Received for publication November 16, 2007.
Revised April 29, 2008.
Accepted for publication April 29, 2008.

Arsenic Trioxide, Arsenic Pentoxide and Arsenic Iodide Inhibit Human Keratinocyte Proliferation through the Induction of Apoptosis

Abstract

Arsenic compounds have been traditionally used to treat a variety of ailments including skin diseases. Our previous study identified the extract of realgar to possess potent anti-proliferative action on HaCaT cells. The present study aimed at evaluating whether a number of inorganic arsenics found in realgar also possess similar anti-proliferative property. The results showed that arsenic trioxide, arsenic pentoxide and arsenic iodide had significant anti-proliferative action on HaCaT cells, with IC₅₀ values at 2.4, 16 and 6.8 µM respectively. These compounds, however, only modestly inhibited the growth of Hs-68 cells, a normal human skin fibroblast cell line, with IC₅₀ at 43.4, 223 and 89 µM respectively, conferring a favorable toxicity profile. In mechanistic studies, all three compounds caused DNA fragmentation as demonstrated by gel electrophoresis and the TUNEL method. Morphologically, nuclear condensation and DNA fragmentation were observed when the cells were exposed to the arsenic compounds. Cell cycle analysis with propidium iodide (PI) staining demonstrated the appearance of sub-G1 peak and cell arrest at the G1 phase in the presence of these compounds. Quantitative analysis by annexin V-PI staining revealed that the arsenics-induced apoptotic event was dose-dependent. Moreover, the arsenic compounds were able to activate caspase-3 expression when examined by Western blot analysis. Our experimental data unambiguously demonstrated that induction of cellular apoptosis was mainly responsible for the observed anti-proliferation brought about by the arsenic compounds on HaCaT keratinocytes, suggesting that these arsenic compounds are putative agents from which psoriasis-treating topical formulae could be developed.

Key words: Apoptosis, Arsenic iodide, Arsenic pentoxide, Arsenic trioxide, Keratinocytes, Psoriasis