Orotic acid (Vitamin B13) is an intermediate product in pyrimidine metabolism.

Orotic acid increases cell proliferation and decreases apoptosis in serum-starved SK-Hep1 hepatocellular carcinoma cells, which may ascribe to the inhibition of AMP-activated protein kinase (AMPK) phosphorylation and thus activation of mammalian target of rapamycin complex 1 (mTORC1) [1].

Male Fischer 344 rats (130-150 g) to two-thirds PH in the absence or in the presence of Orotic acid (a 300-mg tablet of Orotic acid methyl ester implanted intraperitoneally at the time of two-thirds PH). treatment with Orotic acid resulted in a near-100% inhibition of RNR induced by two-thirds PH in rat liver, as monitored by enzyme activity and protein level [2]. Feeding 1% Orotic acid with diet decreased the phosphorylation of AMPK and increased the maturation of SREBP-1 and the expression of SREBP-responsive genes in the rat liver. Orotic acid-induced lipid accumulation was also completely inhibited by rapamycin. Mouse hepatocytes and mice were resistant to Orotic acid-induced lipogenesis because of little if any response in AMPK and downstream effectors [3].