Distribution of metabolites between mitochondria and cytosol of cultured fibroblastoid rat heart cells

Dual-Targeted Synthetic Nanoparticles for Cardiovascular Diseases

Atherosclerosis is one of the world's most aggressive diseases, claiming over 17.5 million lives per year. This disease is usually caused by high amounts of lipoproteins circulating in the blood stream, which leads to plaque formation. Ultimately, these plaques can undergo thrombosis and lead to major heart damage. A major contributor to these vulnerable plaques is macrophage apoptosis. Development of nanovehicles that carry contrast and therapeutic agents to the mitochondria within these macrophages is attractive for the diagnosis and treatment of atherosclerosis. Here, we report the design and synthesis of a dual-targeted synthetic nanoparticle (NP) to perform the double duty of diagnosis and therapy in atherosclerosis treatment regime. A library of dual-targeted NPs with an encapsulated iron oxide NP, mito-magneto (MM), with a magnetic resonance imaging (MRI) contrast enhancement capability was elucidated. Relaxivity measurements revealed that there is a substantial enhancement in transverse relaxivities upon the encapsulation of MM inside the dual-targeted NPs, highlighting the MRI contrast-enhancing ability of these NPs. Successful in vivo imaging documenting the distribution of MM-encapsulated dual-targeted NPs in the heart and aorta in mice ensured the diagnostic potential. The presence of mannose receptor targeting ligands and the optimization of the NP composition facilitated its ability to perform therapeutic duty by targeting the macrophages at the plaque. These dual-targeted NPs with the encapsulated MM were able to show therapeutic potential and did not trigger any toxic immunogenic response.

Simultaneous extraction of several metabolites of energy metabolism and related substances in mammalian cells: optimization using experimental design

As a basis for the development of predictive mathematical models in systems biology and a quantitative understanding of cellular metabolism, reliable experimental data sets of intracellular metabolites are indispensable. A prerequisite for the acquisition of such data is the identification of a suitable sample preparation method. In this work, the extraction procedure for the simultaneous measurement of a wide range of intracellular metabolites from adherent mammalian cells in culture was optimized. A screening of several commonly used extraction protocols with Madin-Darby canine kidney (MDCK) cells found the methanol/chloroform (MeOH/CHCl(3)) and MeOH/Boil methods to be promising candidates for further analysis by anion-exchange chromatography. Both methods were optimized based on experimental design techniques with four response variables: Nucleotide Content, Energy Charge, Fructose 1,6-Bisphosphate content (F16bP), and Absorption at 280 nm. After data evaluation and with the help of desirability functions, an overall optimum for the extraction conditions was found. Using optimal settings, the extraction performances for MDCK and Vero cell cultivations of both methods were compared. Both methods extracted nearly the same absolute amounts of intracellular metabolites, suggesting that these methods are equal. However, recoveries for nucleotide diphosphates were significantly above 100% for both methods. This most likely was due to remaining nucleotide kinase activity during extraction. After combining individual steps of both methods, recoveries close to 100% for all metabolites could be reached. Absolute values of intracellular metabolites extracted with this modified method are comparable to the results of the two previously optimized methods, indicating a good extraction procedure according to the chosen response variables.

Influence of mitochondrial creatine kinase on the mitochondrial/extramitochondrial distribution of high energy phosphates in muscle tissue: evidence for a leak in the creatine shuttle

The influence of mitochondrial creatine kinase on subcellular high energy systems has been investigated using isolated rat heart mitochondria, mitoplasts and intact heart and skeletal muscle tissue. In isolated mitochondria, the creatine kinase is functionally coupled to oxidative phosphorylation at active respiratory chain, so that it catalyses the formation of creatine phosphate against its thermodynamic equilibrium. Therefore the mass action ratio is shifted from the equilibrium ratio to lower values. At inhibited respiration, it is close to the equilibrium value, irrespective of the mechanism of the inhibition. The same results were obtained for mitoplasts under conditions where the mitochondrial creatine kinase is still associated with the inner membrane. In intact tissue increasing amounts of creatine phosphate are found in the mitochondrial compartment when respiration and/or muscle work are increased. It is suggested that at high rates of oxidative phosphorylation creatine phosphate is accumulated in the intermembrane space due to the high activity of mitochondrial creatine kinase and the restricted permeability of reactants into the extramitochondrial space. A certain amount of this creatine phosphate 'leaks' into the mitochondrial matrix. This leak is confirmed in isolated rat heart mitochondria where creatine phosphate is taken up when it is generated by the mitochondrial creatine kinase reaction. At inhibited creatine kinase, external creatine phosphate is not taken up. Likewise, mitoplasts only take up creatine phosphate when creatine kinase is still associated with the inner membrane. Both findings indicate that uptake is dependent on the functional active creatine kinase coupled to oxidative phosphorylation. Creatine phosphate uptake into mitochondria is inhibited with carboxyatractyloside.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of oxidative phosphorylation in mitochondria of epididymal bull spermatozoa

The regulation of oxidative phosphorylation was studied with digitonin-treated epididymal bull spermatozoa in which mitochondria are directly accessible to low molecular compounds in the extracellular medium. Due to the high extramitochondrial ATPase activity in this cell preparation, it was possible to stimulate respiration to a small extent only by added hexokinase in the presence of glucose and adenine nucleotides. Added pyruvate kinase plus phosphoenol pyruvate, however, strongly suppressed the respiration. Under these conditions, the respiration was found to depend on the extramitochondrial [ATP]/[ADP] ratio in the range of 1-100. The contribution of the adenine nucleotide translocator to this dependence was determined by titration with the irreversible inhibitor carboxyatractyloside in the presence of ADP. Using lactate plus malate as substrate, the active state respiration was controlled to about 30% by the translocator, whereas 12 and 4% were determined in the presence of L-glycerol-3-phosphate and malate alone, respectively. In order to compare the results with those for intact cells, the adenine nucleotide patterns were determined in intact and digitonin-treated spermatozoa under conditions of controlled respiration in the presence of vanadate and carboxyatractyloside, respectively. About 21% of total cellular adenine nucleotides were found in digitonin-treated cells representing the mitochondrial compartment. While allowing for the intramitochondrial amount of adenine nucleotides, the cytosolic [ATP]/[ADP] ratio was estimated to be 6-times higher than the mitochondrial ratio in intact cells. It is concluded from the data presented that the principal mechanism by which oxidative phosphorylation in sperm mitochondria is regulated via the extramitochondrial [ATP]/[ADP] ratio is the same as that demonstrated for other isolated mitochondria.

Function dependent changes in the subcellular distribution of high energy phosphates in fast and slow rat skeletal muscles

Function dependent changes in the subcellular distribution of ATP, ADP, creatine phosphate (CrP) and creatine (Cr) in rat fast-twitch gastrocnemius and slow-twitch soleus muscles were studied by fractionation of freeze-clamped and freeze-dried tissue in non-aqueous solvents. During 5 min of isotonic contraction of gastrocnemius muscles the mitochondrial content of total creatine [sigma(CrP + Cr)] decreases by 9.5 nmol/mg total protein whereas there is an increase in extramitochondrial total creatine by 12.3 nmol/mg total protein, indicating a net transfer of approximately 10 nmol total creatine/mg total protein/5 min across the mitochondrial inner membrane. During short-term stimulation (6 s) of gastrocnemius muscles the socalled "additionally-bound ADP" correlates not only with force (Hebisch et al. 1984) but also with filament overlap. This confirms the previous suggestion that "additionally-bound ADP" represents actomyosin-ADP-complexes. Following long-term stimulation (10 s), the rate of decay of force is at least two orders of magnitude faster than that of "additionally bound ADP". This indicates a decrease of actomyosin-ADP complexes due to formation of myosin-ADP complexes. Short-term stimulation (6 s) of slow-twitch soleus muscles does not lead to any force-dependent change in the content of "additionally-bound ADP", similar to the finding in long-term contracting gastrocnemius muscles. Denervation of soleus muscles leads to a decrease in "additionally-bound ADP" to values comparable to those found in resting fast-twitch gastrocnemius muscles.

Interdependence of mitochondrial ATP production and extramitochondrial ATP utilization in intact spermatozoa

The dependence of both respiration and total activity of ATP-consuming reactions on the cellular adenine nucleotide pattern was investigated in intact bovine spermatozoa. ATP consumption was manipulated by inhibition with vanadate and activation with caffeine, leading to a decrease or increase in the rate of respiration up to 70% or 20%, respectively. Oligomycin blocked the respiration to the same extent as did vanadate, suggesting that the total extramitochondrial ATP-consuming activity is vanadate-sensitive. The major part of ATP utilization must be linked to dynein ATPase, since inhibition of (Na+, K+) ATPase by ouabain showed only a small effect on respiration (-17%). Being a potent inhibitor of dynein ATPase, vanadate drastically reduced the amount of motile cells, whereas caffeine tended to increase the intensity of motion. The effects of vanadate or caffeine on respiration were paralleled by changes in cellular ATP, reflecting the response of mitochondrial respiration on the cellular ATP/ADP ratio. Respiration was found to depend on changes in the ATP/ADP ratio in the range from about 3 (+caffeine) to 9 (+vanadate). The range of response of ATP consumption to the ATP/ADP ratio was determined by varying the mitochondrial ATP production via the concentration of lactate which was used as substrate. The measured effects on both respiratory rate and ATP/ADP ratio suggested that ATP consumption was markedly dependent on ATP/ADP ratios below 5. It is concluded that lactate concentrations above 1 mM sufficiently supply bovine spermatozoa with substrate and the energy turnover is mainly limited by the activity of dynein ATPase rather than by the capacity of mitochondrial oxidative phosphorylation.

Compartmentation of high-energy phosphates in resting and working rat skeletal muscle

The subcellular distribution of high-energy phosphates in various types of skeletal muscle of the rat was analysed by subfractionation of tissues in non-aqueous solvents. Different glycolytic and oxidative capacities were calculated from the ratio of phosphoglycerate kinase and citrate synthase activities, ranging from 25 in m. soleus to 130 in m. tensor fasciae latae. In the resting state, the subcellular contents of ATP, creatine phosphate and creatine were similar in m. soleus, m. vastus intermedius, m. gastrocnemius and m. tensor fasciae latae but, significantly, a higher extramitochondrial ADP-content was found in m. soleus. A similar observation was made in isometrically and isotonically working m. gastrocnemius. The extramitochondrial, bound ADP accounted fully for actin-binding sites in resting fast-twitch muscles, but an excess of bound ADP was found in m. soleus and working m. gastrocnemius. The amount of non-actin-bound ADP reached maximal values of approx. 1.2 nmol/mg total protein. It could not be enhanced further by prolonged isotonic stimulation or by increased isometric force development. It is suggested that non-actin-bound ADP is accounted for by actomyosin-ADP complexes generated during the contraction cycle. Binding of extramitochondrial ADP to actomyosin complexes in working muscles thus acts as a buffer for cytosolic ADP in addition to the creatine system, maintaining a high cytosolic phosphorylation potential also at increasing rates of ATP hydrolysis during muscle contraction.

Response of isolated rat heart cells to hypoxia, re-oxygenation, and acidosis

Responses of isolated adult rat heart cells to conditions that emphasize various aspects of ischemia have been evaluated. Cells maintained in hypoxic media with limited substrate deteriorate more rapidly than aerobic controls supplemented with glucose. Two distinct irreversible pathways for cell alteration can be distinguished as follows: (1) continued anaerobic aging in the absence of glucose results in the production of large numbers of cells which retain the rod-shaped morphology of heart cells in situ, but which have lost sarcolemmal integrity, and (2) after a period of anaerobic aging, reaeration of the cells produces large numbers of rounded cells in irreversible contracture. These cells maintain an intact sarcolemma and are indistinguishable from those produced by addition of 1 mM Ca2+ to Na+-loaded, aerobic cells. Contracture of isolated cells on re-aeration is at least superficially analogous to the oxygen paradox in situ, but since the isolated cells maintain an intact sarcolemma, there is no loss of creatine phosphokinase or other components of the cytosol. Incubation of isolated heart cells at acid pH (pH 6.8 to 6.2) largely prevents both Ca2+-dependent contracture and a Ca2+- dependent loss of respiratory capacity. The acidic conditions virtually eliminate the net influx of 45Ca2+ into isolated cells that occurs at neutral pH, and the inhibition appears to be localized at the sarcolemma.