Roles of Parathyroid Hormone and Fibroblast Growth Factor 23 in Advanced Chronic Kidney Disease.

Parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) each play a central role in the pathogenesis of chronic kidney disease (CKD)-mineral and bone disorder. Levels of both hormones increase progressively in advanced CKD and can lead to damage in multiple organs. Secondary hyperparathyroidism (SHPT), characterized by parathyroid hyperplasia with increased PTH secretion, is associated with fractures and mortality. Emerging evidence suggests that these associations may be partially explained by PTH-induced browning of adipose tissue and increased energy expenditure. Observational studies suggest a survival benefit of PTHlowering therapy, and a recent study comparing parathyroidectomy and calcimimetics further suggests the importance of intensive PTH control. The mechanisms underlying the regulation of FGF23 secretion by osteocytes in response to phosphate load have been unclear, but recent experimental studies have identified glycerol-3-phosphate, a byproduct of glycolysis released by the kidney, as a key regulator of FGF23 production. Elevated FGF23 levels have been shown to be associated with mortality, and experimental data suggest off-target adverse effects of FGF23. However, the causal role of FGF23 in adverse outcomes in CKD patients remains to be established. Further studies are needed to determine whether intensive SHPT control improves clinical outcomes and whether treatment targeting FGF23 can improve patient outcomes.

Association of serum sodium levels with fractures and mortality in patients undergoing maintenance hemodialysis.

BACKGROUND: Hyponatremia is implicated in pathological bone resorption and has been identified as a risk factor for bone fracture in the general population. However, there are limited data on the association between serum sodium levels and fracture risk in patients undergoing hemodialysis (HD). METHODS: We analyzed a historical cohort of 2220 maintenance HD patients to examine the association between serum sodium levels and the risk of fracture and mortality. We also examined the association between serum sodium levels and osteoporosis, based on metacarpal bone mineral density, in a subcohort of 455 patients with available data. In addition, we examined the association between serum sodium levels and bone turnover markers in a separate cross-sectional cohort of 654 maintenance HD patients. RESULTS: During a median follow-up of 5.4 years, 712 patients died, 113 experienced clinical fractures, and 64 experienced asymptomatic vertebral fractures. Lower serum sodium levels were associated with an increased risk of mortality (HR 1.06 per 1 mEq/L decrease; 95% CI 1.03-1.09) but not with the risk of clinical fracture (HR 1.04 per 1 mEq/L decrease; 95% CI 0.97-1.11). A similar lack of association was observed for asymptomatic vertebral fracture and any fracture. Serum sodium levels were also not associated with osteoporosis in a subcohort with available data (n = 455) or with bone alkaline phosphatase or tartrate-resistant acid phosphatase-5b in a separate cross-sectional cohort. CONCLUSION: Serum sodium levels were associated with mortality but not with fracture risk, osteoporosis, or bone turnover markers in maintenance HD patients.

Standardization of PTH measurement by LC-MS/MS: a promising solution for interassay variability.

Parathyroid hormone measurement is critical in managing chronic kidney disease-mineral bone disorders. However, there are several commercially available immunoassays with interassay variability. To address this, Cavalier et al. developed standardization of parathyroid hormone measurement by establishing regression equations of each assay against the liquid chromatography coupled to tandem mass spectrometry method. The recalibration successfully reduced interassay variability, allowing for more consistent interpretation. The proposed approach may pave the way for accurate interpretation of parathyroid hormone in clinical practice.

Impact of beta-tricalcium phosphate on preventing tooth extraction-triggered bisphosphonate-related osteonecrosis of the jaw in rats.

Antiresorptive or antiangiogenic drugs can cause medication-related osteonecrosis of the jaw that is refractory. Bisphosphonate-related osteonecrosis of the jaw (BRONJ) may be caused by procedures such as tooth extraction damage the alveolar bone, release bisphosphonates (BPs) and impede healing. This study investigated strategies for BRONJ prevention and molecular mechanisms of its onset. We assessed the effectiveness of filling extraction sockets with beta-tricalcium phosphate (ß-TCP). Rats were administered zoledronic acid (ZA) 1.2 mg/kg once per week for 2 weeks, and a molar was extracted. They were randomly assigned to the ß-TCP group (bone defects filled with 0.01 g of ß-TCP) or control group. Tissue content measurements indicated 2.2 ng of ZA per socket in the ß-TCP group and 4.9 ng in the control group, confirming BP distribution and BP adsorption by ß-TCP in vivo. At 4 weeks after extraction, the ß-TCP group had normal mucosal coverage without inflammation. Moreover, at 8 weeks after extraction, enhanced bone healing, socket coverage, and new bone formation were observed in the ß-TCP group. Connective tissue in the extraction sockets suggested that local increases in BP concentrations may suppress the local autophagy mechanisms involved in BRONJ. Filling extraction sockets with ß-TCP may prevent BRONJ.

Clinical Phenotypes and the Clinical Course of Bullous Pemphigoid Receiving Dipeptidyl Pepitidase-4 Inhibitor Treatment: An Analysis of Cases in a Single Japanese Center.

Objective Several studies have shown an increased risk of bullous pemphigoid (BP) when receiving dipeptidyl pepitidase-4 inhibitor (DPP-4i) treatment. The present study explored the associations of DPP-4i treatment with the clinical phenotypes and clinical course of BP. Methods We analyzed data of 146 patients with BP at Tokai University School of Medicine from December 1, 2009, to December 31, 2021. We obtained data by a retrospective medical record review and compared the bullous pemphigoid disease area index (BPDAI) between diabetes patients receiving DPP-4i treatment and those not receiving DPP-4i treatment. We employed multivariable linear regression models to explore the association between the DPP-4i treatment and the BPDAI scores. Results Among 53 BP patients with diabetes, 33 had developed BP during treatment with DPP-4i agents, among which vildagliptin was the most frequently used. The urticaria/erythema scores of the BPDAI were significantly lower in patients who developed BP while receiving DPP-4i treatment than among others. Of note, 69.2% of the patients who stopped DPP-4i treatment experienced complete remission, and the clinical course was more favorable in patients with lower scores for urticaria/erythema than among others. Conclusion These findings suggest that, in patients who developed BP while receiving DPP-4i treatment, a noninflammatory phenotype may indicate a high likelihood that DPP-4i treatment contributes to the development of BP. The discontinuation of DPP-4i should be carefully considered in close consultation with dermatologists.

Serum Sclerostin Levels and Mortality in Hemodialysis Patients: An 8-Year Prospective Study.

INTRODUCTION: Sclerostin is an osteocyte-derived inhibitor of bone formation and is increased in kidney failure. Sclerostin might be involved in the pathogenesis of vascular calcification, but few studies have examined the association between sclerostin and mortality in hemodialysis patients. METHODS: We analyzed a prospective cohort of 654 patients undergoing maintenance hemodialysis. The primary exposure variable was the baseline serum sclerostin level measured at study enrollment. The primary outcome was 8-year all-cause mortality. Mortality risk was assessed using Cox regression models adjusted for potential confounders. RESULTS: During a median follow-up of 7.6 years (interquartile range, 4.1-8.0 years), 229 of the 654 participants died. In a univariate analysis, serum sclerostin levels were not associated with mortality (HR per doubling, 0.94; 95% CI, 0.76-1.17). This result was unchanged after adjustment for age, sex, dialysis vintage, diabetes, prior cardiovascular disease, and body mass index (HR per doubling, 0.92; 95% CI, 0.72-1.17). Similar results were obtained for cardiovascular mortality. CONCLUSION: Serum sclerostin levels were not associated with mortality in maintenance hemodialysis patients. Further research is required to determine the role of sclerostin in vascular calcification and cardiovascular disease in kidney failure.

Examination of Suprahyoid Muscle Resection and Other Factors Affecting Swallowing Function in Patients With Advanced Oral Cancer After Surgical Resection and Reconstruction.

Dysphagia is one of the most common adverse effects associated with oral cancer therapy and could greatly impair postoperative quality of life. The objective of this study was to analyze postoperative swallowing outcomes and factors influencing postoperative swallowing function in patients with advanced oral cancer who underwent primary reconstruction after surgical resection to identify patients at risk of experiencing severe dysphagia after immediate reconstruction of surgical defects, and to determine an ideal approach to provide appropriate perioperative interventions. The swallowing status was evaluated at 4 week postoperatively using the Functional Oral Intake Scale. We also analyzed the effects of patient, tumor, surgical, and other factors on postoperative swallowing function. The study included 67 patients. At 4 weeks postoperatively, 11 patients showed reduced swallowing function, whereas 56 patients showed good swallowing function. The number of resected suprahyoid muscles (odds ratio, 1.55; 95% confidence interval, 1.03-2.32; P=0.035) was an independent factor influencing postoperative swallowing function. Thus, among patients who underwent radical resection of oral cancer with primary reconstruction, those with extensive resection of the suprahyoid muscles were at higher risk of developing postoperative dysphagia. These findings are expected to facilitate increased vigilance for dysphagia, better counseling, and appropriate rehabilitation interventions.

Case report: Unilateral masticatory atrophy caused by pure trigeminal motor neuropathy.

Pure trigeminal motor neuropathy (PTMN) is characterized by trigeminal motor weakness without signs of trigeminal sensory dysfunction or involvement of other cranial nerves. We describe a rare case of an 83-year-old man with weakness and atrophy of the right masticatory muscle without any sensory disturbance. Brain computed tomography and magnetic resonance imaging revealed atrophy and fatty infiltration of the right masticatory muscle. Electromyography revealed abnormal spontaneous activity, chronic neurogenic motor unit potentials, and reduced interference patterns in the right temporalis and the masseter muscles. The patient was diagnosed with PTMN based on the clinical symptoms and examinations. Our case presents a rare clinical manifestation with unclear etiology.

Interrelationships Between Sclerostin, Secondary Hyperparathyroidism, and Bone Metabolism in Patients on Hemodialysis.

CONTEXT: Sclerostin is an osteocyte-derived inhibitor of bone formation and is increased in kidney failure, but its role in the pathogenesis of renal bone disease remains unknown. OBJECTIVE: We aimed to explore the association of serum sclerostin with bone metabolism in patients undergoing hemodialysis, with a particular focus on parathyroid hormone (PTH)-dependent and PTH-independent pathways. METHODS: This cross-sectional and prospective cohort study included 654 patients undergoing hemodialysis at 10 facilities in Japan. We employed multivariable linear regression to explore whether sclerostin levels were associated with metacarpal bone mineral density (BMD), intact PTH, bone alkaline phosphatase (BAP), and tartrate-resistant acid phosphatase-5b (TRACP-5b). We employed mediation analyses to explore whether and to what extent the association of PTH with bone turnover markers is mediated by sclerostin. We also compared sclerostin levels between patients with and without previous or incident fractures. RESULTS: The median sclerostin level in hemodialysis patients was 3- to 4-fold higher than that in healthy individuals. Higher sclerostin levels were associated with higher metacarpal BMD and lower levels of intact PTH, BAP, and TRACP-5b. However, the relationships of sclerostin with bone turnover markers were substantially attenuated after adjustment for PTH. Mediation analysis suggested that the effects of PTH on bone turnover markers were mainly direct rather than mediated by sclerostin. Sclerostin levels were not associated with previous or incident fractures. CONCLUSION: These findings suggest that in patients undergoing dialysis, sclerostin has only a limited role in bone metabolism and may not mediate the effect of PTH on bone turnover.

Changes in Fibroblast Growth Factor 23 and Soluble Klotho Levels After Hemodialysis Initiation.

RATIONALE & OBJECTIVE: Patients with chronic kidney failure have markedly elevated fibroblast growth factor 23 (FGF-23) levels and decreased soluble Klotho levels. However, no studies have examined the effects of hemodialysis initiation on the levels of these hormones and other parameters of mineral metabolism. STUDY DESIGN: Prospective single-arm study. SETTING & PARTICIPANTS: 20 individuals with incident kidney failure initiating hemodialysis. EXPOSURE: Initiation of hemodialysis. Dose adjustments of phosphate binders and vitamin D receptor activators and use of calcimimetics, erythropoiesis-stimulating agents, and intravenous iron were prohibited. OUTCOMES: Changes in serum levels of FGF-23, soluble Klotho, and other biochemical parameters of mineral metabolism, measured before and after each hemodialysis session, for a total of 4 sessions over 5 days. ANALYTICAL APPROACH: Repeated-measures analysis of variance. RESULTS: At baseline, participants had 18-fold higher median FGF-23 levels and 1.6-fold lower mean soluble Klotho levels compared with age- and sex-matched healthy individuals. Initiation of hemodialysis led to progressive reductions in serum phosphorus, intact parathyroid hormone, and FGF-23 levels, with dialysis-related fluctuations. No reductions were observed in levels of α1-microglobulin, which has molecular weight comparable to FGF-23. The magnitude of the FGF-23 level reductions was strongly associated with concomitant changes in serum phosphorus levels but not with the changes in intact parathyroid hormone levels. Soluble Klotho levels did not change after the initiation of hemodialysis. LIMITATIONS: Single-arm design, small sample size, short follow-up period. CONCLUSIONS: Initiation of hemodialysis in patients with chronic kidney failure led to progressive reductions in FGF-23 levels in association with reductions in serum phosphorus levels. These results suggest that phosphorus is a strong inducer of FGF-23 production and that regulation of FGF-23 production is a rapid process.

Metacarpal bone mineral density by radiographic absorptiometry predicts fracture risk in patients undergoing maintenance hemodialysis.

The 2017 Kidney Disease: Improving Global Outcomes (KDIGO) guideline update suggests bone mineral density testing to assess fracture risk in patients with chronic kidney disease, but dual-energy X-ray absorptiometry is not available in most dialysis facilities. Radiographic absorptiometry is an inexpensive and quick method for evaluating bone mineral density. Therefore, we analyzed a historical cohort of 456 maintenance hemodialysis patients to determine whether metacarpal bone mineral density measured by digital image processing, a computer-assisted radiographic absorptiometry technique, predicts fracture risk. At baseline, the median metacarpal bone mineral density T-score was -2.05 (interquartile range, -3.35 to -0.99). During a mean follow-up of 5.3 years, there were 16 clinical fractures and 11 asymptomatic vertebral fractures as estimated by height loss. Metacarpal bone mineral density T-score was significantly lower in patients who sustained a clinical fracture than in those remaining event-free. Decreasing metacarpal bone mineral density T-score was significantly associated with increased risk of clinical fracture (hazard ratio, 1.41 per 1 standard deviation decrease in bone mineral density T-score [95% confidence interval, 1.09 to 1.83]; the hazard ratio for lowest versus highest tertile was 4.86 [1.03 to 22.92]. Similar associations were observed between metacarpal bone mineral density T-score and vertebral fracture or any fracture. The results were robust to different analysis strategies and were consistent across different subgroups. Thus, radiographic absorptiometry could be a useful tool for primary screening of hemodialysis patients at high risk for fracture. Additional studies are required to determine the predictive ability of radiographic absorptiometry techniques compared to dual-energy X-ray absorptiometry or other established methods.

Inhibition of the ATR kinase enhances 5-FU sensitivity independently of nonhomologous end-joining and homologous recombination repair pathways.

The anticancer agent 5-fluorouracil (5-FU) is cytotoxic and often used to treat various cancers. 5-FU is thought to inhibit the enzyme thymidylate synthase, which plays a role in nucleotide synthesis and has been found to induce single- and double-strand DNA breaks. ATR Ser/Thr kinase (ATR) is a principal kinase in the DNA damage response and is activated in response to UV- and chemotherapeutic drug-induced DNA replication stress, but its role in cellular responses to 5-FU is unclear. In this study, we examined the effect of ATR inhibition on 5-FU sensitivity of mammalian cells. Using immunoblotting, we found that 5-FU treatment dose-dependently induced the phosphorylation of ATR at the autophosphorylation site Thr-1989 and thereby activated its kinase. Administration of 5-FU with a specific ATR inhibitor remarkably decreased cell survival, compared with 5-FU treatment combined with other major DNA repair kinase inhibitors. Of note, the ATR inhibition enhanced induction of DNA double-strand breaks and apoptosis in 5-FU-treated cells. Using gene expression analysis, we found that 5-FU induced the activation of the intra-S cell-cycle checkpoint. Cells lacking BRCA2 were sensitive to 5-FU in the presence of ATR inhibitor. Moreover, ATR inhibition enhanced the efficacy of the 5-FU treatment, independently of the nonhomologous end-joining and homologous recombination repair pathways. These findings suggest that ATR could be a potential therapeutic target in 5-FU-based chemotherapy.

Magnesium as a Janus-faced inhibitor of calcification.

Vascular calcification is a life-threatening complication in patients with chronic kidney disease. Magnesium is a potent inhibitor of calcification and attracting attention as a new therapeutic candidate. ter Braake and colleagues demonstrate that magnesium supplementation strikingly prevents vascular calcification in Klotho knockout mice. However, these mice also show osteomalacia, indicating that magnesium has a Janus face. Maximizing the beneficial effects of magnesium without causing bone mineralization defects is an important next challenge.

Correction to: Preventive effect of early introduction of everolimus and reduced­exposure tacrolimus on renal interstitial fibrosis in de novo living­donor renal transplant recipients.

In the Original publication of the article, the co-author name has been misspelled as "Yousuke Nakagawa".

[Secondary osteoporosis. Disordered bone metabolism in chronic kidney disease.]

In patients with chronic kidney disease(CKD), mineral metabolism abnormalities such as hyperphosphatemia, decreased 1,25-dihydroxyvitamin D, and elevated parathyroid hormone develop as kidney function declines, which lead to vascular calcification and a variety of skeletal abnormalities, collectively termed renal osteodystrophy. Because CKD patients have increased risk of bone fractures, it is important to assess fracture risk by measuring bone mineral density and bone metabolism markers. In addition to management of secondary hyperparathyroidism, medications for osteoporosis could be a reasonable option for preventing fracture.

Bite injuries caused by transcranial electrical stimulation motor-evoked potentials' monitoring: incidence, associated factors, and clinical course.

PURPOSE: The incidence of bite injuries associated with transcranial electrical stimulation motor-evoked potentials monitoring reportedly ranges from 0.13 to 0.19%. However, in clinical practice, bite injuries appear to occur more frequently than previously reported. Our aim was to identify the incidence of and perioperative risk factors associated with bite injuries caused by transcranial electrical stimulation motor-evoked potential monitoring. METHODS: Patients who underwent elective surgery with transcranial electrical stimulation motor-evoked potential monitoring at a single tertiary hospital in Japan between June 2017 and December 2017 were included in this study. All patients were assessed by oral surgeons preoperatively and postoperatively. The associated factors with bite injuries were explored by the univariate analysis. RESULTS: 12 of 186 patients experienced 13 bite injuries, including three lip, six oral mucosa, and four tongue injuries. No patient required suture repair. 11 of 12 patients had uneventful postoperative courses and were cured within 12 postoperative days. One patient with a tongue ulcer and a hematoma had difficulty in oral intake and persistent dysgeusia. Patient severe movement during transcranial electrical stimulation motor-evoked potential monitoring was associated with bite injuries (p = 0.03). CONCLUSIONS: The incidence of bite injuries assessed by oral surgeons was 6.5% in patients with transcranial electrical stimulation motor-evoked potential monitoring, and the patients with severe movement during the monitoring tended to incur bite injuries. In rare cases, transcranial electrical stimulation motor-evoked potential monitoring may cause difficulty in oral intake and dysgeusia.

BRCA2 protects mammalian cells from heat shock.

PURPOSE: Heat shock induces DNA double-strand breaks (DSBs) in mammalian cells. Mammalian cells are capable of repairing DSBs by utilising the homologous recombination (HR) pathway. Breast cancer susceptibility gene 2 (BRCA2) is known to regulate the HR pathway. Here, we investigate the role of BRCA2 in repairing DNA damage induced by heat shock. MATERIALS AND METHODS: Chinese hamster lung fibroblast cell lines and human tongue squamous cell carcinoma SAS cells were used. RAD51 foci formation assay was used as an HR indicator. Heat sensitivity was analysed with colony forming assays. Phosphorylated histone H2AX (γH2AX) intensity, which correlates with the number of DSBs, was analysed with flow cytometry. RESULTS: RAD51 foci appeared with heat shock, and the number of cells with RAD51 foci was maximal at about 4 h after heat shock. Heat-induced RAD51 foci co-localised with γH2AX foci. BRCA2-deficient cells were sensitive to heat when compared to their parental wild-type cells. Heat-induced γH2AX was higher in BRCA2-deficient cells compared to parental cells. In SAS cells, cells transfected with BRCA2-siRNA were more sensitive to heat than cells transfected with negative control siRNA. Apoptotic bodies increased in number more rapidly in BRCA2-siRNA transfected cells than in cells transfected with negative control siRNA when cells were observed at 48 h after a heat treatment. In addition, cells deficient in BRCA2 were incapable of activating heat-induced G2/M arrest. CONCLUSION: BRCA2 has a protecting role against heat-induced cell death. BRCA2 might be a potential molecular target for hyperthermic cancer therapy.

Homologous recombination preferentially repairs heat-induced DNA double-strand breaks in mammalian cells.

PURPOSE: Heat shock induces DNA double-strand breaks (DSBs), but the precise mechanism of repairing heat-induced damage is unclear. Here, we investigated the DNA repair pathways involved in cell death induced by heat shock. MATERIALS AND METHODS: B02, a specific inhibitor of human RAD51 (homologous recombination; HR), and NU7026, a specific inhibitor of DNA-PK (non-homologous end-joining; NHEJ), were used for survival assays of human cancer cell lines with different p53-gene status. Mouse embryonic fibroblasts (MEFs) lacking Lig4 (NHEJ) and/or Rad54 (HR) were used for survival assays and a phosphorylated histone H2AX at Ser139 (γH2AX) assay. MEFs lacking Rad51d (HR) were used for survival assays. SPD8 cells were used to measure HR frequency after heat shock. RESULTS: Human cancer cells were more sensitive to heat shock in the presence of B02 despite their p53-gene status, and the effect of B02 on heat sensitivity was specific to the G2 phase. Rad54-deficient MEFs were sensitive to heat shock and showed prolonged γH2AX signals following heat shock. Rad51d-deficient MEFs were also sensitive to heat shock. Moreover, heat shock-stimulated cells had increased HR. CONCLUSIONS: The HR pathway plays an important role in the survival of mammalian cells against death induced by heat shock via the repair of heat-induced DNA DSBs.

Comparison of the pharmacokinetics between L-BPA and L-FBPA using the same administration dose and protocol: a validation study for the theranostic approach using [18F]-L-FBPA positron emission tomography in boron neutron capture therapy.

BACKGROUND: Boron neutron capture therapy (BNCT) is a cellular-level particle radiation therapy that combines the selective delivery of boron compounds to tumour tissue with neutron irradiation. L-p-Boronophenylalanine (L-BPA) is a boron compound now widely used in clinical situations. Determination of the boron distribution is required for successful BNCT prior to neutron irradiation. Thus, positron emission tomography with [18F]-L-FBPA, an 18F-labelled radiopharmaceutical analogue of L-BPA, was developed. However, several differences between L-BPA and [18F]-L-FBPA have been highlighted, including the different injection doses and administration protocols. The purpose of this study was to clarify the equivalence between L-BPA and [19F]-L-FBPA as alternatives to [18F]-L-FBPA. METHODS: SCC-VII was subcutaneously inoculated into the legs of C3H/He mice. The same dose of L-BPA or [19F]-L-FBPA was subcutaneously injected. The time courses of the boron concentrations in blood, tumour tissue, and normal tissue were compared between the groups. Next, we administered the therapeutic dose of L-BPA or the same dose of [19F]-L-FBPA by continuous infusion and compared the effects of the administration protocol on boron accumulation in tissues. RESULTS: There were no differences between L-BPA and [19F]-L-FBPA in the transition of boron concentrations in blood, tumour tissue, and normal tissue using the same administration protocol. However, the normal tissue to blood ratio of the boron concentrations in the continuous-infusion group was lower than that in the subcutaneous injection group. CONCLUSIONS: No difference was noted in the time course of the boron concentrations in tumour tissue and normal tissues between L-BPA and [19F]-L-FBPA. However, the administration protocol had effects on the normal tissue to blood ratio of the boron concentration. In estimating the BNCT dose in normal tissue by positron emission tomography (PET), we should consider the possible overestimation of the normal tissue to blood ratio of the boron concentrations derived from the values measured by PET on dose calculation.

Detection of γH2AX foci in mouse normal brain and brain tumor after boron neutron capture therapy.

AIM: In this study, we investigated γH2AX foci as markers of DSBs in normal brain and brain tumor tissue in mouse after BNCT. BACKGROUND: Boron neutron capture therapy (BNCT) is a particle radiation therapy in combination of thermal neutron irradiation and boron compound that specifically accumulates in the tumor. (10)B captures neutrons and produces an alpha ((4)He) particle and a recoiled lithium nucleus ((7)Li). These particles have the characteristics of extremely high linear energy transfer (LET) radiation and therefore have marked biological effects. High LET radiation causes severe DNA damage, DNA DSBs. As the high LET radiation induces complex DNA double strand breaks (DSBs), large proportions of DSBs are considered to remain unrepaired in comparison with exposure to sparsely ionizing radiation. MATERIALS AND METHODS: We analyzed the number of γH2AX foci by immunohistochemistry 30 min or 24 h after neutron irradiation. RESULTS: In both normal brain and brain tumor, γH2AX foci induced by (10)B(n,α)(7)Li reaction remained 24 h after neutron beam irradiation. In contrast, γH2AX foci produced by γ-ray irradiation at contaminated dose in BNCT disappeared 24 h after irradiation in these tissues. CONCLUSION: DSBs produced by (10)B(n,α)(7)Li reaction are supposed to be too complex to repair for cells in normal brain and brain tumor tissue within 24 h. These DSBs would be more difficult to repair than those by γ-ray. Excellent anti-tumor effect of BNCT may result from these unrepaired DSBs induced by (10)B(n,α)(7)Li reaction.