Cloning of the gene for spinocerebellar ataxia 2 reveals a locus with high sensitivity to expanded CAG/glutamine repeats

A 3-day monolithic polyacrylate adhesive dispersion type delivery system containing methadone was fabricated and in vitro permeation through hairless mouse and human cadaver skins was conducted. The effect of skin permeation enhancers was also investigated. Skin permeation rate across human cadaver skin was found to be lower than that of hairless mouse. Skin permeation profiles across both types of skins showed a membrane permeation controlled cumulative amount permeated (Q) versus time (t) relationship. Skin permeation rate was found to be dependent on both adhesive film thickness and loading dose of the drug in the matrix. Effective skin permeation rate across the hairless mouse skin was obtained from a patch with 1.5 mm thickness and 15% w/w loading dose. n-Decylmethyl sulfoxide and Azone were found to produce an effective skin permeation rate of methadone through human cadaver skin at a 5% w/w concentration. These initial studies demonstrated the feasibility of methadone administration through intact skin from a transdermal patch.     

Transdermal delivery of narcotic analgesics: comparative metabolism and permeability of human cadaver skin and hairless mouse skin

The permeation of hairless mouse skin and human cadaver skin by narcotic analgesics was investigated to determine the interspecies variation. Permeability coefficients of morphine, fentanyl, and sufentanil across full-thickness hairless mouse skin were 1 order of magnitude higher than those found for human epidermis. The permeability coefficient of morphine for stripped hairless mouse skin was 500-fold higher than that for intact skin, showing the stratum corneum to be the principal barrier to its penetration. The permeability coefficient of fentanyl for stripped hairless mouse skin was also raised, but stripping caused an inappreciable increase in the permeation rate of sufentanil. The thick dermis of excised mouse skin obviously offered a significant resistance to the permeation of these lipophilic compounds. In comparison, the permeability coefficients of fentanyl and sufentanil through stripped cadaver epidermis (n > or = 25) were 67 and 37 higher than for intact human epidermis, respectively. The skin metabolism of the narcotics was investigated. No significant metabolic degradation of morphine, fentnayl, and sufentanil was observed in either fresh human cadaver skin or hairless mouse skin homogenates in the presence of NADPH cofactor, suggesting a low monooxygenase enzyme presence in skin. Moreover, no measurable glucuronidation of morphine took place in human skin or hairless mouse skin. Both processes proceeded rapidly in liver homogenates (mouse) under identical circumstances. It thus appears that these drugs pass through in intact form.     

Plasminogen activator in acute myeloid leukaemic marrows: u-PA in contrast to t-PA in normal marrow

PURPOSE: The aim of this study is to investigate species differences in the stereoselective hydrolysis for propranolol ester prodrugs in mammalian intestinal mucosa and Caco-2 cells. METHODS: Hydrolase activities for propranolol prodrugs and p-nitrophenylacetate in man (age: 51-71 years), the beagle dog (age: 4 years) and Wistar rat (age: 8 weeks) intestinal mucosa, and also in Caco-2 cells (passage between 60-70) were estimated by determining the rate of production of proparanolol and p-nitrophenol, respectively. RESULTS: The hydrolase activities for both propranolol prodrugs and p-nitrophenylacetate were in the order of man > rat > Caco-2 cells > dog for intestinal microsomes, and rat > Caco-2 cells = man > dog for intestinal cytosol. Dog microsomes showed stereoselective hydrolysis for propranolol prodrugs, but not those from human or rat. Interestingly, both subcellular fractions of Caco-2 cells showed remarkable R-enantioselectivity except acetyl propranolol. Enzyme kinetic experiments for each enantiomer of butyryl propranolol in microsomes revealed that dog possesses both low and high affinity hydrolases. Both Km and Vmax values in rat were largest among examined microsomes, while Vmax/Km was largest in man. Finally, it was shown that the carboxylesterases might contribute to the hydrolysis of propranolol prodrug in all species by inhibition experiments. CONCLUSIONS: The hydrolase activities for propranolol prodrugs and p-nitrophenylacetate in intestinal mucosa showed great species differences and those in human intestine were closer to those of rat intestine than dog intestine or Caco-2 cells.     

Studies on development of pharmaceutical preparation with the purpose of improving controlled-release and bioavailability

During the past fifteen years, the experiments based on three main propositions were proceeded to carry out in our laboratory, that is, (1) Microencapsulation: The method of solvent evaporation in water or oily phases was adopted because of its comparative simplicity in the procedure and its high reproducibility. The application of pharmacokinetic consideration to in vivo evaluation of microencapsulated drugs using beagle dogs intended for obtaining controlled-release by oral administration. The pullulan acetate phthalate microcapsules containing cefadroxil were prepared by the solvent evaporation method in liquid paraffin and showed a zero-order dissolution pattern in pH 6-7.4. (2) Rectal gel preparation: The hydrogels and xerogels were prepared by Eudispert hv. These gels have excellent staying properties in the lower part of the rectum, over a fairly long period. Eudispert hv hydrogels or xerogels containing propentfylline were tested for avoidance of the first-pass metabolism. The absolute bioavailability of propentofylline from gel preparations was almost 100%. (3) Binary vehicle for transdermal delivery: The effects of glycerides, short-chain alcohols and their binary vehicles as donor components on the skin permeation of ketoprofen across the excised hairless mouse skin were evaluated with the diffusion cell. Among single vehicles, Panasate 800 as lipophilic vehicle and ethanol as hydrophilic vehicle showed the effective permeation flux of ketoprofen. The greatest enhancement was observed in an ethanol/Panasate 800 (40/60) binary vehicle. The relationship between lipophilicity and skin permeability of 16 drugs from the ethanol/Panasate 800 (40/60) binary vehicle showed a parabolic shape with a peak at a more hydrophilic range compared with other past references.     

Membrane potential of mesenteric artery from carvedilol-treated spontaneously hypertensive rats

The effect of current, its magnitude and penetration enhancers (propylene glycol/oleic acid) on the transdermal flux of AZT (Zidovudine) across hairless mouse skin was studied and the results were compared. The in vitro iontophoretic flux from AZT solution increased to about 5-40 fold that obtained by passive diffusion, depending on the magnitude of current density. When the donor side was karaya gum matrix, instead of solution, the flux enhancement effect by iontophoresis was much smaller. Incorporation of penetration enhancers into the matrix increased the passive flux 2-50 fold, depending on the amount of penetration enhancers in the matrix. These enhancers worked synergistically with iontophoresis in the transdermal transport: a much larger flux than that expected from a simple additive effect was observed. Electrical resistance data from our previous work is utilized to further discuss this synergistic effect.     

A comparison of the bioconversion rates and the Caco-2 cell permeation characteristics of coumarin-based cyclic prodrugs and methylester-based linear prodrugs of RGD peptidomimetics

PURPOSE: To compare the bioconversion rates in various biological media and the Caco-2 cell permeation characteristics of coumarin based cyclic prodrugs (3a, 3b) and methylester-based linear prodrugs (1b, 2b) of two RGD peptidomimetics (1a, 2a). METHODS: Bioconversion rates of the prodrugs to the RGD peptidomimetics were determined in Hank balances salt solution (HBSS), pH 7,4, at 37 degrees C and in various biological media (human blood plasma, rat liver homogenate, Caco-2 cell homogenate) known to have esterase activity. Transport rates of the prodrugs and the RGD peptidomimetics were determined using Caco-2 cell monolayers, an in vitro cell culture model of the intestinal mucosa. RESULTS. In HBSS, pH 7,4, the coumarin-based cyclic prodrugs 3a and 3b degraded slowly and quantitatively to the RGD peptidomimetics 1a and 2a, respectively (3a, t1/2 = 630+2-14 min; 3b, t1/2 = 301 +/-12 min). The methylester-based linear prodrugs 1b and 2b were more stable to chemical hydrolysis (1b and 2b, t1/2 > 2000 min). Both the coumarin-based cyclic prodrugs and the methylester-based linear prodrugs degraded more rapidly in biological media containing esterase activity (e.g., 90% human blood plasma: 1b, t1/2 < 5 min; 2b, t1/2 < 5 min; 3a, t1/2 < 91+/-1 min; 3b, 1/2 < 57+/-2 min). When the apical (AP)-to-basolateral (BL) permeation characteristics were determined using Caco-2 cell monolayers, it was found that the methylester prodrugs 1b and 2b underwent esterase bioconversion (>80%) to the RGD peptidomimetics 1a and 2a, respectively, In contrast, the cyclic prodrugs 3a and 3b permeated the cell monolayers intact. Considering the appearance of both the prodrug and the RGD peptidomimetic on the BL side, the methylester prodrugs 1b and 2b were approximately 12-fold more able to permeate than were the RGD peptidomimetics 1a and 2a. When similar analysis of the transport data for the coumarin prodrugs 3a and 3b was performed, they were shown to be approximately 6-fold and 5-fold more able to permeate than were the RGD peptidomimetics 1a and 12a, respectively. CONCLUSION: The coumarin-based cyclic prodrugs 3a and 3b were chemically less stable, but metabolically more stable, then the methylester based linear prodrugs. The esterase stability of the cyclic prodrugs 3a and 3b means that they are transported intact across the Caco-2 cell monolayer in contrast to the methylester prodrugs 1b and 2b, which undergo facile bioconversion during their transport to the RGD peptidomimetics. However, both prodrug systems successfully delivered more (5-12-fold) of the RGD peptidomimetic and/or the precursor (prodrug) than did the RGD peptidomimetics themselves.     

Growth hormone treatment in growth retarded children with end stage renal failure: effect on free/dissociable IGF-I levels

PURPOSE: Skin binding of prednisolone and its esters was investigated in the hairless mouse skin in vitro. METHODS: The distribution of the amount of drugs bound in the skin was determined by a skin slicing technique. The model drugs used were prednisolone (PN, M.W. 360) and its esters, senesyonate (PN-C5, M.W. 442), geranate (PN-C10, M.W. 510), farnesylate (PN-C15, M.W. 578), and geranylgeranate (PN-C20, M.W. 646). RESULTS: The distribution of bound drug was nonhomogeneous in the skin; the concentration of PN-C10 and PN-C15 in the skin increased gradually with the distance from the skin surface. The parent drug, PN, however, was hardly bound in the viable skin. CONCLUSIONS: These findings suggest that the prodrugs of prednisolone may prolong the dermal retention of the parent drug and minimize to delivery into the systemic circulation of the prodrug and metabolite.     

An experimental model for interpreting percutaneous penetration of oligonucleotides that incorporates the role of keratinocytes

Oligonucleotides have been extensively studied for their potential as therapeutic agents. Phosphorothioate oligonucleotides have been demonstrated to be particularly useful due to their stability against nucleases, their ability to be internalized by many cell types, and the ease with which they hybridize with target mRNA. These compounds have previously been delivered across the skin with the aid of iontophoresis. During transdermal delivery, the first viable cells exposed to the oligonucleotides are the keratinocytes. The purpose of this study was to determine the relationship between internalization of these compounds by keratinocytes and their transport across the skin. The in vitro uptake of 15 different fluorescently labeled phosphorothioate oligonucleotides into human keratinocytes was quantitatively measured with a fluorometer. Photomicrographs of keratinocytes indicate diffuse cytoplasmic and nuclear localization. The ability of these molecules to enter cells was linearly related to size. Cellular uptake data were inversely correlated with previously reported steady-state transport levels of oligonucleotides that had been transdermally delivered by iontophoresis across hairless mouse skin. Oligonucleotides that readily entered keratinocytes had a decreased ability to penetrate skin under iontophoretic conditions. The results indicate that oligonucleotide sequences may be designed for treating skin diseases (high uptake, low transport) or systemic disorders (low uptake, high transport).     

Iontophoretic transport pathways: dependence on penetrant physicochemical properties

The objective of this work was to investigate how the preferred iontophoretic transport pathways of a molecule depend on its physicochemical properties. Laser scanning confocal microscopy (LSCM) was used to visualize in hairless mouse skin the distribution of two fluorescent penetrants: calcein, a multiply charged (-4), hydrophilic molecule; and nile red, a lipophilic, neutral compound. Iontophoresis and passive delivery of nile red showed that the percutaneous transport of this compound occurred via (inter- and intracellular) pathways that were clearly distinct from those followed by calcein. Although the distribution of nile red was influenced somewhat by the passage of current relative to the passive control, there was relatively little enhancement of the penetration of this compound into the skin. Calcein, on the other hand, did not passively enter the skin. However, with iontophoresis, greatly enhanced transport, with an important contribution from follicular structures, was observed. Sequential (dual) transport of the two fluorophores illustrated clearly the different pathways followed and reflected the transport and visualization studies of the individual species. It may be concluded, therefore, that the iontophoretic pathways followed across the skin are dictated by the physicochemical properties of the penetrant and by its affinity for the different environments available.     

Stereoselective hydrolysis of O-isovaleryl propranolol and its influence on the clearance of propranolol after oral administration

The stereoselective hydrolysis of O-isovaleryl propranolol (isovaleryl-PL) was studied using phosphate and Tris-HCl buffers (pH 7.4), dog plasma, and liver preparations. The 10000g supernatant, microsomes, and cytosol were prepared from the liver homogenate. The hydrolysis rate of isovaleryl-PL was accelerated in the order Tris buffer < plasma = phosphate buffer < 10000g supernatant of liver = liver cytosol < liver microsomes. The high plasma protein binding of the prodrug brought about the extremely slow hydrolysis rate of isovaleryl-PL in plasma. No difference was observed in the hydrolysis rate between the isomers of isovaleryl-PL in buffers. The hydrolysis rate was 2-3 times faster with the (R)-isomer than with the (S)-isomer using racemate in dog plasma and liver preparations. The hydrolysis of each enantiomer was inhibited by the other enantiomer. For hydrolysis in microsomes the Km values of (R)- and (S)-isomers were same, and the Vmax of the (R)-isomer was 3 times greater than that of the (S)-isomer. These data suggested the mutual interaction of (R)- and (S)-isomers during the hydrolysis process and the rapid hydrolysis of isovaleryl-PL in liver after absorption. The AUC of PL enantiomers after oral administration of racemic isovaleryl-PL was about 2 times higher compared to 2 mg/kg equivalent molar dose of racemic PL in beagle dogs, and the corresponding plasma levels were not stereoselective from both PL and prodrug. The amount of (R)-PL absorbed after administration of a 5 mg/kg dose of racemic PL was 2-fold greater than (S)-PL, because of the stereoselective oxidation and glucronidation of (S)-PL.(ABSTRACT TRUNCATED AT 250 WORDS)     

5'-Amino acid esters of antiviral nucleosides, acyclovir, and AZT are absorbed by the intestinal PEPT1 peptide transporter

PURPOSE: General use of nucleoside analogues in the treatment of viral infections and cancer is often limited by poor oral absorption. Valacyclovir, a water soluble amino acid ester prodrug of acyclovir has been reported to increase the oral bioavailability of acyclovir but its absorption mechanism is unknown. This study characterized the intestinal absorption mechanism of 5' -amino acid ester prodrugs of the antiviral drugs and examined the potential of amino acid esters as an effective strategy for improving oral drug absorption. METHODS: Acyclovir (ACV) and Zidovudine (AZT) were selected as the different sugar-modified nucleoside antiviral agents and synthesized to L-valyl esters of ACV and AZT (L-Val-ACV and L-Val-AZT), D-valyl ester of ACV (D-Val-ACV) and glycly ester of ACV (Gly-ACV). The intestinal absorption mechanism of these 5' -amino acid ester prodrugs was characterized in three different experimental systems; in situ rat perfusion model, CHO/hPEPT1 cells and Caco-2 cells. RESULTS: Testing 5' -amino acid ester prodrugs of acyclovir and AZT, we found that the prodrugs increased the intestinal permeability of the parent nucleoside analogue 3- to 10-fold. The dose- dependent permeation enhancement was selective for L-amino acid esters. Competitive inhibition studies in rats and in CHO cells transfected with the human peptide transporter, hPEPT1, demonstrated that membrane transport of the prodrugs was mediated predominantly by the PEPT1 H+/dipeptide cotransporter even though these prodrugs did not possess a peptide bond. Finally, transport studies in Caco-2 cells confirmed that the 5' - amino acid ester prodrugs enhanced the transcellular transport of the parent drug. CONCLUSIONS: This study demonstrates that L-amino acid-nucleoside chimeras can serve as prodrugs to enhance intestinal absorption via the PEPT1 transporter, providing a novel strategy for improving oral therapy of nucleoside drugs.     

Posteroventral medial pallidotomy in levodopa-unresponsive parkinsonism

PURPOSE: The purpose of this study was to test whether structural modifications improve the intestinal absorption of DMP 728 (cyclo(D-Abu-NMeArg-Gly-Asp-Amb)), a GPIIb/IIIa receptor antagonist. METHODS: In vitro permeabilities of prodrugs and analogs of DMP 728 across excised rat intestinal segments were determined. RESULTS: n-Butyl and n-octyl esters of DMP 728 were relatively stable during in vitro permeation of rat intestine. Intestinal permeation rates of these compounds were no greater than that of DMP 728, even though the octyl ester was much more lipophilic. A pivaloyloxymethyl ester, which was hydrolyzed to DMP 728 during intestinal permeation, also did not improve permeability. In another approach, analogs with an additional methyl substituent on various amide nitrogens were evaluated. Cyclo(D-Val-NMeArg-Gly-Asp-NMeAmb), cyclo(D-Abu-diN-MeLys-Gly-Asp-Amb), and cyclo(NMeGly-NMeArg-Gly-Asp-Amb) each had about 2-fold greater permeability than DMP 728. Two other analogs with improved permeability were linear Ac-D-Abu-NMeArg-Gly-Asp-Amb and a DMP 728 derivative in which the Asp was rearranged. An analog in which the charged amino acids were replaced by neutral amino acids had permeability similar to DMP 728. CONCLUSIONS: Within this series of peptides, hydrogen bonding tendency and structural constraint influenced intestinal permeation, but not always in ways consistent with the literature, whereas charge and lipophilicity were not shown to influence intestinal permeability. The failure of these approaches to improve permeation more significantly could be due to the influence of secretory transport.     

Characterization of convective solvent flow during iontophoresis

During iontophoresis under neutral pH conditions, there is a net convective flow of volume (electroosmosis) from anode to cathode leading to the enhanced transport of dissolved polar (but uncharged) solutes in the same direction. The objective of this study was to address the following unresolved questions with respect to electroosmotic transport: [1] Whether the efficiency of electroosmotic transport is solute size-dependent and, if so, how severe is this dependence? [2] Is electroosmosis linearly related to current density in the same way that the iontophoretic flux of charged species appears to be? [3] Are positively charged permeants able to influence their own electrotransport across the skin (by modifying the net charge on the membrane and altering, as a result, the permselectivity) and, if so, why and to what extent? Electroosmosis was assessed from the iontophoreically driven fluxes of mannitol, sucrose and lactose across hairless mouse skin in vitro. It was found that:- (a) The electroosmotic transport rate of mannitol is similar to that of the disaccharides, sucrose and lactose, when examined under identical conditions. The dependence of electroosmotic flux upon molecular size requires study of solutes having a wider range of MW than those considered here. (b) Electroosmotic flow from anode-to-cathode increases with applied current density; similarly, convective flow in the opposite direction diminishes with increasing current density. Apparently, there is correlation between the net movement of solvent and the total flux of ions across the skin. (c) The permselectivity of skin can be 'neutralized' by driving, iontophoretically, a cationic, lipophilic peptide (specifically the leutinizing hormone releasing hormone (LHRH) analog, Nafarelin) into the membrane.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular and functional aspects of the hairless (hr) gene in laboratory rodents and humans

For many years, hairless and rhino mouse mutants have provided a useful and extensively exploited model for studying different aspects of skin physiology, including skin aging, pharmacokinetic evaluation of drug activity and cutaneous absorption, skin carcinogenesis, and skin toxicology. Interestingly, however, hairless and rhino mice have rarely been studied for their primary cellular defect - hairlessness - and thus, the hairless gene itself and its physiological functions have been largely overlooked for decades. The recent identification of the human homolog of the hairless gene on human Chromosome 8p12 confirmed the clinical significance of the phenomenon of "hairlessness" in humans, which was predicted on the basis of similarities between hairless mice and a congenital hair disorder characterized by atrichia with papules. Mutations in the hairless gene of mice provide instructive models for further studies of hr gene function, and may facilitate insights into the pathophysiology of different human disorders associated with the disruption of hr gene activity. We provide an overview of current data on the structure and expression patterns of the hr gene, and of mutations at the hairless locus in mice and humans, including the genetic basis of different alleles, the pathology of hairlessness, reproductive and immunological defects, and susceptibility to dioxin toxicity. On the basis of our current understanding of hairlessness, we speculate on the putative functions of the hr gene product in skin physiology, and particularly, in hair follicle biology.     

Cellular uptake mechanism of amino acid ester prodrugs in Caco-2/hPEPT1 cells overexpressing a human peptide transporter

PURPOSE: This study characterized the cellular uptake mechanism and hydrolysis of the amino acid ester prodrugs of nucleoside antiviral drugs in the transiently transfected Caco-2 cells overexpressing a human intestinal peptide transporter, hPEPT1 (Caco-2/hPEPT1 cells). METHODS: Amino acid ester prodrugs of acyclovir and AZT were synthesized and their apical membrane permeability and hydrolysis were evaluated in Caco-2/hPEPT1 cells. The cellular uptake mechanism of prodrugs was investigated through the competitive inhibition study in Caco-2/hPEPT1 cells. RESULTS: L-Valyl ester of acyclovir (L-Val-ACV) was approximately ten fold more permeable across the apical membrane than acyclovir and four times more permeable than D-valyl ester of acyclovir (D-Val-ACV). Correspondingly, L-valyl ester of AZT (L- Val-AZT) exhibited three fold higher cellular uptake than AZT. Therefore, amino acid ester prodrugs significantly increased the cellular uptake of the parent drugs and exhibited the D,L-stereoselectivity. Furthermore, prodrugs were rapidly hydrolyzed to the parent drugs by the intracellular hydrolysis, following the apical membrane transport. In the inhibition studies, cephalexin and small dipeptides strongly inhibited the cellular uptake of L-Val-ACV while L-valine had no effect, indicating that the peptide transporter is primarily responsible for the apical membrane transport of L-Val-ACV. In addition, the cellular uptake of L-Val-ACV was five times higher in Caco-2/hPEPT1 cells than the uptake in the untransfected Caco-2 cells, implying the cellular uptake of L-Val-ACV was related to the enhancement of the peptide transport activity in Caco-2/hPEPT1 cells. CONCLUSIONS: Caco-2/hPEPT1 system is an efficient in vitro model for the uptake study of peptidyl derivatives. Amino acid ester prodrugs significantly improved the cellular uptake of the parent drugs via peptide transport mechanism and were rapidly converted to the active parent drugs by the intracellular hydrolysis.     

Effect of various marine lipids on transdermal drug delivery--in vitro evaluation

The effects of several marine lipids on the penetration of hydrocortisone and nitroglycerin through excised hairless mouse skin have been studied. Fatty acid extracts obtained by hydrolysis of Portuguese dog-fish-liver-oil or by hydrolysis of cod-liver-oil were shown to be effective skin penetration enhancers. Phospholipid obtained from squid was also shown to be effective enhancer. However, the enhancing effect of the marine products could generally be associated with their content of free unsaturated fatty acids. The fatty acid extract obtained from cod-liver-oil caused insignificant skin irritation when incorporated into an ointment base and applied to human skin.     

In vitro study of the percutaneous absorption of four aromatic amines using hairless rat skin

Using hairless rat skin maintained in a Franz diffusion cell, the percutaneous penetration of four aromatic amines: para-chloroaniline (PCPA), meta-trifluoromethylaniline (mTFMA), dichloro-3,4-aniline (3,4-DCA) and dichloro-3,5-aniline (3,5-DCA) were studied. The purpose of the studies was to determine the permeation parameters (rate of permeation, permeability rat constant) in order to compare the rate of absorption of the four amines. The results show that the four amines penetrate significantly across the skin, but with different rates. 10 h after in vitro application (2 mg/cm2), the extent of permeation was PCPA > mTFMA > 3,4-DCA > 3,5-DCA.     

Ocular penetration and bioconversion of prostaglandin F2alpha prodrugs in rabbit cornea and conjunctiva

The objective of this study was to identify prostaglandin F2alpha (PGF2alpha) prodrugs that have an optimal ocular absorption profile and therefore could be potentially useful for the treatment of glaucoma. Rabbit cornea, conjunctiva, and iris/ciliary body were mounted in a flow-through chamber to evaluate the permeability and bioconversion of PGF2alpha and its prodrugs. The prodrugs tested were PGF2alpha 1-isopropyl, 1,11-lactone, 15-acetyl, 15-pivaloyl, 15-valeryl, and 11,15-dipivaloyl esters. After 4 h in the donor or acceptor compartments, the products and formation of PGF2alpha were analyzed by HPLC. Effects on intraocular pressure and ocular surface hyperemia were also determined. All prodrugs penetrated the rabbit cornea faster than PGF2alpha by 4- to 83-fold. All prodrugs penetrated conjunctiva faster than PGF2alpha, except the 15-acetyl ester prodrug, which was equally permeable. No direct correlation between drug lipophilicity and permeability across the cornea or conjunctiva was apparent. The most metabolically stable prodrug was the 1,11-lactone, followed by the 11,15-dipivaloyl, 15-pivaloyl, 15-acetyl, 1-isopropyl, and the 15-valeryl esters, the latter of which was extensively converted to PGF2alpha. A separation index for various prodrugs was calculated from the ratio of the bioavailable PGF2alpha for ocular hypotension to the bioavailable PGF2alpha for hyperemia. The highest separation index was observed for the 1,11-lactone prodrug (2.33), followed by the 11,15-dipivaloyl ester prodrug (1.80). Thus the 1,11-lactone and 11,15-dipivaloyl ester prodrugs appeared to be superior to the others in providing bioavailable PGF2alpha for ocular hypotension, while minimizing hyperemia. The favorable separation index for these compounds appeared to be due to their metabolic stability at the corneal surface and conjunctiva combined with sufficient bioavailability for ocular hypotension.     

Transdermal delivery of erythromycin lactobionate--implications for the therapy of gastroparesis

BACKGROUND: The treatment of many diseases may be complicated by abnormalities in gastric emptying. Gastric motor dysfunction may lead to unpredictable food and medication delivery to the small intestine, their site of absorption. Prokinetic agents improve gastric motility, but orally administered drugs are unreliably absorbed, thereby limiting their effectiveness. A method of delivering prokinetic agents which bypasses the gastrointestinal tract could lead to more effective treatment. METHODS: Skin samples from rat, hairless mouse and man were placed in an in vitro diffusion chamber. The epidermal side of the skin was exposed to erythromycin lactobionate and passage of the drug across the skin sample monitored and quantitated by high-performance liquid chromatography with UV detection. RESULTS: Erythromycin passes across all skin types tested. Steady-state flux across hairless mouse skin was greater than for rat, full thickness human skin and human epidermis. In the first 3 h following introduction of erythromycin lactobionate, 1.85 mg/cm2 crossed human epidermis. Given that a dose of 50 mg may exert prokinetic effects in vivo in man, increasing the patch size to approximately equal to 28 cm2 should provide therapeutic levels of drug within 3 h. CONCLUSIONS: Erythromycin lactobionate, when administered transdermally, can be delivered at levels sufficient to treat gastroparesis. This technique warrants in vivo investigation.     

Transdermal delivery of peptides by iontophoresis

Transdermal administration by iontophoresis (enhanced transport via the skin using the driving force of an applied electric field) has been successfully demonstrated but no formal relationship between peptide sequence/structure and efficiency of delivery has been established. There are notable examples, such as the lipophilic leutinizing hormone releasing hormone (LHRH) analogs, Nafarelin and Leuprolide, that exhibit down-regulation of their own transport across the skin under the influence of an iontophoretic current. The hypothesis that this phenomenon is due to neutralization of the skin's net negative charge by these cationic peptides was examined with LHRH oligopeptides. The impact of these compounds on the electroosmotic flow of solvent into the skin, which is induced by iontophoresis and which contributes significantly to the electrotransport of large, positively charged ions, was examined and quantified. Close juxtaposition of cationic and lipophilic residues profoundly inhibited electroosmosis and, presumably, peptide flux. The results indicate that the lipophilicity of the oligopeptides facilitates van der Waals interactions with hydrophobic patches along the transport route, thereby permitting the positively charged oligopeptide to interact with carboxylate side chains that give the skin its net negative charge at neutral pH. The lipophilic, cationic oligopeptide, therefore, becomes anchored in the transport path, neutralizing the original charge of the membrane, and completely altering the permselective properties of the skin.