Exploring the antiviral potential of justicidin B and four glycosylated lignans from Phyllanthus brasiliensis against Zika virus: A promising pharmacological approach.

BACKGROUND: Zika virus (ZIKV) is an emerging arbovirus that in recent years has been associated with cases of severe neurological disorders, such as microcephaly in newborns and Guillain-Barré syndrome in adults. As there is no vaccine or treatment, the search for new therapeutic targets is of great relevance. In this sense, plants are extremely rich sources for the discovery of new bioactive compounds and the species Phyllanthus brasiliensis (native to the Amazon region) remains unexplored. PURPOSE: To investigate the potential antiviral activity of compounds isolated from P. brasiliensis leaves against ZIKV infection. METHODS: In vitro antiviral assays were performed with justicidin B (a lignan) and four glycosylated lignans (tuberculatin, phyllanthostatin A, 5-O-ß-d-glucopyranosyljusticidin B, and cleistanthin B) against ZIKV in Vero cells. MTT colorimetric assay was used to assess cell viability and plaque forming unit assay to quantify viral load. In addition, for justicidin B, tests were performed to investigate the mechanism of action (virucidal, adsorption, internalization, post-infection). RESULTS: The isolated compounds showed potent anti-ZIKV activities and high selectivity indexes. Moreover, justicidin B, tuberculatin, and phyllanthostatin A completely reduced the viral load in at least one of the concentrations evaluated. Among them, justicidin B stood out as the main active, and further investigation revealed that justicidin B exerts its antiviral effect during post-infection stages, resulting in a remarkable 99.9 % reduction in viral load when treatment was initiated 24 h after infection. CONCLUSION: Our findings suggest that justicidin B inhibits endosomal internalization and acidification, effectively interrupting the viral multiplication cycle. Therefore, the findings shed light on the promising potential of isolated compounds isolated from P. brasiliensis, especially justicidin B, which could contribute to the drug development and treatments for Zika virus infections.

Oropouche virus infection induces ROS production and oxidative stress in liver and spleen of mice.

Oropouche virus (OROV) is the aetiological agent of Oropouche fever, the symptoms of which are common to most arboviruses, such as fever, headache, malaise, nausea and vomiting. More than half a million people have been infected with OROV since its isolation in 1955. Although Oropouche fever is classified as a neglected and emerging disease, to date, there are no antiviral drugs or vaccines available against the infection and little is known about its pathogenicity. Therefore, it is essential to elucidate the possible mechanisms involved in its pathogenesis. Since oxidative stress plays a pivotal role in the progression of various viral diseases, in this study, redox homeostasis in the target organs of OROV infection was evaluated using an animal model. Infected BALB/c mice exhibited reduced weight gain, splenomegaly, leukopenia, thrombocytopenia, anaemia, development of anti-OROV neutralizing antibodies, increased liver transaminases, and serum levels of pro-inflammatory cytokines tumour necrosis factor (TNF-α) and interferon-γ (IFN-γ). The OROV genome and infectious particles were detected in the liver and spleen of infected animals, with liver inflammation and an increase in the number and total area of lymphoid nodules in the spleen. In relation to redox homeostasis in the liver and spleen, infection led to an increase in reactive oxygen species (ROS) levels, increased oxidative stress biomarkers malondialdehyde (MDA) and carbonyl protein, and decreased activity of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT). Taken together, these results help elucidate some important aspects of OROV infection that may contribute to the pathogenesis of Oropouche.

Zika virus induces oxidative stress and decreases antioxidant enzyme activities in vitro and in vivo.

The first outbreak of Zika virus (ZIKV) infection in the Americas, especially in Brazil, was reported in 2015. Fever, headache, rash, and conjunctivitis are the common symptoms of ZIKV infection. Unexpected clinical outcomes, such as microcephaly and Guillain-Barré syndrome, have also been reported. The recent spread of ZIKV and its association with severe illness has created an urgent need to understand its pathogenesis and find potential therapeutic targets. Studies show that some viruses, including Flavivirus, trigger oxidative stress, which affects cellular metabolism, viral cycle, and pathogenesis. However, the role of oxidative stress in ZIKV infection needs to be investigated. Here, we analyzed ZIKV infection-triggered oxidative stress and modified antioxidant enzyme activities. U87-MG and HepG2 cells were infected to measure reactive oxygen species (ROS), malondialdehyde (MDA), and carbonyl protein levels, the activities of superoxide dismutase (SOD) and catalase (CAT), and the activation of nuclear factor erythroid 2p45-related factor 2 (Nrf2). ZIKV infection induced a significant increase in ROS, lipid peroxidation, and protein carbonylation products and a significant decrease in SOD and CAT activities accompanied by inhibition of Nrf2 activation in both cell lines. Further, MDA and carbonyl protein levels and SOD and CAT activities were evaluated in the brain and liver of ZIKV-infected C57BL/6 mice, and oxidative stress associated with antioxidant depletion was also found to occur in vivo. Together, our findings indicate the potential use of antioxidants as a novel therapeutic approach to Zika disease, and future studies in this direction are warranted.

Antiviral effect of silymarin against Zika virus in vitro.

Zika virus (ZIKV) epidemic and its association with severe neurological syndromes have raised worldwide concern. Despite the great clinical relevance of this infection, no vaccine or specific treatment is available and the search for antiviral compounds against ZIKV is extremely necessary. Several natural compounds, such as silymarin, exhibit antioxidant, hepatoprotective, and antiviral properties; however, the antiviral potential of this compound remains partially investigated. Therefore, the objective of this study was to evaluate in vitro the antiviral activity of silymarin against ZIKV infection. Global antiviral activity, dose-dependent, plaque reduction, and time-of-drug-addition assays were used to determine the anti-ZIKV activity of silymarin. Additionally, to start characterizing the mechanisms of action we determined whether silymarin could have a virucidal effect and inhibit viral adsorption and penetration stages. Regarding its global antiviral activity, silymarin showed significant inhibition of ZIKV infection, protecting cells infected with EC50 equal to 34.17µg/mL, with a selectivity index greater than 17 and 4x greater than that of the positive control (ribavirin). Its greatest efficiency was achieved at 125µg/mL, whose cell viability did not differ from the control without infection and treatment. Furthermore, treatment with silymarin reduced viral load by up to two logs (> 90%) concerning viral control, when evaluating virucidal activity and the precocious times of infection. Thus, our results set to show the promising anti-ZIKV activity of silymarin, which does not seem to have a single inhibition mechanism, acting at different times of infection, and still has the advantage of silymarin be a phytotherapy already available on the market.

Mayaro Virus Induction of Oxidative Stress is Associated With Liver Pathology in a Non-Lethal Mouse Model.

Mayaro virus (MAYV) causes Mayaro fever in humans, a self-limiting acute disease, with persistent arthralgia and arthritis. Although MAYV has a remerging potential, its pathogenic mechanisms remain unclear. Here, we characterized a model of MAYV infection in 3-4-week BALB/c mice. We investigated whether the liver acts as a site of viral replication and if the infection could cause histopathological alterations and an imbalance in redox homeostasis, culminating with oxidative stress. MAYV-infected mice revealed lower weight gain; however, the disease was self-resolving. High virus titre, neutralizing antibodies, and increased levels of aspartate and alanine aminotransferases were detected in the serum. Infectious viral particles were recovered in the liver of infected animals and the histological examination of liver tissues revealed significant increase in the inflammatory infiltrate. MAYV induced significant oxidative stress in the liver of infected animals, as well as a deregulation of enzymatic antioxidant components. Collectively, this is the first study to report that oxidative stress occurs in MAYV infection in vivo, and that it may be crucial in virus pathogenesis. Future studies are warranted to address the alternative therapeutic strategies for Mayaro fever, such as those based on antioxidant compounds.