Relationships between desacylated and acylated ghrelin and insulin sensitivity in the metabolic syndrome

Abstract

Context: Metabolic syndrome shows clustered metabolic abnormalities with major roles for insulin resistance and obesity. Ghrelin is a gastric hormone whose total plasma concentration (T-Ghr) is associated positively with insulin sensitivity and is reduced in obesity. Ghrelin circulates in acylated (A-Ghr) and desacylated (D-Ghr) forms, but their potential differential associations with insulin resistance and whether they are differentially altered in obesity remain undefined.

Objective: Our objective was to determine potential differential associations of ghrelin forms with insulin resistance [homeostasis model assessment of insulin resistance (HOMA-IR)] and the impact of obesity on their plasma concentrations in metabolic syndrome.

Design: This is a cross-sectional study.

Setting: The study was performed in a metabolic outpatient unit.

Patients: Patients with metabolic syndrome (National Cholesterol Education Program-Adult Treatment Panel III; n = 45, 23 males/22 females) were included in the study.

Main outcomes: The main study outcomes were metabolic syndrome criteria, HOMA-IR, and ghrelin forms.

Results: Plasma insulin and HOMA-IR were associated negatively with T-Ghr and D-Ghr but positively with A-Ghr and acylated to desacylated ghrelin (A/D-Ghr) ratio (n = 45; P < 0.05). Compared with nonobese [body mass index (BMI) < 27.5 kg/m(2); n = 12, six males/six females], obese metabolic syndrome patients (BMI > 27.5 kg/m(2); n = 33) had lower T-Ghr and D-Ghr but comparable A-Ghr and higher A/D-Ghr ratio (P < 0.05). BMI and waist circumference (WC) were positively related with HOMA-IR (n = 45; P < 0.05). However, opposite associations between A/D-Ghr ratio and HOMA-IR remained significant after adjustment for sex and BMI (or WC). Additional obese individuals without metabolic syndrome (n = 10: age-, sex-, BMI-, and WC-matched to obese metabolic syndrome patients) had lower T-Ghr but higher A-Ghr (P < 0.05) compared with age-, sex-matched healthy nonobese counterparts (n = 15). T-Ghr and A-Ghr were comparable in obese with or without metabolic syndrome.

Conclusion: Obesity could alter circulating ghrelin profile, and relative A-Ghr excess could contribute to obesity-associated insulin resistance in metabolic syndrome.