Biochemical signs of impaired cobalamin status during and after radiotherapy for rectal cancer

Interactions between Radiation and One-Carbon Metabolism

Metabolic reprogramming is a hallmark of cancer. Cancer cells rewire one-carbon metabolism, a central metabolic pathway, to turn nutritional inputs into essential biomolecules required for cancer cell growth and maintenance. Radiation therapy, a common cancer therapy, also interacts and alters one-carbon metabolism. This review discusses the interactions between radiation therapy, one-carbon metabolism and its component metabolic pathways.

Changes in one-carbon metabolism and DNA methylation in the hearts of mice exposed to space environment-relevant doses of oxygen ions (16O)

Cardiovascular disease constitutes an important threat to humans after space missions beyond the Earth's magnetosphere. Epigenetic alterations have an important role in the etiology and pathogenesis of cardiovascular disease. Previous research in animal models has shown that protons and ⁵⁶Fe ions cause long-term changes in DNA methylation and expression of repetitive elements in the heart. However, astronauts will be exposed to a variety of ions, including the smaller fragmented products of heavy ions after they interact with the walls of the space craft. Here, we investigated the effects of ¹⁶O on the cardiac methylome and one-carbon metabolism in male C57BL/6 J mice. Left ventricles were examined 14 and 90 days after exposure to space-relevant doses of 0.1, 0.25, or 1 Gy of ¹⁶O (600 MeV/n). At 14 days, the two higher radiation doses elicited global DNA hypomethylation in the 5'-UTR of Long Interspersed Nuclear Elements 1 (LINE-1) compared to unirradiated, sham-treated mice, whereas specific LINE-1 elements exhibited hypermethylation at day 90. The pericentromeric major satellites were affected both at the DNA methylation and expression levels at the lowest radiation dose. DNA methylation was elevated, particularly after 90 days, while expression showed first a decrease followed by an increase in transcript abundance. Metabolomics analysis revealed that metabolites involved in homocysteine remethylation, central to DNA methylation, were unaffected by radiation, but the transsulfuration pathway was impacted after 90 days, with a large increase in cystathione levels at the lowest dose. In summary, we observed dynamic changes in the cardiac epigenome and metabolome three months after exposure to a single low dose of oxygen ions.

One-carbon metabolism and ionizing radiation: a multifaceted interaction

Ionizing radiation (IR) is a ubiquitous component of our environment and an important tool in research and medical treatment. At the same time, IR is a potent genotoxic and epigenotoxic stressor, exposure to which may lead to negative health outcomes. While the genotoxocity is well described and characterized, the epigenetic effects of exposure to IR and their mechanisms remain under-investigated. In this conceptual review, we propose the IR-induced changes to one-carbon metabolism as prerequisites to alterations in the cellular epigenome. We also provide evidence from both experimental and clinical studies describing the interactions between IR and one-carbon metabolism. We further discuss the potential for the manipulation of the one-carbon metabolism in clinical applications for the purpose of normal tissue protection and for increasing the radiosensitivity of cancerous cells.

Intestinal malabsorption in long-term survivors of cervical cancer treated with radiotherapy

PURPOSE

The aim of this cross-sectional study is to investigate the associations between pelvic radiotherapy (RT) and markers of intestinal absorption in cervical cancer survivors (CCSs). We compared patient data with normative data from a reference population and explored the associations between cobalamin status and clinically significant diarrhea and depression.

METHODS AND MATERIALS

Fifty-five CCSs treated with RT in 1994-1999 were included in 2005 in a follow-up questionnaire study exploring physical and psychological symptoms. Blood tests, including serum (S)-vitamin B(12,) S-methylmalonic acid, S-folate, erythrocyte-folate, and plasma homocysteine, were analyzed. Differences in median values between CCSs and reference populations were evaluated by using Wilcoxon tests. Associations between variables were examined by means of multiple regression analyses.

RESULTS

Median S-vitamin B(12) level was significantly lower and median S-methylmalonic acid level was significantly higher in CCSs compared with the reference population (p < 0.001). Correction for renal function verified a likely cobalamin deficiency in 20% of CCSs (11 of 55). Diarrhea or depression was not significantly related to any of the mentioned markers of cobalamin or folate status. Fifteen percent of CCSs (8 of 55) had subnormal S-calcium values.

CONCLUSIONS

Significant cobalamin deficiency was observed in 11 (20%) and low calcium level was observed in 8 CCSs (15%) 6-12 years after pelvic RT. Neither diarrhea nor depression was associated with this deficiency. Routine monitoring of S-vitamin B(12) level is recommended, and regular intake of cobalamin should be considered in CCSs treated with RT.

Time patterns of changes in biomarkers, symptoms and histopathology during pelvic radiotherapy

Acute radiation proctitis was evaluated before, during and after radiotherapy (RT) for prostate cancer. The main aims of the study were to examine changes related to the increasing radiation dose, and identify surrogate markers of gastrointestinal (GI) reaction to radiation. Twenty consecutive prostate cancer patients scheduled for 7 weeks of conformal RT were prospectively included in a longitudinal study assessing symptoms, inflammation in rectal mucosa biopsies, and blood and stool samples at four time points (before RT and 2, 6 and 11 weeks after start of RT). Blood samples were examined for acute phase response-related markers, fatty acids (FAs), vitamin E and leukotriene B(4) (LTB(4)). Lactoferrin, calprotectin and S100A12 were measured in stool samples and FAs in biopsies from rectal mucosa. The increase in histopathological inflammation reached a maximum 2 weeks after start of RT. Symptoms of GI toxicity increased with higher radiation dose and had not returned to pre-treatment level 4 weeks after RT. Lactoferrin concentrations in stool increased significantly at week 6. Significant decreases of vitamin E, leukocyte count, hemoglobin and some groups of FAs were discovered, while a few FAs increased significantly during the study period. Time courses vary between the selected indicators of acute radiation proctitis. The biopsy grading of inflammatory changes were most intense 2 weeks into the treatment period while symptoms continued to increase until week 6. Lactoferrin in stool samples could be a non-invasive marker of GI inflammation during RT. A transient decrease in vitamin E and some FAs during RT warrants further studies.