Pharmacokinetic modeling of ascorbate diffusion through normal and tumor tissue

Area of Science:

• Pharmacokinetics and cellular transport
• Biomedical engineering
• Cancer research

Background:

• Ascorbate (vitamin C) delivery to tissues is crucial, but its penetration into avascular regions, common in solid tumors, remains unclear.
• Tumor hypoxia impairs nutrient delivery, potentially depleting essential molecules like ascorbate.
• Understanding ascorbate transport is vital for cancer therapy and nutritional support.

Purpose of the Study:

• To quantify ascorbate diffusion and transport parameters in dense tissues using a 3D pharmacokinetic model.
• To simulate ascorbate distribution in normal and hypoxic tumor tissues under various plasma concentrations.
• To determine the necessary ascorbate levels for effective tumor tissue saturation.

Main Methods:

• Utilized a multicell-layered, three-dimensional pharmacokinetic model for in vitro tissue studies.
• Measured ascorbate diffusion rates and compared them to mannitol.
• Determined cellular uptake parameters and fitted data to a diffusion model for simulations.

Main Results:

• Ascorbate diffused through dense tissue slightly slower than mannitol, primarily via the paracellular route.
• Simulations revealed heterogeneous ascorbate distribution in tumor tissue at physiological levels (10-100 μM).
• Supraphysiological plasma concentrations (>100 μM) are predicted to be necessary for effective ascorbate delivery to poorly vascularized tumor areas.

Conclusions:

• Ascorbate transport in dense tissues is primarily paracellular.
• Achieving adequate ascorbate levels in hypoxic tumor regions requires concentrations significantly above normal physiological levels.
• These findings inform strategies for using ascorbate in cancer treatment and supportive care.