Abstract:Inflammation plays a prominent role in the pathogenesis of Alzheimer's disease, affecting both brain and the peripheral system. Thus, modulation of inflammation in animal models of this neurodegenerative disorder may be of great interest to elucidate the pathological mechanisms underlying this inflammatory component. To this end, a metabolomic investigation on a triple transgenic mouse model obtained by crossing the APP/PS1 mice with interleukin-4 knockout mice (a model of impaired immune function) was performed for the first time. Serum samples from transgenic mice and wild type animals were analyzed by direct infusion mass spectrometry followed by multivariate statistics in order to identify altered metabolites. Subsequently, metabolic pathway analysis allowed the elucidation of potential pathological mechanisms associated with the development of Alzheimer-type disorders in response to interleukin-4 deficiency, such as impaired homeostasis of histamine, altered metabolism of amino acids (threonine, aspartate and tyrosine), deregulated urea cycle and increased production of eicosanoids. Therefore, this work demonstrates the potential of this triple transgenic model with modulated immunity for the study of pathological mechanisms associated with inflammation in Alzheimer's disease.
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COMMENTS FOR THE AUTHOR:Reviewer #1: The authors have not included some important requests for clarification to be added to the manuscript by the reviewer therefor another minor revision is required.
Abstract still poorly writtenFor example this sentence:Thereby, the investigation of this inflammatory component presents a great potential for the elucidation of pathological mechanisms underlying to disease, the discovery of potential markers of diagnosis and the development of novel therapeutic approaches Abstract was rewritten.
Authors commentWe did not use internal standards because we considered that the validation of reproducibility in metabolomic methods is better assessed using QC samples. In this sense, Naz et al. recently described that "although spiking some selected metabolites could give a good approach to the general behaviour of the method, results cannot be assumed for all the components in the sample" (J Chromatogr A 2014;1353:99). Instead, biological QCs show a similar composition to real samples, so they are preferable for validating non-targeted approaches. Thus, "the se of QCs in non-targeted metabolomics analysis can be considered as equivalent to the use of standards in routine target analysis".
Reviewer comment: I don't agree with this statement how can you account for a one off issue and internal standards are also in the sample matrix. You need add this justification to the manuscriptInternal standards must present similar physico-chemical properties to the chemical species of interest in the sample. However, metabolomics approaches are not focused on individual compounds, so the use of internal standards in these method...