It has been well established that hypoxia significantly increases both cellular and tumor resistance to ionizing radiation. Hypoxia associated radiation resistance has been known for some time but there has been limited success in sensitizing cells to radiation under hypoxic conditions. These studies show that, when irradiated with low linear energy transfer (LET) gamma-rays, poly (ADP-ribose), polymerase (PARP), Fanconi Anemia (FANC), and mutant Chinese Hamster Ovary (CHO) cells respond similarly to the non-homologous end joining (NHEJ) and the homologous recombination (HR) repair mutant CHO cells. Comparable results were observed in cells exposed to 13 keV/μm carbon ions. However, when irradiated with higher LET spread out Bragg peak (SOBP) carbon ions, we observed a decrease in the oxygen enhancement ratio (OER) in all the DNA of repair mutant cell lines. Interestingly, PARP mutant cells were observed as having the largest decrease in OER. Finally, these studies show a significant increase in the relative biological effectiveness (RBE) of high LET SOBP carbon and iron ions in HR and PARP mutants. There was also an increase in the RBE of NHEJ mutants when irradiated to SOBP carbon and iron ions. However, this increase was lower than in other mutant cell lines. These findings indicate that high LET radiation produces unique types of DNA damage under hypoxic conditions and PARP and HR repair pathways play a role in repairing this damage.

Sites of acute inflammation become austere environments for the procurement of energy. The combination of oxygen depletion (hypoxia) and decreased glucose availability requires surprising metabolic adaptability. In this issue of the JCI, Watts et al. examined the metabolic adaptability of murine neutrophils to the setting of acute pulmonary inflammation elicited by exposure to nebulized endotoxin. While neutrophils are generally considered a primarily glycolytic cell type, Watts et al. used a combination of labeled amino acids and high-resolution proteomics to reveal that the harsh environment of the inflammatory lesion drives neutrophils toward de novo protein synthesis and extracellular protein scavenging as a primary fuel. This study provides compelling evidence that tissue neutrophils scavenge extracellular proteins to fuel carbon metabolism, which aids in de novo protein synthesis and the promotion of an inflammatory phenotype. These observations reveal the surprisingly creative extent to which cells and tissues might adapt to energy-deficient inflammatory environments.