Two low-molecular-mass inhibitors of
matrix metalloproteinases (
MMPs),
CT1166, a concentration-dependent selective inhibitor of
gelatinases A and B, and
Ro 31-7467, a concentration-dependent selective inhibitor of
collagenase, were examined for their effects on
bone resorption and type-I collagenolysis. The test systems consisted of measuring (1) the release of [3H]
proline from prelabelled mouse calvarial explants; (2) the release of 14C from prelabelled
type-I collagen films by mouse calvarial osteoblasts; and (3) lacunar resorption by isolated rat osteoclasts cultured on ivory slices. In 24 h cultures,
CT1166 and
Ro 31-7467 inhibited both
interleukin-1 alpha- (IL-1 alpha; 10(-10) M) and
1,25-dihydroxyvitamin D3 (10(-8) M)-stimulated
bone resorption in cultured neonatal mouse calvariae at concentration selective for the inhibition of
gelatinase (10(-9) M for
CT1166) and
collagenase (10(-8) M for
Ro 31-7467) respectively. For each compound the inhibition was dose-dependent, reversible, and complete at
a 10(-7) M concentration. However,
CT1166 (10(-9) M) and
Ro 31-7467 (10(-8) M) in combination were required to completely abolish
IL-1 alpha-stimulated
bone resorption in mouse calvariae throughout a 96 h culture period. Neither of the inhibitors affected
protein synthesis,
DNA synthesis nor the
IL-1 alpha-stimulated secretion of the lysosomal
enzyme,
beta-glucuronidase. Both
CT1166 and
Ro 31-7467 partially inhibited
IL-1 alpha-stimulated lacunar resorption by isolated osteoclasts, but were without effect on unstimulated lacunar resorption. Rodent osteoclasts produced
collagenase and
gelatinases-A and -B activity. In contrast the substrate used to assess osteoclast lacunar resorption contained no detectable
collagenase or
gelatinase activity. Both compounds dose-dependently inhibited
1,25-dihydroxyvitamin D3 (10(-8) M)-stimulated degradation of
type-I collagen by mouse calvarial osteoblasts; however, complete inhibition of collagenolysis was only achieved at concentrations at which
CT1166 and
Ro 31-7467 act as general
MMP inhibitors. This study demonstrates that
collagenase and
gelatinases A and/or B participate in
bone resorption. While these
MMPs may be primarily involved in osteoid removal, we conclude that they may also be released by osteoclasts, where they participate in bone
collagen degradation within the resorption lacunae.