Mitsuharu Narita

Biosynthesis of Methylguanidine in Isolated Rat Hepatocytes and in vivo

To clarify the organ in which methylguanidine is synthesized, high doses of creatinine, which is known to stimulate the synthesis of methylguanidine, were administered to male Wistar rats intraperitoneally. Various tissues of the rats were frozen by a freeze clamp method before and 1, 2 and 3 h after injection, and methylguanidine was determined by high-pressure liquid chromatography using 9,10-phenanthrenequinone for fluorometric determination. We found evidence that the liver, kidney, lung, muscle, red blood cells and gut flora synthesize methylguanidine. In addition, we measured the synthesis of methylguanidine in isolated hepatocytes prepared from normal rats following the addition of creatinine, arginine and guanidinoacetic acid to the incubation medium. Synthesis of methylguanidine was observed only in those incubations which contained creatinine, and was dependent on the concentration of creatinine in the media and on the incubation period. Isolated rat hepatocytes also synthesized guanidine in the presence of guanidinoacetic acid. These results indicate that the liver is one of the organs which synthesize methylguanidine and also that creatinine is the precursor.

Active oxygen in methylguanidine synthesis.

Methylguanidine (MG), a toxin reported in uremia, is thought to be a product of creatinine oxidation. This study is designed to demonstrate the role of active oxygen in the oxidation of creatinine under conditions compatible with those found in uremia. MG synthesis is moderately stimulated by the superoxide radical derived from 3 mM hypoxanthine and 0.015 units/ml xanthine oxidase and inhibited by the addition of superoxide dismutase. This is increased markedly by the addition of 0.05% hydrogen peroxide and augmented to about 56,000 times the control rate in the presence of hydroxyl radicals derived from the reaction of 10 mM FeSO4 and 0.05% hydrogen peroxide. In addition, MG synthesis is inhibited by the addition of sorbitol, lactulose or ethanol, the scavengers of hydroxyl radicals. These results indicate that creatinine can be oxidized to MG by various species of active oxygen and that one of the mechanisms of MG synthesis is such oxidation. MG, therefore, may be a useful indicator of peroxidation in vivo.

Glomerular lesions associated with the Crow-Fukase syndrome

Three cases of the Crow-Fukase syndrome without radiographic changes of multiple myeloma are reported, with special reference to the glomerular changes seen. Proteinuria was detected in one case, although decreased renal function was observed in all (GFR: 41.0, 62.0, 74.1 ml/min respectively) at the time of renal biopsy. Glomerular changes were similar in all three cases. The main characteristic changes were mesangial proliferation and thickening of the glomerular capillary walls. Pictures by light microscopy were therefore similar to that of MPGN. On electron microscopy, the thickened capillary walls showed circumferential mesangial interposition and the subendothelial zone was electron-lucent and contained small dense granules or flocculent deposits. By immunofluorescent microscopy, no immunoglobulins, complement components or light chain were detected in the glomeruli except in one case.

FORMATION OF GUANIDINOSUCCINIC ACID, A STABLE NITRIC OXIDE MIMIC, FROM ARGININOSUCCINIC ACID AND NITRIC OXIDE-DERIVED FREE RADICALS

Guanidinosuccinic acid (GSA) is noted for its nitric oxide (NO) mimicking actions such as vasodilatation and activation of the N-methyl-D-aspartate (NMDA) receptor. We have reported that GSA is the product of argininosuccinate (ASA) and some reactive oxygen species, mainly the hydroxyl radical. We tested for GSA synthesis in the presence of NO donors. ASA (1 mM) was incubated with NOR-2, NOC-7 or 3-morpholinosydomine hydrochloride (SIN-1) at 37 degrees C. GSA was determined by HPLC using a cationic resin for separation and phenanthrenequinone as an indicator. Neither NOR-2 or NOC-7 formed GSA. SIN-1, on the other hand, generates NO and the superoxide anion which, in turn, generated peroxynitrite which was then converted to the hydroxyl radical. Incubation of ASA with SIN-1 leads, via this route, to GSA. When ASA was incubated with 1 mM SIN-1, the amount of GSA produced depended on the incubation time and the concentration of ASA. Among the tested SIN-1 concentrations, from 0.5 to 5 mM, GSA synthesis was maximum at 0.5 mM and decreased with increasing concentrations of SIN-1. Carboxy-PTIO, a NO scavenger, completely inhibited GSA synthesis. SOD, a superoxide scavenger, decreased GSA synthesis by 20%, and catalase inhibited GSA synthesis only by 12%; DMSO, a hydroxyl radical scavenger completely inhibited GSA synthesis in the presence of SIN-1. These data suggest that the hydroxyl radical derived from a combination of NO and the superoxide anion generates GSA, a stable NO mimic. Meanwhile, synthesis of GSA by NO produces reactive oxygen and activates the NMDA receptor that generates NO from GSA, suggesting a positive feed back mechanism.

Ultrastructural Study of Gaps of the Glomerular Basement Membrane in IgA Nephropathy

Renal biopsy specimens from 163 patients with IgA nephropathy were examined by electron microscopy to clarify the significance of gaps of the glomerular basement membrane (GBM) in IgA nephropathy. Gaps of the GBM were observed in 21 cases. In 1 case the capillary lumen was partially filled with fibrin-like materials, basement membrane-like materials, and epithelial cells, and in 6 cases wide gaps of the GBM were observed. In 10 cases the gaps of the GBM were covered by epithelial and/or endothelial cells, and in 4 cases spherical microparticles were seen at the gaps of the GBM. Microscopic hematuria of less than 5 red blood cells per high-power field of vision at the time of biopsy was less frequently observed in patients with gaps of the GBM than in patients without (p less than 0.05). Marked local thinning or splitting of the GBM and electron-dense deposits or spherical microparticles on peripheral capillary walls were more frequently observed in patients with gaps of the GBM than in those without (p less than 0.001, less than 0.005, less than 0.05, and less than 0.001, respectively).

Dipyridamole Therapy in the Nephrotic Syndrome

Dipyridamole was used in 30 cases of nephrotic syndrome, mostly of intractable type. The results indicate that the drug therapy proved to be effective in decreasing urinary protein and controlling nephrotic condition in 40% of the cases after an initial period of treatment. Long-term results of the drug on urinary protein and on nephrotic condition were rated as good in 36.7 and 53.3%, respectively, of the cases treated. The exact mechanism of action of dipyridamole in the nephrotic syndrome is still obscure in many respects. However, the fact that the drug shares its anti-platelet action with the non-steroid anti-inflammatory drugs, e.g. aspirin and indomethacin, and the rapidity with which it produces its urinary protein-decreasing effect, strongly suggests that it inhibits the release of vasoactive amines and other chemical mediators from blood platelets. As far as the present study is concerned, adverse side effects of dipyridamole were few or minimal, even when the drug used in large doses over a prolonged period of time. From these results it is considered that dipyridamole provides a new remedy which is worthy of trying in nephrotic syndrome as a means of reducing the requirement of steroids and immunosuppressive drugs.

Urinary Excretion of Creatol, an In Vivo Biomarker of Hydroxyl Radical, in Patients with Chronic Renal Failure

Creatol (CTL) is a hydroxyl radical adduct of creatinine (Cr). The serum methylguanidine (MG) level and the MG/Cr molar ratio are reported to be biomarkers for oxidative stress. The aim of this study was to examine whether urinary excretion of CTL, another oxidative stress-related marker, is increased in patients with chronic renal failure (CRF). One hundred twenty-four non-dialyzed patients with chronic renal failure (serum Cr level, 1.3–10.0 mg/dL) were recruited from our hospitals. Urine and serum levels of CTL and MG were determined by high-performance liquid chromatography with the use of 9, 10- phenanthrenequinone as a fluorogenic reagent. The CTL/Cr and (CTL+MG)/Cr molar ratios in spot urine samples were also compared with those in 24-h urine samples. The urinary CTL/Cr and (CTL+MG)/Cr molar ratios increased with decreases in Cr clearance in patients with CRF. Correlations between serum and spot urine (CTL+MG)/Cr and between serum and spot urine CTL/Cr were quite similar to those in 24-h urine samples. CTL/Cr and (CTL+MG)/Cr molar ratios in both 24-h urine and spot urine samples appear to be useful indices of the severity of CRF.

Studies on platelet function in patients with prostatic cancer: Preliminary report

Platelet function was evaluated as an index of the thromboembolic tendency in patients with untreated, advanced prostatic cancer. Patients with benign prostatic hypertrophy (BPH) and similar age distribution served as a comparison group. Platelet aggregations were elevated in both groups, but not significantly different from each other. Platelet serotonin level in patients with prostatic cancer was lower than in patients with BPH (p less than 0.01), whereas plasma serotonin level in patients with prostatic cancer (within normal ranges in our series) was lower than in patients with BPH (p less than 0.001). Levels of 2 intraplatelet proteins, beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) in the two groups of patients were similar. However, levels of beta-TG were elevated significantly in both groups of patients compared with those of healthy individuals. These studies revealed that the platelet serotonin levels in advanced prostatic cancer patients differed significantly from those in patients with BPH. The platelet serotonin level thus may provide an index of platelet activation in patients with prostatic cancer.

Synthesis of creatol, a hydroxyl radical adduct of creatinine and its increase by puromycin aminonucleoside in isolated rat hepatocytes

Creatol is a hydroxyl radical adduct of creatinine and the precursor of methylguanidine (MG), a uremic toxin. We investigate the synthesis of creatol and MG from creatinine and the effect of substances that affect the hydroxyl radical in isolated rat hepatocytes. In the presence of increasing concentrations of creatinine, rising level of creatol were found after 2 h incubation in Krebs-Henseleit bicarbonate buffer. However, further increase of creatol was not observed after 4 and 6h incubations. On the other hand, MG after 2 h incubation achieved a level of about 50% that of creatol and increased depending on both the creatinine concentration and the incubation period. DMSO, a hydroxyl radical scavenger decreased the generation of creatol and MG by about 50% at 2.5 mM and the inhibition depended on DMSO concentration. Puromycin amino-nucleoside (PAN) increased both by about 170%. These findings demonstrated that hepatocytes synthesize creatol prior to MG and are inhibited by a hydroxyl] radical scavenger. They also show that PAN increased hydroxyl radical generation in tissue cells.

Intraglomerular Monocytes in Human Glomerulonephritis

A total of 246 cases of 166 primary glomerulonephritis (GN) and 80 secondary GN were examined for the presence of intraglomerular monocytes using nonspecific esterase reaction of alpha-naphthyl butyrate methods. The high score of monocyte index (MI) as the numbers of monocytes per glomerulus was found in crescentic GN (n = 5, MI = 3.72 +/- 1.98), endocapillary proliferative GN (n = 8, MI = 2.17 +/- 2.13), lupus nephritis (n = 43, MI = 2.21 +/- 3.35), and cryoglobulinemia-related GN (n = 1, MI = 11.5). The intermediate score of MI was observed in IgA nephropathy (IgA-N, n = 64, MI = 0.63 +/- 0.42) and Henoch-Schönlein purpura nephritis (HSP-N, n = 11, MI = 1.09 +/- 0.87). Out of IgA-N and HSP-N, the scores of MI in patients with more severe proliferation and/or with segmental lesions were higher than those without this histological finding. However, there was not a significant correlation between the glomerular monocytic infiltration and clinical findings in each group. In primary GN including minor glomerular abnormalities, focal glomerular sclerosis and membranous GN, and in secondary renal diseases except for SLE, HSP, and cryoglobulinemia, the score of intraglomerular monocytic infiltration was of little value. The participation of monocytes was predominant in extra- and intracapillary GN, lupus nephritis, and cryoglobulinemia-related GN, as previously reported. Moreover, in some types of proliferative GN, especially IgA-N and HSP-N, some parts of glomerular hypercellularity result from the participation of monocyte-macrophage series, although the main parts of cell proliferation are intrinsic mesangial cells.