N. Siliprandi

Inhibitory action of silymarin of lipid peroxide formation in rat liver mitochondria and microsomes

Abstract Silymarin, a 3-oxyflavone present in Silybum Marianum, protected both liver mitochondria and microsomes from lipid peroxide formation induced by various agents. The antiperoxidative action exhibited by Silymarin was 10-fold higher than that of α-tocopherol, and was present when the drug was added as well as after the peroxidant agents. Data obtained rule out the possibility that the antiperoxidative action of Silymarin was due to an interaction of this drug with Fe 2+ . The reported results are compatible with an interaction of Silymarin with free radical species responsible for lipid peroxidation.

Influence of L-carnitine administration on maximal physical exercise

SummaryThe effects of L-carnitine administration on maximal exercise capacity were studied in a double-blind, cross-over trial on ten moderately trained young men. A quantity of 2 g of L-carnitine or a placebo were administered orally in random order to these subjects 1 h before they began exercise on a cycle ergometer. Exercise intensity was increased by 50-W increments every 3 min until they became exhausted. After 72-h recovery, the same exercise regime was repeated but this time the subjects, who had previously received L-carnitine, were now given the placebo and vice versa. The results showed that at the maximal exercise intensity, treatment with L-carnitine significantly increased both maximal oxygen uptake, and power output. Moreover, at similar exercise intensities in the L-carnitine trial oxygen uptake, carbon dioxide production, pulmonary ventilation and plasma lactate were reduced. It is concluded that under these experimental conditions pretreatment with L-carnitine favoured aerobic processes resulting in a more efficient performance. Possible mechanisms producing this effect are discussed.

Comparative evaluation of antiperoxidative action of silymarin and other flavonoids.

Summary The antiperoxidative action of silymarin has been compared to that of quercetin, dihydroquercetin and quercitrin in microsomes and mitochondria from rat liver exposed in vitro to two peroxidizing systems: dihydroxyfumaric acid plus FeSo 4 and potassium peroxychromate. It has been found that silymarin is about as active as quercetin and dihydroquercetin, and more active than quercitrin as antiperoxidative agent, irrespective to the system used for inducing peroxidation. The results obtained are also consistent with the view that all flavonoids tested act as “scavengers” of free radicals and not simply as metal complexing agents.

L-propionyl-carnitine protection of mitochondria in ischemic rat hearts.

The energy-linked processes (transmembrane potential and oxidative phosphorylation) resulted in impaired mitochondria isolated from ischemic perfused rat hearts. Addition of 1.5 mM L-propionyl-carnitine to the perfusate significantly reduced the ischemic damage and ameliorated mitochondrial Ca2+ homeostasis. In both normoxic and ischemic hearts perfused with L-propionyl-carnitine a consistent amount of propionyl-CoA — otherwise undetectable — was produced. L-propionyl-carnitine treatment also prevented the decrease of succinyl-CoA associated with the ischemic condition. These results and the decrease of myocardial acetyl-CoA induced by exogenous L-propionyl-carnitine points to the anaplerotic effect of this ester. The consequently improved flux in the tricarboxylic-acid cycle may account for the observed protection of mitochondrial functions afforded by L-propionyl-carnitine in the ischemic perfused hearts.

Metabolic changes induced by maximal exercise in human subjects following L-carnitine administration

In double-blind cross-over experiments, ten moderately trained male subjects were submitted to two bouts of maximal cycle ergometer exercise separated by a 3 day interval. Each subject was randomly given either L-carnitine (2 g) or placebo orally 1 h before the beginning of each exercise session. At rest L-carnitine supplementation resulted in an increase of plasma-free carnitine without a change in acid-soluble carnitine esters. Treatment with L-carnitine induced a significant post-exercise decrease of plasma lactate and pyruvate and a concurrent increase of acetylcarnitine. The determination of the individual carnitine esters in urine collected for 24 h after the placebo exercise trial revealed a decrease of acetyl carnitine and a parallel increase of a C4 carnitine ester, probably isobutyrylcarnitine. Conversely, acetylcarnitine was strongly increased and C4 compounds were almost suppressed in the L-carnitine loading trial. These results suggest that L-carnitine administration prior to high-intensity exercise stimulates pyruvate dehydrogenase activity, thus diverting pyruvate from lactate to acetylcarnitine formation.

Uptake of spermine by rat liver mitochondria and its influence on the transport of phosphate

Spermine, a polyamine present in the mammalian cells at rather high concentration, has, among other actions, a remarkable stabilizing effect on mitochondria, functions which have generally been attributed to the capability of this and other polyamines to bind to membrane anionic sites. In the present paper evidence is provided that at physiological concentrations spermine may also be transported into rat liver mitochondrial matrix space, provided that mitochondria are energized and inorganic phosphate is simultaneously transported. The close dependence of spermine transport is also demonstrated by the concurrent efflux of spermine and inorganic phosphate when mitochondria preloaded with the two ionic species are deenergized either with uncouplers or respiratory chain inhibitors. Furthermore, Mersalyl, the known inhibitor of phosphate transport, prevents both spermine uptake and release. Mg2+ inhibits the transport of spermine conceivably by competing for the some binding sites on the mitochondrial membrane. The physiological significance of these results is discussed.

Propionyl-L-carnitine: biochemical significance and possible role in cardiac metabolism.

SummaryPropionyl-CoA is formed principally during amino acid catabolism. It is then converted chiefly to succinate in a described three-step sequence. Free propionate is formed from propionyl-CoA to a very limited extent, but this anion can participate in a futile cycle of activation and hydrolysis, which can significantly deplete mitochondrial ATP. Free CoA and propionyl-CoA cannot enter or leave mitochondria, but propionyl groups are transferred between separate CoA pools by prior conversion to propionyl-L-carnitine. This reaction requires carnitine and carnitine acetyl transferase, and enzyme abundant in heart tissue. Propionyl-L-carnitine traverses both mitochondrial and cell membranes. Within the cell, this mobility helps to maintain the mitochondrial acyl-CoA/CoA ratio. When this ratio is increased, as in carnitine deficiency states, deleterious consequences ensue, which include deficient metabolism of fatty acids and urea synthesis. From outside the cell (in blood plasma), propionyl-L-carnitine can either be excreted in the urine or redistributed by entering other tissues. This process apparently occurs without prior hydrolysis and reformation. It is suggested that heart tissue utilizes such exogenous propionyl-L-carnitine to stimulate the tricarboxylic acid cycle (via succinate synthesis) and that this may explain its known protective effect against ischemia.

Involvement of endogenous phospholipase A2 in Ca2+ and Mg2+ movements induced by inorganic phosphate and diamide in rat liver mitochondria

Abstract Addition to rat liver mitochondria of 2 mM inorganic phosphate or 0.15 mM diamide, a thiol oxidizing agent, induced a respiration dependent efflux of Mg2+ which was prevented by both antimycin A and tetracaine. Tetracaine also inhibited the release of respiration induced by phosphate or diamide. Endogenous Ca2+ were retained by mitochondria until 50–60 per cent of endogenous Mg2+ has been lost. Tetracaine retarded Ca2+ release. The involvement of mitochondrial phospholipase A2 is demonstrated both by its inhibition by tetracaine and its activation by diamide or phosphate. The failure of these compounds to activate phospholipase A2 in the presence of added Ca2+ makes reasonable the assumption that the activation of phospholipase A2 is secondary to respiration dependent Ca2+ movements, which would favour the interaction Ca2+-phospholipase A2.

Carnitine-Related Alterations in Patients With Intermittent Claudication Indication for a Focused Carnitine Therapy

BACKGROUND Carnitine metabolism is altered in peripheral arterial disease. L-carnitine supplementation may correct these alterations and improve walking performance. METHODS AND RESULTS Plasma levels of carnitine and its esters were measured at rest and after maximally tolerated exercise in 22 claudicant patients and 8 normal subjects. One week later, this protocol was repeated in patients after random administration of placebo or L-carnitine (500 mg IV as a single bolus). Two groups of patients emerged. In 10 patients (group IC1), the plasma level of acetylcarnitine at rest was 3.7 +/- 0.2 micromol/L and increased significantly (P<.01) at maximally tolerated exercise. In 12 patients (group IC2), the resting level of plasma acetylcarnitine was elevated (7.9 +/- 0.7 micromol/L, P<.01) and decreased with exercise. Furthermore, group IC2 patients had a significantly lower walking capacity than group IC1 patients. In both groups, placebo did not affect the metabolic profile, nor did it improve exercise performance. Conversely, after L-carnitine administration, all but one patient in group IC2 (n=7) showed an increase in plasma acetylcarnitine concentration during exercise versus the decrease observed without L-carnitine. This metabolic effect was accompanied by a significant increase (P<.01) in walking capacity. Interestingly, in group IC1 patients (n=5), L-carnitine neither improved walking capacity nor modified the metabolic profile. Statistical analysis showed that changes in walking capacity with L-carnitine treatment were influenced exclusively by exercise-induced changes in plasma acetylcarnitine. CONCLUSIONS In patients with intermittent claudication, assessment of plasma acetylcarnitine at rest and after exercise may be a means to select a target population for L-carnitine therapy.

On the mechanism by which Mg2+ and adenine nucleotides restore membrane potential in rat liver mitochondria deenergized by Ca2+ and phosphate.

The presence of ATP or ADP in the incubation medium prevents the collapse of membrane potential induced by external Ca2+ and phosphate. The same adenine nucleotides are unable to restore collapsed membrane potential unless Mg2+ are also added. Bongkrekate is also able to prevent the effects of external Ca2+ and phosphate and when added after membrane potential has collapsed strongly potentiates the restorative action of ATP or ADP. Atractyloside has an opposite effect.