Antiviral activity of an aqueous extract derived from Aloe arborescens Mill. against a broad panel of viruses causing infections of the upper respiratory tract

Abstract

Background: A number of antiviral therapies have evolved that may be effectively administered to treat respiratory viral diseases. But these therapies are very often of limited efficacy or have severe side effects. Therefore there is great interest in developing new efficacious and safe antiviral compounds e.g. based on the identification of compounds of herbal origin.

Hypothesis: Since an aqueous extract of Aloe arborescens Mill. shows antiviral activity against viruses causing infections of the upper respiratory tract in vitro we hypothesised that a product containing it such as Biaron C(®) could have an antiviral activity too.

Study design: Antiviral activity of Bioaron C(®), an herbal medicinal product consisting of an aqueous extract of Aloe arborescens Mill., Vitamin C, and Aronia melanocarpa Elliot. succus, added as an excipient, was tested in vitro against a broad panel of viruses involved in upper respiratory tract infections.

Methods: These studies included human adenovirus and several RNA viruses and were performed either with plaque reduction assays or with tests for the detection of a virus-caused cytopathic effect.

Results: Our studies demonstrated an impressive activity of Bioaron C(®) against members of the orthomyxoviridae - influenza A and influenza B viruses. Replication of both analysed influenza A virus strains - H1N1 and H3N2 - as well as replication of two analysed influenza B viruses - strains Yamagatal and Beiying - was significantly reduced after addition of Bioaron C(®) to the infected cell cultures. In contrast antiviral activity of Bioaron C(®) against other RNA viruses showed a heterogeneous pattern. Bioaron C(®) inhibited the replication of human rhinovirus and coxsackievirus, both viruses belonging to the family of picornaviridae and both representing non-enveloped RNA viruses. In vitro infections with respiratory syncytial virus and parainfluenza virus, both belonging to the paramyxoviridae, were only poorly blocked by the test substance. No antiviral activity of Bioaron C(®) was detected against adenovirus - a non-enveloped DNA virus.

Conclusions: These results represent the first proof of a selective antiviral activity of Bioaron C(®) against influenza viruses and create basis for further analyses of type and molecular mechanisms of the antiviral activity of this herbal medicine.

Keywords: Aloe arborescens Mill.; Antiviral activity; Plant extract; Xanthorrhoeaceae.

Graphical abstract

Fig. 1

Chromatogram profile of Bioaron C^®: Representative HPLC chromatograms of Aloenin A (a) and Bioaron C^® (b). Signals of the reference solution correspond to 0.53 mg/100 ml.

Fig. 2

In vitro cytotoxicity of Bioaron C^®: In vitro cytotoxicity of Bioaron C^® was tested on cells used for propagation of viruses: MDCK (a) HEp-2 (b), BGM (c), and HeLa (d) over a period of several days. The titration curves show the dose-dependent cytotoxicity for day 1 (blue), day 3 (red), and day 5 (green) for each of the cell line. IC50 values were determined graphically and are presented in Table 1. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Antiviral activity of Bioaron C^® against uncoated RNA viruses: Antiviral activity of Bioaron C^® was determined against members of the family of picornaviridae: HRV14 (a) and CA9 (b). Plaque-forming units per ml (PFU/ml) were determined as readout for quantification of the antiviral activity. The figures present the % inhibition of the infectivity of the substance-treated cell cultures in comparison with the non-treated virus control. Data derived from four replicates of at least two independent studies, respectively, and are presented as mean values.

Fig. 4

Antiviral activity of Bioaron C^® against enveloped RNA viruses and a non-enveloped DNA virus: Antiviral activity of Bioaron C^® was determined against enveloped RNA-viruses: Para 3 (a) and RSV (b). Furthermore the reactivity was tested against a non-enveloped DNA virus: Adeno 5 (c). For the RNA viruses plaque-forming units per millilitre (PFU/ml) were determined as readout for the antiviral activity. The effect against Adeno 5 was determined by the detection of the cytopathogenic effect (CPE). The figures present the % inhibition of the infectivity of the substance-treated cell cultures in comparison with the non-treated virus control (100% infection). Data derived from at least four replicates and two independent experiments.

Fig. 5

Antiviral activity of Bioaron C^® against orthomyxoviridae: Antiviral activity of Bioaron C^® against FluA H1N1 (a), FluA H3N2 (b), FluB Yamagatal (c) and FluB Beiying (d) was performed with plaque reduction assays. For FluA H1N1, FluA H3N2, and FluB Yamagatal data derived from six replicates from three independent studies, for FluB Beiying from four replicates (two studies).

Fig. 6

Antiviral activity of Bioaron C^® against FluA H1N1: 6-well plates with authentic plaque reduction assays are presented. MDCK cells were infected with FluA H1N1 and incubated for 3 days with an agarose overlay containing different dilutions of Bioaron C^®. A solvent control (2%), a non-treated virus control, and a positive control with Ribavirin (5 µg/ml) were included in the test. After a 3 day incubation period cells were fixed and stained with crystal-violet. Plates were then analysed with an ELISpot analysing system (AID Diagnostika GmbH). Numbers of plaques are indicated in the lower left corners of the respective wells.