Hydrogel Formulation of Usnic Acid and Antibacterial Activity Test Against Propionibacterium acne
Round 1
Reviewer 1 Report
Authors should give more review in introduction part.
At line 81, authors state that "Solid dispersion of usnic acid PVP K-30 was prepared as described in previous work [15]." Please describe the process in short.
At line 132, authors state that "However, the viscosity of the F1a was the lowest which was relatively as liquid than gel." An explanation should be needed.
At line 179, authors state that "Preparation of hydrogel is influenced by the form of usnic acid used, which solid dispersion of usnic acid with PVP K-30 provides better result in appearance compared to intact usnic acid." Please give some discussions about the underline.
Author Response
Point 1: Authors should give more review in introduction part.
Response 1: We have added the introduction part
Point 2:At line 81, authors state that "Solid dispersion of usnic acid PVP K-30 was prepared as described in previous work [15]." Please describe the process in short.
Response 2:We have added explanation about the preparation of solid dispersion (line 86-90)
Point 3: At line 132, authors state that "However, the viscosity of the F1a was the lowest which wasrelatively as liquid than gel." An explanation should be needed.
Response 3: We have addedexplanation about the viscosity of the F1a in the text (line 129).
This result was likely due toinsufficient amount of gelling agent used to prepare the hydrogel as described in product description [22], thus the concentration of Aqupec hydrogel influenced the viscosity.
Point 4: At line 179, authors state that "Preparation of hydrogel is influenced by the form of usnic acid used, which solid dispersion of usnic acid with PVP K-30 providesbetter result in appearance compared to intact usnic acid." Please give some discussions about the underline.
Response 4: We have added the conclusion part (line 182).
Reviewer 2 Report
This manuscript describes the formulating hydrogel of usnic acid and evaluating the antibacterial activity against Propionibacterium acne. In this study, usnic was prepared in two different forms: intact usnic acid (UA) and solid dispersion of usnic acid with PVP K-30 (UA-SD). They found that the antibacterial activity against Propionibacterium acne by UA and US-SD was almost similar to marketed gel contained synthetic antibiotic and UA-SD provides better result in appearance compared to UA. In conclusion, the hydrogel UA-SD is promising preparation in handling acne. The research design is appropriate, the results appear sound, but lot of issues regarding the interpretation of the data, experimental protocols and additional discussion will need to be addressed!
Major comments
1. There are two enantiomer of usnic acid. Authors did not sign which one is the usnic acid they used. The (+)-usnic acid enantiomer appears to be selective against Streptococcus mutans. On the other hand, the (–)-usnic acid enantiomer is a selective natural herbicide because of its blocking action against a specific key plant enzyme (Cocchietto et al., 2002). It is important to address which kind of usnic acid they used in this study.
2. In cosmetology, it was used to some extent as an antimicrobial and deodorant agent. It is one of many constituents in oakmoss/treemoss extracts that used for perfuming purposes. However, usnic acid has pronounced sensitization potential. Cases of allergic contact dermatitis have been described (Sheu et al., 2006). In addition, usnic acid and its salts are idiosyncratically associated with severe hepatotoxicity and liver failure (Yellapu et al., 2011). In opinion of SCCNFP: “On review of the information presently available, it is the opinion of the SCCNFP that oakmoss/tremoss ectracts, present in cosmetic products, have a well recognized potential to cause allergic reactions in the consumer as fragrance ingredients.”
3. In addition, due to lack of data, it is not possible to reach a conclusion about the safety of using usnic acid in cosmetic products. Therefore, it is more important to investigate the side effect of usnic acid, for example, the allergic effect of UA and/or UA formulate in this study.
Miner comments
1. In materials and methods, 2.3 evaluation of hydrogel base, the experimental protocol should be described straightly instead of listed descriptions.
2. Table 2 and 2.6 evaluation of …… are not necessary, please remove.
3. In 2.8, the sample was measured at 217 nm. However, in your previous study (reference 13), the maximum absorbance of UA is 283 nm. What is the reason for using 217 nm as the wavelength for determination of UA in this study? In addition, authors should provide the standard curve and the linear calibration slope of UA should be listed in supporting information.
References
Cocchietto M, Skert N, Nimis P, Sava G (2002). A review on usnic acid, an interesting natural compound. Naturwissenschaften. 89 (4): 137–146.
SCCNFP (2000): Opinion on Oakmoss/Treemoss extracts and appropriate consumer information, 24 October (SCCNFP/0421/00)
Sheu M, Simpson EL, Law SV, Storrs FJ (2006). Allergic contact dermatitis from a natural deodorant: a report of 4 cases associated with lichen acid mix allergy. J Am Acad Dermatol. 55: 323-337.
Yellapu RK, Mittal V, Grewal P, Fiel M, Schiano T (2011). "Acute liver failure caused by 'fat burners' and dietary supplements: a case report and literature review". Canadian Journal of Gastroenterology. 25 (3): 157–60.
Author Response
Point 1: There are two enantiomers of usnic acid. Authors did not sign which one is the usnic acid they used. The (+)-usnic acid enantiomer appears to be selective against Streptococcus mutans. On the other hand, the (–)-usnic acid enantiomer is a selective natural herbicide because of its blocking action against a specific key plant enzyme (Cocchietto et al., 2002). It is important to address which kind of usnic acid they used in this study.
Response 1: We have characterized our isolated usnic acid using a polarimeter (bellingham stanley limited R91017) at wavelength 589 nm and the result was [α]D27+69 (concentration 0.1% in CHCl3).
Point 2:In cosmetology, it was used to some extent as an antimicrobial and deodorant agent. It is one of many constituents in oakmoss/treemoss extracts that used for perfuming purposes. However, usnic acid has pronounced sensitization potential. Cases of allergic contact dermatitis have been described (Sheu et al., 2006). In addition, usnic acid and its salts are idiosyncratically associated with severe hepatotoxicity and liver failure (Yellapu et al., 2011). In opinion of SCCNFP: “On review of the information presently available, it is the opinion of the SCCNFP that oakmoss/tremoss ectracts, present in cosmetic products, have a well-recognized potential to cause allergic reactions in the consumer as fragrance ingredients.”
Response 2:Our research is a preliminary study about preparation of usnic acid ant its potency as anti-acne preparation. We have added in the manuscript line 55:
As a preliminary study, this research was focused on the pharmaceutical aspects of hydrogel contained usnic acid and the potency of usnic acid in order to confirm the activity against P. acnes.
Point 3: In addition, due to lack of data, it is not possible to reach a conclusion about the safety of using usnic acid in cosmetic products. Therefore, it is more important to investigate the side effect of usnic acid, for example, the allergic effect of UA and/or UA formulate in this study.
Response 3: Despite some findings that usnic acid has allergic effect on the skin, usnic acid and solid dispersion-usnic acid that have been prepared in hydrogel showed its incredible activity against P. acnes in this preliminary study. Regarding allergic reaction and in vivo application on the skin, a further study needs to be addressed for safety use.
Point 4: In materials and methods, 2.3 evaluation of hydrogel base, the experimental protocol should be described straightly instead of listed descriptions.
Response 4: We have omitted the list and added a brief description.
Point 5: Table 2 and 2.6 evaluation of …… are not necessary, please remove.
Response 5: We already removed them as suggested
Point 6: In 2.8, the sample was measured at 217 nm. However, in your previous study (reference 13), the maximum absorbance of UA is 283 nm. What is the reason for using 217 nm as the wavelength for determination of UA in this study? In addition, authors should provide the standard curve and the linear calibration slope of UA should be listed in supporting information.
Response 6: There was an erratum in the manuscript and the wavelength should be 289 nm (as seen in the curve below).
Author Response File: 
Author Response.docx
Round 2
Reviewer 1 Report
I have no further comment.
Reviewer 2 Report
Dear Authors
According to your responses, this research is a preliminary study and was focused on the pharmaceutical aspects of hydrogel contained usnic acid in order to confirm the activity against P. acnes. We agree and hope a further study on allergic effect and safety data will be presented for application needs.
