Oligomycin-induced proton uncoupling

Mitochondrial reprogramming by activating OXPHOS via glutamine metabolism in African American patients with bladder cancer

Bladder cancer (BLCA) mortality is higher in African American (AA) patients compared with European American (EA) patients, but the molecular mechanism underlying race-specific differences are unknown. To address this gap, we conducted comprehensive RNA-Seq, proteomics, and metabolomics analysis of BLCA tumors from AA and EA. Our findings reveal a distinct metabolic phenotype in AA BLCA characterized by elevated mitochondrial oxidative phosphorylation (OXPHOS), particularly through the activation of complex I. The results provide insight into the complex I activation-driven higher OXPHOS activity resulting in glutamine-mediated metabolic rewiring and increased disease progression, which was also confirmed by [U]13C-glutamine tracing. Mechanistic studies further demonstrate that knockdown of NDUFB8, one of the components of complex I in AA BLCA cells, resulted in reduced basal respiration, ATP production, GLS1 expression, and proliferation. Moreover, preclinical studies demonstrate the therapeutic potential of targeting complex I, as evidenced by decreased tumor growth in NDUFB8-depleted AA BLCA tumors. Additionally, genetic and pharmacological inhibition of GLS1 attenuated mitochondrial respiration rates and tumor growth potential in AA BLCA. Taken together, these findings provide insight into BLCA disparity for targeting GLS1-Complex I for future therapy.

Consequences of a 2-Deoxyglucose Exposure on the ATP Content and the Cytosolic Glucose Metabolism of Cultured Primary Rat Astrocytes

The glucose analogue 2-deoxyglucose (2DG) has frequently been used as a tool to study cellular glucose uptake and to inhibit glycolysis. Exposure of primary cultured astrocytes to 2DG caused a time- and concentration-dependent cellular accumulation of 2-deoxyglucose-6-phosphate (2DG6P) that was accompanied by a rapid initial decline in cellular ATP content. Inhibitors of mitochondrial respiration as well as inhibitors of mitochondrial uptake of pyruvate and activated fatty acids accelerated the ATP loss, demonstrating that mitochondrial ATP regeneration contributes to the partial maintenance of the ATP content in 2DG-treated astrocytes. After a 30 min exposure to 10 mM 2DG the specific content of cellular 2DG6P had accumulated to around 150 nmol/mg, while cellular ATP was lowered by 50% to around 16 nmol/mg. Following such a 2DG6P-loading of astrocytes, glycolytic lactate production from applied glucose was severely impaired during the initial 60 min of incubation, but was reestablished during longer incubation concomitant with a loss in cellular 2DG6P content. In contrast to glycolysis, the glucose-dependent NADPH regeneration via the pentose phosphate pathway (PPP) was only weakly affected in 2DG6P-loaded astrocytes and in cells that were coincubated with glucose in the presence of an excess of 2DG. Additionally, in the presence of 2DG PPP-dependent WST1 reduction was found to have doubled compared to hexose-free control incubations, indicating that cellular 2DG6P can serve as substrate for NADPH regeneration by the astrocytic PPP. The data presented provide new insights on the metabolic consequences of a 2DG exposure on the energy and glucose metabolism of astrocytes and demonstrate the reversibility of the inhibitory potential of a 2DG-treatment on the glucose metabolism of cultured astrocytes.

Kinetic modelling of the cellular metabolic responses underpinning in vitro glycolysis assays

This study aims to demonstrate the benefits of augmenting commercially available, real-time, in vitro glycolysis assays with phenomenological rate equation-based kinetic models, describing the contributions of the underpinning metabolic pathways. To this end, a commercially available glycolysis assay, sensitive to changes in extracellular acidification (extracellular pH), was used to derive the glycolysis pathway kinetics. The pathway was numerically modelled using a series of ordinary differential rate equations, to simulate the obtained experimental results. The sensitivity of the model to the key equation parameters was also explored. The cellular glycolysis pathway kinetics were determined for three different cell-lines, under nonmodulated and modulated conditions. Over the timescale studied, the assay demonstrated a two-phase metabolic response, representing the differential kinetics of glycolysis pathway rate as a function of time, and this behaviour was faithfully reproduced by the model simulations. The model enabled quantitative comparison of the pathway kinetics of three cell lines, and also the modulating effect of two known drugs. Moreover, the modelling tool allows the subtle differences between different cell lines to be better elucidated and also allows augmentation of the assay sensitivity. A simplistic numerical model can faithfully reproduce the differential pathway kinetics for three different cell lines, with and without pathway-modulating drugs, and furthermore provides insights into the cellular metabolism by elucidating the underlying mechanisms leading to the pathway end-product. This study demonstrates that augmenting a relatively simple, real-time, in vitro assay with a model of the underpinning metabolic pathway provides considerable insights into the observed differences in cellular systems.

Interaction between mitochondrial homeostasis and barrier function in lipopolysaccharide-induced endothelial cell injury

This study aimed to investigate the effects of mitochondrial homeostasis on lipopolysaccharide (LPS)-induced endothelial cell barrier function and the mechanisms that underlie these effects. Cells were treated with LPS or oligomycin (mitochondrial adenosine triphosphate synthase inhibitor) and the mitochondrial morphology, mitochondrial reactive oxygen species (mtROS), and mitochondrial membrane potential (ΔΨm) were evaluated. Moreover, the shedding of glycocalyx-heparan sulphate (HS), the levels of HS-specific degrading enzyme heparanase (HPA), and the expression of occludin and zonula occludens (ZO-1) of Tight Junctions (TJ)s, which are mediated by myosin light chain phosphorylation (p-MLC), were assessed. Examining the changes in mitochondrial homeostasis showed that adding heparinase III, which is an exogenous HPA, can destroy the integrity of glycocalyx. LPS simultaneously increased mitochondrial swelling, mtROS, and ΔΨm. Without oligomycin effects, HS, HPA levels, and p-MLC were found to be elevated, and the destruction of occludin and ZO-1 increased. Heparinase III not only damaged the glycocalyx by increasing HS shedding but also increased mitochondrial swelling and mtROS and decreased ΔΨm. Mitochondrial homeostasis is involved in LPS-induced endothelial cell barrier dysfunction by aggravating HPA and p-MLC levels. In turn, the integrated glycocalyx protects mitochondrial homeostasis.

Low-Dose Exposure of WS2 Nanosheets Induces Differential Apoptosis in Lung Epithelial Cells

Escalating the production and application of tungsten disulfide (WS2) nanosheets inevitably increases environmental human exposure and warrants the necessity of studies to elucidate their biological impacts. Herein, we assessed the toxicity of WS2 nanosheets and focused on the impacts of low doses (≤10 μg/mL) on normal (BEAS-2B) and tumorigenic (A549) lung epithelial cells. The low doses, which approximate real-world exposures, were found to induce cell apoptosis, while doses ≥ 50 μg/mL cause necrosis. Focused studies on low-dose exposure to WS2 nanosheets revealed more details of the impacts on both cell lines, including reduction of cell metabolic activity, induction of lipid peroxidation in cell membranes, and uncoupling of mitochondrial oxidative phosphorylation that led to the loss of ATP production. These phenomena, along with the expression situations of a few key proteins involved in apoptosis, point toward the occurrence of mitochondria-dependent apoptotic signaling in exposed cells. Substantial differences in responses to WS2 exposure between normal and tumorigenic lung epithelial cells were noticed as well. Specifically, BEAS-2B cells experienced more adverse effects and took up more nanosheets than A549 cells. Our results highlight the importance of dose and cell model selection in the assessment of nanotoxicity. By using doses consistent with real-world exposures and comparing normal and diseased cells, we can gain knowledge to guide the development of safety precautions for mitigating the adverse impacts of nanomaterial exposure on human health.

Ether phospholipids are required for mitochondrial reactive oxygen species homeostasis

Mitochondria are hubs where bioenergetics, redox homeostasis, and anabolic metabolism pathways integrate through a tightly coordinated flux of metabolites. The contributions of mitochondrial metabolism to tumor growth and therapy resistance are evident, but drugs targeting mitochondrial metabolism have repeatedly failed in the clinic. Our study in pancreatic ductal adenocarcinoma (PDAC) finds that cellular and mitochondrial lipid composition influence cancer cell sensitivity to pharmacological inhibition of electron transport chain complex I. Profiling of patient-derived PDAC models revealed that monounsaturated fatty acids (MUFAs) and MUFA-linked ether phospholipids play a critical role in maintaining ROS homeostasis. We show that ether phospholipids support mitochondrial supercomplex assembly and ROS production; accordingly, blocking de novo ether phospholipid biosynthesis sensitized PDAC cells to complex I inhibition by inducing mitochondrial ROS and lipid peroxidation. These data identify ether phospholipids as a regulator of mitochondrial redox control that contributes to the sensitivity of PDAC cells to complex I inhibition.

Antifungal Annona muricata L. (soursop) extract targets the cell envelope of multi-drug resistant Candida albicans

ETNOPHARMACOLOGICAL RELEVANCE

Annona muricata L. (soursop) is traditionally used in the treatment of inflammatory diseases, cancer, and infections caused by fungi. The therapeutic activity explored by its medicinal use is generally associated with its phytoconstituents, such as acetogenins and alkaloids. However, its potential antifungal bioactivity as well as its mechanism of action remains to be established.

AIM OF THE STUDY

To evaluate the antifungal activity of the ethanolic extract of A. muricata leaves against multidrug-resistant Candida albicans (ATCC® 10231).

MATERIAL AND METHODS

Phytoconstituents were detected by UFLC-QTOF-MS. The minimum inhibitory concentration was determined, followed by the determination of the minimum fungicidal concentration. For planktonic cells, the growth curve and cell density were evaluated. Studies to understand the mechanism of action on the cell envelope involved crystal violet permeability, membrane extravasation, sorbitol protection, exogenous ergosterol binding assay, metabolic activity, and cell viability. Furthermore, mitochondrial membrane potential was assessed.

RESULTS

Our analyses demonstrated a significant inhibitory effect of A. muricata, with the ability to reduce fungal growth by 58% and cell density by 65%. The extract affected both the fungal plasma membrane and cell wall integrity, with significant reduction of the cell viability. Depolarization of the fungal mitochondrial membrane was observed after treatment with A. muricata. Rutin, xi-anomuricine, kaempferol-3O-rutinoside, nornuciferine, xylopine, atherosperminine, caffeic acid, asimilobine, s-norcorydine, loliolide, annohexocin, annomuricin, annopentocin, and sucrose were identified as extract bioactive components.

CONCLUSIONS

Our findings show that the A. muricata extract is a source of chemical diversity, which acts as a potential antifungal agent with promising application to the therapy of infections caused by C. albicans.

Modulation and Pharmacology of the Mitochondrial Permeability Transition: A Journey from F-ATP Synthase to ANT

The permeability transition (PT) is an increased permeation of the inner mitochondrial membrane due to the opening of the PT pore (PTP), a Ca²⁺-activated high conductance channel involved in Ca²⁺ homeostasis and cell death. Alterations of the PTP have been associated with many pathological conditions and its targeting represents an incessant challenge in the field. Although the modulation of the PTP has been extensively explored, the lack of a clear picture of its molecular nature increases the degree of complexity for any target-based approach. Recent advances suggest the existence of at least two mitochondrial permeability pathways mediated by the F-ATP synthase and the ANT, although the exact molecular mechanism leading to channel formation remains elusive for both. A full comprehension of this to-pore conversion will help to assist in drug design and to develop pharmacological treatments for a fine-tuned PT regulation. Here, we will focus on regulatory mechanisms that impinge on the PTP and discuss the relevant literature of PTP targeting compounds with particular attention to F-ATP synthase and ANT.

Glucose starvation greatly enhances antiproliferative and antiestrogenic potency of oligomycin A in MCF-7 breast cancer cells

Energy imbalance is one of the key properties of tumour cells, which in certain cases supports fast cancer progression and resistance to therapy. The simultaneous blocking of glycolytic processes and oxidative phosphorylation pathways seems to be a promising strategy for antitumor therapies. The study aimed to evaluate the effect of glucose starvation on the antiproliferative and antiestrogenic potency of oligomycin A against hormone-dependent breast cancer cells. Cell viability was assessed by the MTT test. Estrogen receptor alpha (ERα) activity was evaluated by reporter assay. mTOR, AMPK, Akt, and S6 kinase expression was assessed by immunoblotting. Glucose starvation caused multiple increases in the antiproliferative potency of oligomycin A in the hormone-dependent breast cancer MCF-7 cells, while its effect on the sensitivity of the second hormone-dependent cancer cell line, named T47D, was weak and limited. Glycolytic inhibitors, 3-bromopyruvate and 2-deoxyglucose, greatly enhanced the antiproliferative potency of oligomycin A in MCF-7 cells. Glucose starvation leads to remarkable activation of Akt in MCF-7 cells, whereas oligomycin A enhances its effect. The mTOR, S6 kinase, and AMPK signalling pathways are significantly modulated by oligomycin A under glucose starvation. Oligomycin A demonstrates more pronounced antiestrogenic effects under glucose starvation. Thus, glucose starvation and pharmacological inhibition of glycolysis are of interest for revealing the antitumor potential of macrolide oligomycin A against hormone-dependent breast cancers.