Menthol causes mitochondrial Ca2+-influx, affects structure-function relationship and cools mitochondria

Menthol is a small bioactive compound able to cause several physiological changes and has multiple molecular targets. Therefore, cellular response against menthol is complex, and still poorly understood. In this work, we used a human osteosarcoma cell line (Saos-2) and analysed the effect of menthol, especially in terms of cellular, subcellular and molecular aspects. We demonstrate that menthol causes increased mitochondrial Ca2+ in a complex manner, which is mainly contributed by intracellular sources, including ER. Menthol also changes the Ca2+-load of individual mitochondrial particles in different conditions. Menthol increases ER-mito contact points, causes mitochondrial morphological changes, and increases mitochondrial ATP, cardiolipin, mitochondrial ROS and reduces mitochondrial membrane potential (ΔΨm). Menthol also prevents the mitochondrial quality damaged by sub-lethal and lethal doses of CCCP. In addition, menthol lowers the mitochondrial temperature within cell and also serves as a cooling agent for the isolated mitochondria in a cell free system too. Notably, menthol-induced reduction of mitochondrial temperature is observed in diverse types of cells, including neuronal, immune and cancer cells. As the higher mitochondrial temperature is a hallmark of several inflammatory, metabolic, disease and age-related disorders, we propose that menthol can serve as an active anti-aging compound against all these disorders. These findings may have relevance in case of several pharmacological and clinical applications of menthol. SIGNIFICANCE STATEMENT: Menthol is a plant-derived bioactive compound that is widely used for several physiological, behavioural, addictive, and medicinal purposes. It is a well-established "cooling and analgesic agent". However, the exact cellular and sub-cellular responses of menthol is poorly understood. In this work, we have characterized the effects of menthol on mitochondrial metabolism. Menthol regulates mitochondrial Ca2+, ATP, superoxides, cardiolipin, membrane-potential, and ER-mito contact sites. Moreover, the cooling agent menthol also cools down mitochondria and protects mitochondrial damage by certain toxins. These findings may promote use of menthol as a useful supplementary agent for anti-aging, anti-cancer, anti-inflammatory purposes where higher mitochondrial temperature is prevalent.

TRPV4 acts as a mitochondrial Ca2+-importer and regulates mitochondrial temperature and metabolism

TRPV4 is associated with the development of neuropathic pain, sensory defects, muscular dystrophies, neurodegenerative disorders, Charcot Marie Tooth and skeletal dysplasia. In all these cases, mitochondrial abnormalities are prominent. Here, we demonstrate that TRPV4, localizes to a subpopulation of mitochondria in various cell lines. Improper expression and/or function of TRPV4 induces several mitochondrial abnormalities. TRPV4 is also involved in the regulation of mitochondrial numbers, Ca²⁺-levels and mitochondrial temperature. Accordingly, several naturally occurring TRPV4 mutations affect mitochondrial morphology and distribution. These findings may help in understanding the significance of mitochondria in TRPV4-mediated channelopathies possibly classifying them as mitochondrial diseases.

Regulation of mitochondrial temperature in health and disease

Mitochondrial temperature is produced by various metabolic processes inside the mitochondria, particularly oxidative phosphorylation. It was recently reported that mitochondria could normally operate at high temperatures that can reach 50℃. The aim of this review is to identify mitochondrial temperature differences between normal cells and cancer cells. Herein, we discussed the different types of mitochondrial thermosensors and their advantages and disadvantages. We reviewed the studies assessing the mitochondrial temperature in cancer cells and normal cells. We shed the light on the factors involved in maintaining the mitochondrial temperature of normal cells compared to cancer cells.

A two-step precise targeting nanoplatform for tumor therapy via the alkyl radicals activated by the microenvironment of organelles

With the in-depth research of organelles, the microenvironment characteristics of their own, such as the acid environment of lysosomes and the high temperature environment of mitochondria, could be used as a natural and powerful condition for tumor therapy. Based on this, we constructed a two-step precise targeting nanoplatform which can realize the drug release and drug action triggered by the microenvironment of lysosomes (endosomes) and mitochondria, respectively. To begin with, the mesoporous silica nanoparticles (MSNs) were modified with triphenylphosphonium (TPP) and loaded with 2,2'-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIPH). Then, folic acid (FA) targeted pH-sensitive liposomes containing docetaxel (Lipo/DTX-FA) were prepared by thin-film dispersion method, and the core-shell AIPH/MSN-TPP@Lipo/DTX-FA nanoparticles were constructed by self-assembly during the hydration of the liposomes. When this nanoplatform entered into the tumor cells through FA receptor-mediated endocytosis, the pH-sensitive liposomes were destabilized in the lysosomes, resulting in the release of DTX and AIPH/MSN-TPP nanoparticles. After that, AIPH was delivered to mitochondria by AIPH/MSN-TPP, and the alkyl radicals produced by AIPH under the high temperature environment can cause oxidative damage to mitochondria. Not only that, the DTX could enhance the anti-tumor effect of AIPH by downregulating the expression of anti-apoptotic Bcl-2 protein. The in vitro and in vivo results demonstrate that this delivery system could induce apoptosis based on organelles' s own microenvironment, which provides a new approach for tumor therapy.