The Impact of Dipyridamole on Disease-Associated Microglia Phenotypic Transformation in White Matter Lesions Induced by Chronic Cerebral Hypoperfusion.

White matter lesions (WMLs) resulting from chronic cerebral hypoperfusion (CCH) are the leading cause of vascular dementia (VaD). This study aimed to investigate whether dipyridamole could alleviate WMLs by regulating the phenotype of disease-associated microglia (DAM) through equilibrative nucleoside transporter 2 (ENT2) and adenosine A2A receptor (Adora2a) and to clarify the underlying molecular mechanisms. CCH rat models were constructed to mimic VaD. Morris water maze and Luxol Fast Blue staining were employed to assess cognitive function and quantify the severity of WMLs, respectively. Immunofluorescent staining was performed to analyze the activation of glial cells and the phenotypic transformation of DAM. Additionally, levels of ENT2, proteins in the NF-κB and ERK1/2 pathways and inflammatory cytokines were detected. The results indicated that dipyridamole diminished the activation and proliferation of microglia and astrocytes, increased the expression of myelin basic protein and ameliorated WMLs and cognitive decline in CCH rats. Further study revealed that dipyridamole decreased the expression of ENT2 and inhibited the activation of ERK1/2 and NF-κB signaling pathways, which ultimately converted DAM to anti-inflammatory phenotype and suppressed the levels of TNF-α, IL-1ß, IL-6 in WMLs. However, Adora2a inhibitor (SCH58261) attenuated above effects. Our study demonstrates that dipyridamole facilitates the conversion of DAM to the anti-inflammatory phenotype through ENT2/Adora2a pathway and inhibits the activation of ERK1/2 and NF-κB signaling pathways, thereby alleviating neuroinflammation in WMLs. The current findings establish the basis for using dipyridamole to treat VaD.

Effect of Dipyridamole on Membrane Energization and Energy Transfer in Chromatophores of Rba. sphaeroides.

Effect of dipyridamole (DIP) at concentrations up to 1 mM on fluorescent characteristics of light-harvesting complexes LH2 and LH1, as well as on conditions of photosynthetic electron transport chain in the bacterial chromatophores of Rba. sphaeroides was investigated. DIP was found to affect efficiency of energy transfer from the light-harvesting complex LH2 to the LH1-reaction center core complex and to produce the long-wavelength ("red") shift of the absorption band of light-harvesting bacteriochlorophyll molecules in the IR spectral region at 840-900 nm. This shift is associated with the membrane transition to the energized state. It was shown that DIP is able to reduce the photooxidized bacteriochlorophyll of the reaction center, which accelerated electron flow along the electron transport chain, thereby stimulating generation of the transmembrane potential on the chromatophore membrane. The results are important for clarifying possible mechanisms of DIP influence on the activity of membrane-bound functional proteins. In particular, they might be significant for interpreting numerous therapeutic effects of DIP.

Influence of nitric oxide and phosphodiesterases during in vitro maturation of bovine oocytes on meiotic resumption and embryo production.

This study aimed to examine the effects of nitric oxide (NO) and different phosphodiesterase (PDE) families on meiosis resumption, nucleotides levels and embryo production. Experiment I, COCs were matured in vitro with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) associated or not with the soluble guanylate cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), meiotic resumption and nucleotides levels were assessed. SNAP delayed germinal vesicle breakdown (GVBD) (53.4 ± 1.2 versus 78.4 ± 2.4% for controls, P 0.05). Cyclic GMP levels were higher in SNAP (3.94 ± 0.18, P 0.05). Embryo development did not differ from the control for SNAP and cilostamide groups (38.7 ± 5.8, 37.9 ± 6.2 and 40.5 ± 5.8%, P > 0.05), but SNAP + cilostamide decreased embryo production (25.7 ± 6.9%, P < 0.05). In conclusion, SNAP was confirmed to delay meiosis resumption by the NO/sGC/cGMP pathway, by increasing cGMP, but not cAMP. Inhibiting different PDEs to further increase nucleotides in association with SNAP did not show any additive effects on meiosis resumption, indicating that other pathways are involved. Moreover, SNAP + cilostamide affected the meiosis progression and decreased embryo development.

Generation of radical form of dipyridamole at illumination of photosynthetic reaction centers of Rb. sphaeroides.

The study of the effect of vasodilator, antiplatelet agent, and inhibitor P-glycoprotein dipyridamole (DIP) on the functioning of the transmembrane protein of the reaction center (RC) of Rb. sphaeroides showed that the activation of RC by constant light generates the DIP radical cation, which significantly affects the kinetics of recombination of charges divided between photoactive bacteriochlorophyll and quinone acceptors. Thus, the antioxidant properties of DIP may affect the functional activity of membrane proteins, and this apparently should be taken into account in the studies of the mechanisms of therapeutic action of this drug.

Instrumentation of Flow-Through USP IV Dissolution Apparatus to Assess Poorly Soluble Basic Drug Products: a Technical Note.

Supersaturation and precipitation are common limitations encountered especially with poorly soluble basic drugs. The aims of this work were to explore the pattern of dissolution and precipitation of poorly soluble basic drugs using a United States Pharmacopoeia (USP) IV dissolution apparatus and to compare it to the widely used USP II dissolution apparatus. In order to investigate the influence of gastric emptying time on bioavailability, tables of two model drugs (dipyridamole 100 mg and cinnarizine 15 mg) were investigated and pH change from 1.2 to 6.8 were achieved after 10, 20 or 30 min using USP II or USP IV dissolution apparatuses. Using USP II, dipyridamole and cinnarizine concentrations dropped instantly as a result of drug precipitation with drug crystals evident in the dissolution vessel. At pH change times of 10, 20 and 30 min, the total amount of dissolved drug was dependent on pH change time. Using USP IV, at a flow rate of 8 ml/min, it was possible to have comparable release to agitation at 50 rpm using USP II suggesting that comparable hydrodynamic forces are possible. No drop in drug percentage occurs as the dissolved fraction was readily emptied from the flow cell, preventing drug accumulation in the dissolution medium. However, a negligible percentage of drug release took place following pH change. In conclusion, the use of the flow-through cell dissolution provided laminar flow, use of realistic fluid volumes and avoided precipitation of dissolved drug fraction in the gastric phase as it is discharged before pH change.

Construction and study of blood purification membrane modified with PDE inhibitor: Investigation of antiplatelet activity and hemocompatibility.

The recent "cell-based theory" of coagulation suggests that platelets serve as the site of coagulation factor reactions, making platelets an effective target for inhibiting membrane thrombosis. Unfortunately, there is limited research on how blood purification membranes affect platelet intracellular signaling. In this study, we modified polyethersulfone (PES) membranes with the platelet phosphodiesterase (PDE) inhibitor dipyridamole (DIP) and investigated the effects of the DIP/PES (DP) membranes on platelet adhesion, activation, aggregation, and secretion, as well as the role of the PDE-cyclic adenosine monophosphate (cAMP) intracellular signaling pathway. Additionally, we evaluated the hemocompatibility and preliminary in vivo safety of DP membranes. Our results demonstrate that the modified DP membranes effectively inhibited platelet adhesion, membrane CD62P expression, and plasma soluble P-selectin activation levels. Furthermore, we confirmed that DP membranes achieved platelet aggregation inhibition and reduced platelet factor 4 and ß-thromoglobulin secretion levels by inhibiting platelet intracellular PDE-cAMP signaling. Moreover, the modified DP membranes exhibited good anticoagulant and red blood cell membrane stability and complement resistance and demonstrated preliminary biocompatibility in mouse experiments. Collectively, these findings highlight the potential application of DP dialysis membranes in blood purification for critically ill patients.

Metabolism and accumulation of the lipophilic deoxynucleoside analogs elacytarabine and CP-4126.

Cytarabine (ara-C) and gemcitabine (dFdC) are commonly used anticancer drugs, which depend on the equilibrative (ENT) and concentrative-nucleoside-transporters to enter the cell. To bypass transport-related drug resistance, lipophilic derivatives elacytarabine (CP-4055), ara-C-5'elaidic-acid-ester, and CP-4126, (CO 1.01) gemcitabine-5'elaidic-acid-ester, were investigated for the entry into the cell, distribution, metabolism and retention. The leukemic CEM-cell-line and its deoxycytidine-kinase deficient variant (CEM/dCK-) were exposed for 30 and 60 min to the radiolabeled drugs; followed by culture in drug-free medium in order to determine drug retention in the cell. The cellular fractions were analyzed with thin-layer-chromatography and HPLC. Elacytarabine and CP-4126 were converted to the parent compounds both inside and outside the cell (35-45%). The ENT-inhibitor dipyridamole did not affect their uptake or retention. Inside the cell Elacytarabine and CP-4126 predominantly localized in the membrane and cytosolic fraction, leading to a long retention after removal of the medium. In contrast, in cells exposed to the parent drugs ara-C and dFdC, intracellular drug concentration increased during exposure but decreased to undetectable levels after drug removal. In the dCK- cell line, no metabolism was observed. The concentrations of ara-CTP and dFdCTP reached a peak at the end of the incubation with the drugs, and decreased after drug removal; peak levels of dFdCTP were 35 times higher than ara-CTP and was retained better. In contrast, after exposure to elacytarabine or CP-4126, ara-CTP and dFdCTP levels continued to increase not only during exposure but also during 120 min after removal of the elacytarabine and CP-4126. Levels of ara-CTP and dFdCTP were higher than after exposure to the parent drugs. In conclusion, the lipophilic derivatives elacytarabine and CP-4126 showed a nucleoside-transporter independent uptake, with long retention of the active nucleotides. These lipophilic nucleoside analogues are new chemical entities suitable for novel clinical applications.

An in vitro methodology for forecasting luminal concentrations and precipitation of highly permeable lipophilic weak bases in the fasted upper small intestine.

PURPOSE: To develop an in vitro methodology for prediction of concentrations and potential precipitation of highly permeable, lipophilic weak bases in fasted upper small intestine based on ketoconazole and dipyridamole luminal data. Evaluate usefulness of methodology in predicting luminal precipitation of AZD0865 and SB705498 based on plasma data. METHODS: A three-compartment in vitro setup was used. Depending on the dosage form administered in in vivo studies, a solution or a suspension was placed in the gastric compartment. A medium simulating the luminal environment (FaSSIF-V2plus) was initially placed in the duodenal compartment. Concentrated FaSSIF-V2plus was placed in the reservoir compartment. RESULTS: In vitro ketoconazole and dipyridamole concentrations and precipitated fractions adequately reflected luminal data. Unlike luminal precipitates, in vitro ketoconazole precipitates were crystalline. In vitro AZD0865 data confirmed previously published human pharmacokinetic data suggesting that absorption rates are not affected by luminal precipitation. In vitro SB705498 data predicted that significant luminal precipitation occurs after a 100 mg or 400 mg but not after a 10 mg dose, consistent with human pharmacokinetic data. CONCLUSIONS: An in vitro methodology for predicting concentrations and potential precipitation in fasted upper small intestine, after administration of highly permeable, lipophilic weak bases in fasted upper small intestine was developed and evaluated for its predictability in regard to luminal precipitation.

Assessment of on-treatment platelet reactivity at high and low shear stress and platelet activation status after the addition of dipyridamole to aspirin in the early and late phases after TIA and ischaemic stroke.

BACKGROUND: Data are limited on the ability of dipyridamole to additionally inhibit platelet function/reactivity in ischaemic cerebrovascular disease (CVD) patients on aspirin. AIMS: To assess inhibition of platelet function/reactivity and platelet activation with dipyridamole in CVD. METHODS: This prospective, observational study assessed TIA/ischaemic stroke patients before (baseline; N = 60), at 14 ±7 days (14d, N = 39) and ≥ 90 days (90d, N = 31) after adding dipyridamole to aspirin. Platelet function/reactivity at high shear stress (PFA-100® C-ADP) and low shear stress (VerifyNow® P2Y12 and Multiplate® ADP assays), and platelet activation status (% expression of CD62P, CD63 and leucocyte-platelet complexes on whole blood flow cytometry) were quantified. 'Dipyridamole-high on-treatment platelet reactivity (HTPR)' was defined as failure to inhibit ADP-induced platelet aggregation +/- adhesion compared with the patient's baseline on aspirin monotherapy by more than twice the coefficient-of-variation of the assay after adding dipyridamole to aspirin. RESULTS: Dipyridamole-HTPR was identified in 71.4-75% of patients on PFA-100 C-ADP, 83.9-86.8% of patients on VerifyNow P2Y12, and 81.5-83.3% of patients on Multiplate ADP assays. There were no changes in CD62P/CD63 expression (P ≥ 0.18), or consistent changes in leucocyte-platelet complexes in CVD patients overall at 14d or 90d vs. baseline after commencing dipyridamole. Monocyte-platelet complexes increased in the patient subgroup with dipyridamole-HTPR at 14d and 90d on PFA-100, and at 14d on VerifyNow (P ≤ 0.04), but not in those without dipyridamole-HTPR. DISCUSSION: Additional antiplatelet effects of dipyridamole are detectable under high and low shear stress conditions with user-friendly platelet function/reactivity tests ex vivo. Increasing circulating monocyte-platelet complexes over time are associated with dipyridamole-HTPR.

Dipyridamole ameliorates doxorubicin-induced cardiotoxicity.

Dipyridamole is a platelet inhibitor with antithrombotic properties that can help prevent stroke recurrence. Twenty-eight male rats were divided randomly into four groups (7 rats in each group). Control group: rats received a natural diet and water. Normal saline group: rats received 0.9% normal saline for two weeks. Doxorubicin group (induced group): rats received 2.5 mg/kg three times a week for two weeks. Dipyridamole group (dipyridamole treated group): received dipyridamole (6 mg/kg/daily) orally for two weeks. Doxorubicin caused cardiotoxicity as indicated by a significant increase in tumor necrosis factor-α, interleukin-6, malondialdehyde, and caspase-3 level (P<0.05), while total antioxidant capacity and Bcl-2 levels were significantly reduced in cardiac tissues of rats in the doxorubicin group compared to the normal saline control group (P<0.05). Dipyridamole significantly ameliorates doxorubicin-induced cardiotoxicity, as suggested by a significant decrease in inflammatory markers (tumor necrosis factor-α and interleukin-6) (P<0.05). Moreover, the cardiac tissue level of oxidative marker malondialdehyde was significantly decreased (P<0.05), and total antioxidant capacity significantly increased in the dipyridamole group in comparison to the doxorubicin-only group (P<0.05). Dipyridamole exerted a significant heart-protective effect against doxorubicin-induced cardiotoxicity in rats, probably via interfering with oxidative stress, inflammatory response, and apoptotic pathway. The goal of this study was to investigate the potential protective effect of dipyridamole against doxorubicin-induced cardiotoxicity via interfering with pro-inflammatory, oxidative, and apoptotic pathways.

Evaluation of selective competitive binding of basic drugs to alpha1-acid glycoprotein variants.

We examined the binding of various basic drugs to the F(1)S and A genetic variants of alpha(1)-acid glycoprotein (AGP), which were isolated from native human commercial AGP (total AGP) by chromatography on an immobilized copper(II) affinity adsorbent. The values of the dissociation constant (K(d)) of some basic drugs with the F(1)S variant in equilibrium dialysis differed characteristically from those with the A variant. The selective binding to these variants was evaluated by measuring the displacement ratio of dicumarol bound to the F(1)S variant or that of acridine orange bound to the A variant, using circular dichroism spectroscopy. There was reasonably good agreement between the K(d) values and displacement ratios. There was a characteristic difference between the values of inhibition constant (K(i)) of basic drugs towards dipyridamole binding to F(1)S and towards disopyramide binding to A in total AGP. We found that the K(i) values for dipyridamole binding were well correlated with the K(d) values for the F(1)S variant, whereas those for disopyramide binding were well correlated with the K(d) values for the A variant. In conclusion, the higher the affinity of basic drugs for AGP, the more they inhibit the binding of other basic drugs, and further, the inhibitory potency depends on the selectivity of binding to the AGP variants.

Ginkgo leaf extract and dipyridamole injection for chronic cor pulmonale: a PRISMA-compliant meta-analysis of randomized controlled trials.

Ginkgo leaf extract and dipyridamole injection (GLED), a kind of Chinese herbal medicine preparation, has been considered as a promising supplementary treatment for chronic cor pulmonale (CCP). Although an analysis of the published literature has been performed, the exact effects and safety of GLED have yet to be systematically investigated. Therefore, a wide-ranging systematic search of electronic databases from which to draw conclusions was conducted. All randomized controlled trials concerning the GLED plus conventional treatments for CCP were selected in the present study. Main outcomes were treatment efficacy, blood gas and hemorrheology indexes, and adverse events. Data from 28 trials with 2457 CCP patients were analyzed. The results indicated that, compared with conventional treatments alone, the combination of conventional treatments with GLED obviously improved the markedly effective rate (RR = 1.44, 95% CI = 1.31-1.58, P < 0.00001) and total effective rate (RR = 1.28, 95% CI = 1.18-1.38, P < 0.00001). Moreover, the hemorrheology (PaO2, P < 0.00001; PaCO2, P < 0.00001; SaO2, P < 0.00001; pH value, P = 0.05) and blood gas indexes (PV, WBHSV, WBMSV, WBLSV, hematocrit and FBG, P < 0.01) of CCP patients were also significantly ameliorated after the combined therapy. The frequency of adverse events did not differ significantly between the two groups (P > 0.05). In summary, evidence from the meta-analysis suggested that the combination of conventional treatments and GLED appeared to be effective and relatively safe for CCP. Therefore, GLED mediated therapy could be recommended as an adjuvant treatment for CCP.

Involvement of nucleoside transporters in the transcorneal permeation of topically instilled substrates in rabbits in-vivo.

The objective of the current study was to characterize and evaluate the functional importance of the Nucleoside Transporters (NTs) in the cornea of the rabbits. Reverse transcriptase polymerase chain reaction (RT-PCR) was used for the molecular characterization of the NTs. Their functionality was evaluated using two substrates, ribavirin and cytarabine. Dipyridamole was used as a blocker for the study. All the treatments were given topically. Molecular characterization of NTs revealed presence of ent1, ent2, ent3 and cnt3 in the cornea. The concentration vs time profile for cytarabine in Aqueous Humor (AH) exhibited a statistically significant (p<0.05) drop at 1h with blocker pretreatment. The mean AUC0-2 between the treatments was also differing in a significant (p<0.05) manner. The concentration vs time profile for ribavirin in AH also showed a significant (p<0.05) decrease in its concentration at 1h with blocker pretreatment. Dipyridamole was able to block ribavirin's entry with as low as 40nM concentration while complete blockade was achieved at 8mM and above. When cytarabine and ribavirin were co-administered, ribavirin at a concentration of 6.5mM significantly inhibited (p<0.05) the transcorneal permeation of cytarabine up to 80%. To conclude, this study showed the presence and functional importance of NTs in the transcorneal uptake of nucleoside substrates. This study further revealed the presence of concentration dependent competitive inhibition among substrates for their transcorneal permeation.

Enzymatic oxidation of dipyridamole in homogeneous and micellar solutions in the horseradish peroxidase-hydrogen peroxide system.

Enzymatic oxidation of dipyridamole (DIP) by horseradish peroxidase-hydrogen peroxide system (HRP-H2O2) in aqueous and micellar solutions was carried out. The reaction was monitored by optical absorption and fluorescence techniques. In aqueous solution at pH 7.0 and pH 9.0, the disappearance of the characteristic bands of DIP centered at 400 nm and 280 nm was observed. A new strong band at 260 nm is observed for the oxidation product(s) with shoulders at 322 nm and 390 nm. A non-fluorescent product is formed upon oxidation. In cationic cethyl trimethyl-1-ammonium chloride (CTAC) and zwitterionic 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS) micellar solutions the same results are observed: three, well-defined, isosbestic points in the optical spectra suggest the transformation between two species. In anionic micellar sodium dodecylsulfate solution (SDS), the appearance of a new band centered around 506 nm was observed, associated to a solution color change from the usual yellow to deep blue/violet, characteristic of a radical species associated to the one-electron oxidation of DIP to its cation radical (DIP*+), observed previously in electrochemical oxidation. Experiments of radical decay kinetics monitoring the absorbance change at 506 nm were performed and analyzed in the frame of a kinetic model taking into account the species both in homogeneous and micellar media. The reaction medium is composed of bulk solution, SDS micelle/solution interface and enzyme catalytic site(s). The variation of DIP*+ concentration was analyzed assuming: (1) synthesis of DIP*+ by HRP through one-electron oxidation; (2) decomposition of DIP*+ by further one-electron oxidation; (3) direct two-electron oxidation of DIP by HRP; (4) bimolecular DIP*+ disproportionation. The main results of the analysis are as follows: (1) kinetic data can be divided in two phases, an HRP active phase and another phase which proceeds in the absence of enzyme activity due to consumption of all H2O2; (2) the reactions of DIP*+ formation, DIP*+ decomposition and DIP two-electron oxidation are HRP concentration dependent; (3) since DIP*+ formation constant seems to be overestimated, it is proposed that two-electron oxidation is another source of DIP*+, through the comproportionation reaction. Evidences for this reaction were also observed previously in electrochemical experiments; and (4) the kinetic analysis provides evidences that the bimolecular reaction of DIP*+ takes place mainly in the absence of active HRP and in this phase the combination of, at least, two second-order kinetic processes is needed to model the experimental data. Our data suggest that HRP oxidizes DIP in general by a two-electron process or that the cation radical is very unstable so that the one-electron process is only detected in the presence of anionic surfactant, which stabilizes significantly the DIP*+ intermediate.

Effect of chronic sustained-release dipyridamole on myocardial blood flow and left ventricular function in patients with ischemic cardiomyopathy.

Dipyridamole increases adenosine levels and augments coronary collateralization in patients with coronary ischemia. This pilot study tested whether a 6-month course of sustained-release dipyridamole/aspirin improves coronary flow reserve and left ventricular systolic function in patients with ischemic cardiomyopathy. Six outpatients with coronary artery disease and left ventricular ejection fraction (LVEF) <40% were treated with sustained-release dipyridamole 200 mg/aspirin 25 mg twice daily for 6 months. Myocardial function and perfusion, including coronary sinus flow at rest and during intravenous dipyridamole-induced hyperemia, were measured using velocity-encoded cine magnetic resonance stress perfusion studies at baseline, 3 months, and 6 months. There was no change in heart failure or angina class at 6 months. LVEF increased by 39%+/-64% (31.0%+/-13.3% at baseline vs 38.3%+/-10.7% at 6 months; P=.01), hyperemic coronary sinus flow increased more than 2-fold (219.6+/-121.3 mL/min vs 509.4+/-349.3 mL/min; P=.01), and stress-induced relative myocardial perfusion increased by 35%+/-13% (9.4%+/-3.4% vs 13.9%+/-8.5%; P=.004). Sustained-release dipyridamole improved hyperemic myocardial blood flow and left ventricular systolic function in patients with ischemic cardiomyopathy.

Cellular pharmacokinetics and pharmacodynamics of dipyridamole in vascular smooth muscle cells.

Hemodialysis arteriovenous grafts are often plagued by stenosis at the vein-graft anastomosis, which is due to the proliferation of venous smooth muscle cells (SMCs). Perivascular delivery of dipyridamole, a potent antiproliferative agent, has been proposed for the prevention of graft stenosis. In order to develop an optimal delivery system for dipyridamole, we examined its pharmacokinetics and pharmacodynamics in human and porcine venous and arterial SMCs in vitro. SMCs were incubated with dipyridamole for various durations, and visualized for the uptake and release by fluorescence microscopy, which were further quantified by fluorospectrometry. The antiproliferative effect of dipyridamole was examined by cell counting or the methylthiazoletetrazolium (MTT) dye-reduction assay. Cytotoxicity was examined by the lactate dehydrogenase (LDH)-release assay. The kinetics of dipyridamole transport through the cell membrane was compatible with a passive diffusion mechanism. Dipyridamole inhibited SMC proliferation in a dose-dependent manner and was more effective in venous than arterial cells in both species. The inhibition was completely reversible at 15microg/ml upon drug removal from the medium. At 25microg/ml, however, the effect was partially irreversible, which might be attributed to the cytotoxicity of dipyridamole. These data support the need for sustained delivery of dipyridamole to achieve the long-term inhibition of SMC proliferation in the prevention of stenosis since SMCs are continuously stimulated at the anastomosis of hemodialysis arteriovenous grafts.

Development of a sustained-release system for perivascular delivery of dipyridamole.

Vascular access grafts implanted in dialysis patients are prone to failure in the long-term because of stenosis and occlusion caused by neointimal hyperplasia. Local delivery of antiproliferative drugs may be effective to prevent this consequence while minimizing the systemic side effects they cause. We developed a combination of poly(lactide-co-glycolide) (PLGA) microspheres with ReGel, an injectable copolymer, as a sustained-release system for perivascular delivery of an antiproliferative drug, dipyridamole. Dipyridamole-incorporated PLGA microspheres with various molecular weights (MWs) of PLGA were prepared by oil-in-water emulsion method. Encapsulation efficiency and surface morphology of microspheres were characterized. In vitro release kinetics of dipyridamole from ReGel or from microspheres/ReGel was experimentally determined. Without microspheres, 40% of the dipyridamole was released from ReGel as an initial burst in the first 3 days followed by continuous release in the subsequent 2 weeks. The use of PLGA microspheres decreased the initial burst and extended dipyridamole release from 23 to 35 days with increasing MW of PLGA. The highest MW PLGA showed a lag time of 17 days before consistent drug release occurred. Mixing microspheres and ReGel with two different MW PLGA achieved a continuous release for 35 days with little initial burst. In vivo release of dipyridamole from microspheres/ReGel exhibited a comparable release pattern to that seen in vitro. This injectable platform is a promising technique for sustained perivascular delivery of antiproliferative drugs.

[New poly-(3-hydroxybutyrate)-based systems for controlled release of dipyridamole and indomethacin].

New poly-(3-hydroxybutyrate)-based systems for controlled release of anti-inflammatory and antithrombogenic drugs have been studied. The release occurs via two mechanisms (diffusion and degradation) operating simultaneously. Dipyridamole and indomethacin diffusion processes determine the rate of the release at the early stages of the contact of the system with the environment (the first 6-8 days). The coefficient of the release diffusion of a drug depends on its nature, the thickness of the poly-(3-hydroxybutyrate) films containing the drug, the concentrations of dipyridamole and indomethacin, and the molecular weight of the poly-(3-hydroxybutyrate). The results obtained are critical for developing systems of release of diverse drugs, thus, enabling the attainment of the requisite physiological effects on tissues and organs of humans.

Prediction of the precipitation profiles of weak base drugs in the small intestine using a simplified transfer ("dumping") model coupled with in silico modeling and simulation approach.

BACKGROUND: Precipitation of poorly soluble, weakly basic drugs upon entering the small intestine may lead to poor bioavailability. It would be useful to be able to predict the extent of in vivo precipitation so that formulation measures to counteract this problem can be taken. AIM: The aim of this research was to characterize the precipitation kinetics of two representative weak base drugs, dipyridamole and ketoconazole in vitro using a simplified transfer model approach, and to establish a predictive model for the total and dissolved concentrations in the small intestine after oral administration using in silico modeling and simulation. METHODS: A simplified transfer ("dumping") method based on the USP paddle apparatus was used to obtain the precipitation profiles of the two weak base drugs by adding a solution of the drug in 0.02N hydrochloric acid to FaSSIF-V2. The observed precipitation curves obtained with various initial concentrations were fitted to first order kinetics. An in silico pharmacokinetic model for weak base drugs with precipitation in the small intestine was designed using STELLA® software and coupled with the precipitation profiles in order to simulate the total and dissolved drug concentrations in the small intestinal lumen in the fasted state in humans. RESULTS: The predicted total and dissolved concentration curves in small intestine for the two weak base drugs were similar to the concentration profiles observed in vivo. The fraction precipitated of the drugs in the small intestine was also well predicted, although the precipitation of ketoconazole at higher initial concentrations was somewhat overestimated. A sensitivity analysis conducted on the simulation of the precipitation of the drugs indicated that a higher fraction precipitated when gastric emptying was faster and/or the concentration of the drug in the added solution was higher. CONCLUSION: The dumping method provides a useful screen for precipitation in the small intestine, especially in the context of early development.

An in vitro biorelevant gastrointestinal transfer (BioGIT) system for forecasting concentrations in the fasted upper small intestine: Design, implementation, and evaluation.

PURPOSE: Design an in vitro methodology for studying gastrointestinal transfer in the fasted state and implement the methodology in vitro by using a biorelevant gastrointestinal transfer system(BioGIT); evaluate the usefulness of BioGIT in predicting luminal concentrations of lipophilic weak bases in the fasted upper small intestine. METHODS: The methodology was designed after modeling existing luminal data. Its implementation in vitro was based on a three compartment setup. Reproducibility of the transfer process was evaluated under conditions where solutions and/or suspensions were present in gastric and/or duodenal compartment and by using ranitidine, dipyridamole, ketoconazole, and posaconazole as model drugs. The transfer process as well as concentrations of dipyridamole, ketoconazole and posaconazole measured in the duodenal compartment were compared with data previously collected in the upper small intestine, after administration of identical preparations/dosage forms to fasted adults. RESULTS: Using BioGIT, the transfer process was performed reproducibly in all cases (RSD b 12.9%); data with dipyridamole and ketoconazole were in line with luminal data in humans. Dipyridamole, ketoconazole and posaconazole concentrations in duodenal compartment were also in line with previously measured concentrations in the fasted upper small intestine of healthy adults. CONCLUSIONS: BioGIT system could be useful for the evaluation of the impact of gastrointestinal transfer on concentrations in the upper intestinal lumen during the first hour, after oral administration of dispersing/solution dosage forms of lipophilic weak bases.