Date of Completion

12-18-2013

Embargo Period

12-18-2013

Keywords

amino acids, calcium absorption, dietary protein

Major Advisor

Jane Kerstetter

Associate Advisor

Karl Insogna

Associate Advisor

Nancy Rodriguez

Associate Advisor

Yih-Woei Fridell

Associate Advisor

Anne Kenny

Field of Study

Nutritional Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

We undertook a randomized, double-blind, crossover study in 14 healthy women who were required to ingest a 6-day low protein diet supplemented with CaSR-AAA (calcium-sensing receptor-activating amino acids), DAA (dibasic amino acids) or methylcellulose capsules (control). All subjects ingested all three diets in random order. Prior to each experimental diet subjects consumed an 11 day adjustment diet. Calcium absorption was measured on day 5 of each dietary intervention using dual-stable calcium isotopes. The clinical trial tested the hypothesis that dietary protein affects the efficiency of intestinal calcium absorption by activating the calcium sensing receptor (CaSR). Supplementation with CaSR-AAA did not significantly increase Ca absorption. However, a trend towards improved Ca absorption was observed with DAA (25.2±1.4% vs. 22.3±1.4%, P=0.094).

To further elucidate the mechanisms by which dietary protein improves Ca absorption, we established and validated a 45Ca in vitro transport model. Differentiated Caco-2 cells were exposed to different concentrations of amino acids for 6 and 72 hours. Prolonged amino acid treatment significantly enhanced total transepithelial Ca transport (P=0.0048).

Subsequent in vitro studies utilized our recently validated transport model and focused on the functional role of Cldn-2 in total transepithelial Ca transport. Cldn-2 is a tight junction protein that was previously shown to be upregulated by dietary protein in rats. Total transepithelial Ca transport was significantly reduced when Cldn-2 was stably knocked down in Caco-2 cells (P< 0.0001). The contribution of Cldn-2 to amino acid-induced increases in Ca transport will be explored in future studies.

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