ABSTRACT
Recent studies have shown that sparse distribution of regulatory T cells (Tregs) in the skin might be involved in the onset of severe cutaneous adverse drug reactions such as Stevens-Johnson syndrome and toxic epidermal necrolysis. Treg migration toward epithelial cells is regulated by certain chemokines, including TARC/CCL17 and MDC/CCL22. In this study, we analyzed the effect of allopurinol (APN), a drug known to cause severe adverse reactions, on the expression of factors affecting Treg migration and the mechanisms involved. APN inhibited the tumor necrosis factor (TNF)-α- and interferon (IFN)-γ-associated expression of TARC/CCL17 and MDC/CCL22 mRNA in HaCaT cells in a dose-dependent manner. Consistent with this, APN also suppressed TNF-α- and IFN-γ-induced production of TARC/CCL17 and MDC/CCL22 proteins and the migration of C-C chemokine receptor type 4-positive cells. Activity of the transcription factors NF-κB and STAT1, which are involved in TARC/CCL17 and MDC/CCL22 expression, was also investigated. APN inhibited activation of NF-κB, but not that of STAT1. Furthermore, it restricted p38 MAPK phosphorylation. These results suggest that APN inhibits TNF-α- and IFN-γ-induced TARC/CCL17 and MDC/CCL22 production through downregulation of p38 MAPK and NF-κB signaling, resulting in the sparse distribution of Tregs in the skin of patients with APN-associated Stevens-Johnson syndrome/toxic epidermal necrolysis.
Subject(s)
Allopurinol/toxicity , Cell Movement/drug effects , Chemokine CCL17/antagonists & inhibitors , Chemokine CCL22/antagonists & inhibitors , Keratinocytes/drug effects , NF-kappa B/metabolism , T-Lymphocytes, Regulatory/drug effects , Chemokine CCL17/metabolism , Chemokine CCL22/metabolism , HEK293 Cells , Humans , K562 Cells , Keratinocytes/immunology , Oxypurinol/toxicity , Stevens-Johnson Syndrome/etiology , Stevens-Johnson Syndrome/immunology , T-Lymphocytes, Regulatory/immunologyABSTRACT
Nitric oxide (NO), now almost synonymous with endothelium-derived relaxing factor (EDRF), reacts with superoxide anion radical (O2-) and forms a potentially toxic molecular species, peroxynitrite (ONOO-). Because xanthine oxidase (XO) seems to be a major O2- -producing enzyme in the vascular system, it is important to clarify the mechanism of XO regulation of NO/EDRF. We first characterized the inhibition of XO in vitro by three types of pyrazolopyrimidine derivatives. Kinetic studies indicated that 4-amino-6-hydroxpyrazolo[3,4-d]pyrimidine (AHPP) and allopurinol competitively inhibited the conversion of xanthine to uric acid catalyzed by XO, with apparent Ki values of 0.17 +/- 0.02 and 0.50 +/- 0.03 micro M respectively; alloxanthine inhibited this conversion in a noncompetitive manner with an apparent Ki value of 3.54 +/- 1.12 microM. O2- generation in the xanthine/XO system assayed by lucigenin-dependent chemiluminescence was suppressed most strongly by AHPP in a dose-dependent fashion; allopurinol itself appears to reduce the enzyme by transfer of an electron to O2, thus generating O(2-). AHPP significantly augmented EDRF-mediated relaxation of aortic rings from both rabbits and spontaneously hypertensive rats (SHR) in a dose-dependent manner, whereas allopurinol did not affect the relaxation and only marginal potentiation of the vasorelaxation was observed with alloxanthine. Finally, iv injection of AHPP (50.4 mg/kg; 100 micromol/300 g rat) reduced the blood pressure of SHR rats to 70% of the initial pressure; this pressure is almost the blood pressure of normal rats. Allopurinol (100 micromol/300 g rat; iv) showed transient decrease in blood pressure and moderate reduction of hypertension of SHR (10%) was observed with iv injection of alloxanthine (100 mumol/300 g rat). On the basis of these results, it seems that XO regulates EDRF/NO via production of O2-.
