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In vitro reversal of hyperglycemia normalizes insulin action in fat cells from type 2 diabetes patients: is cellular insulin resistance caused by glucotoxicity in vivo?
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine.
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine.
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine.
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine.
2002 (English)In: Metabolism: Clinical and Experimental, ISSN 0026-0495, E-ISSN 1532-8600, Vol. 52, no 2, 239-245 p.Article in journal (Refereed) Published
Abstract [en]

Chronic hyperglycemia promotes the development of insulin resistance. The aim of this study was to investigate whether cellular insulin resistance is secondary to the diabetic state in human type 2 diabetes. Subcutaneous fat biopsies were taken from 3 age-, sex-, and body mass index (BMI)-matched groups with 10 subjects in each group: type 2 diabetes patients with either good (hemoglobin A1c [HbA1c] [lt ] 7%, G) or poor (HbA1c [gt ] 7.5%, P) metabolic control and healthy control subjects (C). Insulin action in vitro was studied by measurements of glucose uptake both directly after cell isolation and following a 24-hour incubation at a physiological glucose level (6 mmol/L). The relationship with insulin action in vivo was addressed by employing the euglycemic clamp technique. Freshly isolated fat cells from type 2 diabetes patients with poor metabolic control had [sim ]55% lower maximal insulin response (1,000 [mu ]U/mL) on glucose uptake (P [lt ] .05) compared to C. Cells from P were more insulin-resistant (P [lt ] .05) than cells from G at a low (5 [mu ]U/mL) but not at a high (1,000 [mu ]U/mL) insulin concentration, suggesting insulin insensitivity. However, following 24 hours of incubation at physiological glucose levels, insulin resistance was completely reversed in the diabetes cells and no differences in insulin-stimulated glucose uptake were found among the 3 groups. Insulin sensitivity in vivo assessed with hyperinsulinemic, euglycemic clamp (M-value) was significantly associated with insulin action on glucose uptake in fresh adipocytes in vitro (r = 0.50, P [lt ] .01). Fasting blood glucose at the time of biopsy and HbA1c, but not serum insulin, were negatively correlated to insulin's effect to stimulate glucose uptake in vitro (r = [minus ]0.36, P = .064 and r = [minus ] 0.41, P [lt ].05, respectively) in all groups taken together. In the in vivo situation, fasting blood glucose, HbA1c, and serum insulin were all negatively correlated to insulin sensitivity (M-value; r = [minus ]0.62, P[lt ] .001, r= [minus ]0.61, P[lt ] .001, and r = [minus ]0.56, p [lt ] .01, respectively). Cell size, waist-to-hip ration (WHR), and BMI correlated negatively with insulin's effect to stimulate glucose uptake both in vitro (r = [minus ]0.55, P [lt ] .01, r = [minus ]0.54, P [lt ] .01, and r = [minus ]0.43, P [lt ] .05, respectively) and in vivo (r = [minus ]0.43, P [lt ] .05, r = [minus ]0.50, P [lt ] .01, and r = [minus ]0.36, P [lt ] .05, respectively). Multiple regression analyses revealed that adipocyte cell size and WHR independently predicted insulin resistance in vitro. Furthermore, insulin sensitivity in vivo could be predicted by fasting blood glucose and serum insulin levels. We conclude that insulin resistance in fat cells from type 2 diabetes patients is fully reversible following incubation at physiological glucose concentrations. Thus, cellular insulin resistance may be mainly secondary to the hyperglycemic state in vivo.

Place, publisher, year, edition, pages
Elsevier Science , 2002. Vol. 52, no 2, 239-245 p.
Identifiers
URN: urn:nbn:se:umu:diva-3933DOI: 10.1053/meta.2003.50041OAI: oai:DiVA.org:umu-3933DiVA: diva2:142846
Available from: 2002-12-06 Created: 2002-12-06 Last updated: 2010-06-17Bibliographically approved
In thesis
1. Glucose and lipid metabolism in insulin resistance: an experimental study in fat cells
Open this publication in new window or tab >>Glucose and lipid metabolism in insulin resistance: an experimental study in fat cells
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Type 2 diabetes is usually caused by a combination of pancreatic β-cell failure and insulin resistance in target tissues like liver, muscle and fat. Insulin resistance is characterised by an impaired effect of insulin to reduce hepatic glucose production and to promote glucose uptake in peripheral tissues. The focus of this study was to further elucidate cellular mechanisms for insulin resistance that may be of relevance for type 2 diabetes in humans. We used rat and human adipocytes as an established model of insulin’s target cells.

Glucocorticoids, e.g. cortisol, can induce insulin resistance in vivo. In the present study, pretreatment of rat adipocytes in vitro for 24 h with the cortisol analogue dexamethasone produced a downregulation of glucose uptake capacity as well as a marked depletion of cellular insulin receptor substrate 1 (IRS-1) and protein kinase B (PKB), two proteins suggested to play a critical role in the intracellular signal transduction pathway of insulin. The amount of phosphorylated PKB in response to acute insulin treatment was decreased in parallel to total PKB content. The basal rate of lipolysis was enhanced, but insulin’s antilipolytic effect was not consistently altered following dexamethasone pretreatment.

Alterations in blood glucose as well as insulin levels may be of great importance for cellular as well as whole-body insulin resistance. High glucose (≥15 mM) for 24 h induced a decrease in glucose uptake capacity in rat adipocytes and IRS-1 content was reduced whereas IRS-2 was increased. Long-term pretreatment with a high insulin concentration downregulated insulin binding capacity and when combined with high glucose, it produced a pronounced

reduction of cellular IRS-1 and 2 content together with insensitivity to insulin’s effect to activate PKB and a decrease in glucose uptake capacity. A common denominator for a decrease in glucose uptake capacity in our rat adipocyte studies seems to be a decrease in IRS-1 content.

Adipocytes from type 2 diabetes patients are insulin-resistant, but in our work the insulin resistance could be reversed by incubation of the cells at a physiological glucose level for 24 h. Insulin resistance in fresh adipocytes from type 2 diabetes patients was associated with in vivo insulin resistance and glycemic level and with adipocyte cell size and waist-hip ratio

(WHR).

As a potential mechanism for postprandial dyslipidemia in type 2 diabetes, we examined the nutritional regulation of subcutaneous adipose tissue lipoprotein lipase (LPL) activity. It was upregulated by ~40-50 % after a standardised lipid-enriched meal and this was very similar in type 2 diabetes patients and control subjects, suggesting that the postprandial

hypertriglyceridemia found in type 2 diabetes is not explained by an altered nutritional regulation of LPL in subcutaneous fat.

In conclusion, the present work provides evidence for novel interactions between glucocorticoids and insulin in the regulation of glucose metabolism that may potentially contribute to the development of insulin resistance. High levels of glucose and insulin produce perturbations in the insulin signalling pathway that may be of relevance for human type 2 diabetes. Cellular insulin resistance may be secondary to the diabetic state in vivo, e.g. via glucotoxicity. This is supported by our finding that insulin resistance in adipocytes from type 2 diabetes patients can be reversed after incubation at a physiological glucose level.

Key words: adipocyte, insulin resistance, type 2 diabetes, insulin signalling, glucose uptake,

insulin, glucose, dexamethasone, insulin receptor substrate, protein kinase B, GLUT4,

lipoprotein lipase.

Place, publisher, year, edition, pages
Umeå: Folkhälsa och klinisk medicin, 2003. 63 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 817
Keyword
Public health, adipocyte, insulin resistance, type 2 diabetes, insulin signalling, glucose uptake, insulin, glucose, dexamethasone, insulin receptor substrate, protein kinase B, GLUT4, lipoprotein lipase, Folkhälsomedicin
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Research subject
Medicine
Identifiers
urn:nbn:se:umu:diva-26 (URN)91-7305-359-7 (ISBN)
Public defence
2002-12-06, Umeå, 13:00
Available from: 2002-12-06 Created: 2002-12-06 Last updated: 2010-06-17Bibliographically approved

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