The in vitro cytotoxicities of the ethanol extract of Andrographis paniculata (APE) and its main diterpenoid components were evaluated in various cancer cells. APE was found to be significantly growth inhibitory to human acute myeloid leukemic HL-60 cells with an IC (50) value of 14.01 microg/mL after 24 h of treatment. Among the three main diterpenoids in A. paniculata, andrographolide exhibited the highest degree of cytotoxicity followed by deoxyandrographolide while neoandrographolide was the least effective. Laser confocal microscopy and gel electrophoresis studies revealed chromosomal DNA fragmentations suggesting the occurrence of apoptosis. An increase of G (0)/G (1) phase cells from 51.88 % to 78.69 % was noted after andrographolide treatment for 36 h. The G (0)/G (1) phase arrest and apoptosis were associated with disappearance of mitochondrial cytochrome c and increased expression of Bax but decreased expression of Bcl-2 proteins in the inhibited cells. Although the order of all these events has not been determined, it is concluded that APE and andrographolide induce cell cycle arrest and affect an intrinsic mitochondria-dependent pathway of apoptosis by regulating the expression of some pro-apoptotic markers in HL-60 cells.

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Herpes simplex virus type I (HSV-1) is a neurotropic virus that is capable of infecting not only neurons, but also microglia and astrocytes and can establish latent infection in the central nervous system (CNS). We investigated whether IFN lambda (IFN-λ), a newly identified member of IFN family, has the ability to inhibit HSV-1 infection of primary human astrocytes and neurons. Both astrocytes and neurons were found to be highly susceptible to HSV-1 infection. However, upon IFN-λ treatment, HSV-1 replication in both astrocytes and neurons was significantly suppressed, which was evidenced by the reduced expression of HSV-1 DNA and proteins. This IFN-λ-mediated action on HSV-1 could be partially neutralized by antibody to IFN-λ receptor. Investigation of the mechanisms showed that IFN-λ treatment of astrocytes and neurons resulted in the upregulation of endogenous IFN-α/β and several IFN-stimulated genes (ISGs). To block IFN-α/β receptor by a specific antibody could compromise the IFN-λ actions on HSV-1 inhibition and ISG induction. In addition, IFN-λ treatment induced the expression of IFN regulatory factors (IRFs) in astrocytes and neurons. Furthermore, IFN-λ treatment of astrocytes and neurons resulted in the suppression of suppressor of cytokine signaling 1 (SOCS-1), a key negative regulator of IFN pathway. These data suggest that IFN-λ possesses the anti-HSV-1 function by promoting type I IFN-mediated innate antiviral immune response in the CNS cells.

Toll-like receptor 3 (TLR3) plays a critical role in initiating type I IFN-mediated innate immunity against viral infections. TLR3 recognizes various forms of double stranded (ds) RNA, including viral dsRNA and a synthetic mimic of dsRNA, poly I:C, which has been used extensively as a TLR3 ligand to induce antiviral immunity. The activation efficiency of TLR3 by poly I:C is influenced by various factors, including size of the ligands, delivery methods and cell types. In this study, we examined the stimulatory effect of two commercially-available poly I:Cs [high molecular mass (HMM) and low molecular mass (LMM)] on TLR3 activation in various human cell types by determining the induction of type I and type III IFNs, as well as the antiviral effect. We demonstrated that the direct addition of both HMM- and LMM-poly I:C to the cultures of primary macrophages or a neuroplastoma cell line could activate TLR3. However, the transfection of poly I:C was necessary to induce TLR3 activation in other cell types studied. In all the cell lines tested, the efficiency of TLR3 activation by HMM-poly I:C was significantly higher than that by LMM-poly I:C. These observations indicate the importance and necessity of developing effective TLR3 ligands for antiviral therapy.

Toll-like receptors (TLRs) play an essential role in initiating intracellular type I interferon (IFN)-mediated innate immunity against viral infections. We examined whether human neuronal cells (primary human neurons, NT2-N and CHP-212 cells) express TLRs and mount type I IFN-mediated innate immunity against herpes simplex virus-1 (HSV-1) infection. Human neuronal cells expressed TLR family members 1–10 and IFN-α/β. The activation of TLR3 or TLR8 by double-stranded RNA (poly-I:C) or single-stranded RNA (ssRNA) induced IFN-α/β expression. In addition, HSV-1 infection of human neuronal cells induced IFN-α expression. Investigation of the mechanisms showed that poly-I:C or ssRNA treatment enhanced the expression of several IFN regulatory factors. Importantly, the activation of TLR3 or TLR8 by poly-I:C or ssRNA prior to HSV-1 infection reduced the susceptibility of the neuronal cells to infection. These observations indicate that human neuronal cells possess intracellular TLR-mediated innate immune protection against HSV-1 infection.