Adaptive iron utilization compensates for the lack of an inducible uptake system in Naegleria fowleri and represents a potential target for therapeutic intervention

Abstract

Naegleria fowleri is a single-cell organism living in warm freshwater that can become a deadly human pathogen known as a brain-eating amoeba. The condition caused by N. fowleri, primary amoebic meningoencephalitis, is usually a fatal infection of the brain with rapid and severe onset. Iron is a common element on earth and a crucial cofactor for all living organisms. However, its bioavailable form can be scarce in certain niches, where it becomes a factor that limits growth. To obtain iron, many pathogens use different machineries to exploit an iron-withholding strategy that has evolved in mammals and is important to host-parasite interactions. The present study demonstrates the importance of iron in the biology of N. fowleri and explores the plausibility of exploiting iron as a potential target for therapeutic intervention. We used different biochemical and analytical methods to explore the effect of decreased iron availability on the cellular processes of the amoeba. We show that, under iron starvation, nonessential, iron-dependent, mostly cytosolic pathways in N. fowleri are downregulated, while the metal is utilized in the mitochondria to maintain vital respiratory processes. Surprisingly, N. fowleri fails to respond to acute shortages of iron by inducing the reductive iron uptake system that seems to be the main iron-obtaining strategy of the parasite. Our findings suggest that iron restriction may be used to slow the progression of infection, which may make the difference between life and death for patients.

Novel aspects of iron homeostasis in pathogenic bloodstream form Trypanosoma brucei

“…Such a mechanism was reported for PCFs and is backed by the presence of two putative iron reductases and iron transporters in the T. brucei genome whose function and location remain unknown (20). This two-step reductive mechanism has been described for S. cerevisiae (48), Naegleria fowleri (49) and the closely related Kinetoplastid Leishmania.…”

Novel aspects of iron homeostasis in pathogenic bloodstream form Trypanosoma brucei

“…Such a mechanism was reported for PCFs and is backed by the presence of two putative iron reductases and iron transporters in the T. brucei genome whose function and location remain unknown [19]. This two-step reductive mechanism has been described for S. cerevisiae [46], Naegleria fowleri [47] and the closely related Kinetoplastid Leishmania. Leishmania ferric reductase 1 (LFR1) reduces Fe 3+ to Fe 2+ which is subsequently transported to the cytosol by Leishmania iron transporter 1 (LIT1) [48,49].…”

“…This two-step reductive mechanism has been described for S . cerevisiae [ 46 ], Naegleria fowleri [ 47 ] and the closely related Kinetoplastid Leishmania . Leishmania ferric reductase 1 (LFR1) reduces Fe 3+ to Fe 2+ which is subsequently transported to the cytosol by Leishmania iron transporter 1 (LIT1) [ 48 , 49 ].…”

Differential growth rates and in vitro drug susceptibility to currently used drugs for multiple isolates of Naegleria fowleri

“…Nf69 (ATCC 30215), a clinical isolate used as a reference strain in these studies was obtained from a 9-year-old boy in Adelaide, Australia who died in 1969 (34)(35)(36), and 6088 (ATCC 30896), obtained from a 9-year-old girl in California who survived in 1978 (37,38), were purchased from the American Type Culture Collection (ATCC). V067, isolated from a 30year-old male in Arizona who died in 1987 (39,40), V206, isolated from a man in Mexico who died in 1990 (39), V413, isolated from a 17-year-old boy in Texas who died in 1998 (39,40), V597, isolated from a 10-year-old boy in Florida who died in 2007, V631, isolated from a 28year-old man in in Louisiana who died in 2011 (41), Davis, isolated from an individual in Florida who died in 1998 (30), HB1, isolated from a 16-year-old boy in Florida who died in 1966 (25,(42)(43)(44), HB4, isolated from a female in Virginia who died in 1977 (38,45,46), and Ty, obtained from a 14-year-old boy in Virginia who died in 1969 (30,32,38,47,48) were all kindly provided by Dr. Ibne Ali at the Centers for Disease Control and Prevention (CDC).…”

“…There are numerous studies that report the susceptibility of 1 to 3 clinical isolates of N. fowleri to a variety of drugs (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28) and only 4 studies that use 5 or more different isolates (29)(30)(31)(32). As such, we selected amphotericin B, fluconazole, ketoconazole, miconazole, posaconazole, azithromycin, rifampin, and miltefosine to assess their efficacy and determine the consistency in the response among N. fowleri clinical isolates of various genotypes, geographical locales, and temporal origins.…”