Pancreatic Elastase-1 in Stools, a Marker of Exocrine Pancreas Function, Correlates With Both Residual β-Cell Secretion and Metabolic Control in Type 1 Diabetic Subjects

RESEARCH DESIGN AND METHODS

We studied 37 consecutive type 1 diabetic patients and performed follow-up at the outpatient clinic of our diabetes unit (16 men and 21 women, aged 34 ± 2 years [mean ± SE]). Diabetes duration was 10.4 ± 1.3 years, BMI 23.9 ± 0.6 kg/m², caloric intake 2,047 ± 71 kcal/day, fasting plasma glucose 8.76 ± 0.40 mmol/l, C-peptide (radioimmunoassay kit; Adaltis Italia, Bologna, Italy) 0.30 ± 0.07 ng/ml, and HbA_1c (high-performance liquid chromatography method, Variant II; BioRad, Milan, Italy) 8.1 ± 0.24%. A total of 20 healthy subjects, matched for age, sex, BMI, and daily caloric intake, were used as control subjects (Table 1). Patients were on steady metabolic control, presented a stable body weight in the previous 6 months, did not report a history or symptoms of gastrointestinal disease, and tested negative for antibodies to gliadin and endomysium. They were on a normocaloric diet with a carbohydrate content accounting for 55–60% of calories, with restriction of simple sugars, a protein content of 1 g/kg body wt, and a lipid content of ∼25–30% of total calories. Subjects received three premeal rapid insulin injections and one bedtime intermediate insulin injection. Two patients were macroalbuminuric (albumin excretion rate >200 μg/min), and six were microalbuminuric (albumin excretion rate between 20 and 200 μg/min); seven subjects had background and two had preproliferative retinopathy.

PE-1 concentrations in stools were determined by enzyme-linked immunosorbent assay (ScheBo Pancreatic Elastase 1 ELISA kit; ScheBo-Tech, Giessen, Germany; intra-assay and interassay coefficients of variation [CVs] 5.8 and 7.7%, respectively). In patients with chronic pancreatitis, the cutoff at 200 μg/g stools shows 100% sensitivity for moderate and severe pancreatic insufficiency, while for patients with exocrine pancreatic insufficiency of any kind, both sensitivity and specificity are 93% (4). Individual daily variations of PE-1 concentrations are very low (mean CV 15%) (4). PE-1 values are not affected by gastric resection, malabsorption, alteration of gastric motility, and therapy with exogenous enzymes (3).

RESULTS

Results have been evaluated by the Mann-Whitney nonparametric test for unpaired data and by linear and multiple regression analyses utilizing StatView software.

PE-1 values in stools in type 1 diabetic patients were significantly lower than in the 20 control subjects (i.e., 263 ± 30 vs. 438 ± 38 μg/g stools; P = 0.0004; 21 of 37 patients had PE-1 values below the lower limit of normal). Sex did not influence PE-1 (men 241 ± 37, women 291 ± 50 μg/g stools; P = NS). PE-1 was correlated to C-peptide (r = 0.565; P = 0.0003) (Fig. 1A). All but one patient with PE-1 <200 μg/g stools had C-peptide ≤0.5 ng/ml. On the contrary, 7 of 30 patients with C-peptide ≤0.5 ng/ml had PE-1 in the normal range. In patients with C-peptide ≤0.5 ng/ml, PE-1 values were ∼50% compared with those in patients with C-peptide >0.5 ng/ml (211 ± 29 vs. 424 ± 62 μg/g stools; P = 0.0044). PE-1 values in patients with C-peptide >0.5 ng/ml were similar to those measured in control subjects (424 ± 62 and 438 ± 38 μg/g stools, respectively; P = NS).

PE-1 was inversely correlated to HbA_1c (r = −0.519; P = 0.0001) (Fig. 1B). In patients with HbA_1c >8% (cutoff value of bad glycemic control), PE-1 was lower than in those with HbA_1c ≤8% (175 ± 26 vs. 346 ± 46 μg/g stools; P = 0.0023). Among patients with HbA_1c >8.0%, 14 of 19 had PE-1 <200 μg/g stools compared with 9 of 18 with HbA_1c ≤8.0%. HbA_1c correlated to C-peptide (r = −0.350; P = 0.033) and diabetes duration (r = 0.450; P = 0.0045).

PE-1 was inversely correlated to diabetes duration (r = −0.470; P = 0.0032) (Fig. 1C). All subjects with diabetes duration >15 years had PE-1 <200 μg/g stools. Also, C-peptide showed an inverse relationship with diabetes duration (r = −0.455; P = 0.0049). Subjects with C-peptide >0.5 ng/ml had shorter diabetes duration than subjects with C-peptide ≤0.5 ng/ml (4.2 ± 1.3 vs. 12.4 ± 1.5 years, respectively; P = 0.0018). Furthermore, only two patients with diabetes duration >5 years presented C-peptide >0.5 ng/ml.

PE-1 values <100 μg/g stools, a marker of a very severe impairment of exocrine pancreas function, were found in four subjects, all with C-peptide ≤0.5 ng/ml and HbA_1c >8.0%, three of whom had a diabetes duration >15 years. We measured a fecal fat excretion ≥6 g/day (i.e., over the threshold for steatorrhea) in all of these subjects.

PE-1 was not related to BMI (r = 0.252; P = NS), daily insulin dose (r = 0.233; P = NS), daily insulin dose per kilogram body weight (r = 0.220; P = NS), daily caloric intake (r = 0.085; P = NS), daily urea nitrogen excretion (r = 0.038; P = NS), and albumin excretion rate (r = 0.220; P = NS).

By multiple regression analysis, when PE-1 was considered the independent variable, C-peptide and HbA_1c remained significantly correlated to PE-1 (standard coefficient 0.398; P = 0.0134 and standard coefficient −0.331; P = 0.041, respectively), while BMI and diabetes duration did not (Table 2).

CONCLUSIONS

PE-1 concentrations in stools, a reliable marker of exocrine pancreas function, are independently correlated to both glycemic control and residual β-cell function in type 1 diabetic patients, suggesting that also at low levels of β-cell function, residual insulin secretion is important in maintaining exocrine pancreas activity. Furthermore, since patients with C-peptide >0.5 ng/ml showed PE-1 values in stools similar to control subjects, our study suggests that this level could be considered the cutoff point over which endocrine pancreatic function does not impair the exocrine-one. On the other hand, the occurrence of normal PE-1 values in a few patients with C-peptide ≤0.5 ng/ml suggests that insulin secretion is not the only determinant of PE-1 concentrations in stools in type 1 diabetic subjects.

The observation that a small residual insulin secretion modulates exocrine pancreatic function, even in the presence of exogenous insulin treatment, is explained by the fact that the concentrations of insulin needed to exert local effects on acinar cells are much higher than those reached by subcutaneous insulin administration. Insulin concentrations physiologically measured in the immediate periphery of islet cells are two to three orders of magnitude higher than usual circulating values (7). PE-1 concentrations in stools also correlated to glycemic control when residual β-cell secretion was taken into account. The occurrence of glucose toxicity at the exocrine pancreas level could be supposed, since acute hyperglycemia at 15 mmol/l during a hyperglycemic clamp inhibits both basal and low-dose colecystokinin-stimulated exocrine pancreas secretion (8).

The observation that eight patients presented low PE-1 concentrations despite good glycemic control and a relatively short diabetes duration is explained by the fact that seven of eight patients had C-peptide values ≤0.5 ng/ml and five of eight had ≤0.1 ng/ml. Thus, a good glycemic control does not offset the effects of insulin deficiency. Since the correlation of diabetes duration with PE-1 disappears when insulin secretion and glycemic control are taken into account, we suppose that the influence of diabetes duration on PE-1 is attributable to the progressive reduction of β-cell function with time and to the consequent impairment of blood glucose control.

The clinical meaning of our results could also be interpreted in light of our unpublished observation that PE-1 values correlate with fecal fat excretion. In this light, it is not surprising that patients with a PE-1 value <100 μg/g stools presented steatorrhea.

In conclusion, this study shows for the first time that both residual insulin secretion and glycemic control play relevant and independent effects on exocrine pancreatic function in type 1 diabetic patients and confirms the frequent occurrence of a asymptomatic exocrine pancreas deficiency in these patients.