Gastric carcinogenesis by N-Methyl-N-nitrosourea is enhanced in db/db diabetic mice

Abstract

In 2005, a Japanese epidemiological study showed that increase in plasma glucose levels is a risk factor for gastric cancer. However, no animal model has hitherto shown any association between diabetes mellitus and neoplasia in the stomach. Diabetic (db/db) mice have obese and diabetic phenotypes, including hyperglycemia, because of disruption of the leptin receptor. In the present study, effects of hyperglycemia and/or hyperinsulinemia on the development of proliferative lesions were therefore examined in db/db mice given N-methyl-N-nitrosourea (MNU). A total of 120 mice were assigned to four groups: Group A, 40 db/db mice with MNU; Group B, 40 + /db mice with MNU; Group C, 30 misty (wild-type) mice with MNU; Group D, 10 db/db mice without MNU. MNU was given at 60 ppm in drinking water for 20 weeks. Subgroups of animals were sacrificed at weeks 21 and 30 and blood samples were collected to measure glucose, insulin, leptin, and adiponectin concentrations. The removed stomachs were fixed in formalin, and embedded in paraffin for histological examination and immunohistochemistry. At week 30 in Groups A, B, C and D, hyperplasia was observed in 100, 79, 57, and 0%, and dysplasia in 91, 43, 71, and 0%, respectively. Adenocarcinomas and pepsinogen-altered pyloric glands (PAPG), putative preneoplastic lesions, were observed only in Group A, at an incidence of 45%. The serum levels of insulin and leptin were also elevated in Group A. Gastric carcinogenesis by MNU was enhanced in db/db mice, possibly in association with hyperinsulinemia and hyperleptinemia.

Figure 1

Changes in body weight in each group. The bars attached on each value show SD.

Figure 2

Cysts (a) or dilated glands (A) and hyperplasia (B) were frequent in the groups treated with N‐methyl‐N‐nitrosourea (MNU), dysplasia (C) being significantly increased in diabetic (db/db) mice treated with MNU. At week 30, adenocarcinomas were observed in 45% of db/db mice treated with MNU (D,E). H&E (d), p53 (E). Parietal cells recognized as H+/K+‐exchanging ATPase (H/K‐ATPase)‐positive were decreased or lacking in a hyperplastic area (F). Foveolar hyperplasia was recognized by a proliferation of periodic acid‐Schiff‐positive cells (G) and mucous cell hyperplasia, by mostly trefoil factor 2 (TFF2)‐positive cells (H). A tumor in which the expression of pepsinogen was decreased or lacking (I). Bar = 100 µM in (A–C, E–I), 20 µM in (D).

Figure 3

BrdU staining in the normal fundic gland of Group C (A), and Group A (B). In hyperplasia cases, BrdU staining showed an expansion of the proliferating S‐phase cell compartment (×40; C, ×100; D). Bar = 100 µM.