Broadened quantum critical ground state in a disordered superconducting thin film

A superconductor-insulator transition (SIT) in two dimensions is a prototypical quantum phase transition (QPT) with a clear quantum critical point (QCP) at zero temperature (T = 0). The SIT is induced by a field B and observed in disordered thin films. In some of weakly disordered or crystalline thin films, however, an anomalous metallic (AM) ground state emerges over a wide B range between the superconducting and insulating phases. It remains a fundamental open question how the QPT picture of the SIT is modified when the AM state appears. Here we present measurements of the Nernst effect N, which has great sensitivity to the fluctuations of the superconducting order parameter. From a thorough contour map of N in the B-T plane, we found a thermal-to-quantum crossover line of the superconducting fluctuations, a so-called ghost-temperature line associated with the QPT, as well as a ghost-field line associated with a thermal transition. The QCP is identified as a T = 0 intercept of the ghost-temperature line inside the AM state, which verifies that the AM state is a broadened critical state of the SIT.

Evidence of second-order transition and critical scaling for the dynamical ordering transition in current-driven vortices

Dynamical ordering from a disordered plastic flow to an anisotropically ordered smectic flow induced by a dc force has been studied in various many-particle systems, including vortices in type-II superconductors. However, it remains unclear whether the dynamical ordering is a true phase transition because of lack of suitable experimental methods. Here, we study the response of vortex flow to the transverse force using a cross-shaped amorphous Mo[Formula: see text]Ge[Formula: see text] film. From transverse current-voltage (force-velocity) characteristics under various longitudinal currents, we find a change of the transverse response in low voltage (velocity) regions from a nonlinear to linear behavior at a well-defined longitudinal current that marks the dynamical ordering transition. We also find the scaling collapse of the transverse current-voltage curves to a universal scaling function, providing evidence of the second-order transition for the dynamical ordering transition.

Kibble-Zurek Mechanism for Dynamical Ordering in a Driven Vortex System

The Kibble-Zurek mechanism describes the formation of topological defects in systems crossing a continuous symmetry-breaking phase transition at a finite quench rate. While this mechanism has been extensively studied for equilibrium transitions, its applicability to nonequilibrium transitions has not yet been fully examined. Recent simulation has shown the applicability of the Kibble-Zurek mechanism to dynamical ordering transitions in particlelike assemblies, including superconducting vortices, driven over random disorder. Here, we experimentally study the configurational order of vortices in the course of dynamical ordering with various quench rates. We verify a power-law scaling of the defect density with the quench rate and an impulse-adiabatic crossover on the ordered side of the transition, which are key predictions of the Kibble-Zurek mechanism. Our results suggest the applicability of the Kibble-Zurek mechanism to other nonequilibrium phase transitions.

Critical behavior of nonequilibrium depinning transitions for vortices driven by current and vortex density

We study the critical dynamics of vortices associated with dynamic disordering near the depinning transitions driven by dc force (dc current I) and vortex density (magnetic field B). Independent of the driving parameters, I and B, we observe the critical behavior of the depinning transitions, not only on the moving side, but also on the pinned side of the transition, which is the first convincing verification of the theoretical prediction. Relaxation times, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau (I)$$\end{document}τ(I) and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau (B)$$\end{document}τ(B), to reach either the moving or pinned state, plotted against I and B, respectively, exhibit a power-law divergence at the depinning thresholds. The critical exponents of both transitions are, within errors, identical to each other, which are in agreement with the values expected for an absorbing phase transition in the two-dimensional directed-percolation universality class. With an increase in B under constant I, the depinning transition at low B is replaced by the repinning transition at high B in the peak-effect regime. We find a trend that the critical exponents in the peak-effect regime are slightly smaller than those in the low-B regime and the theoretical one, which is attributed to the slight difference in the depinning mechanism in the peak-effect regime.

Critical behavior of density-driven and shear-driven reversible-irreversible transitions in cyclically sheared vortices

Random assemblies of particles subjected to cyclic shear undergo a reversible–irreversible transition (RIT) with increasing a shear amplitude d or particle density n, while the latter type of RIT has not been verified experimentally. Here, we measure the time-dependent velocity of cyclically sheared vortices and observe the critical behavior of RIT driven by vortex density B as well as d. At the critical point of each RIT, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$B_{\mathrm {c}}$$\end{document}Bc and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d_{\mathrm {c}}$$\end{document}dc, the relaxation time \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau $$\end{document}τ to reach the steady state shows a power-law divergence. The critical exponent for B-driven RIT is in agreement with that for d-driven RIT and both types of RIT fall into the same universality class as the absorbing transition in the two-dimensional directed-percolation universality class. As d is decreased to the average intervortex spacing in the reversible regime, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau (d)$$\end{document}τ(d) shows a significant drop, indicating a transition or crossover from a loop-reversible state with vortex-vortex collisions to a collisionless point-reversible state. In either regime, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau (d)$$\end{document}τ(d) exhibits a power-law divergence at the same \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d_{\mathrm {c}}$$\end{document}dc with nearly the same exponent.

Quantum Criticality inside the Anomalous Metallic State of a Disordered Superconducting Thin Film

The field-induced superconductor-insulator transition (SIT) in two-dimensional (2D) systems is a famous example of a quantum phase transition. However, an emergence of an anomalous metallic state induced by field has been a long-standing problem in 2D superconductors. While theories predicted that the emergence is attributed to strong phase fluctuations of the superconducting order parameter due to quantum fluctuations, usual resistance measurements have not probed them directly. Here, using Nernst effect measurements, we uncover superconducting fluctuations in the vicinity of the field-induced metallic state in an amorphous Mo_{x}Ge_{1-x} thin film. The field range where the vortex Nernst signals are detectable remains nonzero toward zero temperature, and it locates inside the metallic state defined by the magnetoresistance, indicating that the metallic state results from quantum vortex liquid (QVL) with phase fluctuations due to quantum fluctuations. Slow decay of transport entropy of vortices in the QVL with decreasing temperature suggests that the metallic state originates from broadening of a quantum critical point in SIT.

Natural van der Waals heterostructural single crystals with both magnetic and topological properties

Heterostructures having both magnetism and topology are promising materials for the realization of exotic topological quantum states while challenging in synthesis and engineering. Here, we report natural magnetic van der Waals heterostructures of (MnBi₂Te₄) _m (Bi₂Te₃) _n that exhibit controllable magnetic properties while maintaining their topological surface states. The interlayer antiferromagnetic exchange coupling is gradually weakened as the separation of magnetic layers increases, and an anomalous Hall effect that is well coupled with magnetization and shows ferromagnetic hysteresis was observed below 5 K. The obtained homogeneous heterostructure with atomically sharp interface and intrinsic magnetic properties will be an ideal platform for studying the quantum anomalous Hall effect, axion insulator states, and the topological magnetoelectric effect.

Modulation of Electron-Phonon Coupling in One-Dimensionally Nanorippled Graphene on a Macrofacet of 6H-SiC

Local electron-phonon coupling of a one-dimensionally nanorippled graphene is studied on a SiC(0001) vicinal substrate. We have characterized local atomic and electronic structures of a periodically nanorippled graphene (3.4 nm period) prepared on a macrofacet of the 6H-SiC crystal using scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoelectron spectroscopy (ARPES). The rippled graphene on the macrofacets distributes homogeneously over the 6H-SiC substrate in a millimeter scale, and thus replica bands are detected by the macroscopic ARPES. The STM/STS results indicate the strength of electron-phonon coupling to the out-of-plane phonon at the K̅ points of graphene is periodically modified in accordance with the ripple structure. We propose an interface carbon nanostructure with graphene nanoribbons between the surface rippled graphene and the substrate SiC that periodically modifies the electron-phonon coupling in the surface graphene.

Orbital Selectivity in Scanning Tunneling Microscopy: Distance-Dependent Tunneling Process Observed in Iron Nitride

In scanning tunneling microscopy, orbital selectivity of the tunneling process can make the topographic image dependent on a tip-surface distance. We have found reproducible dependence of the images on the distance for a monatomic layer of iron nitride formed on a Cu(001) surface. Observed atomic images systematically change between a regular dot array and a dimerized structure depending on the tip-surface distance, which turns out to be the only relevant parameter in the image variation. An accompanied change in the weight of Fe-3d local density of states to a tunneling background was detected in dI/dV spectra. These have been attributed to a shift in surface orbitals detected by the tip from the d states to the s/p states with increasing the tip-surface distance, consistent with an orbital assignment from first-principles calculations.

Crosslines, fluorophores in the AGE-related cross-linked proteins

We can summarize our results as follows: (1) A pair of fluorescent crosslines were isolated from the Maillard reaction mixture; (2) AGE-proteins contained crossline-like structures, and (3) crossline-like immunoreactivities were accumulated in renal tissues of diabetic rats. From these results we concluded that fluorophores in AGE proteins have crossline-like structures and we had the first indication that XLs could be markers for renal disorders.

Creatinine and HMH (5-hydroxy-1-methylhydantoin, NZ-419) as intrinsic hydroxyl radical scavengers

Creatinine (Crn) is one of the main intrinsic hydroxyl radical (•OH) scavengers and an ideal one for healthy or normal mammals, although this fact has not yet become widely accepted. Our results from urinary data estimated that ca. 0.4-0.6% of Crn is used daily to scavenge •OH in normal mammals [ca. 50 μmole and ca. 400 pmole of •OH in healthy subjects and normal rats, respectively]. In human subjects, Crn reacts non-enzymatically with •OH to form creatol (CTL: 5-hydroxycreatinine) and demethylcreatinine (DMC) in a one to one ratio, and CTL partially decomposes to methylguanidine (MG). And so, the scavenged mole of •OH by Crn is nearly equal to their molar total sum (CTL + MG + DMC) or 2 × (CTL + MG). The molar ratio of (scavenged •OH)/Crn in healthy subjects and normal rats are 4.4 and 6.0 mmole/mole, respectively, i.e. almost similar, but in patients with chronic kidney disease (CKD) the ratio increases up to ca. 60 mmole/mole in proportion to the severity of CKD. Since the level of Crn might not be enough to scavenge all •OH, and MG starts accumulating as a uremic toxin, Crn is not really the ideal scavenger. 5-Hydroxy-1-methylhydantoin (HMH, NZ-419), a Crn metabolite, is another antioxidant, having •OH scavenging ability, and has been shown to inhibit the progression of CKD in rats in stead of Crn, if sufficient amounts are given orally.

The role of protein kinase C in the increased generation in isolated rat hepatocytes of the hydroxyl radical by puromycin aminonucleoside

Puromycin aminonucleoside (PAN) has been known to induce proteinuria. The increased generation of reactive oxygen species (ROS) has been implicated in this toxicity of PAN. We have reported that PAN increases the synthesis of methylguanidine (MG) and creatol which are the products of the reaction of creatinine and the hydroxyl radical in isolated rat hepatocytes. However, the mechanism for the increased ROS induced by PAN is still unclear. In this paper, we investigate the role of protein kinase C (PKC) on the PAN induced reactive oxygen generation in isolated rat hepatocytes. Isolated hepatocytes were incubated in Krebs-Henseleit bicarbonate buffer containing 3% BSA, 16.6 mM creatinine and tested reagents. MG and creatol were determined by high-performance liquid chromatography using 9,10-phenanthrenequinone for the post-labeling. PAN increased MG and creatol synthesis in isolated rat hepatocytes by 60%. 1-(5-Isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), a PKC inhibitor, at 10 and 100 microM significantly inhibited MG and creatol synthesis with or without PAN. The inhibition rate is dose dependent from 10 to 100 microM. H1004, a reagent used as control for H-7, did not affect (at 10 microM) or increased little (at 100 microM) the synthesis of MG and creatol. Ro31-8425, a potent PKC inhibitor, significantly inhibited (at 10 microM) MG synthesis in the presence of PAN. PKC in the membrane fraction, a marker of PKC activation, increased over the initial concentration by a factor of 1.65-fold at 60 min incubation and 2.16-fold at 120 min with PAN, while it changed little without PAN. These results indicate that PAN activates PKC resulting in increased hydroxyl radical generation in isolated rat hepatocytes.

Crossline levels in serum and erythrocyte membrane proteins from patients with diabetic nephropathy

Crossline is one of the structurally defined adducts of advanced glycation endproducts (AGEs) which has both a crosslink and fluorescence similar to AGE-protein in vivo. Crossline was measured in serum and erythrocyte membrane proteins (EMP) from 52 type 2 diabetic patients using a specific enzyme-linked immunosorbent assay system. Serum and EMP crossline levels in the diabetic patients were significantly higher than those in normal control. The patients with advanced diabetic nephropathy (serum creatinine levels of more than 1.2 mg/dl) had markedly elevated serum crossline levels compared to those with moderate diabetic nephropathy (clinical proteinuria) (180. 7+/-51.7 vs. 71.8+/-18.4 pmol/ml; P<0.01). On the other hand, there were no significant differences in EMP crossline levels between the two. EMP crossline levels in the patients with moderate diabetic nephropathy (8.8+/-2.9 pmol/mg protein) and those with advanced diabetic nephropathy (9.7+/-3.0 pmol/mg protein) were significantly higher than those without clinical proteinuria (6.4+/-1.9 pmol/mg protein; P<0.01). The present study demonstrated that EMP crossline levels were associated with the presence of nephropathy in patients with type 2 diabetes mellitus. Serum crossline levels were significantly influenced by remaining renal function. The measurement of crossline from a blood sample could provide us with important information for the study of clinical evaluation and pathogenesis of diabetic complications.

A protein kinase C-beta-selective inhibitor ameliorates neural dysfunction in streptozotocin-induced diabetic rats

Increased protein kinase C (PKC) activity has been implicated in the pathogenesis of diabetic retinopathy and nephropathy. However, the role of PKC in diabetic neuropathy remains unclear. The present study was conducted to compare the effect of PKC inhibition by a PKC-beta-selective inhibitor, LY333531 (LY), on diabetic nerve dysfunction with that of an aldose reductase inhibitor, NZ-314 (NZ). Streptozotocin-induced diabetic rats were treated with or without LY and/or NZ for 4 weeks, and motor nerve conduction velocity (MNCV), coefficient of variation of R-R interval (CVR-R), sciatic nerve blood flow (SNBF), peak latencies of oscillatory potentials on electroretinogram, PKC activities in membranous and cytosolic fractions of sciatic nerves, and polyol contents in the tail nerves were measured. Untreated diabetic rats demonstrated delayed MNCV, decreased CVR-R, reduced SNBF, and prolonged peak latencies of oscillatory potentials. Treatment with LY as well as NZ prevented all these deficits in diabetic rats. There were no significant differences in PKC activities in membranous or cytosolic fractions of sciatic nerves between normal and diabetic rats. Treatment with neither LY nor NZ altered PKC activities. Nerve myo-inositol depletion in diabetic rats was ameliorated not only by NZ, but also by LY. These observations suggest that inhibition of PKC-beta by LY may have a beneficial effect in preventing the development of diabetic nerve dysfunction, and that this effect may be mediated through its action on the endoneurial micro-vasculature.

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.

Immunochemical quantification of crossline as a fluorescent advanced glycation endproduct in erythrocyte membrane proteins from diabetic patients with or without retinopathy

Crossline is a novel advanced glycation endproduct (AGE) which has both a crosslink and fluorescence similar to AGE-protein in vivo. To assess the association of AGEs to the development of diabetic retinopathy we developed a sensitive and specific enzyme-linked immunosorbent assay (ELISA) for crossline in blood samples and investigated the association of the development of retinopathy and erythrocyte membrane protein (EMP)-crossline concentrations in patients with Type 2 diabetes mellitus (Type 2 DM). Crossline formation in EMP exceeded that in haemoglobin and was detectable in normal EMP samples without pretreatment by this ELISA system. Mean (+/-SE) EMP crossline levels were elevated 1.6-fold in diabetic patients without retinopathy (7.6 +/- 0.5 pmol mg(-1), p < 0.005), 2.2-fold in diabetic patients with non-proliferative retinopathy (10.5 +/- 0.6 pmol mg(-1), p < 0.001) and 2.6-fold in diabetic patients with proliferative retinopathy (12.0 +/- 0.6 pmol mg(-1), p < 0.001) compared with healthy control subjects (4.7 +/- 0.5 pmol mg(-1)). Type 2 DM patients with retinopathy had significantly higher EMP-crossline levels than those without retinopathy (p < 0.005). Our data suggest that elevated EMP-crossline concentrations are associated with the presence of retinopathy in patients with Type 2 DM and EMP-crossline measured by our ELISA may provide a useful marker for assessing the role of glycation in the development of diabetic retinopathy.

Neurotropin induces antinociceptive effect by enhancing descending pain inhibitory systems involving 5-HT3 and noradrenergic alpha2 receptors in spinal dorsal horn

Neurotropin, a non-protein extract from the inflamed skin of rabbits inoculated with vaccinia virus, has been clinically used as an analgesic drug in Japan. Its analgesic effect has been demonstrated by reduced mechano-nociception in hyperalgesic rats exposed to SART-stress (a repeated cold stress) for 5 days. In order to clarify the mechanism of the analgesic effect of neurotropin at the spinal cord level, we examined the effects of several neurotransmitter receptor antagonists given by intrathecal (i.t.) injection on the antinociceptive effect of intraperitoneally (i.p.) injected neurotropin [100 and 200 Neurotropin Unit (NU)/kg]. The analgesic effect of neurotropin was significantly inhibited not only by methysergide (100 nmol/rat, i.t.), a non-selective antagonist against serotonin (5-HT), but also MDL 72222 (30 nmol/rat, i.t.), a selective 5-HT3 antagonist, but not influenced by ketanserin (100 nmol/rat, i.t.), a 5-HT2A antagonist. The antinociceptive effect of neurotropin (200 NU/kg, i. p.) was significantly inhibited also by yohimbine (30 nmol/rat, i.t.), a noradrenergic alpha2 antagonist. However, the analgesic effect of neurotropin (100 and 200 NU/kg, i.p.) was not influenced by naloxone (30 nmol/rat, i.t.), an opioid antagonist. These results suggest that the mechanism of the antinociceptive effect of neurotropin is via enhancement of endogenous descending pain inhibitory pathways of the serotonergic and noradrenergic systems, especially involving 5-HT3 and noradrenergic alpha2 receptors in spinal dorsal horn in which these neurons terminate. No influence of opioid receptors at the spinal cord level is indicated.

Immunochemical quantification of crossline as a fluorescent advanced glycation endproduct in erythrocyte membrane proteins from diabetic patients with or without retinopathy

Crossline is a novel advanced glycation endproduct (AGE) which has both a crosslink and fluorescence similar to AGE-protein in vivo. To assess the association of AGEs to the development of diabetic retinopathy we developed a sensitive and specific enzyme-linked immunosorbent assay (ELISA) for crossline in blood samples and investigated the association of the development of retinopathy and erythrocyte membrane protein (EMP)-crossline concentrations in patients with Type 2 diabetes mellitus (Type 2 DM). Crossline formation in EMP exceeded that in haemoglobin and was detectable in normal EMP samples without pretreatment by this ELISA system. Mean (+/-SE) EMP crossline levels were elevated 1.6-fold in diabetic patients without retinopathy (7.6 +/- 0.5 pmol mg(-1), p < 0.005), 2.2-fold in diabetic patients with non-proliferative retinopathy (10.5 +/- 0.6 pmol mg(-1), p < 0.001) and 2.6-fold in diabetic patients with proliferative retinopathy (12.0 +/- 0.6 pmol mg(-1), p < 0.001) compared with healthy control subjects (4.7 +/- 0.5 pmol mg(-1)). Type 2 DM patients with retinopathy had significantly higher EMP-crossline levels than those without retinopathy (p < 0.005). Our data suggest that elevated EMP-crossline concentrations are associated with the presence of retinopathy in patients with Type 2 DM and EMP-crossline measured by our ELISA may provide a useful marker for assessing the role of glycation in the development of diabetic retinopathy.

Effect of neurotropin on the binding of high molecular weight kininogen and Hageman factor to human umbilical vein endothelial cells and the autoactivation of bound Hageman factor

Bradykinin is generated by activation of the plasma kallikrein-kinin (K-K) cascade and contributes to the symptoms of allergic reactions and the perception of pain. Neurotropin is a biological material obtained from inflamed rabbit skin inoculated with vaccinia virus, which is widely used clinically in Japan as an effective agent for these disorders. Factor XII (FXII) and high molecular weight kininogen (HK), two critical constituents of the plasma K-K cascade, bind to endothelial cells, and bound FXII is autoactivated in the presence of zinc ions. We have investigated the effects of Neurotropin on the interactions of FXII and HK with endothelial cells. Neurotropin inhibited the binding of both proteins to cultured human umbilical vein endothelial cells (HUVEC) and inhibited autoactivation of FXII upon HUVEC in a concentration-dependent manner. These data suggest that the ameliorating effects of Neurotropin in allergic disorders and pain syndromes may be related to this ability to inhibit activation of the K-K cascade and, consequently, the formation of bradykinin.

Naturally occurring 2'-O-methylpurine nucleosides with hypotensive properties

2'-O-Methylinosine (1) has been isolated for the first time and shown to be an intrinsic hypotensive principle. Its probable in vivo precursor, 2'-O-methyladenosine (3), showed stronger and even orally potent hypotensive activity. Resistance of the methyladenosine (3) against adenosine deaminase is thought to contribute to its long-lasting activity. The effect of both nucleosides (1 and 3) was not accompanied with any significant change in heart rate, which is often observed with adenosine.

Advanced glycation end products induce expression of vascular endothelial growth factor by retinal Muller cells

Recent studies have suggested that advanced glycation end products (AGEs) are involved in the development of diabetic complications. To assess the pathogenic role of AGEs and vascular endothelial growth factor (VEGF) in the development of retinal neovascularization in diabetic retinopathy, we investigated the effect of AGEs on induction of VEGF by retinal Muller cells and measured AGE and VEGF concentrations in the vitreous of patients with proliferative diabetic retinopathy (PDR) and nondiabetic patients. The expression of VEGF mRNA and the production of VEGF protein by cultured Muller cells were enhanced by the presence of AGEs. The vitreous concentrations of AGEs and VEGF were both elevated in patients with PDR compared with patients without diabetes (P < 0.01). There was a moderate positive correlation between the levels of crossline and VEGF (r=0.698, P < 0.01). Elevation of AGEs in the vitreous may promote intraocular neovascularization in diabetic retinopathy through production of VEGF from Muller cells.

Acid-stable fluorescent advanced glycation end products: vesperlysines A, B, and C are formed as crosslinked products in the Maillard reaction between lysine or proteins with glucose

Vesperlysines A and B, 6-hydroxy-1,4-di{6-(L-norleucyl)}-1H-pyrrolo[3,2-b]pyridinium and its 5-methyl derivative, respectively, and Vesperlysine C, 5-hydroxy-methyl-1,6-di{6-(L-norleucyl)}-1H-pyrrolo[3,4-b] pyridinium, are isolated as major fluorescent advanced glycation end products (AGEs) from hydrochloric acid hydrolysis of AGE-BSA, bovine serum albumin (BSA) modified by the Maillard reaction with glucose. These fluorophores are glycation products and not artifacts of hydrolysis, since they are also detected in the reaction mixture of lysine and glucose prior to hydrolysis. Vesperlysines are crosslinked products from two lysine side-chains in proteins and are considered to be generated from lysines and the oxidative degradation of glucose, because the six carbon skeleton of glucose in its original form was not incorporated into each structure. These compounds are most likely glycoxidation products like pentosidine. This reasoning is supported by the formation of the same compounds in the Maillard reactions in which ascorbic acid or other sugars with shorter carbon chains are used.

Changes in serum levels of creatol and methylguanidine in renal injury induced by lipid peroxide produced by vitamin E deficiency and GSH depletion in rats

A novel creatinine metabolite, creatol (5-hydroxycreatinine), is a key precursor in the synthesis of the uremic toxin methylguanidine (MG). Creatinine is converted to creatol within the mammalian body and this conversion is mediated specifically by hydroxyl radicals. We investigated the production of creatol and MG from creatinine in rats with renal failure induced by the lipid peroxide produced as a consequence of vitamin E deficiency and depletion of the reduced form of glutathione (GSH). In addition, we examined serum levels of other guanidino compounds, namely guanidinoacetic acid (GAA) and guanidinosuccinic acid (GSA). The injury to kidneys induced by the depletion of GSH in combination with vitamin E deficiency caused markedly elevated serum levels of creatol, MG and GSA and decreased serum GAA. The molar ratio of creatol to creatinine in the serum, which should be an index of the oxygen stress mediated by hydroxyl radicals, increased with time. Therefore, the enhanced production of creatol in vitamin-E-deficient rats that have been depleted of GSH might be due to the enhanced production of oxygen radicals in this system.

Formation of crossline as a fluorescent advanced glycation end product in vitro and in vivo

Crossline is one of the major advanced glycation end products resulting the reaction mixture of free amino group(s) such as epsilon-one in lysine with D-glucose in vitro. To study crossline formation on proteins in vitro and in vivo, polyclonal antiserum to the crossline hapten was prepared. This antiserum reacted with bovine and human serum albumin that had been modified by prolonged incubation with glucose as well as with crossline itself. Antisera did not react with unmodified serum albumin or the other Maillard-related compounds. Crossline was formed in a time-dependent manner when a mixture of six different proteins was incubated with glucose at pH 7.2 or 9.0. Crossline levels could be measured in rat lens proteins and the levels increased with age. The crossline content of lens proteins in diabetic rats was more than two-fold higher than that of age-matched controls. Results of this study suggest that most proteins containing advanced glycation end products have crossline-like structures. Measurement of crossline-like structures in biological specimens may provide an index of aging and of the development of diabetic complications.

Highly selective aldose reductase inhibitors. 1. 3-(Arylalkyl)-2,4,5-trioxoimidazolidine-1-acetic acids

A series of 3-(arylalkyl)-2,4,5-trioxoimidazolidine-1-acetic acids (1) was prepared and tested for aldose reductase (AR) and aldehyde reductase (ALR) inhibitory activities. These compounds showed strong inhibitory activity against AR without significant inhibitory activity for ALR. The ratio of IC50(ALR)/IC50(AR) was > 1000 in some compounds. On the basis of pharmacological tests such as the recovery of reduced motor nerve conduction velocity and toxicological profile, 3-(3-nitrobenzyl)-2,4,5-trioxoimidazolidine-1-acetic acid (NZ-314) was selected as the candidate for clinical development.

Diabetic renal failure and serum accumulation of the creatinine oxidative metabolites creatol and methylguanidine

Diabetic patients (n = 23) with chronic renal failure (CRF) accumulate the creatinine (Cr) oxidative metabolites creatol (CTL) and methylguanidine (MG; a uremic toxin) in their sera. Analysis of serum CTL, a key intermediate in mammalian Cr catabolism into MG, is shown to offer some useful diagnostic information on CRF, especially in the determination of an initial stage of pathological renal failure. The sera of all diabetic (n = 23) and nondiabetic (n = 20) patients with CRF (s-Cr > 1.25 mg/dl) contained s-CTL (> 2 micrograms/dl), whereas those from normal subjects (n = 18) and diabetic patients (n = 18) without CRF contained no detectable s-CTL. A similar accumulation of s-MG was observed, but only when s-Cr was higher than 2.0 mg/dl. Although each s-CTL (Y: microgram/dl, Y': mol/l) and s-MG level (Z: microgram/dl, Z': mol/l) is highly correlated with s-Cr (X: mg/dl, X': mol/l) in a normal equation, Y or Z = AX + B, an alternative correlation in a second-order equation, Y or Z = alpha X2 + beta X, could also fit well. Since the quadratic equation can be convertible to Y/X or Z/X = alpha X + beta [Y'/X' or Z'/X' = alpha' X+ beta'] and active oxygen species, especially hydroxyl radicals, convert Cr into CTL, Y/X, Y'/X', Z/X and Z'/X' values which might be a kind of indices for oxygen stress (oxidative stress) increased in proportion to the increased severity of CRF in such patients. Although its meaning and interpretation are still debatable, diabetic CRF patients had a significantly higher alpha' value (2.2) than that (0.89) of nondiabetic CRF patients. All serum values for Cr, CTL and MG were measured with HPLC.

Creatol, a creatinine metabolite, as a useful determinant of renal function

Analysis of creatol (CTL, 5-hydroxycreatinine), an oxidative creatinine (Cr) metabolite, in serum and urine of human subjects has indicated that CTL is a useful determinant of renal function. The existence itself of serum CTL (s-CTL) could be a diagnostic sign for chronic renal failure (CRF): in all normal subjects, s-CTL was undetectable, but s-CTL was detectable in sera of all patients with CRF (s-Cr: > 2.0 mg/dl). And the s-CTL values increased in proportion to the severity of CRF in such patients. Furthermore, the molar ratio (CTL/Cr) in both urine and serum increased significantly in proportion to the severity of CRF. Our results indicated not only hyperproduction of CTL but also higher oxygen stress in patients according to the progression of CRF. The diagnostic importance of the CTL value and the CTL/Cr ratio are discussed.

Comparison of renal effects of creatinine, creatol and methylguanidine in rats with adenine-induced chronic renal failure

Creatinine (Cr), creatol and methylguanidine (MG), which accumulate in the body with the progress of renal failure after adenine administration, were given separately to rats in order to compare their toxicities. Food containing adenine was given to rats for 20 days to induce renal failure. Then each of the test substances was administered intraperitoneally, and renal function of the rats was determined. The changes in glomerular filtration rate, renal plasma flow and renal blood flow after administration of Cr were only slight in comparison with those of the control group. Creatol or MG administration induced a significant decrease in renal function. In addition, the level of MG in serum, liver and kidney was extraordinarily high in rats given creatol or MG. The toxic effects are discussed on the basis of these results.

L-gulono-gamma-lactone oxidase is the enzyme responsible for the production of methylguanidine in the rat liver

A methylguanidine-synthesizing enzyme localized in rat liver microsomes produces methylguanidine via the intermediates creatone A and creatone B from the substrate, creatol, a substance produced from creatinine mainly by reaction with hydroxyl radicals. This enzyme has been identified as L-gulono-gamma-lactone oxidase (EC 1.1.3.8). However, no corresponding activity was found in extracts from human livers.

Purification of methylguanidine synthase from the rat kidney

Methylguanidine (MG)-synthesizing enzyme was purified from rat kidney lysosomes and peroxisomes. The enzyme was a flavoprotein with a molecular weight of about 37,000 and oxidized creatol to produce MG. The present results suggest that the reaction mechanism of this enzyme is different from that of L-gulono-gamma-lactone oxidase (EC 1.1.3.8) isolated from rat liver microsomes.

Gamma-glutamyltaurine has potent and long-lasting antiepileptic action as demonstrated by intra-amygdaloid injection in amygdala-kindled rats

Intra-amygdaloid injections of gamma-glutamyltaurine, a recently identified brain dipeptide, strongly suppressed seizures in amygdala-kindled rats stimulated with intensities 10 or 50 microA above the generalized seizure triggering threshold (mean 82 microA). The suppressive effect persisted as long as 3 days. Taurine had relatively weak suppressive effects. Thus gamma-glutamyltaurine seems much more potent than taurine in the suppression of epileptic seizures when injected directly into the kindling site.

Effects of creatinine, creatol and methylguanidine on renal function

Creatinine (Cr), creatol or methylguanidine (MG) was administered intraperitoneally to normal rats, and several renal function parameters were examined in an attempt to clarify the pathology under the various conditions. The glomerular filtration rate, renal plasma flow and renal blood flow after administration of Cr remained virtually unchanged when compared to those in the control group. In contrast, administration of creatol induced a significant decrease in these renal functions. Further decreases in the renal functions were observed in the rats given MG. However, the level of serum MG was extraordinarily high in the rats given creatol or MG. The toxic effects are discussed on the basis of the above results.

First isolation of gamma-L-glutamyl-gamma-aminobutyric acid from bovine brains

We had obtained some immunohistochemical indications which suggested that peptide(s) containing GABA at the C-terminal could exist in specific neurons in brains. We therefore sought such GABA conjugate(s) by isolating an acidic GABA-dipeptide from bovine brains and determined its structure as gamma-L-glutamyl-gamma-aminobutyric acid (gamma-L-Glu-gamma Abu:GluGABA). Its gamma-linkage was determined by a mass-spectrometric (B/E linked scan SIMS) analysis; its chirality was established by a chiral column HPLC technique. This peptide is the first acidic GABA-peptide recognized in brain and the first brain peptide containing GABA at the C-terminal.

Possible role of tumor necrosis factor and interleukin-1 in the development of diabetic nephropathy

The possibility that tumor necrosis factor (TNF) and interleukin-1 (IL-1) could participate in the development of diabetic nephropathy was evaluated in streptozocin (STZ)-treated diabetic rats. Diabetic rats were divided into two groups: aminoguanidine treated group (25 mg/kg body wt, daily i.p. injection; DM-AG group) and untreated group (DM group). Non-diabetic age-matched rats were also divided into two groups with the same manner and used as controls. After twelve weeks of treatment, glomerular basement membranes (GBM) were isolated from rats of each experimental group. When thioglycollate-elicited peritoneal macrophages (M phi) from normal rats were incubated with these GBM materials, GBM from DM group induced significantly greater levels of TNF and IL-1 production than did GBM from other three groups with at doses of 2.5 to 10 mg. The TNF and IL-1 production by stimulation of GBM from the DM-AG group were similar to those from each control group. Aminoguanidine treatment significantly decreased the accumulation of advanced glycation end-products (AGEs) in GBM of diabetic rats. These findings suggest that AGE-proteins may be involved in the production of TNF and IL-1 from M phi. AGE-induced cytokines may be implicated in the development of diabetic nephropathy.

Effects of intraamygdaloid injection of taurine and valyltaurine on amygdaloid kindled seizure in rats

Antiepileptic effects of intracerebral injections of taurine and valyltaurine were examined in amygdaloid kindled rats. The effects were assessed whether the animals can evoke generalized seizures by a 10 microA higher stimulation intensity than triggering thresholds. In all fully-kindled animals that have received intraamygdaloid injection of 500 nmol taurine, the kindled seizure was completely abolished. Such a significant seizure suppression (p less than 0.05) was observed 12-24 h after the taurine injection. Valyltaurine (500 nmol) also suppressed the seizure in 60% of animals tested, but the effect was not statistically significant. The results indicate that taurine may effectively suppress epileptic seizures when it acts directly at the stimulation site amygdala.

Production of methylguanidine from creatinine via creatol by active oxygen species: analyses of the catabolism in vitro

The chemical oxidative conversion of creatinine (Cr) into methylguanidine (MG) has been followed by 1H-NMR and HPLC. By using active oxygen species generated by Fenton's reagent (Fe2+ and H2O2) or the similar reagent (Fe3+ and H2O2), creatol (CTL), a metabolite newly isolated from the urine of uremic patients, and creatones A and B were experimentally detected in the reaction mixture and implicated as successive intermediates in the pathway from CR to MG. An alternative oxidation of Cr to demethylcreatinine (glycocyamidine) was also observed. The importance of CTL in this in vitro oxidation mechanism is discussed.

Isolation of glutamyltaurine from bovine brains and proof of its gamma-linkage by the B/E linked scan SIMS technique

We isolated a glutamyltaurine from bovine brains and determined its structure as gamma-glutamyltaurine (gamma-Glu-Tau; glutaurine) by use of a new mass spectrometric technique [B/E linked scan sputtered ion mass spectrometry (SIMS)], which we have recently shown to be useful for distinguishing the gamma- from the alpha-isomer of glutamyl-dipeptides. Neither the alpha-isomer of glutamyltaurine nor any aspartyltaurines could be detected in bovine brain.

Creatol (5-hydroxycreatinine), a new toxin candidate in uremic patients

Both 5-hydroxy-1-methylhydantoin (3) and the hitherto unrecognized 5-hydroxycreatinine (2-amino-5-hydroxy-1-methyl-imidazol-4(5H)-one or creatol) (6) can be isolated from the urine of uremic patients, in whom these compounds probably arise as oxidative metabolites of creatinine (1). The enhanced production of the well-known uremic toxin, methylguanidine (8), from creatinine (1) in such patients, almost certainly occurs via the newly recognized metabolite.

Simple method for determination of A1c-type glycated hemoglobin(s) in rats using high performance liquid chromatography

We have developed a new chromatographic method for the determination of rat glycated hemoglobins by cation exchange high-performance liquid chromatography. The hemoglobins were eluted by a two-step gradient, and the total assay time, including re-equilibration of the column, was 27 min. Two A1c type and one pre-A1c type rat glycated hemoglobins were separated and measured. The change in major HbA1c of rats, in which diabetes was induced by streptozotocin and which were subsequently treated with insulin, was monitored. In diabetic rats (n = 10, average blood glucose greater than 300 mg/dL), major HbA1c rose to 3.39 +/- 0.06% compared with controls (n = 10, 1.20 +/- 0.03%) during 5 wk. Insulin treatment decreased the HbA1c from 3.48 +/- 0.16% to 2.74 +/- 0.15% (p less than 0.01) in 6 wk. This method was also effective for the determination of mouse HbA1c.

The metabolism of 1-methylhydantoin via 5-hydroxy-1-methylhydantoin in mammals

The metabolic pathway of 1-methylhydantoin (2) via 5-hydroxy-1-methylhydantoin (3), methylparabanic acid (4) and N5-methyloxaluric acid (5) proved to be a major and general one in mammals. Hence the formation of (3), which has not been detected in normal tissue, is likely to be indirect in inflamed tissue, probably depending on the arising formation of (2) from creatinine (1).

The Dimroth rearrangement. XVII. The rearrangement of some 1,6-Dihydro-6-imino-1,2-polymethylenepyrimidines into 2,N6-polymethylene-bridged 6-aminopyrimidines

The cyclic imino ether, 2-ethoxy-3,4,5,6,7,8-hexahydroazocine (4; n = 6), condenses with amino-methylenemalononitrile (3; R = CN) to give the bicyclic imine, 6,7,8,9,10,11-hexahydro-4-imino-4H-pyrimido[1,2- alazocine-3-carbonitrile (5f), which undergoes Dimroth rearrangement in boiling butanol to yield a β-bridged isomer, 2,10,13- triazabicyclo[7,3,1]trideca-1(13),9,11-triene-12-carbo-nitrile (7a). Imino ethers (4) with fewer than six methylene groups give bicyclic imines which are incapable of rearrangement; those with more than six methylene groups give imines which cannot be isolated on account of their extremely facile rearrangement into β-bridged isomers. Ionization constants and the ultraviolet, infrared, proton magnetic resonance and mass spectra of the main products are discussed.