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The effect of nutrients on the rate of protein degradation in isolated small intestinal enterocytes from Sprague-Dawley rats Taghadomy Saberi, Mohsen


Nutrients affect small intestinal protein mass and metabolism. Studies on the effect of nutrients on small intestinal protein degradation are limited due to a lack of a proper method. The objectives of this study were to establish a method to directly estimate protein degradation in isolated enterocytes from rats, and to test the effect of energy substrates and amino acids on protein degradation. Male Sprague-Dawley rats (150-200 g, n ≥8 per treatment) were used. Cell viability, tyrosine release as an indicator of protein degradation, and the effect of osmolarity were measured to establish the method. The effects of energy substrates (50 mM glucose, 20 mM (β-hydroxybutyrate, 4.7 mM butyrate, and 30 mM glutamine) and amino acid solutions (30 mM amino acids mix, 30 mM glutamate, 1% ammonium, and 30 mM amino acids mix plus 50 mM glucose) on protein degradation were measured. Average viability at time 30 min was 85.8% (range 81-94%). Tyrosine release was linear over the course of experiments, indicating constant protein degradation (R²= 0.9943) (p<0.05). Osmolarity, glucose, and glutamine had no effect on protein degradation. [β-hydroxybutyrate significantly decreased it (-16%; p<0.05), whereas butyrate slightly increased it (+ 5%; p<0.05). The mixture of amino acids and glutamate increased (p<0.05) protein degradation (+ 10%) compared to control. Ammonium had no effect. The mixture of amino acids plus glucose decreased (-13%; p<0.05) protein degradation compared to the mix of amino acids only. High viability and constant rate of protein degradation indicate successful establishment of a method to estimate protein degradation in isolated small intestinal enterocytes from rats. The mixture of amino acids or glutamate may have acted as an energy source for the highly energy dependent enterocyte. Addition of glucose to the mixture of amino acids may have decreased the concentration of amino acids in tissue and abolished their effect. The large effect of β-hydroxybutyrate suggests a potential positive role for ketone bodies to limit the loss of small intestinal protein mass by decreasing protein degradation. These findings might be particularly important in catabolic conditions such as starvation or total parenteral nutrition, where the loss of small intestinal protein mass is substantial.

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