Diffusion Kurtosis Imaging Reflects GFAP, TopoIIα, and MGMT Expression in Astrocytomas
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.310109
Source of Support: None, Conflict of Interest: None
Keywords: Astrocytomas, GFAP, MGMT, MR diffusion kurtosis imaging, TopoIIα
Astrocytomas is the most common adult primary neuroepithelial tumors. Factors affecting the biological behavior of astrocytomas are very complex. Although routine pathological diagnosis and classification is an important criterion to assess the prognosis of clinical treatment, it does not fully reflect the biological behavior of tumors. In order to better assess the biological behavior of the tumor, it is necessary to reveal the development of astrocytomas at the molecular biological level, and then we can adopt appropriate treatment measures to achieve targeted therapy. Recent studies have shown that glial fibrillary acidic protein (GFAP),, DNA topoisomeraseIIα(Topo-IIα),, and O6-methylguanine-DNA-methyltransferase (MGMT), may reflect the biological behavior of a tumor.
As commonly used in clinic, magnetic resonance (MR) is noninvasive, and is widely used in the grading of astrocytomas. Fractional anisotropy (FA) and mean diffusivity (MD) obtained from diffusion tensor imaging (DTI) have been used to grade gliomas. However, FA and MD have limitations in accurately evaluating GFAP, Topo-IIα, and MGMT.
New technologies, such as diffusion kurtosis imaging (DKI), can provide information on the pathophysiology of cancer. Finding a relationship between DKI parameters and the corresponding expression of GFAP, Topo-IIα, and MGMT can provide more abundant imaging information to better assess the biological behavior of the tumor and guide cancer diagnosis and treatment.
DKI has been used to measure non-Gaussian diffusion, which has the potential to better characterize both normal and pathological tissue than DTI. However, to our knowledge, no comparison of these different diffusion imaging approaches in assessing the GFAP, TopoIIα, and MGMT expression in astrocytomas has been investigated so far.
The purpose of this study was to quantitatively compare the potential of parameters obtained from the DTI and DKI in assessing the GFAP, TopoIIα, and MGMT expression in astrocytomas.
Sixty-six cases with pathologically proven astrocytomas (22 males and 44 females, aged 22 years to 71 years, with a mean 42 years) were enrolled from March 2012 to September 2014 in the First Hospital of Shanxi Medical. All the participants underwent preoperative conventional MRI head scan, DKI scan, and enhanced scan under the same conditions. Then, they underwent surgery in 2 weeks, Immunohistochemistry of GFAP, Topo-IIα, and MGMT were also available.
All pathological specimens made by experienced experts were in accordance with neuropathological 2007 World Health Organization (WHO) classification criteria for the diagnosis of central nervous system tumors, and there were 34 cases in astrocytomas high-grade group (WHO III-IV grade) and 32 cases in low-grade group (WHO I-II grade). This study was approved by the local ethics committee, and informed consent was obtained from all the participants.
Image acquisition and quantitative imaging analysis
GE 3.0T MRI and head and neck joint eight-channel phased-array coil were used for scanning. Conventional MRI head scan, DKI scan, and enhanced scan under the same conditions were obtained. T1-weighted images (WI) fluid-attenuated inversion recovery (FLAIR) sequence parameters were: TR 1686 ms, TE 24.2 ms, thickness: 6.0 mm, FOV = 24 cm; T2WI sequence parameters: TR 6600 ms, TE 107.2 ms, thickness: 6.0 mm, FOV = 24 cm; T2WI FLAIR sequence parameters: TR 8000 ms, TE 126.8 ms, thickness: 6.0 mm, FOV = 24 cm; DWI using echo-planar sequence (echo planar sequence, EPI), scan parameters: TR 6550 ms, TE 116 ms, FOV = 24 cm, thickness: 6. 0 mm, 15 diffusers sensitive gradient field, b values were 0,1000 s/mm2; DKI using EPI sequence scanning, scanning parameters: TR 6550 ms, TE 116 ms, FOV = 24 cm, thickness: 6.0 mm, 30 diffusers sensitive gradient field, b values were 0,1000 s/mm2, 2000 s/mm2. T1WI enhanced scan: TR = 2002.2 ms, TE = 24.2 ms, thickness: 6.0 mm, FOV = 24 cm.
Images were transferred to a workstation (Advantage Workstation4.4; GE Medical System) for processing. FA and MK of DKI parameter was calculated. The region of interest (ROI) was measured at the solid portion of the tumors. The ROIs varied from 25 to 50 mm2 (mean size: 36 mm2) to avoid cystic degeneration, necrosis, large blood vessels, bleeding, and calcification area.
Statistical Package for the Social Sciences (SPSS) version 16.0 statistical software was used to process all statistical data, measurement data. We performed two-sample t-test to compare parameter values between the two groups DKI and GFAP, Topo-IIα and MGMT expression level differences. Spearman rank correlation analysis was conducted to analyze DKI parameter value that was correlated with GFAP, Topo-IIα, MGMT expression. P < 0.05 was considered to be statistically significant.
Diffusion kurtosis imaging parameter values in astrocytomas
MK values of the high-grade astrocytomas were significantly higher than that of the low-grade group (P < 0.05); FA values between the high and low-grade group had no significant difference (P = 0.331) [Table 1].
Glial fibrillary acidic protein, Topo-IIα, O 6-methylguanine–DNA methyltransferase expression analysis in astrocytomas
The expression of GFAP was positive or strongly positive in the low-grade group, however, it was weakly positive or there was no expression in the high-grade group. The expression of GFAP between high and low grade groups were significantly different (P < 0.05). The expression of Topo-IIα was weakly positive or there was no expression in the low-grade group, but it was positive or strongly positive in the high-grade group; the expression of Topo-IIα in high and low-grade group was significantly different (P < 0.05). The expression of MGMT in high and low grade groups showed no statistically significant difference (P = 0.679) [Table 2].
Correlation between diffusion kurtosis imaging parameter values and expression of glial fibrillary acidic protein, Topo-IIα, and O 6-methylguanine–DNA methyltransferase in astrocytomas
Spearman rank correlation analysis showed that MK value was negatively correlated (r = −0.836; P = 0.03) with the expression of GFAP, was positively correlated (r = 0.896; P = 0.01) with the expression of Topo-IIα, and there was no linear correlation with the expression of MGMT (r = 0.362; P = 0.05); there was no linear correlation between FA values and the expression of GFAP (r = 0.366; P = 0.05), Topo-IIα (r = −0.562; P = 0.05) and MGMT (r = −0.153; P = 0.10) [Figure 1], [Figure 2], [Figure 3], [Figure 4].
Role of diffusion kurtosis imaging in brain astrocytomas grading
DKI has the potential to measure the non-Gaussian diffusion in biological tissue. Based on our results, there was no significant difference in FA between high and low-grade astrocytomas, whereas there was a significant difference in MK between high and low-grade astrocytomas.
MK is the true state of diffusion of water molecules. Its size depends on the degree of tissue cell structure, the more complicated structure of water molecules, (non-Gaussian distribution restricted diffusion) the higher MK value is. The degree of tumor differentiation in brain astrocytomas malignancy, invasion, and metastasis is associated with the organizational structure,, the tumor may render brain tissue lose its structural integrity and tumor tissue cells can increase internal and external diffusion barrier and restrict the movement of water molecules., In this study, FA value was not significantly different between the high and low grade glioma groups, which showed that directional diffusion of water molecules in the brain astrocytomas was not significantly different. This suggests that infiltrative tumor growth, white matter irregular fiber structure damage, normal white matter fiber tissue and tumor tissue are mixed and only part of the water molecules diffusion in normal nerve fibers myelin is restricted. Therefore there is no significant difference in FA values between the two groups. MK in the high-grade gliomas was significantly higher than that of the low-grade gliomas, suggesting that there are more complex organizational structures, atypical cells, and polymorphonuclear cell nucleus in the high-grade astrocytomas.
Diffusion kurtosis imaging and glial fibrillary acidic protein expression and its clinical significance
GFAP, an intermediate filament cytoskeletal proteins, is specifically expressed in the star-shaped cells, and determines the function and structure of the astrocytes, Schmidt, and Pekny reported that GFAP expression status and the biological behavior of the and prognosis of astrocytomas are closely related. Our research shows that the pathology of high-grade astrocytomas is related to low expression of GFAP, immature cells, messy tissue structure, poor prognosis, suggesting, that GFAP is important for astrocytomas's grade. Missing GFAP expression can lead to structural changes in the star cytoskeleton, with loss of important intercellular interconnection. This leads to the infiltration of the tumor cells into the adjacent tissues, thereby limiting the movement of the water molecules in the tumor cells. DKI dispersion degree in different grades of astrocytomas can be used to evaluate tumor cell infiltration depth, differentiation, degree of malignancy, and other biological behavior., This study shows that GFAP expression of brain astrocytomas is associated with MK, the astrocytomas GFAP expression was not correlated with the FA value, as GFAP expression may be decreased or absent, causing change the skeletal structure of the tissue and weakening of the cellular interconnections.
Tumor cell easily infiltrate into the adjacent tissue, normal white matter fiber tissue mixed with tumor tissue, white matter fiber structure was irregularly damaged, only part of the water molecules can diffuse, normal nerve fibers myelin constraints will loss. Therefore, FA values and GFAP had no linear correlation, whereas MK, the DKI parameter value, is reflected with GFAP expression grades of astrocytomas.
Diffusion kurtosis imaging and TopoIIα expression and its clinical significance
TopoIIα, an important nuclear enzyme, is required for the transcription of DNA replication, and it is important to many chemotherapeutic drugs target enzymes. It is an important biological marker of brain astrocytomas prognosis., At the same time, studies show that Topo-IIα expression is correlated with cell activity cycle M phase, S phase, and G2 phase; also, it can better reflect tumor cell proliferation. In the present study, the Topo-IIαexpression of astrocytomas in high-grade group is significantly higher than that of the low-grade group, which confirmed that Topo-IIα expression of brain is important for astrocytomas tumor grade, Higher the expression of the totp-II alpha, greater will be the proliferation of cells and poorer the prognosis. If there is higher degree of malignancy, more tumor tissue density, more nuclear atypia, richer tumor blood vessels, and more severe necrotic tissue, the tumor tissue will have more diffuse barrier, and microscopic structure would be more complex, and diffusion limited extent would be more pronounced, and the water molecules Gaussian diffusion displacement deviation will be greater. DKI is to describe a non-Gaussian diffusion displacement of the body's water molecules, to quantify the diffusion of water molecules that are not homogeneous, and to quantify its diffusion limited extent., The study found that MK values were significantly correlated with Topo-IIα expression grades. Topo-IIα expression is in higher-grade tumor, which suggested that the proliferation of malignant tumor cells is quicker, and that there is denser tissue, and that the movement of water molecules is more obviously limited, and resulting in organizational MK parameter values significantly increased. The Topo-IIα expression in astrocytomas was not correlated with FA values, may be due to brain astrocytomas growth is infiltrative, also, normal white matter fiber tissue and tumor tissue are mixed, there are irregular fiber structure of white matter damage, only a part of the water molecular diffusion is lost in normal nerve fibers myelin constraint, FA value is not obviously different among tumor, FA values had no significant linear correlation with Topo-IIα, therefore, MK, the DKI parameters, can reflect the Topo-IIα expression grade in astrocytomas.
Diffusion kurtosis imaging and O 6-methylguanine–DNA methyltransferase expression and its clinical significance
Temozolomide, a kind of chemotherapy drug, can be used to treat brain astrocytomas, MGMT can repair DNA damage by using induced temozolomide alkyl, reducing for chemotherapy temozolomide in MGMT expression in brain astrocytomas can be important indicators of chemotherapy temozolomide's sensitivity. Sun Yanhui's, Ting's, and other studies regarding different pathological grade glioma expression of MGMT has reached the opposite conclusion. Our study found that the overall expression level of MGMT in high-grade brain astrocytomas is higher than that of lower-grade group, suggesting that the high-grade expression of MGMT overall in astrocytomas astrocytomas lower grades of temozolomide tolerance prognosis than difference. However, the expression of MGMT between high-grade group and low-grade group was not statistically significant, which implies that the differences of MGMT's expression on individual are significant, we need further study in the future. In recent years, Li found that 42 cases of patients with glioblastoma tumor MGMT expression was measured in surgery by using immunohistochemistry staining T2WI MRI, which showed edema, the performance of MGMT expression level was associated with edema. Moon used DTI and DSC-PWI to analyze MGMT and MRI correlation of multiparameter analysis in high-grade glioma and it showed that MGMT expression was negatively correlated with the ADC value, and the value of MGMT expression and FA showed a significant positive correlation. DKI is evolved from the DTI technology evolution, it can describe the organization's non-Gaussian distribution of water molecules diffuse displacement, displacement quantization ideal state of Gaussian diffusion, and diffusion of water molecules deviate from the true state of size, relatively, the DTI can better reflect the organization Microstructure changes. However, studies suggest that FA value and MK value had no linear correlation with MGMT expression from Moon's different results, suggesting that using MRI to assess the level of significance of MGMT expression is not clear, we need further studies in the future.
In conclusion, our results suggest that MK could provide more valuable information about the grading of astrocytomas than that of FA. In addition, MK was significantly correlated with GFAP and Topo-IIα expression. To a certain extent, applying DKI may provide the biological behavior of tumor cell differentiation, proliferation activity, invasion and metastasis, and can guide individual treatment.
Financial support and sponsorship
This study was supported by grants from the National Natural Science Foundation of China (81471652) to Hui Zhang; grants from the Natural Science Foundation of Shanxi Province to Xiao-chun Wang (2015011092) and to Yan Tan (201601D021162); grants from the Youth Innovation Fund in the First Hospital of Shanxi Medical University (YC1416) to Xiao-chun Wang; grants from the Scientific and Technological Project of Shanxi Province Health Department (201201071) to Yan Tan.
Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]