Bioactive Metabolites from Yeasts Presumptively Qualified as Safe as Functional Agents in the Management of Type 2 Diabetes
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
- At the beginning, it is affirmative to praise one author who presented a systematic review with a significantly low degree
text matches determined via iThenticate of 13%.
-Abstract is sufficiently informative and speaks to the content of the text!
- With reference 8 must be supplemented with adequate studies (when it is stated that there are numerous studies)? It must be supplemented with those that speak in favor of that thesis!
- after the sentence "An alternative method, proposed by Metchnikoff, relied on the consumption of fermented foods to isolate potentially probiotic microorganisms". Check the reference if it is appropriate!
- The conclusion must be more specific! what is the effect on HgbA1c, c peptide, insulin ... something more specific for clinical practice!
Author Response
Thank you for taking the time to carefully review this manuscript and for your pertinent comments and suggestions. Please find the detailed responses below and the corresponding highlighted revisions in the resubmitted files.
Comment 1: At the beginning, it is affirmative to praise one author who presented a systematic review with a significantly low degree text matches determined via iThenticate of 13%.
Response 1: Thank you, dear reviewer, for your comment.
Comment 2: Abstract is sufficiently informative and speaks to the content of the text!
Response 2: Thank you, dear reviewer, for this comment which reflects the depth of your observation.
Comment 3: With reference 8 must be supplemented with adequate studies (when it is stated that there are numerous studies)? It must be supplemented with those that speak in favor of that thesis!
Response 3: Thank you for your comment. I agree with you. In fact, the paragraph dealing with the concern has been virtually restructured to incorporate both your concern and that of the other reviewer. The reformulation is therefore as follows (lines 44-56 of the revised manuscript):
A few preclinical studies in rats have demonstrated that administration of the Saccharomyces boulardii THT 500101 strain moderately improves blood glucose levels, reduces systemic inflammation, normalises the renin-angiotensin II system, and corrects the lipid profile [6, 8-10]. In addition to Saccharomyces boulardii, the most well-known and commercially available species, this list includes Saccharomyces bayanus, S. pastorianus, Kluyveromyces lactis, Komagataella phaffii, K. pastoris, Schizosaccharomyces pombe, Cyberlindnera jadinii, Hanseniaspora uvarum, Xanthophyllomyces dendrorhous, Ogataea angusta, Limtongozyma cylindracea, Yarrowia lipolytica, and Zygosaccharomyces rouxii [11]. However, their application in the management of diabetes remains very limited or even ineffective, despite the presence in their fermentates of bioactive molecules (organic acids, bioactive peptides, polysaccharides, carotenoids) known for their ability to alleviate diabetes and/or its complications [12-16]. These metabolites may act as signalling molecules, interpreted by host cells and triggering a cascade of reactions likely to regulate energy metabolism, insulin resistance, and oxidative stress. Therefore, exploring these bioactive compounds could pave the way for a postbiotic approach aimed at formulating food supplements or nutraceuticals that are more stable over time than living cells [17].
Comment 4: After the sentence "An alternative method, proposed by Metchnikoff, relied on the consumption of fermented foods to isolate potentially probiotic microorganisms". Check the reference if it is appropriate!
Response 4 : After verification, I agree with your comment, and I thank you for that. The sentence has been rephrased as indicated below, and the appropriate references have been included (lines 67-69 of the revised manuscript).
“An alternative method, based on the exploration of fermented foods to isolate potentially probiotic micro-organisms, corresponds to the initial approach adopted by Metchnikoff for the isolation and identification of Lactobacillus bulgaricus.”
Comment 5: The conclusion must be more specific! what is the effect on HgbA1c, c peptide, insulin ... something more specific for clinical practice!
Response 5 : Thank you for this suggestion, which will help make the reading more digestible and beneficial for the reader. The specific effects of the different categories of molecules studied have been briefly clarified in the conclusion (lines 399-408 of the revised manuscript).
“Exploring the under-explored metabolic profile of probiotic yeasts in the context of type 2 diabetes reveals promising therapeutic potential. The metabolites identified (SCFAs, BSCFAs, bioactive peptides, carotenoids, and polysaccharides) have complementary anti-diabetic effects. SCFAs and BSCFAs improve insulin sensitivity and glucose tolerance whilst modulating lipid and immune homeostasis. Bioactive peptides inhibit α-glucosidase and DPP-IV, stimulate the secretion of incretins (GLP-1, GIP) and protect β-cells without inducing hypoglycaemia. Carotenoids bolster antioxidant defences, reduce oxidative stress and inflammation (NF-κB, COX-2), and lower HbA1c whilst improving the lipid profile. Finally, β-glucans and mannan oligosaccharides regulate blood glucose, triglycerides, insulin resistance and inflammation (TNF-α), promote bile acid excretion, and positively modulate the gut microbiota. Exploiting these metabolites for postbiotic purposes could provide a standardised and stable alternative to probiotics. Nevertheless, the validation of these results, via complementary in vitro tests, will enable us to gain a deeper understanding of the mechanisms of action and to envisage clinical trials, the data from which, via meta-analyses, will enable us to make more generalised recommendations.”
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript needs careful revision, as it is difficult to understand in its current form. This manuscript contains many instances of incorrect citations of publications. The reviewer believes that the author needs to revise the list of publications with which the author supports his theses.
Introduction Section. After reading this section, it is not clear why the author wrote this manuscript. A Google Scholar search (for the phrase anti-diabetic effects of yeast) yields 3700 review articles published in the last five years. This section needs revision.
Lines 29-31, "...provide us with the elements we need to induce metabolic dysfunctions." This sentence should be reformulated. The reviewer assumes that the author meant that dietary habits could cause metabolic dysfunctions.
In this section, the author conveys ideas to the reader that are not supported by data from the cited publications. This is the text in lines 48-52, where the author states that the mushrooms listed in lines 43-48 produce biologically active substances with an antidiabetic effect; the author here refers to publications [9] and [10], the first one states that brewer's yeast improves glycemic indices in type 2 diabetes mellitus, the second one states that brewer's yeast extract stimulates glucose metabolism and inhibits lipolysis in rat adipocytes in vitro. Thus, using these publications for citation is incorrect. In lines 53-56, the author states that there are few studies on the antidiabetic effect of yeast metabolites; the reviewer would like to remind once again about the 3700 review articles published over the past five years, where this problem has been studied to one degree or another. A thorough revision of this fragment is needed here. There is an excellent review (https://doi.org/10.3390/jof10070489) that describes both the metabolites and their effects well.
Section 2 is titled "Discovery of Probiotics and Characteristics of Probiotic Yeasts". The section contains fragmentary information about the history of the discovery of probiotics and the methods of selecting probiotics. All this concerns bacterial probiotics, and there is nothing about probiotic yeast. Thus, the content of this section does not correspond to its title.
In Section 3, the author incorrectly interprets the information contained in the cited publications. This concerns publications [15], [16], and [17].
In Subsection 3.1 (Metabolite Profile of Probiotic Yeasts), information on the metabolic profile of probiotic yeast is very poorly presented. Incorrect citation is in lines 93-96; Publications [4] and [21] say nothing about fungal digestive enzymes and antimicrobial peptides. The same remark applies to lines 96-100 and [23] and [24]; these publications contain nothing about the effect of beta-glucans, in the context mentioned by the author.
In subsection 3.2 (Variability According to Culture Conditions), subsections 3.2.1 and 3.2.2 (3.2.1. Branched and Non-Branched Short Chain Fatty Acids and 3.2.2. Other Organic Acid) suddenly appear. These subsections talk about the potential antidiabetic effects of various organic acids. Firstly, this is out of context with subsection 3.2; secondly, this section contains data that are not related to probiotic yeast, this also applies to the cited literature. Is this section necessary in this form?
Author Response
Thank you for taking the time to thoroughly review this manuscript and for providing your valuable comments and suggestions. Below, you will find detailed responses along with the corresponding revisions, which have been highlighted in the revised manuscript.
Comment 1: Introduction Section. After reading this section, it is not clear why the author wrote this manuscript. A Google Scholar search (for the phrase anti-diabetic effects of yeast) yields 3700 review articles published in the last five years. This section needs revision.
Response 1: Thank you for your comment. We have taken it into consideration and noted that, indeed, a search on Google Scholar using the expression "anti-diabetic effects of yeast" yields over 3,700 raw results (narrative reviews). However, upon closer examination, it appears that these reviews do not address the current topic; rather, the high number of results seems to be due to noise associated with one or more of the search terms used. A more refined search on Web of Science, Scopus, and PubMed yields only 2, 2, and 0 results respectively. Upon further inspection, these few results are not directly related to the theme of this manuscript. These are:
The Many Faces of Kefir Fermented Dairy Products: Quality Characteristics, Flavour Chemistry, Nutritional Value, Health Benefits, and Safety (Scopus, Web of Science)
The compositional and functional properties of Kombucha: A literature review (Scopus)
Analysis of Health Benefits Conferred by Lactobacillus Species from Kefir (Web of Science)
The present manuscript stems from the observation that only a limited number of studies on yeasts have undertaken comprehensive characterisations aimed at their potential use in diabetes management. Although the effects of Saccharomyces boulardii in diabetic rats are often modest or inconclusive, this yeast secretes molecules with demonstrated antidiabetic properties or with the ability to mitigate diabetes-related complications. Investigating these bioactive compounds could therefore lead to the development of supernatant- or extract-based interventions, potentially offering more effective nutraceutical or dietary supplement options than whole-cell formulations.
Comment 2: Lines 29-31, "...provide us with the elements we need to induce metabolic dysfunctions." This sentence should be reformulated. The reviewer assumes that the author meant that dietary habits could cause metabolic dysfunctions.
Response 2: Thank you for your thoughtful comment, as the meaning of that sentence was neither precise nor accurate. It has been rephrased as shown below in the revised manuscript (lines 29 to 31 of the revised manuscript).
“Modern dietary habits, combined with an increasing consumption of highly calorific, salty, and fatty processed foods, promote the development of metabolic dysfunctions that underlie chronic diseases.”
Comment 3:
In this section, the author conveys ideas to the reader that are not supported by data from the cited publications. This is the text in lines 48-52, where the author states that the mushrooms listed in lines 43-48 produce biologically active substances with an antidiabetic effect; the author here refers to publications [9] and [10], the first one states that brewer's yeast improves glycaemic indices in type 2 diabetes mellitus, the second one states that brewer's yeast extract stimulates glucose metabolism and inhibits lipolysis in rat adipocytes in vitro. Thus, using these publications for citation is incorrect.
Response 3: Thank you for this remark. The references related to the ideas discussed have been added. Furthermore, the text has been reformulated to align with the content of the cited references. The revised version included in the manuscript (lines 44 to 56) is as follows:
“A few preclinical studies in rats have demonstrated that administration of the Saccharomyces boulardii THT 500101 strain moderately improves blood glucose levels, reduces systemic inflammation, normalises the renin-angiotensin II system, and corrects the lipid profile [6, 8-10]. In addition to Saccharomyces boulardii, the most well-known and commercially available species, this list includes Saccharomyces bayanus, S. pastorianus, Kluyveromyces lactis, Komagataella phaffii, K. pastoris, Schizosaccharomyces pombe, Cyberlindnera jadinii, Hanseniaspora uvarum, Xanthophyllomyces dendrorhous, Ogataea angusta, Limtongozyma cylindracea, Yarrowia lipolytica, and Zygosaccharomyces rouxii [11]. However, their application in the management of diabetes remains very limited or even ineffective, despite the presence in their fermentates of bioactive molecules (organic acids, bioactive peptides, polysaccharides, carotenoids) known for their ability to alleviate diabetes and/or its complications [12-16]. These metabolites may act as signalling molecules, interpreted by host cells and triggering a cascade of reactions likely to regulate energy metabolism, insulin resistance, and oxidative stress. Therefore, exploring these bioactive compounds could pave the way for a postbiotic approach aimed at formulating food supplements or nutraceuticals that are more stable over time than living cells [17].”
Comment 4: In lines 53-56, the author states that there are few studies on the antidiabetic effect of yeast metabolites; the reviewer would like to remind once again about the 3700 review articles published over the past five years, where this problem has been studied to one degree or another. A thorough revision of this fragment is needed here. There is an excellent review (https://doi.org/10.3390/jof10070489) that describes both the metabolites and their effects well.
Response 4: We thank the reviewer for this remark. We agree that when searching Google Scholar or other databases using the expression “anti-diabetic metabolites of yeast”, more than 3700 results are retrieved. However, a careful analysis shows that the majority of these refer to studies on filamentous fungi, as well as noise related to the use of yeast-derived α-glucosidase in in vitro assays. Ultimately, very few studies actually assess the effect of probiotic yeasts and/or their fermentates in the management of diabetes.
Furthermore, the article suggested by the reviewer is highly relevant and has indeed been used in the present manuscript (line 97, reference 31). However, it mainly describes the biological properties (antioxidant, anti-inflammatory, etc.) of Saccharomyces and non-Saccharomyces yeasts, rather than identifying specific bioactive compounds or directly assessing their antidiabetic activity.
Comment 5: Section 2 is titled "Discovery of Probiotics and Characteristics of Probiotic Yeasts". The section contains fragmentary information about the history of the discovery of probiotics and the methods of selecting probiotics. All this concerns bacterial probiotics, and there is nothing about probiotic yeast. Thus, the content of this section does not correspond to its title.
Response 5: This comment is entirely justified, and we thank you for it. In this section, the subheading “2.1. Exploration of yeasts” has been removed, as there is only one subsection. Furthermore, a new paragraph linking to the previous one and focusing on the characteristics of probiotic yeasts has been added as follows (lines 78 to 90 in the revised manuscript).
“Probiotics are live microorganisms that provide health benefits to humans and animals when consumed in adequate amounts. They enhance the activity of the host’s endogenous microflora, modulate the immune system, support digestion and metabolism, and influence the gut–brain axis [25-27]. Yeasts represent a valuable alternative to bacterial probiotics, especially in contexts where antibiotics are frequently used in therapeutic treatments may suppress or eliminate bacterial strains [28]. Their strong resistance to gastric acidity ensures their survival through the stomach and enables them to reach the intestine, where they can colonise effectively thanks to specific surface proteins and glycoproteins [29]. Once established, yeast probiotics exert immunomodulatory effects by stimulating cytokine production and enhancing immune cell activity. They also exhibit antimicrobial action by secreting organic acids, hydrogen peroxide, and antifungal peptides [28]. However, the beneficial effects may be attributed either to the yeast cells themselves or to the various metabolites they produce.”
Comment 6: In Section 3, the author incorrectly interprets the information contained in the cited publications. This concerns publications [15], [16], and [17].
Response 6: Thank you, we agree with your comment. To avoid associating inappropriate information, the first sentence has been slightly reworded, and a reference has been added. In the second sentence, a reference has been modified to remain in the context of diabetes. It is presented in the revised manuscript (lines 92-94) as follows:
“Contemporary research reveals a growing interest in the constituents of yeast extract and metabolites secreted by probiotic yeasts in the management of chronic diseases such as T2DM [12].”
Comment 7: In Subsection 3.1 (Metabolite Profile of Probiotic Yeasts), information on the metabolic profile of probiotic yeast is very poorly presented.
Response 7: Your suggestion is relevant, and we thank you for it. It has been taken into account, and this section has been restructured to highlight a number of yeast-derived metabolites, although not exhaustively. This revision is presented in the revised manuscript (lines 104-131) as follows:
« 3.1. Metabolite profile of QPS yeasts
Yeast metabolism can be likened to the components of a factory, where each stage yields an intermediate product and a final product at the end of the chain, including waste. Each of these products or by-products plays a role in the cell, although they can become harmful depending on their concentration. Their nature also varies according to the metabolic pathway employed, which itself is selected based on several factors such as the type and concentration of substrate, oxygen availability, temperature, and more [33].
In addition to ethanol abundantly produced by species of the genera Saccharomyces, Pichia, Schizosaccharomyces, Kluyveromyces, Candida, among others, yeasts generate a wide range of metabolites. Food-relevant metabolites are the most extensively documented, including glycerol, succinate, butyrate, acetate, α-ketoglutarate, and malate [33, 34]. Except for malate, ethanol, and glycerol, many of these compounds can be utilised by colonocytes as an energy source [35]. Yeasts also synthesise a variety of amino acids via the shikimate pathway and produce numerous volatile organic compounds such as phenyllactic acid, isoamyl alcohols, ethyl acetate, ethyl butyrate, ethyl isobutyrate, acetaldehyde, 1,1-diethoxyethane, 2-hydroxyisocaproic acid, and limonene [36-38]. They also release GABA (γ-aminobutyric acid), shikimic acid (a precursor to phenylalanine, tyrosine, and tryptophan), p-aminobenzoic acid, and tyrosol [39]. Yeasts, particularly Saccharomyces boulardii, produce bioactive peptides involved in regulating carbohydrate metabolism of interest for diabetes management and inhibiting pathogenic microorganisms. In addition to these compounds, certain strains are capable of synthesising polysaccharides and carotenoids, which possess antioxidant properties, modulate inflammation, and stimulate the immune system [9, 40].
It is important to note that the metabolomic profile is not fixed; it varies depending on the culture medium in which the microorganism is grown. In the following sections of this manuscript, metabolites with antidiabetic potential are grouped into organic acids (including short-chain fatty acids, branched-chain short-chain fatty acids, and other organic acids), bioactive peptides, and carotenoids, to highlight their relevance in diabetes management. »
Comment 8: Incorrect citation is in lines 93-96; Publications [4] and [21] say nothing about fungal digestive enzymes and antimicrobial peptides. The same remark applies to lines 96-100 and [23] and [24]; these publications contain nothing about the effect of beta-glucans, in the context mentioned by the author.
Response 8: Thank you for this comment. In response to comment 8, we have restructured the indicated section, ensuring that relevant and appropriate references were consulted and included.
Comment 9: In subsection 3.2 (Variability According to Culture Conditions), subsections 3.2.1 and 3.2.2 (3.2.1. Branched and Non-Branched Short Chain Fatty Acids and 3.2.2. Other Organic Acid) suddenly appear. These subsections talk about the potential antidiabetic effects of various organic acids. Firstly, this is out of context with subsection 3.2; secondly, this section contains data that are not related to probiotic yeast, this also applies to the cited literature. Is this section necessary in this form?
Response 9 : We fully agree with your view; this section can indeed be removed. The section entitled “Variability according to culture conditions” does divert the flow of the narrative and may distract the reader’s attention. Accordingly, this section has been deleted, and a new heading, “Antidiabetic potential of yeast-secreted metabolites,” has been added (line 129).
Regarding the second concern, yes, this section includes a reference that does not relate to probiotic yeasts, as we are targeting a broader group (QPS yeasts). As a result, the title 3.1 ‘Metabolite profile of probiotic yeasts’ has been amended as follows:
“3.1. Metabolite profile of QPS yeasts” see line 103 of the revised manuscript.
Written as such, the yeasts mentioned in this section remain on topic since QPS represent the large group of non-pathogenic yeasts, some of which are recognised as probiotics.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsNo
Author Response
Thank you for your contribution.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe author has done a significant amount of work to improve the quality of the manuscript. The reviewer is satisfied with the author's responses and believes that the manuscript is suitable for publication after correcting some errors. This concerns the content of line 18 in the abstract. The author wrote GLP-1 (Glucose-Like Protein-1) there; it seems that this is a mistake, and the author meant glucagon-like peptide-1.
Author Response
Comment 1: The author has done a significant amount of work to improve the quality of the manuscript. The reviewer is satisfied with the author's responses and believes that the manuscript is suitable for publication after correcting some errors. This concerns the content of line 18 in the abstract. The author wrote GLP-1 (Glucose-Like Protein-1) there; it seems that this is a mistake, and the author meant glucagon-like peptide-1.
Response 1: Thank you for your remark. The correction has been made in the revised manuscript as suggested. See line 18
