Doxycycline Indirectly Inhibits Proteolytic Activation of Tryptic Kallikrein-Related Peptidases and Activation of Cathelicidin

Abstract

The increased abundance and activity of cathelicidin and kallikrein 5 (KLK5), a predominant trypsin-like serine protease (TLSP) in the stratum corneum, have been implicated in the pathogenesis of rosacea, a disorder treated by the use of low-dose doxycycline. Here we hypothesized that doxycycline can inhibit activation of tryptic KLKs through an indirect mechanism by inhibition of matrix metalloproteinases (MMPs) in keratinocytes. The capacity of doxycycline to directly inhibit enzyme activity was measured in surface collections of human facial skin and extracts of cultured keratinocytes by fluorescence polarization assay against fluorogenic substrates specific for MMPs or TLSPs. Doxycycline did inhibit MMP activity but did not directly inhibit serine protease activity against a fluorogenic substrate specific for TLSPs. However, when doxycycline or other MMP inhibitors were added to live keratinocytes during the production of tryptic KLKs, this treatment indirectly resulted in decreased TLSP activity. Furthermore, doxycycline under these conditions inhibited the generation of the cathelicidin peptide LL-37 from its precursor protein hCAP18, a process dependent on KLK activity. These results demonstrate that doxycycline can prevent cathelicidin activation, and suggest a previously unknown mechanism of action for doxycycline through inhibiting generation of active cathelicidin peptides.

New and Emerging Treatments for Rosacea

“…Traditional US Food and Drug Administration (FDA)-approved topical treatments include topical sodium sulfacetamide, azelaic acid, and metronidazole. The only FDAapproved systemic medication for rosacea is subantimicrobial-dose doxycycline [11,12]. Several new treatment options were recently FDA approved or are in clinical trials.…”

Current Drug Therapies for Rosacea: A Chronic Vascular and Inflammatory Skin Disease

“…One potential mechanism of action for doxycycline in the treatment of rosacea is indirect inhibition of KLK proteolytic activities and cathelicidin peptide LL-37 production by inhibiting MMPs in keratinocytes. 37 Decreased KLK activity is reported when doxycycline or other MMP inhibitors are added to live keratinocytes during KLK production. 37 …”

“…37 Decreased KLK activity is reported when doxycycline or other MMP inhibitors are added to live keratinocytes during KLK production. 37 …”

“…37 Neovascularization occurs when LL-37 is applied in a rabbit model, suggesting that LL-37 may play a role in creating a chronic vascular environment in rosacea skin. 26 Adrenergic receptors have also been implicated to play a role in neurovascular regulation.…”

Update on the Management of Rosacea

“…48 Through inhibition of numerous matrix metalloproteinases, a reduction in the quantity and activity of serine protease kallikrein 5 results in decreased production of cathelicidin LL-37, the same AMP that has been highlighted in the pathogenesis of rosacea. 49 Key anti-inflammatory actions of doxycycline in rosacea include: downregulation of cytokines, reducing neutrophil infiltration, inhibition of nitric oxide and its vasodilatory effects, reduction of reactive oxygen species, slowing connective tissue destruction, and inhibition of matrix metalloproteinases. 50 Several studies have shown the effectiveness of doxycycline at subantimicrobial doses in the treatment of PPR, both as monotherapy and in conjunction with topical agents.…”