Pompilia Ispas-Szabo

N-acylated chitosan: hydrophobic matrices for controlled drug release.

N-acylation of chitosan with various fatty acid (C(6)-C(16)) chlorides increased its hydrophobic character and made important changes in its structural features. Unmodified chitosan exhibited a low degree of order (DO) and a weak tablet crushing strength. Chitosan acylated with a short chain length (C(6)) possessed similar properties, but exhibited significant swelling. Acylation with longer side chains (C(8)-C(16)) resulted in a higher DO and crushing strength but lower swelling. The best mechanical characteristics and drug release properties were found for palmitoyl chitosan (substitution degree 40-50%) tablets with 20% acetaminophen as a tracer. The high stability of these monolithic tablets appears to be due to hydrophobic interactions between side chains, as shown by a more organized structure. Infrared spectroscopy, X-ray diffractometry and proton nuclear magnetic resonance analyses of palmitoyl chitosan were consistent with a hydrophobic self-assembling model. Drug dissolution kinetics showed longer release times for higher degrees of functionalization, i.e. 30 h (for 47% substitution) and 90 h (for 69% substitution), suggesting palmitoyl chitosan excipients as interesting candidates for oral and subdermal pharmaceutical applications.

Cross-linked high amylose starch derivatives as matrices for controlled release of high drug loadings

Selection of hydrogels as excipients in controlled drug release systems depends on the characteristics of the gel and of the drug. Three types of derivatives were synthesized from cross-linked high amylose starch (HASCL-6) by substitution of hydroxylic groups with cationic (carboxymethyl: CM), anionic (aminoethyl: AE) and acetate (Ac) groups. These new polymeric excipients are able to control the release over 20 h from monolithic tablets loaded with 20 to 60% drug. Three drugs were used as model tracer: acetaminophen (uncharged), acetylsalicylic acid (having an acidic group) and metformin (having a basic group). It was found that the release of ionic drugs from CM-HASCL-6 and AE-HASCL-6 matrices can be partially controlled by ionic interaction between pendant groups of polymer and drugs. The substitution degree of HASCL-6 derivatives can also be varied to modulate the drugs release time. These derivatives represent a novel generation of pharmaceutical excipients, recommended for high loading dosage formulations.

Structure–properties relationship in cross-linked high-amylose starch for use in controlled drug release

Cross-linked high-amylose starch (CLHAS), obtained by high-amylose starch cross-linking, was recently introduced as an excipient (Contramid) for monolithic dosage forms that are able to control drug release over 18-24 h. These control properties are related to tablet swelling and are strongly dependent on the degree of the cross-linking of CLHAS. The permeability of solutes through CLHAS hydrogels depends on the chemical structure of the polymer. The aim of this study was to obtain a better understanding of how modifications in CLHAS molecular structures at the level of long-range and short-range order during the cross-linking and processing conditions relate to the release properties of the CLHAS matrices. Structural parameters such as crystallinity contribute significantly to the physical and mechanical aspects of starch products. X-ray diffractometry, FTIR spectroscopy, dissolution tests in vitro, and mechanical hardness (of dry tablets) were found to be sensitive to the cross-linking degree (cld) variation. Best release properties and highest mechanical hardness were obtained from CLHAS matrices with low-to-moderate crystallinity, where the V- and the B-type structures coexist with amorphous regions. X-ray and FTIR profiles of dry CLHAS powders were found to be predictive for release properties of CLHAS tablets.

Carboxymethyl starch and lecithin complex as matrix for targeted drug delivery: I. Monolithic Mesalamine forms for colon delivery

For drugs expected to act locally in the colon, and for successful treatment, a delivery device is necessary, in order to limit the systemic absorption which decreases effectiveness and causes important side effects. Various delayed release systems are currently commercialized; most of them based on pH-dependent release which is sensitive to gastrointestinal pH variation. This study proposes a novel excipient for colon delivery. This new preparation consists in the complexation between carboxymethyl starch (CMS) and Lecithin (L). As opposed to existing excipients, the new complex is pH-independent, inexpensive, and easy to manufacture and allows a high drug loading. FTIR, X-ray, and SEM structural analysis all support the hypothesis of the formation of a complex. By minor variation of the excipient content within the tablet, it is possible to modulate the release time and delivery at specific sites of the gastrointestinal tract. This study opens the door to a new pH-independent delivery system for mesalamine targeted administration. Our novel formulation fits well with the posology of mesalamine, used in the treatment of Inflammatory Bowel Disease (IBD), which requires repeated administrations (1g orally four times a day) to maintain a good quality of life.

NMR imaging of chitosan and carboxymethyl starch tablets: swelling and hydration of the polyelectrolyte complex.

The hydration and swelling properties of the tablets made of chitosan, carboxymethyl starch, and a polyelectrolyte complex of these two polysaccharides have been studied by NMR imaging. We studied the effect of pH and ionic strength on the swelling of the tablets and on the diffusion of fluid into the tablets in water and simulated physiological fluids. The pH value of the fluids exerts a more significant effect than their ionic strengths on the swelling of the tablets. The tablets are compared also with those made of cross-linked high amylose starch. The formation of complex helps to keep the integrity of the tablets in various media and render a slow and restricted swelling similar to that of the tablets of the cross-linked high amylase starch, which is significantly lower than the swelling of chitosan and of carboxymethyl starch. The capacities to modulate the release rate of drugs in different media are discussed by comparing the matrices and evaluating the preparation process of the complex. A sustained release of less soluble drugs such as aspirin in gastrointestinal fluids can be provided by the complex, due to the ionic interaction and hydrogen bonding between the drug and the biopolymer complex.

Carboxymethyl starch: Chitosan monolithic matrices containing diamine oxidase and catalase for intestinal delivery

The capacity of carboxymethyl starch (CMS):Chitosan monolithic tablets to protect diamine oxidase and/or catalase therapeutic enzymes against simulated gastric fluid (SGF) and to control their delivery in simulated intestinal fluid (SIF) was investigated. Enzyme formulations loaded with grass pea seedlings diamine oxidase (PSDAO) vegetal extract, catalase, or PSDAO associated to catalase, were obtained by direct compression. The CMS:Chitosan (1:1) matrix afforded a good gastric protection to PSDAO and to catalase, when each enzyme was formulated separately. Variable amounts of DAO were delivered in the SIF containing pancreatin, with maximal release reached at about 8h, a time convenient for tablets to attain the colon. Up to 50% of the initial enzymatic activity of catalase formulated with CMS:Chitosan was found after 8 h in SIF. For the CMS:Chitosan tablets of bi-enzymatic formulations containing PSDAO:Catalase, the releases of DAO and of catalase were synchronized. The hydrogen peroxide (product of DAO activity) was decomposed by the catalase liberated in the same SIF environment. The proposed formulations could allow novel therapeutic approaches for the treatment of inflammatory bowel diseases, intestinal cancers or pseudo-allergic reactions.

Modified high amylose starch for immobilization of uricase for therapeutic application

Urate oxidase (uricase) was immobilized on carboxymethyl high amylose starch cross‐linked 35 (CM‐HASCL‐35), on aminoethyl high amylose starch cross‐linked 35, as well as on commercial supports, CNBr‐activated Sepharose and diaminodipropylamine agarose. The N‐ethyl‐5‐phenylisoxazolium‐3′‐sulphonate (Woodward reagent K) gave a high binding but totally inhibited the enzyme activity. Best results were obtained with CM‐HASCL‐35 using 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodi‐imide as a coupling agent. The immobilized enzyme retained 88% of its initial limit rate [Vmax(app)=16 EU/mg for immobilized uricase versus Vmax=18 EU/mg for the free enzyme], with an apparent decrease of affinity for urate substrate [Km(app)=0.17 mM versus Km=0.03 mM for the free enzyme]. The coupling yield was 60% and the modified uricase was found more resistant to proteolysis than the free enzyme. The immobilized uricase retained 25% of its initial activity after 60 min in pancreatic proteolysis medium (pancreatin), whereas the free enzyme retained only 5% of its initial activity. The best immobilization yield was obtained with the polymeric support based on CM‐HASCL‐35 (53%), which gave better results than commercial supports based on agarose.

Starch materials as biocompatible supports and procedure for fast separation of macrophages

Different starch derivatives were evaluated as supports for attachment and recovery of macrophages (RAW 264.7 line). Gelatinized starch (G-St), acetate starch (Ac-St), carboxymethyl starch and aminoethyl starch were synthesized and characterized by FTIR, 1H NMR, SEM and static water contact angle. These polymers are filmogenic and may coat well the holder devices used for macrophage adhesion. They also present a susceptibility to mild hydrolysis with alpha-amylase, liberating the adhered macrophages. Cell counts, percentage of dead cells and level of tumor necrosis factor (TNF-α) were used to evaluate the possible interaction between macrophages and starch films. The high percentage of cell adhesion (90-95% on G-St and on Ac-St) associated with enzymatic detachment of macrophages from film-coated inserts, resulted in higher viabilities compared with those obtained with cells detached by current methods scrapping or vortex. This novel method allows a fast macrophage separation, with excellent yields and high viability of recovered cells.

Ampholytic starch excipients for high loaded drug formulations: Mechanistic insights

Ampholytic starch derivatives are proposed as a new class of excipients carrying simultaneously anionic carboxymethyl (CM) and cationic aminoethyl (AE) groups on starch (St) polymeric chains. Three different types of derivatives were obtained by using the same reagents and varying only the order of their addition in the reaction medium: in one step method (OS) the two reactants were added simultaneously, whereas in two steps method (TS) either CMSt or AESt were prepared separately in the first step, followed by subsequent addition of the second reactant. It was found that all ampholytic derivatives were able to generate monolithic tablets by direct compression and allowed 60% loading of acidic (Acetylsalicylic acid), basic (Metformin), zwitterion (Mesalamine) or neutral (Acetaminophen) as drug models. The in vitro dissolution tests followed for 2 h in SGF and then in SIF, showed that the mentioned starch derivatives were stabilized by self-assembling and generated matrices able to control the release of drugs for about 24 h. The addition order of reagents has an impact on ampholytic starch properties offering thus a high versatility of this new class of starch excipients that can be tailored for challenging formulations with high dosages of several drugs.

Chitosan-doxycycline hydrogel: An MMP inhibitor/sclerosing embolizing agent as a new approach to endoleak prevention and treatment after endovascular aneurysm repair

The success of endovascular repair of abdominal aortic aneurysms remains limited due to the development of endoleaks. Sac embolization has been proposed to manage endoleaks, but current embolizing materials are associated with frequent recurrence. An injectable agent that combines vascular occlusion and sclerosing properties has demonstrated promise for the treatment of endoleaks. Moreover, the inhibition of aneurysmal wall degradation via matrix metalloproteinases (MMPs) may further prevent aneurysm progression. Thus, an embolization agent that promotes occlusion, MMP inhibition and endothelial ablation was hypothesized to provide a multi-faceted approach for endoleak treatment. In this study, an injectable, occlusive chitosan (CH) hydrogel containing doxycycline (DOX)-a sclerosant and MMP inhibitor-was developed. Several CH-DOX hydrogel formulations were characterized for their mechanical and sclerosing properties, injectability, DOX release rate, and MMP inhibition. An optimized formulation was assessed for its short-term ability to occlude blood vessels in vivo. All formulations were injectable and gelled rapidly at body temperature. Only hydrogels prepared with 0.075M sodium bicarbonate and 0.08M phosphate buffer as the gelling agent presented sufficient mechanical properties to immediately impede physiological flow. DOX release from this gel was in a two-stage pattern: a burst release followed by a slow continuous release. Released DOX was bioactive and able to inhibit MMP-2 activity in human glioblastoma cells. Preliminary in vivo testing in pig renal arteries showed immediate and delayed embolization success of 96% and 86%, respectively. Altogether, CH-DOX hydrogels appear to be promising new multifunctional embolic agents for the treatment of endoleaks. STATEMENT OF SIGNIFICANCE An injectable embolizing chitosan hydrogel releasing doxycycline (DOX) was developed as the first multi-faceted approach for the occlusion of blood vessels. It combines occlusive properties with DOX sclerosing and MMP inhibition properties, respectively known to prevent recanalization process and to counteract the underlying pathophysiology of vessel wall degradation and aneurysm progression. After drug release, the biocompatible scaffold can be invaded by cells and slowly degrade. Local DOX delivery requires lower drug amount and decreases risks of side effects compared to systemic administration. This new gel could be used for the prevention or treatment of endoleaks after endovascular aneurysm repair, but also for the embolization of other blood vessels such as venous or vascular malformations.