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Ganciclovir permeation of the human erythrocyte membrane
W B Mahony1, B A Domin, T P Zimmerman
1Experimental Therapy Division, Wellcome Research Laboratories, Research Triangle Park, NC 27709.
Abstract:
The membrane permeation of ganciclovir (DHPG)--a structural analogue of acyclovir (ACV) with activity against cytomegalovirus--was investigated in human erythrocytes at 37 degrees with an "inhibitor-stop" assay. DHPG influx was nonconcentrative, occurred without permeant metabolism, and was rate-saturable. While substantial inhibition of the influx of 13 microM DHPG occurred only in the presence of permeants of the purine nucleobase carrier, nucleosides and inhibitors of nucleoside transport markedly inhibited DHPG influx at higher DHPG concentrations (greater than or equal to 200 microM). Adenine and dilazep (a potent inhibitor of the nucleoside carrier) each inhibited the influx of DHPG only partially; when present together, however, they inhibited DHPG permeation completely. DHPG permeation via the purine nucleobase carrier (Km = 0.89 mM) was characterized by assessing influx in the presence of 1.0 microM dilazep. Adenine and ACV were shown to competitively inhibit this process, while DHPG (Ki = 0.90 mM) was found to competitively inhibit adenine influx. DHPG influx via the nucleoside carrier (Km = 14 mM) was characterized by assessing influx in the presence of 2 mM adenine. DHPG (Ki = 10 mM) also appeared to competitively inhibit the influx of 5-iodo-2'-deoxyuridine. These results indicate that DHPG permeates the human erythrocyte membrane primarily by the purine nucleobase carrier and secondarily by the nucleoside transporter.
Insights
Ganciclovir (DHPG) enters human red blood cells through two main pathways: the purine nucleobase carrier and, to a lesser extent, the nucleoside transporter. This understanding is crucial for drug delivery and antiviral research.
Area of Science:
- Pharmacokinetics
- Membrane Transport Biology
Background:
- Ganciclovir (DHPG) is an acyclovir (ACV) analogue effective against cytomegalovirus.
- Understanding DHPG membrane permeation is key for optimizing its therapeutic use.
Purpose of the Study:
- To investigate the membrane permeation mechanisms of ganciclovir (DHPG) in human erythrocytes.
- To identify the specific transporters involved in DHPG uptake.
Main Methods:
- Utilized an "inhibitor-stop" assay in human erythrocytes at 37°C.
- Investigated the effects of various permeants and inhibitors on DHPG influx.
Main Results:
- DHPG influx is nonconcentrative, not metabolism-dependent, and exhibits saturation kinetics.
- Purine nucleobase carrier is the primary route for DHPG permeation (Km = 0.89 mM).
- Nucleoside transporter is a secondary route (Km = 14 mM), particularly at higher DHPG concentrations.
Conclusions:
- DHPG utilizes both the purine nucleobase carrier and the nucleoside transporter for erythrocyte membrane permeation.
- The purine nucleobase carrier is the predominant pathway for DHPG uptake.