Effects of Salicylate and Other Enhancers on Rectal Absorption of Erythropoietin in Rats

Intestinal permeation enhancers for oral peptide delivery

Intestinal permeation enhancers (PEs) are one of the most widely tested strategies to improve oral delivery of therapeutic peptides. This article assesses the intestinal permeation enhancement action of over 250 PEs that have been tested in intestinal delivery models. In depth analysis of pre-clinical data is presented for PEs as components of proprietary delivery systems that have progressed to clinical trials. Given the importance of co-presentation of sufficiently high concentrations of PE and peptide at the small intestinal epithelium, there is an emphasis on studies where PEs have been formulated with poorly permeable molecules in solid dosage forms and lipoidal dispersions.

Safety and efficacy of sodium caprate in promoting oral drug absorption: from in vitro to the clinic

A major challenge in oral drug delivery is the development of novel dosage forms to promote absorption of poorly permeable drugs across the intestinal epithelium. To date, no absorption promoter has been approved in a formulation specifically designed for oral delivery of Class III molecules. Promoters that are designated safe for human consumption have been licensed for use in a recently approved buccal insulin spray delivery system and also for many years as part of an ampicillin rectal suppository. Unlike buccal and rectal delivery, oral formulations containing absorption promoters have the additional technical hurdle whereby the promoter and payload must be co-released in high concentrations at the small intestinal epithelium in order to generate significant but rapidly reversible increases in permeability. An advanced promoter in the clinic is the medium chain fatty acid (MCFA), sodium caprate (C(10)), a compound already approved as a food additive. We discuss how it has evolved to a matrix tablet format suitable for administration to humans under the headings of mechanism of action at the cellular and tissue level as well as in vitro and in vivo efficacy and safety studies. In specific clinical examples, we review how C(10)-based formulations are being tested for oral delivery of bisphosphonates using Gastro Intestinal Permeation Enhancement Technology, GIPET (Merrion Pharmaceuticals, Ireland) and in a related solid dose format for antisense oligonucleotides (ISIS Pharmaceuticals, USA).

Self-dissolving microneedles for the percutaneous absorption of EPO in mice

Erythropoietin (EPO) loaded microneedles were prepared using thread-forming polymer as a base for the percutaneous administration of EPO. The used polymers were dextrin, chondroitin sulfate and albumin. Under room temperature, EPO solution was added to high concentration of polymer solution and microneedles were prepared by forming thread with polypropylene tips. The mean weight of microneedle was 0.59 +/- 0.01 mg and length and basal diameter were 3.24 +/- 0.16 and 0.55 +/- 0.03 mm, respectively. Four microneedles were percutaneously (pc) administered to mice at the EPO dose levels of 100 IU/kg. After administration, blood samples were collected for 24 h and serum EPO levels were measured. Dextrin EPO microneedles were administered both pc and subcutaneously (sc) to mice. Serum EPO levels vs. time profiles showed Cmax of 138.6 +/- 16.1 and 146.5 +/- 8.0 mIU/ml, respectively. Tmax were 7.5 h. The values of bioavailability (BA) of EPO were 82.1 and 99.4%, respectively. By decreasing the dose from 100 to 50 and 25 IU/kg, dose-dependent serum EPO levels vs. time profiles were not clearly obtained. When chondroitin sulfate and albumin were used as the microneedle base, the serum EPO levels vs. time profiles showed almost the same pattern. Cmax of chondroitin sulfate and albumin microneedles were 96.3 +/- 8.8 and 132.2 +/- 18.9 mIU/ml, respectively. AUCs were 835.1 and 1098.7 mIU h/ml. Tmax were 8 and 6.8 h. These results suggest the usefulness of microneedles for the percutaneous administration of EPO.

Pharmacokinetic and pharmacodynamic studies following percutaneous absorption of erythropoietin micropiles to rats

To ascertain the pharmacological activity of erythropoietin (EPO) administered by self-dissolving micropiles (SDMP), four kinds of EPO SDMPs were prepared and were administered to rats in 4 consecutive days at 200, 500, 1000 and 2300 IU/kg. After the start of the experiment, blood samples were obtained once a day for 10 days and percent circulating reticulocytes were counted using Miller technique. At the lower doses, 200 and 500 IU/kg, pharmacological activity of EPO was not obtained. By increasing EPO dose to 1000 IU/kg, circulating reticulocytes significantly increased at days 4, 5, 6 and 7 after the start of the experiment and the average value for the change in reticulocyte levels during day 1 and day 5 was 170.9%. With the highest dose, 2300 IU/kg, higher circulating reticulocytes levels started to increase at the 4th day after the start of the experiment and maintained from day 5 to day 10. The average of the changes in reticulocyte from day 5 to day 10 was 251%. Dose-dependent circulating reticulocytes increase was observed at the higher dose range, 1000 and 2300 IU/kg. To study the linearity on the serum EPO level vs. time curves, pharmacokinetic experiment was performed with rats. After the administration of EPO SDMPs to rats, 200, 500, 1000 and 2300 IU/kg, serum EPO levels gradually increased and reached to the maximum level, C(max), at 18 h after administration. The C(max)s were 100.4+/-11.7 mIU/ml (200 IU/kg), 346.6+/-11.8 mIU/ml (500 IU/kg), 391.6+/-17.6 mIU/ml (1000 IU/kg), and 1094.9+/-114.8 mIU/ml (2300 IU/kg), respectively. AUCs were 1407+/-231, 3843+/-402, 5363+/-482 and 15,566+/-1894 mIU h/ml. Linear relation was obtained between serum EPO level and EPO dose administered as SDMP. With histological study, any adverse effect was not found out on the skin where SDMPs were administered for consecutive 4 days. These results suggest the usefulness of SDMP as a new percutaneous delivery system of EPO.

Pharmacokinetic and pharmacodynamic studies following oral administration of erythropoietin mucoadhesive tablets to beagle dogs

Oral administration of mucoadhesive tablets containing erythropoietin (EPO) and an absorption enhancer Labrasol was studied in rats and dogs. Mucoadhesive tablets were prepared using Sylysia 550 holding the absorption enhancer and Carbopol 974P as a mucoadhesive agent. Mucoadhesive tablets were covered with a water-insoluble backing layer made of cellulose acetate and a pH-sensitive covering layer made of Eudragit L/Eudragit S. Tablet was administered into the rat jejunum at EPO dose of 100 IU/kg and serum samples were collected for 6h. Serum EPO level was analysed with a standard ELISA procedure. After administration, rats showed a maximum serum EPO level of C(max) 70.6 +/- 8.9 mIU/ml. Oral administration of a single tablet containing 100 IU/kg EPO to beagle dogs showed a C(max) of 24.6 +/- 4.1. When EPO dose was increased to 500 IU/kg and the number of tablets was also increased to 5, the C(max) was 54.8 +/- 9.0 mIU/ml. However, when EPO, 100 IU/kg dose was divided into five tablets, the C(max) was 15.5 +/- 1.8 mIU/ml. In the absence of absorption enhancer, the C(max) was 35.8 +/- 3.8 with 500 IU/kg dose distributed among five tablets. Pharmacodynamic studies were carried out following oral administration of mucoadhesive tablets for 6 consecutive days at an EPO dose of 500 IU/kg. Whole blood samples were collected and percent circulating reticulocytes were counted using Miller technique. The increase in percent circulating reticulocytes was found to be 1.7% on day 8 following oral administration. As a control study, EPO was administered by i.v. route at a dose of 300 IU/kg for 3 consecutive days and the percent circulating reticulocytes were counted. Mucoadhesive tablets showed promising results as an oral drug delivery system for protein therapeutics.

Gastro-intestinal patch system for the delivery of erythropoietin

The absorption of erythropoietin (EPO) from rat small intestine was studied using gastro-intestinal patches (GI-PS) in the presence of absorption enhancers. Surfactants such as a saturated polyglycolysed C8-C18 glyceride (Gelucire 44/14), PEG-8 capryl/caprylic acid glycerides (Labrasol), and polyoxyethylene hydrogenated castor oil derivative (HCO-60) were used as absorption enhancers at 143, 94 and 20 mg/kg, respectively. The absorption of EPO was studied by measuring serum EPO levels by an ELISA method after small intestinal administration of EPO-GI-PS preparation in rats at the EPO dose level of 100 IU/kg. Labrasol showed the highest absorption enhancing effect after intrajejunum administration with maximum serum EPO level of 84.1+/-11.4 mIU/ml while Gelucire 44/14 and HCO-60 showed 43.5+/-9.8 and 26.5+/-2.3 mIU/ml, respectively. The appropriate site for EPO absorption was also investigated. Jejunum was found to be the most efficient absorption site for the absorption of EPO from GI-PS. Using Labrasol as the absorption enhancer and jejunum as the absorption site, the effect of EPO dose on EPO absorption was studied by increasing the EPO dose from 50, to 100, 300 and 600 IU/kg. It was found that 100 IU/kg was the optimum dose with a serum EPO level of 84.1+/-11.4 mIU/ml while escalating doses showed decreases in serum EPO levels 48.3+/-5.6 for 300 IU/kg and 50.6+/-10.3 mIU/ml for 600 IU/kg. The percent bioavailability (BA) of EPO-GI-PS with Labrasol as absorption enhancer was 7.9 at 50 IU/kg, 12.1 at 100 IU/kg, 3.2 at 300 IU/kg and 1.2 at 600 IU/kg. Histological studies showed no adverse effect at the site of administration.

Liquid filled nanoparticles as a drug delivery tool for protein therapeutics

In the present study, an attempt was made to study the feasibility of nanoparticulate adsorbents in the presence of an absorption enhancer, as a drug delivery tool for the administration of erythropoietin (EPO) to the small intestine. Liquid filled nano- and micro-particles (LFNPS/LFMPS) were prepared using solid adsorbents such as porous silicon dioxide (Sylysia 550), carbon nanotubes (CNTs), carbon nanohorns, fullerene, charcoal and bamboo charcoal. Surfactants such as a saturated polyglycolysed C8-C18 glyceride (Gelucire 44/14), PEG-8 capryl/caprylic acid glycerides (Labrasol) and polyoxyethylene hydrogenated castor oil derivative (HCO-60) were used as an absorption enhancer at 50mg/kg along with casein/lactoferrin as enzyme inhibitors. The absorption of EPO was studied by measuring serum EPO levels by an ELISA method after small intestinal administration of EPO-LFNPS preparation to rats at the EPO dose level of 100 IU/kg. Among the adsorbents studied, CNTs showed the highest serum EPO level of 62.7 +/- 11.6 mIU/ml. In addition, with the use of casein, EPO absorption was improved, C(max) 143.1 +/- 15.2 mIU/ml. Labrasol showed the highest absorption enhancing effect after intra-jejunum administration than Gelucire 44/14 and HCO-60, 25.6 +/- 3.2 and 22.2 +/- 3.6 mIU/ml, respectively. Jejunum was found to be the best absorption site for the absorption of EPO from LFNPS. The use of CNTs as LFNPS, improved the bioavailability of EPO to 11.5% following intra-small intestinal administration.

Roles of erythropoietin in human milk

Erythropoietin (Epo) is one of many biologically active growth factors present in human and animal milk. Accumulating evidence shows important developmental roles for these milk-borne growth factors. Although Epo is present in biologically relevant amounts in mammalian milk, the roles of Epo in milk are incompletely defined. A significant proportion of milk-borne Epo resists proteolytic degradation. Epo receptors (EpoR) have been found on gastric mucosa and intestinal mucosa, and in mesenteric vessel endothelium. Evidence to date shows that intact Epo reaches these local organs, as well as distal organs. After feeding Epo, local gastrointestinal physiological effects are seen in suckling rats. In humans and rats, short-term feeding of high-dose Epo increases reticulocytes, but it is unclear whether sustained treatment increases red cell mass.

CONCLUSION

Further work towards understanding the physiological and potential pharmacological roles of enterally administered Epo is necessary.

Enteral absorption of erythropoietin in the suckling rat

Milk contains biologically relevant concentrations of erythropoietin (Epo), the primary hormone responsible for erythrocyte production. In animals, milk-borne Epo stimulates erythropoiesis. Epo receptors have been found in nonerythropoietic tissues including gastrointestinal tract. We hypothesized that milk-borne Epo is distributed to local gastrointestinal tissues, absorbed intact, and then distributed peripherally via the systemic circulation. Rat milk protected recombinant human Epo (rhEpo) from degradation in the suckling rat gastrointestinal tract. Simulated digestion of (125)I-rhEpo in suckling rat gastrointestinal juices was performed. When measured by acid precipitation and immunoassay, rat milk protected rhEpo from gastrointestinal juices better than saline (p < 0.0001). The fate of enterally administered milk-borne (125)I-rhEpo was examined in 10-d-old rats. RhEpo fed in rat milk was better protected from in vivo proteolytic degradation than rhEpo in saline (p < 0.05). After enteral (125)I-rhEpo dosing, radiolabeled protein from gastric tissue comigrated on SDS-PAGE with intact rhEpo at 36.5 kD. To determine the local and systemic distribution of physiologic intakes of rhEpo, suckling rats were fed (125)I-rhEpo in rat milk, and tissues were harvested 1, 2, and 4 h later. Intact (125)I-rhEpo was found in gastric and small intestinal walls and lumens. Five percent of total administered dose was found intact in the plasma, whereas another 8 to 10% of total administered dose was localized to bone marrow, percentages comparable to those seen after parenteral administration. Radiolabel was also localized to liver and peripheral solid tissues. These patterns of localization and degradation of rhEpo after acute administration support both systemic absorption and gastrointestinal cellular processing.

Absorption enhancement in intestinal epithelial Caco-2 monolayers by sodium caprate: assessment of molecular weight dependence and demonstration of transport routes

Sodium caprate (C10), a medium chain fatty acid, is used clinically to enhance rectal absorption of the low molecular weight (MW) drug ampicillin. The main aim of this study was to investigate whether C10 also enhances the permeability of high MW model drugs in a model of the intestinal epithelium. The second aim was to present visual evidence of the route of enhanced transport across the epithelial cell layer. The studies were performed in Caco-2 monolayers cultured on permeable supports. The effects of non-toxic concentrations (< or = 13 mM) of C10 on drug transport across the monolayers was studied using monodisperse 14C-polyethylene glycols (MW 238-502; 14C-PEGs), 125I-Arg5-vasopressin (MW 1,208), 125I-insulin (MW 6,000) and FITC-labelled dextrans (MW 4,400 and 19,600; FD4 and FD20 respectively) as model drugs. Electron and confocal laser scanning microscopy were used to demonstrate transport routes across the epithelium. 10 mM C10 increased the permeability of all 14C-PEGs to approximately the same extent. 13 mM C10 increased the permeability of 125I-Arg8-vasopressin 10-fold. Only small increases in FD4 and FD20 permeabilities were observed. After C10 exposure, both tight junctions with normal morphology and those with dilatations showed an increased permeability to ruthenium red, indicating that C10 enhanced the paracellular transport of molecules with a MW < 1,000. Confocal microscopy showed that C10 increased the transport of FD4 and FD20 by the paracellular route. In conclusion, non-toxic concentrations of C10 can be used to enhance the permeability of drugs of MW up to approximately 1,200. Enhancement of the absorption of molecules larger than 4,000 is quantitatively insignificant. The enhanced permeability occurred via the paracellular pathway.

Human milk as a potential enteral source of erythropoietin

In addition to its content of traditional nutrients, milk is a rich source of hormones and peptides, which survive digestion in the neonatal gastrointestinal tract secondary to lower proteolytic activity and increased protein permeability. Previous studies have shown accelerated erythropoiesis or elevated serum erythropoietin (Epo) levels in neonatal (suckling) animals after maternal phlebotomy or maternal hypoxia exposure. We sought to determine whether significant quantities of Epo are present in human milk and whether Epo remains intact under physiologic digestion conditions. Immunoreactive Epo concentrations were determined in 409 human milk samples obtained from mothers of term and premature infants. Samples collected between birth and postpartum d 134 were divided into 11 postpartum day groups. Mean milk-borne Epo concentrations were within the normal range for plasma Epo concentrations and rose with postpartum day (F10,398 = 5.82, p < 0.0001). No differences were observed between milk collected from mothers of premature versus term infants. Estimated weekly human milk-borne Epo intakes approximated the lower range of published parenteral therapeutic doses. In simulated digestion at physiologic pH levels of 3.2, 5.8, and 7.4, milk-borne Epo resisted degradation at 1 and 2 h, compared with baseline. Therefore, we conclude that human milk contains considerable amounts of Epo which resist degradation after exposure to gastric juices at physiologic pH levels. These results support continued investigation into the fate and developmental roles of Epo in human milk.