Evgenov et al. reply:
Saudek et al.1 express two major concerns regarding our analysis of their results. First, they object to our interpretation of their reported cellular iron uptake. We would like to point out that we did not interpret, but only reiterated their own statement that the reported amount of iron was unrealistically high: “If we assume that one islet is composed of roughly 3000 cells, this may represent approximately 90 pg of iron per cell. This amount is, however, much higher than that found in other cell types”1. We do not believe that it is reasonable for Saudek et al. to criticize us for simply repeating a statement from their own manuscript. Indeed, the authors provide some justification for this observation: “...some iron could remain trapped inside the islet, that is, did not enter the cells but was not washed out.” Although we do not object to this possibility, we believe that, until proven experimentally, it remains speculative.
Second, Saudek et al. express disappointment that we did not acknowledge their primacy on the use of magnetic resonance imaging for islet visualization. Fair scientific discourse is founded upon the responsibility for citing the work of others, both as a means of giving credit and as part of an open research dialogue. In agreement with this principle, we expressed our concerns regarding the statements and conclusions made in Jirak et al.1 Although we are not disputing the fact that their manuscript came out first, we would like to emphasize that, in our opinion, their publication has important shortcomings. T2 relaxation times in the hundreds of milliseconds showing no correlation with the number of labeled islets, different pulse sequences for experimental and control images, the unknown nature of the causes behind the reported detrimental drop in insulin secretion, and the absence of basic histological studies supporting the imaging data are a few of them. Consequently, we were reluctant to discuss this study in detail and focused only on some results relevant to our manuscript2.
Noninvasive imaging of transplanted pancreatic islets has the potential to advance the successful implementation of clinical islet transplantation for diabetes treatment. Hence, the translation of this technique into clinical trials imposes a tremendous responsibility on researchers and requires a thorough and reliable investigation of all possible mechanisms behind islet labeling and all the consequences that it might have on patient health.
Jirak, D. et al. Magn. Reson. Med. 52, 1228–1233 (2004).
Evgenov, N. V., Medarova, Z., Dai, G., Bonner-Weir, S. & Moore, A. Nat. Med. 12, 144–148 (2006).
The authors declare no competing financial interests.
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Moore, A., Medarova, Z., Evgenov, N. et al. Reply to 'In vivo imaging of islet transplantation'. Nat Med 13, 773 (2007). https://doi.org/10.1038/nm0707-773b