Abstract
Bilirubin-IX-alpha (BR) is the final product of heme metabolism through the heme oxygenase/biliverdin reductase (HO/BVR) system. Previous papers reported on the microbicidal effects of the HO by-products biliverdin-IX-alpha, carbon monoxide and iron, through either direct or indirect mechanisms. In this paper the evidence of a virucidal effect of BR against human herpes simplex virus type 1 (HSV-1) and the enterovirus EV71 was provided. Bilirubin-IX-alpha, at concentrations 1–10 μM, close to those found in blood and tissues, significantly reduced HSV-1 and EV71 replication in Hep-2 and Vero cell lines, respectively. Bilirubin-IX-alpha inhibited viral infection of Hep-2 and Vero cells when given 2 h before, concomitantly and 2 h after viral infection. Furthermore, BR retained its antiviral activity even complexed with a saturating concentration of human serum-albumin. Moreover, 10 μM BR increased the formation of nitric oxide and the phosphorylation of c-Jun N-terminal kinase in Vero and Hep-2 cell lines, respectively, thus implying a role of these two pathways in the mechanism of antiviral activity of the bile pigment. In conclusion, these results support the antiviral effect of BR against HSV-1 and enterovirus in vitro, and put the basis for further basic and clinical studies to understand the real role of BR as an endogenous antiviral molecule.
Highlights
The heme oxygenase/biliverdin reductase (HO/BVR) axis is the main metabolic pathway by which heme is degraded
With regard to the by-products of the HO system involved in this antiviral activity, BV was shown to interfere with human hepatitis C virus (HCV) and human herpes virus (HHV)-6 replication as well as to reduce the cytopathic effect of human immunodeficiency type 1 virus (HIV) in Huh or MT4 cells (Mori et al, 1991; Nakagami et al, 1992; Lehmann et al, 2010; Zhu et al, 2010)
Biliverdin-IX-alpha was shown to inhibit the replication of HCV, HHV-6, and human immunodeficiency type virus (HIV) (Mori et al, 1991; Nakagami et al, 1992; Lehmann et al, 2010; Zhu et al, 2010), carbon monoxide (CO) reduced the growth of E. coli, P. aeruginosa, and S. aureus (Nobre et al, 2007, 2009; Davidge et al, 2009; Desmard et al, 2012) and iron almost completely decreased HCV core mRNA and protein (Hou et al, 2009)
Summary
The heme oxygenase/biliverdin reductase (HO/BVR) axis is the main metabolic pathway by which heme is degraded. Bilirubin-IX-alpha helps maintain the cell’s redox equilibrium by activating important pro-survival signaling pathways, such as those involving the proto-oncogene Akt or the mitogenactivated protein kinase family (MAPK), and by scavenging reactive oxygen and nitrogen species (ROS and RNS, respectively; Stocker et al, 1987b; Minetti et al, 1998; Kaur et al, 2003; Mancuso et al, 2006b, 2008) These findings suggest that up-regulation of the HO/BVR axis is a useful mechanism for improving cells’ responses to stress, and substances known to increase HO activity in vitro are being explored as potential drugs for the treatment of free radical-induced diseases (Mancuso and Barone, 2009).
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