-Exposure to high concentrations of glucose and insulin results in insulin resistance of metabolic target tissues, a characteristic feature of type 2 diabetes. High glucose has also been associated with oxidative stress, and increased levels of reactive oxygen species have been proposed to cause insulin resistance. To determine whether oxidative stress contributes to insulin resistance induced by hyperglycemia in vivo, nondiabetic rats were infused with glucose for 6 h to maintain a circulating glucose concentration of 15 mM with and without coinfusion of the antioxidant N-acetylcysteine (NAC), followed by a 2-h hyperinsulinemic-euglycemic clamp. High glucose (HG) induced a significant decrease in insulin-stimulated glucose uptake [tracer-determined disappearance rate (R d), control 41.2 Ϯ 1.7 vs. HG 32.4 Ϯ 1.9 mg ⅐ kg Ϫ1 ⅐ min Ϫ1 , P Ͻ 0.05], which was prevented by NAC (HG ϩ NAC 45.9 Ϯ 3.5 mg ⅐ kg Ϫ1 ⅐ min Ϫ1 ). Similar results were obtained with the antioxidant taurine. Neither NAC nor taurine alone altered Rd. HG caused a significant (5-fold) increase in soleus muscle protein carbonyl content, a marker of oxidative stress that was blocked by NAC, as well as elevated levels of malondialdehyde and 4-hydroxynonenal, markers of lipid peroxidation, which were reduced by taurine. In contrast to findings after long-term hyperglycemia, there was no membrane translocation of novel isoforms of protein kinase C in skeletal muscle after 6 h. These data support the concept that oxidative stress contributes to the pathogenesis of hyperglycemia-induced insulin resistance. euglycemic clamp; insulin resistance; protein carbonyls; protein kinase C; antioxidants INSULIN RESISTANCE is one of the earliest detectable predictors of type 2 diabetes (47, 51, 39) and, along with relative insulin deficiency (39, 56), strongly contributes to the development of overt hyperglycemia. Hyperglycemia is in large part responsible for a host of complications found in diabetic subjects (15,83,86) and can worsen insulin resistance (11,38,72,73,75). The effect of hyperglycemia per se to induce insulin resistance in vivo was first demonstrated by Rossetti et al. (75) in the partially pancreatectomized rat model, which is characterized by moderate fasting hyperglycemia, glucose intolerance, and normal fasting insulin levels. In that study, phlorizin was used to normalize plasma glucose without affecting insulin secretion. Use of a hyperinsulinemic-euglycemic clamp revealed that the decreased insulin-stimulated glucose utilization was completely normalized in the phlorizin-treated rats, indicating a direct role of glucose in the induction of insulin resistance. Several mechanisms have been proposed to mediate hyperglycemia-induced insulin resistance, including the hexosamine biosynthetic pathway (4,31,67,74,87) and protein kinase C (55,68,78

Prolonged exposure of pancreatic islets to free fatty acids (FFAs) inhibits glucose-stimulated insulin secretion (GSIS) in vitro. However, FFA inhibition of GSIS has not been clearly demonstrated in vivo. We examined the in vivo effect of prolonged elevation of plasma FFAs on GSIS using a two-step hyperglycemic clamp in rats treated with a 48-h intravenous infusion of either 20% Intralipid plus heparin (INT) (5 microl/min plus heparin, 0.1 U/min; n = 8), oleate (OLE) (1.3 microEq/min; n = 6), saline (SAL) (n = 6), or bovine serum albumin (BSA) (vehicle for OLE; n = 5). Because there was no difference in any of the parameters between BSA and SAL rats, these groups were combined as control rats (CONT) (n = 11). At the end of the 48-h OLE/INT/CONT infusions, after an overnight fast, plasma glucose was clamped for 2 h at 13 mmol/l and for another 2 h at 22 mmol/l. Preclamp plasma FFAs were elevated twofold (P < 0.01) versus CONT with both INT and OLE (NS, INT vs. OLE). Preclamp glucose, insulin, and C-peptide levels were higher in INT than in CONT rats (P < 0.05), suggesting insulin resistance, but they were not different in OLE and CONT rats. The insulin and C-peptide responses to the rise in plasma glucose from basal to 13 mmol/l were lower in OLE (336 +/- 72 pmol/l and 1.2 +/- 0.1 nmol/l, P < 0.01 and P < 0.05, respectively) than in CONT (552 +/- 54 and 1.9 +/- 0.1) rats, but they were not different between CONT and INT rats (648 +/- 150 and 2.0 +/- 0.4). The insulin and C-peptide responses to the rise in plasma glucose from 13 to 22 mmol/l were lower in both INT (1,188 +/- 204 pmol/l and 3.0 +/- 0.3 nmol/l, P < 0.01 and P < 0.001) and OLE (432 +/- 60 and 1.7 +/- 0.2, P < 0.001 vs. CONT or INT) rats than in CONT rats (1,662 +/- 174 and 5.0 +/- 0.6). In summary, 1) both INT and OLE decreased GSIS in vivo in rats, and 2) the impairing effect of INT on GSIS was less than that of OLE, which might be due to the different type of fatty acid (mostly polyunsaturated in INT versus monounsaturated as OLE) and/or to differential effects of INT and OLE on insulin sensitivity. In conclusion, prolonged elevation of plasma FFAs can desensitize the insulin secretory response to glucose in vivo, thus inducing a beta-cell defect that is similar to that found in type 2 diabetes.

We determined the effect of 48-h elevation of plasma free fatty acids (FFA) on insulin secretion during hyperglycemic clamps in control female Wistar rats (group a) and in the following female rat models of progressive ␤-cell dysfunction: lean Zucker diabetic fatty (ZDF) rats, both wild-type (group b) and heterozygous for the fa mutation in the leptin receptor gene (group c); obese (fa/fa) Zucker rats (nonprediabetic; group d); obese prediabetic (fa/fa) ZDF rats (group e); and obese (fa/fa) diabetic ZDF rats (group f). FFA induced insulin resistance in all groups but increased Cpeptide levels (index of absolute insulin secretion) only in obese prediabetic ZDF rats. Insulin secretion corrected for insulin sensitivity using a hyperbolic or power relationship (disposition index or compensation index, respectively, both indexes of ␤-cell function) was decreased by FFA. The decrease was greater in normoglycemic heterozygous lean ZDF rats than in Wistar controls. In obese "prediabetic" ZDF rats with mild hyperglycemia, the FFA-induced decrease in ␤-cell function was no greater than that in obese Zucker rats. However, in overtly diabetic obese ZDF rats, FFA further impaired ␤-cell function. In conclusion, 1) the FFA-induced impairment in ␤-cell function is accentuated in the presence of a single copy of a mutated leptin receptor gene, independent of hyperglycemia. 2) In prediabetic ZDF rats with mild hyperglycemia, lipotoxicity is not accentuated, as the ␤-cell mounts a partial compensatory response for FFA-induced insulin resistance. 3) This compensation is lost in diabetic rats with more marked hyperglycemia and loss of glucose sensing.free fatty acid; obesity; insulin secretion; hyperglycemic clamp; Zucker diabetic fatty rat TYPE 2 DIABETES IS CHARACTERIZED by impaired insulin secretion and action (19,24). An early characteristic of the defect in insulin secretion is selective impairment of glucose-stimulated insulin secretion (GSIS). More than 80% of type 2 diabetic individuals are obese, and obese individuals often have elevated plasma levels of free fatty acids (FFA) (4) because of their expanded (3, 4) and more lipolytically active (41) adipose tissue stores. It is well known that FFA can impair insulin action (4); however, it is less clear whether FFA can also impair ␤-cell function, thus playing a role in the defect in GSIS that characterizes type 2 diabetes. Acutely, FFA increase insulin secretion both in vitro (13, 46) and in vivo (15, 21, 45). However, in vitro and ex vivo studies (8,28,43,47,48) have shown that, chronically, FFA impair GSIS. The effect of prolonged FFA elevation on GSIS in vivo is more controversial. We have found that prolonged elevation of plasma FFA results in decreased GSIS in vivo in normal female Wistar rats (34). The decrease was marked with oleate infusion but was also seen at high glucose levels with infusion of Intralipid ϩ heparin (IH). In that study, a mild elevation of FFA was obtained that did not significantly decrease insulin sensitivity during a hyperglycemic clamp. Howeve...

BackgroundPatient diaries and pain scales can capture the course and complications of pain managed at home in children. The Faces Pain Scale-Revised (FPS-R) is a validated scale showing reliability in children, but it has not been validated in children with sickle cell disease (SCD).ObjectiveThe purpose of this study was to evaluate comprehension and usability of an electronic modified version of the FPS-R among pediatric patients with SCD.MethodsThis was a cross-sectional, qualitative study involving in-person interviews with children/adolescents from the USA and their parents/legal guardians. Interviews involved cognitive debriefing and usability testing of the FPS-R.ResultsIn total, 22 children with SCD aged 4–17 years participated. Children aged 4–6 were generally unable to demonstrate clear understanding of the FPS-R and its response scale. Overall, children aged ≥7 years understood the instrument and could complete it on the electronic device, although children aged 7–8 often needed assistance from the parent. Children aged 9–17 years were able to read and complete the instrument independently. Most participants considered the electronic device easy to use.ConclusionsThe FPS-R was shown to be a comprehensible and usable pain measure for children aged 7–17 with SCD and to be beneficial for future clinical studies.