Free-Radical-Mediated Formation of Trans-Cardiolipin Isomers, Analytical Approaches for Lipidomics and Consequences of the Structural Organization of Membranes

Abstract

Free-radical-mediated processes, such as peroxidation, isomerization and hydrogenation affecting fatty acid integrity and biological functions, have a trans-disciplinary relevance. Cardiolipins (CL, (1,3-diphosphatidyl-sn-glycerol)) and tetra-linoleoyl-CL are complex phospholipids, exclusively present in the Inner Mitochondrial Membrane (IMM) lipids, where they maintain membrane integrity and regulate enzyme functionalities. Peroxidation pathways and fatty acid remodeling are known causes of mitochondrial disfunctions and pathologies, including cancer. Free-radical-mediated isomerization with the change of the cis CL into geometrical trans isomers is an unknown process with possible consequences on the supramolecular membrane lipid organization. Here, the formation of mono-trans CL (MT-CL) and other trans CL isomers (T-CL) is reported using CL from bovine heart mitochondria and thiyl radicals generated by UV-photolysis from 2-mercaptoethanol. Analytical approaches for CL isomer separation and identification via 1H/13C NMR are provided, together with the chemical study of CL derivatization to fatty acid methyl esters (FAME), useful for lipidomics and metabolomics research. Kinetics information of the radical chain isomerization process was obtained using γ-irradiation conditions. The CL isomerization affected the structural organization of membranes, as tested by the reduction in unilamellar liposome diameter, and accompanied the well-known process of oxidative consumption induced by Fenton reagents. These results highlight a potential new molecular modification pathway of mitochondrial lipids with wide applications to membrane functions and biological consequences.

Biomimetic Ketone Reduction by Disulfide Radical Anion

“…The comprehension of free radical reactivity taking place in naturally occurring processes can be very important for chemistry in two main ways: (1) inspiring new synthetic methods based on the same mechanisms that nature uses to prepare biomolecules, and (2) designing biomimetic models to simulate the free radical damages and to provide molecular libraries for mechanistic and biomarker discovery. Two successful examples of these approaches from our group are the syntheses of 5 ,8-cyclopurine lesions [1][2][3] and mono-trans PUFA isomers [4][5][6]. Indeed, there are strict relationships between reactivity involving free radicals and processes taking place in nature [7].…”

“…The forward rate constant (k 1 ) was measured in the range pH 10-11 and found to be k 1 = 1.2 × 10 9 M −1 s −1 , whereas the reverse rate constant (k −1 ) strongly depends on whether the amino group is protonated or not, affecting the disulfide radical anion equilibrium (Equation (1)) and the reduction potential of CysSSCys/CysSSCys •− redox couple (Figure 2B). The stability of (CysSSCys) •− increases when protonated amino groups are present and is reflected in equilibrium constants K 1 : 438 M −1 (with zero protonated amino groups) (5), 317 M −1 (with one protonated amino group) (6), and 8900 M −1 (with two protonated amino groups) (7). Increases in stability of these species are indicated by progressively less negative reduction potentials: −1.50 V, −1.38 V, and −1.30 V, for 0, 1, and 2 protonated amino groups, respectively [18].…”

Melatonin: Regulation of Biomolecular Condensates in Neurodegenerative Disorders

“…Cristae are dynamic, independent, bioenergetic IMM invaginations capable of remodeling in seconds to organize respiratory chain supercomplex assembly and ATP synthase for efficient ATP production [ 221 , 222 ]. Mitochondrial membrane lipid composition may contain up to 24–25% of cardiolipin (CL) [ 223 , 224 , 225 ]—an anionic, high-curvature, four-acyl chain lipid with a unique cone shape that can stabilize negative membrane curvatures in cristae and increase bending elasticity of the IMM [ 226 , 227 , 228 , 229 , 230 , 231 ]. Embedded in the IMM cristae, the F 0 motor of the ATP synthase controls proton flux that powers the rotation of the F 1 subunit protruding into the mitochondrial matrix, driving the synthesis of ATP [ 232 ].…”

A convenient route to mono-trans polyunsaturated free fatty acids

“…11,17 Such reactivity has been recently investigated in complex lipids like cardiolipins, giving again evidence of the formation of mt-cardiolipins as first isomers. 18…”