The dimerization of ferrihaems. IV. Studies on haematoferrihaem and a general appraisal of the nature and implications of dimerization.

The dimerization of haematoferrihaem was studied in phosphate buffer in the pH range 7.02--8.14. The absorbance of dilute solutions decreased over a period of several hours due to adsorption of haematoferrihaem to glass vessels. This problem was overcome by using dilute solutions within 10 min of preparation. Spectrophotometric data were consistent with a dimerization process according to the equation 2 monomer in equilibrium dimer + H+ as found earlier for other ferrihaems studied. The value of K, defined as K = [dimer] [H+]/[monomer]2, was found to be 1.00 . 10(-2). Rate constants for the forward and reverse steps in dimerization were determined at pH values of 6.63, 7.01 and 7.44, using the temperature-jump technique. The reaction pathway for dimerization was found to be similar to those of deuteroferrihaem and mesoferrihaem, but different from that of coproferrihaem. A general appraisal of the factors influencing dimerization is attempted in the light of accumulated data on various ferrihaems. With the exception of protoferrihaem, it is suggested that dimerzation increases with the hydrophobicity of the 2,4 substituents. The additional stability of the protoferrihaem dimer is explained in terms of increased interaction due to conjugation of the vinyl groups with the porphyrin macrocycle.

Fluorescence bronchoscopy for detection of lung cancer.

A system using the fluorescence bronchoscope has been designed for localization of small, early bronchogenic carcinoma by the fluorescence of previously injected hematoporphyrin derivative. The system included a 200W mercury vapor lamp and primary filter, flexible fiberoptic bronchoscope with special violet-transmitting light conductor, secondary filter, and image intensifier tube. Tests indicated the system could detect a tumor only 100 micron thick at the expected concentration of hematoporphyrin derivative: 1 microgram/gm at 48 to 96 hours following intravenous injection at a dosage of 2.5 mg/kg. Examination of resected specimens (six of lung, one of esophagus) showed positive fluorescence in all cases, with fluorescence visible beyond the region visible under conventional white light examination. Fluorescence bronchoscopy has been performed on four patients thus far. Positive fluorescence was observed in all three cases where the tumor had been known to occur. Positive fluorescence was also observed in the patient with sputum positive for lung cancer, but negative x-ray film findings. However, additional examinations are required to demonstrate the smallest lesion that can be detected in vivo.

The effect of haematoporphyrin derivative on the uptake of 67Ga, 59Fe and 65Zn in tumours.

The effect of prior administration of haematoporphyrin derivative on the uptake in tumours of 67Ga, 59Fe and 65Zn has been studied in tumour-bearing rats and mice. An approximately two-fold increase in the uptake of 67Ga was observed in the August 15 rat tumour when the nuclide was administered 17 to 24 hr after haematoporphyrin. No increase in the uptake of 67Ga occurred in three mouse tumours. Haematoporphyrin administration did not affect the uptake of 65Zn and 59Fe in any of the tumour systems. It is concluded that the presence of haematoporphyrin does not markedly increase the ability of tumours to accummulate metallic radionuclides.

Catalase model systems. Decomposition of hydrogen peroxide catalysed by mesoferrihaem, deuteroferrihaem, coproferrihaem and haematoferrihaem.

The catalytic decomposition of H2O2 by deuteroferrihaem, mesoferrihaem, coproferrihaem and haematoferrihaem was studied as a model for the mechanism of action of catalase. For haematoferrihaem, anomalous but reproducible results were obtained, which could not be adequately explained. For each of the other ferrihaems studied, both monomeric and dimeric species catalysed decomposition, although the activity of monomer (aM) was much greater than that of dimer (aD). The pH variation of aD in the range 6.5--11 was consistent with an inverse dependence on [H+]1/2. The molecular mechanism whereby such a dependence could be achieved is not apparent. A study of the pH-dependence of aM in the range 6.5--11 revealed a linear inverse relationship with [H+]. This is interpreted in terms of attack by HO2- on ferrihaem monomer. The specific pH-independent rate constants for this reaction were in the order coproferrihaem greater than protoferrihaem greater than or equal to mesoferrihaem congruent to deuteroferrihaem. The order of magnitude of these rate constants is the same as that for catalysis by Fe(H2O)63+ and the second-order rate constant for decomposition of H2O2 by catalase. The implications on the mechanism of action of catalase are discussed.

Hematoporphyrin derivative: a possible aid in the diagnosis and therapy of carcinoma of the bladder.

The distribution of hematoporphyrin derivative has been studied in patients undergoing transurethral resections and total cystectomy for carcinoma of the bladder. Although hematoporphyrin derivative fluorescence was not confined to malignant tissues with the dose used there was preferential localization in malignant and pre-malignant epithelium. Also high intensity illumination of an area of hematoporphyrin derivative sensitized carcinoma caused tumor destruction. Therefore, it is suggested that hematoporphyrin derivative could be used as an aid to the diagnosis and treatment of carcinoma of the bladder.