Plasma levels of leptin, omentin, collagenous repeat-containing sequence of 26-kDa protein (CORS-26) and adiponectin before and after oral glucose uptake in slim adults

Abstract

Background: Adipose tissue secreted proteins are collectively named adipocytokines and include leptin, adiponectin, resistin, collagenous repeat-containing sequence of 26-kDa protein (CORS-26) and omentin. Several of these adipocytokines influence insulin sensitivity and glucose metabolism and therefore systemic levels may be affected by oral glucose uptake. Whereas contradictory results have been published for leptin and adiponectin, resistin has not been extensively investigated and no reports on omentin and CORS-26 do exist.

Methods: Therefore the plasma levels of these proteins before and 120 min after an oral glucose load were analyzed in 20 highly-insulin sensitive, young adults by ELISA or immunoblot.

Results: Circulating leptin was reduced 2 h after glucose uptake whereas adiponectin and resistin levels are not changed. Distribution of adiponectin and CORS-26 isoforms were similar before and after glucose ingestion. Omentin is highly abundant in plasma and immunoblot analysis revealed no alterations when plasma levels before and 2 h after glucose intake were compared.

Conclusion: Taken together our data indicate that only leptin is reduced by glucose uptake in insulin-sensitive probands whereas adiponectin and resistin are not altered. CORS-26 was demonstrated for the first time to circulate as high molecular weight form in plasma and like omentin was not influenced by oral glucose load. Omentin was shown to enhance insulin-stimulated glucose uptake but systemic levels are not correlated to postprandial blood glucose.

Figure 1

Leptin and adiponectin in fasting plasma and plasma after glucose challenge. (A) Leptin was determined in the plasma of 20 probands after an overnight fast and 2 h after glucose uptake by ELISA (B) Adiponectin was analyzed by non-denaturing SDS-PAGE (high-molecular weight, HMW) and denaturing SDS-PAGE (low-molecular weight, LMW) and a representative result after fasting (0) and 2 h (2) after glucose uptake is shown for probands 1 to 4. The molecular mass of standard proteins in kDa is indicated on the left side of the immunoblot.

Figure 2

Specificity of the CORS-26 antiserum and CORS-26 in fasting plasma and plasma after glucose challenge. (A) Recombinant adiponectin (Apm) and CORS-26 on a silver-stained SDS-PAGE gel and upon detection by the respective antibodies using immunoblot. (B) High-molecular weight (HMW) CORS-26 was analyzed by non-denaturing SDS-PAGE and low-molecular weight (LMW) CORS-26 by denaturing SDS-PAGE and a representative result of 4 donors (1 to 4) after fasting (0) and 2 h (2) after glucose uptake is shown. The molecular mass of standard proteins in kDa is indicated on the left side of the immunoblot.

Figure 3

Specificity of the omentin antiserum and omentin in fasting plasma and plasma after glucose challenge. (A) In vitro translated omentin and a control protein were used to determine the specificity of the omentin antiserum. (B) Omentin was analyzed in the plasma of all probands and a representative result of the probands 1 to 4 after an overnight fast (0) and 2 h (2) after glucose uptake by immunoblot is shown. (C) Omentin in the plasma of women (F9, F10, F12, F17) and men (M4, M8, M11, M13, M14, M15, M18, M19, M20) was determined by immunoblot.