Metallothioneins (MTs) and various other metal binding proteins release metals when exposed to nitric oxide (NO). We investigated the structural consequences of the interaction between MTs and NO by using ¹ H‐ and ¹¹³ Cd‐NMR spectroscopy and found that only the three metals from the N ‐terminal β‐domain were selectively released whereas the C ‐terminal α‐domain remains intact. Since it has been proposed that the β‐domain is responsible for the postulated role of MTs in zinc homeostasis, whereas the tight binding of metals in the α‐domain appears to play a role in heavy metal detoxification, our results suggest a potential regulatory role of NO in zinc distribution. Specifically, we present a mechanism whereby MT counteracts the cytotoxic effects of NO at inflammatory sites.

Sulfation of resveratrol, a polyphenolic compound present in grapes and wine with anticancer and cardioprotective activities, was studied in human liver cytosol. In the presence of 3′-phosphoadenosine-5′-phosphosulfate, three metabolites (M1–3) whose structures were identified by mass spectrometry and NMR as trans-resveratrol-3-O-sulfate, trans-resveratrol-4′-O-sulfate, and trans-resveratrol-3-O-4′-O-disulfate, respectively. The kinetics of M1 formation in human liver cytosol exhibited an pattern of substrate inhibition with a K_i of 21.3 ± 8.73 µM and a V_max/K_m of 1.63 ± 0.41 µL min⁻¹mg⁻¹ protein. Formation of M2 and M3 showed sigmoidal kinetics with about 56-fold higher V_max/K_m values for M3 than for M2 (2.23 ± 0.14 and 0.04 ± 0.01 µL min⁻¹ mg⁻¹). Incubation in the presence of human recombinant sulfotransferases (SULTs) demonstrated that M1 is almost exclusively catalysed by SULT1A1 and only to a minor extent by SULT 1A2, 1A3 and 1E1, whereas M2 is selectively formed by SULT1A2. M3 is mainly catalysed by SULT1A2 and 1A3. In conclusion, the results elucidate the enzymatic pathways of resveratrol in human liver, which must be considered in humans following oral uptake of dietary resveratrol.

Activity-guided fractionation of a petroleum ether-soluble extract of the roots of Onosma paniculata, which has been shown to affect the cell cycle and to induce apoptosis in melanoma cells, led to the isolation of several shikonin derivatives, namely, β-hydroxyisovalerylshikonin (1), acetylshikonin (2), dimethylacrylshikonin (3), and a mixture of α-methylbutyrylshikonin and isovalerylshikonin (4+5). All compounds exhibited strong cytotoxicity against eight cancer cell lines and MRC-5 lung fibroblasts, with 3 found to possess the most potent cytotoxicity toward four melanoma cell lines (SBcl2, WM35, WM9, and WM164). Furthermore, 3 and the mixture of 4+5 were found to interfere with cell-cycle progression in these cell lines and led to an increasing number of cells in the subG1 region as well as to caspase-3/7 activation, indicating apoptotic cell death.

Resveratrol (3,4′,5-trihydroxy-trans-stilbene) is a naturally occurring polyphenolic compound found in grapes, wine and medicinal plants with a variety of biological and pharmacological activities including pronounced anticancer properties. These effects are observed despite its extremely low bioavailability and rapid clearance from the circulation due to extensive sulfation and glucuronidation in the intestine and liver. In order to determine whether its metabolites demonstrate any cytotoxic properties, three major human sulfated conjugates of resveratrol were synthesized and their anticancer activity evaluated against three breast cancer cell lines (two hormone-dependent: MCF-7 and ZR-75-1; one hormone-independent: MDA‐MB‐231) and one immortalized breast epithelial cell line (MCF-10A). We found that, in contrast to resveratrol, all three sulfated metabolites were less potent against MCF-7, MDA‐MB‐231 and ZR-75-1 cells (trans-resveratrol 3-O-sulfate < trans-resveratrol 4′-O-sulfate < trans-resveratrol 3-O-4′-O-disulfate) indicating that any conjugation of the phenolic groups with sulfuric acid strongly affecting the cytotoxicity. Interestingly, all sulfated metabolites were reduced about 10-fold, but showed nearly equal cytotoxicity towards nonmalignant MCF-10A breast cells (IC_50 s: 202–228 µM). In summary, in contrast to resveratrol its sulfated metabolites showed poor cytotoxicity in human malignant and nonmalignant breast cancer cell lines. However, the in vitro activity of the metabolites may not necessarily reflect their in vivo function, given the fact that the ubiquitously existing human sulfatases could convert the metabolites back to resveratrol in humans.