The secondary plant metabolites, polyphenols, have a wide spectrum of actions such as modulation of lipid peroxidation, free radical scavenging, inhibition of hydrolytic and oxidative enzymes (phospholipase A2, cyclooxygenase), and anti-inflammatory activity (Lu et al. 2016). The current focus is on the antioxidant activity of polyphenols. It is this activity that determines the pharmacological effects. Antioxidants play an important role in protecting human cells against free radicals, which cause several physiological and pathological abnormalities, such as cardiovascular disease, rheumatoid arthritis, cancer, and aging (Atanassova et al., 2011; Ghafar et al., 2017).

Scientists are constantly searching for plants whose organs contain substances with high antioxidant activity, namely Cydonia Mill. and Pseudocydonia C.K. Schneid. (Monka et al., 2014; Grygorieva et al., 2020), Cornus mas L. (Klymenko, Grygorieva and Brindza, 2017), Diospyros virginiana L. (Grygorieva et al., 2018), Sambucus nigra L. (Horčinová Sedláčková et al., 2018, 2019), Ziziphus jujuba Mill. (Ivanišová et al., 2017), Hippophae rhamnoides L. (Ivanišová et al., 2020), Lycium spp. (Szot, Zhurba and Klymenko, 2020). However, a whole group of invasive plants is little studied in this respect. Meanwhile, the secondary distribution range of invasive species expands year by year and their resource reserves in the new homeland are very large. Our previous studies have already demonstrated very high antioxidant activity in several invasive species: Aronia mitschurinii A.K.Skvortsov & Maitul. (Vinogradova et al., 2017, 2020) and Solidago canadensis L. (Shelepova et al., 2020).

In this context, we began to study a North American Echinocystis lobata (Mich.) Torr. et Gray, which have been unintentionally introduced in Europe at the beginning of the XX century, no later than 1904, but had only isolated localities until World War II. From 1946 onwards, it gradually expanded its range and moved north-east. This species became established in Central and South-Eastern Europe, and the Far East, forming a secondary distribution range. The northern limit of the range in Russia runs along the line St. Petersburg – Vologda – Perm – Krasnoyarsk – Irkutsk – Tynda – Komsomolsk-on-Amur (Vinogradova et al., 2010). Over the past 30 years, its secondary range has expanded considerably and the species has invaded natural riverine plant communities, becoming a “transformer” (Richardson and Pyšek, 2006). Invasive populations have been very stable: Echinocystis lobata actively displaces native riparian species from their habitats, producing a lot of seeds.

Echinocystis lobata belongs to the family Cucurbitaceae, and closely related species in the same family contain cucurbitacins that are used as antiproliferative, antiinflammatory, and antioxidant agents. Several species of this family, widely used in folk medicine, are now attracting the increasing attention of biochemists as valuable raw materials for new medicinal preparations. For example, the oil isolated from the seeds of Ecballium elaterium (L.) A. Rich. has antitumor activity and is promising for use in oncology (Touihri et al., 2019). The presence of cucurbitacins in seeds of the Cucurbitaceae family (and Echinocystis in particular) is known from the literature (Sokolov, 1986). All these compounds have a bitter, unpleasant taste, but can induce cytotoxicity against malignant cells in mammals (Panosyan, 1985) and are used to treat benign tumors and to kill worms (pumpkin seeds are known to have this pharmacological effect).

North American Indians use Echinocystis roots as a remedy: the bitterness extracted from the roots contains analgesics (Burton et al., 2015). Traditional medicine refers to its use for headaches, menstrual disorders, rheumatism, fever, kidney, or stomach problems (Melymuka et al., 2005). However, there is little scientific information on the composition of bioactive compounds of Echinocystis. There are indications of the presence of quercetin and isorhamnetin derivatives (Krauze- Baranowska and Cisowski, 1996). Various enzymes (Gillard and Walton, 1976) and trypsin inhibitors (Stachowiak et al., 1996) have been reported. The fruit contains carbohydrates: galactose, xylose, rhamnose, arabinose, and mucus (Budantsev and Lesiovskaya, 2014).

The presence in Echinocystis lobata of substances with a wide range of pharmacological effects, in particular, antitumor and antioxidant activity, increases interest in detailing the chemical composition of this species. Such studies may be promising and relevant, as they will allow evaluating the phytotherapeutic prospects of the plant and its resource potential.

Phenolic content and antioxidant activity have been studied in detail only in Romania. However, only the leaves, flowers, and above-ground parts of the plants have been studied; the seeds have not been examined. Ethanolic extracts from leaves and aerial parts of Echinocystis lobata contain mainly p-coumaric acid, isoquercitrin, rutin, quercitrin, and kaempferol (Ielciu et al., 2017). The flowers contained the same substances and in addition ferulic acid. Biological assays showed a significant antioxidant effect and no cytotoxic and anti-plasmodial activity (Ielciu et al., 2018).

When analyzing seeds of Echinocystis from geographically different populations of Central Russia, it was found that climatic and soil conditions of growth influence the accumulation of flavonoids – the total content of these compounds in the seeds of Echinocystis from the Moscow population was 0.085 ±0.005%, and in seeds from the Tver population was 0.105 ±0.009%. The flavonoid composition of seeds of this plant is practically not studied. Thus, only one literary source (Krauze- Baranowska and Cisowski, 1996) knows that Cglycosides are distinguished in flavonoid complex. Considering the significant content of flavonoids in the seeds of Echinocystis lobata and their undoubted importance in the biological activity of the raw material, furthermore, detailed study of the flavonoid composition of Echinocystis seeds seems to be advisable.

This work aims to compare the total content of polyphenols and flavonoids in different organs of Echinocystis in Central Russia and Slovakia.

Echinocystis lobata is an annual vine with stems that can be as long as 6 m (Vinogradova, 2006) and which climb, with the help of coiling, branched tendrils, over shrubs and fences or trail across the ground. The leaves are alternate with long petioles and five palmate lobes. The flowers are monoecious, with separate male and female blooms on the same plant. The male flowers are in long-stemmed, upright panicles. Each flower has a white, or greenish-yellow, corolla with six slender lobes and a single central stamen with a yellow anther. The female flower has a single stigma with the spiky globular inferior ovary. The fruit is a prickly, inflated capsule up to 5 cm long with two pores and four seeds. It persists all winter and then opens at the bottom, liberating the seeds.

The seed of Echinocystis lobata, collected from a single individual, has its shape, color, and seed coat pattern (like a person's fingerprints). Only seed weight and size vary. Seeds of 17 discrete variations (phenotypes) have been identified, occurring both in the natural and in secondary habitat. The spermoderm texture can be smooth or wrinkled, with or without a pattern. The shape of the semen varies from rounded to oval or, less frequently, lanceolate. Spermoderm coloring may be black, brown, or grey, with or without a stripe along the lateral seam. Spermoderm pattern may be marbled or spotted, in the latter case, the spots may be rounded, triangular, or shapeless. In all populations, oval-shaped seeds with wrinkled patterned spermoderm prevailed (Vinogradova, et al., 2010). High variability in seed size and coloration has also been noted by other researchers (Golivets, 2014).

The biochemical composition of Echinocystis seed oil has been best studied. Linoleic, oleic, palmitic, stearic, and linolenic acids, as well as phytosteroids (spinasterol, sigmastadiene) and glycoside of echinocystic acid, were isolated in seed oil (Sokolov, 1986). Our previous studies (Shelepova, et al., 2016) have also shown that the component composition of Echinocystis seed oil from populations of the secondary distribution range of Central Russia is almost similar to that of plants from North American populations. The seeds of Echinocystis lobata are of interest for their possible use in phytotherapy. They can be used for the prevention of some diseases and, in particular, as an anti-inflammatory component, as they contain up to 1% of triterpene saponins, up to 0.1% of flavonoids, and up to 40% of oil. Fatty acid oil composition is represented by almost 60% linoleic acid (Shelepova and Vinogradova, 2016, 2017).

As a result, numerous reports are dedicated to the study of useful properties of invasive plants, among which different biological activities. The antioxidant activity of these plants demonstrated valuable results comparing with widely used species (Guzzetti, et al., 2017; Sari, et al., 2018; Maema, Potgieter and Samie, 2019). Several studies showed that the content of polyphenol compounds of invasive plants had higher values than native (Kim and Lee, 2011).

The fruits and seeds of Echinocystis lobata are of interest for further investigation into their possible use in phytotherapy. They can be used for the prevention of several diseases and, in particular, as an anti-inflammatory component as they contain up to 1% triterpene saponins, up to 40% oil, whose fatty acid composition is represented by almost 60% linoleic acid, and up to 0.1% flavonoids. Echinocystis is superior to many other plants in terms of the total amount of flavonoids contained in its fruits and seeds. The dried fruits contain more flavonoids than the seeds. Seeds from Slovak populations of Echinocystis have a higher flavonoid content than those from Russian populations. The results demonstrated that Echinocystis lobata can be a valuable raw material resource for the bioeconomy and there is the possibility of its wider application in the future.