Differential regulation of protein synthesis in hepatic and intestinal tissues by amino acids: Studies in patients recovering from major abdominal operations

Enteral delivery of proteins enhances the expression of proteins involved in the cytoskeleton and protein biosynthesis in human duodenal mucosa

BACKGROUND

Amino acids are well known to be key effectors of gut protein turnover. We recently reported that enteral delivery of proteins markedly stimulated global duodenal protein synthesis in carbohydrate-fed healthy humans, but specifically affected proteins remain unknown.

OBJECTIVE

We aimed to assess the influence of an enteral protein supply on the duodenal mucosal proteome in carbohydrate-fed humans.

DESIGN

Six healthy volunteers received for 5 h, on 2 occasions and in random order, either an enteral infusion of maltodextrins alone (0.25 g · kg⁻¹ · h⁻¹) mimicking the fed state or maltodextrins with a protein powder (0.14 g proteins · kg⁻¹ · h⁻¹). Endoscopic duodenal biopsy specimens were then collected and frozen until analysis. A 2-dimensional polyacrylamide gel electrophoresis-based comparative proteomics analysis was then performed, and differentially expressed proteins (at least ±1.5-fold change; Student's t test, P < 0.05) were identified by mass spectrometry. Protein expression changes were confirmed by Western blot analysis.

RESULTS

Thirty-two protein spots were differentially expressed after protein delivery compared with maltodextrins alone: 28 and 4 spots were up- or downregulated, respectively. Among the 22 identified proteins, 11 upregulated proteins were involved either in the cytoskeleton (ezrin, moesin, plastin 1, lamin B1, vimentin, and β-actin) or in protein biosynthesis (glutamyl-prolyl-transfer RNA synthetase, glutaminyl-transfer RNA synthetase, elongation factor 2, elongation factor 1δ, and eukaryotic translation and initiation factor 3 subunit f).

CONCLUSIONS

Enteral delivery of proteins altered the duodenal mucosal proteome and mainly stimulated the expression of proteins involved in cytoskeleton and protein biosynthesis. These results suggest that protein supply may affect intestinal morphology by stimulating actin cytoskeleton remodeling.

Albumin synthesis rates are not responsive to hyperglycemic hyperinsulinemia in postoperative patients

BACKGROUND

Insulin regulates albumin synthesis in vitro and in various experimental models. The current study was undertaken to determine the effects of a physiologic hyperinsulinemia on albumin synthesis in postoperative patients in whom plasma albumin concentrations are decreased.

METHODS

Studies were performed in postabsorptive patients after major abdominal operations. Mass spectrometry techniques were used to directly determine the incorporation rate of 1-[(13)C]-leucine into albumin. Consecutive blood samples were taken during a continuous isotope (D-Glc) infusion (0.16 µmol/kg/min). Isotopic enrichments were determined at baseline (period I) and after a 4-hour D-glucose (D-Glc) infusion at currently recommended rates (170 mg/kg/h, n = 10) or after infusion of saline (control group, n = 8) (period II).

RESULTS

After D-Glc infusion, plasma insulin concentrations increased significantly (period I, 6.6 ± 1.8 µU/mL; period II, 21.4 ± 2.1 µU/mL; P < .01). In contrast, plasma insulin concentration remained constant in control patients (period I, 3.8 ± 0.9 µU/mL(-1); period II, 5.9 ± 1.1 µU/mL; not significant vs period I, but P < .005 vs the corresponding value at the end of period II in the control group). Hyperinsulinemia was without effect on fractional albumin synthesis (period I, 12.8% ± 1.9%/d; period II, 11.9% ± 1.9%/d; not significant), and synthesis rates corresponded to those measured in controls (period I, 13.0% ± 1.2%/d; period II, 12.1% ± 0.1%/d; not significant vs period I and vs D-Glc infusion).

CONCLUSIONS

A standard D-Glc infusion is insufficient to increase albumin synthesis in postoperative patients.

Postoperative hypoproteinemia in cancer patients following extensive abdominal surgery despite parenteral nutritional support

Determination of the predictors of hypoproteinemia among cancer patients following extensive surgery may enhance their nutritional management and clinical outcome. This study evaluated the predictive factors of postoperative hypoproteinemia among cancer patients following extensive abdominal surgery. An age- and gender-matched case-control study (n = 115) was conducted among cancer patients undergoing extensive (cases; n = 81) and moderate (controls; n = 34) abdominal surgery. Case patients received total parenteral nutrition (TPN), including 3 units of fresh frozen plasma and 200 mL 5% human albumin solution, for 8 postoperative days (POD). Case patients had lower mean total serum protein (TSP) levels throughout POD 8 (F value = 13.81; P = 0.001). Despite TPN, cases had greatest mean (±SD) TSP percent change on POD 1 (-24.6% ± 13.0, vs. -12.6% ± 9.2; P < 0.0001) and did not regain preoperative levels (POD 8: -14.3% ± 12.5 vs. 6.9% ± 13.4; P = 0.006). The likelihood of hypoproteinemia in this group was greatest on POD 3 (OR = 30.57; 95% CI 5.44-171.83). Multivariate regression analyses indicated that the determinants of postoperative hypoproteinemia were age [Adjusted OR (AOR) = 1.04; 95% CI 1.00-1.08), preoperative TSP (AOR = 0.46; 95% CI 0.23-0.92), and extensive surgery (AOR = 2.65; 95% CI 1.01-6.95). Tailored nutritional support, regarding extent of surgery, preoperative TSP, and patient age are needed to deter the occurrence of postoperative hypoproteinemia and consequent adverse surgical outcome among cancer patients.