Related Experiment Videos
Kinetics of the uptake of antimicrobial agents by human polymorphonuclear leucocytes
1Research and Development Division, Heinrich Mack Nachf., Illertissen, Fed. Rep. of Germany.
Abstract:
The in-vitro rate constants of the cellular uptake and elimination of the antimicrobial agents josamycin (Wilprafen), erythromycin and tetracycline were measured in normal human polymorphonuclear leucocytes (PMNs) using the velocity gradient centrifugation technique with radiolabelled drugs at extracellular concentrations corresponding to therapeutically effective serum levels. The rate of antibiotic uptake increased stepwise in the order tetracycline less than erythromycin less than josamycin. The half-lives of the uptake came to 0.8 min for josamycin, 4.7 min for erythromycin, and 14.8 min for tetracycline. The extraordinarily rapid uptake of josamycin by PMNs corresponds to the high lipophility of the drug. The accumulation of the three tested antibiotics in PMNs occurred much faster than their elimination from the cells, suggesting directional transport of the molecules through the leucocyte membrane and/or rate limiting dissociation from intracellular binding sites. Significant differences between the drugs tested were observed in the temperature dependence of their rates of uptake. The apparent activation energies of cellular uptake amounted to 114.2 kJ mol-1 (josamycin), 68.6 kJ mol-1 (erythromycin) and 52.2 kJ mol-1 (tetracycline). There is experimental support for a contribution of the nucleoside carrier system to the membrane transport of josamycin.
Insights
Josamycin, erythromycin, and tetracycline uptake by human immune cells (PMNs) varies significantly, with josamycin showing the fastest cellular accumulation. This research highlights differential antibiotic transport mechanisms in immune cells.
Area of Science:
- Pharmacology
- Cell Biology
- Immunology
Background:
- Antimicrobial agents are crucial for treating infections.
- Understanding cellular uptake mechanisms of antibiotics by immune cells is vital for optimizing therapeutic efficacy.
- Polymorphonuclear leucocytes (PMNs) play a key role in host defense against microbial pathogens.
Purpose of the Study:
- To quantify and compare the in-vitro cellular uptake and elimination rates of josamycin, erythromycin, and tetracycline in human PMNs.
- To investigate the influence of drug lipophilicity and temperature on antibiotic transport kinetics.
- To explore potential mechanisms involved in the cellular accumulation of these antimicrobial agents.
Main Methods:
- Utilized radiolabelled antimicrobial drugs to measure in-vitro uptake and elimination rate constants.
- Employed the velocity gradient centrifugation technique for cellular analysis.
- Assayed drug concentrations in normal human PMNs at therapeutically relevant extracellular levels.
Main Results:
- Antibiotic uptake rates increased in the order: tetracycline < erythromycin < josamycin.
- Observed rapid josamycin uptake (half-life: 0.8 min) attributed to its high lipophilicity.
- Accumulation significantly exceeded elimination, suggesting directional transport or rate-limiting intracellular dissociation.
- Identified distinct temperature dependencies for uptake, with activation energies of 114.2 kJ/mol (josamycin), 68.6 kJ/mol (erythromycin), and 52.2 kJ/mol (tetracycline).
Conclusions:
- Josamycin exhibits exceptionally rapid cellular uptake by PMNs compared to erythromycin and tetracycline.
- Differences in uptake kinetics are linked to drug lipophilicity and membrane transport mechanisms.
- Evidence suggests the nucleoside carrier system may contribute to josamycin transport into PMNs.
- Findings provide insights into the pharmacokinetics of macrolides and tetracyclines within immune cells.