Type I collagen fibers account for 90% of the organic matrix of bone. The degradation of this collagen is a major event during bone resorption, but its mechanism is unknown. A series of data obtained in biological models strongly suggests that the recently discovered cysteine proteinase cathepsin K plays a key role in bone resorption. Little is known, however, about the actual action of cathepsin K on type I collagen. Here, we show that the activity of cathepsin K alone is sufficient to dissolve completely insoluble collagen of adult human cortical bone. We found that the collagenolytic activity of cathepsin K is directed both outside the helical region of the molecule, i.e. the typical activity of cysteine proteinases, and at various sites inside the helical region, hitherto believed to resist all mammalian proteinases but the collagenases of the matrix metalloproteinase family and the neutrophil elastase. This property of cathepsin K is unique among mammalian proteinases and is reminiscent of bacterial collagenases. It is likely to be responsible for the key role of cathepsin K in bone resorption.The only mammalian proteinases that have been shown to attack the native triple helical region of type I collagen are the collagenases of the MMP 1 family (1-3) and the neutrophil serine elastase (4) They cleave the type I collagen triple helix across all three chains (i.e. two ␣1 chains and one ␣2 chain) only at a specific point three-quarters of the way to the Nterminal end of the collagen molecule. Proteinases with broad specificity, such as cysteine proteinases, attack only the extrahelical regions that are located at either end of native collagen (telopeptides) and that represent only 4% of the molecule (5). Because the telopeptides are involved in intra-and intermolecular links, this attack may separate individual molecules. The latter proteinases may also attack destabilized triple helices, acting thereby as gelatinases. At 37°C, such a destabilization may transiently affect a small proportion of collagen molecules, because the melting temperature of soluble collagen is only a few degrees higher. It has also been emphasized that when collagen molecules are cross-linked and arranged in insoluble fibers they become more resistant to proteolysis (6). However, the co-operation of proteinases with distinct specificities toward the chemical bonds of collagen fibers has been shown to favor the efficiency of collagenolysis (7).Insoluble type I collagen fibers constitute 90% of the organic matrix of bone, and their degradation is necessary for bone resorption (8). The test tube experiments that have been performed so far showed that it is difficult to achieve complete degradation of adult lamellar bone with a single bone proteinase (9, 10). On the other hand, various biological approaches have shown that both MMPs and cysteine proteinases participate in the bone resorption processes (8,(11)(12)(13). Representatives of these two types of proteinases were identified in osteoclasts, the cells responsible for bone resorptio...

IMPORTANCE Sprifermin is under investigation as a disease-modifying osteoarthritis drug.OBJECTIVE To evaluate the effects of sprifermin on changes in total femorotibial joint cartilage thickness in the more symptomatic knee of patients with osteoarthritis. Osteoarthritis Randomized Trial with Administration of Repeated Doses) was a 5-year, dose-finding, multicenter randomized clinical trial conducted at 10 sites. Eligible participants were aged 40 to 85 years with symptomatic, radiographic knee osteoarthritis and Kellgren-Lawrence grade 2 or 3. Enrollment began in July 2013 and ended in May 2014; the last participant visit occurred on May 8, 2017. The primary outcome at 2 years and a follow-up analysis at 3 years are reported. DESIGN, SETTING, AND PARTICIPANTSINTERVENTIONS Participants were randomized to 1 of 5 groups: intra-articular injections of 100 μg of sprifermin administered every 6 months (n = 110) or every 12 months (n = 110), 30 μg of sprifermin every 6 months (n = 111) or every 12 months (n = 110), or placebo every 6 months (n = 108). Each treatment consisted of weekly injections over 3 weeks. MAIN OUTCOMES AND MEASURESThe primary end point was change in total femorotibial joint cartilage thickness measured by quantitative magnetic resonance imaging at 2 years. The secondary end points (of 15 total) included 2-year change from baseline in total Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores. The minimal clinically important difference (MCID) is unknown for the primary outcome; for total WOMAC score in patients with hip and knee osteoarthritis, the absolute MCID is 7 U (95% CI, 4 to 10 U) and the percentage MCID is 14% (95% CI, 9% to 18%). RESULTS Among 549 participants (median age, 65.0 years; 379 female [69.0%]), 474 (86.3%) completed 2-year follow-up. Compared with placebo, the changes from baseline to 2 years in total femorotibial joint cartilage thickness were 0.05 mm (95% CI, 0.03 to 0.07 mm) for 100 μg of sprifermin administered every 6 months; 0.04 mm (95% CI, 0.02 to 0.06 mm) for 100 μg of sprifermin every 12 months; 0.02 mm (95% CI, −0.01 to 0.04 mm) for 30 μg of sprifermin every 6 months; and 0.01 mm (95% CI, −0.01 to 0.03 mm) for 30 μg of sprifermin every 12 months. Compared with placebo, there were no statistically significant differences in mean absolute change from baseline in total WOMAC scores for 100 μg of sprifermin administered every 6 months or every 12 months, or for 30 μg of sprifermin every 6 months or every 12 months. The most frequently reported treatment-emergent adverse event was arthralgia (placebo: n = 46 [43.0%]; 100 μg of sprifermin administered every 6 months: n = 45 [41.3%]; 100 μg of sprifermin every 12 months: n = 50 [45.0%]; 30 μg of sprifermin every 6 months: n = 40 [36.0%]; and 30 μg of sprifermin every 12 months: n = 48 [44.0%]).CONCLUSIONS AND RELEVANCE Among participants with symptomatic radiographic knee osteoarthritis, the intra-articular administration of 100 μg of sprifermin every 6 or 12 months vs placebo resulted in an impro...

Collagen type I fragments, reflecting bone resorption, and release of gut hormones were investigated after a meal. Investigations led to a dose escalation study with glucagon like peptide-2 (GLP-2) in postmenopausal women. We found a dose-dependent effect of GLP-2 on the reduction of bone resorption.Introduction: The C-terminal telopeptide region of type I collagen as measured in serum (s-CTX) can be used to assess bone resorption. This marker of bone resorption has a significant circadian variation that is influenced by food intake. However, the mediator of this variation has not been identified. Materials and Methods:We studied the release of the gut hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-2 (GLP-2; a representative of the intestinal proglucagon-derived peptides) after ingestion of glucose, fat, protein, and fructose, as well as their effects after parenteral administration in relation to bone turnover processes in healthy volunteers. Furthermore, we studied the effect on bone turnover of a single subcutaneous injection of GLP-2 in four different dosages (100, 200, 400, or 800 g GLP-2) or placebo in 60 postmenopausal women (mean age, 61 Ϯ 5 years). Results: All macronutrients significantly (p Ͻ 0.05) reduced bone resorption as assessed by s-CTX (39 -52% from baseline), and only the glucagon-like peptides were secreted in parallel. Parenteral administration of GIP and GLP-1 did not result in a reduction of the s-CTX level, whereas GLP-2 caused a statistically significant and dose-dependent reduction in the s-CTX level from baseline compared with placebo (p Ͻ 0.05). Urine DPD/creatinine, a marker of bone resorption, was significantly reduced by 25% from baseline in the 800-g GLP-2 group (p Ͻ 0.01). An area under the curve (AUC 0 -8h ) analysis for s-CTX after GLP-2 injection confirmed the dose-dependent decrease (ANOVA, p ϭ 0.05). The s-osteocalcin level was unaffected by the GLP-2 treatment. Conclusion: These studies exclude both GIP and GLP-1 as key mediators for the immediate reduction in bone resorption seen after a meal. The dose-dependent reduction of bone resorption markers found after subcutaneous injection of GLP-2 warrants further investigation into the mechanism and importance of GLP-2 for the bone turnover processes.

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The aim of this review is to discuss the potential usefulness of a novel class of biochemical markers, neoepitopes, in the context of the US Food and Drug Administration (FDA) Critical Path Initiative, which emphasizes biomarkers of safety and efficacy as areas of pivotal interest. Examples of protein degradation fragments--neoepitopes--that have proven useful for research on bone and cartilage are collagen type I and collagen type II degradation products, respectively. These markers have utility in the translational approach, as they can be used to estimate safety and efficacy in both preclinical models and clinical settings. Biochemical markers of tissue degradation may provide optimal tools, which in combination with other techniques, prove essential to drug discovery and development.