Search PubMed⌕ Search

Biomedical subjects

H Okamoto

Publications and source records attributed to H Okamoto.

At least 253 records · Page 14Linked to original sources
PubMed1999

Cyclic ADP-ribose-mediated insulin secretion and Reg, regenerating gene.

Glucose is the primary stimulus of insulin secretion in pancreatic beta-cells of the islets of Langerhans. CD38 has both ADP-ribosyl cyclase, which catalyzes the formation of cyclic ADP-ribose from NAD+, and cyclic ADP-ribose hydrolase, which converts cyclic ADP-ribose to ADP-ribose. ATP, produced by glucose metabolism, inhibits the cyclic ADP-ribose hydrolase of CD38 and therefore causes cyclic ADP-ribose accumulation in beta-cells. Then, cyclic ADP-ribose acts as a second messenger for Ca2+ mobilization from the endoplasmic reticulum to secrete insulin. The mechanism of insulin secretion as described above is completely different from the conventional hypothesis in which Ca2+ influx from extracellular sources was assumed to play a role in insulin secretion by glucose. On the other hand, strategies for influencing the replication of islet beta-cells and the growth of the beta-cell mass may be more important for ameliorating diabetes. Reg, regenerating gene, is involved in the growth of the beta-cell mass, and Reg protein has been shown to increase the beta-cell mass in a 90% depancreatized diabetic rat model, thereby ameliorating the diabetes. CD38 is involved in the formation of cyclic ADP-ribose and is essential for the glucose sensitivity of beta-cells for insulin secretion. Therefore, CD38 gene and Reg gene will become targets for genetic engineering for diabetic beta-cells.

ADP-ribosyl Cyclase↗
PubMed1999

The Reg gene family and Reg proteins: with special attention to the regeneration of pancreatic beta-cells.

Pancreatic beta-cells of the islets of Langerhans are the only cells that produce insulin in humans, as well as in most animals, but they have been thought to have a limited capacity for regeneration, which is a predisposing factor for the development of diabetes mellitus. Strategies for influencing the replication and growth of the beta-cell mass are therefore important for the prevention and/or treatment of diabetes. We have established a model for islet regeneration in 90% depancreatized rats by the administration of poly(ADP-ribose) synthetase inhibitors such as nicotinamide. The regenerating islets in the remaining pancreas of poly(ADP-ribose) synthetase inhibitor-treated rats were markedly enlarged and consisted largely of insulin-producing beta-cells, preventing the development of diabetes mellitus that would otherwise be caused by the 90% pancreatectomy. In screening the regenerating islet-derived cDNA library, we found a novel gene and named it Reg (i.e., regenerating gene). The rate Reg cDNA had a single open reading frame that encoded a 165-amino acid protein with a 21-amino acid signal peptide. We also isolated the human REG cDNA which encoded a 166-amino acid protein with a 22-amino acid signal peptide. The amino acid sequence of human REG protein has 68% homology to that of rat Reg protein. Recombinant rat Reg protein without the signal peptide, produced in yeast, stimulated beta-cell replication and increased the beta-cell mass in the residual pancreas of 90% depancreatized rats, ameliorating the surgical diabetes. Recombinant human REG protein also induced an expansion of the beta-cell mass in non-obese diabetic (NOD) mice, resulting in the amelioration of diabetes. These results, as well as several other lines of evidence, indicate that Reg protein is a growth factor for pancreatic beta-cells and also suggest that the administration of Reg protein and/or activation of the Reg gene can be used as a potential therapeutic approach for diabetes mellitus. We have further isolated several Reg and Reg-related genes from human, rat and mouse, and revealed that they constitute a multigene family, the Reg gene family. Based on the primary structures of proteins encoded by the Reg gene family, we have grouped the members of the family into three subclasses, type I, II, and III. Type I Reg (Reg I) encodes a beta-cell growth factor, Reg I protein, as mentioned above. Some of the type III Reg (Reg III) have recently been suggested to play roles in the regeneration of cells other than pancreatic beta-cells, such as neuronal cells and epithelial cells in the alimentary tract.

Amino Acid Sequence↗
PubMed1999

Rubber-like elasticity and volume changes in the isolated spasmoneme of giant Zoothamnium sp. under Ca2+-induced contraction.

Using glycerinated spasmoneme of giant Zoothamnium sp., the physical properties of spasmoneme before and after Ca2+-induced contraction (pCa 4.5) were investigated. The volume change of spasmoneme contraction was measured under zero tension. The length and diameter decreased by about 50% of their initial value as a result of contraction, which means that contraction is nearly isotropic. Thus the volume of spasmoneme decreased drastically by 86% of its original value. The swollen ratio of extended and contracted spasmoneme were 0.07 and 0.37, respectively. Tension-extension relationships of extended and contracted spasmonemes were measured. By applying the theory of rubber elasticity, the number of segments of a chain in originally extended spasmoneme was only 3.3, i.e., the chain was almost a straight one. On the other hand, the number of segments of a chain in contracted spasmoneme was more than 100, i.e., the chain was essentially a random one. Furthermore, the total number of chains in single spasmoneme was the same in extended and contracted spasmoneme. This means that the interchain cross-links of chains were not influenced by addition or removal of Ca2+. Moreover, the molecular weight of a chain is estimated to be at most about 50 kd. By considering all these results, it is concluded that the contractile mechanism of spasmoneme originates in the intramolecular folding and unfolding induced by Ca2+ binding and detaching.

Animals↗
PubMed1999

Secretion of prebeta HDL increases with the suppression of cholesteryl ester transfer protein in Hep G2 cells.

Prebeta HDL are small, protein rich lipoproteins that are predominantly composed of apo A-I, without apo A-II. Prebeta HDL are secreted from the liver as nascent HDL and/or are produced in the incubated plasma by cholesteryl ester transfer protein (CETP). However, the role of CETP in the secretion of HDL from the liver has yet to be determined. In the present study, we examined the effect of the suppression of hepatic CETP by antisense oligodeoxynucleotides (ODNs) against CETP targeted to the liver on the secretion of apo A-I using a Hep G2 cell culture. The ODNs against CETP were coupled to asialoglycoprotein (ASOR) carrier molecules, which serve as an important method for the regulation of liver gene expression. Hep G2 cells were cultured in DMEM supplemented with 10 FBS. After 2 days, the medium was changed to DMEM with EGF and the cells were divided into three groups. The control group received saline, while the sense group was mixed with the sense ODNs complex and the antisense group was mixed with the antisense ODNs complex, respectively, for 2 days. Both the hepatic CETP mRNA and the CETP mass in the medium in the antisense group decreased significantly more than in the sense and the control groups (CETP mass: 1.697 + /- 0.410 ng/mg cell protein vs. 2.367 + /- 0.22 and 2.360 + /- 0.139, n = 3 in each determination). In contrast, both the hepatic apo A-I mRNA and the apo A-I mass in the medium in the antisense group were significantly higher than those in the sense and the control groups (apo A-I mass; 1.877 + /- 0.215 micro/mg cell protein vs. 1.213 + /- 0.282 and 1.097 + /- 0.144, n = 3 in each determination). The increase in apo A-I was mainly due to the increase in prebeta apo A-I. These findings may partly explain why HDL and apo A-I increase in patients with CETP deficiency, while also indicating the possibility that the original level of prebeta HDL is sufficient in such patients.

Apolipoprotein A-I↗
PubMed1999

Detection of bikunin mRNA in limited portions of rat brain.

Tissue distribution of bikunin mRNA, which encodes a Kunitz-type serine protease inhibitor of the inter-alpha-inhibitor family (IalphaI), was studied in rats and mice by the reverse-transcripsion polymerase chain reaction (RT-PCR). We found that the liver as well as other tissues, such as the kidney, testis and adrenal gland, expressed bikunin mRNA. Although signals of bikunin mRNA were faint in the whole brain of rats and mice, distinct signals were found in limited portions of rat brain, such as the hippocampus, cerebral cortex and pituitary, but undetectable in cerebellum, medulla oblongata, hypothalamus, striatum, midbrain and choroid plexus. In three distinct types of cells, such as neurons, astrocytes and meningeal cells, in primary cultures isolated from the cerebral cortex and meninges of 1-day-old newborn rats, only neurons positively expressed bikunin mRNA. These results suggest that, in addition to peripheral tissues, neurons in the hippocampus and cerebral cortex produce bikunin, suggesting a potential role of bikunin/IalphaI family in these brain regions.

Animals↗
PubMed1999

MT neurons in the macaque exhibited two types of bimodal direction tuning as predicted by a model for visual motion detection.

We previously proposed a model for detecting local image velocity on the magnocellular visual pathway (Kawakami & Okamoto (1996) Vision Research, 36, 117-147). The model detects visual motion in two stages using the hierarchical network that includes component and pattern cells in area MT. To validate the model, we predicted two types of bimodal direction tuning for MT neurons. The first type is characteristic of component cells. The tuning is bimodal when stimulated with high-speed spots, but unimodal for low-speed spots or for bars. The interval between the two peaks widens as the spot's speed increases. The second type is characteristic of pattern cells. The tuning is bimodal when stimulated with low-speed bars, but unimodal for high-speed bars or for spots. The interval widens as the bar's speed decreases. To confirm this prediction, we studied the change of direction tuning curves for moving spots and bars in area MT of macaque monkeys. Out of 35 neurons measured at various speeds, six component cells and four pattern cells revealed the predicted bimodal tunings. This result provided neurophysiological support for the validity of the model. We believe ours is the first systematic study that records the two types of bimodality in MT neurons.

Animals↗
PubMed1999

Expression of kininogen mRNAs and plasma kallikrein mRNA by cultured neurons, astrocytes and meningeal cells in the rat brain.

Expression of kininogen mRNAs has been studied in cultures of three different types of cells in rat brain, including neurons and astrocytes from cerebral cortex and meningeal cells from the leptomeninges/choroid plexus. T-kininogen mRNA was expressed by meningeal cells, but not by neurons and astrocytes, and the expression in meningeal cells was enhanced by culture with prostaglandin E2 (PGE2) or dibutyryl cAMP (Bt2cAMP). Low-molecular-weight kininogen mRNA was not detected in these cultures of cells, even after treatment with PGE2. Although expression of high-molecular-weight kininogen mRNA was very low in these cultures of cells, PGE2 or Bt2cAMP markedly stimulated its expression in cultures of meningeal cells and slightly in neurons, but not in astrocytes. We also found that expression of plasma kallikrein mRNA was strong in cultures of meningeal cells and slight in astrocytes, but absent in neurons. These results suggest that cells in the leptomeninges/choroid plexus are major sources of kininogens in rat brain which may function as precursor proteins for kinins and/or potent cysteine proteinase inhibitors during cerebral inflammation.

Animals↗
PubMed1999

Determination of antibodies to TT virus (TTV) and application to blood donors and patients with post-transfusion non-A to G hepatitis in Japan.

Recently, a nonenveloped single-stranded DNA virus named TT virus (TTV) has been reported in association with non-A to G post-transfusion as well as sporadic acute and chronic liver disease. A method was developed for the detection of antibody to TTV (anti-TTV) by means of immune precipitation and detection of TTV DNA by the polymerase chain reaction. The test serum was incubated with TTV, recovered from feces of a carrier, and after incubation, the formed immune complexes were precipitated with goat antiserum to human IgG. TTV DNA was sought for by the polymerase chain reaction in both precipitate and supernatant. The detection of TTV DNA in the precipitate, but not in the supernatant, was considered to represent anti-TTV in the test serum. Of the 44 healthy blood donors in Japan, anti-TTV was detected in one of the six (17%) with TTV DNA and 11 of the 38 (29%) without TTV DNA. In the two patients with post-transfusion non-A to G hepatitis, free anti-TTV developed as they cleared TTV in serum. Anti-TTV complexed with TTV in serum, detectable by precipitating sera with goat anti-human IgG and testing for TTV DNA, elicited while the patients had elevated alanine transaminase levels. The determination of anti-TTV would be useful for detecting resolved infection in surveys for exposure to TTV in the general population, and for establishing the mechanism of liver injury associated with TTV infection.

Adult↗
PubMed1999

Serological detection of hepatitis B virus genotypes by ELISA with monoclonal antibodies to type-specific epitopes in the preS2-region product.

An ELISA was developed for serological determination of the six genotypes of hepatitis B virus (HBV) designated A, B, C, D, E, and F. Monoclonal antibodies were raised against genotype-specific epitopes in the preS2-region product, and labeled with horseradish peroxidase. Hepatitis B surface antigen (HBsAg) in sera was captured by immobilized antibodies against the common determinant, and evaluated for reactivity with genotype-specific monoclonal antibodies labeled with the enzyme. Serological genotyping was in complete accord with genotypes determined by S-gene sequences in a panel of 68 sera containing HBV/HBsAg of different genotypes. Of 514 sera with HBsAg from Japan, 507 (98.6%) were genotyped serologically: genotype A was identified in 24 (4.7%); B in 196 (38.1%); C in 282 (54.9%); D in 2 (0.4%); and F in 3 (0.6%). There were no sera containing HBV of genotype E. Likewise, 425 of 446 (95.3%) sera with HBsAg from Brazil, China, India, Indonesia, Kenya, Korea, Nepal, Papua New Guinea, the Philippines, and Thailand were classified into A (25.6%), B (24.2%), C (33.9%), and D (11.7%) genotypes; there were no sera with HBsAg of genotype E or F among them. Some sera unclassifiable by ELISA revealed mixed infection with HBV of distinct genotypes, or contained HBsAg deprived of genotype-specific epitopes by point mutations. The ELISA would be useful for large-scale surveys, because it allows serological detection of HBV genotypes without sequencing nucleotides.

Amino Acid Sequence↗
PubMed1999

Infection with an unenveloped DNA virus (TTV) in patients with acute or chronic liver disease of unknown etiology and in those positive for hepatitis C virus RNA.

BACKGROUND/AIMS: An unenveloped single-stranded DNA virus (TTV) has been reported in association with elevated transaminase levels in patients with posttransfusion hepatitis and in those with acute or chronic liver disease of unknown etiology. To further evaluate the association of TTV with liver disease, TTV DNA was searched for in patients with acute or chronic liver disease of various etiologies. METHODS: TTV DNA was determined by polymerase chain reaction with hemi-nested primers in 64 patients with acute or chronic liver disease of unknown etiology and in 100 with acute or chronic liver disease positive for antibody to hepatitis C virus (HCV) as well as HCV RNA. RESULTS: TTV DNA was detected in two of the seven (29%) patients with acute hepatitis of unknown etiology, but in none of the four patients with acute HCV-associated hepatitis. It was detected in 27 of the 57 (47%) patients with chronic liver disease of unknown etiology at a frequency significantly higher (p<0.001) than that in 17 of the 96 (18%) patients with chronic HCV-associated liver disease. By contrast, RNA of hepatitis G virus was detected in none of the patients with acute hepatitis, and only in one of the 57 (2%) patients with chronic liver disease of unknown etiology as well as in six of the 96 (6%) patients with chronic HCV-associated liver disease. CONCLUSIONS: Based on the obtained results, TTV has a role in the development of acute and chronic liver disease of unknown etiology.

Acute Disease↗
PubMed1999

Compartmentalized expression of zebrafish ten-m3 and ten-m4, homologues of the Drosophila ten(m)/odd Oz gene, in the central nervous system.

Zebrafish ten-m3 and ten-m4 encode proteins highly similar to the product of Drosophila pair-rule gene ten(m)/odd Oz (odz). Their products contain eight epidermal growth factor (EGF)-like repeats that resemble mostly those of the extracellular matrix molecule tenascin. During segmentation period, ten-m3 is expressed in the somites, notochord, pharyngeal arches, and the brain, while expression of ten-m4 is mainly restricted to the brain. In the developing brain, ten-m3 and ten-m4 expression delineates several compartments. Interestingly, ten-m3 and ten-m4 show expression patterns complementary to each other in the developing forebrain and midbrain along both rostrocaudal and dorsoventral axes, depending on developmental stages and locations.

Amino Acid Sequence↗
PubMed1999

Effects of mono-ADP-ribosylation on cytoskeletal actin in chromaffin cells and their release of catecholamine.

To better understand the physiological role of mono-ADP-ribosylation in animals, we examined its role in chromaffin cells. Monoclonal antibodies against rat brain ADP-ribosylhydrolase were prepared, one of which (9E7) completely inhibited the enzyme's activity with ADP-ribosylated actin as the substrate. After actin monomers were polymerized by the addition of Mg2+, mono-ADP-ribosylation induced actin depolymerization. After mono-ADP-ribosylation, the actin monomers did not polymerize by the addition of Mg2+. Polymerized actin cosedimented with chromaffin granules but mono-ADP-ribosylated actin did not. After ADP-ribosylhydrolase on the membrane of chromaffin granules was incubated with 9E7, mono-ADP-ribosylated actin did not cosediment with chromaffin granules. When chromaffin cells permeabilized with saponin were incubated with NAD and 9E7, actin and rho protein was mono-ADP-ribosylated and stimulated catecholamine release from the cells. In histochemical experiments, catecholamine and actin filaments disappeared when the permeabilized chromaffin cells were treated with NAD and 9E7. These findings indicate that mono-ADP-ribosylation breaks the actin barrier in order to move granules during exocytosis, and ADP-ribosylactin hydrolase may keep the granules within the actin barrier.

Actins↗
PubMed1999

Ultraviolet radiation-induced suppression of natural killer cell activity is enhanced in xeroderma pigmentosum group A (XPA) model mice.

Xeroderma pigmentosum group A gene-deficient mice easily develop skin cancers by ultraviolet radiation. Natural killer cells play an important part in tumor surveillance. To study whether ultraviolet radiation-induced suppression of natural killer cell function is involved in the high incidence of skin tumors in patients with xeroderma pigmentosum, we analyzed the number and activity of natural killer cells in ultraviolet B-irradiated xeroderma pigmentosum A model mice. The number of natural killer cells in peripheral blood significantly decreased after ultraviolet B-irradiation only in xeroderma pigmentosum A mice, but those in the spleen were not affected. As compared with the wild-type mice, the xeroderma pigmentosum A mice displayed a higher level of spontaneous splenic natural killer cell activity (10%-15% vs 3%) and inducible natural killer activity (30%-50% vs 20%-25%) after injection of polyinosinic:polycytidylic acid. At 24 h after the last irradiation of three and five daily consecutive exposures to 500 mJ per cm2-ultraviolet B, however, the natural killer activity in xeroderma pigmentosum A mice decreased to 60 and 30% of the preirradiated level, respectively, but it did not in the wild-type mice. The depression of natural killer activity in xeroderma pigmentosum A mice recovered to a normal level at 10 and 15 d after the last irradiation, respectively. The high incidence of skin cancers in xeroderma pigmentosum patients may be mainly due to a defect in the repair of ultraviolet-damaged DNA of cutaneous cells, and possibly also due to an intensified ultraviolet-induced immunosuppression. Moreover, the present study suggests that the enhanced ultraviolet-induced impairment of natural killer function could be partially involved in cancer development.

Animals↗
PubMed1999

Evaluation of apoptotic cells induced by ultraviolet light B radiation in epidermal sheets stained by the TUNEL technique.

Two major components of epidermal cells, keratinocytes and Langerhans cells, are injured by ultraviolet light B radiation, resulting in sunburn cell (apoptotic cell) formation, impaired function, and a reduced number of Langerhans cells. Quantitative analysis of Langerhans cell damage is usually performed using epidermal sheets, whereas that of keratinocytes has been performed by counting the number of sunburn cells in vertical tissue sections. In this study we assessed the influences of ultraviolet light B radiation on epidermal cells by apoptotic cell formation, using murine epidermal sheets stained by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling technique. Ten to 75 mJ per cm2 of ultraviolet light B radiation induced apoptotic cells in abdominal skin of C3H mice. The cells were induced in 6 h after 50 mJ per cm2 of ultraviolet light B irradiation with the peak in number in 24 h, 18.8 +/- 5.0 per mm2 and 97.7 +/- 7.4 per mm2, respectively. One week later, the apoptotic cells were not visualized. As C3H/He, BALB/C, and C57BL/6 mice showed almost the same frequency of apoptosis in epidermal sheets from 50 mJ per cm2 ultraviolet light B-irradiated skin, the induction of the cells by ultraviolet light B radiation did not depend on the genetic trait of the mouse. Xeroderma pigmentosum type A gene-deficient mice, however, showed a greater induction of apoptotic cells (216.9 +/- 25.2 per mm2) by ultraviolet light B radiation than xeroderma pigmentosum type A wild-type mice (89.5 +/- 13.6 per mm2) and conventional mice. Pretreatment with a SPF 60 sunscreen agent was quite effective in reducing the induction of apoptotic cells. Using confocal laser scanning microscopy and double staining, 1.5 +/- 2.7% of apoptotic cells were Ia-positive cells in 24 h after 50 mJ per cm2 of ultraviolet light B radiation. Apoptotic Ia-positive cells were not observed 48 h after the radiation. On the other hand, no apoptotic dendritic epidermal T cells were observed in up to 75 mJ per cm2 of ultraviolet light B radiated skin. Thus, nearly all apoptotic cells were keratinocytes, and Langerhans cells and dendritic epidermal T cells appeared resistant to ultraviolet light B-induced apoptosis. Compared with the assessment in vertical tissue sections, the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling technique with epidermal sheets appeared to be a more physiologically relevant method for quantitative evaluation of apoptotic epidermal cells induced by ultraviolet light B radiation.

Animals↗
PubMed1999

Infection by an unenveloped DNA virus associated with non-A to -G hepatitis in Japanese blood donors with or without elevated ALT levels.

BACKGROUND: An unenveloped, single-stranded DNA virus named TT virus has been found in association with elevated alanine aminotransferase (ALT) levels in recipients of transfusions and has been detected frequently in patients with acute or chronic hepatitis of non-A to -G etiology in Japan. DNA of the TT virus was searched for in blood donors with or without elevated ALT levels. STUDY DESIGN AND METHODS: A total of 861 blood donors without previous transfusions and who were negative for markers of hepatitis B or C virus infection were tested. DNA of the TT virus was detected by polymerize chain reaction with hemi-nested primers. RESULTS: TT virus DNA was detected in 62 of 280 (22.1% [95% CI: 18.1-26.6]) donors with elevated ALT levels (mean +/- SD, 89.3 +/- 36.4 U/L; range, 61-301 U/L), which is significantly more frequently (p<0.02) than its detection in 91 of 581 (15.7% [95% CI: 13.2-18.4]) donors with normal ALT (< or = 45 U/L). The frequency of TT virus DNA increased with age, in donors with and without elevated ALT. CONCLUSION: The detection of TT virus DNA, at a frequency higher in donors with elevated ALT than in those without, strengthens the association of TT virus with non-A to -G hepatitis.

Adolescent↗
PubMed1999

Excretion into bile of a novel unenveloped DNA virus (TT virus) associated with acute and chronic non-A-G hepatitis.

Recently, an unenveloped, single-stranded DNA virus named TT virus (TTV) has been reported in association with hepatitis of non-A-G etiology. Five patients with TTV viremia, who received bile drainage or cholecystectomy, were tested for TTV DNA in bile by polymerase chain reaction with heminested primers. TTV DNA was detected in bile from all patients; titers were 10-100 times higher than in serum in 4 and at a comparable level in the remaining 1 patient. TTV DNA was detected in feces, also, in 1 of the 2 patients tested. The buoyant density of TTV in bile from 1 tested patient (1.33-1.35 g/cm3) was the same as that in feces (1.32-1.35 g/cm3). TTV may be secreted via bile into feces in a transmissible form and would spread by a fecal-oral route for deep and wide penetration into the general population.

Acute Disease↗