A Leckström

Linköping University, Linköping, OEstergoetland, Sweden

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Publications (13)40.35 Total impact

  • A Leckström, I Lundquist, Z Ma, P Westermark
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    ABSTRACT: Obese mice (Umeå ob/ob) and their lean litter-mates were investigated from 7 to 52 weeks of age with respect to the plasma concentration of islet amyloid polypeptide (IAPP) and insulin. Plasma levels of IAPP were highly elevated in the ob/ob mice and remained unchanged until age 33 weeks, after which a sudden significant increase occurred at age 40 weeks. The plasma concentration of insulin gradually increased from start to end and reached extremely high levels. In the lean mice, there were no age-related differences in plasma levels of IAPP and insulin, being of the same magnitude as in normal NMRI mice. The plasma IAPP/insulin molar ratio was similar in lean and obese mice until age 14 weeks. At 21 weeks, the ratio in the ob/ob mice had decreased dramatically and remained markedly (sixfold) lower than in the lean mice until the end of the study. The IAPP concentration in the pancreata of 21-week-old ob/ob mice was 25-fold higher than that in the lean mice. Immunohistochemically, a majority of the ob/ob mice displayed enlarged and more numerous pancreatic islets, compared with the lean mice, and the IAPP- and insulin-labeling intensity was equal for all animals. At the electron-microscopic level, there was an increase in the number of IAPP- and insulin-immunoreactive gold particles per whole granule area as well as per core granule area. We conclude that the dramatically increased IAPP levels in severely hyperinsulinemic ob/ob mice may be of importance for the development of insulin resistance. Further, the disproportionate secretion of IAPP and insulin in the adult obese mouse might indicate a disturbed negative feedback effect of IAPP on insulin secretory mechanisms, resulting in very high plasma insulin levels.
    Pancreas 05/1999; 18(3):266-73. · 2.95 Impact Factor
  • G T Westermark, A Leckström, Z Ma, P Westermark
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    ABSTRACT: In the present study, mice were fed high-fat diet or standard animal chow during 6 months. Animals fed high-fat diet showed a 4.5-fold increase in the fasting plasma IAPP levels compared to animals fed standard chow. No significant change in plasma insulin levels occurred between the groups. These differences in hormone response result in a change of the molar ratio between IAPP and insulin in the group fed high-fat diet. An increased IAPP to insulin molar ratio might be important in the pathogenesis of islet amyloid in man.
    Hormone and Metabolic Research 06/1998; 30(5):256-8. · 2.15 Impact Factor
  • A Leckström, E Ziv, E Shafrir, P Westermark
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    ABSTRACT: We investigated the possible relationship between islet amyloid polypeptide (IAPP) and the hyperinsulinemia and/or hyperglycemia that is seen in the desert-adapted gerbil Psammomys obesus, when the animal is transferred from a low-energy (LE) diet to a high-energy (HE) diet. The effects of vanadyl sulfate and transition from a HE to a LE diet on the diabetic state of the Psammomys were also studied. Psammomys maintained on a LE diet, showing normoinsulinemia and normoglycemia (group A), were used as controls. IAPP and insulin immunoreactivity in the islets of Langerhans was studied using the peroxidase-antiperoxidase technique and plasma levels of the two hormones were determined by radioimmunoassays. The islet immunoreactivity of both IAPP and insulin was significantly weaker in the hyperinsulinemic and hyperglycemic Psammomys (group C) compared to group A. Transfer to a LE diet resulted in complete recovery of the IAPP- and insulin-staining pattern to that seen in group A [group A--Rec (nutrition)]. The plasma IAPP levels of the group C animals were not significantly higher than in group A, while after vanadyl sulfate treatment the IAPP levels and IAPP/insulin ratios remained significantly higher [group A--Rec (vanadyl)]. At the same time the circulating levels of glucose and insulin were restored to normal. Conclusively, islet IAPP and insulin immunoreactivity disappeared and reappeared in parallel in Psammomys transferred to a HE diet and back to a LE diet. Furthermore, vanadyl sulfate treatment of the hyperinsulinemic and hyperglycemic animals normalized circulating glucose and insulin levels, but not IAPP levels, possibly due to a negative feedback effect of IAPP on insulin release.
    Pancreas 12/1997; 15(4):358-66. · 2.95 Impact Factor
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    ABSTRACT: Six healthy volunteers showed significantly higher plasma islet amyloid polypeptide levels following an oral glucose tolerance test compared to fasting levels. The urine IAPP concentration before and after the OGTT was comparable to that in plasma. Reverse phase HPLC and radioimmunoassay analysis of urine samples revealed a single IAPP-immunoreactive peak. Before hemodialysis, the plasma levels of IAPP and C-peptide, but not of insulin, were significantly elevated in eight fasting patients with chronic renal failure, compared to eight healthy matched control subjects. After hemodialysis, there was a tendency for decreased IAPP levels compared to before dialysis. In summary, elevated levels of plasma IAPP were found in patients with chronic renal failure and the peptide is eliminated by hemodialysis. Furthermore, immunoreactive IAPP is normally present in the urine. These results suggest that IAPP is, at least in part, renally eliminated from the plasma by excretion (glomerular filtration and/or tubular secretion.
    Biochemical and Biophysical Research Communications 11/1997; 239(1):265-8. · 2.41 Impact Factor
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    ABSTRACT: The objective was to evaluate the effect of insulin treatment on circulating islet amyloid polypeptide (IAPP). Twelve patients with NIDDM and secondary failure were studied on oral agents and then switched to insulin treatment. Fasting and postprandial IAPP concentrations were measured on oral treatment and on insulin treatment. In 5 of the patients no postprandial concentrations were determined. In the 7 patients who were investigated both fasting and postprandially the fasting IAPP concentration was 6.5 +/- 1.2 pmol l(-1) (mean +/- SEM) during oral treatment with a rise to 13.5 +/- 3.1 90 min after breakfast (p = 0.028). On insulin treatment HbA1c decreased from 8.6 +/- 0.5 to 7.5 +/- 0.4% (p< 0.03) and plasma C-peptide concentration was significantly lowered (p< 0.01). There was a close correlation using simple regression between the per cent change of IAPP concentration and the per cent change of C-peptide concentration during this period (r = 0.88; p< 0.01). In the total patient material of 12 patients there was a significant correlation using simple regression analysis between per cent change of IAPP concentration and per cent change of C-peptide concentration using all 48 measurements available (r = 0.58: p< 0.001). These data suggest that secretion of IAPP is lowered when endogenous insulin secretion is lowered by administration of exogenous insulin in patients with NIDDM. Thus, if IAPP secretion has a pathogenetic role in the development of beta cell failure in NIDDM, insulin treatment might delay this deterioration.
    Diabetic Medicine 07/1997; 14(6):472-6. · 3.24 Impact Factor
  • Experimental and Clinical Endocrinology & Diabetes - EXP CLIN ENDOCRINOL DIABETES. 01/1997; 105:70-71.
  • Experimental and Clinical Endocrinology & Diabetes - EXP CLIN ENDOCRINOL DIABETES. 01/1997; 105:67-67.
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    ABSTRACT: We have investigated whether a possible dysregulation of the storage and function of islet amyloid polypeptide (IAPP) in the endocrine pancreas of 4-month-old spontaneously diabetic Goto-Kakizaki (GK) rats might contribute to the impairment of glucose-induced insulin secretion previously reported in these rats. Immunocytochemical studies indicated a significantly lower degree of labeling per beta-cell granule of insulin but not of IAPP in GK islets compared to control islets. Further, the GK rats displayed lower plasma levels of both insulin and IAPP in the fasting state. The pancreatic concentrations of both IAPP and insulin were also significantly lower in the GK rats than in the controls. Following an intraperitoneal glucose injection, the plasma IAPP and insulin concentration of the GK rats did not increase at all, whereas a significant increase in both IAPP and insulin concentration was recorded in the control animals. However, the plasma IAPP/insulin ratio was significantly higher in the GK rats at both 30 and 60 min after glucose injection, which may be a reflection of an increased negative feedback effect of IAPP on insulin release. A relative hypersecretion of IAPP might be one of several factors contributing to the impairment of glucose-induced insulin secretion in this rat model of non-insulin-dependent diabetes mellitus. This is further supported by our electron microscopic observations showing disproportionate IAPP/insulin labeling of beta-cell granules in the GK islets.
    Pancreas 11/1996; 13(3):259-67. · 2.95 Impact Factor
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    ABSTRACT: Amylin, also named islet amyloid polypeptide (IAPP), is a protein that is processed and released from pancreatic beta-cells in parallel with insulin. Islet amyloid polypeptide is currently studied with regard to a role for insulin resistance in non-insulin-dependent diabetes. To elucidate a possible function of IAPP for impaired glucose tolerance in primary hyperparathyroidism (pHPT), we studied plasma IAPP levels during an oral glucose tolerance test (OGTT) in seven pHPT patients before and 8 weeks after surgery and in six healthy subjects. The B-glucose level of the patient groups was 4.34 +/- 0.12 mmol/l before and 3.97 +/- 0.16 mmol/l after surgery (NS), while the serum level of insulin was significantly higher before (16.9 +/- 2.8 mlU/l) than after (8.9 +/- 1.9 mlU/l) the operation (p < 0.05), indicating a moderately increased insulin resistance in pHPT. The basal plasma levels of IAPP were significantly higher in pHPT patients before than 8 weeks after surgery (9.71 +/- 1.05 and 4.30 +/- 0.82 pmol/l, respectively: p < 0.01). When compared to the plasma IAPP level of the controls at 1.80 +/- 0.38 pmol/l, pHPT patients had higher IAPP values both before (p < 0.01) and at 8 weeks after (p < 0.05) operation. There was a significant correlation between the serum levels of insulin and plasma levels of IAPP in pHPT patients before (r = 0.87, p < 0.01) as well as 8 weeks after surgery (r = 0.69, p < 0.05). The area under the curve for IAPP during OGTT in pHPT patients was 1872.4 +/- 187.7 pmol.min/l, which is significantly higher than after surgery (1010.8 +/- 93.7 pmol.min/l) (p<0.05) and compared to the area for the controls at 840.3 +/- 49.9 pmol.min/l (p<0.01). In conclusion, pHPT is associated with an increased plasma level of IAPP, correlated to the serum insulin level, but persistently higher than in controls also 8 weeks after surgery. Possibly, increased IAPP levels can have a role for impaired glucose tolerance in pHPT. The hyperparathyroid state might have a specific role for the release of this peptide, otherwise closely connected to insulin secretion
    European Journal of Endocrinology 03/1996; 134(3):320-5. · 3.14 Impact Factor
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    ABSTRACT: Formation of amyloid-like fibrils in a solution of human islet amyloid polypeptide (hIAPP) with and without the presence of other beta-cell granule components was studied in vitro. Insulin at less than equimolar concentration strongly inhibited hIAPP fibrillogenesis. Proinsulin had a weaker inhibitory effect while C-peptide, Ca2+ and Zn2+ each individually enhanced fibril formation. C-peptide combined with Ca2+ had an inhibitory effect. Since IAPP was found almost exclusively in the halo fractions of isolated islet secretory granules, primarily the concentrations of C-peptide, Ca2+ and possibly proinsulin may be crucial for the native state of IAPP. It is concluded that an imbalance between fibril formation enhancers and inhibitors may be of importance in the pathogenesis of amyloid in the islets of Langerhans.
    FEBS Letters 03/1996; 379(3):203-6. · 3.58 Impact Factor
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    ABSTRACT: Islet amyloid polypeptide (IAPP) or amylin is a hormone candidate predominantly expressed in insulin cells. A role for IAPP in the regulation of glucose homeostasis and the development of non-insulin-dependent diabetes mellitus has been proposed. IAPP is structurally related to the sensory neuropeptide calcitonin gene-related peptide. In the present study, using in situ hybridization, immunocytochemistry, and immunochemistry, the expression of IAPP in sensory neurons in the rat was investigated. IAPP was expressed in a population of small- to medium-sized nerve cell bodies in dorsal root ganglia from all levels and in the jugular-nodose and trigeminal ganglion; IAPP-expressing nerve cell bodies constituted a subpopulation of those expressing calcitonin gene-related peptide. In addition, IAPP-like immunoreactivity occurred in nerve cell bodies storing substance P and pituitary adenylate cyclase-activating polypeptide. IAPP-immunoreactive nerve fibers were encountered in the dorsal horns of the spinal cord, and to a lesser extent in peripheral tissues receiving sensory innervation; IAPP-immunoreactive fibers constituted a subpopulation of those containing calcitonin gene-related peptide and/or substance P. The immunochemical determinations demonstrated a low level of IAPP-like immunoreactivity in the dorsal root ganglia and spinal cord, which chromatographically coeluted with authentic rat IAPP. We conclude that IAPP is expressed in sensory neurons, thus being a novel sensory neuropeptide candidate for which a physiological role remains to be identified.
    Journal of Neuroscience 12/1995; 15(11):7625-32. · 6.91 Impact Factor
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    ABSTRACT: To model islet amyloidogenesis in NIDDM and explore the glucoregulatory role of islet amyloid polypeptide (IAPP), we have created transgenic micye containing a rat insulin-I promoter-human IAPP fusion gene. Expression of human IAPP was localized to the islets of Langerhans, anterior pituitary and brain in transgenic animals; blood IAPP levels were elevated 5-fold while fasting glucose levels remained normal. Amyloid deposits have not been detected in transgenic islets suggesting that other co-existing abnormalitites in NIDDM may be required for the formation of islet amyloid. These animals provide a unique model for exploring this hypothesis and other proposed functions of IAPP.
    FEBS Letters 06/1993; · 3.58 Impact Factor
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    ABSTRACT: In this study, we determined the cDNA-predicted amino acid sequence of positions 9-31 of islet amyloid polypeptide from the rabbit and European hare. A synthetic rabbit/hare islet amyloid polypeptide 20-29 peptide was subsequently shown to be strongly fibrillogenic in vitro even though the putative amyloidogenic AILS sequence at positions 25-28 of human and cat islet amyloid polypeptide is modified in the rabbit and hare by a substitution of phenylalanine for leucine at position 27 (i.e. AIFS). Although islet amyloid polypeptide of both the rabbit and hare has an amyloidogenic sequence and is in fact amyloidogenic in vitro, the apparent lack of in vivo islet amyloidosis in rabbits and hares may be related to relatively low levels of islet amyloid polypeptide production by the islet beta cells in these species. This was supported by our findings that there is no substantial immunoreactivity in either rabbit or hare islets, and no measurable amount either in extracts of rabbit pancreases, or in rabbit plasma. This study supports the need for at least two prerequisites for the development of islet amyloidosis in vivo: an inherent fibrillogenic sequence within the islet amyloid polypeptide molecule and an adequate local concentration of islet amyloid polypeptide to promote self aggregation and formation of islet amyloid.
    Diabetologia 04/1993; 36(3):183-8. · 6.49 Impact Factor