Minimal heating dose: a novel biological unit to measure infrared irradiation

Skin Protection by Carotenoid Pigments

Sunlight, despite its benefits, can pose a threat to the skin, which is a natural protective barrier. Phototoxicity caused by overexposure, especially to ultraviolet radiation (UVR), results in burns, accelerates photoaging, and causes skin cancer formation. Natural substances of plant origin, i.e., polyphenols, flavonoids, and photosynthetic pigments, can protect the skin against the effects of radiation, acting not only as photoprotectors like natural filters but as antioxidant and anti-inflammatory remedies, alleviating the effects of photodamage to the skin. Plant-based formulations are gaining popularity as an attractive alternative to synthetic filters. Over the past 20 years, a large number of studies have been published to assess the photoprotective effects of natural plant products, primarily through their antioxidant, antimutagenic, and anti-immunosuppressive activities. This review selects the most important data on skin photodamage and photoprotective efficacy of selected plant carotenoid representatives from in vivo studies on animal models and humans, as well as in vitro experiments performed on fibroblast and keratinocyte cell lines. Recent research on carotenoids associated with lipid nanoparticles, nanoemulsions, liposomes, and micelles is reviewed. The focus was on collecting those nanomaterials that serve to improve the bioavailability and stability of carotenoids as natural antioxidants with photoprotective activity.

Exosomes: A Promising Strategy for Repair, Regeneration and Treatment of Skin Disorders

The skin is the organ that serves as the outermost layer of protection against injury, pathogens, and homeostasis with external factors; in turn, it can be damaged by factors such as burns, trauma, exposure to ultraviolet light (UV), infrared radiation (IR), activating signaling pathways such as Toll-like receptors (TLR) and Nuclear factor erythroid 2-related factor 2 (NRF2), among others, causing a need to subsequently repair and regenerate the skin. However, pathologies such as diabetes lengthen the inflammatory stage, complicating the healing process and, in some cases, completely inhibiting it, generating susceptibility to infections. Exosomes are nano-sized extracellular vesicles that can be isolated and purified from different sources such as blood, urine, breast milk, saliva, urine, umbilical cord bile cells, and mesenchymal stem cells. They have bioactive compounds that, thanks to their paracrine activity, have proven to be effective as anti-inflammatory agents, inducers of macrophage polarization and accelerators of skin repair and regeneration, reducing the possible complications relating to poor wound repair, and prolonged inflammation. This review provides information on the use of exosomes as a promising therapy against damage from UV light, infrared radiation, burns, and skin disorders.

Ultraviolet Light Protection: Is It Really Enough?

Our current understanding of the pathogenesis of skin aging includes the role of ultraviolet light, visible light, infrared, pollution, cigarette smoke and other environmental exposures. The mechanism of action common to these exposures is the disruption of the cellular redox balance by the directly or indirectly increased formation of reactive oxygen species that overwhelm the intrinsic antioxidant defense system, resulting in an oxidative stress condition. Altered redox homeostasis triggers downstream pathways that contribute to tissue oxinflammation (cross-talk between inflammation and altered redox status) and accelerate skin aging. In addition, both ultraviolet light and pollution increase intracellular free iron that catalyzes reactive oxygen species generation via the Fenton reaction. This disruption of iron homeostasis within the cell further promotes oxidative stress and contributes to extrinsic skin aging. More recent studies have demonstrated that iron chelators can be used topically and can enhance the benefits of topically applied antioxidants. Thus, an updated, more comprehensive approach to environmental or atmospheric aging protection should include sun protective measures, broad spectrum sunscreens, antioxidants, chelating agents, and DNA repair enzymes.

To study the effect of acute infrared radiation-induced alterations in human skin at cellular and molecular level using in vivo confocal Raman spectroscopy

BACKGROUND

Solar radiations are classified in terms of wavelengths, including visible light, infrared, and ultraviolet. Infrared radiation (IR) accounts the largest proportion of solar radiations that cause oxidative stress-induced aging of human skin. This study investigates the biochemical changes in proteins, lipids, and DNA associated with acute exposure to IR radiations.

METHOD

In vivo confocal Raman spectroscopy was used to examine the forearms region of 20 healthy participants with phototype II skin, aged between 18 and 30 years, without IR incidence (T0), with IR incidence 30 minutes (T30) at day 1 and 30 minutes at day 2 (T60). One-way ANOVA and two-tailed t test along with post hoc Bonferroni correction were used to detect the existence of significant differences in the timestamps of stratum corneum, stratum basale, and dermis at all IR wavenumbers under test.

RESULTS

An increase in the Raman peaks of stratum corneum lipids, decrease in stratum basal DNA peaks, and a shift in the amide I peak of collagen in the skin dermis were observed. One-way ANOVA results showed significant differences among timestamps of stratum corneum, stratum basale, and dermis at all wavenumbers under test (P < .001). Furthermore, paired timestamps also showed significant differences (P < .016) except at two wavenumbers 1293 cm^-1 and 852 cm^-1 in stratum corneum and basale layer clusters on timestamps (T0 & T30 and T30 & T60, P > .016). This study proved that confocal Raman spectroscopy is an useful technique for early evaluation of IR-induced skin changes.

Impact of physiologically relevant temperatures on dermal absorption of active substances - an ex-vivo study in human skin

Skin temperature plays a certain role in the dermal absorption of substances, but the extent and mechanisms of skin temperatures-induced modulation in ranges caused by physiological thermoregulation or environmental conditions are largely unknown. The influence of dermal temperature on the absorption of the model lipophilic compound (anisole) and the model hydrophilic compounds (1,4-dioxane, ethanol) through human skin was investigated at three dermal temperatures (25, 32 and 39 °C) in an ex-vivo diffusion cell model. The substances were applied to the skin and transdermal penetration was monitored. All substances showed temperature dependent variations in their penetration behavior (3 h: 25-39 °C: 202-275% increase in cumulative, transdermally penetrated amounts). The relative differences in absorption in relation to temperature were greatest within 45 min after exposure (25-39 °C: 347-653% rise in cumulated penetration), although absolute amounts absorbed were small (45 min vs. 3 h: 4.5-14.5%). Regardless of blood circulation, skin temperature significantly influences the amount and kinetics of dermal absorption. Substance-dependent, temperature-related changes of the lipid layer order or the porous pathway may facilitate penetration. The early-stage modulation of transdermal penetration indicates transappendageal absorption, which may be relevant for short-term exposures. For both, toxicological evaluation and perfusion cell studies, it is important to consider the thermal influence on absorption or to perform the latter at a standardized temperature (32±1 °C).

Inhibitory Effect of Manassantin B Isolated from Saururus chinensis on Skin Heat Aging

Heat shock treatment-induced skin aging causes a thickened epidermis, increased matrix metalloproteinase (MMP)-1 expression, collagen degradation, and deep wrinkles. In this study, we investigated the effect of manassantin B in preventing heat shock treatment-induced aging. We first separated manassantin B (MB) from the roots of Saururus chinensis, and the structure was identified using 1H- and 13C-NMR spectroscopy. RT-PCR and western blotting were applied to investigate the anti-aging effect of manassantin B. Manassantin B decreased MMP-1 expression through transient receptor potential vanilloid (TRPV) 1 channel inhibition and significantly increased procollagen expression. In addition, manassantin B suppressed MAPK phosphorylation in a dose-dependent manner. Our results suggest that manassantin B, the active ingredient in S. chinensis, can be effectively used to inhibit heat shock treatment-induced skin aging.

Assessment of Laser Effects on Skin Rejuvenation

Laser skin resurfacing has changed the approach of facial skin rejuvenation over the past decade. This article evaluates the laser effects on skin rejuvenation by the assessment of laser characteristics and histological and molecular changes, accompanied by the expression of proteins during and after laser-assisted rejuvenation of skin. It is important to note that different layers of skin with different cells are normally exposed to the sun's UV radiation which is the most likely factor in aging and damaging healthy skin. To identify the expression of proteins, using validated databases and reviewing existing data could reveal altered proteins which could be analyzed and mapped to investigate their expression and their different effects on cell biological responses. In this regard, proteomics data can be used for better investigation of the changes in the proteomic profile of the treated skin. Different assessments have revealed the survival and activation of fibroblasts and new keratinocytes with an increase of collagen and elastin fibers in the dermis and the reduction of matrix metalloproteinases (MMPs) and heat shock proteins (HSPs) as a result of different low-power laser therapies of skin. There are a wide range of biological effects associated with laser application in skin rejuvenation; therefore, more safety considerations should be regarded in the application of lasers in skin rejuvenation.

The anti-inflammatory and anti-apoptotic effects of advanced anti-inflammation composition (AAIC) in heat shock-induced human HaCaT keratinocytes

BACKGROUND

The development of natural cosmetic materials without side effects to protect skin from heat shock is necessary. We recently reported that advanced cooling composition (ACC) has anti-inflammatory effect in RAW 264.7 cells stimulated with lipopolysaccharide (LPS) and strong anti-microbial effect against Pseudomonas aeruginosa, Staphylococcus aureus, MRSA (Methicillin-resistant Staphylococcus aureus), Candida albicans, and Streptococcus mutans.

AIMS

To further investigate whether advanced anti-inflammation composition (AAIC), newly developed from existing ACC has beneficial effects in heat shock-induced immortalized human keratinocytes (HaCaT cells), HaCaT cells were pretreated with AAIC before heat shock treatment.

METHODS

Cell viability for heat shock treatment and different concentrations of AAIC in HaCaT cells were assessed by MTT assay. Anti-oxidative activity of AAIC was measured using the DPPH assay. The protein expression in heat shock-induced HaCaT cells treated with AAIC was evaluated by immunofluorescence staining and western blot analysis.

RESULTS

AAIC, which is effective at 100 µg/mL concentration, was nontoxic in HaCaT cells and had an anti-oxidative effect demonstrated by scavenging DPPH free radicals. AAIC treatment significantly attenuated the aberrant levels of pro-inflammatory and pro-apoptotic signaling molecules in heat shock-induced HaCaT cells compared with control cells.

CONCLUSION

AAIC potentially includes effective anti-oxidative activity, anti-inflammatory, and anti-apoptotic properties against heat shock-induced keratinocytes, suggesting that it can be provided as a raw material for imparting skin health.

Heat shock antagonizes UVA-induced responses in murine melanocytes and melanoma cells: an unexpected interaction

The skin is under the influence of oscillatory factors such as light and temperature. This organ possesses a local system that controls several aspects in a time-dependent manner; moreover, the skin has a well-known set of opsins whose function is still unknown. We demonstrate that heat shock reduces Opn2 expression in normal Melan-a melanocytes, while the opposite effect is found in malignant B16-F10 cells. In both cell lines, UVA radiation increases the expression of Opn4 and melanin content. Clock genes and Xpa, a DNA repair gene, of malignant melanocytes are more responsive to UVA radiation when compared to normal cells. Most UVA-induced effects are antagonized by heat shock, a phenomenon shown for the first time. Based on our data, the heat produced during UV experiments should be carefully monitored since temperature represents, according to our results, an important confounding factor, and therefore it should, when possible, be dissociated from UV radiation. The responses displayed by murine melanoma cells, if proven to also take place in human melanoma, may represent an important step in cancer development and progression.

Brazilian consensus on photoprotection

Brazil is a country of continental dimensions with a large heterogeneity of climates and massive mixing of the population. Almost the entire national territory is located between the Equator and the Tropic of Capricorn, and the Earth axial tilt to the south certainly makes Brazil one of the countries of the world with greater extent of land in proximity to the sun. The Brazilian coastline, where most of its population lives, is more than 8,500 km long. Due to geographic characteristics and cultural trends, Brazilians are among the peoples with the highest annual exposure to the sun. Epidemiological data show a continuing increase in the incidence of non-melanoma and melanoma skin cancers. Photoprotection can be understood as a set of measures aimed at reducing sun exposure and at preventing the development of acute and chronic actinic damage. Due to the peculiarities of Brazilian territory and culture, it would not be advisable to replicate the concepts of photoprotection from other developed countries, places with completely different climates and populations. Thus the Brazilian Society of Dermatology has developed the Brazilian Consensus on Photoprotection, the first official document on photoprotection developed in Brazil for Brazilians, with recommendations on matters involving photoprotection.

Metal oxide-coating PMMA or Talc as a new IR blocker inhibits IR-induced decrease of collagens in human dermal fibroblasts

OBJECTIVES

The purpose of this study was whether P/M or T/M inhibits IR-induced decrease of collagens in human dermal fibroblasts, using P/M or T/M blocked near-IR (NIR) transmittance significantly in spectrophotometer measurement.

METHODS

As metal oxides are effective inorganic molecules for intercepting IR radiation, we have developed metal oxide-coating PMMA (P/M) or Talc (T/M) as a new IR blocker. Inhibitory effect of the new IR blocker on collagen degradation was measured by gene and protein expressions of procollagens and MMPs, respectively, in IR-irradiated Hs68 cell line.

RESULTS

Using P/M or T/M inhibited IR-induced increases of MMP-1, MMP-3 and MMP-9, and IR-induced decreases of type 1 and 4 procollagen in a dose-dependent manner in dermal fibroblasts. In addition, using both P/M and T/M blocked the increase of cell media temperature induced by IR lamp.

CONCLUSION

The results suggest that P/M or T/M can inhibit decrease of collagens by blocking IR-induced heat transmission in human dermal fibroblasts.

Molecular action mechanisms of solar infrared radiation and heat on human skin

The generation of ROS underlies all solar infrared-affected therapeutic and pathological cutaneous effects. The signaling pathway NF-kB is responsible for the induced therapeutic effects, while the AP-1 for the pathological effects. The different signaling pathways of infrared-induced ROS and infrared-induced heat shock ROS were shown to act independently multiplying the influence on each other by increasing the doses of irradiation and/or increasing the temperature. The molecular action mechanisms of solar infrared radiation and heat on human skin are summarized and discussed in detail in the present paper. The critical doses are determined. Protection strategies against infrared-induced skin damage are proposed.

Might outdoor heat stress be considered a proxy for the unperceivable effect of the ultraviolet-induced risk of erythema in Florence?

Erythema is the most familiar short-term symptom of human skin associated with overexposure to unperceivable ultraviolet radiation (UV). However, people are able to perceive the warm infrared component of the solar radiation by means of thermal (dis)comfort. This study investigated the potentiality of perceived outdoor heat stress as a valuable proxy for the unperceivable effect of UV-induced risk of erythema in a Mediterranean city. Meteorological data and UVB (280-320nm) measurements were obtained for the 2004-2012 period by a weather station located in the municipality of Florence. Continuous measurements of erythemally effective UV (UVEry) were performed by means of a broadband temperature-corrected radiometer with the spectral response close to the erythemal action spectrum. Hourly UVEry doses were expressed as Standard Erythemal Doses (SEDs). The newly developed Universal Thermal Climate Index (UTCI), that represents the state-of-the-art of outdoor thermal (dis)comfort evaluation, was also assessed. Descriptive analyses of the hourly distribution per month of the frequencies of days with heat stress and UVEry exceeding 2.0, 3.0, 4.5 and 6.0 SEDs were carried out based on the general skin-type characteristics. The association between UVEry and UTCI was analyzed by a two-way contingency table approach. The probability of UVEry exceeding specific SED thresholds when heat stress occurs was often significantly higher than the same probability when no heat stress is perceived. Furthermore, increased magnitudes of the ratios, ranging from the very sensitive to the minimally sensitive skin types, were also found. However, during several months, too many days occur without any signs of heat discomfort, even when people may be exposed to relevant doses of harmful UVEry for the skin of various phototypes. These findings underlie the need for public health authorities to provide differentiated advice per month in relation to potential UV skin damage in the city of Florence.

Effects of ultraviolet radiation, visible light, and infrared radiation on erythema and pigmentation: a review

The effects of ultraviolet radiation, visible light, and infrared radiation on cutaneous erythema, immediate pigment darkening, persistent pigment darkening, and delayed tanning are affected by a variety of factors. Some of these factors include the depth of cutaneous penetration of the specific wavelength, the individual skin type, and the absorption spectra of the different chromophores in the skin. UVB is an effective spectrum to induce erythema, which is followed by delayed tanning. UVA induces immediate pigment darkening, persistent pigment darkening, and delayed tanning. At high doses, UVA (primarily UVA2) can also induce erythema in individuals with skin types I-II. Visible light has been shown to induce erythema and a tanning response in dark skin, but not in fair skinned individuals. Infrared radiation produces erythema, which is probably a thermal effect. In this article we reviewed the available literature on the effects of ultraviolet radiation, visible light, and infrared radiation on the skin in regards to erythema and pigmentation. Much remains to be learned on the cutaneous effects of visible light and infrared radiation.

Modulation of tropoelastin and fibrillin-1 by infrared radiation in human skin in vivo

BACKGROUND

The heat produced by exposure to infrared radiation (IR) has been demonstrated to modulate the expression of tropoelastin and fibrillin-1, the two main components of elastic fibers in human skin in vivo. However, the effect of IR range of radiations on tropoelastin and fibrillin-1 expression has not been thoroughly investigated.

METHODS

Eighteen volunteers were enrolled in this study involving three trials. Time-dependent, dose-dependent and cumulative effects of IR were investigated, respectively. Tropoelastin and fibrillin-1 expression was measured by immunohistochemical staining on skin biopsy samples from volunteers. In addition, we also measured tropoelastin mRNA expression by a real-time RT-polymerase chain reaction.

RESULTS

A single dose of IR (2 minimal heating dose) induced a time-dependent increase in tropoelastin expression at the protein level. An inverse correlation was found between the alterations of tropoelastin and fibrillin-1. Furthermore, IR was found to increase tropoelastin expression in a dose-dependent manner at both the mRNA and the protein level. Repeated low doses of IR increased tropoelastin expression and decreased fibrillin-1 expression at the protein level in the dermis. Meanwhile, the number of both fibers along the dermal-epidermal junction was increased.

CONCLUSION

IR can alter the expression of tropoelastin and fibrillin-1, which may result in abnormal elastic fiber formation.

Effects of infrared radiation and heat on human skin aging in vivo

Sunlight damages human skin, resulting in a wrinkled appearance. Since natural sunlight is polychromatic, its ultimate effects on the human skin are the result of not only the action of each wavelength separately, but also interactions among the many wavelengths, including UV, visible light, and infrared (IR). In direct sunlight, the temperature of human skin rises to about 40 degrees C following the conversion of absorbed IR into heat. So far, our knowledge of the effects of IR radiation or heat on skin aging is limited. Recent work demonstrates that IR and heat exposure each induces cutaneous angiogenesis and inflammatory cellular infiltration, disrupts the dermal extracellular matrix by inducing matrix metalloproteinases, and alters dermal structural proteins, thereby adding to premature skin aging. This review provides a summary of current research on the effects of IR radiation and heat on aging in human skin in vivo.Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 15-19; doi:10.1038/jidsymp.2009.7.

Acute exposure of human skin to ultraviolet or infrared radiation or heat stimuli increases mast cell numbers and tryptase expression in human skin in vivo

BACKGROUND

Mast cells are key effector cells in diverse immunological and pathological processes. It is still unclear why there are more mast cells at peripheral and sun-exposed skin sites than at sun-protected sites.

OBJECTIVES

To investigate changes in mast cell numbers associated with natural ageing and photoageing, and to observe the effects of ultraviolet (UV) and infrared (IR) radiation and heat on the prevalence of mast cells and tryptase expression in human skin in vivo.

METHODS

Sun-exposed and sun-protected skin samples were taken from individuals in four different age groups. UV, IR or heat-treated buttock skin of young volunteers was also obtained. Mast cells were quantified by immunohistochemical staining of mast cell-specific tryptase and chymase. The expression of tryptase was determined by Western blotting.

RESULTS

Both sun-exposed and sun-protected skin showed a gradual decrease in total mast cells (MC(Total)) number with ageing. The number of mast cells in sun-exposed skin was significantly higher than that in sun-protected skin. After UV irradiation (2 minimal erythema doses), MC(Total) and mast cells expressing tryptase and chymase were significantly increased at 24 and 48 h postirradiation. After IR irradiation (3 minimal heating doses) and heat treatment (43 degrees C for 90 min), MC(Total) reached peak induction at 8 and 48 h after stimulation, respectively. Tryptase expression was also clearly upregulated by UV, IR and heat.

CONCLUSIONS

Our data demonstrate that mast cell numbers decreased with ageing in human skin. Also, mast cells may be activated and recruited by UV, IR and heat. These findings should further our understanding of the reason for the high prevalence of mast cells at peripheral sun-exposed skin sites.

Infrared exposure induces an angiogenic switch in human skin that is partially mediated by heat

BACKGROUND

Angiogenesis plays an important role in physiological and pathological conditions of the skin. Although acute ultraviolet-induced skin angiogenesis has been investigated, little is known about the distinct effects of acute infrared (IR) radiation on angiogenesis in human skin.

OBJECTIVES

To elucidate the molecular regulation of the angiogenic switch by acute near-IR radiation or by a single heat treatment in human skin in vivo.

METHODS

We subjected 16 healthy volunteers to near-IR irradiation (six minimal heating doses) and 14 healthy volunteers to heat treatment (43 degrees C for 90 min), and skin specimens were obtained by punch biopsy for immunohistochemical, Western blot and reverse transcription-polymerase chain reaction analyses.

RESULTS

We observed that CD31-stained vessels in the upper dermis were increased after acute near-IR exposure, and that this was associated with the upregulation of vascular endothelial growth factor (VEGF) and the downregulation of thrombospondin (TSP)-2. During the application of near-IR to buttock skin, skin temperatures immediately increased from 32 degrees C up to 42 degrees C, as measured using a digital thermometer. Moreover, the expression of inducible heat shock protein 70 was increased after near-IR irradiation in human skin. Therefore, we investigated the effects of a single heat treatment on angiogenesis and on the expression of VEGF and TSP-2 in skin, and found that vascularization and VEGF expression were increased, whereas TSP-2 expression was reduced.

CONCLUSIONS

Our results suggest that IR radiation plays an important role in skin angiogenesis via regulation of the balance between the angiogenic inducer VEGF and the angiogenic inhibitor TSP-2, and that IR-induced skin angiogenesis might be partially caused by the effects of heat in human skin in vivo.

Regulation of type I procollagen and MMP-1 expression after single or repeated exposure to infrared radiation in human skin

Human skin is daily exposed to infrared (IR) radiation from natural sunlight. However, the effects of IR irradiation on collagen metabolism have not been investigated in human skin in vivo. Here, we examined whether single or repeated (three times a week for 4 weeks) exposure to IR irradiation changes the expressions of type I procollagen and interstitial collagenase (MMP-1). By using immunostaining, Western blotting, and semi-quantitative RT-PCR, we analyzed the protein and mRNA levels of type I procollagen and MMP-1 in young buttock skin. A single dose of IR to human skin increased the expression of type I procollagen within 24h, but did not change the expression of MMP-1. On the other hand, multiple IR doses reduced the expression of type I procollagen and increased the expression of MMP-1. We also found that TGF-betas may mediate type I procollagen synthesis in IR-irradiated human skin. Our results demonstrate that the regulations of the expressions of type I procollagen and MMP-1 differ in acute and chronically IR-irradiated skin. In particular, decreased collagen levels and increased MMP-1 levels in chronic IR-irradiated skin may be associated with connective tissue damage. Thus, we suggest that repeated exposure to IR irradiation might induce premature skin aging (photoaging) in human skin in vivo.