Shigeru Sassa* Pages 273 - 290 ( 18 )
Heme and heme-related compounds such as porphyrins have a variety of biological and clinical activities. This review highlights some of the novel effects of these compounds in medicinal chemistry. Heme which has no photoreactive properties, can serve as the prosthetic group for various hemoproteins, or as a substrate for microsomal heme oxygenase (HO). In contrast, porphyrins have photodynamic activities but usually do not serve as substrates in biological systems. Thus, heme and heme analogues are often used to influence enzyme activities in tissues, while porphyrins by taking advantage of their photoreactive properties are used as drugs in medicine. There are four major applications of these compounds, namely the use of (i) heme in the treatment of porphyrias and hematological disorders, (ii) synthetic metalloporphyrins in the treatment of hyperbilirubinemia, (iii) metal-free porphyrins in photodynamic therapy of malignant tumors, and (iv) porphyrin derivatives as contrast reagents in radiography. Solubility, stability, pharmacokinetics, pharmacodynamics and analytical techniques are all important considerations in the medicinal chemistry of these compounds. In man and animals in vivo, the rate of synthesis and catabolism of heme, as well as disorders of heme synthesis are important in understanding pathophysiological effects of these compounds.