Cassiae semen contains structurally diverse and biologically active anthraquinones. Thus far, ~53 anthraquinones have been isolated and identified. The predominant anthraquinones are emodin-type anthraquinones, which include emodin, chrysophanol, physcion, aloe-emodin, rhein, obtusin, chryso-obtusin, aurantio-obtusin, obtusifolin, questin, 1-desmethylaurantio-obtusin, 1-desmethylobtusin, 1-desmethylchryso-obtusin, chrysophanol-10,10′-bianthrone, 1,2-dihydroxyanthraquinone, 2-hydroxyemodin-1-methylether, alaternin, 1,3-dihydroxy-6-methoxy-7-methyl anthraquinone, 1-hydroxy-3,7-diformyl anthraquinone, chrysarobin, 8-O-methylchrysophanol, 1-O-methylemodin, 1,2-dimethoxy-8-hydroxy-3-methyl-9,10-anthraquinone and l,2,7-trimethoxyl-6,8-dihydroxy-3-methylanthraquinone (compounds 1–24, respectively; Fig. 1); these have all been isolated from Cassiae semen (29–38). There are also many combined anthraquinones (compounds 25–46; Fig. 1), which have been isolated from the seeds of C. obtusifolia or C. tora (3,7,30,36,39–46).

Naphthopyrones are the other characteristic components in Cassiae semen. In 1969, torachrysone, rubrofusarin and rubrofusarin-6-O-β-D-gentiobioside were isolated from C. tora seeds (compounds 47–49, respectively; Fig. 2) (47,48). Subsequently, toralactone, rubrofusarin triglucoside, cassiaside, nor-rubrofusarin gentiobioside, cassiaside B, cassiaside C, torachrysone apiglucoside, torachrysone gentiobioside, torachrysone tetraglucoside, cassiatoroside, demethylflavasperone gentiobioside and cassialactone gentiobioside were isolated from C. tora seeds (compounds 50–61, respectively; Fig. 2) (17,28,49–51). In addition, cassiaside B and cassiaside C were identified in the seeds of C. obtusifolia (52). Other naphthopyrones, including torosachrysone, isotoralactone, cassialactone, cassiaside B2, cassiaside C2, nor-rubrofusarin-6-O-β-D (6′-O-acetyl) glucopyranoside and l-hydroxyl-2-acetyl-3,8-dimethoxy-6-O-[β-D-apiofuranosyl- (l→2)-β-D-glucopyranosyl]-naphthalene were also isolated from C. obtusifolia seeds (compounds 62–68, respectively; Fig. 2) (19,53–55).

Li (56) extracted the volatile oils from Cassiae semen by steam distillation, and subsequently identified 37 components according to the gas chromatography/mass spectrometry analysis. Among these peaks, the major volatile components were 9-octadecenoic acid (E) (22.15%), n-hexadecanoic acid (12.53%), 9,10-anthracenedione, 1,8-dihydroxy-3-methyl (7.66%), octadecanoic acid (4.56%) and 13-octadecenoic acid methyl ester (Z) (3.84%) (56).

A range of other components have been isolated from Cassiae semen, including malvalic acid, sterculic acid, mandelic acid, campesterol, aspidinol and 5,7-dihydroxychromone (compounds 69–74, respectively; Fig. 3) (5,57,58). In addition, the four flavonoid compounds, chrysin, chrysin-7-O-β-D-glucoside, galangin and cyanidenon, were also obtained and identified from Cassiae semen (compounds 75–78, respectively; Fig. 3) (58).

An overview of the pharmacological studies on Cassiae semen is presented in detail in the following sections.

In traditional Chinese herbal medicine, Cassiae semen is used for the prevention and treatment of hyperlipidemia. Several Chinese herbal formulations containing Cassiae semen is available in the Chinese market for preventing the formation of atherosclerotic plaques (59). In certain Asian countries, including China and Korea, it is also commonly drunk as a roasted tea to reduce body weight (60,61). Previous studies using mice have evaluated the reductions in blood lipid contents induced by different Cassiae semen extracts obtained through different methods, including supercritical fluid extraction, systematic solvents (petroleum ether, ethyl acetate, n-butanol, 70% ethanol and water) and ethanol precipitation following water extraction. The results revealed that the n-butanol and ethyl acetate extracts were the most effective (62,63). In addition, the ethanol and aqueous extracts of Cassiae emen significantly decreased the serum levels of total cholesterol (TC), triglyceride (TG) and low-density lipoprotein cholesterol (LDL-C), however, they increased the levels of high-density lipoprotein cholesterol (HDL-C) (13,64,65). Similarly, He et al (66) reported that treatment with the water extract form of C. obtusifolia seeds decreased the blood-lipid level by inhibiting cholesterol synthesis. Cho et al (67) demonstrated that soluble fibers from C. tora seeds markedly decreased liver TC and TG levels in rats fed with a high-cholesterol diet. The underlying mechanism may be mediated by increasing fecal bile acid excretion and downregulating the production of lipogenic enzymes (67). In addition, soluble fibers decreased the serum levels of TC, TG and LDL-C in patients with type II diabetes without serious adverse effects (2). Liu et al (68) revealed that the ethanol extract of Cassiae semen upregulated the expression levels of peroxisome proliferator-activated receptor (PPAR)-γ, sterol regulatory element-binding protein-1c, hormone-sensitive lipase and triacylglycerol hydrolase, however, tumor necrosis factor receptor superfamily member 6 was downregulated in adipose tissue. The anti-hyperlipidemia activity of Cassiae semen is primarily due to its antioxidant components, such as anthraquinones and polysaccharides. There are a variety of bioactive anthraquinone components in Cassiae semen, including chrysophanol, physcion, aurantio-obtusin, obtusifolin and emodin, which have been observed to decrease the levels of TC and TG (69,70). Previous studies have demonstrated that anthraquinones isolated from Cassiae semen were effective substances during hypolipidemic activities (71,72). These results were verified by a previous study, which applied an experimental hyperlipidemic rat model to investigate anthraquinone treatment (80 and 20 mg/kg, per os, for 20 days). The TC, TG and LDL-C levels were significantly reduced in a dose-dependent manner, however, the levels of HDL-C increased. Inhibition of cholesterol synthesis may be one of the underlying mechanisms involved in decreasing blood lipid levels (73). Water-soluble polysaccharides (WSPs) from Cassiae semen markedly inhibited the activities of α-amylase and pancreatic lipase, however, protease activity increased. The results demonstrated that WSPs had the ability to bind to bile acids and reduce the absorption of cholesterol, indicating that WSPs may have potential as an effective herbal ingredient in functional food applications (74).

A number of studies have demonstrated that Cassiae semen exhibits anti-diabetic activity. A total of three naphthopyrone glucosides (compounds 49, 52 and 55) isolated from the butanol-soluble extract of Cassia semen have been evaluated for their inhibitory activity on advanced glycation end products (AGEs) formation in vitro. The results revealed that these compounds possessed more potent inhibitory activity against AGEs compared with the aminoguanidine positive control (15). In addition, rubrofusarin-6-O-β-d-gentiobioside (compound 49) and cassiaside (compound 52) significantly inhibited the expression of transforming growth factor (TGF)-1 and extracellular matrix protein in glomerular mesangial cells cultured under diabetic conditions, suggesting that the active compounds in Cassiae semen may be effective in the treatment of renal complications associated with diabetes (16). Similarly, Kim et al (75) evaluated the preventive effects of the methanol extract of Cassia semen (200 mg/kg/day, for 12 weeks) on the development of diabetic nephropathy in streptozotocin (STZ)-induced diabetic rats. The results indicated that oral treatment with the Cassia semen methanol extract inhibited the development of diabetic nephropathy by inhibiting AGEs accumulation, receptor for advanced glycosylation end product and cyclooxygenase-2 expression in the renal cortex of STZ-diabetic rats (75,76). In addition, Zhu (77) reported that the water extract of Cassia semen exhibited protective activity against STZ-induced renal fibrosis in diabetic rats. The underlying mechanisms may be associated with its ability to downregulate the expression of TGF-β1, connective tissue growth factor and mothers against decapentaplegic homolog 3 (smad3), as well as upregulating the protein expression of smad6 (77).

The ethanolic extract from the seeds of C. obtusifolia has been reported to have a neuroprotective effect in brain disease models. Kim et al (6) suggested that C. obtusifolia (25, 50 or 100 mg/kg) significantly attenuated scopolamine or transient bilateral common carotid artery occlusion (2VO)-induced memory impairment. These effects are mediated by the enhancement of the cholinergic nervous system via acetylcholinesterase inhibition in a dose-dependent manner [half maximal inhibitory concentration (IC₅₀)=81.6 µg/ml] (6). In addition, C. obtusifolia (10 or 50 mg/kg/day) exhibited a neuroprotective effect in a mouse transient global ischemia model due to its anti-inflammatory properties and the induced upregulated expression of phosphorylated cyclic AMP response element binding protein and brain-derived neurotrophic factor (78).

Drever et al (79) demonstrated that treatment with C. obtusifolia (0.1–10 µg/ml) significantly attenuated secondary calcium dysregulation and cell death induced by N-methyl-D-aspartate and 3-nitropropionic acid in mouse hippocampal cultures, and no significant effect on cell death was induced by incubation with naturally-secreted oligomers of amyloid (A)β. Yi et al (80) reported for the first time, that C. obtusifolia (10 µg/ml) ameliorated the Aβ-induced synaptic dysfunction model through anti-inflammatory and protein kinase B (Akt)/glycogen synthase kinase-3β pathways. The results suggested that the neuroprotective effect may be attributable to obtusifolin (compound 9) and/or alaternin (compound 17) (80). In a further experiment, C. obtusifolia (0.1–1 µg/ml) inhibited cell damage against oxidopamine (6-OHDA)-induced dopaminergic (DA) neural toxicity in PC12 cells through an anti-oxidant and antimitochondrial-mediated apoptosis mechanism. In a mesencephalic DA culture, C. obtusifolia (0.1–1 µg/ml) protected the DA cells against 6-OHDA- and N-methyl-4-phenylpyridinium iodide-induced toxicities. In addition, C. obtusifolia (50 mg/kg/day for 15 days) significantly protected DA neuronal degeneration in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced mouse Parkinson's disease (PD) model by inhibiting the movement impairment and the loss of DA neurons, indicating that C. obtusifolia may be a useful neuroprotective candidate for PD (81). In addition, protein and anthraquinone glucosides from Cassia semen improved learning and memory capacity, inhibited the malondialdehyde (MDA) and monoamine oxidase levels, and enhanced the level of superoxide dismutase (SOD) in the cerebrum of senile mice (82).

It was recorded in the Compendium of Materia Medica that Cassiae semen exhibited the functions of nourishing the liver and improving vision (83). In Korea, the aqueous extract of C. tora L. seeds has been used for the protection of the liver. A weak anti-hepatotoxic activity in CCl4-induced mice was observed when the drug was administered orally at a dose of 670 mg/kg (84). The methanol extract of C. tora L. seeds exhibited significantly protective effects in primary cultured hepatocytes against CCl4 and toxicity. A total of two anthraquinone glycosides (compounds 44 and 45) and three naphthoypyrone glycosides (compounds 49, 51 and 53) from the methanol extract of C. tora seeds were the primary chemical constituents (42,50). The preventative effects of Cassiae semen on acute liver injury in mice induced by CCl4 have also been investigated (85,86). When compared with the control group, varying concentrations of the aqueous extract of Cassiae semen significantly increased the serum levels of SOD, and decreased the serum levels of aspartate transaminase (AST), alanine transaminase (ALT) and MDA. These results indicate that Cassiae semen is potentially beneficial in the treatment or prevention of hepatic damage (85,86). In addition, the ethanol extract of Cassiae semen has been observed to increase the serum levels of SOD and to decrease the serum levels of TG, TC, MDA, AST and ALT (86). Total anthraquinones from Cassiae semen exhibited a protective effect on alcohol-induced acute liver injury in mice by regulating fat metabolism, improving liver function and increasing the mRNA and protein expression levels of PPAR-γ (10,87).

Antibacterial activity, an important effect of Cassiae semen, has been comprehensively investigated. Naphthalenes (compounds 47 and 50) and anthraquinones (compounds 1, 4 and 5) isolated from C. tora seeds exhibited significant antibacterial effects on four strains of methicillin-resistant Staphylococcus aureus [minimal inhibitory concentration (MIC) was 2–64 µg/ml] and a strain of methicillin-sensitive S. aureus. In addition, rhein (compound 5) and torachrysone (compound 47) from the seeds of C. tora exhibited antibacterial activity against Escherichia coli K12 with MIC values of 512 and 128 µg/ml, respectively (17). Kim et al (88) were the first to demonstrate that emodin (compound 1) from C. tora seeds has a median lethal dose (LC50) value of 0.102, 0.163, 0.385 and 0.046 g/l against Rhizoctonia solani, Botrytis cinerea, Phytophthora infestans and Erysiphe graminis, respectively, and physcion (compound 3) has an LC50 value of 0.248, 0.263, 0.518, and 0.073 g/l against R. solani, B. cinerea, P. infestans and E. graminis, respectively. In addition, the LC50 value of rhein (compound 5) is 0.375, 0.478, and 0.047 g/l against R. solani, B. cinerea and P. infestans, respectively (88).

It has been reported that ethanol and aqueous extracts of C. obtusifolia seeds were inhibitory against Helicobacter pylori strains (MIC were 100 and 60 µg/ml, respectively) (89). In addition, 1,2-dihydroxyanthraquinone (compound 15) isolated from C. obtusifolia seeds was revealed to inhibit the growth of Clostridium perfringens and E. coli., indicating that this drug exhibited potent growth-inhibiting activities towards human intestinal bacteria (90). Li et al (91) demonstrated that the chloroform extract of the seeds of C. obtusifolia also exhibited different inhibitory activities against Fusarium oxysporum and B. cinerea (IC₅₀ values were 0.57 mg/ml and 0.97 mg/ml).

The water extract of C. tora seeds accelerated the oxidation of deoxyribose induced by Fe³⁺-EDTA/H₂O₂ and exhibited 94% inhibition of linoleic acid peroxidation at a concentration of 0.2 mg/ml. The underlying mechanisms of this may be mediated by reducing metal ions, scavenging hydroxyl radical and chelating ferrousion (92,93). Xv and Hu (94) demonstrated that the water extract of Cassiae semen exhibited a potent ability to scavenge free oxygen radicals [IC₅₀ values were 2 mg/ml and 2 µg/ml for hydroxyl radicals (OH_-) and hydrogen peroxide (H₂O₂), respectively]. WSP from Cassiae semen (0.022 mg/ml) effectively inhibited superoxide radicals (O_2-) induced by pyrogallol autoxidation (95). The inhibitory effects of WSP on serum levels of MDA were used to evaluate its antioxidation capabilities. The results demonstrated that WSP decreased MDA serum levels with an IC₅₀ value of 15.80% (96). In another study, Liu et al (97) optimized the extraction conditions for WSP of Cassiae semen (temperature 80°C, extraction time 3.5 h, solid-liquid ratio 1:30) and observed that WSP (94.03 µg/ml) had the ability to scavenge hydroxyl and superoxide radicals with scavenging rates of 43.32 and 64.97%, respectively.

In addition, ethyl acetate fraction and n-butanol fraction of Cassiae semen were evaluated by DPPH radical scavenging activity. The results revealed that the ethyl acetate fraction had a lower IC₅₀ value of 56.4 g/ml, when compared with the value of 80.6 g/ml for n-butanol fraction. 1-Desmethylaurantio-obtusin (compound 11) exhibited good scavenging activity on DPPH with an IC₅₀ value of 4.5±0.7 g/ml, while aurantio-obtusin-6-O-β-D-glucopyranoside (compound 34) and questin (compound 10) exhibited moderate antioxidant activity, and their IC₅₀ values were 103.2±1.5 g/ml and 185.2±1.8 g/ml, respectively. When compared with these results, chryso-obtusin (compound 7) and aurantio-obtusin (compound 8) demonstrated weaker antioxidant activity (IC₅₀ >200 µg/ml) (98). The methanolic extract of C. tora seeds exhibited a high antioxidant activity on lipid peroxidation (99). Similarly, in another study, Yen et al (12) demonstrated that the methanolic extract of C. tora seeds exerted a greater antioxidant activity than the other organic solvents (n-hexane and ethyl acetate). Emodin was also revealed to be an antioxidative component (12). In addition, alaternin (compound 17), cassiaside (compound 52) and rubrofusarin-6-O-β-D-gentiobioside (compound 49) isolated from C. tora seeds exhibited good scavenging activity against DPPH radicals with IC₅₀ values of 17.59, 32.52 and 18.04 µg/ml, respectively (100).

Aqueous and ethanol extracts of Cassiae semen have been reported to possess hypotensive effects (101). Koo et al (101) reported that the water extract of C. tora seeds (3.75, 7.5, 15, 30, 60 and 250 mg/kg) consistently reduced arterial blood pressure in anesthetized rats. A potential reflex mechanism of this hypotensive action may involve a vagal reflex, which reciprocally inhibits the peripheral vasomotor tone via a reflex reduction in the sympathetic neural outflow to blood vessels (102). In addition, the media portion of the medullary reticular formation has been revealed to be directly involved in the hypotensive effect of C. tora seeds (103). Furthermore, the ethanol extract of Cassiae semen significantly decreased blood pressure in hypertensive rats by inhibiting receptor-controlled calcium channels on vessels and regulating the secretion of nitric oxide and inducible nitric oxide synthase (104).

In addition to the pharmacological effects described above, Cassiae semen and its ingredients have other pharmacological effects, including estrogenic, anti-allergic, antigenotoxic, anti-aggregatory, antimutagenic and cardioprotective effects. Some of these effects are discussed briefly below.

The estrogenic activity of C. obtusifolia seeds was evaluated by a recombinant yeast screening assay. The results revealed that 70% EtOH extracts of this drug exhibited estrogenic relative potency [half maximal effective concentration (EC₅₀) was 60.2 µg/ml) (105). Cassiaside C₂ (compound 66) isolated from C. obtusifolia seeds exhibited a potent anti-allergic activity by inhibiting the histamine release from mast cells induced by antigen-antibody reaction (19). Furthermore, gluco-aurantioobtusin (compound 25) from C. obtusifolia seeds possessed potent inhibitory activities against arachidonic-acid-, ADP- and collagen-induced platelet aggregations (39). Wu and Yen (106) demonstrated that the water extract of C. tora seeds exhibited potential antigenotoxic activities against the dietary mutagens Glu-P-1 and TrpP-1 in the Ames test and the Comet assay. The potential mechanisms may be associated with neutralization of the reactive intermediate of Trp-P-1 and an antioxidant effect of the tested compounds (106). Anthraquinone aglycones (compounds 2, 7 and 8) and naphthopyrone glycosides (compounds 49 and 52) from C. tora seeds exhibited significant antimutagenic activity in vitro. The mechanism associated with these compounds may be mediated via interactions with a microsomal activating system (14). Fu et al (107) reported that the water extract of Cassiae semen (10 mg/kg/day, for one week) effectively improved myocardial function, and attenuated myocardial ischemia and reperfusion-induced injury and apoptosis in diabetic animals, which is potentially attributable to the reduced plasma lipid levels and the triggered cell survival Akt and extracellular signal-regulated kinases 1/2 signaling.