Topical Plant Polyphenols Prevent Type I Interferon Signaling in the Skin and Suppress Contact Hypersensitivity.

Human keratinocytes were recently shown to respond to anti-EGFR (epidermal growth factor receptor) drugs with activation of an interferon-κ-driven autocrine loop, leading to enhanced expression of innate antiviral effectors and of the pro-inflammatory chemokines CXCL10 (C-X-C motif chemokine 10) and CCL2 (C-C motif ligand 2). Here we showed active type I interferon signaling in the skin lesions of cancer patients undergoing treatment with the anti-EGFR drug cetuximab. Strong nuclear positivity for Interferon Regulatory Factor 1 and phosphorylated Signal Transducer and Activator of Transcription 1, enhanced interferon-κ expression and CXCL10 was associated to the epidermal compartment. Notably, 50 micromolar resveratrol and quercetin fully suppressed the low constitutive levels of type I interferon signaling and prevented its activation by the anti-EGFR cetuximab or gefitinib in cultured keratinocytes. In sensitized mice undergoing DNFB (2,4-dinitro-1-fluorobenzene)-induced contact hypersensitivity, local administration of gefitinib prior to elicitation further amplified hapten-induced type I interferon activation, tissue edema, and infiltration by T cells, whereas resveratrol or quercetin suppressed this inflammatory cascade. Overall, these data suggest that topical application of resveratrol or quercetin could be potentially effective in preventing pathological conditions due to overactivation of type I IFN (interferon)-driven circuits in the skin, including the inflammatory manifestations of anti-EGFR drug-induced skin-targeted toxicity.

Purinergic signaling in scarring.

Adenosine (ADO) and nucleotides such as ATP, ADP, and uridine 5'-triphosphate (UTP), among others, may serve as extracellular signaling molecules. These mediators activate specific cell-surface receptors-namely, purinergic 1 and 2 (P1 and P2)-to modulate crucial pathophysiological responses. Regulation of this process is maintained by nucleoside and nucleotide transporters, as well as the ectonucleotidases ectonucleoside triphosphate diphosphohydrolase [ENTPD; cluster of differentiation (CD)39] and ecto-5'-nucleotidase (5'-NT; CD73), among others. Cells involved in tissue repair, healing, and scarring respond to both ADO and ATP. Our recent investigations have shown that modulation of purinergic signaling regulates matrix deposition during tissue repair and fibrosis in several organs. Cells release adenine nucleotides into the extracellular space, where these mediators are converted by CD39 and CD73 into ADO, which is anti-inflammatory in the short term but may also promote dermal, heart, liver, and lung fibrosis with repetitive signaling under defined circumstances. Extracellular ATP stimulates cardiac fibroblast proliferation, lung inflammation, and fibrosis. P2Y2 (UTP/ATP) and P2Y6 [ADP/UTP/uridine 5'-diphosphate (UDP)] have been shown to have profibrotic effects, as well. Modulation of purinergic signaling represents a novel approach to preventing or diminishing fibrosis. We provide an overview of the current understanding of purinergic signaling in scarring and discuss its potential to prevent or decrease fibrosis.

The MEK Inhibitors Trametinib and Cobimetinib Induce a Type I Interferon Response in Human Keratinocytes.

Mitogen-activated protein kinase kinases (MEK) 1 and 2 have crucial roles in tumorigenesis, cell proliferation, and protection from apoptosis, and their inhibition is therefore an attractive therapeutic strategy in cancer. Orally available and highly selective MEK inhibitors have been developed and assessed in numerous clinical trials, either alone or in combination with cytotoxic chemotherapy and/or other targeted agents. Of note, a complex picture of class-specific adverse effects associates with these drugs, frequently including inflammatory skin rash. Here, we investigated the response of normal human keratinocytes to the MEK inhibitors trametinib and cobimetinib, alone and in combination with the v-Raf murine sarcoma viral oncogene homolog B (BRAF) inhibitors dabrafenib and vemurafenib, in terms of signal transduction and de novo gene expression. MEK inhibitors triggered enhanced expression of interferon regulatory factor 1 (IRF1) and phosphorylation of signal transducer and activator of transcription 1 (STAT1), and up-regulated the keratinocyte-specific type I interferon κ (IFN-κ), the anti-viral effectors interferon-induced tetratricopeptide repeats (IFIT) 1 and 2, and the pro-inflammatory chemokine (C-C motif) ligand 2 (CCL2) and the C-X-C motif chemokine 10 (CXCL10), both at the mRNA and protein level. Impairment of IRF1 expression, or abrogation of STAT1 phosphorylation due to IFN-κ gene silencing, suppressed anti-viral and pro-inflammatory gene expression. These data suggest that, similar to what we observed for epidermal growth factor receptor (EGFR) blockade, MEK inhibition activates a type I interferon response, which is now recognized as an effective anti-cancer response, in human epidermal keratinocytes.

Epidermal growth factor receptor signalling in keratinocyte biology: implications for skin toxicity of tyrosine kinase inhibitors.

The epidermal growth factor receptor (EGFR) and its ligands have been long recognized as centrally involved in the growth and repair process of epithelia, as well as in carcinogenesis. In addition, the EGFR has been demonstrated to be importantly involved in the control of inflammatory responses. During this last decade, a number of highly specific agents targeting this system have become an integral component of pharmacologic strategies against many solid malignancies. These drugs have led to increased patient survival and made therapy more tolerant when compared to conventional cytotoxic drugs. Nonetheless, their use is associated with a constellation of toxic effects on the skin, including follicular pustules, persistent inflammation, xerosis and pruritus, and enhanced susceptibility to infections. This dramatic impairment of skin homoeostasis underscores the centrality of the EGFR-ligand system in the whole skin immune system. So far, no mechanism-based approaches are available to specifically counteract the adverse effects of anti-EGFR drugs or any other class of tyrosine kinase inhibitors. Only the knowledge of the cellular and molecular events underlying these adverse effects in humans, combined with in vitro/in vivo models able to mimic these toxic responses, may guide the development of mechanism-based treatment or prevention strategies.

Plant polyphenols differentially modulate inflammatory responses of human keratinocytes by interfering with activation of transcription factors NFκB and AhR and EGFR-ERK pathway.

Molecular mechanisms underlying modulation of inflammatory responses in primary human keratinocytes by plant polyphenols (PPs), namely the glycosylated phenylpropanoid verbascoside, the stilbenoid resveratrol and its glycoside polydatin, and the flavonoid quercetin and its glycoside rutin were evaluated. As non-lethal stimuli, the prototypic ligand for epidermal growth factor receptor (EGFR) transforming growth factor alpha (TGFalpha), the combination of tumor necrosis factor (TNFalpha) and interferon (IFNgamma) (T/I), UVA+UVB irradiation, and bacterial lipopolysaccharide (LPS) were used. We demonstrated differential modulation of inflammatory responses in keratinocytes at signal transduction, gene transcription, and protein synthesis levels as a function of PP chemical structure, the pro-inflammatory trigger used, and PP interaction with intracellular detoxifying systems. The PPs remarkably inhibited constitutive, LPS- and T/I-induced but not TGFalpha-induced ERK phosphorylation. They also suppressed NFkappaB activation by LPS and T/I. Verbascoside and quercetin invariably impaired EGFR phosphorylation and UV-associated aryl hydrocarbon receptor (AhR)-mediated signaling, while rutin, polydatin and resveratrol did not affect EGFR phosphorylation and further activated AhR machinery in UV-exposed keratinocytes. In general, PPs down-regulated gene expression of pro-inflammatory cytokines/enzymes, except significant up-regulation of IL-8 observed under stimulation with TGFalpha. Both spontaneous and T/I-induced release of IL-8 and IP-10 was suppressed, although 50µM resveratrol and polydatin up-regulated IL-8. At this concentration, resveratrol activated both gene expression and de novo synthesis of IL-8 and AhR-mediated mechanisms were involved. We conclude that PPs differentially modulate the inflammatory response of human keratinocytes through distinct signal transduction pathways, including AhR and EGFR.

Pollen-derived E1-phytoprostanes signal via PPAR-gamma and NF-kappaB-dependent mechanisms.

In a humid milieu such as mucosal surfaces, pollen grains do not only release allergens but also proinflammatory and immunomodulatory lipids, termed pollen-associated lipid mediators. Among these, the E(1)-phytoprostanes (PPE(1)) were identified to modulate dendritic cell (DC) function: PPE(1) inhibit the DC's capacity to produce IL-12 and enhance DC mediated T(H)2 polarization of naive T cells. The mechanism(s) by which PPE(1) act on DC remained elusive. We thus analyzed candidate signaling elements and their role in PPE(1)-mediated regulation of DC function. Aqueous birch pollen extracts induced a marked cAMP response in DC that could be blocked partially by EP2 and EP4 antagonists. In contrast, PPE(1) hardly induced cAMP and the inhibitory effect on IL-12 production was mostly independent of EP2 and EP4. Instead, PPE(1) inhibited the LPS-induced production of IL-12 p70 by a mechanism involving the nuclear receptor PPAR-gamma. Finally, PPE(1) efficiently blocked NF-kappaB signaling in DCs by inhibiting IkappaB-alpha degradation, translocation of p65 to the nucleus, and binding to its target DNA elements. We conclude that pollen-derived PPE(1) modulate DC function via PPAR-gamma dependent pathways that lead to inhibition of NFkappaB activation and result in reduced DC IL-12 production and consecutive T(H)2 polarization.

Wide-spectrum profile of inflammatory mediators in the plasma and scales of patients with psoriatic disease.

Psoriasis is a chronic recurrent inflammatory disorder of the skin. Clinical subtypes include psoriasis vulgaris (PV), psoriatic arthropathy, and erythrodermic psoriasis. Aim of this study was to analyse relevant inflammatory mediators in the plasma of patients with distinct subtypes of active psoriasis, and in the scales of mild-to-moderate PV patients, and correlation to disease severity. Compared to healthy controls (n=10), patients affected by very severe forms of psoriasis (n=30) were characterized by increased plasma levels of IL-4, IL-6, MCP-1, VEGF and in particular PDGFbb. Each group with severe psoriasis had distinct characteristic features of plasma cytokine profile. Mild-to-moderate PV patients (n=35) showed higher levels of IL-4, IL-6, IL-10, and IL-13 when compared to healthy controls. No correlation was found between PV severity assessed by PASI (Psoriasis Area and Severity Index) and levels of these mediators. By contrast, disease severity correlated to scale levels of IP-10. For the first time, we found exaggerated circulating levels of the pro-angiogenic PDGFbb and VEGF in severe psoriasis. Evidence that the severity of skin symptoms correlated exclusively with scale levels of IP-10, but not with any up-regulated inflammatory mediator in plasma, suggests that distinct skin-independent processes contribute to the circulating cytokine profile in psoriasis.

Biological definition of multiple chemical sensitivity from redox state and cytokine profiling and not from polymorphisms of xenobiotic-metabolizing enzymes.

BACKGROUND: Multiple chemical sensitivity (MCS) is a poorly clinically and biologically defined environment-associated syndrome. Although dysfunctions of phase I/phase II metabolizing enzymes and redox imbalance have been hypothesized, corresponding genetic and metabolic parameters in MCS have not been systematically examined. OBJECTIVES: We sought for genetic, immunological, and metabolic markers in MCS. METHODS: We genotyped patients with diagnosis of MCS, suspected MCS and Italian healthy controls for allelic variants of cytochrome P450 isoforms (CYP2C9, CYP2C19, CYP2D6, and CYP3A5), UDP-glucuronosyl transferase (UGT1A1), and glutathione S-transferases (GSTP1, GSTM1, and GSTT1). Erythrocyte membrane fatty acids, antioxidant (catalase, superoxide dismutase (SOD)) and glutathione metabolizing (GST, glutathione peroxidase (Gpx)) enzymes, whole blood chemiluminescence, total antioxidant capacity, levels of nitrites/nitrates, glutathione, HNE-protein adducts, and a wide spectrum of cytokines in the plasma were determined. RESULTS: Allele and genotype frequencies of CYPs, UGT, GSTM, GSTT, and GSTP were similar in the Italian MCS patients and in the control populations. The activities of erythrocyte catalase and GST were lower, whereas Gpx was higher than normal. Both reduced and oxidised glutathione were decreased, whereas nitrites/nitrates were increased in the MCS groups. The MCS fatty acid profile was shifted to saturated compartment and IFNgamma, IL-8, IL-10, MCP-1, PDGFbb, and VEGF were increased. CONCLUSIONS: Altered redox and cytokine patterns suggest inhibition of expression/activity of metabolizing and antioxidant enzymes in MCS. Metabolic parameters indicating accelerated lipid oxidation, increased nitric oxide production and glutathione depletion in combination with increased plasma inflammatory cytokines should be considered in biological definition and diagnosis of MCS.

Redox imbalance in T cell-mediated skin diseases.

The skin is permanently exposed to physical, chemical, and biological aggression by the environment. In addition, acute and chronic inflammatory events taking place in the skin are accompanied by abnormal release of pro-oxidative mediators. In this paper, we will briefly overview the homeostatic systems active in the skin to maintain the redox balance and also to counteract abnormal oxidative stress. We will concentrate on the evidence that a local and/or systemic redox dysregulation accompanies the chronic inflammatory disorder events associated to psoriasis, contact dermatitis, and atopic dermatitis. We will also discuss the fact that several well-established treatments for the therapy of chronic inflammatory skin disorders are based on the application of strong physical or chemical oxidants onto the skin, indicating that, in selected conditions, a further increase of the oxidative imbalance may lead to a beneficial outcome.

Intracellular Insulin-like growth factor binding protein 2 (IGFBP2) contributes to the senescence of keratinocytes in psoriasis by stabilizing cytoplasmic p21.

Psoriasis is a chronic Th1/Th17 lymphocytes-mediated inflammatory skin disease, in which epidermal keratinocytes exhibit a peculiar senescent state, resistance to apoptosis and the acquisition of senescence-associated secretory phenotype (SASP). SASP consists of the release of soluble factors, including IGFBPs, that exert extracellular and intracellular functions in IGF-dependent or independent manner.In this report, we investigated the expression and function of IGFBP2 in senescent keratinocytes isolated from the skin of patients with plaque psoriasis. We found that IGFBP2 is aberrantly expressed and released by these cells in vivo, as well as in vitro in keratinocyte cultures undergoing progressive senescence, and it associates with the cyclin-dependent kinase inhibitors p21 and p16 expression. For the first time, we provide evidence for a dual action of IGFBP2 in psoriatic keratinocytes during growth and senescence processes. While extracellular IGFBP2 counter-regulates IGF-induced keratinocyte hyper-proliferation, intracellular IGFBP2 inhibits apoptosis by interacting with p21 and protecting it from ubiquitin-dependent degradation. Indeed, we found that cytoplasmic p21 sustains anti-apoptotic processes, by inhibiting pro-caspase 3 cleavage and JNK phosphorylation in senescent psoriatic keratinocytes. As a consequence, abrogation of p21, as well as that of IGFBP2, found to stabilize cytoplasmic p21 levels, lead to the restoration of apoptosis mechanisms in psoriatic keratinocytes, commonly observed in healthy cells.

CXCR2 ligands and G-CSF mediate PKCalpha-induced intraepidermal inflammation.

Transgenic mice overexpressing PKCalpha in the epidermis (K5-PKCalpha mice) exhibit an inducible severe intraepidermal neutrophilic inflammation and systemic neutrophilia when PKCalpha is activated by topical 12-O-tetradecanoylphorbol-13-acetate (TPA). This inducible model of cutaneous inflammation was used to define mediators of skin inflammation that may have clinical relevance. Activation of cutaneous PKCalpha increased the production of the chemotactic factors cytokine-induced neutrophil chemoattractant (KC) and macrophage inflammatory protein 2 (MIP-2) in murine plasma. TPA treatment of cultured K5-PKCalpha keratinocytes also released KC and MIP-2 into culture supernatants through an NF-kappaB-dependent pathway. MIP-2 and KC mediated the infiltration of neutrophils into the epidermis, since this was prevented by ablating CXCR2 in K5-PKCalpha mice or administering neutralizing antibodies against KC or MIP-2. The neutrophilia resulted from PKCalpha-mediated upregulation of cutaneous G-CSF released into the plasma independent of CXCR2. These responses could be inhibited by topical treatment with a PKCalpha-selective inhibitor. Inhibiting PKCalpha also reduced the basal and TNF-alpha- or TPA-induced expression of CXCL8 in cultured psoriatic keratinocytes, suggesting that PKCalpha activity may contribute to psoriatic inflammation. Thus, skin can be the source of circulating factors that have both local and systemic consequences, and these factors, their receptors, and possibly PKCalpha could be therapeutic targets for inhibition of cutaneous inflammation.

Metabolism of plant polyphenols in the skin: beneficial versus deleterious effects.

Polyphenols are produced by all higher plants in order to protect them against biotic and abiotic stress such as UV radiation, temperature changes, infections, wounding, and herbivores. When in contact with human skin, polyphenols exert either curative or damaging action depending on their physical-chemical properties, bioavailability through cutaneous barrier, metabolism in the skin, and individual sensitivity. This review will focus on 1) synthesis and metabolism of polyphenols and their role in the plant physiology, 2) non-enzymatic and enzymatic polyphenol transformation in the skin, 3) polyphenols as inhibitors or inducers of inflammatory response in the skin, and 4) photo-protective versus photo-toxic effects of polyphenols. The potential consequences of these controversial effects on the use of plant polyphenols in dermatology and cosmetology will be also discussed.

The contribution of keratinocytes to the pathogenesis of atopic dermatitis.

Atopic dermatitis (AD) develops from a complex interplay between environmental, genetic, immunologic and biochemical factors. Relevant to the amplification and persistence of inflammatory and immune responses in AD skin are keratinocytes, which can be induced to secrete proinflammatory mediators in response to a variety of stimuli, including epidermal barrier perturbation. Moreover, keratinocytes from AD patients synthesize exaggerated amounts of mediators (e.g., GM-CSF and RANTES/CCL5) important for enhanced recruitment as well as sustained survival and activation of T cells and dendritic cells. AD keratinocytes have a constitutive dysregulated activity of transcription factors that modulate the expression of inflammatory genes, suggesting the existence of predetermined mechanisms targeting atopic inflammation to the skin. Among these, the existence of a defective epidermal barrier, which appears related to decreased ceramide generation and abnormal degradation of corneodesmosomes, certainly plays a central role in the predisposition to AD.

Epidermal growth factor receptor inhibitors trigger a type I interferon response in human skin.

The Epidermal Growth Factor Receptor (EGFR) is centrally involved in the regulation of key processes of the epithelia, including cell proliferation, survival, differentiation, and also tumorigenesis. Humanized antibodies and small-molecule inhibitors targeting EGFR were developed to disrupt these functions in cancer cells and are currently used in the treatment of diverse metastatic epithelial cancers. By contrast, these drugs possess significant skin-specific toxic effects, comprising the establishment of a persistent inflammatory milieu. So far, the molecular mechanisms underlying these epiphenomena have been investigated rather poorly. Here we showed that keratinocytes respond to anti-EGFR drugs with the development of a type I interferon molecular signature. Upregulation of the transcription factor IRF1 is early implicated in the enhanced expression of interferon-kappa, leading to persistent activation of STAT1 and further amplification of downstream interferon-induced genes, including anti-viral effectors and chemokines. When anti-EGFR drugs are associated to TNF-α, whose expression is enhanced by the drugs themselves, all these molecular events undergo a dramatic enhancement by synergy mechanisms. Finally, high levels of interferon-kappa can be observed in epidermal keratinocytes and also in leukocytes infiltrating the upper dermis of cetuximab-driven skin lesions. Our data suggest that dysregulated activation of type I interferon innate immunity is implicated in the molecular processes triggered by anti-EGFR drugs and leading to persistent skin inflammation.

Interleukin-10 downregulates anti-microbial peptide expression in atopic dermatitis.

Recurrent skin infections in extrinsic atopic dermatitis (EAD) may be because of the suppression of anti-microbial peptide (AMP) expression by interleukin (IL)-4 and IL-13. Twenty to thirty percent of AD, however, are classified as intrinsic atopic dermatitis (IAD). They exhibit normal serum IgE levels, no allergen-specific sensitization, and lower levels of IL-4 and IL-13 than EAD. Both forms of AD have increased propensity to skin infection, suggesting a novel mechanism for infection in IAD. In this study, we observed significantly decreased human beta-defensin (HBD)-2 gene expression in the skin of both IAD (p = 0.010) and EAD (p = 0.004), as compared with psoriasis patients. Conversely, IAD (p = 0.019) and EAD (p = 0.002) skin lesions exhibited elevated IL-10 gene expression when compared with psoriasis. Using primary keratinocytes, we found that the deficiency in AMP expression is an acquired rather than a constitutive defect. Interestingly, neutralizing antibodies to IL-10 augmented the production of tumor necrosis factor-alpha and interferon-gamma by peripheral blood mononuclear cell from AD patients. Additionally, treatment of AD skin explants with anti-IL-10 augmented the expression of both HBD-2 and LL-37. Thus, increased levels of IL-10 may contribute to the AMP deficiency in both IAD and EAD by reducing cytokines that induce AMP.

Regulatory role of nitric oxide on monocyte-derived dendritic cell functions.

Nitric oxide (NO) has an established role in the defense against bacterial infections and exerts multiple modulatory activities on both inflammatory and immune responses. However, the relevance of NO on dendritic cell (DC) functions has been poorly investigated. In this study, we found that addition of the NO donor S-nitrosoglutathione (GSNO) to monocyte-derived DCs matured by lipopolysaccharide (LPS) or soluble CD40 ligand led to a decreased capacity to activate naive allogeneic T cells but a more prominent Th1 polarization, with increased interferon-gamma (IFN-gamma) secretion and reduced interleukin-5 (IL-5) release. The presence of GSNO during maturation of DCs caused a reduced expression of surface CD86, whereas CD80, CD83, and MHC molecule expression was not affected. Moreover, GSNO induced a dose-dependent decrease of IL-10 and enhancement of tumor necrosis factor-alpha (TNF-alpha) release from mature DCs. In parallel, a marked reduced production of IL-12 p40 subunit but no significant perturbation of the bioactive IL-12 p70 production was observed. Finally, GSNO significantly reduced the release of IP-10/CXCL10 and RANTES/CCL5 but not IL-8/CXCL8 by mature DCs. Although GSNO can strengthen the capacity of mature DCs to induce type 1 polarization of T lymphocytes, our data suggest that it elicits distinct anti-inflammatory functions, eventually reducing T lymphocyte proliferation and recruitment.

Targeting tumor necrosis factor-alpha as a potential therapy in inflammatory skin diseases.

Tumor necrosis factor-a (TNFalpha) plays an important role in the initiation and persistence of inflammation in a variety of skin disorders. The availability of selective TNFalpha blockers has provided new therapeutic opportunities. TNFa inhibitors have been employed with success in treating psoriasis in controlled trials, although further studies are warranted to better define which subgroup of patients can benefit most from this treatment and modalities of combination therapy. In addition, an increasing number of case reports indicates that anti-TNFalpha agents are of value in the treatment of other skin diseases, such as pyoderma gangrenosum and Behcet's syndrome, and in the treatment of graft-versus-host disease.

Chemokine networks in inflammatory skin diseases.

The superfamily of chemokines comprises numerous small, cytokine-like chemotactic proteins, which have a fundamental role in the regulation of leukocyte trafficking. The chemokine-chemokine receptor system is highly redundant and promiscuous, and forms a complex network relevantly involved in the expression of chronic inflammatory skin diseases, including allergic contact dermatitis, atopic dermatitis and psoriasis. The pattern of chemokine expression shows overlapping features but also important differences in these diseases due to distinct sources and types of pro-inflammatory signals involved in chemokine induction, and the inherent capacity of resident skin cells to produce chemokines. Chemokine receptors (G-protein coupled receptors) rather than chemokines appear the appropriate therapeutic targets as they are more chemically tractable and play less redundant functions.

Insulin-like growth factor-1 induces regulatory T cell-mediated suppression of allergic contact dermatitis in mice.

Allergic contact dermatitis (ACD) is triggered by an aberrant hyperinflammatory immune response to innocuous chemical compounds and ranks as the world's most prevalent occupational skin condition. Although a variety of immune effector cells are activated during ACD, regulatory T (Treg) cells are crucial in controlling the resulting inflammation. Insulin-like growth factor-1 (IGF-1) regulates cell proliferation and differentiation and accelerates wound healing and regeneration in several organs including the skin. Recently IGF-1 has also been implicated in protection from autoimmune inflammation by expansion of Treg cells. Here, we demonstrate that ectopic expression of IGF-1 in mouse skin suppresses ACD in a Treg cell-specific manner, increasing the number of Foxp3+ Treg cells in the affected area and stimulating lymphocyte production of the anti-inflammatory cytokine interleukin 10. Similar therapeutic effects can be achieved with systemic or topical delivery of IGF-1, implicating this growth factor as a promising new therapeutic option for the treatment of ACD.