Solution equilibria and the X-ray structure of Cu(ii) complexation with 3-amino-N-(pyridin-2-ylmethyl)propanamide, a pseudo-mimic of human serum albumin.

Copper complexes have anti-inflammatory activity in the treatment of inflammation associated with rheumatoid arthritis (RA). The preferred route of administration is through the skin, so the rate of dermal absorption and bioavailability of copper is important. Based on previous studies, 3-amino-N-(pyridin-2-ylmethyl)-propanamide, [H(56)NH2], was designed as a potential chelator of copper. The stability constant measurements revealed that MLH-1 is the most stable species at the physiological pH of 7.4. The X-ray crystal structure of this species was solved and copper was found in a rectangular pyramidal geometry. The ligand occupied three coordination sites while bridging chloride linked copper ions together in a chain. The ligand bound to the metal ion through the pyridyl nitrogen, the amide nitrogen and the terminal amino group. Spectroscopic studies confirmed that this structure persisted in aqueous solution. Octanol/water partition coefficients and Franz cell permeation studies showed that [H(56)NH2] is able to promote the dermal absorption of Cu(ii).

The cytotoxicity of garlic-related disulphides and thiosulfonates in WHCO1 oesophageal cancer cells is dependent on S-thiolation and not production of ROS.

BACKGROUND: Garlic has been used for centuries in folk medicine for its health promoting and cancer preventative properties. The bioactive principles in crushed garlic are allyl sulphur compounds which are proposed to chemically react through (i) protein S-thiolation and (ii) production of ROS. METHODS: A collection of R-propyl disulphide and R-thiosulfonate compounds were synthesised to probe the importance of thiolysis and ROS generation in the cytotoxicity of garlic-related compounds in WHCO1 oesophageal cancer cells. RESULTS: A significant correlation (R(2)=0.78, Fcrit (7,1) α=0.005) was found between the cytotoxicity IC(50) and the leaving group pK(a) of the R-propyl disulphides and thiosulfonates, supporting a mechanism that relies on the thermodynamics of a mixed disulphide exchange reaction. Disulphide (1) and thiosulfonate (11) were further evaluated mechanistically and found to induce G(2)/M cell-cycle arrest and apoptosis, inhibit cell proliferation, and generate ROS. When the ROS produced by 1 and 11 were quenched with Trolox, ascorbic acid or N-acetyl cysteine (NAC), only NAC was found to counter the cytotoxicity of both compounds. However, NAC was found to chemically react with 11 through mixed disulphide formation, providing an explanation for this apparent inhibitory result. CONCLUSION: Cellular S-thiolation by garlic related disulphides appears to be the cause of cytotoxicity in WHCO1 cells. Generation of ROS appears to only play a secondary role. GENERAL SIGNIFICANCE: Our findings do not support ROS production causing the cytotoxicity of garlic-related disulphides in WHCO1 cells. Importantly, it was found that the popular ROS inhibitor NAC interferes with the assay.