Defects in resting metabolic rates and mitochondrial respiration in Kwashiorkor and dietary obese rats.

Resting metabolic rates have been measured and compared with hepatic mitochondrial respiration in Kwashiorkor and diet-induced obese weaned rats. In Kwashiorkor, resting metabolic rate was 21% lower than the value of controls, while that of the obese rats was 14% higher than in control animals. The resting metabolic rate for Kwashiorkor animals was 50% of the predicted basal metabolic rate (BMR), whereas that of the obese rats was 23% higher than the predicted BMR. The mitochondrial oxygen consumption patterns, using malate plus glutamate or succinate as respiratory substrates, revealed that the resting respiration (state 4) was 23.9% higher in Kwashiorkor and 29.1% higher in obese animals, while the active (state 3) respiration was 34.8% lower in Kwashiorkor and 43.3% lower in obese rats compared to controls. The respiratory control ratios (RCR) were 51.1% and 43.8% in Kwashiorkor and obese rats, respectively, relative to the values in control rats. It is concluded from these studies that Kwashiorkor disease and diet-induced obesity appear to interfere with oxygen utilization at the level of state 3 mitochondrial respiration, which is markedly decreased when compared to the values for control animals.

Interaction of benzoquinones with mitochondria interferes with oxidative phosphorylation characteristics.

Studies with four benzoquinones, viz. juglone, embelin, maesaquinone and maesanin, on rat liver mitochondria oxidative phosphorylation have been carried out. Three of the benzoquinones are uncouplers in the order juglone greater than maesoquinone greater than embelin, while maesanin is an inhibitor of electron transport and oxidative phosphorylation.

Effects of defective in vivo synthesis of mitochondrial proteins on cellular biochemistry and physiology of malnourished rats.

Investigations were carried out to find the biochemical and bioenergetic implications of a defective in vivo synthesis of mitochondrial proteins during dietary-protein depletion. 3.4% dietary protein was fed to 21-day-old weanling rats for 30 days (experimental), while 21.0% dietary protein was fed to controls. A close simulation of marasmic-kwashiorkor syndrome was obtained in the experimental group. Rat liver mitochondria were isolated, and the functional and structural integrity was determined using biochemical standard parameters. Results show that the respiratory control ratio (RCR) is reduced by 50% in the experimental group, using any of the pyruvate/malate, beta-hydroxybutyrate or succinate as substrate. The effects of storage at 0 degree C were more pronounced in mitochondria from protein-depleted rats as these mitochondria are more leaky to protons (H+); hence they are defective in carrying out chemiosmotic oxidative phosphorylation. There is a drastic reduction in the basal ATPase and cytochrome oxidase activities with low ATP production and a decline in energy expenditure. This led to serious bioenergetic consequences culminating in heavy dependence on glycolysis and other biochemical aberrations.

Mechanism of action of thyroxine (T4) on the biogenesis of mitochondria using antibiotic-free system: a gerontological survey.

For the biogenesis of mitochondria from rat liver two different genetic systems are responsible, the nucleo-cytoplasmic system, covering 85-90% of the protein, and the mitochondrial system (10-15%). These data have been confirmed by experiment. Both protein fractions were separated by phosphate buffer (pH 11.5), in which only one of them is soluble. The experiments were performed with 3 age groups of rat: 1, 3 and 24 months. The ratio of both protein fractions was not dependent on rat age. The activities of the two genetic systems were examined by the in-vivo incorporation rate of 14 C-leucine. For the mitochondrial genetic system this rate was approximately equal in all of the age groups, while that for the nucleo-cytoplasmic genetic system was reduced in the 24 month group. Hence an age-dependence is demonstrated for the nucleo-cytoplasmic genetic system. The results of our investigation permit the conclusion that the role of the mitochondrial genetic system increases at senescence. To investigate the effect of T4 on the biogenesis of mitochondria, both protein fractions were estimated also in liver of rats treated with T4. The result showed that there was an increase for all the age groups for protein only of nucleo-cytoplasmic origin. Since it is known that T4 stimulates the biogenesis of mitochondria and increases its protein content, it could be inferred that the action of T4 is channelled through the nucleo-cytoplasmic system independent on age, and that the nucleus plays the major regulatory role in the biogenesis of mitochondria.

The peculiarities of protein and RNA syntheses in the hepatic mitochondria of young and old animals: studies without the use of an antibiotic.

Pulse-labelling in the presence of antibiotics is so widely used for studying mitochondriogenesis that the shortcomings of the method is usually overlooked. In this article, we present the results of experiments on the biogenesis of mitochondria done without the use of antibiotics. The method of Kitagawa and Sugimoto (1980) for the estimation of in vivo translational activity of rat liver mitochondria without the use of antibiotics was employed. The syntheses of RNA and protein in rat liver mitochondria of young and old animals was investigated. Incorporation of 14C-ATP into the RNA of isolated mitochondria occurs at the same level in both young and old animals. However, the incorporation of 14C-leucine into the two fractions of mitochondria, i.e. mitochondria protein of nucleo-cytoplasmic origin and those of intrinsic mitochondrial origin are at the same level for young animals. In old animals, the incorporation of the tracer into mitochondrial protein of intrinsic mitochondrial origin (which is at the same level as that of young animals) is three times greater than the incorporation of the tracer into mitochondrial protein of nucleo-cytoplasmic origin. These findings suggest that the role of the mitochondrial genome in the biogenesis of mitochondria increases at senesence and that the synthesis of corresponding regulatory proteins which are of nucleo-cytoplasmic origin decreases at senesence.

Cytochrome oxidase status in protein-energy-deficient rats.

Effects of changes in dietary protein have been investigated on three mitochondrial enzymes, succinate dehydrogenase, isocitrate dehydrogenase and cytochrome oxidase. Weanling rats (21 days old) were fed for 30 days on (a) a commercially produced diet (CPD) containing 21.0% dietary protein and (b) a low protein-high carbohydrate diet (LPD) containing 3.47% dietary protein. Signs of protein-energy malnutrition developed in the animals having the low protein diet. The mitochondrial enzymes were assayed. Some of the experimental rats were repleted by feeding them on a protein-rich diet for 3 weeks, and the same mitochondrial enzymes were assayed. The activity of mitochondrial cytochrome oxidase, which fell to 24% of the control values during the period of deficiency, rose to 91% of the values for control rats during rehabilitation. The activities of succinate dehydrogenase and NAD+-isocitrate dehydrogenase fell to 75 and 73% of the control values, respectively, during depletion and rose to 83 and 88% during repletion in line with the general rate of recovery of the malnourished rats as reflected by the changes in the body weights during repletion. These results show that mitochondrial cytochrome oxidase is very sensitive to changes in dietary protein. Its activity drops sharply with reduction in dietary protein intake and rises rapidly, outstripping the rate of general recovery on reverting to a protein-rich diet.

Consequences of defective vitamin A transportation on mitochondrial membrane integrity during protein depletion.

The relationships between the structural integrity and functionality of rat liver mitochondrial membranes, and different levels of dietary protein and vitamin A transportation during protein depletion in animals have been investigated. Although the vitamin A content of the protein-depleted diet was 1680 +/- 35 IU/kg diet, and that of the control diet was 1,650 +/- 30 IU/kg diet, the vitamin A content of the liver of depleted rats was reduced to 16.7% of controls. The hepatic mitochondria of rats fed a protein-depleted diet showed excessive passive swelling (about 3-fold of controls) in isotonic solutions. Whereas a seemingly inverse relationship existed between the vitamin A content of the liver and the osmotic behaviour of hepatic mitochondria of rats fed a protein-depleted diet, there is a direct relationship between their hepatic mitochondrial vitamin A and the respiratory control ratio. The implications of these observations are discussed.

Possible defect in xenobiotic activation before glycine conjugation in protein-energy malnutrition.

1. [14C]Benzoic acid administered to rats fed a normal diet was excreted mainly (99% of 24h excretion) as hippuric acid. 2. In protein-energy malnourished rats, only about 74% of [14C]benzoic acid administered was excreted as hippuric acid. The remainder was excreted as the glucuronide conjugate. 3. The oxidative phosphorylation capacity of liver mitochondria of malnourished rats was 30% less than that of normal rat liver mitochondria. 4. The decreased rate in oxidative phosphorylation is discussed in relationship to the observed decrease in glycine conjugation.