Bridging the Gap: Harnessing Plant Bioactive Molecules to Target Gut Microbiome Dysfunctions in Amyotrophic Lateral Sclerosis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors highlight in their review the importance of the microbiome in the development of a very important neurodegenerative disease: ALS. The work is very important and represents a different and certainly valuable beginning. It is well structured, I ask the authors to expose points where they better highlight how the metabolic aspect of bacteria can lead to the production of substances that affect the neuronal aspect. I ask the authors to search the literature for work that highlights the presence of conotoxins and similar toxins in ALS and to argue. In addition, it is also important to evaluate studies that relate this disease to certain viruses and that perhaps contamination of the microbiome with certain viruses may be an additional avenue to evaluate.

Author Response

Thank you for your valuable feedback and for your time dedicated to our article. We have addressed your questions as follows:

1. COMMENT 1: Metabolic aspect of bacteria that leads to the production of substances that affect the neuronal aspect

Thank you for pointing this out! We have introduced the following paragraph in the article at page 2 / lines 84-93:

Serotonin, a microbial metabolite, heavily depends on dietary tryptophan for its synthesis which takes place mainly in the gut [17]. Research found that treating murine microglial cells and primary microglia cultures with serotonin heightens exosome-associated proteins and insulin-degrading enzyme. Specific serotonin receptor antagonists impede this effect [18]. Exosomes emerge from recent studies as a type of extracellular vesicles that importantly mediate intercellular communication as well as in other physiological mechanisms such as cytokine secretion [19]. Given these mechanisms, serotonin likely plays a pivotal role in cytokine-carrying exomes' release from microglia [18]. Hence, serotonin-induced microglial exosomes could significantly impact neuroinflammation and associated disorders such as ALS [19].

2. COMMENT 2 & 3: Conotoxins and viruses

I totally agree, adding specific information about the virome and conotoxins enriches our text. We have introduced the following paragraph in the article at page 2 / lines 54-61:

Viral genes, such as endogenous retrovirus-K have been linked to ALS neuropathology due to their ability to interact with neuronal pathways via both cell-associated (retrotransposition) and cell-free (virion) mechanisms [6]. New findings indicate the potential impact of a conotoxin-like protein within the ERVK transcription genes with more specific potential role in ALS neuropathology, through its impact on inflammation, immune gene expression, and motor neuron degeneration [7]. However given the complex viral genomic mutations, more studies are needed to investigate the gut virome epigenetic regulation of brain disorders.

Best regards!

Reviewer 2 Report

Comments and Suggestions for Authors

The submitted review summarizes the role of plant-derived molecules in modulating gut microbiota in amyotrophic lateral sclerosis. The topic is very important due to the fatal and progressive nature of the disease.

A major concern authors have to state is whether the alterations of microbiota in each of the reported studies reflect causation (appear at disease onset) or association (appear at a later stage of disease progression). Section 2.2 should be updated accordingly.

The word “ALS” in the title should be written in full.

Author affiliation #4 is not matched in the author list.

Remove the Arabic number following each keyword.

Line 87: starting paragraphs with abbreviations is not recommended.

Line 109: The count of gut microbiota is in trillions, about 10¹³–10¹⁴. Please correct!

Line 116,117: It is widely accepted that the “microbiome” refers to the microorganisms and their genes while the “microbiota” only refers to the microbes themselves. Thus, the words "gut microbiota" should be with "gut microbiome" here.

 

 

Figure 2, though appears interesting, the effects of plant-derived oils on the gastrointestinal tract are not clearly shown. Elaborations should be added to the Figure legend to cover all figure contents. 

Comments on the Quality of English Language

The English of the manuscript is acceptable.

Author Response

Thank you very much for taking the time to review our manuscript.

Please find the detailed responses below and the corresponding revisions in track changes in the re-submitted files.

COMMENT 1. A major concern authors have to state is whether the alterations of microbiota in each of the reported studies reflect causation (appear at disease onset) or association (appear at a later stage of disease progression). Section 2.2 should be updated accordingly.

I have updated section 2.2 accordingly as can be seen in tracked changes on page 6.

COMMENT 2. The word “ALS” in the title should be written in full.

Thank you very much for this one, we cannot understand how we skipped such an important detail. Has been corrected.

COMMENT 3. Author affiliation #4 is not matched in the author list.

I am not sure how to change this one, we based our choice on the following recommendations for authors on the journal website:

“If one or all the authors are not currently affiliated with a university, institution or company, or have not been during the development of the manuscript, they should list themselves as an “Independent Researcher”."

https://www.mdpi.com/journal/cimb/instructions

We hope this can work since Elena Mardale is not affiliated at the moment.

COMMENT 4. Remove the Arabic number following each keyword.

Thank you, we removed them.

COMMENT 5. Line 87: starting paragraphs with abbreviations is not recommended.

Thank you, I have also proceeded in correcting all the paragraphs starting with abbreviations, as can be seen in track changes.

COMMENT 6. Line 109: The count of gut microbiota is in trillions, about 10¹³–10¹⁴. Please correct!

Thank you, we apologize for this error, it has now been corrected!

COMMENT 7. Line 116,117: It is widely accepted that the “microbiome” refers to the microorganisms and their genes while the “microbiota” only refers to the microbes themselves. Thus, the words "gut microbiota" should be with "gut microbiome" here.

Thank you, this has been corrected.

Best regards!

Reviewer 3 Report

Comments and Suggestions for Authors

In this review, Pribac et al. discussed the significant role of gut microbiome dysfunctions in amyotrophic lateral sclerosis (ALS) and explored the therapeutic potential of plant bioactive molecules, particularly essential oils, due to their anti-inflammatory properties and ability to modulate the gut. This review highlighted specific bacteria associated with ALS pathogenesis and the promising effects of bioactive plant molecules in improving the microbiome and enriching current ALS treatments. This review presents an interesting topic, but it has some issues. Here are some comments on this review:

 

1.        ALS in the title should be defined.

2.        Numbers in keywords should be removed.

3.        Line 41, please define all abbreviations when they are first used.

4.        Lines 63-65 appear to express the same meaning as the lines 58-61.

5.        Lines 71-73, it is recommended that some background related to gut microbiome metabolites be introduced before concluding.

6.        Lines 94-96, specific beneficial bacteria need to be pointed out and references cited.

7.        It is suggested that the authors could organize some tables to display how gut microbiome changes in ALS.

8.        Line 155, B. fragilis and E. coli need to be italicized.

 

9.        The structure of section 3.2 needs to be adjusted; the paragraph contains only one sentence that needs to be revised.

Author Response

Thank you very much for taking the time to review our manuscript in such detail. Please find the detailed responses below and the corresponding revisions in track changes in the re-submitted files.

COMMENT 1. ALS in the title should be defined.

The abbreviation has been changed in the title, thank you.

COMMENT 2.  Numbers in keywords should be removed.

Thank you, we removed them.

COMMENT 3. Line 41, please define all abbreviations when they are first used.

Thank you, correction can be seen line 42 and 43.

COMMENT 4. Lines 63-65 appear to express the same meaning as the lines 58-61.

Thank you, we removed one paragraph that indeed what a repetition of the previous one.

COMMENT 5. Lines 71-73, it is recommended that some background related to gut microbiome metabolites be introduced before concluding.

Thank you, I changed the end of that paragraph as following:

Therefore, manipulating the microbiota to regulate bacterial metabolite production such as short chain fatty acids (SCFA), secondary bile acids, Gamma-Aminobutyric Acid, or serotonin, emerges as a crucial strategy in ALS inflammation management [13,14].

COMMENT 6. Lines 94-96, specific beneficial bacteria need to be pointed out and references cited.

Thank you, we have updated according to your well pointed notes. The following paragraph has been extended:

Moreover, oral supplementation with Wild Orange (Citrus sinensis) EO has been observed to enhance the growth of beneficial bacterial species suc as Bifidobacterium spp. in the colon, leading to modifications in the composition and function of the intestinal microbiome [28].

COMMENT 7.       It is suggested that the authors could organize some tables to display how gut microbiome changes in ALS.

As for this aspect, we thought the list of bacteria in the figure acts as a sort of table to show how the microbiome composition changes – using a common denominator from most studies comprised in this review. We hope this works. Thank you!

COMMENT 8.       Line 155, B. fragilis and E. coli need to be italicized.

 Thank you, this has been changed.

COMMENT 9.        The structure of section 3.2 needs to be adjusted; the paragraph contains only one sentence that needs to be revised.

Thank you, we have made some corrections that can be seen in track changes.

Best regards.