Linking chondrocyte and synovial transcriptional profile to clinical phenotype in osteoarthritis.

OBJECTIVES: To determine how gene expression profiles in osteoarthritis joint tissues relate to patient phenotypes and whether molecular subtypes can be reproducibly captured by a molecular classification algorithm. METHODS: We analysed RNA sequencing data from cartilage and synovium in 113 osteoarthritis patients, applying unsupervised clustering and Multi-Omics Factor Analysis to characterise transcriptional profiles. We tested the association of the molecularly defined patient subgroups with clinical characteristics from electronic health records. RESULTS: We detected two patient subgroups in low-grade cartilage (showing no/minimal degeneration, cartilage normal/softening only), with differences associated with inflammation, extracellular matrix-related and cell adhesion pathways. The high-inflammation subgroup was associated with female sex (OR 4.12, p=0.0024) and prescription of proton pump inhibitors (OR 4.21, p=0.0040). We identified two independent patient subgroupings in osteoarthritis synovium: one related to inflammation and the other to extracellular matrix and cell adhesion processes. A seven-gene classifier including MMP13, APOD, MMP2, MMP1, CYTL1, IL6 and C15orf48 recapitulated the main axis of molecular heterogeneity in low-grade knee osteoarthritis cartilage (correlation ρ=-0.88, p<10-10) and was reproducible in an independent patient cohort (ρ=-0.85, p<10-10). CONCLUSIONS: These data support the reproducible stratification of osteoarthritis patients by molecular subtype and the exploration of new avenues for tailored treatments.

A molecular quantitative trait locus map for osteoarthritis.

Osteoarthritis causes pain and functional disability for over 500 million people worldwide. To develop disease-stratifying tools and modifying therapies, we need a better understanding of the molecular basis of the disease in relevant tissue and cell types. Here, we study primary cartilage and synovium from 115 patients with osteoarthritis to construct a deep molecular signature map of the disease. By integrating genetics with transcriptomics and proteomics, we discover molecular trait loci in each tissue type and omics level, identify likely effector genes for osteoarthritis-associated genetic signals and highlight high-value targets for drug development and repurposing. These findings provide insights into disease aetiopathology, and offer translational opportunities in response to the global clinical challenge of osteoarthritis.

Effect of denosumab on osteolytic lesion activity after total hip arthroplasty: a single-centre, randomised, double-blind, placebo-controlled, proof of concept trial.

BACKGROUND: Osteolysis causes recurrent pain and disability after total hip arthroplasty. We investigated the effect of the human monoclonal antibody denosumab on osteolytic lesion activity in patients undergoing revision total hip arthroplasty surgery to show the biological proof of concept for a non-surgical treatment for the disease. METHODS: We did a phase 2, randomised, double-blind, placebo-controlled, proof of concept superiority trial at Sheffield Teaching Hospitals, Sheffield, UK. Eligible patients aged 30 years or older and scheduled for revision surgery for symptomatic, radiographically confirmed osteolysis were randomly allocated (1:1) to subcutaneous denosumab (60 mg single-dose) or placebo by an independent pharmacist using a random number table. The primary outcome was the between-group difference in osteoclast number per mm of bone surface of biopsies taken from the osteolytic membrane-bone interface at surgery 8 weeks later, measured by quantitative histomorphometry in all patients who underwent revision surgery. Adverse events were analysed in all randomly assigned participants. This trial is registered with the EU Clinical Trials Register (EudraCT 2011-000541-20). FINDINGS: Between Dec 12, 2012, and June 24, 2018, 51 patients were assessed for eligibility, of whom 24 were randomly assigned to study treatment. Two patients had their revision surgery cancelled for unrelated reasons, leaving 22 patients (ten in the denosumab group) for analysis of the primary outcome. There were 83% fewer osteoclasts at the osteolysis membrane-bone interface in the denosumab versus the placebo group (median 0·05 per mm [IQR 0·11] vs 0·30 mm [0·40], p=0·011). No deaths or treatment-related serious adverse events occurred. Seven adverse events, including one severe adverse event, occurred in four (36%) of 11 patients in the denosumab group. In the placebo group ten adverse events, including three severe adverse events, occurred in five (38%) of 13 patients. INTERPRETATION: To our knowledge, this is the first clinical trial of an investigational drug for osteolysis that shows tissue-specific biological efficacy. These results justify the need for future trials that target earlier-stage disease to test for clinical efficacy in reducing the need for revision surgery. FUNDING: Amgen.

Integrative epigenomics, transcriptomics and proteomics of patient chondrocytes reveal genes and pathways involved in osteoarthritis.

Osteoarthritis (OA) is a common disease characterized by cartilage degeneration and joint remodeling. The underlying molecular changes underpinning disease progression are incompletely understood. We investigated genes and pathways that mark OA progression in isolated primary chondrocytes taken from paired intact versus degraded articular cartilage samples across 38 patients undergoing joint replacement surgery (discovery cohort: 12 knee OA, replication cohorts: 17 knee OA, 9 hip OA patients). We combined genome-wide DNA methylation, RNA sequencing, and quantitative proteomics data. We identified 49 genes differentially regulated between intact and degraded cartilage in at least two -omics levels, 16 of which have not previously been implicated in OA progression. Integrated pathway analysis implicated the involvement of extracellular matrix degradation, collagen catabolism and angiogenesis in disease progression. Using independent replication datasets, we showed that the direction of change is consistent for over 90% of differentially expressed genes and differentially methylated CpG probes. AQP1, COL1A1 and CLEC3B were significantly differentially regulated across all three -omics levels, confirming their differential expression in human disease. Through integration of genome-wide methylation, gene and protein expression data in human primary chondrocytes, we identified consistent molecular players in OA progression that replicated across independent datasets and that have translational potential.

Diagnostic accuracy of bone turnover markers as a screening tool for aseptic loosening after total hip arthroplasty.

Aseptic loosening is the most common cause of prosthesis failure after total hip arthroplasty (THA). We measured serum cross-linked carboxyterminal telopeptide of type I collagen (ICTP), tartrate-resistant acid phosphatase 5b (TRAP5b), dickkopf-1 (dkk-1) and sclerostin; and urinary α isomer of C-terminal cross-linked telopeptide of type I collagen (αCTX-I) to investigate their potential diagnostic value detecting aseptic loosening after THA. Biomarkers were measured in 24 subjects with aseptic loosening of THA versus 26 control subjects without loosening after THA. Serum ICTP in the loose group (7.04 ng/mL) was higher than controls (5.15 ng/mL), (p = 0.0007). ROC analysis demonstrated that a serum ICTP >5.5 ng/L had a sensitivity of 91% and specificity of 69% for detecting aseptic loosening (area under ROC curve = 0.77, p = 0.0001), resulting in a positive predictive value (PPV) of 73% and a negative predictive value (NPV) of 90%. Serum TRAP5b in the aseptic loosening group (4.17U/L) was higher than controls (3.44 U/L), (p = 0.03). A serum TRAP5b >2.46 U/L had sensitivity of 100% and a specificity of 31% to detect aseptic loosening (AUC 0.67, p = 0.031), resulting in a PPV of 57% and a NPV of 100%. Serum dkk-1, serum sclerostin and urinary αCTX-I were not elevated in subjects with aseptic loosening (p>0.05). Serum ICTP and TRAP5b show potential utility as screening biomarkers for excluding aseptic loosening, because of their ability to discriminate individuals without disease. Our finding of elevated ICTP, generated by the action of matrix metalloproteinases, suggests a role for this group of endopeptidases in aseptic loosening.

Pelvic periprosthetic bone mineral density measurement around cemented vs cementless acetabular prostheses.

We compared the short-term precision of pelvic periprosthetic bone mineral density (BMD) measurement around a cementless acetabular prosthesis (n = 29) vs a cemented all-polyethylene acetabular prosthesis (n = 19) in patients after total hip arthroplasty. Two dual-energy x-ray absorptiometry scans of the pelvis were made on the same day in each subject with subject repositioning between scans and analyzed independently with a 4-region of interest model. Precision was expressed as coefficient of variation (CV%). The measured BMD around the cemented prostheses was greater than the cementless prostheses p < 0.004, all analyses). The net CV for pelvic BMD measurements around the cementless prosthesis was 1.9% vs 3.6% around the cemented prosthesis (F-test p < 0.001). The CVs of individual regions of interest was between 2.8% and 4.8% for the cementless prosthesis vs 4.4% to 8.4% for the cemented prosthesis (F-test; p < 0.05, all comparisons). Prospective studies would require 57 subjects to detect a 10% change in net pelvic BMD around a cementless prosthesis and 122 to detect a similar change around a cemented prosthesis with 90% power and with an alpha error of 0.05. In conclusion, the precision of pelvic BMD measurements made around cementless prostheses are better vs those for cemented prostheses. Dual-energy x-ray absorptiometry studies of cemented prosthesis require approximately double the number of subjects vs cementless prostheses to achieve a similar level of power.

Effect of sliding-taper compared with composite-beam cemented femoral prosthesis loading regime on proximal femoral bone remodeling: a randomized clinical trial.

BACKGROUND: This two-year randomized clinical trial was performed to examine whether the geometry of the cemented femoral prosthesis affects the pattern of strain-adaptive bone remodeling in the proximal aspect of the femur after primary total hip arthroplasty. METHODS: One hundred and twenty patients were randomized to receive a Charnley (composite-beam), Exeter (double-tapered), or C-Stem (triple-tapered) prosthesis. The change in proximal femoral bone mineral density over two years was measured by dual x-ray absorptiometry (DXA). Bone turnover markers were measured in urine and serum samples collected at the preoperative baseline and during the first postoperative year. N-telopeptide of type-I collagen was measured in urine as a marker of osteoclast activity, and osteocalcin was measured in serum as a marker of osteoblast activity. Clinical outcome was measured with use of the Harris and Oxford hip scores and prosthesis migration was measured with use of digitized radiographs during the first two postoperative years. RESULTS: The baseline characteristics of the subjects in each group were similar (p > 0.05). Decreases in femoral bone mineral density were observed over the first year for all prosthesis designs, with no further loss during the second year. The decreases were similar in regional distribution and magnitude between the composite-beam and sliding-taper designs (p > 0.05). Bone loss was greatest (14%) in the proximal medial aspect of the femur (Gruen zone 7). Transient increases in both N-telopeptide of type-I collagen and osteocalcin activity also occurred over the first year, and these increases were similar in pattern among the three prosthesis groups (p > 0.05). All prostheses showed migration patterns that were consistent with their design type, and similar improvements in clinical hip scores were observed over the two-year course of the study. CONCLUSIONS: Differences in the mechanism of load transfer between the prosthesis and host bone in composite-beam or sliding-taper cemented femoral prosthesis designs were not a major determinant of proximal femoral bone loss after total hip arthroplasty, and the design that included a third taper exhibited a remodeling profile that was similar to those of the double-tapered design.