Ursodeoxycholyl lysophosphatidylethanolamide is a first-in-class hepatoprotectant being superior to UDCA or PC capable of inhibiting hepatocellular apoptosis (Chamulitrat et al., 2009
) and inflammation in vivo
under acute liver injury (Pathil et al., 2011a
). PC controls liver homeostasis by membrane stabilization and the loss of PC levels results in an on-set of development of liver disease. It is of a question whether UDCA-LPE could increase PC to replenish PC for cytoprotection. We herein demonstrated that UDCA-LPE enhanced PC concentrations in vitro
and in vivo
, and these increases were associated with upregulation of CDS1. This ability of UDCA-LPE to increase PC can enhance hepatoprotection and renders it appropriate to treat acute hepatotoxicity.
We have shown that UDCA-LPE is able to induce survival signaling pathway by activating PI3K/Akt and MAPK/ERK1/2 pathways within 0.5–7
h in cultured hepatocytes (Chamulitrat et al., 2009
). At the rapid time point of 4
h where increased PC was observed (Figures and ), it is unlikely that UDCA-LPE could induce PC synthesis genes on the transcriptional and translational levels. In cultured hepatocytes, the early PC response obtainable at 4-h treatment with UDCA-LPE may thus likely due to some unknown signaling pathways triggered by UDCA-LPE which result in increases of PC abundance. For such rapid activation, it is possible that UDCA-LPE may interact with G-protein coupled receptors on plasma membrane or nuclear receptors intracellularly. The immediate PC increases were also observed in vivo
h after intraperitoneal injection. Specific signaling pathways in regulating PC metabolism responsible for a rapid rise of PC have not been identified. PPAR alpha and gamma as well as glucocorticoid receptors are among nuclear receptors proposed to be affected by UDCA-LPE. These receptors are known to modulate the syntheses of phospholipids (Lee et al., 2004
) including PC (Pan et al., 2006
). After prolonged hepatocyte treatment with UDCA-LPE for 20
h, we found that CDS1 mRNA was upregulated. CDS1 generates PC from phosphatidic acid. CDS1 upregulation could explain the increased and sustained PC levels observed even after 24
h under in vivo
conditions. The immediate and prolonged increases of hepatic PC levels by UDCA-LPE may provide feasibility for its use in the clinics, for an example, for effective reduction of acute severe hepatotoxicity from acetaminophen overdose. UDCA-LPE may be used as an antidote against hepatotoxins in humans.
Ursodeoxycholyl lysophosphatidylethanolamide is better than UDCA or PC in inhibiting apoptosis and liver injury (Chamulitrat et al., 2009
; Pathil et al., 2011a
). PC synthesis is known to be downregulated during apoptosis, and that PC supplementation provides protection (Cui and Houweling, 2002
). In addition to UDCA-LPE’s ability to inhibit apoptosis, the PC generated by UDCA-LPE by ways of CDS1 upregulation could also be a mechanism for its anti-apoptosis effects (Figure C). In support of this notion, the contents of product of CDS1 CDP-diacylglycerol contents are found to be decreased in livers of diabetic rats (Whiting et al., 1977
), and increased CDS1 is found during the development of heart failure and identified to be involved in compensatory mechanisms (Saini-Chohan et al., 2009
). These data suggest protective function of CDS1 and consistent with UDCA-LPE protection.
In addition to UDCA (Simko and Michael, 1994
), other protective bile acids, such as 5 beta-scymnol (Slitt et al., 2004
), have been shown to reduce liver injury and acetaminophen toxicity. UDCA-LPE may be hepatoprotective in these settings as UDCA-LPE is superior to UDCA. Furthermore, UDCA-LPE inhibits activities of hepatic phospholipase A2 thus decreasing the levels of cytotoxic lyso PC (Pathil et al., 2011a
). It has been shown that CDS1 activity is inhibited by lyso PC in vitro
(Lin et al., 1991
). UDCA-LPE’s ability to lower lyso PC concentrations may lead to increases in CDS1 activity and hence increased PC. Increased CDS1 and PC abundance by UDCA-LPE could also provide dilinoleyl- or polyenyl PC (Aleynik et al., 1997
; Lieber et al., 2003
) as well as PC-containing medium-chain fatty acids, such as dilauroyl PC, which is a new PC molecule recently identified to elicit protective anti-diabetic effects (Lee et al., 2011
). Alternatively, UDCA-LPE may prevent PC export to extracellular space thus allowing more PC for maintaining cell integrity during stress. Further analyses of PC export genes affected by UDCA-LPE are still yet to be determined.
It is possible that increases of PC may indicate increased availability of free fatty acids due to upregulation of lipogenic genes by drug treatment (Anthérieu et al., 2011
). This possibility may be applicable for treatment longer than 4
h to allow protein translation. UDCA-LPE’s ability to increase lipogenic genes such as fatty acid synthase and elongase genes has previously been observed (unpublished data). These de novo
lipogenic lipids including PC in fact reflect the protection against cell death during palmitate stress after 20
h (Collins et al., 2010
; Green and Olsen, 2011
). It has been shown that CDS1 expression is concomitantly increased with lipogenesis genes fatty acid synthase during fetal lung development (Zhang et al., 2004
), it is surmised that CDS1 may be similarly regulated by de novo
lipogenesis transcription factors. As UDCA-LPE elicits lipoprotection after 20
h treatment, UDCA-LPE may be found most effective in treatment of pathological acute hepatotoxicity as to compare with normal physiological conditions. While many cationic amphiphilic drugs such as chlorpromazine and tamoxifen are known to be cytotoxic to hepatocytes by inducing phospholipidosis (Chatman et al., 2009
), it is still to be determined whether UDCA-LPE could accumulate phospholipids in lysosomes (which are the organelles for phospholipidosis). As UDCA-LPE targets mitochondria by inhibiting the loss of mitochondrial membrane potentials (Chamulitrat et al., 2009
), UCDA-LPE may elicit protection during acute liver injury at this organelle (Pathil et al., 2011a
). PC could likely be accumulated in the mitochondrial membrane for protection.
We herein demonstrated that UDCA-LPE rapidly caused accumulation of hepatic PC likely by stimulation of specific signaling pathways of PC metabolism. Further experiments are still yet to be performed to investigate UDCA-LPE protective effects against severe hepatotoxicity induced by drugs such as acetaminophen.