Reanalysis of study of pancreatic effects of incretin therapy: methodological deficiencies

Abstract

A recently published study by Butler et al. concluded that incretin treatment had adverse effects on the human type 2 diabetic pancreas including 'a marked expansion of the exocrine and endocrine pancreatic compartments, the former being accompanied by increased proliferation and dysplasia and the latter by α-cell hyperplasia with the potential for evolution into neuroendocrine tumours'. Incretin therapy has become widely used for type 2 diabetes, so these conclusions have instigated major concerns with regard to patient safety. We reassessed both the clinical case information and virtual microscopy images of the same 34 cases that were used in the Butler study as well as Network for Pancreatic Organ Donation (nPOD) cases that were not included. Whereas we would like to stress that it is important to investigate in depth any indication that incretin treatment may lead to inflammation or dysplasia in the pancreas, we find that the data presented in the Butler paper have serious methodological deficiencies that preclude any meaningful conclusions.

Keywords: incretin therapy; islets; type 2 diabetes.

Figure 1

Graphic display of ages of nPOD cases used in Butler et al (1) showing the lack of age matching of studied cohorts. Solid black circles= type 2 diabetes +Incretin (I) therapy; white circles = type 2 diabetes; grey circles = non-diabetic cases. The dotted line indicates 45 years of age, which is that of the youngest case in the type 2 diabetes + incretin group.

Figure 2

Variability of immunostaining is problematic for accurate quantification of relative areas of the α- and β-cells. A, B. Staining with Fast Red chromogen was excessive and “bleeds over” adjacent non-endocrine tissue and luminal space (asterix). Here are shown images from two type 2 diabetes +I cases with overstaining for glucagon. C, D In other sections staining was very faint for insulin (C) or glucagon (D). In the case shown staining for both insulin and glucagon are very faint as seen in the same field of adjacent sections from the glucagon-rich tail of the pancreas stained for each (arrows indicate the islets).

Figure 3

Overstaining for both insulin and glucagon distorts the quantification of relative areas of beta and alpha cells respectively. The same islets on adjacent sections stained for insulin (A) and glucagon (B) show imprecise discrimination of cell types due to overstaining.

Figure 4

Graphic display of the pancreatic weights of the nPOD cases used Butler et al (1) suggesting the 204 g pancreas (nPOD 6185) as an outlier. Solid black circles= type 2 diabetes +I; white circles = type 2 diabetes; grey circles = non-diabetic. The dashed line indicates of the mean (92.4 g) of all the cases used in Butler et al (1); the dotted lines indicate ± two standard deviations.

Figure 5

Substantial hormone-positive cells (here shown glucagon: red) associated with PanINs and focal areas of pancreatitis-associated changes in type 2 diabetes were present in subjects with (A, case nPOD 6206) and without (B, case nPOD 6139) incretin therapy. In both, characteristic focal areas of pancreatitis-associated changes are seen with multiple ductal profiles, many of which have tall columnar ductal cells typical of early PanINs. In B, the large duct has the papillary lesion characteristic of PanIN1B.