Melatonin modulates mitophagy, innate immunity and circadian clocks in a model of viral-induced fulminant hepatic failure.

The haemorrhagic disease virus (RHDV) is a non-cultivable virus that promotes in rabbits an acute disease which accomplishes many characteristics of an animal model of fulminant hepatic failure (FHF). Beneficial effects of melatonin have been reported in RHDV-infected rabbits. This study investigated whether protection against viral-derived liver injury by melatonin is associated with modulation of mitophagy, innate immunity and clock signalling. Rabbits were experimentally infected with 2 × 104 haemagglutination units of a RHDV isolate and killed at 18, 24 and 30 hours after infection (hpi). Melatonin (20 mg/kg body weight ip) was administered at 0, 12 and 24 hpi. RHDV infection induced mitophagy, with the presence of a high number of mitophagosomes in hepatocytes and increased expression of mitophagy genes. Greater expression of main innate immune intermediaries and inflammasome components was also found in livers with RHDV-induced FHF. Both mitophagy and innate immunity activation was significantly hindered by melatonin. FHF induction also elicited an early dysregulation in clock signalling, and melatonin was able to prevent such circadian disruption. Our study discloses novel molecular routes contributing to RHDV-induced damage progression and supports the potential of melatonin as a promising therapeutic option in human FHF.

Evaluation of the Therapeutic Effect of a Flavonoid Prescription against Rabbit Hemorrhagic Disease In Vivo.

Rabbit hemorrhagic disease (RHD) is an acute, high fatal contagious disease induced by rabbit hemorrhagic disease virus (RHDV) with acute severe hepatic injury and causes huge economic loss worldwide. In order to develop an effective and reliable drug to treat this disease in clinic, a prescription formulated with baicalin, linarin, icariin, and notoginsenoside R1 (BLIN) according to the theory of syndrome differentiation and treatment in traditional Chinese veterinary medicine was applied to investigate its curative effects against RHD in vivo. The preliminary study results showed that BLIN prescription exerted good curative effect on RHD therapy. To further validate the curative effect and to investigate the possible related curative mechanisms of this drug, the survival rates, the plasma biochemical indexes of hepatic function, the plasma evaluation indexes of oxidative injury, and the RHDV gene expression levels were detected and then the correlation among these indexes was also analyzed. These results showed that BLIN prescription could significantly increase the survival rate, reduce the hepatic injury severity, alleviate the oxidative injury, and decrease the RHDV gene expression level in rabbits infected with RHDV. All these results indicate that BLIN prescription possesses outstanding curative effect against RHD, and the curative mechanism may be related to its antioxidant and anti-RHDV activities. Therefore, this prescription can be expected to be exploited into a new candidate for RHD therapy in clinic.

Purification and Biochemical Characterisation of Rabbit Calicivirus RNA-Dependent RNA Polymerases and Identification of Non-Nucleoside Inhibitors.

Rabbit haemorrhagic disease virus (RHDV) is a calicivirus that causes acute infections in both domestic and wild European rabbits (Oryctolagus cuniculus). The virus causes significant economic losses in rabbit farming and reduces wild rabbit populations. The recent emergence of RHDV variants capable of overcoming immunity to other strains emphasises the need to develop universally effective antivirals to enable quick responses during outbreaks until new vaccines become available. The RNA-dependent RNA polymerase (RdRp) is a primary target for the development of such antiviral drugs. In this study, we used cell-free in vitro assays to examine the biochemical characteristics of two rabbit calicivirus RdRps and the effects of several antivirals that were previously identified as human norovirus RdRp inhibitors. The non-nucleoside inhibitor NIC02 was identified as a potential scaffold for further drug development against rabbit caliciviruses. Our experiments revealed an unusually high temperature optimum (between 40 and 45 °C) for RdRps derived from both a pathogenic and a non-pathogenic rabbit calicivirus, possibly demonstrating an adaptation to a host with a physiological body temperature of more than 38 °C. Interestingly, the in vitro polymerase activity of the non-pathogenic calicivirus RdRp was at least two times higher than that of the RdRp of the highly virulent RHDV.