Calcium Threshold Research Articles

Assessment of Coronary Artery Calcium on Low-Dose Coronary Computed Tomography Angiography With Iterative Reconstruction.

This study aims to evaluate whether coronary calcium scoring (CCS) is also feasible using low-radiation-dose coronary computed tomography angiography (CCTA) in combination with iterative reconstruction. Forty-three individuals without known coronary artery disease underwent both noncontrast CCS (±1 mSv) for reference Agatston scores and low-dose CCTA (±3 mSv). Raw CCTA data were reconstructed with filtered back projection (FBP), hybrid iterative reconstruction (HIR), and model-based iterative reconstruction (MIR). Calcification volumes were derived with thresholds of >351 and >600 Hounsfield units (HU) and converted to proxy Agatston scores with linear regression analysis. Intraclass correlation coefficients for Agatston scores versus CCTA volumes with FBP and iterative reconstruction were excellent (ranges 0.94-0.99 and 0.96-0.99 for >351 HU and >600 HU thresholds, respectively). The >351 HU threshold resulted in higher CCTA volume scores ranging from 65.9 (15.1-347.0) for HIR to 94.8 (42.0-423.0) for MIR (P = 0.001 and <0.001, respectively). The >600 HU threshold scores ranged from 14.1 (0.0-159.3) for HIR to 28.6 (0.0-215.6) for MIR (P = 0.003 and 0.027, respectively). At >351 HU, reclassification occurred in 21 individuals (49%) for FBP and HIR and 25 individuals (58%) for MIR. Reclassifications decreased with >600 HU to 10 (HIR, 23%), 8 (FBP, 19%), and 4 (MIR, 9%). The CCS is feasible using iteratively reconstructed low-dose CCTA with a calcium threshold of >600 HU. Using MIR, only 9% of individuals were reclassified.

Coronary calcium scoring from contrast coronary CT angiography using a semiautomated standardized method

BackgroundWhen coronary calcium scoring is performed in patients with suspected coronary artery disease, a separate noncontrast scan is acquired before contrast-enhanced coronary CT angiography (CTA). ObjectiveOur aim was to develop and validate an automated method for calculating the coronary calcium score (CCS) from coronary CTA. MethodsWe analyzed coronary CTA and noncontrast CT data sets of 84 patients (Agatston score >0). The CCS on noncontrast CT was measured using commercial methods. Coronary calcium volume was measured on coronary CTA using an automated standardized method with scan-specific calcium thresholds. Data sets were split into derivation (n = 40) and validation groups (n = 44). To calculate the CCS on coronary CTA, a conversion factor between calcium scores measured in noncontrast CT and the calcium volume measured on coronary CTA was derived by linear regression. ResultsIn the validation group, the median calculated CCS derived from CTA was 277 and 244 on noncontrast images (P = .12). This CCS showed an excellent correlation with the CCS from noncontrast images (Pearson, r = 0.95). In the validation group, 39 of 44 patients (88.6%) were classified into the same standard category (1–10, 11–100, 101–400, or >400) with an excellent agreement (weighted κ of 0.87). ConclusionCCSs can be accurately measured from contrast-enhanced coronary CTA by using an automated, standardized method, obviating the need for a noncontrast scan.

Coronary Artery Calcium: 0.5 mm Slice-Thickness Reconstruction with Adjusted Attenuation Threshold Outperforms 3.0 mm by Validating Against Spatially Registered Intravascular Ultrasound with Radiofrequency Backscatter

Coronary artery calcium (CAC) images can be reconstructed with thinner slice thickness on some modern multidetector-row computed tomography scanners without additional radiation. We hypothesized that the isotropic 0.5-mm CAC reconstruction outperforms the conventional 3.0-mm reconstruction in detecting and quantifying coronary calcium, and we proposed to compare them by validating against spatially registered intravascular ultrasound with radiofrequency backscatter-virtual histology (IVUS-VH). Twenty-seven patients were enrolled, and 5976 mm of coronary arteries were analyzed. A semiautomatic software was developed to coregister CAC and IVUS-VH on a detailed slice-by-slice basis. Calcium detection and calcium volume quantification were evaluated and compared using varying calcium attenuation thresholds. Algorithms for deriving individualized optimal threshold and comparable Agatston score on the 0.5-mm reconstruction were developed. The isotropic 0.5-mm reconstruction achieved significantly higher area under receiver-operating curve than the conventional 3.0-mm reconstruction (0.9 vs. 0.74, P < .001). Using the optimal threshold, the 0.5-mm reconstruction had higher sensitivity (0.79 vs. 0.65), specificity (0.85 vs. 0.77), positive predictive value (0.42 vs. 0.29), and negative predictive value (0.97 vs. 0.94) than the 3.0 mm. Individualized optimal threshold was significantly correlated with the image noise (r = 0.66, P < .001) in the 0.5-mm reconstruction. By optimizing the calcium threshold, the 0.5-mm reconstruction is superior to the conventional 3.0-mm in detecting and quantifying calcium, which may improve the clinical value of CAC without additional radiation.

Abstract 203: Differences Between Mammalian and Drosophila Mitochondrial Calcium Handling Help Identify Mechanisms Regulating the Permeability Transition.

Studies of cardiomyocyte death during calcium overload induced by ischemia-reperfusion injury or heart failure have implicated the mitochondrial permeability transition as a key pathway. During the permeability transition, an opening of a channel in the inner membrane leads to mitochondrial depolarization and swelling. Despite extensive studies in mammalian systems, the machinery responsible for this phenomenon remains only partially identified. If present in non-mammalian species, the components of the permeability transition may be further elucidated, given potential advantages within these systems for high-throughput screens. However, the existence of a permeability transition remains controversial in non-mammalian organisms. In Drosophila , prior studies have documented calcium-induced mitochondrial depolarization, but no obvious swelling. Here we show that Drosophila S2R+ cells do possess the machinery for permeability transition, but that the threshold for a calcium trigger is significantly higher than in mammalian systems. Using a calcein-loading method, we show that Drosophila permeability transition can be triggered by calcium overload, using ionomycin, and by cysteine oxidation, using phenylarsine oxide. As in mammalian systems, blockade of mitochondrial cyclophilin or the ATP/ADP transporter appears to inhibit the Drosophila permeability transition. Finally, we examine three alternative hypotheses that may explain these differences in permeability transition. First, we test if perturbing the pathways for calcium influx into S2R+ mitochondria can trigger this phenomenon. Second, we test if the discrepancy in the calcium threshold is due to structural differences in the key regulators, particularly the mitochondrial cyclophilin. Third, we compare Drosophila and human genomes to see if any novel molecules may be responsible for setting the lower threshold for calcium-induced permeability transition in mammalian cells. Since the Drosophila cells possess such significant resistance to permeability transition, the results of our investigations suggest potential new strategies for the development of therapeutics inhibiting mitochondrial permeability transition in cardiac calcium-induced injury.

Association of cross-reactive antibodies targeting peptidyl-arginine deiminase 3 and 4 with rheumatoid arthritis-associated interstitial lung disease.

BackgroundA subset of rheumatoid arthritis (RA) patients have detectable antibodies directed against the peptidyl-arginine deiminase (PAD) enzyme isoforms 3 and 4. Anti-PAD3/4 cross-reactive antibodies (anti-PAD3/4XR) have been shown to lower the calcium threshold required for PAD4 activation, an effect potentially relevant to the pathogenesis of RA-associated interstitial lung disease (ILD).MethodsRA patients underwent multi-detector computed tomography (MDCT) of the chest with interpretation by a pulmonary radiologist for ILD features. A semi-quantitative ILD Score (range 0–32) was calculated. Concurrent serum samples were assessed for antibodies against PAD by immunoprecipitation with radiolabeled PAD3 and PAD4.ResultsAmong the 176 RA patients studied, any ILD was observed in 58 (33%) and anti-PAD3/4XR was detected in 19 (11%). The frequency of any ILD among those with anti-PAD3/4XR was 68% vs. 29% among those with no anti-PAD (crude OR = 5.39; p = 0.002) and vs. 27% among those with anti-PAD4 that was not cross-reactive with PAD3 (crude OR = 5.74; p = 0.001). Both associations were stronger after adjustment for relevant confounders (adjusted ORs = 7.22 and 6.61, respectively; both p-values<0.01). Among ever smokers with anti-PAD3/4XR, the adjusted frequency of any ILD was 93% vs. 17% for never smokers without the antibody (adjusted OR = 61.4; p = 0.001, p-value for the interaction of smoking with anti-PAD3/4XR<0.05).ConclusionsThe prevalence and extent of ILD was markedly higher among RA patients with anti-PAD3/4 cross-reactive antibodies, even after accounting for relevant confounders, particularly among ever smokers. These findings may suggest etiopathologic mechanisms of RA-ILD, and their clinical utility for predicting ILD warrants additional study.

Protective role of amantadine in mitochondrial dysfunction and oxidative stress mediated by hepatitis C virus protein expression

Amantadine is an antiviral and antiparkinsonian drug that has been evaluated in combination therapies against hepatitis C virus (HCV) infection. Controversial results have been reported concerning its efficacy, and its mechanism of action remains unclear. Data obtained in vitro suggested a role of amantadine in inhibiting HCV p7-mediated cation conductance. In keeping with the fact that mitochondria are responsible to ionic fluxes and that HCV infection impairs mitochondrial function, we investigated a potential role of amantadine in modulating mitochondrial function. Using a well-characterized inducible cell line expressing the full-length HCV polyprotein, we found that amantadine not only prevented but also rescued HCV protein-mediated mitochondrial dysfunction. Specifically, amantadine corrected (i) overload of mitochondrial Ca2+; (ii) inhibition of respiratory chain activity and oxidative phosphorylation; (iii) reduction of membrane potential; and (iv) overproduction of reactive oxygen species. The effects of amantadine were observed within 15min following drug administration and confirmed in Huh-7.5 cells transfected with an infectious HCV genome. These effects were also observed in cells expressing subgenomic HCV constructs, indicating that they are not mediated or only in part mediated by p7. Single organelle analyzes carried out on isolated mouse liver mitochondria demonstrated that amantadine induces hyperpolarization of the membrane potential. Moreover, amantadine treatment increased the calcium threshold required to trigger mitochondrial permeability transition opening. In conclusion, these results support a role of amantadine in preserving cellular bioenergetics and redox homeostasis in HCV-infected cells and unveil an effect of the drug which might be exploited for a broader therapeutic utilization.

The Association of Calcium Intake and Other Risk Factors with Cardiovascular Disease among Obese Adults in USA

In this study, we used a cross-sectional study design to examine the relationship between the calcium intake and risk factors for CVD among obese adults by using continuous waves of National Health and Nutrition Examination Survey (NHANES) data 1999-2010. The association between calcium intake and risk factors of CVD (hypertension, total cholesterol, HDL, glycohemoglobin), CRP, albuminuria) is assessed among obese adults in USA. The incidence of Cardiovascular Disease (CVD) is high among obese people. The potential effects of inadequate calcium intake on CVD are receiving increased epidemiologic attention. Understanding the association between risk factors for CVD and calcium intake among obese adults is important for the advancement of CVD, nutrition and obesity research. Data collected from the National Health and Nutrition Examination Survey from 1999-2010 were examined, utilizing a subset of 14,856 obese subjects. Analysis of Variance statistical tests were conducted to determine associations between calcium intake and CVD risk. Simple and multiple linear and logistic regression analyses were conducted to determine the predicted value of calcium intake with CVD. After adjusting for energy intake and other potential risk factors, systolic blood pressure, diastolic blood pressure, C-reactive protein, glycosylated hemoglobin and albuminuria were negatively associated with calcium intake at α = 0.05 level in both linear and logistic regression analyses. In a comparison of calcium intake by quartiles, results reveal that total cholesterol had a weak negative association with calcium intake at α = 0.1 level. The implications of these study results are important as the importance of adequate calcium intake and its potential to decrease CVD among obese adults has incredible preventive value for populations. Additional research that focuses on dietary intake, calcium thresholds and impacts on total cholesterol levels in the body is warranted.

American ginseng (Panax quinquefolius L.) floristic associations in Pennsylvania: guidance for identifying calcium-rich forest farming sites

In the eastern United States, there is interest among forest landowners in American ginseng husbandry, and particularly in cultivating this plant on forestlands using a wild-simulated forest farming approach. This study documented the flora and soil conditions associated with wild and wild-simulated ginseng populations throughout Pennsylvania (PA) to develop floristic “indicators” that can be used to identify supportive growing sites on forestlands. A total of 243 plant species were documented associates of ginseng across PA: 32 over-story trees, 37 shrubs and understory trees, 15 vines, 143 herbs, and 16 ferns. Statistical analysis revealed a largely shared floristic assemblage throughout the state although some associates did differ according to region and physiographic province. Previous studies have suggested that a soil calcium content, especially soils having at least 3,360 kg ha−1 (3,000 lbs ac), appear to be particularly conducive to wild and wild-simulated ginseng occurrence and/or vigor, and indicator species analysis in this study revealed that three of the top plant associates that can be used for determining sites that meet this calcium threshold in PA are white ash, Jack-in-the-pulpit, and rattlesnake fern. These results suggest that successful adoption of wild-simulated ginseng forest farming is likely to be improved in forested areas where these species are found collectively as a dominant component of local plant assemblages.

Controversies about effects of low-kilovoltage MDCT acquisition on Agatston calcium scoring

Recent articles have advocated the possibility of obtaining Agatston coronary calcium scoring at 100 kVp by using a single adapted elevated calcium threshold. To evaluate the influence of kilovoltage potential protocols on the Agatston score, we acquired successive scans of a calcium scoring phantom at 4 levels of kilovoltage potential (80, 100, 120, and 140 kVp, 55 mAs) and measured semiautomatically the individual and the total Agatston score of 6 inserts (of 5-mm and 3-mm diameter) containing hydroxyapatite at different concentrations (800, 400, 200 mg/cm3). Our results showed that Agatston scores obtained at various low-kilovoltage potential protocols can be highly overestimated in some particular cases. At 80 kVp, for example, mean measured Agatston score was multiplied by a factor from 1.06 (5-mm highest density insert) to 2.67 (3-mm lowest density insert) compared with the Agatston scores performed at 120 kVp. Indeed in the one hand, reducing kilovoltage potential in multidetector CT acquisitions increase the CT density of coronary calcifications that can be measured on the reconstructed images. On the other hand, Agatston score is a multi-threshold measurement (with a step weighting function). Consequently low kilovoltage potential can lead to overweight some calcifications scores. For these reasons, Agatston score with low kilovoltage potential acquisition cannot be reliably adapted by a unique recalibration of the standard calcium attenuation threshold of 130 HU and requires a standardized CT acquisition protocol at 120 kVp. Alternatives to performing low-dose coronary artery calcium scans are either using coronary calcium scans with reduced tube current (low mAs) at 120 kVp with the iterative reconstructions or using mass/volume scoring (not influenced by kilovoltage potential variations). Finally, we emphasized that incorrect Agatston score evaluation may have important clinical, financial, and health care implications.

Salivary calcium concentration as a screening tool for postmenopausal osteoporosis

Measurements of salivary calcium level may be a useful screening tool for osteoporosis in postmenopausal women. The purpose of this study was to clarify whether this measure is valid compared with dual-energy X-ray (Bone Mineral Density) screening tools in osteoporosis. A case-control study was carried out in 40 postmenopausal women with osteoporosis (T-score ≤-2.5) and 40 women without osteoporosis (T-score >-1 bone mineral density). Salivary samples were collected and calcium concentrations were measured and expressed as mg/dL. Receiver operating characteristic curve analyses was used to determine the optimal cut-off thresholds for salivary calcium in healthy postmenopausal women. The cut-off point for salivary calcium was 6.1mg/dL. The sensitivity and specificity, respectively, for identifying women with osteoporosis, were 67.5 (95%CI 52.33-82.67) and 60% (95%CI 44.62-75.38). The area under curve (AUC) was 0.678 (95%CI 0.56-0.79), the positive predictive value (PPV) was 62.79 (95%CI 47.74-77.84) and negative predictive value (NPV) was 64.86% (95%CI 49.27-80.46). The positive likelihood ratio was 1.688 and the negative likelihood ratio was 0.542. Salivary calcium concentration discriminates between women with and without osteoporosis and constitutes a useful tool for screening for osteoporosis.

Fatty-acid oxidation and calcium homeostasis are involved in the rescue of bupivacaine-induced cardiotoxicity by lipid emulsion in rats*

Lipid emulsion has been shown to be effective in resuscitating bupivacaine-induced cardiac arrest but its mechanism of action is not clear. Here we investigated whether fatty-acid oxidation is required for rescue of bupivacaine-induced cardiotoxicity by lipid emulsion in rats. We also compared the mitochondrial function and calcium threshold for triggering of mitochondrial permeability transition pore opening in bupivacaine-induced cardiac arrest before and after resuscitation with lipid emulsion. Prospective, randomized animal study. University research laboratory. Adult male Sprague-Dawley rats. Asystole was achieved with a single dose of bupivacaine (10 mg/kg over 20 secs, intravenously) and 20% lipid emulsion infusion (5 mL/kg bolus, and 0.5 mL/kg/min maintenance), and cardiac massage started immediately. The rats in CVT-4325 (CVT) group were pretreated with a single dose of fatty-acid oxidation inhibitor CVT (0.5, 0.25, 0.125, or 0.0625 mg/kg bolus intravenously) 5 mins prior to inducing asystole by bupivacaine overdose. Heart rate, ejection fraction, fractional shortening, the threshold for opening of mitochondrial permeability transition pore, oxygen consumption, and membrane potential were measured. The values are mean ± SEM. Administration of bupivacaine resulted in asystole. Lipid Emulsion infusion improved the cardiac function gradually as the ejection fraction was fully recovered within 5 mins (ejection fraction=64±4% and fractional shortening=36±3%, n=6) and heart rate increased to 239±9 beats/min (71% recovery, n=6) within 10 mins. Lipid emulsion was only able to rescue rats pretreated with low dose of CVT (0.0625 mg/kg; heart rate~181±11 beats/min at 10 mins, recovery of 56%; ejection fraction=50±1%; fractional shortening=26±0.6% at 5 mins, n=3), but was unable to resuscitate rats pretreated with higher doses of CVT (0.5, 0.25, or 0.125 mg/kg). The calcium-retention capacity in response to Ca²⁺ overload was significantly higher in cardiac mitochondria isolated from rats resuscitated with 20% lipid emulsion compared to the group that did not receive Lipid Emulsion after bupivacaine overdose (330±42 nmol/mg vs. 180±8.2 nmol/mg of mitochondrial protein, p<.05, n=3 in each group). The mitochondrial oxidative rate and membrane potential were similar in the bupivacaine group before and after resuscitation with lipid emulsion infusion. Fatty-acid oxidation is required for successful rescue of bupivacaine-induced cardiotoxicity by lipid emulsion. This rescue action is associated with inhibition of mitochondrial permeability transition pore opening.

Interaction of inhibition and triplets of excitatory spikes modulates the NMDA-R-mediated synaptic plasticity in a computational model of spike timing-dependent plasticity

Spike timing-dependent plasticity (STDP) experiments have shown that a synapse is strengthened when a presynaptic spike precedes a postsynaptic one and depressed vice versa. The canonical form of STDP has been shown to have an asymmetric shape with the peak long-term potentiation at +6 ms and the peak long-term depression at -5 ms. Experiments in hippocampal cultures with more complex stimuli such as triplets (one presynaptic spike combined with two postsynaptic spikes or one postsynaptic spike with two presynaptic spikes) have shown that pre-post-pre spike triplets result in no change in synaptic strength, whereas post-pre-post spike triplets lead to significant potentiation. The sign and magnitude of STDP have also been experimentally hypothesized to be modulated by inhibition. Recently, a computational study showed that the asymmetrical form of STDP in the CA1 pyramidal cell dendrite when two spikes interact switches to a symmetrical one in the presence of inhibition under certain conditions. In the present study, I investigate computationally how inhibition modulates STDP in the CA1 pyramidal neuron dendrite when it is driven by triplets. The model uses calcium as the postsynaptic signaling agent for STDP and is shown to be consistent with the experimental triplet observations in the absence of inhibition: simulated pre-post-pre spike triplets result in no change in synaptic strength, whereas simulated post-pre-post spike triplets lead to significant potentiation. When inhibition is bounded by the onset and offset of the triplet stimulation, then the strength of the synapse is decreased as the strength of inhibition increases. When inhibition arrives either few milliseconds before or at the onset of the last spike in the pre-post-pre triplet stimulation, then the synapse is potentiated. Variability in the frequency of inhibition (50 vs. 100 Hz) produces no change in synaptic strength. Finally, a 5% variation in model's calcium parameters (calcium thresholds) proves that the model's performance is robust.

Measuring coronary artery calcification using positron emission tomography-computed tomography attenuation correction images

Cardiac computed tomography (CT) measured coronary artery calcium (CAC-CT) is a well-validated and accurate tool for estimating atherosclerotic burden and prognosis. Computed tomography attenuation correction (ACCT) obtained during cardiac positron emission tomography (PET) has been used to visually estimate CAC; however, quantification using a non-gated ACCT images has not been described. We sought to understand the relationship between CAC measured using cardiac computed tomography (CT) and CAC using ACCT images obtained during cardiac PET perfusion imaging. Patients with both CAC-CT and cardiac PET within 6 months of each other were identified. CAC-CT images were scored using the Agatston scoring method, while ACCT images were scored using different attenuation thresholds for calcium. CAC-CT and ACCT scores were compared. Between August 2007 and October 2010, 91 patients were included in the analysis. Interobserver reliability was excellent at all thresholds of detection tested. Pearson correlation was strongest between CAC-CT and ACCT at 50 HU threshold of detection (ACCT(50)). Implementing CAC categories (0, 1-100, 101-400, >400), there was a high degree of agreement between observers as well as between CAC-CT and ACCT(50). Correlation was best for lower CAC scores; however, as CAC-CT increased, ACCT(50) underestimated CAC. Quantifying CAC using ACCT images appears to be feasible and accurate. In a single cardiac PET examination, information regarding perfusion, LV function, flow quantification, and CAC can be obtained without additional radiation.

Calcium-based plasticity model explains sensitivity of synaptic changes to spike pattern, rate, and dendritic location

Multiple stimulation protocols have been found to be effective in changing synaptic efficacy by inducing long-term potentiation or depression. In many of those protocols, increases in postsynaptic calcium concentration have been shown to play a crucial role. However, it is still unclear whether and how the dynamics of the postsynaptic calcium alone determine the outcome of synaptic plasticity. Here, we propose a calcium-based model of a synapse in which potentiation and depression are activated above calcium thresholds. We show that this model gives rise to a large diversity of spike timing-dependent plasticity curves, most of which have been observed experimentally in different systems. It accounts quantitatively for plasticity outcomes evoked by protocols involving patterns with variable spike timing and firing rate in hippocampus and neocortex. Furthermore, it allows us to predict that differences in plasticity outcomes in different studies are due to differences in parameters defining the calcium dynamics. The model provides a mechanistic understanding of how various stimulation protocols provoke specific synaptic changes through the dynamics of calcium concentration and thresholds implementing in simplified fashion protein signaling cascades, leading to long-term potentiation and long-term depression. The combination of biophysical realism and analytical tractability makes it the ideal candidate to study plasticity at the synapse, neuron, and network levels.

Post-translational Membrane Insertion of Tail-anchored Transmembrane EF-hand Ca2+ Sensor Calneurons Requires the TRC40/Asna1 Protein Chaperone

Calneuron-1 and -2 are neuronal EF-hand-type calcium sensor proteins that are prominently targeted to trans-Golgi network membranes and impose a calcium threshold at the Golgi for phosphatidylinositol 4-OH kinase IIIβ activation and the regulated local synthesis of phospholipids that are crucial for TGN-to-plasma membrane trafficking. In this study, we show that calneurons are nonclassical type II tail-anchored proteins that are post-translationally inserted into the endoplasmic reticulum membrane via an association of a 23-amino acid-long transmembrane domain (TMD) with the TRC40/Asna1 chaperone complex. Following trafficking to the Golgi, calneurons are probably retained in the TGN because of the length of the TMD and phosphatidylinositol 4-phosphate lipid binding. Both calneurons rapidly self-associate in vitro and in vivo via their TMD and EF-hand containing the N terminus. Although dimerization and potentially multimerization precludes TRC40/Asna1 binding and thereby membrane insertion, we found no evidence for a cytosolic pool of calneurons and could demonstrate that self-association of calneurons is restricted to membrane-inserted protein. The dimerization properties and the fact that they, unlike every other EF-hand calmodulin-like Ca(2+) sensor, are always associated with membranes of the secretory pathway, including vesicles and plasma membrane, suggests a high degree of spatial segregation for physiological target interactions.

Evaluating the Clinical Utility of a Biomarker

Biomarkers, broadly defined, are markers of a biological process or state.1 Biomarkers are often used in research studies, but they may also be useful for clinicians and patients if they provide information about current status or future risk of disease. It is not always clear, however, when a novel biomarker provides enough useful information to justify measuring it in the context of clinical care. Evaluating the clinical utility of a novel biomarker requires a phased approach.2 Early-phase studies must prove that the biomarker is associated statistically with the clinical state of interest and adds information about presence or risk of disease above and beyond established markers. Midphase studies describe how often this incremental information might alter physician prescribing decisions. Early- and mid-phase studies are useful because they help investigators compare biomarker performance in terms that are generic (ie, not dependent on the specifics of the disease state being studied). Generic measures of biomarker performance have been reviewed previously2,–,16 and are described in Table 1 along with relevant published examples.17,–,32 View this table: Table 1. Generic Measures of Biomarker Performance Measuring biomarker performance in generic terms, however, is not sufficient for demonstrating clinical utility.6 The decision to use a biomarker in clinical practice should be based on an expectation that it will have a positive net health impact, and measuring health impact, by definition, requires use of measurements that consider the specific disease state being studied and its consequences. The goal of this review is to describe the methods by which evidence about the health impact of measuring a biomarker may be generated (late-phase evidence2) using examples relevant to cardiovascular disease and with a focus on the use of randomized clinical trials and modeling for estimating health impact. ### Mechanisms by Which Biomarker Measurement Can Impact Health There are 3 fundamental …

The Value of Postoperative Parathyroid Hormone Levels in Predicting the Need for Long-Term Vitamin D Supplementation after Total Thyroidectomy

Few studies have examined the need for vitamin D supplementation after total thyroidectomy. This study examines the role of postoperative day (POD) 1 serum calcium and parathyroid hormone (PTH) levels in predicting the need for long-term vitamin D supplementation after total thyroidectomy. A retrospective, single institutional study of patients who underwent total thyroidectomy between January 2007 and December 2008 was performed. Data collected included extent of surgery, final pathology, postoperative calcium (mg/dl) and PTH (pg/ml) values, and duration of vitamin D supplementation. Patients were divided into 4 groups based on POD1 PTH values: group 1 (<5.0); group 2 (5.0-10); group 3 (10.1-20); and group 4 (>20). Of the 104 patients, 26 were in group 1, 12 in group 2, 18 in group 3, and 48 in group 4, with median PTH values of <2.5, 8.2, 14.1, and 30pg/ml, respectively. All 7 (7%) patients who required vitamin D supplementation >1month were in group 1. The positive predictive value of POD1 PTH <5.0 in predicting supplementation >1month was 27% (sensitivity 100%, specificity 80%). Seventy-eight patients had a POD1 PTH level ≥5, and none required vitamin D supplementation >1month (100% negative predictive value). The positive predictive value of various POD1 calcium thresholds (<7.5, <8.0, and <8.5mg/dl) was 17, 14, and 15%, respectively. Postoperative PTH levels better predict long-term hypocalcemia requiring vitamin D supplementation than serum calcium levels. A PTH level ≥5.0 may identify patients who can be safely discharged without routine vitamin D supplementation.

Coronary artery calcium scoring using a reduced tube voltage and radiation dose protocol with dual-source computed tomography

Technical advances to minimize radiation exposure because of imaging are in accord with the "as low as reasonably achievable" principle. We aimed to determine whether coronary calcium scoring (CCS) by multidetector CT at a tube voltage of 100 kVp yields comparable results to the standard 120-kVp protocol while reducing radiation dose. Sixty consecutive outpatients were scanned with a dual-source CT scanner with both the120- and 100-kVp protocols. The calcium threshold was 130 Hounsfield units (HUs) for 120 kVp and 147 HU for 100 kVp, as determined from phantom data. All 100-kVp scans were scored by an experienced reader blinded to 120-kVp data. Image quality was comparable for 100- and 120- kVp scans. Mean Agatston scores for 100 and 120 kVp were 189 +/- 484 and 189 +/- 498 (P = 0.92), with perfect correlation (r = 1.0; P < 0.0001; 95% limits of agreement, -36 to 37; bias, 0.6). Mean coronary calcium volume scores for 100 and 120 kVp were 143 +/- 370 mm(3) and 149 +/- 392 mm(3) (P = 0.26), with perfect correlation (r = 1.0; P < 0.0001; 95% limits of agreement, -35 to 32 mm(3); bias, -1.4 mm(3)). The mean absolute difference for Agatston scores between the protocols was 16.9, with excellent agreement (kappa = 0.95; P < 0.0001). Mean effective radiation dose for the 100-kVp protocol was significantly lower (1.17 mSv versus 1.70 mSv; P < 0.0001). A reduced tube current protocol using 100 kVp gives equivalent CCS results at reduced radiation exposure compared with a standard protocol at 120 kVp.

Prediction of hypocalcemia after using 1‐ to 6‐hour postoperative parathyroid hormone and calcium levels: An analysis of pooled individual patient data from 3 observational studies

Parathyroid hormone (PTH) levels up to 6 hours postthyroidectomy have been shown to have excellent predictive power in determining hypocalcemia. In this study, we investigate the usefulness of combining calcium and PTH to increase the predictive power. Individual patient data were obtained from 3 studies (152 patients) that fulfilled our criteria (using PTH assay within hours postthyroidectomy to predict symptomatic hypocalcemia). Changes in combined PTH and calcium threshold levels checked 1 to 6 hours after thyroidectomy were excellent in predicting postoperative hypocalcemia. A decrease in PTH of 60%, coupled with a simultaneous decrease in calcium of 10%, 5 to 6 hours postoperatively resulted in a sensitivity and specificity of 100%. However, combined PTH and calcium threshold changes were not significantly better than using PTH threshold changes alone. Threshold changes in serum calcium and PTH, checked hours after surgery, can be used together to accurately predict whether a patient will become hypocalcemic after thyroidectomy.

Ca2+ and calmodulin initiate all forms of endocytosis during depolarization at a nerve terminal

Although endocytosis maintains synaptic transmission, how endocytosis is initiated is unclear. We found that calcium influx initiated all forms of endocytosis at a single nerve terminal in rodents, including clathrin-dependent slow endocytosis, bulk endocytosis, rapid endocytosis and endocytosis overshoot (excess endocytosis), with each being evoked with a correspondingly higher calcium threshold. As calcium influx increased, endocytosis gradually switched from very slow endocytosis to slow endocytosis to bulk endocytosis to rapid endocytosis and to endocytosis overshoot. The calcium-induced endocytosis rate increase was a result of the speeding up of membrane invagination and fission. Pharmacological experiments suggested that the calcium sensor mediating these forms of endocytosis is calmodulin. In addition to its role in recycling vesicles, calcium/calmodulin-initiated endocytosis facilitated vesicle mobilization to the readily releasable pool, probably by clearing fused vesicle membrane at release sites. Our findings provide a unifying mechanism for the initiation of various forms of endocytosis that are critical in maintaining exocytosis.