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

Background

Diabetes 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.

Methods

Diabetes 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.

Results

After 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.

Conclusion

Our 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.

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.

In vivo detection of c-MET expression in a rat hepatocarcinogenesis model using molecularly targeted magnetic resonance imaging

The multifunctional growth factor scatter factor/hepatocyte growth factor and its tyrosine kinase receptor, c-MET, have been implicated in the genesis and malignant progression of numerous human malignancies, including hepatocellular carcinomas. The incidence of hepatocellular carcinomas in the United States has increased noticeably over the past two decades and is listed as the fifth major cancer in men worldwide. In this study, we used a choline-deficient l-amino acid (CDAA)-defined rat hepatocarcinogenesis model to visualize increased in vivo expression of the c-MET antigen in neoplastic lesion formation with the use of a super paramagnetic iron oxide (SPIO)-anti-c-MET molecularly targeted magnetic resonance imaging (MRI) contrast agent. SPIO-anti-c-MET was used for the first time to detect overexpression of c-MET in neoplastic nodules and tumors within the livers of CDAA-treated rats, as determined by a decrease in MRI signal intensity and a decrease in regional T(2) values. Specificity for the binding of the molecularly targeted anti-c-MET contrast agent was determined using rat hepatoma (H4-II-E-C3) cell cultures and immunofluorescence microscopic imaging of the targeting agents within neoplastic liver tissue 1 to 2 hours following intravenous administration of SPIO-anti-c-MET and MRI investigation. This method has the ability to visualize in vivo the overexpression of c-MET at early developmental stages of tumor formation.

LINE-1 hypomethylation in a choline-deficiency-induced liver cancer in rats: dependence on feeding period

Chronic feeding of methyl-donor (methionine, choline, folic acid, and vitamin B12) deficient diet induces hepatocellular carcinoma formation in rats. Previous studies have shown that promoter CpG islands in various cancer-related genes are aberrantly methylated in this model. Moreover, the global genome in methyl-donor-deficient diet fed rats contains a lesser amount of 5-methylcytosine than control livers. It is speculated that more than 90% of all 5-methylcytosines lie within the CpG islands of the transposons, including the long/short interspersed nucleotide elements (LINE and SINE). It is considered that the 5-methylcytosines in LINE-1 limit the ability of retrotransposons to be activated and transcribed; therefore, the extent of hypomethylation of LINE-1 could be a surrogate marker for aberrant methylation in other tumor-related genes as well as genome instability. Additionally, LINE-1 methylation status has been shown to be a good indicator of genome-wide methylation. In this study, we determined cytosine methylation status in the LINE-1 repetitive sequences of rats fed a choline-deficient (CD) diet for various durations and compared these with rats fed a choline-sufficient (CS) diet. The methylation status of LINE-1 was assessed by the combined bisulfite restriction analysis (COBRA) method, where the amount of bisulfite-modified and RsaI-cleaved DNA was quantified using gel electrophoresis. Progressive hypomethylation was observed in LINE-1 of CD livers as a function of feeding time; that is, the amount of cytosine in total cytosine (methylated and unmethylated) increased from 11.1% (1 week) to 19.3% (56 weeks), whereas in the control CS livers, it increased from 9.2% to 12.9%. Hypomethylation in tumor tissues was slightly higher (6%) than the nontumorous surrounding tissue. The present result also indicates that age is a factor influencing the extent of cytosine methylation.

Application of proton NMR spectroscopy in the study of lipid metabolites in a rat hepatocarcinogenesis model

Liver cancer is one of the most common cancers worldwide. Altered lipid metabolism in the liver is a key feature of developing liver nodules and tumors. Methods of analysis vary from the most sophisticated chromatography to the in vivo nuclear magnetic resonance (NMR) spectroscopy. In this study, we present a systematic method for the identification and quantitation of signature signals from lipid metabolites using 1D NMR proton spectroscopy. We assessed lipid metabolites in an epigenetic rat hepatocarcinogenesis model induced by treatment with a choline-deficient diet (CDAA, choline-deficient l-amino acid defined) over a period of 1 year, from the formation of steatosis, to the development of nodules and adenomas. A comparable choline-sufficient (CSAA) diet was used for the controls. The resonances of the methylene protons of the glycerol backbone in phospholipids were used to quantify the total concentration of such compounds. CDAA rat livers were found to have significantly higher levels of phospholipids, when compared to CSAA, throughout the entire carcinogenesis period. The tri-methyl protons of choline compounds serves to quantify total choline, and the vinyl and bis-allyl proton resonances can be used to not only quantify fatty acid concentrations but also to probe the number of double bonds in a fatty acid moiety. Early stages of carcinogenesis indicate a lower degree of double bonds in fatty acyl containing compounds in CDAA rat livers, when compared to CSAA. The results of this study are in agreement with those previously published in the literature on other rat hepatocarcinogenesis models.

In vivo identification of aflatoxin-induced free radicals in rat bile

Aflatoxin B1 (AFB1) is a potent hepatocarcinogen. We have recently detected [via electron spin resonance (ESR) spectroscopy] free radicals in vivo in rat bile following AFB1 metabolism using the spin trapping [alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone (4-POBN)] technique. The aim of the present study was to identify the trapped free radical intermediates from the in vivo hepatic metabolism of AFB1. Rats were treated simultaneously with AFB1 (3 mg/kg i.p.) and the spin trapping agent 4-POBN (1 g/kg i.p.), and bile was collected over a period of 1 h at 20 min intervals. On-line high performance liquid chromatography (HPLC) coupled to ESR was used to identify an arachidonic acid-derived radical adduct of 4-POBN in rat bile, and a methyl adduct of 4-POBN from the reaction of hydroxyl radicals with carbon-13-labeled dimethyl sulfoxide ((13)C-DMSO). The effect of metabolic inhibitors, such as desferoxamine mesylate (DFO), an iron chelator, 2-dimethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF) 525A, a cytochrome P-450 inhibitor, and gadolinium chloride (GdCl(3)), a Kupffer cell inactivator, on in vivo aflatoxin-induced free radical formation were also studied. It was found that there was a significant decrease in radical formation as a result of DFO, SKF525A and GdCl(3) inhibition. Trapped 4-POBN radical adducts were also detected in rat bile following the in vivo metabolism of aflatoxin-M1, one of the hydroxylated metabolites of AFB1.

In vivo detection of aflatoxin-induced lipid free radicals in rat bile

Aflatoxin B1 (AFB1), a potent hepatotoxin and hepatocarcinogen, is metabolized in the liver via cytochrome P-450 to an AFB1-8,9-epoxide intermediate. The formation of the AFB1-8,9-epoxide correlates with the pathological changes observed in numerous mammalian species. Oxidative damage has been postulated to play a major role in the mechanisms associated with AFB1-induced cytotoxicity and carcinogenecity in mammalian species. The aim of this study was to detect and identify free radical intermediates from the hepatic metabolism of AFB1 in vivo. Rat bile ducts were cannulated and rats were treated simultaneously with AFB1 (3 mg/kg i.p.) and the spin trapping agent 4-POBN (alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone) (1 g/kg i.p.), and bile was collected over a period of 2 h at 20-min intervals. ESR spectroscopy was used to detect a carbon-centered radical adduct of 4-POBN in rat bile. The effect of metabolic inhibitors, such as deferoxamine mesylate (DFO), an iron chelator, and SKF 525A, a cytochrome P-450 inhibitor, on in vivo aflatoxin-induced free radical formation were also studied. It was found that there was a significant decrease in free radical formation by pre-treatment with both DFO and SKF 525A. This indicates that oxidation of AFB1 generates free radical species via CYP metabolism and an iron-mediated redox mechanism.

In vivo assessment of nodularin-induced hepatotoxicity in the rat using magnetic resonance techniques (MRI, MRS and EPR oximetry)

Acute nodularin-induced hepatotoxicity was assessed in vivo, in rats using magnetic resonance (MR) techniques, including MR imaging (MRI), MR spectroscopy (MRS), and electron paramagnetic resonance (EPR) oximetry. Nodularin is a cyclic hepatotoxin isolated from the cyanobacterium Nodularia spumigena. Three hours following the intraperitoneal (i.p.) administration of nodularin (LD50), a region of 'damage', characterized by an increase in signal intensity, was observed proximal to the porta hepatis (PH) region in T2-weighted MR images of rat liver. Image analysis of these regions of apparent 'damage' indicated a statistically significant increase in signal intensity around the PH region following nodularin administration, in comparison with controls and regions peripheral to the PH region. An increase in signal intensity was also observed proximal to the PH region in water chemical shift selective images (CSSI) of nodularin-treated rat livers, indicating that the increased signal observed by MRI is an oedematous response to the toxin. Microscopic assessment (histology and electron microscopy) and serum liver enzyme function tests (aminotransferase (ALT) and aspartate ALT (AST)) confirmed the nodularin-induced tissue injury observed by MRI. In vivo and in vitro MRS was used to detect alterations in metabolites, such as lipids, Glu+Gln, and choline, during the hepatotoxic response (2-3 h post-exposure). Biochemical assessment of perchloric acid extracts of nodularin-treated rat livers were used to confirm the MRS results. In vivo EPR oximetry was used to monitor decreasing hepatic pO2 (approximately 2-fold from controls) 2-3 h following nodularin exposure. In vivo MR techniques (MRI, MRS and EPR oximetry) are able to highlight effects that may not have been evident in single end point studies, and are ideal methods to follow tissue injury progression in longitudinally, increasing the power of a study through repeated measures, and decreasing the number of animals to perform a similar study using histological or biochemical techniques.

Assessment of in vivo oxidative lipid metabolism following acute microcystin-LR-induced hepatotoxicity in rats

Oxidative lipid metabolism as a result of acute cyanobacterial toxin-induced hepatotoxicity was monitored in male Sprague-Dawley rats using electron spin resonance (ESR) spectroscopy and image-guided proton nuclear magnetic resonance (1H-NMR) spectroscopy. ESR spectroscopy, coupled with spin trapping, was used to trap and detect lipid-derived radicals, formed in rat livers after acute in vivo exposure (LD50) to the cyanobacterial toxin, microcystin-LR (MCLR). A statistically significant increase in the levels (spectral peak integrals) of lipid radicals was detected in MCLR-treated livers (p < 0.05) (n = 8), in comparison to control livers (n = 6). In order to monitor lipid metabolism, before and for a period of 3 h, following toxin exposure, in vivo proton image-guided NMR spectroscopy was used. A statistically significant decrease in the levels of lipid methylene hydrogen resonances (spectral peak integrals) was observed from MCLR-treated livers (n = 6) 2 and 3 h post-exposure (p < 0.05), in comparison to controls (n = 6). Image-guided NMR spectroscopy was also used to detect significant decreasing levels of in vivo glutamine/glutamate, following exposure to MCLR. Biochemical assessment of perchloric extracts of liver glutamine and glutamate levels correlated with NMR spectroscopy results. Lactate levels measured as perchloric acid extracts, were also found to significantly decrease. In addition, assessment of serum enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were used to confirm hepatotoxicity (n = 20). This study strongly suggests that oxidative stress related processes are involved in in vivo microcystin-induced hepatotoxicity in mammals, and may play an integral role in MCLR-induced toxicity.

Magnetic resonance imaging of pulmonary damage in the term and premature rat neonate exposed to hyperoxia

Immaturity and oxygen toxicity have been implicated in the pathogenesis of the neonatal disease bronchopulmonary dysplasia. The present study aimed to investigate the use of magnetic resonance imaging (MRI) to assess hyperoxia-mediated lung injury in the term and premature neonate. Term (gestation, 22 d) and premature (21 d) rat pups were exposed to hyperoxia (>95%) or air for a 6-d period (n = 7) and assessed for lung damage by MRI. Pulmonary signal intensities of T1-weighted images were significantly increased in both hyperoxia-exposed term and premature neonates, relative to air-breathing controls (p < 0.01). T2-weighted MRI signal intensities were also greater in premature and term rat pups exposed to hyperoxia, but failed to reach significance (p > 0.05). Elevated MRI pulmonary signal intensities may have represented an increase in magnetic resonance-detectable free water, possibly indicating an increase in edema. Corresponding histologic evidence of lung injury was detected in both term and premature rat pups exposed to hyperoxia. Histologic samples indicated focal regions of alveolar hemorrhage, immune cell infiltration, edema, and collapse in both term and premature rat neonates exposed to hyperoxia. Alveolar air space was assessed (n = 5) by light microscopy within a 0.5 mm2 region of the superior left and inferior right pulmonary lobes of each treatment group. Alveolar area of the superior left lung lobe of the premature hyperoxia treatment group was significantly smaller than other treatment groups (p < 0.05). Reduced area for respiratory exchange was probably a result of observed focal areas of edema and collapse. MRI-detectable increases in lung signal intensity may have represented an increase in hyperoxia-induced pulmonary edema in the 6-d-old rat neonate. Increases in signal intensity correlated with the appearance of edema in pulmonary histologic samples. Premature delivery had a less defined effect on lung injury but possibly exacerbated hyperoxia-mediated pulmonary damage.

In vivo image-guided (1)H-magnetic resonance spectroscopy of the serial development of hepatocarcinogenesis in an experimental animal model

Histology on a core or open biopsy is considered the gold standard for the diagnosis of tumours. While the non-invasive technique of magnetic resonance imaging can direct some of the decision diagnostic making, it has limitations and disadvantages, that can be partly overcome with the use of in vivo magnetic resonance spectroscopy (MRS). In vivo MRS is able to provide a specific biochemical profile on tumour tissue, compared with normal tissue. The capability of this technique is demonstrated here by the long-term development of hepatocellular carcinoma in an animal model. It allows the observation of the biochemical changes that occur in tumour tissue during its progression from preneoplastic nodules to hepatocellular carcinoma. Specifically the changes in the lipid profiles of tumour tissue at various stages of development are observed with proton ((1)H) MRS. Significant increases occurred in the lipid acyl chain methylene and methyl hydrogens during the early developmental stages of hepatocarcinogenesis, whereas during later stages associated with tumour development there was a significant increase in the levels of olefinic acyl chain hydrogens from unsaturated lipids. It is anticipated that this model will precede the application of the same technology to the non-invasive diagnosis and grading of human hepatocellular carcinoma.

Non-invasive in vivo magnetic resonance imaging assessment of acute aflatoxin B1 hepatotoxicity in rats

Acute aflatoxin B1 (AFB1)-induced hepatotoxicity was assessed in vivo in male Sprague-Dawley rats (150-300 g) using magnetic resonance imaging (MRI). MRI results were compared to serum enzyme levels, histology and electron microscopy. Twenty-four hours following intraperitoneal delivery of AFB1 (3 mg/kg body weight in a saline/dimethyl sulfoxide (DMSO; 0.03 ml/kg body weight) solution), regions of damage, characterised by increased proton signal intensities in T2-weighted images, were observed in the vicinity of the hepatic portal vein (HPV) and in the right medial regions of the liver. Image analysis of regions of apparent damage around the HPV and right medial regions, following 24 h of AFB1 exposure, indicated statistically significant (P<0.05) increases in proton image signal intensities, when compared to saline/DMSO-treated rats. No significant difference in proton image signal intensities were observed 1-2 h following AFB1 exposure. Twenty-four hours following AFB1 exposure, histopathological assessment was characterised by portal/central vein/artery congestion, sinusoid congestion, nuclear pyknosis and karyolysis, and hepatocyte vacuolation; electron microscopy (EM) examination indicated nuclear debris, swollen cytoplasmic compartments, vacuolation, and the disappearance of the smooth endoplasmic reticulum, and elevated levels of serum aspartate aminotransferase and alanine aminotransferase were found to be significantly different (P<0.01) than controls.

In vivo assessment of microcystin-LR-induced hepatotoxicity in the rat using proton nuclear magnetic resonance (1H-NMR) imaging

Microcystin-LR (MCLR)-induced hepatotoxicity was assessed in vivo in male Sprague-Dawley rats (150-350 g) using magnetic resonance imaging (MRI). Following the intraperitoneal administration of MCLR (LD(50)), a region of damage, characterised by increased signal intensity on T(2)-weighted images, was seen proximal to the hepatic portal vein in the liver. Similarly, increased signal intensity was seen in the chemical-shift selective images (CSSI) of water frequency, proximal to the hepatic portal vein in the liver. This indicates that the increased signal intensity observed in the T(2)-weighted images was due to an increased amount of magnetic resonance (MR) visible protons in the tissue which represents an oedematous response. Image analysis of regions of apparent damage around the hepatic portal vein indicated a statistically significant increase in signal intensity in this region. Mitochondrial swelling and lipid inclusions were observed by transmission electron microscopy (TEM) in samples obtained from the oedematous regions of the liver using spatial coordinates from the magnetic resonance (MR) images. Massive haemorrhagic necrosis and nuclear swelling were observed by light microscopy in the centrilobular regions of the lobules.

In vivo study of halothane hepatotoxicity in the rat using magnetic resonance imaging and 31P spectroscopy

Using magnetic resonance imaging (MRI) and spectroscopy (MRS), in vivo halothane hepatotoxicity was assessed in male Wistar rats. With 1.5% halothane in 100 or 20% O2, an edematous region, characterized by increased intensity on T2 weighted images and an increase in regional tissue water content (rho water), was seen proximal to the hepatic portal vein in the liver. Both spin-lattice relaxation (T1) and spin-spin relaxation (T2) increased in this region, relative to distal regions of the liver. Similarly, a high signal intensity on proton density weighted images was observed in this area. As halothane anaesthesia progressed, a decrease in the adenosine triphosphate-inorganic phosphate ratio (ATP/Pi) and an increase in the phosphomonoester-phosphodiester (PME/PDE) ratio was detected in the liver. In addition, intracellular pH decreased and intracellular free magnesium concentration [Mg2+] increased with time of exposure. Excessive vacuolation, ribosomal disappearance from rough endoplasmic reticulum, mitochondrial swelling and fragmentation of smooth endoplasmic reticulum were observed by transmission electron microscopy (TEM) in samples from the edematous region of the liver.

Detection of hydroxyl and carbon-centred radicals by EPR spectroscopy after ischaemia and reperfusion of the rat kidney

Recent studies suggest that oxygen-derived free radicals are involved in mediating renal reperfusion injury. EPR spectroscopy and spin trapping with the spin traps DMPO and PBN, were used to detect and quantitate the formation of hydroxyl radicals in rat kidney after ischaemia-reperfusion in vivo and in vitro in the isolated rat kidney perfused in the absence of leucocytes. EPR analysis of homogenised kidneys and of venous samples did not detect radical adducts with either spin trap. With PBN, radical adducts were not detected in vitro. When DMPO was used as the spin trap in kidneys perfused without albumin in the perfusate, EPR signals characteristic of hydroxyl and carbon-centred radical adducts were detected during early reperfusion following ischaemia. These studies confirm the generation of hydroxyl radicals during ischaemia-reperfusion in kidney. During reperfusion the total DMPO adduct concentration reached 4.35 +/- 1.05 nmol/g kidney/3 min, p < 0.05. In control kidneys total adduct were present at lower concentration (2.55 +/- 1.1 nmol/g kidney/3 min). Addition of 15 mM dimethylthiourea abolished formation of these adducts following ischaemia-reperfusion but did not prevent a reduction in glomerular filtration rate. These results indicate that significant levels of hydroxyl and carbon-centred radicals are formed in the absence of circulating neutrophils during early renal reperfusion following ischaemia.

Hydroxyl radical generation following ischaemia-reperfusion in cell-free perfused rat kidney

The difficulty in direct detection of oxygen-derived free radicals (OFR) in the intact kidney has left uncertain the role of OFR in renal hypoperfusion injury. Salicylate hydroxylation was used as a sensitive method of estimating the extent of production of highly reactive hydroxyl radicals in renal ischaemia-reperfusion injury in the intact rat kidney perfused with recirculating cell-free medium. The reaction products were detected and quantified by HPLC with electrochemical detection. Hydroxyl radicals were detected as 2,5-dihydroxybenzoic acid (2,5-DHBA). Ischaemia for 15 min followed by reperfusion for 15 min caused more than a twofold increase in 2,5-DHBA concentration (to 2279 +/- 225 pg/g tissue weight) compared to controls (933 +/- 103, P < 0.001). Addition of 15 mM dimethylthiourea (DMTU) before induction of ischaemia prevented this increase. Induction of hypoxia for 15 min with continued perfusion (as a model of low-flow ischaemia) had no significant effect on hydroxyl radical formation. We conclude that significant quantities of hydroxyl radicals form in the absence of circulating leucocytes during reperfusion following ischaemia, but not during hypoxia in the perfused rat kidney.

Diagnosis of persistent intestinal ischemia in the rabbit using proton magnetic resonance imaging

Noninvasive diagnosis of persistent intestinal ischemia remains an elusive goal. Magnetic resonance imaging (MRI) recognizes changes in tissue water content, and several authors have demonstrated increased intensity within 6 hours of intestinal ischemia. To simulate the clinical situation more closely, we studied the efficacy of MRI in differentiating ischemic from viable segments of bowel 24 hours after injury in a rabbit model. A segment of distal ileum was rendered ischemic by vascular isolation and ligation. Controls underwent sham operation without vascular ligation. After 24 hours, multislice transverse scans were done using both T1 and T2 weighting. Image intensity was calculated from the isolated loop (absolute intensity), and paraspinal muscle intensity was used as an internal standard to calculate relative intensity (isolated bowel/paraspinal muscle). Animals were killed and bowel necrosis was confirmed histologically. Both absolute and relative intensity were significantly higher in animals undergoing persistent intestinal ischemia. This was true using both T1 and T2 weighting. In a further group of rabbits using the same model, intensity was calculated both before and after intravenous gadolinium. No significant difference was seen between sham and ischemic animals. Our data show that (1) MRI can differentiate ischemic from viable bowel 24 hours after ischemic injury, and (2) the use of intravenous contrast does not improve accuracy. We conclude that MRI may represent a useful noninvasive technique for the diagnosis of persistent intestinal ischemia and that clinical studies should be initiated.

Influences of dietary deoxycholic acid on progression of hepatocellular neoplasms and expression of glutathione S-transferases in rats

Serial magnetic resonance imaging (MRI) was used to evaluate the influences of dietary deoxycholic acid (DCA) on the rate of progression of chemically induced hepatocellular neoplasms in rats. Male Fischer-344 rats with established persistent hepatocellular nodules generated by the Solt-Farber protocol were exposed to dietary DCA (0.3%) between 6 and 12 mo of age. Growth of nodules and carcinomas in vivo was measured by morphometric quantification of tumor images obtained every 6 wk. The final stages of neoplastic progression were determined by terminal histopathological examination and by expression and functional evaluation of glutathione S-transferase (GST) isoenzyme phenotypes. Dietary DCA increased the number of hepatocellular neoplasms per rat, accelerated the rate of growth of persistent nodules, and increased the histological progression of liver tumors. Expression of immunoreactive GST subunits Yf, Ya, and Yb1 was induced in early persistent nodules, a pattern that was maintained throughout the study in both basal diet and DCA-fed groups. However, 5% of early nodules and about 75% of advanced neoplasms were partially or completely deficient in GST Yb2 expression in both groups. DCA did not alter the cytosolic activity for the GST substrates 1-chloro-2,4-dinitrobenzene (CDNB) or trans-4-phenyl-3-buten-2-one (tPBO) in tumors or surrounding liver. However, in both groups, CDNB activity was increased in the tumors relative to the surrounding nonneoplastic tissue, whereas activity for tPBO, a substrate more specific for the Yb2 subunit, was reduced in the tumors. All advanced neoplasms were similarly more resistant than surrounding liver to DNA-binding metabolites of aflatoxin B1 or benzo[a]pyrene. These data demonstrate that DCA can increase the progression of established hepatocellular nodules to larger, more advanced neoplasms but does not preferentially select for a specific GST phenotype. Preferential loss of constitutively expressed GST Yb2 in both basal diet and DCA-fed groups may be an important aspect of progression from resistant nodules to advanced cancers in this model. These studies also demonstrate that serial MRI is a useful tool for measuring the rates of enlargement and patterns of growth in established hepatocellular neoplasms.

In vivo magnetic resonance imaging study of Kupffer cell involvement in CCl4-induced hepatotoxicity in rats

When carbon tetrachloride (CCl4) was administered to rats, a localized region of hepatic edema could be detected within 1 h by in vivo proton magnetic resonance imaging. However, if rats were pretreated with gadolinium chloride (GdCl3), an inhibitor of Kupffer cell function, the CCl4-induced edema was greatly decreased. Methyl palmitate, another Kupffer cell inhibitor, also decreased the degree of edema caused by the administration of CCl4. Electron micrographs of samples that were taken from regions of the liver where the edema was localized indicated formation of vacuoles and lipid droplets in parenchymal cells and enlargement of Kupffer cells, which exhibited numerous phagosomes and extensive pseudopod formation. These electron micrograph changes were also attenuated by pretreatment of the rats with GdCl3 and methyl palmitate. In vivo spin trapping and electron paramagnetic resonance experiments indicated that GdCl3 did not affect the metabolism of CCl4 to the trichloromethyl radical. The data in this report suggest that localized hepatic edema which occurs soon after administration of CCl4 involves activation of Kupffer cells, and that trichloromethyl radical production may be a separate but related process occurring in parenchymal cells. These observations support reports from other laboratories that Kupffer cells may be involved in CCl4-induced hepatotoxicity.

The use of in vivo magnetic resonance imaging and spectroscopy to study porcine stress syndrome in young, halothane-susceptible pigs: Preliminary results

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) studies on young, halothane-susceptible pigs (4 wk old) are reported. The proton image shows distinct changes in shape of the hindleg muscle as the stress syndrome develops. Simultaneous evaluations of the "free water" content by volume selective spectroscopy shows an increase of about 40% after onset of the syndrome. The in vivo phosphorus spectrum obtained as a function of time before and after the stress event clearly shows a drop in phosphocreatine with simultaneous increase in inorganic phosphate. A drop in pH can also be detected after some delay. This study illustrates the broad applicability of noninvasive MRI and MRS in investigations of porcine stress syndrome. Key words: PSS, porcine stress syndrome, MRI, magnetic resonance imaging, 31P MRS, phosphorus-31 magnetic resonance spectroscopy

Use of nitroxides as MRI contrast agents to study in vivo carbon tetrachloride induced hepatotoxicity in rats

CCl4 and related compounds, such as halothane, are metabolized by the liver to form free radical intermediates, which are thought to be implicated in the hepatotoxic response. Two to three hours following CCl4 exposure (i.p.) there is a localized edematous region surrounding the portal vein which is observable by proton MRI in vivo. Enhancement of the CCl4-induced edematous region was possible using Gd-DTPA, a paramagnetic contrast agent. However, with the use of a nitroxide contrast agent (3-PCA) there was no enhancement, but rather a significant diminution of the CCl4-induced edematous response. These results suggest that the nitroxide contrast agents, which are themselves free radicals, act as free radical scavengers and therefore reduce the formation of the CCl4-induced hepatic 'damage' observed in proton MR images.

In vivo nuclear magnetic resonance spectroscopy of chicken embryos from two broiler strains of varying fat content

In vivo nuclear magnetic resonance (NMR) imaging and spectroscopy techniques were used to monitor changes in P- and H-containing molecules in embryos of two broiler strains (30 and 31) differing genetically in fat content and ranging in age from 0 to 20 days of incubation. Chemical analysis showed that Strain 30 has more carcass fat than Strain 31 at market age (7 wk). Proton (1H) and 31P spectra were obtained on four eggs per strain at Days 0, 2, 4, 6, 8, 11, 12, 14, 16, 17, 19, and 20 of incubation. Fat:water, phosphomonoester (PME):phosphodiester (PDE), and adenosine triphosphate (ATP):PDE ratios were calculated. Chicks were hatched, grown to market weight (2,000 g for females and 2,300 g for males at 7 wk), and the whole intact carcasses were analyzed for crude fat. Hydrogen-1 NMR spectroscopy studies of incubated eggs indicated no significant difference (P > .05) in the fat:water ratio between the two strains. The difference in the PME:PDE ratios between the two strains as obtained by 31P-NMR spectroscopy over all days of incubation analyzed was not significant (P > .05); however, there was a significant difference in this ratio between the two strains at Days 4, 6, and 11. Up to Day 16, Strain 30 had a slightly, but not significantly (P > .05), higher ATP:PDE ratio as shown on 31P-NMR spectra, whereas after Day 17 the ATP:PDE ratio was significantly higher (P < .01) for Strain 31. Strain 31 birds had a significantly lower (P < .05) crude fat content. There was a significant difference (P < .05) in 7-wk carcass fat content between sexes, males having significantly (P < .01) less fat than females, which was correlated with a significantly higher (P < .01) ATP:PDE ratio in male embryos. It might be possible to use ATP:PDE ratios obtained during embryonic development by 31P-NMR to select strains of birds for low fat content at market weight and to distinguish between sexes during late embryonic development.

Magnetic resonance imaging of the canine and feline eye, orbit, and optic nerves and its clinical application

The purpose of this study was to investigate magnetic resonance imaging of the normal canine and feline eye, orbit and optic nerves using proton density-weighted, T(1)-weighted and T(2)-weighted images. The clinical application of magnetic resonance imaging in veterinary ophthalmology was also investigated using three clinical cases: a feline orbital melanoma, a feline optic nerve meningioma, and a canine orbital fibrosarcoma. Gadolinium diethylenetriamine pentaacetic acid enhanced magnetic resonance imaging was completed on the case of feline optic nerve meningioma. Magnetic resonance imaging provides excellent anatomical detail of the canine and feline eye, orbit, and optic nerves due to its superior soft tissue contrast, and its multiplanar and multislice imaging capability. Therefore it is of value for diagnostic imaging of some ophthalmic and neuro-ophthalmic conditions in the dog and cat.

MRI study of the inhibitory effect of new spin traps on in vivo CCl4-induced hepatotoxicity in rats

Acute CCl4 hepatotoxicity is thought to occur as a result of free radicals generated from the metabolism of CCl4 in the liver. With the use of MRI it is possible to detect in vivo a CCl4-induced localized edematous region surrounding the major branch of the hepatic portal vein in the right lobe. Inhibition of the CCl4-induced response has been obtained by pretreatment with the spin trap, PBN, 30 min prior to CCl4 exposure. The inhibitory effect of two new spin traps, M3PO or methyl-DMPO, and PhM2PO or phenyl-DMPO, on in vivo CCl4-induced acute hepatotoxicity was investigated. Both PhM2PO and M3PO were found to inhibit the CCl4-induced response at lower concentrations (0.35 M/kg body weight) than PBN (0.70 M/kg body weight). However, both M3PO and PhM2PO were also found to induce an edematous response at the same concentrations used for the PBN studies (0.70 M/kg body weight). PhM2PO, at a concentration of 0.35 M/kg body weight, was 93% as efficient as PBN, at a concentration of 0.70 M/kg body weight; whereas M3PO, at a concentration of 0.35 M/kg, was 89% as efficient as PBN at 0.70 M/kg body weight. Electron micrographs were obtained from small liver sections taken in proximity to the major branch of the hepatic portal veins of all treatment groups. The electron microscopy investigations support the MRI findings.

Diagnosis of intestinal ischemia in the rat using magnetic resonance imaging

Noninvasive diagnosis of persistent ischemia after intestinal revascularization has remained an elusive goal. Because magnetic resonance imaging (MRI) can detect changes in tissue water, we studied its efficacy in differentiating ischemic from perfused intestine in an animal model. Six-week-old rats were subjected to (1) 30-min superior mesenteric artery (SMA) occlusion and reperfusion, (2) permanent SMA ligation, or (3) sham operation, and were then imaged for 90 min using a small-animal MRI scanner with T1 weighting (TR = 1000 msec, TE = 25 msec). In an additional group of rats, the experiment was repeated using a new contrast technique consisting of oral ferrite to decrease luminal signal and intravenous gadolinium to increase bowel wall signal. Mean abdominal intensity over the scanning period was calculated for each animal (n = 5 rats per experimental group). Definition of individual bowel loops was subjectively improved in animals scanned with intravenous and oral contrast. Mean abdominal intensity was significantly lower in ligated vs sham rats (43.90 +/- 8 vs 59.63 +/- 6 and 46.19 +/- 6 vs 54.26 +/- 6, with and without contrast, respectively). There was no significant difference in intensity between reperfused and sham animals. MRI differentiated persistently ischemic bowel from viable bowel in this model, both with and without the use of contrast. These data suggest that MRI may have a potential role in the noninvasive diagnosis of persistent intestinal ischemia.

In vivo 31P NMR spectroscopy studies of halothane induced porcine stress syndrome. No effect of C-phenyl N-tert-butyl nitrone (PBN)

Porcine stress syndrome (PSS) which is an example of malignant hyperthermia (MH) in swine has previously been attributed to oxidative stress primarily due to an inherited antioxidant abnormality in MH susceptible (MHS) animals. C-phenyl-N-tert-butyl nitrone (PBN), a free radical spin trap, was selected to investigate whether free radicals are involved in MH. If free radicals cause the MH stress attack, then PBN should alter the time required for the onset of the stress attack, or perhaps protect the animal from experiencing the stress attack. In vivo phosphorus-31 (31P) magnetic resonance spectroscopy (MRS) was used to monitor metabolism in three to four week old normal and MHS piglets administered halothane as the stress challenge. Malignant hyperthermia was not reproducibly induced by halothane anesthesia. For those animals which did develop MH a dramatic fall in the level of PCr and a rise in the level of Pi was detected by 31P MRS. Intravenous administration of PBN prior to halothane exposure had no effect on the number of animals experiencing the stress attack. PBN does not appear to prevent, delay or reverse the onset of halothane-induced MH in three to four week old MHS piglets. The primary events leading to the MH syndrome do not appear to be influenced by the intervention of the type of free radicals normally trapped by PBN.

Comparison of magnetic resonance images and the histopathological findings of lesions induced by interstitial laser photocoagulation in the brain

Interest has developed in using magnetic resonance (MR) imaging to monitor the volume of tissue destroyed by interstitial laser photocoagulation (ILP). In these experiments, ILP was induced in the normal brains of 9 anesthetized cats by delivering 1.5 W of continuous-wave Nd:YAG laser energy (1,064 nm) from a single 400-microns core optical fiber for 1,000 s. The irradiations were monitored using proton spin-echo MR imaging during and immediately after ILP and at postirradiation survival times of 2, 5, and 14 days. At 2 days postirradiation, the necrotic thermal lesion consisted of a central cavity surrounded by 2 concentric zones of coagulative necrosis, one dense and the other dispersed. The lesion shrank and the zonal appearance became less obvious over the 14 day survival period. An enhancing halo on contrast-enhanced T1-weighted images acquired immediately postirradiation best approximated the total lesion diameter at 2 days. These images also indicated that the volume of tissue destroyed during ILP corresponded better to the necrotic volume determined at 2 days than at 5 days and 14 days postirradiation. T2-weighted images acquired during and immediately after ILP consistently underestimated the total lesion diameter at 2 days.

Research note: an assessment of egg yolk structure using magnetic resonance imaging

The purpose of the present experiment was to examine the inner structure of the egg using magnetic resonance imaging (MRI). Proton images of fertile and infertile eggs and eggs from hens fed a corn-based or a flax-based diet were generated using a Spectroscopy Imaging Systems unit. Phantom eggs, made from homogenized albumen and homogenized yolk in a plastic shell, were imaged as controls. Eggs were imaged individually on their side, in the sagittal plane. A single image was generated through the center of the yolk. Images clearly distinguished the eggshell, air space, albumen, and yolk. Within the yolk of both fertile and infertile eggs, the latebra, the neck of the latebra, and four to six pairs of concentric yolk rings were visible, although the rings were less clearly defined in eggs from hens fed the flax-based diet. The embryo was not visible after 24 h of incubation but yolk stratification could still be resolved. Rings were not evident in the phantom eggs. It was concluded that MRI can be used successfully in assessing the microanatomy of eggs.

The use of magnetic resonance imaging in the diagnosis of neurological disease

Magnetic resonance imaging (MRI) data were correlated with clinical and cerebrospinal fluid (CSF) findings in one cat and two dogs with brain lesions. In all three cases, localization of the lesions, as determined clinically, was confirmed using MRI. Magnetic resonance imaging also helped us to define the full extent of the lesion(s) in each case. In one case, the lesion would have been diagnosed as purely inflammatory based on the abnormalities in the CSF. The MRI study, however, showed a homogeneous mass with circumferential changes characteristic of peritumoral edema or inflammation. In two cases, the MRI findings were confirmed at necropsy. An MRI study was also done on a normal dog, demonstrating the variable contrast and anatomical detail possible using this technique. We also discuss difficulties in identifying tumor type using MRI.

Use of 1H/23Na and 1H/31P double frequency tuned birdcage coils to study in vivo carbon tetrachloride-induced hepatotoxicity in rats

In vivo 1H and 23Na magnetic resonance imaging (MRI) and 31P magnetic resonance spectroscopy (MRS) techniques were used to study CCl4-induced acute hepatotoxicity in rats in situ. One or two hours following exposure to CCl4, a localized edematous region was detected in the liver by 1H MRI. The CCl4-induced edema was localized in a region surrounding the hepatic portal vein. With the use of a 23Na/1H double frequency tuned bird-cage imaging coil an increase in Na+ ion flux was also observed in the same region as the edematous region detected by 1H-MRI. Pretreatment with alpha-phenyl-tert-butyl nitrone (PBN), a free radical spin trap, 30 min prior to CCl4 exposure, was found to reduce the CCl4-induced edematous response in the liver observed in either 1H or 23Na-NMR images. Inhibition of the CCl4-induced edematous response in rat liver by PBN demonstrates that free radical intermediates, arising from the metabolism of CCl4, are possibly the key causal agents in the initiation of the edematous response. In addition, with the use of a 31P/1H double frequency tuned bird-cage imaging/spectroscopy coil, localized 31P spectra (ISIS) were obtained from the regions of CCl4-induced "tissue damage" observed in the 1H-MRI images. The most notable changes observed from the 31P spectra were an increase in inorganic phosphate (Pi) and a decrease in hepatocytosolic pH in the CCl4-treated rat livers in comparison to saline-treated control livers.

Spin trapping of free radical metabolites of carbon tetrachloride in vitro and in vivo: effect of acute ethanol administration

A single dose of ethanol, when administered 18 hr prior to CCl4, potentiates the hepatotoxicity of the halocarbon. In these studies, spin trapping and electron spin resonance (ESR) spectroscopy methods were utilized to determine whether a single ethanol dose increased the metabolism of CCl4 to free radical intermediates. When hepatic microsomes from ethanol-treated or control rats were incubated with CCl4 and the spin trapping agent alpha-phenyl-N-tert-butylnitrone (PBN), the ESR signal of the trichloromethyl radical adduct of PBN was of similar intensity in both groups. The ethanol dose also failed to induce p-nitrophenol hydroxylase activity. When PBN and CCl4 were administered to rats, liver extracts contained ESR signals resulting primarily from the trichloromethyl radical adduct of PBN, and the signals were of similar intensity in both experimental groups. Higher concentrations of the carbon dioxide anion radical adduct of PBN were detected in plasma samples from ethanol-treated rats. However, when hepatocytes from ethanol-treated and control rats were incubated with PBN and CCl4, ESR signals of the carbon dioxide adduct were of similar intensity. These data suggest that the higher concentrations of the carbon dioxide adduct in the blood of ethanol-treated rats may be explained by early CCl4-induced damage to liver cell membranes, rather than increased rates of formation. The data in this report fail to support the hypothesis that a single dose of ethanol stimulates the hepatic metabolism of CCl4 to the trichloromethyl radical. Alternatively, ethanol may potentiate CCl4 toxicity by affecting some critical metabolic step subsequent to trichloromethyl radical formation.

Magnetic resonance imaging of interstitial laser photocoagulation in brain

Magnetic resonance (MR) imaging can be used to monitor the development of thermal lesions induced in tissue using interstitial laser photocoagulation (ILP). A potential application for ILP is the treatment of surgically inaccessible brain tumors. For the successful clinical application of MR-monitored ILP, it is necessary to relate MR images of ILP lesions to the actual induced lesions. In this preliminary study we performed ILP in the normal brains of anesthetized cats by delivering interstitially 1.0, 1.5, and 2.0 W of continuous-wave Nd:YAG laser energy (1,064 nm) for 1,000 s via a plane-cut 400 microns core optical fiber. At 48 h post-irradiation the lesions consisted of four sharply demarcated concentric zones of thermal damage. Lesion diameter increased linearly with delivered power. T2-weighted proton spin-echo images acquired during ILP showed a region of complete or near signal loss that underestimated the actual lesion at 48 h. Gadolinium-enhanced T1-weighted spin-echo images acquired immediately post-irradiation showed the actual lesion precisely.

Enhancement of carbon tetrachloride-induced liver injury by a single dose of ethanol: proton magnetic resonance imaging (MRI) studies in vivo

Magnetic resonance imaging (MRI) and localized magnetic resonance spectroscopy (MRS) were used to study the effects of a single dose of ethanol, given 18 h prior to experiments, on CC14-induced acute hepatotoxicity in rats in situ. Localized edema in the centrilobular region of the liver, following exposure to ethanol and CCl4, was detected by 1H-MRI techniques. The edema was characterized by a volume selective spectroscopy (VOSY) method, which measured an increase in water concentration from ethanol and CCl4-treated rat livers, in comparison to control livers. Electron microscopy (EM) of the high intensity regions of the ethanol/CCl4 treated liver sections revealed dramatic subcellular changes such as fragmentation of the granular endoplasmic reticulum (ER), formation of large vacuoles and lipid droplets in the cytoplasmic matrix and extensive swelling of the mitochondria as well as disruption of the cristae. Pretreatment with alpha-phenyl tert-butyl nitrone (PBN), a free radical spin trap, prior to halocarbon exposure, was found to reduce the CC14-mediated high intensity region in the liver images. Electron microscopy of the PBN pretreated CCl4 exposed rat liver sections revealed only minor observable differences in subcellular organization, such as some swelling of the mitochondria, when compared to controls. In addition, these data suggest that ethanol may potentiate CCl4 hepatotoxicity by increased formation of free radical intermediates. Inhibition of the CCl4-induced edematous response in rat liver by PBN demonstrates that free radical intermediates, arising from the metabolism of CCl4, are possibly the causal factor in the initiation of the edema.

In vivo proton magnetic resonance imaging and localized spectroscopic analysis of polycystic kidney disease in DBA/2FG-pyc mice

Proton magnetic resonance imaging (MRI) and localized spectroscopy techniques were used to study polycystic kidney disease (PKD) in DBA/2FG-pcy (pcy) mice, which are an animal model for the adult form of human PKD. A volume selective spectroscopy (VOSY) method was used to obtain localized proton spectra as well as apparent T1 and T2 relaxation times of the kidneys of either pcy or DBA/2FG normal (DBA) mice. Localization of the proton spectra was based on spatial coordinates determined from the proton images. Increases in apparent kidney T1 and T2 relaxation times were observed for pcy mice in comparison to those measured in DBA mice. Localized kidney T1 values from pcy mice were found to range from 799 to 1395 msec whereas DBA mice kidney T1 values were 617 to 774 msec. Localized T2 values measured from pcy mice kidneys ranged from 90 to 172 msec in comparison to kidney T2 values of 50 to 72 msec for DBA mice. The onset of cyst formation in the kidneys of pcy mice as a function of age was also studied. As early as 4 to 5 weeks of age it was possible to detect in vivo changes in pcy mice kidney T1 and T2 values.

Mass spectroscopy and chromatography of the trichloromethyl radical adduct of phenyl tert-butyl nitrone

Positive structural identification of the PBN-trichloromethyl spin adduct in vitro was accomplished with the use of high pressure liquid chromatography and/or gas chromatography coupled with mass spectrometry. Both thin layer and liquid chromatography were used to separate a complex mixture of compounds from rat liver extracts treated with CCl4 in vitro and in vivo. Deuterated PBN's (PBN-d9; tert-butyl deuteration, or PBN-d14; both phenyl and tert-butyl deuteration) were also used to aid in the mass spectral analysis of spin adducts from liver extracts of CCl4 exposed rat livers, since the tert-butyl group fragment ion. C4D9+ (m/z = 66) is always present for PBN and PBN spin adducts. In addition, the masses of the ion peaks increase by the amount of deuteration, i.e. an increase of 9 for PBN-d9 or PBN-d14 in comparison to normally synthesized PBN.

Sodium-23 and proton nuclear magnetic resonance imaging studies of carbon tetrachloride-induced liver damage in the rat

Magnetic resonance imaging techniques were used to investigate the response of the liver of the rat in situ to a toxicological challenge by carbon tetrachloride. Proton images were taken as transverse slices through the rat before and after intraperitoneal administration of the hepatotoxin. Two to three hours after carbon tetrachloride was given, a region of high proton signal intensity was observed where the portal vein enters the liver. Sodium-23 images were also taken, and a region of high sodium intensity was observed in the same location within the liver as the increased proton intensity. The results suggest that acute administration of carbon tetrachloride induces localized liver damage in the region where the hepatotoxin first enters the liver. This liver damage is manifest as edema with a buildup of sodium ion and water, which can be readily detected by sodium-23 and proton NMR imaging techniques, respectively.

Structure identification of free radicals by ESR and GC/MS of PBN spin adducts from the in vitro and in vivo rat liver metabolism of halothane

Free radicals were detected from the in vitro metabolism of halothane (rat liver microsomes) by the PBN spin trapping method. The detected radical species include the 1-chloro-2,2,2-trifluoro-1-ethyl radical (I), as determined by mass spectral analysis, and lipid-type radicals assigned by high resolution ESR spectroscopy with the use of d14-deuterated PBN. The lipid-derived radicals are a carbon-centred radical with the partially assigned structure CH2R and an oxygen-centred radical of the OR' type. From the mass spectral analysis of the spin adduct mixture there is also evidence for a halocarbon double adduct of PBN of the type I-PBN-I.

MRI detection of hyperoxia-induced lung edema in Zn-deficient rats

In a pioneering application of proton Magnetic Resonance Imaging (MRI), lung edema has been monitored in vivo in Zn-deficient rats exposed to 85% oxygen. Dietary Zn appears to play a role in protecting against hyperoxia-induced lung damage.

The effect of phenyl tert-butyl nitrone (PBN) on CCl4-induced rat liver injury detected by proton magnetic resonance imaging (MRI) in vivo and electron microscopy (EM)

Acute intoxication by CCl4 induces morphological changes in rat liver which are readily detectable by 1H-NMR imaging techniques in situ. Two to four hours after the administration of CCl4, regions of high proton signal intensity are observed in the centrilobular region of the liver. The regions of high signal intensity are attributed to the formation of local edema as a result of CCl4-induced damage. Electron microscopy of the high intensity regions of CCl4 treated liver sections revealed characteristic subcellular changes which include the disapperance of ribosomes from the rough endoplasmic reticulum (RER), the fragmented appearance of the smooth endoplasmic reticulum (SER), formation of vacuoles in the cisternae and swelling of the mitochondria. Pretreatment of rats with alpha-phenyl-tert-butyl nitrone (PBN), a free radical spin trap, prior to halocarbon exposure, was found to reduce the halocarbon-induced edema in the liver. Electron microscopy of the PBN pretreated CCl4 exposed rat liver sections revealed no observable changes in subcellular organization when compared to controls.

Investigations of the horse conceptus via magnetic resonance imaging (MRI) and nitroxide spin labels as contrast agents

Results are presented which illustrate the usefulness of Magnetic Resonance Imaging as applied to the study of living embryos. Nitroxide spin labels were employed as contrast agents to study the structure and properties of the embryos. These spin labels offer the additional advantage that they may potentially be bound to biologically important molecules thereby imparting the ability to produce contrast in the MR images to these new molecules. The horse conceptus was chosen over other embryos due to its large size. Whereas the embryos of cattle and swine are sub-millimetre in size, the horse conceptus is on the order of 10 millimetres in diameter. The availability of microscopic imaging gradient coils will allow the techniques developed in this study to be applied to the smaller embryos of other species.

In vivo and in vitro 31P-NMR spectroscopy of rat liver treated with halocarbons

Both in vivo and in vitro 31P-NMR spectroscopy were used to demonstrate metabolic changes in rat liver as a function of time after exposure to either carbon tetrachloride (CCl4) or bromotrichloromethane (BrCCl3). The inorganic phosphate resonance, measured in vivo, moves upfield, which is associated with a decrease in cytosolic pH over a 12 or 20 h period (for BrCCl3 or CCl4, respectively). Intoxication by CCl4 or BrCCl3 causes an intracellular acidosis to pH 7.05 or 6.82 (+/- 0.05), respectively. Also, it has been found that halocarbon exposure increases the amounts of phosphomonoesters (PME) detected. High resolution in vitro 31P-NMR spectroscopy studies of perchloric acid extracts of CCl4-treated rat livers indicated a significant increase in the height of the phosphocholine resonance in the PME region 4-5 h after CCl4 exposure.

In vivo proton nuclear magnetic resonance imaging and spectroscopy studies of halocarbon-induced liver damage

Proton magnetic resonance imaging and localized NMR spectroscopy were used to study the rat liver in situ. Respiratory gating was used in both the imaging and the localized spectroscopy studies to control for the movement of the upper abdomen of the rat during breathing. After administration of carbon tetrachloride, bromotrichloromethane, or halothane, localized regions of high proton signal intensity were observed in the NMR images of the liver. Localized (VOSY) proton NMR spectra from within these regions indicated that the increase in a signal intensity was due to a longer T2 relaxation time for the water resonance, indicating acute edema in the region of tissue damage.

Factors influencing the formation of the carbon dioxide radical anion (.CO2-) spin adduct of PBN in the rat liver metabolism of halocarbons

Spin trapping techniques have been used to detect free radicals generated from the in vitro metabolism by rat liver microsomes of carbon tetrachloride (CCl4) and bromotrichloromethane (BrCCl3) under conditions of varying oxygen tension and pH. Dispersions of rat liver microsomes incubated with 12CCl4, 13CCl4 or Br12CCl3, alpha-phenyl-tert-butyl nitrone (PBN) and NADPH/NADH in a phosphate buffer varying in pH from 6.6 to 8.0 under varying oxygen tensions produced various amounts of four different PBN adducts: PBN-CCl3, PBN-L, PBN-OL and PBN-CO2- where L is a carbon-centered lipid type radical and LO is an oxygen-centered lipid type radical. The relative amount of PBN-CO2- increases with the absence of oxygen. With the use of 31P-NMR in vivo spectroscopy it was possible to detect a pH change from 7.4 to 6.8 in the livers of rats treated with CCl4 or BrCCl3. These results suggest that halocarbon metabolism in biological systems may depend on both oxygen tension as well as pH.

Detection of free radicals generated from the in vitro metabolism of carbon tetrachloride using improved ESR spin trapping techniques

The spin trapping chemistry of carbon tetrachloride has been previously investigated in rat liver, both in vitro and in vivo. In addition to the trichloromethyl radical, both a 'carbon-centered' and an 'oxygen-centered' radical have been detected in vitro. These spin adducts have been assigned to 'lipid' and 'lipid oxyl' radicals. However, no specific structural characterization has been provided to date. The spin trapping chemistry of this system was reinvestigated with the use of deuterated alpha-phenyl N-tert-butyl nitrones to obtain better spectral resolution. Results indicate that the PBN trapped carbon-centered lipid radical is of a primary alkyl type.

Effects of individual terphenyls and polychlorinated terphenyls on rat hepatic microsomal cytochrome P-450-dependent monooxygenases: structure-activity relationships

The effects of o-, m- and p-terphenyl, 2,4-dichloro-, 2,4,6-trichloro-, 2,3,5,6-tetrachloro-, 2,3,4,6-tetrachloro-, 2,4,4''',6- tetrachloro- and 2,3,4,5-tetrachloro-p-terphenyl, 2,3,4,5-tetrachloro-m- and o-terphenyl as inducers of hepatic drug-metabolizing enzymes were determined in immature male Wistar rats. o-Terphenyl, 2,4-dichloro-, 2,4,6-trichloro-p-terphenyl and 2,3,4,5-tetrachloro-o-terphenyl induced 4,4'-dimethylamino antipyrine N-demethylase at total dose levels of 300 mumol/kg and the 2,3,4,5-tetrachloro-p-terphenyl induced ethoxyresorufin O-deethylase (EROD). In contrast, none of the other terphenyls or polychlorinated terphenyls (PCTs) induced these enzyme activities. Previous studies have demonstrated that 2,3,4,5-tetrachloro-p-terphenyl did not exhibit a high affinity for the 2,3,7,8-tetrachlorodibenzo-p-trachlorodibenzo-p-dioxin (TCDD) receptor protein (EC50 = 6.6 X 10(-6) M). In contrast, this study showed that 2,3,4,5-tetrachloro-p-terphenyl was more active than either 2,3,4,5-tetrachloro-o- or m-terphenyl as an inducer of EROD. Moreover, the competitive receptor binding EC50 values for the latter two isomers were greater than 10(-5) M and this result was also consistent with their lack of EROD induction activity. Previous studies showed that analysis of the data for a series of 4'-substituted-2,3,4,5-tetrachlorobiphenyls indicated that the p-terphenyl structural moiety (i.e. 4'-substituent = phenyl) did not interact with high affinity with the receptor protein binding site. Since the 2,3,4,5-tetrachloro o- and m-terphenyls are also poor ligands for the receptor protein, this data and results from other studies indicate that PCT congeners (and commercial mixtures) are therefore unlikely to elicit significant 2,3,7,8-TCDD-like biologic or toxic effects in target species.