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Biomedical subjects

N Shirai

Publications and source records attributed to N Shirai.

68 records · Page 4Linked to original sources
PubMed1986

High tumorigenicity of the 3,4-dihydrodiol of 7-methylbenz[c]acridine on mouse skin and in newborn mice.

The tumorigenicities of 7-methylbenz[c]acridine (7MB[c]ACR) and its five metabolically possible trans-dihydrodiols were determined in two mouse tumor models. In initiation-promotion studies on mouse skin, a single topical application of 0.15 to 0.75 mumol of compound was followed 9 days later by twice weekly applications of 12-O-tetradecanoylphorbol-13-acetate for 20 wk. Comparison of the average number of skin tumors per mouse indicated that 7MB[c]ACR 3,4-dihydrodiol, the metabolic precursor of a bay-region diol-epoxide, was 4- to 6-fold more active than the parent compound as a tumor initiator. The 1,2-, 5,6-, 8,9-, and 10,11-dihydrodiols of 7MB[c]ACR had no significant tumor-initiating activity at the doses tested. In newborn mice, a total dose of 0.35 mumol of compound was administered i.p. during the first 15 days of life, and tumorigenic activity was determined when the mice were 32 to 36 wk old. 7MB[c]ACR 3,4-dihydrodiol induced about 8-fold more pulmonary tumors per mouse and 9-fold more hepatic tumors per male mouse than the parent aza-substituted hydrocarbon. The other four dihydrodiols of 7MB[c]ACR had no significant tumorigenic activity. The high tumorigenic activity of 7MB[c]ACR 3,4-dihydrodiol in both tumor models suggests that a bay-region 3,4-diol-1,2-epoxide may be an ultimate carcinogenic metabolite of 7MB[c]ACR. 7MB[c]ACR was at least 5-fold more active as a tumor initiator on mouse skin than was the unsubstituted aza-aromatic compound, benz[c]acridine. This latter result indicates that substitution of a methyl group at position 7 of benz[c]acridine leads to enhanced tumor-initiating activity, as has been previously demonstrated for benz[a]anthracene and its 7-methyl derivative.

Acridines↗
PubMed1984

Relationship between the inotropy speeds in guinea-pig myocardium and lipophilic character of cardenolides and ericaceous toxins.

Interrelation between lipophilic characters and speeds of positive inotropic effect (PIE) of cardenolides and ericaceous toxins was studied by determining both parameters of lipophilicity and inotropy speeds. The lipophilic characters of 8 kinds of cardenolides, evaluated from Rm or log k' values by means of thin layer chromatography (Rf) or high performance liquid chromatography (retention time), increased in the order of ouabain, digoxin, digitoxigenin, digitoxigenin-monodigitoxoside, digitoxigenin-bis-digitoxoside, digitoxin, alpha-acetyl-digitoxin, triacetyl-digitoxin. Lipophilic character, evaluated from Rm values of 6 kinds of ericaceous toxins, was in decreasing order of 10S-grayanotoxin II, 6-acetyl grayanotoxin I, asebotoxin I, grayanotoxin I, asebotoxin III, asebotoxin X. The speed with which PIE developed was evaluated from the time to half maximum PIE (T50) of cardenolides and ericaceous toxins at a pD2 concentration. The speed of positive inotropy of cardenolides was independent of their concentration tested in the range from half to twice the concentration of pD2, while the speeds of PIE of ericaceous toxins depended on their concentration in the same range used in case of cardenolides. Inotropy speed of these two classes of cardiotoxins correlated well with the lipophilic character: a) In the case of cardenolides, a positive and close correlation (r = 0.98) was observed between T50 and Rm. The more lipophilic the cardenolides, the more time was required to reach the fully development of PIE. b) In contrast, a negative correlation (r = -0.82, between Rm and T50) was obtained in the case of ericaceous toxins; Toxins with more lipophilic nature caused faster development of PIE. The present results can be interpreted to mean that the PIE receptor for cardenolides in myocardial cells is located on the outer surface of the sarcolemma, while that for ericaceous toxins is located on the inside of the myocardial cell.

Animals↗
PubMed1983

Postoperative deep venous thrombosis in Japan. Incidence and prophylaxis.

The incidence of postoperative deep venous thrombosis was investigated using the iodine-125-fibrinogen method in 256 patients undergoing major surgery. Deep venous thrombosis was found in 49 patients (15.3 percent), and nonfatal pulmonary embolism developed in one of seven patients in whom the thrombus extended to the popliteal vein. The same investigation was performed in 110 patients who wore a graduated compression stocking on one leg, with the other leg serving as a control. Deep venous thrombosis was found in 4 of 110 stockinged legs (3.6 percent) and in 16 of 110 control legs (14.5 percent). The incidence of deep venous thrombosis decreased significantly in patients who wore the stocking. An increase in femoral venous flow velocity was found in the stockinged legs by the Doppler method. The mean velocity of venous return by xenon-133 clearance was significantly greater in the stockinged legs than in the control legs. These findings were considered to support the efficacy of graduated compression stockings for the prevention of deep venous thrombosis.

Adolescent↗
PubMed1983

Quantitative structure-inotropy relationship applied to substituted grayanotoxins.

Nine 14 beta-O-acylated grayanotoxins were synthesized by ozonolysis of 14,16-alkylidenegrayanotoxin III. The correlation between positive inotropic potency (PIE) in guinea pigs and physicochemical parameters (Vw, Mw, and Rm50) in 14 14-substituted grayanotoxins were quantitatively analyzed. It became clear that a parabolic relation existed between the bulkiness of the 14-substituents and PIE and that some electronic factor and the hydrophilic-hydrophobic balance would be related to the development of PIE.

Animals↗
PubMed1980

Relationship between structure, positive inotropic potency and lethal dose of grayanotoxins in guinea pig.

Relationship between chemical structure, positive inotropic potency and lethal dose of grayanotoxins and the related compounds was studied using guinea pigs. The positive inotropic effect (PIE) was examined in their papillary muscle isolated from the heart. The potency of these compounds was expressed by pD2 values, and was determined by depicting the concentration-PIE curve for each compound. The study has clarified the contribution of functional groups in the molecule; the presence of 3 beta-hydroxyl, 6 beta-hydroxyl and 10 beta-methyl groups attached to the grayanane skeleton is established to be essential for the development of PIE. The inotropic potency of compounds carrying these essential groups is increased by a 10 alpha-hydroxyl group and the acylation of the 14 beta-hydroxyl group. LD50 value of 10 compounds with a high cardiotonic potency (pD2 greater than 4) was determined by up and down method using male guinea pigs. The relation of LD50 to pD2 bore a significant correlation (r = 0.68, p less than 0.05). The most cardiotropic and toxic compound found in this study was asebotoxin III.

Animals↗
PubMedDate not supplied

Expression of cyclin kinase inhibitor p27(Kip1) in skin tumours of dogs.

Skin tumours (n=148) of epidermal or hair follicle origin were examined immunohistochemically to determine the expression of p27(Kip1)(p27), a cyclin-dependent kinase inhibitor (CDKI), and of Ki-67. In normal skin, a large number of basal cells of the epidermis and hair follicles were positive for Ki-67 and many suprabasal epithelial cells were positive for p27. Most of the hair matrix cells were positive for Ki-67 but negative for p27. Hair papillae were strongly positive for p27. Squamous cell carcinomas had a p27 positive index (PI) significantly lower than that of trichoepitheliomas (P<0.005), basal cell tumours (P<0.05) and intracutaneous cornifying epitheliomas (P<0.001). In contrast, Ki-67 PIs of squamous cell carcinomas and pilomatrixomas were significantly higher than those of trichoepitheliomas, basal cell tumours and intracutaneous cornifying epitheliomas (P<0.01 to P<0.001). No significant difference was observed between the Ki-67 PI values of squamous cell carcinomas and pilomatrixomas. The results suggested that p27 is capable of suppressing cell proliferation in the differentiation of normal canine skin. In spite of being a benign neoplasm, pilomatrixomas had a low p27 expression; this may be a reflection of the proliferative potential of the hair matrix. The expression of p27 may be a useful marker for the analysis of cell kinetics.

Animals↗
PubMedDate not supplied

Cardiac Na(+) channel dysfunction in Brugada syndrome is aggravated by beta(1)-subunit.

BACKGROUND: Mutations in the gene encoding the human cardiac Na(+) channel alpha-subunit (hH1) are responsible for chromosome 3-linked congenital long-QT syndrome (LQT3) and idiopathic ventricular fibrillation (IVF). An auxiliary beta(1)-subunit, widely expressed in excitable tissues, shifts the voltage dependence of steady-state inactivation toward more negative potentials and restores normal gating kinetics of brain and skeletal muscle Na(+) channels expressed in Xenopus oocytes but has little if any functional effect on the cardiac isoform. Here, we characterize the altered effects of a human beta(1)-subunit (hbeta(1)) on the heterologously expressed hH1 mutation (T1620M) previously associated with IVF. METHODS AND RESULTS: When expressed alone in Xenopus oocytes, T1620M exhibited no persistent currents, in contrast to the LQT3 mutant channels, but the midpoint of steady-state inactivation (V(1/2)) was significantly shifted toward more positive potentials than for wild-type hH1. Coexpression of hbeta(1) did not significantly alter current decay or recovery from inactivation of wild-type hH1; however, it further shifted the V(1/2) and accelerated the recovery from inactivation of T1620M. Oocyte macropatch analysis revealed that the activation kinetics of T1620M were normal. CONCLUSIONS: It is suggested that coexpression of hbeta(1) exposes a more severe functional defect that results in a greater overlap in the relationship between channel inactivation and activation (window current) in T1620M, which is proposed to be a potential pathophysiological mechanism of IVF in vivo. One possible explanation for our finding is an altered alpha-/beta(1)-subunit association in the mutant.

Amino Acid Substitution↗