Peptide-based treatment with mesoporous silica particles for mycobacterial infections

Abstract

Tuberculosis (TB) and other mycobacterial infections have become more difficult to treat since the strains need to be screened for resistance. Furthermore, the half-year long treatment time could harm hepatocytes as a side effect of the treatment. This calls for discovery of new compounds for a successful treatment.

One such promising peptide was recently discovered and called NZX. In this study, the antimicrobial property of this peptide was tested on nontuberculous mycobacterial (NTM) strains. In addition, the peptide’s interaction with current TB drugs was tested to look for synergy. Most of the current TB drugs have low efficiency due to their inability to access live bacteria inside cellular compartments. To resolve this issue, we investigate mesoporous silica nanoparticles (MSN) as potential carriers for NZX, regard to cellular uptake and toxicity.

The results presented show that all NTMs tested were susceptible to NZX. However, even though no synergy was observed with the TB drugs, an additive effect was seen. Two different sized MSPs were tested by observing uptake pattern into macrophages and both were taken up efficiently. However, some cytotoxicity was seen for both particles.

Overall, NZX appears to be a good drug candidate for TB/mycobacterial infections. MSNs as drug-carrier has to be further explored.

Popular Abstract

Fungal peptide: A cure to mycobacterial infections?

Despite the decline in frequency of new tuberculosis cases, this disease is still recognized as the leading cause of death via an infectious agent. Effective drug treatment was first introduced in 1940s followed by discovery of other tuberculosis (TB) drugs in the coming years. Resistance to many of these drugs has been reported and the pursuit to find new drugs is eminent. Another prominent issue with TB drugs are their poor ability to enter white blood cells where the bacteria resides.

Antimicrobial peptides are small proteins produced by all living organisms and they are known to be a part of the immune system. In this thesis we worked with one such peptide named NZX discovered from Pseudoplectania nigrella. From previous studies we have proven that NZX can kill M. tuberculosis (Mtb) which causes TB. One part of this study was to understand its killing effect in other bacterial species, hence we tested out the peptide on nontuberculous mycobacteria (NTM), that are known for causing infections in lung and other organs. The latter part of this study involved analysing different sized mesoporous silica nanoparticles (MSNs) as a drug-carrier for intracellular killing of Mtb with NZX.

Fourteen NTM strains, originally isolated from patients, were treated with NZX to obtain minimum inhibitory concentration (MIC) per strain. MIC is defined as the lowest concentration of the drug at which bacteria stops growing. Treatment for NTM/TB involves multiple drug therapy. A set of experiments was performed to see interactions between NZX and the current TB drugs used. MSNs were evaluated for their potential drug-carrier role by looking at uptake of these cells into specific white blood cells. These particles were also screened for any toxic effects on human cells.

We observed promising results for NZX’s activity towards NTMs. Most strains tested against the peptide were killed at lower concentrations whereas some strains needed higher concentrations. Peptide was further tested on a gram-positive and gram-negative bacterium as well. Like NTM’s S. aureus (gram-positive) was killed at low concentrations, but no effect was observed for E. coli (gram-negative). An assay to examine interaction between NZX and current TB drugs was carried out and the results showed no synergy, but most had additive effect. However, neither of the drug combinations showed antagonism. Two MSNs, named after their diameter 1500 and 200, were analysed for uptake into white blood cells. Smaller particles were taken up faster and particles were picked up faster at higher concentrations. With higher concentrations toxic effect on cells was detected for both particles.

With the results obtained, NZX seems like an excellent candidate for both NTM/TB infections. We can also speculate a bit on the peptide’s process of killing from the varied results (MIC) seen within different NTM strains. Even though no synergistic property was observed for NZX, additive effect was seen with certain drugs. This opens up for the possibility to treat patients with lower drug concentrations and that could possibly improve their quality of life. Delivery of NZX via MSNs has proven to be beneficial as they are efficiently taken up by the cells. However, some cytotoxicity observed calls for careful use. In conclusion NZX’s therapeutic value has potential and the future of this project will be to understand its mode of action/killing.

Master’s Degree Project in Molecular Biology, 60 credits 2017-2018
Department of Biology, Lund University
Advisor: Gabriela Godaly
Advisors affiliation: Department: Division of Microbiology, Immunology and Glycobiology, BMC, Lund University.

• author: Umashankar Rao, Komal
• supervisor: Gabriela Godaly
• organization: Degree Projects in Molecular Biology
• course: MOBN03 20172
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8952947
• date added to LUP: 2018-06-26 08:37:20
• date last changed: 2018-06-26 08:37:20