Although GLP-1 has been suggested as a major factor for the marked improvement of glucose tolerance commonly seen after sleeve gastrectomy (SG), several observations challenge this hypothesis. To better understand the role of GLP-1 in the remission of type 2 diabetes mellitus (T2DM) long term after SG in humans, we conducted two separate cross-sectional studies: 1) the GLP-1 response to a standardized mixed liquid meal (SMLM) was compared in subjects with T2DM antedating SG but with different long-term (>2 years) T2DM outcomes (remission, relapse, or lack of remission) (study 1) and 2) the effect of GLP-1 receptor blockade with exendin (9-39) on glucose tolerance was examined in subjects with T2DM antedating surgery, who had undergone SG and presented with long-term T2DM remission (study 2). In study 1, we observed a comparable GLP-1 response to the SMLM regardless of the post-SG outcome of T2DM. In study 2, the blockade of GLP-1 action resulted in impaired insulin secretion but limited deterioration of glucose tolerance. Thus, our data suggest the enhanced GLP-1 secretion observed long term after SG is neither sufficient nor critical to maintain normal glucose tolerance in subjects with T2DM antedating the surgery.

GLP-1 has been suggested as a critical mediator for the marked improvement of glucose tolerance in subjects with type 2 diabetes mellitus (T2DM) commonly seen after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) (1). However, this view has been challenged by 1) studies in humans—performed long after RYGB using the GLP-1 receptor antagonist exendin (9-39) (Ex 9-39)—showing that blockade of GLP-1 action results in marked decrease in insulin secretion but limited impact on glucose tolerance (2,3); 2) data showing the GLP-1 response to meal stimuli does not differ between T2DM patients who after RYGB presented with lack of remission, partial remission, or relapse of T2DM (4); and 3) mouse data demonstrating that whole-body GLP-1 receptor deficiency does not influence the glycemic response to SG (5).

To gain further insight into the role of GLP-1 in the remission of T2DM long term after SG in humans, We conducted two separate cross-sectional studies: 1) we compared the GLP-1 response to a standardized mixed liquid meal (SMLM) in subjects with T2DM antedating SG but with different long-term (>2 years) T2DM outcomes (remission, relapse, or lack of remission) (study 1) and 2) we examined the effect of GLP-1 receptor blockade with Ex 9-39 on glucose tolerance in subjects with T2DM antedating surgery, who had undergone SG and presented with long-term T2DM remission (study 2).

Participants in study 1 (n = 23) were selected out of our series of T2DM patients who had undergone SG at least 2 years before study entry (n = 55), of whom 18 (33%), 31 (56%), and 6 (11%) presented with nonremission, remission, or relapse of T2DM, respectively (6,7). All subjects in the relapse group and 10 and 7 subjects from the remission and nonremission group with similar sex distribution, presurgical BMI, and length of follow-up volunteered to participate. The GLP-1, glucose, C-peptide, and glucagon response to a SMLM (398 kcal, 50% carbohydrate, 35% from fat, 15% protein, Isosource Energy; Novartis, Switzerland) challenge were assessed as previously reported (4).

Study 2 was a case-control study involving three groups of subjects: 1) individuals who had undergone SG ≥24 months before inclusion in the study, had pharmacologically treated T2DM prior to surgery with duration of >6 months, and presented T2DM remission at the time of evaluation (SG-DMR group; n = 8); 2) nondiabetic individuals who underwent SG ≥24 months prior to the study (SG-control group; n = 6); and 3) normal-weight, nonoperated, healthy subjects (NO-control group; n = 8). The three groups were matched for age and sex distribution. The SG-DMR and SG-control groups were also matched by BMI and length of postsurgical follow-up. Sample size was calculated to detect differences among groups with a statistical power of 80% and an α error of 0.05 based on our previously published observation of a 10% increase in the area under the curve of plasma glucose (AUC0–120) during Ex 9-39 versus saline infusion in control subjects (2) and based on the expectation of at least a 30% increase in the AUC0–120 with Ex 9-39 versus saline infusion in the SG-DMR group. The assessment of plasma glucose, insulin, C-peptide, GLP-1, and gastric inhibitory polypeptide (GIP) to an SMLM, during Ex 9-39 (Clinalfa Basic; Bachem, Weil am Rhein, Germany) or saline infusion was performed as previously described (2).

In both studies, β-cell function parameters were derived from mathematical modeling of plasma glucose and C-peptide concentrations measured during SMLM, as previously described (8). Insulin sensitivity was estimated either from fasting plasma insulin and glucose measurements (homeostasis model assessment of insulin resistance) or from glucose and C-peptide plasma concentrations throughout the SMLM, as described by Matsuda and DeFronzo (9), using C-peptide instead of insulin as proposed by Radaelli et al. (10). AUC was calculated using the trapezoidal method.

Both studies received approval by the hospital ethics committee. Written informed consent from all participants was obtained.

Data are expressed as mean (SD) unless otherwise specified. Parametric tests were used in statistical analysis, as all variables followed Gaussian distribution (Kolmogorov-Smirnov test, P > 0.05). Paired t test was used for within-group comparisons in studies with Ex 9-39 or saline. Group comparisons in study 1 and study 2 were performed using ANOVA with post hoc analysis. In study 2, parameters obtained during Ex 9-39 or saline infusions were compared among groups using two-way ANOVA for repeated measures. Statistical analysis was performed using SPSS 17.0. Statistical significance was set at P < 0.05.

Study 1

As shown in Table 1 and Supplementary Fig. 1, the glucose response to the SMLM challenge differed among groups (P < 0.001). In addition, β-cell glucose and rate sensitivity were impaired in relapsing and nonremitting patients—to a larger extent in the latter in whom total insulin output and potentiation were also lower than in the remission group. Of note, no differences were found among the three groups in the GLP-1 AUC0–120 or the GLP-1 concentrations during the test. In contrast, the glucagon response was significantly enhanced in relapsing and nonremitting patients alike compared with patients who were in remission.

Table 1

Clinical and biochemical characteristics and glucose and hormonal responses to a SMLM in participants in study 1 according to glucose tolerance at the time of evaluation

RemissionRelapseNonremissionP
n 10  
Age (years) 50.9 ± 10.6 59.4 ± 13.6 58.7 ± 5.5 0.199 
Sex (female/male) 7/3 4/2 4/3 0.500 
Presurgery BMI (kg/m246.1 ± 5.0 44.9 ± 5.3 43.1 ± 7.2 0.588 
T2DM duration (years) 3.8 ± 2.1 5.2 ± 1.9 12.0 ± 6.0*,a 0.002 
Presurgery HbA1c [% (mmol/mol)] 6.8 ± 1.2 (51 ± 13.1) 6.9 ± 1.9 (52 ± 20.8) 9.4 ± 1.9*,a (79 ± 20.8) 0.010 
Presurgery insulin treatment (%) 17 100*,a <0.001 
BMI at evaluation (kg/m232.7 ± 3.0 37.5 ± 7.4 32.4 ± 4.7 0.149 
EWL at evaluation (%) 63 ± 15 42 ± 27 62 ± 11 0.069 
HbA1c at evaluation [% (mmol/mol)] 5.1 ± 0.3 (32 ± 3.3) 6.4 ± 0.2* (46 ± 2.2) 7.7 ± 0.8*,a (61 ± 8.7) <0.001 
Follow-up period (years) 3.0 ± 1.0 3.9 ± 1.3 3.2 ± 0.8 0.216 
Fasting glucose (mg/dL) 90 ± 8 140 ± 42 222 ± 79*,a <0.001 
2-h plasma glucose (mg/dL) 106 ± 21 186 ± 33* 350 ± 92*,a <0.001 
AUC0–120 glucose (mg ⋅ dL−1 ⋅min) 16,719 ± 2,030 27,487 ± 7,304* 40,476 ± 10,789*,a <0.001 
AUC0–120 C-peptide (nmol ⋅ L−1 ⋅ min) 312 ± 47 289 ± 85 190 ± 92*,a 0.009 
Total insulin output (nmol ⋅ m−249 ± 8 40 ± 13 28 ± 13* 0.004 
β-Cell glucose sensitivity (pmol ⋅ min−1 ⋅ m−2 ⋅ mmol/L−186 ± 39 38 ± 22* 16 ± 8* <0.001 
Rate sensitivity (nmol ⋅ m−2 ⋅ mmol/L) 1.64 ± 1.23 0.48 ± 0.60* 0.42 ± 0.19* 0.016 
Potentiation factor 1.29 ± 0.34 1.31 ± 0.46 0.83 ± 0.20*,a 0.022 
IS (mL ⋅ min−1 ⋅ m−23.5 ± 1.0 2.1 ± 1.2 2.6 ± 1.9 0.149 
AUC0–120 glucagon (pg ⋅ dL−1 ⋅ min ⋅ 1038.8 ± 2.5 14.1 ± 5.6* 13.1 ± 2.5 0.014 
AUC0–120 GLP-1 (pmol ⋅ L−1 ⋅ min ⋅ 1034.56 ± 2.83 4.95 ± 1.78 5.06 ± 1.37 0.900 
RemissionRelapseNonremissionP
n 10  
Age (years) 50.9 ± 10.6 59.4 ± 13.6 58.7 ± 5.5 0.199 
Sex (female/male) 7/3 4/2 4/3 0.500 
Presurgery BMI (kg/m246.1 ± 5.0 44.9 ± 5.3 43.1 ± 7.2 0.588 
T2DM duration (years) 3.8 ± 2.1 5.2 ± 1.9 12.0 ± 6.0*,a 0.002 
Presurgery HbA1c [% (mmol/mol)] 6.8 ± 1.2 (51 ± 13.1) 6.9 ± 1.9 (52 ± 20.8) 9.4 ± 1.9*,a (79 ± 20.8) 0.010 
Presurgery insulin treatment (%) 17 100*,a <0.001 
BMI at evaluation (kg/m232.7 ± 3.0 37.5 ± 7.4 32.4 ± 4.7 0.149 
EWL at evaluation (%) 63 ± 15 42 ± 27 62 ± 11 0.069 
HbA1c at evaluation [% (mmol/mol)] 5.1 ± 0.3 (32 ± 3.3) 6.4 ± 0.2* (46 ± 2.2) 7.7 ± 0.8*,a (61 ± 8.7) <0.001 
Follow-up period (years) 3.0 ± 1.0 3.9 ± 1.3 3.2 ± 0.8 0.216 
Fasting glucose (mg/dL) 90 ± 8 140 ± 42 222 ± 79*,a <0.001 
2-h plasma glucose (mg/dL) 106 ± 21 186 ± 33* 350 ± 92*,a <0.001 
AUC0–120 glucose (mg ⋅ dL−1 ⋅min) 16,719 ± 2,030 27,487 ± 7,304* 40,476 ± 10,789*,a <0.001 
AUC0–120 C-peptide (nmol ⋅ L−1 ⋅ min) 312 ± 47 289 ± 85 190 ± 92*,a 0.009 
Total insulin output (nmol ⋅ m−249 ± 8 40 ± 13 28 ± 13* 0.004 
β-Cell glucose sensitivity (pmol ⋅ min−1 ⋅ m−2 ⋅ mmol/L−186 ± 39 38 ± 22* 16 ± 8* <0.001 
Rate sensitivity (nmol ⋅ m−2 ⋅ mmol/L) 1.64 ± 1.23 0.48 ± 0.60* 0.42 ± 0.19* 0.016 
Potentiation factor 1.29 ± 0.34 1.31 ± 0.46 0.83 ± 0.20*,a 0.022 
IS (mL ⋅ min−1 ⋅ m−23.5 ± 1.0 2.1 ± 1.2 2.6 ± 1.9 0.149 
AUC0–120 glucagon (pg ⋅ dL−1 ⋅ min ⋅ 1038.8 ± 2.5 14.1 ± 5.6* 13.1 ± 2.5 0.014 
AUC0–120 GLP-1 (pmol ⋅ L−1 ⋅ min ⋅ 1034.56 ± 2.83 4.95 ± 1.78 5.06 ± 1.37 0.900 

Data are means ± SD. EWL, excess of weight loss; IS, insulin sensitivity.

*P < 0.05 compared with remission group.

aP < 0.05 compared with relapse group.

Study 2

The clinical features of participants in study 2 are shown in Table 2. Time since surgery ranged from 2.0 to 5.2 years. As shown in Fig. 1 and Table 3, patients in the SG-control group had slightly lower fasting glucose levels than the SG-DMR (P = 0.013) or NO-control group. Ex 9-39 infusion was associated with a significant increase in fasting glucose, similarly in the three groups. Meal ingestion gave rise to similar peak and 2-h glucose levels in the three groups. GLP-1 blockade was associated with higher and earlier glucose peak, higher 2-h glucose, higher mean glucose, and greater glucose AUC0–120, with no differences in the magnitude of the effect across groups. This was also true of the incremental glucose AUCs during the meal. Fasting insulin levels did not differ across groups and were not influenced by Ex 9-39. As expected from their higher glucose levels, individuals in the SG-DMR group presented with higher fasting insulin secretion rates than the SG-control group; however, Ex 9-39 had no effect on this parameter. Total insulin output did not differ among groups prior to Ex 9-39 infusion, but Ex 9-39 was associated with a blunted insulin response in both SG groups compared with the NO-control group (Pinteraction = 0.040). In the SG-DMR group, Ex 9-39 resulted in decreased β-cell glucose sensitivity (P = 0.013) but no significant change in the potentiation factor or rate sensitivity.

Table 2

Clinical features of participants in study 2

NO-control groupSG-control groupSG-DMR groupP
n  
Age (years) 50.0 ± 13.0 52.1 ± 13.1 49.8 ± 12.4 0.936 
Sex (female/male) 6/2 4/2 6/2 0.926 
Presurgery BMI (kg/m2— 44.9 ± 5.3 47.7 ± 5.5 0.506 
T2DM duration (years) — — 2.8 ± 1.8  
Presurgery HbA1c [% (mmol/mol)] — 5.0 ± 0.3 (31 ± 3.3) 7.1 ± 2.1 (54 ± 23.0) 0.025 
BMI at evaluation (kg/m223.3 ± 2.0 31.1 ± 4.2* 32.7 ± 2.3* <0.001 
EWL at evaluation (%) — 75 ± 19 64 ± 16 0.265 
Fasting plasma glucose (mg/dL) 88 ± 7 81 ± 11 91 ± 8 0.086 
HbA1c at evaluation [% (mmol/mol)] 5.5 ± 0.3 (37 ± 3.3) 5.4 ± 0.4 (36 ± 4.4) 5.3 ± 0.2 (34 ± 2.2) 0.369 
HOMA-IR 1.3 ± 0.8 1.4 ± 0.8 2.4 ± 0.6 0.021 
Time of postsurgical follow-up (years) — 2.9 ± 0.9 3.4 ± 0.9 0.433 
NO-control groupSG-control groupSG-DMR groupP
n  
Age (years) 50.0 ± 13.0 52.1 ± 13.1 49.8 ± 12.4 0.936 
Sex (female/male) 6/2 4/2 6/2 0.926 
Presurgery BMI (kg/m2— 44.9 ± 5.3 47.7 ± 5.5 0.506 
T2DM duration (years) — — 2.8 ± 1.8  
Presurgery HbA1c [% (mmol/mol)] — 5.0 ± 0.3 (31 ± 3.3) 7.1 ± 2.1 (54 ± 23.0) 0.025 
BMI at evaluation (kg/m223.3 ± 2.0 31.1 ± 4.2* 32.7 ± 2.3* <0.001 
EWL at evaluation (%) — 75 ± 19 64 ± 16 0.265 
Fasting plasma glucose (mg/dL) 88 ± 7 81 ± 11 91 ± 8 0.086 
HbA1c at evaluation [% (mmol/mol)] 5.5 ± 0.3 (37 ± 3.3) 5.4 ± 0.4 (36 ± 4.4) 5.3 ± 0.2 (34 ± 2.2) 0.369 
HOMA-IR 1.3 ± 0.8 1.4 ± 0.8 2.4 ± 0.6 0.021 
Time of postsurgical follow-up (years) — 2.9 ± 0.9 3.4 ± 0.9 0.433 

Data are expressed as means ± SD. EWL, excess of weight loss; HOMA-IR, homeostasis model assessment of insulin resistance.

*P < 0.05 compared with NO-control group.

Figure 1

Blood glucose and insulin secretion in response to a SMLM during saline (□) or Ex 9-39 (♦) infusion in normal-weight NO-control subjects (A), nondiabetic SG-control subjects (B), and SG-DMR subjects (C). Data are presented as mean ± SEM. *P < 0.05 relative to the saline condition.

Figure 1

Blood glucose and insulin secretion in response to a SMLM during saline (□) or Ex 9-39 (♦) infusion in normal-weight NO-control subjects (A), nondiabetic SG-control subjects (B), and SG-DMR subjects (C). Data are presented as mean ± SEM. *P < 0.05 relative to the saline condition.

Table 3

Glucose and insulin responses to a SMLM with or without Ex 9-39

NO-control group (n = 8)
SG-control group (n = 6)
SG-DMR group (n = 8)
PgroupPEx 9-39
SalineEx 9-39SalineEx 9-39SalineEx 9-39
Glucose at −30 min (mg/dL) 88 ± 7 93 ± 5 81 ± 11 81 ± 13 91 ± 8 92 ± 8 <0.019 0.444 
Glucose at 0 min (mg/dL) 92 ± 6 101 ± 9 84 ± 8 91 ± 10 92 ± 8 100 ± 12 0.130 <0.001 
Peak glucose (mg/dL) 149 ± 28 170 ± 36 149 ± 39 150 ± 37 178 ± 18 196 ± 15 0.176 0.013 
Time to peak glucose (min) 68 ± 26 56 ± 29 43 ± 20 32 ± 16 53 ± 10 38 ± 6 0.066 0.032 
2-h glucose (mg/dL) 118 ± 25 133 ± 45 90 ± 29.5 105 ± 39 114 ± 31 141 ± 31 0.206 0.008 
Mean glucose (mg/dL) 123 ± 18 135 ± 17 114 ± 28 118 ± 35 139 ± 32 156 ± 36 0.817 0.018 
AUC glucose0–120 (mg ⋅ dL−1 ⋅ min ⋅ 10314.9 ± 2.2 16.3 ± 2.0 14.0 ± 3.4 14.4 ± 4.3 17.0 ± 1.4 19.1 ± 1.6 0.124 0.005 
Insulin at −30 min (pmol/L) 45 ± 24 55 ± 43 51 ± 25 38 ± 19 77 ± 19 63 ± 22 0.142 0.232 
Insulin at 0 min (pmol/L) 35 ± 19 47 ± 35 34 ± 16 36 ± 18 49 ± 13 45 ± 12 0.521 0.275 
Mean insulin (pmol/L) 239 ± 110 243 ± 93 492 ± 228 350 ± 95 400 ± 158 309 ± 122 0.023 0.039 
Fasting ISR (pmol ⋅ min−1 ⋅ m−269 ± 28 72 ± 26 50 ± 18 53 ± 13 88 ± 14 80 ± 14 0.013 0.892 
Total insulin output (nmol ⋅ m−241 ± 12 42 ± 8 36 ± 8 32 ± 8 49 ± 11 40 ± 11 0.132 0.017 
β-Cell glucose sensitivity 151 ± 100 100 ± 56 91 ± 29 94 ± 42 120 ± 72 73 ± 46 0.512 0.008 
Rate sensitivity (nmol ⋅ m−2 ⋅ mmol/L) 1.85 ± 1.62 1.30 ± 0.65 1.41 ± 1.02 1.48 ± 0.95 2.38 ± 1.08 2.27 ± 1.29 0.234 0.517 
Potentiation factor 1.02 ± 0.40 1.31 ± 0.65 1.40 ± 1.01 1.48 ± 0.95 1.50 ± 0.32 1.37 ± 0.56 0.725 0.909 
NO-control group (n = 8)
SG-control group (n = 6)
SG-DMR group (n = 8)
PgroupPEx 9-39
SalineEx 9-39SalineEx 9-39SalineEx 9-39
Glucose at −30 min (mg/dL) 88 ± 7 93 ± 5 81 ± 11 81 ± 13 91 ± 8 92 ± 8 <0.019 0.444 
Glucose at 0 min (mg/dL) 92 ± 6 101 ± 9 84 ± 8 91 ± 10 92 ± 8 100 ± 12 0.130 <0.001 
Peak glucose (mg/dL) 149 ± 28 170 ± 36 149 ± 39 150 ± 37 178 ± 18 196 ± 15 0.176 0.013 
Time to peak glucose (min) 68 ± 26 56 ± 29 43 ± 20 32 ± 16 53 ± 10 38 ± 6 0.066 0.032 
2-h glucose (mg/dL) 118 ± 25 133 ± 45 90 ± 29.5 105 ± 39 114 ± 31 141 ± 31 0.206 0.008 
Mean glucose (mg/dL) 123 ± 18 135 ± 17 114 ± 28 118 ± 35 139 ± 32 156 ± 36 0.817 0.018 
AUC glucose0–120 (mg ⋅ dL−1 ⋅ min ⋅ 10314.9 ± 2.2 16.3 ± 2.0 14.0 ± 3.4 14.4 ± 4.3 17.0 ± 1.4 19.1 ± 1.6 0.124 0.005 
Insulin at −30 min (pmol/L) 45 ± 24 55 ± 43 51 ± 25 38 ± 19 77 ± 19 63 ± 22 0.142 0.232 
Insulin at 0 min (pmol/L) 35 ± 19 47 ± 35 34 ± 16 36 ± 18 49 ± 13 45 ± 12 0.521 0.275 
Mean insulin (pmol/L) 239 ± 110 243 ± 93 492 ± 228 350 ± 95 400 ± 158 309 ± 122 0.023 0.039 
Fasting ISR (pmol ⋅ min−1 ⋅ m−269 ± 28 72 ± 26 50 ± 18 53 ± 13 88 ± 14 80 ± 14 0.013 0.892 
Total insulin output (nmol ⋅ m−241 ± 12 42 ± 8 36 ± 8 32 ± 8 49 ± 11 40 ± 11 0.132 0.017 
β-Cell glucose sensitivity 151 ± 100 100 ± 56 91 ± 29 94 ± 42 120 ± 72 73 ± 46 0.512 0.008 
Rate sensitivity (nmol ⋅ m−2 ⋅ mmol/L) 1.85 ± 1.62 1.30 ± 0.65 1.41 ± 1.02 1.48 ± 0.95 2.38 ± 1.08 2.27 ± 1.29 0.234 0.517 
Potentiation factor 1.02 ± 0.40 1.31 ± 0.65 1.40 ± 1.01 1.48 ± 0.95 1.50 ± 0.32 1.37 ± 0.56 0.725 0.909 

Data are expressed as means ± SD. ISR, insulin secretion rate.

Prior to meal ingestion, Ex 9-39 had no effect on glucagon or GIP plasma concentrations but was associated with a significant increase in GLP-1 in the three groups (P < 0.001) with no treatment-group interaction (P = 0.793) (Supplementary Table 1 and Supplementary Fig. 2). As expected, meal ingestion per se elicited a higher GLP-1 response in the two surgical groups compared with the NO-control group (P = 0.015), which was not coupled to a suppression of the glucagon response (Supplementary Fig. 2). Ex 9-39 was associated with a further increase in the GLP-1 response in all groups (P < 0.001), which was associated with increases in the glucagon response.

Our data show that 1) the striking GLP-1 response to meal intake observed long term after SG is not sufficient to maintain normal glucose tolerance in subjects with T2DM antedating the surgery and 2) that in subjects with surgically induced long-term T2DM remission, blockade of GLP-1 action results in limited deterioration of glucose tolerance. Thus, our results strongly suggest that enhanced GLP-1 secretion commonly described after SG is not the key determinant of the long-term beneficial effects of this type of surgery on T2DM.

Because of the well-established role of GLP-1 in glucose homeostasis and the parallel improvement in glucose tolerance, β-cell function, and GLP-1 response after SG in several association studies, a causative role of GLP-1 in the amelioration of glucose homeostasis commonly seen after SG has been proposed (1,11,12). According to this hypothesis, a larger incretin response should have been observed in SG subjects in remission in our study 1 compared with those with lack of T2DM remission. In contrast, in study 1, GLP-1 release was almost superimposable regardless of glucose tolerance status. Admittedly, postsurgical restoration of the GLP-1 response was an independent determinant of restored glucose tolerance in a recent prospective study of T2DM patients who had undergone SG or RYGB (11). Nonetheless, in line with our data, in that study the postsurgical GLP-1 response was not an independent predictor of glucose tolerance status. We also acknowledge data obtained in rodents suggesting that differences in the sensitivity to GLP-1 could be implicated in the effects of RYGB on glucose tolerance (13). Nonetheless, though limited by our cross-sectional design, the current association study supports the notion that GLP-1 secretion does not play a critical role in the outcome of T2DM after SG.

To circumvent the limitations inherent in association studies, we conducted study 2, in which glucose tolerance was evaluated with or without GLP-1 blockade. In support of the findings in study 1, GLP-1 blockade resulted in limited deterioration of glucose tolerance. In particular, in subjects in remission of T2DM the blockade resulted in only a 13.2 ± 15.9% increase in the glucose response, similar to the change seen in the NO-control group (10.1 ± 8.4%) (P = 0.281) (Table 3). These results are similar to those recently reported by our group and others in subjects in T2DM remission after RYGB (2,14). Importantly, our subjects with postsurgical remission were also compared with a nondiabetic group that had undergone SG, thereby excluding anatomical differences as a potential source of confounding. Although the use of a mixed-meal challenge rather than a standard oral glucose tolerance test precluded formal assessment of glucose tolerance, under Ex 9-39 infusion only one of eight patients each in the SG-DMR and the NO-control group presented with 2-h glucose levels above the diagnostic threshold for T2DM.

In agreement with previous studies, in our studies β-cell function emerged as the dominant factor influencing the outcome at 2 years after surgery (11). The impairment in β-cell function found in study 1 is concordant with the altered insulin secretion after a meal challenge as well as intravenous glucose administration previously reported by our group in subjects who had undergone RYGB (4). Although the β-cell response to other stimuli was not tested in the current study, recent evidence consistently shows that residual β-cell function is required for a sustained beneficial effect of RYGB on glucose tolerance even in the context of marked GLP-1 secretion (15). Of note, in study 2 Ex 9-39 was associated with a significant decrease in insulin secretion and total insulin output in both surgical groups, supporting the notion that GLP-1 does potentiate insulin secretion after SG and RYGB (16). Nonetheless, the limited impact of the GLP-1 blockade on both insulin secretion and glucose tolerance after SG suggests that other factors are important.

Rapid gastric emptying could be viewed as a potentially unifying mechanism for the hormonal changes after SG. In a recent study in a rodent model, Chambers et al. (17) demonstrated that SG causes accelerated emptying of gastric contents into the intestine and failure to respond to many of the regulatory signals that normally control gastric emptying rate, including GLP-1. On the other hand, postprandial hyperglucagonemia, such as that found in our studies (11,12), has also been described after pharmacological or surgical acceleration of gastric emptying in human subjects (18,19). Although the mechanism(s) underlying this phenomenon remain unclear, it has been hypothesized that rapid increases in portal vein glycemia—due to accelerated intestinal glucose flux—could activate portal glucose sensors influencing neural regulation of α-cell activity (20). Under these circumstances, the enhanced GLP-1 response after SG could be aimed not only, or not so much, to potentiate insulin secretion but also, or primarily, to restore gastric motility. On the other hand, the paradoxical rise in glucagon release in SG-operated subjects may result from signal(s) overriding the normal regulation of the α-cell, which our Ex 9-39 results suggest is at least partly retained postsurgery.

Within its limitations (the cross-sectional design, use of a mixed meal rather than an oral glucose tolerance test, lack of measures of gastric emptying, and other physiological determinants of glucose tolerance), the current study is the first to analyze the contribution of GLP-1 to glucose tolerance after SG using an outcome and a GLP-1 blockade protocol. Although our data do not rule out a role of GLP-1 in improving glucose tolerance shortly after surgery (11,12) and sustaining weight loss (21), they strongly suggest that at a time when weight loss after SG has occurred, the impact of GLP-1 on glucose tolerance is limited.

See accompanying article, p. 3172.

Acknowledgments. The authors thank Judith Viaplana, RN (Institut d’Investigacions Biomèdiques August Pi i Sunyer), for her excellent technical support.

Funding. This work was supported by a grant from the Fondo de Investigacíon Sanitarias (PI11/00892), Instituto de Salud Carlos III (Madrid, Spain), and European Regional Development Fund from the European Union.

Duality of Interest. No potential conflicts of interest relevant to this article were reported.

Author Contributions. A.J. and J.V. researched and discussed data and wrote the manuscript. A.M. and E.F. researched and discussed data and edited the manuscript. R.C. performed the hormonal measurements and reviewed and edited the manuscript. A.L. reviewed and edited the manuscript. J.V. is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

1.
Dirksen
C
,
Bojsen-Møller
KN
,
Jørgensen
NB
, et al
.
Exaggerated release and preserved insulinotropic action of glucagon-like peptide-1 underlie insulin hypersecretion in glucose-tolerant individuals after Roux-en-Y gastric bypass
.
Diabetologia
2013
;
56
:
2679
2687
[PubMed]
2.
Jiménez
A
,
Casamitjana
R
,
Viaplana-Masclans
J
,
Lacy
A
,
Vidal
J
.
GLP-1 action and glucose tolerance in subjects with remission of type 2 diabetes after gastric bypass surgery
.
Diabetes Care
2013
;
36
:
2062
2069
[PubMed]
3.
Shah
M
,
Law
JH
,
Micheletto
F
, et al
.
Contribution of endogenous glucagon-like peptide 1 to glucose metabolism after Roux-en-Y gastric bypass
.
Diabetes
2014
;
63
:
483
493
[PubMed]
4.
Jiménez
A
,
Casamitjana
R
,
Flores
L
,
Delgado
S
,
Lacy
A
,
Vidal
J
.
GLP-1 and the long-term outcome of type 2 diabetes mellitus after Roux-en-Y gastric bypass surgery in morbidly obese subjects
.
Ann Surg
2013
;
257
:
894
899
[PubMed]
5.
Wilson-Perez
HE
,
Chambers
AP
,
Ryan
KK
, et al
.
Vertical sleeve gastrectomy is effective in two genetic mouse models of glucagon-like peptide-1 receptor deficiency
.
Diabetes
2013
;
62
:
2308
2385
6.
Buse
JB
,
Caprio
S
,
Cefalu
WT
, et al
.
How do we define cure of diabetes
?
Diabetes Care
2009
;
32
:
2133
2135
[PubMed]
7.
Jiménez
A
,
Casamitjana
R
,
Flores
L
, et al
.
Long-term effects of sleeve gastrectomy and Roux-en-Y gastric bypass surgery on type 2 diabetes mellitus in morbidly obese subjects
.
Ann Surg
2012
;
256
:
1023
1029
[PubMed]
8.
Mari
A
,
Schmitz
O
,
Gastaldelli
A
,
Oestergaard
T
,
Nyholm
B
,
Ferrannini
E
.
Meal and oral glucose tests for assessment of beta -cell function: modeling analysis in normal subjects
.
Am J Physiol Endocrinol Metab
2002
;
283
:
E1159
E1166
[PubMed]
9.
Matsuda
M
,
DeFronzo
RA
.
Insulin sensitivity indices obtained from oral glucose tolerance testing: comparison with the euglycemic insulin clamp
.
Diabetes Care
1999
;
22
:
1462
1470
[PubMed]
10.
Radaelli
T
,
Farrell
KA
,
Huston-Presley
L
, et al
.
Estimates of insulin sensitivity using glucose and C-Peptide from the hyperglycemia and adverse pregnancy outcome glucose tolerance test
.
Diabetes Care
2010
;
33
:
490
494
[PubMed]
11.
Nannipieri
M
,
Baldi
S
,
Mari
A
, et al
.
Roux-en-Y gastric bypass and sleeve gastrectomy: mechanisms of diabetes remission and role of gut hormones
.
J Clin Endocrinol Metab
2013
;
98
:
4391
4399
[PubMed]
12.
Romero
F
,
Nicolau
J
,
Flores
L
, et al
.
Comparable early changes in gastrointestinal hormones after sleeve gastrectomy and Roux-En-Y gastric bypass surgery for morbidly obese type 2 diabetic subjects
.
Surg Endosc
2012
;
26
:
2231
2239
[PubMed]
13.
Habegger
KM
,
Heppner
KM
,
Amburgy
SE
, et al
.
GLP-1R responsiveness predicts individual gastric bypass efficacy on glucose tolerance in rats
.
Diabetes
2014
;
63
:
505
513
[PubMed]
14.
Jørgensen
NB
,
Dirksen
C
,
Bojsen-Møller
KN
, et al
.
Exaggerated glucagon-like peptide 1 response is important for improved β-cell function and glucose tolerance after Roux-en-Y gastric bypass in patients with type 2 diabetes
.
Diabetes
2013
;
62
:
3044
3052
[PubMed]
15.
Blanco
J
,
Jiménez
A
,
Casamitjana
R
, et al
.
Relevance of beta-cell function for improved glycemic control after gastric bypass surgery
.
Surg Obes Relat Dis
2014
;
10
:
9
13
[PubMed]
16.
Dutia
R
,
Brakoniecki
K
,
Bunker
P
, et al
.
Limited recovery of β-cell function after gastric bypass despite clinical diabetes remission
.
Diabetes
2014
;
63
:
1214
1223
17.
Chambers
AP
,
Smith
EP
,
Begg
DP
, et al
.
Regulation of gastric emptying rate and its role in nutrient-induced GLP-1 secretion in rats after vertical sleeve gastrectomy
.
Am J Physiol Endocrinol Metab
2014
;
306
:
E424
E432
[PubMed]
18.
Meier
JJ
,
Kemmeries
G
,
Holst
JJ
,
Nauck
MA
.
Erythromycin antagonizes the deceleration of gastric emptying by glucagon-like peptide 1 and unmasks its insulinotropic effect in healthy subjects
.
Diabetes
2005
;
54
:
2212
2218
[PubMed]
19.
Plamboeck
A
,
Veedfald
S
,
Deacon
CF
, et al
.
Characterisation of oral and i.v. glucose handling in truncally vagotomised subjects with pyloroplasty
.
Eur J Endocrinol
2013
;
169
:
187
201
[PubMed]
20.
Salehi
M
,
D’Alessio
DA
.
Going with the flow: adaptation of β-cell function to glucose fluxes after bariatric surgery
.
Diabetes
2013
;
62
:
3671
3673
[PubMed]
21.
le Roux
CW
,
Welbourn
R
,
Werling
M
, et al
.
Gut hormones as mediators of appetite and weight loss after Roux-en-Y gastric bypass
.
Ann Surg
2007
;
246
:
780
785
[PubMed]

Supplementary data