Biomedical subjects

Shinjiro Kobayashi

Publications and source records attributed to Shinjiro Kobayashi.

10 recordsLinked to original sources

PubMed2005

Kinetics of the reactions of halide anions with carbocations: quantitative energy profiles for s(n)1 reactions.

Rate constants for the reactions of Laser flash photolytically generated benzhydrylium ions (diarylcarbenium ions) with halide ions have been determined in various solvents, including neat and aqueous acetonitrile as well as some alcohols. Substitution of the rate constants into the correlation equation log k = s(N + E) yields the nucleophilicity parameters N for the halide ions in different solvents. Linear correlations with negative slopes are found between the nucleophilicity parameters N for Cl(-) and Br(-) in different solvents and the solvent ionizing powers Y of the corresponding solvents. Increasing halide solvation reduces the rates of carbocation/chloride combinations by approximately half as much as it increases the rates of ionizations of benzhydryl chlorides. Comparison of the solvent dependent nucleophilicity parameters N of halide anions and the nucleophilicity parameters N(1) for solvents yields a quantitative prediction of common ion rate depression, as demonstrated by the analysis of a variety of literature reported mass-law constants alpha. Combination of the rate constants for the reactions of benzhydrylium ions with halide ions (k(-)()(1)) reported in this work with the ionization constants of benzhydryl halides (k(1)) and the recently reported rate constants for the reactions of benzhydrylium ions with solvents (k(2)) yields complete quantitative free energy profiles for solvolysis reactions. The applicability of Hammond's postulate for interpreting solvolysis reactions can thus be examined quantitatively.

Journal Article↗

PubMed2005

Inhibitory effect of nifedipine on tumor necrosis factor alpha-induced neovascularization in cultured choroidal explants of streptozotocin-diabetic rat.

We have previously reported that the Nepsilon (carboxymethyl)lysine (CML) adduct, a major structure of an advanced glycation end product, facilitates proliferation of CD34+ endothelial progenitor cells budded from cultured choroidal explants and produces immature vessel-like structures in fibrin gel. The CML adduct is accumulated and facilitates immature neovascularization in cultured choroidal explants of streptozotocin (STZ)-induced diabetic rat. The CML-enhanced neovascularization activity is associated with the actions of tumor necrosis factor (TNF) alpha, vascular endothelial growth factor and platelet-derived growth factor released from the choroidal explant (Kobayashi et al., Biol. Pharm. Bull., 27, 1382-1387 (2004); 27, 1565-1571 (2004)). The present study was investigated an inhibitory effect of a dihydropyridine calcium antagonist nifedipine on TNF alpha-induced choroidal neovascularization in the STZ-diabetic rat. TNF alpha (1-100 ng/ml) increased neovascularization of cultured choroidal explants in the age-matched normal rat but did not increase it in the diabetic rat. Anti-TNF alpha antibody (1 : 1000) decreased the neovascularization in the diabetic rat but not in the normal rat. Nifedipine (1 microM) inhibited TNF alpha-induced neovascularization of the normal choroidal explant in a non-competitive manner. Nifedipine (1 microM) also inhibited the diabetic state-induced neovascularization and its inhibitory action was reversed by TNF alpha (1-10 ng/ml). In conclusion, STZ-diabetic state facilitated choroidal neovascularization through the release of TNF alpha. Nifedipine inhibited the action of TNF alpha probably by blocking voltage-dependent Ca2+ channels in the endothelial progenitor cells of the diabetic choroid.

Animals↗

PubMed2004

Solvent nucleophilicity.

The rates of the reactions of benzhydrylium ions (diarylcarbenium ions) with solvent mixtures of variable composition (water/acetonitrile, methanol/acetonitrile, ethanol/acetonitrile, ethanol/water, and trifluoroethanol/water) have been determined photometrically by conventional UV-vis spectroscopy, stopped-flow methods, and laser flash techniques. It has been shown that the first-order rate constants follow the previously published relationship log k(20 degrees C) = s(N + E), where E is an empirical electrophilicity parameter, N is an empirical nucleophilicity parameter, and s is a nucleophile-specific slope parameter. From plots of log k versus E of the benzhydrylium ions are derived the solvent nucleophilicity parameters s and N, the latter of which are designated as N1 to emphasize that their use in the quoted correlation equation gives rise to first-order rate constants. A linear correlation between N1 and Kevill's solvent nucleophilicity NT based on S-methyldibenzothiophenium ions is reported, which allows one to interconvert the two sets of data. Because the N1 values are directly comparable to the previously reported nucleophilicity parameters N for pi-systems (www.cup.uni-muenchen.de/oc/mayr/), the systematic design of Friedel-Crafts reactions with solvolytically generated carbocations becomes possible.

Journal Article↗

PubMed2004

Vascular change of hippocampal capillary is associated with vascular change of retinal capillary in aging.

Vascular deficiency, such as deleterious change of endothelial cells, becomes the prominent feature of hippocampal microvessels during the processes of aging in rodents and it seems to be associated with deficiency of intellectual behavior in aged subjects. The hippocampal microvessels and hippocampal pyramidal neurons form and accumulate intermediates of advanced Maillard reaction (glycation) end products, specifically N()-carboxymethyl lysine (CML) and CML in rodents during the processes of aging. CML facilitates proliferation of endothelial cells in culture. However, further conjugation of CML with the substance(s) seems to occur in the microvessels and pyramidal neurons of hippocampus and it brings about deleterious change of endothelial cells and pyramidal neuron death. This would cause deficiency of recognition and reference memory in rodents during the processes of aging. In man in Alzheimer's disease (AD), one might speculate that formation and accumulation of CML in the hippocampal microvessels initiate the accumulation of amyloid to produce cerebral amyloid angiopathy and it brings about hypoglycemia and hypoxia in the hippocampal pyramidal neurons. Furthermore, formation and accumulation of CML in the hippocampal pyramidal neurons initiate the deposition of neurofibrillary tangles and senile plaques which cause neuronal death. In this way, vascular deficiency of hippocampal microvessels seems to be associated with the demented disease, the atrophic process of the brain and accumulation of amyloid in the brain in man. In terms of vascular deficiency concerns, the vascular change of the retinal capillaries becomes also a prominent feature during the processes of aging and it has a positive correlation with the vascular change of hippocampal capillary. In man during senescence, one might also speculate that vascular change of eye capillaries would become the early market for diagnosis of dementia in AD.

Aging↗

PubMed2004

N(epsilon)-(carboxymethyl)lysine proliferated CD34(+) cells from rat choroidal explant in culture.

Action of N(epsilon)-(carboxymethyl)lysine-human serum albumin (CML-HSA) on neovascularization was investigated in cultured rat choroidal explant. Choroidal explants of normal male Wistar rats were cultured in fibrin gel with Dulbecco's modified Eagle medium containing fetal bovine serum in the presence or absence of CML-HSA. Migrated cells were budded from 2nd day in culture and developed from cultured choroidal explants in a time-dependent manner. Budded and developed cells from the choroidal explant had a feature of fibroblasts, which had attenuated long cytoplasmic processes, long ellipsoid nuclei and numerous membrane-bound polymorphic vesicles. Immunostaining of the attenuated cells in fibrin bed with CD34 (a marker protein of vascular endothelial cells and endothelial progenitor cells) failed to disclose positive result. However the cells which were isolated from fibrin bed by collagenase were specifically stained with anti-CD34 antibody. The isolated cells did not form tube-like structures on collagen gel by 3 weeks in culture. CML-HSA significantly increased the number of total isolated cells and CD34(+) cells as well as the number of vessel-like structures. These results indicate that CML-HSA overproduced immature blood vessels from cultured choroidal explants in fibrin gel, which consisted of CD34(+) cells. The CML-HSA-induced formation of immature blood vessel may be implicated in various choroidal diseases such as age-related macular degeneration.

Animals↗

PubMed2004

Overproduction of N(epsilon)-(carboxymethyl)lysine-induced neovascularization in cultured choroidal explant of streptozotocin-diabetic rat.

Action of N(epsilon)-(carboxymethyl)lysine (CML) adduct, an advanced glycation end product, was investigated on neovascularization of cultured choroidal explants in streptozotocin (STZ)-diabetic rat. The choroidal explants of early (4 weeks after an injection of 60 mg/kg STZ) and advanced (8 months after the STZ injection) diabetic rats, and age-matched normal rats were cultured in fibrin gel with Dulbecco's modified Eagle medium containing fetal bovine serum. The number of budded microvessel-like structures was counted and used as an index of in vitro neovascularization. Choroidal explants in the early diabetic stage released vascular endothelial growth factor (VEGF) and tended to increase tumor necrosis factor (TNF) alpha and platelet-derived growth factor (PDGF)-B, and concomitantly facilitated growth of sprout and buds, compared to the normal control. When choroidal explants were stimulated with CML-human serum albumin (HSA), its releasing effect was in the order VEGF>TNFalpha>PDGF-B. CML-HSA and CML-bovine serum albumin augmented the neovascularization in the cultured diabetic explant and their actions did not virtually differ. A monoclonal anti-CML antibody (6D12) inhibited the neovascularization in the advanced diabetes greater than that in the early diabetes. Inhibitory actions of anti-VEGF and anti-TNFalpha antibodies on the neovascularization were similar to that of the anti-CML antibody in the diabetes. In conclusion, CML adducts were accumulated and over-produced the actions of VEGF, TNFalpha and PDGF-B in the choroidal explant during diabetes in an age-dependent manner. TNFalpha and VEGF are likely to play a predominant role for the CML-induced choroidal neovascularization.

Animals↗

PubMed2003

Ambident reactivity of the thiocyanate anion revisited: can the product ratio be explained by the hard soft acid base principle?

Laser flash photolysis and stopped-flow methods have been employed to determine the kinetics of the reactions of benzhydrylium ions with both termini of the thiocyanate ion. In contrast to previous investigations which reported sulfur/nitrogen ratios of k(S)/k(N) = 2-10 for the reactions of carbocations with SCN(-), values of k(S)/k(N) = 10(3)-10(4) are now derived from absolute rate constants. This discrepancy is explained by the fact that the data determined in this investigation are the first which refer to activation-controlled attack of carbocations at both termini of the thiocyanate ion, while previous reactivity ratios included diffusion-controlled reactions. It is concluded that the selectivities of the reactions of carbocations with the thiocyanate ion cannot be explained by the hard soft acid base principle.

Journal Article↗

PubMed2003

Iron twin-coronet porphyrins as models of myoglobin and hemoglobin: amphibious electrostatic effects of overhanging hydroxyl groups for successful CO/O2 discrimination.

Inspired by the observation of polar interactions between CO and O(2) ligands and the peptide residues at the active site of hemoglobin and myoglobin, we synthesized two kinds of superstructured porphyrins: TCP-IM, which contains a linked imidazole ligand, and TCP-PY, which contains a linked pyridine ligand, and examined the thermodynamic, kinetic, and spectroscopic (UV/Vis, IR, NMR, and resonance Raman) properties of their CO and O(2) complexes. On both sides of each porphyrin plane, bulky binaphthyl bridges form hydrophobic cavities that are suitable for the binding of small molecules. In the proximal site, an imidazole or pyridine residue is covalently fixed and coordinates axially to the central iron atom. In the distal site, two naphtholic hydroxyl groups overhang toward the center above the heme. The CO affinities of TCPs are significantly lower than those of other heme models. In contrast, TCPs have moderate O(2) binding ability. Compared with reported model hemes, the binding selectivity of O(2) over CO in TCP-IM and TCP-PY complexes is greatly improved. The high O(2) selectivity of the TCPs is mainly attributable to a low CO affinity. The comparison of k(on)(CO) values of TCPs with those of unhindered hemes indicates the absence of steric hindrance to the intrinsically linear CO coordination to Fe(II) in TCP-IM and TCP-PY. The abnormally large k(off)(CO) values are responsible for the low CO affinities. In contrast, k(off)(O(2)) of TCP-PY is smaller than those of other pyridine-coordinated model hemes. For the CO adducts of TCPs, unusually low nu(Fe-CO) and unusually high nu(C-O) frequencies are observed. These results can be ascribed to decreased back-bonding from the iron atom to the bound CO. The lone pairs of the oxygen atoms of the hydroxyl groups prevent back-bonding by exertion of a strong negative electrostatic interaction. On the other hand, high nu(Fe-O(2)) frequencies are observed for the O(2) adducts of TCPs. In the resonance Raman (RR) spectrum of oxy-TCP-IM, we observed simultaneous enhancement of the Fe-O(2) and O-O stretching modes. Furthermore, direct evidence for hydrogen bonding between the hydroxyl groups and bound dioxygen was obtained by RR and IR spectroscopy. These spectroscopic data strongly suggest that O(2) and CO binding to TCPs is controlled mainly by the two different electrostatic effects exerted by the overhanging OH groups: destabilization of CO binding by decreasing back-bonding and stabilization of O(2) binding by hydrogen bonding.

Algorithms↗

PubMed2003

Anti-hyperglycemic effect of fangchinoline isolated from Stephania tetrandra Radix in streptozotocin-diabetic mice.

Kampo medicine, Stephania tetrandra Radix (Stephania) in Boi-ogi-to increases the blood insulin level and falls the blood glucose level in streptozotocin (STZ)-diabetic ddY mice. These actions of Stephania are potentiated by Astragalus membranaceus Bunge Radix (Astragali) in Boi-ogi-to (Liu et al., J. Traditional Med., 17, 253-260, 2000). In the present study, actions of bis-benzylisoquinoline alkaloids isolated from Stephania were investigated in the hyperglycemia of STZ-diabetic mice. A main bis-benzylisoquinoline alkaloid, fangchinoline (0.3-3 mg/kg) significantly fell the blood glucose level of the diabetic mice in a dose-dependent manner. The effect of fangchinoline was 3.9-fold greater than that of water extract of Stephania. However, another main compound, tetrandrine (1-100 mg/kg) did not have any effect. The water extract of Astragali did not affect singly but potentiated the anti-hyperglycemic action of fangchinoline (0.3 mg/kg). Out of used compounds (1 mg/kg) isolated from Stephania, fangchinoline, fangchinoline 2'-N-alpha-oxide and 2'-N-norfangchinoline, which are substituted with 7-hydroxy side chain for 7-O-methyl side chain, decreased to near 50% of high blood glucose level. In addition, tetrandrine 2'-N-beta-oxide, tetrandrine 2'-N-alpha-oxide, tetrandrine 2-N-beta-oxide, fangchinoline 2'-N-alpha-oxide, which are added to 2- or 2'-N-oxide side chain, also decreased to near 50% of the high blood glucose level. In conclusion, fangchinoline but not tetrandrine from Stephania shows the anti-hyperglycemic action in the STZ-diabetic mice. The demethylation of 7-O-position and/or addition of 2- or 2'-N-oxide side chain in bis-benzylisoquinoline compounds in Stephania have a role for the induction of the anti-hyperglycemic actions.

Alkaloids↗

PubMed2002

Therapeutic efficacy of Stephania tetrandra S. Moore for treatment of neovascularization of retinal capillary (retinopathy) in diabetes--in vitro study.

The present study was designed to examine therapeutic efficacy of the root extract of Stephania Tetrandra S. Moore (STMS) (traditional Chinese medicine; Han Fang Ji) for treatment of neovascularization of the retinal capillary (retinopathy) in streptozotocin (STZ)-induced diabetic rats (STZ diabetic rats) in culture. Recently we have established the culture system in which fetal bovine serum (FBS) in Dulbecco modified Eagle medium (DMEM) induced neovascularization of the retinal capillary and choroidal capillary in normal rats in culture. STZ diabetic rats showed more neovascularization of the retinal capillary and choroidal capillary than did normal rats in culture. In this study, the retinal tissue was removed for the posterior ocular region and cultured in DMEM containing FBS. The choroidal tissue of the posterior ocular region was also removed and cultured as an internal reference. Administration of STSM (0.91, 9.1 and 91 microg/ml) significantly suppressed neovascularization of the retinal capillary in both STZ diabetic rats and normal rats in a dose-dependent manner. Similar results were obtained with the choroidal capillary; administration of STSM suppressed neovascularization of the choroidal capillary in both STZ diabetic rats and normal rats. In order to determine the component of STSM inhibiting neovascularization of the retinal capillary, tetrandrine (a major chemical constituent of STSM) was administered and neovascularization of the retinal capillary was examined in culture. The effect of tetrandrine on the choroidal capillary was also examined as an internal reference. Administration of tetrandrine (0.1, 1.0 and 10 microM) suppressed neovascularization of the retinal capillary in both STZ diabetic rats and normal rats in a dose-dependent manner. Similar results were obtained with the choroidal capillary of both STZ diabetic rats and normal rats. We infer, therefore, that STSM has a direct effect on the retinal capillary of posterior ocular region and suppresses neovascularization of retinal capillary in STZ diabetic rats through the activation of tetrandrine. These results suggest that STSM may prevent for delay the progression of retinopathy in diabetic patients.

Alkaloids↗