Removal of metals from aqueous solutions using natural chitinous materials

Four naturally derived chitinous materials, commercial cryogenically milled carapace (CCMC), mechanically milled carapace (MMC), chitin and chitosan, were assessed for their ability to remove a range of alkali, alkaline earth, transition and heavy metals from aqueous media in flow-through column trials. The materials showed a poor affinity for the alkali metals and alkaline earth metals but significantly greater affinity for transition and heavy metals. In general, chitin was the least efficient material for removal of transition and heavy metals (≈35%) while chitosan was most effective (>99%). CCMC and MMC both removed >90% of transition and heavy metals tested from solution. Batch studies conducted using copper as a reference metal demonstrated that removal was dependent on a number of variables including pH, contact time, particle size, metal concentration, metal type and the physio-chemical characteristics of the materials. Detailed analysis of the results from these studies indicate that removal is a complex process and that metals can be sequestered from solution by a number of mechanisms including adsorption, absorption and precipitaion.

Nitric oxide-dependent pro-oxidant and pro-apoptotic effect of metallothioneins in HL-60 cells challenged with cupric nitrilotriacetate

Intracellular safeguarding functions of metallothioneins (MTs) include sequestering transition and heavy metals, scavenging free radicals and protecting against electrophiles. We report that MT protection against Cu-induced cytotoxicity can be reversed and pro-oxidant and pro-apoptotic effects can be induced in HL-60 cells exposed to NO. We demonstrate that in ZnCl2-pretreated HL-60 cells loaded with copper nitrilotriacetate (Cu-NTA), exposure to an NO donor, S-nitroso-N-acetyl penicillamine, resulted in S-nitrosylation and oxidation of MT cysteines. This disruption of MT Cu-binding thiolate clusters caused loosening and release of redox-active Cu, enhanced redox-cycling activity of Cu and increased peroxidation of major classes of membrane phospholipids. We also found that Cu-induced oxidative stress in ZnCl2-pretreated/Cu-NTA-loaded HL-60 cells was accompanied by apoptosis documented by characteristic changes of nuclear morphology, internucleosomal DNA cleavage, externalization of phosphatidylserine, release of cytochrome c from mitochondria into cytosol and activation of caspase-3. We conclude that in Cu-challenged cells, NO can reverse the protective role of MTs and convert them into pro-oxidant, pro-apoptotic implements.