Exploration of retinoid activity and the role of inflammation in acne: issues affecting future directions for acne therapy

Formulation of lemongrass oil (Cymbopogon citratus)-loaded solid lipid nanoparticles: an in vitro assessment study

Cymbopogon citratus (DC) stapf. (Gramineae) is a herb known worldwide as lemongrass. The oil obtained, i.e., lemongrass oil has emerged as one among the most relevant natural oils in the pharmaceutical industry owing to its extensive pharmacological and therapeutic benefits including antioxidant, antimicrobial, antiviral and anticancer properties. However, its usage in novel formulations is constrained because of its instability and volatility. To address these concerns, the present study aims to formulate lemongrass-loaded SLN (LGSLN) using hot water titration technique. In the Smix, Tween 80 was selected as a surfactant component, while ethanol was taken as a co-surfactant. Different ratios of Smix (1:1, 1:2, 1:3, 2:1 and 3:1) were utilized to formulate LG-loaded SLN. The results indicated the fact that the LGSLN formulation (abbreviated as LGSLN1), containing lipid phase 10% w/w (i.e., LG 3.33% and SA 6.67%), Tween 80 (20% w/w), ethanol (20% w/w) and distilled water (50% w/w), revealed suitable nanometric size (142.3 ± 5.96 nm) with a high zeta potential value (- 29.12 ± 1.7 mV) and a high entrapment efficiency (77.02 ± 8.12%). A rapid drug release (71.65 ± 5.33%) was observed for LGSLN1 in a time span of 24 h. Additionally, the highest values for steady-state flux (Jss; 0.6133 ± 0.0361 mg/cm2/h), permeability coefficient (Kp; 0.4573 ± 0.0141 (cm/h) × 102) and enhancement ratio (Er; 13.50) was also conferred by LGSLN1. Based on in vitro study results, the developed SLN appeared as a potential carrier for enhanced topical administration of lemongrass oil. The observed results also indicated the fact that the phyto-cosmeceutical prospective of the nanolipidic carrier for topical administration of lemongrass oil utilizing pharmaceutically acceptable components can be explored further for widespread clinical applicability.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03726-5.

Guidance for the pharmacological management of acne vulgaris

INTRODUCTION

Many international guidelines and expert consensuses are available to help the clinician diagnose and treat acne vulgaris; however, a simplified practical guidance that integrates current existing published recommendations is still lacking. This article aims to give practical and simplified insight into the treatment of acne.

AREAS COVERED

Herein, the author discusses the treatment of comedonal, papulopustular, and nodular/cystic/conglobate acne. The author also proposes a simplified treatment escalation strategy that is based on disease severity and extension, starting with topical treatments for mild cases and progressing over to systemic therapies in more severe cases.

EXPERT OPINION

The ideal acne treatment would simultaneously and safely target all the pathogenic factors implicated in the appearance of acne lesions with minimal side effects. Since no such treatment currently exists, combination therapies are usually recommended for most types of acne. A major limitation in choosing an appropriate treatment plan is the discrepant use of classification systems across the published literature making it difficult to draw clear and succinct conclusions about the recommendations given. Acne is not a traditional infectious disease and so while antibiotics may improve symptoms, they do not reliably resolve the condition. Thus, there is currently a tendency to opt for antibiotic-sparing treatment strategies whenever possible.

Involvement of Pattern Recognition Receptors in the Direct Influence of Bacterial Components and Standard Antiacne Compounds on Human Sebaceous Gland Cells

INTRODUCTION

Pattern recognition receptors are involved in innate and adaptive immunity by detecting microbial components. Bacteria have been accused to play a role in inflammatory acne. We investigated the potential involvement of Toll-like receptor (TLR)2, TLR4, TLR6, and CD14 in the direct influence of bacterial components and standard antiacne compounds on human sebocytes.

METHODS

mRNA and protein expression of TLR2, TLR4, TLR6, and CD14 in SZ95 sebocytes was evaluated by real-time qRT-PCR and immunocytochemistry. The effects of lipopolysaccharides (LPS) and lipoteichoic acid on TLR2, TLR4, and CD14 expression and of cytokine/chemokine secretion by 13-cis-retinoic acid, all-trans-retinoic acid, retinol, and hydrocortisone at the mRNA and protein levels were assessed by real-time qRT-PCR and ELISA and verified by cocultivation with neutralizing antibodies.

RESULTS

The constitutive expression of TLR2, TLR4, and CD14 in SZ95 sebocytes was augmented by exposure to LPS. Hydrocortisone induced TLR2, but markedly reduced TLR4 expression. 13-cis-retinoic acid and all-trans-retinoic acid regulated IL-6 release. LPS enhanced and hydrocortisone reduced cytokine and chemokine release. Anti-TLR4 and anti-CD14 mAb blocked LPS-induced IL-8 and IL-6 release.

CONCLUSIONS

Microbial components use pattern recognition receptors to directly activate sebocytes to express a wide range of proinflammatory molecules and especially IL-8 and IL-6 in a TLR4- and CD14-specific manner. Retinoids, but mostly corticosteroids, also use this pathway to exhibit anti-inflammatory effects.

Comparison of guidelines and consensus articles on the management of patients with acne with oral isotretinoin

Guidelines and consensus on the management of patients with acne aim to give evidence-based, expert-group recommendations. This review compares current guidelines and consensus articles to provide a compilation of recommendations on the treatment of acne with oral isotretinoin. Ten common, relevant, clinical questions are addressed, based on published recommendations, including the indications of isotretinoin, the proposed daily dose, the cumulative isotretinoin dose and the laboratory monitoring needed. Recommendations on special considerations are also addressed, including the timing of procedures and the question of an association of depression or inflammatory bowel disease with isotretinoin. A major limitation is the use of different classification systems for acne across guidelines. The recommended daily dose ranges from 0.3 to 0.5 mg/kg in the European guidelines to up to 1 mg/kg in the US guidelines. A specific duration of treatment of at least 6 months is only recommended in the European guidelines. All guidelines report the need of strict pregnancy prevention measures. The European, French and US guidelines recommend to monitor for symptoms of depression. Important clinical questions that are inconsistently addressed in guidelines include the age indication, the recommendation for a cumulative dose, the timing of procedures, the association of isotretinoin with IBD, the recommendation for preventing acne flares and for appropriate laboratory monitoring. These topics should be clearly included in the recommendations of guidelines as they are often raised in everyday clinical practice.

Comparison of Efficacy of Doxycycline and Isotretinoin on Cutaneous Human Beta-Defensin-1 and -2 Levels in Acne Vulgaris

Background:

Recent studies have shown that human beta-defensin-1 (hBD-1) and (human beta-defensin-2 hBD-2), which are antimicrobial peptides produced by the skin, play a role in the pathogenesis of acne vulgaris (AV).

Objective:

The aim of this study was to determine the role of antimicrobial peptides in the pathogenesis of AV and enlighten the effects of doxycycline and isotretinoin in the expression of these defensins in AV.

Materials and Methods:

A total of 44 patients (22 patients in each group) with Grade 6 and 8 AV who were indicated doxycycline or isotretinoin for their treatment, and 20 healthy volunteers were included in this study. Pretreatment cutaneous samples were obtained from pustular lesions and uninvolved skin of AV patients and were repeated after the treatment. Only one biopsy was obtained from controls.

Results:

Cutaneous levels of hBD-1 and hBD-2 were significantly increased in AV patients when compared with healthy controls (P<0.05). Doxycycline therapy achieved a decrease in hBD-1 levels (P<0.05), whereas isotretinoin therapy achieved a reduction in hBD-2 levels when compared with pretreatment levels (P<0.05). Posttreatment hBD-1 and hBD-2 levels were not different between doxycycline and isotretinoin groups (P>0.05).

Conclusion:

In the light of these results, it was reasonable to assume the role of hBD-1 and hBD-2 in the pathogenesis of AV. Our results showing a significant reduction in hBD-1 staining with doxycycline treatment and in hBD-2 with isotretinoin suggested that some part of their anti-acne effect worked through these mechanisms.

Cutaneous induction of corticotropin releasing hormone by Propionibacterium acnes extracts

The skin commensal bacillus Propionibacterium acnes is known to play a major role in the development of acne vulgaris and it is established that this bacteria is involved both in the induction and maintenance of the inflammatory phase of acne. The corticotropin releasing hormone (CRH), a neuropeptide originally isolated from the hypothalamus, is also produced by the skin. CRH has been reported to play a role in the inflammation, the production of sebum and finally the differentiation of keratinocytes. At the therapeutic level, zinc is known to act specifically on inflammatory lesions with still partially known mechanisms and thus could play an important role in the development of inflammatory acne lesions. Our objective was to study the modulation of CRH expression by keratinocytes induced by P. acnes extracts. CRH expression was examined using immunohistochemistry technique on deep-frozen sections of normal human skin explants incubated with two different extracts of P. acnes and with or without zinc salts. We observed that the membrane fraction (FM) of P. acnes increased the CRH expression in the epidermis. This result indicates that P. acnes, by stimulating the production of CRH, can both modulate the differentiation of keratinocytes and increase the local inflammation, arguing that this bacterium plays a role not only in the development of inflammatory acne lesions but also in the formation of the microcomedo in the early stages of acne.

Efficacy and safety of acnecutan for acne treatment

Acnecutan represents an innovative form of isotretinoin, having bioavailability The aim of our study was to evaluate safety and clinical efficacy of the drug isotretinoin (Acnecutan) in the treatment of patients with acne of medium-severe and severe. The treatment of 56 patients with acne, until the exchange rate dose of 100-120 mg/kg. The clinical results of the drug Acnecutan indicate a high level of safety and tolerability

Studies on effectiveness and safety of system retinoids use in therapy ofadolescent acne

The article describes up-to-date data on mechanics of epigenetic effects of system retinoid - isotretinoin (Roaccutane). It is noted, that modern acne therapy is able not only to pathogenetically influence consequences of the process, but effect genetical causes of desease, leading to persistant changes and normalization of regulatory segments DNA structure under influence of isotretinoin. Also this article lists data on the use of isotretinoin (Roaccutane) for acne treatment of 237 adolescents. Studies were performed on frequency of occurrence, degree of manifestation of secondary effects and methods of levereging this effects in practical use. Authors state that correctly prescribed treatments are safe and do not cause serious secondary effects with in case of long treatmetns.

Pharmacotherapy of diseases mediated by 5-lipoxygenase pathway eicosanoids

Inflammatory eicosanoids generated by the 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism are now known to have at least 6 receptors: OXE, which recognizes 5-HETE and 5-oxo-ETE; a putative receptor recognizing a potent 5-oxo-ETE metabolite, FOG(7); the LTB(4) receptors, BLT1 and BLT2; the cysteinyl leukotriene receptors, CysLT(1) and CysLT(2), which recognize leukotrienes LTC(4), LTD(4), LTE(4) and LTF(4). The 5-LO pathway is activated in many diseases and invokes inflammatory responses not affected by glucocorticoids, but therapy with selective BLT1 or CysLT(1) antagonists in asthma has met with variable success. Studies show that 5-LO pathway eicosanoids are not primary mediators in all cases of asthma, but may be especially important in severe persistent asthma, aspirin- and exercise-induced asthma, allergic rhinitis, COPD, idiopathic pulmonary fibrosis, atherosclerosis, atopic dermatitis, acne and ischemia-related organ injury. These disorders appear to involve multiple 5-LO pathway eicosanoids and receptor subtypes, suggesting that inhibition of the pathway at the level of 5-LO may be necessary for maximal efficacy.

Skin Retinoid Concentrations Are Modulated by CYP26AI Expression Restricted to Basal Keratinocytes in Normal Human Skin and Differentiated 3D Skin Models

Cellular levels of all-trans retinoic acid (RA) are meticulously regulated utilizing an array of systems to balance uptake, biosynthesis, catabolism, and efflux transport. Metabolic transformation of all-trans RA to 4-hydroxylated RA appears to be primarily catalyzed by the cytochrome P450 (CYP) 26AI. Analysis of monolayer cultures of normal human epidermal keratinocytes (NHEKs) and dermal fibroblasts by quantitative real-time PCR and reverse transcription-PCR revealed no basal levels of CYP26AI mRNA expression, whereas specific transcripts were detectable following addition of 10(-6) M all-trans RA. Immunofluorescence and Western blot analysis showed a weak expression of CYP26AI in NHEK, which was increased by stimulation with all-trans RA. Using a newly developed peptide antibody, we further examined the localization of CYP26AI expression in normal skin and three-dimensional (3D) skin models. In contrast to cell culture monolayers where CYP26AI was only weakly detectable, strong constitutive expression of CYP26AI in vivo and in organotypic culture was found to be restricted to basal epidermal keratinocytes, as well as eccrine sweat glands and sebaceous glands. These studies verify the capacity of human skin to metabolize RA, although substantial differences exist in CYP expression between normal skin and 3D skin models compared to monolayer cultures. Complex metabolic processes that maintain retinoid homeostasis may therefore be better studied in model systems more closely resembling in vivo skin. In light of our prior studies documenting the functional activity of RA metabolites, expression of CYP26 in the sebaceous gland epithelium supports the suggestion that altered RA metabolism may be involved in the pathogenesis of acne.

Matrix metalloproteinases of epithelial origin in facial sebum of patients with acne and their regulation by isotretinoin

Acne vulgaris is a skin disorder of the sebaceous follicles, involving hyperkeratinization and perifollicular inflammation. Matrix metalloproteinases (MMP) have a predominant role in inflammatory matrix remodeling and hyperproliferative skin disorders. We investigated the expression of MMP and tissue inhibitors of MMP (TIMP) in facial sebum specimens from acne patients, before and after treatment with isotretinoin. Gelatin zymography and Western-blot analysis revealed that sebum contains proMMP-9, which was decreased following per os or topical treatment with isotretinoin and in parallel to the clinical improvement of acne. Sebum also contains MMP-1, MMP-13, TIMP-1, and TIMP-2, as assessed by ELISA and western blot, but only MMP-13 was decreased following treatment with isotretinoin. The origin of MMP and TIMP in sebum is attributed to keratinocytes and sebocytes, since we found that HaCaT keratinocytes in culture secrete proMMP-2, proMMP-9, MMP-1, MMP-13, TIMP-1, and TIMP-2. SZ95 sebocytes in culture secreted proMMP-2 and proMMP-9, which was also confirmed by microarray analysis. Isotretinoin inhibited the arachidonic acid-induced secretion and mRNA expression of proMMP-2 and -9 in both cell types and of MMP-13 in HaCaT keratinocytes. These data indicate that MMP and TIMP of epithelial origin may be involved in acne pathogenesis, and that isotretinoin-induced reduction in MMP-9 and -13 may contribute to the therapeutic effects of the agent in acne.

Peroxisome proliferator-activated receptor and farnesoid X receptor ligands differentially regulate sebaceous differentiation in human sebaceous gland organ cultures in vitro

BACKGROUND

Nuclear hormone receptors are important in the regulation of epidermal differentiation and have been implicated in lipid metabolism. In particular, there is evidence suggesting that the activation of peroxisome proliferator-activated receptors (PPARs) is an important factor in the regulation of sebocyte lipogenesis.

OBJECTIVES

To determine the role of PPARs, farnesoid X receptor (FXR) and other orphan nuclear hormone receptors in sebaceous gland function in vitro by investigating the biochemical effects of appropriate ligands, and by establishing the RNA and protein expression patterns of a number of nuclear receptors in sebaceous glands ex vivo.

METHODS

Human chest sebaceous glands were maintained in vitro as freshly isolated and as 7-day cultured whole organs. We then studied the effects of appropriate ligands on the glandular rates of lipogenesis and DNA synthesis, as well as determining the mRNA (reverse transcription-polymerase chain reaction) and protein expression patterns (immunohistochemistry/immunoblotting) of the nuclear hormone receptors of interest.

RESULTS

PPAR ligands, but not FXR ligands, inhibited sebaceous lipogenesis, in particular the PPARalpha ligands LY 171883 and WY 14643, and the PPARgamma ligands BRL 49653 and 15-deoxy-Delta-12,14-prostaglandin J(2). We detected RNA expression of PPARalpha, PPARbeta, PPARgamma, retinoid X receptor alpha, liver X receptor alpha (LXRalpha) and pregnane X receptor but not FXR in freshly isolated and 7-day maintained sebaceous glands. PPARalpha, PPARbeta, PPARgamma and LXRalpha protein were detected in nuclear extracts of sebaceous glands.

CONCLUSIONS

We conclude that activation of nuclear hormone receptors, in particular activation of PPARalpha and PPARgamma, can regulate lipogenesis in human sebaceous glands. As suppression of sebum secretion is associated with reduced acne activity, the nuclear hormone receptors involved may open new avenues in the development of novel acne treatments.

Acne and sebaceous gland function

The embryologic development of the human sebaceous gland is closely related to the differentiation of the hair follicle and the epidermis. The number of sebaceous glands remains approximately the same throughout life, whereas their size tends to increase with age. The development and function of the sebaceous gland in the fetal and neonatal periods appear to be regulated by maternal androgens and by endogenous steroid synthesis, as well as by other morphogens. The most apparent function of the glands is to excrete sebum. A strong increase in sebum excretion occurs a few hours after birth; this peaks during the first week and slowly subsides thereafter. A new rise takes place at about age 9 years with adrenarche and continues up to age 17 years, when the adult level is reached. The sebaceous gland is an important formation site of active androgens. Androgens are well known for their effects on sebum excretion, whereas terminal sebocyte differentiation is assisted by peroxisome proliferator-activated receptor ligands. Estrogens, glucocorticoids, and prolactin also influence sebaceous gland function. In addition, stress-sensing cutaneous signals lead to the production and release of corticotrophin-releasing hormone from dermal nerves and sebocytes with subsequent dose-dependent regulation of sebaceous nonpolar lipids. Among other lipid fractions, sebaceous glands have been shown to synthesize considerable amounts of free fatty acids without exogenous influence. Sebaceous lipids are responsible for the three-dimensional skin surface lipid organization. Contributing to the integrity of the skin barrier. They also exhibit strong innate antimicrobial activity, transport antioxidants to the skin surface, and express proinflammatory and anti-inflammatory properties. Acne in childhood has been suggested to be strongly associated with the development of severe acne during adolescence. Increased sebum excretion is a major factor in the pathophysiology of acne vulgaris. Other sebaceous gland functions are also associated with the development of acne, including sebaceous proinflammatory lipids; different cytokines produced locally; periglandular peptides and neuropeptides, such as corticotrophin-releasing hormone, which is produced by sebocytes; and substance P, which is expressed in the nerve endings at the vicinity of healthy-looking glands of acne patients. Current data indicate that acne vulgaris may be a primary inflammatory disease. Future drugs developed to treat acne not only should reduce sebum production and Propionibacterium acnes populations, but also should be targeted to reduce proinflammatory lipids in sebum, down-regulate proinflammatory signals in the pilosebaceous unit, and inhibit leukotriene B(4)-induced accumulation of inflammatory cells. They should also influence peroxisome proliferator-activated receptor regulation. Isotretinoin is still the most active available drug for the treatment of severe acne.

Acne: Topical treatment

Acne vulgaris is a common skin disease, affecting about 70-80% of adolescents and young adults. It is a multifactorial disease of the pilosebaceous unit.(1) The influence of androgens at the onset of adolescence leads to an enlargement of the sebaceous gland and a rise in sebum production. Additional increased proliferation and altered differentiation of the follicular epithelium eventually blocks the pilosebaceous duct, leading to development of the microcomedo as the primary acne lesion. Concomitantly and subsequently, colonization with Propionibacterium acnes increases, followed by induction of inflammatory reactions from bacteria, ductal corneocytes, and sebaceous proinflammatory agents (Fig 1).(2-5)