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J Sakakibara

Publications and source records attributed to J Sakakibara.

At least 37 records · Page 2Linked to original sources
PubMed1997

Studies on cardiac ingredients of plants. XIII: Chemical modification of gitoxin to cardiotonic compounds without vascular effect.

Nitrated gitoxins (4) and bufotoxin homologues with various lengths of alkyl chain at C-3 of the steroid nucleus (10) were prepared from gitoxin (1). The pharmacological activities of the resulting compounds (4 and 10) were evaluated by measurement of inhibitory effect on NA+, K(+)-adenosine triphosphatase (ATPase) prepared from dog kidney, positive inotropic effect (PIE) on isolated guinea-pig papillary muscle preparations, and the effect on smooth muscle using the mesenteric artery from spontaneously hypertensive rats. Most of the compounds showed a smaller contractile effect on the arterial muscle. Among these compounds, gitoxin 3"-nitrate (4g) exhibited the most desirable biological activities, such as PIE comparable to that of 1, 1.25 times wider concentration-dependent range than 1, and lack of contractile activity on vascular muscle.

Animals↗
PubMed1997

Studies on chemical modification of monensin. VI. Preparation of C-7 modified monensins via protected 7-oxomonensin and evaluation of their ion transport activity.

7-Carboxymethylmonensin (3), 7-aminomonensin (4), and 7-oxomonensin (5) were synthesized via protected 7-oxomonensin (2), which is expected to be a useful intermediate for the preparation of various monensin derivatives. intermediate for the preparation of various monensin derivatives. Compounds 3-5 exhibited smaller ion transport activity than monensin (1).

Calcium↗
PubMed1997

[Transformation of natural products into more potent compounds: chemical modification of monensin].

Monensin (1) is a representative compound of polyether ionophore antibiotics, which selectively transport Na+ ions. In order to obtain potent Na+ ionophores, the modification of the carboxyl group of monensin was carried out to yield monensylamino acids (2) and monensylamino acid-1,29-lactones (3). The Na+ permeability of ion through the erythrocyte membrane of 2 and 3 was evaluated by the 23Na-NMR method. Compound 2 showed less Na+ ion transport activity than monensin, probably due to the lower lipophilicity caused by the conformational change of the chain moiety of the molecules. Although 3 showed higher lipophilisity than 1, 3 had no Na+ ion permeability, probably due to loss of the carboxyl group. As more lipophilic compounds possessing a carboxyl group was supposed to have more ion transport activity, 7-O-acylmonensins (8) and 7-O-alkylmonensins (11) were synthesized. Among these compounds, the value of Na+ ion permeability of 7-O-benzylmonensin (11c) was 1.4 time that of 1. Further investigation was carried out by preparing various 7-O-(substituted benzyl)monensins (13), and 7-O-(p-ethylbenzyl)monensin (13b) exhibited the largest Na+ ion permeability, about twice the value of 1. In order to convert monensin (1) to Ca2+ ionophore, 7-carboxylmethylmonensin (18) via protected 7-oxomonensin (15), and 25-carboxylmonensin (26) were prepared. In the course of the synthesis, 15 was clarified as a useful intermediate to give 7-amino and 7-alkyl derivatives. Ca2+ ion transport activities of 18 and 26 were determined by a CHCl3 liquid membrane system. 25-carboxylmonensin (26) showed 70% of the activity of Ca2+ ionophore, lasalocid A, and compound 26 could be the lead compound for the preparation of a new Ca2+ ionophore.

Chemical Phenomena↗
PubMed1996

Inhibition of 12-O-tetradecanoylphorbol-13-acetate promoted mouse skin papilloma by digalactosyl diacylglycerols from the fresh water cyanobacterium Phormidium tenue.

To search for possible antitumor-promoters, two digalactosyl diacylglycerols (DGDGs), which were obtained from the freshwater cyanobacterium Phormidium tenue and possessed a single pair of acyl residues, were evaluated for their inhibitory effects on the two-stage carcinogenesis test in mouse skin. Papillomas in mouse skin were initiated with 390 nmol of 7,12-O-dimethylbenz[a]anthracene and 1 week later, were promoted twice a week with 1.7 nmol of 12-O-tetradecanoylphorbol-13-acetate (TPA). Two DGDGs effectively inhibited tumor formation in the sensitive mouse stock even when these compounds were given 1 h before TPA treatment.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1996

Transcriptional regulation of squalene epoxidase by sterols and inhibitors in HeLa cells.

Regulation of squalene epoxidase (SE) gene expression was studied in comparison with those of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase and low density lipoprotein (LDL) receptor. An increased expression of SE mRNA and protein content in mouse L929 cells grown in 10% lipoprotein-deficient fetal bovine serum (LPDS) for 48 h was found by performing immunoblot and Northern blot analyses when compared with the culture in the presence of fetal bovine serum (FBS). The same results in mRNA levels were seen using human cell lines HepG2, HeLa, and Chang liver cells. The increase of SE mRNA in HeLa cells grown in LPDS was preventable in a dose-dependent manner by feeding cells with 25-hydroxycholesterol or cholesterol. When an SE inhibitor, NB-598, was fed to HeLa cells grown in LPDS, it caused further increases in mRNA levels of SE, HMG-CoA reductase, and LDL receptor. In contrast, NB-598 had no effect on the message levels of these genes when fed to HeLa cells grown in FBS. These results suggest that sterol produced endogenously can also regulate SE expression at the level of transcription.

Animals↗
PubMed1996

Antitumor-promoting activities of various synthetic 1-O-acyl-3-O-(6'-O-acyl-beta-D-galactopyranosyl)-sn-glycerols related to natural product from freshwater cyanobacterium Anabaena flos-aquae f. flos-aquae.

1-O-Acyl-3-O-(6'-O-acyl-beta-D-galactopyranosyl)-sn-glycerol, which was isolated from a nitrogen-fixing fresh water cyanobacterium, Anabaena flos-aquae f. flos-aquae, was synthesized by utilizing lipase-catalyzed acylation. The antitumor-promoting activities of these galactolipids were evaluated using a short-term in vitro assay of Epstein-Barr virus activation in Raji cells induced by 12-O-tetradecanoyl- phorbol 13-acetate (TPA). The glyceroglycolipids which have a palmitoleoyl residue at the 1-O-position exhibited more potent activities than the others in this assay.

Anabaena↗
PubMed1995

Different effects of isoproterenol and dihydroouabain on cardiac Ca2+ transients.

Cytosolic fura-2 Ca2+ transient signals (TCa) and the left ventricular pressure or contraction of myocardium under the positive inotropic effects of the beta-adrenoceptor agonist, isoproterenol, and the cardiac glycoside, dihydroouabain, were measured simultaneously and the results were compared. TCa was observed preceding the onset of force development and showed a steeper rise and slower decay than did the contraction curve of papillary muscle. Isoproterenol increased the steepness and the amplitude of TCa, reflecting the speed and peak force of contraction, and clearly biphasic TCa were observed with biphasic contractions developed at low frequency. Ryanodine reduced not only the early component of the contraction but also TCa, without affecting the diastolic Ca2+ level. These effects of isoproterenol were attributed to the enhanced uptake of Ca2+ by the sarcoplasmic reticulum. In contrast, dihydroouabain elevated the Ca2+ level at diastole without any change in the amplitude of TCa, suggesting that dihydroouabain inhibits the membrane Na pump thereby increasing the intracellular Ca2+ via Na(+)-Ca2+ exchange. Furthermore, a comparison of the time course of the isometric twitch curve with that of TCa in rested state contraction indicated that there are distinct differences between the mechanisms of the positive inotropic effects of isoproterenol and of dihydroouabain.

Adrenergic beta-Agonists↗
PubMed1995

Tissue-specific suppression of aortic fatty-acid-binding protein in streptozotocin-induced diabetic rats.

Fatty-acid-binding protein (FABP) expressed in rat aorta has been shown to be homologous to heart FABP (H-FABP) but its precise primary structure, cellular localization and function are not known. To establish the nucleotide identity between heart and aorta FABP, we performed an RNase protection assay with antisense RNA of rat H-FABP. The results demonstrate that the primary nucleotide sequence of aortic FABP is identical to that of rat H-FABP. In situ hybridization analysis revealed that aortic H-FABP mRNA is present in both smooth muscle cells and endothelial cells. In order to explore the function of aortic H-FABP, we examined whether a quantitative change in aortic H-FABP occurred in diabetes mellitus, since this pathological state has been shown to cause abnormalities in fatty acid metabolism. Northern blot analysis revealed that the level of aortic H-FABP mRNA was markedly decreased in rats made diabetic by streptozotocin treatment. The suppression of the mRNA level paralleled that of the protein level, as assessed by Western blot analysis. In distinct contrast, no major changes in the H-FABP mRNA level were observed in any other tissues examined, including heart, kidney and skeletal muscle, suggesting that this decrease is highly tissue-specific. The suppression of the aortic H-FABP in streptozotocin-diabetic rats was abolished by insulin supplementation. Taken together, these results suggest that the expression of the H-FABP gene in aorta may be specifically and dramatically suppressed in streptozotocin-diabetic rats, and that this suppression appears to be regulated by insulin.

Animals↗
PubMed1995

Nucleotide sequence of a cDNA for mouse squalene epoxidase.

A full-length cDNA encoding mouse squalene epoxidase was isolated by screening a mouse liver cDNA library with the rat squalene epoxidase gene as a probe. The cDNA had an open reading frame for a 572 amino acid polypeptide with a calculated molecular mass of 63.8 kDa. The predicted amino acid sequence of the mouse enzyme contained an FAD-binding motif, and was 93% identical to that of the rat enzyme. The former is one amino acid shorter than the latter. Blotting analyses showed that the mRNA is 2.8 kb in size and that a single copy of the gene is present in the mouse genome.

Amino Acid Sequence↗
PubMed1995

Molecular cloning and expression of rat squalene epoxidase.

Squalene epoxidase (SE) (EC 1.14.99.7) catalyzes the first oxygenation step in sterol biosynthesis and is suggested to be one of the rate-limiting enzymes in this pathway. Rat SE cDNA was isolated by selecting yeast transformants expressing rat cDNA in the presence of transformants expressing rat cDNA in the presence of terbinafine, an inhibitor specific for fungal SE. The expression of rat SE in the isolated terbinafine-resistant clone was confirmed by its survival in the presence of either terbinafine or an inhibitor specific for mammalian SE, NB-598, but not in the presence of both terbinafine and NB-598. Rat SE polypeptide deduced from the nucleotide sequence contains 573 amino acids, and its molecular weight is 63,950 Da. The amino acid sequence reveals one potential transmembrane domain, a hydrophobic segment (Leu27 to Tyr43) in the NH2-terminal region. This region also contains a beta 1-alpha A-beta 2 motif, which is the consensus sequence for an FAD binding domain, suggesting that SE is a flavoenzyme. This deduced rat SE sequence is 30.2% identical to the ERG 1 gene, which encodes SE from an allylamine-resistant Saccharomyces cerevisiae mutant. Expression of a full-length rat SE protein in Escherichia coli confirms this polypeptide as a functional SE. This is the first report of the molecular cloning of mammalian SE.

Amino Acid Sequence↗
PubMed1995

Anti-tumour-promoting glyceroglycolipids from the green alga, Chlorella vulgaris.

Two new monogalactosyl diacylglycerols were isolated from the freshwater green alga, Chlorella vulgaris, as anti-tumour promoters, together with three monogalactosyl diacylglycerols and two digalactosyl diacylglycerols. The new monogalactosyl diacylglycerol containing (7Z,10Z)-hexadecadienoic acid showed a more potent inhibitory effect toward tumour promotion than the other glycerolipids isolated.

Anticarcinogenic Agents↗
PubMed1995

Novel antioxidants from roasted perilla seed.

Novel antioxidants, 5-(3,4-dihydroxyphenylmethyl)oxazolidine-2,4-dione (1) and 3-(3,4-dihydroxyphenyl)lactamide (2), have been isolated from roasted perilla seed. Compound 1 was the first example of non-synthetic oxazolidinedione.

Antioxidants↗
PubMed1995

Purification and characterization of recombinant squalene epoxidase.

Recombinant rat squalene epoxidase (rSE) was expressed in E. coli and purified to an apparent homogeneity. This expression system was constructed using squalene epoxidase (SE) cDNA in which nucleotides coding 99 amino acids in the N-terminal were deleted and nucleotides coding hexa-histidine in the C-terminal were added. Purification was carried out using Ni-chelate affinity agarose and Cibacron Blue Sepharose column chromatography. Purification was achieved 100-fold over the crude E. coli extract with a yield of about 50%. The purified enzyme demonstrated a single band on SDS-polyacrylamide gel electrophoresis. The enzyme showed no distinct absorption spectrum in the visible regions. The properties of rSE were compared with those of rat liver microsomal SE. The requirement of the co-factors, the S105 fraction or Triton X-100, and NADPH-cytochrome c reductase, the pH dependency for enzyme activity, and the sensitivity to NB-598 seen with both enzymes suggest that rSE has properties very similar to rat microsomal SE. 2,3-Oxi-dosqualene (OSQ) and 2,3;22,23-dioxidosqualene (DOSQ) were formed by rSE in a completely reconstituted system. It is suggested that recombinant squalene epoxidase catalyzes the conversion of squalene to 2,3-oxidosqualene and of 2,3-oxidosqualene to 2,3;22,23-dioxidosqualene.

Animals↗
PubMed1994

Direct measurement of increased myocardial cellular 23Na NMR signals in perfused guinea-pig heart induced by dihydroouabain and grayanotoxin-I.

The effects of the cardiac glycoside dihydroouabain (DHO), and the ericaceous toxin grayanotoxin-I (GTX-I) on myocardial cellular sodium (Nai) concentrations were investigated using sodium-23 nuclear magnetic resonance (23Na NMR) spectroscopy at 30 degrees C in isolated perfused guinea-pig hearts. The Nai NMR signals from perfused Langendorff heart preparations were obtained by the modified inversion recovery (IR) method based on the previous observation that the spin-lattice relaxation time (T1) of the Nai (25 or 34 msec at 8.46 Tesla (T)) is much faster than that of extracellular sodium (64 msec at 9.4 T). Nai was estimated from the calibration curve of the frequency area of the 23Na NMR FT spectra plotted against the standard Na concentration. The Nai concentration of the heart increased concomitantly with the positive inotropic effects (PIE) of DHO, GTX-I and monensin (MON). The cumulative sequential addition of DHO (5 x 10(-6) M), GTX-I (7 x 10(-8) M) and MON (5 x 10(-6) M), each of which alone induced no appreciable PIE, produced a 22% elevation in Nai concentration relative to that of the control (100%) accompanying a PIE of 44%. The mechanism of this Nai elevation induced by combinational addition of DHO, GTX-I and MON may be mediated as follows: GTX-I increases the net Na-influx via Na+ channels; DHO inhibits the pumping out of Na+ from the cell; and MON transports external Na+ into the cell, acting as a sodium ionophore. Consequently, these drugs act synergistically to increase the Nai, thereby increasing the intracellular Ca2+ concentration via Na(+)-Ca2+. exchange.

Animals↗
PubMed1994

Molecular cloning of a cDNA encoding a novel fatty acid-binding protein from rat skin.

A novel skin-type fatty acid-binding protein, termed cutaneous(C)-FABP, has been purified from rat skin and a cDNA clone for this protein has been identified. The purified protein had the ability to bind long chain fatty acids like other rat FABPs. The deduced amino acid sequence of the cDNA clone comprises residues yielding a molecular mass for the polypeptide of 15.1 kDa and exhibits around 50% identity to myelin P2 protein, adipocyte FABP and heart FABP. Our results propose that C-FABP is a new member of the FABP family.

Adipocytes↗
PubMed1994

Mechanism of an early lysis by fatty acids from axenic Phormidium tenue (musty odor-producing cyanobacterium) and its growth prolongation by bacteria.

We have previously demonstrated that bacteria-containing Phormidium tenue, a cyanobacterium which produces musty odor 2-methylisoborneol, grew beyond 8 weeks, whereas axenic alga perished suddenly between the 3rd week and the 4th week while being cultured in the laboratory. This mechanism was investigated. It is assumed that when algal cells grow beyond a certain level, the supply of CO2 becomes inadequate and results in the rapid lysis of axenic alga. At that time, inhibitory substances liberated from algal cells kill the surviving alga. Since the process occurs continuously, this alga is finally annihilated. On the other hand, since inhibitory substances are metabolized or degraded by bacteria coexistent with alga, bacteria-containing P. tenue maintains growth for a long time. The growth-inhibitory substance was found to be unsaturated free fatty acids.

Bacteria↗
PubMed1994

Studies on chemical modification of monensin. V. Synthesis, sodium ion permeability, antibacterial activity, and crystal structure of 7-O-(4-substituted benzyl)monensins.

7-O-(4-Substituted benzyl)monensins (3a-g) were synthesized from monensin (1), and their lipophilicity, antibacterial activity, and Na+ ion permeability were examined. 7-O-(4-Ethylbenzyl)monensin (3e) showed the largest Na+ ion permeability, but 3c,f,g showed smaller Na+ ion permeability than 7-O-benzylmonensin (2) in spite of higher lipophilicity. An X-ray study of the sodium salt of 3e revealed that the benzyl group was located over the position between the D and E rings, and that the ethyl substituent on the benzyl group was close to the C(28) methyl group on the E ring.

Anti-Bacterial Agents↗