| BackgroundContinuous glucose monitoring system (CGMS) is a tpye of glucose monitoring technology which has been improving and generalizing in recently years.CGMS can play a unique role in comprehensively understanding glucose information and in guiding therapies.Clinical and basic studies have shown that glucose excursion is closely associated with the occurrence of chronic complications of diabetes. Compared with absolutely high level of blood glucose, the damage that high glucose excursion impact on tissues or cells may be greater. Currently, the mean amplitude of glycemic excursions (MAGE) computed from CGMS data is a reliable parameter to assess the glucose excursion.The parameter excludes the fluctuation which excursion is less than one standard deviation, weaks interference factor and objectively reflects changes of the blood glucose.After Monnier reported that patients with type 2 diabetes mellitus (T2DM) have a significantly positive correlation between MAGE and Oxidative Stress in 2006, MAGE has gradually been recognized as the gold standard for assessing glucose excursion.Studies suggest that clinical hyperglycemia occurs only when the quality and quantity of insulin secretion are too severely insufficient to maintain glucose homeostasis. Therefore, the dysfunction of pancreatic isletβcells is far earlier than the occurrence of diabetes.So it is important to judge the early abnormal changes of islet function. Oral glucose tolerance test (OGTT) together with insulin release test are commonly screening methods for diabetes in clinical work, which are also usually used to evaluate the early function ofβcells.The early insulin secretion index (ΔI30/ΔG30) is a reliable parameter and is widely used to reflect the early insulin secretion at home and abroad. Currently views consider that the early phase insulin response may paly an important role in maintaining glucose homeostasis, especially postprandial glucose homeostasis. Further studies found that whenΔI30/ΔG30 is higher, the impact on body glucose homeostasis is greater;ΔI30/ΔG30 is lower, the increase of postprandial glucose level is greater.It suggests that the early phase insulin secretion is closely related with suppression of postprandial glucose excursion. Since the p cells function is decreased progressively from normal glucose tolerance (NGT) to impaired glucose regulation (IGR). and then to T2DM. to realize the characteristics of this changes earlily may contribute to improve the function ofβcells and to prevent T2DM.Glucagon (Gg) is a increase glucose hormone secreted by a cells.Glucagon also plays an important role in the occurrence and development of diabetes. Under normal circumstances, glucose can directly regulate the secretion of glucagon after meals, or indirectly regulate its secretion by stimulating insuin secretion. When levels of glucose are too low, a cells can stimulate hepatic glucose output to prevent hypoglycemia through increasing the glucagon secretion. But hyperinsulinemia and hyperglucagonemia may co-exist in some diabetic high-risk subjects, such as obese patients, whose abilities that insulin inhibits glucagon secretion are markedly decreased.It is known as that the pancreatic islet a cells appear insulin resistance. Studies have shown that absolutely or relatively excess of glucagon is an important factor to cause hyperglycemia.Therefore, abnormal secretion of glucagon may also be involved in pathogenesis of T2DM.Incretin plays an important role in regulating glucose homeostasis. As one of the most important incretin hormone, glucagon like peptide-1 (GLP-1) is the current hotspot. In addition to enhancing glucose-dependently insulin secretion and synthesis, GLP-1 can also inhibit glucagon secretion, delay gastric emptying, reduce appetite and food intake, increase glucose oxidation and utilization, induceβcells regeneration and differentiation, and inhibit apoptosis ofβcells.Studies also have shown that the GLP-1 level in blood is increased by between two and three times response to meals in NGT, but significantly reduced in T2DM patients. GLP-1 not only can alleviate hyperglycemia and protect islet function, but also may play an important role in pathogenesis of T2DM.In this study, subjects with different statuses of glucose metabolism were conducted with OGTT during CGMS period.The dynamic changes of plasma glucose, insulin, glucagon and total GLP-1 during OGTT were assayed.The aim was to observe characteristics of glucose profiles during the OGTT, the early phase insulin secretion and glucose excursion, and to preliminaryly analyze impact of glucagon and GLP-1 on early phase insulin secretion and glucose excursion, and to provide preliminary experimental evidence for exploring the roles of glucagon and GLP-1 in the pathogenesis of T2DM.Objective1. To compare the characteristics of glucose profiles during OGTT in subjects with different statuses of glucose metabolism, such as the glucose peak, added glucose, and time to glucose peak. 2. To analyze relationships between glucagon, GLP-1, early phase insulin secretion, glucose excursion and the characteristics indexes of glucose profiles during OGTT, respectively.3. To preliminaryly analyze the characteristics of dynamic changes of plasma glucose, insulin, glucagon, and GLP-1 levels during OGTT in subjects with different statuses of glucose metabolism.4. To compare CGMS values and venous blood glucose values to evaluate the accuracy of CGMS during OGTT of which glucose changes rapidly.Materials and methods1. SubjectsIn this study,48 volunteers were recruited in outpatient department of Endocrinology & Metabolism of NangFang Hospital, from March,2010 to November,2010. Inclusion criteria:1)more than 20 years old, venous fasting plasma glucose is normal or elevated at the first time, the range is 3.9～11.0mmol/L.2) Not suffering from a variety of serious acute and chronic complications, and no history of infection and ketosis in nearly 3 months.3) ALT and AST are less than 2 times the upper limit of normal, renal function is normal.4)Blood pressure is less than or equal to 140/90mmHg.5) The compliance is good enough to go with the experiment. Exclusion criteria:1) T1DM patients or IGR and T2DM patients who have used hypoglycemic drugs.2) Secondary diabetes or drug-induced glucose abnormal patients.3) Severe lipid metabolic disorder patients.4) Pregnant and lactating women.5) A history of gastric resection or severe gastrointestinal disorders.6) Other diseases that may affect glucose metabolism.2. GroupsGroups baseded on results of OGTT during the experiment and the diabetes diagnostic criteria of WHO in 1999.NGT group included 16 subjects,8 males and 8 females, (40.4±12.5) years old; IGR group included 13 subjects,7 males and 6 females, (49.3±9.9)years old; newly diagnosed T2DM group included 19 patients, 10 males and 9 females, (46.1±13.4) years old.3. ProcessTrained all subjects before the experiment so as to familiar with the general use of CGMS and common blood glucose meter. Specialists installed the CGMS and placed the probe in abdominal subcutaneous fat layer uniformly, and the CGMS was conducted for 72h continuously.Subjects were accepted 75g-OGTT in the morning of the 3rd CGMS day.Blood pressure, height, weight, circumference of waist and hip were measured at 8:00 AM. Collected forearm venous blood at 0,30,60,90, and 120 min during OGTT.Plasma glucose was detected by glucose oxidase method, and plasma insulin, glucagon, and total GLP-1 were assayed with radioimmunoassay.4. Evaluation parameters4.1 Glucose excursion was assessed by MAGE, and the value used for statistical analysis was the average of 2 days.4.2 Early phase insulin secretion was assessed byΔI30/ΔG30.ΔI30/ΔG30= (30min INS-0min INS)/(30min PG-Omin PG)4.3 Area under the curve (AUC) was calculated by approximately trapezoidal formula.120minAUC= (Omin value+120min value)/2+30min value+60min value +90min value.4.4 The CGMS accuracy during daily life was assessed by the mean absolute difference (MAD) calculated by the CGMS software.The criteria is following:When the difference between the fingertip blood glucose values≥5.6mmol/L, MAD≤28% and the correlation coefficient≥0.79.When the difference between the fingertip blood glucose values<5.6mmol/L, MAD≤18%. The CGMS accuracy during OGTT was assessed by correlation coefficient between CGMS values and venous glucose values and by Clarke error grid ananlysis (EGA). If EGA has more than 95% of results in A and B zones, the CGMS accuracy is acceptable.5. Statistical analysisStatistical analysis were conducted with the SPSS 13.0 for windows.All data were presented as mean±standard deviation.Differences between groups of which data belonged completely random design were analyzed by using One-way analysis of variance (ANOVA), and multiple comparisons were analyzed by LSD method when P value is less than 0.05.Welch method was used when equal variances not assumed, and multiple comparisons was analyzed by Dunnett's T3 method when P value is less than 0.05. The correlation analysis between two variables used Spearman correlation method.The comparisons among the same indicator's data that are from multiple time points were analyzed by Repeated Measures analysis of variance.The comparison between two variables that are from the same indicator but different time points was analyzed by paired samples t test. Statistical significance was accepted at a value of P≤0.05.Results1.General InformationAll the subjects successfully completed the experiment.The gender, age, BMI, WHR, SBP and DBP among groups were matched (P all<0.05)2.The comparisons of the main detection indexes2.1 GlucoseThe comparison of values of the OGTT time points was significantly different (F=176.849, P<0.001), and NGT, IGR, and T2DM groups had the same results (P all<0.001). All groups' lowest values were at Omin and largest values were at 30min,60min, and 90min, respectively. After reaching peak, NGT group decreased rapidly, T2DM group continued at a high level, and the change of IGR group was between aboved two groups. The glucose level of T2DM group was the highest, IGR group followed, and NGT group was the lowest (F=58.052, P<0.001).The comparisons of each point value among groups were all significantly different (P all <0.001).There was interaction effect between time points of OGTT and groups (F=23.132, P<0.001)2.2 InsulinThe comparison of values of the OGTT time points was significantly different (F=77.321, P<0.001), and NGT, IGR, and T2DM groups had the same results (P all<0.001). All groups' lowest values were at 0min and largest values were at 60,90, and 90min, respectively. After reaching peak, NGT group decreased rapidly, and IGR group continued at a high level. T2DM group' peak was the smallest and its curve was low and flat. The insulin level of IGR group was the highest, NGT group followed, and T2DM group was the lowest (F=7.130, P=0.002).The comparisons of each point value among groups were all significantly different (P all≤0.05).There was interaction effect between time points of OGTT and groups (F=7.221, P<0.001)2.3 GlucagonThe comparison of values of the OGTT time points was significantly different (F=20.467, P<0.001), and NGT, IGR, and T2DM groups had the same results (P all<0.05). All groups' lowest values were at 0min and largest values were at 30min. After reaching peak, all groups were decreased, but T2DM group was continuously at a high level during OGTT.The glucagon level of T2DM group was the highest, IGR group followed, and NGT group was the lowest (F=16.921, P<0.001).The comparisons of each point value among groups were all significantly different (P all<0.01).There was no interaction effect between time points of OGTT and groups (F=0.393, P=0.876). 2.4 GLP-1The comparison of values of the OGTT time points was significantly different (F=27.917, P<0.001), and NGT, IGR, and T2DM groups had the same results (P all<0.05). All groups' lowest values were at Omin and highest values were at 60min. After reaching peak, NGT group was decreased rapidly, and IGR group was decreased slowly. T2DM group' peak was the smallest and its curve was low and flat. The GLP-1 level of NGT group was the highest, IGR group followed, and T2DM group was the lowest (F=14.799, P<0.001).The comparisons of 30,60,90, and 120min values among groups were all significantly different (P all<0.05).There was interaction effect between time points of OGTT and groups (F=6.233, P<0.001)3. The comparison of 120min AUCPG-AUC was increased gradually from NGT, IGR to T2DM groups.The comparison among the groups was significantly different (F=72.296, P<0.001). The IGR group had the highest INS-AUC, NGT group followed, and T2DM group had the lowest.The comparison among the groups was significantly different (F=7.389, P=0.002). Gg-AUC was increased gradually from NGT, IGR to T2DM groups.The comparison among the groups was significantly different (F=12.054, P<0.001) GLP-1-AUC was decreased gradually from NGT, IGR to T2DM groups. The comparison among the groups was significantly different (F=13.849, P<0.001)4.The glucose characteristics in subjects with different statuses of glucose metabolism.4.1 HbA1cHbA1c was increased gradually from NGT, IGR to T2DM groups. The comparison among groups was significantly different (F=18.409, P<0.001)4.2 MAGEMAGE was increased gradually from NGT, IGR to T2DM groups.The comparison among groups was significantly different (F=66.181, P<0.001)4.3 The glucose characteristics during OGTTThe glucose peak, added value, and time to peak were all increased gradually from NGT, IGR to T2DM groups. The comparisons among groups were all significantly different (F=46.232,26.376, and 20.730, respectively; P all<0.001)5. The comparison of early phase insulin secretion among groupsΔI30/ΔG30 was decreased gradually from NGT, IGR to T2DM groups. The comparison among groups was significantly different (F=13.272, P<0.001)6. Correlation analysis6.1 Correlations between 120min-Gg-AUC,120min-GLP-1-AUC and MAGE, orΔI30/ΔG30The correlation coefficient r between Gg-AUC andΔI30/ΔG30 was -0.389, and correlation was significantly different (P=0.006); The correlation coefficient r between Gg-AUC and MAGE was 0.519, and correlation was significantly different (P<0.001).The correlation coefficient r between GLP-1-AUC andΔI30/ΔG30 was 0.455, and correlation was significantly different (P=0.001); The correlation coefficient r between GLP-1-AUC and MAGE was -0.578, and correlation was significantly different (P<0.001).6.2 Correlations between 120min-Gg-AUC,120min-GLP-1-AUC,ΔI30ΔG30, MAGE, and glucose characteristics indexes during OGTTThe correlation coefficient r between Gg-AUC and glucose peak, added value, time to peak during OGTT were 0.551,0.480, and 0.333, respectively. Correlations were all significantly different (P all<0.05).The correlation coefficient r between GLP-1-AUC and glucose peak, added value, time to peak during OGTT were -0.538,-0.564, and -0.442, respective -ly.Correlations were all significantly different (P all<0.01)The correlation coefficient r betweenΔI30/ΔG30 and glucose peak, added value, time to peak during OGTT were -0.741,-0.678, and -0.552, respectively.Correlations were all significantly different (P all<0.001)The correlation coefficient r between MAGE and glucose peak, added value, time to peak during OGTT were 0.831,0.816, and 0.644, respectively.Correlations were all significantly different (P all<0.001)7. The dynamic changes of glucose, insulin, glucagon, and GLP-1 among groups.7.1 The NGT groupThe glucose peaked at 30min after glucose load(r=-12.726, P<0.001 vs.0min), and then decreased rapidly (t=6.737, P<0.001 vs.120min).The changes of insulin and GLP-1 were consistent, and their peaks were at 60min, about 12.5, and 2.9 times more than Omin value (t values were -8.690 and -0.5667, respectively, P all<0.001 vs.Omin), and then decreased rapidly (t values were 4.383 and 5.674, respectively, P all<0.01 vs.120min).The change of glucagon was consistent with that of glucose, and glucagon peaked at 30min (t=-5.027, P<0.001 vs.0min).With secretion of insulin and GLP-1 increased, glucagon was significantly decreased (t=3.959, P=0.001 vs.120min).7.2 The IGR groupGlucose peaked at 60min after glucose load (t=-24.142, P<0.001 vs.0min). The response of insulin and GLP-1 to glucose load were relatively slow.The insulin peak delayed at 90min (t=-9.044, P<0.001 vs.0min), with staying at a high level after reaching peak.GLP-1 peaked at 60min (t=-2.574, P=0.024 vs.0min), and the curve of GLP-1 was relatively flat.Glucagon peaked at 30min (t=-5.245, P<0.001 vs.Omin), and decreased significantly after reaching peak (t=4.663, P=0.001 vs.120min). 7.3 The T2DM groupGlucose peaked at 90min after glucose load (t=-14.087, P<0.001 vs.Omin). The curves of insulin and GLP-1 were flat.Insulin peaked at 90min (t=-7.430, P<0.001 vs.Omin) and GLP-1 peaked at 60min (t=-4.584, P<0.001 vs.Omin), and both peak values were apparently low.The glucagon peaked at 30min (t=-2.976,P=0.008 vs.Omin), but decreased insignificantly after reaching peak (t=2.091, P=0.051 vs.120min).8.CGMS accuracy evaluationMAD of NGT, IGR and T2DM group were (10.37±3.10)%, (9.82±3.39) %, and (9.25±3.26)%, respectively.There was no significant difference among groups (F=0.515, P=0.601).The number of paired CGMS values and venous blood glucose values measured during the whole OGTT, stable, rapid rising, and falling glucose period were 240,48,91, and 101, and the correlation coefficient r were 0.932,0.811,0.913, and 0.919, respectively.All correlations were significantly different (P all<0.001).Application of EGA showed that there were 97.9%,97.9%, 98.9%, and 97.0% of results in A and B zones in the whole OGTT, stable, rapid rising,and falling glucose period, respectively.Conclusion1. The glucose peak, added value, and time to peak during OGTT are all gradually increased from NGT, IGR to T2DM.2. With early phase insulin secretion decreased or glucose excursion elevated, the glucose peak, added value, and time to peak during OGTT are all increased.3. With secretion of glucagon increased, or GLP-1 decreased after glucose load, early phase insulin secretion is decreased, glucose excursion is elevated, and the glucose peak, added value, time to peak during OGTT are all increased.4. The changes of insulin and GLP-1 are consistent only in NGT during OGTT. 5. CGMS has an acceptable accuracy during OGTT of which glucose changes rapidly. |
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