Yasvir A. Tesiram

Early myocardial dysfunction in streptozotocin-induced diabetic mice: a study using in vivo magnetic resonance imaging (MRI)

BackgroundDiabetes is associated with a cardiomyopathy that is independent of coronary artery disease or hypertension. In the present study we used in vivo magnetic resonance imaging (MRI) and echocardiographic techniques to examine and characterize early changes in myocardial function in a mouse model of type 1 diabetes.MethodsDiabetes was induced in 8-week old C57BL/6 mice with two intraperitoneal injections of streptozotocin. The blood glucose levels were maintained at 19–25 mmol/l using intermittent low dosages of long acting insulin glargine. MRI and echocardiography were performed at 4 weeks of diabetes (age of 12 weeks) in diabetic mice and age-matched controls.ResultsAfter 4 weeks of hyperglycemia one marker of mitochondrial function, NADH oxidase activity, was decreased to 50% of control animals. MRI studies of diabetic mice at 4 weeks demonstrated significant deficits in myocardial morphology and functionality including: a decreased left ventricular (LV) wall thickness, an increased LV end-systolic diameter and volume, a diminished LV ejection fraction and cardiac output, a decreased LV circumferential shortening, and decreased LV peak ejection and filling rates. M-mode echocardiographic and Doppler flow studies of diabetic mice at 4 weeks showed a decreased wall thickening and increased E/A ratio, supporting both systolic and diastolic dysfunction.ConclusionOur study demonstrates that MRI interrogation can identify the onset of diabetic cardiomyopathy in mice with its impaired functional capacity and altered morphology. The MRI technique will lend itself to repetitive study of early changes in cardiac function in small animal models of diabetic cardiomyopathy.

Brain injury: neuro-inflammation, cognitive deficit, and magnetic resonance imaging in a model of blast induced traumatic brain injury

Blast wave-induced traumatic injury from terrorist explosive devices can occur at any time in either military or civilian environments. To date, little work has focused on the central nervous system response to a non-penetrating blast injury. We have evaluated the effect of a single 80-psi blast-overpressure wave in a rat model. Histological and immunochemical studies showed an early inflammatory response, tissue damage and the initiation of apoptosis. With regard to inflammation, polymorphonuclear leukocytes and lymphocytes infiltrated brain parenchyma within 1 h post-blast. Glial-fibrillary protein, cyclo-oxygenase-2ir, interleukin-1β and tumor necrosis factor were present by 1 h and remained detectable at three weeks post-injury. High mobility group box-1 protein was detectable at three weeks. With regard to tissue damage, S100β and 4-hydroxynonenal were present at 1 h and remained detectable at three weeks. Amyloid precursor protein was detectable at three weeks. As for apoptosis, Cleaved Caspase-3 was detectable at three weeks. Morris water maze assessment of cognitive function showed that blast injured animals required significantly more time to reach the platform on day 1 of training and traveled a greater distance to get to the platform on days 1 and 2. Blast-injured animals showed a significant increase in swimming speed (p<0.001), increased total distance traveled (p<0.001) and increased number of entries into the previous quadrant that had contained the escape platform (p<0.05). Magnetic resonance imaging showed hyperintense regions in the somatosensory area within 1 h. T2 relaxation times and apparent diffusion coefficients show increasing trends in both somatosensory and cortical regions. These data indicate an early and lasting response of brain tissue to non-penetrating blast over-pressure injury. This early inflammatory response is indicative of a mild traumatic brain injury. There is evidence of early hippocampal dysfunction.

In vivo detection of c-Met expression in a rat C6 glioma model

The tyrosine kinase receptor, c‐Met, and its substrate, the hepatocyte growth factor (HGF), are implicated in the malignant progression of glioblastomas. In vivo detection of c‐Met expression may be helpful in the diagnosis of malignant tumours. The C6 rat glioma model is a widely used intracranial brain tumour model used to study gliomas experimentally. We used a magnetic resonance imaging (MRI) molecular targeting agent to specifically tag the cell surface receptor, c‐Met, with an anti‐c‐Met antibody (Ab) linked to biotinylated Gd (gadolinium)‐DTPA (diethylene triamine penta acetic acid)‐albumin in rat gliomas to detect overexpression of this antigen in vivo. The anti‐c‐Met probe (anti‐c‐Met‐Gd‐DTPA‐albumin) was administered intravenously, and as determined by an increase in MRI signal intensity and a corresponding decrease in regional T1 relaxation values, this probe was found to detect increased expression of c‐Met protein levels in C6 gliomas. In addition, specificity for the binding of the anti‐c‐Met contrast agent was determined by using fluorescence microscopic imaging of the biotinylated portion of the targeting agent within neoplastic and ‘normal’brain tissues following in vivo administration of the anti‐c‐Met probe. Controls with no Ab or with a normal rat IgG attached to the contrast agent component indicated no non‐specific binding to glioma tissue. This is the first successful visualization of in vivo overexpression of c‐Met in gliomas.

Hippocampal T2 signal change during amygdala kindling epileptogenesis.

Summary:  Purpose: The rat electrical amygdala kindling model is one of the most widely studied animal models of temporal lobe epilepsy (TLE); however, the processes underlying epileptogenesis in this model remain incompletely understood. Magnetic resonance imaging (MRI) is a powerful method to investigate epileptogenesis, allowing serial imaging of associated structural and functional changes in vivo. Here we report on the results of serial MRI acquisitions during epileptogenesis in this model.

Non-mammalian fat-1 gene prevents neoplasia when introduced to a mouse hepatocarcinogenesis model Omega-3 fatty acids prevent liver neoplasia

We investigated the effect of a non-mammalian omega-3 desaturase in a mouse hepatocarcinogenesis model. Mice containing double mutations (DM) in c-myc and TGF-alpha (transforming growth factor-alpha), leading to liver neoplasia, were crossed with mice containing omega-3 desaturase. MRI analysis of triple mutant (TM) mice showed the absence of neoplasia at all time points for 92% of mice in the study. Pathological changes of TM (TGFalpha/c-myc/fat-1) mouse liver tissue was similar to control mouse liver tissue. Magnetic resonance spectroscopy (MRS) measurements of unsaturated fatty acids found a significant difference (p<0.005) between DM and TM transgenic (Tg) mice at 34 and 40 weeks of age. HPLC analysis of mouse liver tissue revealed markedly decreased levels of omega-6 fatty acids in TM mice when compared to DM (TGFalpha/c-myc) and control (CD1) mice. Mass spectrometry (MS) analysis indicated significantly decreased 16:0/20:4 and 18:1/20:4 and elevated 16:0/22:6 fatty acyl groups in both GPCho and GPEtn, and elevated 16:0/20:5, 18:0/18:2, 18:0/18:1 and 18:0/22:6 in GPCho, within TM mice compared to DM mice. Total fatty acid analysis indicated a significant decrease in 18:1n9 in TM mice compared to DM mice. Western blot analysis of liver tissue showed a significant (p<0.05) decrease in NF-kappaB (nuclear factor-kappaB) levels at 40 weeks of age in TM mice compared to DM mice. Microarray analysis of TM versus DM mice livers at 40 weeks revealed alterations in genes involved in cell cycle regulation, cell-to-cell signaling, p53 signaling, and arachidonic acid (20:4) metabolism. Endogenous omega-3 fatty acids were found to prevent HCC development in mice.

Visualization of the protective ability of a free radical trapping compound against rat C6 and F98 gliomas with diffusion tensor fiber tractography

To apply fiber tractography to assess the effect of a possible antiglioma drug, phenyl N‐tert‐butyl nitrone (PBN), on glioma‐affected neuronal fibers. The fiber tractography method was able to differentiate between different tumor types, such as the C6 and F98 rat glioma models.

In vivo MRS assessment of altered fatty acyl unsaturation in liver tumor formation of a TGFα/c-myc transgenic mouse model

Current detection methods (computed tomography, ultrasound, and MRI) for hepatocarcinogenesis in humans rely on visual confirmation of neoplastic formations. A more effective early detection method is needed. Using in vivo magnetic resonance spectroscopy (MRS), we show that alterations in the integral ratios of the bis-allyl to vinyl hydrogen protons in unsaturated lipid fatty acyl groups correlate with the development of neoplastic formations in vivo in a TGFalpha/c-myc mouse hepatocellular carcinoma (HCC) model. HPLC analysis of the TGFalpha/c-myc mice liver tissue revealed a significant increase in the amount of oleic acid, along with alterations in linoleic and gamma-linolenic acids, as compared with control CD1 mice. Electrospray ionization tandem mass spectrometry analysis indicated a significant increase in the abundance of specific glycerol phosphatidylcholine (GPCho) lipids containing palmitic and oleic acids between control CD1 and TGFalpha/c-myc mice liver tissue extracts. Western blot analysis of the mice liver tissue indicates alterations in the desaturase enzyme stearoyl CoA desaturase (SCD)1, responsible for palmitic and oleic acid formation. Microarray analysis detected alterations in several genes involved with fatty acid metabolism, particularly SCD2, in transgenic mouse liver tissue. In correlation with the HPLC, mass spectrometry, Western blot, and microarray analyses, we are able to confirm the ability of in vivo MRS to detect precancerous lesions in the mouse liver before visual neoplastic formations were detectable by MRI.

Magnetic resonance imaging guidance for laser photothermal therapy.

Temperature distribution is a crucial factor in determining the outcome of laser phototherapy in cancer treatment. Magnetic resonance imaging (MRI) is an ideal method for 3-D noninvasive temperature measurement. A 7.1-T MRI was used to determine laser-induced high thermal gradient temperature distribution of target tissue with high spatial resolution. Using a proton density phase shift method, thermal mapping is validated for in vivo thermal measurement with light-absorbing enhancement dye. Tissue-simulating phantom gels, biological tissues, and tumor-bearing animals were used in the experiments. An 805-nm laser was used to irradiate the samples, with laser power in the range of 1 to 3 W. A clear temperature distribution matrix within the target and surrounding tissue was obtained with a specially developed processing algorithm. The temperature mapping showed that the selective laser photothermal effect could result in temperature elevation in a range of 10 to 45 degrees C. The temperature resolution of the measurement was about 0.37 degrees C with 0.4-mm spatial resolution. The results of this study provide in vivo thermal information and future reference for optimizing laser dosage and dye concentration in cancer treatment.

Utility of nuclear magnetic resonance spectroscopy for pancreatic cancer studies

Objectives The aims of this study were (1) to determine nuclear magnetic resonance spectroscopic characteristics and metabolite profiles of serum samples from patients with pancreatic cancer compared with noncancerous control samples and (2) to ascertain if the accuracy of metabolite identification by 1D spectra can be improved upon by confirmation of spin-system assignment using more sophisticated experiments. Methods Nuclear magnetic resonance spectra, including 1D, total correlation spectroscopy, and heteronuclear multiple/single quantum coherence, were obtained from serum samples from patients with pancreatic cancer and control subjects and used to determine serum levels of a range of metabolites. Results The data show that total choline (P = 0.03), taurine (P = 0.03), and glucose plus triglycerides (P = 0.01) are significantly higher in cancer versus control samples. Also detected were species that could not be individually identified and that were designated UCM (unresolved complex matter). Levels of UCM are significantly higher in subjects with cancer, being almost double those of control samples. Conclusions Although metabolites such as lactate, taurine, glucose, choline, and triglycerides can be determined from 1D spectra, accuracy is improved by confirmation of spin-system assignment with total correlation spectroscopy and heteronuclear multiple/single quantum coherence spectral analysis. In addition, we introduce a new metric, UCM, which is at higher concentrations in cancer compared with control samples.

Diffusion tensor imaging and fiber tractography of C6 rat glioma

To apply diffusion tensor images using 30 noncollinear directions for diffusion‐weighted gradient schemes to characterize diffusion tensor imaging (DTI) features associated with C6 glioma‐bearing rat brains, and ideally visualize fiber tractography datasets.