The Clinical Efficacy and Mechanism of Action of Alitretinoin in the Treatment of Alopecia Areata

Abstract

Background

Alitretinoin, a pan-retinoid receptor agonist approved for chronic hand eczema, exhibits immunomodulatory effects that may benefit alopecia areata (AA). However, clinical evidence for its use in AA is limited.

Objective

To evaluate alitretinoin's clinical efficacy and immunological mechanism in patients with AA.

Methods

We reviewed retrospectively twenty-one patients with AA who were treated with alitretinoin, either as monotherapy (n=9) or add-on therapy (n=12). Treatment response was assessed using the Severity of Alopecia Tool (SALT) scores, and in vitro studies used human outer root sheath cells stimulated with interferon-γ and polyinosinic:polycytidylic acid to investigate the drug’s effects on inflammatory pathways.

Results

Both groups showed significant reductions in SALT scores (p=0.04 and p=0.02, respectively). Patients with baseline SALT scores below 50 demonstrated superior improvement. Adverse events were mild, with headache (33.3%) and cheilitis (4.8%) being the most common. In vitro, alitretinoin suppressed interleukin-6 and tumor necrosis factor-α expression, decreased phosphorylation of signal transducer and activator of transcription (STAT) 1/STAT3, and downregulated major histocompatibility complex class I expression, suggesting restoration of hair follicle immune privilege.

Conclusion

Alitretinoin appears to be a safe and potentially effective treatment for patients with mild to moderate AA unresponsive to conventional therapies. Its role as a monotherapy or adjunctive option in selected cases warrants further investigation through larger controlled studies.

INTRODUCTION

Alopecia areata (AA) is a chronic, immune-mediated disorder characterized by non-scarring hair loss resulting from an autoimmune attack on anagen hair follicles. The condition follows a relapsing-remitting course. Clinical presentations range from localized patchy hair loss to complete scalp or body involvement, such as alopecia totalis or universalis. The collapse of the immune privilege of the hair follicle is a key event in disease initiation, followed by T-cell-driven inflammation¹.

Treatment guidelines recommend stepwise therapeutic approaches based on disease extent, duration, and patient age²,³. First-line treatments for limited disease include topical corticosteroids and intralesional triamcinolone injections, whereas patients with more extensive involvement may require systemic immunosuppressants or contact immunotherapy, such as diphenylcyclopropenone (DPCP). Janus kinase (JAK) inhibitors have recently demonstrated efficacy in severe AA and received regulatory approval; however, their long-term use is limited by cost, safety concerns, and restricted indications in pediatric and comorbid populations⁴.

Despite the availability of multiple therapies, a subset of patients with mild to moderate AA remains refractory to conventional treatments and may not be candidates for systemic agents. This highlights an unmet need for alternative options that are both immunomodulatory and safe for long-term use.

Alitretinoin (9-cis-retinoic acid) is a pan-retinoid receptor agonist with anti-inflammatory and immunoregulatory properties. It is approved for chronic hand eczema unresponsive to corticosteroids. It downregulates pro-inflammatory cytokines, inhibits antigen-presenting cell activation, and modulates MHC expresion⁵,⁶. Although not routinely used in AA, case reports have suggested its therapeutic potential in treatment-resistant forms, including alopecia universalis and ophiasis-type AA⁷,⁸,⁹.

In this study, we retrospectively analyzed the clinical outcomes of patients with AA treated with alitretinoin and investigated its immunomodulatory effects in vitro using outer root sheath (ORS) cells under inflammatory conditions relevant to AA pathogenesis.

MATERIALS AND METHODS

Participants

We retrospectively evaluated 21 AA patients diagnosed by board-certified dermatologists and treated with alitretinoin. The patients' demographics and clinical characteristics were recorded, including sex, age at onset, nail change, family history of AA, presence of other comorbidities, the Severity of Alopecia Tool (SALT) score, hair pull test result, and concurrent treatment methods. Of the 21 patients, 9 received alitretinoin exclusively. The remaining 12 patients received either baricitinib, cyclosporin, DPCP, triamcinolone intramuscular injection, or triamcinolone intralesional injection for a minimum of five months without demonstrating a response to the therapy. Alitretinoin was prescribed as adjunctive therapy to 12 patients receiving concurrent treatments, and these 12 patients were designated as the alitretinoin add-on group. Alitretinoin was administered at a dose of 30 mg/day and was adjusted according to patient tolerance and clinical response.

Evaluation of treatment efficacy

To determine the degree of severity and improvement in the AA lesions, we measured the SALT score, then divided the patients into five groups according to their scores: S1 (0%–24%), S2 (25%–49%) S3 (50%–74%), S4 (75%–99%), and S5 (100%), as previously described¹⁰. An analysis assessed the treatment response to alitretinoin, distinguishing between monotherapy and add-on therapy cases. Furthermore, the treatment response was evaluated by the severity of AA, with values recorded in the SALT score of less than 50 and more than 50.

Cell culture

Human scalp tissues were obtained with written informed consent, in accordance with the protocol approved by the Institutional Review Board (IRB) of Chungnam National University Hospital (IRB No. 2016-07-009). ORS cells were isolated from scalp hair follicles using a previously described protocol¹¹. Briefly, hair follicles were treated with 0.25% trypsin and 0.02% ethylenediaminetetraacetic acid in phosphate-buffered saline for 10 minutes, followed by mechanical dissociation through pipetting to generate a single-cell suspension. The resulting cell mixture was washed with Dulbecco’s Modified Eagle Medium (HyClone, Logan, UT, USA) supplemented with 10% fetal bovine serum (Gibco, Grand Island, NY, USA), and centrifuged at 200 × g for 5 minutes. Cells were resuspended in keratinocyte serum-free medium (Gibco) containing epidermal growth factor and bovine pituitary extract, and subsequently seeded onto culture dishes. The cultures were maintained at 37°C in a humidified incubator with 5% CO₂.

Western blot analysis

Cells were lysed using Proprep buffer (Intron, Daejeon, Korea), and total protein concentrations were determined with a bicinchoninic acid protein assay kit (Pierce Biotechnology, Rockford, IL, USA), following the manufacturer's instructions. Equal amounts of protein were separated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and subsequently transferred onto nitrocellulose membranes. The membranes were blocked and incubated with primary antibodies overnight at 4°C. After washing, membranes were probed with horseradish peroxidase–conjugated secondary antibodies and visualized using an enhanced chemiluminescence detection system (Translab, Daejeon, Korea). The following primary antibodies were used: phospho-signal transducer and activator of transcription (STAT) 1 and phospho-STAT3 (Cell Signaling Technology, Danvers, MA, USA), major histocompatibility complex (MHC) class I (Abcam, Cambridge, MA, USA), and actin (Santa Cruz Biotechnology, Dallas, TX, USA).

Quantitative real-time polymerase chain reaction (PCR)

Total RNA was extracted using the Easy-Blue RNA extraction kit (Intron), following the manufacturer's protocol. Complementary DNA was synthesized from the extracted RNA using moloney murine leukemia virus reverse transcriptase (Enzynomics, Daejeon, Korea). Quantitative real-time PCR was performed using SYBR Green Real-Time PCR Master Mix (Thermo Fisher Scientific, Waltham, MA, USA) with gene-specific primers. The primer sequences used for amplification are as follows: interleukin-6 (IL-6), 5’-CCATGCTACATTTGCCGA-3’ and 5’-CTGCGCAGCTTTAAGGAG-3’; tumor necrosis factor-α (TNF-α), 5’-TGGCCCAGGCAGTCAGAT-3’ and 5’-GGTTTGCTACAACATGGGCTA-3’; Actin, 5’-ATTGGCAATGAGCGGTTCC-3’ and 5’-GGTAGTTTCGTGGATGCCACA-3’.

Statistical analysis

Statistical analyses were performed using GraphPad Prism version 8.0.1 for Windows (GraphPad Software, San Diego, CA, USA). Comparisons between groups were evaluated using one-way analysis of variance, unpaired t-tests or paired t-tests, as appropriate. A p-value of less than 0.05 was considered to indicate statistical significance.

Ethics approval

The study design was reviewed and approved by the IRB of Pusan National University Hospital (IRB No. 2505-009-151) and Chungnam National University Hospital (IRB No. 2016-07-009).

RESULTS

Demographic and clinical features

A total of 21 patients with AA were enrolled in the study, including 9 who received alitretinoin monotherapy and 12 who received alitretinoin as an add-on to other treatments (Table 1). The mean age at onset was 41.56±17.70 years in the monotherapy group and 45.17±12.93 years in the add-on group (overall 43.62±14.85 years).

Table 1. Demographics and clinical characteristics of patients.

Characteristic		Alitretinoin monotherapy	Alitretinoin add-on therapy	Total
Total number of patients		9	12	21
Mean age at onset of AA (yr)		41.56±17.70	45.17±12.93	43.62±14.85
Sex
	Male	2 (22.2)	5 (41.7)	7 (33.3)
	Female	7 (77.8)	7 (58.3)	14 (66.7)
Clinical severity (SALT)
	S1 (0–24)	3 (33.3)	2 (16.7)	5 (23.8)
	S2 (25–49)	2 (22.2)	3 (25.0)	5 (23.8)
	S3 (50–74)	1 (11.1)	2 (16.7)	3 (14.3)
	S4 (75–99)	3 (33.3)	5 (41.7)	8 (38.1)
	S5 (100)	0 (0.0)	0 (0.0)	0 (0.0)
Baseline SALT score		46.44±32.87	60.75±25.76	54.62±29.15
Disease duration (mo)		239.33±220.44	123.50±103.35	173.14±169.60
Treatment duration (wk)		24.11±12.60	16.83±7.71	19.95±10.48
Nail change		2 (22.2)	0 (0.0)	2 (9.5)
Autoimmune disease		0 (0.0)	1 (8.3)	1 (4.8)
Atopic diseases		4 (44.4)	1 (8.3)	5 (23.8)
	Atopic dermatitis	1 (11.1)	1 (8.3)	2 (9.5)
	Allergic rhinitis	2 (22.2)	0 (0.0)	2 (9.5)
	Asthma	1 (11.1)	0 (0.0)	1 (4.8)
Concurrent treatment in add-on group
	Baricitinib		3 (25.0)
	Cyclosporine		1 (8.3)
	Diphenylcyclopropenone		6 (50.0)
	Triamcinolone intramuscular injection		1 (8.3)
	Triamcinolone intralesional injection		1 (8.3)

Data are presented as mean ± standard deviation or number (%), as appropriate.

AA: alopecia areata, SALT: Severity of Alopecia Tool.

Among the participants, 7 were male (33.3%) and 14 were female (66.7%). Clinical severity, assessed by SALT, was predominantly moderate to severe in both groups. The most common SALT category was S4 (75%–99% hair loss), observed in 33.33% of the monotherapy group and 41.67% of the add-on group. No patients were classified as S5 (complete hair loss). The baseline SALT scores were 46.44±32.87 and 60.75±25.76 for the monotherapy and add-on groups.

The mean disease duration was longer in the monotherapy group (239.33±220.44 months) compared to the add-on group (123.50±103.35 months). Nail involvement was noted in 2 patients (22.2%) in the monotherapy group only. One patient (8.3%) in the add-on group had a coexisting autoimmune disease.

Atopic conditions, including atopic dermatitis, allergic rhinitis, and asthma, were more frequent in the monotherapy group (44.4%) than in the add-on group (8.3%). In the add-on group, concurrent treatments included DPCP (50.0%), baricitinib (25.0%), and cyclosporine, intramuscular triamcinolone, or intralesional triamcinolone (each 8.3%).

Clinical efficacy of alitretinoin in patients with AA

Fig. 1 presents two representative cases demonstrating the therapeutic potential of alitretinoin in AA. A 43-year-old female with a 67-month disease duration showed marked improvement after 12 months of alitretinoin monotherapy (Fig. 1A and B). Similarly, a 54-year-old female with a 78-month history (Fig. 1C), who had failed to respond to DPCP and statins for 5 months (Fig. 1D), exhibited notable hair regrowth following 6 months of alitretinoin add-on therapy (Fig. 1E).

Fig. 1. Representative clinical responses to alitretinoin therapy in alopecia areata. (A, B) Serial clinical photographs of a 43-year-old female patient demonstrate marked hair regrowth following 12 months of alitretinoin monotherapy. Sequential images of a 54-year-old female patient show (C) initial presentation, (D) lack of response after 5 months of combined diphenylcyclopropenone and statin therapy, and (E) substantial improvement with notable hair regrowth after 6 months of adjunctive alitretinoin treatment.

Changes in SALT scores before and after therapy were analyzed to evaluate overall treatment efficacy (Table 2). A significant reduction in SALT scores was observed in the alitretinoin monotherapy group (Fig. 2A) (p=0.04). A similar improvement was seen in the add-on therapy group (Fig. 2B, p=0.02). Subgroup analysis revealed that patients with baseline SALT scores <50 responded particularly well (Fig. 2C, p=0.001), whereas those with SALT scores ≥50 showed no statistically significant change (Fig. 2D).

Table 2. Distribution of patients achieving SALT score reduction according to treatment modality and baseline disease severity.

% change from baseline in SALT score	Alitretinoin monotherapy (n=9)	Alitretinoin add-on therapy (n=12)	SALT score <50 (n=10)	SALT score ≥50 (n=11)
<25	4 (44.4)	6 (50.0)	0 (0.0)	10 (90.9)
26–50	0 (0.0)	1 (8.3)	1 (10.0)	0 (0.0)
>50	5 (55.6)	5 (41.7)	9 (90.0)	1 (9.1)

Data are presented as mean ± standard deviation or number (%), as appropriate.

SALT: Severity of Alopecia Tool.

Fig. 2. Changes in SALT scores following alitretinoin therapy in alopecia areata. (A) The monotherapy group significantly reduced SALT scores (p<0.05). (B) The add-on therapy group showed comparable efficacy with statistically significant improvement (p<0.05). (C) Stratified analysis revealed pronounced therapeutic response in patients with baseline SALT <50 (p<0.01). (D) Those with SALT ≥50 exhibited no statistically significant improvement. Data are presented as mean ± standard deviation. A paired t-test was done.

SALT: Severity of Alopecia Tool.

^*p<0.05, ^**p<0.01.

There was no significant difference in baseline SALT scores between the two groups. Since the add-on group largely included patients refractory to previous therapies, the observed clinical improvement suggests that alitretinoin may offer additional benefit in treatment-resistant cases of AA. Regarding safety, treatment was generally well tolerated. Seven out of 21 patients (33.3%) reported mild headaches, and one patient (4.8%) developed cheilitis. No serious adverse events were observed during the study period. Based on these findings, we considered alitretinoin a viable adjunctive treatment option in recalcitrant AA.

Effects of alitretinoin on inflammatory responses

To further explore its mechanism of action, we examined the immunomodulatory effects of alitretinoin in primary cultured human ORS cells. As shown in Fig. 3A, treatment with increasing concentrations of alitretinoin did not induce cytotoxicity, confirming its safety in this cellular context.

Fig. 3. Immunomodulatory effects of alitretinoin on inflammatory signaling in human ORS cells. (A) Alitretinoin treatment at concentrations up to 1,000 nM did not affect ORS cell viability, as assessed by the cell viability assay. (B) Stimulation with IFN-γ and poly(I:C) significantly increased IL-6 mRNA expression and protein secretion, which were markedly attenuated by alitretinoin in a dose-dependent manner. (C) Similarly, alitretinoin significantly reduced TNF-α mRNA expression and protein secretion induced by IFN-γ and poly(I:C) stimulation. (D) In contrast, alitretinoin did not significantly alter the expression of IFN-γ-responsive chemokines CXCL9, CXCL10, and CXCL11 under inflammatory conditions. (E) Western blot analysis demonstrated that alitretinoin decreased phosphorylation of STAT1 and STAT3 and MHC class I expression in ORS cells exposed to IFN-γ and poly(I:C). Data are presented as mean ± standard deviation.

ORS: outer root sheath, IFN-γ: interferon-γ, poly(I:C): polyinosinic:polycytidylic acid, IL-6: interleukin-6, mRNA: messenger RNA, TNF-α: tumor necrosis factor-α, CXCL: C-X-C motif chemokine ligand, STAT: signal transducer and activator of transcription, MHC: major histocompatibility complex.

^*p<0.05, ^**p<0.01.

To mimic the inflammatory environment observed in AA, ORS cells were stimulated with interferon-γ (IFN-γ) and polyinosinic:polycytidylic acid (poly[I:C])¹². Under these conditions, alitretinoin significantly reduced both messenger RNA expression and secretion of IL-6 (Fig. 3B) and TNF-α (Fig. 3C), two key pro-inflammatory cytokines implicated in AA pathogenesis. In contrast, alitretinoin did not significantly affect the expression of C-X-C motif chemokine ligand (CXCL) 9, CXCL10, and CXCL11, which are canonical IFN-γ–responsive genes (Fig. 3D), suggesting that its action is selective rather than broadly immunosuppressive.

At the molecular level, alitretinoin treatment reduced phosphorylated STAT1 and STAT3 and decreased MHC class I expression under IFN-γ and poly(I:C)-induced inflammatory conditions (Fig. 3E), which may help restore immune privilege in the hair follicle by limiting antigen presentation.

These findings suggest that alitretinoin selectively suppresses inflammatory signaling and cytokine production without impairing general interferon responsiveness, supporting its therapeutic potential in AA through modulation of local immune responses.

DISCUSSION

Alitretinoin (9-cis-retinoic acid) is a pan-retinoid receptor agonist that binds to both retinoic acid receptors (RAR-α, -β, -γ) and retinoid X receptors (RXR-α, -β, -γ), exerting broad immunomodulatory and anti-inflammatory effects. It is currently approved for the treatment of severe chronic hand eczema unresponsive to corticosteroids, and its efficacy has also been reported in various T cell-mediated inflammatory dermatoses, including lichen planus and palmoplantar pustular psoriasis¹³,¹⁴.

Although limited, case reports suggest that alitretinoin may offer therapeutic benefits in AA. In one case, a patient with alopecia universalis achieved 86.8% hair regrowth over four months of treatment⁷. Another reported complete remission of ophiasis-type AA during long-term therapy for chronic hand eczema⁸. Improvement has also been observed in frontal fibrosing alopecia with coexisting lichen planus, supporting its potential in inflammatory hair disorders⁹. Previous studies suggest that these effects may be mediated by the downregulation of pro-inflammatory cytokines, attenuation of immune cell activation, and modulation of antigen presentation - all of which may contribute to restoring hair follicle immune privilege, a key mechanism disrupted in AA pathogenesis.

Managing mild to moderate AA poses a clinical challenge, particularly when patients fail to respond to first-line treatments such as topical corticosteroids, intralesional injections, or contact immunotherapy. Although systemic agents like cyclosporine or JAK inhibitors are available, their use is often constrained by adverse effects, cost, or accessibility². These limitations underscore the need for safer and more accessible alternatives. Alitretinoin's unique receptor profile and well-established long-term safety may represent a viable option in this context.

In our study, monotherapy and add-on therapy with alitretinoin led to significant reductions in SALT scores, indicating clinical efficacy. The lack of significant differences in baseline disease severity between groups, combined with the observed response in patients previously refractory to standard treatments, supports the potential of alitretinoin as both a monotherapy in localized cases and as an adjunct in more extensive disease.

It is not possible to completely rule out the delayed effects of baseline treatments in the add-on therapy group, which is a limitation of our study. However, considering the efficacy of alitretinoin observed in the monotherapy group, some of the improvement seen in the add-on therapy group is attributable to alitretinoin. Furthermore, in clinical practice, patients with AA often experience significant anxiety, and it is quite common to add a new medication to existing therapies rather than switching treatments to improve compliance. Considering add-on therapy in real-world practice, our study results are meaningful despite this limitation.

We conducted in vitro experiments using ORS cells under IFN-γ and poly(I:C)-induced inflammatory conditions to further investigate the underlying mechanisms. Alitretinoin treatment suppressed pro-inflammatory cytokines, reduced phosphorylation of STAT1 and STAT3, and downregulated MHC class I expression. These effects are consistent with restoring immune privilege in the hair follicle and align with the clinical outcomes observed in our patient cohort. We also tested alitretinoin under poly(I:C)-only stimulation to clarify whether the observed effects were IFN-γ–independent. Alitretinoin reduced IL-6 but did not affect CXCL9/10/11, TNF-α, or MHC class I, suggesting that its impact on MHC class I is IFN-γ-dependent (data not shown).

Given its favorable safety profile and moderate efficacy, alitretinoin can be considered a monotherapy for patients who require long-term management but cannot tolerate potent immunosuppressants or an add-on therapy for patients who do not respond even with immunosuppressants. However, limited efficacy was observed in severe AA cases SALT ≥50, as reflected by non-responding cases from our analysis.

Overall, alitretinoin may help bridge a therapeutic gap in AA, offering a safe and effective option for patients with recalcitrant disease who fall between mild cases responsive to topical therapy and severe cases requiring intensive systemic immunosuppression. Further large-scale, controlled studies are needed to define its precise role and to identify patient subgroups most likely to benefit from this treatment.