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Biomedical subjects

A Krook

Publications and source records attributed to A Krook.

At least 55 records · Page 3Linked to original sources
PubMed1996

Two naturally occurring mutant insulin receptors phosphorylate insulin receptor substrate-1 (IRS-1) but fail to mediate the biological effects of insulin. Evidence that IRS-1 phosphorylation is not sufficient for normal insulin action.

Two naturally occurring mutant insulin receptors, Arg-1174 --> Gln and Leu-1178 --> Pro, found in patients with dominantly inherited Type A insulin resistance, showed unusual signaling properties when stably expressed in Chinese hamster ovary (CHO) cells. Both mutant receptors were expressed on the cell surface and bound insulin normally, but showed markedly impaired autophosphorylation in response to insulin. In addition, the in vitro tyrosine kinase activity of both mutant receptors toward an artificial substrate was also severely impaired. Despite these defects of kinase activity, anti-phosphotyrosine immunoblotting of whole cell lysates and anti-phosphotyrosine immunoprecipitation of 32P-labeled cells showed insulin-stimulated tyrosine phosphorylation of a protein of approximately 185 kDa to an extent comparable to that seen in CHO cells expressing wild-type human insulin receptors. Anti-insulin receptor substrate-1 (IRS-1) immunoprecipitation followed by anti-phosphotyrosine immunoblotting confirmed that this tyrosine-phosphorylated protein was IRS-1. In contrast, CHO cells expressing an insulin receptor mutated at the ATP binding site (Lys-1030 --> Arg) showed no insulin-stimulated autophosphorylation or phosphorylation of IRS-1. Despite exhibiting apparently normal insulin stimulation of IRS-1 tyrosine-phosphorylation, cells expressing the Arg-1174 --> Gln or Pro-1178 --> Leu receptors showed marked impairment in insulin stimulation of glycogen synthesis, thymidine incorporation, and activation of MAP kinase. The inability of these mutant receptors to signal normally to metabolic and mitogenic responses suggests that insulin-stimulated tyrosine phosphorylation of IRS-1 alone is insufficient to fully mediate insulin action.

Adolescent↗
PubMed1996

Mutant insulin receptors in syndromes of insulin resistance.

To date, mutations of the insulin receptor remain the only well-established causes of severe insulin resistance. There is a broad correlation between the extent of impairment of signal transduction seen when the mutant receptors are expressed in vitro with the severity of the clinical phenotype. Thus leprechaunism, Rabson-Mendenhall syndrome and Type A insulin resistance appear to represent points on a continuum of severity of receptor dysfunction, rather than completely distinct syndromes. In other syndromes of insulin resistance, insulin receptor abnormalities remain the exception. However, functional studies of expressed naturally occurring insulin receptor mutations have acted as experiments of nature and greatly aided attempts to dissect the structure-function relationships of the receptor. The next few years will no doubt begin to reveal the contributions made by defects in the post-receptor signalling cascade to the syndromes of insulin resistance in man.

Humans↗
PubMed1996

Molecular scanning of the insulin receptor gene in women with polycystic ovarian syndrome.

Polycystic ovary syndrome (PCOS) is a common disorder characterized by chronic anovulation and infertility, hyperandrogenaemia, and frequently insulin resistance. This study investigated whether mutations in the insulin receptor gene could explain the insulin resistance in subjects with PCOS. From a total of 108 women with PCOS, a subgroup of 24 were selected on the criteria of being in the upper quartile for insulin resistance as assessed by fasting serum insulin, insulin area under the curve following 75 g oral glucose tolerance test, and endogenous glucose disposal as a measure of insulin sensitivity. An additional five normal women were also investigated. The entire coding region of the insulin receptor gene, comprising of 22 exons, was amplified by the PCR using genomic DNA and then subjected to single-stranded conformation polymorphism (SSCP) analysis to screen for single-base DNA sequence changes. DNA sequencing revealed that SSCP variants were detected in regions encompassing exons 3, 6-8, 11, 13, 15, 17, and 22. SSCP variants in regions of exons 3, 6, 7, 11, 15 and 22 were caused by nucleotide substitutions within intronic regions flanking the exon. The considerable variation seen in the 5' intron of exon 3 was found to be caused by variation in the number of (ATTT, 8-11) and (TC, 10-13) short sequence repeats. SSCP variants in exons 8 (Asp519, Ala523), 13 (Asn 838), and 17 (Tyr984, His1058) were caused by known silent polymorphisms. Southern blotting experiments excluded major gene deletions, insertions, or rearrangements. We conclude that insulin resistance in subjects with PCOS is not commonly a consequence of missense or nonsense mutations in the insulin receptor gene.

Blotting, Southern↗
PubMed1995

Prenatal analysis of the insulin receptor gene in a family with leprechaunism.

We report on the prenatal diagnosis of a fetus at risk of leprechaunism. We had previously determined the nature of the causative mutation in the insulin receptor gene in this family. The mutation removes a restriction site for the enzyme Mbo II. Genomic DNA was extracted from a chorionic villus sample and the 3' half of exon 2 was amplified by the polymerase chain reaction (PCR) followed by restriction digest. Using this method, we correctly predicted an unaffected child.

Chorionic Villi↗
PubMed1995

Lack of serotype-specific antibody response to lipopolysaccharide antigens of Moraxella catarrhalis during lower respiratory tract infection.

An enzyme immunoassay (EIA) was used to determine the antibody response to different serotypes of lipopolysaccharide (LPS) antigens of Moraxella catarrhalis in adult patients with lower respiratory tract infections (LRTI). Moraxella catarrhalis was isolated from sputum or nasopharyngeal samples from 20 patients with LRTI. Sixteen of the isolates were serotype A, four were type B and none were type C. The antibody response to the different LPS serotypes was determined in paired sera from patients suffering from LRTI. In addition to the 20 patients with Moraxella catarrhalis isolated (Group 1), a group of seven patients with LRTI of unknown etiology (Group 2) and a group of ten patients with LRTI of known other bacterial etiology (Group 3) were selected for this study. An increase in antibody levels of > 1.5-fold (convalescent-/acute-phase serum) was recorded in approximately half of the patients, not only in the first group (Moraxella catarrhalis isolated) but also in the other two groups. However, in the first and second groups there was a correlation between an increase in antibody levels in the LPS EIA and in an EIA using whole bacterial cells as antigen. In the group of patients in whom Moraxella catarrhalis was isolated, the antibody response to LPS antigens was not serotype specific. The antibody response to type-A and type-B LPS was more predominant than the response to type-C LPS in most patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Somatic care wanted by HIV-infected intravenous drug abusers: the patients' opinions and experiences.

The somatic care of HIV-infected intravenous drug abusers (IVDUs) is often combined with many problems. The addict is often an unpopular patient, but society must assume responsibility for him or her and it is important to solve care problems in an appropriate way. This study was undertaken in order to investigate what kind of care addicts want when they become somatically ill. A questionnaire was given to patients who acquired HIV infection due to intravenous drug abuse, who visited an outpatient clinic for HIV-infected patients at the Department of Infectious Disease, Huddinge Hospital, Stockholm, Sweden. A total of 72 of the original 78 questionnaires could be evaluated. Thirty respondents took part in the Stockholm Methadone Programme. The patients were asked to rank the importance of professional competence among the staff. The patients ranked competence in pain treatment highest followed by competence in somatic medical care. Lower ranked, but still perceived as important, was competence in psychiatric medical care and social welfare work. Experience in treatment of addiction was ranked as less important. It can be concluded that it is fruitful to ask IVDUs about their preferences concerning care.

AIDS-Related Opportunistic Infections↗
PubMed1995

HTLV infections among Swedish intravenous drug users in 1992.

Serum samples collected in 1992 from 1158 intravenous drug users (IVDUs) in Stockholm, Sweden, were tested retrospectively for antibodies to human T-lymphotropic virus type I and II (HTLV-I and II). The overall prevalence rate of HTLV infections was 2.4% (28/1158). A majority of the HTLV infections were caused by HTLV-II (27/28). A significant association between HTLV-II and HIV-1 seropositivity was found, the prevalence of HTLV-II infection being 11.4% (11/96) in HIV-seropositive individuals compared with 1.5% (16/1062) in HIV-seronegative persons (p < 0.001). All the HTLV-infected individuals were of Scandinavian origin. No significant differences in age and sex distribution were observed in HTLV-infected persons compared to seronegative individuals. This study confirms that HTLV-II infection is present in the Swedish IVDU population and the findings provide baseline information for future epidemiological studies.

Adolescent↗
PubMed1994

Molecular scanning of the insulin receptor gene in syndromes of insulin resistance.

Using the molecular scanning technique of single-stranded conformational polymorphism (SSCP), we have examined the exons encoding the insulin receptor gene in 26 patients with syndromes of insulin resistance. We found 27 variant sequences, 4 of which were mutations that altered an amino acid. One patient with the Rabson-Mendenhall syndrome was homozygous for a mutation in the extracellular alpha-subunit (Ser to Leu323), one type A insulin-resistant patient was heterozygous for Pro to Leu1178, and another type A insulin-resistant patient was heterozygous for a mutation in the COOH-terminus of the receptor (Arg to Gln1351). The previously reported, and probably functionally insignificant, variant Val to Met985 was detected in one patient. No missense or nonsense insulin receptor mutations were found in any patients whose insulin resistance was associated with gross obesity, lipoatrophy, or acromegaloid features. No missense or nonsense mutations were found in subjects with polycystic ovary syndrome or Syndrome X. Putting these findings in the context of other work in this field, we conclude that subjects with leprechaunism or Rabson-Mendenhall syndrome have a high probability of having a missense or nonsense insulin receptor mutation. Nonobese, nondysmorphic, severely insulin-resistant females with hirsutism, acanthosis nigricans, and menstrual disturbance (type A phenotype) have an intermediate probability of having this type of insulin receptor mutation. Although insulin receptor mutations have been occasionally described in other phenotypes of insulin resistance, the frequency of point mutations in the exons of the insulin receptor gene in patients with those phenotypes appears to be low.

Adolescent↗
PubMed1994

HTLV-II among injecting drug users in Stockholm.

134 injecting drug users (IDUs) treated at the Department of Infectious Diseases of Roslagstull Hospital, Stockholm, were tested for antibodies to human T-lymphotropic virus, types I and II, by means of 2 HTLV-I/-II peptide-based enzyme immunoassays (EIAs), followed by a whole-virus EIA. Positive EIA reactions were checked and typed by electrophoretic immunoblotting with native HTLV-I and recombinant HTLV-I and -II proteins. 10 IDUs were diagnosed as HTLV-II seropositive. All 10 were of Scandinavian descent. Thus, like HIV-1, HTLV-II infection has entered the injecting drug user population in Stockholm.

Adult↗
PubMed1994

Significance of isolation of Moraxella catarrhalis in routine cultures from the respiratory tract in adults: antibody response studied in a whole cell EIA.

The significance of the isolation of Moraxella catarrhalis from sputum or nasopharynx was studied in patients treated at an infectious disease clinic. A whole-cell enzyme immunoassay was used to detect a specific antibody response to M. catarrhalis during infection. In all, 27 patients with respiratory tract infections and 4 with other infections were studied. Titre rises were recorded in 11/23 patients with lower respiratory tract infections, whereas patients with common cold or infections elsewhere all had negative serology. In patients with acute bronchitis, 7/10 patients responded with a significant titre rise. Patients with a low titre in their acute serum sample were those who responded with a titre increase during infection. The findings indicate that isolation of M. catarrhalis from sputa and nasopharyngeal samples in adults is of value for the etiological diagnosis of acute bronchitis and other lower respiratory tract infections, and is therefore important for the choice of drug for treatment, as many isolates are resistant to beta-lactam antibiotics.

Adolescent↗
PubMed1993

Homozygous nonsense mutation in the insulin receptor gene in infant with leprechaunism.

Mutations in the insulin receptor gene have been detected in patients with severe insulin resistance, but the absence of insulin receptors has not been recorded. We report a severely insulin resistant newborn baby, the offspring of consainguineous parents, who was homozygous for a nonsense mutation (Lys 121-Amber) in this gene. Translation of this very truncated N-terminal fragment would not be expected to result in a functional insulin receptor. The infant had all the typical features of the syndrome of leprechaunism. The baby probably represents the null phenotype with respect to the insulin receptor. Because insulin receptors are expressed very early in the developing embryo, the absence of functional insulin receptors is thought to be incompatible with fetal viability: the normal organogenesis in this infant who survived beyond term implies that this assumption is probably incorrect.

Base Sequence↗
PubMed1993

Serological cross-reactions between Moraxella (Branhamella) catarrhalis and other oropharyngeal bacteria.

Oropharyngeal bacteria belonging to different species were tested for serological cross-reactions with Moraxella catarrhalis using sera from immunized rabbits. Sera were tested using immunofluorescence, an enzyme immunoassay (EIA) and immunoblotting. On immunofluorescence, significant cross-reactions were demonstrated with beta-hemolytic streptococci group A and group G, as well as with streptococci of the viridans group. Some cross-reactions were also noted with Neisseria meningitidis. In the EIA, strong cross-reactions were demonstrated with beta-hemolytic streptococci. No cross-reactions were obtained with Streptococcus pneumoniae, Haemophilus influenzae or common oral Neisseria. The results are of importance for the interpretation of serological tests to detect infections with Moraxella catarrhalis, and for the development of methods for detection of antigens in samples from the respiratory tract.

Animals↗
PubMed1993

p21ras and protein kinase C function in distinct and interdependent signaling pathways in C3H 10T1/2 fibroblasts.

Both p21ras and protein kinase C (PKC) are believed to function downstream of plasma membrane-associated tyrosine kinases in cellular signal transduction pathways. However, it has remained controversial whether they function in the same pathway and, if so, what their relative position and functional relationship in such a pathway are. We investigated the possibilities that p21ras and PKC function either upstream or downstream of each other in a common linear pathway or that they function independently in colinear signal pathways. Either decreased expression of endogenous normal ras in fibroblasts transfected with an inducible antisense ras construct or overexpression of a mutant ras gene reduced the capacity of the phorbol ester tetradecanoyl phorbol acetate to trigger expression of the tetradecanoyl phorbol acetate-responsive and ras-dependent reporter gene osteopontin (OPN). PKC depletion decreased basal OPN mRNA levels, and the overexpression of ras restored OPN expression to the level of non-PKC-depleted cells. We propose a model in which ras and PKC function in distinct and interdependent signaling pathways.

Animals↗