YKL-40 as a biomarker in various inflammatory diseases: A review

Abstract

YKL-40 or Chitinase-3-Like Protein 1 (CHI3L1) is a highly conserved glycoprotein that binds heparin and chitin in a non-enzymatic manner. It is a member of the chitinase protein family 18, subfamily A, and unlike true chitinases, YKL-40 is a chitinase-like protein without enzymatic activity for chitin. Although its accurate function is yet unknown, the pattern of its expression in the normal and disease states suggests its possible engagement in apoptosis, inflammation and remodeling or degradation of the extracellular matrix. During an inflammatory response, YKL-40 is involved in a complicated interaction between host and bacteria, both promoting and attenuating immune response and potentially being served as an autoantigen in a vicious circle of autoimmunity. Based on its pathophysiology and mechanism of action, the aim of this review was to summarize research on the growing role of YKL-40 as a persuasive biomarker for inflammatory diseases' early diagnosis, prediction and follow-up (e.g., cardiovascular, gastrointestinal, endocrinological, immunological, musculoskeletal, neurological, respiratory, urinary, infectious) with detailed structural and functional background of YKL-40.

Keywords: Chitinase-3-Like Protein 1; YKL-40; biomarkers; chitinases; inflammation.

Figure 1

Flow chart demonstrating literature search.

Figure 2

Summary of YKL-40 concentrations in reported studies including healthy population and various inflammatory states. Results of the original studies are summarized with data points representing mean concentration in µg/L (values annotated above/below points) with brackets representing standard deviation. Sample type is annotated individually. Mean and standard deviation was approximated from median and range if not reported in original study. Y-axis is log₁₀ transformed for easier readability due to large range of values. Ref. N - reference number. CSF - cerebrospinal fluid. CVD - cardiovascular disease. STEMI - ST-elevation myocardial infarction. DM - diabetes mellitus. CP - chronic pancreatitis. IBD - inflammatory bowel disease. CKD - chronic kidney disease. AKI - acute kidney injury. AD - Alzheimer’s disease. AME - antibody mediated encephalitis. COPD - chronic obstructive lung disease.