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Anatomy, physiology, and histology of the skin
Published in Michael Parker, Charlie James, Fundamentals for Cosmetic Practice, 2022
When keratinocytes reach the stratum corneum, they will differentiate no further, a stage known as terminal differentiation. Once they have terminally differentiated, these cells are known as corneocytes. Corneocytes are to all intents and purposes are dead cells, as during the process of terminal differentiation their nucleus, organelles and plasma membrane disintegrate. This disintegration process is driven by an influx of calcium, which, in turn, stimulates the release of tissue transglutaminases, which catalyse the cross-linking of proteins such as loricrin. These crosslinked proteins form a strong, waterproof sac to encase corneocytes. Whilst cross-linking is occurring, a lipid matrix is formed from lipids exuded from the terminally differentiating keratinocytes, acting as a glue to tightly bind these cells together. Once this process has finished, the terminally differentiated keratinocytes are stuck together in a strong, waterproof sheet. This structure is further strengthened by junctional proteins such as tight junctions and desmosomes between keratinocytes, which strongly adhere these cells to one another. By being both tightly bound and waterproof, the stratum corneum forms a barrier to protect deeper tissues from dehydration, poisonous chemicals and opportunistic pathogens. After approximately two weeks from the initial differentiation into a transit-amplifying cells, terminally differentiated keratinocytes are shed from the body via a process known as desquamation.
Atopic Dermatitis
Published in Pudupakkam K Vedanthan, Harold S Nelson, Shripad N Agashe, PA Mahesh, Rohit Katial, Textbook of Allergy for the Clinician, 2021
Luz Fonacier, Amanda Schneider
Atopic dermatitis has a pathogenesis of complex immune dysregulation and interplay of genetic, environmental, epidermal and psychological factors. The stratum corneum of healthy skin functions as a barrier and provides water-retaining properties. It contains an extracellular lipid matrix including ceramides, cholesterol and free fatty acids (Leung 2001). When this layer becomes dry and fissured, it becomes a portal of entry for bacteria, mostly commonly Staphylococcus aureus. Disruption of the integrity of the stratum corneum exposes epidermal and dermal extracellular matrix proteins, such as fibronectin and collagen which can serve as anchors for S. aureus binding via adhesions (Cho et al. 2001). In AD, the stratum corneum lipid composition contains decreased levels of ceramides and sphingosine which normally act as water-retaining molecules. Deficient ceramide increases secretion of ceramidases, which leads to increased transepidermal water loss, resulting in dry, cracked skin of AD (Cardona et al. 2006, Arikawa et al. 2002). Sphingosine has been shown to normally possess antimicrobial properties, thus deficiencies may favor bacterial colonization (Arikawa et al. 2002).
Cutaneous Photosensitization
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
The integument has certain intrinsic protective barriers to minimize damage from light exposure. Skin is an optically inhomogeneous medium that serves to modify the radiation that reaches deeper structures via the mechanisms of reflection, refraction, scattering, and absorption. The stratum corneum reflects 5 to 10% of incident solar radiation. In addition, the dead cells of the stratum corneum are composed primarily of keratin, a fibrous protein that absorbs significantly in the UVB and UVC spectral bands and also scatters most visible radiation because of its structural characteristics. The DNA present in these outer epidermal layers will absorb incident UV radiation allowing only 5 to 10% of solar radiation in the 290 to 310 nm band to actually penetrate to the basal epidermal cell layer and superficial dermal vasculature. However, wavelengths above 330 nm readily penetrate the epidermis to reach the deeper photosensitive dermal layers. In Caucasian skin, as much as 50% of incident UVA radiation may be transmitted to the basal cell layer and dermis. There is a significant reduction in UVA transmission in blacks, and those individuals with very dark skin may have as little as 5 to 10% of the incident UVA penetrate the epidermis. This phenomenon is due to the quantitative differences in the light-absorbing pigment, melanin, which serves to further protect the skin from light-induced damage. A more thorough review of these principles is available in other sources.1
Acacetin-loaded microemulsion for transdermal delivery: preparation, optimization and evaluation
Published in Pharmaceutical Biology, 2023
Yajing Wang, Qian Chen, Xianfeng Huang, Xiaojing Yan
Ex vivo permeation studies were conducted to compare the skin permeation ability among formulations of FA, FB and FC. Enhanced skin permeability of ME could be achieved by 10% DMSO (FB) and 50% DMSO(FC) at every time point. The enhanced permeability mechanisms of DMSO might due to (1) DMSO is a polar aprotic solvent able to dissolve polar and nonpolar small molecules, fluidize skin lipid molecules for vesicles permeation (Simoes et al. 2016), it also increases the entrapment of several drugs in lipid carriers by enhancing their solubility (Farooqui et al. 2022); (2) DMSO may also enhance transdermal penetration by improving partitioning of drug into skin layers (Omar et al. 2019). After 120 min, FB showed some advantages compared with FC, which probably attributing to improved skin hydration during transportation (Santos et al. 2008; Hathout and Elshafeey 2012). There should keep balance between enhancing the permeability and hydration of the skin stratum corneum (Fouad et al. 2013; Todosijević et al. 2015).
Solid lipid nanoparticles and nanostructured lipid carriers: a review of the methods of manufacture and routes of administration
Published in Pharmaceutical Development and Technology, 2022
Jafar Akbari, Majid Saeedi, Fatemeh Ahmadi, Seyyed Mohammad Hassan Hashemi, Amirhossein Babaei, Sadra Yaddollahi, Seyyed Sohrab Rostamkalaei, Kofi Asare-Addo, Ali Nokhodchi
Skin correlation is a common illness all over the world (Seth et al. 2017). The main challenge for curing this illness is the low efficiency of drugs to permeate through the skin. The stratum corneum is the main skin barrier. This can however be bypassed by changing the permeation from follicles or transcellular to paracellular. SLNs and NLCs have been fabricated to enhance permeation or penetration in the skin. Topical amphotericin B SLNs were prepared by a novel solvent diffusion technique with slight modification and lyophilized with and without cryoprotectants to determine their stability. It was reported that the SLNs particle size considerably enlarged in the SLN formulations lyophilized without cryoprotectants. Lipid nanoparticles have several benefits for manipulating drug delivery profiles (Table 5) (Butani et al. 2016; Chen et al. 2017).
Overcoming hydrolytic degradation challenges in topical delivery: non-aqueous nano-emulsions
Published in Expert Opinion on Drug Delivery, 2022
Arya Kadukkattil Ramanunny, Sachin Kumar Singh, Sheetu Wadhwa, Monica Gulati, Bhupinder Kapoor, Rubiya Khursheed, Gowthamarajan Kuppusamy, Kamal Dua, Harish Dureja, Dinesh Kumar Chellappan, Niraj Kumar Jha, Piyush Kumar Gupta, Sukriti Vishwas
As natural emulsifiers, such as phospholipids, polysaccharides, and proteins, are not effective in the preparation of NANEs, synthetic emulsifies have been commonly used. Among them, ionic surfactants are considered to be more toxic than nonionic ones. The anionic (negative) head group of the anionic surfactants such as dodecyl phosphate ester sodium salt, alcohol ethoxysulfate [84] binds to the cationic sites of the protein in the body through strong hydrophobic interaction leading to protein denaturation. This causes significant changes in the lipid bilayer that may enhance permeability or retention of the droplets [85]. The positive hydrophilic head of the cationic surfactants (cetyl trimethyl ammonium chloride, octadecyl trimethyl ammonium chloride) [84] interacts with the skin proteins through polar or hydrophobic interaction. This causes stratum corneum to swell, leading to destruction of skin tissue. Hence, nonionic surfactants are preferred [86]. The non-dissociable nature as well as lower critical micellar concentration of the nonionic surfactants make them less irritant than ionic surfactants. They promote penetration across intercellular regions of SC by increasing the fluidity and also improve solubilization and extraction of lipid components. The weak hydrophobic interaction with the keratin filaments results in disruption within the corneocytes [87]. However, toxicity-related issues do get exhibited at higher concentration of these surfactants also [88].