Isolation of Natural Compounds—Emphasis on Antioxidants' Purification

Dear Colleagues,

The structural variety of natural products is endless. Since the dawn of humanity, nature has provided many molecules that possess beneficial effects; a larger number of these are still utilized to this day. Natural products are a challenge both in their chemical and pharmacological aspects. Due to the complex compositions of extracts, their activity is difficult to investigate. For this reason, the isolation of natural products from complex extracts is of significant importance. More than 70% of all nature-derived extracts studied these days come from plants. Plant metabolism is a complex process, capable of producing primary and secondary metabolites. From a chemical point of view, secondary metabolites are more diverse, but they are found in complex mixtures in extracts. Many secondary metabolites (phenols, flavonoids, triterpenoid saponins) are highly (or poly)-glycosylated. Polar compounds remain a challenge for isolation, even with the use of modern methods and chromatographic sorbents. Their potential as antioxidants is yet to be revealed. These are prerequisites for future drug discovery and product development. This Special Issue aims to publish high-quality articles and reviews, discussing modern, eco-friendly, and practical methods for the extraction, separation, purification, and isolation of natural compounds, particularly those with antioxidant activity.

Dr. Aleksandar Shkondrov
Guest Editor

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• separation
• antioxidant activity
• chromatography
• isolation
• purification
• extracts
• phytochemistry
• chemistry of natural compounds
• extracts
• biological activity
• radical scavenging
• pharmacognosy

Title: Hepatoprotective and antioxidant effects of a defatted extract from the aerial parts of Phlomis russeliana
Authors: Magdalena Kondeva-Burdina; Aleksandar Shkondrov; Georgi Popov; Vasil Manov; Ilina Krasteva
Affiliation: Department of Pharmacognosy, Faculty of Pharmacy, Medical University of Sofia, 2 Dunav st., 1000 Sofia, Bulgaria
Abstract: An evaluation of the possible hepatotoxicity/hepatoprotective activity of a defatted extract of the aerial parts of Phlomis russeliana was conducted in vitro and in vivo. The extract was applied alone and in a model of carbon tetrachloride (CCl4)-induced metabolic bio activation on isolated rat hepatocytes and on old Wistar rats. The extract was standardised by high performance liquid chromatography (HPLC), as the total flavonoids as well as verbascoside were quantified. Gallic acid equivalents were used to express its total phenolic content. In addition, the main flavonoids in the extract were identified. On isolated rat hepatocytes in vitro the extract (5, 10 and 50 µg/mL) did not exhibit any statistically significant hepatotoxicity. On a model of CCl4-induced hepatotoxicity, the extract showed significant hepatoprotective activity, which was concentration – dependant (the highest at 50 µg/mL). The in vivo study on old rats confirmed the observed antioxidant and hepatoprotective effects. The histological findings were favourable for the animals, treated with CCl4 and the extract. They had unchanged organ structure, commensurable with those animals, treated with CCl4 and Silymarin.

Title: Phytochemical analysis and in vitro effects on isolated murine lymphocytes and macrophages of polymeric micelles loaded with a cycloartane saponin
Authors: Aleksandar Shkondrov1, Denitsa Stefanova2, Ivan Stambolov1, Krassimira Yoncheva3, Virginia Tzankova2, Ilina Krasteva1*
Affiliation: 1Department of Pharmacognosy, Faculty of Pharmacy, Medical University of Sofia, 2 Dunav st., 1000 Sofia, Bulgaria. 2Department of Pharmacology, Pharmacotherapy and Toxicology, Faculty of Pharmacy, Medical University of Sofia, 2 Dunav st., 1000 Sofia, Bulgaria. 3 Department of Pharmaceutical Technology and Biopharmaceutics, Faculty of Pharmacy, Medical University of Sofia, 2 Dunav st., 1000 Sofia, Bulgaria. *Corresponding author: Prof. Ilina Krasteva, [email protected]
Abstract: Triterpenoid saponins from Astragalus species possess valuable effects (cytotoxic, adjuvant, hepatoprotective, neuroprotective, antiviral, etc.). Some have also immunomodulatory activity. Astragalus glycyphyllos is distributed in Bulgaria and accumulates mainly cycloartane saponins. From the overground parts of the species, a triterpenoid cyloartane-type saponin (AGOS3) was isolated by different chromatographic techniques. A quantitative LC-MS method for the determination of the saponin was developed and validated. Further, the saponin was loaded in copolymeric micelles based on triblock copolymers of polyethylene oxide and polypropylene oxide (Pluronics). The LC-MS method was applied on the developed micelles to determine their loading degree and the rate of saponin release. Afterwards, the possible pharmacological effects of free and encapsulated in polymeric nanoparticles triterpenoid saponin (1, 5, 10, 25, 50 and 100 µg/ml) were evaluated in isolated murine macrophages and lymphocytes in vitro. Free AGOS3 stimulated the proliferation only at highest tested concentrations (50 - 100 µg/ml) and the effect was more evident in isolated macrophages. Interestingly, AGOS3 loaded polymeric micelles caused concentration dependent and statistically significant increase in the proliferation of both isolated lymphocytes and macrophages, even at lower concentration (10 µg/ml). These results could serve as the basis for further research on the immunomodulatory effect of saponins.