Plasma acylated and plasma unacylated ghrelin: useful new biomarkers in patients with neuroendocrine tumors?

Abstract

To date, the value of fasting plasma acylated ghrelin (AG) and unacylated ghrelin (UAG) as potential novel biomarkers in patients with neuroendocrine tumors (NETs) is unknown. The aims of this study are to (i) compare fasting AG and UAG levels between nonobese, nondiabetic NET patients (N=28) and age- (±3 years) and sex-matched nonobese, nondiabetic controls (N=28); and (ii) study the relationship between AG, UAG, and AG/UAG ratios and biochemical (chromogranin-A (CgA) and neuron-specific enolase (NSE) levels) and clinical parameters (age at diagnosis, sex, primary tumor location, carcinoid syndrome, ENETS TNM classification, Ki-67 proliferation index, grading, prior incomplete surgery) in NET patients. Fasting venous blood samples (N=56) were collected and directly stabilized with 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride after withdrawal. Plasma AG and UAG levels were determined by ELISA. Expression of ghrelin was examined in tumor tissue by immunohistochemistry. There were no significant differences between NET patients and controls in AG (median: 62.5 pg/mL, IQR: 33.1-112.8 vs median: 57.2pg/mL, IQR: 26.7-128.3, P=0.66) and UAG in levels (median: 76.6pg/mL, IQR: 35.23-121.7 vs median: 64.9, IQR: 27.5-93.1, P=0.44). No significant correlations were found between AG, UAG, and AG/UAG ratios versus biochemical and clinical parameters in NET patients with the exception of age at diagnosis (AG: ρ= -0.47, P=0.012; AG/UAG ratio: ρ= -0.50, P=0.007) and baseline chromogranin-A levels (AG/UAG ratio: ρ= -0.44, P=0.019). In our view, fasting plasma acylated and unacylated ghrelin appear to have no value as diagnostic biomarkers in the clinical follow-up of patients with NETs.

Keywords: biomarker; human acylated ghrelin (AG); human unacylated ghrelin (UAG); neuroendocrine tumors (NETs).

Figure 1

Plasma acylated ghrelin (AG), plasma unacylated ghrelin (UAG), and acylated ghrelin/unacylated ghrelin (AG/UAG) ratio in Caucasian, nonobese, nondiabetic NET patients (N=28) versus sex- and age-matched healthy Caucasian, nonobese, nondiabetic controls (N=28). Data are expressed as median±interquartile range (IQR).

Figure 2

Primary tumor localization in patients with neuroendocrine tumors (NETs), and the distribution of plasma acylated ghrelin (AG), plasma unacylated ghrelin (UAG), and acylated ghrelin/unacylated ghrelin (AG/UAG) ratio. Data are expressed as median±interquartile range (IQR).

Figure 3

Plasma acylated ghrelin (AG) and plasma unacylated ghrelin (UAG) in Caucasian, nonobese, nondiabetic NET patients (N=28) distributed according to tumor grading. Data are expressed as median±interquartile range (IQR).

Figure 4

Immunohistochemistry: section of normal stomach tissue (panel A, magnification 10×), immunohistochemical staining of ghrelin on normal stomach tissue (panel B, magnification 10×), section of small intestine NET tissue (panel C magnification 20×), and immunohistochemical staining of ghrelin small intestine NET tissue (panel D, magnification 20×). The scale bar is set on 1mm.