Background and aim The pathophysiology of rheumatoid arthritis (RA) is characterized by excess production of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) by neutrophils and macrophages in synovium. Additionally, these cytokines promote the production of reactive oxygen species (ROS), and increased production of matrix metalloproteinases (MMPs), including MMP-3, in synoviocytes that result in joint destruction. There is limited information on how proteolytic enzymes such as MMP-3 can be regulated. We evaluated the effect of the antioxidant N -acetylcysteine (NAC) on RA and identified the relationship between the c-Jun N terminal kinase (JNK) pathway and MMP-3. We hypothesized that elucidating this relationship would lead to novel therapeutic approaches to RA treatment and management. Methods We investigated the effect of administering a low dose (1000 μM or less) of an antioxidant (NAC) to human rheumatoid fibroblast-like synoviocytes (MH7A cells). We also investigated the response of antioxidant genes such as nuclear factor erythroid -derived 2-related factor 2 (Nrf2) and Sequestosome 1 (p62). The influence of MMP-3 expression on the JNK pathway leading to joint destruction and the mechanisms underlying this relationship were investigated through primary dispersion culture cells collected from the synovial membranes of RA patients, consisting of rheumatoid arthritis-fibroblast-like synoviocytes (RA-FLS). Results Low-dose NAC (1000 μM) increased the expression of Nrf2 and phospho-p62 in MH7A cells, activating antioxidant genes, suppressing the expression of MMP-3, and inhibiting the phosphorylation of JNK. ROS, MMP-3 expression, and IL-6 was suppressed by administering 30 μM of SP600125 (a JNK inhibitor) in MH7A cells. Furthermore, the administration of SP600125 (30 μM) to RA-FLS suppressed MMP-3. Conclusions We demonstrated the existence of an MMP-3 suppression mechanism that utilizes the JNK pathway in RA-FLS. We consider that the JNK pathway could be a target for future RA therapies.

Bone modeling is a biological process of bone formation that adapts bone size and shape to mechanical loads, especially during childhood and adolescence. Bone modeling in cortical bone can be easily detected using sequential radiographic images, while its assessment in trabecular bone is challenging. Here, we performed histomorphometric analysis in 21 bone specimens from biopsies collected during hip arthroplasty, and we proposed the criteria for histologically identifying an active modeling-based bone formation, which we call a “forming minimodeling structure” (FMiS). Evidence of FMiSs was found in 9 of 20 specimens (45%). In histomorphometric analysis, bone volume was significant higher in specimens displaying FMiSs compared with the specimens without these structures (BV/TV, 31.7 ± 10.2 vs. 23.1 ± 3.9%; p < 0.05). Osteoid parameters were raised in FMiS-containing bone specimens (OV/BV, 2.1 ± 1.6 vs. 0.6 ± 0.3%; p < 0.001, OS/BS, 23.6 ± 15.5 vs. 7.6 ± 4.2%; p < 0.001, and O.Th, 7.4 µm ± 2.0 vs. 5.2 ± 1.0; p < 0.05). Our results showed that the modeling-based bone formation on trabecular bone surfaces occurs even during adulthood. As FMiSs can represent histological evidence of modeling-based bone formation, understanding of this physiology in relation to bone homeostasis is crucial.

Pustulotic arthro‐osteitis (PAO) is a major complication of palmoplantar pustulosis (PPP). In orthopedic surgery outpatient clinics, PPP patients with osteoarticular symptoms are seen frequently, but PAO's clinical features remain not well known. To determine Japanese patients’ clinical features and treatment status with PAO, we conducted a single‐center retrospective epidemiologic survey. Clinical features, including gender, age, smoking habit, the onset pattern, interval between skin manifestation and osteoarticular symptoms, and the incidence of sternoclavicular joint lesions, axial and peripheral joint lesions, were examined. The association between physical status and image findings by X‐ray, computed tomography, bone scintigraphy with Technetium99, or magnetic resonance imaging was evaluated. The distribution pattern of peripheral joint lesions and the treatment status were evaluated. We identified 51 patients, 10 men and 41 women, with PAO. The average age was 48 years and 59% were smokers. The frequency of onset patterns was skin‐leading type (63%), simultaneous onset (18%), and osteoarticular leading type (16%). The average interval between skin involvement and osteoarticular involvement in skin‐leading type was significantly longer than that in osteoarticular leading type (7.1 years vs. 2.0 years). A sternoclavicular joint (SCJ) lesion was detected in 65% cases, and the physical findings of SCJ were significantly related to the image findings. Axial and peripheral joint lesions were detected in the same ratio (23 cases, 45%). In the peripheral joints, the finger joint was the most common (26%), followed by the shoulder joint (21%). Patients were treated with nonsteroidal anti‐inflammatory drugs (76%), followed by conventional synthetic disease‐modifying antirheumatic drugs (DMARDs) (29%) and biological DMARDs (9.8%). Tonsillectomy was performed in 11 cases. In conclusion, PAO more frequently involves SCJ in middle‐aged women who smoke. Given that osteoarticular leading type was detected in 16% cases, seronegative oligoarthritis patients should be monitored for PPP, leading to a diagnosis of PAO.

This technique may be useful in assisting repair of scaphoid bone fracture.

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