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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mitochondrial and peroxisomal fatty acid oxidation were compared in whole liver homogenates. Oxidation of 0.2 mM palmitoyl-CoA or oleate by mitochondria increased rapidly with increasing molar substrate:albumin ratios and became saturated at ratios below 3, while peroxisomal oxidation increased more slowly and continued to rise to reach maximal activity in the absence of albumin. Under the latter condition mitochondrial oxidation was severely depressed. In homogenates from normal liver peroxisomal oxidation was lower than mitochondrial oxidation at all ratios tested except when albumin was absent. In contrast with mitochondrial oxidation, peroxisomal oxidation did not produce ketones, was cyanide-insensitive, was not dependent on carnitine, and was not inhibited by (+)-octanoylcarnitine, malonyl-CoA and 4-pentenoate. Mitochondrial oxidation was inhibited by CoASH concentrations that were optimal for peroxisomal oxidation. In the presence of albumin, peroxisomal oxidation was stimulated by Triton X-100 but unaffected by freeze-thawing; both treatments suppressed mitochondrial oxidation. Clofibrate treatment increased mitochondrial and peroxisomal oxidation 2- and 6- to 8-fold, respectively. Peroxisomal oxidation remained unchanged in starvation and diabetes. Fatty acid oxidation was severely depressed by cyanide and (+)-octanoylcarnitine in hepatocytes from normal rats. Hepatocytes from clofibrate-treated rats, which displayed a 3- to 4-fold increase in fatty acid oxidation, were less inhibited by (+)-octanoylcarnitine. Hydrogen peroxide production was severalfold higher in hepatocytes from treated animals oxidizing fatty acids than in control hepatocytes. Assuming that all H2O2 produced during fatty acid oxidation was due to peroxisomal oxidation, it was calculated that the contribution of the peroxisomes to fatty acid oxidation was less than 10% both in cells from control and clofibrate-treated animals.
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PMID:Mitochondrial and peroxisomal fatty acid oxidation in liver homogenates and isolated hepatocytes from control and clofibrate-treated rats. 43 7

Conditions for the isolation of rat hepatocytes that are responsive to insulin with regard to fatty acid synthesis were explored. Cells prepared according to the procedure of Ingebretsen and Wagle require the presence of fetal calf serum for insulin expression. Cells isolated by the Seglen method are the preparation of choice, since they respond to insulin in a simple, well-defined medium and, moreover, show much higher basal rates of fatty acid synthesis. In the latter cells isolated from fed male rats, the rate of fatty acid synthesis, as determined by tritium incorporation from [3H]H2O at 37 degrees C, is enhanced within 30 min after addition of insulin to the incubation medium; with glucagon, it is depressed. In the presence of insulin, the cellular content of malonyl coenzyme A is noticeably increased, whereas the concentrations of pyruvate, lactate, and citrate are not markedly affected. Glucagon, on the other hand, decreases the concentrations of all four intermediates. The activity of acetyl-CoA carboxylase is stimulated and depressed after addition of insulin and glucagon, respectively. In all conditions tested, the activity of acetyl-CoA carboxylase correlates with the rate of fatty acid synthesis, which in turn correlates with the cellular level of malonyl-CoA.
Diabetes 1979 Sep
PMID:Opposite effects of insulin and glucagon in acute hormonal control of hepatic lipogenesis. 46 8

1. Liver mitochondrial outer membranes were pre-exposed to media of low (20 mM phosphate) or high salt concentration (20 mM phosphate + 0.3 M KCl) before assay of carnitine palmitoyltransferase (CPT) at 25 degrees C. 2. With membranes from fed rats, exposure to high salt decreased sensitivity of CPT to malonyl-CoA whereas high salt increased sensitivity of CPT to malonyl-CoA in membranes from 48 hr-fasted rats. These changes were paralleled by alterations in the KD for high affinity binding of [14C]malonyl-CoA to outer membranes. 3. Decreasing the CPT assay temperatures from 25 to 10 degrees C caused qualitatively similar changes to those seen on exposure to high salt. 4. The relative content of sphingomyelin was increased 2-fold and 4-fold in liver mitochondrial outer membranes from fasted and diabetic rats respectively. Fasting had no effect on the content of cholesterol whereas diabetes decreased this by a third.
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PMID:Physiological state and the sensitivity of liver mitochondrial outer membrane carnitine palmitoyltransferase to malonyl-CoA. Correlations with assay temperature, salt concentration and membrane lipid composition. 139 5

Saponin-permeabilization (30 micrograms/ml) of the platelet plasma membrane, which enables access of added compounds to mitochondrial overt carnitine palmitoyltransferase (CPT I), was applied to allow the rapid determination of CPT I activity in situ. The effects of diabetes and short-term incubation with insulin in vitro on the kinetic parameters and malonyl-CoA sensitivity of CPT I were also studied in rat platelets. CPT I exhibited ordinary Michaelis-Menten kinetics when platelets were incubated with palmitoyl-CoA. Malonyl-CoA showed an I50 (concentration giving 50% inhibition of CPT activity) of 0.92 +/- 0.11 microM in permeabilized platelets. Platelets obtained from diabetic rats (induced by streptozotocin injection) exhibited an increased Vmax and I50 for malonyl-CoA, and an unaltered Km for palmitoyl-CoA. In contrast, preincubation of platelets prepared from both fed control rats and diabetic rats with insulin (100 and 150 microU/ml) led to a decrease in enzyme activity when assayed with 75 microM palmitoyl-CoA and 0.5 mM L-carnitine as substrates. These in vivo and in vitro results suggested that insulin directly modulated rat platelet CPT I activity, as it does in the liver.
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PMID:Characterization of overt carnitine palmitoyltransferase in rat platelets; involvement of insulin on its regulation. 185 44

1. Liver mitochondrial outer and inner membranes were isolated from normal, 48 h-fasted, streptozotocin-diabetic and hypothyroid rats. 2. Relative to membrane protein, fasting and diabetes substantially increased the activity of carnitine palmitoyltransferase (CPT) in outer membranes. Inner-membrane CPT specific activity was only slightly altered, being increased in diabetes and decreased in hypothyroidism. Abundance of an inner-membrane Mr-68,000 polypeptide that cross-reacted with an anti-CPT serum was significantly increased in diabetes and hypothyroidism. Relative to inner-membrane CPT activity, this cross-reactivity was increased by 37% in diabetes and by 400% in hypothyroidism, suggesting modification of the intrinsic activity of the CPT in these states. 3. CPT in outer membranes was inhibitable by malonyl-CoA, whereas inner-membrane CPT was insensitive to malonyl-CoA. Fasting and diabetes increased the IC50 (concentration of malonyl-CoA causing 50% inhibition) for outer-membrane CPT, whereas the IC50 was decreased in hypothyroidism. 4. Binding of [14C]malonyl-CoA was observed with both outer and inner membranes and was fitted to two-site models in each case. Fasting, diabetes and hypothyroidism changed the KD for binding at the higher-affinity site in outer membranes in a manner that correlated closely with changes in IC50 for inhibition of outer-membrane CPT by malonyl-CoA. Fasting and diabetes increased the abundance of this outer-membrane high-affinity malonyl-CoA-binding site, whereas hypothyroidism decreased its abundance.
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PMID:A study of properties and abundance of the components of liver carnitine palmitoyltransferases in mitochondrial inner and outer membranes. Effects of hypothyroidism, fasting and a ketotic diabetic state. 187 97

Fluorometry and high-performance liquid chromatography were used to measure the content of free CoA and the esters of acetate, malonate, succinate, and long-chain fatty acids in isolated perifused rat pancreatic islets exposed to 25 mM glucose or a mixture of fuels (25 mM glucose plus 10 mM glutamine, 10 mM lactate, and 1 mM pyruvate) to assess the role of intermediates of lipid metabolism as candidate metabolic coupling factors in the mechanism of fuel-induced insulin secretion. Insulin secretion was stimulated in a biphasic manner with the fuel mixture, showing twice the potency compared with high glucose alone. Islets perifused for 3 min with high glucose alone or the fuel mixture compared with 2.5 mM glucose showed a significant increase in malonyl-CoA and succinyl-CoA and a decrease in acetyl-CoA. Free CoA and long-chain acyl-CoA levels were unaltered. Perifused islets stimulated with 25 mM glucose for 30 min showed a significant increase in succinyl-CoA and long-chain acyl-CoA and decrease in acetyl-CoA, whereas malonyl-CoA was not affected. However, when islets were stimulated by the fuel mixture for 30 min, malonyl-CoA was maintained at a high level, and the change in succinyl-CoA and long-chain acyl-CoA was similar to that observed in islets stimulated with 25 mM glucose alone. The acetyl-CoA concentration in the islets stimulated with the fuel mixture decreased slightly. These results confirm the viability of the hypothesis that malonyl-CoA and long-chain acyl-CoA serve as metabolic coupling factors in signal transduction when islets are stimulated by high glucose or glucose combined with other fuels.
Diabetes 1991 Mar
PMID:Content of CoA-esters in perifused rat islets stimulated by glucose and other fuels. 199 74

Administration to normal rats of 100 mg of streptozotocin/kg body weight produced ketotic diabetic rats in which the affinity of carnitine palmitoyltransferase for malonyl-CoA was decreased by 10-fold and its activity was increased by 30%, but the injection of insulin brought the affinity and the activity back to normal within 4 h. Administration of 60 mg of streptozotocin/kg produced non-ketotic diabetic rats and caused a less substantial change in the affinity of carnitine palmitoyltransferase for malonyl-CoA. In the BB Wistar diabetic rat, the onset of diabetes also increased the activity of carnitine palmitoyltransferase and decreased its affinity for malonyl-CoA. Injection of insulin brought both of these values back to normal within 2 h. The total activity of mitochondrial carnitine palmitoyltransferase (outer + inner activities) was 40% greater in the BB Wistar diabetic rat, but treatment with insulin did not decrease the total activity to normal values within 2 h. The elevated activity and decreased affinity for malonyl-CoA found in fasting rats did not respond to short-term insulin treatment. The evaluation of a previous report that cycloheximide blocks the effects of starvation indicated that cycloheximide did not act by inhibiting protein synthesis, but produced its effect by preventing gastric emptying. Current data suggest that diabetes increases the activity of carnitine palmitoyltransferase and greatly diminishes the affinity of the enzyme for malonyl-CoA and that the severity of diabetes is associated with differences in the affinity of the enzyme for its inhibitor. Insulin acts on the outer carnitine palmitoyltransferase to reverse these effects very rapidly, but diabetes produces some change in the total activity that is not reversed by short-term treatment with insulin.
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PMID:Regulation of carnitine palmitoyltransferase by insulin results in decreased activity and decreased apparent Ki values for malonyl-CoA. 295 85

1. The kinetic properties of overt carnitine palmitoyltransferase (CPT I, EC 2.3.1.21) were studied in rat liver mitochondria isolated from untreated, diabetic and insulin-treated diabetic animals. A comparison was made of the time courses required for the changes in these properties of CPT I to occur and for the development of ketosis during the induction of chronic diabetes and its reversal by insulin treatment. 2. The development of hyperketonaemia over the first 5 days of insulin withdrawal from streptozotocin-treated rats was accompanied by parallel increases in the activity of CPT I and in the I0.5 (concentration required to produce 50% inhibition) of the enzyme for malonyl-CoA. 3. The rapid reversal of the ketotic state by treatment of chronically diabetic rats with 6 units of regular insulin was not accompanied by any change in the properties of CPT I over the first 4 h. Higher doses of insulin (15 units), delivered throughout a 4 h period, resulted in an increase in the affinity of CPT I for malonyl-CoA, but the sensitivity of the enzyme to the inhibitor was still significantly lower than in mitochondria from normal animals. 4. Conversely, when insulin treatment was continued over a 24 h period, full restoration of the sensitivity of the enzyme to malonyl-CoA was achieved. However, the activity of the enzyme was only decreased marginally. 5. These results are discussed in terms of the possibility that the major regulatory sites of the rate of hepatic oxidation may vary in different phases of the induction and reversal of chronic diabetes.
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PMID:Role of carnitine palmitoyltransferase I in the regulation of hepatic ketogenesis during the onset and reversal of chronic diabetes. 327 23

1. A permeabilized isolated rat liver cell preparation was developed to achieve selective permeabilization of the cell membrane to metabolites and to allow the assay of mitochondrial overt carnitine palmitoyltransferase (CPT I) activity in situ. By performing the digitonin-induced permeabilization in the presence of fluoride and bivalent-metal-cation sequestrants, it was possible to demonstrate that the activity of other enzymes, which are regulated by reversible phosphorylation, was preserved during the procedure and subsequent washing of cells before assay. 2. CPT activity at a sub-optimal palmitoyl-CoA concentration was almost totally (approximately 90%) inhibited by malonyl-CoA, indicating that mitochondrial CPT I was largely measured in this preparation. 3. The palmitoyl-CoA-saturation and malonyl-CoA-inhibition curves for CPT activity in permeabilized cells were very similar to those obtained previously for the enzyme in isolated liver mitochondria. Moreover, starvation and diabetes had the same effects on enzyme activity, affinity for palmitoyl-CoA and malonyl-CoA sensitivity of CPT I in isolated cells as found in isolated mitochondria. These physiologically induced changes persisted through the cell preparation and incubation period. 4. Neither incubation of cells with glucagon or insulin nor incubation with pyruvate and lactate before permeabilization resulted in alterations of these parameters of CPT I in isolated cells. 5. The results are discussed in relation to the temporal relationships of changes in the activity and properties of CPT I in vivo in relation to the effects of insulin and glucagon on fatty acid metabolism in vivo.
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PMID:Use of a selectively permeabilized isolated rat hepatocyte preparation to study changes in the properties of overt carnitine palmitoyltransferase activity in situ. 328 53

Several investigators have demonstrated a diminished rate of ketogenesis during inflammatory or infectious states despite the availability of free fatty acids supplied to the liver. The biochemical mechanism for this effect is unknown. Malonyl-CoA has been proposed to be a regulator of ketogenesis. Malonyl-CoA levels are low in states of rapid ketogenesis such as starvation or diabetes and high in states of reduced ketogenesis such as carbohydrate feeding. In the present study, the effect of an intra-abdominal abscess on the level of hepatic malonyl-CoA was investigated in four groups of animals (fed control, sterile inflammation, small chronic septic abscess, large chronic septic abscess). Liver samples were frozen in situ 5 days following the intraperitoneal introduction of a rat-fecal agar pellet inoculated with a known bacterial flora which generated an abscess [sterile inflammatory; B. fragilis 10(8)/ml + E. coli 10(2)/ml (small, 0.8 ml or large, 1.5 ml) abscess pellet]. The level of malonyl-CoA in normal fed rats was 5.0 +/- 0.6 nmol/gm wet wt (n = 9). The malonyl-CoA level was not altered in animals with a sterile inflammation. However, hepatic malonyl-CoA levels were significantly increased in small (10 +/- 1 nmole/gm wet wt) (p less than 0.05; n = 9) or large (12 +/- 1 nmol/gm wet wt) (p less than 0.01; n = 14) septic abscess rats compared to control fed and sterile inflammatory rats. Hepatic ketone bodies (beta-hydroxybutyrate and acetoacetate) did not increase in sepsis over control or sterile inflammation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:A biochemical basis for depressed ketogenesis in sepsis. 370 91


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