Detection Of Plasma Levels Of Ghrelin, Leptin, Insulin And Proinsulin In Patients With Pancreatic Endocrine Tumors And Expression Of Ghrelin And GHS-R 1A In Tumor Tissues

Background Insulinoma is the most common type in pancreatic endocrine tumors(PETs).Hypersecretion of insulin or proinsulin by the tumor results in hypoglycemia of the patients.Most of patients with insulinoma are overweight or obesity partly due to frequent food intaking for preventing hypoglycemia.Recently,it has been shown that gastrointestinal peptide hormones ghrelin and leptin are associated with obesity and secretion of insulin. However,it is not clear that plasma levels of ghrelin and leptin correlate with hyperinsulinemia and obesity.Whether ghrelin and its receptor are expressed in insulinoma has not been documented.Objective 1,To study if plasma levels of ghrelin and leptin are associated with high levels of insulin/proinsulin and obesity in patients with insulinoma or PETs;2,To investigate whether ghrelin and its receptor are expressed in insulinoma,and correlate the expression as well as the blood levels of peptides with clinical characteristics.Methods Preoperative blood samples from 40 insulinoma patients and 11 patients with PETs except insulinoma were collected during September 2003 to July 2008,and blood samples from 30 healthy volunteers(matching age, gender and body weight to the patients) were used as controls.Plasma levels of ghrelin,leptin,insulin and proinsulin were detected by ELISA,and the relationships between these hormones were analyzed.Twenty-two tumors from patients with insulinoma and 8 tumors from patients with PETs were used for detecting expression of ghrelin and its functional receptor GHS-R 1A by immunohistochemical staining,while 5 normal pancreatic tissues and 19 paired pancreatic tissues were used as controls.The data was correlated with plasma ghrelin levels.The clinical-pathological characteristics were analyzed and correlated with the plasma levels of the hormones and expression of ghrelin and its receptor. Mann-Whitney U test,Kruskal-Wallis H test,Spearman rank correlation,Fisher's exact probabilities test and factorial design ANOVA were used for statistical analysis in skewness distribution data.P＜0.05 was considered significant.Results Of 40 patients with insulinoma,17 patients were male and 23 patients were female.The range of age of the patients was 18～74,the median age was 45,while the range of BMI of the patients was 19.3～39.6 kg/m²,the average BMI of the patients was 28.3±0.8 kg/m²(median 27.9 kg/m²).The plasma ghrelin levels in patients with insulinoma were significantly lower than those in the normal controls(0.017±0.001 ng/ml vs.0.021±0.002 ng/ml,P=0.044). The plasma levels of leptin,insulin and proinsulin in patients with insulinoma were significantly higher than those in the controls(leptin:0.47±0.04 ng/ml vs. 0.38±0.04 ng/ml,P=0.003;true insulin:29.2±9.8 mU/L vs.4.0±0.7 mU/L,P=1.29×10^-6;proinsulin:24.7±4.9 pmol/L vs.2.1±0.3 pmol/L,P=3.00×10^-9).The plasma ghrelin levels were affected by tumor independently(P=0.019) or by tumor and body weight simultaneously(P=0.017).The plasma ghrelin levels in patients with insulinoma located in head and neck of the pancreas were significantly higher than those in patients with tumor located in body and tail of the pancreas(P=0.039),and the plasma ghrelin levels were not correlated with BMI and other clinical characteristics.The plasma leptin levels in patients with insulinoma were positively correlated with insulin levels and BMI(both of the P value was 0.028),and the plasma leptin levels in male patients were significantly lower than the levels in female patients(P=0.0001).Body weight could impact the plasma leptin levels independently.The plasma insulin levels in patients with insulinoma were positively correlated with BMI(P=0.002).Of 11 patients with PETs,4 patients were male and 7 were female.The range of age of the patients was 33～66,the median age was 45,while the range of BMI of the patients was 15.8～25.9 kg/m²,the average BMI of the patients was 21.2±1.1 kg/m²(median 20.7 kg/m²).The plasma levels of ghrelin,leptin,insulin and proinsulin in patients with PETs were 0.016±0.005 ng/ml,0.34±0.03 ng/ml, 5.5±1.4 mU/L and 8.8±6.5 pmol/L respectively,in which the plasma levels of ghrelin were significantly lower than the levels in normal controls(P=0.047),and plasma levels of leptin,insulin and proinsulin were significantly lower than the levels in patients with insulinoma(the P values were 0.049,0.007 and 0.001 respectively).The plasma ghrelin levels in patients with PETs were positively correlated with leptin levels(P=0.015),and there were no relationships among other hormones and between hormones and clinical characteristics.Positive staining of ghrelin and GHS-R 1A were shown in 82%and 64%of insulinoma tissues,respectively,and the expression rate of GHS-R 1A was significantly higher in the tumor tissues with expression of ghrelin than that in the tumors without expression of ghrelin(78%vs.0%,P=0.010).The expression of ghrelin in the tumor tissues was not correlated with the plasma ghrelin levels in patients with insulinoma.The average age of the patients whose tumor tissues expressed GHS-R 1A was much older than the ones whose tumor tissues did not express the receptor(49.7±4.1 vs.37.1±3.0,P=0.035).The expression of ghrelin and GHS-R 1A were not correlated with other clinical characteristics.Positive staining of ghrelin and GHS-R 1A were shown in 75%and 88%of PETs tissues,respectively.There was no difference of the expression of ghrelin and GHS-R 1A between insulinoma and other types of PETs.The expression of ghrelin and GHS-R 1A were not correlated with the plasma ghrelin levels in patients with PETs and clinical characteristics.Conclusions The plasma levels of the ghrelin,leptin and insulin in patients with insulinoma were significantly different to the controls,suggesting the disorders of peptides secretion occurred in insulinoma.The high expression of ghrelin and its functional receptor in the tumor tissues indicated that ghrelin might act on the tumor through autocrine or paracrine pathway.