Influence of melanin on pO2 measurement in vitro and in vivo.
In a previous study an apparent discrepancy was found between the radiobiological hypoxic fraction of tumours and the tumour oxygenation: the lowest percentage of low pO2 values was observed in the most hypoxic tumour, a heavily pigmented melanoma Na11+. This report describes a similar study with two other less pigmented melanomas. The influence of melanin on pO2 readings was also studied using synthetic melanin and L-tyrosine. Tumour oxygenation was measured using the KIMOC 6650 histograph, apparent pO2 was also measured in the calibration chamber in a buffer containing melanin or L-Tyr at three pHs (6.5, 7.0, 7.5) and bubbled with three different oxygen concentrations (0.2, 2.0, 20.9%). The proportion of hypoxic cells, measured by an in vivo/in vitro colony assay, was 58% for Na11+, 30% for Be11 and 51% for Ma11 tumours. The melanin content (microgram/10(6) cells) was 6.5 (Na11+), 2.0 (Be11), and 4.3 (Ma11). The percentages of radiobiologically hypoxic cells and low pO2 reading values (<2 mmHg) were inversely correlated, contrary to what was expected. In buffer, the pO2 values increased significantly with the melanin concentration: the lower the oxygen concentration, the greater was the increase in pO2. The pO2 readings values increased to a lesser extent with L-Tyr concentration. These results indicate that clinical determination of pO2 in melanoma tumours requires careful attention.
Thomas
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CD
Laboratoire de Radiobiologie Cellulaire, Institut Gustave Roussy, Villejuif, France.
Guichard
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D000818:Animals; D006801:Humans; D008543:Melanins / Q000737:chemistry*; D008545:Melanoma / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D010100:Oxygen / Q000032:analysis* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000737:chemistry
D008543:Melanins; D014443:Tyrosine; D010100:Oxygen