A tobacco smoking mixture and/or a cigarette wrapper with high-temperature ammonia-release agents therein are provided, wherein the high-temperature ammonia-release agents are present in an amount effective to reduce the cytotoxicity of gas phase or particulate matter formed during smoking of the cigarette. The high-temperature ammonia-release agents are capable of reducing the cytotoxicity of gas phase or particulate matter by evolving ammonia at temperatures greater than about 200° C., wherein the ammonia can interact with the particulate matter. Additionally, the high-temperature ammonia-release agents can be formed by heating an aqueous mixture of an iron precursor compound, an ammonia source compound and an acid.