Enzyme histochemistry of the tissue response to pure metal implants

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Abstract
Techniques of enzyme histochemistry have been used to augment those of histology and scanning electron microscopy in the study of the tissue response to pure metals. In this article the distribution of acid and alkaline phosphatase, lactate and succinate dehydrogenases, leucine aminopeptidase, and nonspecific esterase in association with implants of aluminium, copper, cobalt, nickel, and lead is described, and its significance for the tissue response is discussed. The toxic nature of cobalt was demonstrated especially by the intense acid phosphatase activity associated with macrophages and the virtual absence of LDH and SDH activity, implying a low level of respiration. Pigmented deposits noted previously from histological examination of the tissue surrounding copper implants was shown to be cellular in origin with many individual cells of macrophagic morphology being discernible following histochemical staining, suggesting that pigmentation has resulted from copper overload, similar to that of liver cells in Wilson's Disease. Generally, observations with nickel were qualitatively similar to those with copper, but not so prominent. Although lead is well known as a toxic metal, and indeed its effect on nervous tissue was apparent in this study from observation of unusual enzyme activity in muscle, the local response was minimal in contrast to that associated with several other pure metals. On the other hand, aluminium, normally considered a relatively nontoxic metal, induced intense activity of certain enzymes, noticeably acid phosphatase and leucine aminopeptidase, indicating its toxicity under implant conditions.