Stimulation of non-sodium-dependent water, electrolyte, and glucose transport in rat small intestine by gum arabic

Salt reduction in liquid/semi-solid foods based on the mucopenetration ability of gum arabic

Gum arabic enhances the saltiness perception of liquid/semi-solid foods via a mucopenetration effect.

Modulation of Small Intestinal Nitric Oxide Synthase by Gum Arabic

Preceding studies have revealed that gum arabic (GA), a natural proteoglycan (≥250, 000 Da), has proabsorptive properties—as shown by increased sodium and water absorption—in normal rats, and especially in two animal models of diarrhea. Because nitric oxide (NO) metabolism is linked to gastrointestinal Physiology, the goals of this study were to determine whether GA modulated NO and to determine intestinal function in vivo when NO production was enhanced by l-arginine (Arg), added at either 1 or 20 mM. Mechanistically, the goal was also to determine whether GA was a NO scavenger and a small intestinal NO synthase (NOS) inhibitor. Using a glucose-electrolyte solution in rat jejunal perfusions we found that GA at ± 10 μM (2.5 g/l) decreased nitrite and nitrate formation, tending to normalize water, sodium, and glucose absorption when modified by Arg addition. In vitro tests, with oxyhemoglobin as a marker, showed that GA at ≥5 μM scavenged NO. For GA effects on NOS, small intestinal homogenate supematants (10, 000 g) from frozen tissues of either adult or 2-day-old rats were incubated for 1 hour at 37°C in the presence of 2 mM Arg and increasing GA concentrations (0-100 μM). GA produced a concentration-dependent inhibition of NOS, reaching approximately 31% inhibition with 5 μM GA and up to 51% with 50 μM GA. GA at 100 μM produced no further inhibition. The data indicate that GA, in addition to its ability to remove NO diffused into the intestinal lumen, may also partially inhibit intestinal NOS end thus modulate intestinal absorption through these mechanisms. Use of GA as a food additive may help in restoring or improving small Intestinal function in conditions where functional damage has occurred.

Biological effects of gum arabic: a review of some recent research

Gum arabic (GA) is a branched-chain, complex polysaccharide, either neutral or slightly acidic, found as a mixed calcium, magnesium and potassium salt of a polysaccharidic acid. The backbone is composed of 1,3-linked beta-D-galactopyranosyl units. The side chains are composed of two to five 1,3-linked beta-D-galactopyranosyl units, joined to the main chain by 1,6-linkages. Pharmacologically, GA has been claimed to act as an anti-oxidant, and to protect against experimental hepatic-, renal- and cardiac toxicities in rats. These reports could not be confirmed by others. GA has been claimed to alleviate the adverse effects of chronic renal failure in humans. This could not be corroborated experimentally in rats. Reports on the effects of GA on lipid metabolism in humans and rats are at variance, but mostly suggest that GA ingestion can reduce plasma cholesterol concentrations in rats. GA has proabsorptive properties and can be used in diarrhoea. It enhances dental remineralization, and has some antimicrobial activity, suggesting a possible use in dentistry. GA has been shown to have an adverse effect on electrolyte balance and vitamin D in mice, and to cause hypersensitivity in humans. More studies are needed before the pharmacological properties of GA can be utilized in therapy.

Modulation of rat intestinal nuclear factor NF-kappaB by gum arabic

The objective of this study was to test the hypothesis that in an animal model of cathartic-induce intestinal dysfunction the proabsorptive effects of gum arabic (GA) could be associated with modulation of nuclear factor-kappaB (NF-kappaB) and with reduction of the inflammatory response caused by cathartics, as evidenced by intestinal mucosa cytokine production and gene expression. Juvenile male rats were given a phenolphthalein-magnesium citrate solution for 6 days, by itself or supplemented with either 10 or 20 g L(-1) GA, as a sole source of fluid. The controls given were tap water alone or with added 20 g L(-1) GA. The animals were euthanized and small-intestinal mucosa nuclear fractions and RNA were isolated. NF-kappaB p65 activity was highest after administration of cathartics, lowest in controls, and intermediate in GA-treated rats. Mucosal IL-1beta was overexpressed in tissues from cathartic-treated rats and from rats given high-GA solutions. Gene-array analysis revealed a complex pattern of gene regulation by cathartics which selectively upregulated several subfamilies of cytochrome P-450 family 2 genes. Co-administration of GA did not block this effect. These findings suggest that local anti-inflammatory effects on the small intestine could be obtained by administration of a nonabsorbable proteoglycan such as GA.

Enhancement of absorption by gum arabic in a model of gastrointestinal dysfunction

OBJECTIVE

Diarrhea is a common and deadly threat to millions of infants and children. Similarly, malabsorption can aggravate the health status of the chronically sick and especially the elderly. Prompt recovery from intestinal dysfunction may have a substantial impact on many populations. The aim of this study was to test the hypothesis that, in an animal model of cathartic-induce diarrhea, the previously shown proabsorptive effects of gum arabic (GA) could directly reduce and ameliorate intestinal dysfunction.

METHODS

Young male rats were offered a standard solid feed and as a sole source of fluid a phenolphthalein-magnesium citrate solution for 3 or 6 days (PC), or the same plus either 10 (GA1) or 20 (GA2) g/L of GA. Other groups had tap water without (CTL) or with 20 g/L GA (CTL + GA), after which the animals were jejunally perfused under anesthesia to test their absorptive capacity. Similarly treated rats were killed and the small intestinal mucosa scraped and processed for nitric oxide synthase (NOS) determination.

RESULTS

In 6-day studies addition of GA to the cathartic solution led to increases in net water, sodium and glucose absorption with the higher GA2, relatively to the PC rats. For water (means +/- SEM): PC = 42.4 +/- 3.6; GA2 = 57.9 +/- 3.9 nmol/g.min, p < 0.05. For sodium: PC = 2,139 +/- 334; GA2 = 4,465 +/- 444 nmol/g.min, p < 0.05. After only 3-day exposure, effects were less marked. Total NOS activity was increased in the PC, GA1 and GA2 groups (333 +/- 26; 334 +/- 27; 336 +/- 23 nmol/h.g) compared to CTL (233 +/- 27 nmol/h.g, p < 0.05), while CTL + GA showed a further reduction of activity (190 +/- 18 nmol/h.g, p < 0.05 vs. CTL).

CONCLUSIONS

These findings substantiate earlier physiologic and biochemical effects of GA on the gastrointestinal tract, presently conducted in a model of gastrointestinal dysfunction. The data further suggest that a natural proteoglycan such as GA can reduce secretory effects induced by cathartics and, hence, are predictive of potential effectiveness in the context of diarrhea or malabsorption by infectious or functional causes.

Proabsorptive effect of gum arabic in isotonic solutions orally administered to rats: effect on zinc and other solutes

We have previously shown that the addition of gum arabic (GA) to oral rehydration solution (ORS) enhances water and electrolyte absorption during jejunal perfusion in rats under anesthesia. This study investigates whether GA by oral administration could be equally effective in rats. Isotonic solutions containing 25 g/L GA (AG), or without GA (A0) were administered via oral tube to lightly anesthetized adult female rats. Similar experiments were conducted with hypertonic solutions containing no GA (B0), or either 10 (B10) or 50 g/L GA (B50). Blood concentrations of sodium, glucose, glutamate, zinc, and tritiated water were determined at 0, 15, 30, 60, 90, 120, and 180 minutes, and results between treatments were compared. Administration of the isotonic, GA-containing solution (AG) resulted in a higher blood zinc level than with the isotonic GA-free solution (A0) from 15 minutes throughout 180 minutes. Blood zinc at 15 minutes (means +/- SEM) was as follows: for A0: 69.3 +/- 2.0, for AG: 83.4 +/- 3.5 nmol/L, P=0.002. At 180 minutes, A0: 52.6 +/- 1.8; AG: 68.1 +/- 4.6 nmol/L, P=0.004. The corresponding areas under the curve (AUC) were as follows: for A0: 10,737 +/- 214; for AG: 13,919 +/- 765 nmol x min/L, P<0.001). Glucose, glutamate, sodium, and tritiated water body distribution presented no differences in blood concentrations. For sodium and tritiated water body distribution, there was a significant time effect (P<0.0001). In hypertonic solutions, blood zinc levels declined over time, possibly due to their osmotic, counter-absorptive action, thus obscuring possible opposite effects of GA. GA appears to be an effective enhancer of zinc absorption when orally administered in isotonic solutions to laboratory animals. This proabsorptive capacity could be attributed to some of the physicochemical and biochemical properties of GA and suggest possible applications of GA in liquid formulas and solid food preparations.

Gum arabic (GA) modifies paracellular water and electrolyte transport in the small intestine

Previous experiments have shown that a soluble fiber, gum arabic (GA), enhances water, electrolyte, and glucose absorption in animal models of diarrhea. The mechanisms implicated in this effect have not been fully elucidated. This study examined the possibility that paracellular transport is modulated by luminal GA, resulting in an enhanced rate of absorption in the small intestine. This hypothesis was tested by 3-hr jejunal perfusions on anesthetized rats with solutions containing 140 mM NaCl, 5 mM KCl, and 2 microCi/liter (74 kBq) 3H2O, with either 2.5 g/liter GA [+GA] or in its absence [CTL], and one of the following agents, capable of altering paracellular transport: chenodeoxycholic acid at 0.5 mM (CDC), 2,4,6-triaminopyrimidine (TAP) at 20 mM, and protamine at 100 mg/liter (PTM). Sodium, potassium, net water, and unidirectional water movement were measured. The addition of GA increased sodium absorption in perfusions with CDC, TAP, or PTM only. Similar effects by GA on net water absorption rates were obtained in tissues permeabilized with CDC and PTM; however, GA added to TAP did not normalize the reduction caused by TAP. Although PTM did not alter net water absorption, addition of GA to perfusates with PTM enhanced absorption values above those of CTL. GA reversed the strong negative effects of CDC on potassium absorption but was ineffective in this regard with TAP and PTM. The data obtained with those reagents that affect paracellular transport and the histological evidence support the view that GA promotes net absorption by this route in the small intestine of normal rats.

Transepithelial ultrafiltration and fractal power diffusion of D-glucose in the perfused rat intestine

Despite an enormous body of research investigating the mass transfer of D-glucose through biological membranes, carrier-mediated and first-order models have remained the prevalent models describing glucose's quantitative behavior even though they have proven to be inadequate over extended concentration ranges. Recent evidence from GLUT2 knockout studies further questions our understanding of molecular models, especially those employing Michaelis-Menten (MM)-type kinetic models. In this report, evidence is provided that D-glucose is absorbed by rat intestinal epithelium by a combination of convective ultrafiltration and nonlinear diffusion. The diffusive component of mass transfer is described by a concentration-dependent permeability coefficient, modeled as a fractal power function. Glucose and sodium chloride-dependent-induced aqueous convection currents are the result of prevailing oncotic and osmotic pressure effects, and a direct effect of glucose and sodium chloride on intestinal epithelium resulting in enhanced glucose, sodium ion, and water mobility. The fractal power model of glucose diffusion was superior to the conventional MM description. A convection-diffusion model of mass transfer adequately characterized glucose mass transfer over a 105-fold glucose concentration range in the presence and absence of sodium ion.