Antimicrobial peptides (AMPs) have been identified as important therapeutic agents that can be developed as new multifunctional antibiotic compounds, which may address antibiotic resistance. AMPs have a wide range of bioactivities, including antimicrobial, antioxidant, anti-inflammatory and anticancer properties. Os and Os-C (a derivative of Os, lacking cysteine residues) are two synthetic AMPs derived from the tick defensin OsDef2 which have been shown to have antibacterial, antioxidant and anti-inflammatory activity. Differences in bacterial killing times between these peptides indicate differences in the modes of bacterial killing. For the further development of Os and Os-C for therapeutic application, the aim of this study was to establish the mode of bacterial killing, to determine if these peptides are cytotoxic to human erythrocytes and leukocytes. Lastly, to determine if these peptides have additional beneficial cellular effects such as antioxidant activity. Ultrastructural analysis with electron microscopy techniques revealed that both peptides adversely affected the membranes and intracellular structures of both Gram-negative Escherichia coli and Gram-positive Bacillus subtilis bacteria. Effects included membrane ruffling, cytoplasmic retraction, intracellular granulation and the formation of dense fibres. At the minimum bactericidal concentrations (MBCs) of 0.77 μM for Os and 1.74 μM for Os-C membrane permeabilisation measured with the SYTOX green assay was found not to be the principle mode of action. In stationary phase bacteria, fluorescent triple staining showed that both peptides caused permeabilisation. Studies using fluorescently labelled peptides revealed that the membrane penetrating activities of Os and Os-C were similar to buforin II, a cell-penetrating peptide. Os was able to enter stationary phase E. coli and B. subtilis while Os-C was unable to enter E. coli cells and accumulated on B. subtilis septa. Using plasmid binding and fluorescence displacement assays both peptides could bind DNA, while a dosage effect was only observed for Os. Evaluation of cytotoxicity revealed that Os and Os-C caused no erythrocyte haemolysis or changes to erythrocyte morphology. Only the highest concentration of Os (100 μM), which is 130 fold greater than the MBC for E. coli and B. subtilis, caused cellular damage to peripheral mononuclear (MN) and polymorphonuclear (PMN) cells. In contrast, Os-C caused leukocyte activation identified by associated morphological features and reactive oxygen species (ROS) formation. Chemical and erythrocyte antioxidant assays indicated that both Os and Os-C had antioxidant activity. Both peptides provided extracellular protection of erythrocytes against 2,2'-azobis(2-amidinopropane) dihydrochloride induced oxidative damage. In MN and PMN cells Os showed low levels of antioxidant activity while Os-C had minimal activity. In conclusion, both peptides showed a dual mechanism of bacterial killing, targeting both the membrane and intracellular elements. Os had a predominant membrane effect while Os-C targeted the septa of B. subtilis and had a higher affinity for DNA. Cytotoxicity in erythrocytes and leukocytes was minimal. In addition, Os exhibited antioxidant properties while Os-C caused leukocyte activation. Both peptides have been identified as promising therapeutic agents although activity in plasma and the effect on coagulation must still be determined. / Thesis (PhD)--University of Pretoria, 2017. / Anatomy / PhD / Unrestricted

Since ticks are classified as hematophagous ectoparasites, the primary feeding event involves a bloodmeal on a vertebrate host. Such activities facilitate the ingestion of microorganisms which may be detrimental to the survival of a tick. It is observed, however, that ticks are able to survive such invasion by microorganisms and in several cases, facilitate the transmission of pathogens, while themselves remaining unaffected. This phenomenon is attributed to the innate immune system of ticks. The focus of this project is on stimulus-induced immunoreactive peptides known as antimicrobial peptides. In chapter 2, an attempt was made to identify a homolog of the anti Gram-positive and bacteriostatic peptide microplusin, in the salivary glands of the argasid tick Ornithodoros savignyi. It was reported previously that tissue and life stage specific expression of this transcript occurs in the fat body of adult, fully fed, female Rhipicephalus (Boophilus) microplus ticks. The positive control used for this study was unsuccessful due to the incorrect tissue and life stage of R. (B.) microplus ticks. No significant homolog was identified due to the possible existence of stringent regulation of expression as well as differences in the induction stimuli between argasid and ixodid ticks. Lysozyme catalyzes the cleavage of the β-1,4 glycosidic bond between N-acetyl muramic acid and N-acetyl glucosamine of the peptidoglycan layer of bacterial cell walls affording the molecule antibacterial activity. In argasid ticks, lysozyme was observed to be induced by feeding. In chapter 3, an attempt was made to elucidate the O. savignyi homolog of the O. moubata lysozyme molecule. The partial sequence obtained revealed the presence of a lysozyme homolog in O. savignyi. The tissue expression profile revealed constitutive expression in the midgut and ovaries and induction of transcription in the hemolymph upon feeding. In salivary glands, upregulation was observed following ingestion of Gram-positive bacteria. In chapter 4, the tissue expression profile of O. savignyi defensin was investigated. It was found that transcription is induced following the ingestion of Gram-positive bacteria, while in the hemolymph upregulation was observed upon feeding. Furthermore, chapter 4 saw the attempts made at the RNAi mediated silencing of the lysozyme and defensin transcripts. Silencing, analysed by real time PCR, was not efficient as no statistically significant silencing was observed. Observation of the phenotype revealed mortality. However, statistical analysis of silencing revealed that the mortality observed was not due to silencing, but non-specific and possibly the result of injury during injection. Overall, the abovementioned experiments revealed the tissue specificity of expression of ixodid microplusin and that a more strategic approach is required for the elucidation of the argasid homolog. The partial O. savignyi lysozyme sequence was elucidated together with the tissue expression profile of this molecule and O. savignyi defensin. The RNAi experiments require optimization for future studies. / Dissertation (MSc)--University of Pretoria, 2010. / Biochemistry / unrestricted

Overuse of conventional antibiotics has led to increased multidrug resistant micro-organisms. Therefore, development of alternative drugs with new mechanisms of action in the control of resistant micro-organisms is urgently needed. Defensins, one of the larger groups of naturally occurring antimicrobial peptides (AMPs), found in a variety of species, may serve as templates for the development of novel therapeutic agents. The work completed in this study is based on an antimicrobial peptide (AMP), Os, derived from the C-terminus of a tick Ornithodoros savignyi defensin isoform 2 (OsDef2). OsDef2 was found to be active against Gram-positive bacteria only, whereas Os, showed bactericidal activity towards both Gram-positive and Gram-negative bacteria. In this study a series of synthetic shorter peptides, based on the sequence of Os, was utilised in order to determine whether shorter peptides would retain their antibacterial activity and selectivity. Initial screening indicated that only two fragments, Os(3-12) and Os(11-22), were active towards the tested Gram-negative and Gram-positive bacteria. The minimum bactericidal concentrations (MBCs) of the two fragments were determined and ranged from 30 μg/ml to 120 μg/ml. The MBCs of the parent peptide, Os (1.88 to 15 μg/ml), was considerably lower than that of Os(3-12) and Os(11-22). As previously observed for Os, neither of the peptides showed cytotoxic effects towards eukaryotic cells. The amidated analogue of one of the active peptides, Os(11-22)NH2, was further evaluated in terms of its secondary structure, antibacterial and antioxidant activities as well as cytotoxicity. Amidation increased the activity of Os(11-22) 16 fold towards B. subtilis (MBC of 1.88 μg/ml) and 32 fold towards both Escherichia coli and Pseudomonas aeruginosa (MBC of 3.75 μg/ml), whereas a 2 fold decrease in activity was observed against Staphylococcus aureus (MBC of 60 μg/ml). Circular dichroism data showed that amidation altered the secondary structure of Os(11-22) from α-helical to mostly random coiled. In the presence of 30% serum the activity of Os(11-22)NH2 unexpectedly increased 8 fold against S. aureus (MBC of 7.5 μg/ml), but decreased 32 fold against E. coli (MBC of 120 μg/ml). The activity of Os(11-22)NH2 in 100 mM NaCl decreased 4 fold against E. coli (MBC of 15 μg/ml), but was completely lost (MBC >120 μg/ml) against S. aureus. The kinetics of bactericidal activity indicated that Os(11-22)NH2 killed B. subtilis and E. coli within 30 min and 120 min, respectively, whereas Os killed both bacteria within 5 min. Even at high concentrations Os(Os(11-22)NH2 was non-toxic towards human erythrocytes and SC-1 cells, moreover an increase in SC-1 cell number was observed at 120 μg/ml. The peptide showed strong antioxidant activity and was found to be 4 fold more active than glutathione (GSH), however Os was 3.4 fold more antioxidative than Os(11-22)NH2. Os(11-22)NH2 can be considered a dual functional peptide, since it possesses both antibacterial and antioxidant activity. The amidated peptide has the potential for use against the damaging effects of oxidative stress associated with infectious diseases and recovery of chronic wounds. Further investigation into structure-function properties of Os(11-22)NH2 is necessary. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Biochemistry / Unrestricted

Bakterier som är resistenta mot antibiotika har de senaste åren blivit ett stort hot mot mänskligheten. Att utveckla nya antibiotikaläkemedel är väldigt tidskrävande samt kommer med en dyr prislapp. Det är några av anledningarna att forskare har inriktat sig på antimikrobiella peptider (AMPs) som ett alternativ till traditionella antibiotika. Dessa peptider finns i alla levande organismer och uppvisar en snabb och ospecifik mekanism. Vidare så är de mindre benägna att utveckla resistens hos bakterierna. Däremot så har dessa AMPar visat sig ha låg stabilitet och en del toxiska biverkningar. Olika typer av nanobärare kan användas för att överkomma dessa kommakortanden. Syftet med denna studie var att utveckla en optimerad nanobärare för AMPen AP114. Peptiden har blivit inkluderad i nanostrukturerade lipidbärare (NLC) samt liposomer. Dessa har producerats med smält emulsifieringsmetod och lösningsinjektion metoden. De fysikalkemiska karaktäristik hos olika blanka samt AP115 laddade nanoformuleringar har analyserats samt jämförts. Resultaten indikerade att liposomformuleringarna hade den lägsta partikelstorleken och storleksfördelning men en kontrollerad in vitro frisättning av peptiden över 48 timmar. Generellt, så indikerar de preliminära resultaten en potential nanoformulering för peptiden AP114. / In the past few years, bacterial resistance to antibiotics has posed a major threat to humankind. Development of substitutes for traditional antibiotics is a highly time consuming and expensive venture. For this reason, researchers are focusing on using antimicrobial peptides (AMP) as an alternate. These peptides are found in all living organisms and exhibit a fast and non-targeted mechanism of action. Besides, they are less susceptible to microbial resistance. However, these therapeutic peptides are not stable and have toxic side effects. To overcome these limitations, drug delivery systems have been explored. In this study, the aim was to develop an optimized drug delivery system for AP114. The peptide has been encapsulated in nanostructured lipid carriers (NLC) and liposomes, produced by melt emulsification method and solvent injection method, respectively. The physicochemical characterization of different blank and AP114 loaded nanoformulations were analyzed and compared. The results indicated the liposome samples to have the lowest particle size distribution and polydispersity, with a controlled in vitro release of the peptide over 48 hours. Overall, these preliminary findings suggest a promising potential for the formulation of a nanocarrier for AP114 peptide.

The designer proline-rich antimicrobial peptide (PrAMP) Chex1-Arg20 amide (ARV-1502) is active against Gram-negative and Gram-positive pathogens in differentmurine infection models when administered parenterally and possesses a wide therapeutic index. Here we studied the pharmacokinetics of ARV-1502 for the first time when administered intramuscularly or intravenously (IV) in Sprague Dawley rats and Beagle dogs. First, a specific and robust quantitation method relying on parallel reaction monitoring (PRM) using a high-resolution hybrid quadrupole-Orbitrap mass spectrometer coupled on-line to reversed-phase uHPLC was established and validated. The limit of detection was 2 ng/mL and the limit of quantitation was 4 ng/mL when spiked to pooled rat and dog plasma. When ARV-1502 was administered IV at doses of 75 and 250 μg/kg in dogs and rats, the plasma concentrations were 0.7 and 3.4μg/mL 2min post-administration, respectively. ARV-1502 plasma concentrations declined exponentially reaching levels between 2 and 4 ng/mL after 2 h. Intramuscular administration of 0.75 mg/kg in dogs and 2.5 mg/kg in rats resulted in a different pharmacokinetics profile. The plasma concentrations peaked at 15min post-injection at 1μg/mL (dogs) and 12μg/mL (rats) and decreased exponentially within 3 h to 4 and 16 ng/mL, respectively. The initial plasma concentrations of ARV-1502 and the decay timing afterwards indicated that the peptide circulated in the blood stream for several hours, at some point above the minimal inhibitory concentration against multidrug-resistant Enterobacteriaceae, with blood concentrations sufficient to suppress bacterial growth and to modulate the immune system.