Cytoprotection by Achyrocline satureioides (Lam) D.C. and some of its main flavonoids against oxidative stress

Abstract

Epidemiological studies indicate that dietary antioxidants can influence the incidence of neurodegenerative diseases. Among them flavonoids have been proposed to be effective cytoprotectors. Consequently, herbs with a high concentration of these compounds such as Achyrocline satureioides, Ginkgo biloba and Epilobium parviflorum are of special interest. In this context a comparative study of the cytoprotective capacity of infusions from the three plants against an oxidative insult was performed. Hence, the cytoprotective activity of each infusion against H₂O₂ injury to PC12 cells was tested and the antioxidant capacity was assessed by the ABTS⁺ radical bleaching assay. Free and glycosylated flavonoids contained in the infusions were identified by HPLC and the cytoprotective effect of some of these individual flavonoids was tested. The analysis of the flavonoid content of the infusions revealed different profiles. Epilobium parviflorum infusion showed the highest antioxidant capacity but only Achyrocline satureioides infusion proved to be cytoprotective. Moreover, the free flavonoids quercetin and luteolin contained in this infusion were also cytoprotective. In conclusion, the free radical scavenger capacity did not correlate with the cytoprotective profile of the infusions. The special mixture of unglycosylated Achyrocline satureioides flavonoids could be a clue to explain the unique effect of this plant.

Introduction

Oxidative stress has been implicated in the pathogenesis of neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases (Simonian and Coyle, 1996, Gilgun-Sherki et al., 2001). The lack of effective therapeutic agents to treat these disorders has led to an intensive search for therapeutic alternatives against oxidative stress-induced neuronal damage.

Although the available data are still limited, epidemiological studies indicate that dietary habits can influence the incidence of neurodegenerative diseases (De Rijk et al., 1997, Orgogozo et al., 1997, Golbe et al., 1998, Lemeshow et al., 1998, Youdim et al., 2002). It is likely that antioxidants included in the diet could be responsible for such beneficial effects. Natural dietary antioxidants include Vitamins C and E, carotenoids, flavonoids, and other polyphenols. Results of clinical trials assessing the effectiveness of Vitamins C and E are still controversial (Hellenbrand et al., 1996, Logroscino et al., 1996, De Rijk et al., 1997, Golbe et al., 1998). Flavonoids, the most ubiquitous group of polyphenolic phytochemicals, can be found in fruit, vegetables, grains, flowers, tea and wine (Schroeter et al., 2002). These compounds can prevent oxidative injury in various ways: besides direct scavenging of free radicals, they can chelate metal ions and inhibit the activities of several enzymes including lipoxygenase, cyclo-oxygenase, xanthine-oxidase, phospholipase A₂, and protein kinases (Ratty et al., 1988, Cushman et al., 1991, Laughton et al., 1991, Gil et al., 1994, Hoult et al., 1994, Cotelle et al., 1996). Given the growing importance of flavonoids as putative protectors of cells against different kinds of insults (Joyeux et al., 1995, Harborne and Williams, 2000, Ishige et al., 2001, Schroeter et al., 2002), including oxidative stress, herbs with a high concentration of these compounds could be of special interest.

In this sense, the cytoprotective effects of flavonoid-rich plant extracts are receiving experimental confirmation in a number of laboratory studies: Ginkgo biloba L. (Ginkgoaceae) extract has been shown to protect hippocampal neurons from nitric oxide or β-amyloid peptide-induced neurotoxicity (Bastianetto et al., 2000a, Bastianetto et al., 2000b), and green and black tea extracts have been shown to prevent 6-hydroxydopamine (6-OHDA)-induced neuronal death (Levites et al., 2002).

In spite of the widespread use of medicinal herbs for hundred of years, only a few have demonstrated protective effects on neuronal cells (Jang et al., 2002, Maclennan et al., 2002). Considering that only 10% of higher plants has been pharmacologically investigated (Ruffa et al., 2002), it seems very likely that medicinal herbs with previously unknown cytoprotective activity could be discovered among known plant species.

Achyrocline satureioides (LAM) D.C. (Compositae) is a native medicinal herb known by the popular name of “marcela” that grows in extensive regions of Uruguay, Paraguay, Brazil and Argentina. Its infusion is widely utilized for the treatment of several digestive ailments, as an anti-inflammatory preparation, as a sedative, anti-atherosclerotic and for some nervous system disorders (Ruffa et al., 2002, Taylor, 2002). Up to now, reported studies have focused on hepatoprotection, antitumor, antiviral, cytotoxic and immunomodulatory properties of Achyrocline satureioides extracts (Puhlmann et al., 1992, Zanon et al., 1999, Kadarian et al., 2002, Ruffa et al., 2002). Two studies addressed the antioxidant properties of Achyrocline satureioides, utilizing a liver microsomal model (Desmarchelier et al., 1998) or different models of low-density lipoprotein (LDL) oxidation (Gugliucci and Menini, 2002). This property was attributed mainly to its elevated content of flavonoids. However, no study has been conducted so far exploring the cytoprotective activity of Achyrocline satureioides against an oxidative insult in cell culture models.

Ginkgo biloba and Epilobium parviflorum L. (Onagraceae) are also two plants traditionally and frequently utilized in the South American region for the treatment of diverse ailments. As these plants are also known to contain an important amount of flavonoids, it appeared worthwhile to perform a comparative study of the cytoprotective capacity of Achyrocline satureioides, Ginkgo biloba and Epilobium parviflorum infusions against an oxidative insult. For this purpose, the cytoprotective activity of each infusion against hydrogen peroxide (H₂O₂)-induced death in PC12 cells was studied. Antioxidant capacity of the three plant infusions was quantified, and these results were compared with cytoprotective data. To investigate the role of flavonoids in the cytoprotective capacity of each infusion, free and glycosylated flavonoids contained in the infusions were identified, and finally, the cytoprotective effect of some of these individual flavonoids was tested.