Assessing the Putative Anticryptococcal Properties of Crude and Clarified Extracts from Mollusks

Summary

The human fungal pathogen Cryptococcus neoformans produces a variety of virulence factors (e.g., peptidases) to promote its survival within the host. Environmental niches represent a promising source of novel natural peptidase inhibitors. This protocol outlines the preparation of extracts from mollusks and the assessment of their effect on fungal virulence factor production.

Abstract

Cryptococcus neoformans is an encapsulated human fungal pathogen with a global distribution that primarily infects immunocompromised individuals. The widespread use of antifungals in clinical settings, their use in agriculture, and strain hybridization have led to increased evolution of resistance. This rising rate of resistance against antifungals is a growing concern among clinicians and scientists worldwide, and there is heightened urgency to develop novel antifungal therapies. For instance, C. neoformans produces several virulence factors, including intra- and extra-cellular enzymes (e.g., peptidases) with roles in tissue degradation, cellular regulation, and nutrient acquisition. The disruption of such peptidase activity by inhibitors perturbs fungal growth and proliferation, suggesting this may be an important strategy for combating the pathogen. Importantly, invertebrates such as mollusks produce peptidase inhibitors with biomedical applications and anti-microbial activity, but they are underexplored in terms of their usage against fungal pathogens. In this protocol, a global extraction from mollusks was performed to isolate potential peptidase inhibitors in crude and clarified extracts, and their effects against classical cryptococcal virulence factors were assessed. This method supports the prioritization of mollusks with antifungal properties and provides opportunities for the discovery of anti-virulence agents by harnessing the natural inhibitors found in mollusks.

Introduction

Cryptococcus neoformans is a human fungal pathogen that produces severe disease in immunocompromised hosts, such as individuals living with HIV/AIDS¹, and leads to approximately 19% of AIDS-related deaths². The fungus is susceptible to several classes of antifungals, including azoles, polyenes, and flucytosine, which exert fungicidal and fungistatic activity using distinct mechanisms^3,4. However, the extensive use of antifungals in clinical and agricultural settings combined with strain hybridization have amplified the evolution of ....

Protocol

1. Protein extraction from mollusks

1. Collect mollusks from a designated and approved natural area (e.g., Speed River, Guelph, Ontario). For this study, both native and invasive species were selected to assess a broad range of potential antifungal effects.
2. Gently break the shell of the mollusks (e.g., Cepaea nemoralis, Planorbella pilsbryi, and Cipangopaludina chinensis) using a pestle and mortar, and remove the solid pieces with a pair of tweezers. Generally, 10 mollusks are pooled for use throughout the protocol.
3. Collect and weigh the organs. Approximately 15-20 g of sample is optimal. Use sci....

Results

The workflow described herein enables the isolation of proteins and peptides from mollusks with potential anti-virulence properties against C. neoformans. Similarly, assessing different forms of extracts (i.e., crude and clarified) allows for the semi-purification of the potential active compounds and supports downstream assessment (e.g., mass spectrometry-based proteomics). Typically, the protein extraction workflow produces homogenized solutions with protein concentrations of 4-8 mg/mL. Here, the representativ.......

Discussion

The extraction protocol described here outlines the isolation of compounds from mollusks collected from Ontario, Canada, and demonstrates a novel investigation of using mollusk extracts against the human fungal pathogen, C. neoformans. This protocol adds to a growing body of research investigating peptidase inhibitor activity from invertebrates¹³. During the extraction, some extract samples were difficult to filter-sterilize, possibly due to the presence of soluble polysaccharides and/or .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.2 μm Filters	VWR	28145-477 (North America)
1.5 mL Tubes (Safe-Lock)	Eppendorf	0030120086
2 mL Tubes (Safe-Lock)	Eppendorf	0030120094
3,4-Dihydroxy-L-phenylalanine (L-DOPA)	Sigma-Aldrich	D9628-5G	CAS #: 59-92-7
96-well plates	Costar (Corning)	3370
Bullet Blender Storm 24	NEXT ADVANCE	BBY24M
Centrifuge 5430R	Eppendorf	5428000010
Chelex 100 Resin	BioRad	142-1253
CO2 Incubator (Static)	SANYO	Not available
Cryptococcus neoformans H99	ATCC	208821
DIC Microscope	Olympus
DIC Microscope software	Zeiss
DMEM	Corning	10-013-CV
Glucose (D-Glucose, Anhydrous, Reagent Grade)	BioShop	GLU501	CAS #: 50-99-7
Glycine	Fisher Chemical	G46-1	CAS #: 56-40-6
GraphPad Prism 9	Dotmatics
Hemocytometer	VWR	15170-208
HEPES	Sigma Aldrich	H3375
Magnesium sulfate heptahydrate (MgSO4.7 H2O)	Honeywell	M1880-500G	CAS #: 10034-99-8
Peptone	BioShop	PEP403
Phosohate buffer salt pH 7.4	BioShop	PBS408	SKU: PBS408.500
Plate reader (Synergy-H1)	BioTek (Agilent)	Not available
Potassium phosphate monobasic (KH2PO4)	Fisher Chemical	P285-500	CAS #: 7778-77-0
Subtilisin A	Sigma-Aldrich	P4860	CAS #: 9014-01-01
Succinyl-Ala-Ala-Pro-Phe-p-nitroanilide	Sigma-Aldrich	573462	CAS #: 70967-97-4
Thermal bath	VWR	76308-834
Thiamine Hydrochloride	Fisher-Bioreagents	BP892-100	CAS #: 67-03-8
Yeast extract	BioShop	YEX401	CAS #: 8013-01-2
Yeast nitrogen base (with Amino Acids)	Sigma-Aldrich	Y1250-250G	YNB