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Biomedical subjects

M Mita

Publications and source records attributed to M Mita.

At least 19 recordsLinked to original sources
PubMed2001

Interaction of N1-substituted adenines with 1-methyladenine receptors of starfish oocytes in induction of maturation.

Starfish oocytes are arrested naturally in the late G(2) phase of the first meiotic division. In response to the natural maturation-inducing hormone, 1-methyladenine (1-MA), oocytes undergo reinitiation of meiosis with germinal vesicle breakdown. We tested 10 newly synthesized N1-substituted adenines that are 1-MA analogues to analyze the interaction between 1-MA and its stereo-specific receptors on the oocyte plasma membranes of the starfish Asterina pectinifera. Among these analogues, 1-(beta-naphthylmethyl)adenine, 1-aminoadenine and 1-(p-nitrobenzyl)adenine played agonistic roles in the induction of oocyte maturation. 1-(o-Nitrobenzyl)adenine, 1-(m-nitrobenzyl)adenine, 1-phenethyladenine and 1-(p-nitrophenethyl)adenine had antagonist effects on 1-MA-induced oocyte maturation. These agonists and antagonists behaved competitively in the binding of [3H]1-MA to receptors in oocyte cortices. In contrast, 1-(alpha-naphthylmethyl)adenine, 1-(2,4-dinitrobenzyl)adenine and 1-(p-methoxybenzyl)adenine had no effects on oocyte maturation. Our results suggest that regional-specific sterical structures at the N1-site of adenine are important in the interaction between 1-MA and its receptors in oocytes. In addition, a negative charge at the N1-site of adenine is required for binding with the receptors.

Adenine↗
PubMed2001

[Effects of stimulus intensity on multifocal electroretinograms].

PURPOSE: To investigate origins of responses of the second order kernel components of multifocal electroretinograms (m-ERGs), the influence of stimulus intensities on the waveform were studied. SUBJECTS AND METHODS: M-ERGs were recorded from 20 normal eyes of 14 normal adults using a Visual Evoked Response Imaging System with 19 hexagonal stimulus elements with light intensities of 6.3, 20, 63, 200, or 331 cd/m2. The response densities and implicit times of the first (N1, P1, N2) and the second order kernel components (P1, N1, P2, N2, P3, N3) of the m-ERGs were measured. RESULTS: The components were divided into two groups based on the behavior of the each component to the stimulus intensity change. The first group consisted of all the first order kernel components and P1 and N1 of the second order kernel components whose response densities were significantly larger (p < 0.05) than those of components elicited by stimulus of one grade lower intensity. The second group consisted of N2, P3, and N3 of the second order kernel components whose response densities did not increase when the stimulus intensity was increased from 200 to 331 cd/m2. CONCLUSION: It is probable that in the second order kernel components, the origin of P1, N1, and P2 is different from N2, P3, and N3 because the response to stimulus intensity of the two groups of components was different.

Adult↗
PubMed2000

Three episodes of delayed hemolytic transfusion reactions due to multiple red cell antibodies, anti-Di, anti-Jk and anti-E.

There is no report in which three episodes of delayed hemolytic transfusion reaction (DHTR) occurred from multiple antibodies to red cells (RBCs) in the course of treatment of a patient. This paper describes episodes of anemia and hyperbilirubinemia in concert with the development of three alloantibodies in a multiple transfused patient. The patient was a 71-year-old male suffering from valvular heart disease and hemophilia B with a history of transfusions. Although he received compatible RBCs from 14 donors as judged by a crossmatch test using the albumin-antiglobulin method, three episodes of DHTR occurred after surgery. The first hemolytic episode on day 7 after surgery was due to anti-Di(a) because of clinical and laboratory evidence which included jaundice, sudden increases in total bilirubin (T-Bil) and lactate dehydrogenase (LD) levels, and a decrease (2.2 g/dl) in hemoglobin (Hb) level. The second hemolytic episode on day 16 resulted from newly producted anti-Jk(b). The patient experienced fever, fatigue, nausea and anorexia, and laboratory data showed a second increase in T-Bil, a second decrease (3 g/dl) in Hb, and moderate elevations of blood urea nitrogen (BUN) and creatinine (CRE) levels. The third hemolytic episode on day 39 was due to anti-E. The patient complained of fever and fatigue and had a third unexplained drop (1.5 g/dl) in Hb despite no bleeding. This is the first reported case in which three episodes of DHTR occurred from different red cell antibodies.

Aged↗
PubMed2000

Reduction of stilbene oxide and styrene oxide to the corresponding alkenes by intestinal bacteria.

1. This study provides the first evidence that stilbene oxide and styrene oxide are reductively metabolized to the corresponding alkenes by intestinal bacteria in animals. 2. When trans- or cis-stilbene oxide were incubated with the caecal contents of rat under anaerobic conditions, both trans- and cis-stilbene were isolated from the incubation mixture. Styrene oxide was also reduced to styrene by rat caecal contents. 3. Caecal contents of mouse, hamster and guinea pig also exhibited alkene oxide reductase activities toward cis- and trans-stilbene oxides, and styrene oxide. In contrast, liver microsomes or cytosol exhibited no epoxide reductase activities toward these substrates. 4. Seven pure strains of intestinal bacteria exhibited alkene oxide reductase activities of varying degrees under anaerobic conditions, with the highest activity being observed in Clostridium sporogenes. 5. Cell-free extracts of either the intestinal bacteria in rat caecal contents or C. sporogenes exhibited reductase activity when supplemented with both NAD(P)H and FMN under anaerobic conditions. Reductase activity was also observed on addition of the photochemically reduced form of FMN instead of both NAD(P)H and FMN.

Animals↗
PubMed2000

HeLa cell transformants overproducing mouse metallothionein show in vivo resistance to cis-platinum in nude mice.

Plasmid pSV2MT-I encoding mouse metallothionein-I (MT-I) designed to be expressed under the control of an SV40 promoter was introduced into human HeLa S3 cells. Several transformants (HeLa/MTH) carrying multi-copies of mouse MT-I cDNA in their genomes were isolated. These transformants produced 4 to 20-fold larger amounts of MT than their parent cells. The MT levels in HeLa/MTH were well correlated with the extent of resistance to cadmium, but not with that to cis-platinum (cis-DDP) in vitro. To study the role of MT in resistance to cis-DDP in vivo, nude mice were inoculated subcutaneously with two independent HeLa/MTH clones. MT levels in these tumors were about 3-fold higher than those in the parental cells. The growth of tumors derived from either HeLa/MTH clone was not inhibited in the presence of 15 micromol/kg of cis-DDP, which completely inhibited the growth of tumors derived from the parental HeLa cells. These data strongly suggest that the elevated level of MT confers resistance to cis-DDP in vivo but not in vitro. Thus, the results of this study indicate that in vitro determinations of the influence of MT on cis-DDP resistance may underestimate its importance in in vivo situations.

Animals↗
PubMed2000

Activity of exemestane in metastatic breast cancer after failure of nonsteroidal aromatase inhibitors: a phase II trial.

PURPOSE: To evaluate the antitumor activity and toxicity of a new steroidal aromatase inactivator, exemestane, in postmenopausal women with metastatic breast cancer who had progressive disease (PD) after treatment with a nonsteroidal aromatase inhibitor. PATIENTS AND METHODS: In this phase II trial, eligible patients were treated with exemestane 25 mg daily (n = 241) followed, at the time PD was determined, by exemestane 100 mg daily (n = 58). RESULTS: On the basis of the intent-to-treat analysis by independent review, exemestane 25 mg produced objective responses in 6.6% of patients (95% confidence interval [CI], 3.8% to 10.6%) and overall success (complete response + partial response + no change for 24 weeks or longer) in 24.3% (95% CI, 19.0% to 30.2%). The median durations of objective response and overall success were 58.4 weeks (95% CI, 49.7 to 71.1 weeks) and 37.0 weeks (95% CI, 35.0 to 39.4 weeks), respectively. Increasing the dose of exemestane to 100 mg upon the development of PD produced one partial response (1.7%; 95% CI, 0.0% to 9.2%). Both dosages were well tolerated and were discontinued because of adverse events in only 1.7% of patients. CONCLUSION: Exemestane 25 mg once daily seems to be an attractive alternative to chemotherapy for the treatment of patients with metastatic breast cancer after multiple hormonal therapies have failed.

Administration, Oral↗
PubMed2000

Reductive metabolism of stilbene oxide and styrene oxide to the olefins in rats.

The present study provides the first evidence that stilbene oxide and styrene oxide are reductively metabolized to the corresponding olefins in rats. When cis- or trans-stilbene oxide was given orally to rats, both cis- and trans-stilbene were isolated from the urine and feces. Styrene was also isolated from the urine and feces of rats given styrene oxide. These metabolites were identified unequivocally by UV and mass spectral comparison with authentic samples, and on the basis of their TLC and HPLC behavior. However, these olefins were not detected in the urine or feces of antibiotics-treated rats dosed with cis- or trans-stilbene oxide. Cecal contents of the untreated rats exhibited olefin oxide reductase activities toward cis- and trans-stilbene oxides under anaerobic conditions. The results suggest that intestinal bacteria play an important role in the reduction of olefin oxides to the corresponding olefins in the animal body.

Alkenes↗
PubMed1999

1-Methyladenine production from ATP by starfish ovarian follicle cells.

1-Methyladenine (1-MeAde), the oocyte maturation-inducing substance in starfish, is produced by ovarian follicle cells upon stimulation with a gonad-stimulating substance (GSS) released from the radial nerves. We have shown previously that GSS causes a reduction in the intracellular levels of ATP coincident with 1-MeAde production. The present study examined whether the adenine molecule of 1-MeAde is directly derived from ATP. When isolated follicle cells from the starfish Asterina pectinifera were preloaded with [U-14C]adenine or [U-14C]adenosine, there was an increase in the intracellular levels of radiolabeled adenine nucleotides, particularly ATP. Following further incubation with GSS, the intracellular levels of radiolabeled ATP decreased, concomitant with a marked increase in the levels of [14C]1-MeAde in the medium. The amount of ATP consumed under the influence of GSS was similar to the amount of 1-MeAde produced. However, there was no change in the levels of ADP and AMP regardless of the presence or absence of GSS. These findings strongly suggest that 1-MeAde is synthesized from ATP as a substrate in follicle cells under the influence of GSS. Furthermore, using [methyl-3H]methionine, the methyl group of 1-MeAde was found to be derived from methionine. Thus GSS appears to stimulate the synthesis of 1-MeAde from ATP via the methylation process in starfish ovarian follicle cells.

Adenine↗
PubMed1999

Methyl donor for 1-methyladenine biosynthesis in starfish ovarian follicle cells.

1-Methyladenine (1-MeAde), the oocyte maturation-inducing substance of starfish, is produced by ovarian follicle cells upon stimulation with a gonad-stimulating substance (GSS) released from radial nerves. It has been reported that a process of methylation is involved in GSS-induced 1-MeAde production by starfish ovarian follicle cells. The present study sought to identify a possible methyl donor for 1-MeAde biosynthesis in follicle cells of the starfish Asterina pectinifera. When isolated follicle cells were incubated with [methyl-(14)C]methionine (Met), there was an increase in the level of radiolabeled S-adenosylmethionine (SAM). After further incubation with GSS, the [methyl-(14)C]SAM level decreased, concomitant with a marked increase in radiolabeled 1-MeAde production. The amount of [methyl-(14)C]SAM consumed under the influence of GSS was similar to the amount of [methyl-(14)C]1-MeAde produced. Therefore, it is concluded that SAM is a methyl donor for 1-MeAde biosynthesis in starfish ovarian follicle cells. On the other hand, it is likely that the purine molecule of 1-MeAde is not derived from SAM but from ATP. 3-Isobutyl-1-methylxanthine, a potent inhibitor of cyclic AMP phosphodiesterase, also caused a reduction in the level of radiolabeled SAM following 1-MeAde production. This suggests that the methylation process of 1-MeAde biosynthesis in starfish ovarian follicle cells upon stimulation with GSS is mediated by a second messenger, cyclic AMP.

1-Methyl-3-isobutylxanthine↗
PubMed1999

Protein kinase C promotes spontaneous relaxation of streptolysin-O-permeabilized smooth muscle cells from the guinea-pig stomach.

Isolated single smooth muscle cells from the fundus of a guinea-pig stomach were permeabilized by use of streptolysin-O (0.5 U/ml). Most of the permeabilized cells responded to 0.6 microM Ca2+, but not to 0.2 microM Ca2+, with a resulting maximal cell shortening to approximately 71% of the resting cell length. These cells were relaxed again by washing with the Ca2+-free solution (2.5 nM free Ca2+) for 3-5 min. Addition of 10 microM acetylcholine (ACh) resulted in both a marked decrease in the concentration of Ca2+ required to trigger a threshold response and an increase in the maximal cell shortening, indicating that the cells retained the muscarinic receptor function. When the cell treated with a protein kinase C (PKC) inhibitor, K-252b (1 microM), for 3 min was exposed to 10 microM ACh in the presence of K-252b, the cell shortened within 2 min with a maximal cell shortening. When the cell shortening was induced by 10 microM ACh plus 1 microM Ca2+ in the presence of K-252b (1 microM) or more selective PKC inhibitors, such as calphostin C (1 microM) or PKC pseudosubstrate peptide (100 microM), the extension of the shortened cells, by washing with the Ca2+-free solution, was significantly inhibited. In contrast, K-252b (1 microM) did not inhibit the relaxation of Ca2+-induced shortened cells. These results suggest that the receptor-mediated activation of PKC in the process of ACh-induced cell shortening plays a role in the subsequent relaxation of the shortened cells.

Acetylcholine↗
PubMed1999

Metallothionein modulates the carcinogenicity of N-butyl-N-(4-hydroxybutyl)nitrosamine in mice.

We examined the carcinogenicity of N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in transgenic mice deficient in the metallothionein (MT) I and II genes and in control (129/Sv) mice. Both strains of mice were given BBN for 8 weeks with or without Zn treatment. All mice were killed at 12 weeks after the cessation of BBN administration. BBN induced bladder tumors in 75% of MT null mice and in 43% of 129/Sv mice. The average number of bladder tumors per mouse was significantly higher in MT null mice (1. 18 +/- 0.27) than in 129/Sv mice (0.43 +/- 0.20). Zn treatment suppressed the carcinogenicity of BBN in 129/Sv mice but not in MT null mice. Histopathological examination of the tumors revealed that the malignant potential of bladder tumors in 129/Sv mice was greater than that in MT null mice. These results indicate that MT is an important modulator of carcinogenicity of BBN in the bladder of mice.

Animals↗
PubMed1999

Conversion of dieldrin to aldrin by intestinal bacteria in rats.

The present study provides the evidence that dieldrin is reductively metabolized to aldrin by intestinal bacteria in rats. When dieldrin was incubated with the cecal contents of rats, aldrin, a reduced metabolite of the epoxide, was isolated from the incubation mixture. The metabolite was identified unequivocally by UV and mass spectral comparison with an authentic sample, and on the basis of its TLC and HPLC behavior. The cecal contents of rats exhibited epoxide reductase activity toward dieldrin under anaerobic conditions. However, only marginal activity was observed under aerobic conditions. Four pure strains of intestinal bacteria exhibited epoxide reductase activities to varying degrees under anaerobic conditions. The highest activity was observed in Clostridium sporogenes. Cell-free extracts of the intestinal bacteria in rat cecal contents showed reductase activity when supplemented with both NAD(P)H and FMN under anaerobic conditions.

Aldrin↗
PubMed1998

[Myositis caused by hydroxyurea in a patient with chronic myelogenous leukemia].

A 59-year-old man with chronic myelogenous leukemia (CML) had a white-blood-cell (WBC) count of 55,400/microliter when admitted in July 1997, and was placed on oral hydroxyurea (HU) of 1,500 mg/day. Treatment with 600 MU/day of interferon alpha (IFN alpha) was started on August 5. HU was discontinued when the patient's WBC count dropped to 8,100/microliter on August 18. However, HU was resumed about a month later, after his WBC count increased to 10,100/microliter, but discontinued when the patient started to complain of chills, high fever, and bilateral femoral pain. HU treatment was initiated again one week later, after the patient's WBC count had begun rising but ceased again after he experienced chills, high fever, and bilateral femoral pain. The patient's myogenetic enzymes were found to be increasing the following day, and a lymphocyte stimulation test (LST) with HU showed a high stimulation index of 41.7%. The elevation of myogenetic enzymes and the results of the LST suggested that myositis due to HU was the cause of the patient's clinical manifestations. His myositis spontaneously disappeared after HU was discontinued. Although the patient is no longer receiving HU, IFN alpha has brought his CML under control. To our knowledge, this is the first reported case of myositis caused by HU.

Antineoplastic Agents↗
PubMed1997

alpha1-Adrenoceptor-mediated phosphorylation of myosin in rat-tail arterial smooth muscle.

The mechanism of alpha1-adrenoceptor-mediated contraction was investigated in helical strips of the rat-tail artery. Muscle strips with the endothelium removed contracted in response to the alpha1-adrenoceptor agonist cirazoline, with half-maximal contraction at 0.23 microM. The contractile response to a submaximal concentration of cirazoline (0.3 microM) was biphasic, with a rapid phasic component peaking at approx. 30 s, followed by sustained tonic contraction. Phosphorylation of the 20 kDa light chain of myosin (LC20) in response to 0.3 microM cirazoline was also biphasic and closely matched the time-course of contraction. Resting LC20 phosphorylation levels were 0.22+/-0.06 mol of Pi/mol of LC20 (n=3) and reached a maximum of 0.58+/-0.08 mol of Pi/mol of LC20 (n=3). Phosphopeptide mapping and phosphoamino acid analysis revealed that LC20 phosphorylation occurred exclusively at serine-19. The sustained phase of contraction was eliminated by removal of extracellular Ca2+ and the phasic response was eliminated by depletion of endogenous Ca2+ stores. Both phases of the contractile response were restored by re-addition of Ca2+ to the bathing medium. LC20 phosphorylation and both phases of the contractile response to 0.3 microM cirazoline were inhibited by the myosin light-chain kinase inhibitor ML-9 (30 microM). Resting LC20 phosphorylation, however, was unaffected by ML-9. Finally, both phasic and tonic responses to 0.3 microM cirazoline were partially inhibited by chloroethylclonidine (50 microM), suggesting the involvement of both alpha1A and alpha1B adrenoceptors in these contractile responses.

Adrenergic alpha-1 Receptor Antagonists↗
PubMed1997

Inhibitory guanine-nucleotide-binding-regulatory protein alpha subunits in medaka (Oryzias latipes) oocytes--cDNA cloning and decreased expression of proteins during oocyte maturation.

We have previously shown that pertussis-toxin-sensitive inhibitory guanine-nucleotide-binding-regulatory proteins (G proteins) are involved in the signal transduction of steroidal maturation-inducing hormone (MIH) of rainbow trout (Oncorhynchus mykiss) oocytes, 17alpha,20beta-dihydroxy-4-pregnen-3-one (17alpha,20beta-DP) [Yoshikuni, M. & Nagahama, Y. (1994) Dev. Biol. 166, 615-622]. In this study, we obtained five different cDNA fragments of G protein alpha subunits from medaka (Oryzias latipes) intact ovarian follicles (three subtypes of G(i alpha), G(i alpha a), G(i alpha b) and G(i alpha c); two subtypes of G(s alpha), G(s alpha d), and G(s alpha e)). Using a newly developed extraction method for medaka oocyte RNA, we demonstrated that oocytes expressed both G(i alpha a) and G(i alpha c), but not G(i alpha b). Full-length cDNA clones for G(i alpha a) and G(i alpha c) were then isolated from a medaka ovarian follicle cDNA library. The predicted amino acid sequences of G(i alpha a) and G(i alpha c) exhibited significant similarity with G(i alpha1) and G(i alpha2) of other species, respectively. Both G(i alpha a) and G(i alpha c) possessed a specific Cys residue in the C-terminal region that was the site for ADP-ribosylation by pertussis toxin. G(o alpha), another G protein that is ADP-ribosylated by pertussis toxin, was not detected in oocytes, although it was expressed in brain tissue. Western blot analyses using a specific antibody against G(i alpha1) and G(i alpha2) subunit proteins revealed that in both medaka and rainbow trout G(i alpha) subunit protein (40 kDa) contents were abundant in plasma membranes of postvitellogenic immature oocytes, decreased in mature oocytes, and were absent in ovulated eggs. Furthermore, specific 17alpha,20beta-DP binding to plasma membranes was higher in postvitellogenic immature oocytes than in ovulated eggs. Taken together, these results suggest that G(i alpha a) and/or G(i alpha c) may be involved in the transduction of the signal from 17alpha,20beta-DP receptors during oocyte maturation of fish oocytes.

Amino Acid Sequence↗