الفهرس 
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Abstract
Despite the successes in the treatment of some virus diseases during the past three decades, the search for new antiviral drugs remains an area of active investigation. Effective treatment is not available for many viral infections. Moreover, the selection of resistant and cross-resistant mutants caused partially by the narrow spectrum of the mechanism of action, as well as potential toxic side-effects demand the discovery of new drugs.
One of the possible methods which can be used for the discovery of active substances is the screening of plant extracts for biological activities followed by bioassay guided fractionation of active extracts to identify the active substance. The selection of the plant species for the present study was mainly based on the common use of these species for the treatment of various diseases, as indicated by traditional health care systems.
In addition, there has been increasing interest in the possibility of using herbal extracts as antioxidants, the possible use of natural antioxidants for the prevention of some human diseases has stimulated increasing interest in this field.
In this study, the work aimed at investigating the antiviral activity of some medicinal herbal extracts on the influenza virus H5N1. It included the determination of cytotoxic activities of the selected extracts for choosing the safe concentration needed for the antiviral plaque reduction assay. In addition the present work aimed at the determination of the antioxidant activity of the extracted herbs.
A total of seven herbal plants collected from herbarium stores in Alexandria namely, Glycyrrhiza glabra, Pimpinella anisum, Foeniculum vulgare, Nigella sativa, Hibiscus sabdarifa, Origanum majorana, Zingiber officcinale. The hydroethanolic crude extracts from those species were prepared by soaking 500 g of dried, ground plant materials at room temperature in ethanol (1 L of 98%) separately for 5-7 days. The final extracts were filtered and concentrated under vacuum on a rotary evaporator at 50 o C and stored at 4 o C for further use.
The stock solution of crude extracts were prepared by dissolving a known amount of dry extract in 98% ethanol. The working solutions (10, 15, 25, 50, 75, 100, 250, 500 and 750 µg/ml) of the extracts were prepared from the stock solution using suitable dilution.
Experimental Biossays were done as follow:
1- Evaluation of cytotoxic activity of the selected plant extracts by MTT colorimetric assay.
2- Detrermination of TC50 for each extract from the dose effect curve, then selection of the safe concentration for the antiviral assay.
3- Evaluation of the antiviral activity of the selected extracts against Influenza viruses H5N1 in vitro by plaque reduction assay.
4- Antioxidant activity: Determination of percentage radical scavenging activity by DPPH assay for evaluation of the antioxidant effect of the extracted plants.
5- Comparison of the bioactivities of the selected extracts in vitro.
The results of this study showed that:
1. Concerning the cytototoxicity assay; Zingiberofficcinale and Glycyrrhiza glabra showed the lowest TC50 values which are 50 and 40 μg/μl respectively, so they exhibited the highest cytotoxic effect of the all tested extracts.
2. Nigella sativa exhibited also a high cytotoxic effect but less than that of Ginger and Liquorice, with TC50 equal to 102 μg/ml.
3. Foeniculun vulgare, Pimpinella anisum and Origanum majoranahad a medium and nearly similar range values of TC 50 that were 308, 368, 353respectively.
4. The highest value of TC50 was for Hibscus sabdariffa, equal to 487 μg/ml indicating that it had the lowest cytotoxic effect with respect to the other tested herbs.
5. Regarding to the antiviral activity of the tested extracts; five of the tested herbal extracts showed antiviral activities with varying degree against the tested virus H5N1.
6. Origanum majorana extract showed the maximum antiviral activity with 100% inhibition of plaque formation.
7. Effective antiviral activity were determined by Foeniculum vulgare and Pimpinella anisum with percentage plaque inhibition 83 and 75.5 respectively.
8. Medium antiviral activity were observed in Nigella sativa and Hibiscus sabdariffa extracts.
9. The antioxidant assay showed that all the tested extracts had antioxidant activity with little variation in the percentage of radical scavenging activity.
10. Origanum majorana and Pimpinella anisum exhibited the best antioxidant activity compared to the other herbal extracts with percentage of radical scavenging91.9 and 90.2 respectively.
11. Glyccyhriza glabra, Zingiber officcinale and Nigella sativa exhibited also a high antioxidant activity with percentage of radical scavenging89.3, 88.9 and 84.4 respectively.