Effects of aqueous extracts from Ceratonia siliqua L. pods on small intestinal motility in rats and jejunal permeability in mice

Abstract

The current study was performed to assess the effects of carob pod aqueous extracts (CPAE, pulp, seeds or mixture) on gastrointestinal transit (GIT) and intestinal epithelium permeability. In this aspect, male rats fasted for 16 hours were used and given by oral administration NaCl (0.9%, control group) or various doses of CPAE (50, 100 and 200 mg kg⁻¹, b.w.). Two other groups of rats (batch tests) received clonidine (an alpha-2 adrenergic agonist, 1 mg kg⁻¹) or yohimbine (an alpha-2 adrenergic antagonist, 2 mg kg⁻¹). Two hours later, all animals were given a test meal containing charcoal and gum arabic in water. 30 minutes later, rats were anesthetized, a laparotomy was performed and the distance traveled by the meal compared to the total length of the small intestine was measured. Regarding the effect of CPAE on diarrhoea, the extract was administered orally to three groups of rats (ten in each group). Two other groups received normal saline (10 mL kg⁻¹) and loperamide (10 mg kg⁻¹) as a negative and standard group. Compared with the control group, the animals treated with the CPAE of pulp, seeds or a mixture (50% pulp and 50% seeds) of mature carob, showed a significant increase (3–25%) of GIT in a dose-dependent manner. By contrast, the CPAE of immature carob pods significantly and dose dependently decreased (3–19%) the GIT and diarrhoea (66–87%). However, clonidine and yohimbine respectively decreased (58%) and increased (30%) the GIT. More importantly, using the Ussing chamber system, we found that aqueous extracts of mature and immature carob pods significantly and dose-dependently increased or decreased intestinal epithelium permeability. The results indicate that carob possesses significant laxative and anti-diarrheal activities due to its opposite effects both on gastrointestinal propulsion and permeability. These findings confirm that the degree of maturity of carob characterized by a different phytochemical composition may be responsible for these actions.

---

1. Introduction

Several medicinal plants have been largely used to protect against digestive diseases both in experimental and clinical situations. The carob tree (Ceratonia siliqua L.) has been widely cultivated for years in Mediterranean countries including Tunisia.¹ The chemical composition of carob pods differs widely according to carob species and climate as well as the degree of maturity.² The carob fruit, a brown pod, is known for its richness in sugars, dietary fibers and polyphenols.^3–5 The sugars contained in the pods are almost entirely sucrose, fructose and glucose, but their relative proportions are variable.⁶ Dietary fibers are known for exerting a variety of physiological effects, including improved digestion⁷ and attenuation of blood cholesterol.^8,9 Because the carob juice is rich in electrolytes such as potassium, sodium, iron, copper, manganese and zinc, it is used for the treatment of diarrhea.¹⁰

For this reason, carob extract has several beneficial effects on health such as cholesterol lowering activities in humans suffering from hypercholesterolemia^11,12 and antioxidant properties in different in vitro test systems.^13,14 Its bark and leaves are also used in Turkish folk medicine as an antidiarrheal and diuretic.¹⁵

Constipation and diarrhea are multifactorial gastrointestinal disorders characterized by the disruption of intestinal secretions leading to unexplained abdominal pain, discomfort and bloating in association with altered bowel habits.¹⁶ Constipation frequently affects adults^17,18 and it is a risk factor of colorectal cancer,¹⁹ whereas diarrheal disease is one of the most common causes of morbidity and mortality in many developing countries.²⁰ Anti-secretory, anti-inflammatory agents and some rehydration may be recommended. However the majority of these drugs induce a complication in the gastrointestinal tract of severe diarrhea or constipation leading in some cases to colorectal cancer.²¹ Intestinal transports of water, electrolytes, and nutrient substances maintain homeostasis for organisms and fulfil a nutritive role. There are several aspects of gastrointestinal barrier function, such as ion secretion, permeability, and mucosal secretion.²² The small intestine secretes water and electrolytes under basal conditions and in response to a variety of physiological stimuli, notably following the ingestion of food. Secretion occurs predominantly from the small intestinal crypts. Fluid is required to solubilise complex foods in preparation for digestion and to produce an isotonic absorbate consisting of small molecules by which nutrient absorption can take place. The secretory process is balanced by fluid absorption largely by the villous epithelium.²³

Using Ussing chambers gastrointestinal barrier function can be studied, with a primary focus on gastrointestinal epithelium permeability. Indeed, many researchers consider the Ussing chambers to be the gold standard for determining intestinal barrier function,^22,24,25 which reflects the ability of the gastrointestinal epithelium to protect against invasion by pathogenic antigens.

Hence, the present study aimed to investigate the putative effects of carob pod extracts on gastrointestinal transit, diarrhoea and intestinal epithelium permeability in healthy rats and mice depending on its degree of maturity.

2. Materials and methods

2.1. Chemicals

Clonidine, yohimbine hydrochloride, forskolin, charcoal meal, loperamide and gum arabic were from Sigma-Aldrich Co, St Louis, USA. All other chemicals were of analytical grade.

2.2. Preparation of carob extracts

Carob pods (Ceratonia siliqua L.) were cultivated from the region of Tabarka (North-West of Tunisia) during June and October 2013 and identified by Mrs Mouhiba Ben-Naceur, professor of taxonomy at the Higher Institute of Biotechnology of Béja, Tunisia. The voucher specimens were deposited with the herbarium of the Higher Institute of Biotechnology of Béja and also with the Department of Life Sciences in the Faculty of Sciences of Tunis. Plant material (pulp and seeds) was subsequently dried in an incubator at 50 °C for 72 hours and powdered in an electric blender.

The aqueous extracts were prepared with distilled water (1/5; w/v) under magnetic agitation for 24 h and the homogenate was filtered through a colander (0.5 mm mesh size). Finally, the supernatants were lyophilised (extraction yield = 10%) and stored at −80 °C until use.

2.3. Phytochemical screening

The total content of tannins was determined spectrophotometrically using the method of Folin–Ciocalteu reaction using tannic acid as a standard.²⁶ We used dinitrosalicylic acid (DNS) as a reagent for the determination of total and reducing sugars.²⁷ The fiber content was determined using AOAC method 991.42.²⁸

2.4. Analysis of phenolic compounds using RP-HPLC

Dried samples from the pulp and seeds were hydrolyzed according to the slightly modified method of Proestos et al.²⁹ Phenolic compounds were identified by congruent retention times compared with standards. Analyses were performed in triplicate.

2.5. Animals

Healthy adult male Wistar rats (weighing 220–240 g; housed five per cage) and adult male Swiss Albino mice (weighing approximately 25 g; housed ten per cage) were purchased from the Society of Pharmaceutical Industries of Tunisia (SIPHAT, Ben-Arours, TN). Experimental protocols were approved with the guidelines of the Ethical Committee of the Science Faculty of Tunis, Tunisia. The test was performed in compliance with Commission Directive 2000/32/EC and OECD Guideline 474. They were provided with standard food (standard pellet diet – Badr, Utique, TN) and water ad libitum and maintained in an animal house at a controlled temperature (22 ± 2 °C) with a 12 h light–dark cycle.

2.6. Gastrointestinal propulsion

Six groups of 10 animals each were fasted for 16 h and treated as follows:

Group 1 served as a control and received 1 mL of physiological solution (NaCl, 0.9%, p.o.).

Group 2 received yohimbine (1 mg kg⁻¹, b.w. i.p.).

Group 3 received clonidine (2 mg kg⁻¹, b.w. i.p.).

Groups 4, 5 and 6 were pretreated with various doses of carob pulp extract (50, 100 and 200 mg kg⁻¹, b.w. p.o.).

Groups 7, 8 and 9 were pretreated with various doses of carob seed extract (50, 100 and 200 mg kg⁻¹, b.w. p.o.).

Groups 10, 11 and 12 were pretreated with various doses of carob mixture (50% pulp and 50% seeds; 50, 100 and 200 mg kg⁻¹, b.w. p.o.).

GIT was measured using the charcoal meal test.³⁰ Briefly, two hours after treatment, different groups of rats received the standard charcoal meal (10% charcoal in 5% gum arabic). Animals were anesthetized 30 min later. A laparotomy was performed and the distance traveled by the meal compared to the total length of the small intestine was measured.

2.7. Evaluation of antidiarrheal activity

Rats were divided into six groups of 10 animals each. Groups 1 and 2 served as controls and received bidistilled water (5 mL kg⁻¹, b.w., p.o.). Groups 3, 4 and 5 were pre-treated with various doses of CPAE (50, 100 and 200 mg kg⁻¹, b.w., p.o.), while group 6 was pre-treated with loperamide (10 mg kg⁻¹, b.w., p.o.). After 60 min, each animal, except group 1, received castor oil (5 mL kg⁻¹, b.w., p.o.) by gavage and placed in a separate cage for antidiarrhoeal activity evaluation.

The antidiarrhoeal activity of CPAE was evaluated according to the method of Awouters et al.,³¹ modified by Mukherjee et al.³² Briefly, after castor oil administration, animals were observed for defecation for up to 4 h. Transparent plastic dishes were placed beneath each cage and the characteristic diarrheal droppings were noted.

The intestinal fluid accumulation was determined according to Dicarlo et al.,³³ with some modifications. Briefly, 2 h after castor oil administration, animals were anesthetized with urethane (1.25 g kg⁻¹, i.p.). A laparotomy was performed and the small intestine was removed, after ligation at the pyloric end and ileo-caecal junction, and weighed. The intestinal content was then expelled into a graduated tube and the volume was determined. The small intestine was reweighed and the difference between the full and empty intestine was calculated.³⁴

2.8. Absorptive and secretory process test

Mice were fasted for 16 h with water ad libitum, killed by pentobarbital overdose and the jejunum was dissected out and rinsed in cold saline solution.³⁵ We focused our functional studies on the jejunum, which is the major site of nutrient absorption in the small intestine. The mesenteric border was carefully stripped off, and the serosa was stripped away using forceps. The intestine was then opened along the mesenteric border, and four adjacent proximal samples were mounted in Ussing chambers (exposed area, 0.30 cm²). The tissues were bathed with 3 mL of carbogen-gassed Krebs-Ringer bicarbonate (KRB) solution on each side. In the solution bathing the mucosal side of the tissue, the aqueous extract of carob (mature or immature) was added in various concentrations (50–2000 μg mL⁻¹) with or without an activator of adenylyl cyclase, forskolin (reference molecule, 10 μM), in the serosal side. The measure of the short-circuit current reflects more accurately the secretory and absorptive capacity of the tissue.³⁶

2.9. Statistical analysis

The data were analyzed using one-way analysis of variance (ANOVA) and were expressed as means ± the standard error of the mean (SEM). The data are representative of 10 independent experiments. All statistical tests were two-tailed, and a p value of 0.05 or less was considered significant.

3. Results

3.1. Total tannin and dietary fiber contents

We firstly showed a significant difference between the immature (7.2 mg g⁻¹ dry matter, DM) and mature pulp (4.2 mg g⁻¹ DM). Also, the immature seed extract is more rich in total tannins compared to the mature seeds.

A higher rate of dietary fiber was found in mature pulp (15.2% of DM) compared to immature pulp (6.2% of DM) (p < 0.01). Indeed, the difference is also significant between mature and immature seeds (p < 0.05) (Table 1).

Table 1 Contents of tannins, dietary fiber, and total and reducing sugars in immature and mature carob pods. The data are expressed as means ± standard error of the mean (SEM) (n = 5)

	Immature carob		Mature carob
	Pulp	Seeds	Pulp	Seeds
Tannins (mg g^−1 DM)	7.2 ± 1.3	5.2 ± 0.75	4.2 ± 0.7	2.6 ± 0.5
Dietary fibers (%)	6.3 ± 2.02	6.4 ± 0.7	15.2 ± 1.1	8.6 ± 1.5
Total sugars (g L^−1)	112.5 ± 4.2	98.5 ± 5	242.4 ± 10	106.2 ± 3.4
Reducing sugars (g L^−1)	90.2 ± 6.4	50.2 ± 2.4	48.8 ± 3.2	54.5 ± 4.1

---

3.2. Total and reducing sugars levels

The total sugar content varied between 112 and 242 g L⁻¹ in the immature and mature carob pods, respectively. On the other hand, the levels of reducing sugars varied between 10 and 200 g L⁻¹, respectively, in the immature and mature carob pulp.

It was found that no significant (p > 0.05) difference was observed between the total and reducing sugar values in mature and immature seeds (Table 1).

3.3. Hydrolysis and analysis of phenolic compounds using RP-HPLC

The phenolic compounds detected in CPAE (immature carob) are shown in Table 2. The principal compounds are: pyrogallol (26.45 ± 3.03 and 10 ± 1.43%), catechin (16.52 ± 2.34 and 6.51 ± 1.23%), gallic acid (15.12 ± 2.31 and 1.01 ± 0.06%), tannic acid (4.23 ± 0.74 and 18.81 ± 2.12), chlorogenic acid (15.01 ± 1.72 and 00%) and epicatechin (12.26 ± 1.04 and 00%) (Fig. 1).

Table 2 Identification and quantification of phenolic compounds in immature carob pods by HPLC analysis

	% of phenolic compounds detected
	Pulp	Seeds
1 Tannic acid	4.23 ± 0.74	18.81 ± 2.12
2 Pyrogallol	26.45 ± 3.03	10 ± 1.43
3 Catechin	16.52 ± 2.34	6.51 ± 1.23
4 Chlorogenic acid	15.01 ± 1.72	00
5 Gallic acid	15.12 ± 2.31	1.01 ± 0.06
6 Epicatechin	12.26 ± 1.04	00
7 Vanillic acid	5.33 ± 0.65	3.02 ± 0.15
8 Coumarin	1.24 ± 0.16	00

---

Fig. 1 Chromatographic profiles of aqueous extract of immature carob pods ((A) pulp and (B) seeds).

3.4. Gastrointestinal transit

The results of gastrointestinal transit are shown in Table 3. The water extracts of the pulp, seeds and mixture (50/50%) of mature carob at 50, 100 and 200 mg kg⁻¹ significantly and dose-dependently increased the GIT. The increase ranged from 3 to 25%. On the other hand, the water extract of the pulp, seeds and mixture of immature carob, also at 50, 100 and 200 mg kg⁻¹, significantly and dose-dependently decreased the GIT (3–19%). Moreover, contrasting effects have been observed using clonidine (decreased 58%) and yohimbine (increased 30%) on the GIT assessment.

Table 3 Effect of immature and mature carob extracts and reference molecules on gastrointestinal transit (GIT) in rats^a

		NaCl or reference molecules		Immature carob		Mature carob
		GIT (%)	% of increase or decrease	GIT (%)	% of decrease	GIT (%)	% of increase
a Animals were pre-treated with immature and mature carob extract, reference molecules (yohimbine and clonidine) or vehicle (NaCl 0.9%). Two hours after, rats received the standard charcoal meal (10% charcoal in 5% gum arabic). Values are means + SEM. (n = 10). Values with different superscripts differ significantly from each other (p < 0.05).
Control (NaCl)		72.12 ± 0.77^a	—	—	—	—	—
Yohimbine (2 mg kg^−1)		94.22 ± 3.3^b	30.64	—	—	—	—
Clonidine (1 mg kg^−1)		30.13 ± 2.15^c	58.22	—	—	—	—
Pulp	50 mg kg^−1	—	—	68.32 ± 1.02^a	5.27^1	75.2 ± 1.7^a	4.3^1
	100 mg kg^−1	—	—	62.25 ± 0.95^e	13.7^2	84.5 ± 0.5^d	17.2^2
	200 mg kg^−1	—	—	58.12 ± 1.3^e	19.4^4	90.7 ± 0.53^b	25.7^4
Seeds	50 mg kg^−1	—	—	69.6 ± 0.72^a	3.5^1	72.2 ± 0.63^a	—
	100 mg kg^−1	—	—	66.83 ± 1^a	7.3^3	80.6 ± 0.6^d	11.8^3
	200 mg kg^−1	—	—	60.13 ± 0.8^e	16.6^4	85.3 ± 1.03^d	18.3^2
Mixture (50/50%)	50 mg kg^−1	—	—	69.42 ± 1.35^a	3.7^1	74.2 ± 1.4^a	2.9^1
	100 mg kg^−1	—	—	65.42 ± 0.32^e	9.3^3	82.2 ± 0.5^d	14^3
	200 mg kg^−1	—	—	59.62 ± 1.24^e	17.4^4	86.2 ± 0.73^d	19.5^2

---

3.5. Castor oil-induced hypersecretion

In the present study, we demonstrated that the administration of castor oil (5 mL kg⁻¹, b.w., p.o.) caused copious diarrhea for all rats. However, the pre-treatment of animals with various doses of CPAE (50, 100 and 200 mg kg⁻¹, b.w., p.o.) significantly and dose-dependently reduced the number of defecations. Administration of loperamide (10 mg kg⁻¹, b.w., p.o.), a standard antidiarrheal molecule, produced a more marked antidiarrheal effect but this effect is less than that of the high dose of aqueous extract of pulp. The castor oil caused a significant increase of the volume and the weight of intestinal fluid in rats when compared to the control group while loperamide reduced it to near the control level. The CPAE pre-treatment reduced significantly and dose dependently castor oil-induced enteropooling (Table 4).

Table 4 Effect of carob pod aqueous extract (CPAE) and loperamide on castor oil-induced diarrhea and enteropooling in rats^a

		Dose (mg kg^−1)	Number of faeces in 4 h	Reduction (%)	Intestinal fluid (mL)	Weight of intestinal content (g)	Reduction (%)
a Animals were pre-treated with various doses of CPAE (50, 100 and 200 mg kg^−1 b.w., p.o.), reference molecule (loperamide, 10 mg kg^−1 b.w., o.p.) or vehicle (NaCl, 0.9%). One hour after, animals received castor oil (5 mL kg^−1 b.w., o.p.) by gavage and were observed for defecation and enteropooling for up to 4 h. Results are expressed as mean ± SEM; n = 10 in each group. Data was analyzed using Statview ANOVA. ^a p < 0.05 when compared to castor-oil group. ^b p > 0.05 when compared to control group. ^c p < 0.05 when compared to standard group (loperamide).
	Control	10 mL kg^−1	0.35 ± 0.05	97.31	0.5 ± 0.03	0.33 ± 0.02	91.4
	Castor-oil	5 mL kg^−1	13.5 ± 0.8	—	4 ± 0.2	3.84 ± 0.1	—
Pulp	CPAE-50	50	4.5 ± 0.4^a,b,c	66.7	2.2 ± 0.16^a,b	2.1 ± 0.24^a,b	45
	CPAE-100	100	3 ± 0.4^a,b	77.8	1.72 ± 0.14^a	1.65 ± 0.21^a,b	57
	CPAE-200	200	1.5 ± 0.23^a,b	89.0	0.65 ± 0.12^a,c	0.9 ± 0.15^a,b,c	83.75
Seeds	CPAE-50	50	7.5 ± 0.4^a,b,c	44.4	3.22 ± 0.14^b,c	3.5 ± 0.16^b,c	19.5
	CPAE-100	100	6.5 ± 1^a,b,c	52	2.6 ± 0.21^a,b	2.9 ± 0.26^a,b,c	36
	CPAE-200	200	5 ± 0.4^a,b,c	63.1	1.8 ± 0.15^a,b	1.8 ± 0.15^a,b	56
	Loperamide	10	2 ± 0.6	85.2	1.6 ± 01.15	1.7 ± 0.25	61.25

---

3.6. Effect of carob extracts on intestinal epithelium permeability using the Ussing chamber system

The effect of aqueous extracts of immature and mature carob pods on intestinal epithelium permeability (absorption and secretion) was studied in mice jejunal mucosa in Ussing chambers. The potential difference and short-circuit current (I_sc) were measured in stripped mucosa under voltage-clamp conditions. I_sc measurements during the addition of forskolin (10 μM, serosal addition) showed an increase in the short-circuit current indicating the Cl⁻ channel opening and a drastic increase in the intestinal secretory process. The addition of the aqueous extract of immature carob (pulp and seeds) induced a significant dose-dependent diminution of intestinal secretions with or without forskolin (Fig. 2), in opposition to the aqueous extract of mature carob which results in a significant and dose-dependent increase of intestinal basal secretion and after the addition of the reference molecule (Fig. 3). The effect of the aqueous extract of the immature pulp of carob on absorption is completely reversed to its effect on secretion (Fig. 4).

Fig. 2 Effect of various concentrations of immature carob pod aqueous extract (pulp and seeds) on the basal short circuit current (I_sc) and after forskolin (reference molecule) stimulation in mice jejunum. Means ± SEM of 6 to 8 preparations per group.

Fig. 3 Effect of various concentrations of mature carob pod aqueous extract (pulp) on the basal short circuit current (I_sc) (basal secretion) and after forskolin (reference molecule) stimulation in mice jejunum. Means ± SEM of 6 to 8 preparations per group.

Fig. 4 Effect of various concentrations of immature carob pod aqueous extract (pulp) on basal short circuit current (I_sc) (basal absorption) in mice jejunum. I_sc is expressed as the difference to the basal level (ΔI_sc). Means ± SEM of 6 to 8 preparations per group.

4. Discussion

The gastrointestinal tract is dedicated to processing and absorbing the nutrients and fluids essential for the maintenance of good health.³⁷ A major function of the intestinal epithelium is to control the amount of fluid entering into and being absorbed from the lumen.³⁸ In healthy conditions, net fluid movement follows an absorptive vector, although significant secretion also takes place to subserve digestive function. Thus, the secretion of fluid, driven by the active secretion of electrolytes, is important for maintaining the fluidity of intestinal contents during various stages of digestion and thereby allowing for the diffusion of enzymes and nutrients.³⁹

The Ussing chambers have been used extensively to study nutrient absorption across gut epithelial tissues for a range of different animal species, including rats and mice. It provides a physiologically relevant system for measuring the transport of ions, nutrients, and drugs across various epithelial tissues. One of the most studied epithelial tissues is the intestine, which has been used in several landmark discoveries regarding the mechanisms of ion transport.^8,40 Furthermore, the simplicity of the Ussing chambers makes it an attractive in vitro model system for studying drug transport.^41,42

In the present study, we compared the effects of aqueous extracts of mature and immature carob on GIT and intestinal epithelium permeability in healthy rats and mice.

We firstly found that a water extract of mature carob pods significantly and dose-dependently increased the GIT. However, GIT has been shown to be increased by many plant extracts, such as Musa sapientum leaves,⁴³ Mareya micrantha⁴⁴ and Urginea indica⁴⁵, or isolated molecules such as jatrorrhizine⁴⁶ and melatonin.⁴⁷

Carob pods are widely consumed in our region. It is a common observation that these fruits enhance intestinal motility in humans. The proportions of the contents of the total and reducing sugars in pulp show a great difference between the mature and immature carob pods. This difference seems to exist according to the degree of maturity.

The mechanism of this action has not been investigated, but judging from the chemical composition of pulp and seeds, it seems that the relatively high fiber content may be an important factor in the enhanced GIT. It is established that fiber acts (by a physical action) as a major laxative which causes the acceleration of the process of GIT. In addition, the carob pulp has a high content of total sugar, consisting of mainly sucrose, glucose, fructose and maltose. The presence of sucrose in high concentration may be involved in the increase in GIT.⁴⁸

The aqueous extracts of the pulp, seeds and the mixture (pulp and seeds) of the immature pods of carob induced a significant decrease in the GIT, indicating that the substances responsible for accelerating food transit time in the intestine are absent or present in low quantity. The fact that the extract significantly reduced the distance moved by activated charcoal in the intestines of the treated animals showed that it had a potent relaxant effect on the intestine.

The gastrointestinal motility inhibition of an aqueous extract of Ficus exasperata shown in the animals may be due to the presence of the saponins, tannins and flavonoids.⁴⁹ In addition, we found that immature carob pods are richer in total tannins, suggesting that aqueous extracts of immature carob pods have an astringent property. Tannins are present in many plants and can denature protein to form the protein-tannate complex, which makes the intestinal mucosa more resistant and reduces secretion. The tannins present in the plant extracts may be responsible for the inhibition of GIT and diarrhoea. On the other hand, HPLC analyses were performed and showed that the principal compounds are: pyrogallol (48.02 ± 3.55 and 9.12 ± 2.04%), catechin (19.10 ± 2.11 and 6.25 ± 1.10%) and tannic acid (9.01 ± 1.40 and 19.03 ± 2.13%), in mature pulp and seed compartments, respectively.⁵⁰ However, this technique revealed that in immature carob pods the pyrogallol, catechin, gallic acid, chlorogenic acid and epicatechin are main compounds in the pulp and tannic acid in the seeds.

In the present study we also measured GIT following the administration of two established drugs, clonidine, an α₂-adrenoceptor agonist and yohimbine, an α₂-adrenoceptor antagonist. The results indicated that the two drugs produced their expected action, since α₂-adrenoceptors are known to be involved in the control of gastrointestinal motility.⁵¹

Active absorption of sodium is necessary for water conservation by the body in health, and becomes critical in disease conditions characterized by excessive fluid losses from the body. The absorptive process involves either Na⁺ channels (electrogenic absorption) or Na exchange (electroneutral absorption).⁵² Moreover, intestinal secretion is a normal phenomenon, indispensible to solubilizing and diluting nutrients and to maintaining fluidity in the intestinal lumen.⁵³ The immediate action of the aqueous extract of carob on intestinal physiology can be assessed in Ussing chambers. However, the technology of the chambers allows the bringing of such substances into contact with the tissue for a short period of time, provided these substances are soluble. The measure of the short-circuit current more accurately reflects the absorptive and secretory capacity of the tissue. The effect of these substances on I_sc, the epithelial barrier function or responses to secretagogues can be measured immediately or after a short period of incubation. In this context, we have shown that the aqueous extracts of carob (mature and immature) have opposite effects on the intestinal permeability. In fact, the aqueous extract of immature carob pulp and seeds causes an inhibition of the secretion which shows a slowdown in transit. In contrast, we showed that the aqueous extract of mature carob pulp causes an increase in intestinal secretion which facilitates the gastrointestinal transit. This may be due to the effect of the extract on the Cl⁻ channels. Electrogenic Cl⁻ secretion, via chloride channels in the apical membrane of epithelial cells, is the fundamental means by which mucosal surfaces are hydrated in health. On the other hand, we have shown that the aqueous extract of immature carob pulp has opposite effects on intestinal absorption. Some substances can be detrimental to the intestine, inducing electrolyte secretion or decreasing barrier function. Although this approach has limits and should be combined with in vivo measurements, it constitutes a rapid way to evaluate the effect of substances on intestinal physiology and can also, at least partly, elucidate the mechanisms of action of those alternatives.

Measuring I_sc in Ussing chambers can therefore give indications on possible water movement in vivo and be useful to understand the pathophysiology of diarrhea and constipation.^54,55 This can be done at a basal level, without stimulation of the tissue, or after addition to the chambers of pharmacological or natural substances inducing an active transport of ions.

Because most flavonoids naturally occur in plants and plant-derived food as various glycosides rather than in the aglycone form, we tested the effect of quercetin-3-rutinoside (rutin) on I_sc in the proximal colon. In contrast to quercetin, rutin had no effect on I_sc or PD (potential difference).⁵⁶ For instance, the flavonol quercetin, the most abundant dietary flavonoid, on the intestinal mucosa, has been shown to induce Cl⁻ and HCO₃⁻ secretion in the rat colon in Ussing chambers.⁵⁷ Flavonoids, including quercetin, have been also found to inhibit cAMP phosphodiesterase.^58,59

5. Conclusion

The present work supports the claims by traditional medicine practitioners about the usefulness of mature and immature carob pods for the treatment of constipation and diarrhoea. However, more detailed phytochemical studies are necessary to identify the active principle(s) and exact mechanism(s) of action.

Conflict of interest

The authors alone are responsible for the content of this paper.

Abbreviations

GIT	Gastrointestinal transit
CPAE	Carob pod aqueous extract
Isc	Short-circuit current
PD	Potential difference

Acknowledgements

The financial support of INSERM and the Tunisian Ministry of Higher Education and Scientific Research is gratefully acknowledged. Financial disclosures: none declared. The authors would like to thank all members of the TransCell-Lab Laboratory (Faculty of Medicine Xavier Bichat, Université Paris Diderot – Paris 7) for assistance and helpful discussion.

References

1. M. N. Rejeb, Le caroubier en Tunisie: Situations et perspectives d’amélioration, Dans Quel avenir pour l’amélioration des plantes?, AUPELF-UREF, John LibbeyEurotext, Paris, 1995, pp. 79–85.
2. R. W. Owen, R. Haubner, W. E. Hull, G. Erben, B. Spiegelhalder, H. Bartsch and B. Haber, Isolation and structure elucidation of major individual polyphenols in carob fibre, Food Chem. Toxicol., 2003, 41, 1727–1738.
3. S. Marakis, Carob bean in food and feed: current status and future potentials-A critical appraisal, J. Food Sci. Technol., 1996, 33, 365–383.
4. M. Khair, J. El-Shatnawi and K. I. Ereifej, Chemical composition and livestock ingestion of carob (Ceratonia siliqua L.) seeds, J. Range Manage., 2001, 54, 669–673.
5. H. Sebai, A. Souli, L. Chehimi, K. Rtibi, M. Amri, J. El-Benna and S. M. Sakly, In vitro and in vivo antioxidant properties of Tunisian carob (Ceratonia siliqua L.), J. Med. Plants Res., 2013, 7, 85–90.
6. M. Karkacier and N. Artik, Determination of physical properties, chemical composition and extraction conditions of carob bean (Ceratonia siliqua L.), Gida, 1995, 3, 131–136.
7. J. H. Cummings, The effect of dietary fiber on fecal weight and composition, in Dietary Fiber in Human Nutrition, ed. G. A. Spiller, CRC Press, Boca Raton, Ann Arbor, London, Tokyo, 1993, pp. 263–350.
8. S. R. Glore, D. Van Treeck, A. W. Knehans and M. Guild, Soluble fiber and serum lipids: a literature review, J. Am. Diet. Assoc., 1994, 94, 425–436.
9. L. Brown, B. Rosner, W. W. Willett and F. M. Sacks, Cholesterol lowering effects of dietary fiber: a meta-analysis, Am. J. Clin. Nutr., 1999, 69, 30–42.
10. M. S. Gulay, O. Yildiz-Gulay, A. Ata, A. Balic and A. Demirtas, Toxicological Evaluation of carob (Ceratonia siliqua L.) Bean Extracts in Male New Zealand white Rabbits, J. Anim. Vet. Adv., 2012, 11, 1853–1857.
11. H. J. Zunft, W. Luder, A. Harde, B. Haber, H. J. Graubaumn and J. Gruenwald, Carob pulp preparation for treatment of hypercholesterolemia, Adv. Ther., 2001, 18, 230–236.
12. H. J. Zunft, W. Luder, A. Harde, B. Haber, H. J. Graubaum, C. Koebnick and J. Grunwald, Carob pulp preparation rich in insoluble fibre lowers total and LDL cholesterol in hypercholesterolemic patients, Eur. J. Nutr., 2003, 42, 235–242.
13. B. Haber, Carobberbenets and applications, Cereal Foods World, 2002, 47, 365–373.
14. S. Kumazawa, M. Taniguchi, Y. Suzuki, M. Kwon and T. Nakayama, Antioxidant activity of polyphenols in carob pods, J. Agric. Food Chem., 2002, 50, 373–377.
15. T. Baytop, Therapy with Medicinal Plants in Turkey (Past and Present), Publications of the Istanbul University, Istanbul, 1984, p. 3255.
16. W. G. Thompson and M. D. Frcpc, Irritable bowel syndrome: a management strategy, Baillière’s Clinical Gastroenterology, 1999, vol. 13, pp. 453–460.
17. W. Bosshard, R. Dreher, J. F. Schnegg and C. J. Büla, The treatment of chronic constipation in elderly people: An update, Drugs Aging, 2004, 21, 911–930.
18. S. A. Müller-Lissner, A. K. Michael, S. Carmelo and W. Arnold, Myths and Misconceptions about Chronic Constipation Myths and Misconceptions in Chronic Constipation, Am. J. Gastroenterol., 2005, 100, 232–242.
19. N. Tashiro, S. Budhathoki, K. Ohnaka, K. Toyomura, S. Kono, T. Ueki, M. Tanaka, Y. Kakeji, Y. Maehara, T. Okamura, K. Ikejiri, K. Futami, T. Maekawa, Y. Yasunami, K. Takenaka, H. Ichimiya and R. Terasaka, Constipation and colorectal cancer risk: the Fukuoka Colorectal Cancer Study, Asian Pac. J. Cancer Prev., 2011, 12, 2025–2030.
20. F. G. Shoba and M. Thomas, Study of antidiarrhoeal activity of four medicinal plants in castor oil induced diarrhoea, J. Ethnopharmacol., 2001, 76, 73–76.
21. C. P Siegers, E. Hertzberg-Lottin, M. Otte and B. Schneider, Anthranoid laxative abuse a risk for colorectal cancer?, Gut, 1993, 34, 1099–1101.
22. L. L. Clarke, A guide to Ussing chamber studies of mouse intestine, Am. J. Physiol.: Gastrointest., 2009, 296, 1151–1166.
23. M. J. G. Farthing, A. Casburn-Jones and M. R. Banks, Getting control of intestinal secretion: thoughts for 2003, Dig. Liver Dis., 2003, 35, 378–385.
24. P. Mardones, D. Andrinolo, A. Csendes and N. Lagos, Permeability of human jejunal segments to gonyautoxins measured by the Using chamber technique, Toxicon, 2004, 44, 521–528.
25. H. Li, D. N. Sheppard and M. J. Hug, Transepithelial electrical measurements with the Ussing chamber, J. Cystic Fibrosis, 2004, 3, 123–126.
26. F. Pizzaro, M. Olivares, E. Hertrampf and T. Walter, Factors which modify the nutritional status of iron: tannic content of herbal teas, Archivos Latinoamericanos De Nutrucion, 1994, vol. 44, pp. 277–280.
27. L. M. Gail, Use of Dinitrosalicylic Acid Reagent for Determination of Reducing Sugar, Anal. Chem., 1959, 31, 3.
28. AOA, Method 991.42, Official Methods of Analysis of AOAC International, The Association, Gaithersburg, MD, 16th edn, 1995b.
29. C. Proestos, I. S. Boziaris, G. J. E. Nychas and M. Komaitis, Analysis of flavonoids and phenolic acids in Greek aromatic plants: Investigation of their antioxidant capacity and antimicrobial activity, Food Chem., 2006, 95, 664–671.
30. B. H. Ali and A. A. Bashir, The effect of alpha 2-receptor agonists and antagonistis on gastrointestinal transit time, Clin. Exp. Pharmacol. Physiol., 1993, 20, 1–6.
31. F. Awouters, C. J. E. Niemegeers, F. M. Lenaerts and P. A. J. Janssen, Delay of castor oil diarrhea in rats: a new way to evaluate inhibitors of prostaglandin biosynthesis, J. Pharmacol. Pharmacother., 1978, 30, 41–45.
32. P. K. Mukherjee, K. Saha, T. Murugesan, S. C. Mandal, M. Pal and B. P. Saha, Screening of antidiarrhoeal profile of some plant extracts of specific regions of West Bengal, India, J. Ethnopharmacol., 1998, 60, 85–89.
33. G. D. Dicarlo, N. Mascolo, A. A. Izzo, F. Capasso and G. Autore, Effects of quercetin on gastrointestinal tract in rats and mice, Phytother. Res., 1994, 8, 42–45.
34. S. W. R. Inayathulla, A. A. Karigar and M. Sikarwar, Evaluation of anti-diarrhoeal activity of Crataeva nurvala root bark in experimental animals, Int. J. Pharm. Sci., 2010, 2, 158–161.
35. R. Ducroc, S. Guilmeau, K. Akasbi, H. Devaud, M. Buyse and A. Bado, Luminal leptin induces rapid inhibition of active intestinal absorption of glucose mediated by sodium–glucose cotransporter 1, Diabetes, 2005, 54, 348–354.
36. B. Eto, M. Boisset, B. Griesmar and J. F. Desjeux, Effect of sorbin on electrolyte transport in rat and human intestine, Am. J. Physiol., 1999, 276, G107–G114.
37. O. Martínez-Augustin, I. Romero-Calvo, M. D. Suárez, A. D. Zarzuelo and F. S. Medina, Molecular bases of impaired water and ion movements in inflammatory bowel diseases, Inflammatory Bowel Dis., 2009, 15, 114–127.
38. M. H. Montrose, S. J. Keely and K. E. Barrett, Secretion and absorption: small intestine and colon, in Textbook of Gastroenterology, Lippincott, Williams and Wilkins, Philadelphia, 1999, pp. 320–355.
39. E. B. Kim, New insights into the pathogenesis of intestinal dysfunction: secretory diarrhea and cystic fibrosis, World J. Gastroenterol., 2000, 6, 470–474.
40. Y. Tang, L. He, C. Nyachoti and L. Yin, Applications of small intestinal segment perfusion and Ussing chambers technique in pig intestinal function, Research of Agriculture Modernization, 2012, 33, 741–744.
41. F. E. Le, C. Chesne, P. Artusson, D. Brayden, G. Fabre, P. Gires, F. Guillou, M. Rousset, W. Rubas and M. L. Scarino, In Vitro Models of the intestinal barrier, ATLA, Altern. Lab. Anim., 2001, 29, 649–668.
42. J. Rombeau, Physiologic and Metabolic Effects of Intestinal Stomas, Atlas of Intestinal stomas, 2012, pp. 59–67,  DOI:10.1007/978-0-387-78851-74.
43. E. O. Adewoye, A. O. Ige and C. T. Latona, Effect of Methanolic extract of Musa sapientum leaves on Gastrointestinal Transit time in Normal and Alloxan-induced Diabetic rats: Possible Mechanism of Action, Niger. J. Physiol. Sci., 2011, 26, 83–88.
44. M. Souleymane, B. Calixte, Y. Dodéhé, Y. D. Jacques, A. D. Joseph and J. N. David, Laxative activities of Mareya micrantha (Benth.) Müll. Arg. (Euphorbiaceae) leaf aqueous extract in rats, BMC Complementary Altern. Med., 2010, 10–17,  DOI:10.1186/1472-6882-10-7.
45. A. Saima, B. Samra, K. Aslam, H. M. Malik and H. G. Anwarul, Gastrointestinal Stimulant Effect of Urginea indica Kunth and Involvement of Muscarinic Receptors, Phytother. Res., 2011, 26, 704–708.
46. B. B. Zhang, A. L. Cao, J. Y. Zhou, Z. B. Hu and D. Z. Wu, Effect of jatrorrhizine on delayed gastrointestinal transit in rat postoperative ileus, J. Pharmacol. Pharmacother., 2012, 64, 413–419.
47. G. A. Bubenik, Localization physiological significance and possibleclinical implication of gastrointestinal melatonin, Biol. Signals Recept., 2001, 10, 350–366.
48. A. Al-Qarawi, B. H. Ali, S. A. Al-Mougy and H. M. Mousa, Gastrointestinal transit in mice treated with various extracts of date (Phoenix dactylifera L.), Food Chem. Toxicol., 2003, 41, 37–39.
49. B. A. Ayinde and O. J. Owolabi, Effects of the aqueous extract of Ficus capensis thunb (Moraceae) leaf on gastrointestinal motility, J. Pharmacogn. Phytother., 2009, 1, 031–035.
50. K. Rtibi, M. A. Jabri, S. Selmi, A. Souli, H. Sebai, J. El-Benna, M. Amri and L. Marzouki, Carob pods (Ceratonia siliqua L.) inhibit human neutrophils myeloperoxidase and in vitro ROS-scavenging activity, RSC Adv., 2015, 5, 84207–84215.
51. M. J. Fargeas, J. Fioramont and L. Bueno, Central α₂-adrenergic control of the pattern of small intestinal motility in rat, Gastroenterology, 1986, 91, 1470–1475.
52. S. Vidyasagar and B. S. Ramakrishna, Effects of butyrate on active sodium and chloride transport in rat and rabbit distal colon, J. Physiol., 2002, 539, 163–173.
53. A. W. Raul and T. Saul, Regulation mechanisms of intestinal secretion: implications in nutrient absorption, J. Nutr. Biochem., 2002, 13, 190–199.
54. K. H. Erlwanger, M. A. Unmack, M. L. Grondahl, E. Skadhauge and J. E. Thorboll, Effect of age on vasoactive intestinal polypeptide-induced short-circuit current in porcine jejunum, Comp. Biochem. Physiol., 1999, 124, 29–33.
55. K. Holtug, M. B. Hansen and E. Skadhauge, Experimental studies of intestinal ion and water transport, Scand. J. Gastroenterol., 1996, 31, 95–110.
56. C. Rainer, F. Ursula and W. Siegfried, Dietary flavonol quercetin induces chloride secretion in rat colon, American Physiological Society, 1998, 0193, 1857–1898.
57. R. Cermak, U. Föllmer and S. Wolffram, Dietary flavonol quercitin induces chloride secretion in rat colon, Am. J. Physiol., 1998, 275, 1166–1172.
58. A. Beretz, R. Anton and J. C. Stoclet, Flavonoid compounds are potent inhibitors of cyclic AMP phosphodiesterase, Experientia, 1978, 34, 1054–1055.
59. T. Nikaido, T. Ohmoto, U. Sankawa, T. Hamanaka and K. Totsuka, Inhibition of cyclic AMP phosphodiesterase by flavonoids, Planta Med., 1982, 46, 162–216.

---