Yasuhiko Ueda

Angiotensin II Receptor Antagonists and Angiotensin-Converting Enzyme Inhibitors Lower In Vitro the Formation of Advanced Glycation End Products: Biochemical Mechanisms

The implication of advanced glycation end products (AGE) in the pathogenesis of atherosclerosis and of diabetic and uremic complications has stimulated a search for AGE inhibitors. This study evaluates the AGE inhibitory potential of several well-tolerated hypotensive drugs. Olmesartan, an angiotensin II type 1 receptor (AIIR) antagonist, as well as temocaprilat, an angiotensin-converting enzyme (ACE) inhibitor, unlike nifedipine, a calcium blocker, inhibit in vitro the formation of two AGE, pentosidine and N(epsilon)-carboxymethyllysine (CML), during incubation of nonuremic diabetic, nondiabetic uremic, or diabetic uremic plasma or of BSA fortified with arabinose. This effect is shared by all tested AIIR antagonists and ACE inhibitors. On an equimolar basis, they are more efficient than aminoguanidine or pyridoxamine. Unlike the latter two compounds, they do not trap reactive carbonyl precursors for AGE, but impact on the production of reactive carbonyl precursors for AGE by chelating transition metals and inhibiting various oxidative steps, including carbon-centered and hydroxyl radicals, at both the pre- and post-Amadori steps. Their effect is paralleled by a lowered production of reactive carbonyl precursors. Finally, they do not bind pyridoxal, unlike aminoguanidine. Altogether, this study demonstrates for the first time that widely used hypotensive agents, AIIR antagonists and ACE inhibitors, significantly attenuate AGE production. This study provides a new framework for the assessment of families of AGE-lowering compounds according to their mechanisms of action.

Renal Proximal Tubular Metabolism of Protein-Linked Pentosidine, an Advanced Glycation End Product

Background: Pentosidine, an advanced glycation end product, accumulates in plasma proteins of uremic patients. Its fate is, however, yet to be fully understood. Methods: Three cell lines, JTC-12 (proximal tubular cells), MDCK (distal tubular cells), and BALB3T3 (nonrenal cells), were cultured in a double chamber system and were exposed to uremic serum, and the contents of protein-linked pentosidine derived from uremic sera were determined in each medium by HPLC assay. The presence of pentosidine in the cytoplasm of these cells was assessed by immunoperoxidase staining. Results: When the apical cell membrane was exposed to uremic serum (fortified in the upper chamber), the contents of protein-linked pentosidine in the upper medium decreased by up to 30% after 24- and 48-hour incubations of JTC-12 cells but not of other cells. On the other hand, the contents of protein-linked pentosidine in the lower medium did not change. By contrast, exposure of the basolateral cell membrane of the three cell lines to uremic serum (fortified in the lower chamber) did not change the contents of protein-linked pentosidine both in the upper and lower medium after a 24-hour incubation. Pentosidine was detected immunohistochemically in the cytoplasm of JTC-12 cells, but not of BALB3T3 and MDCK cells, the apical membranes of which were exposed to uremic sera for 8 h. The immunoreaction disappeared 48 h after exposure. Pentosidine was not detected in the cytoplasm of JTC-12 cells, the basolateral membranes of which were exposed to uremic sera. The relevance of the in vitro results to humans was demonstrated by immunohistochemical studies in normal human kidney tissues showing that pentosidine was identified in the proximal renal tubules. Conclusion: These results suggest that the proximal tubular cells play a role in the disposal of plasma pentosidine.

Microscopic characterization and electrochemical behavior of high-dose carbon-implanted stainless steels

Abstract A study was made of the electrochemical properties and microscopic characteristics of types 304 and 430 stainless steel implanted at room temperature with carbon at a dosed of 10 18 ions cm -2 at 100 keV. The electrochemical properties were measured by multisweep cyclic voltammetry in a solution of H 2 SO 4 + Na 2 SO 4 . X-ray diffraction and X-ray photoelectron spectroscopy were used to analyze the structure, composition depth profiles and chemical bonding states of carbon-implanted layers. Carbon implantation suppressed the dissolution with transpassivation of stainless steels without influencing adversely their excellent passivity. The amorphized carbon-implanted layers were composed of graphitic solid state carbon, which had a gaussian depth profile corresponding to the distribution of implanted carbon, and metallic carbide with a uniform chemical state in the region containing more than approximately 20 at.% carbon. From these investigations, it is proposed that room-temperature carbon implantation at a very high dose can improve the aqueous corrosion resistance of stainless steels owing to the formation of amorphous layers consisting of graphitic solid state carbon and metallic carbide.

Microscopic characteristics and electrochemical properties of carbon-implanted steels in a non-aqueous acetic acid medium

Abstract A study has been made of the microscopic characteristics such as surface composition and structure, and electrochemical properties of C + -implanted low carbon steel (JIS-SS41) and Type 304 stainless steel. Implantation of 12 C + was performed with 10 18 ions/cm 2 at 100 keV, and at nearly room temperature. XPS and XRD were used to analyze the depth dependence of the atomic fraction and the chemical bonding states of carbon, and the crystal structure of implanted layers, respectively. The electrochemical reaction was measured in a non-aqueous acetic acid medium. The implanted C-atoms showed a Gaussian-like distribution and formed bonds with both matrix elements and carbon itself. In particular, C + -implantation formed metastable iron-carbides in SS41, but such crystalline carbides were hardly observed in 304SS. High-dose C + -implantation resulted in passivation of the anodic reaction of steels most probably by forming inert CC bonds.

Accelerated glomerular injury in hemi-nephrectomized transgenic mice of mesangial cell-predominant serpin, megsin.

Mesangial cells play a critical role in the maintenance of normal glomerular functions such as matrix remodeling and immune complex disposal. We recently identified a novel human mesangium-predominant gene, megsin, which is a new member of the serine protease inhibitor (serpin) superfamily. While our previous studies demonstrated progressive mesangial matrix expansion and an increase in the number of mesangial cells in megsin transgenic mice, it took 40 weeks to develop these manifestations. Here we performed hemi-nephrectomy to accelerate glomerular injury in megsin transgenic mice. Hemi-nephrectomized transgenic mice developed focal segmental mesangial expansion, which was associated with proteinuria. Megsin has thus a biologically relevant influence on the development of glomerular damage. The hemi-nephrectomized model of this transgenic mouse might serve as a tool to investigate the mechanisms of glomerular disease.

Glyoxalase I deficiency is associated with an unusual level of advanced glycation end products in a hemodialysis patient

Abstract Advanced glycation of proteins and their attendant advanced glycation end products (AGEs) contribute to the complications associated with diabetes mellitus or uremia. Here we report a patient in whom the glyoxalase detoxification system of precursor reactive carbonyl compounds (RCOs) is implicated in the in vivo AGE formation. This 69-year-old lady had been on hemodialysis (HD) for 3 years and had suffered from recurrent cardiovascular complications despite the absence of risk factors. Plasma levels of pentosidine and carboxymethyllysine (CML) were markedly elevated as compared to other HD patients. Plasma level of RCO precursors for pentosidine and CML was also higher than in other HD patients. Further investigation disclosed a very low activity in red blood cells (RBC) of glyoxalase I, an enzyme essential for the detoxification of oxoaldehydes. The glycoxalase I protein level, assessed in RBC by immunoblot analysis with a specific antibody, was also markedly lower than that observed in HD patients and normal subjects. Nucleotide sequencing of the products of RT-PCR from the patients mononuclear cells revealed no genetic mutation within the coding region of the glyoxalase I gene. Plasma d -lactate level, the final product resulting from the glyoxalase detoxification pathway, was also in the lower range of the values measured in the other HD patients and normal subjects. The plasma levels of various compounds known to generate AGE precursors as well as the surrogate markers for oxidative stress such as antioxidant enzymes and glutathione were all within the range observed in the other HD patients. These data suggest that the unusually high levels of AGEs in this patient implicates a deficient glyoxalase detoxification of carbonyl precursors.