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John R Griffiths

Publications and source records attributed to John R Griffiths.

At least 37 records · Page 2Linked to original sources
PubMed2004

Tumor R2* is a prognostic indicator of acute radiotherapeutic response in rodent tumors.

PURPOSE: To test the prognostic potential of tumor R2* with respect to radiotherapeutic outcome. Blood oxygenation level dependent (BOLD) MRI images are sensitive to changes in deoxyhemoglobin concentration through the transverse MRI relaxation rate R2* of tissue water, hence the quantitative measurement of tumor R2* may be related to tissue oxygenation. METHODS AND MATERIALS: Tumor growth inhibition in response to radiation was established for both GH3 prolactinomas and RIF-1 fibrosarcomas with animals breathing either air or carbogen during radiation. In a separate cohort, the baseline R2* and carbogen (95% O2, 5% CO2)-induced DeltaR2* of rat GH3 prolactinomas and murine RIF-1 fibrosarcomas were quantified using multigradient echo (MGRE) MRI prior to radiotherapy, and correlated with subsequent tumor growth inhibition in response to ionizing radiation, while the animals breathed air. RESULTS: A radiation dose of 15 Gy caused pronounced growth delay in both tumor models and transient regression of the GH3 prolactinomas. When the animals breathed carbogen during radiation, the growth delay/regression was enhanced only in the GH3 prolactinomas. The GH3 prolactinomas, which exhibit a relatively fast baseline R2* and large DeltaR2* in response to carbogen breathing prior to radiotherapy, showed a substantial reduction in normalized tumor volume to 66 +/- 3% with air breathing and 36 +/- 5% with carbogen seven days after 15 Gy irradiation. In contrast, the effect of 15 Gy on the RIF-1 fibrosarcomas, which give a relatively slow baseline R2* and negligible DeltaR2* response to carbogen prior to treatment, showed a much smaller growth inhibition (143 +/- 3% with air, 133 +/- 12% with carbogen). CONCLUSION: Quantitation of tumor R2* and carbogen-induced DeltaR2* by MGRE MRI provides completely noninvasive prognostic indicators of a potential acute radiotherapeutic response.

Animals↗
PubMed2004

Differentiation of metastases from high-grade gliomas using short echo time 1H spectroscopy.

PURPOSE: To determine if short echo time (TE) (1)H magnetic resonance spectroscopy (MRS) can distinguish between intracranial metastases and glioblastomas. MATERIALS AND METHODS: TE 30-msec spectra were acquired (1.5 T) from voxels entirely within tumors from 23 glioblastoma patients and 24 metastases patients (3 breast carcinomas, 1 bladder carcinoma, 8 lung carcinomas, 3 probable lung carcinomas, 6 melanomas, 1 stomach carcinoma, and 2 undetermined). Spectra were analyzed quantitatively (LCModel) to determine metabolite, lipid, and macromolecule concentrations. All tumors were previously untreated and classified histopathologically. RESULTS: The lipid peak area (LPA) ratio (total peak area at ca. delta1.3 to that at ca. delta0.9) was 2.6 +/- 0.6 (N = 25) for glioblastomas and 3.8 +/- 1.4 (N = 34) for metastases (P < 0.0001). There were no significant differences in metabolite or lipid concentrations between the tumor groups. The LPA ratio provided 80% sensitivity and 80% specificity for discriminating metastases from glioblastomas. CONCLUSION: Lipid and macromolecule (LM) signals can dominate (1)H spectra of high-grade tumors and have characteristics that allow significant discrimination of metastases from glioblastomas. Work is now needed to determine the source and biophysical characteristics of these LM signals to further improve differentiation by optimizing the data acquisition and analysis protocol.

Brain Neoplasms↗
PubMed2004

A method for interleaved acquisition of a vascular input function for dynamic contrast-enhanced MRI in experimental rat tumours.

Dynamic contrast-enhanced MRI is widely used for the evaluation of the response of experimental rodent tumours to antitumour therapy, particularly for the newly developing antiangiogenic and antivascular agents. However, standard models require a time-course for the plasma concentration of contrast agent (usually referred to as the arterial input function) to calculate the transfer constant K(trans) from the dynamic time-course data. Ideally, the plasma concentration time-course should be measured during each experiment to obtain the most accurate measure of K(trans). This is technically difficult in rodents, so assumed values are generally used. A method is presented here using interleaved acquisitions from a tail coil to obtain the plasma concentration simultaneously with DCE-MRI data obtained from a solenoid coil around the tumour. The SNR of the resulting vascular input function data is high compared with methods using a volume coil to acquire plasma concentrations from the aorta and vena cava.

Animals↗
PubMed2004

Vascular proteomics: linking proteomic and metabolomic changes.

Cardiovascular diseases constitute the largest of death in the Western world. Various stressors, including elevated blood pressure, smoking, diabetes, and hypercholesterolemia directly or indirectly damage the vessel wall, eventually inducing arterial stiffness (arteriosclerosis) and lipid accumulation (atherosclerosis). However, the molecular mechanisms of atheroma formation are not yet fully clarified. While many investigators have used proteomic techniques to study cardiac diseases, vascular proteomics is still in its infancy. The present review highlights studies, in which proteomics has been successfully applied to study protein alterations in the vasculature. Furthermore, we will summarize our recent progress in combining proteomic and metabolomic techniques to reveal protein and metabolite alterations in the cardiovascular system: two-dimensional (2-D) gel electrophoresis proved to be highly complementary to nuclear magnetic resonance (NMR) spectroscopy, in that post-translational modifications of the most abundant enzymes were displayed on 2-D gels while NMR spectroscopy revealed changes in the corresponding metabolites. Importantly, the simultaneous assessment of protein and metabolite changes translated purely descriptive proteomic and metabolomic profiles into a functional context and provided important insights into pathophysiological mechanisms that would not have been obtained by other techniques.

Animals↗
PubMed2004

Loss of PKC-delta alters cardiac metabolism.

PKC-delta is believed to play an essential role in cardiomyocyte growth. In the present study, we investigated the effect of PKC-delta on cardiac metabolism using PKC-delta knockout mice generated in our laboratories. Proteomic analysis of heart protein extracts revealed profound changes in enzymes related to energy metabolism: certain isoforms of glycolytic enzymes, e.g., lactate dehydrogenase and pyruvate kinase, were absent or decreased, whereas several enzymes involved in lipid metabolism, e.g., phosphorylated isoforms of acyl-CoA dehydrogenases, showed a marked increase in PKC-delta(-/-) hearts. Moreover, PKC-delta deficiency was associated with changes in antioxidants, namely, 1-Cys peroxiredoxin and selenium-binding protein 1, and posttranslational modifications of chaperones involved in cytoskeleton regulation, such as heat shock protein (HSP)20, HSP27, and the zeta-subunit of the cytosolic chaperone containing the T-complex polypeptide 1. High-resolution NMR analysis of cardiac metabolites confirmed a significant decrease in the ratio of glycolytic end products (alanine + lactate) to end products of lipid metabolism (acetate) in PKC-delta(-/-) hearts. Taken together, our data demonstrate that loss of PKC-delta causes a shift from glucose to lipid metabolism in murine hearts, and we provide a detailed description of the enzymatic changes on a proteomic level. The consequences of these metabolic alterations on sensitivity to myocardial ischemia are further explored in the accompanyingpaper (20).

Animals↗
PubMed2004

Ischemic preconditioning exaggerates cardiac damage in PKC-delta null mice.

Ischemic preconditioning confers cardiac protection during subsequent ischemia-reperfusion, in which protein kinase C (PKC) is believed to play an essential role, but controversial data exist concerning the PKC-delta isoform. In an accompanying study (26), we described metabolic changes in PKC-delta knockout mice. We now wanted to explore their effect on early preconditioning. Both PKC-delta(-/-) and PKC-delta(+/+) mice underwent three cycles of 5-min left descending artery occlusion/5-min reperfusion, followed by 30-min occlusion and 2-h reperfusion. Unexpectedly, preconditioning exaggerated ischemia-reperfusion injury in PKC-delta(-/-) mice. Whereas ischemic preconditioning increased superoxide anion production in PKC-delta(+/+) hearts, no increase in reactive oxygen species was observed in PKC-delta(-/-) hearts. Proteomic analysis of preconditioned PKC-delta(+/+) hearts revealed profound changes in enzymes related to energy metabolism, e.g., NADH dehydrogenase and ATP synthase, with partial fragmentation of these mitochondrial enzymes and of the E(2) component of the pyruvate dehydrogenase complex. Interestingly, fragmentation of mitochondrial enzymes was not observed in PKC-delta(-/-) hearts. High-resolution NMR analysis of cardiac metabolites demonstrated a similar rise of phosphocreatine in PKC-delta(+/+) and PKC-delta(-/-) hearts, but the preconditioning-induced increase in phosphocholine, alanine, carnitine, and glycine was restricted to PKC-delta(+/+) hearts, whereas lactate concentrations were higher in PKC-delta(-/-) hearts. Taken together, our results suggest that reactive oxygen species generated during ischemic preconditioning might alter mitochondrial metabolism by oxidizing key mitochondrial enzymes and that metabolic adaptation to preconditioning is impaired in PKC-delta(-/-) hearts.

Acetyltransferases↗
PubMed2003

Magnetic resonance spectroscopic pharmacodynamic markers of the heat shock protein 90 inhibitor 17-allylamino,17-demethoxygeldanamycin (17AAG) in human colon cancer models.

BACKGROUND: 17-allylamino,17-demethoxygeldanamycin (17AAG) is a novel anticancer drug that inhibits heat shock protein 90 (Hsp90), resulting in proteasomal degradation of several oncogenic proteins. We used phosphorus magnetic resonance spectroscopy (31P-MRS) to determine whether 17AAG treatment leads to alterations in phospholipids that could serve as pharmacodynamic markers for tumor response to 17AAG. METHODS: HCT116, HT29, and SW620 colon cancer cells were treated with 17AAG, and extracts were examined by 31P-MRS. HT29 cells were also treated with the active metabolite of 17AAG, 17-amino,17-demethoxygeldanamycin (17AG), or the inactive 17AAG analog NSC683666. MF-1 nude mice carrying HT29 xenografts were examined using in vivo 31P-MRS before and after 17AAG treatment; xenograft tumor extracts were examined by 31P-MRS and proton MRS (1H-MRS). Hsp90 client protein expression was determined by using western blots. Two-tailed t tests were used to compare metabolite concentrations and ratios, and a Mann-Whitney U test was used to compare proportions. All statistical tests were two-sided. RESULTS: 17AAG treatment led to statistically significantly increased phosphocholine levels in all three cell lines (P =.02). 17AG treatment also increased phosphocholine levels in HT29 cells, whereas NSC683666 had no effect. The phosphomonoester/phosphodiester ratio was statistically significantly increased in the HT29 xenografts after 17AAG treatment relative to the pretreatment ratio (P =.02), whereas no statistically significant change was observed after vehicle treatment (P =.62). Statistically significant increases in phosphocholine, phosphoethanolamine, and valine levels were also observed in tumor extracts treated with 17AAG. CONCLUSIONS: Inhibition of Hsp90 by 17AAG resulted in altered phospholipid metabolism in cultured tumor cells and in tumor xenografts. The increases observed in phosphocholine and phosphomonoester levels suggest that these metabolites may have the potential to act as noninvasive pharmacodynamic markers for analyzing tumor response to treatment with 17AAG or other Hsp90 inhibitors.

Animals↗
PubMed2003

Effects of overexpression of dimethylarginine dimethylaminohydrolase on tumor angiogenesis assessed by susceptibility magnetic resonance imaging.

Intracellular factors that regulate nitric oxide (NO) synthesis represent important targets in tumor progression. Overexpression of dimethylarginine dimethylaminohydrolase (DDAH), which metabolizes the endogenous inhibitors of NO synthesis asymmetric dimethylarginine and N-monomethyl-L-arginine, results in C6 gliomas with enhanced growth rate compared with wild type. To investigate the effects of DDAH on tumor vascular morphogenesis in vivo, we have measured the transverse relaxation rates R(2)* and R(2) in clone D27 gliomas overexpressing DDAH and C6 wild-type gliomas using intrinsic susceptibility magnetic resonance imaging (MRI), sensitive to changes in endogenous [deoxyhemoglobin], and susceptibility contrast-enhanced MRI using the intravascular blood pool contrast agent NC100150, and we compared the results with fluorescence microscopy of the tumor uptake of the perfusion marker Hoechst 33342. The baseline R(2)* was significantly faster in the D27 tumors, consistent with a greater vascular development (P < 0.02, ANOVA). There was no significant difference between the response of the two tumor types to hypercapnia (5% CO(2)/95% air), used as a probe for vascular maturation, or hyperoxia (5% CO(2)/95% O(2)), used as a probe for vascular function. NC100150 increased the R(2)* and R(2) rates of both tumor types and demonstrated a significantly larger blood volume in the D27 tumors (P < 0.02, ANOVA). This correlated with a significantly greater uptake of Hoechst 33342 in the D27 tumors compared with C6 wild-type tumors (P < 0.02, ANOVA). Despite the increased tumor blood volume, the Delta R(2)*/Delta R(2) ratio, an index of microvessel size, showed that the capillaries in the two tumor types were of a similar caliber. The data highlight the potential of susceptibility MRI-derived quantitative end points to noninvasively assess tumor angiogenesis, and in this regard, the use of intravascular blood pool contrast agents such as NC100150 appears very promising. Overexpression of DDAH results in increased neovascularization of C6 gliomas in vivo. The lack of significant difference in hypercapnic/hyperoxic response between the C6 and D27 tumors and the similar vessel caliber are also consistent with a role for DDAH in the initial stages of vasculogenesis.

Amidohydrolases↗
PubMed2003

Tumor vascular architecture and function evaluated by non-invasive susceptibility MRI methods and immunohistochemistry.

PURPOSE: To investigate the physiological origins responsible for the varying blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) responses to carbogen (95% O(2)/5% CO(2)) breathing observed with different tumor types. MATERIALS AND METHODS: Susceptibility contrast-enhanced MRI using the exogenous blood pool contrast agent NC100150 to determine blood volume and vessel size, and immunohistochemical-derived morphometric parameters, were determined in GH3 prolactinomas and RIF-1 fibrosarcomas, both grown in mice, which exhibited very different BOLD responses to carbogen. RESULTS: Administration of NC100150 increased the R(2)* and R(2) rates of both tumor types, and indicated a significant four-fold larger blood volume in the GH3 tumor. The ratio deltaR(2)*/deltaR(2) showed that the capillaries in the GH3 were two-fold larger than those in the RIF-1, in agreement with morphometric analysis. Carbogen breathing induced a significant 25% decrease in R(2)* in the GH3 prolactinoma, whereas the response in the RIF-1 fibrosarcoma was negligible. CONCLUSION: Low blood volume and small vessel size (and hence reduced hematocrit) are two reasons for the lack of R(2)* change in the RIF-1 with carbogen breathing. BOLD MRI is sensitive to erythrocyte-perfused vessels, whereas exogenous contrast agents interrogate the total perfused vascular volume. BOLD MRI, coupled with a carbogen challenge, provides information on functional, hemodynamic tumor vasculature.

Animals↗
PubMed2003

Automated classification of short echo time in in vivo 1H brain tumor spectra: a multicenter study.

Automated pattern recognition techniques are needed to help radiologists categorize MRS data of brain tumors according to histological type and grade. A major question is whether a computer program "trained" on spectra from one hospital will be able to classify those from another, particularly if the acquisition protocol is different. A subset of 144 histopathologically validated brain tumor spectra in the INTERPRET database, obtained from three of the collaborating centers, was grouped into meningiomas, low-grade astrocytomas, and "aggressive tumors" (glioblastomas and metastases). Spectra from two centers formed the training set (94 spectra) while the third acted as the test set (50 spectra). Linear discriminant analysis successfully classified 48/50 in the test set; the remaining two were atypical cases. When the training and test sets were combined, 133 of the 144 spectra were correctly classified using the leave-one-out procedure. These spectra had been obtained using different sequences (STEAM and PRESS), different echo times (20, 30, 31, and 32 ms), different repetition times (1600 and 2000 ms), and different manufacturers' instruments (GE and Philips). Pattern recognition algorithms are less sensitive to acquisition parameters than had been expected.

Astrocytoma↗
PubMed2003

Independent component analysis for automated decomposition of in vivo magnetic resonance spectra.

Fully automated methods for analyzing MR spectra would be of great benefit for clinical diagnosis, in particular for the extraction of relevant information from large databases for subsequent pattern recognition analysis. Independent component analysis (ICA) provides a means of decomposing signals into their constituent components. This work investigates the use of ICA for automatically extracting features from in vivo MR spectra. After its limits are assessed on artificial data, the method is applied to a set of brain tumor spectra. ICA automatically, and in an unsupervised fashion, decomposes the signals into interpretable components. Moreover, the spectral decomposition achieved by the ICA leads to the separation of some tissue types, which confirms the biochemical relevance of the components.

Brain Neoplasms↗
PubMed2003

Issues in GRE & SE magnetic resonance imaging to probe tumor oxygenation.

Tumor oxygenation determines the efficacy of radiotherapy, but there is no non-invasive way to image this parameter. Since gradient recalled echo (GRE) images are sensitive to blood deoxyhaemoglobin concentration ([dHb]) they could have a role in assessing tumor oxygenation. In brain, linear relationships have been demonstrated between brain tissue R2* relaxation rate and tissue [dHb] or oxygen saturation, but in tumors, vascular and tissue heterogeneity, and the presence of simultaneous oxidative and glycolytic metabolism, complicate the analysis. We have studied the effects of vascular challenge in a rat prolactinoma tumor model by MR imaging and spectroscopy and comment on the implications of these results for calibrating GRE images for blood or tissue pO2.

Animals↗
PubMed2002

Metabolic changes detected by in vivo magnetic resonance studies of HEPA-1 wild-type tumors and tumors deficient in hypoxia-inducible factor-1beta (HIF-1beta): evidence of an anabolic role for the HIF-1 pathway.

Hypoxia-inducible factor-1 (HIF-1) regulates many pathways potentially important for tumor growth, including angiogenesis and glycolysis. Most attention has focused on its role in the response to hypoxia, but HIF-1 is also constitutively expressed in many tumors. To analyze the role of this pathway in vivo, we used magnetic resonance (MR) methods and complementary techniques to monitor metabolic changes in tumors derived from HEPA-1 mouse hepatoma lines that were either wild type (WT) or deficient in hypoxia-inducible transcription factor HIF-1beta (c4). The c4 tumors grew significantly more slowly than the WT tumors (P < 0.05), but were examined at a similar size (0.4-0.6 g). At the tumor size used in these studies, no differences in vascularity were observed, and MR parameters measured that related to tumor blood flow, vascularity, and oxygenation demonstrated no significant differences between the two tumor types. Unexpectedly, the ATP content of the c4 tumor was approximately 5 times less than in the WT tumor [measured in tumor extracts (P < 0.001) and by metabolic imaging (P < 0.05)]. Noninvasive (31)P MR spectroscopy showed that the nucleoside triphosphate/P(i) ratio of the two tumor types was similar, so the low ATP content of the c4 tumors was not caused by (or a cause of) impaired cellular bioenergetics. Rather, glycine, an essential precursor for de novo purine formation, was significantly lower in the c4 tumors (P < 0.05), suggesting that ATP synthesis was impaired in the mutant tumor cells. Supporting evidence for this hypothesis came from the significantly lower concentrations of betaine, phosphocholine, and choline in the c4 tumors (P < 0.05); these are intermediates in an alternative pathway for glycine synthesis. No significant differences were seen in lactate or glucose content. MR resonances from phosphodiesters, which relate to the metabolic turnover of phospholipid membranes, were significantly lower in the WT tumors than in the c4 tumors, both in vivo (P < 0.05) and in extracts (P < 0.01). We propose that loss of up-regulation of expression of the genes for glucose transporters and glycolytic enzymes in the c4 tumors decreased formation of glycine, an essential precursor of ATP synthesis, and thus caused the low ATP content of the c4 tumors. In summary, these data suggest that disruption of the HIF-1 pathway in these tumor cells impairs the supply of anabolic precursors required for cell synthesis. They suggest potential biochemical targets that may be modified by therapy blocking HIF-1 function.

Animals↗
PubMed2002

Magnetic resonance neurography of peripheral nerve following experimental crush injury, and correlation with functional deficit.

OBJECT: In a number of clinical studies magnetic resonance (MR) neurography has been used to examine patients with peripheral nerve damage, but little is understood about the sequence of imaging changes following nerve injuries, and how they correlate with functional deficit. The goal of this study was to further understanding of these changes and their implications. METHODS: Using the rat sciatic nerve crush model, the sciatic nerve was imaged at intervals over 70 days in 12 rats. Sham-operated contralateral nerves served as controls. A 4.7-tesla MR imager with a custom-made surface coil was used. The T2 maps were calculated from images obtained at four echo times and from regions of interest designated on the nerve at three sites. Walking-track analysis was performed at the same intervals as imaging. Magnetic resonance neurography revealed a mean T2 of normal sciatic nerve of 36 msec (standard deviation [SD] 1.2 msec). Crushed nerves demonstrated a sequence of changes in signal intensity that were maximal at 14 days, with a mean T2 of 64 msec (SD 5.2 msec), then falling to a T2 of 53 msec (SD 3.7 msec). Sham-operated nerves had a short and nonsustained rise in signal at 7 days. Walking-track analysis revealed maximum deficit immediately postinjury, with an improvement in function approaching that of control nerves at 30 days. CONCLUSIONS: In this study the authors demonstrate that quantitative assessment of nerve signals with MR neurography allows the sequence of events following nerve crush injury to be followed in vivo, and that a return toward a normal signal correlates with functional improvement. Assessment of peripheral nerve injury in patients by using MR neurography has the potential to confirm acute nerve injury as well as to monitor the recovery process.

Animals↗
PubMedDate not supplied

Enhanced uptake of ifosfamide into GH3 prolactinomas with hypercapnic hyperoxic gases monitored in vivo by (31)P MRS.

Previously, (31)P magnetic resonance spectroscopy (MRS) has been used to detect ifosfamide (IF) in vivo and to show that breathing carbogen (5% CO(2)/95% O(2)) enhances the uptake and increases the efficacy of IF in rat GH3 prolactinomas [Rodrigues LM, Maxwell RJ, McSheehy PMJ, Pinkerton CR, Robinson SP, Stubbs M, and Griffiths JR (1997). In vivo detection of ifosfamide by (31)P MRS in rat tumours; increased uptake and cytotoxicity induced by carbogen breathing in GH3 prolactinomas. Br J Cancer 75, 62-68]. We now show that other hypercapnic and/or hyperoxic (5% CO(2) in air, 2.5% CO(2) in O(2)) gas mixtures also increase the uptake of IF into tumors, measured by (31)P MRS. All gases caused an increased uptake (C(max)) of IF compared to air breathing, with carbogen inducing the largest increase (85% (P<.02) compared to 46% with 2.5% CO(2) in O(2) (P<.004) and 48% with 5% CO(2) in air (P<.004)). The T(max) (time of maximum concentration in tumor posintravenous injection of IF) was significantly (P<.04) later in the cohort that breathed 5% CO(2) in air. The increased uptake of IF with carbogen breathing was selective to tumor tissue and there were no significant increases in any of the normal tissues studied, suggesting that any host tissue toxicity would be minimal. Carbogen breathing by patients causes breathlessness. There was no significant difference in IF uptake between breathing carbogen and 2.5% CO(2) in O(2) and, therefore, the ability of 2.5% CO(2) in O(2) to also increase IF uptake may be clinically useful as it causes less patient discomfort.

Animals↗
PubMedDate not supplied

Single dose of the antivascular agent, ZD6126 (N-acetylcolchinol-O-phosphate), reduces perfusion for at least 96 hours in the GH3 prolactinoma rat tumor model.

Tumor vasculature is an attractive therapeutic target as it differs structurally from normal vasculature, and the destruction of a single vessel can lead to the death of many tumor cells. The effects of antivascular drugs are frequently short term, with regrowth beginning less than 24 hours posttreatment. This study investigated the duration of the response to the vascular targeting agent, ZD6126, of the GH3 prolactinoma, in which efficacy and dose-response have previously been demonstrated. GH3 prolactinomas were grown in the flanks of eight Wistar Furth rats. All animals were treated with 50 mg/kg ZD6126. The tumors were examined with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) 24 hours pretreatment and posttreatment, and at a single time between 48 and 96 hours posttreatment. No evidence of recovery of perfusion was observed even at the longest (96-hour) time point. Involvement of a statistician at the project planning stage and the use of DCE-MRI, which permits noninvasive quantitation of parameters related to blood flow in intact animals, allowed this highly significant result to be obtained using only eight rats.

Animals↗