Ca. Scotchford et Sy. Ali, ASSOCIATION OF MAGNESIUM WHITLOCKITE CRYSTALS WITH LIPID COMPONENTS OF THE EXTRACELLULAR-MATRIX IN HUMAN ARTICULAR-CARTILAGE, Osteoarthritis and cartilage, 5(2), 1997, pp. 107-119
Several basic calcium phosphate mineral phases have been reported to b
e associated with osteoarthritis joint disease. Magnesium whitlockite
crystal deposition has been reported in both osteoarthritic and normal
human articular cartilage. Existing data suggest that likely prevaili
ng conditions within cartilage would not support de novo whitlockite f
ormation. It would appear, therefore, that additional factors must be
extant at sites of crystal deposition. In this study normal articular
cartilage specimens were examined for the presence and distribution of
lipids relative to crystal deposition within the extracellular matrix
. Specimens were examined using light and transmission electron micros
copy (TEM), with standard processing protocols plus a malachite green-
glutaraldehyde-osmium tetroxide (MGO) method, used to retain lipids no
rmally removed from tissues during preparation for electron microscopy
. Elemental maps of sections produced using this method were also made
using X-ray microanalysis. Positive oil red O staining for lipid was
clearly apparent immediately below and parallel to the articular surfa
ce of cartilage specimens using light microscopy. The extent and distr
ibution of staining correlated well with the distribution of crystals,
observed by TEM, in sections of tissue from adjacent sites of the sam
e specimens. Using standard TEM, crystals were frequently observed sca
ttered amongst intramatrical lipidic debris, particularly pericellular
ly, in areas of cell necrosis and amongst close packed tangential fibe
rs between the articular surface and initial superficial zone chondroc
ytes. Cartilage specimens processed using the MGO method demonstrated
electron dense features, not apparent using standard techniques, ident
ified as lipid. Such extracellular lipid deposition varied with depth,
with 100nm globular bodies present in the superficial region, where c
olocalization of crystals and lipid were observed in about 10% of crys
tal observations. The association of lipid and crystal deposition is d
iscussed in the context of phospholipid associated mineral formation a
nd the potential role of such magnesium whitlockite deposition assesse
d.