Diabetes Care Volume 37, September 2014 2451

Lalitha Gudipaty,1 Nora K. Rosenfeld,1 Effect of , Sitagliptin, or Carissa S. Fuller,1 Robert Gallop,2 CARE/EDUCATION/NUTRITION/PSYCHOSOCIAL CLIN on b-Cell Secretory Mark H. Schutta,1 and Michael R. Rickels1 Capacity in Early Type 2 Diabetes Care 2014;37:2451–2458 | DOI: 10.2337/dc14-0398

OBJECTIVE Agents that augment GLP-1 effects enhance glucose-dependent b-cell pro- duction and secretion and thus are hoped to prevent progressive impairment in insulin secretion characteristic of (T2D). The purpose of this study was to evaluate GLP-1 effects on b-cell secretory capacity, an in vivo measure of functional b-cell mass, early in the course of T2D.

RESEARCH DESIGN AND METHODS We conducted a randomized controlled trial in 40 subjects with early T2D who received the GLP-1 analog exenatide (n = 14), the dipeptidyl peptidase IV inhibitor sitagliptin (n = 12), or the glimepiride (n = 14) as an active comparator insulin secretagogue for 6 months. Acute insulin responses to arginine (AIRarg) were measured at baseline and after 6 months of treatment with 5 days of drug washout under fasting, 230 mg/dL (glucose potentiation of arginine-induced in- sulin release [AIRpot]), and 340 mg/dL (maximum arginine-induced insulin release [AIRmax]) hyperglycemic clamp conditions, in which AIRmax provides the b-cell secretory capacity.

RESULTS

The change in AIRpot was significantly greater with glimepiride versus exenatide treatment (P < 0.05), and a similar trend was notable for the change in AIRmax (P = 0.1). Within each group, the primary outcome measure, AIRmax,wasun- changed after 6 months of treatment with exenatide or sitagliptin compared with 1 P < a Division of Endocrinology, Diabetes, and Me- baseline but was increased with glimepiride ( 0.05). -Cell secretion tabolism, Department of Medicine, Perelman (AGRmin) was also increased with glimepiride treatment (P < 0.05), and the change School of Medicine at the University of Pennsyl- vania, Philadelphia, PA in AGRmin trended higher with glimepiride than with exenatide (P = 0.06). 2Department of Mathematics, West Chester Uni- CONCLUSIONS versity of Pennsylvania, West Chester, PA After 6 months of treatment, exenatide or sitagliptin had no significant effect on Corresponding author: Michael R. Rickels, rickels@ mail.med.upenn.edu. functional b-cell mass as measured by b-cell secretory capacity, whereas glime- b a Received 12 February 2014 and accepted 22 May piride appeared to enhance -and -cell secretion. 2014. reg. no. NCT00775684, clinicaltrials The main pathophysiologic abnormalities in type 2 diabetes (T2D) are impaired .gov. tissue sensitivity to insulin action (i.e., insulin resistance) and impaired b-cell insulin This article contains Supplementary Data online secretion (1). Autopsy studies have observed a relative b-cell mass reduction of 40% at http://care.diabetesjournals.org/lookup/ suppl/doi:10.2337/dc14-0398/-/DC1. from normal by the time impaired fasting glucose develops ($110 mg/dL) and . b © 2014 by the American Diabetes Association. 60% reduction with overt T2D (2). This decline in -cell mass has been associated Readers may use this article as long as the work with increased b-cell apoptosis (2), and an emerging role of defective autophagy- is properly cited, the use is educational and not associated cell death is linked with the onset of b-cell dysfunction (3,4). Functional for profit, and the work is not altered. 2452 Therapy in Early Type 2 Diabetes Diabetes Care Volume 37, September 2014

b-cell mass is best estimated in vivo as either drug on functional b-cell mass. weeks (6 weeks for thiazolinediones) the b-cell secretory capacity derived These conflicting GLP-1 effects in ro- and of stable body weight (65%) for at from glucose potentiation of arginine- dents versus human T2D may be due least 2 weeks. Exclusion criteria in- induced insulin secretion (5). Consistent to the lengthy duration of the washout cluded any prior exposure to GLP-1 ana- with the autopsy data, metabolic studies period, during which glycemic control logues or DPP4 inhibitors and active have reported a relative b-cell secretory worsened in both clinical studies such cardiovascular, , or disease capacity reduction of .50% from normal that glucotoxicity may have obviated and are provided in full detail under as the fasting glucose increases over 110 any previous improvement in b-cell se- ClinicalTrials.gov identification number mg/dL (1,5). The preservation of func- cretory capacity (11–13). NCT00775684. The study protocol was tional b-cell mass in T2D remains a major The purpose of this investigation was approved by the University of Pennsyl- focus of research in hopes of stabilizing or to address if increasing GLP-1 effects vania Institutional Review Board, and all reversing disease progression (6). early in the course of T2D would pre- subjects provided written informed con- Agents that enhance GLP-1 action are serve or increase functional b-cell mass sent. One hundred seventy subjects un- purported to hold promise for the pre- as measured by b-cell secretory capacity derwent the screening process, out of servation of b-cell mass in T2D. GLP-1 is derived from the glucose-potentiated which 50 subjects were enrolled (Sup- an incretin hormone secreted by L cells arginine (GPA) test. In this study, we plementary Fig. 1). Randomization was of the intestine in response to nutrient present the results of a randomized con- performed with stratification designed ingestion, enhances insulin production trolled trial comparing the effects of ex- to balance sex and tiers of age (18–44 and secretion, and inhibits a-cell gluca- enatide or sitagliptin with glimepiride as and 45–70 years), fasting glucose level gon secretion in a glucose-dependent an active comparator insulin secreto- (110–126 and 127–159 mg/dL), and BMI manner (7). The biologically active gogue on b-cell secretory capacity be- (,35 and 35–44 kg/m2) among the GLP-17–36 amide is rapidly inactivated fore and after 6 months of treatment 5 three groups. by the ubiquitous protease dipeptidyl days off drug in subjects with impaired peptidase IV (DPP4). Raising GLP-1 to fasting glucose or early T2D (fasting glu- Study Design supraphysiologic levels improves b-cell cose $110 but ,160 mg/dL). The 5-day This study was a randomized controlled sensitivity to glucose in T2D (8). Current washout period was designed to elimi- trial of open-label exenatide or sitaglip- strategies to enhance GLP-1 effects in nate any acute effects of the study drugs tin versus an active comparator insulin T2D include the use of injectable GLP-1 on b-cell sensitivity to glucose while secretagogue, glimepiride. The sulfonyl- analogues that resist inactivation by avoiding any deterioration in glycemic urea glimepiride was chosen rather DPP4 and oral inhibitors of DPP4 that control to ensure that any trophic effects than a placebo to ensure adequate gly- effectively increase endogenous GLP-1 of the drugs would not be negated by the cemic control was maintained in the levels. In rodent models, GLP-1 stimulates development of glucotoxicity. GLP-1 comparator group while preventing b-cell proliferation and exerts antiapo- analogues and DPP4 inhibitors have confounding of b-cell effects by use of ptotic effects, which, together with in- been shown to increase both insulin pro- other agents that affect insulin sensitiv- creased insulin production, is expected duction and secretion (14–16) and so ity. bind to their receptor to augment functional b-cell mass in were expected to have a positive effect that inhibits the KATP on the b-cell mem- vivo (9,10). Whether GLP-1 can increase on functional b-cell mass. A sulfonylurea brane, leading to depolarization trigger- functional b-cell mass in human diabetes was selected as an active comparator in- ing insulin release (17–19). Glimepiride, in vivo remains to be elucidated. sulin secretogogue rather than a placebo in particular, was selected, as it has been Current investigations suggest the to provide an agent that would control shown to carry the least risk of hypogly- acute improvement in b-cell sensitivity glycemia by increasing insulin secretion cemia among the sulfonylureas (20). Af- to glucose observed with enhancing without affecting the functional b-cell ter completing a baseline oral glucose GLP-1 effects in human T2D (8) may mass. Since sulfonylureas induce insulin tolerance test (OGTT) and GPA test on not extend to long-term effects on func- secretion without affecting production, separate days, subjects were random- tional b-cell mass. Bunck et al. (11,12) they have been theorized to deplete ized to receive exenatide 5 mg subcuta- demonstrated that 1-year treatment insulin stores (17). We, therefore, hy- neous twice daily, sitagliptin 100 mg, or with exenatide in T2D significantly im- pothesized that exenatide and/or sita- glimepiride 0.5 mg orally each morning. proved b-cell secretory capacity while gliptin would increase b-cell secretory All subjects received a study glucometer on the drug; however, this benefitwas capacity compared with a decrease and test strips (OneTouch Ultra; LifeScan, not sustained 1 month after discontinu- with glimepiride. Milpitas, CA) to monitor glucose each ation. Similarly, there was a significant morning and evening to detect and re- increase in b-cell secretory capacity in RESEARCH DESIGN AND METHODS port any (blood glucose drug-naive T2D subjects treated with Subjects ,70 mg/dL). Exenatide was increased the DPP4 inhibitor for 1 Subjects were males and females age after 1 month per labeling to 10 mg year that again was not maintained 18–70 years with impaired fasting twice daily. All subjects remained on after a 3-month washout period (13). plasma glucose or early T2D as defined this dose until completion of the study These studies indicate an acute effect by a plasma glucose concentration be- except for two subjects who experi- of GLP-1 analogues or DPP4 inhibitors tween 110 and 159 mg/dL following a enced side effects but tolerated 5 or to increase b-cell secretion but do not .12-h overnight fast performed off 10 mg once daily in each case. Sitagliptin demonstrate a modifying effect of any antidiabetogenic agent for $2 remained at 100 mg for the duration of care.diabetesjournals.org Gudipaty and Associates 2453

study and was well tolerated by all sub- achieve a plasma glucose level of 230 performed during the 230 mg/dL glucose jects. Glimepiride was increased by 0.5– mg/dL. Blood samples were taken every clamp enables determination of glucose 1.0-mg increments in the morning or 5 min and measured at the bedside by potentiation of arginine-induced insulin evening at weekly intervals (maximum an automated glucose analyzer (YSI release (AIRpot). The AIRarg performed total daily dose 4.0 mg, divided) to 2300; Yellow Springs Instruments, Yel- during the 340 mg/dL glucose clamp al- achieve an average fasting glucose level low Springs, OH) and used to adjust lows for determination of the b-cell se- ,110 mg/dL while avoiding any hypogly- the infusion rate to achieve the desired cretory capacity (AIRmax) since the AIRarg cemia. No clinically significant hypoglyce- level. After 45-min of the glucose infu- is maximal at plasma glucose concentra- mia was detected with any treatment sion, the AST was performed again. It tions .315 mg/dL (26,27). Between ;60 arm. Augmentation of meal-related in- has been demonstrated that the first and 250 mg/dL, the magnitude of AIRarg creases in levels of active GLP-17–36 amide administration of arginine has no effect is a linear function of the plasma glu- in the sitagliptin group was documented on the subsequent response to arginine cose level, so the difference in AIRarg by repeating the OGTT at the 5-month using this protocol (23). Then, after a 2-h at fasting and 230 mg/dL glucose levels visit. Following 6 months of therapy, all period without glucose infusion, a hy- divided by the difference in plasma glu- drugs were held for 5–7days(.10 half- perglycemic clamp was performed to cose (DAIRarg/DPG) gives the glucose- lives; see Supplementary Data) prior to achieve a plasma glucose level of 340 potentiation slope (GPS) (8,24–26). Using completing a final GPA test. The washout mg/dL. Forty-five minutes after initia- the y-intercept (b) from the line created by period was used to obviate any acute ef- tion of the glucose infusion, another these two points, the plasma glucose level fect of exenatide, sitagliptin, or glimepir- AST was performed. at which half-maximal insulin secretion is ide on b-cell insulin or a-cell glucagon achieved (PG50) is derived from solving the secretion during testing. Biochemical Analysis equation 1/2 (AIR )=(GPSz PG )+ Samples were collected on ice into tubes max 50 b, and provides a measure of b-cell containing EDTA and protease inhibitor Subject Preparation for Metabolic sensitivity to glucose (8,24–26). Insulin cocktail (and for OGTT samples, DPP4 Testing sensitivity (M/I) was determined by di- inhibitor; Sigma-Aldrich, St. Louis, MO), All subjects arrived at the University of viding the mean glucose infusion rate re- centrifuged at 48C, separated, and fro- Pennsylvania Clinical and Translational quired during the 230 mg/dL glucose zen at 2808C for subsequent analysis. Research Center on the morning of test- clamp (M) by the mean prestimulus in- Plasma glucose was determined in dupli- ing having fasted overnight after 2000 h sulin level (I) between 40 and 45 min of cate by an automated glucose analyzer for 12 h. By 0700 h, one catheter was the glucose infusion (28). The proinsulin- (YSI 2300; Yellow Springs Instruments). placed in an antecubital vein for infu- to-insulin (PI/I) ratio was calculated as Plasma insulin, proinsulin, and gluca- sions, and one catheter was placed in a the molar concentration of proinsulin di- gonweremeasuredinduplicateby contralateral hand or forearm vein, ret- vided by the molar concentration of in- double-antibody radioimmunoassays rograde when possible, for blood sam- sulin 3 100. Estimation of the PI/I ratio and GLP-1 – amide by ELISA (Millipore, pling, with the hand or arm warmed by a 7 36 within the secretory granules of the Billerica, MA). Each immunoassay for all heating pad to promote arterialization b-cell is most reliable after acute stimu- time points in a given subject was con- of venous blood (21). Patency of the lation of release (29); therefore, we ex- ducted simultaneously, with representa- catheters was maintained with slow in- amined the proinsulin secretory ratio in tive subjects from each group included fusions of 0.9% saline. At least 20 min of response to each injection of arginine with each assay run. acclimatization to catheter placement from the respective acute PI/I responses transpired prior to testing. Calculations to arginine by dividing the acute proin- Plasma glucose, insulin, and GLP-1 re- sulin responses by the acute insulin re- OGTT After baseline blood sampling at 25and sponses during the OGTT were evalu- sponses. The acute glucagon response to 21 min, 75 g of anhydrous glucose in ated by the incremental area under the arginine (AGRarg), glucose inhibition of solution was ingested over a 5-min pe- curve (AUC) calculated by the trapezoi- arginine-induced glucagon release riod. Blood samples were collected at dal rule with the mean of the baseline (AGRinh), and minimum arginine-induced 15, 30, 60, 90, and 120 min postinges- values subtracted using the computer glucagon secretion (AGRmin) were calcu- tion. At the 5-month visit, morning software Origin (Northampton, MA). lated similarly as the mean of the post- study medication was held until the The GPA test enables characterization arginine values minus the mean of the completion of testing. of glucose-dependent insulin secretion prestimulus values under the fasting, from the glucose dose-response curve 230 mg/dL, and 340 mg/dL glucose GPA Test for acute insulin response to arginine clamp conditions (26). After baseline blood sampling at 25and (AIRarg) performed at fasting, 230 mg/dL, 21 min, 5 g arginine hydrochloride (10% and 340 mg/dL glucose levels. The AST Statistical Analysis solution) was injected over a 1-min pe- measures first-phase insulin release to a The primary outcome was to determine riod. Blood samples were collected at 2, maximally stimulating dose of the non- if increasing GLP-1 effects by exenatide 3, 4, and 5 min postinjection. After this glucose secretagogue arginine as the or sitagliptin preserved or increased baseline arginine stimulation test AIRarg.TheAIRarg was determined as functional b-cell mass measured as (AST), a hyperglycemic clamp technique themeanofthe2-,3-,4-,and5-min b-cell secretory capacity compared (22) utilizing a variable rate of a 20% insulin levels minus the mean of the with glimepiride in subjects with early glucose solution was performed to baseline values (8,24,25). The AIRarg T2D. During year 4 of the study, a 2454 Incretin Therapy in Early Type 2 Diabetes Diabetes Care Volume 37, September 2014

prespecified interim analysis was in the glimepiride group completed the (DAUC 284 6 70 vs. 31 6 24 pmol z performed after 30 subjects had com- study for a total of 40 subjects used in min/L; P , 0.01; Supplementary Fig. 2, pleted the study (10 subjects in each the analysis. Reasons for discontinua- bottom). study group). This interim analysis dem- tion included noncompliance with study onstrated that the change in b-cell se- medication and/or procedures and ad- Effects on Insulin, Proinsulin, and cretory capacity (AIRmax) was less in verse events (Supplementary Fig. 1). Glucagon Responses During the GPA exenatide (P , 0.05) and not different Baseline demographic measures were Test in sitagliptin compared with the glime- similar across all three groups (Table 1). There were no significant differences in piride group, an effect driven by an in- At 6 months, change in weight or BMI the change in AIRarg after 6 months of crease in b-cell secretory capacity in the were not significantly different across exenatide or sitagliptin treatment com- glimepiride group (P , 0.05). These re- all three groups. Within the exenatide pared with glimepiride (Supplementary sults effectively refuted our initial hy- group, subjects had a decrease in Fig. 3 and Table 2), whereas the change pothesis such that no further subjects weight over the 6-month course of in AIRpot was significantly lower in the were enrolled, although those already study (D22.6 6 0.8; P , 0.05; Fig. 1) exenatide group, but not in the sitaglip- active in the study completed the clini- that was also reflected by a decrease in tin group, when compared with the gli- cal trial to yield the final number of sub- BMI (P , 0.05; Table 1). Fasting plasma mepiride group (P , 0.05 for exenatide jects reported. Subjects who did not glucose, insulin, and glucagon were sim- vs. glimepiride; Table 2), and a similar complete the final GPA test were not ilar at baseline and 6 months in all three trend was also evident for the change included in the primary analysis. groups (Table 1). The change in average in AIRmax (P = 0.1 for exenatide vs. gli- All data are expressed as means 6 SE. capillary blood glucose over time was mepiride; Table 2). In fact, within each This was a two-factor experimental de- significantly different across all three group, b-cell secretory capacity (AIRmax) sign with one repeated measure (base- groups (P , 0.01; Fig. 1). The glimepir- increased only in the glimepiride group line and final) and one nonrepeated ide group had a greater reduction in at 6 months compared with baseline measure (exenatide, sitagliptin, and gli- capillary blood glucose than the sita- (P , 0.05; Table 2). b-Cell sensitivity to mepiride). To determine if exenatide or gliptin group (P , 0.01) and the exena- glucose (PG50) was not different at base- sitagliptin induced significant changes tide group by trend (P , 0.1). The lower line and remained unchanged following from baseline, the change for each mea- glucose levels were achieved by 3 any treatment (Table 2). The glucose in- sure (Δ = final 2 baseline) for each months when the average dose of gli- fusion rates (M), second-phase insulin group was compared with the change mepiride was 3 mg. Change in HbA1c levels (I), and the resulting estimate of in the glimepiride group using inde- over time was different by trend across insulin sensitivity (M/I) were not differ- pendent Student t tests or the Mann- all three groups (P = 0.07). The change in entatbaselineandafter6months Whitney U test for nonparametric HbA1c in the exenatide group was not across all three groups (Table 2). data. One-way ANOVA was used to com- different from that in the glimepiride Fasting proinsulin and APRs were not pare baseline measures across all three group, but the change in HbA1c in the different across the groups at baseline groups. Repeated-measures ANOVA was sitagliptingroupwaslessfromthatin or in response to treatment. PI/I ratios used to compare changes in weight, cap- the glimepiride group (P , 0.05; Fig. 1). and proinsulin secretory ratios were un- illary blood glucose, and HbA1c over time Within group, HbA1c trended lower changed from baseline to 6 months with between groups. When a statistical trend within the exenatide group (P =0.09) no significant differences between the (P , 0.1) was evident with at least one of at the end of 6 months, whereas it de- exenatide or sitagliptin and glimepiride the between-group differences with gli- creased significantly with glimepiride groups (data not shown). mepiride, within-group changes from (P , 0.05). Lipid profiles were similar There were no significant differences baseline to final measures were com- across all three groups at baseline, but inthechangeinAGRarg and AGRinh with pared with dependent Student t tests at 6 months, there was an increase exenatide or sitagliptin treatment after or the Wilcoxon matched-pairs test as in HDL cholesterol with exenatide, but 6 months compared with glimepiride; appropriate. All comparisons were not sitagliptin treatment, that was however, there was a statistical trend conducted using Statistica software significantly greater than that seen when comparing the change in AGRmin (StatSoft, Inc., Tulsa, OK). Significance with glimepiride treatment (P , 0.05; with exenatide, but not sitagliptin, to was considered at P , 0.05 (two-tailed). Table 1). glimepiride (P = 0.06 for exenatide vs. glimepiride; Table 2). Within each group, RESULTS Effects on Glucose, Insulin, and glucagon secretion was increased only in Subject Characteristics and Endogenous GLP-1 During the OGTT the glimepiride group at 6 months com- , Disposition At 5 months, the changes in plasma glu- pared with baseline for AGRmin (P Of the 50 subjects enrolled, 47 subjects cose (Supplementary Fig. 2, top)andin- 0.05; Table 2). underwent randomization and com- sulin (Supplementary Fig. 2, middle) pleted baseline GPA testing (Supple- responses were not significantly differ- CONCLUSIONS mentary Fig. 1) with 17 subjects ent with either exenatide or sitagliptin This study evaluated functional b-cell randomized to exenatide, 13 to sitaglip- when compared with glimepiride treat- mass as determined by the b-cell secre- tin, and 17 to glimepiride. There were 7 ment. The change in endogenous GLP-1 tory capacity in subjects with early T2D dropouts, such that 14 subjects in the response was increased with sitagliptin treated with exenatide, a GLP-1 ana- exenatide, 12 in the sitagliptin, and 14 compared with glimepiride treatment logue, or sitagliptin, a DPP4 inhibitor, care.diabetesjournals.org Gudipaty and Associates 2455

Table 1—Subject demographics at baseline and final (after 6 months of therapy) visits Exenatide (n = 14) Sitagliptin (n = 12) Glimepiride (n =14) Baseline 6 monthsa D Baseline 6 monthsa D Baseline 6 monthsa D Age (years) 57 6 2 dd57 6 3 dd52 6 3 dd Sex (% female) 36 dd33 dd43 dd Race (% African American) 50 dd42 dd64 dd Duration of T2D (years) 3.3 6 0.6 dd5.3 6 1.7 dd3.4 6 0.9 dd BMI (kg/m2)336 2326 2* 21 6 0336 1336 106 0316 2316 206 1 b HbA1c,% (mmol/mol) 6.4 6 0.1 6.2 6 0.1 20.2 6 0.1 6.5 6 0.1 6.5 6 0.2 20.01 6 0.1 6.7 6 0.1 6.2 6 0.2 20.5 6 0.2 (46) (44) (48) (48) (50) (44)* Fasting glucose (mg/dL) 129 6 31286 5 22 6 51316 41326 816 91346 41266 5 28 6 6 Fasting insulin (mU/mL) 24 6 6216 3 23 6 4176 2146 2 22.6 6 2176 2156 1.3 22 6 2 Fasting glucagon (pg/mL) 40 6 4426 826 6506 6476 7 23 6 6516 4516 5 20.2 6 4 Total cholesterol (mg/dL) 168 6 71576 6 210 6 71596 12 162 6 10 4 6 61726 10 168 6 11 24 6 7 Triglycerides (mg/dL) 110 6 15 85 6 9 225 6 14 104 6 17 118 6 20 11 6 10 107 6 18 93 6 11 214 6 16 LDL cholesterol (mg/dL) 104 6 5926 6 212 6 6946 10 101 6 956 61106 71116 11 2 6 7 HDL cholesterol (mg/dL) 41 6 2486 3* 7 6 2† 44 6 5386 2 23 6 1416 3386 2 23 6 2 Data are means 6 SE. D, change from baseline to 6 months with each value. aFinal visits after 6 months of therapy were conducted following a 5- to 7-day drug washout. bTo convert to mmol/mol, multiply by 10.93 and subtract 23.50. *P , 0.05 when comparing values within each group. †P , 0.05 when comparing D between the exenatide and glimepiride groups. compared against an active comparator group. In the exenatide-treated sub- glimepiride (4–8 mg) titrated rapidly sulfonylurea, glimepiride. Our results jects, there was also an increase in over a 1–4-week period (34). Similar to demonstrate that in early T2D, 6-month plasma HDL cholesterol that has previ- our finding of an increase in b-cell secre- treatment with a GLP-1 analogue or ously been demonstrated (30). Sitaglip- tory capacity evident after 6 months, DPP4 inhibitor does not increase func- tin treatment was effective in increasing Karunakaran et al. (35) demonstrate a tional b-cell mass relative to treatment the endogenous GLP-1 response 2.3- significant improvement in b-cell func- with a sulfonylurea. While these data fold to oral glucose in our study that is tion with glicazide treatment for 1 year were contrary to our hypothesis, they consistent with previous reports (31). In while demonstrating lower fasting are consistent with previous reports contrast to previous studies, there was plasma glucose and HbA1c without ad- demonstrating no sustained effects of no significant effect of exenatide or si- versely effecting weight. Interpretation GLP-1 on b-cell secretory capacity (11– tagliptin on HbA1c. This is likely attribut- of our study’s results with glimepiride 13). Unlike previous studies in which the able to the early T2D in our subjects who must be made cautiously, however, as drug washout period was $1month, were at the threshold of overt diabetes glimepiride was included as an active during which any potential beneficial ef- (average HbA1c of 6.5% [48 mmol/mol]), comparator without a placebo group fects could be reversed by documented while most outcomes studies have in- for comparison. worsening glycemic control, our results cluded subjects with more advanced While the increase in b-cell secretory were obtained 5 days after discontinua- T2D (average HbA1c $8.5% [69 mmol/ capacity after 6 months of treatment tion of the study medication to ensure mol]) (32,33). Our study is limited by its with glimepiride observed in this study effective drug washout while avoiding small sample size and short duration requires confirmation and further as- development of hyperglycemia. Indeed, and thus does not allow us to determine sessment of durability, there are a few fasting plasma glucose was controlled whether prolonged treatment with exe- speculative mechanisms to explain such within each group at the 6-month visit natide or sitagliptin early in the course an effect. Compared with the exenatide compared with baseline. Thus, these are of T2D may prevent deterioration in gly- and sitagliptin groups, the glimepiride- the first data to demonstrate a lack of cemic control, perhaps through mecha- treated subjects experienced a reduc- improvement in b-cell secretory capac- nisms other than affecting the b-cell tion in capillary glucose. This improved ity with a GLP-1 analogue or a DPP4 in- secretory capacity. glycemic control may have positively af- hibitor off drug and in the absence of Six months of treatment with glime- fected the b-cell secretory capacity. An- overt hyperglycemia, while demon- piride was effective in decreasing capil- other possibility may be a more specific strating a remarkable increase in b-cell lary blood glucose and lowering HbA1c effect of sulfonylureas against autophagy- secretory capacity with sulfonylurea without producing hypoglycemic epi- associated cell death. Autophagy is a treatment. sodes or weight gain with careful dose self-digestive mechanism that regulates Exenatide-treated subjects experi- titration. Postmarketing reports and clin- protein turnover, and current evidence enced a decrease in weight and conse- ical trials have demonstrated significant links impaired autophagy with accumu- quently BMI, although this was not increases in weight with glimepiride lation of autophagic vacuoles in the statistically different from a neutral treatment but these observations were b-cells of T2D when compared with non- weight effect seen in the glimepiride notably with higher concentrations of diabetic islets (4). Altered autophagic 2456 Incretin Therapy in Early Type 2 Diabetes Diabetes Care Volume 37, September 2014

Figure 1—Subject characteristics over the 6-month study period. Means 6 SE of weight, fasting capillary glucose as determined by glucometer readings, and HbA1c in each group. Also shown for the glimepiride group is the average dose at each monthly visit. Changes in weight over time were not significantly different across the three groups [F(12, 222) = 1.1013; P = 0.4]. Average capillary glucose was significantly different [F(12, 204) = 2.53; P , 0.01] when comparing across all three groups. HbA1c was different by trend [F(4, 74) = 2.28; P , 0.1] when comparing across all three groups. *P , 0.05 when comparing D from baseline within each group at each time point.

mechanisms are evident when there is a on a-cells remains unclear at present due of the a-cell, and under normal, nondis- mismatch between insulin production to conflicting results that may be attrib- eased conditions, glucose, insulin, and/or and secretion, as may occur in T2D, in uted to variation in model systemsdi.e., somatostatin via paracrine action can in- which there is impaired b-cell sensitivity with intact islets in which paracrine sig- hibit glucagon release. However, in T2D, to glucose (36). As sulfonylureas such as naling remains intact versus diseased there may be an uncoupling phenome- glimepiride have no effect on insulin pro- islets in which paracrine signaling is dis- non in which glucagon secretion can duction but stimulate insulin secretion rupted versus isolated a-cells (37,38). become independent of these paracrine (36), these agents may correct a syn- For example, Cheng-Xue et al. (37) inhibitory signals, and the stimulatory thetic mismatch and protect against demonstrated a glucagontrophic effect effect of sulfonylureas at the a-cells pre- autophagy-associated cell death. Wheth- of when paracrine signaling dominates such that 6-month treatment er such effects may be associated with by somatostatin was disrupted. These may be glucagontrophic, as reported in increases in functional b-cell mass as authors postulate that glucagon secretion this study. Whether long-term benefits measured by b-cell secretory capacity is controlled by two mechanisms, one of sulfonylureas that may enhance func- warrants further study. that is direct from the closure of KATP tional b-cell mass outweigh any adverse Curiously, a-cell glucagon secretion channels and one that is indirect via con- consequence of the increased glucagon was increased after 6 months of exposure trol from paracrine signaling (37). Thus, secretion on glycemic control remains to glimepiride. The effect of sulfonylureas glimepiride may induce depolarization to be determined. care.diabetesjournals.org Gudipaty and Associates 2457

Table 2—Measures of b-cell secretory capacity, b-cell sensitivity to glucose, insulin sensitivity, and glucagon secretion derived from the GPA test Exenatide (n = 14) Sitagliptin (n = 12) Glimepiride (n =14) Baseline 6 monthsa D Baseline 6 monthsa D Baseline 6 monthsa D

AIRarg (mU/mL) 52 6 14 52 6 11 20.2 6 9356 4346 6 22 6 7446 6426 4 22 6 7

AIRpot (mU/mL) 138 6 31 108 6 21 230 6 20† 83 6 12 80 6 15 22 6 8976 16 119 6 19 22 6 12

AIRmax (mU/mL) 214 6 60 188 6 34 225 6 50‡ 149 6 20 158 6 30 9 6 21 133 6 19 202 6 35* 69 6 33

PG50 (mg/dL) 175 6 13 190 6 14 25 6 20 226 6 12 209 6 16 25 6 24 168 6 17 182 6 10 10 6 26 M(mgz kg21 z min21)5.56 0.3 5.8 6 0.4 0.27 6 0.4 5.4 6 0.4 5.3 6 0.4 20.1 6 0.4 5.5 6 0.4 5.8 6 0.4 0.35 6 0.4 I(mU/mL) 41 6 13 39 6 9 22 6 9226 2236 416 3286 7266 2 22 6 5 M/I (mg z kg21 z min21/mU/mL) 0.3 6 0.1 0.3 6 0.1 20.01 6 0.0 0.3 6 0.0 0.3 6 0.1 0.04 6 0.1 0.3 6 0.1 0.3 6 0.1 20.04 6 0.0

AGRarg (pg/mL) 60 6 12 63 6 836 17 77 6 13 60 6 11 217 6 6406 9626 8226 17

AGRinh (pg/mL) 63 6 12 58 6 13 23 6 6646 13 55 6 16 210 6 10 46 6 7596 7116 7

AGRmin (pg/mL) 51 6 12 52 6 12 2 6 5‡ 55 6 8596 19 4 6 21 37 6 6596 8* 21 6 8 Data are means 6 SE. D, change from baseline to 6 months with each value. aFinal visits after 6 months of therapy were conducted following a 5- to 7-day drug washout. *P , 0.05 when comparing values within each group. †P , 0.05 when comparing D between the exenatide and glimepiride groups. ‡P # 0.1 (statistical trend) when comparing D between exenatide and glimepiride groups.

In conclusion, the implication of the Human Metabolism Resource of the University of 6. U.K. Prospective Diabetes Study Group. U.K. current study is that a 6-month treat- Pennsylvania Institute for Diabetes, Obesity and Prospective Diabetes Study 16. Overview of 6 ’ ment with the GLP-1 analogue exena- Metabolism. The study drugs used were pur- years therapy of type II diabetes: a progressive chased commercially and not provided by any disease. Diabetes 1995;44:1249–1258 tide or DPP4 inhibitor sitagliptin does company. 7. Nauck MA, Homberger E, Siegel EG, et al. not increase b-cell secretory capacity Duality of Interest. No potential conflicts of Incretin effects of increasing glucose loads in human T2D as purported in rodent interest relevant to this article were reported. in man calculated from venous insulin and models. Furthermore, our study indi- Author Contributions. L.G. participated in the C-peptide responses. J Clin Endocrinol Metab conduct of the study, analyzed the data, and cates that the sulfonylurea glimepiride 1986;63:492–498 wrote the manuscript. N.K.R. coordinated the 8. Ahren´ B, Larsson H, Holst JJ. Effects of may be effective in at least short-term study and managed data acquisition and entry. glucagon-like peptide-1 on islet function and improvement in b-cell secretory capac- C.S.F. participated in the conduct of the study. insulin sensitivity in noninsulin-dependent dia- ity associated with improved glycemic R.G. assisted with the study design, randomiza- betes mellitus. J Clin Endocrinol Metab 1997; control early in the course of T2D. Clini- tion procedures, and statistical analysis. M.H.S. 82:473–478 fi assisted with the study design, in particular with 9. Mu J, Petrov A, Eiermann GJ, et al. Inhibition cally, these ndings support T2D treat- drug selection and dosing. M.R.R. served as the ment algorithms that place sulfonylureas of DPP-4 with sitagliptin improves glycemic con- principal investigator. All authors reviewed, ed- trol and restores islet cell mass and function in a ahead of incretin-based approaches (39), ited, and approved the submitted manuscript. rodent model of type 2 diabetes. Eur J Pharma- M.R.R. is the guarantor of this work and, as with special consideration for third- col 2009;623:148–154 such, had full access to all the data in the study generation sulfonylureas such as glimepir- 10. Xu G, Stoffers DA, Habener JF, Bonner-Weir and takes responsibility for the integrity of the S. Exendin-4 stimulates both beta-cell replica- ide, in which careful dose titration as data and the accuracy of the data analysis. tion and neogenesis, resulting in increased conducted in this study may avoid weight Prior Presentation. 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