Virus-Inspired Glucose and Polydopamine (GPDA)-Coating as an Effective Strategy for the Construction of Brain Delivery Platforms.

The ability of drugs to cross the blood-brain barrier (BBB) is crucial for treating central nervous system (CNS) disorders. Inspired by natural viruses, here we report a glucose and polydopamine (GPDA) coating method for the construction of delivery platforms for efficient BBB crossing. Such platforms are composed of nanoparticles (NPs) as the inner core and surface functionalized with glucose-poly(ethylene glycol) (Glu-PEG) and polydopamine (PDA) coating. Glu-PEG provides selective targeting of the NPs to brain capillary endothelial cells (BCECs), while PDA enhances the transcytosis of the NPs. This strategy is applicable to gold NPs (AuNPs), silica, and polymeric NPs, which achieves as high as 1.87% of the injected dose/g of brain in healthy brain tissues. In addition, the GPDA coating manages to deliver NPs into the tumor tissue in the orthotopic glioblastoma model. Our study may provide a universal strategy for the construction of delivery platforms for efficient BBB crossing and brain drug delivery.

Nanoparticle-Enabled Dual Modulation of Phagocytic Signals to Improve Macrophage-Mediated Cancer Immunotherapy.

Activation of the phagocytosis of macrophages to tumor cells is an attractive strategy for cancer immunotherapy, but the effectiveness is limited by the fact that many tumor cells express an increased level of anti-phagocytic signals (e.g., CD47 molecules) on their surface. To promote phagocytosis of macrophages, a pro-phagocytic nanoparticle (SNPACALR&aCD47 ) that concurrently carries CD47 antibody (aCD47) and a pro-phagocytic molecule calreticulin (CALR) is constructed to simultaneously modulate the phagocytic signals of macrophages. SNPACALR&aCD47 can achieve targeted delivery to tumor cells by specifically binding to the cell-surface CD47 and block the CD47-SIRPα pathway to inhibit the "don't eat me" signal. Tumor cell-targeted delivery increases the exposure of recombinant CALR on the cell surface and stimulates an "eat me" signal. Simultaneous modulation of the two signals enhances the phagocytosis of 4T1 tumor cells by macrophages, which leads to significantly improved anti-tumor efficacy in vivo. The findings demonstrate that the concurrent blockade of anti-phagocytic signals and activation of pro-phagocytic signals can be effective in macrophage-mediated cancer immunotherapy.

[Changes in ambulatory electrocardiographic findings after oral administration of low-dose propranolol in infants with hemangioma].

OBJECTIVE: To investigate the effects of oral administration of low-dose propranolol on heart rate variability (HRV), acceleration capacity (AC), deceleration capacity (DC), and cardiac conduction in the treatment of infantile hemangioma. METHODS: A total of 118 infants with hemangioma (≤1 year) were enrolled, and 24-hour ambulatory electrocardiography was performed before oral administration of low-dose propranolol and after one month of administration. The changes in time-domain indices [standard deviation of all normal sinus RR intervals (SDNN), standard deviation of all mean 5-minute RR intervals (SDANN), root mean squared successive difference (RMSSD), and percentage of successive normal sinus RR intervals >50 ms (PNN50)] and frequency-domain indices [low frequency (LF) and high frequency (HF)] for HRV, AC, and DC were observed, as well as abnormalities in cardiac conduction and other aspects after administration of propranolol. RESULTS: After administration of propranolol, the infants had significantly increased SDNN, RMSSD, LF, HF, and PNN50 (P<0.01), and significantly reduced AC, mean heart rate (HR) and minimum HR (P<0.01). The 24-hour ambulatory electrocardiographic findings showed a nonsignificantly higher abnormal rate after administration of propranolol. CONCLUSIONS: In the treatment of infantile hemangioma, propranolol can inhibit the activity of sympathetic nerve and block cardiac conduction, but without any serious adverse effect.

Recent Progress on Nanomedicine-Mediated Repolarization of Tumor-Associated Macrophages for Cancer Immunotherapy.

Tumor-associated macrophages (TAMs) constitute the largest number of immune cells in the tumor microenvironment (TME). They play an essential role in promoting tumor progression and metastasis, which makes them a potential therapeutic target for cancer treatment. TAMs are usually divided into two categories: pro-tumoral M2-like TAMs and antitumoral M1 phenotypes at either extreme. The reprogramming of M2-like TAMs toward a tumoricidal M1 phenotype is of particular interest for the restoration of antitumor immunity in cancer immunotherapy. Notably, nanomedicines have shown great potential for cancer therapy due to their unique structures and properties. This review will briefly describe the biological features and roles of TAMs in tumor, and then discuss recent advances in nanomedicine-mediated repolarization of TAMs for cancer immunotherapy. Finally, perspectives on nanomedicine-mediated repolarization of TAMs for effective cancer immunotherapy are also presented.

Self-Assembled Nanoparticles from the Amphiphilic Prodrug of Resiquimod for Improved Cancer Immunotherapy.

Tumor-associated macrophages (TAMs) usually adopt a tumor-promoting M2-like phenotype, which largely impedes the immune response and therapeutic efficacy of solid tumors. Repolarizing TAMs from M2 to the antitumor M1 phenotype is crucial for reshaping the tumor immunosuppressive microenvironment (TIME). Herein, we developed self-assembled nanoparticles from the polymeric prodrug of resiquimod (R848) to reprogram the TIME for robust cancer immunotherapy. The polymeric prodrug was constructed by conjugating the R848 derivative to terminal amino groups of the linear dendritic polymer composed of linear poly(ethylene glycol) and lysine dendrimer. The amphiphilic prodrug self-assembled into nanoparticles (PLRS) of around 35 nm with a spherical morphology. PLRS nanoparticles could be internalized by antigen-presenting cells (APCs) in vitro and thus efficiently repolarized macrophages from M2 to M1 and facilitated the maturation of APCs. In addition, PLRS significantly inhibited tumor growth in the 4T1 orthotopic breast cancer model with much lower systemic side effects. Mechanistic studies suggested that PLRS significantly stimulated the TIME by repolarizing TAMs into the M1 phenotype and increased the infiltration of cytotoxic T cells into the tumor. This study provides an effective polymeric prodrug-based strategy to improve the therapeutic efficacy of R848 in cancer immunotherapy.

Electroacupuncture activates the peroxisome proliferators-activated receptor pathway to improve the phenotype of cerebral palsy.

AIM: This study explores the efficacy of electroacupuncture (EA) in treating cerebral palsy (CP) in Sprague-Dawley (SD) pups, specifically CP animal models, and its molecular mechanisms. METHODS: Gait analysis and Y-maze were used to detect the improvement of motor ability and cognitive function of CP rats after EA treatment. Transcription sequencing was used to determine the key pathway for EA to improve the symptoms of CP. PPAR agonists were used to verify the causal relationship between the pathway and the improvement of CP phenotype. RESULTS: The motor ability and cognitive function of CP pups were improved after EA treatment. The results of transcriptome sequencing suggest that the improvement of CP phenotype may be caused by the activation of PPAR pathway. PPAR pathway is widely activated in the epithelium of CP pups treated with EA, which is verified by qPCR. Rosiglitazone (Ros), a PPAR agonist, can improve CP phenotype while activating PPAR pathway, which proves the causal relationship between PPAR pathway activation and CP phenotype improvement. CONCLUSION: Our study demonstrated behavioral improvements and enhanced cognitive functions in CP models after EA treatment by activating PPAR pathway, suggesting new perspectives for CP rehabilitation, and providing theoretical support for acupuncture treatment of CP.

Nanoparticle-Mediated CD47-SIRPα Blockade and Calreticulin Exposure for Improved Cancer Chemo-Immunotherapy.

Enabling macrophages to phagocytose tumor cells holds great potential for cancer therapy but suffers from tremendous challenges because the tumor cells upregulate antiphagocytosis molecules (such as CD47) on their surface. The blockade of CD47 alone is insufficient to stimulate tumor cell phagocytosis in solid tumors due to the lack of "eat me" signals. Herein, a degradable mesoporous silica nanoparticle (MSN) is reported to simultaneously deliver anti-CD47 antibodies (aCD47) and doxorubicin (DOX) for cancer chemo-immunotherapy. The codelivery nanocarrier aCD47-DMSN was constructed by accommodating DOX within the mesoporous cavity, while adsorbing aCD47 on the surface of MSN. aCD47 blocks the CD47-SIRPα axis to disable the "don't eat me" signal, while DOX induces immunogenic tumor cell death (ICD) for calreticulin exposure as an "eat me" signal. This design facilitated the phagocytosis of tumor cells by macrophages, which enhanced antigen cross-presentation and elicited efficient T cell-mediated immune response. In 4T1 and B16F10 murine tumor models, aCD47-DMSN generated a strong antitumor effect after intravenous injection by increasing tumor-infiltration of CD8+ T cells. Taken together, this study offers a nanoplatform to modulate the phagocytosis of macrophages for efficacious cancer chemo-immunotherapy.

An Injectable Nanocomposite Hydrogel Improves Tumor Penetration and Cancer Treatment Efficacy.

Hydrogel as a local drug depot can increase drug concentration at the tumor site. However, conventional drug-loaded hydrogel is typically formed by direct dissolution of drug molecules inside the hydrogel, which usually suffers from limited drug retention and poor tumor penetration. In this study, a nanocomposite hydrogel consisting of oxaliplatin (OXA)-conjugated G5 polyamidoamine (G5-OXA) and oxidized dextran (Dex-CHO) is constructed to improve local drug delivery. The OXA-containing nanocomposite hydrogel (denoted as PDO gel) is injectable and could maintain in vivo up to more than three weeks, which increases drug retention in tumor tissues. More interestingly, G5-OXA released from the PDO gel show potent tumor penetration mainly through an active transcytosis process. In vivo antitumor studies in an orthotopic 4T1 tumor model show that PDO gel significantly inhibits primary tumor growth as well as the metastasis. In addition, the PDO gel can also activate the immunosuppressive tumor microenvironment through immunogenic cell death effect, and further improves therapeutic efficacy with the combination of PD-1 antibody. These results demonstrate that the nanocomposite hydrogel can simultaneously enhance the retention and penetration of chemotherapeutic drugs via the combination of both advantages of hydrogel and nanoparticles, which provides new insights for the design of local drug delivery systems. STATEMENT OF SIGNIFICANCE: Hydrogel represents an important class of local drug delivery depot. However, conventional drug-loaded hydrogel is usually achieved by direct dissolution of small drug molecules inside the hydrogel, which typically suffers from limited drug retention and poor tumor penetration. Herein, we developed a nanocomposite hydrogel, which could gradually degrade and release drug-conjugated small nanoparticles (∼ 6 nm) for improved tumor penetration through the combination of an active transcytosis process and a passive diffusion process. This nanocomposite hydrogel system improved tumor penetration and retention of drug in primary tumors as well as the drug deposition in lymph nodes, which significantly suppressed tumor growth and metastasis.

Engineering nanoparticles to tackle tumor barriers.

Engineering nanoparticles (NPs) as delivery systems of anticancer therapeutics has attracted tremendous attention in recent decades, and some nanoscale drug formulations have been approved for clinical use. However, their therapeutic efficacies are still limited by the presence of a series of biological barriers during the delivery process. Among these obstacles, tumor barriers are generally recognized as the bottleneck, because they dominate the NP extravasation from the tumor vasculature and penetration into the tumor parenchyma. Therefore, this review first discussed tumor barriers from two aspects: tumor vascular barriers and tumor stromal barriers. Pathological features of the two sets of barriers as well as their influence on the delivery efficacy were described. Then, we outlined strategies for engineering NPs to overcome these challenges: increasing extravasation through physical property optimization and tumor vascular targeting; and facilitating deep penetration through particle size manipulation, modulation of the tumor extracellular matrix, and some new mechanisms. This review will provide a critical perspective on engineering strategies for more efficient nanomedicine in oncology.

Gelsemine and koumine, principal active ingredients of Gelsemium, exhibit mechanical antiallodynia via spinal glycine receptor activation-induced allopregnanolone biosynthesis.

Gelsemine, the principal active alkaloid from Gelsemium sempervirens Ait., and koumine, the most dominant alkaloids from Gelsemium elegans Benth., produced antinociception in a variety of rodent models of painful hypersensitivity. The present study explored the molecular mechanisms underlying gelsemine- and koumine-induced mechanical antiallodynia in neuropathic pain. The radioligand binding and displacement assays indicated that gelsemine and koumine, like glycine, were reversible and orthosteric agonists of glycine receptors with full efficacy and probably acted on same binding site as the glycine receptor antagonist strychnine. Treatment with gelsemine, koumine and glycine in primary cultures of spinal neurons (but not microglia or astrocytes) concentration dependently increased 3α-hydroxysteroid oxidoreductase (3α-HSOR) mRNA expression, which was inhibited by pretreatment with strychnine but not the glial inhibitor minocycline. Intrathecal injection of gelsemine, koumine and glycine stimulated 3α-HSOR mRNA expression in the spinal cords of neuropathic rats and produced mechanical antiallodynia. Their spinal mechanical antiallodynia was completely blocked by strychnine, the selective 3α-HSOR inhibitor medroxyprogesterone acetate (MPA), 3α-HSOR gene silencer siRNA/3α-HSOR and specific GABAA receptor antagonist isoallopregnanolone, but not minocycline. All the results taken together uncovered that gelsemine and koumine are orthosteric agonists of glycine receptors, and produce mechanical antiallodynia through neuronal glycine receptor/3α-HSOR/allopregnanolone/GABAA receptor pathway.

Correlation analysis of levels of inflammatory cytokines and nitric oxide in peripheral blood with urine proteins and renal function in patients with gestational hypertension.

The aim of the study was to investigate correlations among inflammatory cytokines, nitric oxide (NO) level, urine protein, renal function and blood pressure in peripheral blood of patients with hypertensive disorder complicating pregnancy (HDCP). A total of 60 patients diagnosed with HDCP in the Obstetrics Department of Wuhan Children's Hospital, Tongji Medical College, Huazhong University of Science and Technology from May 2016 to April 2017 were selected. The patients were divided into the HDCP (n=20), mild pre-eclampsia (n=20) and severe pre-eclampsia (n=20) groups. Additionally, 20 healthy pregnant women were selected as the control group. General data of the patients were collected. NO, renal function and 24-h urine protein were measured. The systolic and diastolic blood pressure, C-reactive protein (CRP), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the HDCP group was significantly higher than that in the control group. The CRP, TNF-α and IL-6 levels in the pre-eclampsia groups were higher than those in the gestational hypertension group (P<0.05). The NO level in peripheral blood of patients in the pre-eclampsia groups was lower than that in the gestational hypertension group (P<0.05). The levels of 24-h urine protein, homocysteine (Hcy), cystatin-C (Cys-C), serum creatinine (SCr), urea and ß2 microglobulin in the pre-eclampsia groups were higher than those in the gestational hypertension group (P<0.05). Gestational age and the levels of baseline blood pressure, inflammatory cytokines, 24-h urine protein and renal function have independent predictive value for the occurrence of HDCP (P<0.05). The results show that, 24-h urine protein, renal function and inflammatory cytokines are closely correlated with the occurrence of HDCP, which can reflect the severity and prognosis of the disease to a certain extent. In addition, it has important reference value for the assessment and treatment of the disease.

Enhanced CO2 capture by reducing cation-anion interactions in hydroxyl-pyridine anion-based ionic liquids.

In this work, an efficient strategy for improving CO2 capture based on anion-functionalized ionic liquids (ILs) by reducing cation-anion interactions in ILs was reported. The influence of the cationic species on CO2 absorption was investigated using 2-hydroxyl pyridium anions ([2-Op]) as a probe. CO2 capture experiments indicated that the CO2 absorption capacity in [2-Op] anion-based ILs varied from 0.94 to 1.69 mol CO2 per mol IL at 30 °C and 1 atm. Spectroscopic analysis and quantum chemical calculations suggested that the increase of the CO2 absorption capacity may be ascribed to the reduction of the strength of cation-anion interactions in ILs, and stronger cation-anion interactions would make one CO2 site in the [2-Op] anion inactive. Furthermore, the effect of the cation unit on the anion was evidenced by FT-IR spectra, implying that strong interactions between ions may lead to the decrease of the IR absorption wavenumber of hydroxy pyridium and work against CO2 capture. Following this strategy, it was finally found that [Ph-C8eim][2-Op] (Ph-C8eim = 1-N-ethyl-3-N-octyl-2-phenylimidazolium) with weaker cation-anion interactions exhibited a significant increase in the CO2 uptake capacity, and extremely high capacities of 1.69 and 1.83 mol CO2 per mol IL could be achieved at 30 and 20 °C, respectively. The study presented here would be helpful for further designing novel and effective ILs for advancing CO2 capturing performance.

[Three-year retrospective clinical evaluation of pulp-less molars with defects of varying degree repaired by cast ceramic onlays of three marginal types].

OBJECTIVE: This study aimed to evaluate the clinical effect of pulp-less molars with defects of different degrees repaired by cast ceramic onlays of three marginal types. METHODS: A total of 165 endodontically treated molars of 105 patients were included in this study and were divided into three kinds of defect (mild, moderate, severe) according to the number of remaining axial walls. Each defect was divided into three groups according to the shape of edge to edge, bevel edge, and concave shoulder. After tooth preparation, the casting of ceramic onlays was performed. Treatment follow-up was done for the evaluation of the success and survival rates of three groups under the same defect. RESULTS: The average follow-up was 925.44 days. Under the mild defect, the success and survival rates of the edge to edge onlays were respectively 100% and 100%; bevel edge onlays, 100% and 100%; and concave shoulder onlays, 94.4% and 100%. Under the moderate defect, the success and survival rates of the edge to edge onlays were respectively 96.0% and 100%; bevel edge onlays, 80.0% and 93.3%; and concave shoulder onlays, 95.2% and 95.2%. Under the severe defect, the success and survival rates of the edge to edge onlays were respectively 95.2% and 100%; bevel edge onlays, 73.7% and 89.5%; and concave shoulder onlays, 73.3% and 80.0%. Under different defects, the success or survival rates of the three kinds of onlays had no significant difference (P>0.05). CONCLUSIONS: The edge to edge type is the most preferable way of onlay tooth preparation and can achieve good clinical results in the mild, middle, and severe tooth defection with root canal treatment.

Luteolin inhibits cell proliferation and induces cell apoptosis via down-regulation of mitochondrial membrane potential in esophageal carcinoma cells EC1 and KYSE450.

In current study, we investigated the anti-tumor effect of luteolin in human ESCC cell lines in vitro and in vivo and tried to explore the potential mechanisms. Results from flow cytometry showed that luteolin could induce apoptosis and caspase-3 activation and induce cell cycle arrest at G2/M phase in a dose- and time-dependent manner in EC1 and KYSE450 cells. JC-1 test results showed that membrane potential of mitochondria after luteolin treatment was down-regulated and this was an indicator for intrinsic apoptosis. Western Blot results showed the expression of cell cycle regulatory protein p21 and p53 increased and three apoptosis related proteins that participate in mitochondrial apoptotic pathway, namely, Bim, CYT-c and cPARP, also increased in luteolin treated cells compared with control groups. We further confirmed that luteolin could significantly inhibit the growth of ESCC tumors in xenograft mouse models and no evidence of systemic toxicity was observed. Our results suggest that luteolin can induce cell apoptosis and cell cycle arrest in G2/M phase through mitochondrial pathway in EC1 and KYSE450 cell lines and proper utilization of luteolin might be a practical approach in ESCC chemotherapy.

Effect of high energy X-ray irradiation on the nano-mechanical properties of human enamel and dentine.

Radiotherapy for malignancies in the head and neck can cause common complications that can result in tooth damage that are also known as radiation caries. The aim of this study was to examine damage to the surface topography and calculate changes in friction behavior and the nano-mechanical properties (elastic modulus, nanohardness and friction coefficient) of enamel and dentine from extracted human third molars caused by exposure to radiation. Enamel and dentine samples from 50 human third molars were randomly assigned to four test groups or a control group. The test groups were exposed to high energy X-rays at 2 Gy/day, 5 days/week for 5 days (10 Gy group), 15 days (30 Gy group), 25 days (50 Gy group), 35 days (70 Gy group); the control group was not exposed. The nanohardness, elastic modulus, and friction coefficient were analyzed using a Hysitron Triboindenter. The nano-mechanical properties of both enamel and dentine showed significant dose-response relationships. The nanohardness and elastic modulus were most variable between 30-50 Gy, while the friction coefficient was most variable between 0-10 Gy for dentine and 30-50 Gy for enamel. After exposure to X-rays, the fracture resistance of the teeth clearly decreased (rapidly increasing friction coefficient with increasing doses under the same load), and they were more fragile. These nano-mechanical changes in dental hard tissue may increase the susceptibility to caries. Radiotherapy caused nano-mechanical changes in dentine and enamel that were dose related. The key doses were 30-50 Gy and the key time points occurred during the 15th-25th days of treatment, which is when application of measures to prevent radiation caries should be considered.

Gelsemium analgesia and the spinal glycine receptor/allopregnanolone pathway.

Gelsemium, a small genus of flowering plant from the family Loganiaceae, comprises five species including the popular Gelsemium sempervirens Ait. and Gelsemium elegans Benth., which are indigenous to North America and China/East Asia, respectively. Approximately 120 alkaloids have been isolated and identified from Gelsemium, with the predominant indole alkaloids including gelsemine, koumine, gelsemicine, gelsenicine, gelsedine, sempervirine, koumidine, koumicine and humantenine. Gelsemine is the principal active alkaloid in G. sempervirens Ait., and koumine and gelsemine are the most and second-most dominant alkaloids in G. elegans Benth. Gelsemium extract and its active alkaloids serve a variety of biological functions, including neurobiological, immunosuppressive and antitumor effects, and have traditionally been used to treat pain, neuralgia, anxiety, insomnia, asthma, respiratory ailments and cancers. This review focuses on animal-based studies of Gelsemium as a pain treatment and its mechanism of action. In contrast to morphine, when administered intrathecally and systemically, koumine, gelsemine and gelsenicine have marked antinociception in inflammatory, neuropathic and bone cancer pains without inducing antinociceptive tolerance. Gelsemium and its active alkaloids may produce antinociception by activating the spinal α3 glycine/allopregnanolone pathway. The results of this review support the clinical use of Gelsemium and suggest that its active alkaloids may be developed to treat intractable and other types of pain, preferably after chemical modification. However, Gelsemium is a known toxic plant, and its toxicity limits its appropriate dosage and clinical use. To avoid or decrease the side/toxic effects of Gelsemium, an individual monomer of highly potent alkaloids must be selected, or alkaloids that exhibit greater α3 glycine receptor selectivity may be discovered or modified.

Gelsemine, a principal alkaloid from Gelsemium sempervirens Ait., exhibits potent and specific antinociception in chronic pain by acting at spinal α3 glycine receptors.

The present study examined the antinociceptive effects of gelsemine, the principal alkaloid in Gelsemium sempervirens Ait. A single intrathecal injection of gelsemine produced potent and specific antinociception in formalin-induced tonic pain, bone cancer-induced mechanical allodynia, and spinal nerve ligation-induced painful neuropathy. The antinociception was dose-dependent, with maximal inhibition of 50% to 60% and ED50 values of 0.5 to 0.6 µg. Multiple daily intrathecal injections of gelsemine for 7 days induced no tolerance to antinociception in the rat model of bone cancer pain. Spinal gelsemine was not effective in altering contralateral paw withdrawal thresholds, and had only a slight inhibitory effect on formalin-induced acute nociception. The specific antinociception of gelsemine in chronic pain was blocked dose-dependently by the glycine receptor (GlyR) antagonist strychnine with an apparent ID50 value of 3.8 µg. Gelsemine concentration-dependently displaced H(3)-strychnine binding to the membrane fraction of rat spinal cord homogenates, with a 100% displacement and a Ki of 21.9µM. Gene ablation of the GlyR α3 subunit (α3 GlyR) but not α1 GlyR, by a 7-day intrathecal injection of small interfering RNA (siRNA) targeting α3 GlyR or α1 GlyR, nearly completely prevented gelsemine-induced antinociception in neuropathic pain. Our results demonstrate that gelsemine produces potent and specific antinociception in chronic pain states without induction of apparent tolerance. The results also suggest that gelsemine produces antinociception by activation of spinal α3 glycine receptors, and support the notion that spinal α3 glycine receptors are a potential therapeutic target molecule for the management of chronic pain.

Effect of high energy X-ray irradiation on the nano-mechanical properties of human enamel and dentine

Abstract Radiotherapy for malignancies in the head and neck can cause common complications that can result in tooth damage that are also known as radiation caries. The aim of this study was to examine damage to the surface topography and calculate changes in friction behavior and the nano-mechanical properties (elastic modulus, nanohardness and friction coefficient) of enamel and dentine from extracted human third molars caused by exposure to radiation. Enamel and dentine samples from 50 human third molars were randomly assigned to four test groups or a control group. The test groups were exposed to high energy X-rays at 2 Gy/day, 5 days/week for 5 days (10 Gy group), 15 days (30 Gy group), 25 days (50 Gy group), 35 days (70 Gy group); the control group was not exposed. The nanohardness, elastic modulus, and friction coefficient were analyzed using a Hysitron Triboindenter. The nano-mechanical properties of both enamel and dentine showed significant dose-response relationships. The nanohardness and elastic modulus were most variable between 30-50 Gy, while the friction coefficient was most variable between 0-10 Gy for dentine and 30-50 Gy for enamel. After exposure to X-rays, the fracture resistance of the teeth clearly decreased (rapidly increasing friction coefficient with increasing doses under the same load), and they were more fragile. These nano-mechanical changes in dental hard tissue may increase the susceptibility to caries. Radiotherapy caused nano-mechanical changes in dentine and enamel that were dose related. The key doses were 30-50 Gy and the key time points occurred during the 15th-25th days of treatment, which is when application of measures to prevent radiation caries should be considered.