Biochemical Journal

Research article

High cellular accumulation of sulphoraphane, a dietary anticarcinogen, is followed by rapid transporter-mediated export as a glutathione conjugate

Yuesheng ZHANG, Eileen C. CALLAWAY

Abstract

Sulphoraphane (SF), a naturally occurring isothiocyanate, is a potent anticarcinogen in animal experiments. The mechanism of action of sulphoraphane includes induction of Phase 2 detoxification enzymes, inhibition of carcinogen-activating Phase 1 enzymes, induction of apoptosis and cell cycle arrest, and anti-inflammation. We have recently found that it was accumulated in mammalian cells by up to several hundred-fold over the extracellular concentration, primarily by conjugation with intracellular GSH. The intracellular accumulation levels of SF can reach millimolar concentrations. The anticarcinogenic activity of SF is at least partly dependent on its accumulation levels in cells. Here we show, however, that the accumulated SF was rapidly exported mainly in the form of GSH conjugate (GS—SF) in cultured human cells. It appeared that to sustain the intracellular accumulation levels required a continuous uptake of SF to offset the rapid export of SF/GS—SF. These findings may have important implications for the development of an effective dosing regimen for SF. Moreover, the export was temperature-sensitive and was inhibited by known inhibitors of membrane pumps, suggesting the involvement of such a pump in exporting accumulated SF/GS—SF. Indeed, studies with human leukemia cells (HL60) with or without overexpression of multidrug resistance associated protein-1(MRP-1) and human myeloma cells (8226) with or without overexpression of P-glycoprotein-1 (Pgp-1) indicated that both MRP-1 and Pgp-1 are involved in the export of intracellular SF/GS—SF.

  • anticarcinogen
  • isothiocyanate
  • MRP-1
  • P-glycoprotein-1
  • sulphoraphane transport

Footnotes

  • Abbreviations used: BSO, dl-buthionine (R,S)-sulphoximine; DPBS, Dulbecco's phosphate buffered saline; GST, glutathione S-transferase; HL60/S, human leukemia cells; HL60/AR, adriamycin-resistant derivative of HL60; LNCaP, human prostate carcinoma cells; MCF-7, human breast cancer cells; MK571, 3-[({3-[2-(7-chloro-2-quinolinyl)ethenyl]phenyl}-{(3-dimethyl amino-3-oxopropyl)-thio}methyl)thio]propanoic acid; MRP-1, multidrug resistance associated protein-1; Pgp-1, P-glycoprotein-1; SF, sulphoraphane [1-isothiocyanato-4-(methylsulphinyl)butane]; 8226/S, human myeloma cells; 8226/Dox40, adriamycin-resistant derivative of 8226/S cells.