Use of Bombyx mori silk fibroin as a substratum for cultivation of animal cells

The growth of animal cells on silk fibroin-coated plates was examined. The anchorage-dependent cells showed almost the same growth on both fibroin- and collagen-coated plates, and it was 30-50% higher than that on polystyrene plates coated with hydrophilic groups. On the other hand, the growth of the anchorage-independent hybridomas on the three different plates did not show a significant difference. The cells grown on the respective plates produced their products with the same efficiency despite the difference in the chemical properties of the plates. In this paper, it is demonstrated that silk fibroin can be used as the substratum for the culture of animal cells in place of collagen.

A cross-sectional observation of the health effects of hydrazine hydrate and differences of its metabolism by NAT2 polymorphism

OBJECTIVES

To summarize the results of two studies that attempted to clarify: (1) the health effects of hydrazine hydrate (HH) (N2H4 x H2O: CAS No. 7803-57-8); and (2) the influence of allelic polymorphism of N-acetyltransferase (NAT2) on the metabolism of HH.

METHODS

A cross-sectional survey was carried out on 172 male HH-exposed workers and 125 male referent workers at five factories in Japan. The biological half-lives of HH after 1 h of exposure were determined in 12 workers, four workers in each of three NAT2 phenotypes. Clinical examinations were performed and acute and chronic subjective symptoms related to HH were examined by self-administered questionnaires. NAT2 phenotypes were assessed.

RESULTS

No hydrazine was detected in either the breathing zones or the urine of the referent workers. The mean hydrazine concentration in the breathing zones, hydrazine and acetylhydrazine in urine, and the cumulative exposure level were 0.0109 ppm, 0.8660 micromol/g x Cr, and 2.80 ppm-years, respectively. There was no difference and no dose-dependent change in the health examination items between HH-exposed and referent workers after adjusting confounding factors, nor in terms of the differences of NAT2 phenotypes. Of 90 subjective symptoms, complaints of nightmares were significantly related to HH exposure. The half-life of urinary hydrazine and acetylhydrazine on rapid, intermediate, and slow phenotypes was 1.68, 3.01, and 4.46 h, respectively.

CONCLUSION

This study suggested that current and cumulative exposure to HH did not affect the workers' health, and the half-life of the slow phenotype was longer than those of the rapid and intermediate phenotypes.

Effects of recombinant human serum albumin on ascites in rats with puromycin aminonucleoside-induced nephropathy

1. Recombinant human serum albumin (rHSA) (1 g/kg) significantly decreased the weight of ascites in rats with puromycin aminonucleoside-induced nephropathy. 2. Furosemide (1-30 mg/kg) did not significantly reduce the weight of ascites in this model. 3. A combination of rHSA (1 g/kg) with furosemide (5 mg/kg) significantly decreased the weight of ascites in this model compared with furosemide alone. 4. In consideration of these results, rHSA can be a substitute for human serum albumin products prepared from human plasma in therapy for ascites or edema in furosemide-resistant nephrotic syndrome.

Effect of the chemical modification of the arginyl residue in Bombyx mori silk fibroin on the attachment and growth of fibroblast cells

We prepared matrices of Bombyx mori silk fibroin (SF) with different degrees of modification of arginyl residues by reaction between 1,2-cyclohexanedione (CHD) and SF. Two kinds of SF, namely native SF (NSF), obtained from the silk gland of silkworm larvae, and regenerated SF (RSF), prepared from cocoons of the same silkworm, were used in this study because their amino acid compositions were slightly different from each other. The attachment and growth of mouse fibroblast (L-929) cells on the matrices of the NSF and RSF, in which half or almost all of the arginyl residues were modified (NSF50, RSF50, NSF100, and RSF100), were studied using a cell culture method. Both NSF50 and NSF100 exhibited higher cell attachment than did the unmodified NSF. While the cell growth on NSF50 was not significantly different from that on NSF and NSF100, the growth on NSF100 was higher than that on NSF. The cells attached to NSF50 and NSF100 were extensively spread out and their filopodia were visible by SEM. The cell attachment and growth on RSF were comparable to those on NSF100. Although RSF50 exhibited almost the same cell attachment as did the unmodified RSF, RSF100 exhibited a lower cell attachment than did the unmodified RSF and RSF50. There were no significant differences in the cell growth among RSF series. The cells attached to RSF50 and RSF100 aggregated to form masses, and their filopodia could not be found. The relationship of cell attachment to the basicity of the substrate is considered because the modification of the positively charged arginyl residue changed the basicity of the substrate and the cell attachment on the substrate.

Evidence on N-acetyltransferase allele-associated metabolism of hydrazine in Japanese workers

Hydrazine (N2H4), which has been categorized as a weak carcinogen, is a chemical with the one of the largest production rates in Japan. We have investigated the effects of acetylation phenotypes on the metabolism of hydrazine. Genotypes of N-acetyl transferases, NAT2*, were determined using polymerase chain reaction for 297 male workers. Biological and exposure monitoring were also conducted. The rapid and intermediate acetylators accounted for 45% each, and the slow acetylators accounted for 10%. Biological half-lives were significantly different among the three acetylation phenotypes (analysis of variance, P < 0.05): 3.94+/-1.70 hours for slow acetylators, 2.25+/-0.37 hours for intermediate acetylators, and 1.86+/-0.67 hours for rapid acetylators. Among Japanese, rapid and intermediate acetylators are the major phenotypes, which is in sharp contrast with those among Caucasians. We conclude that biological monitoring should take genetic factors, which may vary dramatically among different populations, into account.

Electrophysiological evidence of an increase in cold tolerance of cardiac muscles in mice after energy restriction

Life-prolonging energy restriction (ER) has been known to extend longevity. The heart was selected as the target organ of ER and the electrophysiological properties of ER on the heart were investigated. Action potential parameters were measured on ventricular papillary muscles of C57BL/6 mice (2-6 months of age). Resting membrane potential (Rm) did not change even when the temperature was lowered to 20 degrees C in ER mice (-67.5 +/- 0.8 mV), however, the membrane was depolarized in the control (-61.1 +/- 1.1 mV). Action potential duration measured at 30 and 50% repolarization was significantly prolonged in ER mice at 20-35 degrees C. Ouabain (10 microM) decreased Rm in ER mice at 20 degrees C (-68.6 +/- 1.0 to -63.6 +/- 0.8 mV), but failed to decrease Rm in the control (-60.6 +/- 1.8 to -62.1 +/- 1.2 mV). There were no significant differences in extracted Na, K-ATPase activity or affinity and binding capacity of ouabain between ER and control hearts. These results indicate that in ER mice the lack of effect of temperature on Rm was not due to a change in the physicochemical properties of Na, K-ATPase. The present study collectively suggests that ER increases cold tolerance in the heart of mice.

Apg1p, a novel protein kinase required for the autophagic process in Saccharomyces cerevisiae

Autophagic protein degradation includes bulk protein turnover with dynamic membrane reorganization, in which formation of novel organelles autophagosomes play key roles. We have shown that Saccharomyces cerevisiae performs the autophagy in the vacuole, a lytic compartment of yeast, in response to various kinds of nutrient starvation. Here we show that the APG1 gene, involved in the autophagic process in yeast, encodes a novel type of Ser/Thr protein kinase. Our results provide direct evidence for involvement of protein phosphorylation in regulation of the autophagic process. We found overall homology of Apglp with C. elegans Unc-51 protein, suggesting that homologous molecular mechanisms, conserved from unicellular to multicellular organisms, are involved in dynamic membrane flow.

Mechanisms for histamine H1 receptor-mediated vasodilation in isolated canine lingual arteries

Histamine and selective histamine receptor subtype agonists' effects on isolated and perfused canine lingual arteries were investigated with the cannula insertion method. In preparations preconstricted with phenylephrine, histamine and a selective histamine H1 receptor agonist, 2-pyridylethylamine induced a biphasic vascular response in a dose-related manner, i.e., vasoconstriction followed by vasodilatation. The biphasic responses to histamine and 2-pyridylethylamine were inhibited by diphenhydramine, a selective histamine H1 receptor antagonist, but were not influenced by cimetidine, a selective histamine H2 receptor antagonist. Dimaprit, a selective histamine H2 receptor agonist, induced only a slight vasoconstriction which was not modified by cimetidine. Dimaprit never induced vasodilation even at a large dose. A histamine H3 receptor agonist, R-alpha-methylhistamine, did not produce any significant vascular responses. Moreover, histamine-induced vasodilation was in part inhibited by removal of the endothelium, and the vasodilation remaining was abolished by H1 blockade. Thus, it is concluded that in canine lingual arteries there are abundant histamine H1 receptors which mediate both vasoconstriction and vasodilation, and that the histamine-induced vasodilation is in part due to endothelium-dependent mechanisms.

Synthesis of poly(ethylene glycol)-silk fibroin conjugates and surface interaction between L-929 cells and the conjugates

Poly(ethylene glycol) (PEG)-silk fibroin (SF) conjugates (PEG2-SF) were prepared by the chemical modification of solubilized SF with 2,4-bis[O-methoxypoly(ethylene glycol)]-6-chloro-s-triazine (actPEG2) in borate buffer at 37 degrees C. The IR spectra and DSC curves of PEG2-SF and SF suggested the introduction of PEG into SF by the modification and the beta-sheet structure of both SF and PEG2-SF induced by the treatment with methanol aqueous solutions. The content of the PEG component in PEG2-SF was evaluated to be 67% by weight from the melting enthalpy change of PEG observed on the DSC thermogram of PEG2-SF. Water content and contact angle measurements of SF before and after the modification indicated that the hydrophilicity of the PEG2-SF surface increased compared with that of SF. The attachment and growth of fibroblast cells (L-929) on the matrix of PEG2-SF were studied by a cell culture method. PEG2-SF exhibited very low cell attachment and growth, though SF exhibited high cell attachment and growth. The filopodium of the cells attached to PEG2-SF could not be found, and the cells aggregated to form masses in scanning electron microscopy images. These results could be explained in terms of the increased hydrophilicity of the PEG2-SF surface.

Stimulus-dependent induction of long-term potentiation in CA1 area of the hippocampus: experiment and model

In the CA1 area of the hippocampus, the magnitude of long-term potentiation (LTP) depends not only on the frequency of applied stimuli, but also on their number. With a slice preparation using extracellular recording in the hippocampus CA1 of a guinea pig, we investigate the magnitude of LTP induced by electrical stimuli with a range of frequencies and the number of applied stimuli. We find that the magnitude of the saturated potentiation obtained with periodic stimuli largely depends on the frequency and is insensitive to the number of stimuli, once the saturation level has been obtained. Furthermore, we investigated nonperiodic stimuli and found that the magnitude of the saturated potentiation is also sensitive to the statistical correlation between successive interstimulus intervals, even when their average frequency is held constant. In order to explain the LTP dependence on these various experimental parameters, we propose a simple mathematical model for the induction of LTP. In the model, an exponentially decaying element released as a result of previous stimuli is coupled with a new stimulus to act as the potentiation force, and the magnitude of potentiation is determined by this potentiation force. We can determine the decaying time constant of this hypothetical element as a model parameter by fitting the model to the experimental data. The time scale is found to be of the order of 200 msc. A molecular or cellular factor with this decaying time constant is likely to be induced in LTP induction.

Isolation and characterization of SYS genes from yeast, multicopy suppressors of the functional loss of the transport GTPase Ypt6p

In Saccharomyces cerevisiae, the YPT6 gene encodes the homologue of the mammalian Rab6 protein found in the Golgi apparatus. Deletion of YPT6 in yeast produces a phenotype showing temperature-sensitive growth and partial missorting of the vacuolar enzyme, carboxypeptidase Y. To identify proteins that might: (1) interact with Ypt6p; or (2) act in the same pathway, we have isolated four multicopy suppressors, named SYS1, SYS2, SYS3 and SYS5, that can complement the temperature-sensitive growth phenotype of the ypt6 null mutant. On high expression, these genes are also able to partially suppress the missorting of carboxypeptidase Y.SYS2 on a multicopy plasmid suppresses in addition the temperature-sensitive phenotype of sec7-1, a mutant defective in transport between and from the Golgi compartment. Gene disruption of SYS1 and SYS2 did not result in significant growth defects. However, deletion of SYS1 and/or SYS2 in the ypt6 null mutant enhances defects in vacuolar protein sorting and in cell growth. Whereas protein secretion was not significantly affected in these mutants, the processing of alpha-factor precursor by the Kex2 protease was inhibited, suggesting a function of YPT6 and its null mutant suppressors in transport between the late Golgi and a prevacuolar, endosome-like compartment.

Possible involvement of muscarinic M1 and M3 receptor subtypes mediating vasodilation in isolated, perfused canine lingual arteries

1. Using the cannula insertion method, muscarinic receptor subtypes were analysed in isolated, perfused canine lingual arteries preconstricted with phenylephrine. 2. Both acetylcholine and McN-A-343 induced a profound vasodilation in a dose-related manner. Acetylcholine-induced dilations were approximately 1000-times more potent than McN-A-343-induced dilation. 3. Acetylcholine-induced dilations were abolished after removal of the endothelium by intraluminal treatment with 1 mg saponin. 4. Acetylcholine-induced dilations were markedly inhibited by an M1/M3 receptor antagonist, 4-DAMP. Moreover, they were slightly, but significantly, inhibited by an M1 antagonist, pirenzepine, but never influenced by an M2 antagonist, AF-DX 116. Mc-N-A-343-induced vasodilations were inhibited by both 4-DAMP or pirenzepine. 5. These results suggest that there are abundant functional M3 and a few M1 receptors in the canine lingual artery that mediate vasodilation and that this vasodilation is dependent on the presence of an intact endothelium.

Chemical modification of the arginyl residue in silk fibroin: 2. Reaction of 1,2-cyclohexanedione in aqueous alkaline medium

The arginyl residue of solubilized silk fibroin was chemically modified with 1,2-cyclohexanedione in aqueous alkaline medium to form a stable imidazolidinone ring, and its positive charge was masked. CD spectra of the modified silk fibroin in aqueous solution showed an increase in the fraction of random coil conformation. The increase may be caused by the exposure to alkaline medium in the modification reaction. FT-IR and CD spectra of the silk fibroin films before and after the modification indicated that the conformational change in the modified silk fibroin in the solid state did not occur by the modification of its arginyl residue with 1,2-cyclohexanedione. The chemical stability of the modified silk fibroin film was investigated in vitro with phosphate-buffered saline solution. The modified arginyl residue in the film was stable in the phosphate-buffered solution.

A novel endogenous mouse mammary tumor virus locus in Asian wild mice and its evolutionary divergency

The divergency of endogenous mouse mammary tumor virus (MMTV) in European mouse strains indicates acquisition of exogenous MMTV into their genomes during evolution. In the present study, we selected two strains of Asian wild mice, Cas-Hmi (Mus musculus castaneus) and Sub-Kjr (M. m. subspecies) to investigate a possible divergency of endogenous MMTVs among Asian mouse strains. Southern blot analysis and polymerase chain reaction (PCR) demonstrated that Cas-Hmi and Sub-Kjr have the full structure of integrated endogenous MMTVs, suggesting that these mice were diverged during evolution after MMTV endemics.

Chemical modification of silk fibroin with N-acetyl-chito-oligosaccharides

N-Acetyl-chito-oligosaccharides (NACOS)-silk fibroin (SF) conjugates (NACOS-CY-SF) were prepared by the reaction of solubilized SF and cyanuric chloride (CY)-activated NACOS modifier (NACOS-CY). N-Acetyl-D-glucosamine (NAG), as a model compound, was reacted with CY to clarify the chemical structure of the modifier. The 1H- and 13C-NMR spectra of the reactant suggest that the anomeric hydroxyl group of NACOS reacted with the chlorine atom of CY. The content of NACOS in the NACOS-CY-SF conjugates was calculated by comparing the integral values of the signals in the 1H-NMR spectra of the conjugates and the mixture of NACOS and SF. As the 1H-NMR spectrum of the conjugates showed a downfield shift of the aromatic protons of the tyrosine residue, the tyrosine residue in SF reacted with another chlorine atom of the triazine ring of the modifier. The result of the amino acid analysis of the conjugates suggests that lysine residues also reacted with the modifier.

Attachment and growth of cultured fibroblast cells on silk protein matrices

The attachment and growth of L-929 cells on films made of Bombyx mori silk proteins--fibroin and sericin and their mixtures--was studied by a cell culture method. Both cell attachment and growth were dependent on a minimum of around 90% sericin in the mixture. The results from electron micrography as well as from the DSC measurements supported the notion that the mixture of the two proteins fibroin and sericin has a phase-separated structure in the solid state. The observed minimum of sericin in the cell attachment and growth is thought to be a result of this phase-separated structure. Films of pure component proteins (i.e., 100% fibroin or sericin) exhibited as high a cell attachment and growth as collagen, a widely used mammalian cell culture substrate. However, a morphological study of the attached cells revealed that the cells attached to silk fibroin were extended and had a spindle shape, just like the cells attached to collagen, while the cells attached to the silk sericin had a different shape. It is concluded, therefore, that the attachment condition on silk fibroin is ideal for the viability, growth and function of the cells.