Mapping Metabolism: Monitoring Lactate Dehydrogenase Activity Directly in Tissue

2-deoxy-2-[18F]fluoro-D-glucose Positron Emission Tomography to Monitor Lung Inflammation and Therapeutic Response to Dexamethasone in a Murine Model of Acute Lung Injury

PURPOSE

To image inflammation and monitor therapeutic response to anti-inflammatory intervention using 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) positron emission tomography (PET) in a preclinical model of acute lung injury (ALI).

PROCEDURES

Mice were intratracheally administered lipopolysaccharide (LPS, 2.5 mg/kg) to induce ALI or phosphate-buffered saline as the vehicle control. A subset of mice in the ALI group received two intraperitoneal doses of dexamethasone 1 and 24 h after LPS. [18F]FDG PET/CT was performed 2 days after the induction of ALI. [18F]FDG uptake in the lungs was quantified by PET (%ID/mLmean and standardized uptake value (SUVmean)) and ex vivo γ-counting (%ID/g). The severity of lung inflammation was determined by quantifying the protein level of inflammatory cytokines/chemokines and the activity of neutrophil elastase and glycolytic enzymes. In separate groups of mice, flow cytometry was performed to estimate the contribution of individual immune cell types to the total pulmonary inflammatory cell burden under different treatment conditions.

RESULTS

Lung uptake of [18F]FDG was significantly increased during LPS-induced ALI, and a decreased [18F]FDG uptake was observed following dexamethasone treatment to an intermediate level between that of LPS-treated and control mice. Protein expression of inflammatory biomarkers and the activity of neutrophil elastase and glycolytic enzymes were increased in the lungs of LPS-treated mice versus those of control mice, and correlated with [18F]FDG uptake. Furthermore, dexamethasone-induced decreases in cytokine/chemokine protein levels and enzyme activities correlated with [18F]FDG uptake. Neutrophils were the most abundant cells in LPS-induced ALI, and the pattern of total cell burden during ALI with or without dexamethasone therapy mirrored that of [18F]FDG uptake.

CONCLUSIONS

[18F]FDG PET noninvasively detects lung inflammation in ALI and its response to anti-inflammatory therapy in a preclinical model. However, high [18F]FDG uptake by bone, brown fat, and myocardium remains a technical limitation for quantification of [18F]FDG in the lungs.

Deletion of Lactate Dehydrogenase-A Impairs Oncogene-Induced Mouse Hepatocellular Carcinoma Development

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is a multistep process whereby abnormally proliferating cancer cells undergo extensive metabolic reprogramming. Metabolic alterations in hepatocarcinogenesis depend on the activation of specific oncogenes, thus partially explaining HCC heterogeneity. c-Myc oncogene overexpression, frequently observed in human HCCs, leads to a metabolic rewiring toward a Warburg phenotype and production of lactate, resulting in the acidification of the extracellular space, favoring the emergence of an immune-permissive tumor microenvironment. Here, we investigated whether Ldha genetic ablation interferes with metabolic reprogramming and HCC development in the mouse.

METHODS

We characterized the metabolic reprogramming in tumors induced in C57BL/6J mice hydrodynamically cotransfected with c-Myc and h-Ras. Using the same experimental model, we investigated the effect of Ldha inhibition-gained through the inducible and hepatocyte-specific Ldha knockout-on cancer cell metabolic reprogramming, number and size of HCC lesions, and tumor microenvironment alterations.

RESULTS

c-Myc/h-Ras-driven tumors display a striking glycolytic metabolism, suggesting a switch to a Warburg phenotype. The tumors also exhibited enhanced pentose phosphate pathway activity, the switch of glutamine to sustain glutathione synthesis instead of the tricarboxylic acid cycle, and the impairment of oxidative phosphorylation. In addition, Ldha abrogation significantly hampered tumor number and size together with an evident inhibition of the Warburg-like metabolic feature and a remarkable increase of CD4⁺ lymphocytes compared with Ldha wild-type livers.

CONCLUSIONS

These results demonstrate that Ldha deletion significantly impairs mouse HCC development and suggest lactate dehydrogenase as a potential target to enhance the efficacy of the current therapeutic options.

Lactate dehydrogenase activity staining demonstrates time-dependent immune cell infiltration in human ex-vivo burn-injured skin

Burn injuries constitute one of the most serious accidental injuries. Increased metabolic rate is a hallmark feature of burn injury. Visualising lactate dehydrogenase (LDH) activity has been previously used to identify metabolic activity differences, hence cell viability and burn depth in burn skin. LDH activity was visualised in injured and uninjured skin from 38 sub-acute burn patients. LDH activity aided the identification of spatially correlating immunocompetent cells in a sub-group of six patients. Desorption Electrospray Ionisation Mass Spectrometry Imaging (DESI MSI) was used to describe relative lactate and pyruvate abundance in burned and uninjured tissue. LDH activity was significantly increased in the middle and deep regions of burnt skin compared with superficial areas in burnt skin and uninjured tissue and positively correlated with post-burn time. Regions of increased LDH activity showed high pyruvate and low lactate abundance when examined with DESI-MSI. Areas of increased LDH activity exhibited cellular infiltration, including CD3 + and CD4 + T-lymphocytes and CD68 + macrophages. Our data demonstrate a steady increase in functional LDH activity in sub-acute burn wounds linked to cellular infiltration. The cell types associated are related to tissue restructuring and inflammation. This region in burn wounds is likely the focus of dysregulated inflammation and hypermetabolism.

Analysis of Colorectal Carcinogenesis Paradigm between Cold Constitution and Heat Constitution: Earlier ECM Collagen Deposition

Colorectal cancer (CRC) is a common malignant tumor around the world. Studying the unique constitution of CRC patients is conducive to the application of personalized medical treatment for CRC. The most common types of constitution in CRC are cold and heat constitution. A previous study has suggested that the malignant progression in cold and heat constitution CRC are different; however, the mechanism remains unclear. The tumor microenvironment (TME) is likely to vary with each individual constitution, which may affect the tumor growth in different constitutions. The extracellular matrix (ECM), the most important component of TME, plays a critical role in disease progression and outcome in patients with CRC. Moreover, collagen, the major component of the ECM, determines the main functional characteristics of ECM and tissue fibrosis caused by collagen deposition, which is one of the signs of CRC malignant progression. This study aimed to explore the mechanisms leading to different colorectal carcinogenesis paradigms between the cold constitution and heat constitution within the context of ECM collagen deposition. We established the CRC rat models and enrolled 30 CRC patients with cold and heat constitution. The collagen-related parameters were detected by using Sirius red staining combined with polarized light microscope, and expressions of collagen (COL I and COL III) and lysyl oxidase (LOX and LOXL2) were determined using immunohistochemistry, while the mRNA levels of COL1A1, COL3A1, LOX, and LOXL2 were measured by qRT-PCR. We found that a higher degree of collagen deposition in the cold-constitution group. The results suggest cold and heat constitution may affect the colorectal carcinogenesis paradigm by influencing the early collagen deposition in colon tissue. The study may provide an effective idea for clinicians to improve the prognosis of CRC patients with different constitutions.

The paradox of metabolism in quiescent stem cells

The shift between a proliferating and a nonproliferating state is associated with significant changes in metabolic needs. Proliferating cells tend to have higher metabolic rates, and their metabolic profiles facilitate biosynthesis, as compared to those of nondividing cells of the same sort. Recent studies have elucidated specific molecules that control metabolic changes while cells shift between proliferation and quiescence. Embryonic stem cells, which are rapidly proliferating, tend to have metabolic patterns that are similar to those of nonstem cells in a proliferative state. Moreover, although adult stem cells tend to be quiescent, their metabolic profiles have been reported in multiple organs to more closely resemble those of proliferating than those of nondividing cells in some respects. The findings raise questions about whether there are metabolic profiles that are required for stemness, and whether these profiles relate to the metabolic properties that may be required for quiescence. Here, we review the literature on how metabolism changes upon commitment to proliferation and compare the proliferating and nonproliferating metabolic states of differentiated cells and embryonic and adult stem cells.

Functional and Morphological Characterization of Small and Large Steroidogenic Luteal Cells From Domestic Cats Before and During Culture

The current study aimed to isolate, culture and characterize small (SLC) and large (LLC) steroidogenic cells from the corpora lutea (CL) of non-pregnant domestic cats. Isolation of feline SLC was based on an enzymatic digestion of luteal tissue, whereas LLC were obtained by mechanical disruption of CL. To assess function of both cell types, progesterone secretion and mRNA expression of selected genes involved in steroid and prostaglandin synthesis were measured, as well as relative transcript abundance of hormone receptors and anti-oxidative enzymes, before and during culture. The cells were cultured for 3 or 5 days without gonadotropins. Isolated feline SLC and LLC had different sizes (12 ± 3 μm vs. 34 ± 5 μm, respectively), morphologies (amount of lipid droplets) and behaved differently in culture. SLC attached and proliferated or spread quickly, but lost their steroidogenic function during culture (significant decrease in progesterone secretion and expression of steroidogenic genes). The expression of receptors for gonadotropins and prolactin also decreased. Prostaglandin synthase (PTGS2) decreased steadily over time, whereas mRNA expression of PGE2 synthase (PGES) increased. The gene expression of anti-oxidative enzyme glutathione peroxidase 4 (GPX4), also increased during culture, but not of superoxide dismutase 1 (SOD1). In comparison to SLC, LLC did not attach to culture plates, secreted more progesterone per inoculated cells and maintained steroidogenic function during culture. Expression of prostaglandin synthases (PTGS2 and PGES) was almost non-detectable. The gene expression of hormone receptors for prostaglandin F2 alpha (PTGFR), gonadotropins (LHCHR and FSHR), and prolactin (PRLR), as well as of anti-oxidative enzymes (GPX4, SOD1), increased over time. To conclude, we successfully isolated and cultured different types of feline steroidogenic luteal cells and comprehensively characterized both isolated cell types. This knowledge can be used to better understand the CL lifecycle in felines more broadly, and the established cell cultures will provide a foundation for future studies on luteolytic and luteotrophic factors in the domestic cat, and for comparison with other feline species, particularly lynx.