Synthetic ¹³C-dipeptide breath test for the rapid assessment of pancreatic exocrine insufficiency in rats

Abstract

Objective. ¹³C-breath tests have been investigated in order to assess pancreatic exocrine function using various ¹³C-compounds, but they have not been accepted for routine clinical use. One of the barriers to their acceptance is that these tests are time-consuming and require up to several hours for breath collection. The purpose of this study was to design a novel ¹³C-compound that would make a rapid ¹³C-breath test for assessing exocrine pancreatic function possible. Material and methods. N-benzoyl-L-tyrosyl-1-¹³C-L-alanine was synthesized, and the characteristics of its cleavage in duodenal juice and in the duodenum of rats were examined. Thereafter, a ¹³C-breath test was carried out in which N-benzoyl-L-tyrosyl-1-¹³C-L-alanine was given orally to pancreatic exocrine-insufficient and normal control rats. Results. N-benzoyl-L-tyrosyl-1-¹³C-L-alanine was readily cleaved and liberated 1-¹³C-L-alanine in the duodenal juice. Carboxypeptidase was a major contributor to the cleavage. When N-benzoyl-L-tyrosyl-1-¹³C-L-alanine was injected into the duodenum and orally administered to the rats, the ¹³C atom% of CO₂ in breath increased rapidly. This indicated that N-benzoyl-L-tyrosyl-1-¹³C-L-alanine in the duodenum liberated ¹³C-Ala on cleavage. ¹³C-Ala is absorbed and metabolized to liberate ¹³CO₂, which is exhaled. It was shown that the Δ¹³CO₂ (‰) in the N-benzoyl-L-tyrosyl-1-¹³C-L-alanine breath test in the pancreatic exocrine-insufficient rats, in whom the absorption and metabolism of ¹³C-Ala was unimpaired, was significantly lower than that in the control rats. Conclusions. The rate of increase in the Δ¹³CO₂ (‰) in the N-benzoyl-L-tyrosyl-1-¹³C-L-alanine breath test is expected to be proportional to the rate of N-benzoyl-L-tyrosyl-1-¹³C-L-alanine cleavage by pancreatic proteases in the duodenum. We propose the N-benzoyl-L-tyrosyl-1-¹³C-L-alanine breath test as a rapid test for assessing pancreatic exocrine function.

• Carboxypeptidase
• 13C breath test
• dipeptide
• pancreatic exocrine function
• pancreatic protease