Stability of spectrofluorimetric spectra of hematoporphyrin–serum albumin complexes: in vitro study

Introduction: Hematoporphyrin is a photosensitizer used in photodynamic therapy of various malignant diseases. It is carried to the cancer tissue by serum albumins. Spectrofluorimetric spectra of hematoporphyrin–serum albumin complexes were examined in vitro. Material and methods: The chemicals were: hematoporphyrin, human serum albumin and bovine serum albumin. The spectra were recorded on a Kontron SFM-25 Instrument AG at two excitation wavelengths: λex = 280 nm and λex = 295 nm. The spectra of hematoporphyrin 1.5 × 10 –5 M as well as spectra of complexes of hematoporphyrin–human serum albumin (1.5 × 10–5 M Hp – 1.25 × 10–6 M HSA) and hematoporphyrin–bovine serum albumin (1.5 × 10–5 M Hp – 3.5 × 10–7 M BSA) were recorded repetitively for 8 days and compared to the initial spectrum. Results: Formation of a complex with human serum albumin extends the stability of the hematoporphyrin spectrum. This extension is greater at excitation λex = 295 nm. Different stability of complexes with bovine and human serum albumins most likely does not result from an actual lower stability of bovine serum albumin complexes, but from the fact that dissimilarity in the structure of both albumins enables additional spectroscopic observations within subdomain IB in the bovine serum albumin molecule. Conclusions: Spectrofluorimetric spectra are stable longer when hematoporphyrin forms a complex with human serum albumin. The present data may be important for understanding the mechanism of hematoporphyrin transportation to the target cancer tissue and effectiveness of photodynamic therapy.