Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 16 de 16
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
2.
Am J Cardiovasc Drugs ; 19(1): 11-20, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30144016

RESUMO

Distributive shock is a subset of shock marked by decreased systemic vascular resistance, organ hypoperfusion and altered oxygen extraction. Despite the use of intravenous fluids and either higher dose of catecholamines or other additional exogenous vasopressors to maintain blood pressure in the target range, the rate of mortality remains higher in patients with septic shock. Therefore, there is clearly an unmet need for additional safe and effective treatments. The use of angiotensin II to raise the mean arterial pressure (MAP) could provide additional therapy and the opportunity to evaluate a catecholamine-sparing effect by decreasing the dose of concomitant catecholamines while maintaining a target MAP. ATHOS-3 (Angiotensin II for the Treatment of High-Output Shock phase 3; ClinicalTrials.gov number, NCT02338843) was an adequate and well-controlled trial. The primary endpoint was the rate of MAP response at hour 3 of treatment with study drug, defined as either a 10-mmHg increase from baseline in MAP or a MAP of at least 75 mmHg. The secondary endpoints were changes from baseline in Sequential Organ Failure Assessment (SOFA) scores (total and cardiovascular). Mortality was an exploratory endpoint. The trial provided substantial evidence of the effectiveness of angiotensin II in raising blood pressure over placebo in patients with distributive shock, while keeping catecholamine levels constant. There was no change in the secondary endpoint of total SOFA scores relative to placebo when catecholamine use was reduced in lieu of angiotensin II treatment. There was a slight decrease in the secondary endpoint of cardiovascular SOFA score relative to placebo during the catecholamine-sparing phase, reflecting the catecholamine-sparing effect. There was a consistent trend in decreased mortality relative to placebo over the 28-day study period. Based on the agreements emanating from the special protocol assessment to assess blood pressure effects, the data from this single study supported approval of angiotensin II by the Food and Drug Administration for marketing in the USA.


Assuntos
Angiotensina II/uso terapêutico , Hipotensão/tratamento farmacológico , Choque Séptico/tratamento farmacológico , Vasoconstritores/uso terapêutico , Adulto , Idoso , Idoso de 80 Anos ou mais , Pressão Sanguínea/efeitos dos fármacos , Sistema Cardiovascular/efeitos dos fármacos , Método Duplo-Cego , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Resultado do Tratamento , Estados Unidos , United States Food and Drug Administration , Adulto Jovem
3.
AAPS PharmSciTech ; 15(6): 1454-67, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-24980081

RESUMO

The purpose of this study was to develop a clear aqueous mixed nanomicellar formulation (MNF) of dexamethasone utilizing both D-α-tocopherol polyethylene glycol-1000 succinate (Vit E TPGS) and octoxynol-40 (Oc-40). In this study, Vit E TPGS and Oc-40 are independent variables. Formulations were prepared following solvent evaporation method. A three level full-factorial design was applied to optimize the formulation based on entrapment efficiency, size, and polydispersity index (PDI). A specific blend of Vit E TPGS and Oc-40 at a particular wt% ratio (4.5:2.0) produced excellent drug entrapment, loading, small mixed nanomicellar size and narrow PDI. Solubility of DEX in MNF is improved by ~6.3-fold relative to normal aqueous solubility. Critical micellar concentration (CMC) for blend of polymers (4.5:2.0) was found to be lower (0.012 wt%) than the individual polymers (Vit E TPGS (0.025 wt%) and Oc-40 (0.107 wt%)). No significant effect on mixed nanomicellar size and PDI with one-factor or multi-factor interactions was observed. Qualitative (1)H NMR studies confirmed absence of free drug in the outer aqueous MNF medium. MNF appeared to be highly stable. Cytotoxicity studies on rabbit primary corneal epithelial cells did not indicate any toxicity suggesting MNF of dexamethasone is safe and suitable for human topical ocular drops after further in vivo evaluations.


Assuntos
Dexametasona/química , Glucocorticoides/química , Nanopartículas , Administração Oftálmica , Animais , Células Cultivadas , Química Farmacêutica , Dexametasona/administração & dosagem , Dexametasona/toxicidade , Epitélio Anterior/efeitos dos fármacos , Glucocorticoides/administração & dosagem , Glucocorticoides/toxicidade , Cinética , Análise dos Mínimos Quadrados , Micelas , Modelos Estatísticos , Nanotecnologia , Octoxinol/química , Soluções Oftálmicas , Tamanho da Partícula , Polietilenoglicóis/química , Espectroscopia de Prótons por Ressonância Magnética , Coelhos , Solubilidade , Propriedades de Superfície , Tecnologia Farmacêutica/métodos , Viscosidade , Vitamina E/análogos & derivados , Vitamina E/química
5.
J Clin Pharmacol ; 52(1 Suppl): 119S-25S, 2012 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-21956605

RESUMO

The objective of this work was to derive a dosing regimen for dabigatran in patients with severe renal impairment by modeling and simulation. Data from a dedicated renal impairment study were used to model the pharmacokinetics of dabigatran in normal and renal-impaired subjects. Model parameters were used to simulate the average concentration time-course of dabigatran following various dosing regimens. Pharmacokinetics of dabigatran in normal and renal-impaired subjects were best described by a 2-compartment open model with first-order absorption and elimination. Simulations were performed to select an appropriate regimen that reasonably matched the exposures on an average with those observed in subjects with moderate renal impairment who did not require a dose adjustment because of a favorable benefit-risk. Dabigatran 150 mg given once daily resulted in 35% higher average C(max, ss), whereas a 75 mg once daily regimen resulted in 42% lower average Cτ, relative to that observed with 150 mg administered twice daily in subjects with moderate renal impairment. A twice daily regimen of dabigatran 75 mg resulted in a reasonable matching of exposures and was selected as an appropriate dosing regimen in patients with severe renal impairment. This recommendation was incorporated in the dosing and recommendation section of dabigatran product insert.


Assuntos
Antitrombinas/administração & dosagem , Benzimidazóis/administração & dosagem , Nefropatias/metabolismo , Modelos Biológicos , beta-Alanina/análogos & derivados , Adulto , Idoso , Antitrombinas/sangue , Antitrombinas/farmacocinética , Benzimidazóis/sangue , Benzimidazóis/farmacocinética , Simulação por Computador , Dabigatrana , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Adulto Jovem , beta-Alanina/administração & dosagem , beta-Alanina/sangue , beta-Alanina/farmacocinética
6.
J Pharm Biomed Anal ; 52(4): 525-33, 2010 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-20172680

RESUMO

A sensitive, selective, accurate and robust LC-MS/MS method was developed and validated for the quantitative determination of glucocorticoids in rabbit ocular tissues. Samples were processed by a simple liquid-liquid extraction procedure. Chromatographic separation was performed on Phenomenex reversed phase C18 gemini column (50mmx4.6mm i.d.,) with an isocratic mobile phase composed of 30% of acetonitrile in water containing 0.1% of formic acid, at a flow rate 0.2mL/min. Dexamethasone (DEX), prednisolone (PD) and hydrocortisone (HD) were detected with proton adducts at m/z 393.20-->355.30, 361.30-->147.20 and 363.20-->121.0 in multiple reaction monitoring (MRM) positive mode respectively. Finally, 50microL of 0.1% novel DEX mixed micellar formulation was topically administered to a rabbit eye and concentrations were measured. The method was validated over a linear concentration range of 2.7-617.6ng/mL. Lower limit of quantitation (LLOQ) of DEX and PD was measured in the concentration range of 2.7 and 11.0ng/mL respectively. The resulting method demonstrated intra and inter-day precision within 13.3% and 11.1% and accuracy within 19.3% and 12.5% for DEX and PD, respectively. Both analytes were found to be stable throughout freeze-thaw cycles and during bench top and postoperative stability studies (r(2)>0.999). DEX concentrations in various ocular tissue samples i.e., aqueous humor, cornea, iris ciliary body, sclera and retina choroid were found to be 344.0, 1050.07, 529.6, 103.9 and 48.5ng/mg protein respectively. Absorption of DEX after topical administration from a novel aqueous mixed micellar formulation achieved therapeutic concentration levels in posterior segment of the rabbit eye.


Assuntos
Dexametasona/análise , Olho/metabolismo , Glucocorticoides/análise , Espectrometria de Massas em Tandem/métodos , Animais , Cromatografia Líquida/métodos , Dexametasona/administração & dosagem , Dexametasona/farmacocinética , Avaliação Pré-Clínica de Medicamentos/métodos , Olho/efeitos dos fármacos , Glucocorticoides/administração & dosagem , Glucocorticoides/farmacocinética , Masculino , Coelhos , Reprodutibilidade dos Testes
7.
J Ocul Pharmacol Ther ; 25(6): 487-98, 2009 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-20028257

RESUMO

PURPOSE: The objectives of this work were (i) to screen ocular hypotensive prostaglandin (PGF2 alpha) analogs--bimatoprost, latanoprost, and travoprost as well as their free acid forms--for interaction with efflux pumps on the cornea and (ii) to assess the modulation of efflux upon co-administration of these prostaglandin analogs. METHODS: Cultured rabbit primary corneal epithelial cells (rPCEC) were employed as an in vitro model for rabbit cornea. Transporter-specific interaction studies were carried out using Madin-Darby canine kidney (MDCK) cells overexpressing MDR1, MRP1, MRP2, MRP5, and BCRP. Freshly excised rabbit cornea was used as an ex vivo model to determine transcorneal permeability. RESULTS: Cellular accumulation studies clearly showed that all prostaglandin analogs and their free acid forms are substrates of MRP1, MRP2, and MRP5. Bimatoprost was the only prostaglandin analog in this study to interact with P-gp. In addition, none of these molecules showed any affinity for BCRP. K (i) values of these prostaglandin analogs obtained from dose-dependent inhibition of erythromycin efflux in rPCEC showed bimatoprost (82.54 microM) and travoprost (94.77 microM) to have similar but higher affinity to efflux pumps than latanoprost (163.20 microM). Ex vivo studies showed that the permeation of these molecules across cornea was significantly elevated in the presence of specific efflux modulators. Finally, both in vitro and ex vivo experiments demonstrated that the efflux of these prostaglandin analogs could be modulated by co-administering them together. CONCLUSION: Bimatoprost, latanoprost, travoprost, and their free acid forms are substrates of multiple drug efflux pumps on the cornea. Co-administration of these molecules together is a viable strategy to overcome efflux, which could simultaneously elicit a synergistic pharmacological effect, since these molecules have been shown to activate different receptor population for the reduction of intraocular pressure (IOP).


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Anti-Hipertensivos/farmacocinética , Epitélio Anterior/metabolismo , Amidas/administração & dosagem , Amidas/farmacocinética , Animais , Anti-Hipertensivos/administração & dosagem , Bimatoprost , Linhagem Celular , Cloprostenol/administração & dosagem , Cloprostenol/análogos & derivados , Cloprostenol/farmacocinética , Córnea/metabolismo , Cães , Relação Dose-Resposta a Droga , Sinergismo Farmacológico , Epitélio Anterior/citologia , Eritromicina/farmacocinética , Latanoprosta , Masculino , Permeabilidade , Prostaglandinas F Sintéticas/administração & dosagem , Prostaglandinas F Sintéticas/farmacocinética , Coelhos , Travoprost
8.
Clin Res Regul Aff ; 26(3): 65-72, 2009 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-21278830

RESUMO

The objective of this work was to study the disposition kinetics of valine-valine-acyclovir (VVACV), a dipeptide ester prodrug of acyclovir following intravenous and oral administrations in rat. A validated LC-MS/MS analytical method was developed for the analysis VVACV, Valine-Acyclovir (VACV), and Acyclovir (ACV) using a linear Ion Trap Quadrupole. ACV was administered orally for comparison purpose. In the VVACV group, both blood and urine samples and in the ACV group only blood samples were collected. All the samples were analyzed using LC-MS/MS. The LLOQ for ACV, VACV, and VVACV were 10, 10, and 50 ng/ml, respectively. Relevant pharmacokinetic parameters were obtained by non-compartmental analyses of data with WinNonlin. Following i.v. administration of VVACV, AUC(0-inf) (min*µM) values for VVACV, VACV, and ACV were 55.06, 106, and 466.96, respectively. The AUC obtained after oral administration of ACV was 178.8. However, following oral administration of VVACV, AUC(0-inf) values for VACV and ACV were 89.28 and 810.77, respectively. Thus the exposure of ACV obtained following oral administration of VVACV was almost 6-fold higher than ACV. This preclinical pharmacokinetic data revealed that VVACV has certainly improved the oral bioavailability of ACV and is an effective prodrug for oral delivery of ACV.

9.
Pharm Res ; 26(5): 1270-82, 2009 May.
Artigo em Inglês | MEDLINE | ID: mdl-18958406

RESUMO

PURPOSE: The objectives were (i) to test in vivo functional activity of MRP2 on rabbit corneal epithelium and (ii) to evaluate modulation of P-gp and MRP2 mediated efflux of erythromycin when co-administered with corticosteroids. METHODS: Cultured rabbit primary corneal epithelial cells (rPCECs) was employed as an in vitro model for rabbit cornea. Cellular accumulation and bi-directional transport studies were conducted across Madin-Darby Canine Kidney (MDCK) cells overexpressing MDR1 and MRP2 proteins to delineate transporter specific interaction of steroids. Ocular pharmacokinetic studies were conducted in rabbits following a single-dose infusion of erythromycin in the presence of specific inhibitors and steroids. RESULTS: Bi-directional transport of erythromycin across MDCK-MDR1 and MDCK-MRP2 cells showed significant difference between BL-AP and AP-BL permeability, suggesting that erythromycin is a substrate for P-gp and MRP2. Cellular accumulation of erythromycin in rPCEC was inhibited by steroids in a dose dependent manner. MK571, a specific MRP inhibitor, modulated the aqueous humor concentration of erythromycin in vivo. Even, steroids inhibited P-gp and MRP2 mediated efflux with maximum increase in k(a), AUC(0-infinity), C(max) and C(last) values of erythromycin, observed with 6alpha-methyl prednisolone. CONCLUSION: MRP2 is functionally active along with P-gp in effluxing drug molecules out of corneal epithelium. Steroids were able to significantly inhibit both P-gp and MRP2 mediated efflux of erythromycin.


Assuntos
Membro 1 da Subfamília B de Cassetes de Ligação de ATP/metabolismo , Corticosteroides/farmacologia , Transporte Biológico/efeitos dos fármacos , Epitélio Anterior/efeitos dos fármacos , Eritromicina/farmacocinética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Membro 1 da Subfamília B de Cassetes de Ligação de ATP/antagonistas & inibidores , Absorção , Corticosteroides/toxicidade , Animais , Linhagem Celular , Proliferação de Células/efeitos dos fármacos , Células Cultivadas , Epitélio Anterior/citologia , Epitélio Anterior/metabolismo , Proteínas Associadas à Resistência a Múltiplos Medicamentos/antagonistas & inibidores , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Coelhos , Regulação para Cima
10.
Ophthalmol Eye Dis ; 1: 21-31, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-23861607

RESUMO

OBJECTIVE: To delineate the plasma pharmacokinetics and determine the corneal uptake of valine based stereoisomeric dipeptide prodrugs of acyclovir (ACV) in rats. METHODS: Male Sprague-Dawley rats were used for the study. Pharmacokinetics of ACV, L-valine-acyclovir (LACV), L-valine-D-valine-acyclovir (LDACV) and D-valine-L-valine acyclovir (DLACV) prodrugs were delineated. These compounds were administered intravenously as a bolus via jugular vein cannula and orally by gavage. Samples were purified by protein precipitation method and analyzed by LC-MS/MS. Pertinent pharmacokinetic parameters were obtained by using WinNonlin. Corneal uptake studies of LDACV and LACV were studied following oral administration. RESULTS: Following i.v. administration, the area under the curve (AUC) in µM*min of generated ACV was in the order of LACV > LDACV > DLACV indicating their rate of metabolism. The AUC values of total drug obtained in the systemic circulation after oral administration LACV and LDACV were 1077.93 ± 236.09 and 1141.76 ± 73.67 µM*min, respectively. DLACV exhibited poor oral absorption. Cmax (µM) and AUC of the intact prodrug obtained in the systemic circulation following oral administration of LDACV were almost 4-5 times higher than LACV. Moreover, concentrations achieved in the cornea after oral administration of LDACV were almost two times of LACV. CONCLUSIONS: LDACV increased both the oral bioavailability and subsequent in vivo corneal uptake of ACV. Hence, LDACV can be considered as the most promising drug candidate for delivery of ACV, in treatment of both genital herpes and ocular herpes keratitis after oral administration.

11.
Int J Pharm ; 362(1-2): 93-101, 2008 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-18638532

RESUMO

In vivo systemic absorption of the amino acid prodrugs of acyclovir (ACV) after oral administration was evaluated in rats. Stability of the prodrugs, L-alanine-ACV (AACV), L-serine-ACV (SACV), L-isoleucine-ACV (IACV), gamma-glutamate-ACV (EACV) and L-valine-ACV (VACV) was evaluated in various tissues. Interaction of these prodrugs with the transporters on Caco-2 cells was studied. In vivo systemic bioavailability of these prodrugs upon oral administration was evaluated in jugular vein cannulated rats. The amino acid ester prodrugs showed affinity towards various amino acid transporters as well as the peptide transporter on the Caco-2 cells. In terms of stability, EACV was most enzymatically stable compared to other prodrugs especially in liver homogenate. In oral absorption studies, ACV and AACV showed high terminal elimination rate constants (lambda(z)). SACV and VACV exhibited approximately five-fold increase in area under the curve (AUC) values relative to ACV (p<0.05). C(max(T)) (maximum concentration) of SACV was observed to be 39+/-22 microM in plasma which is 2 times better than VACV and 15 times better than ACV. C(last(T)) (concentration at the last time point) of SACV was observed to be 0.18+/-0.06 microM in plasma which is two times better than VACV and three times better than ACV. Amino acid ester prodrugs of ACV were absorbed at varying amounts (C(max)) and eliminated at varying rates (lambda(z)) thereby leading to varying extents (AUC). The amino acid ester prodrug SACV owing to its enhanced stability, higher AUC and better concentration at last time point seems to be a promising candidate for the oral treatment of herpes infections.


Assuntos
Aciclovir/farmacocinética , Aminoácidos/química , Proteínas de Transporte/metabolismo , Portadores de Fármacos/química , Pró-Fármacos/farmacocinética , Aciclovir/administração & dosagem , Aciclovir/química , Administração Oral , Sistemas de Transporte de Aminoácidos/metabolismo , Animais , Disponibilidade Biológica , Transporte Biológico Ativo , Células CACO-2 , Cromatografia Líquida de Alta Pressão , Ésteres , Humanos , Masculino , Proteínas de Membrana Transportadoras/metabolismo , Pró-Fármacos/administração & dosagem , Pró-Fármacos/química , Ratos , Ratos Sprague-Dawley , Especificidade por Substrato , Espectrometria de Massas em Tandem , Distribuição Tecidual
12.
Int J Pharm ; 359(1-2): 15-24, 2008 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-18472234

RESUMO

PURPOSE: To evaluate in vivo corneal absorption of the amino acid prodrugs of acyclovir (ACV) using a topical well model and microdialysis in rabbits. METHODS: Stability of L-alanine-ACV (AACV), L-serine-ACV (SACV), L-isoleucine-ACV (IACV), gamma-glutamate-ACV (EACV) and L-valine-ACV (VACV) prodrugs was evaluated in various ocular tissues. Dose-dependent toxicity of these prodrugs was also examined in rabbit primary corneal epithelial cell culture (rPCEC) using 96-well based cell proliferation assay. In vivo ocular bioavailability of these compounds was also evaluated with a combination of topical well infusion and aqueous humor microdialysis techniques. RESULTS: Among the amino acid ester prodrugs, SACV was most stable in aqueous humor. Enzymatic degradation of EACV was the least compared to all other prodrugs. Cellular toxicity of all the prodrugs was significantly less compared to trifluorothymidine (TFT) at 5mM. Absorption rate constants of all the compounds were found to be lower than the elimination rate constants. All the prodrugs showed similar terminal elimination rate constants (lambda(z)). SACV and VACV exhibited approximately two-fold increase in area under the curve (AUC) relative to ACV (p<0.05). Clast (concentration at the last time point) of SACV was observed to be 8+/-2.6microM in aqueous humor which is two and three times higher than VACV and ACV, respectively. CONCLUSIONS: Amino acid ester prodrugs of ACV were absorbed through the cornea at varying rates (ka) thereby leading to varying extents (AUC). The amino acid ester prodrug, SACV owing to its enhanced stability, comparable AUC and high concentration at last time point (Clast) seems to be a promising candidate for the treatment of ocular HSV infections.


Assuntos
Aciclovir/farmacocinética , Antivirais/farmacocinética , Ceratite Herpética/tratamento farmacológico , Pró-Fármacos/farmacocinética , Aciclovir/administração & dosagem , Aciclovir/análogos & derivados , Animais , Câmara Anterior/metabolismo , Antivirais/administração & dosagem , Antivirais/química , Humor Aquoso/metabolismo , Área Sob a Curva , Disponibilidade Biológica , Células Cultivadas , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Estabilidade de Medicamentos , Epitélio Anterior/metabolismo , Masculino , Soluções Oftálmicas , Pró-Fármacos/administração & dosagem , Pró-Fármacos/química , Coelhos , Testes de Toxicidade
13.
Recent Pat Drug Deliv Formul ; 1(2): 161-70, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-19075883

RESUMO

Ophthalmic drug delivery has long been a challenging task for pharmaceutical scientists seeking to alleviate various ocular diseases affecting the anterior and posterior segments. In order to deliver therapeutic agents to target tissues, the unique anatomical barriers of the eye must be circumvented effectively, without causing any patient discomfort or alteration in protective physiological mechanisms. This challenge is currently being met with the development of novel non-invasive delivery methods as well as improvements over existing techniques. Over the past decade many advanced technologies have been patented. Nevertheless a need for additional research and continuous innovation is still warranted. Patent literature is often essential for promoting new directions in research as well as for elucidating possibilities for future technologies. Hence, the aim of this review article is to discuss several recently filed patents on non-invasive modes of drug delivery to the ocular tissues. This review will also focus on the role of colloidal/particulate systems in ocular drug delivery and formulation. Recent patents filed on prodrugs as an efficient ophthalmic drug delivery mechanism also have been discussed. As a whole, this article is intended to provide a valuable insight into current trends in the field of ocular drug delivery and highlights advances made in patent literature.


Assuntos
Sistemas de Liberação de Medicamentos , Soluções Oftálmicas/administração & dosagem , Administração Tópica , Disponibilidade Biológica , Coloides , Lentes de Contato , Olho/metabolismo , Oftalmopatias/tratamento farmacológico , Humanos , Lipossomos , Micelas , Nanopartículas , Patentes como Assunto , Polímeros , Pró-Fármacos/administração & dosagem
14.
Curr Eye Res ; 31(10): 811-24, 2006 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-17050273

RESUMO

PURPOSE: To investigate the functional expression of a carrier-mediated transport mechanism for riboflavin (vitamin B2) across cultured rabbit primary corneal epithelial cells (rPCECs) and intact rabbit cornea. The secondary objective was to understand the physiological significance behind the presence of such a transport system for riboflavin on the apical side of the corneal epithelium. METHODS: rPCECs and freshly excised rabbit corneas were selected as in vitro and ex vivo models, respectively. Transport and uptake characteristics of [3H]riboflavin were determined at various time points, concentrations, temperatures, and pH. Substrate specificity, energy, and ion dependence studies were carried out to characterize the translocation mechanism. Rabbit tear analysis was done with liquid chromatography/tandem mass spectrometry (LC-MS/MS) to understand the physiological relevance of this transporter. RESULTS: The uptake process in rPCECs was found to be concentration dependent and saturable at higher concentrations. The process was also independent of pH, Na+, and Cl- but dependent on energy and temperature. Unlabeled riboflavin and its structural analogues caused significant inhibition, whereas unrelated vitamins did not interfere with the process. Transport of [3H]riboflavin across rabbit cornea was also saturable at higher concentration and energy dependent but Na+ independent. Substrate specificity studies across intact rabbit cornea produced results similar to the uptake studies in cultured rPCECs. LC-MS/MS analysis of rabbit tears showed the presence of riboflavin. CONCLUSIONS: Results suggest the presence of a specialized, high-affinity transport mechanism for riboflavin that is expressed on the apical side of rabbit corneal epithelium and may in turn be responsible for influx of riboflavin from tears to cornea.


Assuntos
Epitélio Anterior/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Riboflavina/farmacocinética , 2,4-Dinitrofenol/farmacologia , Animais , Transporte Biológico , Células Cultivadas , Cromatografia Líquida , Colchicina/farmacologia , Inibidores Enzimáticos/farmacologia , Epitélio Anterior/citologia , Epitélio Anterior/efeitos dos fármacos , Cromatografia Gasosa-Espectrometria de Massas , Concentração de Íons de Hidrogênio , Masculino , Coelhos , Lágrimas/metabolismo , Temperatura Ambiente
15.
Curr Eye Res ; 31(10): 797-809, 2006 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-17038304

RESUMO

PURPOSE: The objective of this research was to investigate the presence of sodium-dependent multivitamin transporter (SMVT) on rabbit corneal epithelial cells. METHODS: Primary cultured rabbit corneal epithelial cells (rPCECs)and freshly excised rabbit corneas were used for characterization of biotin uptake and transport, respectively. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to confirm the molecular identity of SMVT. Liquid chromatography/tandem mass spectrometry (LC-MS/MS) analysis was performed to examine the presence of biotin in rabbit tears. RESULTS: Uptake of biotin by rPCECs was found to be time and concentration dependent with Km of 32.52 microM and Vmax of 10.43 pmol min- 1 mg protein- 1. Biotin was significantly inhibited in the presence of pantothenic acid and lipoic acid. Biotin uptake was found to be energy and Na+ dependent but H+ and Cl- independent. The uptake was inhibited by valeric acid in a concentration-dependent manner but not much affected in the presence of biotin methyl ester and biocytin with no free carboxyl group. Modulators of both PKC- and PKA-mediated pathways had no effect on biotin uptake, but calcium-calmodulin inhibitor significantly inhibited its uptake. Sodium-dependent multivitamin transporter was identified by RT-PCR in rPCECs. Transport experiments across the rabbit corneas revealed the functional localization of SMVT on the apical side of the cornea, and thereby corroborating with in vitro results with cultured corneal cells. Finally, LC-MS/MS analysis showed the presence of biotin in rabbit tears. CONCLUSIONS: Results obtained from both in vitro and exvivo studies suggest the possible role of SMVT expressed on corneal epithelial cells for the uptake of biotin, which co-transports pantothenic acid and lipoic acid. Further, the presence of biotin in tears suggests the physiological significance of this transporter in rabbit corneal epithelium.


Assuntos
Biotina/farmacocinética , Epitélio Anterior/metabolismo , Simportadores/fisiologia , Animais , Transporte Biológico Ativo/efeitos dos fármacos , Biotina/antagonistas & inibidores , Células Cultivadas , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Relação Dose-Resposta a Droga , Epitélio Anterior/citologia , Cromatografia Gasosa-Espectrometria de Massas , Concentração de Íons de Hidrogênio , Masculino , Ácido Pantotênico/farmacologia , Ácidos Pentanoicos/farmacologia , Proteína Quinase C/metabolismo , Coelhos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Sódio/farmacologia , Lágrimas/metabolismo , Ácido Tióctico/farmacologia
16.
J Ocul Pharmacol Ther ; 22(6): 465-76, 2006 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-17238815

RESUMO

AIM: The overall aim of this study was to evaluate the corneal absorption of dipeptide monoester prodrugs of ganciclovir (GCV) and compare these results with L-valine-GCV and GCV. Another aim was to evaluate the pharmacokinetics of these prodrugs in aqueous humor. METHODS: A well was placed on the cornea of anesthetized New Zealand albino rabbits with linear probes implanted in the aqueous humor. Two hundred microlitres (200 microL) of a 0.43% w/v (saturation concentration) solution of GCV and equimolar concentrations of its prodrugs, VGCV, glycine-valine-GCV (GVGCV), valine-valine-GCV (VVGCV), and tyrosine-valine- GCV (YVGCV), were placed in the corneal well and were allowed to diffuse for a period of 2 h. Subsequently, the drug solution was aspirated and the well removed. Samples were collected every 20 min throughout the infusion and postinfusion phases and were analyzed by high-performance liquid chromatography to determine the aqueous humor concentrations. RESULTS: Area under the concentration time profile (AUC)infinity and maximum concentration (Cmax) of YVGCV were found to be higher than other prodrugs. AUC of total GCV obtained from YVGCV administration was found to be twelvefold more than AUC of GCV and 6.2-fold more than AUC obtained with total GCV from VGCV administration. VVGCV also exhibited 3.2 times higher AUC relative to VGCV. Also, AUC and Cmax of regenerated GCV from YVGCV was 8.6 and 4.9 times more than GCV, respectively. VVGCV did not produce higher concentrations of GCV. Elimination half-life of regenerated GCV from YVGCV administration was observed to be 157 min. CONCLUSIONS: YVGCV and VVGCV exhibited superior corneal absorption and bioavailability, in comparison with GVGCV, VGCV, and GCV. Such facilitated absorption of prodrugs may be a result of a combination of transcellular passive diffusion and peptide transporter (PEPT1)-mediated transport across the corneal epithelium.


Assuntos
Câmara Anterior/metabolismo , Antivirais/farmacocinética , Córnea/metabolismo , Dipeptídeos/farmacocinética , Ganciclovir/análogos & derivados , Ganciclovir/farmacocinética , Pró-Fármacos/farmacocinética , Absorção , Animais , Disponibilidade Biológica , Relação Dose-Resposta a Droga , Avaliação Pré-Clínica de Medicamentos , Ésteres , Coelhos , Valganciclovir
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA