Metabolites from invasive pests inhibit mitochondrial complex II: A potential strategy for the treatment of human ovarian carcinoma?

The red pigment caulerpin, a secondary metabolite from the marine invasive green algae Caulerpa cylindracea can be accumulated and transferred along the trophic chain, with detrimental consequences on biodiversity and ecosystem functioning. Despite increasing research efforts to understand how caulerpin modifies fish physiology, little is known on the effects of algal metabolites on mammalian cells. Here we report for the first time the mitochondrial targeting activity of both caulerpin, and its closely related derivative caulerpinic acid, by using as experimental model rat liver mitochondria, a system in which bioenergetics mechanisms are not altered. Mitochondrial function was tested by polarographic and spectrophotometric methods. Both compounds were found to selectively inhibit respiratory complex II activity, while complexes I, III, and IV remained functional. These results led us to hypothesize that both algal metabolites could be used as antitumor agents in cell lines with defects in mitochondrial complex I. Ovarian cancer cisplatin-resistant cells are a good example of cell lines with a defective complex I function on which these molecules seem to have a toxic effect on proliferation. This provided novel insight toward the potential use of metabolites from invasive Caulerpa species for the treatment of human ovarian carcinoma cisplatin-resistant cells.

Krill Oil Ameliorates Mitochondrial Dysfunctions in Rats Treated with High-Fat Diet.

In recent years, several studies focused their attention on the role of dietary fats in the pathogenesis of hepatic steatosis. It has been demonstrated that a high-fat diet is able to induce hyperglycemia, hyperinsulinemia, obesity, and nonalcoholic fatty liver disease. On the other hand, krill oil, a novel dietary supplement of n-3 PUFAs, has the ability to improve lipid and glucose metabolism, exerting possible protective effects against hepatic steatosis. In this study we have investigated the effects of krill oil on mitochondrial energetic metabolism in animals fed a high-fat diet. To this end, male Sprague-Dawley rats were divided into three groups and fed for 4 weeks with a standard diet (control group), a diet with 35% fat (HF group), or a high-fat diet supplemented with 2.5% krill oil (HF+KO group). The obtained results suggest that krill oil promotes the burning of fat excess introduced by the high-fat diet. This effect is obtained by stimulating mitochondrial metabolic pathways such as fatty acid oxidation, Krebs cycle, and respiratory chain complexes activity. Modulation of the expression of carrier proteins involved in mitochondrial uncoupling was also observed. Overall, krill oil counteracts the negative effects of a high-fat diet on mitochondrial energetic metabolism.

The dimerization of the yeast cytochrome bc1 complex is an early event and is independent of Rip1.

In Saccharomyces cerevisiae the mature cytochrome bc1 complex exists as an obligate homo-dimer in which each monomer consists of ten distinct protein subunits inserted into or bound to the inner mitochondrial membrane. Among them, the Rieske iron-sulfur protein (Rip1), besides its catalytic role in electron transfer, may be implicated in the bc1 complex dimerization. Indeed, Rip1 has the globular domain containing the catalytic center in one monomer while the transmembrane helix interacts with the adjacent monomer. In addition, the lack of Rip1 leads to the accumulation of an immature bc1 intermediate, only loosely associated with cytochrome c oxidase. In this study we have investigated the biogenesis of the yeast cytochrome bc1 complex using epitope tagged proteins to purify native assembly intermediates. We showed that the dimerization process is an early event during bc1 complex biogenesis and that the presence of Rip1, differently from previous proposals, is not essential for this process. We also investigated the multi-step model of bc1 assembly thereby lending further support to the existence of bona fide subcomplexes during bc1 maturation in the inner mitochondrial membrane. Finally, a new model of cytochrome bc1 complex assembly, in which distinct intermediates sequentially interact during bc1 maturation, has been proposed.

Modulation of the respiratory supercomplexes in yeast: enhanced formation of cytochrome oxidase increases the stability and abundance of respiratory supercomplexes.

Yeast cells deficient in the Rieske iron-sulfur subunit (Rip1) of ubiquinol-cytochrome c reductase (bc1) accumulate a late core assembly intermediate, which weakly associates with cytochrome oxidase (CcO) in a respiratory supercomplex. Expression of the N-terminal half of Rip1, which lacks the C-terminal FeS-containing globular domain (designated N-Rip1), results in a marked stabilization of trimeric and tetrameric bc1-CcO supercomplexes. Another bc1 mutant (qcr9Δ) stalled at the same assembly intermediate is likewise converted to stable supercomplex species by the expression of N-Rip1, but not by expression of intact Rip1. The N-Rip1-induced stabilization of bc1-CcO supercomplexes is independent of the Bcs1 translocase, which mediates Rip1 translocation during bc1 biogenesis. N-Rip1 induces the stabilization of bc1-CcO supercomplexes through an enhanced formation of CcO. The association of N-Rip1 with the late core bc1 assembly intermediate appears to confer stabilization of a CcO assembly intermediate. This induced stabilization of CcO is dependent on the Rcf1 supercomplex stabilization factor and only partially dependent on the presence of cardiolipin. N-Rip1 exerts a related induction of CcO stabilization in WT yeast, resulting in enhanced respiration. Additionally, the impact of CcO stabilization on supercomplexes was observed by means other than expression of N-Rip1 (via overexpression of CcO subunits Cox4 and Cox5a), demonstrating that this is a general phenomenon. This study presents the first evidence showing that supercomplexes can be stabilized by the stimulated formation of CcO.

Differential effects of high-carbohydrate and high-fat diets on hepatic lipogenesis in rats.

PURPOSE: Hepatic fatty acid synthesis is influenced by several nutritional and hormonal factors. In this study, we have investigated the effects of distinct experimental diets enriched in carbohydrate or in fat on hepatic lipogenesis. METHODS: Male Wistar rats were divided into four groups and fed distinct experimental diets enriched in carbohydrates (70% w/w) or in fat (20 and 35% w/w). Activity and expression of the mitochondrial citrate carrier and of the cytosolic enzymes acetyl-CoA carboxylase and fatty acid synthetase were analyzed through the study with assessments at 0, 1, 2, 4, and 6 weeks. Liver lipids and plasma levels of lipids, glucose, and insulin were assayed in parallel. RESULTS: Whereas the high-carbohydrate diet moderately stimulated hepatic lipogenesis, a strong inhibition of this anabolic pathway was found in animals fed high-fat diets. This inhibition was time-dependent and concentration-dependent. Moreover, whereas the high-carbohydrate diet induced an increase in plasma triglycerides, the high-fat diets determined an accumulation of triglycerides in liver. An increase in the plasmatic levels of glucose and insulin was observed in all cases. CONCLUSIONS: The excess of sucrose in the diet is converted into fat that is distributed by bloodstream in the organism in the form of circulating triglycerides. On the other hand, a high amount of dietary fat caused a strong inhibition of lipogenesis and a concomitant increase in the level of hepatic lipids, thereby highlighting, in these conditions, the role of liver as a reservoir of exogenous fat.

A krill oil supplemented diet suppresses hepatic steatosis in high-fat fed rats.

Krill oil (KO) is a dietary source of n-3 polyunsaturated fatty acids, mainly represented by eicosapentaenoic acid and docosahexaenoic acid bound to phospholipids. The supplementation of a high-fat diet with 2.5% KO efficiently prevented triglyceride and cholesterol accumulation in liver of treated rats. This effect was accompanied by a parallel reduction of the plasma levels of triglycerides and glucose and by the prevention of a plasma insulin increase. The investigation of the molecular mechanisms of KO action in high-fat fed animals revealed a strong decrease in the activities of the mitochondrial citrate carrier and of the cytosolic acetyl-CoA carboxylase and fatty acid synthetase, which are both involved in hepatic de novo lipogenesis. In these animals a significant increase in the activity of carnitine palmitoyl-transferase I and in the levels of carnitine was also observed, suggesting a concomitant stimulation of hepatic fatty acid oxidation. The KO supplemented animals also retained an efficient mitochondrial oxidative phosphorylation, most probably as a consequence of a KO-induced arrest of the uncoupling effects of a high-fat diet. Lastly, the KO supplementation prevented an increase in body weight, as well as oxidative damage of lipids and proteins, which is often found in high-fat fed animals.