Pro-inflammatory effects of human apatite crystals extracted from patients suffering from calcific tendinopathy

Abstract

Background Calcific tendonitis of the rotator cuff is due to carbonated apatite deposits in the shoulder tendons. During the evolution of the disease, an acute inflammatory episode may occur leading to the disappearance of the calcification. Although hydroxyapatite crystal-induced inflammation has been previously studied with synthetic crystals, no data are available with calcifications extracted from patients suffering from calcific tendinopathy. The objective of the study was to explore the inflammatory properties of human calcifications and the pathways involved. Methods Human calcifications and synthetic hydroxyapatite were used in vitro to stimulate human monocytes and macrophages, the human myeloid cell line THP-1, and human tenocytes. The release of IL-1β, IL-6, and IL-8 by cells was quantified by ELISA. The gene expression of pro- and anti-inflammatory cytokines was evaluated by quantitative PCR. NF-kB activation and NLRP3 involvement were assessed in THP-1 cells using a NF-kB inhibitor and a caspase-1 inhibitor. The inflammatory properties were then assessed in vivo using a mouse air pouch model. Results Human calcifications were able to induce a significant release of IL-1β when incubated with monocytes, macrophages, and THP-1 only if they were first primed with LPS (monocytes and macrophages) or PMA (THP-1). Stimulation of THP-1 by human calcifications led to similar levels of IL-1β when compared to synthetic hydroxyapatite although these levels were significantly inferior in monocytes and macrophages. The patient’s crystals enhanced mRNA expression of pro-IL-1β, as well as IL-18, NF-kB, and TGFβ when IL-6 and TNFα expression were not. IL-1β production was reduced by the inhibition of caspase-1 indicating the role of NLRP3 inflammasome. In vivo, injection of human calcifications or synthetic hydroxyapatite in the air pouch led to a significant increase in membrane thickness although significant overexpression of IL-1β was only observed for synthetic hydroxyapatite. Conclusions As synthetic hydroxyapatite, human calcifications were able to induce an inflammatory response resulting in the production of IL-1β after NF-kB activation and through NLRP3 inflammasome. In some experiments, IL-1β induction was lower with human calcifications compared to synthetic apatite. Differences in size, shape, and protein content may explain this observation.

Mechanical overload-induced release of extracellular mitochondrial particles from tendon cells leads to inflammation in tendinopathy

“…The present study revealed that the ExtraMito particles within mEPs are fundamental for inducing macrophage infiltration. Several proinflammatory cytokines, such as IL-1β, TNF-α, CXCL1 and IL-6, have been reported to initiate catabolic processes, especially in the early phase of tendinopathy 13 , 47 , 48 . We found that the mechanism underlying the loading-induced release of IL-6, CXCL1, and IL-18 was dependent on the degree of mechanical loading.…”

All that illuminates on radionuclide imaging is not a metastatic lesion: Role of complementary imaging

“…[7] Calcific tendinitis is a cell-mediated disease passing through four stages of development, leading to fibrocartilaginous metaplasia and secondary mineralization which is subsequently resorbed in the resorptive phase by phagocytosis. [1] Crystal deposition incites an inflammatory response with increased tissue metabolism and activated inflammatory cells which are possibly responsible for the increased uptake of tracer on nuclear imaging. [8] A typical clinical picture is characterized by spontaneous onset, pain in the affected joint with referred pain, and spontaneous resolution.…”

“…Although the exact etiology is not known, the development of calcium hydroxyapatite crystals deposition is believed to be due to tissue hypoxia, reduced oxygen tension resulting in cartilaginous metaplasia and secondary mineralization. [1] Characteristically affecting the rotator cuff tendons of the shoulder, it can be asymptomatic or symptomatic in patients and also has been noted at unusual sites such as the elbow, wrist, knee, and hip to name a few. [2] However, its imaging features may mimic a metastatic lesion and this case report highlights the dilemma that can face a clinician.…”

Calcific tendinopathy of the pronator quadratus muscle: A rare site and cause of ulnar sided wrist pain

“…3 The development of calcium hydroxyapatite crystals deposition is thought to be due to decreased oxygen tension, leading to fibrocartilaginous metaplasia and secondary mineralisation. 4 Calcific tendinitis passes through four stages of evolution: (i) precalcific, asymptomatic phase, (ii) calcific or formative phase with varying symptoms, (iii) resorptive, most symptomatic phase due to extravasation of calcium hydroxyapatite into adjacent tissues, and (iv) post calcific phase associated with restriction of joint movements, tendinopathy and associated bursitis. 5 Though the shoulder joint is most frequent location of calcific tendinopathy, symptomatic calcific tendinitis at unusual sites (hip, knee, wrist and elbow) have been well described in literature.…”