Development and in vivo bioavailability study of an oral fondaparinux delivery system

Novel Antithrombotic Agents in Pregnancy Anticoagulants and Antiplatelet Agents

Increasing rates of thromboembolic complications have required increasing use of anticoagulant and antiplatelet agents during and after pregnancy. Furthermore, thromboembolism is both a cause and a complication of severe maternal morbidity requiring intensive care. As a consequence, almost all patients admitted to intensive care units receive an anticoagulant or an antiplatelet agent (or both) for either treatment or prevention of thromboembolism. In this review, we summarize commonly used anticoagulants and antiplatelet agents and outline the potential role of newly developed (novel) antithrombotic agents for pregnant and postpartum patients.

Design, synthesis, crystal structure, in vitro cytotoxicity evaluation, density functional theory calculations and docking studies of 2-(benzamido) benzohydrazide derivatives as potent AChE and BChE inhibitors

A series of hydrazone derivatives of 2-(benzamido) benzohydrazide was designed, synthesized, and characterized utilizing FTIR, NMR and UV spectroscopic techniques along with mass spectrometry. Compound 10 was also characterized through X-ray crystallography. These synthesized compounds were assessed for their potential as anti-Alzheimer's agents by checking their AChE and BChE inhibition properties by in vitro analysis. The synthesized derivatives were also evaluated for their antioxidant potential along with cytotoxicity studies. The results clearly indicated that dual inhibition of both the enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) was achieved by most of the compounds (03–13), showing varying IC₅₀values. Remarkably, compound 06 (IC₅₀ = 0.09 ± 0.05 for AChE and 0.14 ± 0.05 for BChE) and compound 13 (IC₅₀ = 0.11 ± 0.03 for AChE and 0.10 ± 0.06 for BChE) from the series showed IC₅₀ values comparable to the standard donepezil (IC₅₀ = 0.10 ± 0.02 for AChE and 0.14 ± 0.03 for BChE). Moreover, the derivative 11 also exhibited selective inhibition against BChE with IC₅₀ = 0.12 ± 0.09. Meanwhile, compounds 04 and 10 exhibited good anti-oxidant activities, showing % scavenging of 95.06% and 82.55%, respectively. Cytotoxicity studies showed that the synthesized compounds showed cell viability greater than 80%; thus, these compounds can be safely used as drugs. DFT and molecular docking studies also supported the experimental findings.

2-(Benzamido) benzohydrazide derivatives: synthesis from methyl anthranilate and application as potent anti-Alzheimer's agents.

Advanced delivery strategies facilitating oral absorption of heparins

Heparins show great anticoagulant effect with few side effects, and are administered by subcutaneous or intravenous route in clinics. To improve patient compliance, oral administration is an alternative route. Nonetheless, oral administration of heparins still faces enormous challenges due to the multiple obstacles. This review briefly analyzes a series of barriers ranging from poorly physicochemical properties of heparins, to harsh biological barriers including gastrointestinal degradation and pre-systemic metabolism. Moreover, several approaches have been developed to overcome these obstacles, such as improving stability of heparins in the gastrointestinal tract, enhancing the intestinal epithelia permeability and facilitating lymphatic delivery of heparins. Overall, this review aims to provide insights concerning advanced delivery strategies facilitating oral absorption of heparins.

Covalently binding mucoadhesive polymers: N-hydroxysuccinimide grafted polyacrylates

AIM

The aim of the study was to establish a novel type of covalently mucus-binding polymers by targeting selectively amino groups within mucus glycoproteins.

METHODS

N-Hydroxysuccinimide (NHS) was attached to carboxylic groups of polyacrylic acid (PAA). The reaction was mediated by the coupling reagent N,N'-dicyclohexylcarbodiimide (DCC) achieving polymeric NHS esters being able to form amide bonds with free amino groups. The chemical structure of the obtained conjugates was characterized via FTIR- and UV spectroscopy. Reactivity towards mucosal amino groups was evaluated UV spectrometrically upon addition of L-glycine. Furthermore, tensile force evaluations on intestinal mucosa as well as rheological experiments with mucus were performed in order to prove mucoadhesive potential.

RESULTS

Depending on the amount of NHS added to the synthesis, coupling rates of 876 to 1820 µmol NHS per gram polymer were obtained. Kinetic studies of amide bond formation showed a substrate dependent reaction velocity. Rheological synergism of PAA-NHS was proven by a 7.9-fold increased mucus viscosity compared to the control polymer. In further mucoadhesion studies PAA-NHS showed a 5.5-fold improved adhesion time compared to unmodified PAA. Tensile force evaluation confirmed these results with a 1.7-fold higher maximum detachment force (MDF) and 2.7-fold increased total work adhesion (TWA) for PAA-NHS compared to the unmodified control polymer.

CONCLUSION

The results of the present study provide strong evidence that coupling NHS to polymers could be a promising tool for the development of novel mucoadhesive excipients.

S-protected thiolated cyclodextrins as mucoadhesive oligomers for drug delivery

AIM

The purpose of this study was to develop a novel mucoadhesive thiolated and S-protected gamma cyclodextrin (γ-CD) with an intact ring backbone to assure a prolonged residence time at specific target sites.

METHOD

Thiolated γ-CD was generated through bromine substitution of its hydroxyl groups followed by replacement to thiol groups using thiourea. In the second step, thiol groups were protected by disulfide bond formation with 2-mercaptonicotinic acid (2-MNA).

RESULT

Thiolated γ-CD displayed 1385 ± 84 µmol thiol groups per gram of oligomer and the amount of MNA determined in the S-protected oligomer was 1153 ± 41 µmol per gram of oligomer. In-vitro screening of mucoadhesive properties of thiolated and S-protected γ-CD was done by two methods. Rheological investigation revealed the conjugates non-mucolytic with only a slight increase in viscosity of thiolated and S-protected γ-CD as compared to unmodified γ-CD, whereas mucoadhesive properties of the new thiolated and S-protected γ-CD performed on freshly excised porcine intestinal mucosa showed 44.4- and 50.9-fold improvement in mucoadhesion, respectively. The new conjugates did not show any cytotoxicity to Caco-2 cells even at a concentration of 1% (m/v) for 24 h. In addition, in-vitro studies of α-amylase degradation of γ-CD, γ-CD-SH and γ-CD-SS-MNA confirmed that all conjugates are biodegradable.

CONCLUSION

These outcomes predict that these new conjugates of γ-CD might provide a new favorable tool for drug delivery providing a prolonged residence time on mucosal surfaces.

Tailored on demand anti-coagulant dosing: An in vitro and in vivo evaluation of 3D printed purpose-designed oral dosage forms

Coumarin therapy has been associated with high levels of inter- and intra-individual variation in the required dose to reach a therapeutic anticoagulation outcome. Therefore, a dynamic system that is able to achieve accurate delivery of a warfarin dose is of significant importance. Here we assess the ability of 3D printing to fabricate and deliver tailored individualised precision dosing using in-vitro and in-vivo models. Sodium warfarin loaded filaments were compounded using hot melt extrusion (HME) and further fabricated via fused deposition modelling (FDM) 3D printing to produce capsular-ovoid-shaped dosage forms loaded at 200 or 400 µg dose. The solid dosage forms and comparator warfarin aqueous solutions were administered by oral gavage to Sprague-Dawley rats. A novel UV imaging approach indicated that the erosion of the methacrylate matrix was at a rate of 16.4 and 15.2 µm/min for horizontal and vertical planes respectively. In vivo, 3D printed forms were as proportionately effective as their comparative solution form in doubling plasma exposure following a doubling of warfarin dose (184% versus 192% respectively). The 3D printed ovoids showed a lower C_max of warfarin (1.51 and 3.33 mg/mL versus 2.5 and 6.44 mg/mL) and a longer T_max (6 and 3.7 versus 4 and 1.5 h) in comparison to liquid formulation. This work demonstrates for the first time in vivo, the potential of FDM 3D printing to produce a tailored specific dosage form and to accurately titrate coumarin dose response to an individual patient.

2,2'Dithiodinicotinyl ligands: Key to more reactive thiomers

The aim of this study was to establish a novel type of preactivated thiomers exhibiting a comparatively higher reactivity with mucus and consequently improved mucoadhesive properties. In order to achieve this goal, the dimeric form of 2-mercaptonicotinic acid (MNA-MNA) was directly attached to the polymeric backbone of chitosan (CHI) via amide bond formation mediated by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC) used as a coupling reagent. The remaining free amino groups were in the following reacted with succinic anhydride (Succ) in order to obtain a uniformly anionically charged polymer (CHI-Succ-MNA-MNA). Within this study, different coupling rates of up to 170 μmol MNA-MNA per gram polymer were achieved. The attachment of the dimeric ligand resulted in a preactivated thiomer with a comparatively more reactive disulfide substructure due to the additional nitrogen atom in conjugation over the aromatic moieties. Furthermore, the obtained polymer is entirely preactivated and thus prevented against undesired oxidation reactions. Kinetic studies of disulfide exchange reactions showed a 3.8-fold higher reactivity of CHI-Succ-MNA-MNA in comparison to a state-of-the-art preactivated thiomer. Within rheological measurements, CHI-Succ-MNA-MNA with a coupling rate of 170 μmol (CHI-Succ-MNA-MNA 170) led to a 5.7-fold higher mucus viscosity than the non-thiolated control polymer (CHI-Succ) indicating a rheological synergism due to mucoadhesive properties. These results were confirmed by a second mucoadhesion study, which showed a significantly prolonged retention time of CHI-Succ-MNA-MNA on the small intestinal mucosa compared to CHI-Succ (P<0.02). Accordingly, the double preactivation seems to be a promising strategy in order to obtain entirely preactivated polymers with enhanced mucoadhesive properties.

Guidance for the treatment and prevention of obstetric-associated venous thromboembolism

Venous thromboembolism (VTE), which may manifest as pulmonary embolism (PE) or deep vein thrombosis (DVT), is a serious and potentially fatal condition. Treatment and prevention of obstetric-related VTE is complicated by the need to consider fetal, as well as maternal, wellbeing when making management decisions. Although absolute VTE rates in this population are low, obstetric-associated VTE is an important cause of maternal morbidity and mortality. This manuscript, initiated by the Anticoagulation Forum, provides practical clinical guidance on the prevention and treatment of obstetric-associated VTE based on existing guidelines and consensus expert opinion based on available literature where guidelines are lacking.

Trends in the development of oral anticoagulants

Anticoagulation remains the therapy of choice for the prevention and treatment of venous and arterial thromboembolic disorders which can cause major organ damage or death. Heparins represent the antithrombotic drugs of choice in short and medium-term prophylaxis and therapy of thromboembolic diseases. Fondaparinux, a synthetic and structural analog of the antithrombin-binding pentasaccharide domain of heparin, has selective anti-Xa activity and longer half-life. However, anticoagulants are poorly absorbed by oral route because of their high molecular weight, hydrophilicity and negative charges. Long-term anticoagulation therapy is problematic because of side effects and frequent monitoring. Formulation approaches are particularly promising.

Novel self assembling nanoparticles for the oral administration of fondaparinux: synthesis, characterization and in vivo evaluation

Fondaparinux (Fpx) is the anticoagulant of choice in the treatment of short- and medium-term thromboembolic disease. To overcome the low oral bioavailability of Fpx, a new nanoparticulate carrier has been developed. The nanoparticles (NPs) contain squalenyl derivatives, known for their excellent oral bioavailability. They spontaneously self-assemble upon both electrostatic and hydrophobic interactions between the polyanionic Fpx and cationic squalenyl (CSq) derivatives. The preparation conditions were optimized to obtain monodisperse, stable NPs with a mean diameter in the range of 150–200 nm. The encapsulation efficiencies were around 80%. Fpx loadings reached 39 wt.%. According to structural and morphological analysis, Fpx and CSq organized in spherical multilamellar (“onion-type”) nanoparticles. Furthermore, in vivo studies in rats suggested that Fpx was well absorbed from the orally administered NPs, which totally dissociated when reaching the blood stream, leading to the release of free Fpx. The Fpx:CSq NPs improved the plasmatic concentration of Fpx in a dose-dependent manner. However, the oral bioavailability of these new NPs remained low (around 0.3%) but of note, the C_max obtained after oral administration of 50 mg/kg NPs was close to the prophylactic plasma concentration needed to treat venous thromboembolism. Moreover, the oral bioavailability of Fpx could be dramatically increased up to 9% by including the nanoparticles into gastroresistant capsules. This study opens up new perspectives for the oral administration of Fpx and paves the way towards elaborating squalene-based NPs which self assemble without the need of covalently grafting the drug to Sq.

Thiomers--from bench to market

Thiolated polymers or designated thiomers are obtained by immobilization of sulhydryl bearing ligands on the polymeric backbone of well-established polymers such as poly(acrylates) or chitosans. This functionalization leads to significantly improved mucoadhesive properties compared to the corresponding unmodified polymers, as disulfide bonds between thiol groups of thiomers and cysteine-rich glycoproteins of the mucus gel layer are formed. Furthermore, enzyme- and efflux-pump inhibiting as well as improved permeation-enhancing properties are advantages of thiolization. By the covalent attachment of mercaptonicotinamide substructures via disulfide bonds to thiolated polymers these properties are even substantially further improved and stability towards oxidation even in aqueous media can be provided. Meanwhile, more than 50 research groups worldwide are working on thiolated polymers. For certain thiomers the scale up process for industrial production has already been done and GMP material is available. Furthermore, safety of thiolated poly(acrylic acid), thiolated chitosan and thiolated hyaluronic acid could be demonstrated via orientating studies in human volunteers and via various clinical trials. The first product (Lacrimera® eye drops, Croma-Pharma) containing a chitosan-N-acetylcysteine conjugate for treatment of dry eye syndrome will enter the European market this year. It is the only product providing a sustained protective effect on the ocular surface due to its comparatively much more prolonged residence time worldwide. Various further products utilizing, for instance, thiolated hyaluronic acid in ocular surgery are in the pipeline.

Development and in vitro evaluation of slippery nanoparticles for enhanced diffusion through native mucus

Aim: The aim of this study was to investigate the mucus-penetrating properties of neutral nanoparticles comprising poly(acrylic acid) (PAA) and poly(allylamine) (PAM). Materials & methods: PAA and PAM nanoparticles were prepared on the basis of ionic interactions between the two polymers. Nanoparticles were characterized by particle size as well as surface charge. The cytotoxicity was examined via resazurin and lactate dehydrogenase assays. Using a modified Ussing chamber with mucus, the diffusion properties of obtained neutral nanoparticles were compared with control particles. Results: The obtained PAA–PAM nanoparticles demonstrated no significant cytotoxicity and displayed smooth and spherical surfaces, a particle size range of 200 nm and ζ-potential of 0.9 mV. The diffusion efficiency of neutral nanoparticles was 2.5- and 1.8-fold higher than PAM and PAA nanoparticles, respectively. Conclusion: Taking enhanced mucus-penetrating properties into account, neutral nanoparticles were shown to be very promising in drug delivery via mucus membranes of different cavities.

Original submitted 30 May 2012; Revised submitted 21 November 2012; Published online 23 April 2013

Synthesis and in vitro characterization of entirely S-protected thiolated pectin for drug delivery

The study was aimed to synthesize a thiolated polymer (thiomer) that is resistant to oxidation in solutions above pH 5. In order to protect a pectin-cysteine conjugate against premature oxidation, the thiomer was S-protected by a disulfide connected leaving group. Therefore, 2-mercaptonicotinic acid was first coupled to L-cysteine by a disulfide exchange reaction and the purified product was subsequently attached to pectin by a carbodiimide mediated amid bond formation. The obtained fully S-protected thiolated pectin was in vitro characterized with respect to co- and mucoadhesive properties and stability toward oxidation. The results indicated a 1.8-fold and 2.3-fold enhanced disintegration time at pH 6.8 of the S-protected thiolated pectin (Pec-Cys-MNA) compared to thiolated pectin (Pec-Cys) and unmodified pectin (Pec). Moreover, rheological measurements of polymer/mucus mixtures showed a 1.6-fold (compared to Pec-Cys) and 6.7-fold (compared to Pec) increased dynamic viscosity of Pec-Cys-MNA. On the other hand, in the presence of a strong oxidizing agent such as H2O2 (0.3% v/v), no increase in viscosity of Pec-Cys-MNA could be observed. A 6-month experiment also demonstrated the long-term stability of a liquid formulation based on Pec-Cys-MNA. Further investigations proved that the first time all thiol groups on a thiolated polymer could be protected owing to the novel synthesis. Accordingly, these features may help to develop thiomer based liquid or gel formulations targeting mucosal surfaces such as nasal, ocular or vaginal drug delivery systems.

Enzymatic degradation of thiolated chitosan

The objective of this study was to evaluate the biodegradability of thiolated chitosans in comparison to unmodified chitosan. Mediated by carbodiimide, thioglycolic acid (TGA) and mercaptonicotinic acid (MNA) were covalently attached to chitosan via formation an amide bond. Applying two different concentrations of carbodiimide 50 and 100 mM, two chitosan TGA conjugates (TGA A and TGA B) were obtained. According to chitosan solution (3% m/v) thiomer solutions were prepared and chitosanolytic enzyme solutions were added. Lysozyme, pectinase and cellulase were examined in chitosan degrading activity. The enzymatic degradability of these thiomers was investigated by viscosity measurements with a plate-plate viscometer. The obtained chitosan TGA conjugate A displayed 267.7 µmol and conjugate B displayed 116.3 µmol of immobilized thiol groups. With 325.4 µmol immobilized thiol groups, chitosan MNA conjugate displayed the most content of thiol groups. In rheological studies subsequently the modification proved that chitosan TGA conjugates with a higher coupling rate of thiol groups were not only degraded to a lesser extent by 20.9-26.4% but also more slowly. Chitosan mercaptonicotinic acid was degraded by 31.4-50.1% depending the investigated enzyme and even faster than unmodified chitosan. According to these results the biodegradability can be influenced by various modifications of the polymer which showed in particular that the rate of biodegradation is increased when MNA is the ligand, whereas the degradation is hampered when TGA is used as ligand for chitosan.

Pregnancy-associated venous thromboembolism: prevention and treatment

Pregnancy is associated with an increased risk of venous thromboembolism (VTE) and this condition remains an important cause of maternal morbidity and mortality. The use of anticoagulant therapy for treatment and prophylaxis of VTE during pregnancy is challenging because of the potential for fetal, as well as maternal, complications. Although evidence-based recommendations for the use of anticoagulants have been published, given the paucity of available data, guidelines are based largely upon observational studies and from data in nonpregnant patients. This article reviews the available literature and provides guidance for the management and prevention of VTE during pregnancy.

VTE, thrombophilia, antithrombotic therapy, and pregnancy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

The use of anticoagulant therapy during pregnancy is challenging because of the potential for both fetal and maternal complications. This guideline focuses on the management of VTE and thrombophilia as well as the use of antithrombotic agents during pregnancy.

METHODS

The methods of this guideline follow the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement.

RESULTS

We recommend low-molecular-weight heparin for the prevention and treatment of VTE in pregnant women instead of unfractionated heparin (Grade 1B). For pregnant women with acute VTE, we suggest that anticoagulants be continued for at least 6 weeks postpartum (for a minimum duration of therapy of 3 months) compared with shorter durations of treatment (Grade 2C). For women who fulfill the laboratory criteria for antiphospholipid antibody (APLA) syndrome and meet the clinical APLA criteria based on a history of three or more pregnancy losses, we recommend antepartum administration of prophylactic or intermediate-dose unfractionated heparin or prophylactic low-molecular-weight heparin combined with low-dose aspirin (75-100 mg/d) over no treatment (Grade 1B). For women with inherited thrombophilia and a history of pregnancy complications, we suggest not to use antithrombotic prophylaxis (Grade 2C). For women with two or more miscarriages but without APLA or thrombophilia, we recommend against antithrombotic prophylaxis (Grade 1B).

CONCLUSIONS

Most recommendations in this guideline are based on observational studies and extrapolation from other populations. There is an urgent need for appropriately designed studies in this population.

Preactivated thiomers as mucoadhesive polymers for drug delivery

This study was aimed to synthesize polymeric excipients with improved mucoadhesive, cohesive and in situ-gelling properties to assure a prolonged retention time of dosage forms at a given target site, thereby achieving an increased uptake and improved oral bioavailability of certain challenging therapeutic agents such as peptides and proteins. Accordingly, poly(acrylic acid)-cysteine-2-mercaptonicotinic acid (PAA-cys-2MNA) conjugates were synthesized by the oxidative S–S coupling of PAA-cys (100-, 250- and 450 kDa) with 2-mercaptonicotinic acid (2MNA). Unmodified PAAs, PAAs-cys (thiomers) and PAA-cys-2MNA (100-, 250- and 450 kDa) conjugates were compressed into tablets to perform disintegration tests, mucoadhesion studies and rheological measurements. Moreover, cytotoxicty of the polymers was determined using Caco-2 cells. The resulting PAA-cys-2MNA (100-, 250- and 450 kDa) conjugates displayed 113.5 ± 12.7, 122.7 ± 12.2 and 117.3 ± 4.6 μmol/g of 2-mercaptonicotinic acid, respectively. Due to the immobilization of 2MNA, the PAA-cys-2MNA (pre-activated thiomers) conjugates exhibit comparatively higher swelling properties and disintegration time to the corresponding unmodified and thiolated polymers. On the rotating cylinder, tablets based on PAA-cys-2MNA (100-, 250- and 450 kDa) conjugates displayed 5.0-, 5.4- and 960-fold improved mucoadhesion time in comparison to the corresponding unmodified PAAs. Results achieved from tensile studies were found in good agreement with the results obtained by rotating cylinder method. The apparent viscosity of PAA-cys-2MNA (100-, 250- and 450 kDa) conjugates was improved 1.6-, 2.5- and 206.2-fold, respectively, in comparison to the corresponding unmodified PAAs. Moreover, pre-activated thiomers/mucin mixtures showed a time dependent increase in viscosity up to 24 h, leading to 7.0-, 18.9- and 2678-fold increased viscosity in comparison to unmodified PAAs (100-, 250- and 450 kDa), respectively. All polymers were found non-toxic over Caco-2 cells. Thus, on the basis of achieved results the pre-activated thiomers seem to represent a promising generation of mucoadhesive polymers which are safe to use for prolonged residence time of drug delivery systems to target various mucosa.

Oral fondaparinux: use of lipid nanocapsules as nanocarriers and in vivo pharmacokinetic study

Oral anticoagulant therapy could be advanced using lipid-based nanoparticulate systems. This study examined lipid nanocapsules for their oral absorption potential as the first step in developing oral fondaparinux (Fp) novel carriers. Using phase inversion method and cationic surfactants such as hexadecyltrimethyl ammonium bromide (CTAB) or stearylamine (SA), cationic lipid nanocapsules (cLNCs), loaded with Fp on their surface, were prepared and characterized (zeta potential, size and Fp association efficiency and content). In vivo studies were conducted after single oral increasing doses of Fp-loaded cLNCs (0.5 to 5 mg/kg of Fp) in rats and the concentration of Fp in the plasma was measured by anti-factor Xa activity assay. The monodisperse, (~50 nm), positively charged Fp-cLNCs with high drug loadings demonstrated linear pharmacokinetic profiles of the drug with an increased oral absolute bioavailability (up to ~21%) compatible with therapeutic anticoagulant effect (>0.2 μg/mL).