Photoreduction of methemoglobin by irradiation in the near-ultraviolet region.

Ferric metHb can be photoreduced to the ferrous state by direct photoexcitation in the near-ultraviolet region. In this research, we studied the mechanism and facilitating conditions for the photoreduction and the resulting restoration of O(2) binding. MetHb in phosphate-buffered saline or pure water in a CO atmosphere was photoreduced to form HbCO by illuminating the N band (365 nm), one of the porphyrin pi --> pi transitions, whereas the photoreduction did not occur in Ar, N(2), or O(2). The transient absorption spectrum exhibited the generation of deoxyHb within 30 ns in both the CO and Ar atmospheres; however, only in CO did the subsequent CO binding inhibit the back reaction. The photoreduction rate was dependent on the pH and ligand anions, showing that aquametHb in the high-spin state was predominant for the photoreduction. Axial ligand-to-metal charge-transfer (LMCT) bands overlap with the Soret and Q bands in metHb; however, the excitation of these bands showed little photoreduction, indicating that the contribution of these LMCT bands is minimal. Excitation of the N band significantly contributes to the photoreduction, and this is facilitated by the external addition of mannitol, hyaluronic acid, Trp, Tyr, etc. Especially, Trp allowed the photoreduction even in an Ar atmosphere, and the reduced Hb can be converted to HbO(2) by O(2) bubbling. One mechanism of the metHb photoreduction that is proposed on the basis of these results consists of a charge transfer from the porphyrin ring to the central ferric iron to form the porphyrin pi cation radical and ferrous iron by the N band excitation, and the contribution of the amino acid residues in the globin chain as an electron donor or an electron pathway.

[A combination of low-dose carboplatin (CBDCA) and radiation therapy in head and neck cancer patients--response and hematologenic toxicity].

A combination of carboplatin (CBDCA) and radiation therapy was performed in patients with head and neck cancer. The intravenous administration of CBDCA at a weekly dose of 100 mg/body was combined with external irradiation at a dose of 1.8 Gy/day x 5/week during the same therapy period. We evaluated the effects of this method not only on survival and neoadjuvant chemotherapy in patients with advanced cancer but also on local control and prevention of distant metastases in patients with early cancer. The subjects consisted of 31 patients with head and neck cancer who visited the Department of Otolaryngology, Showa University Hospital, Kanto Rosai Hospital and Yokohama Rosai Hospital between March 1993 and March 1995. Squamous cell carcinoma was found in all but one patient who had adenocarcinoma in the parotid gland. The patients were 27 males and 4 females ranging between 40 and 81 years of age (mean, 59 years). Twenty-six patients had previously untreated tumor, while 5 patients had recurrent tumor. The clinical stage was Stage I in 6, Stage II in 10, Stage III in 5 and Stage IV in 10 patients. The original site of cancer was the larynx in 9, hypopharynx in 6, nasopharynx in 6 and elsewhere in 10 patients. The combined therapy was repeated for 2-9 courses (mean, about 5 courses). The total dose of CBDCA was 500 mg on average with a maximum of 900 mg. The total effective rate of the combined therapy was 93.3% with 12 cases of complete response (CR) and 16 cases of partial response (PR). The effective rate in patients with previously untreated tumor was 92% because one patient showed a minor response (MR) and one patient showed no change (NC). The effective rate in patients with recurrent tumor was 100%. Concerning the clinical stage, all patients with Stage I-III disease showed CR or PR, while MR was found in 1, NC in 1 and progressive disease (PD) in 1 of 10 patients with Stage IV disease, resulting in an effective rate of 71.4%. There were no CRs in Stage IV patients. Therapy was terminated due to side effects in 2 patients. Excellent safety was confirmed by laboratory data.