The association between ANKH promoter polymorphism and chondrocalcinosis is independent of age and osteoarthritis: results of a case-control study

High frequency of BCP, but less CPP crystal-mediated calcification in cartilage and synovial membrane of osteoarthritis patients

OBJECTIVE

Ectopic articular calcification is a common phenomenon of osteoarthritic joints, and closely related to disease progression. Identification of the involved calcium crystal types represents an important topic in research and clinical practice. Difficulties in accurate detection and crystal type identification have led to inconsistent data on the prevalence and spatial distribution of Basic calcium phosphate (BCP) and calcium pyrophosphate (CPP) deposition.

METHOD

Combining multiple imaging methods including conventional radiography, histology and Raman spectroscopy, this study provides a comprehensive analysis of BCP and CPP-based calcification, its frequency and distribution in cartilage and synovial membrane samples of 92 osteoarthritis patients undergoing knee replacement surgery.

RESULTS

Conventional radiography showed calcifications in 35% of patients. Von Kossa staining detected calcified deposits in 88% and 57% of cartilage and synovial samples, respectively. BCP crystals presented as brittle deposits on top of the cartilage surface or embedded in synovial tissue. CPP deposits appeared as larger granular needle-shaped clusters or dense circular pockets below the cartilage surface or within synovial tissue. Spectroscopic analysis detected BCP crystals in 75% of cartilage and 43% of synovial samples. CPP deposition was only detected in 18% of cartilage and 15% of synovial samples, often coinciding with BCP deposits.

CONCLUSION

BCP is the predominant crystal type in calcified cartilage and synovium while CPP deposition is rare, often coinciding with BCP. Distinct and qualitative information on BCP and CPP deposits in joint tissues gives rise to the speculation that different disease entities are involved that might need different treatment strategies.

The role of calcium crystals and their effect on osteoarthritis pathogenesis

Osteoarthritis (OA) is a degenerative joint disease characterized by progressive degeneration of articular cartilage. Due to its high prevalence and limited treatment options, OA has become one of the most disabling diseases in developed countries. In recent years, OA has been recognized as a heterogenic disease with various phenotypes. Calcium crystal-related endotypes, which are defined by either a distinct functional or pathobiological mechanism, are present in approximately 60% of all OA patients. Two different calcium crystals can accumulate in the joint and thereby calcify the cartilage matrix, which are basic calcium phosphate (BCP) and calcium pyrophosphate (CPP) crystals. The formation of these crystals depends mainly on the balance of phosphate and pyrophosphate, which is regulated by specific proteins controlling the pyrophosphate metabolism. Dysregulation of these molecules subsequently leads to preferential formation of either BCP or CPP crystals. BCP crystals, on the one hand, are directly associated with OA severity and cartilage degradation. They are mostly located in the deeper cartilage layers and are associated with chondrocyte hypertrophy. CPP crystal deposition, on the other hand, is a hallmark of chondrocalcinosis and is associated with aging and chondrocyte senescence. Therefore, BCP and CPP crystals are associated with different chondrocyte phenotypes. However, BCP and CPP crystals are not mutually exclusive and can coexist in OA, creating a mixed endotype of OA. Both crystals clearly play a role in the pathogenesis of OA. However, the exact impact of each crystal type on either driving the disease progression or being a result of chondrocyte differentiation is still to be elucidated.

Chondrocytes From Osteoarthritic and Chondrocalcinosis Cartilage Represent Different Phenotypes

Basic calcium phosphate (BCP)-based calcification of cartilage is a common finding during osteoarthritis (OA) and is directly linked to the severity of the disease and hypertrophic differentiation of chondrocytes. Chondrocalcinosis (CC) is associated with calcium pyrophosphate dihydrate (CPPD) deposition disease in the joint inducing OA-like symptoms. There is only little knowledge about the effect of CPPD crystals on chondrocytes and the signaling pathways involved in their generation. The aim of this study was to investigate the chondrocyte phenotype in CC cartilage and the effect of CPPD crystals on chondrocytes. Cartilage samples of patients with CC, patients with severe OA, and healthy donors were included in this study. The presence of CC was evaluated using standard X-ray pictures, as well as von Kossa staining of cartilage sections. OA severity was evaluated using the Chambers Score on cartilage sections, as well as the radiological Kellgren–Lawrence Score. Patients with radiologically detectable CC presented calcification mainly on the cartilage surface, whereas OA patients showed calcification mainly in the pericellular matrix of hypertrophic chondrocytes. OA cartilage exhibited increased levels of collagen X and matrix metalloproteinase 13 (MMP13) compared with CC and healthy cartilage. This observation was confirmed by qRT-PCR using cartilage samples. No relevant influence of CPPD crystals on hypertrophic marker genes was observed in vitro, whereas BCP crystals significantly induced hypertrophic differentiation of chondrocytes. Interestingly, we observed an increased expression of p16 and p21 in cartilage samples of CC patients compared with OA patients and healthy controls, indicating cellular senescence. To investigate whether CPPD crystals were sufficient to induce senescence, we incubated chondrocytes with BCP and CPPD crystals and quantified senescence using β-gal staining. No significant difference was observed for the staining, but an increase of p16 expression was observed after 10 days of culture. Primary chondrocytes from CC patients produced CPPD crystals in culture. This phenotype was stabilized by mitomycin C-induced senescence. Healthy and OA chondrocytes did not exhibit this phenotype. BCP and CPPD crystals seem to be associated with two different chondrocyte phenotypes. Whereas BCP deposition is associated with chondrocyte hypertrophy, CPPD deposition is associated with cellular senescence.

Bone status and aortic calcifications in chondrocalcinosis patients

Aim: We aimed to examine the association between several circulating bone turnover markers [ osteocalcin (OC), osteoprotegerin (OPG), beta-CrossLaps (β-CTx)], hip and spine bone mineral density (BMD) and abdominal aortic calcification (AAC) in patients with chondrocalcinosis (CC).

Methods: Thirty-six patients with CC and thirty-seven controls were consecutively enrolled in this pilot case-control, cross-sectional study. The following parameters were assessed: serum levels of OC, OPG and β-CTx by enzyme-linked immunosorbent assay (ELISA); hip and spine BMD by dual-energy X-ray absorptiometry and AAC score by lateral radiography.

Results: Patients with CC had higher levels of serum bone turnover markers and AAC score than the control group: OC [6.5 (3.5-9.9) vs 4.5 (2.6-7.2) ng/ml; p=0.05], OPG [(7.7 (6.2-9.4) vs 6.5 (5.5-8.12) pmol/ml; p=0.02], β-CTx [6078 (5870-6171) vs 5851 (5465-6109) pg/ml; p=0.02] and AAC score (3.6±6.2 vs 0.5±2; p=0.006). Conversely, even if statistical significance was not reached, hip and spine BMD was lower in patients with CC. Additionally, we found a positive correlation between OPG and AAC, but also between OPG and osteoporosis in patients with CC.

Conclusion: Patients with CC are characterized by higher circulating OC, OPG and β-CTx. The presence of AAC was more common in patients with CC, being only associated with serum OPG.

Synthesis of Inorganic Pyrophosphatase-Nanodiamond Conjugates Resistant to Calcium and Fluoride

Pyrophosphate arthropathy is the mineralization defect in humans caused by the deposition of microcrystals of calcium pyrophosphate dihydrate in joint tissues. As a potential therapeutic strategy for the treatment of pyrophosphate arthropathy, delivery of exogenous pyrophosphate-hydrolyzing enzymes, inorganic pyrophosphatases (PPases), to the synovial fluid has been suggested. Previously, we synthesized the conjugates of Escherichia coli PPase (Ec-PPase) with detonation synthesis nanodiamonds (NDs) as a delivery platform, obtaining the hybrid biomaterial retaining high pyrophosphate-hydrolyzing activity in vitro. However, most known PPases including Ec-PPase in the soluble form are strongly inhibited by Ca²⁺ ions. Because synovial fluid contains up to millimolar concentrations of soluble calcium, this inhibition might limit the in vivo application of Ec-PPase-based material in joint tissues. In this work, we proposed other bacterial PPases from Mycobacterium tuberculosis (Mt-PPase), which are resistant to the inhibition by Ca²⁺ ions, as an active PP_i-hydrolyzing agent. We synthesized conjugates of Mt-PPase with NDs and tested their activity under various conditions. Unexpectedly, conjugates of both Ec-PPase and Mt-PPase with aminated NDs retained significant hydrolytic activity in the presence of well-known mechanism-based PPase inhibitors, fluoride or calcium. The incomplete inhibition of PPases by fluoride or calcium was found for the first time.

[Chondrocalcinosis: idiopathic or manifestation of rare metabolic diseases?]

Calcification in hyaline and fibrocartilage is caused by the deposition of calcium pyrophosphate dehydrate, commonly referred to as chondrocalcinosis. Clinically, this can lead to arthritis symptoms similar to a gout attack -"pseudogout". Nonetheless, also chronic or asymptomatic disease courses are possible. The prevalence of chondrocalcinosis increases with age. The diagnostic workup of degenerative joint disease, therefore, often reveals calcifications of articular cartilage as harmless incidental findings. However, particularly in patients younger than 60 years of age, chondrocalcinosis can be the symptom of an underlying metabolic disease. This review article highlights these rare diseases and presents unusual manifestations of chondrocalcinosis.

Severe calcium pyrophosphate dihydrate deposition disease of the metacarpophalangeal joints

We report a case of calcium pyrophosphate deposition disease (CPPD) with an unusual presentation of severe chondrocalcinosis with atypical large burden deposited in the metacarpophalangeal joints as well as more typical deposition in wrists and knees as demonstrated on plain radiographs. A 77-year-old African-American woman 1-year status post parathyroidectomy for hyperparathyroidism initially presented to the rheumatology clinic to treat suspected rheumatoid arthritis given her pattern of joint involvement but was found to have CPPD. The patient’s history is notable for end-stage renal disease which complicates medical management. This case illustrates radiographic findings of CPPD and explores the challenges of treating CPPD in the setting of comorbid conditions.

Inhibition of nucleotide pyrophosphatase/phosphodiesterase 1: implications for developing a calcium pyrophosphate deposition disease modifying drug

Objectives

Calcium pyrophosphate deposition (CPPD) is associated with osteoarthritis and is the cause of a common inflammatory articular disease. Ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (eNPP1) is the major ecto-pyrophosphatase in chondrocytes and cartilage-derived matrix vesicles (MVs). Thus, eNPP1 is a principle contributor to extracellular pyrophosphate levels and a potential target for interventions aimed at preventing CPPD. Recently, we synthesized and described a novel eNPP1-specific inhibitor, SK4A, and we set out to evaluate whether this inhibitor attenuates nucleotide pyrophosphatase activity in human OA cartilage.

Methods

Cartilage tissue, chondrocytes and cartilage-derived MVs were obtained from donors with OA undergoing arthroplasty. The effect of SK4A on cell viability was assayed by the XTT method. eNPP1 expression was evaluated by western blot. Nucleotide pyrophosphatase activity was measured by a colorimetric assay and by HPLC analysis of adenosine triphosphate (ATP) levels. ATP-induced calcium deposition in cultured chondrocytes was visualized and quantified with Alizarin red S staining.

Results

OA chondrocytes expressed eNPP1 in early passages, but this expression was subsequently lost upon further passaging. Similarly, significant nucleotide pyrophosphatase activity was only detected in early-passage chondrocytes. The eNPP1 inhibitor, SK4A, was not toxic to chondrocytes and stable in culture medium and human plasma. SK4A effectively inhibited nucleotide pyrophosphatase activity in whole cartilage tissue, in chondrocytes and in cartilage-derived MVs and reduced ATP-induced CPPD.

Conclusion

Nucleotide analogues such as SK4A may be developed as potent and specific inhibitors of eNPP1 for the purpose of lowering extracellular pyrophosphate levels in human cartilage with the aim of preventing and treating CPPD disease.

Review: Unmet Needs and the Path Forward in Joint Disease Associated With Calcium Pyrophosphate Crystal Deposition

Calcium pyrophosphate (CPP) crystal deposition (CPPD) is prevalent and can be associated with synovitis and joint damage. The population of elderly persons predominantly affected by CPPD is growing rapidly. Since shortfalls exist in many aspects of CPPD, we conducted an anonymous survey of CPPD unmet needs, prioritized by experts from the Gout, Hyperuricemia and Crystal-Associated Disease Network. We provide our perspectives on the survey results, and we propose several CPPD basic and clinical translational research pathways. Chondrocyte and cartilage culture systems for generating CPP crystals in vitro and transgenic small animal CPPD models are needed to better define CPPD mechanism paradigms and help guide new therapies. CPPD recognition, clinical research, and care would be improved by international consensus on CPPD nomenclature and disease phenotype classification, better exploitation of advanced imaging, and pragmatic new point-of-care crystal analytic approaches for detecting CPP crystals. Clinical impacts of CPP crystals in osteoarthritis and in asymptomatic joints in elderly persons remain major unanswered questions that are rendered more difficult by current inability to therapeutically limit or dissolve the crystal deposits and assess the consequent clinical outcome. Going forward, CPPD clinical research studies should define clinical settings in which articular CPPD does substantial harm and should include analyses of diverse clinical phenotypes and populations. Clinical trials should identify the best therapeutic targets to limit CPP crystal deposition and associated inflammation and should include assessment of intraarticular agents. Our perspective is that such advances in basic and clinical science in CPPD are now within reach and can lead to better treatments for this disorder.

DNA and RNA-sequence based GWAS highlights membrane-transport genes as key modulators of milk lactose content

Background

Lactose provides an easily-digested energy source for neonates, and is the primary carbohydrate in milk in most species. Bovine lactose is also a key component of many human food products. However, compared to analyses of other milk components, the genetic control of lactose has been little studied. Here we present the first GWAS focussed on analysis of milk lactose traits.

Results

Using a discovery population of 12,000 taurine dairy cattle, we detail 27 QTL for lactose concentration and yield, and subsequently validate the effects of 26 of these loci in a distinct population of 18,000 cows. We next present data implicating causative genes and variants for these QTL. Fine mapping of these regions using imputed, whole genome sequence-resolution genotypes reveals protein-coding candidate causative variants affecting the ABCG2, DGAT1, STAT5B, KCNH4, NPFFR2 and RNF214 genes. Eleven of the remaining QTL appear to be driven by regulatory effects, suggested by the presence of co-locating, co-segregating eQTL discovered using mammary RNA sequence data from a population of 357 lactating cows. Pathway analysis of genes representing all lactose-associated loci shows significant enrichment of genes located in the endoplasmic reticulum, with functions related to ion channel activity mediated through the LRRC8C, P2RX4, KCNJ2 and ANKH genes. A number of the validated QTL are also found to be associated with additional milk volume, fat and protein phenotypes.

Conclusions

Overall, these findings highlight novel candidate genes and variants involved in milk lactose regulation, whose impacts on membrane transport mechanisms reinforce the key osmo-regulatory roles of lactose in milk.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4320-3) contains supplementary material, which is available to authorized users.

The Role of ANK in Calcium Pyrophosphate Deposition Disease

The protein product of the progressive ankylosis gene, known as ANK, is a 492-amino acid multi-pass transmembrane protein. This protein is critical for the regulation of pyrophosphate, and gain of function ANK mutations is associated with calcium pyrophosphate deposition disease. Much about the structure, function, and regulation of ANK remain unstudied. This review of the current literature examines recent contributions to our understanding of ANK. We focus on new work on the function, binding partners, and regulators of ANK. A more complete understanding of this important protein may help to identify future therapeutic targets for the treatment of calcium pyrophosphate deposition disease.

Calcium pyrophosphate deposition disease: a review of epidemiologic findings

PURPOSE OF REVIEW

The purpose of this review is to summarize the recent advances in the epidemiology of calcium pyrophosphate deposition disease (CPPD), and to discuss their implications. This review is particularly timely as several epidemiological studies that enhance the understanding of CPPD have been published recently.

RECENT FINDINGS

This article will review recent findings on the prevalence of chondrocalcinosis; discuss new data on the associations between bone mineral density and chondrocalcinosis; and between diuretic use, chronic kidney disease 5 and 'pseudogout' (now termed acute calcium pyrophosphate crystal arthritis). It will summarize findings from a large dataset which reported that chondrocalcinosis results from a systemic predisposition, and that the association between chondrocalcinosis and polymorphisms in ANKH gene is independent of age and osteoarthritis. It will also review recent data which suggest that the association between chondrocalcinosis and osteoarthritis may be joint specific, and that chondrocalcinosis associates with radiographic attrition in knees with osteoarthritis.

SUMMARY

The studies reviewed suggest that CPPD occurs due to a generalized predisposition, and that it modifies the radiographic phenotype of osteoarthritis. However, further research is required to confirm if CPPD modifies the clinical phenotype of osteoarthritis.

Mannose-Binding Lectin Gene, MBL2, Polymorphisms Do Not Increase Susceptibility to Invasive Meningococcal Disease in a Population of Danish Children

Background.  Neisseria meningitidis is the cause of meningococcal bacteremia and meningitis, and nasopharyngeal colonization with this pathogen is common. The incidence of invasive disease is highest in infants, whereas adolescents more often are carriers. Altered regulation or dysfunction of the innate immune system may predispose to invasive meningococcal disease (IMD). In this study, we investigated the effect of genetic variation in the mannose-binding lectin gene, MBL2, and its promoter on susceptibility to IMD and IMD-associated mortality among children. Methods.  Children (<5 years) diagnosed during 1982-2007 with IMD and controls were identified through Danish national registries. DNA was obtained from the Danish Neonatal Screening Biobank. The associations between MBL2 diplotypes and IMD susceptibility and 30- and 90-day mortality were investigated using logistic regression analysis. Results.  We included 1351 children: 406 with meningitis, 272 with bacteremia, and 673 age- and sex-matched controls. Of the children studied, 1292 (96%) were successfully genotyped and assigned MBL2 diplotypes. The median age in IMD cases was 19.1 months (interquartile range [IQR], 8.8-32.2 months). Children with defective MBL2 diplotypes were not at higher risk for meningococcal meningitis than children with intermediate and normal diplotypes (odds ratio [OR] = 0.69; 95% confidence interval [CI], .47-1.02). Similar results were found for children with bacteremia and defective diplotypes (OR = 0.84; 95% CI, .53-1.32) as well as for all cases (OR = 0.75; 95% CI, .56-1.01). There was no association between MBL2 diplotypes and mortality. Conclusions.  Defective MBL2 diplotypes did not predict either an increased IMD susceptibility or mortality in a Danish population of children.

Erosive osteoarthritis, psoriatic arthritis and pseudogout; a casual association?

According to recent hypothesis, the inflammation has a pivotal role in the onset and progression of erosive hand osteoarthritis (EHOA), psoriatic arthritis (PsA) and chondrocalcinosis (CC)/pseudogout. Albeit, it has been recognised for years as an association between EHOA and radiographic evidence of CC, but there are few reports of coexistence of microcrystalline arthritis and PsA. This is the first report that described a clinical experience concerning two consecutive cases of patients presented with EHOA, PsA and pseudogout. Two Caucasian women of 71 and 85 years old with a history of OA and mild psoriasis are presented with tenderness and swelling of first interphalangeal (IP) and wrist joint, respectively. Arthrocentesis performed at the first IP and wrist joint, respectively, showed an inflammatory synovial fluid with presence of calcium pyrophosphate dehydrate crystals. X-rays of hands, feet and knees showed characteristic features of EHOA, PsA and CC. Furthermore, HLA typing evinces the presence of HLA C*06; DRB*01 07 and HLA C*07; DRB*01 *11 alleles, respectively, predisposing factors of these inflammatory diseases. The relationship between these aggressive rheumatic diseases along with their clinical, radiographic, laboratory and genetic features is discussed.