A low-protein, high-carbohydrate diet increases de novo fatty acid synthesis from glycerol and glycerokinase content in the liver of growing rats

Abstract

We had previously shown that adipose tissue increased in rats fed a low-protein, high-carbohydrate (LPHC) diet (6% protein, 74% carbohydrate) without a simultaneous increase in the de novo fatty acids (FA) synthesis. In addition, impairment in insulin signaling in adipose tissues was observed in these rats. For this study, we hypothesized that the insulin signaling pathway is preserved in the livers from these rats, which contributes to an increase in liver lipogenesis and, consequently, an increase in the weight of the adipose tissue. We also hypothesized that glycerol from triacylglycerol is an important substrate for FA synthesis. Our results showed that administration of the LPHC diet induced an increase in the in vivo rate of total FA synthesis (150%) as well as FA synthesis from glucose (270%) in the liver. There were also increased rates of [U-¹⁴C]glycerol incorporation into glyceride-FA (15-fold), accompanied by increased glycerokinase content (30%) compared with livers of rats fed the control diet. The LPHC diet did not change the glycerol-3-phosphate generation from either glucose or glyceroneogenesis. There was an increase in the insulin sensitivity in liver from LPHC-fed rats, as evidenced by increases in IR(β) (35%) levels and serine/threonine protein kinase (AKT) levels (75%), and basal (95%) and insulin-stimulated AKT phosphorylation (105%) levels. The LPHC diet also induced an increase in the liver sterol regulatory element-binding protein-1c content (50%). In summary, these data confirmed the hypothesis that lipogenesis and insulin signaling are increased in the livers of LPHC-fed rats and that glycerol is important not only for FA esterification but also for FA synthesis.