[Mechanism and Clinical Significance of NAMPT in Multiple Myeloma]

OBJECTIVE

To investigate the mechanism and clinical value of nicotinamide phosphoribosyltransferase (NAMPT) in multiple myeloma (MM).

METHODS

RT-qPCR and Western blot were used to detect the expression of NAMPT in MM cells and normal bone marrow mononuclear cells. The biological function of NAMPT was analyzed by cell proliferation and apoptosis assay, small interfering RNA silencing, overexpression assay and chromatin immunoprecipitation assay.

RESULTS

The mRNA and protein expression levels of NAMPT in MM cell lines (MM1R, MM1S, U266 and RPMI-8226) were significantly higher than those in normal bone marrow mononuclear cells (P < 0.001), and were most obvious in U266 cells. Compared with Si-NC group, the proliferation of U266 cells in Si-NAMPT group was significantly inhibited at 24, 48 and 72 h after transfection (P =0.006, P < 0.001, P =0.001), and the apoptosis rate of U266 cells was significantly increased at 48 h after transfection (P < 0.001). Compared with Flag-NC group, U266 cell proliferation in Flag-NAMPT group was significantly increased (P =0.003, P =0.002, P < 0.001), while the apoptosis rate decreased significantly at 48 h after transfection. The expression of NAMPT in U266 cells was regulated by XBP1 at transcriptional level. The proliferation rate of U266 cells with XBP1 or NAMPT stable knockout or MKC3946 pretreated with bortezomib was significantly decreased, the levels of BCL-2 mRNA and protein were also significantly decreased, while the levels of BAX mRNA and protein were significantly increased, moreover, the cleavage degree of caspase-3 significantly decreased, while caspase-3/7 activity increased dramatically (P < 0.05).

CONCLUSIONS

The high expression of NAMPT in MM cell line can promote MM cell proliferation and inhibit apoptosis. NAMPT is regulated by IRE1α-XBP1 signaling pathway in U266 cells. Stable knockdown of NAMPT or blocking of IRE1α-XBP1 pathway can significantly increase the sensitivity of U266 cells to bortezomib.

[Efficacy and Safety of Bortezomib or Thalidomide Combined with rhEPO in the Treatment of Multiple Myeloma]

OBJECTIVE

To explore the efficacy and safety of bortezomib or thalidomide combined with recombinant human erythropoietin (rhEPO) in the treatment of multiple myeloma (MM).

METHODS

A total of 80 patients with MM who were treated in the Second People's Hospital of Wuhu from January 2013 to December 2018 were selected as the research subjects, and they were divided into bortezomib group (n=40) and thalidomide group (n=40) by the simple randomization method. The bortezomib group received bortezomib regimen combined with rhEPO therapy, and the thalidomide group was given thalidomide regimen combined with rhEPO therapy, and all patients were treated for 3 courses with every 3 weeks as a course of treatment. The clinical efficacy after 3 courses of treatment, and tumor-related biochemical indicators [lactate dehydrogenase (LDH), β2-microglobulin (β2-MG), vascular endothelial growth factor (VEGF), apoptosis inhibitory protein Survivin], bone marrow-related indicators [serum M-protein, bone marrow plasma cells, hemoglobin (Hb)] and coagulation function indicators [activated partial thromboplastin time (APTT), prothrombin time (PT), plasminogen activator inhibitor (PAI), total circulating microparticles (TMPs)] before treatment and after 3 courses of treatment were compared between the two groups of patients. The occurrence of adverse reactions during the treatment in the two groups of patients was recorded.

RESULTS

After 3 courses of treatment, the ORR rate of 92.5% in bortezomib group was higher than 90.0% in thalidomide group, but the difference was not statistically significant (P >0.05). The levels of LDH, β2-MG, VEGF, Survivin, serum M-protein, bone marrow plasma cells, APTT, PT, PAI and TMPs in the two groups after 3 courses of treatment were significantly lower or shorter than those before treatment, and the above indicators in bortezomib group were significantly lower or shorter than those in thalidomide group (P <0.05). After 3 courses of treatment, the expression level of Hb in the two groups was significantly higher than that before treatment, and the Hb level in bortezomib group was significantly higher than that in thalidomide group (P <0.05). During the treatment process, the incidence rates of adverse reactions in bortezomib group were significantly lower than those in thalidomide group (P <0.05).

CONCLUSION

Thalidomide regimen or bortezomib regimen combined with rhEPO has similar clinical efficacy on MM, but bortezomib regimen combined with rhEPO is more prominent and safer on improving tumor-related biochemical indicators, bone marrow-related indicators and coagulation status in patients with MM.

[Expression and Clinical Significance of NAMPT in Bone Marrow of Patients with Multiple Myeloma]

OBJECTIVE

To study the expression level of nicotinamide phosphoribosyltransferase (NAMPT) in multiple myeloma (MM), its relationship with clinical indicators, prognosis and potential role.

METHODS

Immunohistochemical staining was used to detect the expression of NAMPT in bone marrow biopsies of patients with newly diagnosed multiple myeloma (NDMM) and patients with iron deficiency anemia (IDA) hospitalized during the same period. According to the median expression level of NAMPT, NDMM patients were divided into high expression group and low expression group. The correlation between NAMPT expression level and clinical baseline data was analyzed, and survival analysis was performed to evaluate the relationship between NAMPT expression level and prognosis. The GSE24080 and GSE19784 datasets were used to analyze the effect of NAMPT on the prognosis. Gene set enrichment analysis (GSEA) explored the possible mechanism of NAMPT involved in MM cell function.

RESULTS

The mean staining intensity of NAMPT in bone marrow tissue of 31 NDMM patients was 0.007±0.002, and that of 10 IDA patients was 0.002±0.002 (P < 0.05). The median expression level of NAMPT was 0.0041 in NDMM patients, and the mean staining intensity of high expression group and low expression group was 0.007±0.005 and 0.002±0.001, respectively (P < 0.001). There were certain differences in lactate dehydrogenase (LDH), C-reactive protein (CRP) and ISS staging between high expression group and low expression group (P < 0.001), while no significant differences in other indicators. The overall response rate (ORR) of high expression group was significantly lower than that of low expression group (P < 0.001). The median survival time of patients in high expression group was significantly shorter than that in low expression group (P =0.024). The results of bioinformatics analysis showed that the event-free survival (EFS) rate and overall survival (OS) rate of low NAMPT group were both higher than high NAMPT group (P =0.037, P =0.009), and NAMPT was an independent prognostic factor for EFS and OS (P =0.006, P =0.020). GSEA suggested that NAMPT might affect MM cell function through mTORC1 signaling pathway.

CONCLUSIONS

The expression level of NAMPT in bone marrow of NDMM patients is significantly higher than that of IDA patients, and the high expression of NAMPT may be correlated with late ISS stage, and high level of LDH and CRP. Patients with high expression of NAMPT have worse response to bortezomib and survival time may be shorter. NAMPT may be involved in the occurrence and development of MM through mTORC1 signaling pathway.

[Preliminary Study on the Relationship between the Developmental Stage of Multiple Myeloma Disease and the Results of Bone Marrow Whole Exome Sequencing]

OBJECTIVE

To investigate the genetic results of whole exome sequencing of bone marrow from new onset multiple myeloma (MM) patients to analyze the process of genetic clonal evolution in MM patients.

METHODS

Genomic DNA was extracted from bone marrow samples of 15 MM patients and the whole exomes sequencing was performed using next generation sequencing technology. Using own buccal cells as germline controls, combinated with clinical information, the mutation profile of genes from high-risk asymptomatic myeloma to symptomatic myeloma were analyzed, and genes that may be associated with the efficacy and side effects of bortezomib were screened.

RESULTS

Except for two patients in whom no peripheral neuropathy was observed after a short treatment period, other patients peripheral neuropathy developed of various degrees during treatment with bortezomib containing chemotherapy, and the vast majority of patients achieved remission after receiving this bortezomib-related chemotherapy regimen. All patients had comparable levels of the inherited mutations number, but the somatic mutations was correlated with disease evolution.

CONCLUSION

different gene "mutational spectra" exist in myeloma patients at different stages and are associated with progression through all stages of the disease.

[Regulatory Mechanism of Mangiferin Combined with Bortezomib on Malignant Biological Behavior of Burkitt Lymphoma and Its Effect on Expression of CXC Chemokine Receptors]

OBJECTIVE

To analyze the effects of mangiferin combined with bortezomib on the proliferation, invasion, apoptosis and autophagy of human Burkitt lymphoma Raji cells, as well as the expression of CXC chemokine receptors (CXCRs) family, and explore the molecular mechanism between them to provide scientific basis for basic research and clinical work of Burkitt lymphoma.

METHODS

Raji cells were intervened with different concentrations of mangiferin and bortezomib alone or in combination, then cell proliferation was detected by CCK-8 assay, cell invasion ability was detected by Transwell chamber method, cell apoptosis was detected by Annexin V/PI double-staining flow cytometry, apoptosis, autophagy and Akt/mTOR pathway protein expression were detected by Western blot, and the expression changes of CXCR family was detected by real-time quantitative PCR (RT-qPCR).

RESULTS

Different concentrations of mangiferin intervened Raji cells for different time could inhibit cell viability in a concentration- and time-dependent manner (r =-0.682, r =-0.836). When Raji cells were intervened by combination of mangiferin and bortezomib, compared with single drug group, the proliferation and invasion abilities were significantly decreased, while the apoptosis level was significantly increased (P <0.01). Mangiferin combined with bortezomib could significantly up-regulate the expression of pro-apoptotic protein Bax and down-regulate the expression of anti-apoptotic protein Bcl-2 after intervention in Raji cells. Caspase-3 was also hydrolyzed and activated, and then induced the apoptosis of Raji cells. Mangiferin combined with bortezomib could up-regulate the expression of LC3Ⅱ protein in Raji cells, and the ratio of LC3Ⅱ/LC3Ⅰ in cells was significantly up-regulated compared with single drug or control group (P <0.01). Mangiferin combined with bortezomib could significantly inhibit the phosphorylation levels of Akt and mTOR, inhibit the proliferation and invasion of Raji cells by inhibiting Akt/mTOR pathway, and induce cell autophagy and apoptosis. Mangiferin and bortezomib could down-regulate the expressions of CXCR4 and CXCR7 mRNA after single-agent intervention in Raji cells, and the down-regulations of CXCR4 and CXCR7 mRNA expression were more significant when the two drugs were combined (P <0.01). Mangiferin alone or combined with bortezomib had no significant effect on CXCR5 mRNA expression in Raji cells (P >0.05), while the combination of the two drugs could down-regulate the expression of CXCR3 (P <0.05).

CONCLUSION

Mangiferin combined with bortezomib can synergistically inhibit the proliferation and invasion of Raji cells, and induce autophagy and apoptosis. The mechanism may be related to the inhibition of Akt/mTOR signaling pathway, down-regulation of anti-apoptotic protein Bcl-2 and up-regulation of pro-apoptotic protein Bax, and the inhibition of the expression of CXCR family.

[Research Progress on Mechanism of Bortezomib Resistance in Multiple Myeloma]

Multiple myeloma (MM) is a common plasma cell malignancy, accounting for the second largest hematological malignancy. Proteasome inhibitors represented by bortezomib (BTZ) have been the main treatment for patients with newly diagnosed and relapsed or refractory myeloma in nearly two decades. Although BTZ has improved the prognosis of MM patients, MM remains incurable in most patients, mainly because MM cells become resistant to BTZ. This review is to better understand the mechanism of MM resistance to BTZ and explore possible new therapeutic strategies.

[Clinical Characteristics and Survival Analysis of Patients with Plasma Cell Leukemia]

OBJECTIVE

To investigate the clinical characteristics, therapeutic response and prognosis of patients with plasma cell leukemia (PCL) and improve the understanding of this disease.

METHODS

The clinical manifestations, laboratory tests and treatment response of 27 patients with plasma cell leukemia treated in The Second Hospital of Shanxi Medical University from December 2010 to August 2019 were analyzed retrospectively, and their clinical characteristics were summarized. Kaplan-Meier method was used for survival analysis.

RESULTS

There were 18 cases of primary plasma cell leukemia (pPCL) and 9 cases of secondary plasma cell leukemia (sPCL). The male to female ratio was 1.7∶1. The median age was 62 years old. The first manifestations were bone pain, fatigue, fever, splenomegaly and bleeding, and a large number of plasma cell infiltration was observed in the morphological examination of peripheral blood and bone marrow cells. 13 cases were detected by immunotyping and all of them expressed CD38/CD138. 8 cases underwent karyotype analysis, and 3 cases were normal, clonal abnormalities occurred in 5 cases. FISH detection was performed in 12 cases, of which 8 cases were abnormal. In 17 cases of bortezomib based chemotherapy, the ovevall response rate was 52.9%, which was higher than that in the non-bortezomib group, but there was no significant difference between the two groups (P =0.242). The overall median survival time of 27 patients was 6.4 months, the median progression-free survival time was 3.5 months, and the median survival time of patients with pPCL and sPCL was 8.2 months and 2.4 months, respectively, the difference between the two groups was statistically significant (P =0.031).

CONCLUSION

PCL is highly invasive and has diverse clinical manifestations, and is not sensitive to traditional chemotherapy. The median survival time of patients with pPCL is relatively longer than that of patients with sPCL. The chemotherapy regimen based on bortezomib improves the treatment effectiveness and prolongs the survival time of PCL patients.

[Expression of NAMPT in Patients with Multiple Myeloma and Its Correlation with Clinical Manifestation]

OBJECTIVE

To analyze the expression level of nicotinamide phosphoribosyltransferase (NAMPT ) in bone marrow of multiple myeloma (MM) patients and its correlation with clinicopathological features, clinical efficacy and prognosis.

METHODS

RT-qPCR and Western blot were used to detect the expression of NAMPT mRNA and protein in bone marrow mononuclear cells from 85 newly diagnosed MM patients (including 17 relapsed MM patients) and 15 healthy donors, and explore the correlation of the expression of NAMPT gene with clinicopathological features and efficacy. Kaplan-Meier method was used to analyze the effects of NAMPT on progression-free survival (PFS) and overall survival (OS), and univariate and multivariate survival analysis were performed.

RESULTS

The median expression level of NAMPT mRNA in bone marrow of newly diagnosed and relapsed MM patients was significantly higher than that of healthy donors (P <0.001). The expression of NAMPT mRNA in relapsed MM patients was significantly higher than that in newly diagnosed MM patients (P <0.001), which was consistent with the expression of NAMPT protein. ISS staging, lactate dehydrogenase and C-reactive protein levels, p53 deletion and the proportion of myeloma cells were increased in high NAMPT expression group compared with low NAMPT expression group (P <0.001). Compared with complete remission group, NAMPT mRNA expression was significantly up-regulated in partial remission group, progression group and relapsed group (P <0.001). The median OS and PFS of patients in high NAMPT expression group was 27.3 and 14.9 months, respectively, which was significantly shorter than 39.1 and 27 months in low NAMPT expression group (P =0.048, P <0.001). Both univariate and multivariate analysis showed that NAMPT expression was correlated with PFS and OS.

CONCLUSION

The expression level of NAMPT in newly diagnosed and relapsed MM patients is significantly higher than that in normal controls, and its up-regulation is related to the adverse clinical characteristics, efficacy and prognosis of MM patients. NAMPT is an independent prognostic risk factor of MM.

[IL-6 Regulates the Chemosensitivity of Drug-Resistant Multiple Myeloma Cell Lines to Bortezomib through STAT3/Notch Signaling Pathway]

OBJECTIVE

To investigate the effect of interleukin-6 (IL-6) on the chemosensitivity of drug-resistant multiple myeloma (MM) cell lines to bortezomib (BTZ) and its mechanism.

METHODS

Peripheral blood samples were collected from patients with BTZ-resistant MM before and after treatment. Human MM cell lines KM3 and KM3/BTZ were cultured in vitro. ELISA was used to detect the content of IL-6 in peripheral blood of MM patients, KM3 and KM3/BTZ cells. CCK-8 assay was used to detect the drug sensitivity of KM3 and KM3 / BTZ cells to BTZ. KM3 / BTZ cells were divided into KM3/BTZ control group (normal culture for 48 h), IL-6 neutralizing antibody Anti-IL-6 group (500 ng/ml Anti-IL-6 treated for 48 h), BTZ group (300 ng/ml BTZ treated for 48 h), BTZ + Anti-IL-6 group (300 ng/ml BTZ and 500 ng/ml Anti-IL-6 treated for 48 h). The proliferation activity of KM3 / BTZ cells was detected by CCK-8 assay. The cell cycle distribution of KM3/BTZ cells was detected by flow cytometry. The apoptosis of KM3/BTZ cells was detected by Annexin V-FITC/PI double staining. The mRNA expression levels of IL-6, Notch1, signal transducer and activator of transcription 3 (STAT3) in KM3/BTZ cells were detected by real-time fluorescent quantitative PCR (qRT-PCR), and the protein expression levels of IL-6, Notch1, STAT3 in KM3/BTZ cells were detected by Western blot.

RESULTS

The level of IL-6 in peripheral blood of patients with BTZ-resistant MM after treatment was significantly higher than that before treatment (P<0.05). The level of IL-6 in KM3/BTZ cells was significantly higher than that in KM3 cells (P<0.05). The sensitivity of KM3/BTZ cells to BTZ was significantly lower than that of KM3 cells (P<0.05), and the resistance index (RI) was 19.62. Anti-IL-6 and BTZ could inhibit the proliferation of KM3 / BTZ cells, block cell cycle, and induce apoptosis (P<0.05). Compared with single drug treatment, the combined effect of Anti-IL-6 and BTZ was more obvious on KM3/BTZ cells (P<0.05), and significantly down regulated the mRNA and protein expression of IL-6, Notch1 and STAT3 in KM3/BTZ cells (P<0.05).

CONCLUSION

Antagonizing IL-6 can increase the chemosensitivity of MM cells to BTZ, and IL-6 may reduce the sensitivity of MM cells to BTZ through STAT3/Notch signaling pathway.

[Study on Application of RVD Regimen Sequential Auto-HSCT in the Treatment of Multiple Myeloma Evaluated by Propensity Score Matching]

OBJECTIVE

To investigate the application effect of sequential autologous hematopoietic stem cell transplantation (Auto-HSCT) with lenalidomide, bortezomib and dexamethasone (RVD) in the treatment of multiple myeloma (MM) evaluated by propensity score matching.

METHODS

The clinical data of 49 MM patients treated with RVD scheme and followed-up for 36 months in the hospital from January 2015 to January 2021 were retrospectively analyzed and included in the control group, the clinical data of 54 MM patients who received RVD scheme and sequential Auto-HSCT scheme and completed 36 months of follow-up in the hospital during the same period were collected and included in the observation group. PSM method (1∶1, caliper value=0.01) was used to match the control group with the observation group based on baseline data and laboratory indexes, covariate equilibrium samples were obtained between groups (40 cases in each group). The clinical efficacy of patients in the two groups after 18 weeks of treatment was compared; the incidence of toxic and side effects during treatment of patients in the two groups was compared; the survival of patients in the two groups was compared after 36 months of follow-up.

RESULTS

The ORR and DCR in the observation group were higher than those in the control group, the difference was statistically significant (P<0.05). Compared the incidence of fatigue, rash, thrombocytopenia, anemia and nausea of patients in the two groups, there was no statistical significant difference (P>0.05). After 36 months of follow-up (no loss during follow-up), 4 cases died from illness in the observation group, with a survival rate of 90% and an average survival time of 35.61 (95% CI: 35541-35.685) months, 10 cases died from illness in the control group, with a survival rate of 75% and an average survival time of 34.70 (95% CI: 34.559-34.832) months, the survival rate of the observation group was higher than that of the control group, the difference was statistically significant (P<0.05).

CONCLUSION

Sequential Auto-HSCT with RVD regimen in the treatment of MM can improve the short-term efficacy and increase the survival rate of patients, which will not increase toxic and side effects and has high safety.

[The Relationship between Hematopoietic Scoring System Composed of HB，PLT and MCV and Prognosis and Curative Effect of Multiple Myeloma Patients]

OBJECTIVE

To investigate the prognostic value of hemopoietic scoring system composed of hemoglobin (HB), platelet count (PLT) and mean corpuscular volume (MCV) in MM patients and its correlation with curative effect.

METHODS

The clinical data of 172 newly diagnosed MM patients treated by bortezomib as the first-line regimen in our hospital from May 2014 to December 2019 were collected, three variables (HB≤100 g/L, PLT≤150×10⁹/L, MCV≥96 fl) were introduced, each variable was distributed 1 score, the patients were divided into four groups (0, 1, 2 and 3 points in group 1, 2, 3 and 4, respectively), and the clinical characteristics and prognosis of the patients in the four groups were analyzed. The initial efficacy evaluation after 3-4 courses of treatment was carried out, and the curative effect of the patients in the different hematopoiesis score groups were compared.

RESULTS

The median OS time of the patients in group 1, 2, 3 and 4 was 27.0, 22.5, 20.7 and 18.1 months, while the median PFS time were 23.0, 19.0, 18.0 and 14.0 months, respectively. The OS and PFS of the patients in low score group were significantly better than those in high score group (P=0.045, P=0.048). There was no significant difference in the curative effect of the patients treated by bortezomib after 3-4 courses (P>0.05).

CONCLUSION

Hematopoiesis score can preliminarily predict the overall survival of newly diagnosed MM patients, but there is no significant difference between different scoring groups in the initial curative effect.

[Effect of Celastrol Based on IRAK4/ERK/p38 Signaling Pathway on Proliferation and Apoptosis of Multiple Myeloma Cells]

OBJECTIVE

To investigate the effect of celastrol on the proliferation and apoptosis of human multiple myeloma (MM) cell lines, reveal the relationship between IRAK4/ERK/p38 signaling pathway and celastrol regulating the proliferation and apoptosis of H929 and ARP-1 cells, and explore whether celastrol combined with bortezomib has synergistic effect.

METHODS

CCK-8 method was used to detect the viability of MM cell lines H929 and ARP-1 treated by different concentrations of celastrol, bortezomib, and their combination, and the synergistic effect was determined by Kim's formula. The apoptosis rate of H929 cells and necrosis rate of ARP-1 were detected by Annexin V/PI method. The expression of key proteins and apoptosis proteins in IRAK4/ERK/p38 signaling pathway were detected by Western blot.

RESULTS

Celastrol could significantly inhibit the proliferation of H929 and ARP-1 cells (r=0.9018, r=0.9244) and induce apoptosis in a time-dependent manner. Compared with the control group, celastrol could significantly up-regulate the expression of PARP and cleaved caspase-3 while down-regulate the expression of p-IRAK4, p-ERK, and p-p38 in H929 and ARP-1 cells. Celastrol and bortezomib alone inhibited the proliferation of H929 and ARP-1 cells. Compared with celastrol and bortezomib alone, their combination had lower cell survival rate and higher apoptosis rate (P<0.05).

CONCLUSION

Celastrol can inhibit the proliferation and promote the apoptosis of H929 and ARP-1 cells, which may be related to inhibiting the phosphorylation of IRAK4 and blocking the activation of IRAK4/ERK/p38 signaling pathway. Celastrol combined with bortezomib has synergistic effect, which can more effectively inhibit the proliferation and induce apoptosis of H929 and ARP-1 cells.

[Evaluation of the Efficacy and Safety of Chemotherapy in Elderly Patients with Multiple Myeloma under Different Frailty Scores]

OBJECTIVE

To compare the efficacy and safety of different chemotherapy regimens in elderly multiple myeloma (MM) patients with different Frailty scores.

METHODS

The clinical data of elderly patients with MM were retrospectively analyzed, including age, treatment regimen, efficacy, adverse reactions, and the Frailty score included in the activity of daily living score, the instrumental activity of daily living scale and the Charlson comorbidity index. The patients were divided into fit group, mediate fit group and frail group according to the scoring standard. The treatment efficiency and adverse reaction rates of elderly MM with different physical conditions treated by different chemotherapy regimens were analyzed.

RESULTS

Among the 70 patients, the effective rates of the patients in fit group, the mediate fit group, and the frail group were 79.5%, 81%, and 40%, and the effective rates of the fit patients in double and triple groups were 54.5% and 89.3%, 70% and 90.9% for mediate fit patients, 42.9% and 33.3% for frail patients, the triple regimen in fit patients showed obvious advantages, and the difference showed statistically significant (P<0.05), while the efficacy for mediate patients and frail patients showed no significant difference. During the induction of bortezomib, the incidence of adverse reactions for the patients in the triple group (78.6%) was higher than 67.9% in the double group, and the difference showed no statistically significant (P>0.05).There was no significant difference in the 1-year overall survival rate of the patients and with molecular genetic abnormalities among each groups.

CONCLUSION

The therapeutic effect is related to the patient's physical condition. For patients with healthy physique, the triple regimen should be used first. For patients with weak physical constitution, the chemotherapy regimen with low drug toxicity should be selected for safety.