First Evaluation of Roux-en-Y Gastric Bypass as a Novel Surgical Treatment for Diabetes and Glucose Metabolism Regulation in Cats

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors successfully established a feline diabetes model using partial pancreatectomy, splenectomy, and dexamethasone administration. Their findings indicate that Roux-en-Y gastric bypass (RYGB) is a highly effective intervention for managing feline diabetes, with the potential to induce sustained remission without the need for exogenous insulin. In addition to improving glycemic control, RYGB appears to provide further benefits in liver function and lipid metabolism and may help prevent the progression of diabetic complications.

These results are potentially significant and suggest that, in the future, RYGB could have broader applications in the prevention and treatment of type 2 diabetes and obesity-related complications in both animals and humans. Nevertheless, such implications should be interpreted with caution and substantiated through additional long-term and translational studies.

Author Response

We are very grateful for your high evaluation of this study, and for your precise summary of its core findings and potential broad impacts. We completely agree with your profound insights. Although RYGB has demonstrated highly promising efficacy in the feline diabetes model, a cautious and objective attitude must indeed be maintained when interpreting its application prospects in the broader prevention and treatment of type 2 diabetes and obesity-related complications in both animals and humans. We strongly agree with your suggestion regarding the need to further substantiate these conclusions through additional long-term follow-up and translational studies. In the future, we will further investigate the long-term efficacy of RYGB and its exact role in the progression of diabetic complications in clinical cases of naturally occurring feline diabetes.

Reviewer 2 Report

Comments and Suggestions for Authors

The idea of ​​the article is very innovative.

The major disadvangates:

However, surgically induced diabetes is very different from naturally occurring diabetes (due to obesity, islet amyloidosis, etc.).

Why is the spleen removed? It is redundant and distorts the function of the immune and hematopoietic systems.

ANOVA is not reliable when there are only 24 animals.

Histological analysis is very weak, unclear. No IHC.

A very serious ethical issue - animals die from diabetic coma within weeks. Is this necessary for research?

There are no studies on how hormones related to CD change.

Author Response

1. surgically induced diabetes is very different from naturally occurring diabetes

We completely agree with your viewpoint. The pathological mechanism of naturally occurring feline diabetes is extremely complex and differs from surgically induced models; however, spontaneous cases exhibit enormous individual variations in disease duration, severity, and spontaneous remission rates, and it is difficult for us to collect a sufficient sample size with comparable pathological states to achieve a standardized comparison for the evaluation in this study. We chose to adopt the induction method of "partial pancreatectomy combined with dexamethasone" referenced in the study by Hoenig et al., in order to rapidly and uniformly simulate a physiological baseline of insulin resistance and β-cell dysfunction within a controlled time window, thereby validating the fundamental feasibility of RYGB surgery.

2. Why is the spleen removed? It is redundant and distorts the function of the immune and hematopoietic systems.

The removal of the spleen was not the original intention of the experimental design, but was rather limited by the anatomical structure of cats. In cats, the left lobe of the pancreas is closely adjacent to the splenic artery and vein within the splenorenal ligament. To ensure the complete resection of the left pancreatic lobe and to avoid intraoperative hemorrhage of the splenic vessels or ischemic necrosis of surrounding tissues, a concurrent splenectomy is usually necessary. The absence of the spleen may have an impact on the immune and hematopoietic systems, but it has no direct effect on glycemic regulation and glucose metabolism hormones. Therefore, we believe it has no impact on the experimental results of this study.

3. ANOVA is not reliable when there are only 24 animals.

The small sample size is a limitation of this study. However, during the experimental design, we followed the 3R principles of laboratory animal ethics, aiming to minimize the number of live animals subjected to major surgery while ensuring the minimum statistically effective sample size. Before applying the one-way analysis of variance (ANOVA), we performed normality and homogeneity of variance tests on the data, and selected the LSD or Tamhane's T2 method accordingly.

4. Histological analysis is very weak, unclear. No IHC.

Currently, we have only used traditional H&E staining to observe the morphological changes of hepatic steatosis and islet cell density. The lack of IHC indeed limits our in-depth evaluation of β-cell functional recovery. Due to the limitations of experimental conditions, we are currently unable to perform supplementary IHC, and future studies will further verify these structural changes through IHC.

5. A very serious ethical issue - animals die from diabetic coma within weeks. Is this necessary for research?

This study protocol has been approved by the Animal Ethics Committee of Hunan Agricultural University (HAUCEC2024-35). The original intention of establishing an untreated diabetic control group was to clearly demonstrate the natural progression (i.e., fatality) of this induced model, thereby highlighting the life-saving effect of RYGB surgery. However, we sincerely accept your criticism, and in future studies, we will enforce an earlier humane endpoint.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript entitled “First Evaluation of Roux-en-Y Gastric Bypass as a Novel Surgical Treatment for Diabetes and Glucose Metabolism Regulation in Cats,” authored by Linfeng Li and colleagues, investigates the efficacy of Roux-en-Y gastric bypass (RYGB) surgery as a therapeutic intervention for feline diabetes mellitus (FDM). The study uses an experimental model of induced diabetes and compares the metabolic and hormonal outcomes of the surgical group with insulin-treated groups and untreated diabetic controls. The items described in the manuscript fall within the scope of the journal Veterinary Sciences, specifically within the sections of Nutritional and Metabolic Diseases in Veterinary Medicine and Veterinary Surgery, as the journal covers topics in endocrinology, physiology, metabolism, and surgical techniques in animals. Thirty-two references were used in the construction of the article, the oldest of which dates back to 1975, but the vast majority (approximately 74%) were published in the last 10 years, including relevant journals such as the Journal of the American College of Cardiology (2018) and the Clinical Journal of the American Society of Nephrology (2017). Regarding the issue of conflict of interest, no cross-references were identified in which the authors excessively cite their own previous work with the evident intention of self-promotion; the citations adequately support the hypotheses and methodologies presented (such as Hoenig's induction model). Thus, there is no apparent conflict of interest in the production of this material. According to the Veterinary Sciences (MDPI) guidelines, the abstract should have a maximum of 200 words and be structured, covering context, methods, results, and conclusions. However, the abstract presented has approximately 227 words (counting the body of the abstract text). Although very close to the limit, slight editing is recommended to ensure it does not exceed the 200 words required by the MDPI publisher's technical guidelines. Checking the journal's guidelines, no requirement for a "Simple Summary" was identified; however, a search of recently published articles revealed that they include this section, followed by the abstract. Therefore, authors can follow two approaches: 1) transform the simple summary into an abstract of up to 200 words; 2) maintain the simple summary and construct an abstract of up to 200 words. The manuscript did not explicitly present a list of keywords immediately following the abstract in the analyzed section. With the suggested changes, in order to increase the article's visibility on search engines, the inclusion of the following terms is suggested: Feline diabetes mellitus (specific and common term), Bariatric surgery (connects the study to comparative medicine research), Incretin hormones (relevant due to the GLP-1 and GIP analysis mentioned in the text), Islet cell regeneration (important focus of the histopathological results), and Metabolic surgery (updated term for this type of intervention). The study deals with the "First Evaluation" of Roux-en-Y gastric bypass (RYGB) in cats. Being a well-established technique in humans, but little explored in feline medicine for the treatment of diabetes, its novel nature significantly increases the interest of the scientific community. By using the feline model to study metabolic surgery, the work not only contributes to veterinary medicine but also offers valuable data for human medicine (One Health), since feline diabetes shares many pathophysiological similarities with human Type 2 Diabetes. The experimental design, which includes a surgical group (RYGB), a standard treatment control group (insulin glargine), and an untreated diabetic control group, provides a clear view of the effectiveness of surgery compared to conventional therapies. The study was not limited to glycemic control; it included biochemical parameters (ALT, AST), incretin hormone levels (GLP-1, GIP), and histopathological tissue analysis (liver and pancreas), which lends scientific depth to the results. The introduction is well-written, contextualizing the topic and presenting the issues in a concise and practical way. In the materials and methods section, I found the absence of dosages and routes of administration in the part that describes the medications used interesting, but I liked it because it's not the focus of the work. However, scientific articles should offer the possibility of replicating the study, making it applicable in the routine of researchers and enthusiasts. I would suggest simply placing the dosages used and routes of administration in parentheses next to each medication. This makes the study more complete, although researchers from different locations may use their own protocols for this type of surgery. The citation of the ethics committee approval is perfect. Another suggestion is to indicate a reference that explains the abdominal wall repair technique on line 106. The objective is not to teach the technique to the article's readers, but to indicate that a known technique was followed. This is just to strengthen the material. Figure 1 is excellent, as is its caption. On line 117, replace the number 6, which begins the sentence, with the word "Six". In Figure 2A, the caption indicates that there is an arrow showing the angle of His, but the arrow does not exist in the image. The other images are very good, very clear, and aid in understanding the text. The laboratory analyses are well-adjusted. The statistical analysis is well-defined, and I particularly like SPSS. Congratulations to the authors for choosing the package. I only suggest that the following phrase be inserted in the body of the text, after the terms "Statistics software," on line 189: "a free statistical package that can be downloaded from the internet." Figures 3, 4, 5, and 7 are very good. I, personally, really like column charts, and the authors were very successful in this choice, especially in using standard deviations and intervals with dashed lines. This greatly enriches the material and guides the readers. The only suggestion here is to remove the table from Figure 5, which does not exist in Figures 3 and 4. I believe it was a layout error. Figure 6 is very good, but I suggest improvements that will not compromise its reliability: darken the images and add a little more contrast, without exaggeration. The yellow arrow could be replaced with a more vibrant color such as dark blue or green. If possible, the scale bar could be thicker and its number made sharper. Additionally, the legend should include information on the color, objective lens used, and bar size (HE, 10x. Bar = 50µm). The same applies to Figure 10. The results are well explained and clear. The discussion is very good, but I suggest some specific improvements that will enhance the material. I suggest that the authors discuss in more depth whether the improvement observed after RYGB was purely due to caloric restriction and weight loss or whether there was an immediate hormonal change (incretin effect), as occurs in humans. This would make the article a fundamental reference for those studying feline endocrine physiology. Although the study uses an induced diabetes model (partial pancreatectomy and dexamethasone), readers will be interested in its application to cats with spontaneous diabetes and obesity. I suggest the authors add a paragraph on the surgical challenges and patient selection in routine veterinary clinical practice. Finally, the follow-up was 12 weeks, a limited time. Therefore, I suggest the authors mention the need for long-term follow-up studies (e.g., one year or more) to assess whether diabetes remission is permanent or if there are secondary nutritional deficiencies, something frequently mentioned in bariatric surgery studies. This follow-up could be more punctual, such as every 2 or 3 months, with blood tests being performed.

Author Response

We sincerely thank you for your comprehensive evaluation of our manuscript, and for your positive affirmation of this study's innovation, experimental design, and relevance to the "One Health" concept. We are very grateful for your constructive suggestions, which have significantly enhanced the clarity, reproducibility, and clinical applicability of our work.

We have adjusted the abstract to bring the word count to under 200 words, and added a keywords section after the abstract. Regarding the quality issues of some figures, we have made the necessary modifications: the angle of His in Figure 2 has been marked with an arrow, the outer border of Figure 5 has been removed, and the resolution of the figures has been improved. Since the research design of this paper only targets artificially induced experimental animals, clinical treatment protocols were not discussed. In addition, the 12-week observation period does indeed have certain limitations, as follow-up observations lasting several months were not conducted. However, in the authors' clinical cases, there are already successful cases that are more than one year post-operation.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The article was corrected, however, several conceptual and methodological issues remain and should be addressed before publication.

 

Why were the control group animals later left untreated and left to die? This is a serious breach of ethical norms. 

A surgically induced diabetes model in animals cannot be equated with naturally occurring diabetes in cats.

Does RYGB treat feline diabetes or surgical-pancreatogenic diabetes? This needs to be acknowledged more clearly in the Discussion section.

 

Islet self-repair” interpretation is VERY strong. Authors state: promoted pancreatic islet cell repair (Abstract + Discussion) . However: no Ki-67, no β-cell markers (insulin IHC), no apoptosis analysis. Histology shows only: morphological improvement.

The article: no detailed food intake analysis, no calorie balance.

The study is promising and could potentially be published once conceptual boundaries are resolved and mechanistic claims are refined.

Author Response

Thank you very much for your rigorous review and for recognizing the promising nature of our study. We deeply appreciate your constructive comments, which have been instrumental in refining our manuscript and clarifying our conceptual boundaries.

 

We have carefully addressed each of the concerns raised. Below, please find our point-by-point responses to the reviewer's comments.

 

Point-by-Point Responses to Reviewer Comments

Comment 1: Why were the control group animals later left untreated and left to die? This is a serious breach of ethical norms.

 

Author Response: We sincerely understand and respect the reviewer’s profound ethical concern regarding this outcome. We wish to clarify that all experimental procedures, including the establishment of the control group, were strictly reviewed and authorized in advance by the Animal Ethics Committee of the Hunan Agricultural University, China (HAUCEC2024-35).

 

Scientifically, the diabetic control group was initially established strictly as a positive control for comparative observation, with absolutely no intention of allowing the animals to die. Unfortunately, the onset of severe diabetic complications in this specific surgical-pancreatogenic model was extremely rapid and aggressive. The animals developed severe symptoms and fell into a coma within a very short period. Although we took immediate emergency measures to intervene and attempt to save them, the animals tragically did not survive.

 

We fully acknowledge the reviewer's ethical perspective. In retrospect, observing such a rapid progression to mortality is a harsh endpoint. We deeply regret this outcome and agree that stricter and earlier humane endpoints (e.g., euthanasia upon the initial onset of severe lethargy or weight loss, prior to coma) should have been implemented. We take this ethical feedback very seriously and guarantee that all our future experimental designs will incorporate strict early humane interventions to prevent animal suffering.

 

Action taken: No specific changes were made to the manuscript text regarding this, as the methodology reflects the approved protocol executed, but we assure the reviewer of our commitment to higher ethical vigilance in future studies.

 

Comment 2: A surgically induced diabetes model in animals cannot be equated with naturally occurring diabetes in cats. Does RYGB treat feline diabetes or surgical-pancreatogenic diabetes? This needs to be acknowledged more clearly in the Discussion section.

 

Author Response: We completely agree with your insightful distinction. The surgical-pancreatogenic model, while useful for simulating insulin resistance and β-cell depletion, does not perfectly mirror the complex, multifactorial pathogenesis of naturally occurring feline diabetes. RYGB in our study was specifically evaluated against this surgically induced model. We have now explicitly established this conceptual boundary in the manuscript.

 

Action taken: We have added a new limitation paragraph at the end of the Discussion section to clarify this distinction:

 

"However, certain limitations of the current study should be noted. First, it is important to clarify that RYGB was evaluated using a surgical-pancreatogenic diabetes model, which does not fully replicate the complex, multifactorial pathogenesis of naturally occurring feline diabetes..."

 

We also updated the Conclusions to reflect this specific scope:

 

"This study demonstrates that RYGB is a highly effective intervention for managing feline diabetes in a surgically-induced model..."

 

Comment 3: "Islet self-repair” interpretation is VERY strong. Authors state: promoted pancreatic islet cell repair (Abstract + Discussion). However: no Ki-67, no β-cell markers (insulin IHC), no apoptosis analysis. Histology shows only: morphological improvement.

 

Author Response: We are very grateful to the reviewer for pointing out this overstatement. We entirely agree that without molecular validations—such as Ki-67 proliferation assays, β-cell specific markers, or apoptosis analysis—we cannot definitively claim "cellular repair" or "regeneration." Our current histological data only support a morphological improvement compared to the control groups. We have thoroughly revised the manuscript to temper these mechanistic claims and ensure they strictly align with our histological evidence.

 

Action taken: 1. In the Simple Summary and Abstract, we changed "promoted pancreatic islet cell repair" and "self-repair" to "promoted morphological improvements in pancreatic islets" and "promoting morphological recovery of pancreatic islets".

2. In the Discussion and Conclusions, we removed statements about "restoring the number of islet cells" and "self-repair," replacing them with "morphological improvement."
3. We also explicitly acknowledged the lack of molecular evidence in the newly added limitation paragraph in the Discussion:

 

"...Second, while our histological data demonstrate clear morphological improvements in the pancreas, interpreting these changes as definitive 'islet self-repair' requires further molecular validation. Future studies incorporating specific β-cell markers, Ki-67 proliferation assays, and apoptosis analysis are necessary to substantiate claims of cellular regeneration."

 

Comment 4: The article: no detailed food intake analysis, no calorie balance.

 

Author Response: The reviewer raises an excellent point. Detailed tracking of dietary intake and energy expenditure is undeniably crucial for a comprehensive understanding of metabolic surgeries like RYGB.

 

In this initial study, our primary objective was to evaluate the surgical feasibility, overarching glycemic control, and major shifts in metabolic hormones (GLP-1, GIP) following RYGB. Furthermore, our experimental design deliberately simulated the normal daily rearing conditions of domestic cats, allowing them to eat commercial cat food normally. Because we aimed to observe the therapeutic effects of RYGB under these naturalistic feeding conditions rather than under strict caloric restriction or controlled feeding protocols, granular quantitative data on daily calorie balance were not rigorously tracked.

 

Because we cannot provide robust data to support a detailed discussion on this aspect, we have refrained from over-discussing dietary dynamics in the current manuscript to maintain scientific rigor. We consider this a valuable lesson and will prioritize comprehensive calorie tracking in our subsequent mechanistic studies.

 

Action taken: As we lack the quantitative data to meaningfully expand on this within the manuscript, we have acknowledged this gap in our internal review process and will ensure it is a primary focus in our future research protocols.

 

We hope that these revisions and clarifications address your concerns satisfactorily. Thank you once again for your time and expertise, which have undoubtedly elevated the scientific quality of our work.

 

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

 

The authors should more clearly acknowledge that the induced diabetes model (partial pancreatectomy + dexamethasone) does not fully replicate naturally occurring feline diabetes mellitus and discuss how this limitation may affect the interpretation of the results.

 

The potential systemic effects of splenectomy (immune and metabolic alterations) should be discussed as a possible confounding factor.

 

Conclusions regarding pancreatic islet “repair” or “regeneration” should be moderated, as histological evaluation relied solely on H&E staining without immunohistochemical confirmation of β-cell identity or proliferation.

The ethical considerations regarding the untreated diabetic control group, in which animals died from diabetic complications, should be more thoroughly discussed, including justification and humane endpoints.

 

The use of an untreated diabetic control group that was allowed to progress to fatal diabetic coma raises significant ethical concerns. In modern laboratory animal research, experiments are expected to minimize animal suffering and implement predefined humane endpoints. Allowing animals to reach terminal metabolic decompensation without intervention is difficult to justify scientifically and ethically. In particular, it is generally accepted in contemporary laboratory animal science that experimental designs should not allow animals to progress to predictable, severe, and ultimately fatal disease states when such outcomes can be prevented by predefined humane endpoints or therapeutic intervention. The manuscript should therefore clearly explain why such a design was considered necessary and how it complies with current animal welfare standards and internationally accepted guidelines for animal experimentation.

 

 

Author Response

We sincerely thank you for your rigorous evaluation of our manuscript and for providing such insightful and constructive comments. Your feedback regarding the model's limitations, ethical considerations, and the precision of our histological conclusions has been instrumental in elevating the scientific rigor and integrity of our work.

We have carefully revised the manuscript, particularly the Discussion section, to address each of your concerns. Please note that all modifications and additions in the revised manuscript have been marked in red and blue text for your convenience.

Below, please find our point-by-point responses.

Comment 1: The authors should more clearly acknowledge that the induced diabetes model (partial pancreatectomy + dexamethasone) does not fully replicate naturally occurring feline diabetes mellitus and discuss how this limitation may affect the interpretation of the results.

Author Response: We completely agree with your assessment. The surgically-induced model, while effective for standardizing baseline insulin resistance and β-cell depletion, lacks the chronic, multifactorial complexity of spontaneous feline diabetes (which involves long-term obesity and islet amyloidosis). We have explicitly acknowledged this limitation and cautioned against over-extrapolating our experimental findings to routine clinical cases. Action Taken: We have added a dedicated explanation regarding this limitation in the Discussion section. The newly added text has been marked in red and blue font in the revised manuscript.

Comment 2: The potential systemic effects of splenectomy (immune and metabolic alterations) should be discussed as a possible confounding factor.

Author Response: Thank you for highlighting this important point. The splenectomy was performed purely out of anatomical necessity to safely resect the left pancreatic lobe without causing severe hemorrhage. However, we fully recognize that its removal is not physiologically neutral. We have updated the Discussion to openly acknowledge this as a potential confounding factor. Action Taken: We have inserted a clarification in the Discussion section to address the systemic effects of the splenectomy. These revisions are highlighted in red and blue font in the updated manuscript.

Comment 3: Conclusions regarding pancreatic islet “repair” or “regeneration” should be moderated, as histological evaluation relied solely on H&E staining without immunohistochemical confirmation of β-cell identity or proliferation.

Author Response: We are very grateful for this critical correction. We entirely agree that traditional H&E staining only allows us to observe morphological preservation, not true cellular regeneration. We have meticulously reviewed the manuscript, tempering claims of "regeneration" or "repair" to "structural islet improvements" and "morphological preservation." We have also explicitly stated the need for future molecular studies utilizing immunohistochemical markers (e.g., insulin, Ki-67). Action Taken: We have modified the histopathology discussion and the limitations paragraph accordingly. All related changes are marked in red and blue font in the revised manuscript.

Comment 4: The ethical considerations regarding the untreated diabetic control group, in which animals died from diabetic complications, should be more thoroughly discussed, including justification and humane endpoints.

Author Response: We profoundly respect and accept this ethical critique. Our initial rationale for the untreated group was to establish the aggressive baseline trajectory of this specific surgical model to unequivocally demonstrate the life-saving efficacy of RYGB. However, we agree that allowing animals to reach terminal metabolic decompensation is unacceptable by contemporary animal welfare standards. We have transparently discussed this ethical flaw, justified our initial intent, and firmly committed to enforcing strict, early humane endpoints in all future experimental designs. Action Taken: We have incorporated a new ethical reflection paragraph in the Discussion. These additions are marked in red and blue font in the revised manuscript.

We hope that these revisions satisfactorily address your concerns. Thank you once again for your time, expertise, and guidance, which have significantly improved our manuscript.

Sincerely,

Linfeng Li On behalf of the Authors College of Veterinary Medicine, Hunan Agricultural University