine cation radical (AP+.). The rate of AP+. formation was determined by monitoring the absorbance at 565 nm. The pH optimum of the reaction was around 5.0. The rate of AP+. formation increased with increasing concentration of aminopyrine. Inhibition by excess H2O2 was seen at pH 4.5-5.5. 2. When Cl- was replaced by Br-, the rate of AP+. formation increased significantly, and inhibition by H2O2 became less evident and was observed only at pH 5.5. The rate of chemical oxidation of aminopyrine by HOCl was much slower than that by Br2. 3. Compared with the chlorination of monochlorodimedone (MCD), the reaction between aminopyrine and HOCl, produced by the enzymic peroxidation of Cl-, is rate-limiting in the myeloperoxidase-catalysed oxidation of aminopyrine. The differences in kinetic behaviour between the myeloperoxidase-catalysed chlorination of MCD and oxidation of aminopyrine are explained by the low reactivity of HOCl towards aminopyrine.

Inhibition of mitochondrial respiratory chain by arylthiolated 2,3-ethylenedioxy-1,4-benzoquinones

A series of arylthiolated 2,3-ethylenedioxy-1,4-benzoquinones as a coenzyme Q (CoQ) antagonist was tested for inhibition of succinate oxidase and reduced nicotinamide adenine dinucleotide (NADH) oxidase systems in the mitochondrial respiratory chain. The following characteristics were revealed: (1) 2,3-ethylenedioxy, 5-arylthio and 5,6-diarylthio groups were confirmed to be favorable for inhibition of both systems; (2) these analogs were more effective in the succinate oxidase system than in the NADH oxidase system; (3) 4' substituents on the benzene side ring had little effect on inhibitory activity; (4) the acting sites of these analogs had no strict stereospecificity. The reduced minus oxidized difference spectra revealed that these analogs inhibited the succinate oxidase system at the site between succinate and CoQ, and the NADH oxidase system at the site after cytochrome a + a3, suggesting these analogs might act as antagonists of CoQ in the succinate oxidase system. However, 5-(4'-nitrophenylthio)-2,3-ethylenedioxy-1,4-benzoquinone (If) strongly inhibited only the succinate oxidase system at the site after cytochrome a + a3.

Ethyl hydroperoxide-dependent metabolism of N,N-dimethyl-p-anisidine catalysed by lactoperoxidase

1. Chemical oxidation of N,N-dimethyl-p-anisidine (DMA) with bromine at pH 5-8 gave p-N,N-dimethylaminophenoxy radical irrespective of the DMA/Br2 ratio (1 to 100), whereas the ethyl hydroperoxide-supported oxidation of DMA catalysed by lactoperoxidase gave the phenoxy radical or the cation radical of DMA depending upon the concentration of DMA. 2. The amount of p-benzoquinone produced by the chemical oxidation increased steeply with an increase in pH above 6.0, whereas that produced by the lactoperoxidase-ethyl hydroperoxide-bromide system exhibited a pH optimum centred around pH 6.0. When the concentration of DMA was increased 10-fold, the enzymic formation of p-benzoquinone greatly decreased, whereas that of formaldehyde increased. 3. The rate of formation of the oxidized bromine species by the lactoperoxidase-ethyl hydroperoxide-bromide system showed a similar pH-profile to the formation of p-benzoquinone. 4. The oxidized bromine species is considered to be the predominant oxidizing agent in the lactoperoxidase-ethyl hydroperoxide-bromide system at pH 6.0 and below. The decrease in the amount of p-benzoquinone formed, and the increase in the amount of formaldehyde formed, by the lactoperoxidase-ethyl hydroperoxide-bromide system with increasing concentration of DMA, were interpreted in terms of competition between bromide and DMA for the reaction with compound I of lactoperoxidase.

Chloroperoxidase-catalyzed oxidation of aminopyrine

Although in the absence of halide ion chloroperoxidase did not catalyze the ethylhydroperoxide (EHP)-supported oxidation of aminopyrine, in the presence of Br- or Cl-, chloroperoxidase did catalyze the oxidation of aminopyrine, generating the aminopyrine cation radical (AP+). The initial rate of AP+ formation was determined by monitoring the absorbance at 565 nm. The pH optimum of the reaction was centered around 5.0. The rate of AP+ formation showed typical Michaelis-Menten saturation kinetics with respect to EHP, aminopyrine and Br-. The rate of formation of bromine in the chloroperoxidase-EHP-Br- system was also determined by measuring the change in absorbance at 267 nm. In the system containing 1 mM EHP and 0.2 M KBr at pH 5.0, the rate was 1.8 nmol of bromine/s/micrograms of chloroperoxidase, which was slower than that of AP+ formation under the same conditions. The present results suggest that the formation of AP+ is initiated by the halogenation of the N,N-dimethylamino group followed by the homolysis of the haloammonium cation, and that the most likely halogenating reagent is an enzyme-bound halogenating intermediate.

Oxidative metabolism of propylthiouracil by peroxidases from rat bone marrow

1. Propylthiouracil (PTU) was degraded by myeloperoxidase (MPO) or eosinophil peroxidase (EPO), purified from rat bone marrow, in the presence of H2O2 and Cl-. In the absence of either H2O2 or Cl-, MPO and EPO do not degrade PTU. Optimum concentrations of KCl for MPO and EPO were 50 and 250 mM, respectively. 2. The characteristics of PTU degradation by MPO-H2O2-Cl- were similar to those of the chlorinating activity of the peroxidase. 3. Hypochlorous acid as well as MPO-H2O2-Cl- also degraded PTU. Metabolites of PTU degradation by MPO-H2O2-Cl-, which were separated by C18 reversed phase h.p.l.c., were the same as those produced by hypochlorous acid. 4. Of the metabolites of PTU formed by MPO-H2O2-Cl-, one was identified as PTU sulphonic acid (6-propyl-4-hydroxypyrimidine-2-sulphonate) and another seemed to be propyluracil.

Inactivation of peroxidases of rat bone marrow by repeated administration of propylthiouracil is accompanied by a change in the heme structure

Myeloperoxidase and eosinophil peroxidase were isolated from the bone marrow cells of rats treated with or without propylthiouracil (PTU) which caused bone marrow depression. PTU treatment decreased the activity of myeloperoxidase but not of eosinophil peroxidase using guaiacol as the electron donor. However, when KI,N-N'-dimethyl-p-phenylenediamine and pyrogallol were used as the electron donor, the activity of only eosinophil peroxidase was inhibited by PTU treatment. EPR spectra indicated that the structure of myeloperoxidase surrounding the heme iron changed from a rhombic form into an axial one by the repeated administration of PTU. Therefore, the inactivation of peroxidases by PTU treatment was accompanied by an alteration of their structures surrounding the heme.

Electrochemical immunoassay combined with column liquid chromatography: determination of phenytoin in human serum

A new electrochemical immunoassay combined with column liquid chromatography has been developed for the determination of phenytoin in human serum. Phenytoin was labelled with the electrochemically active nitroxide, and the separation of the free labelled antigen from other electrochemically active compounds in serum was accomplished by the use of gel chromatography. Serum samples were mixed with the antibody and the labelled antigen, incubated for 90 min, and then a 100-microliter aliquot of the mixture was directly injected to the column, which was equipped with an electrochemical detector. With 10 microliter of serum, the smallest detectable concentration of phenytoin was 2 micrograms/ml.

Purification and some properties of peroxidases of rat bone marrow

Myeloperoxidase and eosinophil peroxidase were separated and purified from rat bone marrow cells using cetyltrimethylammonium bromide as the solubilizer and then with column chromatographies on CM-Sephadex C-50 and Con A-Sepharose. Both purified enzymes were observed to be apparently homogeneous by SDS-polyacrylamide gel electrophoresis. Myeloperoxidase consisted of two subunits of Mr 57,000 and 15,000, and eosinophil peroxidase two of 53,000 and 14,000. On structural analysis of the enzymes, their visual and ESR spectra revealed that the structure surrounding the heme in myeloperoxidase was different from that in eosinophil peroxidase. Moreover, substrate specificity and sensitivity to inhibitors such as azide and cyanide differed between the two enzymes. Rat bone marrow possesses two distinct peroxidases, myeloperoxidase and eosinophil peroxidase, which have different subunits and different heme microenvironments. Therefore, the difference in enzymatic function between the two peroxidases may be due to their structures.

ESR studies on the oxidation of N,N-dimethyl-p-anisidine and its analogues catalyzed by myeloperoxidase

N,N-Dimethyl-p-anisidine (DMA) was used as a substrate to differentiate between the direct, or chloride-independent, and the indirect, or chloride-dependent, pathways characteristic of myeloperoxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7). The chemical oxidation by sodium hypochlorite and the horseradish peroxidase-catalyzed oxidation by H2O2 were also investigated for a comparison. The chemical oxidation of DMA by NaOCl (DMA/NaOCl = 1) gave the p-N,N-dimethylaminophenoxy radical at pH 5 and 7. p-Benzoquinone and formaldehyde were determined as stable end-products. On the other hand, the cation radical of DMA was detected and p-benzoquinone was not obtained in the horseradish peroxidase-H2O2-Cl- system. In the presence of Cl- the myeloperoxidase-catalyzed oxidation at pH 5 gave nearly the same result as did the oxidation by NaOCl, whereas in the absence of Cl- the result of the oxidation was similar to that of the horseradish peroxidase-catalyzed oxidation, except for a low yield of formaldehyde formation, which was ascribed to the decomposition of H2O2 by the catalase activity of myeloperoxidase. Although the myeloperoxidase-catalyzed oxidation of DMA at pH 7 in the presence of Cl- gave only the cation radical of DMA, a fairly large amount of p-benzoquinone was obtained as a product. This result indicates that the indirect chloride-dependent oxidation is also operating at pH 7. The reaction mechanism for the myeloperoxidase-catalyzed oxidation of DMA is proposed.