Activities of Synthetic Host Defense Propeptides Processed by Neutrophil Elastase - Book Report/Review Example

Editorial Report on In Vitro Activities of Synthetic Host Defense Propeptides Processed by Neutrophil Elastase against Cystic Fibrosis Pathogens Name Course Professor Institution Date Introduction Research on antimicrobial peptides (AMP) has received a lot of scholarly attention with major focus on the respiratory system. Since the initial findings in 1996 that epithelia present in the linings of the respiratory airways of patients suffering from cystic fibrosis did not eliminate the bacteria, there has been increased research attention on the antimicrobial factors of the air passage secretions and the role played by AMPs in the respiratory system (Devine and Hancock 2004). These findings have been corroborated by empirical findings on AMPs in other fields leading to significant breakthroughs in the study of physiological action of the peptides in the pulmonary tract (Jens-Michael and Kabelitz 2005). Specifically, studies have revealed that peptides play important roles in inflammation, tissue regeneration and host defense and are possibly involved in the pathogenesis of various diseases and development of anti-microbial drugs. Owing to the challenges encountered in sampling the airway surface fluid (ASF), studies on airway peptides have been limited to in vitro experiments (Devine and Hancock 2004). This report is based on an article titled In Vitro Activities of Synthetic Host Defense Propeptides Processed by Neutrophil Elastase against Cystic Fibrosis Pathogens authored in May 2011 by a team of fifteen researchers led by Stephane Desgrandes of the Centre for Synthesis and Chemical Biology; Royal College of Surgeons in Ireland. The article was published in the Antimicrobial Agents and Chemotherapy Journal which is affiliated to the American Society for Microbiology. Research objectives The general objective of the research was to investigate whether the antimicrobial and hemolytic actions of host defense peptides can be stringently controlled through its modification as propeptide. The study was focused on investigating the whether the natural defense mechanisms of the host defense peptides (HDP) can be used to develop a prodrug analogy utilizing neutrophil elastase (NE)against the pathogens involved in Cystic Fibrosis (CF). Background on Peptides It is essential to understand the structural and biochemical characteristics and importance of peptides as they are the fundamental components in the research. Peptides are biochemically active chemical compounds made up of amino acids consisting of an amide group between a carboxyl and an amine group in different amino acids. Peptides are joined together by peptide bonds and are named according to the number of peptide bonds forming the peptide chain. Peptides consisting of less than twenty peptide bonds are termed as oligopeptides while those with more than twenty peptide bonds are called polypeptides (Jens-Michael and Kabelitz 2005). There is controversy as to the size of peptides that qualifies it to become a protein. Depending on their characteristic features and the nature of the amino acids constituting them, peptides can be classified as either L-peptides or D-peptides. L-peptides are derived from amino acids which occur naturally and are degradable by enzymes while D-peptides are derived from artificial amino acids and are not degradable by enzymes (Devine and Hancock 2004). Antimicrobial activity of peptides: advantages and disadvantages A group of peptides termed as antimicrobial peptides (AMPs) have been known to act against bacteria and other susceptible organisms. The basic characteristic of most AMPs is the topological form in which the groups of cationic and hydrophobic amino acids are organized in distinct surface areas (Neote 2006). The ampipathic and cationic characteristic of the AMPs allows them to bind selectively on the negatively charged bacterial plasma membrane. The binding of AMPs on the bacterial plasma membrane leads to disruption of the bacteria functions since their membranes are highly negatively charged in relation to that of the host cells (Devine and Hancock 2004). Due to the electrostatic action of AMPs, they are physiologically active at high concentrations and low electrolyte concentrations (Neote 2006). There is sufficient evidence to support the action of antimicrobial peptides in defending the host against bacterial pathogens especially in the respiratory system. Antimicrobial peptides function as endogenous antimicrobial agents acting as the first line of host defense against respiratory pathogens (Jens-Michael and Kabelitz 2005). For instance, it has been established that the bacterial infection among patients diagnosed with cystic fibrosis is partly as a result of inactivity of the of the peptide-dependent antibacterial action due to the high salt concentration found in the bronco-tracheal fluid of such patients (Neote 2006). The anti-microbial benefit of peptides is largely due to their high selectivity which makes them more effectiveness against the frequent bacterial resistance to common antibiotics. Peptides are also selectively active against bacteria and do not adversely affect the hoist cells. Despite their benefits, peptides also have several limitations in their use against bacterial infections. Firs they are known to have a certain level of toxicity if used excessively. The use of peptides is also limited due to their rapid degradation in physiological conditions. Additionally, peptides do not exhibit biological activity when administered orally hence they have to be given through injection. Cystic Fibrosis and host defense in the human respiratory tract Cystic Fibrosis (CF) is a genetic disorder that affects the endocrine glands especially hose lining the respiratory pathway, pancreatic duct and intestinal lining. The disorder leads to a recurrent bacterial infection affecting the lungs manifesting as a blockage in the bronchial lining as a result of overproduction of mucus by the surrounding glands (Bjorklund 2008). CF is primarily caused by two different bacterial pathogens; Staphylococcus aureus and Pseudomonas aeroginosa. Of the two pathogens, pseudomonas aeroginosa is closely associated with CF in most patients as it has been found to secrete proteins into the extracellular membrane (Braun, Filloux and Tommassen 1996). The pathogenesis of CF is largely due to inflammation of the bronchial linings mediated by the action of the enzyme neutrophil elastase (NE) which is naturally secreted by the host (Neote 2006). The respiratory pathway is usually protected from infection by a combination of host defense mechanisms involving physical, structural and functional systems (Devine and Hancock 2004).The structural host defense in the respiratory tract is provided by the ciliated, small-granule and basal as well as goblet cells (Neote 2006). Antimicrobial peptides present in the lung epithelial lining are derived from epithelial cells or from defense cells like neutrophils and macrophages among others. The anti-inflammatory and defense mechanisms of the respiratory epithelium is due to several mechanisms which include secretion of pro-inflammatory and anti-inflammatory mediating agents and secretion of AMPs among other antimicrobial substances (McCormack 2010). For this reason, AMPs play a major role in the host defense along the airway especially in the case of Cystic Fibrosis. Inflammation in CF patients results from uncontrolled release of NE into the mucosal lining. Research methodology and techniques The research involved various experiments and procedures in order to prepare and analyze the samples. In order to mitigate the effects of excessive secretion of NE present in CF patients, a prodrug that acts analogously to the natural defense mechanism exerted on host defense peptides (HDPs) was suggested (Desgrandes et al 2011). A prodrug can be defined as a compound which is biologically inactive but has the potential of becoming an active drug after undergoing metabolism within the body (Desgrandes et al 2011). Structurally, a prodrug acts as a precursor of the active drug. In this research, the prodrug mimics the propeptide while the actual drug mimics the peptide. Structurally, the prodrug has higher activity than the actual drug. For a peptide to be biologically active, it has to exist in the form of an alpha-helical chain (Desgrandes et al 2011). The prodrug in this case is inactive and requires activation by bacteria and enzymes in order to be converted to the actual drug at the active site. Synthetic propeptides to be used in the study were prepared through HDP modification using an anionic pro-fragment. The synthetic propeptide; L-P18 used was salt-resistant, α-helical in structure and cecropin A-magainin 2-hybrid sequence (Desgrandes et al 2011). Assembly of the peptides was carried out through solid phase synthesis and purified through reverse-phase high-performance liquid chromatography whereas characterization was carried out through matrix-assisted laser desorption spectrometry (Desgrandes et al 2011). The procedure involved elongation of the parent propeptide sequenced at the N- terminal using trialanine linker as the substrate for the NE enzyme (Desgrandes et al 2011). Propeptides were also synthesized from 2-7 glutamic acids in order to cover the + 8 net charges which is the active form of the mature peptide (Desgrandes et al 2011). The antimicrobial activity of the peptides was assessed for Staphylococcus aureus and Pseudomonas aeroginos which are involved in CF (Desgrandes et al 2011). Susceptibility testing was also carried out using a pure form of human NE with concentrations between 0.075 and 0.15µg/ml which is relatively lower than that of sputum present among CF patients (Desgrandes et al 2011). Research findings The findings in this research marked an important breakthrough in the development of an effective therapy for Cystic Fibrosis. The research findings indicated that the propeptide exhibited low activity due to attenuation of its net charge and its hydrophobic nature (Desgrandes et al 2011). After analysis of samples with spectrometric techniques using purified NE, it was discovered that the enzyme hydrolyzes the bond between the two amino acids to generate a reactivated peptide (Desgrandes et al 2011). The synthetic enzyme had a significant Minimum Inhibitory Concentration (MIC) against Staphylococcus aureus. The findings of this research imply that the regulation of HDP by a propeptide can be extended in the development of HDP prodrugs to be targeted at the active sites for bacteria involved in the pathogenesis of CF (Desgrandes et al 2011). Conclusion and implications for future research The research findings lead to the substantial deduction that the antimicrobial and hemolytic activity of HDP can be controlled by the modification of the HDP as a propeptide with a reduced net charge which can subsequently be processed by the action of neutrophil elastase enzyme involved in the inflammatory and pathogenic mechanism of cystic fibrosis (Desgrandes et al 2011). A critical review of the research leads to the conclusion that the study has significant implications for future research. The research opens doors for further studies in the development of prodrugs which have similar effect as the actual antibiotic but is only activated at the site of infection. The prodrugs analogy in this study can be extended in treating a variety of serious infections due to their high specificity. References Bjorklund, R. 2008. Cystic Fibrosis. Singapore: Marshall Cavendish. Braun, P., Filloux A. & Tommassen J. 1996. Role of the propeptide in folding and secretion of elastase of Pseudomonas aeroginosa. Molecular Biology, vol. 19, no. 2, pp. 297-306. Desgrandes, S. et al. 2011. In vitro activities of synthetic of synthetic host defense propeptides processed by neutrophil elastase against cystic fibrosis pathogen. Antimicrobial Agents and Chemotherapy, vol. 55, no. 5, pp. 2487-2489. Devine, D. & Hancock R. E. 2004. Mammalian Host Defense Peptides. Cambridge: Cambridge University Press. Jens-Michael S. & Kabelitz, D. 2005. Mechanisms of Epithelial Defense. Basel, Switzerland: Karger Publishers. McCormack, F. X. 2010. Molecular Basis of Pulmonary Disease: Insights from Rare Lung Disorders. New York: Springer. Neote, K. 2006. Chemokine Biology: Basic Research and Clinical Application. London: Birkhäuser. Read More