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Biomedical subjects

H Kadowaki

Publications and source records attributed to H Kadowaki.

At least 73 records · Page 4Linked to original sources
PubMed1992

Carcinogenicity study of gamma-oryzanol in F344 rats.

The carcinogenic potential of gamma-oryzanol, a drug mainly used for the treatment of hyperlipidaemia, was studied in F344 rats. Groups of 50 males and 50 females were fed a diet containing 0 (control), 200, 600 or 2000 mg gamma-oryzanol/kg body weight/day for 2 yr. Although females in the highest dose group (2000 mg/kg body weight) showed a slight decrease in body weight at 104 wk, there were no treatment-related changes in general condition, food consumption, mortality, organ weight or haematology. Histopathological examination showed various tumours in all groups, including the control group. In the control and 2000-mg/kg groups, high tumour incidences were observed in the testes, pituitary and thyroid of males, and in the pituitary, uterus and mammary gland of females; however, there was no significant increase in the incidence of any tumours between the control and the 2000-mg/kg groups. The findings indicate that under the experimental conditions described gamma-oryzanol was not carcinogenic in F344 rats.

Administration, Oral↗
PubMed1992

Mutations in the insulin receptor gene in patients with genetic syndromes of insulin resistance and acanthosis nigricans.

Mutations of the insulin receptor gene have been identified in patients with genetic syndromes of insulin resistance associated with acanthosis nigricans. These mutations impair insulin responses by reducing the number of insulin receptors on the surface of target cells, or by reducing the receptor's ability to bind insulin or to undergo insulin-stimulated autophosphorylation, an important step in insulin action. Studies of mutant receptors expressed in transfection systems have contributed to our understanding of the structure-function relationships of the insulin receptor.

Acanthosis Nigricans↗
PubMed1992

The role of the seminal vesicles and coagulating glands in fertilization in the rat.

To investigate the role of the seminal vesicles (SV) and coagulating glands (CG) in fertilization in the rat, partial resections of the SV (25%--group B), 50%--group C, and 75%--group D) or bilateral resection of the SV alone (100%--group E), or together with the CG (group F) were undertaken. In other groups, bilateral resection of the CG only (group G), or bilateral resection of the CG with ipsilateral SV resection (group H) were performed. A group of sham-operated rats served as controls (group A). There were no significant differences among groups A, B, C and D in the number of fertile rats post-operatively but significant differences were evident in groups E, F, G, H when compared with the control group (P less than 0.01 for all groups). Only the fertile rats were able to form copulatory plugs (CP) post-operatively. Bilateral ligation of the SV ducts was performed in ten fertile rats. Post-operatively, the proportion of fertile rats was decreased significantly (P less than 0.01). Removal of the ligatures resulted in a significant increase (P less than 0.01) in fertility. It was also demonstrated that the addition of rat seminal vesicular secretions (SVS) to epididymal sperm suspensions resulted in a significant decrease (P less than 0.001) in sperm motility. These results suggest that the SV and CG are necessary for fertility in rats, and that one role of SVS is the formation of a CP and not the maintenance of sperm motility.

Animals↗
PubMed1992

Surgical repair versus medical treatment of varicocele in the rat: pharmacological manipulation of the varicocelized testicle.

Human chorionic gonadotropin, kallikrein, indomethacin, and hydralazine were administered to different groups of varicocelized rats, while surgical repair of the varicocele was performed in another group of rats. The effects of conservative and surgical treatment on epididymal sperm content and motility, the weights of the testes, epididymis, and male accessory genital glands, and fertility were compared between each group and a sham-treated group of rats. Surgical repair significantly improved all the evaluated parameters and all the conservative regimens, except hydralazine, resulted in a significant improvement in most parameters. Our results indicate that stimulation of the Leydig or/and Sertoli cells of a varicocelized testicle can counteract some of the detrimental consequences of the varicocele itself.

Animals↗
PubMed1992

Structure of the human glucokinase gene and identification of a missense mutation in a Japanese patient with early-onset non-insulin-dependent diabetes mellitus.

Glucokinase is thought to play a glucose-sensor role in the pancreas, and abnormalities in its structure, function, and regulation can induce diabetes. We isolated the human glucokinase gene, and determined its genomic structure including exon-intron boundaries. Structure of the glucokinase gene in human was very similar to that in rat. Then, by screening Japanese diabetic patients using polymerase chain reaction--single strand conformation polymorphism (PCR-SSCP) and direct-sequencing strategies, we identified a missense mutation substituting arginine (AGG) for glycine (GGG) at position 261 in exon 7 of the glucokinase gene in a patient with early-onset non-insulin-dependent diabetes (NIDDM).

Base Sequence↗
PubMed1992

Metabolism of high density lipoprotein lipids by the rat liver: evidence for participation of hepatic lipase in the uptake of cholesteryl ester.

In order to determine the role of hepatic lipase in the hepatic uptake and metabolism of high density lipoprotein (HDL) triglycerides, cholesteryl esters, and phospholipids, isolated rat livers were perfused with a reconstituted HDL (rHDL) radiolabeled with [3H]triolein and [14C]cholesteryl oleate or palmitoyl-[14C]linoleoyl phosphatidylcholine. A bolus of radiolabeled rHDL was injected into the portal vein and livers were perfused for 5 min using a nonrecirculating perfusion system. Recovery of rHDL triolein in the liver as intact triolein was used to determine the amount of unmetabolized rHDL remaining in the liver. After correcting for the amount of unmetabolized rHDL remaining in the liver, about 30% of the rHDL triolein was hydrolyzed of which 19% was recovered in the liver and 11% in the perfusate. Moreover, about 7% of the rHDL phosphatidylcholine was hydrolyzed to lysophosphatidylcholine, all of which was recovered in the perfusate. Although there was no hydrolysis of rHDL cholesteryl oleate, about 30% of the cholesteryl oleate was taken up by the liver. Preperfusion of the liver with heparin to deplete the liver of hepatic lipase resulted in about a 70% reduction in rHDL triolein hydrolysis and about a 75% reduction in rHDL cholesteryl oleate uptake. Although hepatic lipase hydrolyzes both triglycerides and phosphatidylcholines, elimination of the triolein from rHDL had no effect on the uptake of rHDL cholesteryl oleate, but replacement of the rHDL phosphatidylcholine with a nonhydrolyzable phosphatidylcholine diether resulted in an 87% reduction in cholesteryl oleate uptake. These results indicate that hepatic lipase is necessary for the hepatic uptake of both HDL triglycerides and cholesteryl esters and that the uptake of cholesteryl esters is not dependent on the hydrolysis of HDL triglycerides but is dependent on the hydrolysis of HDL phospholipids.

Animals↗
PubMed1991

Substitution of arginine for histidine at position 209 in the alpha-subunit of the human insulin receptor. A mutation that impairs receptor dimerization and transport of receptors to the cell surface.

Receptors for insulin and epidermal growth factor contain cysteine-rich domains in the extracellular portion of the molecule. His209 (insulin receptor numbering system) is 1 of 2 amino acid residues that are identically conserved in the cysteine-rich domains of insulin receptors, epidermal growth factor receptors, and other homologous receptors. Previously, we have identified a patient with leprechaunism who is homozygous for a mutation substituting Arg for His209 in the insulin receptor gene (Kadowaki, T., Kadowaki, H., Rechler, M. M., Serrano-Rios, M., Roth, J., Gorden, P., and Taylor, S. I. (1990) J. Clin. Invest. 86, 254-264). In this investigation, the Arg209 mutant receptor was expressed by transfection of mutant cDNA into NIH-3T3 cells. The mutation impairs several steps in the post-translational processing of the insulin receptor:dimerization of 190-kDa proreceptors into a disulfide linked species, proteolytic cleavage of the proreceptor into alpha- and beta-subunits, and terminal processing of the high mannose form of N-linked oligosaccharide into complex carbohydrate. In addition, the defects in post-translational processing within the endoplasmic reticulum and Golgi apparatus are associated with a marked inhibition in transport of receptors to the plasma membrane. Nevertheless, a small number (approximately 10%) of the receptors are transported to the cell surface. These receptors on the cell surface bind insulin with normal affinity and have normal tyrosine kinase activity.

3T3 Cells↗
PubMed1991

Unusual forms of insulin resistance.

Insulin resistance is an important feature in the pathogenesis of non-insulin-dependent diabetes mellitus. Some rare patients have syndromes associated with a severe form of insulin resistance, usually involving acanthosis nigricans and, in premenopausal females, hyperandrogenism. This review discusses two of the causes of insulin resistance: mutations in the insulin receptor gene and autoantibodies directed against the insulin receptor.

Acanthosis Nigricans↗
PubMed1991

Two patients with insulin resistance due to decreased levels of insulin-receptor mRNA.

Mutations have been identified in the insulin-receptor gene in insulin-resistant patients. We studied two patients with acanthosis nigricans and insulin resistance caused by a decrease in the number of cell surface insulin receptors. Patient 1 was an 11-yr-old boy with a fasting insulin level of 2130 pM; patient 2 was a 14-yr-old girl with hyperandrogenism and a fasting insulin level of 580-740 pM. Based on Southern-blotting studies, the structure of both alleles of the insulin-receptor gene in both patients appeared to be grossly normal. There was no evidence of insertions, deletions, or major rearrangements. Moreover, the nucleotide sequences of all 22 exons of the gene were normal in both patients. Thus, the predicted amino acid sequences of both patients' insulin receptors were normal. In Epstein-Barr virus-transformed lymphoblasts from patient 1, insulin-receptor mRNA levels were so low they could not be detected with an RNase A protection assay, whereas mRNA levels from patient 2 were in the lower half of the normal range. By use of a more sensitive assay based on the polymerase chain reaction, insulin-receptor mRNA could be detected in Epstein-Barr virus-transformed lymphoblasts from both patients. Moreover, because of the existence of silent polymorphisms in the nucleotide sequences, it was possible to differentiate the two alleles of the insulin-receptor gene in both patients. In patient 2, the two alleles were expressed asymmetrically, with 90% of the mRNA molecules having been transcribed from one allele but only 10% transcribed from the second allele. This suggests that there is an unidentified mutation in the underexpressed allele that acts in a cis-dominant fashion to decrease insulin-receptor mRNA levels. However, in patient 1, both alleles were expressed symmetrically in similarly low levels. Although not proven, it seems likely that the mutations that decrease insulin-receptor mRNA levels in patient 1 also map to the insulin-receptor locus.

Adolescent↗
PubMed1990

Mutagenesis of lysine 460 in the human insulin receptor. Effects upon receptor recycling and cooperative interactions among binding sites.

Mutations in the insulin receptor gene can cause insulin resistance. Previously, we have identified a mutation substituting glutamic acid for lysine at position 460 in the alpha-subunit of the insulin receptor in a patient with a genetic form of insulin resistance. In the present work, we have investigated the effect upon receptor function of amino acid substitutions at position 460. Decreasing the pH from 8.0 to 5.5 caused a progressive acceleration of the dissociation of 125I-insulin from the wild-type insulin receptor. Substitution of acidic amino acids (Glu or Asp) for Lys460 decreased the ability of acid pH to accelerate dissociation of 125I-insulin. In contrast, substitution of Arg or neutral amino acids (Val, Met, Thr, or Gln) had no effect upon the sensitivity to acid pH. Correlated with decreased sensitivity to acid pH, substitution of Glu or Asp at position 460 retarded the dissociation of 125I-insulin from intracellular receptors subsequent to receptor-mediated endocytosis. Furthermore, retardation of dissociation of 125I-insulin from the internalized receptor was associated with a decreased half-life of the receptor. In summary, the Glu460 mutation appears to cause insulin resistance by accelerating receptor degradation and, thereby, decreasing the number of insulin receptors on the cell surface. Additional studies suggested that Lys460 may provide the amino groups whereby disuccinimidyl suberate cross-links the two alpha-subunits to each other. Consistent with the hypothesis that Lys460 is located at the interface between adjacent alpha-subunits, substitutions at position 460 impair cooperative interactions among insulin binding sites. The Glu460 mutation decreases positively cooperative binding interactions; the Arg460 mutation impairs negative cooperativity. Mutations at position 460 in the alpha-subunit did not decrease the ability of insulin to stimulate receptor tyrosine kinase.

Amino Acid Sequence↗
PubMed1990

Substitution of lysine for asparagine at position 15 in the alpha-subunit of the human insulin receptor. A mutation that impairs transport of receptors to the cell surface and decreases the affinity of insulin binding.

Mutations in the insulin receptor gene can compromise the ability of the receptor to mediate insulin action. Previously, in investigations of a patient with a genetic form of insulin resistance, we have identified a mutant allele encoding an insulin receptor in which lysine is substituted for asparagine at position 15 of the alpha-subunit. In the present study, we have characterized the Lys15-mutant receptor expressed by transfection of mutant cDNA into NIH-3T3 cells. The Lys15-mutation causes at least two defects in insulin receptor function. First, the mutation retards the post-translational processing of the receptor and impairs transport of the receptor to the plasma membrane, thereby reducing the number of receptors on the cell surface. Second, the mutation causes a 5-fold reduction in the affinity of the receptor to bind insulin. These two defects combine to render the target cell resistant to normal physiological concentrations of insulin. It seems likely that both functional defects associated with the Lys15-mutation can be explained by assuming that the mutation distorts the three-dimensional structure of the receptor. Presumably, the abnormal conformation interferes with the transport of the receptor through the endoplasmic reticulum and Golgi, and also inhibits the binding of insulin to its binding site on the receptor.

Animals↗
PubMed1990

A nonsense mutation causing decreased levels of insulin receptor mRNA: detection by a simplified technique for direct sequencing of genomic DNA amplified by the polymerase chain reaction.

Mutations in the insulin receptor gene can render the cell resistant to the biological action of insulin. We have studied a patient with leprechaunism (leprechaun/Minn-1), a genetic syndrome associated with intrauterine growth retardation and extreme insulin resistance. Genomic DNA from the patient was amplified by the polymerase chain reaction catalyzed by Thermus aquaticus (Taq) DNA polymerase, and the amplified DNA was directly sequenced. A nonsense mutation was identified at codon 897 in exon 14 in the paternal allele of the patient's insulin receptor gene. Levels of insulin receptor mRNA are decreased to less than 10% of normal in Epstein-Barr virus-transformed lymphoblasts and cultured skin fibroblasts from this patient. Thus, this nonsense mutation appears to cause a decrease in the levels of insulin receptor mRNA. In addition, we have obtained indirect evidence that the patient's maternal allele of the insulin receptor gene contains a cis-acting dominant mutation that also decreases the level of mRNA, but by a different mechanism. The nucleotide sequence of the entire protein-coding domain and the sequences of the intron-exon boundaries for all 22 exons of the maternal allele were normal. Presumably, the mutation in the maternal allele maps elsewhere in the insulin receptor gene. Thus, we conclude that the patient is a compound heterozygote for two cis-acting dominant mutations in the insulin receptor gene: (i) a nonsense mutation in the paternal allele that reduces the level of insulin receptor mRNA and (ii) an as yet unidentified mutation in the maternal allele that either decreases the rate of transcription or decreases the stability of the mRNA.

Alleles↗
PubMed1990

Effect of differentiation and cell density on glycosphingolipid class and molecular species composition of mouse neuroblastoma NB2a cells.

The effects of cell density and retinoic acid-induced differentiation on the class and molecular species composition of mouse neuroblastoma NB2a cell glycosphingolipids were examined under conditions where the period of culture was controlled. The total amount of neutral glycosphingolipids per cell decreased both with differentiation and as the cells became confluent. The relative amount of the neutral glycosphingolipid classes was not affected by differentiation, whereas there were small but significant changes in the relative amount of the neutral glycosphingolipid classes as the cells became confluent. The total amount of the gangliosides was unaffected by either differentiation or cell density, but there were significant changes in the ganglioside class composition as a result of both cell density and differentiation, and the effects were additive. The molecular species of all the major neutral glycosphingolipid and ganglioside classes were essentially identical, and were altered only slightly by either differentiation or cell density.

Animals↗