Abstract
Giardiasis represents a latent problem in public health due to the exceptionally pathogenic strategies of the parasite Giardia lamblia for evading the human immune system. Strains resistant to first-line drugs are also a challenge. Therefore, new antigiardial therapies are urgently needed. Here, we tested giardial arginine deiminase (GlADI) as a target against giardiasis. GlADI belongs to an essential pathway in Giardia for the synthesis of ATP, which is absent in humans. In silico docking with six thiol-reactive compounds was performed; four of which are approved drugs for humans. Recombinant GlADI was used in enzyme inhibition assays, and computational in silico predictions and spectroscopic studies were applied to follow the enzyme’s structural disturbance and identify possible effective drugs. Inhibition by modification of cysteines was corroborated using Ellman’s method. The efficacy of these drugs on parasite viability was assayed on Giardia trophozoites, along with the inhibition of the endogenous GlADI. The most potent drug against GlADI was assayed on Giardia encystment. The tested drugs inhibited the recombinant GlADI by modifying its cysteines and, potentially, by altering its 3D structure. Only rabeprazole and omeprazole decreased trophozoite survival by inhibiting endogenous GlADI, while rabeprazole also decreased the Giardia encystment rate. These findings demonstrate the potential of GlADI as a target against giardiasis.
Highlights
Current drug discovery techniques against parasites aim at the identification of essential pathogenic targets, which, after inhibiting their functionality, could be lethal for the pathogenic organisms
Human giardiasis is an inflammation-driven diarrhea caused by the protist, Giardia lamblia [1], which has developed a broad range of mechanisms to escape the host immune system [2]
To better support giardial arginine deiminase (GlADI) as a druggable target in Giardia, we studied its reactivity to s-methyl methanethiosulfonate (MMTS) and dithio-bis-nitrobenzoic acid (DTNB), to demonstrate the capacity of thiol-reactive compounds to inactivate this enzyme
Summary
Current drug discovery techniques against parasites aim at the identification of essential pathogenic targets, which, after inhibiting their functionality, could be lethal for the pathogenic organisms. Anti-virulence therapy is based on disarming the pathogens and preventing them from causing disease. The latter is increasing because virulence factors enhance the ability of pathogens to colonize and resist the immunity of their hosts. Therapeutic strategies directed at the molecules that participate at different levels in the life cycle of pathogens might be helpful in the treatment of the illness, and in repressing the dissemination of the disease. Such a strategy might be helpful in the fight against giardiasis. Giardia is a microaerophilic organism that lacks the tricarboxylic acid cycle and oxidative phosphorylation, but has acquired enzymes of likely lateral gene transfer origin that support fermentative glycolysis [3], the arginine dihydrolase pathway [4,5], and substrate-level ATP generation [6,7,8]
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