Hemant K. Gautam

Multifunctional self-assembled cationic peptide nanostructures efficiently carry plasmid DNA in vitro and exhibit antimicrobial activity with minimal toxicity

In this study, a modified dehydropeptide, Boc-FΔF-εAhx-OH, was conjugated with an aminoglycoside antibiotic, neomycin, to construct a multifunctional conjugate, Pep-Neo. The amphiphilic conjugate (Pep-Neo) was able to self-assemble into cationic nanostructures in an aqueous solution at low concentrations. Nanostructure formation was evidenced by TEM and dynamic light scattering analyses. The average hydrodynamic diameter of the self-assembled Pep-Neo nanostructures was found to be ∼279 nm with a zeta potential of +28 mV. The formation of nanostructures with a hydrophobic core and cationic hydrophilic shell resulted in an increased local concentration of cationic charge (ca. in 50% aqueous methanol, i.e. disassembled structure, zeta potential decreased to +17.6 mV), leading to efficient interactions with negatively charged plasmid DNA (pDNA). The size and zeta potential of the resulting Pep-Neo/pDNA complex were found to be ∼154 nm and +19.4 mV, respectively. Having been characterized by physicochemical techniques, the complex was evaluated for its toxicity and ability to deliver nucleic acid therapeutics. The flow cytometry results on MCF-7 cells revealed that Pep-Neo/pDNA complex transfected ∼27% cells at a w/w ratio of 66.6 while the standard transfection reagent, Lipofectamine, could transfect only ∼15% cells. MTT and hemolysis assays showed the non-toxic nature of the projected conjugate at various concentrations. Further, these nanostructures were shown to encapsulate hydrophobic drugs in the core. Finally, Pep-Neo nanostructures showed efficient antibacterial activity against different strains of Gram-positive and -negative bacteria. Interestingly, unlike neomycin, which is highly effective against Gram-negative bacteria, these nanostructures showed considerably high efficiency against Gram-positive strains, highlighting the promising potential of these nanostructures for various biomedical applications.

Synthesis and antimicrobial activity of aminoglycoside-conjugated silica nanoparticles against clinical and resistant bacteria

Functionalization of silica nanoparticles with different cationic moieties makes them suitable for being an effective antimicrobial agent against various clinical pathogenic microbes. Here, we report the synthesis, characterization and evaluation of aminoglycoside-conjugated silica nanoparticles [S–X NPs, where X = gentamicin (G), neomycin (N) or kanamycin (K)] for their antimicrobial activity against clinical pathogens and kanamycin-resistant E. coli. These functionalized silica nanoparticles exhibited enhanced broad-spectrum antimicrobial activity against clinical Gram-positive and Gram-negative bacteria as well as kanamycin-resistant E. coli strain with minimal cytotoxicity. The results show the potential of these conjugates to combat drug resistance.

A cross-sectional pilot study of antibiotic resistance in Propionibacterium acnes strains in Indian acne patients using 16s-RNA polymerase chain reaction: A comparison among treatment modalities including antibiotics, benzoyl peroxide, and isotretinoin

Background: Antibiotic resistance is a worldwide problem in acne patients due to regional prescription practices, patient compliance, and genomic variability in Propionibacterium acnes, though the effect of treatment on the resistance has not been comprehensively analyzed. Aims: Our primary objective was to assess the level of antibiotic resistance in the Indian patients and to assess whether there was a difference in the resistance across common treatment groups. Subjects and Methods: A cross-sectional, institutional based study was undertaken and three groups of patients were analyzed, treatment naïve, those on antibiotics and patients on benzoyl peroxide (BPO) and/isotretinoin. The follicular content was sampled and the culture was verified with 16S rRNA polymerase chain reaction, genomic sequencing, and pulsed-field gel electrophoresis. Minimum inhibitory concentration (MIC) assessment was done for erythromycin (ERY), azithromycin (AZI), clindamycin (CL), tetracycline (TET), doxycycline (DOX), minocycline (MINO), and levofloxacin (LEVO). The four groups of patients were compared for any difference in the resistant strains. Results: Of the 52 P. acnes strains isolated (80 patients), high resistance was observed to AZI (100%), ERY (98%), CL (90.4%), DOX (44.2%), and TETs (30.8%). Low resistance was observed to MINO (1.9%) and LEVO (9.6%). Statistical difference was seen in the resistance between CL and TETs; DOX/LEVO and DOX/MINO (P < 0.001). High MIC90 (≥256 μg/ml) was seen with CL, macrolides, and TETs; moreover, low MIC90 was observed to DOX (16 μg/ml), MINO (8 μg/ml), and LEVO (4 μg/ml). Though the treatment group with isotretinoin/BPO had the least number of resistant strains there was no statistical difference in the antibiotic resistance among the various groups of patients. Conclusions: High resistance was seen among the P. acnes strains to macrolides-lincosamides (AZI and CL) while MINO and LEVO resistance was low.

Enhanced Antimicrobial Activity of Amine-Phosphonium (N-P) Hybrid Polymers Against Gram-Negative and Gram-Positive Bacteria

The authors report synthesis, characterization and evaluation of a series of linear polyethylenimine (lPEI)-grafted butyltriphenylphosphonium bromide (LBTP) polymers (N-P hybrid polymers) for their antimicrobial activity on various Gram-positive and Gram-negative bacteria. Polymers with ∼5.8–13.8% substitution of butyltriphenylphosphonium bromide (BTP) on the backbone of lPEI showed enhanced charge density as compared to native lPEI confirming the conjugation of BTP onto lPEI. These modified polymers displayed low hemolytic activity and excellent antimicrobial activity against these two types of bacteria with one of the modified polymers, LBTP-40, was found to exhibit high antimicrobial activity in all the strains. GRAPHICAL ABSTRACT

Synthesis and antibacterial activity screening of quaternary ammonium derivatives of triazolyl pyranochromenones

AbstractA series of quaternary ammonium derivatives of triazolyl pyranochromen-2-ones have been synthesized and characterized; their antibacterial potential were investigated against two gram negative (Pseudomonas aeruginosa and Escherichia coli) and two gram positive bacterial strains (Bacillus cereus and Staphylococcus aureus). In order to develop structure-activity relationship (SAR), the effect of varying the substituent (R) at the C-10 position of pyranochromen-2-one as well as the length of the spacer (n) between the triazolyl pyranochromen-2-ones and quaternary ammonium group, on the antibacterial activity of compounds has been evaluated. Some of the screened compounds exhibited antibacterial potential against the studied strains in the microgram range. Graphical AbstractA series of quaternary ammonium derivatives of triazolyl pyranochromen-2-ones have been synthesized, characterized AND their antibacterial potential investigated. In order to develop structure-activity relationship (SAR), the effect of varying the substituent (R) at the C-10 position of pyranochromen-2-one as well as the length of the spacer (n) between the triazolyl pyranochromen-2-ones and quaternary ammonium group, on the antibacterial activity of compounds has been evaluated.

Evaluation of antimicrobial efficacy of quaternized poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] against targeted pathogenic and multi-drug-resistant bacteria

Here, we have investigated in vitro antimicrobial efficacy of a quaternized cationic polymer, poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] (polyquaternium-2), against gram-positive as well as gram-negative bacteria along with several multi-drug-resistant bacterial strains. The antimicrobial efficacy of this polymer was first tested against some clinical pathogens followed by microorganisms isolated from acne lesions. Interestingly, polyquaternium-2 exhibited significant antimicrobial activity against methicillin-resistant Staphylococcus aureus, for which very limited drugs are available. Most importantly, the polymer displayed low haemolytic activity and non-toxic behaviour against mammalian cells. The results showed the promising potential of the projected polymer to be utilized as an antibacterial agent for various biomedical applications.

Zinc Oxide Nanoparticles Dispersed in Ionic Liquids Show High Antimicrobial Efficacy to Skin-Specific Bacteria

Zinc oxide (ZnO) nanoparticles have been shown in the literature to have antibacterial properties and have been widely used in antibacterial formulations. However, one of the problems with ZnO nanoparticles is their tendency to aggregate, thereby causing damage to normal cells and lowering their antibacterial efficacy during application. In this work, we have attempted to avoid this by using a combination of ZnO nanoparticles and ionic liquids, a class of low melting salts containing organic cations and organic/inorganic anions that show antibacterial property as well, and tested the antibacterial activity of this dispersion. ZnO nanoparticles of 60 nm were dispersed in two different ionic liquids-choline acetate (IL1) and 1-butyl-3-methylimidazolium chloride (IL2)-to achieve high dispersibility, whereas ZnO dispersed in phosphate-buffered saline was taken as a control. These dispersions were tested on four strains- Escherichia coli, Bacillus subtilis, Klebsiella pneumoniae, and Staphylococcus epidermidis. Maximum efficiency was obtained for ZnO nanoparticles dispersed in imidazolium-based ionic liquids against skin-specific S. epidermidis. Skin infections induced by S. epidermidis are prevalent in hospital-acquired diseases. In most cases, traditional antibiotic-based therapies fail to combat such infections. Our strategy of developing a dispersion of ZnO nanoparticles in ionic liquids shows superior antibacterial efficacy in comparison to that shown individually by ZnO nanoparticles or ionic liquids. We have also established that the mechanism of killing this skin-specific bacterium is possibly through the production of reactive oxygen species leading to bacterial cell lysis. Further, we showed that this formulation is biocompatible and nontoxic to normal keratinocyte cells even under coculture conditions.

Acetamide Derivatives of Chromen‐2‐ones as Potent Cholinesterase Inhibitors

Alzheimers disease (AD), a neurodegenerative disorder, is a serious medical issue worldwide with drastic social consequences. Inhibition of cholinesterase is one of the rational and effective approaches to retard the symptoms of AD and, hence, consistent efforts are being made to develop efficient anti‐cholinesterase agents. In pursuit of this, a series of 19 acetamide derivatives of chromen‐2‐ones were synthesized and evaluated for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory potential. All the synthesized compounds exhibited significant anti‐AChE and anti‐BChE activity, with IC50 values in the range of 0.24–10.19 μM and 0.64–30.08 μM, respectively, using donepezil hydrochloride as the standard. Out of 19 compounds screened, 3 compounds, viz. 22, 40, and 43, caused 50% inhibition of AChE at 0.24, 0.25, and 0.25 μM, respectively. A kinetic study revealed them to be mixed‐type inhibitors, binding with both the CAS and PAS sites of AChE. The above‐selected compounds were found to be effective inhibitors of AChE‐induced and self‐mediated Aβ1–42 aggregation. ADMET predictions demonstrated that these compounds may possess suitable blood–brain barrier (BBB) permeability. Hemolytic assay results revealed that these compounds did not lyse human RBCs up to a thousand times of their IC50 value. MTT assays performed for the shortlisted compounds showed them to be negligibly toxic after 24 h of treatment with the SH‐SY5Y neuroblastoma cells. These results provide insights for further optimization of the scaffolds for designing the next generation of compounds as lead cholinesterase inhibitors.

Amphiphilic azobenzene-neomycin conjugate self-assembles into nanostructures and transports plasmid DNA efficiently into the mammalian cells

The present study demonstrates the use of self-assembled nanostructures of cationic amphiphilic azobenzene-neomycin (a small molecule) conjugate, Azo-Neo, as delivery vector for plasmid DNA. These nanostructures efficiently condensed nucleic acid and formed more compact nanoassemblies. DLS analysis showed size and zeta potential of the resulting Azo-Neo/pDNA nanoassemblies ∼153.7nm and +7.26mV, respectively. The nanoassemblies were characterized by physicochemical techniques and evaluated for its toxicity and ability to deliver nucleic acid therapeutics. The flow cytometry results on MCF-7 and HEK293T cells revealed that Azo-Neo/pDNA nanoassemblies transfected ∼31% and 23% cells, respectively, at a w/w ratio of 250, while the standard transfection reagent, bPEI/pDNA complex, could transfect only ∼21% and 29% cells, respectively, at its best w:w ratio of 2.3. MTT and hemolysis assays showed the non-toxic nature of the projected nanoassemblies and nanostructures, respectively, at various concentrations. Further, Azo-Neo nanostructures showed efficient antibacterial activity against different strains, laboratory strain of Staphylococcus aureus (MTCC 740) as well as MRSA strains (Staphylococcus aureus ATCC 33591, ATCC 43300 and ATCC 700699). These results ensure the great potential of these nanostructures in gene delivery and antimicrobial applications.

Evaluation of antimicrobial activity and cytotoxicity of pegylated aminoglycosides

Here, in this study, we have investigated the antibacterial activity and cytotoxicity of pegylated aminoglycosides (gentamicin, kanamycin, and neomycin). The antibacterial activity of pegylated aminoglycosides, prepared in two different ratios (1:1 and 1:2, aminoglycoside:polyethylene glycol), was determined against some common pathogens, namely, Gram-positive (Bacillus cereus, Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa), by zone of inhibition and minimum inhibitory concentration assays. The activity of pegylated aminoglycosides was found to be decreased as compared to their respective native aminoglycosides. Moreover, aminoglycoside:polyethylene glycol (1:1) derivatives showed much higher activity as compared to aminoglycoside:polyethylene glycol (1:2) derivatives, that is, an increase in the content of polyethylene glycol decreased the activity considerably. This decrease in antibacterial activity was found to be the most prominent in Gram-positive bacteria, S. aureus. On the other hand, pegylation significantly decreased the cytotoxicity as determined by hemolysis and MTT assays. These results advocate exploration of different types of crosslinkers consisting of a small degree of amphiphilicity, which could facilitate better interactions with the bacterial cell membranes and inhibit induction of bacterial resistance.