Fungal cell membrane-promising drug target for antifungal therapy

Increase in invasive fungal infections over the past few years especially in immunocompromised patients prompted the search for new antifungal agents with improved efficacy. Current antifungal armoury includes very few effective drugs like Amphotericin B; new generation azoles, including voriconazole and posaconazole; echinocandins like caspofungin and micafungin to name a few. Azole class of antifungals which target the fungal cell membrane are the first choice of treatment for many years because of their effectiveness. As the fungal cell membrane is predominantly made up of sterols, glycerophospholipids and sphingolipids, the role of lipids in pathogenesis and target identification for improved therapeutics were largely pursued by researchers during the last few years. Present review focuses on cell membrane as an antifungal target with emphasis on membrane biogenesis, structure and function of cell membrane, cell membrane inhibitors, screening assays, recent advances and future prospects.

Mechanism of action of novel synthetic dodecapeptides against Candida albicans

BACKGROUND

Three de novo designed low molecular weight cationic peptides (IJ2, IJ3 and IJ4) containing an unnatural amino acid α,β-didehydrophenylalanine (∆Phe) exhibited potent antifungal activity against fluconazole (FLC) sensitive and resistant clinical isolates of Candida albicans as well as non-albicans and other yeast and filamentous pathogenic fungi. In the present study, their synthesis, susceptibility of different fungi and the mechanism of anti-candidal action have been elucidated.

METHODS

The antimicrobial peptides (AMPs) were synthesized by solid-phase method and checked for antifungal activity against different yeasts and fungi by broth microdilution method. Anti-candidal mode of action of the peptides was investigated through detecting membrane permeabilization by confocal microscopy, Reactive Oxygen Species (ROS) generation by fluorometry, apoptosis and necrosis by flow cytometry and cell wall damage using Scanning and Transmission Electron Microscopy.

RESULTS AND CONCLUSIONS

The MIC of the peptides against C. albicans and other yeast and filamentous fungal pathogens ranged between 3.91 and 250μM. All three peptides exhibited effect on multiple targets in C. albicans including disruption of cell wall structures, compromised cell membrane permeability leading to their enhanced entry into the cells, accumulation of ROS and induction of apoptosis. The peptides also showed synergistic effect when used in combination with fluconazole (FLC) and caspofungin (CAS) against C. albicans.

GENERAL SIGNIFICANCE

The study suggests that the AMPs alone or in combination with conventional antifungals hold promise for the control of fungal pathogens, and need to be further explored for treatment of fungal infections.

A biochemical correlate of dimorphism in a zygomycete Benjaminiella poitrasii: characterization of purified NAD-dependent glutamate dehydrogenase, a target for antifungal agents

The fungal organisms, especially pathogens, change their vegetative (Y, unicellular yeast and H, hypha) morphology reversibly for survival and proliferation in the host environment. NAD-dependent glutamate dehydrogenase (NAD-GDH, EC 1.4.1.2) from a non-pathogenic dimorphic zygomycete Benjaminiella poitrasii was previously reported to be an important biochemical correlate of the transition process. The enzyme was purified to homogeneity and characterized. It is a 371 kDa native molecular weight protein made up of four identical subunits. Kinetic studies showed that unlike other NAD-GDHs, it may act as an anabolic enzyme and has more affinity towards 2-oxoglutarate than L-glutamate. Chemical modifications revealed the involvement of single histidine and lysine residues in the catalytic activity of the enzyme. The phosphorylation and dephosphorylation study showed that the NAD-GDH is present in active phosphorylated form in hyphal cells of B. poitrasii. Two of the 1,2,3 triazole linked β-lactam-bile acid conjugates synthesized in the laboratory (B18, B20) were found to be potent inhibitors of purified NAD-GDH which also significantly affected Y-H transition in B. poitrasii. Furthermore, the compound B20 inhibited germ tube formation during Y-H transition in Candida albicans strains and Yarrowia lipolytica. The possible use of NAD-GDH as a target for antifungal agents is discussed.

Taguchi approach significantly increases bioremediation process efficiency: a case study with Hg (II) removal by Pseudomonas aeruginosa

AIM

Optimization of process parameters for mercury removal by an Hg (II)-reducing Pseudomonas aeruginosa strain.

METHODS AND RESULTS

A strain of Ps. aeruginosa was found to reduce 10 mg l(-1) Hg (II) to Hg0 with 70% efficiency in 24 h. To optimize process performance, a statistical tool--Taguchi design of experiments (DOE)--was used to carry out 18 well-defined experiments (L18 Orthogonal array) with eight variable parameters (viz. agitation, temperature, pH, carbon source, medium volume: flask volume ratio and concentrations of Hg (II), ammonium sulfate and yeast extract). When data obtained were analyzed using specialized software for Taguchi design, Qualitek-4 (Nutek Inc., MI, USA), Hg (II) reduction efficiency was predicted to be 95% in 24 h under the optimized process parameters (also suggested by the software). In the validation experiment, Hg (II) removal of 99.29% in 24 h was indeed obtained.

CONCLUSIONS

Using Taguchi DOE, Hg (II) reduction (and hence its removal) using Ps. aeruginosa could be improved by 29.3%.

SIGNIFICANCE AND IMPACT OF THE STUDY

Taguchi approach could be employed as an efficient and time-saving strategy for parameter optimization in bioremediation processes.