Curcumin accumulates in membrane structures of human Ishikawa and HT-29 cells

A122

Curcumin is the major yellow pigment of the rhizomes of the Asian plant Curcuma longa, which are commonly called turmeric. It is widely used as a food coloring agent and spice, e.g. in curry. Curcumin has a long history in Ayurvedic medicine and exhibits anti-oxidative, anti-inflammatory and anti-carcinogenic properties. Although the chemopreventive activity of curcumin has been shown in several animal studies, little is known about the fate of this compound in cells.
 >In previous studies on the metabolism of curcumin, a high propensity to bind to lipid membranes was noted. The aim of the present study was to characterize the accumulation of curcumin in membrane structures of mammalian cancer cells in more detail. Ishikawa cells, derived from a human endometrial carcinoma, and HT-29 cells, derived from a human colon adenocarcinoma, were incubated with curcumin in culture media with fetal calf serum for various periods of time up to 30 h. Subsequently, cells were harvested, homogenized and separated by ultracentrifugation into three fractions, i.e. cell debris, endoplasmic reticulum and cytoplasm. The cell fractions were extracted with Folch reagent and the incubation media with ethyl acetate, and curcumin was determined in the extracts using HPLC.
 >In Ishikawa cells, a rapid and time-dependent uptake of curcumin was observed. Maximum concentrations were reached after 3 h, followed by a slow decline. Within the cells, the major portion of curcumin was located in cell debris, whereas the endoplasmic reticulum contained less and the cytoplasm very little curcumin. Instead, mostly the reductive curcumin metabolites hexahydro- and octahydro-curcumin were found in the cytoplasm. In cell culture media, parent curcumin decreased and the reductive metabolites increased with time. Cells exposed to hexahydro-curcumin exhibited a reduced uptake of this metabolite as compared to curcumin.
 >In HT-29 cells, the concentration of curcumin found in cell debris and endoplasmic reticulum also exceeded that in cytoplasm. However, curcumin could only be detected in the cell fractions after 1 h. No reductive metabolites but glucuronides of curcumin were formed in HT-29 cells.
 >The results of this study indicate that curcumin rapidly penetrates the plasma membrane of mammalian cells and preferentially binds to the membranes of the endoplasmic reticulum, whereas its reductive metabolites and glucuronides exhibit a lower degree of membrane permeability and binding.