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Antibiotic resistance and re-emergence of highly resistant pathogens is a grave concern everywhere and this has consequences for all kinds of human activities. Herein, we showed that N-palmitoylethanolamine-derived cationic lipid (cN16E) had a lower minimum inhibitory concentration (MIC) against both Gram-positive and Gram-negative bacteria when it was loaded with Butea monosperma seed lectin (BMSL). The analysis using lectin-FITC conjugate labelling indicated that the improved antibacterial activity of BMSL conjugation was due to bacterial cell surface glycan recognition. Live and dead staining experiments revealed that the BMSL-cN16E conjugate (BcN16E) exerts antibacterial activity by damaging the bacterial membrane. BcN16E antimicrobial activity was demonstrated using an infected zebrafish animal model because humans have 70 % genetic similarity to zebrafish. BcN16E therapeutic potential was established successfully by rescuing fish infected with uropathogenic Escherichia coli (UPEC). Remarkably, the rescued infected fish treated with BcN16E prevented reinfection without further therapy, indicating BcN16E immunomodulatory potential. Thus, the study examined the expression of immune-related genes, including tnfα, ifnγ, il-1ß, il-4, il-10, tlr-2, etc. There was a significant elevation in the expression of all these genes compared to control and fish treated with BMSL or cN16E alone. Interestingly, when the rescued zebrafish were reinfected with the same pathogen, the levels of expression of these genes were many folds higher than seen earlier. Radial immune diffusion analyses (RIA) using zebrafish serum revealed antibody production during the initial infection and treatment. Interestingly, reinfected fish had significant immunoprecipitation in RIA, a feature absent in the groups treated with cN16E, BMSL, and control. These results clearly show that the BcN16E complex not only rescued infected zebrafish but also conferred long-lasting protection in terms of immunomodulation that protects against multiple reinfections. The findings support that BcN16E has immense potential as a novel immunostimulant for various biomedical applications.

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Lectins are renowned for recognizing specific carbohydrates, but there is evidence that they can bind to other endogenous ligands. Therefore, lectin can be used as a carrier to recognize glycoconjugates on the cell surface. The anticancer, antibacterial, and immunomodulatory properties of some lectins are established. Metal nanoparticles (MNPs) have been used in various fields recently, but their documented toxicity has raised questions about their suitability for biomedical uses. The advantages of MNPs can be realized if we deliver the NPs to the site of action; as a result, NPs may achieve greater therapeutic efficiency at lower doses with less toxicity. The use of carbohydrate specificity by lectin MNPs conjugates for diagnostics and therapeutics was addressed. The review summarised the multidimensional application of lectins and described their potential for delivery of MNPs in future drug development.

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The disposition of a drug in a biological system may be altered by complex biological fluids; especially, protein binding to drugs influences their activity. Herein, we demonstrated a convenient method involving the noncovalent formulation of butea monosperma seed lectin (BMSL) with an antimicrobial lipid, cationic N-acylethanolamine (cNAE) to mitigate the serum protein interference. Fluorescence spectroscopy and molecular docking study revealed that cNAEs readily formed noncovalent complexes with serum protein, bovine serum albumin. The resulting complexes interfered with the antimicrobial activity of cNAEs. Strikingly, the noncovalent conjugates developed with BMSL and cNAEs (BcNAE) overcame the interference from serum protein and displayed remarkable antimicrobial activity against uropathogenic Escherichia coli (UPEC). Strikingly, the minimum inhibitory concentration (MIC) of the lectin conjugates (7.81 µM) was 4-fold lower than the MIC of pure cNAE. Mechanistic studies showed that BcNAE depolarized the bacterial membrane and affected the integrity to exert the antimicrobial activity. The membrane directed activities of BcNAE on UPEC efficiently eliminated the development of resistance even after 25 passages. The hemocompatibility results and the biosafety assessed in a zebrafish model suggested that BcNAE was nontoxic with good selectivity to bacteria. While testing the therapeutic efficacy against UPEC infected zebrafish, we found that 1× MIC cNAE is ineffective due to interference from biological fluids, which is in agreement with in vitro studies. Remarkably, the infected fish treated with 1× MIC BcNAE conjugates were rescued from infection and restored to the normal life in less than 9 h. Bacterial colony count assay revealed that BcNAE was more efficient in overcoming the biological fluid interference and eliminated the bacterial burden in infected zebrafish. Histopathology analysis supported that BcNAE treatment restored the pathological changes induced by UPEC and, thus, increased survival. The high antimicrobial intensity with limited chance for resistance development and potential to overcome biomolecular interference with a lack of toxicity enhance the merits of exploring lectin conjugates against infectious pathogens.

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The incompetence of conventional antibiotics against bacteria residing in biofilms demands newer therapeutic intervention. In this study, we demonstrated that the interaction between silver nanoparticles (AgNPs) and Butea monosperma seed lectin (BMSL) forms efficient surface-functionalized AgNPs with excellent antibiofilm competency against uropathogenic Escherichia coli (UPEC). The minimum biofilm inhibitory concentration (MBIC) of AgNPs and the BMSL-AgNP conjugate (BAgNP) against UPEC was 75 and 9.37 µM, respectively. The eight-fold reduction in the MBIC of AgNPs was attributed to lectin functionalization. The chemical modification of serine amino acids affects the hemagglutination activity of BMSL but not its interaction with the AgNPs. At the same time, AgNPs surface-functionalized with modified BMSL display poor antibiofilm activity. Molecular docking studies revealed that BMSL binds to galactose with a free energy of -5.72 kcal/mol, whereas the serine residue-modified BMSL showed the lowest free energy values, suggesting incompetence for binding galactose. These results showcase that the sugar binding site of BMSL aids in the adhesion of AgNPs to the biofilm matrix and disturbs the formation of the biofilm, which was confirmed by light microscopy using crystal violet staining. At 37.5 µM, BAgNPs also have the capability to eradicate preformed biofilm. As a proof of concept, UPEC biofilm prevention and eradication were demonstrated on a urinary catheter. A scanning electron microscopy study showed that BAgNPs prevent bacterial colonization and thereby curtail biofilm growth. In addition to antibiofilm activity, BAgNPs exert antibacterial activity at 18.75 µM, which is four-fold lower than the MIC of AgNPs. A mechanistic study revealed that BAgNPs affect the integrity of the bacterial outer membrane and generate an imbalance in the antioxidant defense, which induces cell death. The results highlight that lectin functionalization can be extended to other nanoparticles and different antibiotics to enhance their efficacy against drug-resistant bacteria.

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In this study, the endogenous lipid signalling molecules, N-myristoylethanolamine, were explored as a capping agent to synthesise stable silver nanoparticles (AgNPs) and Ag sulphide NPs (Ag2S NPs). Sulphidation of the AgNPs abolishes the surface plasmon resonance (SPR) maximum of AgNPs at 415 nm with concomitant changes in the SPR, indicating the formation of Ag2S NPs. Transmission electron microscopy revealed that the AgNPs and Ag2S NPs are spherical in shape with a size of 5-30 and 8-30 nm, respectively. AgNPs and Ag2S NPs exhibit antimicrobial activity against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentrations (MIC) of 25 and 50 µM for AgNPs and Ag2S NPs, respectively, were determined from resazurin microtitre plate assay. At or above MIC, both AgNPs and Ag2S NPs decrease the cell viability through the mechanism of membrane damage and generation of excess reactive oxygen species.

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Mercury exists in organic, inorganic, and elemental forms; all of them are highly toxic. A sensor which could detect all forms of mercury below the permissible level in environmental and biological samples would be advantageous. A facile method to synthesize N-acetyl cysteine capped cadmium selenide quantum dots (CdSe QDs) with an emission at 554 nm was reported. CdSe QDs showed high sensitivity and selectivity toward Hg in aqueous media as well as biological fluids like simulated cerebrospinal fluid, saliva, and urine, and also in natural fluids like juices of tomato, sugarcane, and lime. The sensing mechanism is attributed to the interactions between Hg and CdSe QDs inducing fluorescence quenching. The limit of detection is 1.62, 0.75, and 1.27 ppb for organic, inorganic and elemental mercury, respectively, which is below WHO guidelines. The suitability of the sensor for estimating Hg in biological fluids was demonstrated by recovery experiments. Besides sensing, a two color cell imaging method was developed employing CdSe QDs and acridine orange. Using this method, the uptake of Hg in living cells was demonstrated.