1. Introduction
Salsola collina Pall belongs to the family
Chenopodiaceae, and is widespread in northeast, north, northwest, and southwest of China [
1].
S. collina has a long history of use in folk medicine [
2]. The whole herb of
S. collina is commonly used as herbal drink to treat hypertension, headache, insomnia, constipation and vertigo in China and Korea [
3,
4,
5]. In Russia,
S. collina is one component of the biologically active food additive “Heparon”, which has a liver protective, anti-alcohol, anti-inflammatory, and mild cholagogue effect [
6].
Modern medical research has revealed that
S. collina as herbal medicine exhibits beneficial effects on the immune and gastrointestinal system, has anti-inflammatory, anti-bacterial, and anti-hypertensive effects, and prevents cholelithiasis, dry bowel and constipation [
7]. The ethyl acetate extract of
S. collina can improve gastric emptying by regulating gastrointestinal hormone excretion and the c-Kit/SCF signaling pathway, and promote intestinal propulsion by modulating plasma ghrelin, gastrin, the plasma ghrelin receptor, and vasoactive intestinal peptide receptor 2 in the duodenum and activating M-cholinergic receptor [
8,
9,
10]. Meanwhile, the ethanol extract from
S. collina exerts anti-oxidative and anti-cancer activities by regulating the cell cycle [
11]. In addition, the aqueous extract from
S. collina is an effective means for the prophylaxis of cholelithiasis [
12].
Although pharmacological studies have proved that
S. collina has high medicinal value, there are few studies on the identification of active substances. Only about 60 biological active ingredients have been detected from
S. collina, including flavonoids, alkaloids, phenolic acids, organic acids, sterols, etc. [
6,
8,
9,
13,
14,
15,
16,
17,
18,
19,
20]. The main compounds are flavonoids and phenolic acids. The 18 reported flavonoids mainly involve flavones, flavonols and isoflavones [
6,
14,
17,
18,
19,
20]. Twelve phenolic acids have been identified from
S. collina, such as vanillic acid, ferulic acid, salicylic acid, etc. [
8,
9,
17,
18,
19,
20]. It is well-known that there are both chemical and pharmacological differences in different parts of herbs [
21]. Nevertheless, all samples used in previous studies have been collected from the aboveground parts of
S. collina. Hence, the research on the chemical composition of
S. collina at different parts is lacking.
With the development of metabolomics, high-throughput methods such as ultrahigh-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) have been applied to analyze metabolite profiles and detect variations in the compositions of herbs [
21,
22,
23,
24,
25,
26,
27,
28]. In this study, we used a widely targeted metabolomics method to investigate the chemical composition in
S. collina, and identify the differentially accumulated metabolites (DAMs) between the shoots and roots of
S. collina. Our results shed light on the metabolic pathways underlying
S. collina and provide a scientific basis for application of
S. collina.
4. Discussion
S. collina is well known for its medicinal benefits. However, only a few bioactive substances have been reported, and this has focused on flavonoids and phenolic compounds [
6,
8,
9,
10,
14,
17,
20]. In our study, the primary and secondary metabolites of
S. collina were analyzed widely, involving more than ten types of substances. Our results indicated that the main metabolites of
S. collina were flavonoids, phenolic acids, lipids, amino acids and derivatives. Our results have greatly enriched the understanding of the chemical composition in
S. collina.
The fresh
S. collina is used as traditional medicinal materials or food additive, which can ease blood pressure, improve liver function and treat headache and vertigo [
6,
30]. The ethanol extract of
S. collina has a good antihypertensive effect on senile or essential hypertension, and prolongs the hypnotic effect of pentobarbital sodium [
2,
7]. The recent research shows that the ethanol extract of
S. collina also can promote gastric emptying and intestinal propulsion [
8,
9,
10]. Flavonoids, alkaloids, lignins and coumarins, terpenes, polysaccharides, vitamins, etc., are recognized antihypertensive active ingredients. In this study, we identified a variety of hypotensive substances from
S. collina (
Table 1). Most of them belonged to flavonoids, alkaloids, and lignins and coumarins (
Figure 2D). Therefore, we believe that the three substances are the main medicinal substances in
S. collina.In general, different parts of medicinal plants have unique medicinal values. The flower of Saffron is a valuable traditional Chinese medicine. Coniferin and crocin-2 are special components in stigmas and the content of flavonoids is high in tepals [
31]. The root of
Platycodon grandiflorum can be used as medicine. Compared with the stem, leaf and seed, the root contains more saponins [
21]. Cortex moutan is made by drying the roots of peony, and its main roots have higher medicinal value than lateral roots [
22]. Furthermore, the environment and growth age are also important factors affecting the medicinal value [
24,
32]. In this study, we found that the main putative antioxidant compounds showed higher relative concentrations in the shoots of
S. collina, whereas a number of alkaloids and terpenoids were significantly higher in the roots of
S. collina (
Figure 5A and
Table 2). Interestingly, the key of alkaloid, salsoline A, showed higher relative concentrations in the shoots of
S. collina (
Table S2). Therefore, we speculate that the shoots of
S. collina have higher medicinal value.