Enteroids to Study Pediatric Intestinal Drug Transport.

Intestinal maturational changes after birth affect the pharmacokinetics (PK) of drugs, having major implications for drug safety and efficacy. However, little is known about ontogeny-related PK patterns in the intestine. To explore the accuracy of human enteroid monolayers for studying drug transport in the pediatric intestine, we compared the drug transporter functionality and expression in enteroid monolayers and tissue from pediatrics and adults. Enteroid monolayers were cultured of 14 pediatric [median (range) age: 44 weeks (2 days-13 years)] and 5 adult donors, in which bidirectional drug transport experiments were performed. In parallel, we performed similar experiments with tissue explants in Ussing chamber using 11 pediatric [median (range) age: 54 weeks (15 weeks-10 years)] and 6 adult tissues. Enalaprilat, propranolol, talinolol, and rosuvastatin were used to test paracellular, transcellular, and transporter-mediated efflux by P-gp and breast cancer resistance protein (BCRP), respectively. In addition, we compared the expression patterns of ADME-related genes in pediatric and adult enteroid monolayers with tissues using RNA sequencing. Efflux transport by P-gp and BCRP was comparable between the enteroids and tissue. Efflux ratios (ERs) of talinolol and rosuvastatin by P-gp and BCRP, respectively, were higher in enteroid monolayers compared to Ussing chamber, likely caused by experimental differences in model setup and cellular layers present. Explorative statistics on the correlation with age showed trends of increasing ER with age for P-gp in enteroid monolayers; however, it was not significant. In the Ussing chamber setup, lower enalaprilat and propranolol transport was observed with age. Importantly, the RNA sequencing pathway analysis revealed that age-related variation in drug metabolism between neonates and adults was present in both enteroids and intestinal tissue. Age-related differences between 0 and 6 months old and adults were observed in tissue as well as in enteroid monolayers, although to a lesser extent. This study provides the first data for the further development of pediatric enteroids as an in vitro model to study age-related variation in drug transport. Overall, drug transport in enteroids was in line with data obtained from ex vivo tissue (using chamber) experiments. Additionally, pathway analysis showed similar PK-related differences between neonates and adults in both tissue and enteroid monolayers. Given the challenge to elucidate the effect of developmental changes in the pediatric age range in human tissue, intestinal enteroids derived from pediatric patients could provide a versatile experimental platform to study pediatric phenotypes.

Human enteroid monolayers as a potential alternative for Ussing chamber and Caco-2 monolayers to study passive permeability and drug efflux.

After oral administration, the intestine is the first site of drug absorption, making it a key determinant of the bioavailability of a drug, and hence drug efficacy and safety. Existing non-clinical models of the intestinal barrier in vitro often fail to mimic the barrier and absorption of the human intestine. We explore if human enteroid monolayers are a suitable tool for intestinal absorption studies compared to primary tissue (Ussing chamber) and Caco-2 cells. Bidirectional drug transport was determined in enteroid monolayers, fresh tissue (Ussing chamber methodology) and Caco-2 cells. Apparent permeability (Papp) and efflux ratios for enalaprilat (paracellular), propranolol (transcellular), talinolol (P-glycoprotein (P-gp)) and rosuvastatin (Breast cancer resistance protein (BCRP)) were determined and compared between all three methodologies and across intestinal regions. Bulk RNA sequencing was performed to compare gene expression between enteroid monolayers and primary tissue. All three models showed functional efflux transport by P-gp and BCRP with higher basolateral to apical (B-to-A) transport compared to apical-to-basolateral (A-to-B). B-to-A Papp values were similar for talinolol and rosuvastatin in tissue and enteroids. Paracellular transport of enalaprilat was lower and transcellular transport of propranolol was higher in enteroids compared to tissue. Enteroids appeared show more region- specific gene expression compared to tissue. Fresh tissue and enteroid monolayers both show active efflux by P-gp and BCRP in jejunum and ileum. Hence, the use of enteroid monolayers represents a promising and versatile experimental platform to complement current in vitro models.

Absolute quantitation of propranolol from 200-µm regions of mouse brain and liver thin tissues using laser ablation-dropletProbe-mass spectrometry.

RATIONALE: The ability to quantify drugs and metabolites in tissue with sub-mm resolution is a challenging but much needed capability in pharmaceutical research. To fill this void, a novel surface sampling approach combining laser ablation with the commercial dropletProbe automated liquid surface sampling system (LA-dropletProbe) was developed and is presented here. METHODS: Parylene C-coated 200 × 200 µm tissue regions of mouse brain and kidney thin tissue sections were analyzed for propranolol by laser ablation of tissue directly into a preformed liquid junction. Propranolol was detected by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) in positive electrospray ionization mode. Quantitation was achieved via application of a stable-isotope-labeled internal standard and an external calibration curve. RESULTS: The absolute concentrations of propranolol determined from 200 × 200 µm tissue regions were compared with the propranolol concentrations obtained from 2.3-mm-diameter tissue punches of adjacent, non-coated sections using standard bulk tissue extraction protocols followed by regular HPLC/MS/MS analysis. The average concentration of propranolol in both organs determined by the two employed methods agreed to within ±12%. Furthermore, the relative abundances of phase II hydroxypropranolol glucuronide metabolites were recorded and found to be consistent with previous results. CONCLUSIONS: This work illustrates that depositing a thin layer of parylene C onto thin tissue prior to analysis, which seals the surface and prevents direct liquid extraction of the drug from the tissue, coupled to the novel LA-dropletProbe surface sampling system is a viable approach for sub-mm resolution quantitative drug distribution analysis.

Clinical Pharmacokinetics of Propranolol Hydrochloride: A Review.

BACKGROUND: Nobel laureate Sir James Black's molecule, propranolol, still has broad potential in cardiovascular diseases, infantile haemangiomas and anxiety. A comprehensive and systematic review of the literature for the summarization of pharmacokinetic parameters would be effective to explore the new safe uses of propranolol in different scenarios, without exposing humans and using virtual-human modeling approaches. OBJECTIVE: This review encompasses physicochemical properties, pharmacokinetics and drug-drug interaction data of propranolol collected from various studies. METHODS: Clinical pharmacokinetic studies on propranolol were screened using Medline and Google Scholar databases. Eighty-three clinical trials, in which pharmacokinetic profiles and plasma time concentration were available after oral or IV administration, were included in the review. RESULTS: The study depicts that propranolol is well absorbed after oral administration. It has dose-dependent bioavailability, and a 2-fold increase in dose results in a 2.5-fold increase in the area under the curve, a 1.3-fold increase in the time to reach maximum plasma concentration and finally, 2.2 and 1.8-fold increase in maximum plasma concentration in both immediate and long-acting formulations, respectively. Propranolol is a substrate of CYP2D6, CYP1A2 and CYP2C19, retaining potential pharmacokinetic interactions with co-administered drugs. Age, gender, race and ethnicity do not alter its pharmacokinetics. However, in renal and hepatic impairment, it needs a dose adjustment. CONCLUSION: Physiochemical and pooled pharmacokinetic parameters of propranolol are beneficial to establish physiologically based pharmacokinetic modeling among the diseased population.

Vanillin enhances the passive transport rate and absorption of drugs with moderate oral bioavailability in vitro and in vivo by affecting the membrane structure.

Vanillin is a popular flavoring agent in the food, tobacco, and perfume industries. In this paper, we investigated the effect of vanillin on the transport rates of drugs with different levels of permeability (acyclovir, hydrochlorothiazide, propranolol and carbamazepine) through a Caco-2 cell bidirectional transport experiment. We also explored the underlying mechanism using an in silico technique and fluorescence anisotropy measurements. The influence of vanillin on the pharmacokinetics of drugs whose transport rates were affected by vanillin in vitro was then studied in vivo. Results showed that vanillin (100 µM) increased the cumulative amount of passively transported drugs (2.1-fold of hydrochlorothiazide, 1.49-fold of propranolol, 1.35-fold of acyclovir, and 1.34-fold of carbamazepine) in vitro. Molecular dynamics simulations revealed that vanillin disordered the structure of the lipid bilayer and reduced the energy barrier of drugs across the center of the membrane. The anisotropy of TMA-DPH also decreased in Caco-2 cells after treatment with vanillin (25 and 100 µM) and indicated an increase in membrane fluidity, which was dose-dependent. An oral bioavailability study indicated that vanillin (100 mg kg-1) significantly enhanced the Cmax and AUC0-6 of hydrochlorothiazide by 1.42-fold and 1.28-fold, respectively, and slightly elevated the Cmax of propranolol. In conclusion, vanillin can significantly increase the absorption of drugs with moderate oral bioavailability in vitro and in vivo by loosening the membrane. Thus, the concurrent consumption of drugs with food containing vanillin may result in increased drug plasma concentration and pose potential health risks.

Ionic liquid-based transdermal delivery of propranolol: a patent evaluation of US2018/0169033A1.

Ionic liquids (ILs) are organic salts of asymmetric organic cations and inorganic/organic anions and are considered green alternative to organic solvents. ILs have high thermal stability, low volatility, low toxicity and high biodegradability. ILs are frequently used for enhancing the solubility and stability of active pharmaceutical ingredients. This study describes an invention related to the preparation of amorphous melts of propranolol incorporated into transdermal patches for infantile hemangioma intervention. Reduction in skin irritation and a significant increase in transdermal permeability of propranolol from its amorphous melts was reported. However, toxicity and stability issues of the IL-based active pharmaceutical ingredients and their drug delivery systems are yet to be established from regulatory perspective before exploiting commercial viability of these forms.

Thin polymeric films for the topical delivery of propranolol.

BACKGROUND/AIMS: Infantile hemangioma (IH), the most common benign tumor of childhood, is currently treated with propranolol. The aim of this work was to study in vitro propranolol permeation and skin retention from an original polymeric film, composed of polyvinyl alcohol and an acrylic polymer. METHODS: Propranolol polymeric films were applied in occlusive and non-occlusive conditions, on either full thickness skin or isolated epidermis. Experiments were performed also on stripped skin, to simulate the skin permeability of damaged skin. RESULTS: The results obtained underline the importance of determining skin concentration when dealing with drugs that should act on the skin. Skin permeation data are a poor predictor of skin retention data, in particular in critical conditions, such as heavily damaged skin. CONCLUSION: The film proposed for the treatment of IH (and other vascular diseases) with propranolol seems to be a good alternative to semisolid formulations, in particular if used in non-occlusive conditions, because it guarantees high proportions of drug retained in the skin, compared to permeated across the skin, reducing the risks of systemic side effect.

In Vitro Skin Retention and Drug Permeation through Intact and Microneedle Pretreated Skin after Application of Propranolol Loaded Microemulsions.

PURPOSE: Topical beta-blockers are efficacious for treating infantile hemangiomas, but no formulations have been specifically optimized for skin delivery. Our objective was to quantify skin concentrations and drug permeation of propranolol (a nonselective beta-blocker) after application of microemulsions to intact and microneedle pretreated skin. METHODS: Four propranolol-loaded microemulsions were characterized for droplet size, surface charge, conductivity, pH, drug solubility, and drug release. Skin concentrations and drug permeation through skin were quantified using LC-MS. Skin-to-receiver ratios were used to compare the microemulsion formulations to a drug-in-PBS solution. RESULTS: Propranolol solubility was significantly greater in microemulsions vs PBS. Cumulative drug release from the microemulsions over 24 h ranged from 13 to 26%. Skin concentrations and drug permeation through intact skin was significantly higher from PBS; however, the skin-to-receiver ratios were significantly higher for water-rich microemulsions compared to PBS or surfactant-rich microemulsions. Microneedle pretreatment significantly increased skin concentrations for all formulations. Skin-to-receiver ratios significantly increased after microneedle pretreatment for surfactant-rich microemulsions. CONCLUSIONS: Microemulsion formulation can be altered to elicit different drug delivery profiles through MN-treated skin. This could be advantageous for maximizing local skin drug concentrations and improving dosing schedules for infantile hemangioma treatment.

The Influence of Formulation and Excipients on Propranolol Skin Permeation and Retention.

The objective of this work was to study in vitro propranolol permeation and skin retention after topical application of different semisolid vehicles, with the final aim of developing new topical formulations intended for the treatment of infantile hemangioma, able to produce therapeutic drug levels in the skin, avoiding systemic absorption. Propranolol ointments, creams, and gels were prepared and tested on pig skin, an accepted model of human skin. From the results obtained in the present work it is clear that the permeation of propranolol across the skin is a poor predictor of its skin retention, at least in the time-frame considered. With an application time of 4 h, reasonably close to the permanence time of a semisolid formulation on the skin surface, the best performance (high retention and low skin penetration) was obtained with lipophilic formulations, in particular with a lipophilic cream containing olive oil. Hydrophilic formulations, such as gels, are characterized by a significant permeation across the skin, probably leading to systemic side effects, accompanied by a limited skin retention. Overall, the results obtained in the present work pose the basis for the development of new topical formulations, containing propranolol, with better performance and reduced systemic absorption.

Propranolol pharmacokinetics in infants treated for Infantile Hemangiomas requiring systemic therapy: Modeling and dosing regimen recommendations.

Propranolol has become the first choice therapy for complicated Infantile Hemangiomas (IH). The pharmacokinetics of propranolol were evaluated after repeated oral administration of a new pediatric solution of propranolol at 3 mg kg-1 day-1 given twice daily (BID) in infants (77-243 days) with IH. A population model was built to describe the pharmacokinetics of propranolol in infants and to simulate different dosing regimens. One hundred and sixty-seven plasma concentrations from 22 infants were used in the population analysis. Weight effect was tested on apparent clearance and volume of distribution. Monte-Carlo simulations were performed for 4 dosing regimens: BID dosing with irregular or strict 12-hour intervals and 2 different 3 time daily dosing (TID) regimens. The best model was a one-compartment model with first-order absorption and elimination rates. The weight affected the clearance but not the volume. Typical oral clearance was estimated at 3.06 L hour-1 kg-1 (95% CI: 1.14-8.61 L hour-1 kg-1), close to adult clearance data. When regular BID dosing was compared to TID or irregular BID regimens, simulated median Cmin and Cmax were <20% different. To conclude, a model using a weight allometric function on clearance was established and confirmed that the dose in mg/kg should be used without adaptation by range of age in treatment of complicated IH. The simulations support the use of a BID dosing preferably to a TID dosing thanks to close Cmin and Cmax at steady state between both regimen and showed the possibility of irregular BID dosing, allowing early administration in the evening when needed.

Development and characterization of a nanoemulsion containing propranolol for topical delivery.

BACKGROUND: Propranolol (PPN) is a therapeutic option for the treatment of infantile hemangiomas. This study aimed at the development of nanoemulsion (NE) containing 1% PPN, characterization of the system, and safety studies based on ex vivo permeation, cytotoxicity, and biodistribution in vivo. METHODS: The formulation was developed and characterized in relation to the droplet size, polydispersity index (PDI), pH, zeta potential, and electronic microscopy. Ex vivo permeation studies were used to evaluate the cutaneous retention of PPN in the epidermis and dermis. Cytotoxicity studies were performed in fibroblasts, macrophages, and keratinocytes. In vivo biodistribution assay of the formulations was performed by means of labeling with technetium-99m. RESULTS: NE1 exhibited droplet size of 26 nm, PDI <0.4, pH compatible with the skin, and zeta potential of -20 mV, which possibly contributes to the stability. Electron microscopy showed that the NE presented droplets of nanometric size and spherical shape. NE1 provided excellent stability for PPN. In the ex vivo cutaneous permeation assay, the NE provided satisfactory PPN retention particularly in the dermis, which is the site of drug action. In addition, NE1 promoted cutaneous permeation of the PPN in small amount. In vivo biodistribution showed that the radiolabeled formulation remained in the skin and a small amount reached the bloodstream. NE1 presented low cytotoxicity to fibroblasts, macrophages, and keratinocytes in the concentrations evaluated in the cytotoxicity assay. CONCLUSION: We concluded that the formulation is safe for skin administration; however, cutaneous irritation studies should be performed to confirm the safety of the formulation before clinical studies in patients with infantile hemangiomas.

Population Pharmacokinetics and Pharmacodynamics of Oral Propranolol in Pediatric Patients With Infantile Hemangioma.

This study aimed to characterize the population pharmacokinetics and exposure-response relationship of propranolol (Hemangiol® Syrup for Pediatric) in infants with infantile hemangioma. Using nonlinear mixed-effects modeling with 63 pooled sets of plasma concentration-time data from 32 Japanese patients aged 35-150 days, we described the disposition of propranolol adequately by a 1-compartment model with first-order absorption. The estimated population mean apparent clearance and apparent central volume of distribution were 9.34 L/h and 146 L, respectively. Body weight and postnatal age influenced the population pharmacokinetic model. The clinical end points-success (complete or nearly complete resolution of the target hemangioma) and failure-at weeks 12 and 24 were characterized by logistic regression using the area under the concentration-time curve (AUC), estimated from the final population pharmacokinetic model, as an exposure predictor. The logistic regression showed that a higher AUC was associated with a higher probability of successful treatment. At each exposure level, probability of successful treatment was correlated with gestational age and treatment duration. Model-predicted probabilities of successful treatment were consistent with actual results in the clinical trial. Simulations using several dosing regimens indicated that oral propranolol at 3 mg/kg per day was effective and would be appropriate for treating Japanese infants. These simulation results can support optimization of dosing regimens, such as selecting amounts, treatment durations, and dosing intervals, for clinical use.

Radiation preparation of L-arginine/acrylic acid hydrogel matrix patch for transdermal delivery of propranolol HCl in hypertensive rats.

In the present study, L-arginine/acrylic acid (Arg/AAc) batch hydrogel was successfully prepared by gamma irradiation for transdermal delivery of propranolol HCl in hypertensive rats. The resulted system has been characterized by FTIR to confirm the hydrogel formation. The swelling behavior of the prepared hydrogels was investigated as a function of time and pH. The kinetics of swelling has been investigated. In vivo pharmacokinetics evaluation, skin irritation test, and histopathological studies were investigated. Furthermore, the antihypertensive efficacy of transdermal propranolol-loaded Arg/AAc hydrogel on methyl prednisolone acetate-induced hypertensive rats was evaluated. It was found that the prepared patches exhibited a sustained release of the drug into systemic circulation over oral route which is subjected to hepatic first-pass metabolism, coupled with a short plasma half-life. Transdermal administration displayed a prolonged antihypertensive effect in spontaneously hypertensive rats. Moreover, the skin irritation test and histopathological examination indicated that the prepared patches are not irritant and can be safely applied on the skin. These results indicated that the hydrogel system composed of Arg and AAc has potential as a transdermal delivery system.

Continuous delivery of propranolol from liposomes-in-microspheres significantly inhibits infantile hemangioma growth.

PURPOSE: To reduce the adverse effects and high frequency of administration of propranolol to treat infantile hemangioma, we first utilized propranolol-loaded liposomes-in-microsphere (PLIM) as a novel topical release system to realize sustained release of propranolol. METHODS: PLIM was developed from encapsulating propranolol-loaded liposomes (PLs) in microspheres made of poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) copolymers (PLGA-PEG-PLGA). The release profile of propranolol from PLIM was evaluated, and its biological activity was investigated in vitro using proliferation assays on hemangioma stem cells (HemSCs). Tumor inhibition was studied in nude mice bearing human subcutaneous infantile hemangioma. RESULTS: The microspheres were of desired particle size (~77.8 µm) and drug encapsulation efficiency (~23.9%) and achieved sustained drug release for 40 days. PLIM exerted efficient inhibition of the proliferation of HemSCs and significantly reduced the expression of two angiogenesis factors (vascular endothelial growth factor-A [VEGF-A] and basic fibroblast growth factor [bFGF]) in HemSCs. Notably, the therapeutic effect of PLIM in hemangioma was superior to that of propranolol and PL in vivo, as reflected by significantly reduced hemangioma volume, weight, and microvessel density. The mean hemangioma weight of the PLIM-treated group was significantly lower than that of other groups (saline =0.28 g, propranolol =0.21 g, PL =0.13 g, PLIM =0.03 g; PLIM vs saline: P<0.001, PLIM vs propranolol: P<0.001, PLIM vs PL: P<0.001). The mean microvessel density of the PLIM-treated group was significantly lower than that of other groups (saline =40 vessels/mm2, propranolol =31 vessels/mm2, PL =25 vessels/mm2, PLIM =11 vessels/mm2; PLIM vs saline: P<0.001, PLIM vs propranolol: P<0.01, PLIM vs PL: P<0.05). CONCLUSION: Our findings show that PLIM is a very promising approach to locally and efficiently deliver propranolol to the hemangioma site leading to a significant inhibition of infantile hemangioma.

Selectivity in the Efflux of Glucuronides by Human Transporters: MRP4 Is Highly Active toward 4-Methylumbelliferone and 1-Naphthol Glucuronides, while MRP3 Exhibits Stereoselective Propranolol Glucuronide Transport.

Xenobiotic and endobiotic glucuronides, which are generated in hepatic and intestinal epithelial cells, are excreted via efflux transporters. Multidrug resistance proteins 2-4 (MRP2-MRP4) and the breast cancer resistance protein (BCRP) are efflux transporters that are expressed in these polarized cells, on either the basolateral or apical membranes. Their localization, along with expression levels, affects the glucuronide excretion pathways. We have studied the transport of three planar cyclic glucuronides and glucuronides of the two propranolol enantiomers, by the vesicular transport assay, using vesicles from baculovirus-infected insect cells expressing human MRP2, MRP3, MRP4, or BCRP. The transport of estradiol-17ß-glucuronide by recombinant MRP2-4 and BCRP, as demonstrated by kinetic values, were within the ranges previously reported. Our results revealed high transport rates and apparent affinity of MRP4 toward the glucuronides of 4-methylumbelliferone, 1-naphthol, and 1-hydroxypyrene (Km values of 168, 13, and 3 µM, respectively) in comparison to MRP3 (Km values of 278, 98, and 8 µM, respectively). MRP3 exhibited lower rates, but stereoselective transport of propranolol glucuronides, with higher affinity toward the R-enantiomer than the S-enantiomer (Km values 154 vs 434 µM). The glucuronide of propranolol R-enantiomer was not significantly transported by either MRP2, MRP4, or BCRP. Of the tested small glucuronides in this study, BCRP transported only 1-hydroxypyrene glucuronide, at very high rates and high apparent affinity (Vmax and Km values of 4400 pmol/mg/min and 11 µM). The transport activity of MRP2 with all of the studied small glucuronides was relatively very low, even though it transported the reference compound, estradiol-17ß-glucuronide, at a high rate (Vmax = 3500 pmol/mg/min). Our results provide new information, at the molecular level, of efflux transport of the tested glucuronides, which could explain their disposition in vivo, as well as provide new tools for in vitro studies of MRP3, MRP4, and BCRP.

Propranolol.

Propranolol is a noncardioselective ß-blocker. It is reported to have membrane-stabilizing properties, but it does not own intrinsic sympathomimetic activity. Propranolol hydrochloride is used to control hypertension, pheochromocytoma, myocardial infarction, cardiac arrhythmias, angina pectoris, and hypertrophic cardiomyopathy. It is also used to control symptoms of sympathetic overactivity in the management of hyperthyroidism, anxiety disorders, and tremor. Other indications cover the prophylaxis of migraine and of upper gastrointestinal bleeding in patients with portal hypertension. This study provides a detailed, comprehensive profile of propranolol, including formulas, elemental analysis, and the appearance of the drug. In addition, the synthesis of the drug is described. The chapter covers the physicochemical properties, including X-ray powder diffraction, pK, solubility, melting point, and procedures of analysis (spectroscopic, electrochemical, and chromatographic). In-depth pharmacology is also presented (pharmacological actions, therapeutic dosing, uses, Interactions, and adverse effects and precautions). More than 60 references are given as a proof of the abovementioned studies.

Periocular Tissue Concentrations of Propranolol after Ocular Instillation of a Gel-Forming Solution.

BACKGROUND: The aim of this study was to determine the concentrations of propranolol in periocular tissues and plasma after ocular instillation of 0.5% propranolol gel-forming solution (GFS) as compared to 0.5% propranolol non-gelforming solution (non-GFS) for potential use in the treatment of periocular capillary hemangiomas. METHODS: A GFS prepared in 1% sodium alginate or a non-GFS in phosphatebuffered saline was instilled into the eyes of rabbits. At predetermined time intervals after dosing, blood was withdrawn, rabbits were euthanized, and periocular tissues were dissected. RESULTS: Ocular instillation of the GFS resulted in higher concentrations of propranolol in the outer layers of both the upper and lower eyelids (in the range of 9.9-36.9 µg/g) and maintained higher levels of propranolol in these tissues for 24 h after dosing, as compared to the ocular instillation of the non-GFS (in the range of 3.4-15.1 µg/g). While the concentrations of propranolol in the other periocular tissues were generally similar for GFS and non-GFS at 1 h after dosing, the concentrations of propranolol in the extraocular muscles and periocular fat were higher for GFS than those for non-GFS between 4-24 h after dosing. Lower level of propranolol in plasma was observed at 1 h with GFS as compared with non-GFS. CONCLUSION: The use of the propranolol gel-forming solution can prolong drug retention on the ocular surface and increase its distribution to the outer layers of the eyelids while decreasing systemic exposure to the drug.

[Carrier-mediated Transport of Cationic Drugs across the Blood-Tissue Barrier].

Studies of neurological dysfunction have revealed the neuroprotective effect of several cationic drugs, suggesting their usefulness in the treatment of neurological diseases. In the brain and retina, blood-tissue barriers such as blood-brain barrier (BBB) and blood-retinal barrier (BRB) are formed to restrict nonspecific solute transport between the circulating blood and neural tissues. Therefore study of cationic drug transport at these barriers is essential to achieve systemic delivery of neuroprotective agents into the neural tissues. In the retina, severe diseases such as diabetic retinopathy and macular degeneration can cause neurological dysfunction that dramatically affects patients' QOL. The BRB is formed by retinal capillary endothelial cells (inner BRB) and retinal pigment epithelial cells (outer BRB). Blood-to-retina transport of cationic drugs was investigated at the inner BRB, which is known to nourish two thirds of the retina. Blood-to-retinal transport of verapamil suggested that the barrier function of the BRB differs from that of the BBB. Moreover, carrier-mediated transport of verapamil and pyrilamine revealed the involvement of novel organic cation transporters at the inner BRB. The identified transport systems for cationic drugs are sensitive to several cationic neuroprotective and anti-angiogenic agents such as clonidine and propranolol, and the involvement of novel transporters was also suggested in their blood-to-retina transport across the inner BRB.

Metformin reduces hepatic resistance and portal pressure in cirrhotic rats.

Increased hepatic vascular resistance is the primary factor in the development of portal hypertension. Metformin ameliorates vascular cells function in several vascular beds. Our study was aimed at evaluating the effects, and the underlying mechanisms, of metformin on hepatic and systemic hemodynamics in cirrhotic rats and its possible interaction with the effects of propranolol (Prop), the current standard treatment for portal hypertension. CCl4-cirrhotic rats received by gavage metformin 300 mg/kg or its vehicle once a day for 1 wk, before mean arterial pressure (MAP), portal pressure (PP), portal blood flow (PBF), hepatic vascular resistance, and putative molecular/cellular mechanisms were measured. In a subgroup of cirrhotic rats, the hemodynamic response to acute Prop (5 mg/kg iv) was assessed. Effects of metformin ± Prop on PP and MAP were validated in common bile duct ligated-cirrhotic rats. Metformin-treated CCl4-cirrhotic rats had lower PP and hepatic vascular resistance than vehicle-treated rats, without significant changes in MAP or PBF. Metformin caused a significant reduction in liver fibrosis (Sirius red), hepatic stellate cell activation (α-smooth muscle actin, platelet-derived growth factor receptor ß polypeptide, transforming growth factor-ßR1, and Rho kinase), hepatic inflammation (CD68 and CD163), superoxide (dihydroethidium staining), and nitric oxide scavenging (protein nitrotyrosination). Prop, by decreasing PBF, further reduced PP. Similar findings were observed in common bile duct ligated-cirrhotic rats. Metformin administration reduces PP by decreasing the structural and functional components of the elevated hepatic resistance of cirrhosis. This effect is additive to that of Prop. The potential impact of this pharmacological combination, otherwise commonly used in patients with cirrhosis and diabetes, needs clinical evaluation.

Effects of dosing protocol on distribution of propranolol in periocular tissues after topical ocular instillation.

PURPOSE: Our previous study demonstrated that topical ocular instillation can deliver effective concentrations of propranolol in the periocular tissues, and may be superior to oral propranolol in the treatment of periocular capillary hemangiomas. The objective of this study was to investigate the effects of dosing protocol on the distribution of propranolol in the periocular tissues and plasma after topical ocular instillation. METHODS: Each rabbit received propranolol 0.5% ophthalmic solution using one of the following dosing protocols: three drops of 50 µL, one drop of 50 µL, or one drop of 25 µL. The periocular tissues (e.g. eyelids and extraocular muscles) and blood were collected and assayed for propranolol at 1 h after dosing. RESULTS: Decreasing the concentration of eye drops (1% to 0.5%), decreasing the number of eye drops during dosing (three drops to one drop), or decreasing the instilled volume (50 µL to 25 µL) generally lowered the concentration of propranolol in the periocular tissues. Nevertheless, therapeutic levels of propranolol (> 0.4 µg/g) were delivered to the periocular tissues at 1 h after dosing using any of the three protocols examined. Dose-dependent concentrations in some periocular tissues and plasma were observed over the dose range of 0.125 mg to 1.5 mg. The plasma concentration of propranolol was not measurable when a single 25 µL of propranolol 0.5% was instilled in the eye. CONCLUSIONS: The dosing protocol of topical ocular instillation can be tailored to achieve the desired therapeutic concentrations of propranolol in the periocular tissues while minimizing systemic exposure.