ACR Meeting Abstracts

ACR Meeting Abstracts

  • Home
  • Meetings Archive
    • ACR Convergence 2022
    • ACR Convergence 2021
    • ACR Convergence 2020
    • 2020 ACR/ARP PRSYM
    • 2019 ACR/ARP Annual Meeting
    • 2018 ACR/ARHP Annual Meeting
    • 2017-2009 Meetings
    • Download Abstracts
  • Keyword Index
  • Advanced Search
  • Your Favorites
    • Favorites
    • Login
    • View and print all favorites
    • Clear all your favorites
  • Meeting Resource Center

Abstract Number: 0670

Hemochromatosis Is Associated with CPPD Through Iron’s Effect on Bone

Jennifer Velasco, Claudia Gohr, Elizabeth MItton-Fitzgerald and Ann Rosenthal, Medical College of Wisconsin, Milwaukee, WI

Meeting: ACR Convergence 2021

Keywords: bone biology, CPPD, Hemochromatosis

  • Tweet
  • Email
  • Print
Session Information

Date: Sunday, November 7, 2021

Session Title: Metabolic & Crystal Arthropathies – Basic & Clinical Science Poster I (0660–0682)

Session Type: Poster Session B

Session Time: 8:30AM-10:30AM

Background/Purpose: Hemochromatosis (HH) is one of the strongest known risk factors for calcium pyrophosphate (CPP) crystal deposition. The pathogenic mechanisms causing CPP crystal formation in HH patients remain unknown. CPP crystal formation is associated with increased levels of inorganic pyrophosphate (PPi). This process is controlled by transporters of extracellular ATP such as ANK, and a series of ectoenzymes that hydrolyze ATP or degrade PPi. Recently, alterations in bone such as increased osteoclastogenesis, have also been implicated in CPPD. Most end organ damage in HH is attributed to iron deposition; and in vitro studies mimic HH by exposing cells or tissues to high levels of iron. Prior work showed no clear effects of iron on factors affecting CPP crystal formation in articular cartilage. We sought to investigate the hypothesis that iron contributes to CPP crystal formation by stimulating osteoclastogenesis. We also explored other effects of iron on PPi regulatory factors in osteoclasts and osteoblasts.

Methods: RAW264.7 cells (pre-osteoclasts) were incubated with 10-20 ng/ml RANKL and 10-100 µM ferric ammonium citrate (FAC) or no additives for 4-6 days. Osteoclast formation was assessed using a quantitative TRAP assay. Many of the effects of iron are attributed to increased reactive oxygen species (ROS). We measured ROS in RAW cells using DCFDA dye (Sigma). Because high levels of RANKL on osteoblasts stimulate osteoclast formation, we measured RANKL on osteoblasts in the presence of iron. Human osteoblasts (fOBs, Cell Applications) were exposed to 10-100 µM FAC or no additives for 9 days. RANKL levels were measured using RT-PCR. Other factors known to contribute to bone PPi homeostasis were measured in fOBs, including alkaline phosphatase (AP) activity, ANK levels, and levels of PPi. ANK was measured with RT-PCR and AP activity was measured with an assay from Abcam. PPi was measured in the conditioned media of fOBs and RAW cells using a highly sensitive radiometric assay.

Results: Ten-40 µM FAC significantly increased TRAP activity on RAW cells incubated with submaximal concentrations of RANKL at 6 days (p< 0.0001, N=15). Forty µM FAC increased TRAP activity by 2-fold (Figure 1). FAC also increased ROS (p< 0.0001, N=5) (Figure 2). Similar concentrations of FAC had no effects on fOB RANKL levels at 9 days in the absence or presence of differentiation factors (Data not shown). There was a small but significant decrease in alkaline phosphatase in fOBs at 100 µM FAC. Levels were 4.03± 1.3 nmol/well in fOBs with no iron exposure and 2.35± 0.6 U with FAC (p=0.02, n=5). FAC had no effects on ANK mRNA, and PPi levels were unmeasurable in both RAWs and fOBs. FAC toxicity was monitored using an LDH assay and was not significant at the concentrations tested.

Conclusion: We confirm here that iron increases TRAP positive osteoclasts in vitro. Increased osteoclast number is associated with premature severe CPPD caused by a loss of function mutation in osteoprotegerin. Further work will be necessary to determine the mechanisms through which osteoclast excess causes CPPD, but these findings add additional support to the hypothesis that some forms of CPDD are related to primary abnormalities in bone.

Figure 1

Figure 2


Disclosures: J. Velasco, None; C. Gohr, None; E. MItton-Fitzgerald, None; A. Rosenthal, None.

To cite this abstract in AMA style:

Velasco J, Gohr C, MItton-Fitzgerald E, Rosenthal A. Hemochromatosis Is Associated with CPPD Through Iron’s Effect on Bone [abstract]. Arthritis Rheumatol. 2021; 73 (suppl 9). https://acrabstracts.org/abstract/hemochromatosis-is-associated-with-cppd-through-irons-effect-on-bone/. Accessed January 27, 2023.
  • Tweet
  • Email
  • Print

« Back to ACR Convergence 2021

ACR Meeting Abstracts - https://acrabstracts.org/abstract/hemochromatosis-is-associated-with-cppd-through-irons-effect-on-bone/

Advanced Search

Your Favorites

You can save and print a list of your favorite abstracts during your browser session by clicking the “Favorite” button at the bottom of any abstract. View your favorites »

ACR Pediatric Rheumatology Symposium 2020

© COPYRIGHT 2023 AMERICAN COLLEGE OF RHEUMATOLOGY

Wiley

  • Home
  • Meetings Archive
  • Advanced Search
  • Meeting Resource Center
  • Online Journal
  • Privacy Policy
  • Permissions Policies
  • Cookie Preferences