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Biomedical subjects

T Niwa

Publications and source records attributed to T Niwa.

At least 91 records · Page 5Linked to original sources
PubMed1998

RNA metabolism in uremic patients: accumulation of modified ribonucleosides in uremic serum. Technical note.

To determine the metabolism of ribonucleic acid (RNA) in uremia, serum and urine levels of ribonucleosides in uremic patients were analyzed using reversed-phase high-performance liquid chromatography. The serum levels of xanthosine and all modified ribonucleosides were increased in undialyzed patients with chronic renal failure (CRF), and patients undergoing hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD). The serum level of pseudouridine was markedly increased in all the uremic patients especially CAPD patients (32 times higher than normal). By contrast, the serum level of adenosine did not show any significant change in the uremic patients. Interestingly, the serum and urine levels of inosine were significantly decreased in all the uremic patients, suggesting that the production of inosine is decreased in uremic patients. The serum level of uridine was significantly elevated only in the HD patients. The serum levels of all ribonucleosides except inosine and uridine decreased significantly after HD. The urinary excretion of inosine, 1-methyladenosine, 1-methylguanosine, N2,N2-dimethylguanosine and N4-acetylcytidine was significantly decreased in the CRF patients, leading to the accumulation of these modified ribonucleosides in the uremic serum. CAPD patients showed markedly increased serum levels of modified ribonucleosides such as pseudouridine, 1-methylinosine, and N2,N2-dimethylguanosine and N4-acetylcytidine as compared with the HD patients. These results demonstrate that there was an altered metabolism of RNA in uremic patients with marked accumulation of modified ribonucleosides.

Chromatography, High Pressure Liquid↗
PubMed1998

Contribution of human hepatic cytochrome P450 isoforms to regioselective hydroxylation of steroid hormones.

1. Hydroxylation activities toward steroid hormones were determined for eleven forms of human hepatic cytochrome P450s expressed in yeast Saccharomyces cerevisiae cells. Microsomes were prepared from the yeast cells and assayed for their regioselectivity of hydroxylation toward progesterone, pregnenolone, dehydroepiandrosterone (DHEA) and oestrone. 2. 6 beta-Hydroxylation of progesterone was catalysed most efficiently by CYP3A4, followed by CYP2D6. CYP3A4 showed the highest progesterone 16 alpha-hydroxylation activity, followed by CYP1A1 and CYP2D6. 16 alpha-Hydroxylation of pregnenolone was catalysed efficiently by CYP1A1 and CYP3A4. Only CYP3A4 exhibited 16 alpha-hydroxylase activities toward DHEA and oestrone. 3. Addition of nifedipine, a typical substrate of CYP3A4, inhibited the 6 beta- and 16 alpha-hydroxylation of progesterone by CYP3A4. 4. These results suggest that CYP3A4 and CYP1A1 are responsible for the hydroxylation of these endogenous steroids, as well as xenobiotics, in human liver.

Aryl Hydrocarbon Hydroxylases↗
PubMed1998

Involvement of interleukin-8 in dialysis-related arthritis.

To elucidate the role of interleukin (IL)-8, a chemotactic factor for neutrophils, in dialysis-related arthritis (DRA) of patients on long-term hemodialysis, the concentration of IL-8 was measured in the synovial fluids of DRA patients with acute arthralgia and joint swelling, and was compared with those in patients with rheumatoid arthritis (RA) and patients with osteoarthritis (OA). We noted a marked elevation of IL-8 in the joint fluids of patients with DRA and RA as compared with OA. Furthermore, to determine the role of IL-8 in synovitis, we examined the in vivo effect of intra-articular injection of human recombinant IL-8 on leukocyte infiltration into the joint space of rabbits. A single injection of IL-8 to the joints of rabbits induced rapid infiltration of neutrophils into the joint space and synovial tissues, which reached a maximum in four hours. The oral administration of indometacin farnesil (a prodrug that is converted to indomethacin after intestinal absorption) before the injection of IL-8 alleviated the infiltration of neutrophils. When human synovial cells were incubated with tumor necrosis factor (TNF)-alpha, the expression of IL-8 mRNA and IL-8 production in the cultured synovial cells were increased. The TNF-alpha-stimulated expression of IL-8 mRNA and IL-8 production in the cultured synovial cells were markedly inhibited by dexamethasone. In conclusion, IL-8 levels were markedly elevated in the joint fluids of patients with DRA. Interleukin-8 released from synovial cells may be an important factor to induce acute inflammation in DRA. Dexamethasone and indomethacin may be effective for DRA by inhibiting the production and chemotactic actions of IL-8, respectively.

Adult↗
PubMed1998

Urinary excretion of pancreatic stone protein in diabetic nephropathy.

Urinary pancreatic stone protein (PSP) levels were measured in 68 diabetic patients and 170 healthy controls to investigate the relationship between the progression of diabetic nephropathy and PSP excretion. Urinary albumin, N-acetyl-beta-glucosaminidase (NAG), alpha1-microglobulin, creatinine clearance, and the blood PSP level were also determined in the diabetic patients. The urinary glucose level and glycemic control did not influence the urinary PSP level. In patients with normoalbuminuria (urinary albumin <20 mg/gCr, n=31), microalbuminuria (20-200 mg/Cr, n=19), and macroalbuminuria (>200 mg/gCr, n=18), the mean urinary PSP level was 347, 507, and 860 microg/gCr, respectively. These levels were significantly higher than the level in normal volunteers (168 microg/gCr, p<0.01). A significant positive correlation was observed between the urinary PSP level and the NAG or alpha1-microglobulin levels (p<0.01). There was a stronger correlation with alpha1-microglobulin. Blood PSP levels were also elevated in patients who had renal impairment with a decreased creatinine clearance. In conclusion, urinary PSP excretion was increased from the initial stage of diabetic nephropathy and this increase became more marked as nephropathy progressed. Increased PSP excretion may reflect renal tubular dysfunction.

Acetylglucosaminidase↗
PubMed1998

Acetylcholine activates intracellular movement of insulin granules in pancreatic beta-cells via inositol trisphosphate-dependent [correction of triphosphate-dependent] mobilization of intracellular Ca2+.

Intracellular movement of secretory granules is a proximal stage in the secretory cascade that ends in the release product from cells. We investigated mechanisms underlying the control of this movement by acetylcholine using an insulinoma cell line, MIN6, in which acetylcholine increases both insulin secretion and granule movement. The peak activation of movement was observed 3 min after an acetylcholine challenge. The effects were nullified by the muscarinic inhibitor atropine, phospholipase C (PLC) inhibitors (D 609 and compound 48/80), and pretreatment with the Ca2+ pump inhibitor, thapsigargin. Inhibitors of Ca2+-dependent phospholipase A2 (arachidonyl trifluoromethyl ketone and methyl arachidonyl fluorophosphate) also partially inhibited the movement caused by acetylcholine, but downregulation of protein kinase C by overnight incubation with the phorbol ester 12-o-tetradecanoylphorbol-13-acetate failed to exert any influence. Acetylcholine stimulation of granule movement was not reproduced by membrane depolarization with high K+. Phosphorylation of the endogenous myosin light chain in MIN6 cells was increased by addition of acetylcholine and decreased by the Ca2+ chelator BAPTA (1,2-bis[2-aminophenoxy]ethane-N,N,N',N'-tetraacetic acid). The calmodulin inhibitor W-7 and the myosin light-chain kinase inhibitor ML-9 decreased the motile events in the beta-cells under both nonstimulated and acetylcholine-stimulated conditions. These findings led us to conclude that inositol trisphosphate [corrected] causes Ca2+ mobilization by muscarinic activation of PLC, leading to intracellular translocation of insulin granules to the ready-releasable pool in pancreatic beta-cells via Ca2+/calmodulin-dependent phosphorylation of myosin light chains.

Acetylcholine↗
PubMed1998

Immunohistochemical detection of imidazolone and N(epsilon)-(carboxymethyl)lysine in aortas of hemodialysis patients.

The modification of long-lived proteins with advanced glycation endproducts (AGEs) has been hypothesised to contribute to the development of pathologies associated with uremia. Imidazolone and N(epsilon)-(carboxymethyl)lysine (CML) are common epitopes of AGE-modified proteins. Imidazolone is a reaction product of arginine with 3-deoxyglucosone (3-DG) which is markedly accumulated in uremic serum. CML is produced by glycoxidation, and represents a marker of oxidative stress. The specificity of anti-imidazolone antibody that we had developed was further examined using ELISA. The antibody reacted only with imidazolone derived from 3-DG and arginine, but did not react at all with the other imidazolone-like compounds such as reaction products of glyoxal, methylglyoxal, glucosone with arginine or a reaction product of 3-DG with creatine. Further, to determine if AGEs are involved in the development of atherosclerosis in hemodialysis (HD) patients, we studied the localisation of imidazolone and CML in the aortas obtained from HD patients by immunohistochemistry using the anti-imidazolone and anti-CML antibodies. Imidazolone and CML were localised in all atherosclerotic aortic walls of the HD patients. In conclusion, imidazolone and CML are localised in the characteristic lesions of atherosclerosis in HD patients. These results strongly suggest that imidazolone produced by 3-DG, and CML produced by glycoxidation may contribute to the development of atherosclerosis in uremic patients.

Aged↗
PubMed1998

Advanced glycation endproducts (AGE) on IgG, a target for circulating antibodies in North American Indians with rheumatoid arthritis (RA).

Several tribes of North American Indians are known to have poor glucose control and are at a high risk of developing type 2 diabetes. Similarly some tribes also exhibit RA at a high frequency. We have recently determined that a subset of Caucasian patients with RA mount an immune response to IgG modified with advanced glycation endproducts (AGE). The AGE modifications on IgG in vivo include N(epsilon)-(carboxymethyl) lysine, imidazolone and pentosidine. The presence of IgG-AGE and the antibody response to the IgG-AGE in the Ojibwe tribe of First Nations native Indians where both NIDDM and RA are prevalent was investigated. AGE modified IgG and albumin were determined using a modified nitroblue tetrazolium assay. Rheumatoid factors (RFs) and IgM and IgA anti-IgG-AGE were detected by ELISA. Of the 108 individuals tested, 21 had RA only, 3 had both RA and type 2 diabetes, 30 had type 2 diabetes only and 51 had no diagnosed disease. AGE modified IgG was significantly elevated in the RA group compared to the diabetic group. IgM and IgA RFs were detected in 83% and 50% of the RA patients, compared to 31-37% and 7-10% of the diabetics or normal individuals. IgM anti-IgG-AGE was detected in 54% of the RA patients, in contrast to 7-14% in the diabetics or normal individuals. IgA anti-IgG-AGE was detected in 42% of the RA patients and only 7 to 8% of the NIDDM or normal individuals. The IgM or IgA anti-IgG-AGE antibodies likely contribute to the accumulation of IgG-AGE, possibly through blocked clearance through AGE receptors. A trend towards more severe disease was seen in those Ojibwe RA patients with circulating anti-AGE antibodies. Non-enzymatic glycation may be an important pathogenic link in the RA seen in North American Indians.

Adult↗
PubMed1997

Imidazolone, a novel advanced glycation end product, is present at high levels in kidneys of rats with streptozotocin-induced diabetes.

We produced a monoclonal antibody to imidazolones A and B, novel advanced glycation end products formed from the reaction of 3-deoxyglucosone (3-DG) with the guanidino group of arginine. Liquid chromatography/mass spectrometry demonstrated that the formation of imidazolone A by incubating 3-DG with arginine is very rapid, reaching a maximum concentration within 24 h, but the formation of imidazolone B is very slow and low in quantity even after 2 weeks. Thus, at physiological conditions the formation of imidazolone A is dominant, while that of imidazolone B is negligible. Immunochemistry demonstrated that the imidazolone content in the kidneys of streptozotocin-induced diabetic rats was significantly higher than in the control rats. Serum levels of 3-DG in the diabetic rats were also significantly higher than in control rats. 3-DG attacks the arginine residues of the tissue proteins, producing imidazolone at high levels in the kidneys affected by diabetic nephropathy.

Animals↗
PubMed1997

Immunohistochemical detection of imidazolone, a novel advanced glycation end product, in kidneys and aortas of diabetic patients.

To investigate the role of the Maillard reaction in the pathogenesis of diabetic complications, we produced several clones of monoclonal antibodies against advanced glycation end products (AGEs) by immunizing mice with AGE-modified keyhole limpet hemocyanin, and found that one clone (AG-1) of the anti-AGE antibodies reacted specifically with imidazolones A and B, novel AGEs. Thus, the imidazolones, which are the reaction products of the guanidino group of arginine with 3-deoxyglucosone (3-DG), a reactive intermediate of the Maillard reaction, were found to be common epitopes of AGE-modified proteins produced in vitro. We determined the erythrocyte levels of imidazolone in diabetic patients using ELISA with the monoclonal anti-imidazolone antibody. The imidazolone levels in the erythrocytes of diabetic patients were found to be significantly increased as compared with those of healthy subjects. Then we studied the localization of imidazolone in the kidneys and aortas obtained from diabetic patients by immunohistochemistry using the antibody. Specific imidazolone immunoreactivity was detected in nodular lesions and expanded mesangial matrix of glomeruli, and renal arteries in an advanced stage of diabetic nephropathy, as well as in atherosclerotic lesions of aortas. This study first demonstrates the localization of imidazolone in the characteristic lesions of diabetic nephropathy and atherosclerosis. These results, taken together with a recent demonstration of increased serum 3-DG levels in diabetes, strongly suggest that imidazolone produced by 3-DG may contribute to the progression of long-term diabetic complications such as nephropathy and atherosclerosis.

Adolescent↗
PubMed1997

Cytotoxicity of endogenous isoquinolines to human dopaminergic neuroblastoma SH-SY5Y cells.

Endogenous isoquinolines with and without catechol structure have been proposed to be neurotoxins specific for dopamine neurons. In this paper they were examined for the cytotoxicity of human dopaminergic neuroblastoma SH-SY5Y cells. The cytotoxicity was quantitatively determined using Alamar Blue assay, by which the reduction-oxidation potency in the living cells can be measured spectrometrically. 1,2-Dimethyl-6,7-dihydroxyisoquinolinium ion [1,2-DMDHIQ+], an oxidation product of a parkinsonism-inducing isoquinoline, 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahroisoquinoline [N-methyl-(R)salsolinol, NM(R)Sal] was found to be the most potent toxin among isoquinolines examined. In general, catechol isoquinolines were more toxic than isoquinolines without catechol structure. With and without catechol structure, the oxidized isoquinolinium ion having methyl groups at C-1 and N-2 positions proved to be more cytotoxic than the simple isoquinolines. The involvement of 1,2-DMDHIQ+ to the neurotoxicity of NM(R)Sal was suggested and discussed.

Cell Survival↗
PubMed1997

Amyloid beta 2-microglobulin is modified with imidazolone, a novel advanced glycation end product, in dialysis-related amyloidosis.

We have recently demonstrated by immunohistochemistry that amyloid beta 2-microglobulin (beta 2m) is modified with advanced glycation end products (AGEs) in dialysis-related amyloidosis (DRA). To further investigate the role of the Maillard reaction in the pathogenesis of DRA, we produced a monoclonal antibody to imidazolone, a novel AGE, and a reaction product of arginine and 3-deoxyglucosone (3-DG) which was accumulated in uremic serum. Then we determined the localization of imidazolone in the amyloid tissues by immunohistochemistry using the antibody. The connective tissues in carpal tunnel and ligamentum flavum were obtained from six patients with carpal tunnel syndrome and two patients with destructive spondyloarthropathy. Imidazolone was localized to all the beta 2m-positive amyloid deposits in these patients. Western blotting using the antibody demonstrated that beta 2m extracted from the synovium amyloid of hemodialysis patients was modified with imidazolone. Further, beta 2m isolated from the blood ultrafiltrate of hemodialyzed patients was also modified with imidazolone. In vitro incubation of beta 2m with 3-DG produced imidazolone-modified beta 2m. In conclusion, amyloid tissue beta2m is modified with imidazolone in patients with DRA. 3-DG accumulating in uremic serum may be involved in the modification of beta 2m with imidazolone.

Aged↗
PubMed1997

Preventive action of vitamin E-containing liposomes on cataractogenesis in young adult rats fed a 25% galactose diet.

The preventive action of vitamin E (Vit. E)-containing liposomes on cataractogenesis was examined in male Wistar rats (five weeks old) fed a 25% galactose diet. Vit. E-containing liposomes prepared with dipalmitoylphosphatidylcholine were instilled into both eyes three times a day over a 45-day period. Cataract appeared at 18-day galactose feeding and developed gradually thereafter. Simultaneous Vit. E-containing liposome instillation delayed this cataractogenesis. Lenses of 18-day galactose-fed rats showed decreases in Vit. E and reduced glutathione (GSH) contents and Na+, K(+)-ATPase activity and increases in lipid peroxide (LPO), galactitol, and water contents. Lenses of 45-day galactose fed rats showed decreases in GSH content and Na+,K(+)-ATPase activity and increases in Vit. E, LPO, galactitol, and water contents. Serum Vit. E and cholesterol levels decreased in 18-day galactose-fed rats, while both levels increased in 45-day galactose-fed rats. Simultaneous Vit. E-containing liposome instillation prevented these changes except for the changes of lenticular galactitol and water contents and serum Vit. E and cholesterol levels. These results indicate that simultaneously instilled Vit. E-containing liposomes can delay cataractogenesis in young adult rats fed a 25% galactose diet mainly by the antioxidative action of Vit. E contained in the instilled liposomes.

Animals↗
PubMed1997

Determination of advanced glycation end products in serum by fluorescence spectroscopy and competitive ELISA.

Recent studies suggest that advanced glycation endproducts play an important role in cardiovascular complications of ageing, diabetes and end-stage renal failure. Since highly elevated levels of advanced glycation endproducts are present in serum of patients on maintenance haemodialysis, an accurate and rapid assay for their determination would be useful. This would be particularly valuable for monitoring the removal of advanced glycation endproducts by novel dialysis membranes, as well as the effect of new drugs for the inhibition of their formation. Measurement of advanced glycation endproducts in serum was performed by two competitive ELISAs, using a monoclonal antibody directed against imidazolone, an advanced glycation endproduct formed by the reaction of arginine with 3-deoxyglucosone, and a polyclonal antibody directed against keyhole limpet haemocyanin-advanced glycation endproduct, as well as by quantitative fluorescence spectroscopy. Each of the assays showed significant differences between the controls and the maintenance haemodialysis patients. Advanced glycation endproduct levels determined by each of the ELISAs correlated with total and protein-bound fluorescence, but not with each other, suggesting a variable distribution of advanced glycation endproducts on serum proteins among the maintenance haemodialysis patients.

Aged↗
PubMed1997

Indoxyl sulfate increases the gene expressions of TGF-beta 1, TIMP-1 and pro-alpha 1(I) collagen in uremic rat kidneys.

We recently reported that the serum levels of indoxyl sulfate, a dietary protein metabolite, are increased in both uremic rats and patients, and that the administration of indoxyl sulfate to uremic rats accelerates the progression of glomerular sclerosis. Thus, we hypothesize that the overload of protein metabolites such as indoxyl sulfate on nephrons promotes the progression of chronic renal failure (CRF). Recent studies revealed that tubulointerstitial injury is of equal or greater importance than glomerular sclerosis in determining whether progressive renal dysfunction will ensue in various renal diseases. In the present study, to clarify the role of indoxyl sulfate in the progression of CRF, the expressions of genes related to tubulointerstitial fibrosis such as transforming growth factor (TGF)-beta 1, tissue inhibitor of metalloproteinases (TIMP-1) and pro-alpha 1(I) collagen were examined in the renal cortex of 5/6-nephrectomized uremic rats given indoxyl sulfate. In the first experiment, the administration of indoxyl sulfate for five weeks significantly increased the mRNA levels of TGF-beta 1, TIMP-1 and pro-alpha 1(I) collagen in the uremic rats given indoxyl sulfate compared with the control uremic rats, accompanied by a significant decline in renal function and worsening of glomerular sclerosis. In the second experiment, the administration of indoxyl sulfate for 2.5 weeks also increased the expression of the mRNA levels with no significant decline in the renal function. In conclusion, these findings indicate that the overload of the protein metabolite indoxyl sulfate on remnant nephrons is involved in the increased bioactivity of TGF-beta 1 in uremic kidneys, which enhances the renal expression of TIMP-1 and type 1 collagen, leading to the progression of CRF.

Administration, Oral↗
PubMed1997

The protein metabolite hypothesis, a model for the progression of renal failure: an oral adsorbent lowers indoxyl sulfate levels in undialyzed uremic patients.

We have recently demonstrated that indoxyl sulfate promotes the progression of glomerular sclerosis in uremic rats. In the present study, we determined whether an oral adsorbent (AST-120) could reduce the serum and urine levels of indoxyl sulfate and suppress the progression of chronic renal failure (CRF) in undialyzed uremic patients. Twenty-five undialyzed uremic patients were given AST-120 at a dose of 6 g/day for 6 months, while 10 undialyzed uremic patients were not given AST-120. The effects of the oral adsorbent on the slope of the 1/serum creatinine (Scr)-time plot, and the serum and urine levels of indoxyl sulfate were evaluated. Administration of AST-120 significantly decreased the serum and urine levels of indoxyl sulfate, and tended to improve the slope of the 1/SCr-time plot in the CRF patients. Among the patients in whom urinary excretion of indoxyl sulfate was reduced by AST-120, the oral adsorbent significantly improved the slope of the 1/SCr-time plot. The change in the slope of the 1/SCr-time plot showed a significant negative correlation with the change in the urine level of indoxyl sulfate. Thus, patients who showed a greater decrease of urinary indoxyl sulfate also showed more marked suppression of the progression of CRF. These results support the notion that indoxyl sulfate, a protein metabolite, is involved in the progression of CRF, and that an oral adsorbent can delay progression at least partly by reducing the serum and urine levels of indoxyl sulfate.

Administration, Oral↗