NEW THERAPEUTIC PROPOSALS IN THE FIGHT AGAINST ANTIBIOTIC RESISTANCE

SUMMARY

Ever since bacteria have developed resistance to multiple drugs, both clinical and pharmaceutical, efforts have been made to confront these new strains, with ever decreasing success. Advances in other areas, such as nanotechnology, have led to innovations and improvements in the way medicine is applied. An example of this is nanoparticles, which are used in implantable devices and other types of supplies, as well as in the most recently studied system for delivering anti-cancer and antimicrobial drugs. In the latter case, the results have been very favorable for both grampositive and gram-negative bacteria and multi-resistant strains. Recent research has found the important role that “lipid rafts” play in the behavior of multiple bacteria resistant to methicillin, so attacking these microdomains of the membrane with hypolipemiants seems to be an excellent proposal. As for antimicrobial peptides, a response against organisms such as E. coli and S. aureus has also been found, but the specifics in each case are still being investigated, in the aim of determining and modifying the appropriate one. Results seem to indicate that they have a higher sensitivity in studies performed ex vivo.

Keywords: Resistance, antibiotics, nanoparticles, lipid rafts, peptides

INTRODUCTION

Bacterial infections are one of the most frequent causes of morbidity in the world, constituting one of the main reasons for consultations at the first level of care and one of the major complications at the surgical and intrahospital stage. They represent a permanent enemy to human health that will accompany us for as long as we inhabit planet Earth, where they are present in virtually every environment or surface (Belloso, 2009).

Since Fleming and the discovery of antibiotics, however, humanity has had something with which to defend itself (at least until now). Antibiotics are our weapons in fighting infectious processes that in former times were complicated or simply incurable, and that claimed the millions of lives. The impact of these drugs has been such that, since their development, human life expectancy has increased significantly. Their effectiveness and validity are a cornerstone for the survival of our species, and essential to maintaining the stability and lifestyles of human societies today (Belloso, 2009).

There are different kinds of antibiotics and they act in different ways, fulfilling specific functions in accord with the infectious agents they are intended to fight. They are therefore classified according to their chemical composition and their therapeutic use, acting as they do in different sites and on different structural or functional levels of the bacteria they seek to eradicate (see Table 1).

Over time, however, bacteria have managed to adapt to these drugs, diminishing their therapeutic efficacy. This phenomenon is known as bacterial resistance: one of the greatest threats to and challenges for humanity in the short and medium term.

Table 1.- Families of antibiotics: action and resistance mechanisms. Source: Wang et al., 2019 and Daza, 2019.

NANOPARTICLES (NP)

One of the main fields of action of nanotechnology has been medicine. From their use in anti-cancer drug delivery systems to their antimicrobial potential in the treatment of infections, nanoparticles have become one of the most promising areas of study in recent decades.

If you were to define a “nanoparticle,” you might say that it is a nano-object that takes place in all three dimensions and that its size can range from 1 to 100 nanometers. In other words, they are particles smaller than a grain of sand or the diameter of a pin (Lee et al., 2015).

One of the most studied NPs are silver nanoparticles, which are widely used in gauze for burns and in the coatings of implantable devices and dental materials (Pelgrift et al., 2013). Other very promising ones are iron oxide nanoparticles, which have demonstrated bacteriostatic activity against E. coli (Gabrielyan et al., 2020).

Studies show, however, that the morphology of these nanoparticles is especially important to their antimicrobial activity. The study by Ayala-Nuñez et al. (2009) reported that the cytotoxic effect with PN below 10 nm was more effective against methicillin-resistant S. aureus (MRSA) than with sizes above 30-40 or 100 nm. Other studies, such as Gao et al. (2013), revealed that the silver nanospheres showed greater activity against bacteria than in their triangular shape.

Although they are not antibiotics, we can affirm that they act in both gram-positive and gram-negative bacteria. The interaction with gram-positive bacteria, however, is stronger, as their cell wall is thinner and more negative, which attracts more NP (Wang et al., 2017). Studies have been conducted with very common bacteria such as St. aureus, E. coli, Salmonella typhimurium, and other multi-resistant strains, and the results obtained have been very encouraging, so nanoparticles are considered the future of medicine for bacterial resistance (Gabrielyan et al., 2020).

Studies by Gabrielyan et al. (2020) show that, with doses of 10 μg mL-1 of these silver NPs, there is considerable bactericidal activity against E. coli. Some studies have even reported that certain nanoparticles have antifungal effects. One example is chitosan, which inhibits the mycelial growth and spore germination of Colletotrichum gloeosporioides and Alternaria species (Barrera-Necha et al., 2018).

Studies on the mechanisms of action of different nanoparticles have revealed evidence of damage to the bacterial cell wall and increased production of reactive oxygen species (ROS), which produce oxidative stress and cell death (Wang et al., 2017). They also intervene in DNA transcription, inhibiting protein synthesis and the electron transport chain (Pelgrift et al., 2016). A recent study showed that silver NP affected the enzyme FOF1-ATPase in the E. coli membrane, when no activity was detected. The interruption of the activity confers bactericidal effects on this nanoparticle (Gabrielyan et al., 2020).

Among the attributes of PNs reported so far is their ability to produce synergies with conventional antibiotics. Railean-Plugaru et al. (2016) biosynthesized silver NP, used in combination with commercial antibiotics, on bacteria such as K. pneumonia, S. aureus, P. aeruginosa, S. infantis, and P. mirabilis, and concluded that there was an improvement in effect with this synergy.

In addition to their many properties, silver NPs have also shown some adverse effects, mainly in the human keratinocyte cell line, but low doses have a safe profile for these cells (Nakamura et al., 2019). Similarly, other in vitro studies have reported that increased ROS, which are so important in the mechanism of action against bacteria, may affect certain cells in the body and induce apoptosis by the resulting cytotoxicity (Akter et al., 2017). It should be remembered, however, that results so far have been obtained through in vitro studies: much more needs to be done with human subjects in the future.

LIPID RAFTS

These are microdomains made from phospholipids characteristic of the cell’s bilayer, which take advantage of the bilayer’s property as a two-dimensional neutral solvent, favoring the mobility of membrane lipids and proteins and varying in its composition to form glycolipids, sphingolipids, and gangliosides from a sphingoid base, a fatty acid, a neutral polysaccharide head and, according to recent works by Dalton, one or more sialic acid units (Rodríguez and Rodríguez, 2014).

This characteristic has been successfully adapted by various bacteria to resist antibiotic attacks against the membrane. Recent work by the Centro Nacional de Biotecnología in Spain and the Consejo Superior de Investigaciones Científicas (the Spanish Research Council, known by its acronym CSIC) have studied the intervention of these microdomains (“lipid rafts”) present in the bacterium Straphylococcus aureus methicillinresistant (Aguayo-Reyes et al., 2018), by which they activate the PBP2a protein at membrane level, which is the main transpeptidase responsible for this resistance by the bacteria They do so by favoring the crossing of peptidoglycan (PG) strands, particularly between the side chains of amino acid nature with N-acetylmuramic acid binding, preventing its osmotic lysis and membrane commitment.

Following these studies, a new therapeutic perspective has come to light: the use of hypolipemics (statins) to make the pathogen vulnerable and then to act in combination with the antibiotic agent (oxacillin). The panorama has been favorable in trials with mice, which were able to combat the pathogen efficiently and increase their survival (García-Fernández et al., 2017).

PEPTIDES

Antimicrobial peptides (AMPS) may be defined as peptides produced by the immune system for the general protection of the human body against gram-positive and gram-negative bacteria, as well as fungi and viruses, which can be found in different sequences and forms of life, generally formed as either hydrophilic or hydrophobic. They can spread the activation of defense cells by inducing molecules in the case of a potent infection (Sharma et al., 2018).

According to a 2019 study in which different peptides were evaluated, ordered from higher to lower by hydrophobicity level, students in the department of biochemistry and biological sciences of the Universidad Nacional de Litoral in Argentina demonstrated the effectiveness of the Hcl-15 peptide for the inhibition of two very important bacterial strains within the current clinical panorama (E. coli and S. aureus), in which the specific characteristics of the peptides were also evaluated. It was also concluded that they could be used in resistant gram-positive and gram-negative strains, which constitutes an important advance in the technologies of bacterial resistance reduction (Simonutti et al., 2019).

Many of the peptides are under ongoing study to assess their efficacy against various existing pathogens. Peptide 25, for example, has been investigated against resistant cases of C. albicans and Trychophyton rubrum in both in vivo and ex vivo studies. Greater activity was demonstrated in ex vivo studies. Nevertheless, factors such as toxicity, study stability problems, and manufacturing costs should also be considered, considering the studies that are being conducted. It can be affirmed, nevertheless, that synthetic short antimicrobial peptides have great potential as a major area of research and innovation in connection with current technologies (Sharma et al., 2018).

CONCLUSION

The potential antimicrobial effect of nanoparticles, lipid rafts, and peptides has been briefly described above. Each one of these new technologies presents different challenges, which are still being studied. The perspective is encouraging, both now and in the future, as regards the highly resistant bacterial strains that are constantly developing. More detailed studies can be expected to explore their adverse effects, action mechanisms, and antimicrobial spectrum.

Dr. en C. Tonatiuh González Heredia

is coordinator of the post-graduate program in multidisciplinary health research and a category-A research professor at the Centro Universitario de Tonalá of the Universidad de Guadalajara.

David Alejandro Montaño Sánchez

is a student in medicine at CUTonalá, where he is currently deputy director of biochemistry laboratory instructions.

Andrea Neftalí Gaeta Tinoco / Cecilia Isabel Acosta Lemus

are both students in the medical surgery and obstetrics program of the Universidad de Guadalajara (CUTonalá), academic coordinators of the Resfuerzo Intersemestral para Alumnos de Pregrado (RIAP), and logistical coordinators of the Congreso de Urgencias Médico Quirúrgicas (CUMEQ) and the Ciclo de Integración Clínica Médica (CICMED).

References

Aguayo-Reyes, M. Alejandro, Quezada-Aguiluz, S. Mella, G. Riedel, A. Opazo-Capurro, H. Bello-Toledo, M. Domínguez, and G. González-Rocha. (2018). Bases moleculares de la resistencia a meticilina en Staphylococcus aureus. Revista chilena de infectología, 35(1), 7-14. https://dx.doi.org/10.4067/s071610182018000100007

Akter, M., M. T. Sikder, M. M. Rahman, A. Ullah, K. Hossain, S. Banik, T. Hosokawa, T. Saito, and M. Kurasaki. (2017). A systematic review on silver nanoparticles-induced cytotoxicity: Physicochemical properties and perspectives. Journal of advanced research, 9, 1–16. https://doi.org/10.1016/j. jare.2017.10.008

Ayala-Núñez N. V., H.H. Lara, T. L. Ixtepan, and P. C. Rodríguez. (2009). Silver nanoparticles toxicity and bactericidal efect against methicillin-resistant Staphylococcus aureus: nanoscale does matter. Nanobiotechnol 5:2–9. https://doi.org/10.1007/s12030-009-9029-1

Barrera-Necha, L., Z. Correa-Pacheco, S. Bautista-Baños, M. Hernández-López, J. Jiménez, and A. Mejía. (2018). Synthesis and Characterization of Chitosan Nanoparticles Loaded Botanical Extracts with Antifungal Activity on Colletotrichum gloeosporioides and Alternaria species. Advances in Microbiology, 8, 286-296. doi: 10.4236/aim.2018.84019

Belloso, W. H. (2009). Historia de los antibióticos. Rev Hosp Ital B Aires Dic, 29, 102-11. Daza, A. M. (2019). Mecanismos de resistencia a antibióticos de microorganismos patógenos de prioridad. http://147.96.70.122/Web/TFG/TFG/Memoria/ALEJANDRO%20MARTIN%20DAZA.pdf

Gabrielyan, L., H. Badalyan, V. Gevorgyan, et al. (2020). Comparable antibacterial effects and action mechanisms of silver and iron oxide nanoparticles on Escherichia coli and Salmonella typhimurium. Sci Rep 10, 13145. https://doi.org/10.1038/s41598-020-70211-x

Gao M., L. Sun, Z. Wang, and Y. Zhao. (2013). Controlled synthesis of Ag nanoparticles with different morphologies and their antibacterial properties. Mater Sci Eng C Mater Biol Appl 33:397-404.

García-Fernández, E., G. Koch, R. M. Wagner, A. Fekete, S. T. Stengel, J. Schneider, B. Mielich-Suss, S. Geibel, S. M. Markert, C. Stigloher, and D. López. (2017) Membrane Microdomain Disassembly Inhibits MRSA Antibiotic Resistance. Cell. DOI: 10.1016/j.cell.2017.10.012

Lee, B. K., Y. H. Yun, and K. Park. (2015). Smart Nanoparticles for Drug Delivery: Boundaries and Opportunities. Chemical Engineering Science, 125, 158–164. https://doi.org/10.1016/j.ces.2014.06.042

Nakamura, S., M. Sato, Y. Sato, N. Ando, T. Takayama, M. Fujita, and M. Ishihara. (2019). Synthesis and Application of Silver Nanoparticles (Ag NPs) for the Prevention of Infection in Healthcare Workers. International Journal of Molecular Sciences, 20(15), 3620. https://doi.org/10.3390/ijms20153620

Pelgrift, R. Y. and A. J. Friedman. (2013). Nanotechnology as a therapeutic tool to combat microbial resistance. Advanced Drug Delivery Reviews, 65(13-14), 1803-1815. https://doi.org/10.1016/j. addr.2013.07.011

Railean-Plugaru, V., P. Pomastowski, M. Wypij, M. Szultka-Mlynska, K. Rafinska, P. Golinska, H. Dahm, and B. Buszewski. (2016). Study of silver nanoparticles synthesized by acidophilic strain of Actinobacteria isolated from the of Picea sitchensis forest soil. Journal of Applied Microbiology, 120(5), 1250-1263. https://doi.org/10.1111/jam.13093

Rodríguez Padrón, D. and J. Rodríguez Padrón. (2014). Microdominios o balsas lipídicas. Correo Científico Médico, 18(3), 529-531.

Sharma, K., S. Aaghaz, K. Shenmar, and R. Jain. (2018). Short Antimicrobial Peptides. Recent Patents on Anti-Infective Drug Discovery, 13(1), 12-52. https://doi.org/10.2174/1574891x13666180628105928

Simonutti, V. L. (2019). Péptidos antimicrobianos como agentes terapéuticos para el tratamiento de enfermedades infecciosas. Universidad Nacional de Litoral.

Wang, L., C. Hu, and L. Shao. (2017). The antimicrobial activity of nanoparticles: present situation and prospects for the future. International Journal of Nanomedicine, 12, 1227-1249. https://doi.org/10.2147/ IJN.S121956

Wang, T. Z., R. Kodiyanplakkal, and D. P. Calfee. (2019). Antimicrobial resistance in nephrology. Nature Reviews. Nephrology, 15(8), 463-481. https://doi.org/10.1038/s41581-019-0150-7