Intravenous and subcutaneous pharmacokinetics and rectal bioavailability of human epidermal growth factor in the presence of absorption promoter in rats

Exposure assessment of epidermal growth factor to various tissues in mice after intravenous and subcutaneous administration

OBJECTIVES

This study was conducted to examine the tissue distribution of human recombinant epidermal growth factor (EGF) after multiple intravenous and subcutaneous injections in mice.

METHODS

Male BALB/c mice were divided into (1) EGF 1 mg/kg intravenous dose, (2) EGF 5 mg/kg intravenous dose, (3) drug-free intravenous control, (4) EGF 1 mg/kg subcutaneous dose, (5) EGF 5 mg/kg subcutaneous dose and (6) drug-free subcutaneous control groups. EGF and drug-free dosing solutions were injected by intravenous and subcutaneous injections once a day for 3 days. EGF concentrations in serum and tissues of kidney, liver, lung, small intestine and tongue were determined by ELISA.

KEY FINDINGS

As the intravenous and subcutaneous doses were increased from 1 to 5 mg/kg, serum Cmax and area under the concentration-time curve (AUC) values were increased dose-proportionally. In lung, tongue and small intestine, increases in AUC were dose-proportional after intravenous injections, but greater than dose-proportional after subcutaneous injections. The fold-increases in Cmax and AUC values were lowest in liver and highest in kidney.

CONCLUSION

Based on Cmax and AUC data, the systemic exposure achieved by subcutaneous injections was comparable with that achieved by intravenous injections.

Effect of protease inhibitors on degradation of recombinant human epidermal growth factor in skin tissue

Recombinant human epidermal growth factor (rhEGF), a polypeptide of 53 amino acid residues, is subject to degradation by numerous enzymes, especially proteases, when it is applied on the skin for the treatment of open wound. Amastatin, aprotinin, bestatin, EDTA, EGTA, gabexate, gentamicin, leupeptin, and TPCK were investigated for the possible protease inhibitors, which may use to protect rhEGF from degradation by the enzymes in the skin. Skin homogenates containing protease inhibitors and rhEGF were incubated at 37 degrees C for 30 minutes. After the reaction was stopped with trifluoroacetic acid, the amount of rhEGF remaining in the sample was determined with an HPLC method. The percentages of rhEGF degraded, at the skin/PBS ratio of 0.25, in the mouse, rat, and human skin homogenate were 85%, 70%, and 46%, respectively. The degree of degradation of rhEGF in the cytosolic fraction was higher than that in the membrane fraction and these enzyme reactions were completed in 30 minutes. Bestatin, EGTA, and TPCK showed significant inhibitory effects on the degradation of rhEGF in the two fractions (p<0.05), while the other protease inhibitors had no significant inhibitory effects or, even resulted in deleterious effects. Therefore, the formulation containing one or several inhibitors among these effective inhibitors would be a promising topical preparation of rhEGF for the treatment of open wound.

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

To develop a new treatment for patients with anaemia in which erythropoietin (EPO) can be given without injection, the effects of promoters of the rectal absorption of EPO were studied. Recombinant human (rHu) EPO (5000 units) in a dosing solution or in a rectal suppository was placed in the rectum of healthy rats and changes in serum EPO levels were monitored by an enzyme-linked immunosorbent assay. Without a promoter, rHuEPO was not absorbed. Sodium glycocholate, sodium caprate, and sodium salicylate in the solution of rHuEPO increased the absorption of rHuEPO. Sodium salicylate or sodium caprate in the suppository with rHuEPO also increased its absorption. The bioavailability of rHuEPO in a suppository containing 5% sodium salicylate compared with that by an intravenous injection was 1·2%. rHuEPO given in rectal suppositories containing sodium salicylate and inserted once a day for 6 consecutive days increased erythropoiesis in peripheral blood.

Restoration of rat colonic epithelium after in situ intestinal instillation of the absorption promoter, sodium caprate

Background: Sodium caprate (C10) is an oral absorption promoter that is currently in clinical trials as a component of solid dosage forms for poorly permeable small molecules and peptides. Clinical data with zoledronic acid tablets suggest that significant delivery along with acceptable safety can be achieved from a once-a-week dosing regime. C10 has surfactant-like properties at the high doses used in vivo and therefore we examined its effects on rat intestinal epithelium following intestinal instillation. Results: Addition of 100 mM concentrations of C10 with the paracellular flux marker, fluorescein isothiocyanate-dextran 4 kDa, permitted a bioavailability of 33% to be achieved. When C10 was added 10, 30 and 60 min in advance of fluorescein isothiocyanate-dextran 4 kDa, enhancement still occurred, but was progressively reduced. Histology revealed that the permeability increase was likely related in part to superficial epithelial damage caused in the first few minutes of exposure, which was rapidly repaired within 30–60 min. Conclusions: Design of optimized dosage forms containing C10 should corelease the payload and promoter close to the epithelium in high concentrations. While C10 induces some epithelial damage, its remarkable capacity for epithelial repair may render this effect insignificant in vivo.

Effect of excipients on the stability and transport of recombinant human epidermal growth factor (rhEGF) across Caco-2 cell monolayers

The effect of sixteen excipients on the transport of recombinant human epidermal growth factor (rhEGF) across Caco-2 cell monolayers was examined at 37 degrees C. The apparent apical to basolateral (A-B) permeability (Papp) of 30 microM rhEGF was 8.15 x 10(-7) cm/sec, indicative of a poor level of absorption in the GI tract. The Papp was 1.7- and 6.3-fold greater than the Papp in the basolateral to apical (B-A) direction and the A-B permeability of mannitol, respectively, and decreased dramatically to a negligible level at 4 degrees C, consistent with a receptor mediated transcytosis of rhEGF. The stability of rhEGF was very poor, undergoing more than 85% degradation in 2 h in the transport medium at 37 degrees C. A significant increase in the Papp could be achieved by the addition of certain excipients, as exemplified by 23, 21, 20 and 16-fold increases, in the presence of sodium taurochenodeoxycholate (NaTCDC), sodium taurodeoxycholate (NaTDC), sodium glycodeoxycholate (NaGDC) and sodium laurylsulfate (SLS) (all at a concentration of 1% w/v), respectively. A significant increase in stability could also be achieved by the addition of some of the excipients, as represented by 1% SLS, which nearly completely stabilized the rhEGF. Unfortunately, however, an increase in the Papp of rhEGF could not be achieved without a simultaneous and extensive decrease in the integrity of the cell membranes. Thus, more efficient excipients, that specifically enhance the permeation of rhEGF and do not alter the membrane integrity, should be pursued in order to safely enhance the permeation of rhEGF.

Preparation and evaluation of poly(L-lactic acid) microspheres containing rhEGF for chronic gastric ulcer healing

Biodegradable microspheres containing recombinant human epidermal growth factor (rhEGF) were prepared using poly(L-lactic acid) by a solvent evaporation method based on multiple w/o/w emulsion. Encapsulation efficiency and initial release were influenced by the amount of polymer, inner water phase volume and osmotic pressure difference between inner water phase and outer water phase. The effect of osmotic pressure difference between inner water phase and outer water phase in w/o/w emulsion on particle size, porosity and in vitro release of rhEGF from microspheres were also studied. Microspheres prepared with the optimized osmotic pressure, polymer amount and inner water volume produced 21% initial release on the first day with 92% encapsulation efficiency. The blood concentration of rhEGF was maintained at constant levels for 9-11 days after a single subcutaneous (s.c.) administration of rhEGF microspheres. The gastric ulcer healing effect of a single s.c. administration of rhEGF microspheres was increased 1.44-fold compared with twice a day s.c. administration of rhEGF saline solution after 11 days. The enhanced curative ratio of rhEGF loaded microspheres may be due to the optimized osmotic pressure, high encapsulation efficiency and sustained release pattern.

Perturbation of epidermal growth factor clearance after radioiodination and its implications

The clearance of human epidermal growth factor (hEGF1-53) has been thought to be mediated mainly by a high-capacity receptor system, yet relatively low in vivo clearance rates (<10 mL/min/kg) and long terminal elimination half-lives (>120 min) have been observed in rats receiving the peptide that was iodinated by the oxidative chloramine-T (CT) method. We investigated if a mild, less oxidative iodination by the lactoperoxidase (Enzymobeads, EB) method, which is known to yield an iodinated peptide with receptor-binding equivalence, could produce a labeled peptide that behaves pharmacokinetically similar to the native material. For comparison, a parallel study was also conducted with EB-125I-hEGF1-48, which in its native form has a much reduced receptor binding activity due to the loss of the C-terminal pentapeptide. Plasma radioactivity concentrations were determined by trichloroacetic acid (TCA) precipitation and immunoprecipitation. Rats cleared unlabeled hEGF1-53 and hEGF1-48 markedly faster (CL(tot) > 120 mL/min/kg) than their radiolabeled counterparts. Approximately 96% of the hEGF1-53 dose was cleared during the initial phase (0-4 min), as opposed to only 5-14% for the iodinated peptide. Similar change was also observed for EB-125I-hEGF1-48 and CT-125I-hEGF1-53. The pharmacokinetic behavior of EB-125I-hEGF1-53 was, in fact, comparable to that of CT-125I-hEGF1-53. These observations indicate that receptor-binding equivalence does not have direct relationship with in vivo EGF clearance. Both iodination methods (oxidative CT and less oxidative EB) might have perturbed one or more steps in the cascade of ligand-receptor internalization and intracellular procession, which in turn modified the disposition of the peptides. In addition, the two independent precipitation techniques for the same peptide generated different kinetic outcomes. The overall experimental results suggest that it is unacceptable to use an iodinated form to characterize the disposition of peptides/proteins like EGF with a specific receptor system mediating its clearance.

Dose-dependent plasma clearance of human epidermal growth factor in rats

Exogenously administered human epidermal growth factor (hEGF) shows a marked dose-dependent plasma disposition in rats. In the present study, total plasma clearance (CLtotal) of hEGF was examined from the viewpoint of hepatic blood flow and accessible EGF receptors in a dosing range of hEGF from 30 to 1000 micrograms/kg. In rats in which down-regulation of EGF receptors caused a reduction in their number (50% below the normal level) (group 1), the CLtotal of hEGF was decreased only at a medium dose (100 micrograms/kg) compared to those in normal rats. In rats in which hepatic intoxication with carbon tetrachloride caused 50% reduction of both EGF receptor number and hepatic blood flow (group 2), CLtotal was decreased at low and medium hEGF doses. The decrease at a low hEGF dose was proportional to the decrease in the hepatic blood flow. In rats with reduced hepatic blood flow caused by hypothermia (group 3), CLtotal was decreased at all hEGF doses examined, and the decrease at a low hEGF dose (50 micrograms/kg) was proportional to the hepatic blood flow. The decreases of CLtotal at a medium hEGF dose in groups 1, 2 and 3 were well accounted for by the decrease of hepatic blood flow and/or EGF receptor number in a well-stirred model.(ABSTRACT TRUNCATED AT 250 WORDS)

The ulceration-associated cell lineage (UACL) reiterates the Brunner's gland differentiation programme but acquires the proliferative organization of the gastric gland

The ulceration-associated cell lineage (UACL) develops in the human gastrointestinal mucosa after ulceration; it grows out from the bases of adjacent crypts and ramifies in the lamina propria to form a new gland, finally giving rise to a duct by which the glandular secretion and indeed cells are carried to the surface. Using immunocytochemistry and in situ hybridization with 35S-labelled riboprobes, we have defined the pattern of trefoil peptide gene expression (pS2; human spasmolytic polypeptide, hSP), epidermal growth factor/urogastrone (EGF/URO), and the distribution of cell proliferation during the development of the UACL, as indicated by immunostaining for proliferating cell nuclear antigen (PCNA). Our studies reveal that the morphogenesis of the UACL shows a marked morphological resemblance to developing Brunner's glands; the pattern of trefoil peptide gene expression during UACL development is also very similar. However, trefoil peptide gene expression in the mature UACL complex is unique amongst gastrointestinal cells. The mature UACL shows a distinctive proliferative organization: while the early buds and glands are non-proliferative, apparently being fed by cells from the parent crypts, a definitive proliferative zone develops within the duct. This, of course, corresponds to the location of the gastric gland proliferative zone. We propose that while the UACL shows novel features, it shares its differentiation programme with Brunner's glands, but its pattern of cell renewal eventually is that of the gastric gland.

Effect of absorption promoters on subcutaneous absorption of human epidermal growth factor in rats

Subcutaneous administration of human epidermal growth factor (hEGF) to rats gave a significantly smaller value of area under the curve (AUC) of concentration in plasma of immunoreactive hEGF versus time than intravenous administration, probably because the slow entry rate into the blood circulation and consequently the enzymic degradation of hEGF at the injection site. In the present study, absorption promoters such as sodium caprate, N-acylamino acids, disodium ethylenediamine-tetraacetate (EDTA), and sodium glycocholate were used because they were expected to inhibit the enzymic degradation of hEGF at the injection site and to facilitate the entry of hEGF into the blood circulation. Coadministration of an absorption promoter with hEGF significantly increased the entry rate and AUC value of immunoreactive hEGF compared with the case without the absorption promoter. The enzymic degradation of hEGF in the supernatant of the rat subcutaneous tissue homogenates and in the buffer solution containing leucine aminopeptidase or protease was markedly inhibited by the presence of the absorption promoters except EDTA. On the other hand, only EDTA increased the initial entry rate of FITC-dextran (M(r), 4000), which is not metabolized at the injection site, although all absorption promoters including EDTA markedly increased the extravasation of Evans blue. Thus, the increased subcutaneous bioavailability of hEGF in the presence of absorption promoters (except EDTA) was mainly attributed to the inhibitory effect of absorption promoters against the enzymic degradation of hEGF at the subcutaneous tissues.

Transport of peptide and protein drugs across biological membranes

The transport characteristics of peptide and proteins drugs across various epithelial membrane barriers are outlines. These include transport through the intestinal, buccal, nasal and pulmonary absorptive mucosae, as well as transdermal penetration. Because peptides and proteins are hydrophilic and high molecular weight compounds, they commonly show minor permeability across the mentioned biological membranes. In order to improve their transport properties and thereby their systemic bioavailability, several strategies can be undertaken, such as the synthesis of stabilized and lipophilic analogues, the application of absorption enhancers and protease inhibitors, and the design of suitable dosage forms (e.g., liposomes, biodegradable nanocapsules, bioadhesive microspheres).

Possible mechanism of gastric mucosal protection by epidermal growth factor in rats

The mechanism of the protection by human epidermal growth factor (hEGF) against the gastric mucosal lesions induced by acidified ethanol was studied in rats. At different times following the subcutaneous administration of hEGF (30 micrograms/kg), intragastric acidified ethanol (EtOH: 0.125 M HC1 = 50:50 v/v%) was administered to induce an experimental gastric mucosal lesion. Mean length of the lesion in the gastric mucosa was used as a lesion index. Extravasation of intravenously injected Evans blue into the gastric wall and gastric contents was used as an indicator of vascular permeability. Pretreatment with hEGF decreased both the gastric mucosal lesions and the increase of vascular permeability caused by acidified ethanol with similar time profiles relative to pretreatment with hEGF. Maximal protective actions of hEGF occurred about 10 to 30 min after the observed peak plasma concentration of hEGF. Indomethacin and N-ethylmaleimide, but not iodoacetamide, blocked the protective action of hEGF, indicating that endogenous prostaglandins and/or sulfhydryls may participate in the protective action of hEGF. The content of endogenous nonprotein sulfhydryls in the gastric mucosa decreased markedly after acidified ethanol. However, pretreated hEGF did not restore the sulfhydryl contents. Thus, it seemed that endogenous prostaglandins, but not sulfhydryls, are the probable mediators for protection against gastric mucosal injury caused by acidified ethanol.

Protective effect of human epidermal growth factor against the experimental gastric mucosal lesions in rats

The protective effect of human epidermal growth factor (hEGF) on the gastric mucosal lesions in rats was examined in relation to the immunoreactive concentration of plasma. Human EGF (30 micrograms/kg) was administered intravenously, intraperitoneally or subcutaneously. At different times following the administration of hEGF, rats received acidified ethanol solution to induce an experimental gastric mucosal lesion. Sum of lesion length in the gastric mucosa was used as a lesion index. Human EGF administered parenterally markedly decreased the gastric mucosal lesions in 10 min after administration of necrotizing solution, and 10 to 30 min delay was observed in the development of maximal protective action. Profiles of protective potency against the hEGF dose administered intraperitoneally or subcutaneously 30 min before administration of necrotizing solution revealed that the effective dose of hEGF (ED50) was about 5.2 and 2.6 micrograms/kg, for intraperitoneal and subcutaneous administrations, respectively.