Anesthetic modulation of water diffusion: Insights from a diffusion tensor imaging study.

Diffusion tensor imaging (DTI) in animal models are essential for translational neuroscience studies. A critical step in animal studies is the use of anesthetics. Understanding the influence of specific anesthesia regimes on DTI-derived parameters, such as fractional anisotropy (FA) and mean diffusivity (MD), is imperative when comparing results between animal studies using different anesthetics. Here, the quantification of FA and MD under different anesthetic regimes, alpha-chloralose and isoflurane, is discussed. We also used a range of b-values to determine whether the anesthetic effect was b-value dependent. The first group of rats (n = 6) was anesthetized with alpha-chloralose (80 mg/kg), whereas the second group of rats (n = 7) was anesthetized with isoflurane (1.5%). DTI was performed with b-values of 500, 1500, and 1500s/mm2, and the MD and FA were assessed individually. Anesthesia-specific differences in MD were apparent, as manifested by the higher estimated MD under isoflurane anesthesia than that under alpha-chloralose anesthesia (P < 0.001). MD values increased with decreasing b-value in all regions studied, and the degree of increase when rats were anesthetized with isoflurane was more pronounced than that associated with alpha-chloralose (P < 0.05). FA quantitation was also influenced by anesthesia regimens to varying extents, depending on the brain regions and b-values. In conclusion, both scanning parameters and the anesthesia regimens significantly impacted the quantification of DTI indices.

Brain alterations in ovariohysterectomized rats revealed by diffusion tensor imaging.

OBJECTIVES: Women undergoing hysterectomy with oophorectomy have an increased risk of Alzheimer's disease and Parkinson's disease. However, postoperative neuroimaging data on pathogenic processes in the brain are limited. The aim of this study was to investigate the potential effect of ovariohysterectomy on brain integrity in rat model using diffusion tensor imaging (DTI) technique for the first time. METHODS: We enrolled 13 rats each in the control and ovariohysterectomy groups. Rats in the ovariohysterectomy group underwent the ovariohysterectomy at 7 weeks of age, and all rats underwent DTI scans at 9 weeks of age. The DTI-derived parameters, such as fractional anisotropy and mean diffusivity, were compared between the control and ovariohysterectomy groups. RESULTS: Compared to the control group, the ovariohysterectomy group showed significantly lower fractional anisotropy in various brain regions, including the corpus callosum, bilateral striatum, and bilateral cortex (all P  < 0.05), suggesting neuronal injury in ovariohysterectomized rats. Mean diffusivity did not differ significantly between groups (all P  > 0.05). CONCLUSION: Rats undergoing ovariohysterectomy had lower fractional anisotropy compared to control in widespread brain regions, suggesting neuronal injury and demyelination. Therefore, neuroimaging should be performed to monitor brain alterations in women after hysterectomy with bilateral oophorectomy in clinical settings.

Reproducibility of diffusion tensor imaging-derived parameters: implications for the streptozotocin-induced type 1 diabetic rats.

OBJECTIVE: Diffusion tensor imaging (DTI) is a useful approach for studying neuronal integrity in animals. However, the test-retest reproducibility of DTI techniques in animals has not been discussed. Therefore, the first part of this work was to systematically elucidate the reliability of DTI-derived parameters in an animal study. Subsequently, we applied the DTI approach to an animal model of diabetes in a longitudinal manner. MATERIALS AND METHODS: In Study 1, nine rats underwent two DTI sessions using the same scanner and protocols, with a gap of 4 weeks. The reliability of the DTI-derived parameters was evaluated in terms of sessions and raters. In Study 2, nine rats received a single intraperitoneal injection of 70 mg/kg streptozotocin (STZ) to develop diabetes. Longitudinal DTI scans were used to assess brain alterations before and 4 weeks after STZ administration. RESULTS: In the test-retest evaluation, the inter-scan coefficient of variation (CoV) ranged from 3.04 to 3.73% and 2.12-2.59% for fractional anisotropy (FA) and mean diffusivity (MD), respectively, in different brain regions, suggesting excellent reproducibility. Moreover, rater-dependence had minimal effects on FA and MD quantification, with all inter-rater CoV values less than 4%. Following the onset of diabetes, FA in striatum and cortex were noted to be significantly lower relative to the period where they had not developed diabetes (both P < 0.05). However, when compared to the control group, a significant change in FA caused by diabetes was detected only in the striatum (P < 0.05), but not in the cortex. CONCLUSION: These results demonstrate good inter-rater and inter-scan reliability of DTI in animal studies, and the longitudinal setting has a beneficial effect on detecting small changes in the brain due to diseases.

Differences in brain activity between normal and diabetic rats under isoflurane anesthesia: a resting-state functional MRI study.

BACKGROUND: Altered neural activity based on the fractional amplitude of low-frequency fluctuations (fALFF) has been reported in patients with diabetes. However, whether fALFF can differentiate healthy controls from diabetic animals under anesthesia remains unclear. The study aimed to elucidate the changes in fALFF in a rat model of diabetes under isoflurane anesthesia. METHODS: The first group of rats (n = 5) received a single intraperitoneal injection of 70 mg/kg streptozotocin (STZ) to cause the development of diabetes. The second group of rats (n = 7) received a single intraperitoneal injection of the same volume of solvent. Resting-state functional magnetic resonance imaging was used to assess brain activity at 4 weeks after STZ or solvent administration. RESULTS: Compared to the healthy control animals, rats with diabetes showed significantly decreased fALFF in various brain regions, including the cingulate cortex, somatosensory cortex, insula, and striatum (all P < 0.05). The decreased fALFF suggests the aberrant neural activities in the diabetic rats. No regions were detected in which the control group had a lower fALFF than that in the diabetes group. CONCLUSIONS: The results of this study demonstrated that the fALFF could be used to differentiate healthy controls from diabetic animals, providing meaningful information regarding the neurological pathophysiology of diabetes in animal models.

Caffeine enhances BOLD responses to electrical whisker pad stimulation in rats during alpha-chloralose anaesthesia.

By reducing the cerebral blood flow and thereby increasing the resting deoxyhaemoglobin concentration, many human studies have shown that caffeine has a beneficial effect on enhancing the magnitude of blood-oxygenation-level-dependent (BOLD) responses. However, the effect of caffeine on BOLD responses in animals under anaesthesia has not been demonstrated. In this study, we aimed to determine the effect of systemic caffeine administration on BOLD responses in rats under alpha-chloralose. By applying electric whisker pad stimulation to male Sprague-Dawley rats, we performed fMRI measurements before and after the caffeine injection (40 mg/kg, n = 7) or an equivalent volume of saline (n = 6) at 7T. To understand the potential perturbation of animal physiology during stimulation, arterial blood pressure was measured in a separate group of animals (n = 3) outside the scanner. Caffeine significantly decreased baseline BOLD signals (p = .05) due to the increased deoxyhaemoglobin level. Both BOLD responses and t-values in the primary somatosensory cortex were significantly increased (both p < .05). The blood pressure changed insignificantly (p > .05). No significant differences in BOLD responses and t-values were observed in the control condition of saline injection (both p > .05). These findings suggested that, although the cerebral activity was lower under alpha-chloralose anaesthesia, the higher level of deoxygemoglobin at the baseline under the caffeinated condition can benefit the magnitude of BOLD responses in rats. These findings suggest that animal models might serve as potential platforms for further caffeine-related fMRI research studies.

Nanotheranostics With the Combination of Improved Targeting, Therapeutic Effects, and Molecular Imaging.

There is an increasing interest in the design of targeted carrier systems with combined therapeutic and diagnostic modalities. Therapeutic modalities targeting tumors with single ligand-based targeting nanocarriers are insufficient for proficient delivery and for targeting two different surface receptors that are overexpressed in cancer cells. Here, we evaluated an activated nanoparticle delivery system comprising fucoidan/hyaluronic acid to improve therapeutic efficacy. The system comprised polyethylene glycol-gelatin-encapsulated epigallocatechin gallate (EGCG), poly (D,L-lactide-co-glycolide; PLGA), and stable iron oxide nanoparticles (IOs). The latter enables targeting of prostate cancers in their molecular images. We demonstrate the transfer of nanoparticles and their entry into prostate cancer cells through ligand-specific recognition. This system may prove the benefits of drug delivery that enhances the inhibition of cell growth through apoptosis induction. Moreover, the improved targeting of nanotheranostics significantly suppressed orthotopic prostate tumor growth and more accurately targeted tumors compared with systemic combination therapy. In the presence of nanoparticles with iron oxides, the hypointensity of the prostate tumor was visualized on a T2-weignted magnetic resonance image. The diagnostic ability of this system was demonstrated by accumulating fluorescent nanoparticles in the prostate tumor from the in vivo imaging system, computed tomography. It is suggested that theranostic nanoparticles combined with a molecular imaging system can be a promising cancer therapy in the future.

Nanoparticle Delivery of MnO2 and Antiangiogenic Therapy to Overcome Hypoxia-Driven Tumor Escape and Suppress Hepatocellular Carcinoma.

Antiangiogenic therapy is widely administered in many cancers, and the antiangiogenic drug sorafenib offers moderate benefits in advanced hepatocellular carcinoma (HCC). However, antiangiogenic therapy can also lead to hypoxia-driven angiogenesis and immunosuppression in the tumor microenvironment (TME) and metastasis. Here, we report the synthesis and evaluation of NanoMnSor, a tumor-targeted, nanoparticle drug carrier that efficiently codelivers oxygen-generating MnO2 and sorafenib into HCC. We found that MnO2 not only alleviates hypoxia by catalyzing the decomposition of H2O2 to oxygen but also enhances pH/redox-responsive T1-weighted magnetic resonance imaging and drug-release properties upon decomposition into Mn2+ ions in the TME. Moreover, macrophages exposed to MnO2 displayed increased mRNA associated with the immunostimulatory M1 phenotype. We further show that NanoMnSor treatment leads to sorafenib-induced decrease in tumor vascularization and significantly suppresses primary tumor growth and distal metastasis, resulting in improved overall survival in a mouse orthotopic HCC model. Furthermore, NanoMnSor reprograms the immunosuppressive TME by reducing the hypoxia-induced tumor infiltration of tumor-associated macrophages, promoting macrophage polarization toward the immunostimulatory M1 phenotype, and increasing the number of CD8+ cytotoxic T cells in tumors, thereby augmenting the efficacy of anti-PD-1 antibody and whole-cell cancer vaccine immunotherapies. Our study demonstrates the potential of oxygen-generating nanoparticles to deliver antiangiogenic agents, efficiently modulate the hypoxic TME, and overcome hypoxia-driven drug resistance, thereby providing therapeutic benefit in cancer.

DHA Attenuates Cerebral Edema Following Traumatic Brain Injury via the Reduction in Blood-Brain Barrier Permeability.

Traumatic brain injury (TBI) could result in edema and cause an increase in intracranial pressure of the brain resulting in mortality and morbidity. Although there is hyperosmolarity therapy available for this pathophysiological event, it remains controversial. Recently, several groups have shown docosahexaenoic acid (DHA) to improve functional and histological outcomes following brain injury based on reduction of neuroinflammation and apoptosis. However, the effect of DHA on blood-brain barrier (BBB) dysfunction after brain injury has not been fully studied. Here, a controlled cortical impact rat model was used to test the effect of a single dose of DHA administered 30 min post injury. Modified neurological severity score (mNSS) and forelimb asymmetry were used to determine the functional outcomes. Neuroimaging and histology were used to characterize the edema and BBB dysfunction. The study showed that DHA-treated TBI rats had better mNSS and forelimb asymmetry score than vehicle-treated TBI rats. Temporal analysis of edema using MRI revealed a significant reduction in edema level with DHA treatment compared to vehicle in TBI rats. Histological analysis using immunoglobulin G (IgG) extravasation showed that there was less extravasation, which corresponded with a reduction in aquaporin 4 and astrocytic metalloprotease 9 expression, and greater endothelial occludin expression in the peri-contusional site of the TBI rat brain treated with DHA in comparison to vehicle treatment. In conclusion, the study shows that DHA can exert its functional improvement by prevention of the edema formation via prevention of BBB dysfunction after TBI.

Effects of Hemodynamic Response Function Selection on Rat fMRI Statistical Analyses.

The selection of the appropriate hemodynamic response function (HRF) for signal modeling in functional magnetic resonance imaging (fMRI) is important. Although the use of the boxcar-shaped hemodynamic response function (BHRF) and canonical hemodynamic response (CHRF) has gained increasing popularity in rodent fMRI studies, whether the selected HRF affects the results of rodent fMRI has not been fully elucidated. Here we investigated the signal change and t-statistic sensitivities of BHRF, CHRF, and impulse response function (IRF). The effect of HRF selection on different tasks was analyzed by using data collected from two groups of rats receiving either 3 mA whisker pad or 3 mA forepaw electrical stimulations (n = 10 for each group). Under whisker pad stimulation with large blood-oxygen-level dependent (BOLD) signal change (4.31 ± 0.42%), BHRF significantly underestimated signal changes (P < 0.001) and t-statistics (P < 0.001) compared with CHRF or IRF. CHRF and IRF did not provide significantly different t-statistics (P > 0.05). Under forepaw stimulation with small BOLD signal change (1.71 ± 0.34%), different HRFs provided insignificantly different t-statistics (P > 0.05). Therefore, the selected HRF can influence data analysis in rodent fMRI experiments with large BOLD responses but not in those with small BOLD responses.

Diffusion-weighted MRI and 18F-FDG PET correlation with immunity in early radiotherapy response in BNL hepatocellular carcinoma mouse model: timeline validation.

PURPOSE: Imaging probes/biomarkers that are correlated with molecular or microenvironmental alterations in tumors have been used not only in diagnosing cancer but also in assessing the efficacy of cancer treatment. We evaluated the early response of hepatocellular carcinoma (HCC) to radiation treatment using T2-weighted magnetic resonance imaging (MRI), diffusion-weighted (DW) MRI, and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET). METHODS: Orthotopic HCC tumors were established in the right liver lobe of Balb/c mice. Mice were longitudinally scanned using T2-weighted/DW MRI and 18F-FDG PET 1 day before and on days 1, 3, 6, 9 and 13 after irradiation with 15 Gy to the right liver lobe to determine tumor size, apparent diffusion coefficient (ADC) value, and maximum standardized uptake value. Immunohistochemical (IHC) staining was performed to validate the tumor microenvironment. RESULTS: Irradiation markedly retarded tumor growth in the orthotopic HCC model and led to increaes in ADC values as early as on day 1 after irradiation. Irradiation also resulted in increases in 18F-FDG uptake on day 1 that were sustained until the end of the observation period. IHC staining revealed a decrease in the number of proliferative cells and a continuous macrophage influx into irradiated tumors, which dramatically altered the tumor microenvironment. Lastly, in vitro coculture of HCC cells and macrophages led to interaction between the cells and enhanced the cellular uptake of 18F-FDG. CONCLUSION: ADC values and 18F-FDG uptake measured using DW MRI and 18F-FDG PET serve as potential biomarkers for early assessment of HCC tumor responses to radiation therapy.

Heterogeneous Fenton Reaction Enabled Selective Colon Cancerous Cell Treatment.

A selective colon cancer cell therapy was effectively achieved with catalase-mediated intra-cellular heterogeneous Fenton reactions triggered by cellular uptake of SnFe2O4 nanocrystals. The treatment was proven effective for eradicating colon cancer cells, whereas was benign to normal colon cells, thus effectively realizing the selective colon cancer cell therapeutics. Cancer cells possess much higher innate hydrogen peroxide (H2O2) but much lower catalase levels than normal cells. Catalase, an effective H2O2 scavenger, prevented attacks on cells by reactive oxygen species induced from H2O2. The above intrinsic difference between cancer and normal cells was utilized to achieve selective colon cancer cell eradication through endocytosing efficient heterogeneous Fenton catalysts to trigger the formation of highly reactive oxygen species from H2O2. In this paper, SnFe2O4 nanocrystals, a newly noted outstanding paramagnetic heterogeneous Fenton catalyst, have been verified an effective selective colon cancerous cell treatment reagent of satisfactory blood compatibility.

Phase Contrast Magnetic Resonance Imaging in the Rat Common Carotid Artery.

Phase contrast magnetic resonance imaging (PC-MRI) is a noninvasive approach that can quantify flow-related parameters such as blood flow. Previous studies have shown that abnormal blood flow may be associated with systemic vascular risk. Thus, PC-MRI can facilitate the translation of data obtained from animal models of cardiovascular diseases to pertinent clinical investigations. In this report, we describe the procedure for measuring blood flow in the common carotid artery (CCA) of rats using cine-gated PC-MRI and discuss relevant analysis methods. This procedure can be performed in a live, anesthetized animal and does not require euthanasia after the procedure. The proposed scanning parameters yield repeatable measurements for blood flow, indicating excellent reproducibility of the results. The PC-MRI procedure described in this article can be used for pharmacological testing, pathophysiological assessment, and cerebral hemodynamics evaluation.

Early Imaging Biomarker of Myocardial Glucose Adaptations in High-Fat-Diet-Induced Insulin Resistance Model by Using 18F-FDG PET and [U-13C]glucose Nuclear Magnetic Resonance Tracer.

Background: High-fat diet (HFD) induces systemic insulin resistance leading to myocardial dysfunction. We aim to characterize the early adaptations of myocardial glucose utility to HFD-induced insulin resistance. Methods: Male Sprague-Dawley rats were assigned into two groups, fed a regular chow diet or HFD ad libitum for 10 weeks. We used in vivo imaging of cardiac magnetic resonance (CMR), 18F-FDG PET, and ex vivo nuclear magnetic resonance (NMR) metabolomic analysis for the carbon-13-labeled glucose ([U-13C]Glc) perfused myocardium. Results: As compared with controls, HFD rats had a higher ejection fraction and a smaller left ventricular end-systolic volume (P < 0.05), with SUVmax of myocardium on 18F-FDG PET significantly increased in 4 weeks (P < 0.005). The [U-13C]Glc probed the increased glucose uptake being metabolized into pyruvate and acetyl-CoA, undergoing oxidative phosphorylation via the tricarboxylic acid (TCA) cycle, and then synthesized into glutamic acid and glutamine, associated with overexpressed LC3B (P < 0.05). Conclusions: HFD-induced IR associated with increased glucose utility undergoing oxidative phosphorylation via the TCA cycle in the myocardium is supported by overexpression of glucose transporter, acetyl-CoA synthase. Noninvasive imaging biomarker has potentials in detecting the metabolic perturbations prior to the decline of the left ventricular function.

Optimized analysis of blood flow and wall shear stress in the common carotid artery of rat model by phase-contrast MRI.

The present study systemically investigated the influence of gated/non-gated sequences, velocity encoding (VENC), and spatial resolution on blood flow, wall shear stress (WSS), and artery area evaluations when scanning the common carotid artery (CCA) in rats using phase-contrast magnetic resonance imaging (PC-MRI). We first tested whether or not non-gated PC-MRI was appropriate for evaluating blood flow and WSS in rats. For both gated and non-gated techniques, VENC values in the range of 60-120 cm/s with an interval of 10 cm/s were also tested. Second, we optimized the in-plane resolution of PC-MRI for blood flow and WSS measurements. Results showed the usage of a gated instrument can provide more reproducible assessments, whereas VENC had an insignificant influence on all hemodynamic measurements (all P > 0.05). Lower resolutions, such as 0.63 mm, led to significant overestimations in blood flow and artery area quantifications and to an underestimation in WSS measurements (all P < 0.05). However, a higher resolution of 0.16 mm slightly increased measurement variation. As a tradeoff between accuracy and scan time, we propose a gated PC-MRI sequence with a VENC of 120 cm/s and a resolution of 0.21 mm to be used to extract hemodynamic information about rat CCA.

Catalase-Modulated Heterogeneous Fenton Reaction for Selective Cancer Cell Eradication: SnFe2O4 Nanocrystals as an Effective Reagent for Treating Lung Cancer Cells.

Heterogeneous Fenton reactions have been proven to be an effective and promising selective cancer cell treatment method. The key working mechanism for this method to achieve the critical therapeutic selectivity however remains unclear. In this study, we proposed and demonstrated for the first time the critical role played by catalase in realizing the therapeutic selectivity for the heterogeneous Fenton reaction-driven cancer cell treatment. The heterogeneous Fenton reaction, with the lattice ferric ions of the solid catalyst capable of converting H2O2 to highly reactive hydroxyl radicals, can effectively eradicate cancer cells. In this study, SnFe2O4 nanocrystals, a recently discovered outstanding heterogeneous Fenton catalyst, were applied for selective killing of lung cancer cells. The SnFe2O4 nanocrystals, internalized into the cancer cells, can effectively convert endogenous H2O2 into highly reactive hydroxyl radicals to invoke an intensive cytotoxic effect on the cancer cells. On the other hand, catalase, present at a significantly higher concentration in normal cells than in cancer cells, remarkably can impede the apoptotic cell death induced by the internalized SnFe2O4 nanocrystals. According to the results obtained from the in vitro cytotoxicity study, the relevant oxidative attacks were effectively suppressed by the presence of normal physiological levels of catalase. The SnFe2O4 nanocrystals were thus proved to effect apoptotic cancer cell death through the heterogeneous Fenton reaction and were benign to cells possessing normal physiological levels of catalase. The catalase modulation of the involved heterogeneous Fenton reaction plays the key role in achieving selective cancer cell eradication for the heterogeneous Fenton reaction-driven cancer cell treatment.

Fully Automated Quantification of the Striatal Uptake Ratio of [(99m)Tc]-TRODAT with SPECT Imaging: Evaluation of the Diagnostic Performance in Parkinson's Disease and the Temporal Regression of Striatal Tracer Uptake.

PURPOSE: We aimed at improving the existing methods for the fully automatic quantification of striatal uptake of [(99m)Tc]-TRODAT with SPECT imaging. PROCEDURES: A normal [(99m)Tc]-TRODAT template was first formed based on 28 healthy controls. Images from PD patients (n = 365) and nPD subjects (28 healthy controls and 33 essential tremor patients) were spatially normalized to the normal template. We performed an inverse transform on the predefined striatal and reference volumes of interest (VOIs) and applied the transformed VOIs to the original image data to calculate the striatal-to-reference ratio (SRR). The diagnostic performance of the SRR was determined through receiver operating characteristic (ROC) analysis. RESULTS: The SRR measured with our new and automatic method demonstrated excellent diagnostic performance with 92% sensitivity, 90% specificity, 92% accuracy, and an area under the curve (AUC) of 0.94. For the evaluation of the mean SRR and the clinical duration, a quadratic function fit the data with R (2) = 0.84. CONCLUSIONS: We developed and validated a fully automatic method for the quantification of the SRR in a large study sample. This method has an excellent diagnostic performance and exhibits a strong correlation between the mean SRR and the clinical duration in PD patients.

Baculovirus-transduced, VEGF-expressing adipose-derived stem cell sheet for the treatment of myocardium infarction.

Cell sheet technology has been widely employed for the treatment of myocardial infarction (MI), but cell sheet fabrication generally requires the use of thermo-responsive dishes. Here we developed a method for the preparation of adipose-derived stem cell (ASC) sheet that obviated the need of thermo-responsive dishes. This method only required the seeding of rabbit ASC onto 6-well plates at an appropriate cell density and culture in appropriate medium, and the cells were able to develop into ASC sheet in 2 days. The ASC sheet allowed for transduction with the hybrid baculovirus at efficiencies >97%, conferring robust and prolonged (>35 days) overexpression of vascular endothelial growth factor (VEGF). The ASC sheet was easily detached by brief (10 s) trypsinization and saline wash, while retaining the extracellular matrix and desired physical properties. The ASC sheet formation and VEGF expression promoted cell survival under hypoxia in vitro. Epicardial implantation of the VEGF-expressing ASC sheet to rabbit MI models reduced the infarct size and improved cardiac functions to non-diseased levels, as judged from the left ventrical ejection fraction/myocardial perfusion. The VEGF-expressing ASC sheet also effectively prevented myocardial wall thinning, suppressed myocardium fibrosis and enhanced blood vessel formation. These data implicated the potential of this method for the preparation of genetically engineered ASC sheet and future MI treatment.