PONE-D-19-27390

Brain function and metabolism in patients with long-term tacrolimus therapy after kidney transplantation

PLOS ONE

Dear Dr. Pflugrad,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

I would like to first apologize again for the time that it has taken to render a decision on your manuscript. As I wrote to you, I had a very difficult time securing a second review. I appreciate your understanding in this. Between the two reviews, there are a number of issues to be addressed, but these are all relatively minor and will mostly help to clarify certain aspects that are somewhat unclear at the moment and tone done some statements. I encourage you to follow each of the suggestions/comments that have raised by both Reviewers, especially those that concern the presentation of the data.

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PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The manuscript entitled "Brain function and metabolism in patients with long-term tacrolimus therapy after

kidney transplantation" describes the differences in cognitive function and brain ATP levels in kidney transplanted patients, liver tr4ansplanted patients, and healthy controls. The conclusions are, as expected, that kidney transplantation does not restore cognition to normal levels. This has been already mentioned in several reviews on this topic, as well as summarized in a recent review from a Europen group (see e.g. PMID:31071220 ).

However, I find that the manuscript contains important information that merit publication, specifically the use of a liver transplanted group as further control to dissect the effect of tacrolimus from kidney disease.

-the authors should greater strength this latter aspect in the title and the abstract

- the tables are difficult to read: please present the data in graphic form. I would encourage to present a graph with time in the horizontal axis (so that possible time-evolution is evident). (see below regarding the use of symbols)

- in figure 3 please use symbols that could better group the KT patients. e.g. use squares filled with at different gray levels to indicate KT 1, 5 and 10 years (rather than three different symbols). Why no error bars? why are the different cognitive measures connected by a line? this is misleading and makes confusion: please use for this type of graph bar plots.

- I do not agree with the conclusions: liver transplant seems to impinge even more on several cognitive aspects. Is there a dose-response relation between tacrolimus and cognition? please give a scatterplot of the dose of tacrolimus (and cumulative dose, if possible) vs cognitive function. Is it an effect linked to the eGFR (even in the case of liver transplant)? please give a scatterplot of eGFR vs cognitive functions. Is it a problem with liver function in kidney patients? please give a scatterplot of transaminases (or bilirubin, which is more likely to affect the brain) vs cognitive processes.

- ATP seems to be related to kidney transplants and not liver transplants. Therefore, it is not due to tacrolimus: please change the conclusions in the abstract and discuss the possibility that MCI-CKD is due to a loss of ATP into the brain due to CKD (see above reference for MCI-CKD). Please also give the relationship between ATP and cognitive functions (a regression and a scatterplot would be useful).

- I also find fascinating the trend effect of the PVH occipital, which is more present also in the liver transplanted patients. This is a very interesting point. You should demonstrate that these lesions are related to the cognitive measures (by regression, and possibly giving a scatterplot). In general, this finding is intriguing because the hyperintensities have been correlated usually to CKD rather than tacrolimus... is it possible that other drugs are actually causing them? maybe cortisone (which is widely used in CKD diseases)? or diabetes? what is the commonality between CKD, kidney transplant and liver transplant? maybe the data can offer some insight into this question.

Please reformulate the abstract once these points have been addressed.

Reviewer #2: The manuscript entitled “Brain function and metabolism in patients with long-term tacrolimus therapy after kidney transplantation” and submitted to PLOS ONE describes a study into the brain metabolism and cognitive function of kidney transplant recipients. Its cross-sectional study design analyzes patients 10, 5, and 1 years after transplantation under tacrolimus therapy, and compares these to both healthy controls and a group of patients after 10 years post liver transplantation. Methods included both neuropsychological tests, proton MRI and 31P (phosphorus) magnetic resonance spectroscopy. The results indicate that overall the kidney transplant recipients had cognitive impairment compared to healthy controls, but it did not follow that patients 10 years post-transplantation were more impaired than patients 5 and 1 years post.

It is curious that long-term tacrolimus therapy patients were not significantly more impaired than the 5 and 1 year patients, although as the authors state there may be other, more significant factors at work, and the sample size was not overly large. In general the study is well designed with the numerous statistical tests well described. A few keys area should be improved, however, in order to clarify the results and improve the text.

• The authors separate the patients and controls into 5 groups. Although they describe what each group represents (i.e. group 1 is kidney transplant patients 10 years post-transplantation), this gets confusing for the reader, and found myself making notes in order to keep the groups sorted correctly. It would be far easier for the reader if the authors altered their nomenclature for the groups, so that ‘KT10’ could represent kidney transplant patients 10 years post-transplantation. ‘KT5’, ‘KT1’, ‘LT’ and ‘HC’ would follow naturally, and the these should be carried into the various tables. This would be easier for the reader to follow.

• Figure 3 could also be improved as per the previous point. Currently, various symbols indicate which of the groups had significant (p < 0.05) deficits compared to controls. It would be far easier to just list the group names (i.e. LT5) as being significantly less than healthy controls, and state in the figure caption that all group means are being compared to controls.

• A 31P spectra would be interesting to the reader. Consider including an exemplary example as a figure, or at the minimum as supplementary material.

• Line 202-203: The turbo spin echo sequence appears to be a triple echo, with PD (13 ms), intermediate (71 ms) and T2-weighted (130 ms) echo times. It is important that the authors distinguish between this T2-weighted sequence, the T2 FLAIR sequence (see next point).

• Line 206: “an axial turbo inversion recovery magnetic sequence” Do the authors mean a T2-weighted fluid-attenuated inversion recovery (FLAIR) sequence? If so, please state that directly. You should also provide the parameters for this sequence (TR, TE, resolution, etc.) It may be worthwhile to create a new table for the pulse sequences, wherein all the relevant details (field of view, slice thickness, resolution, TR/TE, etc.) could be provided for all sequences. If the parameters were not kept consistent among the subjects (i.e. different FLAIR sequences were used) please state that directly so the reader can evaluate whether this had any effect upon the results.

• Line 208: “(WMH) were assess visually” On what the sequence? It’s almost certainly the FLAIR, but this should be stated directly. If other sequences (i.e. T2* weighted) were also used, this should be stated as well.

• Line 209-210: “ventricular width at the level...” Which sequence was used to measure these widths? The MPRAGE? FLAIR?

• Line 231: “exemplary T2 magnetic resonance image...” This image is almost certainly a T2-weighted FLAIR, not a T2-weighted sequence which was also described (Line 202-203). Please clarify the figure caption.

• Line 360: “Furthermore, KT patients showed enlarged periventricular hyperintensities...” Not sure what the authors mean by enlarged here. Do they mean an increased number of hyperintensities? The same number but increased volume?

• Line 418-419: “despite that they had arterial hypertension...” Consider changing to “despite having arterial hypertension...”

• Line 483-486: “Unfortunately, patients after KT who only received tacrolimus as well as a patient control group with a CNI-free or prednisolone-free immunosuppression since transplantation were not available.” This is not a complete sentence – please revise.

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Reviewer #1: No

Reviewer #2: Yes: Paul Polak

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Brain function and metabolism in patients with long-term tacrolimus therapy after kidney transplantation in comparison to patients after liver transplantation

PONE-D-19-27390R1

Dear Dr. Pflugrad,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

Within one week, you will receive an e-mail containing information on the amendments required prior to publication. When all required modifications have been addressed, you will receive a formal acceptance letter and your manuscript will proceed to our production department and be scheduled for publication.

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With kind regards,

Niels Bergsland

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The revised version is now greatly improved; the authors have implemented all requested changes. The manuscript merits publication

Reviewer #2: (No Response)

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: Yes: Paul Polak