The heme biosynthetic pathway in the regenerating rat liver. The relation between enzymes of heme synthesis and growth

Clinical results of the transurethreal resection and evaluation of superficial bladder carcinomas by means of fluorescence diagnosis after intravesical instillation of 5-aminolevulinic acid

BACKGROUND AND OBJECTIVE

The high recurrence rate of superficial bladder carcinomas requires new approaches in diagnosis and therapy. Particularly, an improvement in detection, resulting in better resection of flat lesions, which are poorly or not detectable under white light, is necessary. The effectiveness of fluorescence diagnosis for detection and transurethral resection of bladder carcinomas was investigated in a prospective study.

MATERIALS AND METHODS

From 120 patients, 347 biopsies were taken or tumors resected with the aid of fluorescence from 5-aminolevulinic acid. Urothelial carcinomas and dysplasias were detected in 124 cases.

RESULTS

Of the lesions, 119 were fluorescence positive (N = 74 pTaG1/2; N = 9 pT1G1/2; N = 11 pT1G3; N = 7 carcinoma in situ; N = 6 p > T1; N = 12 dysplasia II), and 5 were falsely negative (N = 3 pTaG1/2; N = 1 pT1G1/2; N = 1 dysplasia II). The sensitivity of the fluorescence diagnosis (96.0%) was significantly higher than the 67.5% sensitivity of white-light cystoscopy (P < 0.0001). Taking the data for primary or recurrent tumor resection and secondary resection separately, the sensitivity was 100% and 80%, respectively, and was significantly higher than that of white-light cystoscopy, which was 80.8% and 20 %, respectively (P < 0.0001 and P < 0.0008). The lower sensitivity of fluorescence diagnosis in secondary transurethral resection is attributed to the higher rate of false-negative findings in areas of former resection.

CONCLUSIONS

The high rate of false-positive findings limits the correct interpretation of fluorescence findings. In spite of this, fluorescence diagnosis is superior to white-light cystoscopy in every case. By means of better detection of urothelial neoplasias and dysplasias, as well as more thorough and extensive resection under fluorescence control, it should be possible to reduce the recurrence rate of superficial bladder carcinomas.

Porphyrins, porphyrias, cancer and photodynamic therapy--a model for carcinogenesis

Porphyrins are the only and most powerful photosensitizers synthesized internally. To understand better the involvement of porphyrins in photosensitization reactions, the heme biosynthetic pathway is first described, as well as the main features of its regulation in both erythroid and hepatic cells. Most disorders of porphyrin metabolism, known as porphyrias, are characterized by porphyrin accumulation. A full discussion of these diseases, their classification and relevant biochemical and clinical signs are presented. Abnormalities in heme biosynthesis in disorders other than porphyrias, such as iron-deficient and sideroblastic anemias, lead poisoning, hereditary tyrosinemia, chronic renal disease and alcoholism, are briefly considered. A complete survey of the experimental research on the biosynthesis of porphyrins in tumors and of the important association between cancer and porphyrias is dealt with. The link to photodynamic therapy (PDT) emerges naturally and this is treated from the point of view of using porphyrins endogenously formed by the tumors for their localization and PDT. Finally, considering the nature of the alterations occurring in heme metabolism in tumors, and porphyrias and their ubiquity, a model is discussed where the abnormality of heme synthesis is involved in the initiating lesion of carcinogenesis. The model strongly predicts that the incidence of cancer will be high in cells with abnormal heme metabolism, suggesting that porphyric patients may be at greater risk of the development of cancer.

Regulation of heme synthesis in the regenerating rat liver

This investigation shows that the regulation of heme synthesis in the regenerating rat liver does not differ from the regulation in the normal liver. The heme saturation of tryptophan pyrrolase was found to be low, indicating a reduced concentration of heme in the regulatory heme pool of the regenerating rat liver. As expected, ALAS in the mitochondrial fraction was found to be elevated. It was also shown that ALAS in the regenerating rat liver can be induced by the porphyrinogenic drugs AIA and DDC and that heme reduces its activity. The decrease observed in the activity of cytosolic ALAS might be due to impaired synthesis of the enzyme but does not affect the regulation of the heme biosynthetic pathway.

Growth rate determines activity of porphobilinogen deaminase both in nonmalignant and malignant cell lines

PBGD activity and growth rate were determined in cultures of rat embryo fibroblasts, nontransformed and MLV/MS transformed fibroblastic cell lines; NIH-3T3 cells, and in a mouse lymphosarcoma cell line [L-929]. The two parameters examined correlate positively (P less than 0.001). The results of this investigation would seem to indicate clearly that porphobilinogen deaminase activity is related to growth. However, these experiments do not rule out the possibility that malignant transformation per se also causes changes in porphobilinogen deaminase activity.