YKL-40: A biomarker for early nephropathy in type 2 diabetic patients and its association with inflammatory cytokines

Highlights

• YKL-40 also known as chitinase 3-like protein 1 (CHI3L1), is a 40 kDa glycoprotein secreted by neutrophils and activated macrophages.

• Persistent micro and macroalbuminuria are well known predictors of diabetic nephropathy leading to progressive end-stage renal disease.

• We aimed to measure the circulatory YKL-40 in diabetic subjects with and without diabetic nephropathy and investigated its diagnostic accuracy.

• The AUCROC for YKL-40 was found to be high [0.95; (95% CI: 0.88–1.0)], when compared to other acute phase markers.

• Plasma YKL-40 could be a potential biomarker for early diagnosis of incipient DN among South Indian population.

Abstract

Diabetic Nephropathy (DN) is an important cause of morbidity and death amongst diabetes. Persistent micro and macroalbuminuria are well known predictors of DN leading to progressive end-stage renal disease. However, albuminuria has several limitations. Increasing evidences show that YKL-40 is highly expressed in variety of inflammatory diseases and also recognized as a non-invasive prognostic biomarker for inflammation. In the present study, we measured plasma YKL-40 levels in different stages of albuminuria and assessed its diagnostic accuracy as a biomarker for DN and correlated with different families of circulatory cytokines. A total of 306 subjects were recruited and divided into three groups [Group-I, control (n = 83), Group-II, Normoalbuminuria (n = 81), Group-III, DN (n = 142)]. Group-III is further subdivided into: Group-IIIa, microalbuminuria (n = 73), Group-IIIb, macroalbuminuria (n = 69). The median levels of YKL-40 (p = 0.001) showed a marked stepwise increase from normo to macroalbuminuria and positively correlated with eGFR. The AUC_ROC for YKL-40 was found to be high [0.95; (95% CI: 0.88–1.0)], when compared to other acute phase markers. Plasma YKL-40 showed a positive correlation with LIGHT/TNFSF14, sIL-6Ra, gp130/sIL-6Rβ, IFN-β, IL-8, TNFSF14, sCD-30 and eGFR meanwhile a negative correlation with TWEAK/TNFSF12, IL-7 like cytokine and IFN-λ2. Plasma YKL-40 could be a potential biomarker for early diagnosis of incipient DN among South Indian population.

Introduction

Diabetic Nephropathy (DN), a serious and often challenging microvascular complication of diabetes mellitus results with end-stage renal disease, along with a substantial negative impact on both morbidity and mortality rate. Although numerous evidences indicate that the pathogenesis of DN is multifactorial, inflammation has been emerged as a key pathophysiological mechanism (Navarro-Gonzalez et al., 2011). Thus, it is considered that the mediators related to the inflammatory pathways are important in the early stages of diabetic kidney disease. The association of the low-grade inflammation has been evidenced by the presence of an elevated level of various inflammatory cytokines in patients with diabetes as well as with its microvascular complications. Hence, understanding the key features of inflammatory mechanisms involved in the development and progression of DN would enable the identification of therapeutic targets to ameliorate the progression of DN. Currently, microalbuminuria along with estimated glomerular filtration rate (eGFR) is widely used as a diagnostic tool for the occurrence and progression of DN. However, several limitations are associated with microalbuminuria as a biomarker for DN. Although microalbuminuria is a widely used indicator for DN, its diagnostic accuracy is limited by the fact that structural damage might precede albumin excretion (Currie et al., 2014). Further, studies have also confirmed that it is not specific for the presence of DN alone as non-diabetic patients with progressive kidney disease may also develop microalbuminuria (Glassock, 2010). On the other hand, it has been reported that C-reactive protein (CRP), as a diagnostic marker of low-grade inflammation and a determinant of the development of elevated excretion of urinary albumin. Despite a lot of studies addressing the importance of CRP as a prognostic biomarker, there are few reports which highlights that CRP does not seem to have a significant prognostic value, which renders the need for a new biomarker with higher specificity (Olsen et al., 2007; Al-Rubeaan et al., 2017; Peisajovich et al., 2008). Moreover, CRP is primarily produced in response to Interleukin-6 (IL-6) and is not a site specific rather than as a systemic inflammatory marker (Nielsen et al., 2011). Therefore, there is an imperative need to identify an effective, specific and sensitive biomarker that can predict the development of DN among Type 2 Diabetes Mellitus (T2DM) individuals who will develop this life-threatening disease at an early stage.

YKL-40 also known as chitinase 3-like protein 1 (CHI3L1), is a 40 kDa heparin and chitin-binding glycoprotein which has three N terminal amino acids: tyrosine (Y), lysine (K), leucine (L). YKL-40 is secreted by a variety of cells such as neutrophils and activated macrophages in different tissues with inflammation and vascular smooth muscle cells. Increasing evidences support that it is involved in the pathogenesis of diabetes (Zurawska-Plaksej et al., 2015), cardiovascular disease (Kastrup et al., 2009) and cancer (Johansen et al., 2009). YKL-40 act as an inflammatory marker in relation to both acute and chronic inflammation as well as participate in the processes during the early stages of atherosclerosis (Rathcke et al., 2006). Moreover, several reports have demonstrated that circulatory levels of YKL-40 was elevated in T2DM patients and positively correlated with insulin resistance and parameters of the lipid profile (Rathcke et al., 2006; Nielsen et al., 2008). Despite the growing number of studies in recent years, the complete biological function and specific receptor of YKL-40 are still unknown. Recently, few reports have demonstrated that circulating YKL-40 levels were associated with albuminuria in patients with both type 1 diabetes mellitus (T1DM) and T2DM (Brix et al., 2011; Rondbjerg et al., 2011).

Thus, we propose that plasma YKL-40 measurement might become a useful and non-invasive tool for early incipient DN. The present study aimed to measure the levels of circulatory YKL-40 in T2DM subjects with and without DN and further investigated its diagnostic accuracy by comparing with other acute phase markers such as CRP, IL-6 and Tumor Necrosis Factor-α (TNF-α). In addition, to support the role of YKL-40 as a pro-inflammatory marker in the early development of incipient DN, we also explored the direct correlations with other inflammatory cytokines/chemokines.