Fatty-Acid–Induced Apoptosis in Ehrlich Ascites Tumor Cells

Astrocytic metabolic switch is a novel etiology for Cocaine and HIV-1 Tat-mediated neurotoxicity

Calcium (Ca2+) dynamics and oxidative signaling control mitochondrial bioenergetics in the central nervous system, where astrocytes are a major energy source for neurons. Cocaine use exacerbates HIV-associated neurocognitive disorders, but little is known about disruptions in astrocyte metabolism in this context. Our data show that the HIV protein Tat and cocaine induce a metabolic switch from glucose to fatty acid oxidation in astrocytes, thereby limiting lactate transport to neurons. Mechanistic analyses revealed increased Mitochondrial Ca2+ Uniporter (MCU)-mediated Ca2+ uptake in astrocytes exposed to Tat and cocaine due to oxidation of MCU. Since our data suggest that mitochondrial oxidation is dependent in part on MCU-mediated Ca2+ uptake, we targeted MCU to restore glycolysis in astrocytes to normalize extracellular lactate levels. Knocking down MCU in astrocytes prior to Tat and cocaine exposure prevented metabolic switching and protected neurons. These findings identify a novel molecular mechanism underlying neuropathogenesis in HIV and cocaine use.

Molecular mechanisms of the cytotoxicity of human α-lactalbumin made lethal to tumor cells (HAMLET) and other protein-oleic acid complexes

Although HAMLET (human α-lactalbumin made lethal to tumor cells), a complex formed by human α-lactalbumin and oleic acid, has a unique apoptotic activity for the selective killing of tumor cells, the molecular mechanisms of expression of the HAMLET activity are not well understood. Therefore, we studied the molecular properties of HAMLET and its goat counterpart, GAMLET (goat α-lactalbumin made lethal to tumor cells), by pulse field gradient NMR and 920-MHz two-dimensional NMR techniques. We also examined the expression of HAMLET-like activities of complexes between oleic acid and other proteins that form a stable molten globule state. We observed that both HAMLET and GAMLET at pH 7.5 were heterogeneous, composed of the native protein, the monomeric molten globule-like state, and the oligomeric species. At pH 2.0 and 50 °C, HAMLET and GAMLET appeared in the monomeric state, and we identified the oleic acid-binding site in the complexes by two-dimensional NMR. Rather surprisingly, the binding site thus identified was markedly different between HAMLET and GAMLET. Furthermore, canine milk lysozyme, apo-myoglobin, and β2-microglobulin all formed the HAMLET-like complex with the anti-tumor activity, when the protein was treated with oleic acid under conditions in which their molten globule states were stable. From these results, we conclude that the protein portion of HAMLET, GAMLET, and the other HAMLET-like protein-oleic acid complexes is not the origin of their cytotoxicity to tumor cells and that the protein portion of these complexes plays a role in the delivery of cytotoxic oleic acid molecules into tumor cells across the cell membrane.

Low resolution solution structure of HAMLET and the importance of its alpha-domains in tumoricidal activity

HAMLET (Human Alpha-lactalbumin Made LEthal to Tumor cells) is the first member in a new family of protein-lipid complexes with broad tumoricidal activity. Elucidating the molecular structure and the domains crucial for HAMLET formation is fundamental for understanding its tumoricidal function. Here we present the low-resolution solution structure of the complex of oleic acid bound HAMLET, derived from small angle X-ray scattering data. HAMLET shows a two-domain conformation with a large globular domain and an extended part of about 2.22 nm in length and 1.29 nm width. The structure has been superimposed into the related crystallographic structure of human α-lactalbumin, revealing that the major part of α-lactalbumin accommodates well in the shape of HAMLET. However, the C-terminal residues from L105 to L123 of the crystal structure of the human α-lactalbumin do not fit well into the HAMLET structure, resulting in an extended conformation in HAMLET, proposed to be required to form the tumoricidal active HAMLET complex with oleic acid. Consistent with this low resolution structure, we identified biologically active peptide epitopes in the globular as well as the extended domains of HAMLET. Peptides covering the alpha1 and alpha2 domains of the protein triggered rapid ion fluxes in the presence of sodium oleate and were internalized by tumor cells, causing rapid and sustained changes in cell morphology. The alpha peptide-oleate bound forms also triggered tumor cell death with comparable efficiency as HAMLET. In addition, shorter peptides corresponding to those domains are biologically active. These findings provide novel insights into the structural prerequisites for the dramatic effects of HAMLET on tumor cells.

Short-term and long-term effects of fatty acids in rat hepatoma AS-30D cells: The way to apoptosis

Arachidonic acid and, to a smaller extent, oleic acid at micromolar concentrations decreased the mitochondrial membrane potential within AS-30D rat hepatoma cells cultivated in vitro and increased cell respiration. The uncoupling effect of both fatty acids on cell respiration was partly prevented by cyclosporin A, blocker of the mitochondrial permeability transition pore. Arachidonic acid increased the rate of reactive oxygen species (ROS) production, while oleic acid decreased it. Both fatty acids induced apoptotic cell death of AS-30D cells, accompanied by the release of cytochrome c from mitochondria to the cytosol, activation of caspase-3 and association of proapoptotic Bax protein with mitochondria; arachidonic acid being a more potent inducer than oleic acid. Trolox, a potent antioxidant, prevented ROS increase induced by arachidonic acid and protected the cells against apoptosis produced by this fatty acid. It is concluded that arachidonic and oleic acids induce apoptosis of AS-30D hepatoma cells by the mitochondrial pathway but differ in the mechanism of their action: Arachidonic acid induces apoptosis mainly by stimulating ROS production, whereas oleic acid may contribute to programmed cell death by activation of the mitochondrial permeability transition pore.

Effects of N-acylethanolamines on mitochondrial energetics and permeability transition

Effects of N-acylethanolamines (NAEs): N-arachidonoylethanolamine (anandamide), N-oleoylethanolamine and N-palmitoylethanolamine, on energy coupling and permeability of rat heart mitochondria were investigated. In nominally Ca2+-free media, these compounds exerted a weak protonophoric effect manifested by dissipation of the transmembrane potential and stimulation of resting state respiration. The strongest action was exhibited by N-arachidonoylethanolamine, followed by N-oleoylethanolamine, whereas N-palmitoylethanolamine was almost inactive. These protonophoric effects were resistant to cyclosporin A (CsA) and were much weaker than those of corresponding nonesterified fatty acids. In uncoupled mitochondria N-arachidonoylethanolamine and N-oleoylethanolamine partly inhibited mitochondrial respiration with glutamate and succinate but not with tetramethyl-p-phenylenediamine (TMPD) plus ascorbate as respiratory substrates. In mitochondria preloaded with small amounts of Ca2+, NAEs produced a much stronger dissipation of the membrane potential and a release of accumulated calcium, both effects being inhibited by CsA, indicative for opening of the mitochondrial permeability transition pore (PTP). Again, the potency of this action was N-arachidonoylethanolamine>N-oleoylethanolamine>N-palmitoylethanolamine. However, in spite of making the matrix space accessible to external [14C]sucrose, N-arachidonoylethanolamine and N-oleoylethanolamine resulted in only a limited swelling of mitochondria and diminished the rate of swelling produced by high Ca2+ load.