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

Abstract

IntroductionHematoporphyrin 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 methodsThe 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: ex = 280 nm and ex = 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.ResultsFormation of a complex with human serum albumin extends the stability of the hematoporphyrin spectrum. This extension is greater at excitation ex = 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.ConclusionsSpectrofluorimetric 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.

Zinc-Substituted Pheophorbide A Is a Safe and Efficient Antivascular Photodynamic Agent

“…In comparison, the photobleaching of TOOKAD ® was also observed in methanol and acetone [47]. Complexation with albumin is likely to increase the photostability of both PSs, as was similarly observed for hematoporphyrin [48]. Moreover, since Zn-Pheide has a stronger bind to albumin than Pd-BPheide, the complexation of the former may increase its stability to a greater extent.…”