Citrate acts as shock absorber in bone, prevents osteoporosis

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  • Published: Mar 25, 2014
  • Author: Steve Down
  • Channels: X-ray Spectrometry / NMR Knowledge Base
thumbnail image: Citrate acts as shock absorber in bone, prevents osteoporosis

The citrate ions in bone make up layers of "goo" which acts as a shock absorber and allows movement between the calcium phosphate crystals to give bones their flexibility and prevent them from shattering, say UK researchers. "It's this layered structure that's been missing from our knowledge, and we can now see that without it you're stuffed," said Melinda Duer, one of the team.

They used solid-state NMR spectroscopy and X-ray diffraction, backed up by calculations, to propose a bone model in which the citrate ions, produced by cell metabolism, interact with trapped water to produce layers which are sandwiched between thin mineral platelets. The layers allow the crystals to stay flat and move against each other, as they described in Proceedings of the National Academy of Sciences.

When the citrate escapes, it allows the calcium phosphate crystals in the bone to fuse together, leading to clumps of brittle mineral which are likely to be the cause of debilitating diseases such as osteoporosis. "In terms of chemistry, that solid clump of mineral is the most stable structure. Biomechanically, however, it's hopeless – as soon as you stand on it, it shatters. If we want to cure osteoporosis, we need to figure out how to stop the bigger holes forming in the protein matrix," explained Duer.

This new bone model explains several known facts which have been confounding scientists, especially the platelet form of bone mineral crystals. In addition, it accounts for the fact that there is more water in bone mineral than predicted by other models. "Bone mineral was thought to be closely related to this substance called hydroxyapatite. But what we've shown is that a large part of bone mineral – possibly as much as half of it in fact – is made up of this goo," concluded Duer.

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