Absorption of folic acid from the small intestine of the rat

The absorption of folic acid from segments of the small intestine of the rat has been measured in situ with tritium-labelled folic acid. The fraction absorbed was independent of concentration below 10^-6 M but was depressed to half at 4×10^-5 M. Direct measurements of fluxes showed that the mucosal → serosal flux was about 14 times the serosal → mucosal flux, and therefore that uptake of folic acid is an active process. In the ileum but not in the duodeno-jejunum, absorption was depressed by the presence of electrolyte. There was little difference in absorptive capacity between jejunum and ileum nor was there any significant change in animals suffering from a dietary deficiency of folic acid.     

Characterization of norfloxacine release from tablet coated with a new pH-sensitive polymer, P-4135F

A new pH-sensitive polymer, P-4135F, was evaluated as a colon delivery device for norfloxacine (NFLX) which is used for the therapy of patients with Vero toxin-producing Escherichia coli gastroenteritis. P-4135F has a dissolution threshold pH of 7.2 which is higher than the conventional pH-sensitive polymers, Eudragit S100 and L100. To compare the dissolution site of P-4135F coated tablets with other enteric polymer coatings, mini-tablets containing sodium fluorescein (FL) as a model drug were prepared by coating them with the three polymers. After oral administration of FL mini-tablets to rats, the first-appearance time, Ti, of FL into the systemic circulation was measured. The Tis were 0.7+/-0.2 h for Eudragit L100, 1.8+/-0.4 h for S100 and 2.0+/-0.3 h for P-4135F. Direct inspection of the dissolution process of the FL mini-tablets after oral administration to rats was performed by abdominal incision studies. All of the coated FL mini-tablets started to dissolve in the rat ileum. The dissolution sites were identified to be proximal to the ileocecal junction for P-4135F, at the middle part of the ileum for Eudragit S100 and at the proximal part of the ileum for Eudragit L100. NFLX tablets with different membrane thicknesses of P-4135F were prepared and were orally administered to beagle dogs. The colon delivery efficiency was evaluated by measuring the Ti of NFLX into the systemic circulation. The mean Tis were 1.33+/-0.33 h for 56.8+/-0.5 microm membranes, 3.75+/-0.25 h for 64.6+/-0.7 microm membranes, 4.00+/-1.00 h for 70.5+/-0.5 microm membranes and 3.00+/-1.00 h for 74.9+/-0.4 microm membranes. By comparing the Ti, 4.33+/-0.33 h, obtained after oral administration of NFLX in a pressure-controlled colon delivery capsule, and the colon arrival time, 3.5+/-0.3 h, determined by a sulfasalazine test in beagle dogs. P-4135F coated NFLX tablets appeared to dissolve and disintegrate before reaching the colon. Studies using rats and beagle dogs have suggested that P-4135F dissolves in the lower part of the small intestine, i.e., the ileum. These studies also suggest that this new polymer will be useful for the delivery of NFLX to the lower part of the small intestine.     

Drug delivery to the upper small intestine window using gastroretentive technologies

The bioavailability of drugs with an absorption window in the upper small intestine is generally limited with conventional pharmaceutical dosage forms. The residence time of such systems and, thus, of their drug release into the stomach and upper intestine is often short. To overcome this restriction and to increase the bioavailability of these drugs, controlled drug delivery systems with a prolonged residence time in the stomach can be used. Approaches to achieving prolonged residence times of the devices in the upper part of the gastrointestinal tract include the use of bioadhesive, size-increasing, and floating drug delivery systems.     

齐墩果酸磷酸酯二钠盐的小肠吸收动力学

目的研究齐墩果酸磷酸酯二钠盐(OANa2)大鼠小肠的吸收情况。方法采用大鼠在体、离体小肠回流实验装置,利用高效液相色谱法测定肠循环液中OANa2的含量,采用紫外分光光度法测定肠循环液中酚红的含量。结果在体小肠胆管结扎与不结扎的药物吸收百分率(PA)分别为43.4%、43.7%。实验浓度下,离体小肠上、下段的吸收速率常数(Ka)分别为0.318 h、0.300 h。此外,离体小肠实验在3种不同浓度下的吸收速率常数分别为0.270 h、0.322 h、0.284 h。胆管结扎与不结扎的药物吸收百分率无显著性差异(P>0.05);OANa2在小肠不同肠段的吸收速率常数无显著差异(P>0.05)。结论在实验浓度范围内,OANa2的小肠吸收机制属于被动扩散。     

Competitive inhibition between folic acid and methotrexate for transport carrier in the rat small intestine

Folic acid absorption from the lumen of the rat small intestine in situ obeyed Michaelis--Menten kinetics. The values of Vmax and Km for absorption were 4.63 x 10(-7) M/min and 1.21 x 10(-6) M, respectively. Folic acid and methotrexate were mutual competitive inhibitors of absorption. Their Ki values were 1.28 x 10(-6) and 1.9 x 10(-5) M, respectively.     

Pharmacokinetics and delivery of the anti-influenza prodrug oseltamivir to the small intestine and colon using site-specific delivery capsules

This study investigated the site-specific absorption of oseltamivir using targeted delivery and gamma scintigraphy. On four separate occasions, nine healthy male subjects each received a single 150 mg of oseltamivir administered via the Enterion capsule to the stomach, proximal small bowel, distal small bowel and the ascending colon. Pharmacokinetic parameters of oseltamivir and its carboxylate metabolite show that absorption was similar in the proximal and distal small bowel compared to stomach delivery, but reduced from the ascending colon, demonstrating that absorption-rate limited disposition occurred only for the ascending colon. The metabolite-to-parent ratios were minimally reduced. The results support the feasibility of modified-release formulation development whilst confirming the high and consistent oral bioavailability of oseltamivir.     

Effect of systemic anaphylaxis on the absorption of salicylic acid from the rat small intestine

Rats were immunized by intraperitoneal injection of ovalbumin (egg albumin) emulsified in Freund's incomplete adjuvant, and then the effect of an intravenous challenge with ovalbumin on salicylic acid absorption from the small intestine was examined by means of an in situ recirculation technique. The disappearance of salicylic acid from the luminal solution was significantly decreased in rats treated with ovalbumin compared with control groups treated with saline. The decreased absorption of salicylic acid in ovalbumin-immunized rats was related to the anti-ovalbumin antibody responses examined by passive cutaneous anaphylactic reactions. On the other hand, the decreased absorption of salicylic acid was not found in ovalbumin-immunized rats challenged intravenously with bovine gamma-globulin. Similar results were also noted in rats immunized via the footpads with ovalbumin. However, no significant change was observed in the intestinal absorption of salicylic acid in normal (nonimmunized) rats challenged intravenously with ovalbumin. Furthermore, intestinal absorption of sulfadimethoxine and sulfanilamide was significantly decreased during systemic anaphylaxis, whereas no change was observed in the absorption of sulfisoxazole, quinine, sulfanilic acid, and phenolsulfonphthalein. This suggests that the intestinal absorption of rapidly absorbed drugs, including salicylic acid, is more sensitive to systemic anaphylaxis than that of poorly absorbed drugs.     

Studies of chitosan/organic acid/Eudragit RS/RL-coated system for colonic delivery

Prednisolone (PDS) beads were coated sequentially with (i) innermost hydrophobic layer of Eudragit RS/RL, (ii) middle drug release-triggering layer of chitosan, organic acid and Eudragit RS/RL, and (iii) outermost enteric coating layer. Continuous dissolution studies were carried out in artificial gastric fluid (pH 1.2), followed by intestinal fluid (pH 6.8), and finally in colonic fluid (pH 4 and 6) with and without beta-glucosidase. While drug release was prevented in the gastric and small-intestinal fluids, a continuous release was observed in the colonic fluid. Succinic acid provided the fastest rate of release in the colonic fluid compared to citric, tartaric or malic acid. A combined mechanism of drug release is proposed, which considers the swelling of chitosan and Eudragit RS/RL in the presence of succinic acid possibly via electrostatic interaction between the amine groups of chitosan/quaternary ammonium groups of Eudragit RS/RL and the carboxyl groups of succinic acid in aqueous medium. The results of plasma pharmacokinetic studies in Sprague-Dawley rats showed that the developed system provided a significant delay (T(max) 9.3 h) in the absorption profile of PDS compared with simple enteric-coated (T(max) 4 h) or powder (T(max) 1 h) formulation that was taken as proof for the colon-targeted delivery.     

Eudragit RL100 nanoparticle system for the ophthalmic delivery of cloricromene

A Eudragit RL100 polymer nanoparticle system loaded with cloricromene was prepared and characterized on the basis of physicochemical properties, stability and drug release features. To investigate the ocular bioavailability of cloricromene after inclusion in the polymer matrix, the new nanoparticle system was topically administered in the rabbit eye and compared with an aqueous solution of the same drug. The nanoparticle system showed interesting size distribution and surface charge values, suitable for ophthalmic application. The results indicated that the dispersion of cloricromene within Eudragit RL100 polymer nanoparticles increased its ocular bioavailability and enhanced the biopharmaceutical profile. The new cloricromene-loaded nanoparticle system described here may be useful in clinical practice.     

Absorption of benzoic acid in segmental regions of the vascularly perfused rat small intestine preparation.

Oral bioavailability is a consequence of intestinal absorption, exsorption, and metabolism and is further modulated by the difference in activities among segmental regions. The influence of these factors on the net absorption of benzoic acid (BA), a substrate that is metabolized to hippurate and is transported by the monocarboxylic acid transporter 1, was studied in the recirculating, vascularly perfused, rat small intestine preparation. Metabolism of BA was not observed for both systemic and intraluminal injections into segments of varying lengths. But, secretion of BA into lumen was noted. Absorption of BA (0.166-3.68 micromol) introduced at the duodenal end for absorption by the entire intestine was complete (>95% dose at 2 h) and dose-independent, yielding similar absorption rate constants (k(a) of 0.0464 min(-1)). The extent of absorption remained high (92-96% dose) when BA was injected into closed segments of shorter lengths (12 or 20 cm), suggesting a large reserve length of the rat intestine. However, k(a) was higher for the jejunum (0.0519 and 0.0564 min(-1), respectively, for the 12- and 20-cm segments) and exceeded that for the duodenum (12-cm segment, 0.0442 min(-1)) and ileum (20-cm segment, 0.0380 min(-1)) at closed injection sites. The finding paralleled the distribution of monocarboxylic acid transporter isoform 1 detected by Western blotting along the length of the small intestine. Fits of the systemic and oral data (based on duodenal injection for absorption by the whole intestine) to the traditional, physiological model and to the segregated flow model (SFM) that describes partial intestinal flow to the enterocyte region showed a better fit with the SFM even though metabolite data were absent.     

Studies of pectin HM/Eudragit RL/Eudragit NE film-coating formulations intended for colonic drug delivery

Theophylline pellets were coated with Eudragit NE30D aqueous dispersions, containing various pectin HM/Eudragit RL30D ionic complexes, using an Uni-Glatt fluidized-bed apparatus. Dissolution studies were then carried out on the coated pellets at pH 6.0, in absence and in presence of commercial pectinolytic enzymes. The theophylline release from the coated pellets, after an initial latency phase, occurred linearly as a function of time. The theophylline release rate was dependent on the pectin HM content of the complexes incorporated in the coatings. The lowest theophylline release from the coated pellets was obtained when the pectin HM content of the complexes was 20.0% w/w (related to Eudragit RL), i.e. when the complexation between pectin HM and Eudragit RL is optimal. The theophylline release from the coated pellets was slower in presence of the pectinolytic enzymes when the pectin content of complexes is higher than 20% w/w. On the other hand, the effect of the enzymes induced an increase of the theophylline release when the pectin HM content of the coatings ranged between 10.0 and 15.0% w/w (related to Eudragit RL).     

Eudragit RS100 nanosuspensions for the ophthalmic controlled delivery of ibuprofen.

Topical application of non-steroidal anti-inflammatory drugs on the eye is a common treatment used to contrast the miosis induced by surgical traumas, such as cataract extraction. With the aim of improving the availability of sodium ibuprofen (IBU) at the intraocular level, IBU-loaded polymeric nanoparticle suspensions were made from inert polymer resins (Eudragit RS100). The nanosuspensions were prepared by a modification of the quasi-emulsion solvent diffusion technique using variable formulation parameters (drug-to-polymer ratio, total drug and polymer amount, stirring speed). Nanosuspensions had mean sizes around 100 nm and a positive charge (zeta-potential of +40/+60 mV), this makes them suitable for ophthalmic applications. Stability tests (up to 24 months storage at 4 degrees C or at room temperature) or freeze-drying were carried out to optimize a suitable pharmaceutical preparation. In vitro dissolution tests indicated a controlled release profile of IBU from nanoparticles. In vivo efficacy was assessed on the rabbit eye after induction of an ocular trauma (paracentesis). An inhibition of the miotic response to the surgical trauma was achieved, comparable to a control aqueous eye-drop formulation, even though a lower concentration of free drug in the conjunctival sac was reached from the nanoparticle system. Drug levels in the aqueous humour were also higher after application of the nanosuspensions; moreover, IBU-loaded nanosuspensions did not show toxicity on ocular tissues.     

Curcumin reduces indomethacin-induced damage in the rat small intestine

Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used in clinical medicine. Their utility is, however, often limited by the adverse effects they produce in the gastrointestinal tract. Oxidative stress has been shown to occur in the small intestine in response to the oral administration of indomethacin, an NSAID commonly used in toxicity studies. In view of this, the effect of curcumin, an agent with anti-oxidant properties, was evaluated on indomethacin-induced small intestinal damage in a rat model. Rats were pretreated with various doses of curcumin (20 mg kg(-1), 40 mg kg(-1) and 80 mg kg(-1)) before administering indomethacin at 20 mg kg(-1). Various parameters of oxidative stress and the extent of small intestinal damage produced by indomethacin, with and without pretreatment with curcumin, were measured. Macroscopic ulceration was found to occur in the small intestine in response to indomethacin. The viability of enterocytes from indomethacin-treated animals was significantly lower than those from control animals. Drug-induced oxidative stress was also evident as seen by increases in the levels of malondialdehyde and protein carbonyl and in activities of pro-oxidant enzymes such as myeloperoxidase and xanthine oxidase in indomethacin-treated rats. Concomitant decreases were seen in the activities of the antioxidant enzymes catalase and glutathione peroxidase in these animals. Pretreatment with curcumin was found to ameliorate these drug-induced changes. Thus, curcumin appears to hold promise as an agent that can potentially reduce NSAID-induced small intestinal damage.     

Pirfenidone attenuates ischaemia-reperfusion injury in the rat small intestine

1. Pirfenidone, an antifibrotic compound with anti-inflammatory effects, has been investigated in a rat model of acute experimental ischaemia-reperfusion injury of the small intestine. 2. Occlusion of the superior mesenteric artery in young adult female rats for 30 min followed by reperfusion for 120 min induced significant local and systemic effects, including tissue haemorrhage with oedema, elevated serum concentrations of tumour necrosis factor (TNF)-alpha, neutropenia, hypotension and bradycardia. 3. Administration of pirfenidone (200 mg/kg, p.o., i.v. or i.p.) 30 min before occlusion completely inhibited the increase in serum TNF-alpha concentrations. Pirfenidone inhibited, but did not completely prevent, tissue damage in the small intestine, as well as hypotension and oedema, but neutropenia and bradycardia were not significantly changed by treatment. 4. Thus, pirfenidone effectively moderates both local and some systemic effects of ischaemia-reperfusion injury in the rat small intestine model.     

Sildenafil enhances the peripheral antinociceptive effect of ellagic acid in the rat formalin test

Objective:

Ellagic acid (EA), a major polyphenolic compound of pomegranate juice, produces antinociceptive effects, which are mediated through opioidergic and nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathways. The present study was conducted to elucidate the peripheral antinociceptive effect of EA alone and in combination with sildenafil in the rat formalin test.

Materials and Methods:

Pain was produced by intraplantar injection of formalin (2.5%) in rats and nociceptive behavior was measured as the number of flinches every 5 min in 60 min after injection.

Results:

Local administration of EA and sildenafil dose-dependently increased the nociception threshold in both phases of the test. Moreover, sub-effective doses of sildenafil (25 or 50 mcg/paw, i.p.) significantly and dose-dependently enhanced the antinociception induced by a sub-effective dose of EA (60 mcg/paw, i.pl.) in both phases of the test. The antinociception produced by these drugs alone, or in combination, was due to a peripheral site of action, since the administration in the contralateral paw was ineffective.

Conclusion:

Our results suggest that EA has local peripheral antinociceptive activity, and enhancement of this effect with sildenafil probably occurs through the inhibition of cGMP metabolism.KEY WORDS: Ellagic acid, formalin, peripheral antinociception, sildenafil     

Cellular distribution of N-acetyltransferase activity in the rat small intestine

The cellular distribution of AcCoA:arylamine N-acetyltransferase (NAT; EC 2.3.1.5) activities was examined in the rat small intestine to determine if heterogeneous cellular distribution contributes to preferential tumor development in the colonic region after exposure to heterocyclic amines (HAs). A chelation/elution method was used to preferentially isolate villus-tip, mid-villus, and crypt enterocytes. Monomorphic (NAT1) and polymorphic (NAT2) activities were determined using N-acetylprocainamide and N-acetamidobenzoic acid formation, respectively. Sucrase-isomaltase (SI) activity was used to confirm that a villus, mid-villus, and crypt cell gradient had been obtained. Utilizing this marker of villus enrichment, a 4- to 10-fold gradient was achieved. NAT1 and NAT2 activities followed this gradient, with the highest NAT activity occurring in the fraction with the highest SI activity. The ratio of NAT2:NAT1 remained essentially constant along the gradient, indicating a similar pattern of expression for both enzymes. This pattern of cellular distribution for the NATs is similar to that reported for cytochrome P450s. This apparent preferential expression of NAT in the villus cells may result in delivery of bioactivated HAs to the lower regions of the intestines as the villus-tip cells are extruded into the intestinal lumen and enter the fecal stream.     

Characterization of WR-1065 absorption in the rat small intestine

A circulating in situ rat small intestine absorption model was used to study the lumenal metabolism and absorption of [14C]WR-1065. WR-1065 was found to be more tissue reactive and toxic than its phosphorylated form, ethiofos, at equimolar perfusate concentrations. The disappearance profiles of the radiolabeled drug and free WR-1065 indicate that WR-1065 is extensively metabolized in the intestinal lumen prior to absorption. Coadministration of disodium ethylenediaminetetraacetic acid enhances the absorption of the free thiol although not to the same extent as seen with ethiofos. Perfusion of WR-1065 in citrate buffer decreased lumenal degradation of the drug but resulted in decreased absorption. The total material converted to WR-1065 portal blood profiles following ethiofos and WR-1065 perfusion were altered possibly due to distribution and metabolism differences. This study coupled with earlier work completed on ethiofos have increased our understanding of the significant barriers to absorption observed following oral administration of these compounds.     

Carrier-mediated transport of glycerol in the perfused rat small intestine

Studies using the closed loop and everted sacs of the rat small intestine recently prompted us to suggest that carrier-mediated transport is involved in the intestinal absorption of glycerol. Although it could be mediated by a novel carrier system, little information is available. The aim of the present study was to kinetically characterize carrier-mediated glycerol transport in the perfused rat small intestine to help in identifying the carrier involved and to explore the possibility that the carrier might be used as a pathway for oral drug delivery and a target for drug development. In situ single-pass perfusion was conducted using a 10-cm midgut segment of the male Wistar rat, and the absorption of [3H]glycerol was evaluated by its disappearance from the intestinal lumen. The absorption of glycerol was saturable and significantly reduced by removing Na+ from the perfusion solution, suggesting the involvement of a Na+-dependent carrier-mediated transport system. The concentration-dependent absorption profile was successfully analyzed by assuming Michaelis-Menten type carrier-mediated transport and simultaneous passive (diffusive) transport. The maximum transport rate (J(max)) was 77.0 pmol/s/cm2 and the Michaelis constant (K(m)) was 1.04 mM, giving a J(max)/K(m) of 7.39 x 10(-5) cm/s. The membrane permeability coefficient for passive transport (P(m,d)) was 6.89 x 10(-5) cm/s, slightly smaller than J(max)/K(m). Therefore, it could be the major mechanism of intestinal glycerol absorption in the low concentration range where carrier-mediated transport conforms to linear kinetics represented by J(max)/K(m). Furthermore, carrier-mediated glycerol transport was found to be inhibited by glycerol 3-phosphate, monoacetin and diglycerol, indicating that the carrier system may be shared by these structural analogues. Thus, the present study has successfully demonstrated and characterized carrier-mediated glycerol transport in the perfused rat small intestine which is a physiologically relevant model.     

Absorption and metabolism of procaine by the rat small intestine

Summary The aim of this study was to obtain information about the absorption of procaine in the rat small intestine (Fisher-Parsons preparation). In the range from 0.25–10 mmol · l^–1 procaine in the luminal perfusate, much more of the unchanged drug was absorbed in segments of the ileum than of the duodenum and jejunum. Besides procaine, two metabolites, p-aminobenzoic acid (PABA) and acetylated p-aminobenzoic acid (AABA), formed in the intestinal mucosa, appeared in the absorbate. With increasing substrate concentration in the perfusate the PABA in the absorbate increased considerably in all three segments; from 0.75 mmol · l^–1 procaine upwards the PABA produced was highest in the jejunum. AABA formed in the mucosa and measured in the absorbate did not increase in the same manner with increasing substrate concentration; in the absorbate of jejunal segments the amount of AABA was significantly higher than in duodenal and ileal segments. Taking into account that in rats the microclimate of the ileum differs considerably from that of the upper part of the small intestine, the marked difference observed in the absorption of procaine between ileal segments on the one side, and duodenal and jejunal segments on the other, can be explained on the basis of the non-ionic diffusion theory.Send offprint requests to H. P. Büch at the above address