Modified oscillation behavior and decreased D-3-hydroxybutyrate dehydrogenase activity in diabetic rat liver mitochondria

Clusterin overexpression in mice exacerbates diabetic phenotypes but suppresses tumor progression in a mouse melanoma model

Clusterin (CLU) is an ATP-independent small heat shock protein-like chaperone, which functions both intra- and extra-cellularly. Consequently, it has been functionally involved in several physiological (including aging), as well as in pathological conditions and most age-related diseases, e.g., cancer, neurodegeneration, and metabolic syndrome. To address CLU function at an in vivo model we established CLU transgenic (Tg) mice bearing ubiquitous or pancreas-targeted CLU overexpression (OE). Our downstream analyses in established Tg lines showed that ubiquitous or pancreas-targeted CLU OE in mice affected antioxidant, proteostatic and metabolic pathways. Targeted OE of CLU in the pancreas, which also resulted in CLU upregulation in the liver likely via systemic effects, increased basal glucose levels in the circulation and exacerbated diabetic phenotypes. Furthermore, by establishing a syngeneic melanoma mouse tumor model we found that ubiquitous CLU OE suppressed melanoma cells growth, indicating a likely tumor suppressor function in early phases of tumorigenesis. Our observations provide in vivo evidence corroborating the notion that CLU is a potential modulator of metabolic and/or proteostatic pathways playing an important role in diabetes and tumorigenesis.

Streptozotocin-Induced Adaptive Modification of Mitochondrial Supercomplexes in Liver of Wistar Rats and the Protective Effect of Moringa oleifera Lam

The increasing prevalence of diabetes continues to be a major health issue worldwide. Alteration of mitochondrial electron transport chain is a recognized hallmark of the diabetic-associated decline in liver bioenergetics; however, the molecular events involved are only poorly understood. Moringa oleifera is used for the treatment of diabetes. However, its role on mitochondrial functionality is not yet established. This study was aimed to evaluate the effect of M. oleifera extract on supercomplex formation, ATPase activity, ROS production, GSH levels, lipid peroxidation, and protein carbonylation. The levels of lipid peroxidation and protein carbonylation were increased in diabetic group. However, the levels were decreased in Moringa-treated diabetic rats. Analysis of in-gel activity showed an increase in all complex activities in the diabetic group, but spectrophotometric determinations of complex II and IV activities were unaffected in this treatment. However, we found an oxygen consumption abolition through complex I-III-IV pathway in the diabetic group treated with Moringa. While respiration with succinate feeding into complex II-III-IV was increased in the diabetic group. These findings suggest that hyperglycemia modifies oxygen consumption, supercomplexes formation, and increases ROS levels in mitochondria from the liver of STZ-diabetic rats, whereas M. oleifera may have a protective role against some alterations.

Effect of streptozotocin-induced diabetes on oxidative energy metabolism in rat liver mitochondria-A comparative study of early and late effects

The reports in the literature on effects of diabetes on mitochondrial energy-linked functions are conflicting. Hence we carried out systematic studies to evaluate the effects at the early and the late stages of the disease using STZ-diabetic rat as a model. At the end of one week, after induction of diabetes, respiration rates with glutamate and succinate as the substrates increased; respiration rates with other substrates e.g. β-hydroxybutyrate, pyruvate + malate and ascorbate + TMPD were not affected despite substantial decrease in the β-hydroxybutyrate dehydrogenase activity and cytochrome b and c+c(1) contents. Insulin treatment brought about increase in the cytochrome contents beyond control values. The ATPase activity was generally low in the diabetic animals and was not restored by insulin treatment.At the end of one month, the respiratory activities with all the substrates were generally low. Insulin treatment either restored or stimulated the respiration rates beyond control values. The content of cytochromes was differentially affected in the diabetic animals, but insulin treatment caused significant increase beyond control levels. The pattern for ATPase activity was similar to the early effects.At both the stages i.e. early and late stages of diabetes the mitochondria were tightly coupled. The ADP/O ratios were in normal expected ranges and the respiratory control ratios were comparable with the control groups. Insulin treatment resulted in apparent restoration of respiratory activity. However, the effects on the cytochromes and dehydrogenases activities were differential. Taken together the two observations would suggest that the mitochondria were not re-instated to normality despite apparent restoration of respiratory function.

Hexachlorobenzene treatment on hepatic mitochondrial function parameters and intracellular coproporphyrinogen oxidase location

These studies try to elucidate why isocoproporphyrin appears in hexachlorobenzene-poisoned rats' feces. Chronic exposure of hexachlorobenzene to rats produces an experimental model for human porphyria cutanea tarda. After 8 weeks of treatment, rats showed high porphyrin excreta and 50% inhibition of liver uroporphyrinogen decarboxylase activity. Uroporphyrin plus heptacarboxylic porphyrin exceeded coproporphyrin in urine, whereas in feces, isocoproporphyrin, from abnormal pentacarboxylic porphyrinogen III oxidative decarboxylation by liver coproporphyrinogen oxidase, became the main porphyrin. Trypsin-treated mitochondria showed that the outer and inner membrane permeability barrier was highly conserved after hexachlorobenzene intoxication. In digitonin-treated hexachlorobenzene mitochondria, coproporphyrinogen oxidase was free in the mitochondrial intermembrane space, whereas in normal mitochondria, 30% to 50% remained anchored to the inner membrane. Hexachlorobenzene led to a decrease in respiratory control and ADP/O ratios (uncoupled mitochondria). Albumin restored oxidative phosphorylation, indicating no irreversible inner membrane damage. Normal and hexachlorobenzene mitochondria oscillatory studies exhibited similar damping factor values, showing that hexachlorobenzene had no significant effect on membrane fluidity and elasticity. Mitochondrial uncoupling could explain the free state of the enzyme within the intermembrane space. The free state of the enzyme makes it more flexible and would allow pentacarboxylic porphyrinogen III, whose levels are increased, to compete with coproporphyrinogen III and being transformed into dehydroisocoproporphyrinogen, the liver forerunner of fecal isocoproporphyrin.

Insulin-status-dependent modulation of FoF1-ATPase activity in rat liver mitochondria

Early and late effects of alloxan diabetes and insulin treatment on mitochondrial membrane structure and function were evaluated by studying the kinetic properties of mitochondrial membrane marker enzyme FoF1-ATPase and its modulation by membrane lipid/phospholipid composition and membrane fluidity. Under all experimental conditions the enzyme displayed three kinetically distinguishable components. In 1 wk-old diabetic animals the enzyme activity was unchanged; however, K(m) and V(max) of component I increased and K(m) of component II decreased. Insulin treatment resulted in lowering of K(m) and V(max) of components II and Ill. One-mon diabetic state resulted in decreased enzyme activity, whereas insulin treatment caused hyperstimulation. K(m) of components I and II decreased together with decreased V(max) of all the components. Insulin treatment restored the K(m) and V(max) values. In late-stage diabetes the catalytic efficiency of components I and II increased; insulin treatment had drastic adverse effect. Binding pattern of ATP was unchanged under all experimental conditions. Diabetic state resulted in progressive decrease in energy of activation in the low temperature range (E(L)). Insulin treatment lowered the energy of activation in the high temperature range (E(H)) without correcting the E(L) values. The phase transition temperatures increased in diabetic state and were not corrected by insulin treatment. Long-term diabetes lowered the total phospholipid content and elevated the cholesterol content; insulin treatment had partial restorative effect. The membrane fluidity decreased in general in diabetic condition and was not corrected by insulin treatment at late stage. Regression analysis studies suggest that specific phospholipid classes and/or their ratios may play a role in modulation of the enzyme activity.

Insulin status differentially affects energy transduction in cardiac mitochondria from male and female rats

AIM

The incidence of coronary heart diseases (CHD), congestive heart failure (CHF) and myocardial infarction is higher in diabetic patients than in non-diabetic groups, with these incidences being more in women than in the men. Hence, we examined involvement of mitochondrial energy transduction functions.

METHODS

Mitochondrial energy metabolism in cardiomyopathy was studied using streptozotocin (STZ)-diabetic male and female rats as the model system. Effects of insulin treatment were also evaluated.

RESULTS

The body and heart weights decreased in both male and female diabetic rats. Insulin treatments resulted in significant increase in the body and heart weights in the female rats. Mitochondrial respiration rates with all the substrates tested decreased in diabetic condition in both males and females. Treatment with two dose-regimens of insulin had differential restorative effect on mitochondrial substrate oxidation in the males but caused hyper-stimulation in the females. Diabetic state brought about 19% decrease in the cytochrome aa(3) content in the female rats. Treatment with 0.6 units of insulin significantly increased the cytochrome contents in general in both the sexes whereas higher dose (1.0 unit) caused decrease in the cytochromes content in the females. Diabetic state resulted in decreased dehydrogenases activities; insulin treatments had differential effect on the dehydrogenase activity in the males and the females. The results suggest that insulin treatment-induced hyper-stimulation of respiration in female rats may lead to increased production of reactive oxygen species. Besides, increased formation of advanced glycosylated end products may further lead to increased risk of CHF and CHD.

CONCLUSIONS

The results suggest that differential effects of STZ-diabetes and insulin treatments in the female rats than in males may be the underlying cause for increased incidence of diabetic cardiomyopathies in the females.

Effect of streptozotocin-induced diabetes on oxidative energy metabolism in rat kidney mitochondria. A comparative study of early and late effects

AIM

The effects of streptozotocin (STZ)-induced diabetes on oxidative energy metabolism of rat kidney mitochondria were examined at the end of 1 week and 1 month of STZ treatment.

METHODS

At the end of 1 week of induction of diabetes, respiration rates with pyruvate + malate and succinate as the substrates increased while those with beta-hydroxybutyrate and ascorbate + TMPD decreased. Respiration with glutamate was not affected. Insulin treatment had no alleviating effect. The changes persisted through 1 month of induction of diabetes and were not corrected by insulin treatment even at this stage. beta-hydroxybutyrate dehydrogenase activity registered significant decrease while the succinate dehydrogenase activity increased in diabetic and insulin-treated diabetic animals whereas only marginal changes were evident in the composition of the cytochromes.

RESULTS

The ATPase activity tended to be high in the diabetic groups and was restored by insulin treatment. At both the stages, i.e. early and late stages of diabetes the mitochondria were tightly coupled and the ADP/O ratios were in normal expected ranges.

CONCLUSION

Taken together, the results suggest that kidney is the major target tissue to suffer impairment of mitochondrial function with the onset of the disease which persists throughout and that insulin treatment is ineffective in restoring the normal state.

Effect of catecholamine depletion on oxidative energy metabolism in rat liver, brain and heart mitochondria; use of reserpine

Regulation of mitochondrial functions in vivo by catecholamines was examined indirectly by depleting the catecholamines stores by reserpine treatments of the experimental animals. Reserpine treatment resulted in decreased respiratory activity in liver and brain mitochondria with the two NAD+-linked substrates: glutamate and pyruvate + malate with succinate ATP synthesis rate decreased in liver mitochondria only. With ascorbate + TMPD system, the ADP/O ratio and ADP phosphorylation rate decreased in brain mitochondria. For the heart mitochondria, state 3 respiration rates decreased for all substrates. In the liver mitochondria basal ATPase activity decreased by 51%, but in the presence of Mg2+ and/or DNP increased significantly. In the brain and heart mitochondria ATPase activities were unchanged. The energy of activation in high temperature range increased liver mitochondrial ATPase while in brain mitochondria reserpine treatment resulted in abolishment in phase transition. Total phospholipid (TPL) content of the brain mitochondria increased by 22%. For the heart mitochondria TPL content decreased by 19% and CHL content decreased by 34%. Tissue specific differential effects were observed for the mitochondrial phospholipid composition. Liver mitochondrial membranes were more fluidized in the reserpine-treated group. The epinephrine and norepinephrine contents in the adrenals decreased by 68 and 77% after reserpine treatment.

An overview of Argentine contributions to diabetes research in the decade of the 1990s

Argentina has a longstanding tradition of diabetes research, beginning with the seminal work of Prof. Bernardo A. Houssay, who was awarded the first Nobel Prize in Medical Sciences for his studies on the relationship between diabetes and pituitary function. Prof. Luis F. Leloir, who was also awarded the Nobel Prize for his work in carbohydrate metabolism, also inspired younger generations of biologists to work in the field of diabetes research. The aim of this paper is to provide a review of the contributions of Argentine researchers during the 1990s. This manuscript includes only reports of Argentine researchers working on diabetes in local laboratories and quoted in Medline. Thus, important contributions not reported in journals included in Medline or produced by Argentine researchers working abroad may have been omitted. The material consists of a brief description of clinical research (epidemiology and costs, metabolic control, associated risk factors, immunological aspects, and other clinical studies) and basic research (animal model with spontaneous diabetes, islet morphology and function in normal and pathological conditions, insulin action, metabolic disorders related to diabetes, and some miscellaneous effects related to drug-induced diabetes). Altogether, a broad idea of the continuous contribution of our national research to the international field of diabetes is provided, as well as a list of Argentine researchers and research centers devoted to the study of diabetes.

Favourable, significant effect of the dose-dependent treatment with RU 38486 (RU) on the alterations of the hepatic mitochondrial function of diabetic rats

In the present work, the effect "in vivo' of increasing doses of RU 38486 upon the hepatic mitochondrial function of diabetic rats has been studied. At the same time, the action of adrenalectomy and corticosterone restitution on this function were comparatively demonstrated. The parameters measured were oxygen consumption with the substrates: 3-hydroxybutyrate (HB), succinate (Suc) and malate-glutamate (Mal-glut) in intact liver mitochondria and the activities of 3-hydroxybutyrate dehydrogenase (HBD) and cytochrome c oxidase (Cyt.c oxid.) enzymes in broken liver mitochondria. The groups of animals studied were normal controls (N) and the following groups of diabetic rats: rats without any treatment (D), adrenalectomized rats (D+ADX), rats that were adrenalectomized and treated with corticosterone (D+ADX+C) and four groups treated with increasing oral doses of RU (in mg/kg body wt.), that is, 12.5 (D+RU1), 25.0 (D+RU2), 37.5 (D+RU3) and 50.0 (D+RU4). The results showed a tendency of increasing values of mitochondrial oxygen consumption in diabetic animals treated with RU. The favourable effect of increasing doses of RU on O2 consumption of diabetic rat liver mitochondria with each of the substrates showed a significant association as indicated by the values obtained for the correlation coefficients r (0.95, 0.97 and 0.99 according to the substrate HB, Succ or Mal-glut, respectively). Likewise, the correlation between the treatment with increasing doses of RU and the recovery of enzyme activities showed a significant dose-effect association with r 0.94 for HBD and r = 0.95 for Cyt.c oxid. Adrenalectomy showed a similar effect to treatment with the maximum dose of RU while corticosterone restitution gave measured values similar to those of the D group. In conclusion, the favourable, significant variation of the hepatic mitochondrial function of diabetic rats was demonstrated by the dose-dependent treatment with RU as seen by the correlation statistical study performed. At the same time, the pernicious effect that glucocorticoids exert upon such function in experimental diabetes was confirmed.

Stimulation of gluconeogenesis leads to an increased rate of beta-oxidation in hepatocytes from fasted diabetic but not from fasted normal rats

We have investigated the effects of imposing an ATP demand, generated by the addition of lactate, on hepatocytes isolated from fasted normal and streptozocin-induced diabetic rats. The stimulation of O2 consumption upon lactate addition was much greater in hepatocytes from diabetic rats, as a result of a lactate-induced stimulation of beta-oxidation that was not observed in control cells. This lactate-induced increment in beta-oxidation was extremely sensitive to inhibition by low levels of a number of inhibitors of energy transduction, implying that the increment was tightly coupled to ATP synthesis. Such sensitivity of the beta-oxidative pathway to the addition of similar low concentrations of these inhibitors was not seen in control cells. Inhibitors of the gluconeogenic pathway were also more effective in decreasing beta-oxidation in cells from diabetic animals than in cells from normal rats. The increment in beta-oxidation was not accompanied by increased rates of glucose synthesis, fatty acid esterification or ureogenesis. We propose that it may be associated with higher rates of glucose cycling in cells from diabetic rats.

The effect of insulin supplementation on diabetes-induced alterations in the extractable levels of functional mitochondrial anion transport proteins

The effect of insulin supplementation on diabetes-induced alterations in the levels of functional mitochondrial anion transport proteins has been determined. The experimental approach consisted of the extraction of the pyruvate, dicarboxylate, and citrate transport proteins from the mitochondrial inner membrane with Triton X-114 using rat liver mitoplasts (prepared from control, diabetic, or insulin-supplemented diabetic animals) as the starting material, followed by the reconstitution of the function of each transporter in a proteoliposomal system. This experimental strategy permitted the quantification of the functional levels of these three transporters in the absence of the complications that arise when such measurements are carried out with intact mitochondria (or mitoplasts). We found that treatment of diabetic rats (i.e., animals that were injected with streptozotocin 3 weeks earlier) on a daily basis with insulin for 3 weeks resulted in a reversal of the diabetes-induced (a) increase in the extractable and reconstitutable total (and specific) transport activities of the pyruvate and dicarboxylate transporters and (b) decrease in the activity of the citrate transporter. These findings indicate that diabetes-induced alterations in the functional levels of mitochondrial anion transport proteins are a direct consequence of the insulin insufficiency that characterizes this disease. Furthermore, this study provides the first demonstration that insulin participates in the regulation of the functional levels of liver mitochondrial anion transport proteins.

Insulin stimulates mitochondrial protein synthesis and respiration in isolated perfused rat heart

The rates of synthesis of mitochondrial proteins by both the cytoplasmic and mitochondrial protein synthetic systems, as well as parameters of respiration, were measured and compared in mitochondria isolated from fresh, control perfused, and insulin-perfused rat hearts. The respiratory control ratio (RCR) in mitochondria from fresh hearts was 8.1 +/- 0.4 and decreased to 6.0 +/- 0.2 (P less than 0.001 vs. fresh) in mitochondria from control perfused hearts and to 6.7 +/- 0.2 (P less than 0.005 vs. fresh and P less than 0.02 vs. control perfused) for mitochondria from hearts perfused in the presence of insulin. A positive correlation between the RCR and the rate of mitochondrial translation was demonstrated in mitochondria from fresh hearts. In mitochondria isolated from control perfused hearts, the rate of protein synthesis decreased to 84 +/- 3% of the fresh rate after 30 min of perfusion and fell further to 64 +/- 3% after 3 h of perfusion. The inclusion of insulin in the perfusion buffer stimulated mitochondrial protein synthesis 1.2-fold by 1 h (P less than 0.005) and 1.34-fold by 3 h of perfusion (P less than 0.001). The addition of insulin to 1-h control perfused hearts shifted the rate of mitochondrial protein synthesis from the control level to the insulin-perfused level within 30 min of additional perfusion, whereas 1 h was required to shift the RCR values of these mitochondria from control levels to insulin-perfused levels. Thus, whereas RCR was a useful predictor of mitochondrial translation rates, it did not account for the effects of insulin on mitochondrial translation.(ABSTRACT TRUNCATED AT 250 WORDS)

Variations of specific mRNA and polypeptide contents of rat liver D-beta-hydroxybutyrate dehydrogenase during an experimental diabetes mellitus

The expression of the rat liver D-beta-hydroxybutyrate dehydrogenase (BDH) gene was investigated at different levels: the level of its specific mRNA, the protein content and the enzymatic activity. By using a cDNA probe, we found that the BDH mRNA was about 2 kb and we report here that the decrease of BDH activity in diabetic rats is due to a reduction in the content of the enzyme, which is proportional to a diminution in the amount of the BDH mRNA. We also show that insulin is able to reverse this diabetes effect by restoring the level of BDH mRNA, the BDH content and thus its activity. This result indicates that in vivo the control of the expression of the BDH gene by insulin is mainly transcriptional and/or post-transcriptional (mRNA stability).

Metabolic control of the expression of mitochondrial D-beta-hydroxybutyrate dehydrogenase, a ketone body converting enzyme

The effects of various metabolic conditions inducing an overproduction of ketone bodies in the rat were studied at different levels of D-beta-hydroxybutyrate dehydrogenase expression, i.e., enzymatic activity and protein content in purified mitochondria, and translational activity of isolated free cytosolic polysomes. The strongest variations were obtained in diabetes mellitus where the D-beta-hydroxybutyrate dehydrogenase expression is largely decreased. Insulin can reverse this strong effect. Modulation of liver enzyme activity and of enzyme content was observed under the other conditions tested, i.e., a decrease and an increase in starvation and hyperlipidemic conditions, respectively. A comparative study was carried out on the enzyme of extrahepatic tissues, i.e., heart, kidney and brain. The results indicate that the D-beta-hydroxybutyrate dehydrogenase function appears to be controlled, at least at the translational, post-translational and catalytic levels.

Effect of ovarian hormones upon liver mitochondrial function in diabetic rats

In the present study it is shown that streptozotocin (SZ)-induced chronic diabetes of female albino rats produced significant alterations in liver mitochondrial function after 30-35 days of diabetes. The disturbances were as follows: (1) a significant fall of the mean values of the respiratory control ratio and of state 3 of respiration using three substrates, 3-hydroxybutyrate, malate-glutamate and succinate, and (2) a significant increase of the mean damping factor of the oscillatory osmotic variations (with valinomycin as K+ ionophore and succinate as substrate). The same mitochondrial function parameters were analyzed for comparison in control non-diabetic rats (group N) and in the following groups of female rats with chronic diabetes: intact (group I), oophorectomized (6 days after the injection of SZ) (group O), and oophorectomized with restitution therapy of 17 beta-estradiol (from the operation until the day before killing) (group O + Eol). The O group showed significantly higher values of the respiratory control ratio and of state 3 of respiration and significantly lower damping factors than group I. The restitution treatment in the O + Eol group restored the mitochondrial functions assayed to values similar to those of group I. These data provide strong evidence that estrogens exert a negative effect at the molecular level upon impaired liver mitochondrial functions in SZ-induced diabetes.

Ketone-body metabolism in hyperthyroid rats: reduced activity of D-3-hydroxybutyrate dehydrogenase in both liver and heart and of succinyl-coenzyme A: 3-oxoacid coenzyme A-transferase in heart

The specific activity of D-3-hydroxybutyrate dehydrogenase is reduced by about a third in liver and heart mitochondria of hyperthyroid rats. State 3 respiration is also reduced in isolated mitochondria from the same animals when DL-3-hydroxybutyrate is the substrate. Determination of the kinetic parameters of the membrane-bound D-3-hydroxybutyrate dehydrogenase in liver of hyperthyroid rats reveals a decreased in maximal velocity (Vmax). The Michaelis and dissociation constants of NAD+ and D-3-hydroxybutyrate are also significantly influenced, thus indicating that both the affinity and the binding of this enzyme toward its substrates are affected. In hyperthyroid rats a significant ketone-body increase is found in both liver and heart: in blood, an almost doubled concentration can be measured. At the same time, in heart mitochondria of these animals the activity of succinyl-coenzyme A: 3-oxoacid coenzyme A-transferase is significantly reduced. The decrease in both D-3-hydroxybutyrate dehydrogenase and 3-oxoacid coenzyme A-transferase associated with the increase in ketone bodies supports the suggestion that there is a lower utilization of these compounds by peripheral tissues. In the blood of hyperthyroid rats a higher D-3-hydroxybutyrate/acteoacetate ratio is also found, probably resulting from a selective utilization of the two compounds in this pathological state.

Decreased rate of ketone-body oxidation and decreased activity of D-3-hydroxybutyrate dehydrogenase and succinyl-CoA:3-oxo-acid CoA-transferase in heart mitochondria of diabetic rats

Heart mitochondria from chronically diabetic rats ('diabetic mitochondria'), in metabolic State 3, oxidized 3-hydroxybutyrate and acetoacetate at a relatively slow rate, as compared with mitochondria from normal rats ('normal mitochondria'). No significant differences were observed, however, with pyruvate or L-glutamate plus L-malate as substrates. Diabetic mitochondria also showed decreased 3-hydroxybutyrate dehydrogenase and succinyl-CoA: 3-oxoacid CoA-transferase activities, but cytochrome content and NADH-dehydrogenase, succinate dehydrogenase, cytochrome oxidase and acetoacetyl-CoA thiolase activities proved normal. The decrease of 3-hydroxybutyrate dehydrogenase activity was observed in diabetic mitochondria subjected to different disruption procedures, namely freeze-thawing, sonication or hypoosmotic treatment, between pH 7.5 and 8.5, at temperatures in the range 6-36 degrees C, and in the presence of L-cysteine. Determination of the kinetic parameters of the enzyme reaction in diabetic mitochondria revealed diminution of maximal velocity (Vmax) as its outstanding feature. The decrease in 3-hydroxybutyrate dehydrogenase in diabetic mitochondria was a slow-developing effect, which reached full expression 2-3 months after the onset of diabetes; 1 week after onset, no significant difference between enzyme activity in diabetic and normal mitochondria could be established. Insulin administration to chronically diabetic rats for 2 weeks resulted in limited recovery of enzyme activity. G.l.c. analysis of fatty acid composition and measurement of diphenylhexatriene fluorescence anisotropy failed to reveal significant differences between diabetic and normal mitochondria. The Arrhenius-plot characteristics for 3-hydroxybutyrate dehydrogenase in membranes of diabetic and normal mitochondria were similar. It is assumed that the variation of the assayed enzymes in diabetic mitochondria results from a slow adaptation to the metabolic conditions resulting from diabetes, rather than to insulin deficiency itself.

Altered K+ movement in liver mitochondria from alloxan diabetic rats

Potassium movements were monitored in liver mitochondria from control and alloxan diabetic rats with a cationic electrode. There was net accumulation of K+ after Ca2+ addition to the mitochondria with the diabetic but not with the control.

Influence of diabetes on rat liver mitochondria: decreased unsaturation of phospholipid and D-beta-hydroxybutyrate dehydrogenase activity

Liver mitochondria and submitochondrial vesicles have been prepared from rats made diabetic by treatment with streptozotocin (diabetic membranes). The membranes were characterized in terms of phospholipid and fatty acid composition, electron transport functions, and D-beta-hydroxybutyrate dehydrogenase activity and compared with mitochondria and submitochondrial vesicles prepared from control animals (control membranes). No change in the phospholipid composition (44% lecithin, 35% phosphatidylethanolamine, and 21% diphosphatidylglycerol) was found, but a marked alteration in fatty acid composition of both the total phospholipid and lecithin occurred within 3 weeks after streptozotozin treatment and persisted thereafter. In lecithin, the 18:1/18:0 ratio decreases approximately 33% and the 20:4/18:2 ratio decreases approximately 55%. D-beta-hydroxybutyrate dehydrogenase is a lipid-requiring enzyme which has a specific requirement of lecithin for function. In diabetic membranes, there is a progressive decrease in D-beta-hydroxybutyrate dehydrogenase activity with time after streptozotocin treatment to about 40% of control value at 15 weeks. In contrast, succinate oxidase and succinate- or NADH-cytochrome c reductase activities remain essentially unaltered. Further, the Arrhenius plot characteristics differ for D-beta-hydroxybutyrate dehydrogenase in diabetic membranes as compared with control membranes, in that the break point of the biphasic plot increases from 20 +/- 1 degree C in controls to 29 +/- 1 degree C in samples from diabetic animals. The change occurs about 3 weeks after streptozotocin treatment and is correlatable with the increased saturation of the fatty acid moiety of the phospholipids. The observed changes in D-beta-hydroxybutyrate dehydrogenase function and phospholipid composition were prevented by administration of insulin to the diabetic animals and are therefore referable to insulin insufficiency.

Basis for decreased D-beta-hydroxybutyrate dehydrogenase activity in liver mitochondria from diabetic rats

Liver mitochondria from rats made diabetic with streptozotocin have a reduced level of D-beta-hydroxybutyrate dehydrogenase (BDH) activity and decreased ratios of oleic/stearic and arachidonic/linoleic acids in the phospholipids of the mitochondrial membrane. This altered activity and lipid environment result from insulin deprivation since maintenance of the diabetic rats on insulin leads to normal characteristics (J.C. Vidal, J.O. McIntyre, P.F. Churchill, and S. Fleischer (1983) Arch. Biochem, Biophys. 224, 643-658). In the present study, the basis for the reduced enzymatic activity of this lipid-requiring enzyme was analyzed using three approaches: (i) Purified D-beta-hydroxybutyrate, dehydrogenase was inserted into membranes from mitochondria, submitochondrial vesicles, and mitochondrial lipids extracted therefrom. The activation was the same and optimal irrespective of whether the preparations were derived from normal or diabetic rat liver. Therefore, the decreased activity does not appear to be referable to an altered lipid composition. (ii) BDH activity can be released from the mitochondria by phospholipase A2 digestion. The released activity was proportional to the endogenous activity in the submitochondrial vesicles from normal and diabetic membranes. (iii) The BDH activity in submitochondrial vesicles was titrated by inhibition with specific antiserum. Less enzyme was found in mitochondria from diabetic rats as compared with those from normal animals. Hence, the lowered enzymatic activity is due to decreased enzyme in the mitochondrial inner membrane and not to the modified lipid environment.