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Cellular distribution of N-acetyltransferase activity in the rat small intestine
J A Ware1, T P Reilly, C K Svensson
1Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48202, USA.
Abstract:
The cellular distribution of AcCoA:arylamine N-acetyltransferase (NAT; EC 2.3.1.5) activities was examined in the rat small intestine to determine if heterogeneous cellular distribution contributes to preferential tumor development in the colonic region after exposure to heterocyclic amines (HAs). A chelation/elution method was used to preferentially isolate villus-tip, mid-villus, and crypt enterocytes. Monomorphic (NAT1) and polymorphic (NAT2) activities were determined using N-acetylprocainamide and N-acetamidobenzoic acid formation, respectively. Sucrase-isomaltase (SI) activity was used to confirm that a villus, mid-villus, and crypt cell gradient had been obtained. Utilizing this marker of villus enrichment, a 4- to 10-fold gradient was achieved. NAT1 and NAT2 activities followed this gradient, with the highest NAT activity occurring in the fraction with the highest SI activity. The ratio of NAT2:NAT1 remained essentially constant along the gradient, indicating a similar pattern of expression for both enzymes. This pattern of cellular distribution for the NATs is similar to that reported for cytochrome P450s. This apparent preferential expression of NAT in the villus cells may result in delivery of bioactivated HAs to the lower regions of the intestines as the villus-tip cells are extruded into the intestinal lumen and enter the fecal stream.
Insights
N-acetyltransferase (NAT) enzymes show preferential expression in rat small intestine villus cells. This distribution may lead to heterocyclic amine bioactivation and delivery to the colon, potentially influencing tumor development.
Area of Science:
- Gastroenterology
- Toxicology
- Biochemistry
Background:
- Heterocyclic amines (HAs) are linked to colon cancer.
- The cellular distribution of N-acetyltransferase (NAT) enzymes in the rat small intestine is not well understood.
- Understanding NAT distribution is crucial for explaining preferential tumor development in the colon.
Purpose of the Study:
- To investigate the cellular distribution of AcCoA:arylamine N-acetyltransferase (NAT) activities in the rat small intestine.
- To determine if heterogeneous NAT distribution contributes to preferential tumor development after exposure to heterocyclic amines (HAs).
Main Methods:
- Isolated villus-tip, mid-villus, and crypt enterocytes using a chelation/elution method.
- Assessed monomorphic (NAT1) and polymorphic (NAT2) activities using specific substrate formations.
- Utilized Sucrase-isomaltase (SI) activity as a marker for villus enrichment.
Main Results:
- Achieved a 4- to 10-fold gradient of villus enrichment using SI activity.
- NAT1 and NAT2 activities followed the villus enrichment gradient, with highest activity in villus-tip cells.
- The ratio of NAT2:NAT1 remained constant, indicating similar expression patterns for both enzymes.
Conclusions:
- NAT enzymes are preferentially expressed in rat small intestine villus cells.
- This preferential expression may lead to the delivery of bioactivated HAs to the lower intestine.
- This cellular distribution pattern could explain the higher incidence of colonic tumors observed after HA exposure.