Effect of 5-trans Isomer of Arachidonic Acid on Model Liposomal Membranes Studied by a Combined Simulation and Experimental Approach

Geometrical isomerization of arachidonic acid during lipid peroxidation interferes with ferroptosis

Geometrical mono-trans isomers of arachidonic acid (mtAA) are endogenous products of free radical-induced cis-trans double bond isomerization occurring to natural fatty acids during cell metabolism, including lipid peroxidation (LPO). Very little is known about the functional roles of mtAA and in general on the effects of mono-trans isomers of polyunsaturated fatty acids (mtPUFA) in various types of programmed cell death, including ferroptosis. Using HT1080 and MEF cell cultures, supplemented with 20 μM PUFA (i.e., AA, EPA or DHA) and their mtPUFA congeners, ferroptosis occurred in the presence of RSL3 (a direct inhibitor of glutathione peroxidase 4) only with the PUFA in their natural cis configuration, whereas mtPUFA showed an anti-ferroptotic effect. By performing the fatty acid-based membrane lipidome analyses, substantial differences emerged in the membrane fatty acid remodeling of the two different cell fates. In particular, during ferroptosis mtPUFA formation and their incorporation, together with the enrichment of SFA, occurred. This opens new perspectives in the role of the membrane composition for a ferroptotic outcome. While pre-treatment with AA promoted cell death for treatment with H₂O₂ and RSL3, mtAA did not. Cell death by AA supplementation was suppressed also in the presence of either ferroptosis inhibitors, such as the lipophilic antioxidant ferrostatin-1, or NADPH oxidase (NOX) inhibitors, including diphenyleneiodonium chloride and apocynin. Our results confirm a more complex scenario for ferroptosis than actually believed. While LPO processes are active, the importance of environmental lipid levels, balance among SFA, MUFA and PUFA in lipid pools and formation of mtPUFA influence the membrane phospholipid turnover, with crucial effects in the occurrence of cell death by ferroptosis.

Requirements for Designing an Effective Metallic Nanoparticle (NP)-Boosted Radiation Therapy (RT)

Simple Summary

Recent advances in nanotechnology gave rise to trials with various types of metallic nanoparticles (NPs) to enhance the radiosensitization of cancer cells while reducing or maintaining the normal tissue complication probability during radiation therapy. This work reviews the physical and chemical mechanisms leading to the enhancement of ionizing radiation’s detrimental effects on cells and tissues, as well as the plethora of experimental procedures to study these effects of the so-called “NPs’ radiosensitization”. The paper presents the need to a better understanding of all the phases of actions before applying metallic-based NPs in clinical practice to improve the effect of IR therapy. More physical and biological experiments especially in vivo must be performed and simulation Monte Carlo or mathematical codes based on more accurate models for all phases must be developed.

Abstract

Many different tumor-targeted strategies are under development worldwide to limit the side effects and improve the effectiveness of cancer therapies. One promising method is to enhance the radiosensitization of the cancer cells while reducing or maintaining the normal tissue complication probability during radiation therapy using metallic nanoparticles (NPs). Radiotherapy with MV photons is more commonly available and applied in cancer clinics than high LET particle radiotherapy, so the addition of high-Z NPs has the potential to further increase the efficacy of photon radiotherapy in terms of NP radiosensitization. Generally, when using X-rays, mainly the inner electron shells are ionized, which creates cascades of both low and high energy Auger electrons. When using high LET particles, mainly the outer shells are ionized, which give electrons with lower energies than when using X-rays. The amount of the produced low energy electrons is higher when exposing NPs to heavy charged particles than when exposing them to X-rays. Since ions traverse the material along tracks, and therefore give rise to a much more inhomogeneous dose distributions than X-rays, there might be a need to introduce a higher number of NPs when using ions compared to when using X-rays to create enough primary and secondary electrons to get the desired dose escalations. This raises the questions of toxicity. This paper provides a review of the fundamental processes controlling the outcome of metallic NP-boosted photon beam and ion beam radiation therapy and presents some experimental procedures to study the biological effects of NPs’ radiosensitization. The overview shows the need for more systematic studies of the behavior of NPs when exposed to different kinds of ionizing radiation before applying metallic-based NPs in clinical practice to improve the effect of IR therapy.