Duodenal-jejunal bypass normalizes pancreatic islet proliferation rate and function but not hepatic steatosis in hypothalamic obese rats

Abstract

Modifications in life-style and/or pharmacotherapies contribute to weight loss and ameliorate the metabolic profile of diet-induced obese humans and rodents. Since these strategies fail to treat hypothalamic obesity, we have assessed the possible mechanisms by which duodenal-jejunal bypass (DJB) surgery regulates hepatic lipid metabolism and the morphophysiology of pancreatic islets, in hypothalamic obese (HyO) rats. During the first 5 days of life, male Wistar rats received subcutaneous injections of monosodium glutamate (4 g/kg body weight, HyO group), or saline (CTL). At 90 days of age, HyO rats were randomly subjected to DJB (HyO DJB group) or sham surgery (HyO Sham group). HyO Sham rats were morbidly obese, insulin resistant, hypertriglyceridemic and displayed higher serum concentrations of non-esterified fatty acids (NEFA) and hepatic triglyceride (TG). These effects were associated with higher expressions of the lipogenic genes and fatty acid synthase (FASN) protein content in the liver. Furthermore, hepatic genes involved in β-oxidation and TG export were down-regulated in HyO rats. In addition, these rats exhibited hyperinsulinemia, β-cell hypersecretion, a higher percentage of islets and β-cell area/pancreas section, and enhanced nuclear content of Ki67 protein in islet-cells. At 2 months after DJB surgery, serum concentrations of TG and NEFA, but not hepatic TG accumulation and gene and protein expressions, were normalized in HyO rats. Insulin release and Ki67 positive cells were also normalized in HyO DJB islets. In conclusion, DJB decreased islet-cell proliferation, normalized insulinemia, and ameliorated insulin sensitivity and plasma lipid profile, independently of changes in hepatic metabolism.

Figure 1. Body weight (BW) in control (CTL), hypothalamic obese (HyO) Sham and HyO with duodenal-jejunal bypass (DJB) rats, recorded during 5 months. Data are reported as means±SEM (n=13–16). *P<0.05, HyO Sham and HyO DJB groups compared to CTL (one-way ANOVA followed by the Tukey post-test).

Figure 2. LPK, ACC-1, FASN, SCD-1, ACO, CPT-1a and MTP mRNA content in the livers of control (CTL), hypothalamic obese (HyO) Sham and HyO with duodenal-jejunal bypass (DJB) rats. Data are reported as means±SEM (n=5–8). P<0.05, different letters indicate significant differences (one-way ANOVA followed by the Tukey post-test).

Figure 3. Hepatic protein expressions of ACC (A), pACC^Ser79/ACC (B), FASN (C) and CPT-1a (D) in control (CTL), hypothalamic obese (HyO) Sham and HyO with duodenal-jejunal bypass (DJB) rats. Data are reported as means±SEM (n=5–8 rats). P<0.05, different letters indicate significant differences (one-way ANOVA followed by the Tukey post-test).

Figure 4. Means±SEM (n=8-14) of A, serum glucose concentration, B, insulin concentration, and C, insulin sensitivity measured by the HOMA-IR in fasted control (CTL), hypothalamic obese (HyO) Sham and HyO with duodenal-jejunal bypass (DJB) rats. D, Glucose-induced insulin secretion in islets isolated from CTL, HyO Sham and HyO DJB rats. Groups of 4 islets were incubated for 1 h in the presence of 5.6 or 8.3 mM glucose. Data are reported as means±SEM obtained from 8–12 groups of islets in two independent experiments with 4 rats per group. P<0.05, different letters indicate significant differences (one-way ANOVA followed by the Tukey post-test).

Figure 5. A, Representative images of pancreas sections stained for insulin or glucagon. B, Islet, C, β-cell masses, and D, α-cell masses in the CTL, hypothalamic obese (HyO) Sham and HyO with duodenal-jejunal bypass (DJB) pancreases. Data are reported as means±SEM (n=3–4). P<0.05, different letters indicate significant differences (one-way ANOVA followed by the Tukey post-test).

Figure 6. A, Representative images of pancreas sections stained for Ki67. B, Percent of Ki67 positive nucleus in the control (CTL), hypothalamic obese (HyO) Sham and HyO with duodenal-jejunal bypass (DJB) pancreases. Arrows represent the nucleus stained by Ki67. Data are reported as means±SEM (n=3–4). P<0.05, different letters indicate significant differences (one-way ANOVA followed by the Tukey post-test).