Academic literature on the topic 'Lactate-induced hyperpolarization'

Purpose: Inducible Slc4a11 KO leads to corneal edema by disruption of the pump and barrier functions of the corneal endothelium (CE). The loss of Slc4a11 NH3-activated mitochondrial uncoupling leads to mitochondrial membrane potential hyperpolarization-induced oxidative stress. The goal of this study was to investigate the link between oxidative stress and the failure of pump and barrier functions and to test different approaches to revert the process. Methods: Mice which were homozygous for Slc4a11 Flox and Estrogen receptor –Cre Recombinase fusion protein alleles at 8 weeks of age were fed Tamoxifen (Tm)-enriched chow (0.4 g/Kg) for 2 weeks, and controls were fed normal chow. During the initial 14 days, Slc4a11 expression, corneal thickness (CT), stromal [lactate], Na+-K+ ATPase activity, mitochondrial superoxide levels, expression of lactate transporters, and activity of key kinases were assessed. In addition, barrier function was assessed by fluorescein permeability, ZO-1 tight junction integrity, and cortical cytoskeleton F-actin morphology. Results: Tm induced a rapid decay in Slc4a11 expression that was 84% complete at 7 days and 96% complete at 14 days of treatment. Superoxide levels increased significantly by day 7; CT and fluorescein permeability by day 14. Tight junction ZO-1 distribution and the cortical cytoskeleton were disrupted at day 14, concomitant with decreased expression of Cldn1, yet with increased tyrosine phosphorylation. Stromal lactate increased by 60%, Na+-K+ ATPase activity decreased by 40%, and expression of lactate transporters MCT2 and MCT4 significantly decreased, but MCT1 was unchanged at 14 days. Src kinase was activated, but not Rock, PKCα, JNK, or P38Mapk. Mitochondrial antioxidant Visomitin (SkQ1, mitochondrial targeted antioxidant) and Src kinase inhibitor eCF506 significantly slowed the increase in CT, with concomitant decreased stromal lactate retention, improved barrier function, reduced Src activation and Cldn1 phosphorylation, and rescued MCT2 and MCT4 expression. Conclusions: Slc4a11 KO-induced CE oxidative stress triggered increased Src kinase activity that resulted in perturbation of the pump components and barrier function of the CE.

Patients with similar tumour types frequently show different responses to the same therapy. The development of new treatments would benefit, therefore, from imaging methods that allow an early assessment of treatment response in individual patients, allowing rapid selection of the most effective treatment. We have been using 13C MRSI (magnetic resonance spectroscopic imaging) of tumour cell metabolism, using hyperpolarized 13C-labelled cellular metabolites, to detect treatment response. Nuclear spin hyperpolarization can increase sensitivity in the magnetic resonance experiment >10000 times, allowing us to image labelled cell substrates in vivo and their subsequent metabolism. We showed that exchange of hyperpolarized 13C label between lactate and pyruvate, catalysed by lactate dehydrogenase, was decreased in treated tumours undergoing drug-induced cell death, and that tissue pH could be imaged from the ratio of the signal intensities of hyperpolarized H13CO3− and 13CO2 following intravenous injection of hyperpolarized H13CO3. Tumour cell glutaminase activity, a potential measure of cell proliferation, can be determined using hyperpolarized [5-13C]glutamine, and treatment-induced tumour cell necrosis can be imaged in vivo from measurements of the conversion of hyperpolarized [1,4-13C2]fumarate into malate. Since these substrates are endogenous and, in some cases, have already been safely infused into patients, these techniques have the potential to translate to the clinic.

Resveratrol is a stilbene present in different plant species and exerting numerous beneficial effects, including prevention of diabetes and attenuation of some diabetic complications. Its inhibitory effect on insulin secretion was recently documented, but the exact mechanism underlying this action remains unknown. Experiments employing diazoxide and a high concentration of K+revealed that, in depolarized pancreatic islets incubated for 90 min with resveratrol (1, 10, and 100 μM), insulin secretion stimulated by glucose and leucine was impaired. The attenuation of the insulin secretory response to 6.7 mM glucose was not abrogated by blockade of intracellular estrogen receptors and was found to be accompanied by diminished islet glucose oxidation, enhanced lactate production, and reduced ATP levels. Glucose-induced hyperpolarization of the mitochondrial membrane was also reduced in the presence of resveratrol. Moreover, in depolarized islets incubated with 2.8 mM glucose, activation of protein kinase C or protein kinase A potentiated insulin release; however, under these conditions, resveratrol was ineffective. Further studies also revealed that, under conditions of blocked voltage-dependent calcium channels, the stilbene reduced insulin secretion induced by a combination of glucose with forskolin. These data demonstrate that resveratrol 1) inhibits the amplifying pathway of insulin secretion, 2) exerts an insulin-suppressive effect independently of its estrogenic/anti-estrogenic activity, 3) shifts islet glucose metabolism from mitochondrial oxidation to anaerobic, 4) fails to abrogate insulin release promoted without metabolic events, and 5) does not suppress hormone secretion as a result of the direct inhibition of Ca2+influx through voltage-dependent calcium channels.

Abstract Metabolic reprogramming is recognized as one of the key hallmarks in acquiring aggressive phenotype and chemoresistance in solid tumors and hematologic malignancies. We have previously demonstrated that T-ALL are characterized by significant dependency on oxidative phosphorylation (OxPhos) with ability to utilize glutamine either in oxidative or reductive directions of TCA cycle, when mitochondria are blocked by Complex I Inhibitor (Baran N, et al. ASH 2020). To survive upon Complex I blockade leukemic cells require functional monocarboxylate transporter MCT1, that enables excretion of lactate and permissive pyruvate flux (Fig.1 a). Here we show that metabolic intervention utilizing OxPhos blockade can be potentiated by targeting MCT1 transporter and propose a novel metabolic synthetic lethality that could be exploited to eradicate T-ALL and other OxPhos-dependent malignancies. We first demonstrated that Complex I inhibition leads to increased MCT1 expression; on the contrary, MCT1 transporter blockade forces cells to increase OxPhos. In turn, the combinatorial therapy with Complex I inhibitor (IACS-010759) and MCT1 inhibitor (AZD3965) causes loss of ATP content (Fig. 1b), significant reduction of cell number and massive induction of apoptosis. Mechanistically, the combination treatment further reduced oxygen consumption rate (OCR) (Fig. 1c) and increased extracellular acidification rate, as measured by Seahorse. In concert with those results, dual inhibition led to TCA blockade, accumulation of intracellular lactate and depletion of glutamine, cystathionine and glutathione, indicating severe disruption of redox balance as measured by mass spectrometry and confirmed by significant accumulation of intracellular and mitochondrial reactive oxygen species (ROS) (Fig. 1d), loss of mitochondrial membrane potential (ΔΨ) (Fig. 1e) and subsequent mitochondria swelling. RNAseq data showed simultaneous upregulation of glycolysis and glutathione-related processes as possible mechanisms of metabolic compensation, yet strong upregulation of genes regulating apoptosis related to mitochondria dysfunction (Fig. 1f). Real-time hyperpolarized MRI based metabolic imaging studies with [1-13C]-pyruvate in patient-derived xenografts in vivo revealed significant decrease of lactate-to-pyruvate ratio in mice treated with AZD3965 or IACS-010759 alone, and in mice treated with drug combination. [13C]-Glucose isotope tracing analysis in patient-derived xenografts in vivo revealed an increased intracellular trapping of lactate as a marker of treatment effectiveness in mice subjected to dual blockade. While MCT1 inhibition induced only moderate reduction of leukemia growth in vitro and tumor burden in vivo, combination with IACS-010759 depleted significantly both, circulating and marrow/spleen/liver resident leukemia cells. Mechanistically, inhibition of MCT1 by AZD3965 therapy in leukemia-bearing mice led to lactate accumulation, OCR increase, moderate ROS production and mitochondrial membrane hyperpolarization, while Complex I blockade resulted in upregulation of MCT-1, reduction of OCR, lactate production and increase of ROS ; consequently, combinatorial therapy caused complete mitochondria shut-down and drastic inhibition of tumor growth both in vitro and in vivo in two xenografts models and led to significant extension of overall survival (p<0.0001) (Fig. 1g). In summary, these results demonstrate a novel synthetic vulnerability of concomitant blockade of OxPhos and MCT-1, uncovering metabolic checkpoints that can ultimately translate into successful therapies in T-ALL and OxPhos-dependent malignancies. Figure 1 Figure 1. Disclosures Skwarska: Halilovich E, Wang Y, Morris E, Konopleva M, Skwarska A.: Patents & Royalties: Combination of a MCL-1 inhibitor and midostaurin, uses and pharmaceutical composition thereof.. Konopleva: Reata Pharmaceuticals: Current holder of stock options in a privately-held company, Patents & Royalties: intellectual property rights; Rafael Pharmaceuticals: Other: grant support, Research Funding; Stemline Therapeutics: Research Funding; Eli Lilly: Patents & Royalties: intellectual property rights, Research Funding; Ascentage: Other: grant support, Research Funding; Genentech: Consultancy, Honoraria, Other: grant support, Research Funding; Ablynx: Other: grant support, Research Funding; AstraZeneca: Other: grant support, Research Funding; AbbVie: Consultancy, Honoraria, Other: Grant Support, Research Funding; Novartis: Other: research funding pending, Patents & Royalties: intellectual property rights; Cellectis: Other: grant support; Sanofi: Other: grant support, Research Funding; KisoJi: Research Funding; Calithera: Other: grant support, Research Funding; Forty Seven: Other: grant support, Research Funding; Agios: Other: grant support, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Other: grant support.

T cell reconstitution after transplant is critically dependent on the thymus; an inverse relationship between a transplant recipient's age and their capacity to generate T lymphocytes (in particular CD4+T cells) has been found in several studies, and thymic function pre-transplant can have a significant impact on clinical outcomes. Although the thymus has a remarkable ability to repair following damage, the mechanisms underlying this endogenous regeneration remain poorly understood. Despite this regenerative capacity, delayed T cell reconstitution is associated with an increased risk of infections, relapse of malignancy and the development of secondary malignancies. Therefore, there is a clinical demand for therapeutics that restore immune function after damage. Our recent studies have identified two key pathways driving thymic regeneration; centered on the secretion of BMP4 by endothelial cells (ECs) and IL-22 by innate lymphoid cells (Dudakov 2012 Science 336:91; Dudakov 2017 Blood130:933; Wertheimer 2018 Sci Immunol3:19). However, the specific regulatory mechanisms that trigger these regeneration-associated factors after damage remain unclear. Our previous work identified that the presence of homeostatic apoptotic CD4+CD8+ (DP) thymocytes, as apoptotic thymocytes form the bulk of developing T cells, suppress the production of IL-23 in dendritic cells (DCs), a key downstream mediator for IL-22, and BMP4 in ECs (Fig. 1A), and that the depletion of apoptotic thymocytes after damage precedes the production of these regenerative factors. Therefore, together with our findings that the metabolic needs of key thymus populations alter drastically following injury due to damage-induced metabolic remodeling, we hypothesized that further to the loss of DP-specific suppression, metabolic dysfunction in DPs after damage triggers mitochondrial-induced pyroptotic cell death, which can directly promote regeneration of the thymus. Consistent with this hypothesis, our preliminary data shows increased levels of cl-caspase 1 (pyroptotic caspase) and a decrease in cl-caspase 3 (apoptotic caspase) in DPs after SL-TBI (550 cGy), demonstrating a preferential induction of pyroptotic cell death in DPs after damage (Fig. 1B). Furthermore, we demonstrated an increase in extracellular lactate dehydrogenase (LDH) levels, HMGB-1 and TNF⍺[canonical damage-associated molecular patterns (DAMPs) released during ICD] acutely after damage caused by SL-TBI (Fig. 1C).Given our previous findings that stromal cells are more radio-resistant than DP thymocytes (Wertheimer 2018 Sci Immunol3:19), and evidence for mitochondrial-induced pyroptosis, we identified hyperpolarization of the mitochondrial membrane potential accompanied by increased levels of ROS in DPs, an effect not observed in TECs, suggesting metabolic stability confers protection against acute damage (Fig. 1D). Furthermore, co-culture of pyroptotic thymocytes results in increased IL12p40+ DCs and increased Foxn1 expression in TECs (Fig. 1E), strengthening our hypothesis that cell-cell communication drives thymic regeneration after damage by inducing regenerative factors as well as directly promoting TEC function via secreted factors from pyroptotic DPs. One way in which DAMPs, such as ATP, can initiate cell signaling is by the activation of cell surface purinergic receptors, including P2Y2 which is widely expressed on TECs, and here we demonstrate that in vitro treatment with ATP or P2Y2 agonist increases Foxn1 in cTECs, and P2Y2 antagonism reverses this effect (Fig 1F). As P2Y2 activation promotes Ca2+efflux from the ER, we have further demonstrated that stimulating the intracellular release of Ca2+, using tunicamycin, induced Foxn1 expression in cTECs, which was reversed upon inhibition of Ca2+release (Fig. 1G). Importantly, we demonstrate here that this pathway can be therapeutically targeted by activating P2Y2 signaling in vivo with MRS2568 or ATP enhances thymus cellularity and expands cTECs in models of acute injury (Fig. 1H&I). These findings not only reveal a novel metabolic-mediated molecular mechanism governing tissue regeneration; but also by targeting FOXN1 directly offers a potentially superior therapeutic strategy for boosting thymic regeneration and T cell reconstitution after damage such as that caused by HCT, infection or cytoreductive therapy. Disclosures No relevant conflicts of interest to declare.

AbstractHyperpolarization techniques increase nuclear spin polarization by more than four orders of magnitude, enabling metabolic MRI. Even though hyperpolarization has shown clear value in clinical studies, the complexity, cost and slowness of current equipment limits its widespread use. Here, a polarization procedure of [1‐13C]pyruvate based on parahydrogen‐induced polarization by side‐arm hydrogenation (PHIP‐SAH) in an automated polarizer is demonstrated. It is benchmarked in a study with 48 animals against a commercial dissolution dynamic nuclear polarization (d‐DNP) device. Purified, concentrated (≈70–160 mM) and highly hyperpolarized (≈18%) solutions of pyruvate are obtained at physiological pH for volumes up to 2 mL within 85 s in an automated process. The safety profile, image quality, as well as the quantitative perfusion and lactate‐to‐pyruvate ratios, are equivalent for PHIP and d‐DNP, rendering PHIP a viable alternative to established hyperpolarization techniques.

Abstract Background and Aims Gadolinium-based contrast agents are widely used for magnetic resonance imaging, and although they may be considered well tolerated at recommended dosing levels, recent evidences support the deposition of free gadolinium in the tissues, and its slow release into circulation, resulting in long-term toxicity, which is aggravated in renal patients. The kidney, as the major excretion organ of these agents, and particularly the proximal tubule, as a common location of xenobiotics’ bioaccumulation, may be key targets of gadolinium’s deleterious effects. This study aimed at unveiling the nephrotoxic potential and the underlying mechanisms of toxicity of gadolinium, using an in vitro model of normal human proximal tubular cells (HK-2 cell line). Method HK-2 cells were exposed for 24 h to a wide concentration range of gadolinium, in the form of trichloride hexahydrate, and cell viability was assessed to estimate the half maximal effective concentration (EC50) and the subtoxic concentration eliciting 1 % of cell death (EC01). These ECs were further used to determine the effects of gadolinium on the cell’s oxidative status, mitochondrial function, cell death mechanisms and lipid deposition, through variable colorimetric and fluorometric assays. Expression of the pro-inflammatory gene IL6 was also determined through quantitative PCR. Results Gadolinium induced cell death in a concentration-dependent manner, with estimated EC01 and EC50 of 3 and 340 µM, respectively. When compared to control cells, the subtoxic concentration showed no significant effects in terms of reactive oxygen and nitrogen species (ROS and RNS) production, total glutathione levels (tGSH) or total antioxidant status (TAS). On the other hand, the EC50 showed significant disruption of the oxidative status of the cell, with over 60 % depletion of tGSH cell contents (p < 0.01) and a significant decrease of TAS (p < 0.05). However, this effect was not accompanied by an increase, but rather by a significant decline in ROS and RNS production of about 50 % below control (p < 0.0001). At the EC50, but not at EC01, it was also observed the disturbance of the mitochondrial and energetic homeostasis, as showed by the increment of intracellular free calcium levels, hyperpolarization of the mitochondrial membrane, and decay of the ATP levels (p < 0.0001). Cell death induced by gadolinium was characterized by typical morphological changes of late apoptosis and necrosis, with a significant increase in propidium iodide uptake and lactate dehydrogenase leakage (p ≤ 0.0001) at EC50. The presence of neutral lipids-containing vesicles was observed in the cytoplasm of cells exposed to gadolinium using the fluorescent dye BODIPY, already noticeable at the subtoxic concentration. Cells exposed to gadolinium also showed increased expression of IL6, though this effect was only significant at the EC01 (p < 0.05). Conclusion Gadolinium showed marked cytotoxic potential at micromolar levels in HK-2 cells. This cytotoxicity was characterized by increased oxidative stress independent of ROS and RNS production and mitochondrial dysfunction followed by cell death via late apoptosis and necrosis. At a subtoxic concentration, gadolinium was also able to elicit the accumulation of lipidic vesicles within the cells’ cytoplasm, and to trigger a pro-inflammatory response. Although it is still unclear which amount of gadolinium is in fact released from the complexes commonly used as contrast agents, this study shows that gadolinium ion has direct nephrotoxic potential, with noteworthy manifestations at subtoxic concentrations. Acknowledgments This work was supported by Applied Molecular Biosciences Unit (UCIBIO), financed by national funds from FCT/MCTES (UIDB/04378/2020), by North Portugal Regional Coordination and Development Commission (CCDR-N)/NORTE2020/Portugal 2020 (Norte-01-0145-FEDER-000024).

In the present study, we report a lactate-induced hyperpolarization and reduction of epileptiform activity in subicular weak burst firing and regular firing neurons using patch clamp electrophysiology. We showed the expression of lactate receptor Hydroxycarboxylic acid receptor 1 (HCA1) in the subiculum region using immunohistochemistry and found that the inhibitory effect of lactate is through activation of the same receptor because the suppression of epileptiform activity was mimicked by the HCA1 agonist and blocked by the antagonist of HCA1. Lactate-HCA1 interaction leads to activation of Gi-cAMP signaling which was confirmed by pertussis toxin (PTX) experiments by including it in the recording patch pipette. Furthermore, bath perfusion of gallein with lactate after induction of epileptiform activity confirmed the involvement of Gβγ subunit. We hypothesized that Gβγ subunit might activate G protein-coupled inwardly rectifying K+ (GIRK) channel resulting in the observed hyperpolarization with lactate since GIRK channels have been implicated in epilepsy. Using tertiapin-Q (GIRK current blocker) in current-clamp and voltage-clamp experiments validated the activation of GIRK channel by lactate in mediating the inhibition of epileptiform activity. Our findings also suggest that the lactate-induced effect is modulated by the level of cAMP in the cells as treatment with forskolin removed the inhibitory effect of lactate. In conclusion, ours is the first report proposing interaction of lactate with subicular neurons to suppress epileptiform activity through activation of HCA1 and GIRK channel. Our findings suggest future work in exploring the use of lactate as a therapeutic agent in epilepsy research, besides exploring other ion channel targets of lactate.