In vivo detection of free radicals in mouse septic encephalopathy using molecular MRI and immuno-spin trapping.

Free radicals are known to play a major role in sepsis. Combined immuno-spin trapping and molecular magnetic resonance imaging (MRI) was used to detect in vivo and in situ levels of free radicals in murine septic encephalopathy after cecal ligation and puncture (CLP). DMPO (5,5-dimethyl pyrroline N-oxide) was injected over 6h after CLP, before administration of an anti-DMPO probe (anti-DMPO antibody bound to albumin-gadolinium-diethylene triamine pentaacetic acid-biotin MRI targeting contrast agent). In vitro assessment of the anti-DMPO probe in oxidatively stressed mouse astrocytes significantly decreased T1 relaxation (p < 0.0001) compared to controls. MRI detected the presence of anti-DMPO adducts via a substantial decrease in %T1 change within the hippocampus, striatum, occipital, and medial cortex brain regions (p < 0.01 for all) in septic animals compared to shams, which was sustained for over 60 min (p < 0.05 for all). Fluorescently labeled streptavidin was used to target the anti-DMPO probe biotin, which was elevated in septic brain, liver, and lungs compared to sham. Ex vivo DMPO adducts (qualitative) and oxidative products, including 4-hydroxynonenal and 3-nitrotyrosine (quantitative, p < 0.05 for both), were elevated in septic brains compared to shams. This is the first study that has reported on the detection of in vivo and in situ levels of free radicals in murine septic encephalopathy.

Extracellular lipid droplets promote hemozoin crystallization in the gut of the blood fluke Schistosoma mansoni.

Hemozoin (Hz) is a heme crystal produced upon hemoglobin digestion as the main mechanism of heme disposal in several hematophagous organisms. Here, we show that, in the helminth Schistosoma mansoni, Hz formation occurs in extracellular lipid droplets (LDs). Transmission electron microscopy of adult worms revealed the presence of numerous electron-lucent round structures similar to LDs in gut lumen, where multicrystalline Hz assemblies were found associated to their surfaces. Female regurgitates promoted Hz formation in vitro in reactions partially inhibited by boiling. Fractionation of regurgitates showed that Hz crystallization activity was essentially concentrated on lower density fractions, which have small amounts of pre-formed Hz crystals, suggesting that hydrophilic-hydrophobic interfaces, and not Hz itself, play a key catalytic role in Hz formation in S. mansoni. Thus, these data demonstrate that LDs present in the gut lumen of S. mansoni support Hz formation possibly by allowing association of heme to the lipid-water interface of these structures.

Inhibition of heme aggregation by chloroquine reduces Schistosoma mansoni infection.

Adult Schistosoma mansoni digest large amounts of host hemoglobin and release potentially toxic heme inside their guts. We have previously demonstrated that free heme in S. mansoni is detoxified through aggregation, forming hemozoin (Hz). Possible mechanisms of heme aggregation and the effects of chloroquine (CLQ) on formation of Hz and on the viability of this parasite have now been investigated. Different fractions isolated from S. mansoni, such as crude whole-worm homogenates, total lipid extracts, and Hz itself promoted heme aggregation in vitro in a CLQ-sensitive manner. Treatment of S. mansoni-infected mice with CLQ led to remarkable decreases in total protein, Hz content, and viability of the worms, as well as in parasitemia and deposition of eggs in mouse livers. These results indicate that inhibition of formation of Hz in S. mansoni, by CLQ, led to an important decrease in the overall severity of experimental murine schistosomiasis. Taken together, the results presented here suggest that formation of Hz is a major mechanism of heme detoxification and a potential target for chemotherapy in S. mansoni.