RBP4 and metabolic syndrome: Studies from our and others showed that high circulating RBP4 was linked to dyslipidemia, fatty liver, cardiovascular diseases (Graham et al. 2006), as well as insulin resistance (Qi et al. 2007; Sun et al. 2014; Xu et al. 2009) via inflammation in adipose tissue (Moraes-Vieira et al. 2014, 2020) or by inducing expression of gluconeogenic enzyme such as phosphoenolpyruvate carboxykinase and by suppressing muscle insulin signalings (Yang et al. 2005).