NASA-inspired analysis could anticipate bone loss

By Sarah Guy

Measuring naturally occurring calcium (Ca) isotopes in urine could indicate whether someone is experiencing bone loss long before traditional imaging methods are able to, say US researchers.

The findings show that Ca isotopes in urine change rapidly in response to bone mineral balance (BMB), with lighter isotopes entering bone faster than heavy ones, explains the team in a press release accompanying the study.

"Bone is continuously being formed and destroyed," said co-author Joseph Skulan (Arizona State University, Tempe). "In healthy, active humans, these processes are in balance. But if a disease throws the balance off then you ought to see a shift in the calcium isotope ratios."

Skulan and colleagues believe the results could be of great value for the early diagnosis and evaluation of therapies for metabolic bone diseases like osteoporosis and some cancers.

It could also allow "safe, rapid assessment of individual subjects' response to treatment," they write in the Proceedings of the National Academy of Sciences.

The team conducted a 30-day study during which 12 participants (eight men) underwent complete bed rest involving controlled sleep and wake patterns, diet, and room temperature. They gave blood and urine samples that were analyzed for Ca isotope abundance.

Bed rest induces bone loss via skeletal unloading, the same effect that astronauts experience during space flight, explain Skulan and co-investigators. However, while better methods of monitoring and counteracting this effect in space are needed, these methods "are also relevant to general medicine."

Mean Ca isotope values among the participants decreased significantly over the study period, from a pre-bed rest value of 2.4 part per 10,000 (pptt) to 0.9 pptt at day 30.

Indeed, even by day 10 of the study, the average Ca isotope value in the cohort was significantly lower than the pre-bed rest mean, remark Skulan et al.

Furthermore, measurements of the bone resorption marker N-teleopeptide had increased significantly by day 9 of bed rest and remained significantly elevated, indicating that bone resorption increased.

"The next step is to see if [the concept] works in patients with bone-altering diseases," concluded co-author Ariel Anbar.

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