James V Gruber, Nicole Terpak and Sebastien Massard, Vantage12.01.23
It is well established that mammalian skin is a dynamic and constantly evolving structure that prevents humans from dehydrating in the desiccating environments of the earth. Without the protection of a very small layer of stratum corneum (approximately 10µm thick), the human body would rapidly dry out and life on the planet would be impossible (Figure 1). However, because the skin’s stratum corneum is constantly attacked by external forces (UV, weather, aging, pollution, etc.) it must constantly renew itself. The
The skin is bathed in lipids. A recent review by Rudan et al, describes in detail the vast complexity of the skin’s lipids. The science around investigating how they are formed and expressed comprises the emerging science of lipidomics.2-4 Aside from the lipids that emerge from the maturing keratinocytes, the skin also has ancillary appendages that express lipids called sebaceous glands.5 The sebaceous lipids mature in the skin’s sebaceous glands, which are comprised of cells called sebocytes. As the sebocytes mature, they too rupture and spill their oily contents into the sebaceous glands. There, the lipids migrate to the skin’s surface along the hair follicles where the sebaceous glands form an integral part. Sebum spreads across the skin surface forming a kind of first line of defense against external aggressors, including energy, bacterial and chemical aggressors.
For an active ingredient delivered to the skin surface to passively penetrate the lower layers of the stratum corneum and possibly to the viable epidermis, the ingredient must first permeate through the sebaceous lipids on the surface of the skin. To move deeper into the stratum corneum, the active ingredient must circumnavigate the torturous pathway of the complex and tightly organized lipid bilayer. Passive navigation can be bypassed by performing more active delivery of ingredients such as using electrical charge to disrupt the lipid barrier (ionophoresis) or by driving active ingredients through the stratum corneum using small microneedles.6 However, once these delivery mechanisms are employed, the topical applications move out of the realm of cosmetics and into the realm of therapeutics and pharmaceutics. In addition, the chemical nature of the active ingredient can strongly influence how well it can navigate the skin’s protective lipid armaments. If the ingredient itself is lipophilic (oil-loving) then it can more readily assimilate with the skin’s lipids than if the ingredient is hydrophilic (water-loving). Retinol is an example of a well-known lipophilic ingredient while vitamin C is a well-known hydrophilic ingredient commonly used in cosmetic formulations.
Gruber et al, recently reported using an in-situ testing model called skin-PAMPA (Skin Parallel Artificial Membrane Permeability Assay) to enable investigating how lipophilic ingredients like retinol can passively permeate through the skin’s tough lipid barriers.7 This original work examined the influence of jojoba oil and how it helps enhance the retinol’s ability to penetrate a lipid barrier. It demonstrated that jojoba oil possesses a unique ability to enhance skin permeation of retinol. It was suggested that jojoba oil was unique in this application, compared to other types of triglyceride oils, because jojoba seeds do not make triglyceride oils; instead, they make linear liquid wax esters.8 Human sebum is also comprised of similar linear wax esters as shown in Table 1 adapted from a paper by Downing et al.9
It was hypothesized that the linear wax esters of jojoba oil helped to fluidize the sebaceous lipids of the skin and thus better facilitated retinol’s penetration through the lipid barrier of the testing membrane. This hypothesis is supported by studies that demonstrate that sebaceous lipids can naturally be found within the stratum corneum lipid bilayers.10
The fact that jojoba seeds express liquid linear wax esters instead of triglyceride oils is interesting and offers the opportunity to naturally manipulate the chemistry of the linear esters using simple transesterification chemistries (Figure 2). It was recently reported that topical application of jojoba esters can enhance protective features and functionality, particularly when the skin is exposed to chemical irritants like surfactant.11
In the pantheon of skin care active ingredients, several are well-known lipophilic ingredients that offer demonstrable benefits to the skin. Retinol has established itself as one of the premier skin care ingredients due to its remarkable ability to stimulate epidermal barrier improvements.12 However, retinol also has been shown to have profound skin dehydrating effects.13 Resveratrol is also a well-established, naturally-derived ingredient that is found in grapes and Japanese Knotweed.14 In addition to its known antioxidant benefits, resveratrol has been shown to activate certain key proteins in skin called Sirtuin (SIRT) proteins that are involved in skin aging processes.15 These proteins also play important roles in skin barrier formation. Cannabinoids gained recognition as skin beneficial molecules since it was demonstrated that skin cells contain important receptor proteins that are activated by topical application of cannabinoids.16 One notable cannabinoid for skin care is cannabidiol (CBD) and highly purified versions are called isolates.
This article describes studies employing the skin-PAMPA testing methodologies reported earlier to examine how two jojoba esters, Jojoba Esters-1 and Jojoba Esters-2, influenced the permeation of three actives, retinol, resveratrol and CBD isolate. The studies expand on the earlier work done with natural jojoba oil and demonstrate that the linear esters of jojoba seed waxes can help improve the passive skin permeation of important cosmetic active ingredients.
A summary of the various testing formulations used in the skin-PAMPA are shown in Table 2.
Formulas 1 and 2 served as HPLC controls in these studies providing formulations with the jojoba esters without active. These formulations allow for development of the chromatography assay conditions used to determine the amount of each active that permeates into the skin-PAMPA acceptor reservoir but were not included in the analyses of active permeation described here.7
All samples were run in triplicate and the corresponding averages reported in µg/cm2 were statistically analyzed using the Student Paired T-Test in Excel with p≤0.05 demonstrating statistically significant values versus placebo controls (samples without jojoba esters).
The results of the studies using CBD isolate demonstrate that both the Jojoba Esters-1 and the Jojoba Esters-2 demonstrated a positive influence on improving passive lipid permeation of the CBD isolate compared against the placebo formulation. The Jojoba Esters-2 indicates an approximately 7-fold increase in permeation versus the placebo control while the Jojoba Esters-1 demonstrated an approximate 3-fold increase in passive permeation through the skin-PAMPA membrane.
Results from the resveratrol skin-PAMPA permeation study are shown in Figure 4.
The results from the resveratrol study demonstrate that both esters improved the permeation of the resveratrol by approximately 0.5-fold increase in permeation versus the placebo control. The results of the retinol permeations study are shown in Figure 5.
The data indicates the Jojoba Esters-1 demonstrated a statistically significant improvement in retinol permeation versus the placebo control. The increase in permeation of the retinol influenced by the Jojoba Esters-1 was approximately two-fold compared against the placebo formulation. The Jojoba Ester-2 shows some indications of superior skin permeation but did not reach the level of statistical significance in this study.
The results of all three studies continues to demonstrate that jojoba oil and its derivative esters can help improve the permeation of lipophilic actives through a lipophilic membrane employed in the skin-PAMPA permeation testing methodology. The data suggests that formulating these three lipophilic actives with the jojoba esters can likely help to facilitate the permeation of the actives through the skin’s lipid barriers. This conclusion builds on other studies demonstrating jojoba esters’ multifunctionality to improve easing skin inflammation as well as promote skin hydration and barrier recovery.11-16
References
renewal is driven by a process of cellular differentiation that occurs when keratinocytes in the epidermis move through stages of maturation, lose their ability to divide and ultimately die.1 During this process of cellular change, the maturing keratinocytes release lipids that form the skin’s lipid bilayer while the keratinocyte proteins, principally keratin, crosslink to form hardened, non-living shell-like structures called corneocytes. As this process occurs, the nuclear material in the keratinocytes is eliminated and the corneocytes are, essentially, non-living hard particles that reside within a matrix of lipids as shown in Figure 1. The structure of the skin’s stratum corneum is often compared to a brick-and-mortar structure, like a brick wall. Of course, such a comparison would require that the bricks constantly fall off (desquamation) and are replaced by bricks from lower parts of the wall (differentiation).The skin is bathed in lipids. A recent review by Rudan et al, describes in detail the vast complexity of the skin’s lipids. The science around investigating how they are formed and expressed comprises the emerging science of lipidomics.2-4 Aside from the lipids that emerge from the maturing keratinocytes, the skin also has ancillary appendages that express lipids called sebaceous glands.5 The sebaceous lipids mature in the skin’s sebaceous glands, which are comprised of cells called sebocytes. As the sebocytes mature, they too rupture and spill their oily contents into the sebaceous glands. There, the lipids migrate to the skin’s surface along the hair follicles where the sebaceous glands form an integral part. Sebum spreads across the skin surface forming a kind of first line of defense against external aggressors, including energy, bacterial and chemical aggressors.
For an active ingredient delivered to the skin surface to passively penetrate the lower layers of the stratum corneum and possibly to the viable epidermis, the ingredient must first permeate through the sebaceous lipids on the surface of the skin. To move deeper into the stratum corneum, the active ingredient must circumnavigate the torturous pathway of the complex and tightly organized lipid bilayer. Passive navigation can be bypassed by performing more active delivery of ingredients such as using electrical charge to disrupt the lipid barrier (ionophoresis) or by driving active ingredients through the stratum corneum using small microneedles.6 However, once these delivery mechanisms are employed, the topical applications move out of the realm of cosmetics and into the realm of therapeutics and pharmaceutics. In addition, the chemical nature of the active ingredient can strongly influence how well it can navigate the skin’s protective lipid armaments. If the ingredient itself is lipophilic (oil-loving) then it can more readily assimilate with the skin’s lipids than if the ingredient is hydrophilic (water-loving). Retinol is an example of a well-known lipophilic ingredient while vitamin C is a well-known hydrophilic ingredient commonly used in cosmetic formulations.
Jojoba’s Impact on Penetration
Gruber et al, recently reported using an in-situ testing model called skin-PAMPA (Skin Parallel Artificial Membrane Permeability Assay) to enable investigating how lipophilic ingredients like retinol can passively permeate through the skin’s tough lipid barriers.7 This original work examined the influence of jojoba oil and how it helps enhance the retinol’s ability to penetrate a lipid barrier. It demonstrated that jojoba oil possesses a unique ability to enhance skin permeation of retinol. It was suggested that jojoba oil was unique in this application, compared to other types of triglyceride oils, because jojoba seeds do not make triglyceride oils; instead, they make linear liquid wax esters.8 Human sebum is also comprised of similar linear wax esters as shown in Table 1 adapted from a paper by Downing et al.9It was hypothesized that the linear wax esters of jojoba oil helped to fluidize the sebaceous lipids of the skin and thus better facilitated retinol’s penetration through the lipid barrier of the testing membrane. This hypothesis is supported by studies that demonstrate that sebaceous lipids can naturally be found within the stratum corneum lipid bilayers.10
The fact that jojoba seeds express liquid linear wax esters instead of triglyceride oils is interesting and offers the opportunity to naturally manipulate the chemistry of the linear esters using simple transesterification chemistries (Figure 2). It was recently reported that topical application of jojoba esters can enhance protective features and functionality, particularly when the skin is exposed to chemical irritants like surfactant.11
In the pantheon of skin care active ingredients, several are well-known lipophilic ingredients that offer demonstrable benefits to the skin. Retinol has established itself as one of the premier skin care ingredients due to its remarkable ability to stimulate epidermal barrier improvements.12 However, retinol also has been shown to have profound skin dehydrating effects.13 Resveratrol is also a well-established, naturally-derived ingredient that is found in grapes and Japanese Knotweed.14 In addition to its known antioxidant benefits, resveratrol has been shown to activate certain key proteins in skin called Sirtuin (SIRT) proteins that are involved in skin aging processes.15 These proteins also play important roles in skin barrier formation. Cannabinoids gained recognition as skin beneficial molecules since it was demonstrated that skin cells contain important receptor proteins that are activated by topical application of cannabinoids.16 One notable cannabinoid for skin care is cannabidiol (CBD) and highly purified versions are called isolates.
This article describes studies employing the skin-PAMPA testing methodologies reported earlier to examine how two jojoba esters, Jojoba Esters-1 and Jojoba Esters-2, influenced the permeation of three actives, retinol, resveratrol and CBD isolate. The studies expand on the earlier work done with natural jojoba oil and demonstrate that the linear esters of jojoba seed waxes can help improve the passive skin permeation of important cosmetic active ingredients.
Materials and Methods
The methods employed in the present studies were fully described in the earlier work by Gruber et al.7 The Jojoba Esters-1 and Jojoba Esters-2 [INCI: Jojoba Esters] were provided by Vantage Personal Care, Fairfield, NJ, and were used at 10% in each testing formulation to closely mimic the previous study parameters done with jojoba oil.7 The retinol was purchased from BASF and used as is. The resveratrol was derived from Japanese Knotweed and was purchased from PureBulk (Roseburg, OR). The CBD isolate was suggested by the manufacturer to be 98% pure and was provided by OnScent (Norwood, NJ).A summary of the various testing formulations used in the skin-PAMPA are shown in Table 2.
Formulas 1 and 2 served as HPLC controls in these studies providing formulations with the jojoba esters without active. These formulations allow for development of the chromatography assay conditions used to determine the amount of each active that permeates into the skin-PAMPA acceptor reservoir but were not included in the analyses of active permeation described here.7
All samples were run in triplicate and the corresponding averages reported in µg/cm2 were statistically analyzed using the Student Paired T-Test in Excel with p≤0.05 demonstrating statistically significant values versus placebo controls (samples without jojoba esters).
Results and Discussion
The results of the lipid permeation study examining CBD isolate are shown in Figure 3.The results of the studies using CBD isolate demonstrate that both the Jojoba Esters-1 and the Jojoba Esters-2 demonstrated a positive influence on improving passive lipid permeation of the CBD isolate compared against the placebo formulation. The Jojoba Esters-2 indicates an approximately 7-fold increase in permeation versus the placebo control while the Jojoba Esters-1 demonstrated an approximate 3-fold increase in passive permeation through the skin-PAMPA membrane.
Results from the resveratrol skin-PAMPA permeation study are shown in Figure 4.
The results from the resveratrol study demonstrate that both esters improved the permeation of the resveratrol by approximately 0.5-fold increase in permeation versus the placebo control. The results of the retinol permeations study are shown in Figure 5.
The data indicates the Jojoba Esters-1 demonstrated a statistically significant improvement in retinol permeation versus the placebo control. The increase in permeation of the retinol influenced by the Jojoba Esters-1 was approximately two-fold compared against the placebo formulation. The Jojoba Ester-2 shows some indications of superior skin permeation but did not reach the level of statistical significance in this study.
The results of all three studies continues to demonstrate that jojoba oil and its derivative esters can help improve the permeation of lipophilic actives through a lipophilic membrane employed in the skin-PAMPA permeation testing methodology. The data suggests that formulating these three lipophilic actives with the jojoba esters can likely help to facilitate the permeation of the actives through the skin’s lipid barriers. This conclusion builds on other studies demonstrating jojoba esters’ multifunctionality to improve easing skin inflammation as well as promote skin hydration and barrier recovery.11-16
References
- Skin Barrier. Eds: Elias PM and Feingold KR. CRC Press, Taylor & Francis Group, Boca Raton, FL 2006.
- Rudan MV, Watt FM. Mammalian epidermis: A compendium of lipid functionality. Front Physiol. 12:804824. DOI:10.3389/fphys.2021.804824.
- Sochorova M, Vavrova K, Fedorova M, Ni Z, Stenter D, Kutman M, Willighagen EL, Letsiou S, Torocsik D, Marchetti-Deschmann M, Zoratto S, Kremsleher C, Gruber F. Research techniques made simple: Lipidomic analysis in skin research. J Invest Dermatol. 142;4-11:2022.
- He J, Jia Y. Application of omics technologies in dermatological research and skin management. J Cosmet Dermatol. 21;451-460:2022. DOI:10.1111/jocd.14100.
- Géhin C, Tokarska J, Fowler SJ, Barran PE, Trivedi DK. No skin off your back: the sampling and extraction of sebum for metabolomics. Metabolomics 19;21:2023. DOI: 10.1007/s11306-023-01982-3.
- Skin Permeation Fundamentals and Application. Ed. Zatz JL. Allured Publishing Corp.: Wheaton. 1993.
- Gruber JV, Terpak N, Massard S, Schwartz A, Bojanowski K. Passive Enhancement of Retinol Skin Penetration by Jojoba Oil Measured Using the Skin Parallel Artificial Membrane Permeation Assay (Skin-PAMPA): A Pilot Study. Clin Cosmet Invest Dermatol. 16;317-324:2023. DOI: 10.2147/CCID.S391667.
- Sturtevant D, Lu S, Zhou ZW, et al. The genome of jojoba (Simmondsia chinensis): a taxonomically isolated species that directs wax ester accumulation in its seeds. Sci Adv. 2020;6:eaay3240. doi:10.1126/sciadv.aay3240.
- Downing DT, Stewart ME, Wertz PW, Colton SW, Strauss JS. Skin Lipids. Comp Biochem Physiol. 76B;673-678:1983.
- Sadowski T, Klose C, Gerj MJ, Wojcik-Maciejewicz A, Herzog R, Simone K, Reich A, Surma MA. Large-scale human skin lipidomics by quantitative, high-throughput shotgun mass spectroscopy. Sci Rep.7:43761. DOI:10.1038/srep43761.
- Gruber JV, Terpak N, McCormack J, Massard S, Schwartz A, Lyon C. Jojoba oil esters: Ease inflammation, sensitivity, and water loss. Cosmet Toilet.138;36:2023.
- Farris P. Retinol: The ideal retinoid for cosmetic solutions. J Drug Dermatol.2:s4-210:2022. DOI: 10.36849/JDD.SO722.
- Gruber JV, Stojkoska V, Riemer J. Retinol has a skin dehydrating effect that can be improved by a mixture of water-soluble polysaccharides. Cosmetics 7; 80: 2020. DOI:10.3390/cosmetics7040080.
- Leis K, Pisanko K, Jundziłł A, Mazur E, Męcińska-Jundziłł K, Witmanowski H. Resveratrol as a factor preventing skin aging and affecting its regeneration. Adv Dermatol Allergol. 3;439-445:2022. DOI:10.5114.ada.2022.117547.
- Wen S, Zhang J, Yang B, Elias PM, Man MQ. Role of resveratrol in regulating cutaneous functions. Evid Based Complement Alternat Med. 2020:2416837. DOI: 10.1155/2020/2416837.
- Baswan SM, Klosner AE, Glynn K, Malik K, Yim S, Stern. Therapeutic potential of Cannabidiol (CBD) for skin health and disorders. Clin. Cosmet. Invest. Dermatol.13; 927-942:2020. DOI: 10.2147/CCID.S286411.