Chunderika Mocktar

Nanoengineered Drug Delivery Systems for Enhancing Antibiotic Therapy

Formulation scientists are recognizing nanoengineered drug delivery systems as an effective strategy to overcome limitations associated with antibiotic drug therapy. Antibiotics encapsulated into nanodelivery systems will contribute to improved management of patients with various infectious diseases and to overcoming the serious global burden of antibiotic resistance. An extensive review of several antibiotic-loaded nanocarriers that have been formulated to target drugs to infectious sites, achieve controlled drug release profiles, and address formulation challenges, such as low-drug entrapment efficiencies, poor solubility and stability is presented in this paper. The physicochemical properties and the in vitro/in vivo performances of various antibiotic-loaded delivery systems, such as polymeric nanoparticles, micelles, dendrimers, liposomes, solid lipid nanoparticles, lipid-polymer hybrid nanoparticles, nanohybirds, nanofibers/scaffolds, nanosheets, nanoplexes, and nanotubes/horn/rods and nanoemulsions, are highlighted and evaluated. Future studies that will be essential to optimize formulation and commercialization of these antibiotic-loaded nanosystems are also identified. The review presented emphasizes the significant formulation progress achieved and potential that novel nanoengineered antibiotic drug delivery systems have for enhancing the treatment of patients with a range of infections.

Ion pairing with linoleic acid simultaneously enhances encapsulation efficiency and antibacterial activity of vancomycin in solid lipid nanoparticles

Ion pairing of a fatty acid with an antibiotic may be an effective strategy for formulation optimization of a nanoantibiotic system. The aim of this study was therefore to explore the potential of linoleic acid (LA) as an ion pairing agent to simultaneously enhance encapsulation efficiency and antibacterial activity of triethylamine neutralized vancomycin (VCM) in solid lipid nanoparticles (SLNs). The prepared VCM-LA2 conjugate was characterized by Fourier transform-infrared (FT-IR) spectroscopy, logP and binding energy calculations. The shifts in the FT-IR frequencies of COOH, NH2 and CO functionalities, an increase in logP value (1.37) and a lower interaction energy between LA and VCM (-125.54 kcal/mol) confirmed the formation of the conjugate. SLNs were prepared by a hot homogenization and ultrasonication method, and characterized for size, polydispersity index (PI), zeta potential (ZP), entrapment efficiency (%EE), surface morphology and physical stability. In vitro antibacterial activity studies against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) were conducted. Size, PI and ZP for VCM-LA2_SLNs were 102.7±1.01, 0.225±0.02 and -38.8±2.1 (mV) respectively. SLNs were also stable at 4 °C for 3 months. %EE for VCM-HCl_SLNs and VCM-LA2_SLNs were 16.81±3.64 and 70.73±5.96 respectively, indicating a significant improvement in encapsulation of the drug through ion pairing with LA. Transmission electron microscopy images showed spherical nanoparticles with sizes in the range of 95-100 nm. After 36 h, VCM-HCl showed no activity against MRSA. However, the minimum inhibitory concentration for VCM-HCl_SLNs and VCM-LA2_SLNs were 250 and 31.25 μg/ml respectively against S. aureus, while against MRSA it was 500 and 15.62 μg/ml respectively. This confirms the enhanced antibacterial activity of VCM-LA2_SLNs over VCM-HCl_SLNs. These findings therefore suggest that VCM-LA2_SLNs is a promising nanoantibiotic system for effective treatment against both sensitive and resistant S. aureus infections.

Solid lipid nanoparticles of clotrimazole silver complex: An efficient nano antibacterial against Staphylococcus aureus and MRSA.

New and effective strategies to transform current antimicrobials are required to address the increasing issue of microbial resistance and declining introduction of new antibiotic drugs. In this context, metal complexes of known drugs and nano delivery systems for antibiotics are proving to be promising strategies. The aim of the study was therefore to synthesize a silver complex of clotrimazole and formulate it into a nano delivery system for enhanced and sustained antibacterial activity against susceptible and resistant Staphylococcus aureus. A silver complex of clotrimazole was synthesized, characterized and further encapsulated into solid lipid nanoparticles to evaluate its antibacterial activity against S. aureus and methicillin-resistant S. aureus (MRSA). An in vitro cytotoxicity study was performed on HepG2 cell lines to assess the overall biosafety of the synthesized clotrimazole silver complex to mammalian cells, and was found to be non-toxic to mammalian cells (cell viability >80%). The minimum inhibitory concentrations (MIC) of clotrimazole and clotrimazole-silver were 31.25 and 9.76 μg/mL against S. aureus, and 31.25 and 15.62 against MRSA, respectively. Clotrimazole SLNs exhibited MIC values of 104 and 208 μg/mL against both MSSA and MRSA at the end of 18 and 36 h, respectively, but thereafter completely lost its antibacterial activity. Clotrimazole-silver SLNs had an MIC value of 52 μg/mL up to 54 h, after which the MIC value was 104 μg/mL against both strains at the end of 72 h. Thus, clotrimazole-silver SLNs was found to be an efficient nanoantibiotic.

Ultra-small lipid-dendrimer hybrid nanoparticles as a promising strategy for antibiotic delivery: In vitro and in silico studies

The purpose of this study was to explore the preparation of a new lipid-dendrimer hybrid nanoparticle (LDHN) system to effectively deliver vancomycin against methicillin-resistant Staphylococcus aureus (MRSA) infections. Spherical LDHNs with particle size, polydispersity index and zeta potential of 52.21±0.22 nm, 0.105±0.01, and -14.2±1.49 mV respectively were prepared by hot stirring and ultrasonication using Compritol 888 ATO, G4 PAMAM- succinamic acid dendrimer, and Kolliphor RH-40. Vancomycin encapsulation efficiency (%) in LDHNs was almost 4.5-fold greater than in lipid-polymer hybrid nanoparticles formulated using Eudragit RS 100. Differential scanning calorimetry and Fourier transform-infrared studies confirmed the formation of LDHNs. The interactions between the drug-dendrimer complex and lipid molecules using in silico modeling revealed the molecular mechanism behind the enhanced encapsulation and stability. Vancomycin was released from LDHNs over the period of 72 h with zero order kinetics and super case II transport mechanism. The minimum inhibitory concentration (MIC) against S. aureus and MRSA were 15.62 μg/ml and 7.81 μg/ml respectively. Formulation showed sustained activity with MIC of 62.5 μg/ml against S. aureus and 500 μg/ml against MRSA at the end of 72 and 54 h period respectively. The results suggest that the LDHN system can be an effective strategy to combat resistant infections.

Co-encapsulation of multi-lipids and polymers enhances the performance of vancomycin in lipid–polymer hybrid nanoparticles: In vitro and in silico studies

Nano-drug delivery systems are being widely explored to overcome the challenges with existing antibiotics to treat bacterial infections [1]. Lipid-polymer hybrid nanoparticles (LPNs) display unique advantages of both liposomes and polymeric nanoparticles while excluding some of their limitations, particularly the structural integrity of the polymeric particles and the biomimetic properties of the liposome [1]. The use of helper lipids and polymers in LPNs has not been investigated, but has shown potential in other nano-drug delivery systems to improve drug encapsulation, antibacterial activity and drug release. Therefore, LPNs using co-excipients were prepared using vancomycin (VCM), glyceryl triplamitate and Eudragit RS100 as the drug, lipid and polymer respectively. Oleic acid (OA), Chitosan (CHT) and Sodium alginate (ALG) were explored as co-excipients. Results indicated rod-shaped LPNs with suitable size, PDI and zeta potential, while encapsulation efficiency (%EE) increased from 27.8% to 41.5%, 54.3% and 69.3% with the addition of OA, CHT and ALG respectively. Drug release indicated that VCM-CHT had the best performance in sustained drug release of 36.1 ± 5.35% after 24h. The EE and drug release were further corroborated by in silico and release kinetics data. In vitro antibacterial studies of all formulations exhibited better activity against bare VCM and sustained activity up to day 5 against both Staphylococcus aureus and MRSA, with VCM-OA and VCM-CHT showing better activity against MRSA. Therefore, this LPN proves to be a promising system for delivery of VCM as well as other antibiotics.

Silver salts of carboxylic acid terminated generation 1 poly (propyl ether imine) (PETIM) dendron and dendrimers as antimicrobial agents against S. aureus and MRSA

Novel therapeutic strategies are essential to address the current global antimicrobial resistance crisis. Branched molecules with multiple peripheral functionalities, known as dendrimers, have gained interest as antimicrobials and have varying levels of toxicity. Silver displays activity against several micro-organisms only in its positively charged form. In this study, silver salts of generation 1 (G1) poly (propyl ether imine) (PETIM) dendron and dendrimers were synthesised and evaluated for their antimicrobial potential against sensitive and resistant bacteria. The purpose was to exploit the multiple peripheral functionalities of G1 PETIM dendron and dendrimers for the formation of silver salts containing multiple silver ions in a single molecule for enhanced antimicrobial activity at the lowest possible concentration. G1 PETIM dendron, dendrimers and their silver salts were synthesised and characterised by FT-IR, 1H NMR and 13C NMR. PETIM silver salts were evaluated against Hep G2, SKBR-3 and HT-29 cell lines for their cytotoxicity using the MTT assay. The G1 PETIM dendron/dendrimers, silver nitrate and silver salts of the G1 dendron (compound 13), G1 dendrimer with an aromatic core (compound 14) and an oxygen core (compound 15) were evaluated for activity against S. aureus and methicillin-resistant S. aureus (MRSA) by the broth dilution method. PETIM silver salts were found to be non-cytotoxic even up to 100 μg ml−1. Minimum inhibitory concentration values of compounds 13, 14 and 15 against S. aureus were 52.1, 41.7 and 20.8 μg ml−1 while against MRSA they were 125.0, 26.0 and 62.5 μg ml−1, respectively. The calculated fractional inhibitory concentration index further indicated that compound 14 specifically displayed additive effects against S. aureus and synergism against MRSA. The enhanced antimicrobial activities of the PETIM dendron/dendrimer-silver salts against both sensitive and resistant bacterial strains widen the pool of available pharmaceutical materials for optimizing treatment of bacterial infections.

Complexity and diversity of beta-lactamase expression in inhibitor-resistant Escherichia coli from public hospitals in KwaZulu-Natal, South Africa

β-lactamase profles of 38 inhibitor-resistant Escherichia coli isolates obtained from public hospitals in KwaZulu-Natal, selected on the basis of their resistance profles to one/more of amoxicillin/clavulanate, ampicillin/sulbactam and piperacillin/tazobactam were analysed. Isolates were subjected to iso-electric focusing, plasmid profle determination, PCR of the different β-lactamase genes and sequencing thereof to detect the possible mechanism/s of inhibitor-resistance. A range of β-lactamases including two inhibitor-resistant TEM β-lactamases (TEM-145 and TEM-146), a plasmid-mediated AmpC-type β-lactamase (CMY-20), OXA-1, TEM-55, SHV-2, CTX-M1 and TEM-1 was detected. Diverse β-lactamase genes and/or enzyme combinations, and plasmid profles inferred extensive mobilisation of resistance genes. Inhibitor resistance could be attributed to a range of mechanisms including but not limited to inhibitor-resistant TEM β-lactamases, hyper-production of TEM-1, hyper-production of chromosomal AmpC and OXA β-lactamases.

Pegylated oleic acid: A promising amphiphilic polymer for nano-antibiotic delivery

Graphical abstract Figure. No caption available. Abstract Vancomycin (VM), a last resort to control methicillin‐resistant S. aureus (MRSA) infections, is on the verge of becoming ineffective. Novel nano delivery systems of VM have the potential to combat MRSA. The search for novel materials for nanoantibiotic development is therefore an active research area. In this study, oleic acid (OA) was coupled with monomethoxy polyethylene glycol (mPEG) to obtain a novel bio‐safe amphiphilic polymer, mPEG‐OA. The critical micelle concentration of mPEG‐OA, was found to be 4.5 × 10−8 m/L. VM‐loaded polymersomes were prepared from mPEG‐OA and evaluated for size, polydispersity index (PDI), zeta potential (ZP), surface morphology, drug release, in vitro and in vivo antibacterial activity. The size, PDI and ZP of VM‐loaded polymersomes were 142.9 ± 7.5 nm, 0.228 ± 0.03 and −18.3 ± 3.55 mV respectively. Transmission electron microscopy images revealed the spherical shape of polymersomes. The encapsulation efficiency was 53.64 ± 1.86%. The drug release from polymersomes was sustained and in vitro antibacterial activity was 42‐ and 5‐fold more against S. aureus and MRSA, compared with plain VM. An in vivo BALB/c mice, skin infection models revealed that treatment with VM‐loaded polymersomes significantly reduced the MRSA burden compared with plain VM and blank polymersomes. There was a 183 and a 25‐fold reduction in the MRSA colony finding units load in mice skin treated with VM‐loaded polymersomes compared to that treated with blank polymersomes and bare VM respectively. In summary, the developed VM‐loaded polymersomes from novel mPEG‐OA polymer were found to be a promising nanoantibiotic against MRSA.

Transforming linoleic acid into a nanoemulsion for enhanced activity against methicillin susceptible and resistant Staphylococcus aureus

The activity of antibacterial agents can be enhanced by transforming them into the nano form. The aim of this study was therefore to enhance the antibacterial activity of linoleic acid (LA) against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) by formulating it as a nanoemulsion (NE). The mean globule diameter, polydispersity index and zeta potential of the optimized LA NE containing benzalkonium chloride (BAC) as a stabilizer were 75.14 ± 3 nm, 0.145 ± 0.01 and 45.7 ± 1.27 mV respectively. The turbidity absorbance, conductivity and viscosity were 1.773 ± 0.69, 0.0508 ± 0.006 mS cm−1 and 92.74 ± 2.17 mPas respectively, and the formulation was stable at 4 °C for 3 months. The LA NE was non-toxic and exhibited a 205-fold greater increase in the antibacterial activity than plain LA against S. aureus and MRSA. The fractional inhibitory concentration values indicated that the combination of LA and BAC had a synergistic effect. The molecular modeling studies revealed better stability of the LA–BAC system than LA with other surfactants. Bacterial protein degradation and cell morphology studies confirmed that the antibacterial activity of LA NE was due to cell membrane damage. These findings suggest that the developed LA NE could be a promising non-antibiotic drug containing antibacterial nano delivery system.

Enhancing targeted antibiotic therapy via pH responsive solid lipid nanoparticles from an acid cleavable lipid

An acid cleavable lipid (SA-3M) was synthesized and used to develop pH-responsive solid lipid nanoparticles (SLNs) to deliver vancomycin base (VM-FB) to acidic infection sites. The size, polydispersity index and zeta potential of VM-FB_SA-3M_SLNs were 132.9±9.1nm, 0.159±0.01 and -26±4.4mV respectively, with 57.80±1.1% encapsulation efficiency. VM-FB release was significantly faster at pH6.5 than pH7.4. In vitro antibacterial activity against methicillin-susceptible and resistant Staphylococcus aureus (MSSA and MRSA) revealed that SLNs had enhanced activity at pH6.5 than pH7.4. In vivo study showed that the amount of MRSA remaining in the skin of VM-FB_SA-3M_SLNs treated mice was approximately 22-fold lower than VM-FB treated mice. Histological investigations revealed that signs of inflammation in the skin treated with VM-FB_SA-3M_SLNs were minimal. In conclusion, this study confirmed that SA-3M can form pH-responsive SLNs capable of releasing antibiotic specifically at acidic infection sites.