OP0111 PLASMA PROTEOMICS IDENTIFIES CRTAC1 AS BIOMARKER FOR OSTEOARTHRITIS SEVERITY AND PROGRESSION

Background:

Accurate biomarkers for diagnosis and prediction of osteoarthritis (OA) are needed. In addition, biomarkers have the potential to serve as a measure of the different pathological processes underlying OA. Here, we report on a proteomics screen targeted at two important pathways thought to underlie the etiology of OA: the inflammation and metabolic pathways.

Objectives:

The aim of this study was to identify a robust biomarker for OA severity and progression.

Methods:

We used data from the Rotterdam Study, a population based prospective study with participants aged 45 and older. The participants in this study underwent blood measurement at baseline and radiographic measurements at baseline as well as after a mean follow-up time of 5 years. We measured 184 proteins (inflammation and cardiometabolic panel) in plasma from 3,517 participants in the Rotterdam Study using the Olink platform.

We estimated the association for all available proteomic biomarkers with OA in knee, hip and hand in 2 ways: 1) Cross-sectionally in all joints, where we analyzed severity of OA by adding up KL-scores of both joints (knee and hip OA), and all joints of the left and right hand (total amount of joints=30); 2) Longitudinally in Knee and Hip, defining cases of progression of OA as an increase with at least 1 unit in KL-grade per person, excluding progressing from KL0 to KL1. We analyzed the relationship with multivariate regression models using generalized linear models with binomial link function. In model 1 we adjusted for age, sex and cell counts, in model 2 we additionally adjusted for BMI. We report effect estimate(beta) per standard deviation (SD) change in protein levels with 95% Confidence Interval (CI) and nominal p-value (significance level<0.05) for each protein. All statistical analyses were performed in R version 3.5.2.

Results:

We found in total 56 proteins that were significantly associated with one or more OA-outcomes at nominal level. Figure 1 illustrates the 19 significant associations for severity of hand OA ordered by significance level (most significant at top). We observed a very robust association between the level of circulating Cartilage acidic protein 1 (CRTAC1) and severity of OA in the knee (β=0.16, 95%CI 0.09-0.23, p=0.000013, FDR-corrected P:0.0011) hand (β=0.086, 95%CI 0.03-0.14, p=0.00085, FDR-corrected P: 0.0252), while a similar trend was seen in hip (β=0.08, 95%CI -0.02-0.18, p=0.12), although power in hip was limited in our study. The association with CRTAC1was also found for progression in knee (β=0.21, 95%CI 0.03-0.36, p=0.0156, FDR-corrected P>0.2) and hip (β=0.18, 95%CI -0.01-0.38, p=0.0624, FDR-corrected P>0.9). These associations were independent of BMI. Among the findings were several other promising biomarkers, e.g. MMP-10, which we observed to be associated with severity of hand OA (β=-0.09, 95%CI -0.15- -0.04, p=0. 00067, FDR-corrected P:0.0383) and progression of knee OA (β=-0.24, 95%CI -0.42- -0.06, p=0.0073, FDR-corrected P>0.1). Additionally, COMP, a well-known biomarker for OA, was also found significant for OA severity in hand (β=0.10, 95%CI 0.05-0.16, p<0.001, FDR-corrected P:0.0043) and knee (β=0.09, 95%CI 0.02-0.17, p=0.01, FDR-corrected P>0.2).

Conclusion:

We identified the CRTAC1 protein as a robust, promising biomarker for osteoarthritis severity and progression. This protein is a glycosylated extracellular matrix protein that is found in the interterritorial matrix of articular deep zone cartilage. This protein can also be used to distinguish chondrocytes from osteoblasts and mesenchymal stem cells in culture. This suggests that CRTAC1-levels reflects a cartilage-specific process in the joint. Such a biomarker might be useful for targeting the right patients for clinical trials and designing novel therapies for OA.

Disclosure of Interests:

Ingrid Szilagyi: None declared, Costanza Vallerga: None declared, J.H. Waarsing: None declared, Dieuwke Schiphof: None declared, S.M.A. Bierma-Zeinstra Consultant of: Pfizer, one day consultancy, Joyce Van Meurs: None declared

Vitamin K antagonist anticoagulant usage is associated with increased incidence and progression of osteoarthritis

OBJECTIVES

Vitamin K is hypothesised to play a role in osteoarthritis (OA) pathogenesis through effects on vitamin K-dependent bone and cartilage proteins, and therefore may represent a modifiable risk factor. A genetic variant in a vitamin K-dependent protein that is an essential inhibitor for cartilage calcification, matrix Gla protein (MGP), was associated with an increased risk for OA. Vitamin K antagonist anticoagulants (VKAs), such as warfarin and acenocoumarol, act as anticoagulants through inhibition of vitamin K-dependent blood coagulation proteins. VKAs likely also affect the functioning of other vitamin K-dependent proteins such as MGP.

METHODS

We investigated the effect of acenocoumarol usage on progression and incidence of radiographic OA in 3494 participants of the Rotterdam Study cohort. We also examined the effect of MGP and VKORC1 single nucleotide variants on this association.

RESULTS

Acenocoumarol usage was associated with an increased risk of OA incidence and progression (OR=2.50, 95% CI=1.94-3.20), both for knee (OR=2.34, 95% CI=1.67-3.22) and hip OA (OR=2.74, 95% CI=1.82-4.11). Among acenocoumarol users, carriers of the high VKORC1(BB) expression haplotype together with the MGP OA risk allele (rs1800801-T) had an increased risk of OA incidence and progression (OR=4.18, 95% CI=2.69-6.50), while this relationship was not present in non-users of that group (OR=1.01, 95% CI=0.78-1.33).

CONCLUSIONS

These findings support the importance of vitamin K and vitamin K-dependent proteins, as MGP, in the pathogenesis of OA. Additionally, these results may have direct implications for the clinical prevention of OA, supporting the consideration of direct oral anticoagulants in favour of VKAs.

Phenome-wide investigation of health outcomes associated with genetic predisposition to loneliness

Humans are social animals that experience intense suffering when they perceive a lack of social connection. Modern societies are experiencing an epidemic of loneliness. Although the experience of loneliness is universally human, some people report experiencing greater loneliness than others. Loneliness is more strongly associated with mortality than obesity, emphasizing the need to understand the nature of the relationship between loneliness and health. Although it is intuitive that circumstantial factors such as marital status and age influence loneliness, there is also compelling evidence of a genetic predisposition toward loneliness. To better understand the genetic architecture of loneliness and its relationship with associated outcomes, we extended the genome-wide association study meta-analysis of loneliness to 511 280 subjects, and detect 19 significant genetic variants from 16 loci, including four novel loci, as well as 58 significantly associated genes. We investigated the genetic overlap with a wide range of physical and mental health traits by computing genetic correlations and by building loneliness polygenic scores in an independent sample of 18 498 individuals with EHR data to conduct a PheWAS with. A genetic predisposition toward loneliness was associated with cardiovascular, psychiatric, and metabolic disorders and triglycerides and high-density lipoproteins. Mendelian randomization analyses showed evidence of a causal, increasing, the effect of both BMI and body fat on loneliness. Our results provide a framework for future studies of the genetic basis of loneliness and its relationship to mental and physical health.

Absolute and Relative-Rate Kinetics Experiments and Direct Dynamics Computations for the Reaction of Br Atoms with CH2ClBr

Kinetics of the reaction Br + CH2ClBr <--> CHClBr + HBr (1, -1) were studied experimentally in the forward direction. The absolute reaction kinetics method of laser flash photolysis coupled with Br atom resonance fluorescence detection and three different relative-rate methods with gas-chromatographic analysis were applied to carry out the experiments. The rate constants determined were found to obey the Arrhenius law in the wide temperature range of T = 293-785 K providing the kinetic expression k1 = (2.8 +/- 0.1) x 10(13) exp[-(47.6 +/- 0.3) kJ mol(-1)/RT] cm3 mol(-1) s(-1) (the errors given refer to 1sigma precision). An ab initio direct dynamics method was used to study reaction (1, -1) theoretically. The electronic structure information including geometries, gradients, and force constants was obtained at the MP2 level of theory; and energies were improved at higher theoretical levels. Rate constants were calculated using the canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200-1000 K. Theory substantially underestimates k1 compared to experiment. The agreement was found good with k(-1) reported previously predicting positive temperature dependence. The experimental kinetic parameters were utilized in thermochemical calculations yielding the recommended standard enthalpy of formation of delta(f)H degrees (298) (CHClBr) = (140 +/- 4) kJ mol(-1) (with 2sigma accuracy given).