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Surh I, Dunnick JK, Brix AE, et al. NTP Genetically Modified Model Report on the Toxicology Study of Senna (CASRN 8013-11-4) in C57BL/6NTac Mice and Toxicology and Carcinogenesis Study of Senna in Genetically Modified C3B6.129F1/Tac-Trp53tm1Brd N12 Haploinsufficient Mice (Feed Studies): NTP GMM 15 [Internet]. Research Triangle Park (NC): National Toxicology Program; 2012 Apr.

Cover of NTP Genetically Modified Model Report on the Toxicology Study of Senna (CASRN 8013-11-4) in C57BL/6NTac Mice and Toxicology and Carcinogenesis Study of Senna in Genetically Modified C3B6.129F1/Tac-Trp53tm1Brd N12 Haploinsufficient Mice (Feed Studies)

NTP Genetically Modified Model Report on the Toxicology Study of Senna (CASRN 8013-11-4) in C57BL/6NTac Mice and Toxicology and Carcinogenesis Study of Senna in Genetically Modified C3B6.129F1/Tac-Trp53tm1Brd N12 Haploinsufficient Mice (Feed Studies): NTP GMM 15 [Internet].

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CAS No. 8013-11-4

[Senna drawing obtained from Samuelsson (1999)]

Synonyms: Alexandrian senna; Khatoum senna; Tinnevelly senna

Botanical names: Senna alexandrina P. Mill.; Cassia senna L.; Cassia acutifolia Del.; Cassia angustifolia Vahl

Trade names: Ex-Lax®, Fletcher’s Castoria®, Senexon®, Senna-Gen®, Senna Soft®, Senokot®

Chemical and Physical Properties

Senna is a pod (fruit) or leaf of Senna alexandrina P. Mill. (Leguminosae). The plant is a shrub usually 0.7 to 1 m tall, native to Africa, India, and Asia and cultivated in Sudan, China, India, and Pakistan (Blumenthal, 2000; Cupp, 2000). The plants have compound pinnate leaves with three to eight pairs of leaflets per leaf. Lanceolate and pale-green leaflets are 1.5 to 5 cm long and 5 to 15 mm wide. The pale-green pods turn greenish brown during maturity and dark brown after drying. The pods contain five to 10 obovate and green to pale brown seeds (Franz, 1993; WHO, 1999; Blumenthal, 2000; Cupp, 2000; Srivastava et al., 2006).

Fruits and leaves of these plants contain dianthrone O-glycosides (sennoside A, sennoside A1, sennoside B, sennoside C, sennoside D, sennoside D1, sennidin-A-monoglucoside, sennidin-A1-monoglucoside, and sennidin-B-monoglucoside), dianthrones (sennidin A and sennidin B), 1,8-dihydroxy anthraquinones (rhein, aloe-emodin, emodin, and chrysophanol), aloe-emodin diglucoside, rhein glucoside, naphthalene derivatives, flavonoids (kaempferol, isorhamnetin, quercetin diglucoside, kaempferol diglucoside, and isorhamnetin diglucoside), vicenin-2, β-sitosterol, salicylic acid, oxalate, resin, saponins, polyol, sugars, and polysaccharide hydrocolloids (Figure 1; Appendix D) (Lemli et al., 1981; Franz, 1993; WHO, 1999; Blumenthal, 2000; Terreaux et al., 2002).

Figure 1. Primary Structures of Selected Components of Senna.

Figure 1

Primary Structures of Selected Components of Senna. Some are present as glycosides (Franz, 1993; Appendix D). Glu=glucose

Dianthrone O-glycosides are major proactive constituents and make up 1.3% to 3.9% (w/w) of senna pods or leaves (Grimminger and Witthohn, 1993; Shah et al., 2000). Sennosides A and B are stereoisomers. The structure of rhein is similar to danthron, the laxative withdrawn from the market due to possible carcinogenic activity in humans (FDA, 1999; NTP, 2004).

Production, Use, and Human Exposure

Pods and leaves are harvested three times after sowing and dried in shade (Patra et al., 2005). Commercial senna comes from Egypt, Sudan, and India (Blumenthal, 2000). From April 2004 through March 2005, India exported 719,570 kg of senna leaf and pod to the United States (ITC, 2006). From April through September of 2006, India exported 319,900 kg of senna leaf and pod to the United States (ITC, 2007).

Senna is available in over-the-counter laxatives and is classified as a stimulant laxative (Leng-Peschlow, 1992; 21 CFR § 310.545; Rao, 2009). In the United States, senna is available as a tablet (sennosides), fluid extract, leaf, pod, oral solution, or tea (Cupp, 2000). Senna is used clinically for management of constipation resulting from opioid use or when treatment with bulking or osmotic agents has failed (Agra et al., 1998; Foxx-Orenstein et al., 2008; Bouras and Tangalos, 2009). In 1999, due to findings of carcinogenic activity in experimental animal models, the FDA reclassified the stimulant laxatives phenolphthalein and danthron as category II (21 CFR § 310.545) and declared them unsafe for use as over-the-counter laxatives (FDA, 1999). Therefore, it was expected that use of senna as a laxative would increase.

As a laxative, the adult daily dose of senna is 0.5 to 2 g, or 12 to 60 mg of sennosides as a single dose at bedtime. The recommended daily dose is 8.8 to 26.4 mg sennoside in children aged 6 to 12 years and 4.4 to 13.2 mg in children aged 2 to 6 years (Martindale, 1999; PDR for Herbal Medicines, 2007; Novartis, 2010).

In the United States, 2% to 28% of the population suffers from constipation (Higgins and Johanson, 2004). An estimated 7.95 million ambulatory care visits annually (0.18% of the total annual ambulatory care visits) during the period from 2001 to 2004 were for treatment of constipation with 4.6% of patients receiving prescriptions for stimulant laxatives (Shah et al., 2008). The estimated United States population using senna in 2002 was 361,000 (0.9%) (Kennedy, 2005). In the United Kingdom, senna-based products accounted for 23% of laxative use (Heaton and Cripps, 1993). A study of 1,012 patients in Seattle with functional bowel disorders found that 2.4% of those with irritable bowel syndrome and 8.2% of those with functional constipation used senna (van Tilburg et al., 2008). The prevalence of constipation in children is 0.7% to 29.6% (Van den Berg et al., 2006). In interviews with 107 caregivers of African-American children under 2 years of age, seen in a pediatric clinic, 4.7% reported using senna extract to treat colic (Smitherman et al., 2005). Women have approximately a twofold higher prevalence of constipation than men (Higgins and Johanson, 2004). During pregnancy, up to 40% of women have constipation (Cullen and O’Donoghue, 2007). In a study of 3,354 women in the Quebec Pregnancy Registry, 0.4% of pregnant women reported taking senna (Moussally et al., 2009). Adults over age 65 may have a higher risk of constipation (Higgins and Johanson, 2004); this population uses stimulant laxatives more often than bulk laxatives or stool softeners (Ruby et al., 2003). In a survey of 338 geriatric clinic patients aged 65 or older, 1.8% reported using senna tea (Cherniak et al., 2008). A high dose of senna (1 mg/kg, up to 158 mg, of sennosides) is used for cleansing the bowel in preparation for a colonoscopy or surgery (Kleibeuker et al., 1995; Martindale, 1999; Occhipinti and Di Palma, 2009). Senna’s use as a laxative is also listed by the International Association for Hospice and Palliative Care as one of the essential medicines for palliative care (De Lima and Doyle, 2007). Extract of senna leaf is also listed in the European Commission Database (2010) as a skin conditioner.

Regulatory Status

Senna is considered a dietary supplement as specified by the Dietary Supplement Health and Education Act (DSHEA) of 1994 and the DSHEA places dietary supplements in a special category under the general umbrella of “foods” (FDA, 1994). The FDA lists Alexandrian senna (Cassia acutifolia Delile) as a natural flavoring substance for use in food (21 CFR § 172.510). As of November 1993, senna is listed as an over-the-counter category III (safety and effectiveness are not yet established) digestive aid (21 CFR § 310.545; 21 CFR Part 334) Senna is designated pregnancy-category C because no animal reproduction studies and no adequate and well-controlled reproduction studies in humans are available (Tillett et al., 2003; Prather, 2004).

Absorption, Distribution, Metabolism, and Excretion

Experimental Animals

The pharmacological activity of senna is associated with sennosides A and B, the most abundant anthranoids and the precursors of the active metabolite, rhein anthrone (also known as rhein-9-anthrone) (Breimer and Baars, 1976; Sasaki et al., 1979; Lemli and Lemmens, 1980, Hietala et al., 1987; de Witte, 1993; Franz, 1993; Figure 2). The in vivo fate of the sennosides and the other senna anthranoids are described here. Sennosides are not readily absorbed from the mammalian gut; therefore, the activity depends on formation of rhein anthrone following deconjugation and reduction (Figure 2) by microflora in the large intestine (Breimer and Baars, 1976; Sasaki et al., 1979; Lemli and Lemmens, 1980; Dreessen et al., 1981). Lemli and Lemmens (1980) postulated that rhein anthrone arises through formation of a free radical following reduction of sennidin in the gastrointestinal tract. The systemic bioavailability of rhein anthrone is low, putatively due to limited absorption associated with binding to gut contents and rapid oxidation to rhein and sennidin once it is absorbed (Lemli and Lemmens, 1980; Grimminger and Leng-Peschlow, 1988; de Witte, 1993). Lemli and Lemmens (1980) recovered less than 4% of an oral dose Small amounts of free anthraquinones and their glycosides are present in senna (Franz, 1993; Newall et al., 1996; Figure 1; Appendix D), including rhein. Absorption of rhein from the rat gut appears to be greater than absorption of rhein anthrone (de Witte and Lemli, 1988). The cumulative urinary excretion of a single dose of 14C-labeled rhein or 14C-labeled rhein anthrone over 5 days was 37.1% and 2.8%, respectively. Rhein was primarily excreted as glucuronide and/or sulfate conjugates. Most of the rhein anthrone-derived 14C excreted in urine was recovered as rhein following oxidative hydrolysis and extraction of the urine. In a separate study, rhein-derived 14C was highest in the tissues of the gastrointestinal tract in gavaged rats (Lang, 1988). Other tissues contained low levels of radioactivity 7 days following dosing, probably due to protein binding in the blood. The total absorbed dose was estimated to be 50% and was excreted in urine, primarily as conjugates. In a study conducted by Dahms et al. (1997), specific metabolites, mostly glucuronide and sulfate conjugates, were identified in the urine of rats, rabbits, and dogs receiving oral doses of 14C-labeled rhein. Qualitative and quantitative differences in rhein metabolism were observed between species. For instance, rabbit urine contained a glucuronide conjugate of a potentially reactive quinoid metabolite, not evident in the urine of the other species.

Figure 2. Metabolism of Sennosides A and B in Mammals.

Figure 2

Metabolism of Sennosides A and B in Mammals. (Adapted from Lemli and Lemmens, 1980 and Dahms et al., 1997. R, R1, and R2 are H, glucuronic acid, or sulfate; Glu=glucose)

The kinetics of anthraquinones were investigated following oral administration of senna-containing products to rats (Mengs et al., 2004; Mitchell et al., 2006). Concentrations of rhein and aloe-emodin were determined in the blood of rats at various time points on days 90 and 91 of a 13-week gavage study (100 to 1,500 mg/kg) of powdered Tinnevelly senna fruit (Mengs et al., 2004). The concentrations in plasma were proportional to dose from 100 to 750 mg/kg, and were generally higher in females than in males. Chrysophanol was detected in some plasma samples. Blood was sampled at 6, 12, and 24 months in a 2-year oral carcinogenicity study in rats receiving powdered Tinnevelly senna fruit (25 to 300 mg/kg) (Mitchell et al., 2006). In the study, emodin and chrysophanol were generally not detected and aloe-emodin was only detected in the plasma of the high-dose group. Concentrations of rhein were higher in females at 6 and 12 months, but were similar to males at 24 months. In a radiolabeled study of aloe-emodin in gavaged rats, the 14C was absorbed, distributed to all assayed tissues, and 30% of the total dose was excreted in urine as rhein, an unidentified metabolite, and their conjugates (Lang, 1993). The remainder of the dose was excreted in feces. The biotransformation of emodin and chrysophanol were investigated in induced liver microsomes from male and female rats (Mueller et al., 1998). Emodin was metabolized to omega-hydroxyemodin and 2-hydroxyemodin; whereas chrysophanol was metabolized to emodin.


Kobashi et al. (1980) demonstrated that sennosides could be converted to rhein anthrone by specific cultured bacteria strains from the human intestine. Further, Hattori et al. (1993) demonstrated cleavage of the O-glucosyl bond of sennoside B, reduction of sennidin B, and accumulation of rhein anthrone in a coculture of two bacteria strains isolated from human feces.

Concentrations of rhein and aloe-emodin were determined over time in plasma of human volunteers receiving four daily therapeutic doses of either of two senna-containing laxatives (Krumbiegel and Schulz, 1993). No aloe-emodin was detected in any samples. Two peak concentrations of rhein were observed in plasma following each dose, one at 3 to 5 hours and the other at 10 to 11 hours. The authors postulated that the first peak arose from the presence of free or glycosylated rhein in the products and the second peak represented rhein derived from sennosides. In addition to work in animals, Dahms et al. (1997) investigated the metabolism of rhein in human volunteers receiving an oral dose of 14C-labeled diacetylrhein. Diacetylrhein was converted to rhein by gut microflora. Some rheinderived glucuronide and sulfate conjugates excreted in the urine of humans were common to the urine of rats, rabbits, and dogs receiving oral doses of 14C rhein. However, potentially reactive metabolites (i.e., quinoids and diglucuronides) observed in some animals were not present in human urine, and the radioactivity in human serum was highly extractable over time indicating little potential for protein binding.


The glucose in sennosides gives characteristics of a prodrug for laxative effect. Glucose makes the molecule hydrophilic. Therefore, absorption of sennosides is prevented before they reach the target organ (the large intestine). Sennosides precipitate at low pH levels in the stomach further inhibiting absorption (de Witte, 1993; van Gorkom et al., 1999). Due to their β-glycosidic bond, sennosides are not hydrolyzed in the stomach or in the small intestine. Normal microflora in the large intestine are important for the laxative effect of senna. For example, oral administration of sennoside A produced a laxative effect in conventional male and female C3H mice but not in germ-free male and female C3H mice (Dreessen et al., 1981). Sennosides A and B are metabolized by bacteria in the large intestine to rhein-9-anthrone, the active form for laxative effect (Dreessen et al., 1981; Grimminger and Leng-Peschlow, 1988). Sennidins A and B, rhein-9-anthrone, and small amounts of rhein were produced from sennosides A and B incubated with cecal extracts from conventional female Fischer rats, whereas incubation with cecal extracts from germ-free female Fischer rats produced no metabolites (Dreessen et al., 1981). Further, incubation of sennidins A and B with cecal extracts from conventional female Fischer rats produced rhein-9-anthrone and small amounts of rhein; however, no rhein-9-anthrone was detected upon incubation of sennidins with cecal extracts from germ-free female Fischer rats. Rhein-9-anthrone was relatively stable in the rat large intestine in the presence of bacteria but oxidized readily in germ-free rats and in buffers (Dreessen et al., 1981; Grimminger and Leng-Peschlow, 1988). In female albino mice, the ED50s of intracecal administration of rhein anthrone, rhein, and aloe-emodin were 11.4, 91.0, and 246.3 µmol/kg, respectively (Yagi and Yamauchi, 1999). Aloe-emodin anthrone has a weaker laxative effect than rhein anthrone. However, intracecal administration of an equimolar mixture of aloe-emodin anthrone and rhein anthrone produced a synergistic laxative effect in female albino mice (Yagi et al., 1997).

A laxative effect is driven by increasing peristalsis and reduced absorption of water and electrolytes (Leng-Peschlow, 1986). In female Wistar rats, oral administration of 50 mg/kg sennosides reduced large intestinal transit time. Intracecal administration of equimolar doses of sennosides A+B, sennidins A+B, and rhein-9-anthrone produced similar responses in reduced large intestine transit time and increased soft feces (Leng-Peschlow, 1988). Application of rhein anthrone on mucosa of isolated guinea pig ileum dose-dependently increased parameters of peristaltic reflex (longitudinal muscle tension, intraluminal pressure, and volume displacement) (Nijs et al., 1993). In isolated large intestine from male Wistar rats, application of rhein (1 mM) in the lumen increased contractility in the colon, the number of migrating contractions, and fluid flow (Rumsey et al., 1993). In humans, intraluminal introduction of senna, which was preincubated with feces or Escherichia coli, produced peristalsis within 1 hour. Intraluminal application of rhein anthrone also produced peristalsis within 1 hour (Hardcastle and Wilkins, 1970). Oral administration of sennosides in rats in vivo, as well as application of rhein on the mucosal side of isolated rat colon in vitro, decreased absorption of water and sodium; enhanced secretion of water, sodium, and potassium; and reduced Na+, K+-ATPase activity (Leng-Peschlow, 1986, 1989, 1993; Wanitschke and Karbach, 1988). In addition, in humans, perfusion with rhein reversed absorption of water and sodium into secretion in the jejunum and colon, increased chloride secretion in the jejunum, reduced chloride absorption in the colon, and enhanced potassium secretion in the jejunum and colon (Ewe, 1980).


Experimental Animals


The LD50 of senna has not been reported in the literature. Administration of senna induced soft feces and diarrhea, increased water consumption, and reduced body weight gain in rats. Male Wistar rats fed a diet containing 10% senna for 3 or 6 weeks exhibited diarrhea, decreased food intake, and decreased body weight gain compared to controls (Al-Yahya et al., 2002). Oral administration of senna (750 mg/kg or greater) to Sprague-Dawley rats for 13 weeks increased soft feces and water consumption in males and females and reduced body weight gain in males (Mengs et al., 2004).

Male Wistar rats fed a diet containing 10% senna for 3 or 6 weeks had an increased serum index of liver toxicity (alanine aminotransferase and aspartate aminotransferase) and increased urea in serum along with slight degenerative changes in the liver, kidney, and intestines but decreased calcium levels in serum and decreased white blood cell counts compared to controls (Al-Yahya et al., 2002).

Administration of up to 1,500 mg/kg senna for 13 weeks decreased sodium in urine and increased kidney weights in 1,500 mg/kg male and 750 and 1,500 mg/kg female Sprague-Dawley rats compared to controls (Mengs et al., 2004). Minimal to slight hyperplastic changes in the mucosa of the large intestine in rats receiving more than 100 mg/kg of senna and minimal to slight hyperplastic epithelium of the forestomach in rats receiving 1,500 mg/kg were observed. These hyperplastic changes were reversible. Hyperplastic changes were not observed in animals 8 weeks after the 13 weeks of senna administration ended. Several studies in the literature have examined the relationship between the use of senna and damage in the enteric nervous system of the colon. For example, a study by Smith (1968) observed damage to intestinal nerves of mice given senna syrup. However, other rodent studies failed to show damage in the enteric nervous system of the colon after ingestion of senna or sennosides (Dufour and Gendre, 1984; Rudolph and Mengs, 1988; Mengs et al., 2004; Mitchell et al., 2006).

Senna Extract

In mice, the estimated LD50 of senna extracts (calcium sennosides A+B, 20%) administered by gavage was greater than 2.5 g/kg (Marvola et al., 1981). Administration of senna extract also showed a laxative effect and reduced body weight gain in rats. Wistar rats administered 100 mg/kg of senna extract (50% sennoside B) by mouth for 13 weeks had reduced body weight gain and increased water content in feces compared to controls (Mascolo et al., 1999).


For sennosides administered by gavage, the estimated LD50 was greater than 5 g/kg for mice and was greater than 3.5 g/kg for rats (Marvola et al., 1981; Mengs, 1988). In rodents, administration of sennosides produced laxative effects and diarrhea, increased water consumption, and decreased body weight gain compared to controls. In male and female Wistar rats, administration of 25 mg/kg sennosides produced a laxative effect and administration of 100 mg/kg for 6 months induced diarrhea and decreased body weight gain by approximately 50% compared to controls. Single administration of sennosides (2 to 7.5 g/kg) to male and female Wistar rats produced diarrhea, sedation, hunched posture, piloerection, and death (Mengs, 1988). Male Sprague-Dawley rats fed a diet containing 0.2% sennosides for 56 days had diarrhea, reduced body weight gain, and decreased survival compared to controls (Mereto et al., 1996). In NMRI mice, oral administration of 9.35 mg/kg of sennosides induced a laxative effect and 2.5 g/kg of sennosides induced diarrhea (Dufour and Gendre, 1984; Mengs, 1988). A mild laxative effect was induced in male NMRI mice fed a diet containing 0.03% sennosides (86% sennosides) for 20 weeks (Siegers et al., 1993a).

Mild kidney effects of sennosides have been observed. In male and female Wistar rats treated with 2 to 20 mg/kg sennosides for 4 weeks, no changes in hematological, biochemical, or urinary parameters were observed (Mengs, 1988). However, in 20 mg/kg rats, mean kidney weights were higher than that of the control group and small sudanophilic globules within the convoluted tubules of the kidney were observed. In male Wistar rats administered 25 or 100 mg/kg sennosides for 6 months, no hematological or urinary changes were observed, but increased kidney weights as well as dose-related basophilia of convoluted renal tubules were observed.

In male F344 rats fed sennoside A (0.006% to 0.05%) for 7 days, cell proliferation in the colorectum was increased and inflammatory changes in the large intestine were observed (Toyoda et al., 1994). However, in female Wistar rats, administration of 30 mg/kg sennosides for 12 weeks did not affect cell proliferation in the large intestine (Geboes et al., 1993). Administration of 50 mg/kg sennosides did not affect lactic acid dehydrogenase release into the colon lumen of female Wistar rats (Leng-Peschlow, 1993). In male Wistar rats, administration of sennosides (10 or 40 mg/kg) for 23 weeks did not affect the duration or frequency of the long-spike burst in the large intestine in vivo (Fioramonti et al., 1993).


Toxicity studies of emodin in feed were conducted in male and female F344/N rats and B6C3F1 mice (NTP, 2001). Rats were administered up to 50,000 ppm emodin in feed for 16 days. Males and females exposed to 5,500 ppm or greater had reduced body weights compared to controls. Males and females exposed to 17,000 ppm or greater had reduced feed consumption and microscopic kidney lesions. Rats were administered up to 5,000 ppm emodin for 14 weeks. Males exposed to 2,500 ppm or greater and females exposed to 1,250 ppm or greater had reduced body weights compared to controls. Mice were fed diets containing up to 50,000 ppm emodin for 16 days. All mice exposed to 50,000 ppm died before the end of the study. Males and females exposed to 17,000 ppm lost weight during the study. Females receiving 5,500 ppm had greater feed consumption than controls. Males and females exposed to 17,000 ppm had microscopic lesions in the gallbladder and kidney. Mice were fed diets containing up to 5,000 ppm emodin for 14 weeks. Males exposed to 2,500 ppm or greater had reduced body weights compared to controls. In males and females exposed to 1,250 ppm or greater, incidences and severities of nephropathy were increased.



Administration of senna can cause adverse effects such as abdominal cramps and diarrhea in humans (Langmeade and Rampton, 2001).

Three cases of hepatitis were associated with excessive use of senna (Beuers et al., 1991; Seybold et al., 2004; Vanderperren et al., 2005). In two cases, the causal relationship between senna and hepatitis was demonstrated by a change in serum liver test indexes after reexposure of the patients to senna (Beuers et al., 1991; Seybold et al., 2004).

Allergic reactions were induced by senna exposure. A 21-year-old man developed IgE-mediated asthma and rhinoconjunctivitis 5 months after he started handling senna at a hair-dye manufacturer (Helin and Mäkinen-Kiljunen, 1996). The patient’s IgE was specific to protein in crude senna. The patient became asymptomatic upon changing jobs within the factory. At an Australian pharmaceutical manufacturer of laxatives, 15.3% of workers were sensitized to senna (Marks et al., 1991). Incidences of allergic symptoms (upper respiratory tract, eye, and skin) except asthma were higher in workers than in a reference population. In children wearing diapers, unintentional ingestion of senna-containing laxatives was related to severe diaper rash, blisters, and skin sloughing (Spiller et al., 2003).


Stomachache was experienced in 20% of people who took sennosides (Steffen et al., 2006). Treatment with sennosides also caused changes in the colon in humans. Treatment with sennosides A and B (2 mg/kg, maximum 150 mg) substantially increased colonic epithelial cell proliferation compared to untreated controls (Kleibeuker et al., 1995; van Gorkom et al., 2000). At 6 hours after treatment with sennosides A and B (2 mg/kg, maximum 150 mg), more apoptotic bodies in the superficial lamina propria and more intense p53 staining in colonic epithelial crypt cell nuclei were observed in colon biopsies than in untreated controls (van Gorkom et al., 2001).

Like senna, sennosides caused skin irritation in chronic users. A 70-year-old woman who used sennosides for a year developed recurrent pruritic erythema; a patch test showed sennosides to be the causative agents (Sugita et al., 2006). A 55-year-old woman who had taken sennosides for 20 years had suffered from pruritic scaly erythematous plaques for 2 years (Fujita et al., 2004). Withdrawal of sennosides improved her symptoms and similar lesions emerged upon reexposure to sennosides.

Reproductive and Developmental Toxicity

Experimental Animals


Detectable levels of rhein were found in milk after administration of sennosides to monkeys (Cameron et al., 1988). Female Wistar rats were administered diarrhea-inducing oral doses of sennosides (50 to 100 mg/kg) from gestation days 6 to 16; body weight gain was reduced but the numbers of implantation sites, resorption sites, fetuses, and fetal malformations and fetal weight were not affected (Mengs, 1986). White Russian rabbits were administered oral doses of 2, 10, or 20 mg/kg sennosides from gestation days 6 to 18; there was no effect on the numbers of resorption sites, fetuses, or fetal malformations or on fetal weight but body weight gain was decreased in the 20 mg/kg group compared to controls (Mengs, 1986). Female Wistar rats were administered a laxative dose of sennosides (20 mg/kg) from the last third of gestation to the fifth week postpartum; there were no effects on the weight gain in dams, gestation length, litter size, pup weight at birth, or pup weight or survival at 5 weeks (Mengs, 1986). Mengs (1986) also tested the effect of sennosides on fertility in rats. Male rats were treated with 2, 10, or 20 mg/kg sennosides for 10 weeks before mating and female rats were treated with 2, 10, or 20 mg/kg sennosides from 2 weeks before mating to the end of lactation. There were no effects on gestation length, the numbers of implantation or resorption sites, litter size, pup weight at birth, or pup weight or survival at 4 weeks. Pregnant ewes received intracolonic administration of sennosides (60 mg/kg) one to three times at intervals of 7 to 10 days between 75 and 125 days of pregnancy; a laxative effect and reduced uterine motility resulted, but there was no effect on the pregnancy or the fetus (Garcia-Villar, 1988).


In female F344/N rats exposed to 1,250 or 5,000 ppm emodin for 14 weeks, significant increases in estrous cycle lengths were observed (NTP, 2001).

Developmental toxicity of emodin was evaluated in Sprague-Dawley rats and Swiss albino mice (Jahnke et al., 2004). In rats administered up to 1,700 ppm emodin in feed from gestation day 6 to gestation day 20, negative trends in maternal weight gain and feed consumption were observed. However, there were no effects on prenatal mortality, average live litter size, or incidences of fetal malformations or variations. In mice administered up to 6,000 ppm emodin in feed from gestation day 6 to gestation day 17, decreased maternal body weight gain and increased maternal water consumption were observed in the 6,000 ppm group. The only prenatal toxicity was reduced fetal body weight in the 6,000 ppm group. However, there were no effects on incidences of fetal malformations or variations in mice.



The FDA lists senna in pregnancy category C (safety in human pregnancy has not been determined) because there are no adequate reproduction studies available (Tillet et al., 2003; Prather, 2004). Senna is still used for constipation during pregnancy (Moussally et al., 2009). A study of the Hungarian Case Control Surveillance of Congenital Abnormalities database showed that treatment with senna during pregnancy did not increase the risk of congenital abnormalities, and increasing the length of senna exposure during pregnancy did not increase the risk of congenital abnormalities (Ács et al., 2009). Rhein, a metabolite of senna, has been excreted in milk of lactating mothers (Faber and Strenge-Hesse, 1988). However, there are no studies reported in the literature on any developmental effects of senna.


Experimental Animals


Mitchell et al. (2006) studied the carcinogenicity of senna in male and female Sprague-Dawley rats. Rats were administered 25, 100, or 300 mg senna/kg body weight by gavage for 2 years (60 rats per sex per group). Body weights were slightly reduced in 300 mg/kg females. Feed consumption was not affected by senna administration. In 300 mg/kg groups, mucoid feces and darker urine were observed. During the first 65 weeks, increased water consumption was observed in the 300 mg/kg groups. There were changes in electrolytes in serum (increased potassium and chloride) and urine (decreased sodium, potassium, and chloride) in the 300 mg/kg groups. At the end of the study, complete histopathology examinations of control and high-dose groups and histopathology examinations of the intestinal tract, adrenal gland, liver, kidney, brain, and gross lesions in the low- and mid-dose groups were conducted. There were no treatment-related increases in the incidences of neoplasms. However, dose-dependent epithelial hyperplasia of the large intestine and pigment deposition in the kidney were observed.

Senna Extract

Administration of 30 or 60 mg/kg senna pod extract (50% sennoside B) for 110 weeks increased fecal water content, reduced weight gain, and produced no aberrant crypt foci or tumors in the colon of male Wistar rats (Borelli et al., 2005). Sprague-Dawley rats were administered 5, 15, or 25 mg/kg senna extract (35.7% sennosides) in drinking water for 2 years; compared to controls, a laxative effect was induced at 25 mg/kg, reduced body weight gains occurred at 25 mg/kg, and reduced water intake occurred at 15 and 25 mg/kg, but survival and neoplasm incidences were not affected (Lydén-Sokolowski et al., 1993).

The effect of senna extract on azoxymethane-treated rats is controversial. Mascolo et al. (1999) showed that while a laxative-producing dose of senna pod extract (10 mg/kg) administered to male Wistar rats for 13 to 28 weeks did not promote the formation of tumors induced by azoxymethane, a diarrhea-producing dose (100 mg/kg) administered for 13 weeks increased the incidence and multiplicity of tumors induced by azoxymethane. However, oral administration of 30 or 60 mg/kg senna pod extract for 2 years to male Wistar rats treated with the initiating agent azoxymethane (7.5 mg/kg, intraperitoneal) decreased the formation of aberrant crypt foci and colon tumors compared to animals that received azoxymethane alone (Borrelli et al., 2005).


A diet containing 0.03% sennoside (86% sennosides) fed to male NMRI mice for 20 weeks did not induce colorectal tumors; the same diet for 20 weeks with concurrent administration of dimethylhydrazine (20 mg/kg, subcutaneous) for 10 weeks did not promote formation of colorectal tumors (Siegers et al., 1993a).

The numbers and multiplicities of aberrant crypt foci were not affected in dimethylhydrazine-treated male Sprague-Dawley rats fed a 0.1% sennoside-containing diet; rats fed a diarrhea-inducing level of the sennoside-containing diet (0.2%) exhibited a significantly increased number of crypts/foci compared to controls (Mereto et al., 1996).


Dermal application of aloe-emodin (10 µg/mL) before or after UVB (15 kJ/m2) radiation on C3H/HeNCr (MTV) mice did not significantly change the total number of neoplasms or the latency of neoplasm development (Strickland et al., 2000).


Male and female F344/N rats were exposed to up to 2,500 ppm emodin in feed for 2 years (NTP, 2001). Three of 50 females in the 2,500 ppm group had Zymbal’s gland carcinomas. In these studies, male B6C3F1 mice were exposed to up to 625 ppm emodin and female mice were exposed to up to 1,250 ppm emodin for 2 years. The incidences of nephropathy were significantly increased in all exposed groups of females; the incidences of renal tubule pigmentation were significantly increased in all exposed groups and the severity of the lesion increased with increasing exposure concentration.


Studies in the literature suggest that there may be an association between laxative use and colon cancer in humans (Siegers et al., 1993b; Satia et al., 2009). For example, findings from an epidemiology study revealed that more patients with gastrointestinal cancer were senna users than patients without cancer and patients without gastrointestinal disease (Boyd and Doll, 1954). However, the relationship between senna use and colon cancer has not been clearly demonstrated.

Genetic Toxicity

The genetic toxicity of senna products was reviewed in detail by Brusick and Mengs (1997). These authors concluded that most studies of the genetic toxicity of senna products gave negative results, but results from some studies indicated that certain components of senna products, particularly emodin and aloe-emodin, are genotoxic. However, these authors suggested that an overall assessment of the genotoxicity profile of senna, its constituents, and its metabolites, in light of other data from animal and human metabolism or kinetic studies, human clinical trials, and rodent carcinogenicity studies, did not support an increased risk for genotoxicity of senna laxatives in humans when these products were consumed under prescribed-use conditions.

Senna Aqueous Extract

Senna extract (aqueous) did not induce trp+ revertants in Escherichia coli (Silva et al., 2008). There are contradictory results in the literature concerning the ability of senna to induce mutations in Salmonella typhimurium. Al-Dakan et al. (1995) reported a negative response in TA98, whereas Heidemann et al. (1993) showed that senna extract induced his+ revertants in TA98, with and without liver microsomes (S9), and in TA1537 in the absence of S9. Sandnes et al. (1992) reported that extracts of senna folium and senna fructus induced significant dose-related increases in mutations in S. typhimurium strains TA97a, TA98, TA100, and TA102 in the presence of S9; in the absence of S9, mutagenicity was observed in TA97a and TA102. The extract also induced structural chromosomal changes in cultured Chinese hamster ovary (CHO) cells in the presence and absence of S9 (Heidemann et al., 1993). In Chinese hamster lung V79 cells, senna did not induce mutations at the hgprt locus in the presence of S9; in its absence, the results were equivocal (Heidemann et al., 1993). In vivo, senna aqueous extract (2,000 mg/kg, single oral administration) did not induce micronuclei in bone marrow polychromatic erythrocytes of male or female NMRI mice sampled 24 and 48 hours after treatment (Mengs et al., 1999).

Sennosides A and B

The sennosides were generally negative in most genotoxicity tests reported. Sennosides (up to 5,000 µg/plate) did not induce his+ revertants in S. typhimurium strains TA97, TA97a, TA98, TA100, TA1537, or TA1538, or in E. coli, with or without S9 (Mengs, 1988; Sandnes et al., 1992; Heidemann et al., 1993). However, a positive response was reported in S. typhimurium strain TA102, with and without S9 (Sandnes et al., 1992). No mutations were observed at the tk locus in mouse lymphoma cells treated with sennosides (up to 3,000 µg/plate), nor did these glycosides induce chromosomal aberrations in CHO cells exposed to up to 5,000 µg/mL without S9 or 4,000 µg/mL with S9 (Mengs, 1988; Heidemann et al., 1993).

In mice treated with sennosides at doses up to 2,500 mg/kg per day, there were no increases in the frequencies of micronucleated polychromatic erythrocytes and no effect on the ratio of polychromatic to normochromatic erythrocytes (Mengs, 1988, Heidemann et al., 1993). However, a slight elevation in structural chromosomal aberrations was observed in bone marrow cells of mice treated with sennoside B (Mukhopadhyay et al., 1998).


Aloe-emodin was mutagenic in S. typhimurium strains TA97a, TA98, TA100, TA1537 and TA1538, but not in TA102, with and without S9 (Brown and Dietrich, 1979; Westendorf et al., 1990; Kawasaki et al., 1992; Sandnes et al., 1992; Heidemann et al., 1993; Nesslany et al., 2009). In vitro, aloe-emodin induced tk−/− mutants in mouse lymphoma L5178Y cells and human TK6 lymphoblastoid cells, DNA damage as measured by the comet assay, and micronuclei in mouse lymphoma L5178Y cells (Müller et al., 1996; Mueller et al., 1998; Nesslany et al., 2009). DNA damage, measured by the comet assay, was also reported in H460 human lung carcinoma cells exposed to aloe-emodin (Lee et al., 2006). Aloe-emodin induced unscheduled DNA synthesis in male Wistar rat hepatocytes as well as transformed foci in C3H/M2 mouse fibroblasts (Westendorf et al., 1990). The literature is contradictory concerning the ability of aloe-emodin to induce hgprt mutations in Chinese hamster lung V79 cells (Westendorf et al., 1990; Heidemann et al., 1993, 1996). Aloe-emodin induced chromosomal aberrations in CHO cells (Heidemann et al., 1993, 1996). In mice, aloe-emodin induced DNA damage in kidney and colon cells (Nesslany et al., 2009) but did not induce unscheduled DNA synthesis or chromosomal aberrations in Wistar rats nor micronuclei in polychromatic erythrocytes of male and female mice (Heidemann et al., 1993, 1996).


No increase in the frequency of cells with chromosomal aberrations was observed in cultured Chinese hamster ovary cells exposed to chrysophanol, with or without S9 (Mengs et al., 2001).

Rhein (1,8-dihydroxy-3-carboxyl anthraquinone)

Rhein was not found to be mutagenic in S. typhimurium strains TA97a, TA98, TA100, TA1535, or TA1538, with or without S9, or in TA1537 in the absence of S9. However, there are contradictory results with rhein in TA1537 in the presence of S9 and in TA102 with or without S9 (Westendorf et al., 1990; Sandnes et al., 1992; Heidemann et al., 1993; Makena and Chung, 2007). Rhein failed to induce tk−/− mutations in mouse L5178Y lymphoma cells, hgprt mutations in Chinese hamster lung V79 cells, chromosomal aberrations in CHO cells, unscheduled DNA synthesis in male Wistar rat hepatocytes, or transformed foci in C3H/M2 fibroblasts (Westendorf et al., 1990; Sandnes et al., 1992; Heidemann et al., 1993).

Rhein (1,500 mg/kg single oral administration) also failed to induce micronuclei (polychromatic erythrocytes) in bone marrow cells of male NMRI mice sampled 24, 48, or 72 hours after treatment (Heidemann et al., 1993; Mengs and Heidemann, 1993). However, a single oral administration of rhein (2 mg/kg) was reported to induce a small, dose-related increase in the frequency of chromosomally aberrant cells in bone marrow of male Swiss mice (Mukhopadhyay et al., 1998).

Background on the Genetically Modified Mouse (GMM) Model Used in the Senna Study

The p53 tumor suppressor gene suppresses cancer in both humans and mice. The p53 protein is critical to cell cycle control, DNA repair and apoptosis, etc., and is often mutated or lost in human and rodent cancers. The haploinsufficient Trp53 tumor suppressor gene mouse model heterozygous for wildtype and null (+/−) Trp53 alleles (Donehower et al., 1992, 1995) was used in these studies. In this model, a Trp53 null mutation was introduced by homologous recombination in AB1 murine embryonic stem cells which were derived from a black agouti 129Sv inbred mouse. By targeted insertion of a polII neo cassette, an engineered null mutation was induced as a result of the deletion of a 450-base pair gene fragment from the Trp53 gene that included 106 nucleotides of exon 5 and approximately 350 nucleotides of intron 4 that eliminated both mRNA and p53 protein expression from this allele. This Trp53 protein haploinsufficient mouse model has been extensively tested as a short-term cancer bioassay mouse model (Tennant et al., 1995; Dunnick et al., 1997; French et al., 2001a,b; Pritchard et al., 2003; French, 2004) based upon the observation that mice with only a single wildtype Trp53 allele show a significant decrease in the time required for genotoxic carcinogen-induced tumors to develop. These tumors are often associated with either a mutation and/or a loss of heterozygosity of the remaining wildtype Trp53 allele. Few to no sporadic tumors occur in concurrent or historical study control groups in this GMM model, which allows tests to be conducted with fewer animals and direct analysis of the target wildtype Trp53 allele to test for genotoxicity in vivo as a mode of action.

For these studies, an outcross between C3H/HeNTac (C3) female mice homozygous for the wildtype (+) Trp53 allele and the C57BL/6.129Sv-Trp53tm1Brd N12 congenic (abbreviated B6.129-Trp53tm1Brd) N12 backcross generation males homozygous for the Trp53 null (−) allele produced C3B6.129F1/Tac-Trp53tm1Brd N12 progeny heterozygous for a Trp53 wildtype (+) and null allele (−) inbred mouse progeny [hereafter referred to in the abbreviated form as the heterozygous F1 p53+/− mouse, Taconic Laboratory Animals and Services (Germantown, NY)]. The heterozygous F1 p53+/− mouse was selected for the 40-week study of senna because the B6.129-Trp53tm1Brd (N5) haploinsufficient male and female mice (backcrossed to C57BL/6, subline unspecified, for two generations and then to C57BL/6NTac females for an additional three generations) were not sufficiently inbred. The N5 generation of this line retained both C57BL/6 and 129Sv strain allele heterozygosity at both the Trp53 locus and the flanking region on chromosome 11 and at unknown loci throughout the genome of this line. This residual heterozygosity in the B6.129-Trp53tm1Brd N5 backcross generation mice was one covariate that may have been responsible for large variations in the p-cresidine induced urinary bladder tumors (0% to 80%, 10 of 11 studies were positive) in males, which was used as a positive control genotoxic carcinogen in the ILSI/HESI Alternatives to Carcinogenicity Testing initiative (Storer et al., 2001). Therefore, additional inbreeding to the N12 generation was anticipated to decrease the variance in tumor incidence and stabilize the penetrance of tumor phenotypes in NTP studies.

The majority of B6.129-Trp53tm1Brd homozygous null females die in utero and only a few are born alive and most die early. Thus, the B6.129-Trp53tm1Brd N12 line is maintained by intercross of the B6.129-Trp53tm1Brd female heterozygote with the B6.129-Trp53tm1Brd homozygous null male to produce a 1:2 population of homozygous null males and heterozygous null males and females. Therefore it is necessary to select the B6.129-Trp53tm1Brd homozygous null male as the carrier of the null allele. However, the selection of the C3H/HeNTac female as the wildtype Trp53 allele carrier provides 1) increased fecundity and maternal instincts, 2) increased hybrid vigor of an F1 outcross that increases the number of progeny, 3) the advantage of expanding the pattern of tumor susceptibility associated with this genetic background, and 4) a genetic background similar to the B6C3F1 mouse used in NTP studies (NTP, 2010). Together, these factors provided a rational basis for selection of this GMM test model. In addition, the NTP study to be reported on 3′-azido-3′-deoxythymidine (AZT) and 3′-azido-3′-deoxythymidine/lamivudine (AZT/3TC), also used the C3B6.129F1/Tac-Trp53tm1Brd N12 haploinsufficient GMM model (NTP, 2012), and the background rate for spontaneous tumors in the control group C3B6.129F1-Trp53tm1Brd haploinsufficient mice in all three studies (AZT, AZT/3TC, and senna) was not statistically different from the background rates for spontaneous tumors observed in control B6.129-Trp53tm1Brd (N5) haploinsufficient mice used in previous NTP GMM studies (NTP, 2005a,b; 2007a,b,c,d,e; 2008).

Study Rationale

Senna was nominated for study by the Center for Drug Evaluation and Research, United States Food and Drug Administration (FDA) due to the wide use of laxative preparations, positive genotoxicity in vitro for some senna components or metabolites, and unknown carcinogenic potential. Increased use of senna was expected due to the removal of danthron and phenolphthalein from the market. Because the 2-year rat study was ongoing by the manufacturer (Mitchell et al., 2006), the FDA requested that the NTP conduct a senna study in the p53+/− mouse.

Copyright Notice

This is a work of the US government and distributed under the terms of the Public Domain

Bookshelf ID: NBK576229


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