In vivo imaging of schistosomes to assess disease burden using positron emission tomography (PET) - PubMed (original) (raw)
In vivo imaging of schistosomes to assess disease burden using positron emission tomography (PET)
Nicolas Salem et al. PLoS Negl Trop Dis. 2010.
Abstract
Background: Schistosomes are chronic intravascular helminth parasites of humans causing a heavy burden of disease worldwide. Diagnosis of schistosomiasis currently requires the detection of schistosome eggs in the feces and urine of infected individuals. This method unreliably measures disease burden due to poor sensitivity and wide variances in egg shedding. In vivo imaging of schistosome parasites could potentially better assess disease burden, improve management of schistosomiasis, facilitate vaccine development, and enhance study of the parasite's biology. Schistosoma mansoni (S. mansoni) have a high metabolic demand for glucose. In this work we investigated whether the parasite burden in mice could be assessed by positron emission tomography (PET) imaging with 2-deoxy-2[(18)F]fluoro-D-glucose (FDG).
Methodology/principal findings: Live adult S. mansoni worms FDG uptake in vitro increased with the number of worms. Athymic nude mice infected with S. mansoni 5-6 weeks earlier were used in the imaging studies. Fluorescence molecular tomography (FMT) imaging with Prosense 680 was first performed. Accumulation of the imaging probe in the lower abdomen correlated with the number of worms in mice with low infection burden. The total FDG uptake in the common portal vein and/or regions of elevated FDG uptake in the liver linearly correlated to the number of worms recovered from infected animals (R(2) =0.58, P<0.001, n = 40). FDG uptake showed a stronger correlation with the worm burden in mice with more than 50 worms (R(2) = 0.85, P<0.001, n = 17). Cryomicrotome imaging confirmed that most of the worms in a mouse with a high infection burden were in the portal vein, but not in a mouse with a low infection burden. FDG uptake in recovered worms measured by well counting closely correlated with worm number (R(2) = 0.85, P<0.001, n = 21). Infected mice showed a 32% average decrease in total FDG uptake after three days of praziquantel treatment (P = 0.12). The total FDG uptake in untreated mice increased on average by 36% over the same period (P = 0.052).
Conclusion: FDG PET may be useful to non-invasively quantify the worm burden in schistosomiasis-infected animals. Future investigations aiming at minimizing non-specific FDG uptake and to improve the recovery of signal from worms located in the lower abdomen will include the development of more specific radiotracers.
Conflict of interest statement
The authors have declared that no competing interests exist.
Figures
Figure 1. In vitro FDG uptake by S. mansoni.
FDG uptake in counts per minute (cpm) after 60 min incubations of 5-weeks post-infection hepatic young adult-stage schistosomes (live). Iodine killed parasites (dead) of the same developmental age were used as negative controls. Error bars represent the standard deviation (n = 3 experiments each).
Figure 2. FMT and MRI of mice infected with S. mansoni.
(A) Uninfected and mice with different worm burdens were scanned 24 hours after Prosense 680 injections. MRI was also performed on the same mice to provide anatomical references. Arrows indicate fluorescence in the lower abdomen. Arrowheads designate areas of fluorescence in the liver. The dotted boxes indicate the three dimensional ROIs used to quantify the probe amount. Intensity scale [250 (blue)–1500 (red) nM]. (B) Worms were collected on glass slides after perfusion for microscopy. Bright field (BF) and fluorescent images using the Cy5 filter (Cy5) and 50 ms exposures were acquired and co-registered to show that fluorescence was originating in the worms' digestive tract. A male-female pair is shown here. Scale bar = 100 µm. (C) Relationship between the total probe amount in the lower abdomen and the number of worms when considering all mice (n = 10; graph) and only infected mice with less than 60 worms (n = 5; blue inset).
Figure 3. FDG-μPET imaging of mice infected with S. mansoni.
(A) μPET scans were acquired in control and infected mice 90 min after FDG injection. Arrows indicate areas of moderate uptake adjacent to the liver or areas of increased uptake in the liver parenchyma around which ROIs were drawn to quantify FDG uptake (Figure S1). Arrowheads indicate areas of high uptake in the lower abdomen. The mouse with 104 worms had also been imaged with FMT/MRI (Figure 2). Note that mice were in prone position for μPET scanning and in supine position for FMT/MRI scanning. Intensity scale [0 (black)–2×104 (white) nCi/cc]. (B) Photograph of the digestive tract of an infected animal that was removed 60 min after FDG injection (upper panel) and exposed to a phosphor screen for autoradiography showing high FDG uptake in the colon and diffuse FDG uptake in other parts of the digestive tract (lower panel). (C) Cryomicrotome imaging of a mouse with a heavy infection burden. A high number of worms were found in the common portal vein (arrow). (D) Cryomicrotome imaging of the lower abdomen in the same animal showed the presence of a small number of worms scattered in the mesentery (arrows). (E) Worms were found in the liver of one infected mouse that died before FDG injection. H&E staining; scale bar = 100 µm. (F) Lack of an overt inflammatory response to an ova in the liver (H&E staining). Scale bar = 100 µm.
Figure 4. Quantitative analysis of the FDG-μPET images and well-counting data in control and infected mice.
(A) Relationship between the total radioactivity within three-dimensional ROIs drawn around the portal vein and/or areas of abnormal uptake in the liver and the number of worms when considering all datasets (graph) or only datasets obtained from mice with more than 50 worms (blue inset). (B) Radioactivity levels measured by well counting as a function of the number of worms. (C) Total radioactivity measured by μPET graphed as a function of the total radioactivity measured by well counting.
Figure 5. FDG-μPET imaging of praziquantel-treated mice.
(A) μPET imaging performed before (Day 1) and after (Day 4) praziquantel treatment. ROIs on the coronal sections chosen for display are outlined by a green dotted line. Intensity scale [0 (black) –2×104 (white) nCi/cc]. (B) Quantification of FDG uptake in the area of the common portal vein in untreated infected animals at day 1 and day 4 (* and **; Figure S1). (C) Quantification of FDG uptake in the area of the common portal vein in infected animals before and after treatment. (D) Average change in FDG uptake in treated and untreated mice relative to FDG uptake at day 1. Error bars represent the standard deviation.
References
- Chen M. Use of praziquantel for clinical treatment and morbidity control of schistosomiasis japonica in China: a review of 30 years' experience. Acta Trop. 2005;96:168–176. doi: 10.1016/j.actatropica.2005.07.011. - DOI - PubMed
- Xiaonong Z, Minggang C, McManus D, Bergquist R. Schistosomiasis control in the 21st century. Proceedings of the International Symposium on Schistosomiasis, Shanghai, July 4-6, 2001. Acta Trop. 2002;82:95–114. - PubMed
- Hotez PJ, Molyneux DH, Fenwick A, Kumaresan J, Sachs SE, et al. Control of neglected tropical diseases. N Engl J Med. 2007;357:1018–1027. doi: 10.1056/NEJMra064142. - DOI - PubMed
- King CH, Dangerfield-Cha M. The unacknowledged impact of chronic schistosomiasis. Chronic Illn. 2008;4:65–79. doi: 10.1177/1742395307084407. - DOI - PubMed
- Melman SD, Steinauer ML, Cunningham C, Kubatko LS, Mwangi IN, et al. Reduced Susceptibility to Praziquantel among Naturally Occurring Kenyan Isolates of Schistosoma mansoni. PLoS Negl Trop Dis. 2009;3:e504. doi: 10.1371/journal.pntd.0000504. - DOI - PMC - PubMed
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