Na,K-ATPase: a molecular target for Leptospira interrogans endotoxin

Area of Science:

• Biochemistry
• Pathophysiology
• Microbiology

Background:

• Leptospirosis is a significant zoonotic disease.
• A previously identified glycolipoprotein fraction (GLP) from Leptospira interrogans inhibits renal Na,K-ATPase.
• This inhibition was hypothesized as a primary cellular defect in leptospirosis.

Purpose of the Study:

• To investigate the role of GLP in leptospirosis pathogenesis.
• To determine if GLP inhibits all Na,K-ATPase isoforms in affected tissues.
• To assess GLP's effect on Na,K-ATPase in leptospirosis-resistant species and intact cells, and its specificity against H,K-ATPase.

Main Methods:

• Testing GLP inhibition across Na,K-ATPase isoforms in rabbits.
• Comparing GLP sensitivity of Na,K-ATPase in rat (resistant) versus rabbit (sensitive) kidneys.
• Measuring ouabain-sensitive rubidium uptake in rat kidney tubules to assess GLP activity in intact cells.
• Evaluating GLP's effect on renal H,K-ATPase activity.

Main Results:

• GLP effectively inhibited all known Na,K-ATPase isoforms in rabbit tissues (IC50: 120-220 µg/mL).
• Rat kidney Na,K-ATPase showed similar sensitivity to GLP as rabbit, indicating resistance is not due to enzyme insensitivity.
• GLP significantly reduced rubidium uptake in intact rat kidney cells, confirming cellular activity.
• GLP did not affect renal H,K-ATPase activity, showing specificity for Na,K-ATPase.

Conclusions:

• The findings support the hypothesis that GLP-induced Na,K-ATPase inhibition is an initial mechanism in leptospirosis.
• GLP's inhibitory action on Na,K-ATPase isoforms in target tissues is consistent across species.
• GLP demonstrates specificity for Na,K-ATPase over H,K-ATPase, suggesting a targeted pathogenic mechanism.