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Biomedical subjects

A Krook

Publications and source records attributed to A Krook.

At least 37 records · Page 2Linked to original sources
PubMed1999

Comparative evaluation of 14 immunoassays for detection of antibodies to the human T-lymphotropic virus types I and II using panels of sera from Sweden and West Africa.

BACKGROUND: A new generation of assays for the detection of human T-lymphotropic virus types I and II (HTLV-I/II) antibodies has been released. These assays incorporate HTLV-I- and HTLV-II-specific antigens, and some are based on new assay principles. Comparative evaluation data that include these new as well as previous assays are limited. STUDY DESIGN AND METHODS: Fourteen HTLV antibody assays were evaluated by using well-characterized panels of sera from Guinea-Bissau, West Africa, and Sweden. The sera included 127 HTLV-I-positive and 62 HTLV-II-positive specimens, as well as 919 consecutive negative samples. RESULTS: The sensitivity for HTLV-I was 100 percent for all assays, except one, which repeatedly missed one sample. The sensitivity for HTLV-II varied between 86 percent and 100 percent. In general, new-generation assays incorporating HTLV-II-specific antigens, and some of which are based on new assay principles, had a higher sensitivity for HTLV-II than previous assays, which mainly are based on HTLV-I antigens. The specificity was generally higher for new assays than for the previous versions. Testing of Swedish blood donor sera gave higher specificities (94-100%) than did that of African specimens (90-99.7%). Most assays had low delta values (DVs), although there was a tendency toward increased DVs for the new generation of assays. Only two of the new generation of assays came close to a combination of high sensitivity for both HTLV-I and HTLV-II, high specificity, positive and negative predictive values, and high DVs. CONCLUSION: The sensitivity for HTLV-I was generally high and appears to have improved for HTLV-II with the introduction of a new generation of assays incorporating HTLV-II-specific antigens. However, some assays still give false-negative results on HTLV-II-positive specimens. The specificities and the DVs were generally higher for the new assays than for the previous versions.

Africa, Western↗
PubMed1999

Muscle fiber type specificity in insulin signal transduction.

We determined the muscle fiber type-specific response of intracellular signaling proteins to insulin. Epitrochlearis (Epi; 15% type I, 20% type IIa, and 65% type IIb), soleus (84, 16, and 0%), and extensor digitorum longus (EDL; 3, 57, and 40%) muscles from Wistar rats were incubated without or with 120 nM insulin (3-40 min). Peak insulin receptor (IR) tyrosine phosphorylation was reached after 6 (soleus) and 20 (Epi and EDL) min, with sustained activity throughout insulin exposure (40 min). Insulin increased insulin receptor substrate (IRS)-1 and IRS-2 tyrosine phosphorylation and phosphotyrosine-associated phosphatidylinositol (PI)-3-kinase activity to a maximal level after 3-10 min, with subsequent downregulation. Akt kinase phosphorylation peaked at 20 min, with sustained activity throughout insulin exposure. Importantly, the greatest insulin response for all signaling intermediates was observed in soleus, whereas the insulin response between EDL and Epi was similar. Protein expression of the p85alpha-subunit of PI 3-kinase and Akt kinase, but not IR, IRS-1, or IRS-2, was greater in oxidative versus glycolytic muscle. In conclusion, increased function and/or expression of key proteins in the insulin-signaling cascade contribute to fiber type-specific differences in insulin action in skeletal muscle.

Animals↗
PubMed1999

Muscle fiber type-specific defects in insulin signal transduction to glucose transport in diabetic GK rats.

To determine whether defects in the insulin signal transduction pathway to glucose transport occur in a muscle fiber type-specific manner, post-receptor insulin-signaling events were assessed in oxidative (soleus) and glycolytic (extensor digitorum longus [EDL]) skeletal muscle from Wistar or diabetic GK rats. In soleus muscle from GK rats, maximal insulin-stimulated (120 nmol/l) glucose transport was significantly decreased, compared with that of Wistar rats. In EDL muscle from GK rats, maximal insulin-stimulated glucose transport was normal, while the submaximal response was reduced compared with that of Wistar rats. We next treated diabetic GK rats with phlorizin for 4 weeks to determine whether restoration of glycemia would lead to improved insulin signal transduction. Phlorizin treatment of GK rats resulted in full restoration of insulin-stimulated glucose transport in soleus and EDL muscle. In soleus muscle from GK rats, submaximal and maximal insulin-stimulated insulin receptor substrate (IRS)-1 tyrosine phosphorylation and IRS-1-associated phosphatidylinositol (PI) 3-kinase activity were markedly reduced, compared with that of Wistar rats, but only submaximal insulin-stimulated PI 3-kinase was restored after phlorizin treatment. In EDL muscle, insulin-stimulated IRS-1 tyrosine phosphorylation and IRS-1-associated PI-3 kinase were not altered between GK and Wistar rats. Maximal insulin-stimulated Akt (protein kinase B) kinase activity is decreased in soleus muscle from GK rats and restored upon normalization of glycemia (Krook et al., Diabetes 46:2100-2114, 1997). Here, we show that in EDL muscle from GK rats, maximal insulin-stimulated Akt kinase activity is also impaired and restored to Wistar rat levels after phlorizin treatment. In conclusion, functional defects in IRS-1 and PI 3-kinase in skeletal muscle from diabetic GK rats are fiber-type-specific, with alterations observed in oxidative, but not glycolytic, muscle. Furthermore, regardless of muscle fiber type, downstream steps to PI 3-kinase (i.e., Akt and glucose transport) are sensitive to changes in the level of glycemia.

3-O-Methylglucose↗
PubMed1998

Screening for human T cell leukaemia/lymphoma virus among blood donors in Sweden: cost effectiveness analysis.

OBJECTIVE: To analyse the cost effectiveness of a national programme to screen blood donors for infection with the human T cell leukaemia/lymphoma virus. DESIGN: Three models for calculating the costs and benefits of screening were developed. The first model analysed the cost of continuously testing all donations; the second analysed the cost of initially testing new blood donors and then retesting them after five years; the third analysed the cost of testing donors only at the time of their first donation. Patients who had received blood components from donors confirmed to be infected with the virus were offered testing. SETTING: Sweden. MAIN OUTCOME MEASURES: Prevalence of infection with the virus among blood donors, the risk of transmission of the virus, screening costs, and the outcome of infection. RESULTS: 648 497 donations were tested for the virus; 1625 samples tested positive by enzyme linked immunosorbent assay. 6 were confirmed positive by western blotting. The prevalence of infection with the virus was 2/100 000 donors. 35 patients who had received blood infected with the virus were tested; 3 were positive. The cost of testing every donation was calculated to be $3.02m (1.88m pounds); this is 18 times higher than the cost of testing new donors only, and only 1 additional positive donor would be discovered in 7 years. Regardless of the model used, screening was estimated to prevent only 1 death every 200 years at a minimum cost of $36m (22.5m pounds). CONCLUSION: Based on these estimates the Swedish National Board of Health and Welfare decided that only new blood donors would be screened for infection with the virus.

Adult↗
PubMed1998

Divergent effects of exercise on metabolic and mitogenic signaling pathways in human skeletal muscle.

The molecular signaling mechanisms by which muscle contractions lead to changes in glucose metabolism and gene expression remain largely undefined. We assessed whether exercise activates MAP kinase proteins (ERK1/2, SEK1, and p38 MAP kinase) as well as Akt and PYK2 in skeletal muscle from healthy volunteers obtained during and after one-leg cycle ergometry at approximately 70% VO2max. Exercise led to a marked increase in ERK1/2 phosphorylation, which rapidly decreased to resting levels upon recovery. Exercise increased phosphorylation of SEK1 and p38 MAP kinase to a lesser extent than ERK1/2. In contrast to ERK1/2, p38 MAP kinase phosphorylation was increased in nonexercised muscle upon cessation of exercise. Phosphorylation of the transcription factor CREB was increased in nonexercised muscle upon cessation of exercise. Exercise did not activate Akt or increase tyrosine phosphorylation of PYK2. Thus, exercise has divergent effects on parallel MAP kinase pathways, of which only p38 demonstrated a systemic response. However, our data do not support a role of Akt or PYK2 in exercise/contraction-induced signaling in human skeletal. Activation of the different MAP kinase pathways by physical exercise appears to be important in the regulation of transcriptional events in skeletal muscle.

Blood Glucose↗
PubMed1998

Insulin-stimulated Akt kinase activity is reduced in skeletal muscle from NIDDM subjects.

The serine/threonine kinase Akt (PKB/Rac) has been implicated as playing a role in the insulin-signaling pathway to glucose transport. Little is known regarding the regulation of Akt kinase activity in insulin-sensitive tissues, such as skeletal muscle, or whether this regulation is altered in insulin-resistant states such as NIDDM. We examined the effect of insulin on Akt kinase activity in skeletal muscle from six NIDDM patients and six healthy subjects. Whole-body insulin sensitivity, assessed by the euglycemic-hyperinsulinemic clamp, was significantly lower in NIDDM subjects (P < 0.001), and this was accompanied by impaired in vitro insulin-stimulated glucose transport in skeletal muscle. In both groups, insulin induced a significant increase in Akt kinase activity, but the response to maximal insulin (60 nmol/l) was markedly reduced in skeletal muscle from NIDDM subjects (66% of control levels, P < 0.01). Impaired Akt kinase activity was not accompanied by decreased protein expression of Akt. Instead, a trend toward increased Akt expression was noted in skeletal muscle from NIDDM subjects (P < 0.1). These parallel defects in insulin-stimulated Akt kinase activity and glucose transport in diabetic skeletal muscle suggest that reduced Akt kinase activity may play a role in the development of insulin resistance in NIDDM.

Biological Transport↗
PubMed1998

Uncoupling protein 3 is reduced in skeletal muscle of NIDDM patients.

Two recently described proteins in the mitochondrial uncoupling protein (UCP) family, UCP-2 and UCP-3, have been linked to phenotypes of obesity and NIDDM. We determined the mRNA levels of UCP-2 and UCP-3 in skeletal muscle of NIDDM patients and of healthy control subjects. No difference in the mRNA levels or in the protein expression of UCP-2 was observed between the two groups. In contrast, mRNA levels of UCP-3 were significantly reduced in skeletal muscle of NIDDM patients compared with control subjects. In the NIDDM patients, a positive correlation between UCP-3 expression and whole-body insulin-mediated glucose utilization rate was also noted. These results suggest that UCP-3 regulation may be altered in states of insulin resistance.

Blood Glucose↗
PubMed1998

Insulin action in skeletal muscle from patients with NIDDM.

Insulin resistance in peripheral tissues is a common feature of non insulin-dependent diabetes mellitus (NIDDM). The decrease in insulin-mediated peripheral glucose uptake in NIDDM patients can be localized to defects in insulin action on glucose transport in skeletal muscle. Following short term in vitro exposure to both submaximal and maximal concentrations of insulin, 3-O-methylglucose transport rates are 40-50% lower in isolated skeletal muscle strips from NIDDM patients when compared to muscle strips from nondiabetic subjects. In addition, we have shown that physiological levels of insulin induce a 1.6-2.0 fold increase in GLUT4 content in skeletal muscle plasma membranes from control subjects, whereas no significant increase was noted in NIDDM skeletal muscle. Impaired insulin-stimulated GLUT4 translocation and glucose transport in NIDDM skeletal muscle is associated with reduced insulin-stimulated IRS-1 tyrosine phosphorylation and PI3-kinase activity. The reduced IRS-1 phosphorylation cannot be attributed to decreased protein expression, since the IRS-1 protein content is similar between NIDDM subjects and controls. Altered glycemia may contribute to decreased insulin-mediated glucose transport in skeletal muscle from NIDDM patients. We have shown that insulin-stimulated glucose transport is normalized in vitro in the presence of euglycemia, but not in the presence of hyperglycemia. Thus, the circulating level of glucose may independently regulate insulin stimulated glucose transport in skeletal muscle from NIDDM patients via a down regulation of the insulin signaling cascade.

Diabetes Mellitus, Type 2↗
PubMed1997

Two naturally occurring insulin receptor tyrosine kinase domain mutants provide evidence that phosphoinositide 3-kinase activation alone is not sufficient for the mediation of insulin's metabolic and mitogenic effects.

We have recently reported (1) that two naturally occurring mutants of the insulin receptor tyrosine kinase domain, Arg-1174 --> Gln and Pro-1178 --> Leu (Gln-1174 and Leu1178, respectively), both found in patients with inherited severe insulin resistance, markedly impaired receptor tyrosine autophosphorylation, with both mutant receptors being unable to mediate the stimulation of glycogen synthesis or mitogenesis by insulin when expressed in Chinese hamster ovary cells. However, these mutations did not fully prevent IRS-1 phosphorylation in response to insulin in these cells, suggesting that IRS-1 alone may not be sufficient to mediate insulin's metabolic and mitogenic effects. In the present study, we have demonstrated that these mutations also impair the ability of the insulin receptor to activate the transcription factor Elk-1 and promote GLUT4 translocation to the plasma membrane. Although at low concentrations of insulin, the mutant receptors were impaired in their ability to stimulate the tyrosine phosphorylation of IRS-1, at higher insulin concentrations we confirmed that the cells expressing the mutant receptors showed significantly increased tyrosine phosphorylation of IRS-1 compared with parental nontransfected cells. In addition, at comparable insulin concentrations, the association of the p85alpha subunit of phosphoinositide 3-kinase (PI3-kinase) with IRS-1 and the enzymatic activity of IRS-1-associated PI3-kinase were significantly enhanced in cells expressing the mutant receptors. In contrast, no significant stimulation of the tyrosine phosphorylation of Shc, GTP loading of Ras, or mitogen-activated protein kinase phosphorylation was seen in cell lines expressing these mutant receptors. Thus, no activation of any measurable mitogenic or metabolic response was detectable, despite significant insulin-induced phosphorylation of IRS-1 and its association with PI3-kinase in cells stably expressing the mutant insulin receptors. These findings suggest that PI3-kinase activation alone may be insufficient to mediate a wide range of the metabolic and mitogenic effects of insulin. Additionally, the data provide support for the notion that insulin activation of Ras is more closely linked with Shc, and not IRS-1, phosphorylation.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Chloroquine extends the lifetime of the activated insulin receptor complex in endosomes.

Insulin signal transduction, initiated by binding of insulin to its receptor at the plasma membrane, activates the intrinsic receptor tyrosine kinase and leads to internalization of the activated ligand-receptor complex into endosomes. This study addresses the role played by the activated insulin receptor within hepatic endosomes and provides evidence for its central role in insulin-stimulated events in vivo. Rats were treated with chloroquine, an acidotrophic agent that has been shown previously to inhibit endosomal insulin degradation, and then with insulin. Livers were removed and fractionated by density gradient centrifugation to obtain endosomal and plasma membrane preparations. Chloroquine treatment increased the amount of receptor-bound insulin in endosomes at 2 min after insulin injection by 93% as determined by exclusion from G-50 columns and by 90% as determined by polyethylene glycol precipitation (p < 0.02). Chloroquine treatment also increased the insulin receptor content of endosomes after insulin injection (integrated over 0-45 min) by 31% when compared with controls (p < 0.05). Similarly, chloroquine increased both insulin receptor phosphotyrosine content and its exogenous tyrosine kinase activity after insulin injection (64%; p < 0.01 and 96% and p < 0. 001, respectively). In vivo chloroquine treatment was without any observable effect on insulin binding to plasma membrane insulin receptors, nor did it augment insulin-stimulated receptor autophosphorylation or kinase activity in the plasma membrane. Concomitant with its effects on endosomal insulin receptors, chloroquine treatment augmented insulin-stimulated incorporation of glucose into glycogen in diaphragm (p < 0.001). These observations are consistent with the hypothesis that chloroquine-dependent inhibition of endosomal insulin receptor dissociation and subsequent degradation prolongs the half-life of the active endosomal receptor and potentiates insulin signaling from this compartment.

Animals↗
PubMed1997

Prevalence and risk factors for HTLV-II infection in 913 injecting drug users in Stockholm, 1994.

The prevalence and risk factors for acquisition of human T-cell lymphotropic virus type I and II (HTLV-I and II) were investigated in a prospective study of 913 injecting drug users (IDUs) in Stockholm in 1994. Epidemiologic data were recorded, and blood samples were tested for antibodies against HTLV-I and HTLV-II; human immunodeficiency virus (HIV) types 1 and 2; and hepatitis A (HAV), B (HBV), C (HCV), and D (HDV). Positive serologic results for HTLV were confirmed by Western blot (WB) and polymerase chain reaction (PCR). Of the 905 participants with conclusive HTLV-II status, 29 (3.2%) were HTLV-II positive, and all but three were of Nordic descent. None was HTLV-I infected. One person was infected as early as 1981, before HIV had reached the IDU population in Sweden. The prevalence of HTLV-II infection was 12% among HIV-1-seropositive and 1.8% among HIV-1-seronegative participants. The overall seroprevalences were 14% for HIV-1, 0% for HIV-2, 41% for HAV, 75% for HBV, 92% for HCV, and 8% for HDV. Although amphetamine has been the main injecting drug in Sweden for several decades, heroin abuse combined with a debut of injecting drugs before 1975 was identified as the most important risk factor associated with HTLV-II infection. HAV and HIV seropositivity were also independent risk factors.

Adult↗
PubMed1997

Homozygosity for a common polymorphism in the islet-specific promoter of the glucokinase gene is associated with a reduced early insulin response to oral glucose in pregnant women.

A commonly occurring sequence variant in the islet-specific promoter of the glucokinase gene (-30 G to A) has been variably reported to be associated with reduced insulin secretory responses to oral glucose. The effect of this promoter variant may be subtle and only become apparent under conditions of beta-cell 'stress'. As late pregnancy is a time of increased insulin secretory demand, we have examined whether this common genetic variant was associated with impairment of insulin secretory responses to oral glucose in 92 women in the third trimester of pregnancy. The three women who were homozygous for the variant sequence had a markedly diminished 30' insulin incremental response to oral glucose (10.4, 11.4, and 17.2 pmol insulin mmol-1 glucose, respectively) compared to either heterozygous (49.3 (37.6-64.6 pmol insulin mmol-1 glucose)) (p < 0.002) or homozygous wild-type (51.4 (40.9-64.7 pmol insulin mmol-1 glucose)) (p < 0.002) Mann-Whitney U test) women. In a subset of 35 British Caucasian women with gestational diabetes, no mutations resulting in a change of amino acid sequence were detected by molecular scanning of all exons of the glucokinase gene. In summary, in a cohort of 35 British Caucasian women with gestational diabetes neither missense nor nonsense glucokinase mutations were found. However, in women in the third trimester of pregnancy, homozygosity for a common polymorphic variant in the islet-specific promoter of the glucokinase gene was associated with a highly significant reduction of early insulin secretory responsiveness to oral glucose. Under the conditions of increased secretory demand represented by late pregnancy, a promoter variant in the glucokinase gene may influence the early insulin secretory response to oral glucose.

Base Sequence↗
PubMed1997

Human immunoglobulin isotype and IgG subclass response to different antigens of Moraxella catarrhalis.

Enzyme immunoassays were tested for the determination of antibodies of different isotypes and IgG subclasses to Moraxella catarrhalis in human sera. An assay based on an outer membrane protein preparation (OMP) as antigen was compared to assays using whole bacterial cells and a purified lipopolysaccharide preparation. There was a good correlation between the results obtained with the OMP preparation and the whole-cell antigen. In paired sera, optimal sensitivity was obtained by using the OMP preparation as coating antigen and testing for a rise in IgG3 antibodies. However, patients with high levels of antibodies in acute serum had no or only an insignificant antibody response during infection.

Adult↗
PubMed1997

Improved glucose tolerance restores insulin-stimulated Akt kinase activity and glucose transport in skeletal muscle from diabetic Goto-Kakizaki rats.

The serine/threonine kinase Akt (protein kinase B [PKB] or related to A and C protein kinase [RAC]) has recently been implicated to play a role in the signaling pathway to glucose transport. However, little is known concerning the regulation of Akt activity in insulin-sensitive tissues such as skeletal muscle. To explore the role of hyperglycemia on Akt kinase activity in skeletal muscle, normal Wistar rats or Goto-Kakizaki (GK) diabetic rats were treated with phlorizin. Phlorizin treatment normalized fasting blood glucose and significantly improved glucose tolerance (P < 0.001) in GK rats, whereas in Wistar rats, the compound had no effect on glucose homeostasis. In soleus muscle from GK rats, maximal insulin-stimulated (120 nmol/l) Akt kinase activity was reduced by 68% (P < 0.01) and glucose transport was decreased by 39% (P < 0.05), compared with Wistar rats. Importantly, the defects at the level of Akt kinase and glucose transport were completely restored by phlorizin treatment. There was no significant difference in Akt kinase protein expression among the three groups. At a submaximal insulin concentration (2.4 nmol/l), activity of Akt kinase and glucose transport were unaltered. In conclusion, improved glucose tolerance in diabetic GK rats by phlorizin treatment fully restored insulin-stimulated activity of Akt kinase and glucose transport. Thus, hyperglycemia may directly contribute to the development of muscle insulin resistance through alterations in insulin action on Akt kinase and glucose transport.

Animals↗
PubMed1996

Functional activation of mutant human insulin receptor by monoclonal antibody.

BACKGROUND: A mutant insulin receptor, Ser323Leu, has been reported in two severely insulin-resistant patients with Rabson-Mendenhall syndrome. In both cases, extreme hyperglycaemia could not be controlled by conventional antidiabetic therapy. The SER323Leu mutant insulin receptor is inserted normally in the plasma membrane but has very low binding affinity for insulin. A monoclonal antibody directed against the extracellular domain of the insulin receptor (83.14) can mimic the natural ligand as far as the first step after ligand binding--autophosphorylation of the intracellular domain of the receptor. We have investigated whether antibody binding can imitate autophosphorylation of the Ser323Leu mutant receptor and lead to metabolic events within the cell. METHODS: The effects of insulin and the insulin-receptor monoclonal antibody on receptor autophosphorylation and glycogen synthesis were compared in Chinese hamster ovary cells expressing the wild-type human insulin receptor, mock-transfected cells, cells expressing an insulin-receptor mutant without autophosphorylation capacity, and cells expressing the Ser323Leu mutant receptor. FINDINGS: Cells expressing the SER323Leu mutant receptor had very low specific insulin binding and, unlike cells expressing wild-type insulin receptors, did not show autophosphorylation or stimulation of glycogen synthesis in response to insulin. However, exposure of cells expressing the Ser323Leu mutant receptor to monoclonal antibody 83.14 resulted in autophosphorylation and stimulation of glycogen synthesis similar to that seen in cells expressing wild-type insulin receptors. INTERPRETATION: Although insulin does not bind to cells expressing the Ser323Leu mutation, insulin signalling can be mimicked by exposure of the cells to an antibody to the extracellular domain of the insulin receptor. Activation by monoclonal antibodies of mutant transmembrane receptors that show normal cell-surface expression but defective ligand binding may provide an approach to the therapy of some subtypes of inherited hormone resistance for which little effective treatment is available.

Adult↗