Impact of Regional Intestinal pH Modulation on Absorption of Peptide Drugs: Oral Absorption Studies of Salmon Calcitonin in Beagle Dogs

Purpose. To investigate the relationship between the modulation of intestinal pH and the oral absorption properties of a model peptide drug, salmon calcitonin (sCT), in conscious beagle dogs. Methods. Studies were performed to characterize the disintegration of the formulation, intestinal pH changes, and the appearance of the peptide in the blood. Enteric-coated formulations containing sCT and various amounts of citric acid (CA) were tethered to a Heidelberg capsule (HC) and given orally to normal beagle dogs. Blood samples were collected and analyzed by radioimmunoassay (RIA). Intestinal pH was continuously monitored using the Heidelberg pH capsule (HC) system. The integrity of the HC-delivery system tether was verified by fluoroscopy. Results. The intra-individual variation in gastric emptying (GE) of the delivery system was large. There were also large inter-individual differences in the disintegration and absorption properties of the various formulations. However, the peak plasma concentrations of sCT were always observed when the intestinal pH declined. The average baseline intestinal pH was 6.1 ± 0.2 (mean ± SEM, n = 12). The intestinal pH reduction was 2.6 ± 0.4 (mean ± SEM, n = 12, ranged from 0.5 to 4.0 units from baseline). There was a good correlation between the time to reach the trough intestinal pH (t_pH,min) and time to reach the peak plasma concentration (t_conc,max) of sCT (t_conc,max = 0.95 × t_pH,min + 14.1, n = 11, r² = 0.91). Plasma C_max and area under the curve (AUC) increased with increasing amounts of CA in the formulations. Conclusions. The results of these studies demonstrate that the oral absorption properties of a model peptide drug, sCT, can be modulated by changing intestinal pH. sCT is a substrate for the pancreatic serine protease trypsin which has maximal activity at pH 5 to 6. Reducing intestinal pH presumably stabilizes sCT in the GI tract enabling greater absorption of the intact peptide.     

Protein and Peptide Drug Delivery: Oral Approaches

Till recent, injections remained the most common means for administering therapeutic proteins and peptides because of their poor oral bioavailability. However, oral route would be preferred to any other route because of its high levels of patient acceptance and long term compliance, which increases the therapeutic value of the drug. Designing and formulating a polypeptide drug delivery through the gastro intestinal tract has been a persistent challenge because of their unfavorable physicochemical properties, which includes enzymatic degradation, poor membrane permeability and large molecular size. The main challenge is to improve the oral bioavailability from less than 1% to at least 30-50%. Consequently, efforts have intensified over the past few decades, where every oral dosage form used for the conventional small molecule drugs has been used to explore oral protein and peptide delivery. Various strategies currently under investigation include chemical modification, formulation vehicles and use of enzyme inhibitors, absorption enhancers and mucoadhesive polymers. This review summarizes different pharmaceutical approaches which overcome various physiological barriers that help to improve oral bioavailability that ultimately achieve formulation goals for oral delivery.     

Regional Differences in Intestinal Spreading and pH Recovery and the Impact on Salmon Calcitonin Absorption in Dogs

Purpose. To investigate the regional influence of intestinal spreadingand pH recovery on the performance of drug and excipient deliverysystems and their impact on the oral absorption of a model peptidedrug, salmon calcitonin (sCT), in conscious beagle dogs. Methods. Male beagle dogs were surgically prepared with subdermalIntestinal Access Ports (IAP). The catheter from one port was placedin the duodenum and the other in the ileum. Fluoroscopy and HeidelbergpH capsule studies were performed to characterize intestinal spreadingand pH recovery, respectively. Three treatments were performed: (1)a radiopaque dye and citric acid (CA) were infused into the intestinalsegments, (2) a radiopaque powder capsule containing CA was givenorally, and (3) capsules containing CA and sCT were given orally.Regular blood samples were collected and analyzed byradioimmunoassay (RIA) to determine the absorption characteristics of sCT. Results. Since sCT is an excellent substrate for the pancreatic serineprotease trypsin, the rate of degradation of sCT in the GI lumen isdependent upon the regional pH, activity of digestive enzymes and theconcentration of sCT at the site of absorption. Fluoroscopy resultsclearly showed that when the radiopaque dye was infused into theduodenum and capsule disintegration occurred early, there wassignificant dilution and spreading of the excipients throughout a large sectionof the upper small intestine (USI). However, when the radiopaque dyewas infused into the ileum and capsule disintegration occurred in thelower small intestine (LSI), the excipients moved along as a bolus (i.e.,plug). The pH monitoring results were consistent with the fluoroscopyresults. The pH dropped only momentarily and rose quickly in the USIconsistent with well-stirred mixing kinetics. In the LSI, dilution andspreading were minimal and the drop in pH was greater and persistedfor a longer period of time. Plasma levels of sCT were maximal whendisintegration occurred in the LSI. Conclusions. Since significantly less dilution and spreading occurredin the LSI, the exposure of the intestine to pharmaceutical excipientsand sCT was more concentrated resulting in a higher fraction of sCTabsorbed. The results of this study demonstrate that intestinal mixingkinetics have a dramatic impact on the ability of pharmaceuticalexcipients to modulate the oral bioavailability of peptide drugs like sCT.     

In Vivo Evaluation of an Oral Salmon Calcitonin-Delivery System Based on a Thiolated Chitosan Carrier Matrix

PURPOSE: To develop and evaluate an oral delivery system for salmon calcitonin. METHODS: 2-Iminothiolane was covalently bound to chitosan in order to improve the mucoadhesive and cohesive properties of the polymer. The resulting chitosan-TBA conjugate (chitosan-4-thiobutylamidine conjugate) was homogenized with salmon calcitonin. mannitol, and a chitosan-Bowman-Birk inhibitor conjugate and a chitosan-elastatinal conjugate (6.75 + 0.25 + 1 + 1 + 1). Optionally 0.5% (m/m) reduced glutathione. used as permeation mediator, was added. Each mixture was compressed to 2 mg microtablets and enteric coated with a polymethacrylate. Biofeedback studies were performed in rats by oral administration of the delivery system and determination of the decrease in plasma calcium level as a function of time. RESULTS: Test formulations led to a significant (p < 0.005) decrease in the plasma calcium level of the dosed animals in comparison to control tablets being based on unmodified chitosan. The addition of glutathione in the tablets led to a further improvement in the oral bioavailability of salmon calcitonin with an earlier onset of action and a decrease in the calcium level of about 10% for at least 10 h. CONCLUSIONS: The combination of mucoadhesive thiolated chitosan, chitosan-enzyme-inhibitor conjugates and the permeation mediator glutathione seems to represent a promising strategy for the oral delivery of salmon calcitonin.     

Study on Pulmonary Delivery of Salmon Calcitonin in Rats: Effects of Protease Inhibitors and Absorption Enhancers

Effects of protease inhibitors and absorption enhancers on the absorption of salmon calcitonin (sCT) were evaluated after intratracheal coadministration to rats using the plasma Ca level as an index. Remarkable absorption enhancement could be attained with unsaturated fatty acids such as oleic acid and polyoxyethylene oleyl ether (absorption enhancers) and with chymostatin, bacitracin, potato carboxypeptidase inhibitor and phosphoramidon (protease inhibitors). sCT degrading enzymes had four times higher activity per total protein in membrane fraction of lung homogenates than the activity in cytosol fraction. These enzymes are thought to be serine proteases and metalloenzymes from the in vitro action profile of protease inhibitors. A good correlation between the in vitro activity of protease inhibitors and the in vivo enhancing effect on sCT activity suggested that membrane enzymes are responsible for the inactivation of sCT. Metabolic degradation and low permeability of sCT may be possible barriers to the absorption of sCT.     

Aqueous-Soluble,Non-Reversible Lipid Conjugate of Salmon Calcitonin: Synthesis,Characterization and <Emphasis Type="BoldItalic">In Vivo</Emphasis> Activity

Purpose A novel, non-reversible, aqueous-based lipidization strategy with palmitic acid as a model lipid was evaluated for conjugation with salmon calcitonin (sCT).Materials and Methods A water-soluble ε-maleimido lysine derivative of palmitic acid was synthesized from reaction of palmitic acid N-succinimidyl ester and ε-maleimido lysine. The latter was generated from reaction of α-Boc-lysine and methylpyrrolecarboxylate, with subsequent deprotection of the Boc group. The palmitic derivative was further conjugated with sCT via a thio-ether bond to produce Mal-sCT in aqueous solution. The identity and purity of Mal-sCT was confirmed by Electrospray Ionisation Mass spectrometry (ESI–MS) and HPLC.Results Yield of Mal-sCT was 83%. Dynamic light scattering and circular dichroism data suggested that Mal-sCT presented as a stable helical structure in aqueous solutions of varying polarity, with a propensity to aggregate at concentrations above 11 μM. Cellular uptake of Mal-sCT was twice that of sCT in the Caco-2 cell model, and the conjugate was more resistant to liver enzyme degradation. Mal-sCT exhibited comparable hypocalcemic activity to sCT when administered subcutaneously in the rat model at sCT equivalent dose of 0.114 mg/kg. Peroral Mal-sCT, however, produced variability in therapeutic outcome. While four out of six rats did not respond following intragastric gavage with Mal-sCT, two rats showed significantly suppressed plasma calcium levels (∼60% of baseline) for up to 10 h.Conclusion A novel non-reversible, water-soluble lipid conjugate of sCT was successfully synthesized that showed (1) different aggregation behavior and secondary structure, (2) improved enzymatic stability and cellular uptake, and (3) comparable hypocalcemic activity in vivo compared to sCT.     

Oral Delivery of Sodium Cromolyn: Preliminary Studies In Vivo and In Vitro

Purpose. Herein we report the discovery of a group of derivatized -amino acids that increase the oral bioavailability of sodium cromolyn. Methods. We prepared three N-acylated -amino acids and used these compounds to demonstrate the oral delivery of cromolyn in an in vivo rat model. In vitro experiments, including permeation studies and near infrared spectroscopy, were also performed to initiate an understanding of the mechanism by which these compounds facilitate cromolyn oral delivery. Results. Following oral administration to rats of solutions containing a combination of cromolyn and the delivery agent, significant systemic plasma concentrations of the drug were detected. In vitro studies suggest that absorption of the drug across the gastrointestinal membrane is a passive process. Conclusions. The absolute oral bioavailability of sodium cromolyn in the rat model is estimated to be ~5%. Preliminary mechanistic studies suggest that a complex of the cromolyn/delivery agent facilitates permeation across/through the membrane.     

多肽类药物的口服吸收及其剂型研究

根据国外有关文献，分析了多肽类药物口服生物利用度低的原因，包括胃肠道黏膜的低渗透性、胃酸和各种消化酶的降解作用及首过效应等，并介绍从结构修饰、处方和剂型设计三方面提高多肽口服生物利用度的方法。     

In Vitro and In Vivo Characterisation of PEG-Lipid-Based Micellar Complexes of Salmon Calcitonin for Pulmonary Delivery

Purpose

To investigate DSPE-PEG₂₀₀₀-based micellar formulations of salmon calcitonin (sCT) for their ability to improve pulmonary delivery.

Methods

Micelles were characterised by DLS and ³¹P-NMR spectroscopy. Stability against sCT degrading peptidases, trypsin, ??-chymotrypsin and neutrophil elastase as well as their influence on transepithelial absorption was investigated in vitro. In vivo perfomance of sCT micelles was studied in an experimental model of intratracheal aerosolisation into rats.

Results

Micelles with a mean hydrodynamic diameter of 12?nm spontaneously assembled, when a total concentration of 0.02?mM of PEG-lipid and sCT (at 1:1 molar ratio) was exceeded. Nuclear magnetic resonance confirmed the presence of small micellar structures. The micellar formulation showed increased stability against enzymatic digestion. In vitro studies also showed that sCT micelles were able to enhance transepithelial absorption. Data obtained from in vivo experiments provided evidence of significantly (P?AUC _inf and a relative bioavailability of 160?±?55% when compared to plain sCT solution.

Conclusions

The herein described PEG-lipid micelles are promising carriers for enhanced pulmonary delivery of sCT.     

In Vitro/in Vivo Models for Peptide Oral Absorption: Comparison of Caco-2 Cell Permeability with Rat Intestinal Absorption of Renin Inhibitory Peptides

Pharmaceutical Research -     

Thiolated Chitosans: Design and In Vivo Evaluation of a Mucoadhesive Buccal Peptide Drug Delivery System

Purpose Intravenous application of pituitary adenylate cyclase-activating polypeptide (PACAP) has been identified as a promising strategy for the treatment of type 2 diabetes. To generate a more applicable formulation, it was the aim of this study to develop a sustained buccal delivery system for this promising therapeutic peptide. Methods 2-Iminothiolane was covalently bound to chitosan to improve the mucoadhesive and permeation-enhancing properties of chitosan used as drug carrier matrix. The resulting chitosan–4-thiobutylamidine conjugate was homogenized with the enzyme inhibitor and permeation mediator glutathione (gamma-Glu-Cys-Gly), Brij 35, and PACAP (formulation A). The mixture was lyophilized and compressed into flat-faced discs (18 mm in diameter). One formulation was additionally coated on one side with palm wax (formulation B). Tablets consisting of unmodified chitosan and PACAP (formulation C) or of unmodified chitosan, Brij 35, and PACAP (formulation D) served as controls. Bioavailability studies were performed in pigs by buccal administration of these test formulations. Blood samples were analyzed via an ELISA method. Results Formulations A and B led to an absolute bioavailability of 1%, whereas PACAP did not reach the systemic circulation when administered via formulations C and D. Moreover, in the case of formulations A and B, a continuously raised plasma level of the peptide drug being in the therapeutic range could be maintained over the whole period of application (6 h). Formulations A and B were removed by moderate force from the buccal mucosa after 6 h, whereas formulations C and D detached from the mucosa 4 h after application. Conclusion The study reveals this novel mucoadhesive delivery system to be a promising approach for buccal delivery of PACAP.     

Oral Mucosal Permeability and Stability of Transforming Growth Factor Beta-3 In Vitro

Purpose. To investigate the permeability and localization of topically applied ¹²⁵I-TGF-3 in porcine floor-of-mouth mucosa as a function of concentration and exposure. Methods. The ¹²⁵I-TGF-3 diluted in three different vehicles was applied to the tissue samples mounted in perfusion cells maintained at 37°C. Flux and K_p values were calculated from the perfusate collected over a 24 hour period. The quantity of ¹²⁵I-TGF-3 present in the tissue was determined by horizontal sectioning and subsequent counting. The stability of ¹²⁵I-TGF-3 in saliva and in the tissue was analyzed by SDS polyacrylamide gradient gel electrophoresis. Results. ¹²⁵I-TGF-3 was relatively stable in saliva and in the epithelium; approximately 50% of the total counts in the deeper epithelium were resident in the 25kDa TGF-3 homodimer. A steady-state flux was reached 6 hours post application and K_p value was 4.0 ± 0.6 × 10^-6 (mean ± sem). Penetration of ¹²⁵I-TGF-3 to the basal cell layer was concentration dependent but reached nanomolar concentrations even after extensive surface rinsing, representing over one-thousand fold the IC₅₀ for epithelial cell cycle arrest. Conclusions. The data suggest that topical application of TGF-3 to the oral mucosa in an appropriate vehicle can provide effective therapeutic delivery to the tissue.     

Synthesis,Characterization and In Vivo Efficacy of PEGylated Insulin for Oral Delivery with Complexation Hydrogels

Purpose  This work evaluated the feasibility of combining insulin PEGylation with pH responsive hydrogels for oral insulin delivery. Methods  A mono-substituted PEG–insulin conjugate was synthesized and purified. The site of conjugation was determined by MALDI-TOF MS. Uptake and release of PEGylated insulin was performed in complexation hydrogels to simulate oral dosing. The bioactivity of the conjugate and PK/PD profile was measured in vivo in rats. Results  PEGylation was confirmed to be specifically located at the amino terminus of the B-chain of insulin. Higher loading efficiency was achieved with PEGylated insulin than regular human insulin in pH responsive hydrogels. The release of PEGylated insulin was lower than that of human insulin at all pH levels considered. Full retention of bioactivity of the PEG–insulin conjugate was confirmed by intravenous dosing while subcutaneous dosing exhibited a relative hypoglycemic effect 127.8% that of human insulin. Conclusions  Polyethylene glycol conjugated specifically to the amino terminus of the B-chain of insulin maintained the bioactivity of the protein and significantly extended the duration of the hypoglycemic effect. Used in combination with pH responsive hydrogels, PEGylated insulin has significant potential for oral delivery.     

Development and in Vivo Evaluation of an Oral Delivery System for Low Molecular Weight Heparin Based on Thiolated Polycarbophil

Purpose. It was the purpose of this study to develop a new oral drug delivery system for low molecular weight heparin (LMWH) providing an improved bioavailability and a prolonged therapeutic effect. Methods. The permeation enhancing polycarbophil-cysteine conjugate (PCP-Cys) used in this study displayed 111.4 ± 6.4 M thiol groups per gram polymer. Permeation studies on freshly excised intestinal mucosa were performed in Ussing chambers demonstrating a 2-fold improved uptake of heparin as a result of the addition of 0.5% (w/v) PCP-Cys and the permeation mediator glutathione (GSH). Results. Tablets containing PCP-Cys, GSH, and 279 IU of LMWH showed a sustained drug release over 4 h. To guarantee the swelling of the polymeric carrier matrix in the small intestine tablets were enteric coated. They were orally given to rats. For tablets being based on the thiomer/GSH system an absolute bioavailability of 19.9 ± 9.3% (means ± SD; n = 5) vs. intravenous injection could be achieved, whereas tablets comprising unmodified PCP did not lead to a significant (p < 0.01) heparin concentration in plasma. The permeation enhancing effect and subsequently a therapeutic heparin level was maintained for 24 h after a single dose. Conclusions. Because of the strong and prolonged lasting permeation enhancing effect of the thiomer/GSH system, the oral bioavailability of LMWH could be significantly improved. This new delivery system represents therefore a promising tool for the oral administration of heparin.     

Design and In Vivo Evaluation of An Oral Delivery System for Insulin

Purpose. To develop an oral controlled release system for insulin. Methods. The polymer-inhibitor conjugates carboxymethylcellulose (CMC)-Bowman-Birk inhibitor and CMC-elastatinal were homo- genized with polycarbophil-cysteine conjugate, insulin, and mannitol, compressed to 2 mg microtablets and enteric coated with a polymethacrylate. The protective effect of this delivery system for insulin towards enzymatic degradation, as well as the release profile, was evaluated in vitro. In addition, the effect of the dosage form on glucose levels of diabetic mice was determined. Results. Tablets containing the CMC-inhibitor conjugates showed a strong protective effect for insulin. Whereas 91.6 ± 7.4% (mean ± SD, n = 3) of insulin in the dosage form without the inhibitor conjugates has been degraded within 3 h of incubation in an artificial intestinal fluid containing physiological concentrations of trypsin, chymotrypsin, and elastase, 49.7 ± 5.5% (mean ± SD, n = 3) of insulin remained stable in the delivery system containing the polymer-inhibitor conjugates. Additionally, polycarbophil-cysteine (PCP-Cys) provides high cohesiveness of the dosage form, due to the formation of inter- as well as intramolecular disulfide bonds within the polymer matrix. According to this, a controlled release of insulin could be achieved over a time period of 10 h. Furthermore, in vivo studies in diabetic mice showed a decrease in basal glucose levels of 20% to 40% during a time period of 80 h. Conclusions. Mucoadhesive polymer-inhibitor conjugates might represent a promising excipient in delivery systems for oral (poly)peptide delivery.     

In Vitro and in Vivo Investigations of Dihydropyridine-Based Chemical Delivery Systems for Anticonvulsants

A dihydropyridine-based chemical delivery system (CDS), intended to improve drug delivery to the brain, was investigated with a series of analogues of the anticonvulsant stiripentol. In vitro experiments demonstrated that the rates of hydrolysis of the corresponding pyridinium conjugates were influenced markedly by small changes in the structure of the drug moiety to be released. Thus, allylic esters were hydrolyzed rapidly to drug in all aqueous media, while the analogous saturated esters and an allylic amide derivative were almost totally stable. The mechanism of hydrolysis, which is particular to this series of CDS conjugates, appeared to occur via ionization to a resonance-stabilized carbocation intermediate. The same CDS compounds were investigated in vivo and compared to the corresponding drugs after intravenous administration. Only those CDS compounds that were found to hydrolyze in vitro released appreciable amounts of drug in vivo. Prolonged release of the drug from the CDS in the brain could be demonstrated for these compounds, but the gain in the ratio of brain-to-plasma AUC when the CDS was administered depended on the innate distribution characteristics of the drug. Thus, the drug D3, which had a high brain-to-plasma AUC ratio, did not show an improvement in this ratio when administered as CDS3. In contrast, stiripentol with a poor brain-to-plasma AUC ratio showed a two- to threefold increase in this ratio when administered as a CDS. These investigations highlight the need for a thorough understanding of the mechanism of drug release and the importance of the pharmacokinetic properties of the drug in designing a carrier system for delivery of drugs to the brain.     

Efficacy and Mechanism of Action of Chitosan Nanocapsules for Oral Peptide Delivery

Purpose We have previously shown that high molecular weight (MW > 100 kDa) chitosan nanocapsules are efficient vehicles for improving the oral absorption of salmon calcitonin (sCT). In the present work, our objectives were, first, to investigate the influence of some formulation parameters on the efficacy of chitosan nanocapsules as carriers for the oral administration of sCT and, second, to elucidate the mechanism of interaction of chitosan nanocapsules with intestinal model cell lines. Methods sCT-loaded chitosan nanocapsules were prepared by the solvent displacement technique. They were characterized for their size, zeta potential, and sCT loading. The ability of chitosan nanocapsules to enhance the oral absorption of sCT was investigated in rats by monitoring the serum calcium levels. Finally, the mechanism of interaction of chitosan nanocapsules with the Caco-2 cell model or in the coculture of Caco-2 with HT29-M6 cells was investigated by confocal fluorescence microscopy. Results Chitosan nanocapsules presented a particle size in nanometer range, a positive surface charge, and an efficient encapsulation of sCT. Following oral administration to rats, all formulations of nanocapsules exhibited the ability to reduce calcemia levels; however, the intensity of the response varied depending on the formulation conditions. With regard to the mechanism of interaction of chitosan nanocapsules with cell culture, the xz images evidenced that chitosan nanocapsules interact and remain associated to the apical side of both model cell cultures. In addition, chitosan nanocapsules showed a preferable association to the mucus-secreting cells (HT29-M6). Conclusions Chitosan nanocapsules are able to enhance and prolong the intestinal absorption of sCT and this effect could be mainly ascribed to their mucoadhesive character and intimate interaction with the intestinal barrier.     

Visualization of Insulin-Loaded Nanocapsules: In Vitro and in Vivo Studies After Oral Administration to Rats

Purpose. Biodegradable poly(isobutylcyanoacrylate) nanocapsules have been recognized as a promising carrier for oral administration of peptides and proteins. In the present study, we investigate the fate of insulin-loaded nanocapsules by fluorescence and transmission electron microscopy (TEM) after intragastric force-feeding to rats. Methods. Insulin-, Texas-red^®-labeled insulin, or gold-labeled insulin-loaded nanocapsules were first characterized. Rats received a single dose of nanocapsules (diameter 60-300 nm, 57 IU insulin/kg) by intragastric force-feeding. After 90 min, ileum was isolated and prepared for fluorescence and transmission electron microscopy. Results. Nanocapsules were observed on both sides of the gut epithelium and in blood capillaries. In M-cell-free epithelium, apparently intact nanocapsules could be seen in the underlying tissue, suggesting they could cross the epithelium and carry the encapsulated peptide. In M-cell-containing epithelium, nanocapsules appeared degraded in the vicinity of macrophages. It is noteworthy that intestinal absorption of nanocapsules was observed without artifacts forcing the nanocapsules to stay in the gut. Conclusions. Based on TEM observations, this study shows the intestinal absorption of biodegradable nanocapsules leading to the transport of insulin across the epithelium mucosa. The fate of the nanocapsules appeared different depending on the presence or the absence of M cells in the intestinal epithelium.     

Oral Absorption of Peptides: The Effect of Absorption Site and Enzyme Inhibition on the Systemic Availability of Metkephamid

In this study the intestinal degradation and absorption of a synthetic pentapeptide, metkephamid, were investigated in the rat by determination of its wall permeabilities in the small and large intestine and the extent and mechanism of its intestinal degradation. The peptide was metabolized in the gut wall through contact with membrane-bound enzymes in the brush border membrane. The extent of metabolic inactivation depended on the intestinal segment investigated and decreased in the axial direction. No metabolism was found in the colon. The dimensionless wall permeabilities (P _w*), determined by single-pass perfusion, were also site dependent. P _w* was highest in the ileum [1.91 ± 0.24, (SE); n = 4], followed by the jejunum (1.64 ± 0.34; n = 4) and the colon (0.67 ± 0.38; n = 4). Based on the permeability data alone and under the assumption of no presystemic metabolism, complete bioavailability would be predicted for metkephamid. However, following oral administration, the mean absolute bioavailability was only 0.22 ± 0.065% (n = 3), indicating the overall dominance of degradation in the absorption process. Thus future strategies in oral peptide delivery should focus on increasing the stability of the peptide in the intestine by modifying the peptide structure and/or delivering the compound to an intestinal segment showing little or no enzymatic degradation.     

Design of Biodegradable Nanoparticles for Oral Delivery of Doxorubicin: <Emphasis Type="BoldItalic">In vivo</Emphasis> Pharmacokinetics and Toxicity Studies in Rats

Purpose  Doxorubicin, a potent anticancer drug associated with cardiotoxicity and low oral bioavailability, was loaded into nanoparticles with a view to improve its performance. Methods  Doxorubicin loaded PLGA nanoparticles were prepared by a double emulsion method. The pH dependent stability of nanoparticles in simulated fluids was evaluated. DSC and XRD studies were carried out in order to ascertain the nature of doxorubicin in formulations in conjunction with accelerated stability studies. The in vitro release was investigated in phosphate buffer. The pharmacokinetic and toxicity studies were conducted in rats. Results  Nanoparticles had an average size of 185 nm, with 49% entrapment at 10% w/w of polymer. The particles displayed good pH dependent stability in the pH range 1.1–7.4. DSC and XRD studies revealed the amorphous nature of doxorubicin in nanoparticles and the accelerated stability studies revealed the integrity of formulations. Initial biphasic release (20%) followed by a sustained release (80%) for 24 days was observed under in vitro conditions. The doxorubicin loaded nanoparticles demonstrated superior performance in vivo as evident by enhanced bioavailability and lower toxicity. Conclusions  Together, the data indicates the potential of doxorubicin loaded nanoparticles for oral chemotherapy. Further, these formulations could be explored for new indications like leishmaniasis.