Insights into the malfunctioning of the mitochondrial citrate carrier: Implications for cell pathology

The mitochondrial citrate carrier (CIC) is a member of the mitochondrial carrier family and is responsible for the transit of tricarboxylates and dicarboxylates across the inner membrane. By modulating the flux of these molecules, it represents the molecular link between catabolic and anabolic reactions that take place in distinct cellular sub-compartments. Therefore, this transport protein represents an important element of investigation both in physiology and in pathology. In this review we critically analyze the involvement of the mitochondrial CIC in several human pathologies, which can be divided into two subgroups, one characterized by a decrease and the other by an increase in the flux of citrate across the inner mitochondrial membrane. In particular, a decrease in the activity of the mitochondrial CIC is responsible for several congenital diseases of different severity, which are also characterized by the increase in urinary levels of L-2- and D-2-hydroxyglutaric acids. On the other hand, an increase in the activity of the mitochondrial CIC is involved, in various ways, in the onset of inflammation, autoimmune diseases, and cancer. Then, understanding the role of CIC and the mechanisms driving the flux of metabolic intermediates between mitochondria and cytosol would potentially allow for manipulation and control of metabolism in pathological conditions

Multiple roles played by the mitochondrial citrate carrier in cellular metabolism and physiology

The citrate carrier (CIC) is an integral protein of the inner mitochondrial membrane which catalyzes the efflux of mitochondrial citrate (or other tricarboxylates) in exchange with a cytosolic anion represented by a tricarboxylate or a dicarboxylate or phosphoenolpyruvate. In this way, the CIC provides the cytosol with citrate which is involved in many metabolic reactions. Several studies have been carried out over the years on the structure, function and regulation of this metabolite carrier protein both in mammals and in many other organisms. A lot of data on the characteristics of this protein have therefore accumulated over time thereby leading to a complex framework of metabolic and physiological implications connected to the CIC function. In this review we critically analyze these data starting from the multiple roles played by the mitochondrial CIC in many cellular processes and then examining the regulation of its activity in different nutritional and hormonal states. Finally, the metabolic significance of the citrate flux, mediated by the CIC, across distinct subcellular compartments is also discussed

Ctp1 and Yhm2: Two Mitochondrial Citrate Transporters to Support Metabolic Flexibility of Saccharomyces cerevisiae

Differently from higher eukaryotic cells, in the yeast Saccharomyces cerevisiae there are two mitochondrial carrier proteins involved in the transport of citrate: Ctp1 and Yhm2. Very little is known about the physiological role of these proteins. Wild-type and mutant yeast strains deleted in CTP1 and YHM2 were grown in media supplemented with a fermentable (glucose) or a nonfermentable (ethanol) carbon source. To assess changes in Ctp1 and Yhm2 mRNA expression levels, real-time PCR was performed after total RNA extraction. In the wild-type strain, the metabolic switch from the exponential to the stationary phase is associated with an increase in the expression level of the two citrate transporters. In addition, the results obtained in the mutant strains suggest that the presence of a single citrate transporter can partially compensate for the absence of the other. Ctp1 and Yhm2 differently contribute to fermentative and respiratory metabolism. Moreover, the two mitochondrial carriers represent a link between the Krebs cycle and the glyoxylate cycle, which play a key role in the metabolic adaptation strategies of S. cerevisiae

Cytotoxicity of new organometallic Pt(II)-complexes containing 1,10-phenantroline

Among the emerging anti-cancer compounds, phenanthroline derivatives are of high interest. In contrast to cisplatin, phenanthrolines and their metal complexes are potentially intercalant molecules that can interact with DNA by aromatic π-stacking between base pairs. In this study, two new organometallic Pt(II)-complexes containing 1,10-phenantroline (phen), [Pt(phen)(DMSO)(η1CH2CH2OMe)]+, 1, [Pt(phen)(NH3)(η1-CH2CH2OMe)]+, 2, have been taken into consideration in order to evaluate their cytotoxicity in different human cancer cell lines. In addition, maximal intracellular uptake (MIU) was assayed by ICP-AES after incubation of cells with 100 μM 1 and 2 for 0.5-12 hours. Ten different human cancer cell lines (Caco-2, Caki-1, HeLa, Hep-G2, MCF-7, MG-63, SH-SY5Y, Skov-3, ZL-34 and ZL-55) were treated with 1, 2 and cisplatin at increasing concentrations (0.1-200 μM) from 12 to 72 hours to assess their effect on cell viability. While 2 did not show significantly greater cytotoxic effects than cisplatin in any cell line, 1 proved to be highly effective in almost all cell lines and mainly in the first 12-24 hours of treatment (Figure 1). The greater effects were observed in neuroblastoma cells SH-SY5Y (IC50 (12-24 h) between 8.23 ± 1.11 μM and 19.8 ± 3.26 μM) and ovarian adenocarcinoma cells SKOV-3 (IC50 (12-24 h) between 39.8 ± 3.56 μM and 92.13 ± 7.81 μM). ICP-AES in SH-SY5Y and SKOV-3 demonstrated a high intracellular uptake of compound (1) (MIUSH-SY5Y 430.5 ± 40.1 ng Pt/mg protein; MIUSKOV-3 497.6 ± 59.5 ng Pt/mg protein) compared to cisplatin (MIUSH-SY5Y 155.9 ± 31.4 ng Pt/mg protein; MIUSKOV-3 30 ± 10.2 ng Pt/mg protein). Total Pt concentration of compound 2 (MIUSH-SY5Y 300 ± 39.2 ng Pt/mg protein; MIUSKOV-3 140.4 ± 46.3 ng Pt/mg protein) was also higher than cisplatin despite not having significantly greater cytotoxic effects. Further studies are needed in order to evaluate the mechanism of action of both 1 and 2 compounds and therefore understand why compound 1 is more toxic than compound 2. Finally, it is desirable to use healthy cell lines corresponding to the tumor lines used here in order to verify any cellular specificity towards cancer cells of the two compounds