Narendra K. Jain

Dendrimer toxicity: Let's meet the challenge

Dendrimers are well-defined, versatile polymeric architecture with properties resembling biomolecules. Dendritic polymers emerged as outstanding carrier in modern medicine system because of its derivatisable branched architecture and flexibility in modifying it in numerous ways. Dendritic scaffold has been found to be suitable carrier for a variety of drugs including anticancer, anti-viral, anti-bacterial, antitubercular etc., with capacity to improve solubility and bioavailability of poorly soluble drugs. In spite of extensive applicability in pharmaceutical field, the use of dendrimers in biological system is constrained because of inherent toxicity associated with them. This toxicity is attributed to the interaction of surface cationic charge of dendrimers with negatively charged biological membranes in vivo. Interaction of dendrimers with biological membranes results in membrane disruption via nanohole formation, membrane thinning and erosion. Dendrimer toxicity in biological system is generally characterized by hemolytic toxicity, cytotoxicity and hematological toxicity. To minimize this toxicity two strategies have been utilized; first, designing and synthesis of biocompatible dendrimers; and second, masking of peripheral charge of dendrimers by surface engineering. Biocompatible dendrimers can be synthesized by employing biodegradable core and branching units or utilizing intermediates of various metabolic pathways. Dendrimer biocompatibility has been evaluated in vitro and in vivo for efficient presentation of biological performance. Surface engineering masks the cationic charge of dendrimer surface either by neutralization of charge, for example PEGylation, acetylation, carbohydrate and peptide conjugation; or by introducing negative charge such as half generation dendrimers. Neutral and negatively charged dendrimers do not interact with biological environment and hence are compatible for clinical applications as elucidated by various studies examined in this review. Chemical modification of the surface is an important strategy to overcome the toxicity problems associated with the dendrimers. The present review emphasizes on the approaches available to overcome the cationic toxicity inherently associated with the dendrimers.

Folate and folate-PEG-PAMAM dendrimers: synthesis, characterization, and targeted anticancer drug delivery potential in tumor bearing mice.

Ligand-mediated targeting of drugs especially in anticancer drug delivery is an effective approach. Dendrimers, due to unique surface topologies, can be a choice in this context. In the present study, PAMAM (polyamidoamine) dendrimers up to fourth generation were synthesized and characterized through infrared (IR), nuclear magnetic resonance (NMR), electrospray ionization (ESI) mass spectrometric, and transmission electron microscopic (TEM) techniques. Primary amines present on the dendritic surface were conjugated through folic acid and folic acid-PEG (poly(ethylene glycol))-NHS (N-hydroxysuccinimide) conjugates. Tumor in mice was induced through the use of KB cell culture. Prepared dendritic conjugates were evaluated for the anticancer drug delivery potential using 5-FU (5-fluorouracil) in tumor-bearing mice. Approximately 31% of 5-FU was loaded in folate-PEG-dendritic conjugates. Results indicated that folate-PEG-dendrimer conjugate was significantly safe and effective in tumor targeting compared to a non-PEGylated formulation. Tailoring of dendrimers via PEG-folic acid reduced hemolytic toxicity, which led to a sustained drug release pattern as well as highest accumulation in the tumor area.

Proniosome based transdermal delivery of levonorgestrel for effective contraception

A proniosome based transdermal drug delivery system of levonorgestrel (LN) was developed and extensively characterized both in vitro and in vivo. The proniosomal structure was liquid crystalline-compact niosomes hybrid which could be converted into niosomes upon hydration. The system was evaluated in vitro for drug loading, rate of hydration (spontaneity), vesicle size, polydispersity, entrapment efficiency and drug diffusion across rat skin. The effect of composition of formulation, amount of drug, type of Spans, alcohols and sonication time on transdermal permeation profile was observed. The stability studies were performed at 4 degrees C and at room temperature. The biological assay for progestational activity included endometrial assay and inhibition with the formation of corpora lutea. The study demonstrated the utility of proniosomal transdermal patch bearing levonorgestrel for effective contraception.

Transfersomes—A Novel Vesicular Carrier for Enhanced Transdermal Delivery: Development, Characterization, and Performance Evaluation

Abstract This work describes the use of a novel vesicular drug carrier system called transfersomes, which is composed of phospholipid, surfactant, and water for enhanced transdermal delivery. The transfersomal system was much more efficient at delivering a low and high molecular weight drug to the skin in terms of quantity and depth. In the present study transfersomes and liposomes were prepared by using dexamethasone as a model drug. The system was evaluated in vitro for vesicle shape and size, entrapment efficiency, degree of deformability, number of vesicles per cubic mm, and drug diffusion across the artificial membrane and rat skin. The effects of surfactant type, composition, charge, and concentration of surfactant were studied. The in vivo performance of selected formulation was evaluated by using a carrageenan-induced rat paw edema model. Fluorescence microscopy by using rhodamine-123 and 6-carboxyfluorescein as fluorescence probe was performed. The stability study was performed at 4°C and 37°C. An in vitro drug release study has shown a nearly zero order release of drug and no lag phase. The absence of lag phase in comparison to liposomes and ointment is attributed to the greater deformability, which may account for better skin permeability of transfersomes. In vivo studies of transfersomes showed better antiedema activity in comparison to liposomes and ointment, indicating better permeation through the penetration barrier of the skin. This was further confirmed through a fluorescence microscopy study. Finally, it may be concluded from the study that complex lipid molecules, transfersomes, can increase the transdermal flux, prolong the release, and improve the site specificity of bioactive molecules.

A review of nanocarriers for the delivery of small interfering RNA

Increasing knowledge about molecular mechanisms of endogenous RNA interference (RNAi) and small interfering RNAs (siRNAs) has been incorporated into innovative nucleic acid medicines for treatment of diseases such as cancers. Although RNAi and siRNA have the potential to become powerful therapeutic drugs, their delivery to the target site represents a major challenge. The design and creation of nanocarriers for the safe and efficient delivery of siRNA towards their potential applications site is one of the challenging and rapidly growing areas of research since they have to overcome the commonly encountered biological barriers. In this review, we discuss the recent nanotechnological strategies for siRNA delivery by using different carriers such as liposomes, dendrimers and carbon nanotubes.

PULMONARY TOXICITY OF CARBON NANOTUBES: A SYSTEMATIC REPORT

UNLABELLED Carbon nanotubes (CNTs) are nanosized cylindrical hollow tubes consisting entirely of the element carbon. Currently, CNTs are playing an important role in drug delivery as a carrier system because of their several unique physical and chemical properties. Studies show that CNTs are toxic and that the extent of that toxicity depends on properties of the CNTs, such as their structure (single wall or multiple wall), length and aspects ratios, surface area, degree of aggregation, extent of oxidation, bound functional group(s), method of manufacturing, concentration, and dose. People could be exposed to CNTs either accidentally by coming in contact with the aerosol form of CNTs during production or by exposure as a result of biomedical use. Numerous in vitro and in vivo studies have shown that CNTs and/or associated contaminants or catalytic materials that arise during the production process may induce oxidative stress, prominent pulmonary inflammation, apoptosis in different cell types, and induction of cytotoxic effects on lungs. Studies on the toxicity of CNTs have mainly focused on the pulmonary effects of intratracheal or pharyngeally administered CNTs. This review examines the potential pulmonary toxicity of CNTs. FROM THE CLINICAL EDITOR Carbon nanotubes are promising drug delivery agents; however, their pulmonary toxicity may represent a substantial limitation to their applicability. This detailed review discusses critical aspects of the above problem.

Formulation and in vitro, in vivo evaluation of extended- release matrix tablet of Zidovudine: Influence of combination of hydrophilic and hydrophobic matrix formers

The aim of the present study was to prepare and characterize extended-release matrix tablets of zidovudine using hydrophilic Eudragit RLPO and RSPO alone or their combination with hydrophobic ethyl cellulose. Release kinetics was evaluated by using United States Pharmacopeia (USP)-22 type I dissolution apparatus. Scanning electron microscopy was used to visualize the effect of dissolution medium on matrix tablet surface. Furthermore, the in vitro and in vivo newly formulated sustained-release zidovudine tablets were compared with conventional marketed tablet (Zidovir, Cipla Ltd, Mumbai, India). The in-vitro drug release study revealed that either Eudragit preparation was able to sustain the drug release only for 6 hours (94.3%±4.5% release). Combining Eudragit with ethyl cellulose sustained the drug release for 12 hours (88.1%±4.1% release). Fitting the in vitro drug release data to Korsmeyer equation indicated that diffusion along with erosion could be the mechanism of drug release. In vivo investigation in rabbits showed sustained-release pharmacokinetic profile of zidovudine from the matrix tablets formulated using combination of Eudragits and ethylcellulose. In conclusion, the results suggest that the developed sustained-release tablets of zidovudine could perform therapeutically better than conventional dosage forms, leading to improve efficacy and better patient compliance.

A review of glycosylated carriers for drug delivery.

Carbohydrates not only represent a vast potential as structure building blocks of living cells but also have proved as a promising candidate for drug delivery. Glycosylation of nanocarriers instructs some gratifying characteristic, which leads to the evolution of promising delivery systems. Some path-breaking advantages of glycosylated carriers include the engineered release profile of bioactives when introduced into biological system. Being natural product of living system these carriers also upshots as a multifaceted drug delivery vehicle and reduces the toxicity associated with unmodified drug carrier and therapeutic agent. An additional attribute of these carriers is to alter the pharmacokinetic profile of drugs positively with stabilization of drug carrier. The presence of lectin receptors on different cell surfaces makes the glycosylated carrier appreciable for targeted delivery of drugs to improve their therapeutic index. Active participation of some lectin receptors in immune responses to antigen overlaid the application of glycosylated carriers in delivery of antigen and immunotherapy for treatment of ailments like cancer. These advantages revealed the promising potential of glycosylated carriers in each perspective of drug delivery. Collectively this review presents an overview of different applications of glycosylated carriers, with a focus on their applicability in development of a nanoconstruct with GRAS status.

Poly(amidoamine) (PAMAM) dendritic nanostructures for controlled sitespecific delivery of acidic anti-inflammatory active ingredient

The purpose of the investigation was to evaluate the potential of polyamidoamine (PAMAM) dendrimer as nanoscale drug delivery units for controlled release of water insoluble and acidic anti-inflammatory drug. Flurbiprofen (FB) was selected as a model acidic anti-inflammatory drug. The aqueous solutions of 4.0 generation (G) PAMAM dendrimer in different concentrations were prepared and used further for solubilizing FB. Formation of dendrimer complex was characterized by Fourier transform infrared spectroscopy. The effect of pH on the solubility of FB in dendrimer was evaluated. Dendrimer formulations were further evaluated for in vitro release study and hemolytic toxicity. Pharmacokinetic and biodistribution were studied in male albino rats. Efficacy of dendrimer formulation was tested by carrageenan induced paw edema model. It was observed that the loaded drug displayed initial rapid release (more than 40% till 3rd hour) followed by rather slow release. Pharmacodynamic study revealed 75% inhibition at 4th hour that was maintained above 50% till 8th hour. The mean residence time (MRT) and terminal half-life (THF) of the dendritic formulation increased by 2-fold and 3-fold, respectively, compared with free drug. Hence, with dendritic system the drug is retained for longer duration in the biosystem with 5-fold greater distribution. It may be concluded that the drug-loaded dendrimers not only enhanced the solubility but also controlled the delivery of the bioactive with localized action at the site of inflammation.

Formulation and evaluation of ethosomes for transdermal delivery of lamivudine.

The purpose of the present research was to investigate the mechanism for improved intercellular and intracellular drug delivery from ethosomes using visualization techniques and cell line study. Ethosomal formulations were prepared using lamivudine as model drug and characterized in vitro, ex vivo and in vivo. Transmission electron microscopy, scanning electron microscopy, and fluorescence microscopy were employed to determine the effect of ethosome on ultrastructure of skin. Cytotoxicity and cellular uptake of ethosome were determined using T-lymphoid cell line (MT-2). The optimized ethosomal formulation showed 25 times higher transdermal flux (68.4±3.5 µg/cm2/h) across the rat skin as compared with that of lamivudine solution (2.8±0.2 µg/cm2/h). Microscopic studies revealed that ethosomes influenced the ultrastructure of stratum corneum. Distinct regions with lamellar stacks derived from vesicles were observed in intercellular region of deeper skin layers. Results of cellular uptake study showed significantly higher intracellular uptake of ethosomes (85.7%±4.5%) as compared with drug solution (24.9%±1.9%). The results of the characterization studies indicate that lipid perturbation along with elasticity of ethosomes vesicles seems to be the main contributor for improved skin permeation.