Influence of hyperosmotic environment comparable to the renal medulla upon membrane NADPH oxidase of human polymorphonuclear leukocytes
Related Experiment Videos
K Takahashi1, T Matsumoto, S Kubo
1Department of Urology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Abstract:
Hyperosmotic environment in the renal medulla seems important for bacterial pyelonephritis because it exerts inhibitory influences upon the function of polymorphonuclear leukocytes (PMN). Urea and NaCl primarily contribute to high osmolarity in the renal medulla. We previously reported that PMN function was actually suppressed in phagocytosis, intracellular bacterial killing and superoxide generation in the hyperosmotic solution of urea and NaCl. In the present report, to verify the mechanism of this inhibitory effect, a kinetic study for NADPH oxidase in the cell membrane, the key enzyme complex of superoxide generation, was carried out in the cell membrane-solubilizing system under the hyperosmotic condition caused by urea or NaCl. Urea directly denaturated NADPH oxidase, and its inhibitory mechanism was reversible and uncompetitive with a decrease in Vmax and Km, while NaCl had no effect upon it, maintaining Lineweaver-Burk plots in the same position as those of the control. This result suggests that urea at least produces an inhibitory effect upon PMN through the direct inactivation of NADPH oxidase, although NaCl was unable to do so.
Insights
Urea in the renal medulla inhibits polymorphonuclear leukocyte (PMN) function by directly inactivating NADPH oxidase, a key enzyme for superoxide generation. This mechanism explains how high osmolarity affects immune response during pyelonephritis.
Area of Science:
- Nephrology
- Immunology
- Biochemistry
Background:
- The renal medulla's hyperosmotic environment, mainly from urea and NaCl, impacts bacterial pyelonephritis.
- High osmolarity is known to inhibit polymorphonuclear leukocyte (PMN) functions like phagocytosis and bacterial killing.
Purpose of the Study:
- To investigate the mechanism by which hyperosmotic conditions, specifically urea and NaCl, inhibit PMN function.
- To kinetically analyze the effect of urea and NaCl on NADPH oxidase, the key enzyme in superoxide generation.
Main Methods:
- A kinetic study of NADPH oxidase was performed in a cell membrane-solubilizing system.
- Hyperosmotic conditions were created using urea or NaCl.
- Lineweaver-Burk plots were used to analyze enzyme kinetics.
Main Results:
- Urea directly denatured NADPH oxidase, causing reversible, uncompetitive inhibition (decreased Vmax and Km).
- NaCl did not affect NADPH oxidase activity, with Lineweaver-Burk plots remaining unchanged compared to controls.
- This indicates urea, not NaCl, directly inactivates NADPH oxidase.
Conclusions:
- Urea directly inactivates NADPH oxidase, contributing to the inhibitory effect on PMN function in hyperosmotic renal medulla.
- NaCl does not appear to inhibit PMN function through direct inactivation of NADPH oxidase.
- These findings elucidate a specific molecular mechanism underlying immune cell dysfunction in pyelonephritis.