PONE-D-19-26326

Urine dicarboxylic acids change in pre-symptomatic Alzheimer’s disease and reflect loss of energy capacity and hippocampal volume

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Reviewer #1: This is a very interesting paper. The reviewer agree with authors' hypothesis. But would like to suggest an open search for lipid metabolites as urinary biomarkers in the future. The manuscript should be published to show the community the potential of urine. But there is a theory about urinary biomarker which will support the manuscript but not mentioned. The theory is in the paper with recent progress of urinary protein biomarkers on early AD animal model (J Alzheimers Dis. (2018) 66:613–637. doi: 10.3233/JAD-180412).

Reviewer #2:

1. Please give the precise structure of C4-C5 DCAs and C7-C10 DCAs, are they oxidized?

2. Single ion monitoring (SIM) mode based on triple quad mass spectrometry is a Quantitative platform for targeted analysis, but is not suitable for the finding of biomarkers. Therefore, although the authors targeted dicarboxylic acids because they are implicated in several processes associated with AD pathology, I guess readers may also need to explain why and how the C4-C5 DCAs and C7-C10 DCAs were selected for SIM analysis. Specifically, whether some other DCAs such as smaller than C4 or bigger than C 10 were detected in urine, or there is no statistical differences for these DCAS between AD and cognitively healthy groups.

3. The authors have provided well designed and credible results, especially; the samples of CH individuals with normal amyloid/Tau (CH-NAT) and pathological amyloid/Tau (CH-PAT) are very valuable. However, some details of the analysis method may be ignored. For example, gas chromatographic methods coupled with mass spectrometry is widely used for the detection of dicarboxylic acids, but the efficiency and stability of reaction products and several derivatization agents may be different, so the detection limit (LOD) and relative standard deviation (RSD) of C4,C5… C10 should be given, 0therwise, the relationship between signal intensity and content cannot be accurately judged.

4. In Fig 2(B). Changes in urine DCA in clinical groups, if I am not wrong, there are 25 black triangles, which is not inconsistent with 24 AD samples.

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Reviewer #2: Yes: Yong Wang

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Urine dicarboxylic acids change in pre-symptomatic Alzheimer’s disease and reflect loss of energy capacity and hippocampal volume

PONE-D-19-26326R1

Dear Dr. Harrington,

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