Michelle L. Kerns

Induction of the Phase 2 Response in Mouse and Human Skin by Sulforaphane-containing Broccoli Sprout Extracts

The isothiocyanate sulforaphane was isolated from broccoli extracts in a bioactivity-guided fractionation as the principal and very potent inducer of cytoprotective phase 2 enzymes and subsequently shown to inhibit tumor development in animal models that involve various carcinogens and target organs. Because broccoli and broccoli sprouts are widely consumed, extracts obtained from them are viewed as convenient vehicles for sulforaphane delivery to humans. In relation to our current interest in devising strategies for protection against UV light–induced skin cancer, it was necessary to examine the safety and efficacy of topical application of sulforaphane-containing broccoli sprout extracts as single and multiple doses in both mice and humans. Topical application of an extract delivering 100 nmol sulforaphane/cm2 increased the protein levels of NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione S-transferase A1, and heme oxygenase 1, three representative phase 2 enzymes, in mouse skin epidermis. Quantitative assessment of the activity of NQO1 24 h after dosing showed increases of 1.5- and 2.7-fold after application of single and multiple (thrice, every 24 h) doses, respectively. A dose-escalation safety study in healthy human subjects revealed no adverse reactions when doses as high as 340 nmol of sulforaphane in the form of broccoli sprout extracts were applied topically to the center of a 1-cm-diameter circle drawn on the volar forearm. A subsequent efficacy study showed that despite the interindividual differences in basal levels, the enzyme activity of NQO1 in homogenates of 3-mm full thickness skin punch biopsies increased in a dose-dependent manner, with maximum increases of 1.5- and 4.5-fold after application of 150 nmol doses, once or three times (at 24 h-intervals), respectively, thus providing direct evidence for induction of the phase 2 response in humans. (Cancer Epidemiol Biomarkers Prev 2007;16(4):847–51)

Epidermolysis bullosa simplex: a paradigm for disorders of tissue fragility

Epidermolysis bullosa (EB) simplex is a rare genetic condition typified by superficial bullous lesions that result from frictional trauma to the skin. Most cases are due to dominantly acting mutations in either keratin 14 (K14) or K5, the type I and II intermediate filament (IF) proteins tasked with forming a pancytoplasmic network of 10-nm filaments in basal keratinocytes of the epidermis and in other stratified epithelia. Defects in K5/K14 filament network architecture cause basal keratinocytes to become fragile and account for their trauma-induced rupture. Here we review how laboratory investigations centered on keratin biology have deepened our understanding of the etiology and pathophysiology of EB simplex and revealed novel avenues for its therapy.

Keratin 17 promotes epithelial proliferation and tumor growth by polarizing the immune response in skin

Basaloid skin tumors, including basal cell carcinoma (BCC) and basaloid follicular hamartoma, are associated with aberrant Hedgehog (Hh) signaling and, in the case of BCC, an expanding set of genetic variants including keratin 5 (encoded by KRT5), an intermediate filament-forming protein. We here show that genetic ablation of keratin 17 (Krt17) protein, which is induced in basaloid skin tumors and co-polymerizes with Krt5 in vivo, delays basaloid follicular hamartoma tumor initiation and growth in mice with constitutive Hh signaling in epidermis. This delay is preceded by a reduced inflammation and a polarization of inflammatory cytokines from a Th1- and Th17-dominated profile to a Th2-dominated profile. Absence of Krt17 also attenuates hyperplasia and inflammation in models of acute dermatitis. Re-expression of Krt17 in Gli2tg; Krt17−/− keratinocytes induces select Th1 chemokines that have established roles in BCC. Our findings establish an immunomodulatory role for Krt17 in Hh driven basaloid skin tumors that could impact additional tumor settings, psoriasis and wound repair.

Reprogramming of keratin biosynthesis by sulforaphane restores skin integrity in epidermolysis bullosa simplex

Epidermolysis bullosa simplex (EBS) is a rare inherited condition in which the epidermis loses its integrity after mechanical trauma. EBS is typified by the dysfunction of intermediate filaments in basal keratinocytes of epidermis. Most cases of EBS are due to mutations in the keratin 5 or 14 gene (K5 and K14), whose products copolymerize to form intermediate filaments in basal keratinocytes. Available treatments for this disorder are only palliative. Here we exploit functional redundancy within the keratin gene family as the basis for therapy. We show that genetic activation of Gli2 or treatment with a pharmacological activator of Nrf2, two transcription factors eliciting distinct transcriptional programs, alleviates the blistering caused by a K14 deficiency in an EBS mouse model, correlating with K17 induction in basal epidermal keratinocytes. Nrf2 induction is brought about by treatment with sulforaphane, a natural product. Sulforaphane thus represents an attractive option for the prevention of skin blistering associated with K14 mutations in EBS.

Differential Modulation of Keratin Expression by Sulforaphane Occurs via Nrf2-dependent and -independent Pathways in Skin Epithelia

In this study the authors address the mechanistic basis of the therapeutic benefit afforded by treatment with the naturally occurring small molecule sulforaphane in the context of a keratin-based skin blistering disease, epidermolysis bullosa simplex.

Randomized, split-body, single-blinded clinical trial of topical broccoli sprout extract: Assessing the feasibility of its use in keratin-based disorders

Background: Epidermolysis bullosa simplex is a skin‐blistering disorder caused by mutations in keratin (K)14 or K5. Treatment with nuclear factor (erythroid‐derived 2)‐like 2 inducer sulforaphane ameliorated skin blistering in Krt14‐null mice, correlating with induction of K17. To be therapeutically useful for epidermolysis bullosa simplex, topical broccoli sprout extract (BSE), enriched for sulforaphane, would ideally induce the expression of homologous keratins (eg, K6, K17, K16) in the basal layer of human epidermis without impacting expression of defective keratins (K5/K14). Objective: The purpose of this 1‐week, randomized, split‐body, single‐blinded, placebo‐controlled trial was to assess the impact of BSE on keratin expression. Methods: Five subjects (34‐71 years old) applied BSE (500 nmol of sulforaphane/mL) or vehicle alone to the inner aspect of the arm daily. Expression of keratin, nuclear factor (erythroid‐derived 2)‐like 2, and other markers was assessed using reverse transcription‐polymerase chain reaction and indirect immunofluorescence. Results: One subject (age 71 years) was excluded a posteriori because of poor tissue quality. Topical BSE activated nuclear factor (erythroid‐derived 2)‐like 2 and up‐regulated K17 in the epidermis of all subjects, had variable effects on K16 and K6 expression, and did not alter expression of K14 or K5. Limitations: Small sample size is a limitation. Conclusion: BSE represents an attractive therapeutic candidate for K14‐associated epidermolysis bullosa simplex.

Sexual Dimorphism in Response to an NRF2 Inducer in a Model for Pachyonychia Congenita

Sex is an influential factor regarding pathophysiology and therapeutic response in human disease. Pachyonychia congenita is caused by mutations in keratin genes and typified by dystrophic lesions affecting nails, glands, oral mucosa, and palmar-plantar epidermis. Painful palmar-plantar keratoderma (PPK) severely impairs mobility in pachyonychia congenita. Mice genetically null for keratin 16 (Krt16), one of the genes mutated in pachyonychia congenita, develop pachyonychia congenita-like PPK. In male Krt16-/- mice, oxidative stress associated with impaired glutathione synthesis and nuclear factor erythroid-derived 2 related factor 2 (NRF2)-dependent gene expression precedes PPK onset, which can be prevented by topical sulforaphane-mediated activation of NRF2. We report here that sulforaphane treatment fails to activate NRF2 and prevent PPK in female Krt16-/- mice despite a similar set of molecular circumstances. Follow-up studies reveal a temporal shift in PPK onset in Krt16-/- females, coinciding with sex-specific fluctuations in footpad skin glutathione levels. Dual treatment with sulforaphane and diarylpropionitrile, an estrogen receptor beta selective agonist, results in NRF2 activation, normalization of glutathione levels, and prevention of PPK in female Krt16-/- mice. These findings point to a sex difference in NRF2 responsiveness that needs be considered when exploring NRF2 as a therapeutic target in skin disorders.