Assessing HDL Metabolism in Subjects with Elevated Levels of HDL Cholesterol and Coronary Artery Disease

High-density lipoprotein cholesterol (HDL-C) is thought to be atheroprotective yet some patients with elevated HDL-C levels develop cardiovascular disease, possibly due to the presence of dysfunctional HDL. We aimed to assess the metabolic fate of circulating HDL particles in patients with high HDL-C with and without coronary artery disease (CAD) using in vivo dual labeling of its cholesterol and protein moieties. We measured HDL apolipoprotein (apo) A-I, apoA-II, free cholesterol (FC), and cholesteryl ester (CE) kinetics using stable isotope-labeled tracers (D3-leucine and 13C2-acetate) as well as ex vivo cholesterol efflux to HDL in subjects with (n = 6) and without (n = 6) CAD that had HDL-C levels >90th percentile. Healthy controls with HDL-C within the normal range (n = 6) who underwent the same procedures were used as the reference. Subjects with high HDL-C with and without CAD had similar plasma lipid levels and similar apoA-I, apoA-II, HDL FC, and CE pool sizes with no significant differences in fractional clearance rates (FCRs) or production rates (PRs) of these components between groups. Subjects with high HDL-C with and without CAD also had similar basal and cAMP-stimulated ex vivo cholesterol efflux to HDL. When all subjects were considered (n = 18), unstimulated non-ABCA1-mediated efflux (but not ABCA1-specific efflux) was correlated positively with apoA-I production (r = 0.552, p = 0.017) and HDL FC and CE pool sizes, and negatively with the fractional clearance rate of FC (r = −0.759, p = 4.1 × 10−4) and CE (r = −0.652, p = 4.57 × 10−3). Our data are consistent with the concept that ex vivo non-ABCA1 efflux capacity may correlate with slower in vivo turnover of HDL cholesterol moieties. The use of a dual labeling protocol provided for the first time the opportunity to assess the association of ex vivo cholesterol efflux capacity with in vivo HDL cholesterol metabolic parameters.

The Blood Lactate/Pyruvate Equilibrium Affair

The Lactate Shuttle hypothesis is supported by a variety of techniques including mass spectrometry analytics following infusion of carbon labeled isotopic tracers. However, there has been controversy over whether lactate tracers measure lactate (L) or pyruvate (P) turnover. Here we review the analytical errors, use of inappropriate tissue and animal models, failure to consider L and P pool sizes in modeling results, inappropriate tracer and blood sampling sites, and failure to anticipate roles of heart and lung parenchyma on L:P interactions. With support from magnetic resonance spectroscopy (MRS) and immunocytochemistry we conclude that carbon-labeled lactate tracers can be used to quantitate lactate fluxes.

Pyruvate Carboxylase Supports MCF10A-Ras Cell Survival in Extracellular Matrix Detached Conditions

Background: Throughout metastatic progression, cancer cells acquire anchorage independence, or the ability to survive detached from the extracellular matrix (ECM). While untransformed epithelial cells reduce energy metabolism when detached, cancer cells display metabolic flexibility to continue important metabolic processes. Glucose and glutamine are predominant nutrients utilized for energy as well as other purposes, and their metabolism is regulated by cancer cells.Methods: The purpose of the current studies was to determine the effects of detachment on glucose and glutamine metabolism in human breast epithelial MCF10A cells transfected with the Harvey-ras oncogene (MCF10A-ras), a model of early-stage cancer. Detachment was simulated with poly-HEMA coated plates, and intracellular metabolic flux was determined using stably labeled 13C5-glutamine and 13C6-glucose tracers.Results: Results show reduced glutamine flux in detached cells as determined by reduced accumulation of label in glutamate (21%), malate (30%), and aspartate (23%) from 13C5-glutamine. Detachment also reduced flux of 13C6-glucose to pyruvate and lactate pools by 51% and 29%, respectively. Similarly, detachment reduced total intracellular pool sizes of pyruvate (51%), lactate (49%), α-ketoglutarate (43%), fumarate (32%), malate (19%), alanine (35%), serine (35%), and glutamate (28%) compared to attached cells, but citrate and aspartate pool sizes were unchanged. Compared to attached cells, detachment increased pyruvate carboxylase (PC) mRNA abundance and protein expression by 131% and 190%, respectively. In detachment, PC activity, determined by 13C6-glucose derived M + 3 isotopomers, was shown to preferentially replenish malate and aspartate, but not citrate pools. In addition, doxycycline-inducible shRNA depletion of PC significantly decreased, while doxycycline-inducible PC overexpression significantly increased, detached cell viability. Further, a switch from glutamine to PC activity for anaplerosis was demonstrated, as supplementation with the cell permeable analog of the tricarboxylic acid cycle intermediate, α-ketoglutarate, a downstream metabolite of glutamine, decreased PC mRNA abundance in detached cells.Conclusion: Collectively, these results suggest that detached breast cancer cells increase PC activity in response to decreased glutamine-derived anaplerosis to promote cell survival.

Pooled Sample Testing for SARS-CoV-2 Using Rapid RT-PCR COVID-19 Tests

We tested an operationally efficient way to pool samples on a rapid, point-of-care PCR device and examined the limit of detection of SARS-CoV-2 for various pool sizes. Pooled testing maintained testing performance similar to individual sample PCR testing, offering the potential for scalable rapid testing at lower cost with less supplies.

Samples sizes required to accurately quantify viral load and histologic lesion severity at the maternal–fetal interface of PRRSV-inoculated pregnant gilts

Porcine reproductive and respiratory syndrome virus (PRRSV) is transmitted vertically, causing fetal death in late gestation. Spatiotemporal distribution of virus at the maternal–fetal interface (MFI) is variable, and accurate assessment of viral concentration and lesions is thus subject to sampling error. Our objectives were: 1) to assess whether viral load and lesion severity in a single sample of endometrium (END) and placenta (PLC), collected near the base of the umbilical cord (the current standard), are representative of the entire organ; and 2) to compare sampling strategies and evaluate if spatial variation in viral load can be overcome by pooling of like-tissues. Spatially distinct pieces of END and PLC of 24 fetuses from PRRSV-2–infected dams were collected. PRRSV RNA quantified by RT-qPCR was compared in 5 individual pieces per fetus and in respective pools of tissue and extracted RNA. Three distinct pieces of MFI were assessed for histologic severity. Concordance correlation and kappa inter-rater agreement were used to characterize agreement among individual samples and pools. The viral load of individual samples and pools of END had greater concordance to a referent standard than did samples of PLC. Larger pool sizes had greater concordance than smaller pool sizes. Average viral load and lesion severity did not differ by location sampled, and no technical advantages of pooling tissues versus RNA extracts were found. We conclude that multiple pieces of MFI tissues must be evaluated to accurately assess lesion severity and viral load. Three pieces per fetus provided a reasonable balance of cost and logistic feasibility.

Nested pool testing strategy for the reliable identification of individuals infected with SARS-CoV-2

The progress of the SARS-CoV-2 pandemic requires the design of cost-effective testing programs at large scale. To this end, pooling multiple samples can provide a solution. Defining a cost-effective strategy requires the establishment of an efficient deconvolution and re-testing procedure that eventually allows the identifcation of the carrier. Based on Dorfman’s algorithm, we developed an adaptive nested strategy for which we have, for a given prevalence, simple analytic expressions of the optimal number of samples in the starting pool, of the number of partitioning steps (stages) in the optimal path, of the pool sizes in each of these stages and of the expected average number of tests needed to identify the infected individuals. In this paper we analyze the strategy in detail focusing on its practical implementation when there are restrictions that prevent the use of the optimum. More specifically, we analyze how to proceed when the infection prevalence is poorly known a priori or when the optimal requires starting with pool sizes that are too large for the reliable detection of an infected sample. The sensitivity of the RT-qPCR assay, the gold standard RNA detection method, is a major concern in the case of SARS-CoV-2: it is estimated that half of the infected individuals give false negative results. Recently, droplet digital PCR (ddPCR) was shown to be 10 − 100 times more sensitive than RT-qPCR, making this technology suitable for pool testing. ddPCR has the added value of providing the direct quantification of the RNA content at the end of the test. In the paper we show how this feature can be used for verification purposes. The analyses and strategies presented here should be useful to those considering the adoption of a pooling approach for RNA detection, particularly, for the identification of individuals infected with SARS-CoV-2.Author summaryThe progress of the SARS-CoV-2 pandemic requires the design of cost-effective testing programs at large scale. Running tests on pooled samples can provide a solution if the tests sensitivity is high enough. In the case of SARS-CoV-2, the current gold standard test, RT-qPCR, has shown some limitations that only allow the use of pools with relatively few samples. In this regard, Droplet digital PCR (ddPCR) has been shown to be 10 − 100 times more sensitive than RT-qPCR, making it suitable for test pooling. In this paper we describe a nested pool testing method in which the properties that make it optimal are simple analytic functions of the infection prevalence. We discuss how to proceed in practical implementations of the strategy, particularly when there are constraints that prevent the use of the optimal. We also show how its nested nature can be combined with the direct RNA quantification that the ddPCR test provides to identify the presence of unviable samples in the pools and for self-consistency tests. The studies of this paper should be useful for those considering the adoption of test pooling for RNA detection.