Medicinal Plant

Pharmaceutical Chemistry Journal

Vol. 42, No. 1, 2008

MEDICINAL PLANTS ANTIOXIDANT PROPERTIES OF MEDICINAL PLANTS V. F. Gromovaya,1 G. S. Shapoval,1 I. E. Mironyuk,1 and N. V. Nestyuk1 Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 42, No. 1, pp. 26 – 29, January, 2008. Original article submitted May 15, 2006.

Impulse voltamperometry was used to study the antioxidant activity of a series of tinctures from medicinal plants. Effective concentrations were determined and a series of comparative evaluations of their antioxidant and antiradical activities was constructed; these were maximal in St. John’s wort, ginseng, rosewort, and Eleutherococcus. A possible mechanism of the antioxidant action of these plants in the body is suggested.

Interest in studies of the processes of free-radical oxidation and, thus, in agents able to influence the intensity of these processes, has increased significantly in recent years. This is because in conditions of a worsening ecological environment, various extreme factors produce significant increases in the concentrations of active oxygen species (AOS, including O-·, ·OH, H2O2, and others) in the body, able to damage protein and nucleic acid molecules, inactivate enzymes, and damage cell membranes, which in turn leads to the development of various pathological states in the body. The question of the possible blockade of these free-radical processes initiated by AOS at the early stages is therefore particularly acute [1 – 5]. Free-radical processes in the body are controlled using biologically active substances (BAS) with antioxidant properties. These include agents of both synthetic and natural origin; an important place among these is held by plant preparations containing bioflavonoids, carotenoids, essential fatty acids, etc. The use of preparations of this type has enormous potential - as natural antioxidants, they have easy and unlimited access to metabolic processes in the body and produce virtually none of the side effects associated with synthetic agents [6 – 9]. Medicinal plants are widely used in medicine, though as antioxidants they have received only fragmentary investigation. Thus, studies of medicinal plants as potential antioxidants and modeling of the possible mechanisms of their inhibitory actions at defined stages of the reduction of oxygen in the body are of significant interest. The question of selecting effective antioxidants and identifying their antioxidant activity is a quite complex task. 1

Contemporary in vitro assessment methods are time-consuming and laborious and do not allow evaluation of the efficacies of agents in relation to their influences at defined stages of free-radical processes [10 – 14]. Potential approaches to such studies include our previously developed methodological approaches to modeling elementary initiatory redox reactions involving oxygen, as well as the impulse voltamperometry method and its derivative express method, which allows simultaneous evaluation of the antioxidant and antiradical activity of compounds of interest [15 – 16]. The aim of the present work was to investigate the antioxidant activities of a wide range of tinctures of medicinal plants and to model the possible mechanisms of their action at defined stages of the reduction of oxygen in the body. METHODS Studies were performed using pharmaceutical tinctures of motherwort, rosewort, Eleutherococcus, ginseng, Echinacea, and bearberry, as well as laboratory-prepared (as described in [17]) water-alcohol tinctures of St. John’s wort, plantain, mayweed, and sage. Working solutions were prepared in 0.1 M sodium chloride. Electrochemical studies were performed as described in [18, 19], using a PU-1 universal polarigraph in the differential impulse voltamperometry regime with a three-electrode set-up. The working electrode was made from high-purity copper. Potentials were measured relative to a silver chloride reference electrode, and the accessory electrode was a platinum coil. Electrochemical studies and processing of results were performed using a specially developed computer program. All studies were performed in sodium chloride solu-

Institute of Bioorganic Chemistry and Oil Chemistry, Ukrainian National Academy of Sciences, Kiev.

25 0091-150X/08/4201-0025 © 2008 Springer Science+Business Media, Inc.

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V. F. Gromovaya et al. a)

dI/dE, arbitrary units

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Fig. 1. Voltamperometric curves of the reduction of oxygen in the presence of different concentrations of: a) rosewort: 1) baseline 0.1 M NaCl; 2 – 6) 0.2, 0.63, 0.92, 1.11, and 1.16 g/liter; b) Eleutherococcus: 1) baseline 0.1 M NaCl; 2 – 6) 0.523, 0.814, 1.677, 2.532, and 3.142 g/liter.

tion, whose concentration corresponded to physiological saline (0.9%). The oxygen concentration was determined by equilibrium at atmospheric pressure and a temperature of 20 ± 1°C. Antiradical and antioxidant activity of BAS were assessed in terms of changes in the relative height (h/h0) of waves of hydroxyl radicals (I) and hydrogen peroxide (III) respectively during the electrochemical reduction of oxygen in the presence of study compounds, where h0 is the height (mm) of the wave of reduction of hydroxyl radicals, molecular oxygen, or hydrogen peroxide in the absence of study

BAS and h is the height of the corresponding wave in the presence of the study BAS. RESULTS AND DISCUSSION Figure 1 shows voltamperometric curves for the reduction of oxygen obtained in the copper electrode impulse polarization regime in baseline 0.1 M sodium chloride solution. These methodological approaches resulted in recording of three stages of the reduction of oxygen, characterized by the following waves:

TABLE 1. Comparison of the Antioxidant Activities of Medicinal Plant Tinctures.

Preparation studied

Ginseng St. John’s wort Rosewort Eleutherococcus Mayweed Motherwort Bearberry Sage Plantain Echinacea

Maximally effective concentration, g/dm3

0.8 1.13 1.11 2.7 1.32 0.21 0.7 0.88 1.13 1.02

Maximum change in the height of waves of oxygen reduction in the presence of study preparations compared with baseline (h/h0) Wave hydroxyl radicals

molecular oxygen

hydrogen peroxide

0.38 0.68 0.58 0.62 0.63 0.73 0.69 0.86 0.69 0.81

1.05 1.12 1.71 1.04 1.09 0.96 0.93 1.00 0.85 0.91

0.36 0.46 0.34 0.48 0.56 0.77 0.69 0.96 0.82 0.98

·

OH + e- > OH-;

(1)

Wave II

O2 + 2e- + 2H+ > H2O2;

(2)

Wave III

H2O2 + 2e- + 2H+ > 2H2O;

(3)

H2O2 + e- > H2O2- > -OH + ·OH

(4)

Wave I

The ability to define this stepwise reduction of oxygen, which may serve as a model of the elementary initiory redox processes occurring in the body in both two- and one-electron reduction of oxygen, allowed the influences of various BAS on the individual stages of the reduction of oxygen to be studied. Thus, addition of the study medicinal plant tinctures to the baseline solution showed that all induced changes in the voltamperometric curves of the reduction of oxygen, though these changes were of different natures. Addition of rosewort to the oxygen-containing baseline solution induced a significant increase in the wave of reduction of molecular oxygen (wave II) and shifted its potential in the positive direction, providing evidence that the process of reduction of molecular oxygen was facilitated in the presence of this tincture

Antioxidant Properties of Medicinal Plants

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a)

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Fig. 2. Relationship between relative decreases in the heights of waves of oxygen reduction at the copper electrode: wave I (Z); wave II (<); wave III (D) and concentrations of: a) St. John’s wort; b) ginseng.

(Fig. 1a ). There were significant decreases in the waves corresponding to hydroxyl radicals (I) and hydrogen peroxide (III). This effect increased with increases in the rosewort concentration. The most effective concentration was ~1.1 g/dm3. A similar effect on hydroxyl radicals and hydrogen peroxide was seen with Eleutherococcus, though the wave of reduction of molecular oxygen (wave II) remained at essentially the same level as the Eleutherococcus concentration increased and there was no shift in the potential (Fig. 1b ). St. John’s wort (Fig. 2a ) and motherwort increased the magnitude of waves of reduction of molecular oxygen, facilitating the process of reduction and significantly suppressing the waves of reduction of hydroxyl radical and hydrogen peroxide. St. John’s wort was rather more effective than motherwort. Although the maximum effective concentration for motherwort was lower, the changes in the heights of the hydroxyl radical and hydrogen peroxide waves seen with St. John’s wort could not be obtained even using significantly increased concentrations. If we take the interaction with peroxides as a measure of antioxidant activity and the interaction with hydroxyl radicals as a measure of antiradical activity, then the study agent with the most marked antioxidant and antiradical activities was ginseng, probably because of the inhibitory action in relation to hydroxyl radicals formed by one-electron reduction of peroxides (reaction 4), producing a significant decrease in waves I and III on the voltamperometric oxygen reduction curve (Fig. 2b ). Bearberry had marked antioxidant and marked antiradical properties but had virtually no effect on the reduction of molecular oxygen. The results obtained from our studies of tinctures of medicinal plants are presented in Table 1. The present studies identified effective concentrations of medicinal plant extracts and tinctures and allowed construction of a series of comparative evaluations of their antioxidant activity:

ginseng > rosewort > St. John’s wort > Eleutherococcus > mayweed > bearberry > motherwort > plantain > Echinacea > sage; and antiradical activity: ginseng > rosewort > Eleutherococcus > mayweed > St. John’s wort > bearberry = plantain > Echinacea > motherwort > sage. Thus, we believe that the voltamperometric characteristics of the potentially antioxidant BAS studied here allow not only assessment of the antioxidant activity of these agents overall, as described in [20], but also separation of the effects associated with their interactions with hydrogen peroxide, the initial molecular oxygen, and, most importantly, with hydroxyl radicals, which are the most reactive intermediate in the reduction of oxygen. These studies established that the most effective of the medicinal plant extracts studied here were St. John’s wort, ginseng, rosewort, and Eleutherococcus and that they may find application in antioxidant treatment as agents able to reduce the toxic effects of free-radical products of the reduction of oxygen in the body. Extrapolating these data to biological systems suggests that these agents have antiradical activity, decreasing levels of hydroxyl radicals in the study system; they also have antioxidant activity, blocking lipid peroxidation processes. At the same time, they facilitate the process of the reduction of molecular oxygen. This study was performed with financial support from the Ukrainian Science and Technology Center, Project No. 2238. REFERENCES 1. J. F. Ghersiegea, Y. Maupoil, D. Ray, and L. Rochette, Free Rad. Biol. Med., 24, 1074 – 1081 (1998). 2. E. E. Dubinina, Vopr. Med. Khim, 47(6), 562 – 581 (2001).

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