Journal Pre-proof Biomarkers of tissue turnover and systemic inflammation are associated with disease severity and activity in patients with hidradenitis suppurativa

informed consent on their disease severity defined by Hurley stages; mild = Hurley I (n=148), moderate = Hurley II (n=145), severe = Hurley III (n=38) characteristics examination interview. activity score; COPD; Chronic obstructive pulmonary disease; LDL, low-density lipoprotein; HDL, high-density lipoprotein; ALAT, alanine aminotransferase; ALP, alkaline phosphatase.


To the Editor
Hidradenitis suppurativa (HS) is a chronic inflammatory skin condition of the follicular epithelium occurring predominantly in the axillae, inframammary folds, groins and buttocks (Gansevoort et al. 2011). Dependent on the disease severity, various pharmacologic and surgical interventions to prevent and treat new lesions, as well as remove existing inflammatory nodules, abscesses, and sinus tracts, can be initiated. Biomarkers reflecting disease severity and activity of HS could potentially aid the need for better tools to diagnose HS as well as determine treatment effects (Blok et al. 2016). Here both imaging and blood-based techniques have been proposed. For imaging, ultrasound (US) is the most well-characterized method, while other methods such as medical infrared thermography (MIT) and optical coherence tomography (OCT) are emerging methods which demonstrate higher degree of accuracy compared to US (Grand et al. 2019).
The extracellular matrix (ECM) of the skin results in generation of protein fragments released into the blood, which can be quantified as blood-based biomarkers. Such biomarkers reflect scarring and fibrosis of the skin and could be potential emerging targets for HS (Dengjel et al. 2020;Sand et al. 2018). Collagens are the most abundant ECM proteins of the body, where type I, III, IV, VI and VII are the most well described in the skin. Type I and III collagen are primarily found in the dermis, type IV collagen is located in the basement membrane by the junction of epidermis and dermis, type VI collagen is located throughout the dermis, while type VII collagen is known as an anchoring fibril, stabilizing the lower part of the dermo-epidermal basement membrane to the underlying dermis (Dobrota et al. 2021;Sand et al. 2018). In addition to collagens, the interfilament protein vimentin plays a role in macrophage and fibroblast differentiation and keratinocyte differentiation in wound healing (Mortensen et al. 2015), while S100A9, a subunit of calprotectin (S100A8/A9), J o u r n a l P r e -p r o o f contributes to the epithelial cell function including keratinocyte differentiation (Iotzova-Weiss et al. 2015).
We hypothesized that serological biomarkers of ECM remodelling linked to chronic inflammation are upregulated in patients diagnosed with HS compared to healthy subjects and associated with disease severity and activity, and systemic inflammation.  Table   1). All biomarkers are validated for human serum. The inter-and intra-assay coefficients of variation are >15% and 10% respectively for all assays.
A total of 331 patients with HS (228 women and 93 men) with a mean age of 39.98 years (SD=13.93) were included, together with 16 healthy donors (10 women and 6 men) with a mean age of 35.19 years (SD=7.43) as reference (Table 1).
C1M was significantly higher in patients with Hurley stage II and III compared to stage I (p=0.043 and <0.0001 respectively), and between Hurley stage II and III (p<0.0001). C3M and C4M were J o u r n a l P r e -p r o o f significantly elevated in patients with Hurley stage II and III, compared to Hurley stage I (p=0.014 and 0.001; p=0.0001 and p<0.0001, respectively). No significant differences were detected for C5M.
C7M, was significantly elevated in Hurley stage III compared to Hurley stage I and II (p=0.0003 and p=0.0042 respectively). The macrophage activity biomarker, VICM, was significantly higher in patients with Hurley stage II and III compared to stage I (p=0.0167 and p<0.0001 respectively), and between Hurley stage II and III (p=0.0152). The human neutrophil activity biomarker, CPa9-HNE, We evaluated a biomarker panel of ECM turnover and systemic inflammation in a large, wellcharacterized cohort of HS patients with aim to identify potential blood-based biomarkers for HS.
There is a need for HS biomarkers to help understand the pathogenesis and to monitor the disease progression. This need is crucial for use in clinical trials, but also to advance knowledge of the biological complexity behind HS. The evaluated biomarkers in this study represent proteins located in dermis, epidermis, and the epidermal basement membrane, reflecting the individual skin compartments remodeled during HS progression. A balanced ECM is necessary to preserve skin integrity and tissue homeostasis (Dengjel et al. 2020 In summary, this is, to our knowledge, the first study to evaluate novel ECM biomarkers and systemic inflammation in patients with HS. The findings indicate an association between biomarkers of tissue turnover and disease severity and activity. Such biomarkers may be utilized to assess patients' eligibility to targeted treatments and fill the medical need for biomarkers in clinical management and trials.

DATA AVAILABILITY STATEMENT
All data from this study are included in this article. Data are kept on file and are not publicly available due to privacy data legislation. Requests can be directed to the corresponding author.