Ewa Radziszewska

Inhibition of proliferation and apoptosis of human and rat T lymphocytes by curcumin, a curry pigment

Curcumin (diferuoylmethane), the yellow pigment in the rhizome of tumeric (Curcuma longa), an ingredient of curry spice, is known to exhibit a variety of pharmacological effects including antitumor, antiinflammatory, and antiinfectious activities. Although its precise mode of action remains elusive, curcumin has been shown to suppress the activity of the AP-1 transcription factor in cells stimulated to proliferate. In this study, we observed that curcumin (50 microM) inhibited proliferation of rat thymocytes stimulated with concanavalin A (Con A) as well as that of human Jurkat lymphoblastoid cells in the logarithmic growth phase. The pigment also inhibited apoptosis in dexamethasone-treated rat thymocytes and in UV-irradiated Jurkat cells as judged by DNA ladder formation, cellular morphological changes, and flow cytometry analysis. The inhibition of apoptosis by curcumin in rat thymocytes was accompanied by partial suppression of AP-1 activity. Complete suppression of AP-1 activity was observed in Con A-treated, proliferating thymocytes. The capacity of curcumin to inhibit both cell growth and death strongly implies that these two biological processes share a common pathway at some point and that curcumin affects a common step, presumably involving a modulation of the AP-1 transcription factor.

Glutathione-independent mechanism of apoptosis inhibition by curcumin in rat thymocytes

Curcumin (CUR) is a natural yellow dye with antioxidant and scavenging properties present in Curcuma species. It is widely used as an anti-inflammatory, anti-mutagenic and chemopreventive agent. In addition to its inhibitory effect on proliferation, CUR has recently been shown to block dexamethasone-induced programmed cell death (apoptosis) of rat thymocytes. Because cellular thiols seem to play a role in redox regulation of apoptosis, the mechanism of the anti-apoptotic effect of CUR was studied by examining the levels of glutathione and acid-soluble sulfhydryl groups. CUR was shown to prevent the glutathione loss occurring in dexamethasone-treated thymocytes, enhancing intracellular glutathione content at 8 hr to 192% of that of nontreated cells. A 60% increase in acid-soluble sulfhydryl groups was also observed. In the presence of L-buthionine S,R-sulfoximine (BSO, an inhibitor of glutathione synthesis), intracellular glutathione content of thymocytes treated with dexamethasone and CUR fell to 31% and that of the acid-soluble sulfhydryl groups to 23% of control after 8 hr. Unexpectedly, the electrophoretic and flow cytometric studies of DNA fragmentation demonstrated that apoptosis did not occur even after 20 hr of incubation with buthionine S,R-sulfoximine and dexamethasone, while control thymocytes and the cells treated only with buthionine S,R-sulfoximine showed DNA fragmentation at a level corresponding to spontaneous apoptosis. These results show that CUR treatment elevated the concentrations of glutathione and nonprotein sulfhydryl groups, thus preventing their decrease in apoptotic thymocytes. Coadministration of L-buthionine S,R-sulfoximine and CUR did not affect the anti-apoptotic effect of CUR suggesting a glutathione-independent mechanism of cell protection.

Loss of transcription factor AP-1 DNA binding activity during lymphocyte aging in vivo

The main feature of cellular senescence is cessation of cell proliferation. Protooncogene c‐fos, which is required for the cell to enter into DNA synthesis, is repressed in senescent fibroblasts. Diminished expression of c‐fos and impaired formation of AP‐1, which is a complex of c‐Fos and c‐Jun proteins acting as a transcription factor, was found in lymphocytes derived from old (> 18 months) mice and stimulated with Con A. There were no differences in c‐jun expression and formation of other transcription factors (AP‐2 and AP‐3) between lymphocytes isolated front old and young mice.

UVC-induced cell death of IL-2-dependent human lymphocytes.

We compared the in vitro propensity of human IL‐2‐dependent lymphocytes (young proliferating and senescent non‐proliferating), and resting peripheral blood lymphocytes (PBLs) to undergo UVC‐induced apoptosis. The activities of AP‐1 (activator protein‐1), CRE (cAMP response element) and OCT‐1 (octamer‐1) transcription factors in all lymphocytes were also assessed. At 24h after UVC treatment, half of young proliferating T lymphocytes and about a quarter of PBLs and senescent non‐proliferating cells were apoptotic, as shown by flow cytometry. However, only in young lymphocytes were both typical DNA ‘ladder’ and Bcl‐2 downregulation evident. The AP‐1 transcription factor was activated by UVC in IL‐2‐dependent young and senescent, but not resting lymphocytes. Taken together, the data show different propensities of resting, proliferating and senescent human lymphocytes to undergo UVC‐induced apoptosis and AP‐1 activation.