For instance, three studies have been conducted about RBP-4 levels and GDM risk [28, 29, 32]. Although a significant association was reported in a U.S. population [29], there was no significant association in other studies from UK [32] and China [28]. Conflicting results were also reported in the four studies about TNF- levels and risk of GDM, with one study reporting a significant association [18] while another two reporting no significant association [12, 19, 35]. Recently, adipocyte fatty acid-binding protein (AFABP) has been suggested to be a probable candidate involved in the pathophysiology of GDM [37]. However, no prospective study has conducted so far on the association between AFABP and GDM. The only study, which was cross-sectional, reported an elevated AFABP level in women with GDM as compared with healthy pregnant controls [38].Author Manuscript Author Manuscript Author Manuscript Author Manuscript4. DISCUSSIONIn this systematic review and quantitative analysis of available data regarding adipokines and GDM, we observed that adiponectin levels in the first or second trimester of pregnancy are lower among pregnant women who later develop GDM than non-GDM women, whereas leptin levels are higher. Prospective data were sparse and findings were inconsistent for visfatin, RBP-4, resistin, TNF-, IL-6, and vaspin. We did not identify prospective studies for several novel adipokines, including BQ-123 chemical information chemerin, apelin, omentin, or AFABP.Metabolism. Author manuscript; available in PMC 2016 June 01.Bao et al.PageThe observed associations of GDM with adiponectin and leptin levels are biologically plausible. GDM develops when pancreatic cells of pregnant women are unable to increase insulin secretion Procyanidin B1MedChemExpress Procyanidin B1 enough to counteract the corresponding fall in tissue sensitivity to insulin during pregnancy [39]. Adiponectin is a signaling protein that is synthesized and secreted by adipose tissue and is one of the most abundant plasma proteins in humans [40]. Adiponectin can reduce ectopic fat storage through stimulating lipid oxidation and inhibiting lipolysis in adipose tissue [41]. In addition, adiponectin may also display anti-inflammatory properties by suppressing TNF- production [42]. Intravenous administration of recombinant adiponectin in rodent models of insulin resistance restored normal insulin sensitivity [6]. In humans, adiponectin levels were inversely associated with fasting glucose, insulin, and insulin resistance [43], and the risk of developing T2DM [44]. Thus, a reduction in adiponectin levels may be associated with the development of GDM through decreased insulin sensitivity and attenuated anti-inflammatory capacity. In contrast to adiponectin, leptin may contribute to the pathogenesis of GDM through elevated insulin resistance. Leptin is an adipose tissue-derived hormone that plays a key role in the regulation of energy intake and energy expenditure. Circulating leptin levels are elevated with increasing adiposity [45], reflecting a state of leptin resistance [46]. Several studies have positively associated leptin levels with insulin resistance independent of body mass index (BMI), whereas other studies suggest that the relationship between leptin levels and insulin resistance is mainly accounted for by obesity [47, 48]. Elevated leptin levels were also independently associated with a higher risk of incident GDM [14] and T2DM [49]. Animal and human studies have demonstrated that a circulating soluble form of the leptin receptor influence.For instance, three studies have been conducted about RBP-4 levels and GDM risk [28, 29, 32]. Although a significant association was reported in a U.S. population [29], there was no significant association in other studies from UK [32] and China [28]. Conflicting results were also reported in the four studies about TNF- levels and risk of GDM, with one study reporting a significant association [18] while another two reporting no significant association [12, 19, 35]. Recently, adipocyte fatty acid-binding protein (AFABP) has been suggested to be a probable candidate involved in the pathophysiology of GDM [37]. However, no prospective study has conducted so far on the association between AFABP and GDM. The only study, which was cross-sectional, reported an elevated AFABP level in women with GDM as compared with healthy pregnant controls [38].Author Manuscript Author Manuscript Author Manuscript Author Manuscript4. DISCUSSIONIn this systematic review and quantitative analysis of available data regarding adipokines and GDM, we observed that adiponectin levels in the first or second trimester of pregnancy are lower among pregnant women who later develop GDM than non-GDM women, whereas leptin levels are higher. Prospective data were sparse and findings were inconsistent for visfatin, RBP-4, resistin, TNF-, IL-6, and vaspin. We did not identify prospective studies for several novel adipokines, including chemerin, apelin, omentin, or AFABP.Metabolism. Author manuscript; available in PMC 2016 June 01.Bao et al.PageThe observed associations of GDM with adiponectin and leptin levels are biologically plausible. GDM develops when pancreatic cells of pregnant women are unable to increase insulin secretion enough to counteract the corresponding fall in tissue sensitivity to insulin during pregnancy [39]. Adiponectin is a signaling protein that is synthesized and secreted by adipose tissue and is one of the most abundant plasma proteins in humans [40]. Adiponectin can reduce ectopic fat storage through stimulating lipid oxidation and inhibiting lipolysis in adipose tissue [41]. In addition, adiponectin may also display anti-inflammatory properties by suppressing TNF- production [42]. Intravenous administration of recombinant adiponectin in rodent models of insulin resistance restored normal insulin sensitivity [6]. In humans, adiponectin levels were inversely associated with fasting glucose, insulin, and insulin resistance [43], and the risk of developing T2DM [44]. Thus, a reduction in adiponectin levels may be associated with the development of GDM through decreased insulin sensitivity and attenuated anti-inflammatory capacity. In contrast to adiponectin, leptin may contribute to the pathogenesis of GDM through elevated insulin resistance. Leptin is an adipose tissue-derived hormone that plays a key role in the regulation of energy intake and energy expenditure. Circulating leptin levels are elevated with increasing adiposity [45], reflecting a state of leptin resistance [46]. Several studies have positively associated leptin levels with insulin resistance independent of body mass index (BMI), whereas other studies suggest that the relationship between leptin levels and insulin resistance is mainly accounted for by obesity [47, 48]. Elevated leptin levels were also independently associated with a higher risk of incident GDM [14] and T2DM [49]. Animal and human studies have demonstrated that a circulating soluble form of the leptin receptor influence.
