What Active Ingredients Are in Horsetail Extract Powder?

Horsetail (Equisetum arvense) is recorded in *Ben Cao Shi Yi* [2]: “It grows in the islands and shoals of the Yi and Luo rivers, with stems resembling those of wood sorrel, segmented and interconnected, and is also known as ‘continuous grass.’” The entire plant is used medicinally. It has a bitter taste, is neutral in nature, and enters the liver, heart, and bladder meridians. It possesses the effects of clearing heat and promoting urination, cooling the blood and stopping bleeding, activating blood circulation and resolving stasis, and resolving phlegm and stopping cough. It is harvested in summer and autumn by cutting the entire plant and drying it in a well-ventilated area. It is primarily produced in Heilongjiang, Jilin, Liaoning, Shaanxi, Sichuan, Guizhou, Jiangxi, and Anhui provinces [3]. Recently, Horsetail has been found to have clinical applications for hypertension, coronary heart disease, diabetes, dyslipidemia, atherosclerosis, and prostate-related conditions in the elderly. The following is a summary of the various chemical components in Horsetail and their related pharmacological effects.

1 Active components of Horsetail extracts

1.1 Acids and phenolic acids

Phenolic compounds and acids are acidic in nature and often coexist in plants. In 1975, Soviet scholars Syrchina A.I. et al. [4] isolated the following phenolic acids from the aboveground parts of Horsetail: p-hydroxybenzoic acid, vanillic acid, protocatechuic acid, gallic acid, p-coumaric acid, ferulic acid, and caffeic acid. Among these, caffeic acid was the most abundant, while p-hydroxybenzoic acid, vanillic acid, and gallic acid salts were present in very small amounts. Additionally, water-soluble acids such as aconitic acid, arabinonic acid, citric acid, fumaric acid, and gluconic acid were identified [5].

1.2 Flavonoid Compounds

In 1974, researchers identified apigenin-5-glucopyranoside in the aboveground parts of Horsetail. In 1975, Syrchina A.I. et al. [6] isolated three dihydroflavonoids from it, namely: naringenin, dihydrokaempferol, and dihydroquercetin. In 1980, Syrchina A.I. et al. [7] isolated gengkwanin-5-O-β-D-glucopyranoside and luteolin-5-O-β-D-glucopyranoside from the whole plant of Horsetail.

Subsequently, 6-chloropuerarin (6-Chliro-apigenin) and pro-togengkwanin-4'-glucoside were discovered, as shown in Figures 1 and 2. Notably, both compounds were identified for the first time. 

As can be seen from the above, the flavonoid compounds in Horsetail extract are actually two types: one is free flavonoids that have not condensed with sugars; the other is flavonoid glycosides that have condensed with sugars.

1.3 Glycosides

In Horsetail extracts, in addition to flavonoids that can form glycosides with sugars, other structures can also condense with sugars to form glycosides. Changjun et al. [8] isolated 12 compounds from the water-soluble components of Horsetail nutrient stems. After spectral analysis and chemical identification, three new phenolic glycoside compounds were named Horsetail glycoside A, Horsetail glycoside B, and Horsetail glycoside C, as shown in Table 1. Additionally, uridine, hypoxanthine, 2'-deoxyhypoxanthine, 2'-deoxycytidine, tryptophan, thymine, 5-carboxy-2'-deoxyuridine, pinobanksin, and 9-fluorenol-3-O-β-D-glucopyranoside were also identified. These compounds were all isolated from this plant for the first time.

1.4 Alkaloids

Horsetail extracts contain various alkaloids, collectively referred to as Horsetail total alkaloids (TAEP) [9]. The alkaloid content of 95% is (dog) Horsetail alkaloid (palustrine), see Figure 3. Askaric acid was first isolated from E. palustre. Its absolute configuration is (13R,17S,1'S)-17-(1-hydroxypropyl)-1,5,10-triazacyclodec-[11.4.0]dec-17-ene-11-one [9, 10].

1.5 Protein and Amino Acids

In 1971, Aggarwal et al. [11] isolated iron oxidoreductin (I) from Horsetail. This protein exhibits maximum absorption at 465, 421, 330, and 276 nm. Upon hydrolysis, the amino acid composition of the protein was as follows: Lys₄, His₁, Argi, Trpo, Asp₈₋₉, Thr₇, Serg, Glu₁₅₋₁₆, Pro₄, Glyg, Ala₆, 1/₂Cys₄, Valg, Met₁, Iley, Leu, Tyr₂, and Phe₄. The total number of amino acid residues is 93–95, which is fewer than those found in iron redox proteins from other plants.

1.6 Indanone

Semenov et al. [12] also isolated indanone from the sample, whose structural formula is shown in Figure 4.

1.7 Equisetum silicates

Equisetum contains a large amount of Equisetum silicates (SCE), including silicic acid, inorganic silicates, and organic silicates [13].

1.8 Others

Additionally, Horsetail contains lignin (7.1% of dry weight), sugars (9.9% of dry weight), and vitamins [14].

2 Pharmacological Effects of Horsetail

2.1 Effects on the Central Nervous System

Research by Ji Yubin et al. [15] demonstrated that by influencing the activity of monoamine oxidase-B (MAO-B) in mouse brains, the total alkaloids of Horsetail (TAEP) can antagonize the inhibitory effect of hydrazine on MAO-B activity in mouse brains. At a dose of 45 mg/kg, TAEP completely antagonized the inhibitory effect of hydrazine, while 60 mg/kg TAEP reversed the inhibitory effect to an activating effect (P < 0.001).    Based on these findings, it is concluded that TAEP is an agonist of MAO-B, and its agonistic effect on MAO-B is one of the mechanisms underlying its central inhibitory action. Additionally, by observing the effects of horsetail alkaloids on 5-HT and NA levels in the mesolimbic system of rats with morphine withdrawal, it was found that horsetail alkaloids significantly reduced 5-HT and NA levels in the mesolimbic system of rats with morphine withdrawal, demonstrating strong central sedative effects. Furthermore, Ji Yubin et al. [16] conducted a kinetic study on the inhibitory effects of Horsetail alkaloids on Mg²⁺-ATPase and Ca²⁺-ATPase in the brain vesicle membranes of rats, demonstrating that Horsetail alkaloids possess sedative, hypnotic, and anxiolytic effects.

2.2 Hepatoprotective Effects

Studies have shown [17, 18] that Horsetail silicified compounds (SCE) have a protective effect on experimental liver damage. Experiments were conducted using rats as experimental materials, with CCL4, TAA, and prednisolone used to induce liver damage in rats. Although the causes of liver injury differed, Horsetail silicates were able to reduce serum ALT levels in rats.

This finding is consistent with the conclusion that Horsetail decoctions can also reduce serum ALT levels [19].

2.3 Lipid-lowering and blood pressure-lowering effects

Water-soluble silicates extracted from the whole plant of Horsetail can be used to treat atherosclerosis, hypertension, and hyperlipidemia [20, 21]. This is consistent with the conclusion that the decoction of Horsetail can lower blood lipids and blood pressure.

2.4 Diuretic effects

The ethanol-soluble components of fresh whole Horsetail and its extract have diuretic effects, though not strong. Silicic acid is the primary component responsible for diuresis. Horsetail and its silicic compounds can also eliminate metabolic byproducts, foreign substances, and toxins from the body, thereby exerting protective effects such as detoxification and detoxification [22].

3 Discussion

Given that Horsetail contains both acidic phenols, acids, and phenolic acids, as well as alkaline alkaloids, we have reason to believe that alkaloids may exist in the form of salts by combining with phenols, acids, or phenolic acids.

Six flavonoid monomers have been isolated from Horsetail, and relevant pharmacological studies have been reported. Generally, flavonoids exhibit broad and mild physiological activities and are not very potent [23]. Japanese scholars suggest that components that are abundant and widely distributed typically lack strong physiological activity, much like human food. Flavonoids are precisely such compounds: widely distributed, easily separable, yet lacking strong physiological activity. Therefore, to date, the true active components of Horsetail have not been identified, and further research in this area is needed.

Horsetail contains numerous phenolic acids and flavonoids containing phenolic -OH groups. Generally, compounds containing phenolic -OH groups possess the ability to scavenge reactive oxygen species (ROS), and the greater the number of phenolic -OH groups, the stronger the ability [24]. This suggests that Horsetail may possess antioxidant properties. However, when extracting these phenol-OH-containing components, the temperature should not be too high, and exposure to air should be minimized, as prolonged exposure may lead to oxidation into quinones and discoloration.

Further research into the chemical composition and pharmacological effects of Horsetail could contribute to the development of traditional Chinese medicine and have a positive impact on addressing the global challenge of an aging population.

References:

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