Anticryptosporidial activity of ranalexin, lasalocid and azithromycin alone and in combination in cell lines

Molecular cloning and expression of ranalexin, a bioactive antimicrobial peptide from Rana catesbeiana in Escherichia coli and assessments of its biological activities

The coding sequence, which corresponds to the mature antimicrobial peptide ranalexin from the frog Rana catesbeiana, was chemically synthesized with preferred codons for expression in Escherichia coli. It was cloned into the vector pET32c (+) to express a thioredoxin-ranalexin fusion protein which was produced in soluble form in E. coli BL21 (DE3) induced under optimized conditions. After two purification steps through affinity chromatography, about 1 mg of the recombinant ranalexin was obtained from 1 L of culture. Mass spectrometrical analysis of the purified recombinant ranalexin demonstrated its identity with ranalexin. The purified recombinant ranalexin is biologically active. It showed antibacterial activities similar to those of the native peptide against Staphylococcus aureus, Streptococcus pyogenes, E. coli, and multidrug-resistant strains of S. aureus with minimum inhibitory concentration values between 8 and 128 μg/ml. The recombinant ranalexin is also cytotoxic in HeLa and COS7 human cancer cells (IC50 = 13-15 μg/ml).

Antimicrobial peptides from amphibians

Increased prevalence of multi-drug resistance in pathogens has encouraged researchers to focus on finding novel forms of anti-infective agents. Antimicrobial peptides (AMPs) found in animal secretions are components of host innate immune response and have survived eons of pathogen evolution. Thus, they are likely to be active against pathogens and even those that are resistant to conventional drugs. Many peptides have been isolated and shown to be effective against multi-drug resistant pathogens. More than 500 AMPs have been identified from amphibians. The abundance of AMPs in frog skin is remarkable and constitutes a rich source for design of novel pharmaceutical molecules. Expression and post-translational modifications, discovery, activities and probable therapeutic application prospects of amphibian AMPs will be discussed in this article.

[Molecular diversities and functions of antibacterial peptides from the skins of Ranidae of amphibians.]

Granular glands in the frog skins of Ranidae of amphibians, a widely distributed group with over 650 species, synthesize and secrete a remarkably diverse array of peptides with the broad-spectrum antibacterial, antifungal and other biologic activities to protect the organism against a wide range of pathogens, which are believed to have arisen as a result of multiple gene duplication events. Almost without exception, these components are hydrophobic, cationic and form an amphipathic a-helix in a membrane-mimetic solvent. The peptides can be grouped into families on the basis of structural similarity. To date, brevinin-1, esculentin-1, esculentin-2, and temporin peptides, ranalexin, ranatuerin-1, ranatuerin-2 and palustrin, brevinin-2, tigerinin, japonicin, nigrocin and melittin-related peptides have been found in amphibians of Ranidae. In this paper, the molecular diversity, structural feature and the biological ac-tivity of Ranidae antibacterial peptides were reviewed.

Antimicrobial peptides from ranid frogs: taxonomic and phylogenetic markers and a potential source of new therapeutic agents

Granular glands in the skins of frogs of the genus Rana, a widely distributed group with over 250 species, synthesize and secrete a remarkably diverse array of peptides with antimicrobial activity that are believed to have arisen as a result of multiple gene duplication events. Almost without exception, these components are hydrophobic, cationic and form an amphipathic alpha-helix in a membrane-mimetic solvent. The peptides can be grouped into families on the basis of structural similarity. To date, brevinin-1, esculentin-1, esculentin-2, and temporin peptides have been found in ranid frogs of both Eurasian and North American origin; ranalexin, ranatuerin-1, ranatuerin-2 and palustrin peptides only in N. American frogs; and brevinin-2, tigerinin, japonicin, nigrocin and melittin-related peptides only in Eurasian frogs. It is generally assumed that this structurally diversity serves to protect the organism against a wide range of pathogens but convincing evidence in support of this hypothesis is still required. The possibility that "antimicrobial peptides" fulfill additional or alternative biological functions should not be rejected. The molecular heterogeneity of the peptide families, particularly brevinin-1, brevinin-2 and ranatuerin-2, may be exploited for the purposes of unequivocal identification of specimens and for an understanding of phylogenetic interrelationships between species. The broad-spectrum antibacterial and antifungal activities of certain peptides, for example esculentin-1, ranalexin-1 and ranatuerin, together with their relatively low hemolytic activity, make them candidates for development into therapeutically useful anti-infective agents.

In vitro effect of short-term exposure to two synthetic peptides, alone or in combination with clarithromycin or rifabutin, on Cryptosporidium parvum infectivity

The viability of Cryptosporidium parvum after exposure to peptide antibiotics was studied by two different methods, a cell culture system and a double fluorogenic staining. The peptides KFFKFFKFF and IKFLKFLKFL exerted high cytotoxic effects on sporozoites, as demonstrated by cell cultures (complete inhibition after 60 min at 100 microg/ml) and flow cytometry (30% after 20 min at 100 microg/ml), but did not affect consistently the oocysts. Clarithromycin and rifabutin demonstrated less activity against sporozoites but higher activity against oocysts (30% after 180 min at 10 microg/ml). The combination between peptides and azithromycin or rifabutin exerted the highest activities.

Parasitic infections of the intestine

Intestinal protozoal infections cause significant disease not only in the tropics but also in immunocompromised hosts and returning travellers in the developed world. Precise diagnosis of protozoal intestinal infection by microscopy can be difficult. Enzyme immunoassays for antigen detection are being used for some protozoal infections with some limitations which will, it is hoped, be overcome by molecular techniques. Nucleic acid amplification techniques could help improve detection of microsporidial species, which are difficult to detect microscopically and allow differentiation between Entamoeba histolytica and Entamoeba dispar. Definitive treatment for Cryptosporidium parvum infection remains elusive but new drugs are being evaluated. Cessation of thiabendazole production should not affect therapy of intestinal nematode infections as potent alternative therapy is available.

Short-term exposure to membrane-active antibiotics inhibits Cryptosporidium parvum infection in cell culture

A cell culture system and double fluorogenic staining were used to study the susceptibility of Cryptosporidium parvum to membrane-active antibiotics. Buforin II and magainin II exerted a cytotoxic effect on sporozoites but did not consistently affect oocyst viability. Lasalocid and nigericin demonstrated less activity against sporozoites but reduced the infectivity of oocysts.