Analyzing Spatial Heterogeneity in DCE- and DW-MRI Parametric Maps to Optimize Prediction of Pathologic Response to Neoadjuvant Chemotherapy in Breast Cancer

The purpose of this study is to investigate the ability of multivariate analysis of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and diffusion-weighted MRI (DW-MRI) parametric maps, obtained early in the course of therapy, to predict which patients will achieve pathologic complete response (pCR) at the time of surgery. Thirty-three patients underwent DCE-MRI (to estimate K^trans, v_e, k_ep, and v_p) and DW-MRI [to estimate the apparent diffusion coefficient (ADC)] at baseline (t₁) and after the first cycle of neoadjuvant chemotherapy (t₂). Four analyses were performed and evaluated using receiver-operating characteristic (ROC) analysis to test their ability to predict pCR. First, a region of interest (ROI) level analysis input the mean K^trans, v_e, k_ep, v_p, and ADC into the logistic model. Second, a voxel-based analysis was performed in which a longitudinal registration algorithm aligned serial parameters to a common space for each patient. The voxels with an increase in k_ep, K^trans, and v_p or a decrease in ADC or v_e were then detected and input into the regression model. In the third analysis, both the ROI and voxel level data were included in the regression model. In the fourth analysis, the ROI and voxel level data were combined with selected clinical data in the regression model. The overfitting-corrected area under the ROC curve (AUC) with 95% confidence intervals (CIs) was then calculated to evaluate the performance of the four analyses. The combination of k_ep, ADC ROI, and voxel level data achieved the best AUC (95% CI) of 0.87 (0.77–0.98).     

Comparison of DCE-MRI of murine model cancers with a low dose and high dose of contrast agent

There are increasing concerns regarding intracellular accumulation of gadolinium (Gd) after multiple dynamic contrast enhanced (DCE) MRI scans. We investigated whether a low dose (LD) of Gd-based contrast agent is as effective as a high dose (HD) for quantitative analysis of DCE-MRI data, and evaluated the use of a split dose protocol to obtain new diagnostic parameters. Female C3H mice (n = 6) were injected with mammary carcinoma cells in the hind leg. MRI experiments were performed on 9.4 T scanner. DCE-MRI data were acquired with 1.5 s temporal resolution before and after a LD (0.04 mmol/kg), then again after 30 min followed by a HD (0.2 mmol/kg) bolus injection of Omniscan. The standard Tofts model was used to extract physiological parameters (K^trans and v_e) with the arterial input function derived from muscle reference tissue. In addition, an empirical mathematical model was used to characterize maximum contrast agent uptake (A), contrast agent uptake rate (α) and washout rate (β and γ). There were moderate to strong correlations (r = 0.69–0.97, p < 0001) for parameters K^trans, v_e, A, α and β from LD versus HD data. On average, tumor parameters obtained from LD data were significantly larger (p < 0.05) than those from HD data. The parameter ratios, K^trans, v_e, A and α calculated from the LD data divided by the HD data, were all significantly larger than 1.0 (p < 0.003) for tumor. T₂* changes following contrast agent injection affected parameters calculated from HD data, but this was not the case for LD data. The results suggest that quantitative analysis of LD data may be at least as effective for cancer characterization as quantitative analysis of HD data. In addition, the combination of parameters from two different doses may provide useful diagnostic information.     

Variations of Dynamic Contrast-Enhanced Magnetic Resonance Imaging in Evaluation of Breast Cancer Therapy Response: A Multicenter Data Analysis Challenge

Pharmacokinetic analysis of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) time-course data allows estimation of quantitative parameters such as K^trans (rate constant for plasma/interstitium contrast agent transfer), v_e (extravascular extracellular volume fraction), and v_p (plasma volume fraction). A plethora of factors in DCE-MRI data acquisition and analysis can affect accuracy and precision of these parameters and, consequently, the utility of quantitative DCE-MRI for assessing therapy response. In this multicenter data analysis challenge, DCE-MRI data acquired at one center from 10 patients with breast cancer before and after the first cycle of neoadjuvant chemotherapy were shared and processed with 12 software tools based on the Tofts model (TM), extended TM, and Shutter-Speed model. Inputs of tumor region of interest definition, pre-contrast T₁, and arterial input function were controlled to focus on the variations in parameter value and response prediction capability caused by differences in models and associated algorithms. Considerable parameter variations were observed with the within-subject coefficient of variation (wCV) values for K^trans and v_p being as high as 0.59 and 0.82, respectively. Parameter agreement improved when only algorithms based on the same model were compared, e.g., the K^trans intraclass correlation coefficient increased to as high as 0.84. Agreement in parameter percentage change was much better than that in absolute parameter value, e.g., the pairwise concordance correlation coefficient improved from 0.047 (for K^trans) to 0.92 (for K^trans percentage change) in comparing two TM algorithms. Nearly all algorithms provided good to excellent (univariate logistic regression c-statistic value ranging from 0.8 to 1.0) early prediction of therapy response using the metrics of mean tumor K^trans and k_ep (= K^trans/v_e, intravasation rate constant) after the first therapy cycle and the corresponding percentage changes. The results suggest that the interalgorithm parameter variations are largely systematic, which are not likely to significantly affect the utility of DCE-MRI for assessment of therapy response.     

The Microenvironment of Cervical Carcinoma Xenografts: Associations with Lymph Node Metastasis and Its Assessment by DCE-MRI

Poor disease-free and overall survival rates in locally advanced cervical cancer are associated with a tumor micro-environment characterized by extensive hypoxia, interstitial hypertension, and high lactate concentrations. The potential of gadolinium diethylenetriamine pentaacetic acid-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in assessing the microenvironment and microenvironment-associated aggressiveness of cervical carcinomas was investigated in this preclinical study. CK-160 and TS-415 cervical carcinoma xenografts were used as tumor models. DCE-MRI was carried out at 1.5 T, and parametric images of K^trans and v_e were produced by pharmacokinetic analysis of the DCE-MRI series. Pimonidazole was used as a marker of hypoxia. A Millar catheter was used to measure tumor interstitial fluid pressure (IFP). The concentrations of glucose, adenosine triphosphate (ATP), and lactate were measured by induced metabolic bioluminescence imaging. High incidence of lymph node metastases was associated with high hypoxic fraction and high lactate concentration in CK-160 tumors and with high IFP and high lactate concentration in TS-415 tumors. Low K^trans was associated with high hypoxic fraction, low glucose concentration, and high lactate concentration in tumors of both lines and with high incidence of metastases in CK-160 tumors. Associations between v_e and microenvironmental parameters or metastatic propensity were not detected in any of the tumor lines. Taken together, this preclinical study suggests that K^trans is a potentially useful biomarker for poor outcome of treatment in advanced cervical carcinoma. The possibility that K^trans may be used to identify patients with cervical cancer who are likely to benefit from particularly aggressive treatment merits thorough clinical investigations.     

Dynamic Contrast-Enhanced Magnetic Resonance Imaging with Gd-EOB-DTPA for the Evaluation of Liver Fibrosis Induced by Carbon Tetrachloride in Rats

Purpose

To investigate the utility of dynamic contrast-enhanced MRI (DCE-MRI) with Gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) for detecting liver fibrosis induced by carbon tetrachloride (CCl₄) in rats.

Methods

This study was approved by the institutional animal care and use committee. Liver fibrosis in rats was induced by intraperitoneal injection of 1 mL/kg 50% CCl₄ twice a week for 4-13 weeks. Control rats were injected with saline. Liver fibrosis was graded using the Metaviar score: no fibrosis (F0), mild fibrosis (F1-F2) and advanced fibrosis (F3-F4). DCE-MRI with Gd-EOB-DTPA was performed for all rats. K^trans, K_ep, V_e and iAUC of the liver parenchyma were measured. Relative enhancement (RE) value of the liver was calculated on T₁-weighted images at 15, 20 and 25 min after Gd-EOB-DTPA administration.

Results

Thirty-five rats were included: no fibrosis (n=13), mild fibrosis (n=11) and advanced fibrosis (n=11). K^trans and iAUC values were highest in advanced fibrosis group and lowest in no fibrosis group (P＜0.05). The area under the receiver operating characteristic curve (AUROC) for fibrosis (stages F1 and greater) were 0.773 and 0.882 for K^trans and iAUC, respectively. AUROC for advanced fibrosis were 0.835 and 0.867 for K^trans and iAUC, respectively. K_ep and RE values were not able to differentiate fibrosis stages (all P＞0.05).

Conclusion

K^trans and iAUC obtained from DCE-MRI with Gd-EOB-DTPA are useful for the detection and staging of rat liver fibrosis induced by CCl₄.     

In Vivo Correlation of Glucose Metabolism,Cell Density and Microcirculatory Parameters in Patients with Head and Neck Cancer: Initial Results Using Simultaneous PET/MRI

Objective

To demonstrate the feasibility of simultaneous acquisition of ¹⁸F-FDG-PET, diffusion-weighted imaging (DWI) and T1-weighted dynamic contrast-enhanced MRI (T1w-DCE) in an integrated simultaneous PET/MRI in patients with head and neck squamous cell cancer (HNSCC) and to investigate possible correlations between these parameters.

Methods

17 patients that had given informed consent (15 male, 2 female) with biopsy-proven HNSCC underwent simultaneous ¹⁸F-FDG-PET/MRI including DWI and T1w-DCE. SUV_max, SUV_mean, ADC_mean, ADC_min and K ^trans, k _ep and v _e were measured for each tumour and correlated using Spearman’s ρ.

Results

Significant correlations were observed between SUV_mean and K ^trans (ρ = 0.43; p ≤ 0.05); SUV_mean and k _ep (ρ = 0.44; p ≤ 0.05); K ^trans and k _ep (ρ = 0.53; p ≤ 0.05); and between k _ep and v _e (ρ = -0.74; p ≤ 0.01). There was a trend towards statistical significance when correlating SUV_max and ADC_min (ρ = -0.35; p = 0.08); SUV_max and K ^trans (ρ = 0.37; p = 0.07); SUV_max and k _ep (ρ = 0.39; p = 0.06); and ADC_mean and v _e (ρ = 0.4; p = 0.06).

Conclusion

Simultaneous ¹⁸F-FDG-PET/MRI including DWI and T1w-DCE in patients with HNSCC is feasible and allows depiction of complex interactions between glucose metabolism, microcirculatory parameters and cellular density.     

18F-FDG PET Metabolic Parameters and MRI Perfusion and Diffusion Parameters in Hepatocellular Carcinoma: A Preliminary Study

Objectives

Glucose metabolism, perfusion, and water diffusion may have a relationship or affect each other in the same tumor. The understanding of their relationship could expand the knowledge of tumor characteristics and contribute to the field of oncologic imaging. The purpose of this study was to evaluate the relationships between metabolism, vasculature and cellularity of advanced hepatocellular carcinoma (HCC), using multimodality imaging such as ¹⁸F-FDG positron emission tomography (PET), dynamic contrast enhanced (DCE)-MRI, and diffusion weighted imaging(DWI).

Materials and Methods

Twenty-one patients with advanced HCC underwent ¹⁸F-FDG PET, DCE-MRI, and DWI before treatment. Maximum standard uptake values (SUV_max) from ¹⁸F-FDG-PET, variables of the volume transfer constant (K^trans) from DCE-MRI and apparent diffusion coefficient (ADC) from DWI were obtained for the tumor and their relationships were examined by Spearman’s correlation analysis. The influence of portal vein thrombosis on SUV_max and variables of K^trans and ADC was evaluated by Mann-Whitney test.

Results

SUV_max showed significant negative correlation with K^trans _max (ρ = −0.622, p = 0.002). However, variables of ADC showed no relationship with variables of K^trans or SUV_max (p>0.05). Whether portal vein thrombosis was present or not did not influence the SUV _max and variables of ADC and K^trans (p>0.05).

Conclusion

In this study, SUV was shown to be correlated with K_trans in advanced HCCs; the higher the glucose metabolism a tumor had, the lower the perfusion it had, which might help in guiding target therapy.     

Evaluating treatment response using DW-MRI and DCE-MRI in trastuzumab responsive and resistant HER2-overexpressing human breast cancer xenografts

We report longitudinal diffusion-weighted magnetic resonance imaging (DW-MRI) and dynamic contrast enhanced (DCE)-MRI (7 T) studies designed to identify functional changes, prior to volume changes, in trastuzumab-sensitive and resistant HER2 + breast cancer xenografts. Athymic mice (N = 33) were subcutaneously implanted with trastuzumab-sensitive (BT474) or trastuzumab-resistant (HR6) breast cancer cells. Tumor-bearing animals were distributed into four groups: BT474 treated and control, HR6 treated and control. DW- and DCE-MRI were conducted at baseline, day 1, and day 4; trastuzumab (10 mg/kg) or saline was administered at baseline and day 3. Animals were sacrificed on day 4 and tumors resected for histology. Voxel-based DW- and DCE-MRI analyses were performed to generate parametric maps of ADC, K^trans, and v_e. On day 1, no differences in tumor size were observed between any of the groups. On day 4, significant differences in tumor size were observed between treated vs. control BT474, treated BT474 vs. treated HR6, and treated vs. control HR6 (P < .0001). On day 1, v_e was significantly higher in the BT474 treated group compared to BT474 control (P = .002) and HR6 treated (P = .004). On day 4, v_e and K^trans were significantly higher in the treated BT474 tumors compared to BT474 controls (P = .0007, P = .02, respectively). A significant decrease in Ki67 staining reinforced response in the BT474 treated group compared to BT474 controls (P = .02). This work demonstrated that quantitative MRI biomarkers have the sensitivity to differentiate treatment response in HER2 + tumors prior to changes in tumor size.     

Monitoring the Effect of Docetaxel Treatment in MCF7 Xenografts Using Multimodal In Vivo and Ex Vivo Magnetic Resonance Methods,Histopathology, and Gene Expression

The purpose of this study was to evaluate the sensitivity of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), diffusion-weighted (DW)-MRI, in vivo MR spectroscopy (MRS), and ex vivo high-resolution magic angle spinning (HR MAS) MRS for the detection of early treatment effects after docetaxel administration. Docetaxel is an antitumor agent that leads to mitotic arrest, apoptosis, and mitotic catastrophe cell death. Gene expression analysis was performed to detect altered regulation in gene expression pathways related to docetaxel treatment effects. Histopathology was used as a measure of alterations in apoptosis and proliferation due to docetaxel. Experiments were performed using MCF7 mouse xenografts, randomized into a docetaxel (30 mg/kg) treatment group and a control group given saline. MRI/MRS was performed 1 day before treatment and 1, 3, and 6 days after treatment. Parametric images of the extracellular extravascular volume fraction (v_e) transfer constant (K^trans) and the apparent diffusion coefficient (ADC) were calculated from the DCE-MRI and DW-MRI data. Biopsies were analyzed by HR MAS MRS, and histopathology and gene expression profiles were determined (Illumina). A significant increase in the ADC 3 and 6 days after treatment and a significant decrease in total choline and a higher v_e were found in treated tumors 6 days after treatment. No significant difference was found in the K^trans between the two groups. Our results show that docetaxel induces apoptosis and decreases proliferation in MCF7 xenografts. Further, these phenomena can be monitored by in vivo MRS, DW-MRI, and gene expression.     

Reduced Sialylation Impacts Ventricular Repolarization by Modulating Specific K+ Channel Isoforms Distinctly

Voltage-gated K⁺ channels (K_v) are responsible for repolarizing excitable cells and can be heavily glycosylated. Cardiac K_v activity is indispensable where even minimal reductions in function can extend action potential duration, prolong QT intervals, and ultimately contribute to life-threatening arrhythmias. Diseases such as congenital disorders of glycosylation often cause significant cardiac phenotypes that can include arrhythmias. Here we investigated the impact of reduced sialylation on ventricular repolarization through gene deletion of the sialyltransferase ST3Gal4. ST3Gal4-deficient mice (ST3Gal4^−/−) had prolonged QT intervals with a concomitant increase in ventricular action potential duration. Ventricular apex myocytes isolated from ST3Gal4^−/− mice demonstrated depolarizing shifts in activation gating of the transient outward (I_to) and delayed rectifier (I_Kslow) components of K⁺ current with no change in maximum current densities. Consistently, similar protein expression levels of the three K_v isoforms responsible for I_to and I_Kslow were measured for ST3Gal4^−/− versus controls. However, novel non-enzymatic sialic acid labeling indicated a reduction in sialylation of ST3Gal4^−/− ventricular K_v4.2 and K_v1.5, which contribute to I_to and I_Kslow, respectively. Thus, we describe here a novel form of regulating cardiac function through the activities of a specific glycogene product. Namely, reduced ST3Gal4 activity leads to a loss of isoform-specific K_v sialylation and function, thereby limiting K_v activity during the action potential and decreasing repolarization rate, which likely contributes to prolonged ventricular repolarization. These studies elucidate a novel role for individual glycogene products in contributing to a complex network of cardiac regulation under normal and pathologic conditions.     

Diffusion kurtosis imaging in head and neck cancer: A correlation study with dynamic contrast enhanced MRI

PurposeTo investigate the biophysical meaning of Diffusion Kurtosis Imaging (DKI) parameters via correlations with the perfusion parameters obtained from a long Dynamic Contrast Enhanced MRI scan, in head and neck (HN) cancer.MethodsTwenty two patients with newly diagnosed HN tumor were included in the present retrospective study. Some patients had multiple lesions, therefore a total of 26 lesions were analyzed. DKI was acquired using 5b values at 0, 500, 1000,1500 and 2000 s/mm². DCE-MRI was obtained with 130 dynamic volumes, with a temporal resolution of 5 s, to achieve a long scan time (>10 min). The apparent diffusion coefficient D_app and apparent diffusional kurtosis K_app were calculated voxel-by-voxel, removing the point at b value = 0 to eliminate possible perfusion effects on the parameter estimations. The transfer constants K^trans and K_ep, v_e, and the histogram-based entropy (En) and interquartile range (IQR) of each DCE-MRI parameter were quantified. Correlations between all variables were investigated by the Spearman’s Rho correlation test.ResultsModerate relationships emerged between D_app and K_ep (Rho =  − 0.510, p = 0.009), and between D_app and v_e (Rho = 0.418, p = 0.038). En(K_ep) was significantly related to K_app (Rho = 0.407, p = 0.043), while IQR(K_ep) showed an inverse association with D_app (Rho = -0.422, p = 0.035).ConclusionsA weak to intermediate correlation was found between DKI parameters and both K_ep and v_e. The kurtosis was associated to the intratumoral heterogeneity and complexity of the capillary permeability, expressed by En(K_ep).     

Loss of the K+ channel Kv2.1 greatly reduces outward dark current and causes ionic dysregulation and degeneration in rod photoreceptors

Vertebrate retinal photoreceptors signal light by suppressing a circulating “dark current” that maintains their relative depolarization in the dark. This dark current is composed of an inward current through CNG channels and NCKX transporters in the outer segment that is balanced by outward current exiting principally from the inner segment. It has been hypothesized that K_v2.1 channels carry a predominant fraction of the outward current in rods. We examined this hypothesis by comparing whole cell, suction electrode, and electroretinographic recordings from K_v2.1 knockout (K_v2.1^−/−) and wild-type (WT) mouse rods. Single cell recordings revealed flash responses with unusual kinetics, and reduced dark currents that were quantitatively consistent with the measured depolarization of the membrane resting potential in the dark. A two-compartment (outer and inner segment) physiological model based on known ionic mechanisms revealed that the abnormal K_v2.1^−/− rod photoresponses arise principally from the voltage dependencies of the known conductances and the NCKX exchanger, and a highly elevated fraction of inward current carried by Ca²⁺ through CNG channels due to the aberrant depolarization. K_v2.1^−/− rods had shorter outer segments than WT and dysmorphic mitochondria in their inner segments. Optical coherence tomography of knockout animals demonstrated a slow photoreceptor degeneration over a period of 6 mo. Overall, these findings reveal that K_v2.1 channels carry 70–80% of the non-NKX outward dark current of the mouse rod, and that the depolarization caused by the loss of K_v2.1 results in elevated Ca²⁺ influx through CNG channels and elevated free intracellular Ca²⁺, leading to progressive degeneration.     

Can DCEMRI assess the effect of green tea on the angiogenic properties of rodent prostate tumors?

The purpose of this research was to test whether dynamic contrast enhanced MRI could assess the effect of green tea on the angiogenic properties of transplanted rodent tumors. Copenhagen rats bearing AT6.1 prostate tumors inoculated in the hind limbs were randomly assigned to cages in which they were allowed to only drink either plain water (control group) or water containing green tea extract (treated group). Assignments were made after a baseline MRI experiment (week 0) was performed on each rat at 4.7 T. All the rats were subsequently imaged at day 7 (week 1) and day 14 (week 2) to follow tumor growth and vascular development. The two-compartment pharmacokinetic model was used to analyze the dynamic contrast Gd-DTPA enhanced MRI data on a pixel-by-pixel basis over the tumor area to obtain the volume transfer constant (K^trans) and extravascular extracellular space (v_e). An identity Chi-squared test showed that the distributions of averaged histograms (n = 6) of K^trans and v_e were significantly different from week 0 to both weeks 1 and 2 (p < 0.001) in both the control and the treated rats due to increasing areas of tumor necrosis. However, the tumor growth rate was statistically indistinguishable between control and treated rats. There was no significant difference in the distributions of K^trans and v_e between control and treated rats. The results showed that no effects of green tea on tumor micro-vasculature were measurable by dynamic Gd-DTPA enhanced MRI.     

Two Structurally Different Dienelactone Hydrolases (TfdEI and TfdEII) from Cupriavidus necator JMP134 Plasmid pJP4 Catalyse Cis- and Trans-Dienelactones with Similar Efficiency

In this study, dienelactone hydrolases (TfdEI and TfdEII) located on plasmid pJP4 of Cupriavidus necator JMP134 were cloned, purified, characterized and three dimensional structures were predicted. tfdEI and tfdEII genes were cloned into pET21b vector and expressed in E. coli BL21(DE3). The enzymes were purified by applying ultra-membrane filtration, anion-exchange QFF and gel-filtration columns. The enzyme activity was determined by using cis-dienelactone. The three-dimensional structure of enzymes was predicted using SWISS-MODEL workspace and the biophysical properties were determined on ExPASy server. Both TfdEI and TfdEII (M_r 25 kDa) exhibited optimum activity at 37°C and pH 7.0. The enzymes retained approximately 50% of their activity after 1 h of incubation at 50°C and showed high stability against denaturing agents. The TfdEI and TfdEII hydrolysed cis-dienelactone at a rate of 0.258 and 0.182 µMs⁻¹, with a K_m value of 87 µM and 305 µM, respectively. Also, TfdEI and TfdEII hydrolysed trans-dienelactone at a rate of 0.053 µMs⁻¹ and 0.0766 µMs⁻¹, with a K_m value of 84 µM and 178 µM, respectively. The TfdEI and TfdEII k_cat/K_m ratios were 0.12 µM⁻¹s⁻¹and 0.13 µM⁻¹s⁻¹ and 0.216 µM⁻¹s⁻¹ and 0.094 µM⁻¹s⁻¹ for for cis- and trans-dienelactone, respectively. The k_cat/K_m ratios for cis-dienelactone show that both enzymes catalyse the reaction with same efficiency even though K_m value differs significantly. This is the first report to characterize and compare reaction kinetics of purified TfdEI and TfdEII from Cupriavidus necator JMP134 and may be helpful for further exploration of their catalytic mechanisms.     

Kinetic Parameters of the Conversion of Methane Precursors to Methane in a Hypereutrophic Lake Sediment

The kinetic parameters K_m, V_max, T_t (turnover time), and v (natural velocity) were determined for H₂ and acetate conversion to methane by Wintergreen Lake sediment, using short-term (a few hours) methods and incubation temperatures of 10 to 14°C. Estimates of the Michaelis-Menten constant, K_m, for both the consumption of hydrogen and the conversion of hydrogen to methane by sediment microflora averaged about 0.024 μmol g⁻¹ of dry sediment. The maximal velocity, V_max, averaged 4.8 μmol of H₂ g⁻¹ h⁻¹ for hydrogen consumption and 0.64 μmol of CH₄ g⁻¹ h⁻¹ for the conversion of hydrogen to methane during the winter. Estimated natural rates of hydrogen consumption and hydrogen conversion to methane could be calculated from the Michaelis-Menten equation and estimates of K_m, V_max, and the in situ dissolved-hydrogen concentration. These results indicate that methane may not be the only fate of hydrogen in the sediment. Among several potential hydrogen donors tested, only formate stimulated the rate of sediment methanogenesis. Formate conversion to methane was so rapid that an accurate estimate of kinetic parameters was not possible. Kinetic experiments using [2-¹⁴C]acetate and sediments collected in the summer indicated that acetate was being converted to methane at or near the maximal rate. A minimum natural rate of acetate conversion to methane was estimated to be about 110 nmol of CH₄ g⁻¹ h⁻¹, which was 66% of the V_max (163 nmol of CH₄ g⁻¹ h⁻¹). A 15-min preincubation of sediment with 5.0 × 10⁻³ atm of hydrogen had a pronounced effect on the kinetic parameters for the conversion of acetate to methane. The acetate pool size, expressed as the term K_m + S_n (S_n is in situ substrate concentration), decreased by 37% and T_t decreased by 43%. The V_max remained relatively constant. A preincubation with hydrogen also caused a 37% decrease in the amount of labeled carbon dioxide produced from the metabolism of [U-¹⁴C]valine by sediment heterotrophs.     

Suitability of Pharmacokinetic Models for Dynamic Contrast-Enhanced MRI of Abdominal Aortic Aneurysm Vessel Wall: A Comparison

Purpose

Increased microvascularization of the abdominal aortic aneurysm (AAA) vessel wall has been related to AAA progression and rupture. The aim of this study was to compare the suitability of three pharmacokinetic models to describe AAA vessel wall enhancement using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

Materials and Methods

Patients with AAA underwent DCE-MRI at 1.5 Tesla. The volume transfer constant (K^trans), which reflects microvascular flow, permeability and surface area, was calculated by fitting the blood and aneurysm vessel wall gadolinium concentration curves. The relative fit errors, parameter uncertainties and parameter reproducibilities for the Patlak, Tofts and Extended Tofts model were compared to find the most suitable model. Scan-rescan reproducibility was assessed using the interclass correlation coefficient and coefficient of variation (CV). Further, the relationship between K^trans and AAA size was investigated.

Results

DCE-MRI examinations from thirty-nine patients (mean age±SD: 72±6 years; M/F: 35/4) with an mean AAA maximal diameter of 49±6 mm could be included for pharmacokinetic analysis. Relative fit uncertainties for K^trans based on the Patlak model (17%) were significantly lower compared to the Tofts (37%) and Extended Tofts model (42%) (p<0.001). K^trans scan-rescan reproducibility for the Patlak model (ICC = 0.61 and CV = 22%) was comparable with the Tofts (ICC = 0.61, CV = 23%) and Extended Tofts model (ICC = 0.76, CV = 22%). K^trans was positively correlated with maximal AAA diameter (Spearman’s ρ = 0.38, p = 0.02) using the Patlak model.

Conclusion

Using the presented imaging protocol, the Patlak model is most suited to describe DCE-MRI data of the AAA vessel wall with good K^trans scan-rescan reproducibility.     

Respiratory Kinetics of Marine Bacteria Exposed to Decreasing Oxygen Concentrations

During aerobic respiration, microorganisms consume oxygen (O₂) through the use of different types of terminal oxidases which have a wide range of affinities for O₂. The K_m values for O₂ of these enzymes have been determined to be in the range of 3 to 200 nmol liter⁻¹. In this study, we examined the time course of development of aerobic respiratory kinetics of four marine bacterial species (Dinoroseobacter shibae, Roseobacter denitrificans, Idiomarina loihiensis, and Marinobacter daepoensis) during exposure to decreasing O₂ concentrations. The genomes of all four species have genes for both high-affinity and low-affinity terminal oxidases. The respiration rate of the bacteria was measured by the use of extremely sensitive optical trace O₂ sensors (range, 1 to 1,000 nmol liter⁻¹). Three of the four isolates exhibited apparent K_m values of 30 to 60 nmol liter⁻¹ when exposed to submicromolar O₂ concentrations, but a decrease to values below 10 nmol liter⁻¹ was observed when the respiration rate per cell was lowered and the cell size was decreased due to starvation. The fourth isolate did not reach a low respiration rate per cell during starvation and exhibited apparent K_m values of about 20 nmol liter⁻¹ throughout the experiment. The results clearly demonstrate not only that enzyme kinetics may limit O₂ uptake but also that even individual cells may be diffusion limited and that this diffusion limitation is the most pronounced at high respiration rates. A decrease in cell size by starvation, due to limiting organic carbon, and thereby more efficient diffusion uptake may also contribute to lower apparent K_m values.     

Correlations Between DCE MRI and Histopathological Parameters in Head and Neck Squamous Cell Carcinoma

BACKGROUND: Dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) can characterize perfusion and vascularization of tissues. DCE MRI parameters can differentiate between malignant and benign lesions and predict tumor grading. The purpose of this study was to correlate DCE MRI findings and various histopathological parameters in head and neck squamous cell carcinoma (HNSCC). PATIENTS AND METHODS: Sixteen patients with histologically proven HNSCC (11 cases primary tumors and in 5 patients with local tumor recurrence) were included in the study. DCE imaging was performed in all cases and the following parameters were estimated: K^trans, V_e, K_ep, and iAUC. The tumor proliferation index was estimated on Ki 67 antigen stained specimens. Microvessel density parameters (stained vessel area, total vessel area, number of vessels, and mean vessel diameter) were estimated on CD31 antigen stained specimens. Spearman''s non-parametric rank sum correlation coefficients were calculated between DCE and different histopathological parameters. RESULTS: The mean values of DCE perfusion parameters were as follows: K^trans 0.189 ± 0.056 min⁻¹, K_ep 0.390 ± 0.160 min⁻¹, V_e 0.548 ± 0.119%, and iAUC 22.40 ± 12.57. Significant correlations were observed between K_ep and stained vessel areas (r = 0.51, P = .041) and total vessel areas (r = 0.5118, P = .043); between V_e and mean vessel diameter (r = −0.59, P = .017). Cell count had a tendency to correlate with V_e (r = −0.48, P = .058). In an analysis of the primary HNSCC only, a significant inverse correlation between K^trans and KI 67 was identified (r = −0.62, P = .041). Our analysis showed significant correlations between DCE parameters and histopathological findings in HNSCC.Dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) has been reported as a technique which is able to characterize perfusion and vascularization of tissues [1], [2]. It has been shown that DCE MRI can be helpful to differentiate between malignant and benign lesions [1]. For example, Yuan et al. reported that lung cancer had a larger volume transfer constant (K^trans) and a lower volume of the extravascular extracellular leakage space (V_e) in comparison to benign lesions [3]. Similar results were reported by Li et al. for breast lesions [4]. Furthermore, according to Cho et al., DCE MRI parameters can be used to distinguish prostatic cancer from benign changes [5]. Moreover, DCE MRI parameters can also predict tumor grading. As reported previously, K^trans correlated well with Gleason score in prostatic cancer [5], [6]. According to other reports, K^trans and V_e correlated with glioma grade [7], [8].DCE MRI parameters were also associated with prognosis in several malignancies [9], [10]. Koo et al. showed that breast cancers with higher K^trans or lower V_e had poor prognostic factors and were often of the triple-negative subtype [10].According to the literature, DCE MRI parameters can predict response to therapy in different tumors. For instance, some authors mentioned that low pretreatment K^trans in regional lymph node metastases in head and neck cancer was associated with a poor response to concurrent chemoradiation therapy [11].Furthermore, Andersen et al. showed that DCE MR parameters obtained prior to chemoradiotherapy predicted survival of patients with cervical cancer [12].Presumably, DCE MRI parameters may be based on tissue composition, such as cellularity and vascular density. However, in this regard there are contradictory data in the literature. While some studies identified significant correlations between DCE MRI and histopathological parameters, others did not [13], [14], [15], [16].The purpose of this study was to correlate DCE MRI findings and various histopathological parameters in head and neck squamous cell carcinoma (HNSCC).     

Quantitative and Physiological Analyses of Chloride Dependence of Growth of Halobacillus halophilus

A quantitative analysis of the Cl⁻ dependence of growth of Halobacillus halophilus was performed. Optimal growth rates were obtained at Cl⁻ concentrations of between 0.5 and 2.0 M, and the final yield was also strictly dependent on the Cl⁻ concentration. Br⁻ but not I⁻, SO₄²⁻, NO₂⁻, SO₂⁻, OCN⁻, SCN⁻, BO₂⁻, or BrO₃⁻ could substitute for Cl⁻. To analyze the function of chloride, chloride concentration was determined. At low external Cl⁻ (Cl_e⁻) concentrations, the growth rate was low and Cl⁻ was excluded from the cytoplasm; increasing the Cl_e⁻ concentration led to an increase in the growth rate and an energy-dependent uptake of Cl⁻, thus decreasing the Cl_e⁻/internal Cl_i⁻ gradient from ≥10 at 0.1 M Cl_e⁻ to a nearly constant value of 2 at Cl_e⁻ concentrations which allowed optimal growth. Two membrane proteins with apparent molecular masses of 31 and 16 kDa which were identified to be specific for Cl⁻-grown cultures are possible candidates for a chloride uptake system.     

Ion Transport in Isolated Protoplasts from Tobacco Suspension Cells: II. Selectivity and Kinetics

Protoplasts were enzymically isolated from suspension cultured cells of Nicotiana glutinosa L. and aspects of transport selectivity and kinetics were studied. In the presence of Ca²⁺, transport was selective for K⁺ (⁸⁶Rb) over Na⁺. ³⁶Cl⁻ transport was inhibited by Br⁻ or I⁻ but not by H₂PO₄⁻. The kinetic data for short term (30 minutes) K⁺ influx over the range of 0.05 to 100 millimolar KCl were complex but similar to those observed in other plant tissues. In contrast, the kinetic data for Cl⁻ and H₂³²PO₄⁻ over the same concentration range were different from those observed for K⁺, and could be accounted for by a single isotherm in the range of 0.05 to 4 millimolar and by an almost linear increase in influx rate above 4 millimolar. The kinetic data for Cl⁻ transport into intact cultured cells were identical in character to those observed for isolated protoplasts. The results support the view that enzymic removal of the cell wall produced no significant alteration in the transport properties of the protoplast.