We have studied the issues associated with the use of platinum electrodes for transdermal iontophoretic delivery of peptides, using insulin as a model peptide. Insulin permeation was studied using full-thickness rat skin by varying the donor solution pH as a function of electrode polarity. The stability of insulin under the iontophoretic conditions was studied using TLC, SDS-polyacrylamide gel electrophoresis and HPLC. Large pH shifts were observed during anodal iontophoresis (AI), when the donor solution pH was above the isoelectric point of insulin and in cathodal iontophoresis (CI), when the donor solution pH was below the isoelectric point of insulin. The direction and magnitude of electroosmotic flow was influenced by pH of the donor solution and the electrode polarity. On the other hand, the buffer used to maintain the pH governed the contribution of electrorepulsion to the overall transport of insulin. Electrochemical degradation of insulin was significant during AI at pH 7.4. Among the pH investigated, AI of insulin at pH 3.6 and CI at pH 8.35 were better, as the pH shift was relatively less and electrochemically more stable during iontophoresis as compared with other pH. In summary, the pH shift caused by platinum electrodes had a significant influence on the permeation and stability of insulin.

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Different monoclonal antibodies, both commercial and indigenously produced, were evaluated in various combinations to optimize an immunoradiometric assay (IRMA) system for human thyroid stimulating hormone (hTSH). During these studies, it was observed that mixing one of the indigenously produced hTSH monoclonal antibody (2B11) in the hTSH IRMA system using Immunotech (Beckman Coulter, Czech Republic) kit reagents, led to an overall increase in the assay binding and sensitivity (from 0.025 mIU/L to 0.015mIU/L) of this IRMA system. This is not a general property of all monoclonal antibodies against hTSH. The mechanism for this enhancement can be attributed to the formation of a multicomponent complex.

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