Evaluation of a topical cyclosporine A prodrug on corneal graft rejection in rats.

PURPOSE: To assess the efficacy of a topical cyclosporine A (CsA), water-soluble prodrug, for promoting the survival of allogenic rat corneal grafts after penetrating keratoplasty (PKP). METHODS: Corneas of Brown-Norway rats (donors) were transplanted to Lewis rats (recipients). Transplanted rats were divided in three treatment groups: group I (PBS) and group II (0.26% Debio088) received drops five times per day. Group III received a daily intramuscular CsA injection (10 mg/kg/day). Blood CsA concentrations were measured on days 2 and 14. On day 4, 10, 13 after PKP, grafts were scored for corneal transparency, edema and extent of neovascularization. An opacity score of greater than or equal to 3 was considered as a nonreversible graft rejection process. On day 14, the experimental eyes were processed for histology. RESULTS: On day 13, 12 of the 18 corneal transplants (67%) in group I showed irreversible graft rejection. Three of 18 transplants (19%) in group II and 5 of 16 transplants (28%) in group III showed irreversible graft rejection (p=0.013/p=0.019, OR=0.14/0.06 versus vehicle). Each mean clinical score for edema, opacity, and neovessels in group II were significantly lower than those of the grafts in group I (respectively p=0.010, p=0.013, p=0.024) and III except for neovessels (respectively p=0.002, p=0.001, p=0.057). Histology confirmed the clinical results. The mean CsA blood levels for groups II and III were, respectively 54+/-141 mug/l and 755+/-319 mug/l on day 2 and 14+/-34 mug/l and 1318+/-463 mug/l on day 14. CONCLUSIONS: Debio088 CsA prodrug drops given five times daily are as effective as intramuscular injection of 10 mg/kg/day for the prevention of acute corneal graft rejection in rats.

A novel water-soluble cyclosporine A prodrug: ocular tolerance and in vivo kinetics.

The purpose of this study is to demonstrate that a novel water-soluble prodrug of cyclosporine A (CsA) intended for topical ocular administration, does not induce eye irritation in a rabbit model and is able to generate therapeutic concentrations of CsA in the precorneal area immediately after administration. The eye irritancy of the prodrug and CsA control solution was assessed by the Draize test and by confocal laser ophthalmoscopy (CLSO). Residence time and tear concentrations of prodrug and CsA in the rabbit eye were assessed by HPLC. The Draize test showed an excellent tolerance for the prodrug solution while the reference CsA oil solution induced lachrymation and irritation. The CLSO-measured corneal lesions, subsequent to treatment with the prodrug and reference solutions, were 3% and 9%, respectively. The prodrug transformed rapidly, leading to relatively stable CsA concentrations in tears with a maximal concentration of 94 microg ml(-1) over the observation period. This study demonstrated that the prodrug solution was well tolerated and that clinically significant CsA tear concentrations were achieved. UNIL088 is a promising molecule in the treatment of immune-related disorders of the eye.

Conversion of cyclosporine A prodrugs in human tears vs rabbits tears.

The aim of this study was to evaluate the rate and mechanism of conversion of two water-soluble prodrugs of cyclosporine A (CsA) intended for topical delivery to the eye. The new molecules were designed according to the double prodrug concept: a solubilizing moiety was grafted onto CsA via an ester function, which could be hydrolysed via a two-step process (enzymatic and chemical). Prodrug solutions were prepared extemporaneously in an isotonic and neutral aqueous medium compatible with ophthalmic use. The rates of conversion into the parent molecule were determined by incubating the prodrugs in fresh rabbit or human tears or in a phosphate buffer solution (PBS) at pH 7.4. Both prodrugs were converted into CsA within the first minute in the presence of rabbit tears with rate constants of k=5.9x10(-3)min(-1) and k=3.8x10(-3)min(-1), respectively, for UNIL088 and UNIL089, whereas chemical conversion in PBS was negligible (k=0.5x10(-3)min(-1) for both molecules). Incubation of UNIL088 in human tears showed a significantly high conversion rate. It is concluded that the developed double prodrugs underwent a bioconversion in physiological media and thus represent promising candidates for topical delivery of CsA to the eye.

Cyclosporine A delivery to the eye: a pharmaceutical challenge.

Systemic administration of cyclosporine A (CsA) is commonly used in the treatment of local ophthalmic conditions involving cytokines, such as corneal graft rejection, autoimmune uveitis and dry eye syndrome. Local administration is expected to avoid the various side effects associated with systemic delivery. However, the currently available systems using oils to deliver CsA topically are poorly tolerated and provide a low bioavailability. These difficulties may be overcome through formulations aimed at improving CsA water solubility (e.g. cyclodextrins), or those designed to facilitate tissue drug penetration using penetration enhancers. The use of colloidal carriers (micelles, emulsions, liposomes and nanoparticles) as well as the approach using hydrosoluble prodrugs of CsA have shown promising results. Solid devices such as shields and particles of collagen have been investigated to enhance retention time on the eye surface. Some of these topical formulations have shown efficacy in the treatment of extraocular diseases but were inefficient at reaching intraocular targets. Microspheres, implants and liposomes have been developed to be directly administered subconjunctivally or intravitreally in order to enhance CsA concentration in the vitreous. Although progress has been made, there is still room for improvement in CsA ocular application, as none of these formulations is ideal.

Early administration of vapreotide for variceal bleeding in patients with cirrhosis.

BACKGROUND: In patients with cirrhosis, pharmacologic or endoscopic treatment may control variceal bleeding. However, the effects of early administration of a somatostatin analogue followed by endoscopic treatment are unknown. METHODS: We studied the effects of treatment with vapreotide, a somatostatin analogue, begun before endoscopic treatment in 227 patients with cirrhosis who were hospitalized for acute upper gastrointestinal bleeding. The patients were randomly assigned to receive vapreotide (a 50-microg intravenous bolus followed by an infusion at a rate of 50 microg per hour for five days) or placebo within a mean (+/-SD) of 2.3+/-1.5 hours after admission. All the patients received endoscopic treatment a mean of 2.6+/-3.3 hours after the infusion was begun. After the exclusion of 31 patients whose bleeding was not caused by portal hypertension, there were 98 patients in each group. RESULTS: At the time of endoscopy, active bleeding was evident in 28 of 91 patients in the vapreotide group (31 percent), as compared with 43 of 93 patients in the placebo group (46 percent) (P=0.03). During the five-day infusion, the primary objective--survival and control of bleeding--was achieved in 65 of 98 patients in the vapreotide group (66 percent) as compared with 49 of 98 patients in the placebo group (50 percent) (P=0.02). The patients in the vapreotide group received significantly fewer blood transfusions (2.0+/-2.2 vs. 2.8+/-2.8 units, P=0.04). Overall mortality rates at 42 days were not significantly different in the two groups. CONCLUSIONS: In patients with cirrhosis and variceal bleeding, the combination of vapreotide and endoscopic treatment is more effective than endoscopic treatment alone as a method of controlling acute bleeding. However, the use of combination therapy does not affect mortality rates at 42 days.

Prospective study on the application of the Baveno II Consensus Conference criteria in patients with cirrhosis and gastrointestinal bleeding.

BACKGROUND/AIMS: This study aimed to evaluate the Baveno II criteria defining key events in variceal bleeding. METHODS: These criteria were applied to 196 patients with cirrhosis admitted for upper gastrointestinal bleeding due to portal hypertension and enrolled in a trial. Blood pressure, heart rate, hematocrit and clinical signs of upper digestive tract hemorrhage were recorded for 5 days. The blind overall clinical judgment of hemodynamic stability was recorded separately by the Steering Committee. RESULTS: The evaluation of several hemodynamic criteria was left to the judgment of the clinician. The first time point for the control of bleeding, fixed at 6 h after admission, was impractical since 13% of the patients had not yet received specific treatment. The independent judgment did not agree in 38% of 82 cases without control of bleeding. In 15% of cases this was due to tachycardia. Calculation of several judgment criteria was not defined in the Baveno II criteria: survival without bleeding at 5 days, transfusion rate, and length of hospital stay. CONCLUSIONS: Although the Baveno II criteria have improved the definitions of key events, the criteria are hampered by limits such as false positive criteria of failure to control bleeding. We make several proposals for improvement.

Formation of peptide impurities in polyester matrices during implant manufacturing.

Most peptides are susceptible, in vivo, to proteolytic degradation, and it is difficult to formulate and to deliver them without loss of biological activity. In addition, it is often desirable to release them continuously and at a controlled rate over a period of weeks or months. For these reasons, a controlled release system is suitable. Poly(lactic acid) (PLA) is a biocompatible and biodegradable material that can be used for many applications, including the design of injectable controlled release systems for pharmaceutical agents. Development of these delivery systems presents challenges in the assessment of stability, specially for peptide drugs. By means of an extrusion method, long-acting poly(lactic acid) implants containing vapreotide, a somatostatin analogue, were prepared. The nature of the main degradation product obtained after implant manufacturing was elucidated. It was found that the main peptide impurity was a lactoyl lactyl-vapreotide conjugate. Because lactide are found in small quantities in most commercially available PLA, the influence of residual lactide in the polymeric matrix, on the formation of peptide impurities during manufacturing, was specially investigated. This work demonstrates that the degree of purity of the carrier is of great importance with regard to the formation of peptide impurities.

In vitro and in vivo evaluation of a somatostatin analogue released from PLGA microspheres.

The purpose of this study was to design poly(lactide-co-glycolide) (PLGA) microspheres for the continuous delivery of the somatostatin analogue, vapreotide, over 2-4 weeks. The microspheres were produced by spray-drying and the desired characteristics, i.e. high encapsulation efficiency and controlled release over 2-4 weeks, achieved through optimizing the type of polymer, processing solvent, and co-encapsulated additive. The in vitro release was tested in fetal bovine serum preserved with 0.02% of thiomersal. Furthermore, formulations were injected intramuscularly into rats to obtain pharmacokinetic profiles. Encapsulation efficiency was between 34 and 91%, depending on the particular formulation. The initial peptide release (within 6 h) was lowest, i.e. <20%, when acetic acid was used as processing solvent and highest, i.e. 57%, with dichloromethane. The various co-encapsulated additives generally lowered the encapsulation efficiency by 15-30%. The best formulation in terms of low burst and effective drug serum levels (>1 ng/ml) over 21-28 days in rats was the one made with end-group uncapped PLGA 50:50, the solvent acetic acid and the additive polyethyleneglycol. In conclusion, the optimization of formulation parameters allowed us to produce vapreotide-loaded PLGA microspheres of suitable characteristics for therapeutic use.

Injection-molding versus extrusion as manufacturing technique for the preparation of biodegradable implants.

Polylactic acid (PLA) is a biocompatible and biodegradable material with wide utility for many applications, including the design of controlled-release systems for pharmaceutical agents. The factors determining the degradation kinetics of these systems include the composition and the molecular mass of the polymer, the morphology and the structure of the device, and the influence of thermal processes. The processing of the polymer determines the structure and design of the device, and influences to a high degree its morphology, namely its microporous structure, polymeric chain orientation and crystallinity.In this work, we aimed to compare the influence of two different implant manufacturing techniques, extrusion and injection-molding, on the in vitro degradation of the polymeric matrix. Both kinds of implants were loaded with a somatostatin analogue. Decrease in molecular weight, and polydispersity evolution during an accelerated in vitro degradation test were studied by size exclusion chromatography. Morphological changes in the polymeric matrix during degradation were followed after defined time intervals by means of scanning electron microscopy. Crystallinity studies were performed by differential scanning calorimetry and by X-ray analysis. Peptide stability in the polymeric matrix after both manufacturing methods was evaluated. Peptide release profiles, obtained in vitro during a week dissolution test, from both implant samples, were studied. It was shown that both molecular weight and polydispersity decreased after extrusion or injection-molding. This decrease was more pronounced with the latter technique. Crystallinity studies demonstrated that the crystalline network was not destroyed after both manufacturing methods. Peptide release profiles obtained in vitro were in good accordance with scanning electron microscopy. It was found that both manufacturing techniques had to be considered, although the extruded implants degraded more rapidly in vitro than the injection-molded ones.

Importance of the test medium for the release kinetics of a somatostatin analogue from poly(D,L-lactide-co-glycolide) microspheres.

The determination of in vitro release kinetics of peptides from poly(d,l-lactide-co-glycolide) (PLGA) microspheres generally requires optimization of the test conditions for a given formulation. This is particularly important when in vitro/in vivo correlation should be determined. Here, the somatostatin analogue vapreotide pamoate, an octapeptide, was microencapsulated into PLGA 50:50 by spray-drying. The solubility of this peptide and its in vitro release kinetics from the microspheres were studied in various test media. The solubility of vapreotide pamoate was approximately 20-40 microg/ml in 67 mM phosphate buffer saline (PBS) at pH 7.4, but increased to approximately 500-1000 microg/ml at a pH of 3.5. At low pH, the solubility increased with the buffer concentration (1-66 mM). Very importantly, proteins (aqueous bovine serum albumin (BSA) solution or human serum) appeared to solubilize the peptide pamoate, resulting in solubilities ranging from 900 to 6100 microg/ml. The release rate was also greatly affected by the medium composition. Typically, in PBS of pH 7.4, only 33+/-1% of the peptide were released within 4 days, whereas 53+/-2 and 61+/-0.9% were released in 1% BSA solution and serum, respectively. The type of medium was found critical for the estimation of the in vivo release. The in vivo release kinetics of vapreotide pamoate from PLGA microspheres following administration to rats were qualitatively in good agreement with those obtained in vitro using serum as release medium. Finally, sterilization by gamma-irradiation had only a minor effect on the in vivo pharmacokinetics.

Stability studies of a somatostatin analogue in biodegradable implants.

In recent years, peptides and proteins have received much attention as drug candidates. For many polypeptides, particularly hormones, it is desirable to release the drug continuously at a controlled rate over a period of weeks or even months, and thus a controlled release system is needed. Polylactic acid (PLA) is a biocompatible and biodegradable material with wide utility for many applications, including the design of controlled release systems for pharmaceutical agents. Pharmaceutical development of these delivery systems presents new problems in the area of stability assessment, especially for peptide drugs. In this study, we aimed to investigate the influence of different steps, during the manufacturing of an implant, on peptide stability in the polymeric matrix. Polylactic acid implants containing vapreotide, a somatostatin analogue, were prepared by extrusion. The effects of time, extrusion and temperature on the peptide stability were studied. The influence of various gamma sterilization doses, as well as the conditions under which the implants were irradiated, were also investigated. Peptide stability in the polymeric matrix was evaluated at various temperatures and at various time intervals up to 9 months.

Development and evaluation in vivo of a long-term delivery system for vapreotide, a somatostatin analogue.

In recent years peptides and proteins have received much attention as candidate drugs. For many peptides, particularly hormones, it is desirable to release the drug continuously at a controlled rate over a period of weeks or even months. Polylactic acid and poly (lactic-co-glycolic) acid are well known biocompatible biodegradable materials with wide applications including the design of controlled-release systems for pharmaceutical agents. Polylactic acid implants containing vapreotide were prepared by an extrusion method and drug release was evaluated in vivo in rats using an RIA method The development of an injectable, biodegradable depot formulation of a somatostatin analogue (vapreotide) is described which ensures satisfactory peptide blood level in rats over approximately 250 days. A modification of this formulation by means of a wear coating allows minimisation of the initial burst a feature rarely discussed.

Neural tube defects after infertility treatment: a review.

OBJECTIVE: To investigate whether an association exists between ovulation induction and neural tube defects (NTDs). MATERIALS AND METHODS: Risk estimations in the medical literature were identified through Medline, and validity and power were assessed. Large in vitro fertilization-embryo transfer (IVF-ET) registries represent another source of information. The total number of NTDs and the total number of fetuses were computed from five registries. These data were expressed as proportions and compared with data from the general population. RESULTS: Only one study could be identified as both valid and powerful, through literature review. This case-control study concluded there was no association between ovulation induction and NTDs. The pool of IVF-ET registry data represents another powerful epidemiologic tool. Analysis of the registry data confirms the findings of the case-control study. CONCLUSIONS: Ovulation induction does not seem to represent a risk factor for NTDs in the offspring.

Salicylic acid permeability properties of the rabbit cortical collecting duct.

To assess the role of nonionic diffusion of salicylic acid (pKa = 3) in the terminal nephron, we measured the passive permeability of [14C]salicylic acid in rabbit cortical collecting ducts isolated and perfused in vitro. This segment can produce and maintain a maximal pH gradient between blood and tubular fluid. When peritubular pH was kept constant at pH 7.4 the apparent permeability of salicylic acid (P', 10(-6) cm/s) was 6.2 +/- 1.1 at a luminal pH of 6.0, 17.2 +/- 5.3 at a luminal pH of 5.5, and 39.0 +/- 4.7 at a luminal pH of 5.0. These permeabilities were in close correlation with the percentage of nonionized salicylic acid present at each pH, indicating that only the nonionized molecule can diffuse across the collecting duct epithelium. By recalculating the permeability, taking into account only the concentration of the nonionized salicylic acid molecules, we obtained the apparent permeability of nonionized salicylic acid, which was no longer pH dependent and averaged 4,345 +/- 460 x 10(-6) cm/s. The apparent activation energy of this diffusion process was 9.3 +/- 1.2 kcal/mol as calculated from an Arrhenius plot.

Renal secretion of 3'-azido-3'-deoxythymidine by the rat.

The renal excretion of 3'-azido-3'-deoxythymidine (AZT) was investigated in clearance experiments in anesthetized rats. AZT was filtered freely and subsequently secreted, reabsorption being of minor importance. Probenecid, the classical inhibitor organic anion secretion, decreased AZT secretion. AZT, on the other hand, decreased p-aminohippurate secretion. These observations demonstrate that AZT is secreted by the organic anion secretory mechanisms. Cimetidine, an organic cation, also decreased AZT secretion at a concentration which did not inhibit the secretion of the organic anion, p-aminohippurate. This suggests that AZT might also be transported by the mechanisms secreting organic cations. However, as AZT did not inhibit the secretion of the organic cation tetraethylammonium, it cannot be concluded that AZT is transported by the mechanisms secreting organic cations.

Transport of the organic cation N1-methylnicotinamide by the rabbit proximal tubule. I. Accumulation in the isolated nonperfused tubule.

Isolated nonperfused rabbit renal proximal tubules were used to investigate the basolateral step of transport of the organic cation N1-methylnicotinamide (NMN). NMN accumulation was highest and saturable in S2 and S3 segments, but lowest and nonsaturable in S1 segments. In S1 segments, accumulation of [3H]-NMN (0.5-8 microM in the bath) resulted in an average tubular water/medium concentration ratio (T/M) of 8.2, whereas in S2 and S3 segments T/M averaged 19.5 and 18.6, respectively. At these concentrations, about 30% of the label was attached in all segments to a metabolite comigrating with nicotinamide. KCN (10(-2) M) or ouabain (10(-4) M) reduced T/M to about 8 for all segments. NMN accumulation was inhibited (to a T/M of about 3 with mepiperphenidol) by other organic cations (10(-5)-10(-3) M) with the potency sequence mepiperphenidol greater than tetraethylammonium = quinine greater than morphine, these organic cations having no effect on p-aminohippurate accumulation, except for the highest concentration of quinine (10(-3) M). After correction for metabolism, NMN accumulation could be accounted for by simple electrochemical equilibrium across the basolateral membrane. The basolateral step of NMN transport appears therefore to be a carrier-mediated diffusion, in opposition to the active basolateral accumulation described for tetraethylammonium.

Transport of the organic cation N1-methylnicotinamide by the rabbit proximal tubule. II. Reabsorption and secretion in the isolated perfused tubule.

The mechanisms involved in the transport of the organic cation N1-methylnicotinamide (NMN) were investigated in the isolated perfused rabbit S2 proximal tubule. NMN underwent a small reabsorptive transport which appeared to be passive. NMN secretory transport was saturable, inhibited by mepiperphenidol (10(-4) M) and presented a relatively low apparent affinity (apparent Km of 852 microM) for the organic cation transport system, with transport against a concentration gradient being observed only at low flow rates. Acidification of the perfusate, by either buffering it at pH 6.8 with MES, or by bubbling the bath with a mixture of 80% O2-20% CO2, resulted in a decrease, rather than an increase, of NMN secretion. Carbonic anhydrase inhibition with ethoxyzolamide (10(-4) M in the bath) did not modify NMN secretion. Addition of 20 to 40 microM NMN in the perfusate also did not change NMN secretion. Proton or organic cation counterexchange seemed therefore not to play a major role in NMN apical step of secretion, the basolateral step appearing to be the general organic cation system of transport for which NMN shows a low affinity.

Transport of methotrexate by the in vitro isolated rabbit proximal tubule.

The tubular transport of [3H]methotrexate was studied in isolated nonperfused and perfused superficial proximal tubular segments of rabbit kidneys. Reabsorption represented only 5% of perfused methotrexate, and appeared to be mostly of passive nature inasmuch as it was not modified by reducing the temperature or by ouabain. Cellular accumulation in nonperfused segments and secretion in perfused tubules were highest in the S2 segment and lower in the S3 and S1 segments. Secretion against a bath-to-lumen concentration gradient was observed only in S2 segments (with a maximum methotrexate secretory rate of 478 +/- 48 fmol/mm.min and an apparent Km of transport of 363 +/- 32 microM), and was inhibited by probenecid and folate. The low capacity for methotrexate secretion may be explained by a low capacity of transport across the basolateral membrane of the proximal cell as methotrexate was accumulated only to a low extent in nonperfused tubules (tissue water to medium concentration ratio of 8.2 +/- 1 in S2 segments). During secretion a small amount of methotrexate was metabolized; the nature of the metabolite(s) remains to be defined.

Facilitation by serum albumin of renal tubular secretion of organic anions.

The role of albumin in tubular secretion of the organic anions p-aminohippurate (PAH, 21% albumin-bound at 1 microM) and methotrexate (MTX, 55% bound at 1 microM), and of the organic cation N1-methylnicotinamide (NMN, not bound), was investigated in isolated rabbit S2 proximal tubules. PAH or MTX secretory rates were low in the absence of colloids or in the presence of 1 g/dl dextran 40, and were reversibly two- to sevenfold stimulated by either 1 g/dl bovine (BSA, either regular, defatted, and/or dialyzed) or rabbit serum albumin, or by dialyzed native rabbit plasma. NMN secretion was not stimulated by either dextran or albumin. Luminal BSA had no effect, but stimulation of PAH secretion was observed when albumin was present in both lumen and bath. This secretion was BSA concentration-dependent up to a 1 g/dl BSA. Saturation experiments suggested that 1 g/dl BSA may increase PAH apparent affinity for secretion, with no change in its maximum velocity. Albumin appears therefore to facilitate organic anion proximal secretion by an effect unrelated to oncotic pressure or to the extent of organic anion binding.

Net sodium and water movements in the newborn rabbit collecting tubule: lack of modifications by indomethacin.

In contrast to adult tubules, a bath-to-lumen sodium gradient was followed by net sodium entry in the lumen of in vitro isolated perfused newborn (3-5 days) rabbit collecting tubules. In addition, transepithelial voltage and electrical resistance were lower in newborn tubules. The sodium flux into the lumen was unaffected by indomethacin. These observations suggest that the newborn collecting tubule may be unable to maintain an adequate sodium gradient for the optimal function of the urinary concentrating mechanism, and that endogenous prostaglandins are not involved in this defect.