Presence of immunoreactive beta-endorphin in human skin

Opioidergic Signaling-A Neglected, Yet Potentially Important Player in Atopic Dermatitis

Atopic dermatitis (AD) is one of the most common skin diseases, the prevalence of which is especially high among children. Although our understanding about its pathogenesis has substantially grown in recent years, and hence, several novel therapeutic targets have been successfully exploited in the management of the disease, we still lack curative treatments for it. Thus, there is an unmet societal demand to identify further details of its pathogenesis to thereby pave the way for novel therapeutic approaches with favorable side effect profiles. It is commonly accepted that dysfunction of the complex cutaneous barrier plays a central role in the development of AD; therefore, the signaling pathways involved in the regulation of this quite complex process are likely to be involved in the pathogenesis of the disease and can provide novel, promising, yet unexplored therapeutic targets. Thus, in the current review, we aim to summarize the available potentially AD-relevant data regarding one such signaling pathway, namely cutaneous opioidergic signaling.

Genetic Associations with Indoor Tanning Addiction among non-Hispanic White Young Adult Women

BACKGROUND

Some young people may become addicted to indoor tanning in a manner similar to other forms of addiction, but research on genetic associations with indoor tanning addiction remains limited.

PURPOSE

To examine if liabilities in genetic addiction reward pathways and psychiatric comorbidity influence the risk of indoor tanning addiction.

METHODS

This was a cross-sectional study with a community sample of 292 non-Hispanic white young adult women aged 18-30 years who reported indoor tanning in the past year. Self-report measures included indoor tanning frequency, appearance orientation, depressive symptoms, and two screeners of tanning addiction. DNA samples were analyzed for 34 single nucleotide polymorphisms (SNPs) in candidate genes in addiction reward pathways.

RESULTS

No SNPs were significantly associated with tanning addiction in univariate analyses after multiplicity adjustment. In multivariable analyses adjusting for indoor tanning frequency, appearance orientation, and depressive symptoms, variant genotypes (CC or CT) in two DRD2 dopamine receptor gene SNPs were associated with increased odds of indoor tanning addiction (rs4436578, odds ratio [OR]: 2.30, 95% confidence interval [CI]: 1.11-4.77; rs4648318, OR: 1.95, 95% CI: 1.02-3.72). Variant SNP genotypes interacted with depressive symptoms to increase the risk of indoor tanning addiction: OR: 10.79, 95% CI: 3.25, 35.80, OR: 13.60, 95% CI: 4.13, 44.78, respectively.

CONCLUSIONS

This study provides preliminary evidence that DRD2 dopamine receptor gene SNPs are associated with indoor tanning addiction and young women with variant genotypes and elevated depressive symptoms may be at higher risk. These preliminary results support a reward-based model for indoor tanning addiction and warrant further investigation.

Blue light (λ=453 nm) nitric oxide dependently induces β-endorphin production of human skin keratinocytes in-vitro and increases systemic β-endorphin levels in humans in-vivo

β-Endorphin exerts a broad spectrum of physiological activity on mood, immune functions, pain management, reward effects, and behavioral stability. β-Endorphin is produced in certain neurons within the central and peripheral nervous system but also in the skin, especially in response to ultraviolet radiation. In the present study we have investigated the impact of visible blue light at λ = 453 nm (BL) on β-endorphin production of primary human skin keratinocytes (hKC) in-vitro as well as on systemic β-endorphin formation of whole-body exposed subjects in-vivo. We found that BL irradiation significantly enhanced both keratinocytic β-endorphin production of hKC cultures as well as systemic β-endorphin concentrations in light exposed healthy subjects. Interestingly, in hKC cultures elevated β-endorphin formation was paralleled by significantly increased levels of non-enzymatically generated nitric oxide (NO), whereas elevated systemic β-endorphin values of BL-exposed subjects were accompanied by enhanced systemic concentration of bioactive NO-derivates. These findings point to a pivotal role of NO in the molecular mechanism of the observed BL-induced effects, and indeed, exogenously applied NO was able to significantly enhance β-endorphin production in hKC cultures. Thus, our finding of BL-induced increases in systemic β-endorphin concentration in-vivo can be plausibly explained by an event sequence comprising 1.) BL-driven non-enzymatic formation of NO in the exposed skin tissue, 2.) systemic distribution of cutaneously produced NO in the form of bioactive nitroso compounds, 3.) a subsequent NO-dependent induction of β-endorphin synthesis in epidermal keratinocytes, and 4.) probably also a NO-dependent modulation of β-endorphin synthesis in specialized neurons within the central and peripheral nervous system.

Leucine-enkephalin promotes wound repair through the regulation of hemidesmosome dynamics and matrix metalloprotease

The skin responds to environmental stressors by coordinated actions of neuropeptides and their receptors. An endogenous peptide for δ-opioid receptor (DOPr), Leu-enkephalin (L-ENK), is expressed in the skin and its expression is altered in pathological conditions. Although the importance of DOPr is rapidly gaining recognition, the molecular mechanisms underlying its effects on wound healing are largely undefined. We show here that L-ENK induced activation of Erk, P90(RSK), and Elk-1 and promoted the disruption of hemidesmosomes and the expression of matrix metalloprotease (MMP)-2 and MMP-9, important processes for wound healing. Treatment with Erk inhibitor blocked activation of P90(RSK) and Elk-1 and significantly blunted wound repair. Therefore, our results suggest that activation of Erk and its downstream effectors, P90(RSK) and Elk-1, are critical for DOPr-mediated skin homeostasis.

Primary afferent neurons express functional delta opioid receptors in inflamed skin

Peripherally-restricted opiate compounds attenuate hyperalgesia in experimental models of inflammatory pain, but have little discernable effect on nociceptive behavior in normal animals. This suggests that activation of opioid receptors on peripheral sensory axons contributes to decreased afferent activity after injury. Previously, we reported that direct application of morphine to cutaneous receptive fields decreased mechanical and heat-evoked responses in a population of C-fiber nociceptors in inflamed skin. Consistent with reported behavioral studies, direct application of morphine had no effect on fiber activity in control skin. The aim of the present study was to determine whether mechanical responsiveness of nociceptors innervating inflamed skin was attenuated by direct activation of delta opioid receptors (DORs) on peripheral terminals. An ex vivo preparation of rat plantar skin and tibial nerve was used to examine effects of a selective DOR agonist, deltorphin II, on responsiveness of single fibers innervating inflamed skin. Electrical recordings were made eighteen hours after injection of complete Freund's adjuvant into the hindpaw. Deltorphin II produced an inhibition of the mechanical responsiveness of single fibers innervating inflamed skin; an effect blocked by the DOR-selective antagonist, naltrindole. The population of units responsive to deltorphin II was identified as consisting of C fiber mechanical nociceptors.

Topical treatment with the opioid antagonist naltrexone accelerates the remodeling phase of full-thickness wound healing in type 1 diabetic rats

Wound repair involves a series of overlapping phases that include inflammation, proliferation, and tissue remodeling, with the latter phase requiring months for proper healing. Delays in any of these processes can result in infection, chronic ulceration, and possible amputation. Diabetes is a major risk factor for improper wound repair, and impaired wound healing is a major complication for more than 26 million people in the US diagnosed with diabetes. Previous studies have demonstrated that the opioid antagonist naltrexone (NTX) dissolved in moisturizing cream reverses delays in wound closure in streptozotocin-induced type 1 diabetic (T1D) rats. NTX accelerated DNA synthesis and increased the number of epithelial and mast cells, as well as new blood vessel formation. In this study, remodeling was evaluated in T1D rats up to eight weeks after initial wounding. Twenty days following wounding, diabetic rats treated with vehicle had elevated numbers of MMP-2+ fibroblasts, suggesting delayed healing processes; birefringence of granulation tissue stained with Sirius red revealed diminished collagen formation and maturation. Wound tissue from NTX-treated T1D rats had comparable numbers of MMP-2+ fibroblasts to control specimens, as well as accelerated maturation of granulation tissue. The integrity of wounded skin was evaluated by tensile strength measurements. T1D resulted in delayed wound healing, and wounded skin that displayed reduced tensile strength relative to normal rats. Topical NTX applied to wounds in T1D rats resulted in enhanced collagen formation and maturation over a 60-day period of time. Moreover, the force required to tear skin of NTX-treated T1D rats was elevated relative to the force necessary to tear the skin of vehicle-treated T1D rats, and comparable to that for normal rats. These data reveal that complications in wound healing associated with T1D involve the novel OGF-OGFr pathway, and that topical NTX is an effective treatment to enhance wound healing.

Topical naltrexone accelerates full-thickness wound closure in type 1 diabetic rats by stimulating angiogenesis

Delays in wound healing often result in infection, chronic ulceration, and possible amputation of extremities. Impaired wound healing is a major complication of the 23 million people in the USA with diabetes, and financial and medical burdens are demanding new treatments for wound healing. Previous studies have demonstrated that topical application of the opioid antagonist naltrexone (NTX) dissolved in moisturizing cream reverses delays in wound closure in rats with streptozotocin-induced type 1 diabetes. A target of NTX's action is DNA synthesis and cell proliferation. In this study, granulation tissue was evaluated to ascertain the specific cellular targets that were impaired in diabetic wounds, as well as those that were enhanced following NTX application. Mast cell number as well as the number of new blood vessels immunoreactive to fibroblast growth factor-2 (FGF-2), vascular endothelial growth factor (VEGF), and alpha smooth muscle actin (α-SMA) antibodies were recorded at 3, 5, 8, 10, 15, and 20 days following creation of full-thickness dorsal cutaneous wounds in normal and type 1 diabetic rats. Diabetic rats displayed delays in wound closure as well as a reduction in the number of mast cells responding to the injury, and delays in the spatial and temporal expression of FGF-2, VEGF, and α-SMA in capillaries. Topical NTX accelerated the rate of wound closure and stimulated expression of angiogenic factors within granulation tissue of diabetic rats relative to control animals receiving saline in moisturizing cream. These data support observations that a novel biological pathway is impaired under diabetic conditions and can be modulated by topical NTX to enhance proliferative events in wound healing.

Topical treatment with the opioid antagonist naltrexone facilitates closure of full-thickness wounds in diabetic rats

A major problem associated with diabetes is the complication of chronic non-healing wounds that can lead to the formation of debilitating ulcers, and can progress to more serious problems including amputation. There is no fully effective prevention of these complications, constituting an unmet medical need to understand the pathophysiology and treatment of wound healing in diabetes. This study determined whether blockade of opioid receptors from opioid peptides, known to inhibit cell proliferation and be overexpressed in diabetes, by topical application of the opioid antagonist naltrexone (NTX) reverses delays in wound closure. Rats with streptozotocin-induced type 1 diabetes (T1D) received topical applications of NTX (10(-4)-10(-6) mol/L) or vehicle in a variety of carriers; DNA synthesis was evaluated 12 h later. DNA synthesis in the epithelium of T1D rats was significantly reduced from normal animals. Both systemic and topical application of NTX increased DNA synthesis (up to 2-fold higher) within 12 h of administration. In a second study, diabetic and normal rats received full-thickness cutaneous wounds and were treated three times daily with either 10(-5) mol/L NTX or vehicle in topical carriers. Wound sizes were analyzed, and BrdU (5-bromo-2'-deoxyuridine) labeling in the skin was evaluated to determine DNA synthesis. Application of NTX in a variety of carriers to rats with full-thickness wounds resulted in significantly smaller wound areas relative to T1D animals receiving vehicle, and comparable to that of normal rats. Wound contraction in T1D animals was 50% of that in normal rats, with NTX-treated wounds restoring wound contraction to that of normal cohorts. DNA synthesis was also enhanced in NTX-treated T1D animals compared with T1D vehicle controls. These data suggest that topical application of NTX is a non-toxic and efficacious facilitator for healing full thickness wounds in T1D, with wound contraction serving as a particular target of NTX action.

Tanning as a behavioral addiction

BACKGROUND

Persistent tanning despite potentially fatal consequences suggests a compulsive behavior similar to other addictive disorders.

OBJECTIVES

To review the literature supporting tanning addiction from an epidemiological, behavioral, and neurobiological perspective.

METHODS

A comprehensive review of the medical literature was conducted to assess the health consequences of tanning, behaviors and other psychiatric disorders associated with tanning, and central rewarding effects of ultraviolet light.

RESULTS

Many frequent tanners endorse signs and symptoms adapted from Diagnostic and Statistical Manual-IV (DSM IV) substance abuse or dependence criteria. Recent studies suggest biochemical mechanisms may reinforce ultraviolet light seeking behavior.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Frequent and persistent tanning may reveal itself to be a dermatologic-psychiatric disorder with carcinogenic sequelae. Multidisciplinary studies are required to determine the validity of an addiction diagnosis and to explore pharmacologic and cognitive therapeutic options for affected persons.

GaAlAs (830 nm) low-level laser enhances peripheral endogenous opioid analgesia in rats

BACKGROUND

Low-level laser therapy (LLLT) has been reported to relieve pain with minimal side effects. Recent studies have demonstrated that opioid-containing immune cells migrate to inflamed sites and release beta-endorphins to inhibit pain as a mode of peripheral endogenous opioid analgesia. The present study investigates whether LLLT may enhance peripheral endogenous opioid analgesia.

METHODS

The effect of LLLT on opioid analgesia and production was evaluated in vivo in a rat model of inflammation as well as in vitro in Jurkat cells, a human T-cell leukemia cell line. mRNA expression of the beta-endorphin precursors proopiomelanocortin and corticotrophin releasing factor was assessed by reverse transcription polymerase chain reaction.

RESULTS

LLLT produced an analgesic effect in inflamed peripheral tissue which was transiently antagonized by naloxone. Beta-endorphin precursor mRNA expression increased with LLLT, both in vivo and in vitro.

CONCLUSION

This study demonstrates that LLLT produces analgesic effects in a rat model of peripheral inflammation. We further revealed an additional mechanism of LLLT-mediated analgesia via enhancement of peripheral endogenous opioids. These findings suggest that LLLT induces analgesia in rats by enhancing peripheral endogenous opioid production in addition to previously reported mechanisms.

Central role of p53 in the suntan response and pathologic hyperpigmentation

UV-induced pigmentation (suntanning) requires induction of alpha-melanocyte-stimulating hormone (alpha-MSH) secretion by keratinocytes. alpha-MSH and other bioactive peptides are cleavage products of pro-opiomelanocortin (POMC). Here we provide biochemical and genetic evidence demonstrating that UV induction of POMC/MSH in skin is directly controlled by p53. Whereas p53 potently stimulates the POMC promoter in response to UV, the absence of p53, as in knockout mice, is associated with absence of the UV-tanning response. The same pathway produces beta-endorphin, another POMC derivative, which potentially contributes to sun-seeking behaviors. Furthermore, several instances of UV-independent pathologic pigmentation are shown to involve p53 "mimicking" the tanning response. p53 thus functions as a sensor/effector for UV pigmentation, which is a nearly constant environmental exposure. Moreover, this pathway is activated in numerous conditions of pathologic pigmentation and thus mimics the tanning response.

Hair melanocytes as neuro-endocrine sensors--pigments for our imagination

We are currently experiencing a spectacular surge in our knowledge of skin function both at the organ and organismal levels, much of this due to a flurry of cutaneous neuroendocrinologic data, that positions the skin as a major sensor of the periphery. As our body's largest organ, the skin incorporates all major support systems including blood, muscle and innervation as well as its role in immuno-competence, psycho-emotion, ultraviolet radiation sensing, endocrine function, etc. It is integral for maintenance of mammalian homeostasis and utilizes locally-produced melanocortins to neutralize noxious stimuli. In particular, the cutaneous pigmentary system is an important stress response element of the skin's sensing apparatus; where stimuli involving corticotrophin-releasing hormone (CRH) and proopiomelanocortin (POMC) peptides help regulate pigmentation in the hair follicle and the epidermis. These pigmentary units are organized into symmetrical functional pigmentary units composed of corticotropin-releasing hormone, and the melanocortin POMC peptides melanocyte stimulating hormone, adrenocorticotropic hormone and also the opiate beta-endorphin. These new findings have led to the concept of "self-similarity" of melanocortin systems based on their expression both at the local (skin) and systemic (CNS) levels, where the only major apparent difference appears to be one of scale. This review explores this concept and describes how the components of the CRH/POMC systems may help regulate the human hair follicle pigmentary unit.

No significant change of plasma beta-endorphin levels of psoriasis patients after synchronous balneophototherapy

BACKGROUND/PURPOSE

Previous studies suggested that beta-endorphin has a pathogenic role in psoriasis: its increased plasma concentration may play a role in the neuroimmunological processes in the pathomechanism of the disease, and plasma beta-endorphin levels should reflect the changes in the patients' skin status. The purpose of this study was to investigate the changes of peripheral blood beta-endorphin levels in psoriatic patients in conjunction with changes in their skin symptoms after synchronous balneophototherapy.

METHODS

With synchronous balneophototherapy, 12 patients with extended skin symptoms of psoriasis were treated. The therapy followed the Regensburg protocol, consisting of a basic course of 35 sessions. Patients' skin status was characterized by evaluating the Psoriasis Area and Severity Index score before and after the therapy course. Blood samples were taken before treatment, and 1 day after the last session, with symptom-free skin. Plasma beta-endorphin levels were measured by a specific radioimmunoassay developed by the authors.

RESULTS

There was no significant change in plasma levels of beta-endorphin after clinical clearance of psoriatic skin symptoms.

CONCLUSION

In this non-randomized, uncontrolled study no significant difference could be detected between plasma beta-endorphin levels before and after a basic course of synchronous balneophototherapy in patients with psoriasis. Although beta-endorphin has many neuroimmunological effects, the changes of its plasma level do not consistently reflect the skin status. Inflammation in psoriatic skin lesions is probably not mediated directly by circulating beta-endorphin.

beta-Endorphin as a regulator of human hair follicle melanocyte biology

The pro-opiomelanocortin (POMC)-derived peptides, alpha-melanocyte-stimulating hormone, and adrenocorticotropic hormone, are important mediators of human skin pigmentation via action at the melanocortin-1 receptor. Recent data suggests that such a regulatory role also exists for the endogenous opiate, beta-endorphin (beta-END). A role for this beta-END in the regulation of follicular pigmentation, however, has not been determined. This study was designed to examine the involvement of the beta-END/mu-opiate receptor system in human follicular melanocyte biology. We employed RT-PCR, and immunohisto/cytochemistry and immunoelectron microscopy using beta-END and mu-opiate receptor specific antibodies and a functional role for beta-END was assessed by direct stimulation with the peptide. This study has demonstrated that human hair follicle melanocytes (HFM) express mRNA for the mu-opiate receptor and POMC. Furthermore, beta-END and its high affinity mu-opiate receptor are expressed at the protein level in glycoprotein100-positive follicular melanocytes and as a function of their anatomic location and differentiation status during the hair growth cycle. Functional studies revealed that beta-END is a modifier of HFM phenotype via its ability to upregulate melanogenesis, dendricity, and proliferation. These findings suggest a new regulatory role for beta-END in human HFM biology, providing a new research direction into the fundamental regulation of human hair pigmentation.

Solar-Simulated Ultraviolet Radiation-Induced Upregulation of the Melanocortin-1 Receptor, Proopiomelanocortin, and α-Melanocyte-Stimulating Hormone in Human Epidermis In Vivo

Ultraviolet light is one of the most crucial environmental factors with regard to its capacity to induce skin cancer, premature aging of the skin, and immunosuppression. Although ultraviolet directly affects the function of epidermal cells, many of these effects are mediated by induction of cytokines, growth factors, and neuropeptides, such as alpha-melanocyte-stimulating hormone. Recently, in addition to its well-known pigmentation inducing activity, a strong anti-inflammatory as well as an immunomodulatory potential of alpha-melanocyte-stimulating hormone has been recognized. The aim of this study was to determine, whether ultraviolet irradiation affects the expression of both alpha-melanocyte-stimulating hormone and the melanocortin-1 receptor in human epidermis in vivo. The volar aspects of the forearms were exposed to twice the minimal erythema dose of solar-simulating radiation. Three, 6, and 24 h after irradiation, the proopiomelanocortin and interleukin-10 mRNA levels in suction blister induced epidermal sheets were considerably upregulated as detected by semiquantitative reverse transcription-polymerase chain reaction. Furthermore, alpha-melanocyte-stimulating hormone and interleukin-10 protein levels in blister fluids were significantly increased 24 h after ultraviolet irradiation, an effect that could be abolished by application of the broad-spectrum sunscreen Anthélios XL prior to ultraviolet (solar-simulating radiation) exposure. In addition, enhanced melanocortin-1 receptor mRNA and receptor protein expression upon solar-simulating radiation was ascertained by reverse transcription-polymerase chain reaction and immunohistochemistry of the epidermal sheets, respectively. Proopiomelanocortin-derived neuropeptides, such as alpha-melanocyte-stimulating hormone may therefore play an important part in modulating ultraviolet-induced inflammation.

Plasma levels of opioid peptides after sunbed exposures

BACKGROUND

Previous studies have indicated that solar and artificial ultraviolet (UV) radiation have a positive influence on psychological variables such as mood and emotional state. Circulating opioid peptides have been suggested as being important in this effect.

OBJECTIVES

To investigate in a controlled trial the influence of UVA radiation on opioid peptide levels.

METHODS

We determined plasma levels of beta-endorphin immunoreactive material (IRM) and met-enkephalin in UV-exposed (n = 35) and non-exposed (n = 9) healthy volunteers. On the first day of the study, blood samples were taken from the volunteers (time A). UVA irradiation was subsequently administered with an air-conditioned tanning device. During the UV exposures the volunteers wore opaque goggles. Twenty minutes after UV exposure, blood samples were collected again (time B). Within the following 3 weeks the volunteers had a series of five UV exposures. On the last day of the study (24 h after the sixth UV exposure) blood samples were collected (time C). The cumulative UVA doses were 96 J cm-2 for skin type II and 126 J cm-2 for skin type III. The controls had no UV exposures. Plasma beta-endorphin IRM and met-enkephalin levels were determined using radioimmunoassays.

RESULTS

At all times of blood collection (A, B, C), there were no significant differences in plasma levels of beta-endorphin IRM and met-enkephalin between UV-exposed and non-exposed volunteers (P > 0.05).

CONCLUSIONS

UVA irradiation does not significantly elevate plasma levels of beta-endorphin IRM and met-enkephalin. Therefore we suggest that psychological benefits claimed to occur after UV exposure are unlikely to be mediated by the types of circulating opioid peptides measured in this study.

Interactions between opioid and chemokine receptors: heterologous desensitization

The opioid and chemokine receptors are both members of the seven transmembrane G protein-coupled receptor (GPCR) superfamily. Desensitization is believed to be a major element of the regulation of the function of these receptors, and recent findings suggest that both agonist-dependent (homologous) desensitization and heterologous desensitization can control receptor activity. The cross-desensitization between opioid and chemokine receptors has significant implications for our understanding of both the regulation of leukocyte trafficking, as well as the regulation of chemokine receptor function in inflammatory disease states. We also review findings which suggest that pro-inflammatory chemokine receptor-induced heterologous desensitization of opioid receptors has important implications for the regulation of opioid receptor function in the nervous system.