Intake of Lactiplantibacillus plantarum HEAL9 Improves Cognition in Moderately Stressed Subjects: A Randomized Controlled Study
Round 1
Reviewer 1 Report
The authors of the manuscript “Intake of Lactiplantibacillus plantarum HEAL9 improves cognition in moderately stressed subjects: a randomized controlled study” investigated in a cohort of 132 healthy adults with symptoms of moderate stress the effect of supplementation with the probiotc Lactiplantibacillus plantarum HEAL9 on stress, mood, cognition, sleep, awakening cortisol and immune blood markers. The result showed significantly different outcomes for some of the tests while for other tests no or only minor differences were observed between the probiotic and the placebo group.
The authors present very interesting positive results on the use of a specific probiotic strain for stress and cognition that are backed up with results from former studies investigating similar outcomes during probiotic supplementation.
Specific considerations to the authors:
The authors should be more consistent in naming the study product: L. plantarum HAEL9, LPHAEL9, LPHAEL9TM, HAEL9TM, or they should give an explanation why different names are used throughout the text.
Line 220: rephrase the sentence: The per protocol population (PP)….
Line 513: change “applicable” to “applied”
Regarding the changes of tryptophane and kynurenine, the authors discuss that the lower abundance of these metabolites could be due to the metabolic capability of the strain to degrade tryptophane.
Do the authors have knowledge on the genetic equipment of the strain to potentially degrade tryptophane?
What could be the cause of increased amounts in the metabolites in the placebo group?
The authors should make a statement on the persistence of the given strain in the gut after application.
Are any long time effects known from supplementation of this strain, even after stopping supplementation?
The authors should elaborate on the mode of action of this specific strain (e.g. specific bacterial metabolites) to give some explanations for the observed outcomes.
The authors of the manuscript “Intake of Lactiplantibacillus plantarum HEAL9 improves cognition in moderately stressed subjects: a randomized controlled study” investigated in a cohort of 132 healthy adults with symptoms of moderate stress the effect of supplementation with the probiotc Lactiplantibacillus plantarum HEAL9 on stress, mood, cognition, sleep, awakening cortisol and immune blood markers. The result showed significantly different outcomes for some of the tests while for other tests no or only minor differences were observed between the probiotic and the placebo group.
The authors present very interesting positive results on the use of a specific probiotic strain for stress and cognition that are backed up with results from former studies investigating similar outcomes during probiotic supplementation.
Specific considerations to the authors:
The authors should be more consistent in naming the study product: L. plantarum HAEL9, LPHAEL9, LPHAEL9TM, HAEL9TM, or they should give an explanation why different names are used throughout the text.
Line 220: rephrase the sentence: The per protocol population (PP)….
Line 513: change “applicable” to “applied”
Regarding the changes of tryptophane and kynurenine, the authors discuss that the lower abundance of these metabolites could be due to the metabolic capability of the strain to degrade tryptophane.
Do the authors have knowledge on the genetic equipment of the strain to potentially degrade tryptophane?
What could be the cause of increased amounts in the metabolites in the placebo group?
The authors should make a statement on the persistence of the given strain in the gut after application.
Are any long time effects known from supplementation of this strain, even after stopping supplementation?
The authors should elaborate on the mode of action of this specific strain (e.g. specific bacterial metabolites) to give some explanations for the observed outcomes.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Firstly, where is HEAL9TM in its marketing development? It’d behoove the paper to succinctly state where it is in the Introduction section. Moreover, the authors state that this is an exploratory study, but I feel the term exploratory doesn’t quite fit. In fact, I wonder if HEAL9TM isn’t already a marketed product somewhere (is it?), and if so, maybe this is more of a phase-4 post-marketing clinical trial entering a new value category (for people in normalcy)? The term exploratory study in my experience is usually reserved for either phase-1 (safety) or phase-2 (dose-finding) trials. Yet, in this case, from the reference list, we see there have already been two 2020 papers. They both are thorough clinical studies of HEAL9TM in dire human stress situations (acute stress and depressive illness) and both have reported therapeutically good results. So, in the context of the development of this probiotic, the first reports in print were on sick people (stressed or depressed) and only now have the developers of HEAL9TM gotten around to reporting healthy normal effects. I would only therefore agree to call this an exploratory study if the authors define these facts upfront. I would say that although earlier studies with patients have established useful doses and good results, this is the first time that relatively normal people have been studied with HEAL9TM for their mental status.
Overall, I like the design and thoroughness of the study and its analysis. The only statistic that confused me was in Methods section after the non-parametric Mann Whitney U Test, it was stated that within-product-group analysis was also done using paired t-test or the non-parametric test Wilcoxon Signed Rank test or Friedman´s test. Please define what is meant by “within-product-group” and how you rationalized no using Mann Whitney U Test here.
The final statement about limitations is useful but of concern, perhaps warranting a small paragraph. It reads “A final limitation in this study was the very high placebo-effects seen for (line 535) several variables.”… which is claimed to relate to “choosing subjective measurements in healthy and fairly young individuals”. Are you suggesting that depressed or anxiety patients might be better able to distinguish changing subjective mental states that emerge when taking HEAL9TM ? And, if so, why is that? It might be substantiated by the better findings in references #4 and #5! So, perhaps you need to reword this discussion (if you agree) by saying something like: Many of the mental state scores in the present study started so normal at baseline pre-treatment that they couldn’t improve much. Added to this was the challenge of sorting-out a discovered slight placebo effect. Fortunately, you succeeded in identifying separable probiotic changes (vs. placebo) thanks to large enough group numbers and by carefully matching the groups for age, sex, etc…
Here’s something else. “LPHEAL9 intake was found to significantly improve working and spatial memory as seen by the larger reduction in reaction time for the Numeric working memory test, as compared to the placebo group. Learning and visuospatial memory were studied in the Paired Associate Learning test, where LPHEAL9 treatment caused a significant reduction of the mean errors to success compared to the placebo group.” And then it is stated that one of the most significant results in the present study is that intake of LPHEAL9 improved the working memory as compared to the placebo group in the Word recall test.” Aren’t the ‘Numeric working memory test’ and ‘Word recall test’ conceptually related? If so, I think you didn’t say so.
Spelling problem:
in a study with L. plantarum 299v, where intake of this probiotic stain (strain) decreased the kynurenine level and improved the cognitive …
The following makes no sense to me!
“This stabilization of the inflammatory status (fractaline and TGFbeta) in the probiotic group in contrast to the placebo group is likely to be one underlying mechanism of the observed positive effect of LPHEAL9 on cognition.” Why do you say that?
I think with the above changes this paper should be published.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
