RESUMEN
Both L- and D-isomers of S-nitrosocysteine (CSNO) can bind to the intracellular domain of voltage-gated potassium channels in vitro. CSNO binding inhibits these channels in the carotid body, leading to increased minute ventilation in vivo. However, only the l-isomer is active in vivo because it requires the l-amino acid transporter (LAT) for transmembrane transport. In rodents and dogs, the esterified D-CSNO precursor-d-cystine dimethyl ester (ATLX-0199)-overcomes opioid- and benzodiazepine-induced respiratory depression while maintaining analgesia. Although ATLX-0199 can enter cells independently of LAT because it is an ester, its stability in plasma is limited by the presence of esterases. Here, we hypothesized that the drug could be sequestered in erythrocytes to avoid de-esterification in circulation. We developed a liquid chromatography-mass spectrometry method for detecting ATLX-0199 and characterized a new metabolite, S-nitroso-d-cysteine monomethyl ester (DNOCE), which is also a D-CSNO precursor. We found that both ATLX-0199 and DNOCE readily enter erythrocytes and neurons and remain stable over 20 min; thus ATLX-0199 can enter cells where the ester is stable, but the thiol is reduced. Depending on hemoglobin conformation, the reduced ester can be S-nitrosylated and enter carotid body neurons, where it then increases minute ventilation. These data may help explain the paradox that ATLX-0199, a dimethyl ester, can avoid de-esterification in plasma and exert its effects at the level of the carotid body.
Asunto(s)
S-Nitrosotioles , Animales , Perros , S-Nitrosotioles/metabolismo , S-Nitrosotioles/farmacología , Cisteína/metabolismo , Eritrocitos/metabolismo , Compuestos de Sulfhidrilo , ÉsteresRESUMEN
Though endogenous S-nitroso-l-cysteine (l-CSNO) signaling at the level of the carotid body increases minute ventilation (vÌE ), neither the background data nor the potential clinical relevance are well-understood by pulmonologists in general, or by pediatric pulmonologists in particular. Here, we first review how regulation of the synthesis, activation, transmembrane transport, target interaction, and degradation of l-CSNO can affect the ventilatory drive. In particular, we review l-CSNO formation by hemoglobin R to T conformational change and by nitric oxide (NO) synthases (NOS), and the downstream effects on vÌE through interaction with voltage-gated K+ (Kv) channel proteins and other targets in the peripheral and central nervous systems. We will review how these effects are independent of-and, in fact may be opposite to-those of NO. Next, we will review evidence that specific elements of this pathway may underlie disorders of respiratory control in childhood. Finally, we will review the potential clinical implications of this pathway in the development of respiratory stimulants, with a particular focus on potential pediatric applications.
Asunto(s)
Fármacos del Sistema Respiratorio , S-Nitrosotioles , Niño , Cisteína/análogos & derivados , Cisteína/metabolismo , Hemoglobinas , Humanos , Óxido Nítrico/metabolismo , Óxido Nítrico Sintasa , S-Nitrosotioles/metabolismoRESUMEN
Intestinal permeability of PAMAM dendrimers has been observed, giving rationale for their use in oral drug delivery as potential carriers of associated molecules. This study assessed the apparent permeability coefficients (Papp) of dendrimers across isolated rat intestinal regional mucosae, along with estimation of the maximum non-toxic concentration. Caco-2 monolayers were also used to assess the comparative Papp values between isolated mucosae and cell culture models. Concentrations from 0.1 to 10 mM of anionic and cationic dendrimers were tested in mucosae to assess their Papp, membrane TEER, [(14)C]-mannitol Papp, and histology. 0.1 mM concentrations of dendrimers were assessed over 120 min in Caco-2 cell monolayers as concentrations above that were cytotoxic. Jejunal transport of dendrimers was higher than transport in colonic epithelium. Monolayer Papp values of dendrimers were comparable to those of jejunal mucosae. Mucosae exposed to dendrimer concentrations of 10 mM for 120 min caused significant reduction in TEER and changes in tissue morphology; however, G3.5 was the only analogue that caused significant TEER reduction and morphological changes at 1 mM concentrations. Transport in jejunal mucosae appears to be the greatest indicating that the small intestinal will be the most likely region to target for oral drug delivery using PAMAM dendrimers.
Asunto(s)
Colon/metabolismo , Dendrímeros , Sistemas de Liberación de Medicamentos , Mucosa Intestinal/metabolismo , Yeyuno/metabolismo , Modelos Biológicos , Administración Oral , Animales , Transporte Biológico Activo/efectos de los fármacos , Células CACO-2 , Dendrímeros/química , Dendrímeros/farmacocinética , Dendrímeros/farmacología , Femenino , Humanos , Especificidad de Órganos/efectos de los fármacos , Ratas , Ratas Sprague-DawleyRESUMEN
Poly(amido amine) (PAMAM) dendrimers have shown transepithelial transport across intestinal epithelial barrier in rats and across Caco-2 cell monolayers. Caco-2 models innately lack mucous barriers, and rat isolated intestinal tissue has been shown to overestimate human permeability. This study is the first report of transport of PAMAM dendrimers across isolated human intestinal epithelium. It was observed that FITC labeled G4-NH2 and G3.5-COOH PAMAM dendrimers at 1 mM concentration do not have a statistically higher permeability compared to free FITC controls in isolated human jejunum and colonic tissues. Mannitol permeability was increased at 10 mM concentrations of G3.5-COOH and G4-NH2 dendrimers. Significant histological changes in human colonic and jejunal tissues were observed at G3.5-COOH and G4-NH2 concentrations of 10 mM implying that dose limiting toxicity may occur at similar concentrations in vivo. The permeability through human isolated intestinal tissue in this study was compared to previous rat and Caco-2 permeability data. This study implicates that PAMAM dendrimer oral drug delivery may be feasible, but it may be limited to highly potent drugs.
Asunto(s)
Materiales Biocompatibles/farmacocinética , Permeabilidad de la Membrana Celular , Dendrímeros/farmacocinética , Sistemas de Liberación de Medicamentos , Mucosa Intestinal/metabolismo , Manitol/metabolismo , Adulto , Anciano , Anciano de 80 o más Años , Animales , Materiales Biocompatibles/química , Transporte Biológico , Células CACO-2 , Dendrímeros/química , Femenino , Humanos , Mucosa Intestinal/citología , Masculino , Persona de Mediana Edad , Ratas , Adulto JovenRESUMEN
Oral delivery remains a challenge for poorly permeable hydrophilic macromolecules. Poly(amido amine) (PAMAM) dendrimers have shown potential for their possible oral delivery. Transepithelial transport of carboxyl-terminated G3.5 and amine-terminated G4 PAMAM dendrimers was assessed using isolated rat jejunal mucosae mounted in Ussing chambers. The 1 mM FITC-labeled dendrimers were added to the apical side of mucosae. Apparent permeability coefficients (Papp) from the apical to the basolateral side were significantly increased for FITC when conjugated to G3.5 PAMAM dendrimer compared to FITC alone. Minimal signs of toxicity were observed when mucosae were exposed to both dendrimers with respect to transepithelial electrical resistance changes, carbachol-induced short circuit current stimulation, and histological changes. [(14)C]-mannitol fluxes were not altered in the presence of 1 mM dendrimers, suggesting that the paracellular pathway was not affected at this concentration in this model. These results give insight into the mechanism of PAMAM dendrimer transepithelial rat jejunal transport, as well as toxicological considerations important for oral drug delivery.
Asunto(s)
Dendrímeros , Sistemas de Liberación de Medicamentos , Mucosa Intestinal/metabolismo , Yeyuno/metabolismo , Animales , Transporte Biológico/efectos de los fármacos , Dendrímeros/química , Dendrímeros/farmacocinética , Dendrímeros/farmacología , Mucosa Intestinal/citología , Yeyuno/citología , Masculino , RatasRESUMEN
The in vivo biodistribution and pharmacokinetics of silica nanoparticles (SiO(2)) with systematically varied geometries, porosities, and surface characteristics were investigated in immune-competent CD-1 mice via the intravenous injection. The nanoparticles were taken up extensively by the liver and spleen. Mesoporous SiO(2) exhibited higher accumulation in the lung than nonporous SiO(2) of similar size. This accumulation was reduced by primary amine modification of the nanoparticles. High aspect ratio, amine-modified mesoporous nanorods showed enhanced lung accumulation compared to amine-modified mesoporous nanospheres. Accumulation of the nanoparticles was mainly caused by passive entrapment in the discontinuous openings in the endothelium of the liver and spleen or in the pulmonary capillaries, and was highly dependent on nanoparticle hydrodynamic size in circulation. The SiO(2) were likely internalized by the reticulo-endothelial system (RES) following physical sequestration in the liver and spleen. The nanoparticles that were transiently associated with the lung were re-distributed out of this organ without significant internalization. Pharmacokinetic analysis showed that all SiO(2) were rapidly cleared from systemic circulation. Amine-modified or nonporous nanoparticles possessed a higher volume of distribution at steady state than their pristine counterparts or mesoporous SiO(2). In all, surface characteristics and porosity played important roles in influencing SiO(2) biodistribution and pharmacokinetics. Increasing the aspect ratio of amine-modified mesoporous SiO(2) from 1 to 8 resulted in increased accumulation in the lung.
Asunto(s)
Nanopartículas/química , Dióxido de Silicio/química , Dióxido de Silicio/farmacocinética , Animales , Femenino , Ratones , Porosidad , Propiedades de Superficie , Distribución TisularRESUMEN
The influence of size, surface charge and surface functionality of poly(amido amine) dendrimers and silica nanoparticles (SNPs) on their toxicity was studied in immunocompetent mice. After systematic characterization of nanoparticles, they were administered to CD-1 (caesarean derived-1) mice to evaluate acute toxicity. A distinct trend in nanotoxicity based on surface charge and functional group was observed with dendrimers regardless of their size. Amine-terminated dendrimers were fatal at doses >10 mg/kg causing haematological complications such as disseminated intravascular coagulation-like manifestations whereas carboxyl- and hydroxyl-terminated dendrimers of similar sizes were tolerated at 50-fold higher doses. In contrast, larger SNPs were less tolerated than smaller SNPs irrespective of their surface functionality. These findings have important implications in the use of these nanoparticles for various biomedical applications.