• E Toussirot, N U Nguyen, G Dumoulin, J Regnard, and D Wendling.
• Department of Rheumatology, University Hospital J. Minjoz, Besançon, France.
• Br. J. Rheumatol. 1998 Nov 1; 37 (11): 1172-6.

ObjectiveLow bone mass, vertebral osteopenia and fractures have been described in patients with ankylosing spondylitis (AS), but the aetiology of this osteoporosis (OP) remains unknown. Insulin-like growth factor-I (IGF-I), a bone-promoting peptide, may be considered as reflecting osteoblast function as well as its main binding protein, insulin-like growth factor binding protein-3 (IGFBP-3). Both were found to be decreased in post-menopausal women and male patients with idiopathic OP. In this study, we aimed to measure the circulating IGF-I and IGFBP-3 in AS patients.MethodsThirty-three AS patients were compared to 23 healthy controls. Bone mineral density (dual X-ray absorptiometry) was measured at the spine and the femoral neck. We determined the serum levels of growth hormone (GH), insulin, glycaemia, and the IGF-I and IGFBP-3 serum concentrations.ResultsA lowered lumbar spine bone mineral density was found in the AS group (AS: 0.946 g/cm2, controls: 1.02 g/cm2; P = 0.05). AS patients had a higher glycaemia than controls, but results were in the normal range. There were no significant differences in the mean values for GH and insulin. Mean IGF-I serum levels were 218.3 ng/ml (+/-72.4) in patients and 212.1 (+/-71.1) in controls (P = 0.75). The serum concentrations of IGFBP-3 were significantly lower in AS (3.29+/-0.6 microg/ml) than in healthy subjects (3.63+/-0.6 microg/ml; P = 0.05). There was a negative correlation between the serum IGFBP-3 concentration and erythrocyte sedimentation rate (r = -0.39; P = 0.025).ConclusionsSince IGFBP-3 is an important cofactor for IGF-I and modulates its bioavailability and activity in bone, these data suggest that osteoblast cell function could be impaired in AS. Inflammation could play a role in this IGFBP-3/IGF-I axis involvement. However, further studies are warranted to determine the role of the other growth factors and their binding proteins in the OP of AS.

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