In vitro intestinal lead uptake and transport in relation to speciation

Area of Science:

• Environmental Health
• Toxicology
• Biochemistry

Background:

• Children's substantial exposure to lead via soil ingestion necessitates understanding oral bioavailability.
• Oral bioavailability of soilborne lead is a complex process involving ingestion, bioaccessibility, intestinal transport, and first-pass metabolism.
• Previous research characterized lead bioaccessibility and speciation in artificial intestinal fluid.

Purpose of the Study:

• To investigate the transport of bioaccessible lead across the intestinal epithelium using an in vitro model.
• To determine the extent and mechanisms of lead absorption by intestinal cells.
• To assess the implications of these findings for the risk assessment of soilborne lead exposure in children.

Main Methods:

• Utilized the Caco-2 cell line as a model for the human intestinal epithelium.
• Exposed Caco-2 cell monolayers to diluted artificial human intestinal fluid (chyme) containing lead.
• Quantified lead association with cells and transport across the monolayer over 24 hours.
• Analyzed the relationship between lead speciation in chyme and cellular uptake.

Main Results:

• Approximately 27% of lead associated with Caco-2 cells, and 3% transported across the monolayer within 24 hours.
• Lead association with cells showed a linear correlation with the total lead concentration.
• Bile levels did not influence the fraction of lead associated with the cells.
• Lead transport occurred without reaching equilibrium, suggesting ongoing absorption.

Conclusions:

• In vitro intestinal transport studies indicate that only a fraction of bioaccessible lead is absorbed.
• Lead species other than free Pb(2+) ions, such as lead phosphate and lead bile complexes, contribute to intestinal lead transport.
• These findings refine our understanding of soilborne lead's oral bioavailability and inform risk assessments for children.