Differential effects of fish-oil and cocoa-butter based high-fat/high-sucrose diets on endocrine pancreas morphology and function in mice

Abstract

Introduction: A high-fat/high-sucrose diet leads to adverse metabolic changes that affect insulin sensitivity, function, and secretion. The source of fat in the diet might inhibit or increase this adverse effect. Fish oil and cocoa butter are a significant part of our diets. Yet comparisons of these commonly used fat sources with high sucrose on pancreas morphology and function are not made. This study investigated the comparative effects of a fish oil-based high-fat/high-sucrose diet (Fish-HFDS) versus a cocoa butter-based high-fat/high-sucrose diet (Cocoa-HFDS) on endocrine pancreas morphology and function in mice.

Methods: C57BL/6 male mice (n=12) were randomly assigned to dietary intervention either Fish-HFDS (n=6) or Cocoa-HFDS (n=6) for 22 weeks. Intraperitoneal glucose and insulin tolerance tests (IP-GTT and IP-ITT) were performed after 20-21 weeks of dietary intervention. Plasma concentrations of c-peptide, insulin, glucagon, GLP-1, and leptin were measured by Milliplex kit. Pancreatic tissues were collected for immunohistochemistry to measure islet number and composition. Tissues were multi-labelled with antibodies against insulin and glucagon, also including expression on Pdx1-positive cells.

Results and discussion: Fish-HFDS-fed mice showed significantly reduced food intake and body weight gain compared to Cocoa-HFDS-fed mice. Fish-HFDS group had lower fasting blood glucose concentration and area under the curve (AUC) for both GTT and ITT. Plasma c-peptide, insulin, glucagon, and GLP-1 concentrations were increased in the Fish-HFDS group. Interestingly, mice fed the Fish-HFDS diet displayed higher plasma leptin concentration. Histochemical analysis revealed a significant increase in endocrine pancreas β-cells and islet numbers in mice fed Fish-HFDS compared to the Cocoa-HFDS group. Taken together, these findings suggest that in a high-fat/high-sucrose dietary setting, the source of the fat, especially fish oil, can ameliorate the effect of sucrose on glucose homeostasis and endocrine pancreas morphology and function.

Keywords: cocoa butter; fish oil; glucagon; high-fat/sucrose diet; insulin; α-cell; β-cell.

Figure 1

The Effect of different fat-based diets (Fish-HFDS and Cocoa-HFDS) on weight gain and food intake in mice. (A) The starting body weight of both groups. (B) The final body weight of both groups. (C) Weight gain after the diet intervention. (D) Food intake during the diet intervention. Data are mean with ± SEM. P-values for differences between groups by ANOVA and Student’s t-test.

Figure 2

The Effect of different fat-based diets (Fish-HFDS and Cocoa-HFDS) on glucose insulin and glucagon. (A) Fasting blood glucose concentration of both groups. (B) Intraperitoneal glucose tolerance test (IPGTT). (C) AUC _IP-GTT. (D) Insulin tolerance test (ITT). (E) AUC _ITT. (F) Fasting plasma insulin concentration. (G) Fasting plasma glucagon concentration. Data are mean with ± SEM. P-values for differences between groups by ANOVA and Student’s t-test. The asterisk (*) represent a P-value of ≤ 0.05.

Figure 3

The Effect of different fat-based diets (Fish-HFDS and Cocoa-HFDS) on plasma metabolic markers. (A) Fasting plasma GLP-1concentration. (B) Correlation between food intake and GLP-1. (C) Fasting plasma C-peptide concentration. (D) Fasting plasma leptin concentration. (E) Correlation between food intake and leptin. Data are mean with ± SEM. P-values for differences between groups by ANOVA and Student’s t-test.

Figure 4

Representative photomicrographs of double staining of insulin and glucagon. Scale bar 50 µm.

Figure 5

The Effect of different fat-based diets (Fish-HFDS and Cocoa-HFDS) on endocrine pancreas morphology. (A) Number of β-cells. (B) Number of islets. Data are mean with ± SEM. P-values for differences between groups by ANOVA and Student’s t-test.

Figure 6

Representative photomicrographs of double staining of insulin and pdx1. Scale bar 10 µm.