The insulin-like growth factor binding proteins in uncultured human cartilage: increases in insulin-like growth factor binding protein 3 during osteoarthritis.
OBJECTIVE
To assess changes in the insulin-like growth factor binding proteins (IGFBPs) in uncultured cartilage during stages of osteoarthritis (OA), and to determine if OA cartilage is capable of autocrine secretion of IGFBPs.


METHODS
Articular cartilage was dissected from fibrillated and nonfibrillated sites of 11 human femoral heads, and extracted in buffer containing 8M urea. IGFBPs were identified by immunoprecipitation and subsequent analysis by (125)I-IGF-2 Western ligand blotting (WLB), radioimmunoassay, or 2-site immunoradiometric assay (IRMA). IGFBPs were assessed in cartilage extracts by WLB. IGFBP-3 content was determined by IRMA and synthesis by metabolic labeling with (35)S-cysteine in organ cultures.


RESULTS
Sample grouping into 3 distinct OA strata was supported by gross pathology of the femoral heads, histologic grading of cartilage slices, and biochemical analysis of the glycosaminoglycan and protein content of the extracts. Group I was normal/mild OA, group II was intermediate OA, and group III was severe OA. IGFBP-2 was present in all samples, IGFBP-4 in sporadic samples, and BP-3 in group II-III samples. By IRMA, group I had a mean +/- SD of 6.26 +/- 2.6 ng IGFBP-3/mg soluble protein (IGFBP-3) (n = 6), group II had a mean +/- SD 14 +/- 7.5 IGFBP-3 (n = 10), and group III had a mean +/- SD 17.03 +/- 8.94 IGFBP-3 (n = 6). Analysis of variance showed group differences (F[3,19] = 3.84, P = 0.04), and post hoc tests revealed that IGFBP-3 levels were higher for group III versus group I (P = 0.04). OA cartilage synthesized IGFBP-3.


CONCLUSIONS
Increases in net cartilage content of IGFBP-3 occurred in intact OA cartilage, reaching statistically significant elevation in severe disease. There was autocrine IGFBP-3 production in OA cartilage.
D019898:Autocrine Communication; D015153:Blotting, Western; D002358:Cartilage, Articular / Q000737:chemistry / Q000378:metabolism*; D018450:Disease Progression; D005260:Female; D006031:Glycosylation; D006801:Humans; D015592:Immunoradiometric Assay; D066298:In Vitro Techniques; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology; D012720:Severity of Illness Index; D014020:Tissue Extracts / Q000378:metabolism
D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins; D014020:Tissue Extracts