Prediction of pathologic response to neoadjuvant chemotherapy in patients with breast cancer using diffusion‐weighted imaging and MRS

The aim of this study was to determine whether tumor size, MRS parameters and apparent diffusion coefficient (ADC) measurements could be applied to predict pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC). Ninety patients with breast cancer (median size, 4.5 cm; range, 1.6–9.5 cm) were evaluated with single‐voxel ¹H MRS and dynamic contrast‐enhanced MRI. Diffusion‐weighted imaging was performed in 41 of these patients using a 1.5‐T scanner before and after completion of NAC. Pre‐ and post‐treatment measurements and changes in tumor size, MRS parameters [absolute and normalized total choline‐containing compound (tCho) integral and tCho signal‐to‐noise ratio (SNR)] and ADCs in pCR versus non‐pCR were compared using the nonparametric Mann–Whitney test. Receiver operating characteristic (ROC) curve analysis was performed to assess the diagnostic performance of each parameter. After NAC, 30 patients (33%) showed pCR and 60 (67%) showed non‐pCR. At pretreatment, ADC was the only significant parameter in differentiating between pCR and non‐pCR [(0.83 ± 0.05) × 10^–3 versus (0.97 ± 0.14) × 10^–3 mm²/s] (p = 0.014). Post‐treatment measurements after completion of NAC and changes in tumor size (both p < 0.001), MRS parameters (p = 0.027 and p = 0.020 for absolute tCho integral, p = 0.036 and p = 0.023 for normalized tCho integral, and p = 0.032 and p = 0.061 for tCho SNR) and ADC (p = 0.003 and p < 0.001) were significantly different between the pCR and non‐pCR groups, except for changes in tCho SNR. In ROC analysis, the areas under the ROC curve (AUCs) of 0.63–0.73 were obtained for tumor size and MRS parameters. AUCs for pre‐ and post‐treatment ADC and changes in ADC were 0.75, 0.80 and 0.96, respectively. The optimal cut‐off of the percentage change in ADC for predicting pCR was 40.7%, yielding 100% sensitivity and 91% specificity. Patients with pCR showed significantly lower pretreatment ADCs than those with non‐pCR. The change in ADC after NAC was the most accurate predictor of pCR. Copyright © 2012 John Wiley & Sons, Ltd.     

Direct in vivo measurement of glycine and the neurochemical profile in the rat medulla oblongata

The medulla oblongata (MO) contains a high density of glycinergic synapses and a particularly high concentration of glycine. The aims of this study were to measure directly in vivo the neurochemical profile, including glycine, in MO using a spin‐echo‐based ¹H MRS sequence at TE = 2.8 ms and to compare it with three other brain regions (cortex, striatum and hippocampus) in the rat. Glycine was quantified in MO at TE = 2.8 ms with a Cramér–Rao lower bound (CRLB) of approximately 5%. As a result of the relatively low level of glycine in the other three regions, the measurement of glycine was performed at TE = 20 ms, which provides a favorable J‐modulation of overlapping myo‐inositol resonance. The other 14 metabolites composing the neurochemical profile were quantified in vivo in MO with CRLBs below 25%. Absolute concentrations of metabolites in MO, such as glutamate, glutamine, γ‐aminobutyrate, taurine and glycine, were in the range of previous in vitro quantifications in tissue extracts. Compared with the other regions, MO had a three‐fold higher glycine concentration, and was characterised by reduced (p < 0.001) concentrations of glutamate (?50 ± 4%), glutamine (–54 ± 3%) and taurine (?78 ± 3%). This study suggests that the functional specialisation of distinct brain regions is reflected in the neurochemical profile. Copyright © 2010 John Wiley & Sons, Ltd.     

Glycogen synthase kinase‐3β ablation limits pancreatitis‐induced acinar‐to‐ductal metaplasia

Acinar‐to‐ductal metaplasia (ADM) is a reversible epithelial transdifferentiation process that occurs in the pancreas in response to acute inflammation. ADM can rapidly progress towards pre‐malignant pancreatic intraepithelial neoplasia (PanIN) lesions in the presence of mutant KRas and ultimately pancreatic adenocarcinoma (PDAC). In the present work, we elucidate the role and related mechanism of glycogen synthase kinase‐3beta (GSK‐3β) in ADM development using in vitro 3D cultures and genetically engineered mouse models. We show that GSK‐3β promotes TGF‐α‐induced ADM in 3D cultured primary acinar cells, whereas deletion of GSK‐3β attenuates caerulein‐induced ADM formation and PanIN progression in Kras^G12D transgenic mice. Furthermore, we demonstrate that GSK‐3β ablation influences ADM formation and PanIN progression by suppressing oncogenic KRas‐driven cell proliferation. Mechanistically, we show that GSK‐3β regulates proliferation by increasing the activation of S6 kinase. Taken together, these results indicate that GSK‐3β participates in early pancreatitis‐induced ADM and thus could be a target for the treatment of chronic pancreatitis and the prevention of PDAC progression. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Molecular pathology of pancreatic cancer

By genomic and epigenomic screening techniques, substantial progress has been made in our understanding of pancreatic cancer. The comprehensive studies of the pancreatic cancer genome have revealed that most genetic alterations are identified to be associated with specific core signaling pathways including high‐frequency mutated genes such as KRAS, CDKN2A, TP53, and SMAD4 along with several low‐frequency mutated genes. Three types of histological precursors of pancreatic cancer: pancreatic intraepithelial neoplasia, mucinous cystic neoplasm, and intraductal papillary mucinous neoplasm, had been recognized by morphological studies and the recent genomic screening techniques revealed that each of these precursor lesions were associated with specific molecular alterations. In the familial pancreatic cancer cases, several responsible genes were discovered. Epigenetic changes also play an important role in the progression of pancreatic cancer. Several tumor suppressor genes were silenced due to aberrant promoter CpG island hypermethylation. Several genetically engineered mouse models, based on the Kras mutation, were created, and provided reliable tools to identify the key molecules responsible for the development or progression of pancreatic cancer.     

Anti‐stromal treatment together with chemotherapy targets multiple signalling pathways in pancreatic adenocarcinoma

Stromal targeting for pancreatic ductal adenocarcinoma (PDAC) is rapidly becoming an attractive option, due to the lack of efficacy of standard chemotherapy and increased knowledge about PDAC stroma. We postulated that the addition of stromal therapy may enhance the anti‐tumour efficacy of chemotherapy. Gemcitabine and all‐trans retinoic acid (ATRA) were combined in a clinically applicable regimen, to target cancer cells and pancreatic stellate cells (PSCs) respectively, in 3D organotypic culture models and genetically engineered mice (LSL‐Kras^G12D/+;LSL‐Trp53^R172H/+;Pdx‐1‐Cre: KPC mice) representing the spectrum of PDAC. In two distinct sets of organotypic models as well as KPC mice, we demonstrate a reduction in cancer cell proliferation and invasion together with enhanced cancer cell apoptosis when ATRA is combined with gemcitabine, compared to vehicle or either agent alone. Simultaneously, PSC activity (as measured by deposition of extracellular matrix proteins such as collagen and fibronectin) and PSC invasive ability were both diminished in response to combination therapy. These effects were mediated through a range of signalling cascades (Wnt, hedgehog, retinoid, and FGF) in cancer as well as stellate cells, affecting epithelial cellular functions such as epithelial–mesenchymal transition, cellular polarity, and lumen formation. At the tissue level, this resulted in enhanced tumour necrosis, increased vascularity, and diminished hypoxia. Consequently, there was an overall reduction in tumour size. The enhanced effect of stromal co‐targeting (ATRA) alongside chemotherapy (gemcitabine) appears to be mediated by dampening multiple signalling cascades in the tumour–stroma cross‐talk, rather than ablating stroma or targeting a single pathway. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.     

Alterations in creatine metabolism observed in experimental autoimmune myocarditis using ex vivo proton magic angle spinning MRS

Experimental autoimmune myocarditis (EAM) in rodents is an accepted model of myocarditis and dilated cardiomyopathy (DCM). Altered metabolism is thought to play an important role in the pathogenesis of DCM and heart failure (HF). Study of the metabolism may provide new diagnostic information and insights into the mechanisms of myocarditis and HF. Proton MRS (¹H‐MRS) has not yet been used to study the changes occurring in myocarditis and subsequent HF. We aimed to explore the changes in creatine metabolism using this model and compare them with the findings in healthy animals. Myocardial function of male young Lewis rats with EAM was quantified by performing left ventricular ejection fraction (LVEF) analysis in short‐axis cine images throughout the whole heart. Inflammatory cellular infiltrate was assessed by immunohistochemistry. Myocardial tissue was analyzed using ex vivo proton magic angle spinning MRS (¹H‐MAS‐MRS). Myocarditis was confirmed histologically by the presence of an inflammatory cellular infiltrate and CD68 positive staining. A significant increase in the metabolic ratio of Tau/tCr (taurine/total creatine) obtained by ¹H‐MAS‐MRS was observed in myocarditis compared with healthy controls (21 d acute EAM, 4.38 (±0.23); 21 d control, 2.84 (±0.08); 35 d chronic EAM, 4.47 (±0.83); 35 d control, 2.59 (±0.38); P < 0.001). LVEF was reduced in diseased animals (EAM, 55.2% (±11.3%); control, 72.6% (±3.8%); P < 0.01) and correlated with Tau/tCr ratio (R = 0.937, P < 0.001). Metabolic alterations occur acutely with the development of myocarditis. Myocardial Tau/tCr ratio as detected by ¹H‐MRS correlates with LVEF and is able to differentiate between healthy myocardium and myocardium from rats with EAM. Copyright © 2015 John Wiley & Sons, Ltd.     

Non‐invasive diagnosis and metabolic consequences of congenital portosystemic shunts in C57BL/6 J mice

This study demonstrates the suitability of magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) for the imaging of congenital portosystemic shunts (PSS) in mice, a vascular abnormality in which mesenteric blood bypasses the liver and is instead drained directly to the systemic circulation. The non‐invasive diagnosis performed in tandem with other experimental assessments permits further characterization of liver, whole‐body and brain metabolic defects associated with PSS. Magnetic resonance measurements were performed in a 26‐cm, horizontal‐bore, 14.1‐T magnet. MRA was obtained with a three‐dimensional gradient echo sequence (GRE; in‐plane resolution, 234 × 250 × 234 μm³) using a birdcage coil. Two‐dimensional GRE MRI with high spatial resolution (in‐plane resolution, 100 × 130 μm²; slices, 30 × 0.3 mm) was performed using a surface coil. Brain‐ (dorsal hippocampus) and liver‐localized ¹H magnetic resonance spectroscopy (MRS) was also performed with the surface coil. Whole‐body metabolic status was evaluated with an oral glucose tolerance test (OGTT). Both MRA and anatomical MRI allowed the identification of hepatic vessels and the diagnosis of PSS in mice. The incidence of PSS was about 10%. Hepatic lipid content was higher in PSS than in control mice (5.1 ± 2.8% versus 1.8 ± 0.6%, p = 0.02). PSS mice had higher brain glutamine concentration than controls (7.3 ± 1.0 μmol/g versus 2.7 ± 0.6 μmol/g, p < 0.0001) and, conversely, lower myo‐inositol (4.2 ± 0.6 μmol/g versus 6.0 ± 0.4 μmol/g, p < 0.0001), taurine (9.7 ± 1.2 μmol/g versus 11.0 ± 0.4 μmol/g, p < 0.01) and total choline (0.9 ± 0.1 μmol/g versus 1.2 ± 0.1 μmol/g, p < 0.001) concentrations. Fasting blood glucose and plasma insulin were lower in PSS than in control mice (4.7 ± 0.5mM versus 8.8 ± 0.6mM, p < 0.0001; and 0.04 ± 0.03 μg/L versus 0.3 ± 0.2 μg/L, p = 0.02, respectively). Glucose clearance during OGTT was delayed and less efficient in PSS mice than in controls. Thus, given the non‐negligible incidence of PSS in inbred mice, the undiagnosed presence of PSS will, importantly, have an impact on experimental outcomes, notably in studies addressing brain, liver or whole‐body metabolism.     

Early detection of radiation therapy response in non‐Hodgkin's lymphoma xenografts by in vivo 1H magnetic resonance spectroscopy and imaging

The purpose of the study was to investigate the capability of ¹H MRS and MRI methods for detecting early response to radiation therapy in non‐Hodgkin's lymphoma (NHL). Studies were performed on the WSU‐DLCL2 xenograft model in nude mice of human diffuse large B‐cell lymphoma, the most common form of NHL. Radiation treatment was applied as a single 15 Gy dose to the tumor. Tumor lactate, lipids, total choline, T₂ and apparent diffusion coefficients (ADC) were measured before treatment and at 24 h and 72 h after radiation. A Hadamard‐encoded slice‐selective multiple quantum coherence spectroscopy sequence was used for detecting lactate (Lac) while a stimulated echo acquisition mode sequence was used for detection of total choline (tCho) and lipids. T₂‐ and diffusion‐weighted imaging sequences were used for measuring T₂ and ADC. Within 24 h after radiation, significant changes were observed in the normalized integrated resonance intensities of Lac and the methylenes of lipids. Lac/H₂O decreased by 38 ± 15% (p = 0.03), and lipid (1.3 ppm, CH₂)/H₂O increased by 57 ± 14% (p = 0.01). At 72 h after radiation, tCho/H₂O decreased by 45 ± 14% (p = 0.01), and lipid (2.8 ppm, polyunsaturated fatty acid)/H₂O increased by 970 ± 36% (p = 0.001). ADC increased by 14 ± 2% (p = 0.003), and T₂ did not change significantly. Tumor growth delay and regression were observed thereafter. This study enabled comparison of the relative sensitivities of various ¹H MRS and MRI indices to radiation and suggests that ¹H MRS/MRI measurements detect early responses to radiation that precede tumor volume changes. Copyright © 2010 John Wiley & Sons, Ltd.     

Loss of natural killer T cells promotes pancreatic cancer in LSL‐KrasG12D/+ mice

The role of the unique T‐cell population, natural killer T (NKT) cells, which have similar functions to NK cells in pancreatic cancer (PC), is not yet evaluated. To address the regulatory roles of NKT cells on tumour progression through tumour‐associated macrophages (TAM) and their production of microsomal prostaglandin E synthase‐1 (mPGES‐1) and 5‐lipoxygenase (5‐LOX) in (Kras)‐driven pancreatic tumour (KPT) progression, we crossed CD1d^−/− mice deficient in both invariant and variant NKT cells with the Kras^G12D mice. Loss of NKT cells significantly increased pancreatic intraepithelial neoplasia (PanIN) lesions and also increased 5‐LOX and mPGES‐1 expression in M2‐type macrophages and cancer stem‐like cells in pancreatic tumours. Pharmacological inhibition of mPGES‐1 and 5‐LOX in M2 macrophages with specific inhibitor YS‐121 in KPT‐CD1d^−/− mice decreased PanIN lesions and suppressed tumour growth in association with elevated levels of active CD8a cells. Hence, NKT cells regulate PC by modulating TAMs (M2) through mPGES‐1 and 5‐LOX; and the absence of NKT cells leads to aggressive development of PC.     

Long‐TE 1H MRS suggests that liver fat is more saturated than subcutaneous and visceral fat

Cross‐talk between adipose tissue and liver is disturbed in the metabolic syndrome. Moreover, the relative fatty acid composition of adipose and liver fat is poorly characterized. Long‐TE ¹H MRS can determine the unsaturation and polyunsaturation of adipose tissue. The aim of this study was to use long‐TE ¹H MRS to determine the composition of liver fat and its relation to adipose tissue composition. Sixteen subjects with increased liver fat (>5%) were recruited for the study. Using TE = 200 ms, we were able to resolve the olefinic (?CH, 5.3 ppm) and water (H₂O, 4.7 ppm) resonances in liver spectra and to obtain a repeatable estimate of liver fat unsaturation (coefficient of variation, 2.3%). With TE = 135 ms, the diallylic (?C? CH₂? C?, 2.8 ppm) resonance was detectable in subjects with a liver fat content above 15%. Long‐TE ¹H MRS was also used to determine the unsaturation in subcutaneous (n = 16) and visceral (n = 11) adipose tissue in the same subjects. Liver fat was more saturated (double bonds per fatty acid chain, 0.812 ± 0.022) than subcutaneous (double bonds per fatty acid chain, 0.862 ± 0.022, p < 0.0004) or visceral (double bonds per fatty acid chain, 0.865 ± 0.033, p < 0.0004) fat. Liver fat unsaturation correlated with subcutaneous unsaturation (R = 0.837, p < 0.0001) and visceral unsaturation (R = 0.879, p < 0.0004). The present study introduces a new noninvasive method for the assessment of the composition of liver fat. The results suggest that liver fat is more saturated than subcutaneous or visceral adipose tissue, which may be attributed to differences in de novo lipogenesis. Copyright © 2010 John Wiley & Sons, Ltd.     

31P and 1H MRS of DB‐1 melanoma xenografts: lonidamine selectively decreases tumor intracellular pH and energy status and sensitizes tumors to melphalan

In vivo ³¹P MRS demonstrates that human melanoma xenografts in immunosuppressed mice treated with lonidamine (LND, 100 mg/kg intraperitoneally) exhibit a decrease in intracellular pH (pH_i) from 6.90 ± 0.05 to 6.33 ± 0.10 (p < 0.001), a slight decrease in extracellular pH (pH_e) from 7.00 ± 0.04 to 6.80 ± 0.07 (p > 0.05) and a monotonic decline in bioenergetics (nucleoside triphosphate/inorganic phosphate) of 66.8 ± 5.7% (p < 0.001) relative to the baseline level. Both bioenergetics and pH_i decreases were sustained for at least 3 h following LND treatment. Liver exhibited a transient intracellular acidification by 0.2 ± 0.1 pH units (p > 0.05) at 20 min post‐LND, with no significant change in pH_e and a small transient decrease in bioenergetics (32.9 ± 10.6%, p > 0.05) at 40 min post‐LND. No changes in pH_i or adenosine triphosphate/inorganic phosphate were detected in the brain (pH_i, bioenergetics; p > 0.1) or skeletal muscle (pH_i, pH_e, bioenergetics; p > 0.1) for at least 120 min post‐LND. Steady‐state tumor lactate monitored by ¹H MRS with a selective multiquantum pulse sequence with Hadamard localization increased approximately three‐fold (p = 0.009). Treatment with LND increased the systemic melanoma response to melphalan (LPAM; 7.5 mg/kg intravenously), producing a growth delay of 19.9 ± 2.0 days (tumor doubling time, 6.15 ± 0.31 days; log₁₀ cell kill, 0.975 ± 0.110; cell kill, 89.4 ± 2.2%) compared with LND alone of 1.1 ± 0.1 days and LPAM alone of 4.0 ± 0.0 days. The study demonstrates that the effects of LND on tumor pH_i and bioenergetics may sensitize melanoma to pH‐dependent therapeutics, such as chemotherapy with alkylating agents or hyperthermia. Copyright © 2012 John Wiley & Sons, Ltd.     

Diffusion behavior of cerebral metabolites of congenital portal systemic shunt mice assessed noninvasively by diffusion‐weighted 1H magnetic resonance spectroscopy

Diffusion‐weighted ¹H‐MRS (DW‐MRS) allows for noninvasive investigation of the cellular compartmentalization of cerebral metabolites. DW‐MRS applied to the congenital portal systemic shunt (PSS) mouse brain may provide specific insight into alterations of cellular restrictions associated with PSS in humans. At 14.1 T, adult male PSS and their age‐matched healthy (Ctrl) mice were studied using DW‐MRS covering b‐values ranging from 0 to 45 ms/μm² to determine the diffusion behavior of abundant metabolites. The remarkable sensitivity and spectral resolution, in combination with very high diffusion weighting, allowed for precise measurement of the diffusion properties of endogenous N‐acetyl‐aspartate, total creatine, myo‐inositol, total choline with extension to glutamine and glutamate in mouse brains, in vivo. Most metabolites had comparable diffusion properties in PSS and Ctrl mice, suggesting that intracellular distribution space for these metabolites was not affected in the model. The slightly different diffusivity of the slow decaying component of taurine (0.015 ± 0.003 μm²/ms in PSS vs 0.021 ± 0.002 μm²/ms in Ctrl, P < 0.05) might support a cellular redistribution of taurine in the PSS mouse brain.     

Characterisation of mobile lipid resonances in tissue biopsies from patients with cervical cancer and correlation with cytoplasmic lipid droplets

The aims of this study were to characterise the major saturated and unsaturated lipid peaks in histologically normal cervical epithelium and stroma, dysplastic epithelium (low‐grade cervical intraepithelial neoplasia, CIN) and cancer‐containing tissue samples from patients with cervical cancer using diffusion‐weighted ¹H high‐resolution magic angle spinning MRS, to determine whether mobile lipid resonances (MLRs) distinguish tissue types and to test for a correlation between MLRs and the number of cytoplasmic lipid droplets. Diffusion‐weighted spectra of tissue biopsies were acquired using a stimulated echo sequence with bipolar gradients. Major saturated and unsaturated MLRs were identified and multivariate analysis of peak combinations was used to determine the best separation between tissue classes. Lipid droplets were visualised with Nile red staining and fluorescence microscopy. Correlations of saturated lipid resonances (0.9 and 1.3 ppm), polyunsaturated resonances (2.8 ppm), triglycerides (4.3 ppm) and unsaturated resonances (5.3 ppm) with average droplet number (per image) were investigated using a Spearman rank test. A large heterogeneity in lipid content among samples was observed, resulting in no significant differences in MLR intensities of individual peaks between the three tissue classes. Linear discriminant analysis separated ‘no cancer’ from ‘cancer’ based on the intensities at 0.9, 1.3, 2.2 and 2.8 ppm [area under the curve (AUC) = 0.939, p < 0.001], ‘low‐grade CIN’ from ‘cancer’ based on the intensities at 0.9, 4.1, 4.3 and 5.3 ppm (AUC = 0.987, p < 0.001) and ‘no cancer’ from ‘low‐grade CIN’ based on intensities at 0.9, 2.2 and 4.3 ppm (AUC = 0.984, p < 0.001). The distribution of cytoplasmic lipid droplets was nonuniform and was not related to the presence of epithelial or stromal components. On average, there were more droplets visible in low‐grade CIN and cancer‐containing tissues. Significant correlations between MLR peaks and lipid droplet number were seen for 0.9 (p = 0.002), 1.3 (p = 0.003) and 2.8 ppm (p = 0.018). MLR combinations indicative of average lipid structure efficiently separated tissue classes. Increased lipid resonances correlated with increased numbers of cytoplasmic lipid droplets. Copyright © 2013 John Wiley & Sons, Ltd.     

Age‐ and sex‐related differences in muscle phosphocreatine and oxygenation kinetics during high‐intensity exercise in adolescents and adults

The aim of this investigation was to examine the adaptation of the muscle phosphates (e.g. phosphocreatine (PCr) and ADP) implicated in regulating oxidative phosphorylation, and oxygenation at the onset of high intensity exercise in children and adults. The hypotheses were threefold: primary PCr kinetics would be faster in children than adults; the amplitude of the PCr slow component would be attenuated in children; and the amplitude of the deoxyhaemoglobin/myoglobin (HHb) slow component would be reduced in children. Eleven children (5 girls, 6 boys, 13 ± 1 years) and 11 adults (5 women, 6 men, 24 ± 4 years) completed two to four constant work rate exercise tests within a 1.5 T MR scanner. Quadriceps muscle energetics during high intensity exercise were monitored using ³¹P‐MRS. Muscle oxygenation was monitored using near‐infrared spectroscopy. The time constant for the PCr response was not significantly different in boys (31 ± 10 s), girls (31 ± 10 s), men (44 ± 20 s) or women (29 ± 14 s, main effects: age, p = 0.37, sex, p = 0.25). The amplitude of the PCr slow component relative to end‐exercise PCr was not significantly different between children (23 ± 23%) and adults (17 ± 13%, p = 0.47). End‐exercise [PCr] was significantly lower, and [ADP] higher, in females (18 ± 4 mM and 53 ± 16 µM) than males (23 ± 4 mM, p = 0.02 and 37 ± 11 µM, p = 0.02), but did not differ with age ([PCr]: p = 0.96, [ADP]: p = 0.72). The mean response time for muscle tissue deoxygenation was significantly faster in children (22 ± 4 s) than adults (27 ± 7 s, p = 0.01). The results of this study show that the control of oxidative metabolism at the onset of high intensity exercise is adult‐like in 13‐year‐old children, but that matching of oxygen delivery to extraction is more precise in adults. Copyright © 2010 John Wiley & Sons, Ltd.     

In vivo mouse myocardial 31P MRS using three‐dimensional image‐selected in vivo spectroscopy (3D ISIS): technical considerations and biochemical validations

³¹P MRS provides a unique non‐invasive window into myocardial energy homeostasis. Mouse models of cardiac disease are widely used in preclinical studies, but the application of ³¹P MRS in the in vivo mouse heart has been limited. The small‐sized, fast‐beating mouse heart imposes challenges regarding localized signal acquisition devoid of contamination with signal originating from surrounding tissues. Here, we report the implementation and validation of three‐dimensional image‐selected in vivo spectroscopy (3D ISIS) for localized ³¹P MRS of the in vivo mouse heart at 9.4 T. Cardiac ³¹P MR spectra were acquired in vivo in healthy mice (n = 9) and in transverse aortic constricted (TAC) mice (n = 8) using respiratory‐gated, cardiac‐triggered 3D ISIS. Localization and potential signal contamination were assessed with ³¹P MRS experiments in the anterior myocardial wall, liver, skeletal muscle and blood. For healthy hearts, results were validated against ex vivo biochemical assays. Effects of isoflurane anesthesia were assessed by measuring in vivo hemodynamics and blood gases. The myocardial energy status, assessed via the phosphocreatine (PCr) to adenosine 5′‐triphosphate (ATP) ratio, was approximately 25% lower in TAC mice compared with controls (0.76 ± 0.13 versus 1.00 ± 0.15; P < 0.01). Localization with one‐dimensional (1D) ISIS resulted in two‐fold higher PCr/ATP ratios than measured with 3D ISIS, because of the high PCr levels of chest skeletal muscle that contaminate the 1D ISIS measurements. Ex vivo determinations of the myocardial PCr/ATP ratio (0.94 ± 0.24; n = 8) confirmed the in vivo observations in control mice. Heart rate (497 ± 76 beats/min), mean arterial pressure (90 ± 3.3 mmHg) and blood oxygen saturation (96.2 ± 0.6%) during the experimental conditions of in vivo ³¹P MRS were within the normal physiological range. Our results show that respiratory‐gated, cardiac‐triggered 3D ISIS allows for non‐invasive assessments of in vivo mouse myocardial energy homeostasis with ³¹P MRS under physiological conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Cardiac lipid levels show diurnal changes and long‐term variations in healthy human subjects

¹H‐MRS is regularly applied to determine lipid content in ectopic tissue – mostly skeletal muscle and liver – to investigate physiological and/or pathologic conditions, e.g. insulin resistance. Technical developments also allow non‐invasive in vivo assessment of cardiac lipids; however, basic data about methodological reliability (repeatability) and physiological variations are scarce. The aim of the presented work was to determine potential diurnal changes of cardiac lipid stores in humans, and to put the results in relation to methodological repeatability and normal physiological day‐to‐day variations. Optimized cardiac‐ and respiratory‐gated ¹H‐MRS was used for non‐invasive quantification of intracardiomyocellular lipids (ICCL), creatine, trimethyl‐ammonium compounds (TMA), and taurine in nine healthy young men at three time points per day on two days separated by one week. This design allowed determination of (a) diurnal changes, (b) physiological variation over one week and (c) methodological repeatability of the ICCL levels. Comparison of fasted morning to post‐absorptive evening measurements revealed a significant 37 ± 19% decrease of ICCL during the day (p = 0.0001). There was a significant linear correlation between ICCL levels in the morning and their decrease during the day (p = 0.015). Methodological repeatability for the ICCL/creatine ratio was excellent, with a coefficient of variance of ~5%, whereas physiological variation was found to be considerably higher (22%) in spite of a standardized physiological preparation protocol. In contrast, TMA levels remained stable over this time period. The proposed ¹H‐MRS technique provides a robust way to investigate relevant physiological changes in cardiac metabolites, in particular ICCL. The present results suggest that ICCL reveal a diurnal course, with higher levels in the morning as compared to evening. In addition, a considerable long‐term variation of ICCL levels, in both the morning and evening, was documented. Given the high methodological repeatability, these effects should be taken into account in studies investigating the metabolic role of ICCL. Copyright © 2014 John Wiley & Sons, Ltd.     

The cellular origins of cancer with particular reference to the gastrointestinal tract

Stem cells or their closely related committed progenitor cells are the likely founder cells of most neoplasms. In the continually renewing and hierarchically organized epithelia of the oesophagus, stomach and intestine, homeostatic stem cells are located at the beginning of the cell flux, in the basal layer of the oesophagus, the isthmic region of gastric oxyntic glands and at the bottom of gastric pyloric‐antral glands and colonic crypts. The introduction of mutant oncogenes such as Kras^G12D or loss of Tp53 or Apc to specific cell types expressing the likes of Lgr5 and Mist1 can be readily accomplished in genetically engineered mouse models to initiate tumorigenesis. Other origins of cancer are discussed including ‘reserve’ stem cells that may be activated by damage or through disruption of morphogen gradients along the crypt axis. In the liver and pancreas, with little cell turnover and no obvious stem cell markers, the importance of regenerative hyperplasia associated with chronic inflammation to tumour initiation is vividly apparent, though inflammatory conditions in the renewing populations are also permissive for tumour induction. In the liver, hepatocytes, biliary epithelial cells and hepatic progenitor cells are embryologically related, and all can give rise to hepatocellular carcinoma and cholangiocarcinoma. In the exocrine pancreas, both acinar and ductal cells can give rise to pancreatic ductal adenocarcinoma (PDAC), although the preceding preneoplastic states are quite different: acinar‐ductal metaplasia gives rise to pancreatic intraepithelial neoplasia culminating in PDAC, while ducts give rise to PDAC via. mucinous cell metaplasia that may have a polyclonal origin.     

Effects of exercise‐induced intracellular acidosis on the phosphocreatine recovery kinetics: a 31P MRS study in three muscle groups in humans

Little is known about the metabolic differences that exist among different muscle groups within the same subjects. Therefore, we used ³¹P‐magnetic resonance spectroscopy (³¹P‐MRS) to investigate muscle oxidative capacity and the potential effects of pH on PCr recovery kinetics between muscles of different phenotypes (quadriceps (Q), finger (FF) and plantar flexors (PF)) in the same cohort of 16 untrained adults. The estimated muscle oxidative capacity was lower in Q (29 ± 12 mM min^‐1, CV_{inter‐subject} = 42%) as compared with PF (46 ± 20 mM min^‐1, CV_{inter‐subject} = 44%) and tended to be higher in FF (43 ± 35 mM min^‐1, CV_{inter‐subject} = 80%). The coefficient of variation (CV) of oxidative capacity between muscles within the group was 59 ± 24%. PCr recovery time constant was correlated with end‐exercise pH in Q (p < 0.01), FF (p < 0.05) and PF (p <0.05) as well as proton efflux rate in FF (p < 0.01), PF (p < 0.01) and Q (p = 0.12). We also observed a steeper slope of the relationship between end‐exercise acidosis and PCr recovery kinetics in FF compared with either PF or Q muscles. Overall, this study supports the concept of skeletal muscle heterogeneity by revealing a comparable inter‐ and intra‐individual variability in oxidative capacity across three skeletal muscles in untrained individuals. These findings also indicate that the sensitivity of mitochondrial respiration to the inhibition associated with cytosolic acidosis is greater in the finger flexor muscles compared with locomotor muscles, which might be related to differences in permeability in the mitochondrial membrane and, to some extent, to proton efflux rates. Copyright © 2013 John Wiley & Sons, Ltd.     

Automated whole‐brain N‐acetylaspartate proton MRS quantification

Concentration of the neuronal marker, N‐acetylaspartate (NAA), a quantitative metric for the health and density of neurons, is currently obtained by integration of the manually defined peak in whole‐head proton (¹H)‐MRS. Our goal was to develop a full spectral modeling approach for the automatic estimation of the whole‐brain NAA concentration (WBNAA) and to compare the performance of this approach with a manual frequency‐range peak integration approach previously employed. MRI and whole‐head ¹H‐MRS from 18 healthy young adults were examined. Non‐localized, whole‐head ¹H‐MRS obtained at 3 T yielded the NAA peak area through both manually defined frequency‐range integration and the new, full spectral simulation. The NAA peak area was converted into an absolute amount with phantom replacement and normalized for brain volume (segmented from T₁‐weighted MRI) to yield WBNAA. A paired‐sample t test was used to compare the means of the WBNAA paradigms and a likelihood ratio test used to compare their coefficients of variation. While the between‐subject WBNAA means were nearly identical (12.8 ± 2.5 mm for integration, 12.8 ± 1.4 mm for spectral modeling), the latter's standard deviation was significantly smaller (by ~50%, p = 0.026). The within‐subject variability was 11.7% (±1.3 mm ) for integration versus 7.0% (±0.8 mm ) for spectral modeling, i.e., a 40% improvement. The (quantifiable) quality of the modeling approach was high, as reflected by Cramer–Rao lower bounds below 0.1% and vanishingly small (experimental ‐ fitted) residuals. Modeling of the whole‐head ¹H‐MRS increases WBNAA quantification reliability by reducing its variability, its susceptibility to operator bias and baseline roll, and by providing quality‐control feedback. Together, these enhance the usefulness of the technique for monitoring the diffuse progression and treatment response of neurological disorders. Copyright © 2014 John Wiley & Sons, Ltd.