Phytochemical Screening and Assays of Phenolic Compounds in Senna occidentalis L. Leaf and Seed Extracts

Phytochemical screening and assay of secondary metabolites, crude extracts with distilled water, aqueous methanol, aqueous acetone and aqueous ethanol of leaves and seeds of Senna occidentalis L. were studied in this work. The aim was to verify the distribution of secondary metabolites according to S. occidentalis organs. Four leaf samples from four different localities (South, East, West and Central Senegal) and a mixed sample of seeds were used. Functional molecules such as polyphenols, flavonoids and tannins were then assessed in the leaves and seeds using various standard methods. The results show that Senna occidentalis L. leaf and seed samples display an identical and homogeneous profile, regardless of locality. They contain secondary metabolites and the polyphenol content of extracts from southern, eastern, western and central leaves is: 0.620 - 0.539 - 0.811 - 0.573 g GAE/100 g DM;flavonoids: 0.064 - 0.074 - 0.130 - 0.101 g CE/100 g DM and tannins: 0.326 - 0.264 - 0.269 - 0.494 g TAE/100 g DM. The efficacy of S. occidentalis L. infusions in therapy is thus justified by the presence of these metabolites, whose biological properties are well known. It is then possible to explore isolation of active principles of Senna occidentalis L. leaves and even seeds for producing medicines.

Lubiprostone vs Senna in postoperative orthopedic surgery patients with opioid-induced constipation:A double-blind,active-comparator trial

AIM: To investigate the efficacy of lubiprostone compared to Senna on bowel symptoms and constipation in post-operative orthopedic patients treated with opioids.

Same-day colonoscopy preparation with Senna alkaloids and bisacodyl tablets:A pilot study

AIM: To evaluate the efficacy of same-day bowel preparation with Senna alkaloids combined with bisacodyl tablets in routine colonoscopy procedures.

Addition of senna improves quality of colonoscopy preparation with magnesium citrate

AIM: To prospectively investigate the effectiveness and patient’s tolerance of two low-cost bowel cleansing preparation protocols based on magnesium citrate only or the combination of magnesium citrate and senna. METHODS: A total of 342 patients who were referred for colonoscopy underwent a colon cleansing protocol with magnesium citrate alone (n = 160) or magnesium citrate and senna granules (n = 182). The colonoscopist rated the overall efficacy of colon cleansing using an established score on a 4-point scale. Patients were questioned before undergoing colonoscopy for side effects and symptoms during bowel preparation. RESULTS: The percentage of procedures rescheduled because ofinsufficient colon cleansing was 7% in the magnesium citrate group and 4% in the magnesium citrate/senna group (P = 0.44). Adequate visualization of the colonic mucosa was rated superior under the citramag/senna regimen (P = 0.004). Both regimens were well tolerated, and did not significantly differ in the occurrence of nausea, bloating or headache.However, abdominal cramps were observed more often under the senna protocol (29.2%) compared to the magnesium citrate only protocol (9.9%, P < 0.0003). CONCLUSION: The addition of senna to the bowel preparation protocol with magnesium citrate significantly improves the cleansing outcome.

Comparative study of two bowel preparaton regimens for colonoscopy: Senna tablets vs sodium phosphate solution

AIM: To compare the efficacy and acceptance of senna tablet and sodium phosphate solution for bowel preparation before colonoscopy.METHODS: One hundred and thirty four patients, who needed elective colonoscopy, were randomly allocated to take 180 mg senna tablet or 95 mL sodium phosphate solution on the day before colonoscopy. The effi cacies of both laxatives were compared using the mean difference of colon-cleanliness score of the rectum, sigmoid segments, descending colon, transverse colon and cecum. The scores were rated by two observers who were blinded to the laxatives administered. The higher score means that the colon is cleaner. The efficacy of both laxatives were equivalent if the 95% confidence interval of the mean difference of the score of colon lie within -1 to +1. RESULTS: On intention-to-treat analysis, the mean cleanliness scores in the four segments of colon except the cecum were higher in the sodium phosphate group than those in senna group (7.9 ± 1.7 vs 8.3 ± 1.5, 8.0 ± 1.8 vs 8.5 ± 1.4, 7.9 ± 2.0 vs 8.5 ± 1.3, 7.9 ± 2.0 vs 8.2 ± 1.4 and 7.2 ± 1.7 vs 6.9 ± 1.4, respectively). The 95% conf idence intervals (95% CI) of mean difference in each segment of colon were not found to lie within 1 point which indicated that their effi cacies were not equivalent. The taste of senna was better than sodium phosphate solution. Also, senna had fewer side effects. CONCLUSION: The effi cacy of senna is not equivalentto sodium phosphate solution in bowel preparation for colonoscopy, but senna may be considered an alternative laxative.

Organ specific differences in alteration of aquaporin expression in rats treated with sennoside A,senna anthraquinones and rhubarb anthraquinones

OBJECTIVE Senna and rhubarb are classified as stimulative laxatives,and known to have similar effective constituents,the anthraquinones.Being protected by theβ-glucoside bond,the anthraquinones can reach the intestines where they are degraded into complex metabolites by enzymes secreted from the intestinal microbiome.It is these complex metabolites that produce the laxative effects.Then the similarities and differences of action between the anthraquinones require further elucidation.METHODS Here,we studied metabolites of senna anthraquinones(SAQ),rhubarb anthraquinones(RAQ)and their chemical marker,sennoside A(SA),in a rat diarrhea model.In the in vitro biotransformation experiments,SAQ,RAQ and SA were incubated with rat fecal flora solution and the metabolites produced were analyzed using HPLC.In the in vivo studies,the same compounds were investigated for purgation induction,with measurement of histopathology and multiple aquaporins(Aqps)gene expression in six organs.RESULTS SAQ and RAQ had similar principal constituents but could be degraded into different metabolites.A similar profile of Aqps down-regulation for all compounds was seen in the colon,suggesting a similar mechanism of action for purgation.However,in the kidneys and livers of the diarrhea-rats,down-regulation of Aqps was found in the RAQ-rats whereas up-regulation of Aqps was seen in the SAQ-rats.Furthermore,the RAQ-rats showed lower aquaporin 2(Aqp2)protein expression in the kidneys,whilst the SA-rats and SAQ-rats had higher Aqp2 protein expression in the kidneys.This may have implications for side effects of SAQ or RAQ in patients with chronic kidney or liver diseases.CONCLUSION SAQ and RAQ showed similar laxative actions with a similar mechanism,they could display different actions in rat kidneys and livers.We suggest that the clinical usage of senna or rhubarb products should be clarified for patients having chronic kidney or liver diseases.

Free radical scavenging activity of three different flowers-Hibiscus rosa-sinensis,Quisqualis indica and Senna surattensis

Objective:To evaluate three flowers of Hibiscus rosa-sinensis(H.rosa-sinensis),Quisqualis indica(Q.indica) and Senna surattensis(S.surattensis) for their antioxidant activity by different methods in addition to total phenolic,flavonoid and pigment contents.Methods:Antioxidant activity of water,ethanol and absolute ethanol extracts of three flowers; H.rosa-sinensis,Q.indica and S.surattensis was evaluated.The antioxidant activity was assessed by 1,1-diphenyl-2-picrylhydrazyl free radical scavenging activity,ferrous chelating activity,reducing power,nitric oxide scavenging activity,hydroxyl radical scavenging activity as well as total antioxidant capacity.Total flavonoids,total phenols and total pigments including chlorophylls and carotenoids were measured for the three flowers.Results:The results showed that the highest total antioxidant capacity at concentration of 500 mg/L was found in S.surattensis as 0.479 ± 0.001.Scavenging activity of H.rosasinensis,Q.indica and S.surattensis flower extracts against 1,1-diphenyl-2-picrylhydrazyl radical showed the highest activity of(90.20 ± 0.29)% with 500 mg/L.Phytochemical screening of the three flowers extracts were carried out for alkaloids,flavonoids,saponins,tannins,steroids,glycosides,terpenoids,amino acid and mucilages.H.rosa-sinensis showed the total phenolic in water extract of(235.77 ± 14.31) mg/100 g,the other two flowers Q.indica and S.surattensis had the total phenolic in ethanol extracts of(937.70 ± 25.06) and(850.30 ± 13.81) mg/100 g,respectively.On the other hand total flavonoids were identified in absolute ethanol extracts in the three flowers[(32.83 ± 1.34),(49.24 ± 4.87) and(2.79 ± 0.23) mg/100 g,respectively].Conclusions:The extracts in the constituents of the three flowers could be used as additives as supplement fractions in foods.

Anti-lipogenic effect of Senna alata leaf extract in high-fat diet-induced obese mice

Objective: To examine the effect of Senna alata(S. alata) leaf extracts on the regulation of lipid metabolism in high-fat diet-induced obese mice.Methods: The obesity condition was induced in the male ICR mice by feeding them with high-fat diet(45 kcal% fat) for 12 weeks. At the 7th week of diet feeding, the obese mice were treated with the water extract of S. alata leaf at 250 and 500 mg/kg/day, respectively, that continued for six weeks. At the end of the treatment period, the biochemical parameters were determined. The hepatic histology and the gene and protein expressions were also examined.Results: In comparison with the obese control mice, the mice treated with S. alata showed a significant reduction in the elevated blood glucose levels and a decrease in the serum insulin and leptin levels. A reduction in the serum total cholesterol, triglyceride,non-esterified fatty acid, and hepatic triglyceride levels were also observed. The histological examination of the obese mice treated with S. alata showed a reduced lipid accumulation in the liver tissue. Hepatic lipogenic gene expression showed that S. alata decreased the activity of sterol regulatory element binding protein 1c, fatty acid synthase,and acetyl-Co A carboxylase. S. alata could suppress hepatic peroxisome proliferatoractivated receptor gamma(PPARg) protein. Moreover, the protein expression of PPARa in liver tissue was clearly increased by S. alata treatment.Conclusion: The treatment with S. alata could decrease several parameters of impaired lipid metabolism in the obese mice by downregulating sterol regulatory element binding protein 1c and PPARg and upregulating PPARa. This study is the first report on the role of S. alata leaf extract in alleviating the abnormal lipid metabolism in obese conditions.

Protection effect of the anthraquinones, cassiatorin and aurantio-obtusin from seeds of Senna tora against cowpea weevil attack

Objetive: To explore the potential insecticidal, ovipositor deterrent and antifeedant effects of ethyl acetate extract of the seeds of Senna tora(Syn. Cassia tora) against cowpea weevil(Callosobruchus maculatus).Method: The activities were evaluated using standard protocols.In these bioassays, the cowpea seeds were used directly as an insect feed. The activity of the extract and isolated compounds were tested at concentrations of 100, 200 and 300 μg/mL and compared to neem oil and cinnamaldehyde(as standard positive controls). Phytochemical analysis of the ethyl acetate extract was done through a number of chromatographic techniques and the structures of the isolated compounds were established through comprehensive spectroscopic analysis including 2 D-NMR and ESI-MS studies.Results: Fractionation of the active ethyl acetate extract resulted in the isolation of one known anthraquinone,aurantio-obtusin(1) and a novel compound that was named as cassiatorin(2). Compounds1 and 2 showed comparable insect antifeedant properties with the positive controls while their insecticidal and ovipositor deterrent effects were far superior to the standard controls.Conclusions: It is thus concluded that Senna tora extracts and the isolated compounds(1 and2) may be employed in the postharvest management of stored cowpea seeds and as other crop protectants.

Senna petersiana inhibits key digestive enzymes and modulates dysfunctional enzyme activities in oxidative pancreatic injury

Objective:To evaluate the effect of Senna petersiana leaf extracts on key digestive enzymes and FeSO_(4)-induced oxidative injury.Methods:Dried Senna petersiana leaf powder(60 g)was defatted in n-hexane and then extracted sequentially at room temperature with dichloromethane,methanol,and distilled water.The total phytochemical content of the extracts was estimated using established methods.The in vitro antioxidant,anti-lipase,and antidiabetic activities and the effect of the extracts on intestinal glucose absorption and FeSO_(4)-induced pancreatic oxidative injury were determined using different protocols.Moreover,GC-MS analysis was performed to identify the main compounds of the plant extract.Molecular docking analysis was also carried out to evaluate the binding energy of compounds with digestive enzymes.Results:Senna petersiana leaf extracts showed significant antioxidant activities in FRAP,DPPH,and hydroxyl radical scavenging assays.They also inhibited pancreatic lipase and lowered intestinal glucose absorption by suppressing activities ofα-amylase andα-glucosidase.Treatment with the extracts also lowered lipid peroxidation(malondialdehyde),nitric oxide level,acetylcholinesterase,and ATPase activities with simultaneous improvement of antioxidant(catalase,superoxide dismutase,glutathione)capacity in the type 2 diabetes model of oxidative pancreatic injury.GC-MS characterization of the extracts revealed the presence of stilbenoids,alkaloids,and other compounds.Molecular docking screening assay indicated the extract phytochemicals showed strong interaction with the active site amino acids of the targeted digestive enzymes.Among the Senna petersiana compounds,veratramine had the highest affinity forα-amylase and lipase,whereas dihydrostilbestrol was most attracted toα-glucosidase.Conclusions:Senna petersiana inhibits carbohydrate digestive enzymes,reduces intestinal glucose absorption,and exerts ameliorative effects on FeSO_(4)-induced oxidative pancreatic injury with significant antioxidant capabilities.Detailed in vivo studies are underway to understand the plant's therapeutic potential in diabetes management.

Ethnobotanical review and pharmacological properties of selected medicinal plants in Brunei Darussalam:Litsea elliptica,Dillenia suffruticosa,Dillenia excelsa,Aidia racemosa,Vitex pinnata and Senna alata

The aim of the current study is to review the medicinal properties of the plants found in Brunei Darussalam namely Litsea elliptica, Dillenia suffruticosa, Dillenia excelsa, Aidia racemosa, Vitex pinnata and Senna alata. The known phytochemical constituents of these plants and their ability to bring about a range of biological activities are included in this review. These plants have been used traditionally for a multitude of diseases and illnesses. There is a lot of untapped potential in these medicinal plants which could cure multiple diseases.

Nutritional Potential of Two Leafy Vegetables <i>Leptadenia hastata</i>Decne and <i>Senna obtusifolia</i>Link Consumed in Senegal

This study focused on two woody leafy vegetables Leptadenia hastata Decne and Senna obtusifolia Link, commonly consumed in Senegal. Leaves were col-lected from three regions. Then, proximate analyses and micronutrients were carried out to evaluate their nutritional values. Results revealed that protein level of S. obtusifolia (SO) is richer (21.75%) than Leptadenia hastata (LH) (18.16%). The cellulose and carbohydrate contents of the two vegetable’s leaves are in the same order except those of LH from Widou which are less rich in cellulose (8.31%) and richest in carbohydrate (6.35%). These leaves are also good sources of various mineral elements and especially iron. Leaves of LH appear to be richer in iron and magnesium, while SO appears to be richer in calcium. Vitamin C intakes of SO leaves are better than those of LH and respectively range from 142 to 196.5 and 22.5 to 159.5 mg/100 g. According to the use of this leafy vegetable by the populations, a domestication opportunity is thus justified to ensure availability and accessibility of these significant sources of micronutrients.

Crude Extracts of <i>Senna alata</i>(L.) Roxb. Mimics Plant Growth Hormones in Promotion of Vegetative and Reproductive Growth in <i>Celosia argentea</i>L.

The efficacy of crude extracts of Senna alata in the improvement of vegetative and reproductive growth in Celosia aregentea was investigated. Fresh leaves of S. alata were blended with a homogenizer in 1 litre of distilled water. The resultant green paste was filtered under suction. Different concentrations (75%, 50%, 40%, 30%, 25%, 12%, 10%, and 5%) were prepared from the 100% crude extract. Seeds of C. argentea were presoaked in these different concentrations including a control (0%) and planted out after 24 hours. Results obtained showed that seedling height, leaf area, dry weight and leaf area ratio were promoted and enhanced by presoaking seeds in the extract. At the end of the experimental period (six weeks), seedling height in 75% and 100% treatments were 109 ± 16.12 cm and 117 ± 19.32 cm, leaf area 128 ± 17.91 cm2 and 125 ± 18.12 cm2, dry weight 7.48 kg and 7.0 kg respectively. Seedlings raised from seeds presoaked in water (control) however, flowered earlier (8 weeks) than the treatments (10 weeks in 75% and 100%). Presoaking seeds of C. argentea in crude extracts of S. alata before planting is recommended for optimum production of the leafy vegetable. The procedure is cheap and easily implementable by resource-poor farmers who are the main growers of C. argentea.

Biological Control Potential of <i>Colletotrichum gloeosporioides</i>for Coffee Senna (<i>Cassia occidentalis</i>)

A fungal pathogen, Colletotrichum gloeosporioides was isolated from a greenhouse-grown seedling of coffee senna (Cassia occidentalis) and evaluated as a mycoherbicide for that weed. Host range tests revealed that coffee senna, wild senna (C. marilandica), and sicklepod (C. obtusifolia) were also affected by this pathogen, but 35 other crop and weed species, representing 8 botanical families were not affected. The fungus sporulated prolifically on solid and liquid media with maximum spore germination and growth occurring at 20°C - 30°C. Optimal environmental conditions included at least 12 h of free moisture (dew) at 20°C - 30°C. Spray mixtures containing approximately 1.0 × 105 or more conidia·ml–1 gave maximum control when coffee senna seedlings were sprayed until runoff occurred. Coffee senna seedlings that were in the cotyledon to first-leaf growth stage were most susceptible to this pathogen. Weed control efficacy studies under field conditions demonstrated that control of coffee senna was directly proportional to the inoculum concentration applied. Results of these tests suggest that this fungus has potential as a mycoherbicide to control coffee senna, a serious weed in the southeastern U.S.

Chemical Constituents and Antimicrobial Activity of Essential Oil of <i>Senna podocarpa</i>(Guill. et Perr.) Lock

The chemistry of essential obtained from the leaves of Senna podocarpa (Guill. Et Perr.) Lock from Nigeria is being reported. The hydrodistilled oil was analyzed by gas chromatography-flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS) techniques. The main constituents of the oil were 1,2-benzenedicarboxylic acid, mono (2-ethylhexyl) ester phthalate (26.6%) and β-elemene (27.9%). There were significant amounts of caryophyllene oxide (7.3%) and urs-12-en-24-oic acid, 3-oxo-methyl ester (5.5%). The antimicrobial activity of the essential oil was evaluated against a panel of seven bacteria and two fungal strain using agar diffusion and broth microdilution methods. Results had shown that the oil exhibited moderate to strong antimicrobial activity against the tested microorganisms. The activity zones of inhibition (ZI) ranged between 10.0 ± 0.2 mm and 28.3 ± 2.9 mm while the minimum inhibitory concentrations (MIC) ranged between 0.3 mg/mL 5.0 mg/mL, respectively. The chemical constituents and antimicrobial activity of the essential oil of Senna podocarpa were being reported for the first time.

Safety of the Aqueous Extract of the Leaves of Senna alata (L.) Roxb. (Leguminosae-Caesalpinioideae), a Plant Used in Benin to Treat Infections

Description of the Subject: Senna alata (L.) was a plant in the Benin pharmacopoeia used to treat skin infections. Objectives: The aim of our work was to test its harmlessness in vivo. Method: Wistar rats received by gavage a single dose of 2000 mg/kg of Senna alata leaves aqueous extract for the Acute Oral Toxicity (AOT) test. For the sub-Chronic Oral Toxicity (SCT) test, rats force-fed the extract at a daily dose of 300 mg/Kg of body weight for 28 days. The weight of the rats was taken and the blood samples were collected on Day 0, then respectively day 14 for the AOT and Day 28 for the SCT. The renal balance was carried out by dosage of the creatinine, the liver balance by the transaminases AST and ALT and the blood balance by the hemogram. The liver, kidneys and spleen were removed for histological analysis. The results were analyzed using the Student test, with the significance level set at 5%. Results: The weight of the rats did not change significantly in the acute or subchronic oral toxicity tests suggesting an absence of physical disturbance in the rats. Serum creatinine did not vary significantly, suggesting preservation of renal function. That was the same for ASAT and ALAT transaminases, indicating an absence of hepatic cytolysis. In hematology, the hemoglobin level and the number of blood platelets did not vary significantly, suggesting that the extract did not create anemia and did not influence blood coagulation. Hepatic, renal and splenic parenchyma showed no atypia. Conclusion: The aqueous extract of Senna alata (L.) leaves did not reveal any acute or subchronic toxicity and offered prospects for its use in the treatment of infections.

Phytochemical Composition, Anti-Inflammatory and Cytotoxic Activities of Chloroform Extract of <i>Senna crotalarioides</i>Kunth

Senna crotalarioides is used in traditional medicine to treat inflammation. The aim of this work was to investigate the anti-inflammatory and cytotoxic activities and the possible mechanism of action of the chloroform extract washed with hexane of S. crotalarioides (CESC). The anti-inflammatory effect was tested on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ear edema in mice. The levels of TNF-α, IL-1β, IL-6 and IL-10 were determined in macrophages J774A.1 stimulated by lipopolysaccharide (LPS). The cytotoxic activity was evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay against six human cancer cell lines: HeLa (cervical cancer), SKLU-1 and A549 (lung cancer), LNCaP (prostate cancer), SW620 (colon cancer) and MCF7 (breast cancer). The composition of the CESC was determined by GC-MS analysis, and standardized by HPLC-ELSD with ursolic acid as the phytochemical marker. CESC inhibited ear edema 61.45%. In chronic ear edema, CESC diminished the inflammation by 53.77%. CESC decreased TNF-α, IL-1β and IL-6 concentrations, and increased the concentration of IL-10. The extract showed IC50 values on HeLa, SKLU-1, A549, LNCaP, SW620 and MCF7 by 48, 21, 8.16, 6.82, 1.81, 4.06 and 12.5 μg/mL, respectively. The main components were ursolic acid, 1-octacosanol, stigmasterol, β-sitosterol, 1-triacontanol, (Z, Z) hexadec-9-enoic acid octadec-9-enyl ester. CESC might be useful for developing a phytomedicine with anti-inflammatory and cytotoxic activities.

Assessment of Anti-Salmonella Activity of Aqueous and Ethanolic Extract of Senna siamae, Used in Traditional Management of Salmonellosis in Benin

Recent ethnopharmacological data cited Senna siamea as one of the most widely used medicinal plants in the management of salmonellosis in Benin. However, data related to its activity on non-typhoidal Salmonella spp are limited. This study aimed to assess the antibacterial activity of Senna siamea on multidrug-resistant Salmonella. Ethanolic and aqueous extracts of S. siamea were tested for their antibacterial activity on four multidrug-resistant Salmonella: Salmonella Typhimurium ATCC 14028 and three Salmonella spp. isolated from animals intended for human consumption in Benin. Well diffusion technique combined with the determination by microdilution of Minimum Bactericidal Concentration (MBC) and Minimum Inhibitory Concentration (MIC) were used for antibacterial testing. From antibacterial testing, inhibition diameters of the extracts ranged from 7 to 11 mm, for the susceptible strains. Colistin (reference antibiotic) was active on all Salmonella spp. with inhibition diameters between 18 and 19 mm. The MICs ranged from 3.125 to 25 mg/ml while MBCs of the extracts are greater than 100 mg/ml, so none of the extracts have antibacterial power (p.a). From these results, it appears that the use of Senna siamea in the traditional treatment of salmonellosis is justified. These results must be valued in the development of anti-salmonella phytomedicines.

迈凯伦Senna

这款迈凯伦Senna乃是迈凯伦的最新作品,全球限量500辆。这款全新跑车在外观上仍采用一些迈凯伦家族式DNA。不过前灯组的尺寸轮廓却更为夸张,与下方进气口连为一体。同时,灯组中碳纤维结构前的LED光带也与前脸形成一条直线,视觉冲击感极强。而大尺寸碳纤维前唇在营造极强的运动感的同时,也更加优化空气动力属性。

慢传输型便秘的中医中药治疗进展

慢传输型便秘(STC)是临床上常见的慢性顽固性便秘类型,综合的保守治疗往往效果欠佳,临床滥用泻剂的现象较为普遍,最终导致便秘的进行性加重。STC的病理生理机制多见于长期的不良生活习惯导致肠道刺激不足,排便动作缺乏,粪便在肠腔内滞留时间过久。而中医通过物理治疗(如按摩、针灸、耳穴按压)以及中药方剂治疗STC取得理想效果,与西医治疗相比不良反应少且安全性较高,临床应用价值显著。但目前中药临床与实验研究方面仍存在不足,未来应开展并设计更加严谨、质量高且样本量大的临床研究,以明确中药有效成分治疗STC的作用及机制。