The experimental design rested on two embryonic mammalian cell lines of different origin: EBTr cells, derived from embryonic bovine trachea, and 3T3 cells, a mouse embryonic fibroblast line. These lines are standard tools in virology and toxicology laboratories, valued for their robust growth in culture and their well-characterized responses to viral infection and chemical stress. Using two cell lines from different species allowed the investigators to ask whether any observed effects were consistent across mammalian backgrounds or were instead specific to one cellular context. This cross-species comparison is particularly important in pilot studies, where the goal is to establish whether a phenomenon is general enough to justify further, more resource-intensive investigation.

To create the infections, the researchers inoculated cultures of both cell lines with a mixture of two vaccine strains of avipoxvirus, designated FK from fowl and Dessau from pigeon. Avipoxviruses are poxviruses that infect birds, and vaccine strains of these viruses are widely used in research because they can enter and express their genes in mammalian cells while producing a controlled, measurable cytopathogenic effect. By inoculating the cultures and then treating sub-populations of the infected cells with each of the two derivatives twenty-four hours after viral inoculation, the team could separate the effects of the compounds on established infection from their effects on uninfected cells. This timing is technically significant: a compound added after infection is tested for its ability to interfere with viral processes already underway inside the host cell, rather than merely blocking initial attachment or entry.

The readouts of the study were deliberately simple and complementary. The investigators determined the viral cytopathogenic effect, the visible damage that virus-infected cells sustain as replication proceeds, alongside the cytotoxic and antiviral influences of a range of concentrations of each substance. All values were assessed against control cultures of each cell line that had been neither inoculated with virus nor treated with the compounds. This dual control structure is what allows the separation of two phenomena that are otherwise easily conflated: a loss of cell viability in a treated, infected culture could reflect direct chemical toxicity, viral damage, or a combination of both. By comparing infected treated cultures against uninfected untreated controls, and by tracking viability at multiple time points after treatment, the researchers could begin to attribute observed changes to their most likely causes.

The headline finding of the study concerns the relative performance of the two derivatives. As a whole, the purine derivative aminophylline showed lower cytotoxicity but a stronger antiviral effect on virus-inoculated cells from both embryonic mammalian lines compared with the indole derivative 61-tartrat. In other words, across both the bovine EBTr and the mouse 3T3 backgrounds, aminophylline appeared to suppress the viral infection more effectively while harming the host cells less. This combination of properties is exactly what antiviral screening seeks: a compound that widens rather than narrows the gap between the concentration that inhibits the virus and the concentration that damages the cell.

A particularly informative technical observation came from comparing cell viability at the twenty-fourth and forty-eighth hours after treatment. The researchers determined a decrease in the viability of the inoculated cells from both cell types at the forty-eighth hour after treatment compared with the twenty-fourth hour. Crucially, they interpreted this result differently depending on the concentration of the derivatives. At low concentrations of the two compounds, the decline in viability was taken as evidence relevant to the antiviral comparison between them. At higher concentrations, however, the decreased viability of cells from both types was probably mainly attributable to the viral cytopathogenic effect itself rather than to the compounds. This kind of time- and concentration-dependent interpretation reflects a mature approach to cytotoxicity data, in which the same numerical change can carry different biological meanings in different experimental contexts.

From these data, the team was able to determine non-cytotoxic antiviral concentrations of each of the two derivatives that were nonetheless high enough to influence the cells of both types. Establishing such concentrations is the practical deliverable of a pilot study of this kind. It converts a qualitative observation, that a compound seems to help infected cells, into a quantitative starting point for future experiments: specific concentration ranges at which the compound can be applied without confounding the results by killing or stressing the host cells. The authors note that in this regard a strong analogy was assessed between the embryonic mammalian cells of bovine and mouse origin, meaning that the two lines behaved similarly enough that findings in one appear transferable to the other.

This cross-species consistency carries a broader implication that the authors highlight in their conclusions. The data, they write, suggest a possibility for future studies using mouse embryonic cells as a proven appropriate experimental in vitro model analogue to the respective human systems. The 3T3 mouse embryonic line is one of the most extensively characterized cell lines in biomedical research, and if antiviral and cytotoxic responses observed in EBTr cells are mirrored in 3T3 cells, researchers can design follow-up experiments on a well-standardized platform. The authors also situate their work within a wider literature on purine and indole chemistry in antiviral research, referencing work on Epstein-Barr virus, HIV, N6-methyladenosine modification of viral and cellular RNA, and epigenetic targets such as the histone methyltransferase DOT1L, whose inhibition by the compound EPZ004777 alters methylation at lysine 79 of histone H3. These references sketch the mechanistic landscape in which purine- and indole-based molecules are increasingly studied as modulators of viral and epigenetic processes.

It is worth being clear about the scope of what this pilot study does and does not establish. The experiments were performed in vitro, on vaccine strains of an avian poxvirus in rodent and bovine embryonic cells, and the compounds were tested at defined concentrations under controlled laboratory conditions. The results do not demonstrate efficacy against any human virus, nor do they establish clinical safety or dosing for either compound. Aminophylline itself is a familiar drug, long used in respiratory medicine as a bronchodilator, which gives it an established pharmacological profile in humans; however, the concentrations and mechanisms relevant to its observed antiviral activity in this cell culture system are a separate question from its classical clinical use. The value of the present work lies in defining the experimental conditions under which antiviral effects can be studied without cytotoxic confounding, and in validating a model system for that purpose.

Nevertheless, the study offers a useful methodological template for early-stage antiviral screening. By pairing two embryonic cell lines from different species, applying compounds after infection rather than before, measuring both cytopathogenic effect and cell viability over time, and interpreting viability losses in a concentration-dependent manner, the researchers assembled a picture in which aminophylline emerges as the more promising of the two derivatives for further antiviral investigation. The determination of non-cytotoxic, virus-suppressing concentrations for both aminophylline and 61-tartrat provides a concrete foundation on which subsequent studies, whether extending to additional viruses, to human cell systems, or to mechanistic dissection of how these purine and indole scaffolds interfere with viral replication, can now be built. As with all pilot studies, the findings are preliminary, but they are a documented, quantified first step rather than a speculative one.

Subject of Research: Non-cytotoxic, virus-suppressing concentrations of purine and indole derivatives in infected mammalian cell cultures

Article Title: A pilot study of non-cytotoxic, virus-suppressing concentrations of purine and indole derivatives on infected mammalian cells

Article References: Sainova, I., Kolyovska, V., Mihaylova, E., Dimitrova-Dikanarova, D., Hadjiolova, R., & Markova, T. (2026). A pilot study of non-cytotoxic, virus-suppressing concentrations of purine and indole derivatives on infected mammalian cells. BMC Pharmacology and Toxicology. https://doi.org/10.1186/s40360-026-01228-7

Image Credits: AI Generated

DOI: 10.1186/s40360-026-01228-7

Keywords: aminophylline, indole derivatives, purine derivatives, antiviral activity, cytotoxicity, avipoxvirus, embryonic mammalian cells, EBTr cells, 3T3 cells, viral cytopathogenic effect, in vitro model, pharmacology

In a study published in BMC Complementary Medicine and Therapies, a team led by Fahime Edalat, Fatemeh Jahedi, Neda Pirbonyeh and Afagh Moattari of Shiraz University of Medical Sciences, working with colleagues at Tehran University of Medical Sciences, Ardakan University and Tarbiat Modares University, systematically evaluated the antiviral activity of an aqueous-alcoholic extract of Adiantum capillus-veneris against influenza A(H1N1) in cell culture. The research was conceived against a backdrop of increasing concern about antiviral resistance and a growing interest in herbal medicines that combine anti-inflammatory and antioxidant properties with potential direct antiviral effects. Although A. capillus-veneris has a long history of folk use for respiratory complaints, its potential to inhibit influenza viruses had never been rigorously tested, making the new work the first detailed in vitro characterization of its anti-influenza activity.

The team adopted a carefully staged experimental design to disentangle the different ways in which a botanical extract might interfere with viral infection. The first step was to establish the safety profile of the extract for the host cells. Using Madin-Darby Canine Kidney cells, the standard laboratory substrate for influenza research, the investigators applied the MTT assay, a colorimetric test that measures metabolic activity and therefore cell viability, to determine the 50 percent cytotoxic concentration, or CC50, of the extract. This value defines the dose at which the extract harms half of the host cells and thus sets the ceiling for any antiviral testing. The extract exhibited a CC50 of approximately 1 milligram per milliliter, a result the researchers describe as indicating moderate cytotoxicity. Armed with this safety threshold, they could then probe concentrations well below the toxic limit for genuine antiviral effects.

To explore how the extract might interact with the viral life cycle, the researchers introduced it at three distinct stages relative to infection. In the pre-treatment scenario, cells were exposed to the extract before the virus arrived, testing whether the plant preparation could prime the cellular environment or block viral attachment in some way. In the co-treatment scenario, extract and virus were applied simultaneously, probing interactions during the earliest steps of infection such as binding and entry. In the post-treatment scenario, the extract was added after viral inoculation, asking whether it could suppress replication once the virus had already gained entry to the cells. For comparison, oseltamivir was tested separately, added one hour after viral inoculation, replicating its clinical role as a post-exposure inhibitor of viral spread.

The readouts were equally comprehensive. Cytopathic effects, the visible damage that influenza inflicts on infected cell monolayers, were monitored 48 to 72 hours after inoculation. Viral titers were then quantified using three independent methods: the hemagglutination assay, which measures the ability of viral particles to agglutinate red blood cells; quantitative real-time PCR, which tracks viral RNA load; and the TCID50 assay, which calculates the tissue culture infectious dose, a functional measure of how much infectious virus remains. Together these assays provided a multi-angle view of viral burden, reducing the risk that a single methodological artifact could be mistaken for a true antiviral effect.

The results were striking. In the TCID50 assays, the extract demonstrated strong antiviral activity across concentrations ranging from 0.02 to 0.5 milligrams per milliliter, all comfortably below the cytotoxic threshold. The most impressive finding came from the pre-treatment arm: at a concentration of just 0.1 milligrams per milliliter, extract administered before infection reduced viral load by 99.9 percent, a reduction of three orders of magnitude in infectious virus. Meanwhile, at 0.5 milligrams per milliliter, the extract suppressed viral replication when applied during the infection window itself. The fact that pre-treatment produced the most dramatic suppression suggests that the extract may interfere with early events in the viral life cycle, perhaps by altering host cell surface receptors, blocking viral binding or entry, or inducing intracellular states less hospitable to the virus. The researchers caution, however, that the precise molecular stage at which the inhibition occurs remains to be determined.

Perhaps the most clinically relevant discovery, though, emerged when the extract was tested in combination with oseltamivir. When oseltamivir at concentrations of 0.5 and 0.05 milligrams per milliliter was paired with the extract at 0.5, 0.1 and 0.05 milligrams per milliliter, the combination produced a synergistic effect against influenza A(H1N1), delivering suppression that clearly surpassed what oseltamivir alone could achieve. Synergy of this kind is a significant observation for several reasons. First, it suggests that the extract and the neuraminidase inhibitor act on different aspects of the viral life cycle or on complementary molecular targets, since compounds competing for the same target typically show additive rather than synergistic effects. Second, combination approaches can lower the effective dose of each agent, potentially reducing side effects and, critically, slowing the emergence of drug-resistant viral variants, which thrive under monotherapy pressure. If the in vitro findings can be extended in animal models and eventually in clinical settings, an extract-based adjunct to standard antiviral therapy could offer a valuable hedge against oseltamivir resistance.

The biological plausibility of such effects is grounded in what is already known about Adiantum capillus-veneris. The fern, found across temperate and tropical regions, has featured in traditional medical systems as a remedy for coughs, bronchitis and other respiratory conditions. Previous phytochemical and pharmacological studies have attributed anti-inflammatory and antioxidant properties to its preparations, characteristics that could modulate the host environment in ways unfavorable to viral replication. The new study adds a direct antiviral dimension to this picture, although the authors emphasize that the specific chemical constituents responsible for the observed activity have not yet been identified. Flavonoids, phenolic acids and triterpenoids are common candidates in fern extracts, but confirming the active molecules will require bioassay-guided fractionation, a process of progressively separating and testing extract components to pinpoint the compounds carrying the antiviral punch.

The researchers are candid about the limits of their work. The experiments were conducted entirely in vitro, in a cell culture system that cannot capture the complexity of a living host, including immune responses, pharmacokinetics, metabolism and tissue distribution. The moderate cytotoxicity profile, with a CC50 close to the antiviral concentrations used, means that any future therapeutic application will require careful optimization of dose, formulation and potentially the isolation of active compounds to improve the therapeutic window. The study was performed in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Shiraz University of Medical Sciences, and it was funded by Shiraz University of Medical Sciences. The authors also disclosed that they used ChatGPT for assistance with English language editing while retaining full responsibility for the scientific content, data analysis, interpretation and conclusions.

Looking forward, the research team recommends two priorities: identifying the specific active components of the extract and determining the exact stage of viral replication at which inhibition occurs. Both are essential steps on the long road from cell culture to clinic. If a discrete molecule can be isolated, characterized and shown to inhibit influenza A(H1N1) at achievable, non-toxic concentrations, it could become a lead compound for drug development or a standardized herbal medicine candidate. Even short of that, the demonstration that a traditional fern remedy can achieve a 99.9 percent reduction in viral load in pre-treated cells, and can synergize with a widely used antiviral drug, adds weight to the growing argument that ethnobotanical knowledge remains a rich and underexplored reservoir of antiviral potential. As influenza continues to mutate and evade single-target drugs, the maidenhair fern, a humble plant steeping in a laboratory beaker in Shiraz, may yet contribute something unexpected to the arsenal against one of humanity’s oldest viral adversaries.

Subject of Research: Antiviral activity of Adiantum capillus-veneris L. plant extract against influenza A(H1N1) in vitro

Article Title: Unveiling the antiviral activity of Adiantum capillus-veneris L. against influenza A(H1N1)

Article References: Edalat, F., Jahedi, F., Taghiabadi, Z., Letafati, A., Pirbonyeh, N., Pourghanbari, G., Shatizadeh Malekshahi, S., & Moattari, A. (2026). Unveiling the antiviral activity of Adiantum capillus-veneris L. against influenza A(H1N1). BMC Complementary Medicine and Therapies. https://doi.org/10.1186/s12906-026-05584-z

Image Credits: AI Generated

DOI: 10.1186/s12906-026-05584-z

Keywords: influenza A(H1N1), Adiantum capillus-veneris, antiviral activity, herbal extract, oseltamivir, TCID50, MDCK cells, real-time PCR, hemagglutination assay, cytotoxicity, synergy, natural remedies