Effects of microgravity on urinary osteopontin

Area of Science:

• Space medicine
• Nephrology
• Biochemistry

Background:

• Space flight increases renal stone formation risk due to bone demineralization and altered urinary composition.
• Key factors include increased calcium oxalate supersaturation and decreased urinary citrate, magnesium, and volume.
• Current stone risk profiles lack comprehensive assessment of crystallization inhibitors.

Purpose of the Study:

• To evaluate urinary protein inhibitors of calcium crystallization for improved space flight renal stone risk prediction.
• To correlate mineral saturation with inhibitor protein concentrations in astronauts.
• To analyze urinary osteopontin (uropontin) excretion patterns in astronauts before, during, and after space flight.

Main Methods:

• Studied 14 astronauts, measuring urinary osteopontin (uropontin) levels.
• Collected samples pre-flight, in-flight, and post-flight.
• Analyzed molecular size shifts in uropontin.

Main Results:

• No compensatory increase in uropontin excretion was observed during space flight.
• A majority of astronauts showed increased uropontin excretion post-flight, peaking at 2 weeks after landing.
• Observed molecular size shifts in uropontin were attributed to storage conditions, not microgravity effects.

Conclusions:

• Urinary osteopontin (uropontin) excretion does not increase during space flight.
• Post-flight increases in uropontin suggest its potential role in assessing renal stone risk after space missions.
• Storage conditions, not microgravity, altered uropontin molecular size during flight.