Oxygen Levels in Normal and Previously Irradiated Human Skin as Assessed by EF5 Binding

Abstract

The oxygen status of skin is a controversial topic. Skin is radiosensitive, suggesting it is well-oxygenated. However, it can be further sensitized with nitroimidazole drugs, implying that it is partially hypoxic. Skin oxygen levels are difficult to measure with either electrodes or the hypoxia-monitoring agent (3)H-misonidazole. For the latter, binding has previously been reported to be high in murine skin, but this could be attributed to either non-oxygen-dependent variations in nitroreductase activity, drug metabolism, and/or actual oxygen gradients. We obtained tumor and skin from patients given EF5, a 2-nitroimidazole tissue hypoxia monitor. We performed immunohistochemical studies using highly specific monoclonal antibodies for the hypoxia-dependent production of EF5 tissue adducts. Some tissue sections were counterstained using either Ki67 for proliferation or CD31 for vessels. We found that the human dermis is well-oxygenated, the epidermis is modestly hypoxic and portions of some sebaceous glands and hair follicles are moderately to severely hypoxic. Normal and irradiated skin had similar oxygenation patterns. Control studies demonstrated that these observations are not due to tissue variations in nitroreductase activity. The importance of the highly heterogeneous distribution of oxygen in skin requires further study, but recent investigations suggest that skin hypoxia may have important clinical ramifications including mediating cellular transformation.

Patterns and Levels of Hypoxia in Head and Neck Squamous Cell Carcinomas and Their Relationship to Patient Outcome

“…It should be noted however, that although the number of patients presented herein is small (n=22), it is similar to studies using the Eppendorf needle electrode Intriguing observations from this study include the varied patterns of EF5 binding in HNSCC. Type 1 binding pattern is most similar to EF5 binding in sarcomas and brain tumors 24,25 and Type 2 binding is most reminiscent of the EF5 binding patterns described in normal human skin 30 . Using pimonidazole, similar patterns of binding have been reported 45,46 .…”

“…Based on these observations, they conclude that involucrin is a hypoxia-inducible protein, but its expression is altered by cellular differentiation. Our studies performed in human skin, which contain regions of squamous cell differentiation, suggests that "Type 2" EF5 binding is dominantly a reflection of tissue pO 2 rather than expression of other cellular proteins, state of differentiation or an artifact of elevated reductase enzymes 30 . This conclusion is supported by images of the spatial relationship between EF5 binding and CD31 staining (blood vessels) or Ki67 staining (proliferation) (Figure 3).…”

“…The quantitative analysis of tumor sections stained for EF3/EF5 has been previously described 30 24 , 31 . Briefly, tissue sections were counterstained with Hoechst 33342 to identify the location of intact nuclei.…”

Notch1 is an effector of Akt and hypoxia in melanoma development

“…For example, Notch1 is required by tissue hypoxia to maintain cells in an undifferentiated state (26). This is particularly relevant to melanoma, because we and others previously demonstrated that the skin is normally mildly hypoxic and that melanocytes reside in this environment (27,28). Taken together, these findings strongly suggest that the Notch1 signaling pathway can be under control of both oncogene activation and environmental conditions, although how these factors regulate Notch1 is still not fully understood.…”

Altered cellular redox homeostasis and redox responses under standard oxygen cell culture conditions versus physioxia

“…air). Two percent O 2 was chosen to represent a physioxic environment as this concentration falls within the range of O 2 concentrations measured in healthy epidermal skin [17] and superficial epidermoid carcinomas in vivo [18]. Thus, our investigations were carried out under three different O 2 conditions (Fig.…”