Assessment of Mitochondrial Cell Metabolism by Respiratory Chain Electron Flow Assays.

Cellular energy metabolism is regulated by complex metabolic pathways. Although anaerobic glycolysis was reported as a primary source of energy in cancer leading to a high rate of lactate production, current evidence shows that the main energy source supporting cancer cell metabolism relies on mitochondrial metabolism. Mitochondria are the key organelle maintaining optimal cellular energy levels.

Natural modulators of the hallmarks of immunogenic cell death.

Natural compounds act as immunoadjuvants as their therapeutic effects trigger cancer stress response and release of damage-associated molecular patterns (DAMPs). These reactions occur through an increase in the immunogenicity of cancer cells that undergo stress followed by immunogenic cell death (ICD). These processes result in a chemotherapeutic response with a potent immune-mediating reaction.

Stress-induced cellular responses in immunogenic cell death: Implications for cancer immunotherapy.

Cancer is evading the host's defense mechanisms leading to avoidance of immune destruction. During tumor progression, immune-evading cancer cells arise due to selective pressure from the hypoxic and nutrient-deprived microenvironment. Thus, therapies aiming at re-establishing immune destruction of pathological cells constitute innovating anti-cancer strategies.

Tubulin-binding anticancer polysulfides induce cell death via mitotic arrest and autophagic interference in colorectal cancer.

Polysulfanes show chemopreventive effects against gastrointestinal tumors. We identified diallyl tetrasulfide and its derivative, dibenzyl tetrasulfide (DBTTS), to be mitotic inhibitors and apoptosis inducers. Here, we translate their application in colorectal cancer (CRC).

Effects of Natural Products on Mcl-1 Expression and Function.

Cancer development is mostly due to a deregulation of cell death as cancer cells become resistant to apoptosis by increasing expression of anti-apoptotic proteins belonging to the Bcl-2 family. Mcl-1 is one anti-apoptotic protein, which is mainly responsible for cancer cell resistance as it is overexpressed by most cancer cell types. Many research projects aim to restore cancer cell death by using natural pharmacological scaffolds targeting anti-apoptotic proteins to inhibit their effect in cancer development.

Cancer-type-specific crosstalk between autophagy, necroptosis and apoptosis as a pharmacological target.

Cell death plays an essential role in the development of organs, homeostasis, and cancer. Apoptosis and programmed necrosis are two major types of cell death, characterized by different cell morphology and pathways. Accumulating evidence shows autophagy as a new alternative target to treat tumor resistance.

From nature to bedside: pro-survival and cell death mechanisms as therapeutic targets in cancer treatment.

Cell death is an important physiological regulator during development, tissue homeostasis and stress response but it is also a protective tumor suppressive mechanism. Tumor cells almost universally acquire the ability to evade cell death pathways that in normal cells act as a protective mechanism to remove damaged cells. As a result, a population of death-resistant cells with accumulating genetic and epigenetic abnormalities contributes to malignant transformation.

Natural compounds as regulators of the cancer cell metabolism.

Even though altered metabolism is an "old" physiological mechanism, only recently its targeting became a therapeutically interesting strategy and by now it is considered an emerging hallmark of cancer. Nevertheless, a very poor number of compounds are under investigation as potential modulators of cell metabolism. Candidate agents should display selectivity of action towards cancer cells without side effects.

Melatonin: a pleiotropic molecule regulating inflammation.

Melatonin is a neurohormone produced by the pineal gland that regulates sleep and circadian functions. Melatonin also regulates inflammatory and immune processes acting as both an activator and inhibitor of these responses. Melatonin demonstrates endocrine, but also paracrine and autocrine effects in the leukocyte compartment: on one side, leukocytes respond to melatonin in a circadian fashion; on the other side, leukocytes are able to synthesize melatonin by themselves.

Subapoptogenic oxidative stress strongly increases the activity of the glycolytic key enzyme glyceraldehyde 3-phosphate dehydrogenase.

We have previously shown that oxidative stress induced by an apoptogenic dose of H(2)O(2) leads to a temporary block of glycolytic flux via inactivation of the glycolytic key enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in U937 cells. This corresponds to the activation of a cell defense pathway that is triggered to repair stress-induced damage and to rescue cells from death. Here, we show that subapoptogenic doses of H(2)O(2) affect GAPDH activity in an opposite way, leading to strong hyperactivation.

Multiple mechanisms for hydrogen peroxide-induced apoptosis.

The mechanisms of cell killing by oxidative stress, in particular by hydrogen peroxide, are not yet well clarified. Here, we show that during recovery after H(2)O(2) treatment, apoptosis occurs in two different waves, peaking at 8 h (early) and 18 h (late) of recovery from oxidative stress. The two peaks are differentially modulated by a set of inhibitors of metabolic processes, which suggests that the first peak depends on DNA break formation, whereas the second may be correlated with H(2)O(2)-induced mitochondrial alterations.

Neuroprotection by melatonin on astrocytoma cell death.

Glial cells play an active role in the homeostatic regulation of the central nervous system (CNS). Astrocytes, the most abundant glial cell types in the brain, provide mechanical and metabolic support for neurons. The regulation of astrocyte apoptosis, therefore, is important for physiological and pathological processes in the CNS.

Intracellular prooxidant activity of melatonin induces a survival pathway involving NF-kappaB activation.

We have shown that melatonin exerts a prooxidant activity in U937 cells, a tumor human promonocytic cell line. (1) Here we show that melatonin induces a strong canonical activation of NF-kappaB, inducing IkappaBalpha degradation and the consequential nuclear translocation of p50/p65 subunits. The timing of NF-kappaB activation overlaps with the timing of reactive oxygen species (ROS) production due to melatonin.

Melatonin as a modulator of apoptosis in B-lymphoma cells.

Melatonin is considered a promising antitumor agent, promoting apoptosis in tumor cells and contrasting it in normal cells. The basis for this selectivity is presumed to be the ability of melatonin to stimulate reactive oxygen species (ROS) production in tumor cells. Here we investigate the effect of melatonin on three types of human lymphocytes: normal blood lymphocytes, BL41 Burkitt lymphoma, and the cognate Epstein-Barr virus (EBV)-converted E2r.

Rapid and transient stimulation of intracellular reactive oxygen species by melatonin in normal and tumor leukocytes.

Melatonin is a modified tryptophan with potent biological activity, exerted by stimulation of specific plasma membrane (MT1/MT2) receptors, by lower affinity intracellular enzymatic targets (quinone reductase, calmodulin), or through its strong anti-oxidant ability. Scattered studies also report a perplexing pro-oxidant activity, showing that melatonin is able to stimulate production of intracellular reactive oxygen species (ROS). Here we show that on U937 human monocytes melatonin promotes intracellular ROS in a fast (<1 min) and transient (up to 5-6 h) way.

Melatonin antagonizes the intrinsic pathway of apoptosis via mitochondrial targeting of Bcl-2.

We have recently shown that melatonin antagonizes damage-induced apoptosis by interaction with the MT-1/MT-2 plasma membrane receptors. Here, we show that melatonin interferes with the intrinsic pathway of apoptosis at the mitochondrial level. In response to an apoptogenic stimulus, melatonin allows mitochondrial translocation of the pro-apoptotic protein Bax, but it impairs its activation/dimerization The downstream apoptotic events, i.

Melatonin antagonizes apoptosis via receptor interaction in U937 monocytic cells.

Among the non-neurological functions of melatonin, much attention is being directed to the ability of melatonin to modulate the immune system, whose cells possess melatonin-specific receptors and biosynthetic enzymes. Melatonin controls cell behaviour by eliciting specific signal transduction actions after its interaction with plasma membrane receptors (MT(1), MT(2)); additionally, melatonin potently neutralizes free radicals. Melatonin regulates immune cell loss by antagonizing apoptosis.

Melatonin as an apoptosis antagonist.

The pineal hormone melatonin (Mel), in addition to having a well-established role as a regulator of circadian rhythms, modulates nonneural compartments by acting on specific plasma membrane receptors (MT1/MT2) present in many different cell types. Mel plays immunomodulatory roles and is an oncostatic and antiproliferative agent; this led to the widespread belief that Mel may induce or potentiate apoptosis on tumor cells, even though no clear indications have been presented so far. Here we report that Mel is not apoptogenic on U937 human monocytic cells, which are known to possess MT1 receptors at the times (up to 48 h) and doses (up to 1 mM) tested.

Intracellular pro-oxidant activity of melatonin deprives U937 cells of reduced glutathione without affecting glutathione peroxidase activity.

It was long believed that melatonin might counteract intracellular oxidative stress because it was shown to potentiate antioxidant endogenous defences, and to increase the activity of many antioxidant enzymes. However, it is now becoming evident that when radicals are measured within cells, melatonin increases, rather than decreasing, radical production. Herein we demonstrate a pro-oxidant effect of melatonin in U937 cells by showing an increase of intracellular oxidative species and a depletion of glutathione (GSH).

Oxidative upregulation of Bcl-2 in healthy lymphocytes.

In many cell systems, pharmacological glutathione (GSH) depletion with the GSH neosynthesis inhibitor buthionine sulfoximine (BSO) leads to cell death and highly sensitizes tumor cells to apoptosis induced by standard chemotherapeutic agents. However, some tumor cells upregulate Bcl-2 in response to BSO, thus surviving the treatment and failing to be chemosensitized. Cell lines of monocytic and lymphocytic origins respond to BSO treatment in an opposite way, lymphocytes being chemosensitized and unable to transactivate Bcl-2.