Continuous parenteral and enteral nutrition induces metabolic dysfunction in neonatal pigs

Abstract

Background: We previously showed that parenteral nutrition (PN) compared with formula feeding results in hepatic insulin resistance and steatosis in neonatal pigs. The current aim was to test whether the route of feeding (intravenous [IV] vs enteral) rather than other feeding modalities (diet, pattern) had contributed to the outcome.

Methods: Neonatal pigs were fed enterally or parenterally for 14 days with 1 of 4 feeding modalities as follows: (1) enteral polymeric formula intermittently (FORM), (2) enteral elemental diet (ED) intermittently (IEN), (3) enteral ED continuously (CEN), and (4) parenteral ED continuously (PN). Subgroups of pigs underwent IV glucose tolerance tests (IVGTT) and hyperinsulinemic-euglycemic clamps (CLAMP). Following CLAMP, pigs were euthanized and tissues collected for further analysis.

Results: Insulin secretion during IVGTT was significantly higher and glucose infusion rates during CLAMP were lower in CEN and PN than in FORM and IEN. Endogenous glucose production rate was suppressed to zero in all groups during CLAMP. In the fed state, plasma glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide (GLP)-1, and GLP-2 were different between feeding modalities. Insulin receptor phosphorylation in liver and muscle was decreased in IEN, CEN, and PN compared with FORM. Liver weight was highest in PN. Steatosis and myeloperoxidase (MPO) activity tended to be highest in PN and CEN. Enterally fed groups had higher plasma GLP-2 and jejunum weight compared with PN.

Conclusions: PN and enteral nutrition (EN) when given continuously as an elemental diet reduces insulin sensitivity and the secretion of key gut incretins. The intermittent vs continuous pattern of EN produced the optimal effect on metabolic function.

Figure 1

Intravenous glucose tolerance tests (IVGTT). Plasma glucose and insulin concentrations and respective AUC values during IVGTT on day 7 (A, B) and on day 14 (C, D) in FORM, IEN, CEN, and PN pigs. Results are expressed as mean ± SEM; n = 5–8 per group;^abcd different from PN, CEN, IEN, and FORM, respectively; P < .05. CEN, continuous enteral nutrition; FORM, intermittent formula feeding; IEN, intermittent enteral nutrition; PN, parenteral nutrition.

Figure 2

Hyperinsulinemic-euglycemic clamp (CLAMP). Glucose, insulin, and glucagon during 6-hour infusion of D[¹³C₆] glucose (0.005 mmol/kg·min) during fasting (0–2 hours) and CLAMP (3–6 hours) with insulin infusion of 31 pmol/kg^0.66·min. Plasma glucose during fasting (A), glucose infusion rates during CLAMP (B), endogenous glucose production and plasma glucagon during fasting (C, E), and CLAMP (D, F). Plasma insulin (pmol/L) between groups was not different during fasting (12 ± 1), n = 54, or CLAMP (378 ± 12), n = 32. Results are expressed as mean ± SEM; n = 6–20 per group; ^abcd different from PN, CEN, IEN, and FORM, respectively; P < .05. CEN, continuous enteral nutrition; FORM, intermittent formula feeding; IEN, intermittent enteral nutrition; PN, parenteral nutrition.

Figure 3

Incretin hormones. Plasma GLP-1 (A) and GIP (B) concentrations in the fed state after 9–12 days of treatment. Results are expressed as mean ± SEM; n = 6–20 per group;^abcd different from PN, CEN, IEN, and FORM, respectively; P < .05. GLP-1, glucagon-like peptide-1; GIP, glucose-dependent insulinotropic polypeptide; CEN, continuous enteral nutrition; FORM, intermittent formula feeding; IEN, intermittent enteral nutrition; PN, parenteral nutrition.

Figure 4

Insulin signaling. Relative abundance and phosphorylation of proteins in liver and skeletal muscle tissue samples from neonatal pigs treated for 14 days after a 4-hour hyperinsulinemic-euglycemic clamp (CLAMP) on day 14. Liver tissue relative abundance of phospho-IR (pIR) (A), phospho-IRS-1 (pIRS-1) (B), and PI3K (C). Muscle tissue relative abundance of phospho-IR (pIR) (D), phospho-IRS-1 (pIRS-1) (E), and PI3K (F). Phosphorylated proteins expressed relative to total protein and PI3K protein expressed relative to tubulin. Results are expressed in arbitrary units as mean ± SEM; n = 6 per group;^abcd different from PN, CEN, IEN, and FORM, respectively; P < .05. IR, insulin receptor; IRS-1, insulin receptor substrate 1; PI3K, phosphatidylinositol 3 kinase; CEN, continuous enteral nutrition; FORM, intermittent formula feeding; IEN, intermittent enteral nutrition; PN, parenteral nutrition.

Figure 5

Hepatic steatosis and inflammation. Livers from neonatal pigs treated for 14 days. Representative Oil Red O–stained liver sections showing lipid droplets (red) (A); liver weight per kilogram of body weight (BW) (B), hepatic triglyceride (TG) content per gram of liver tissue (C) and per kilogram of BW (D); hepatic myeloperoxidase (MPO) activity (E). Results are expressed as mean ± SEM; n = 7–17 per group;^abcd different from PN, CEN, IEN, and FORM, respectively; P < .05. CEN, continuous enteral nutrition; FORM, intermittent formula feeding; IEN, intermittent enteral nutrition; PN, parenteral nutrition.

Figure 6

Hepatic steatosis is associated with increased insulin resistance. Nonlinear regression analysis of hepatic triglyceride (TG) content and glucose infusion rate during hyperinsulinemic euglycemic clamp (y = 1.72E−4 x² – 8.67E−3×+ 1.82E−1; R² = 0.637; P < .0001; n = 32). CEN, continuous enteral nutrition; FORM, intermittent formula feeding; IEN, intermittent enteral nutrition; PN, parenteral nutrition.

Figure 7

Intestinal growth. Plasma GLP-2 concentrations in the fed state after 9–12 days of treatment (A). Jejunum (B) and ileum (C) weight per kilogram of body weight (BW) of neonatal pigs treated for 14 days. Results are expressed as mean ± SEM; n = 5–20 per group;^abcd different from PN, CEN, IEN, and FORM, respectively; P < .05. GLP-2, glucagon-like peptide-2; CEN, continuous enteral nutrition; FORM, intermittent formula feeding; IEN, intermittent enteral nutrition; PN, parenteral nutrition.