June R. Aprille

Delocalized lipophilic cations selectively target the mitochondria of carcinoma cells

Traditional chemotherapies, aimed at DNA replication in rapidly dividing cells, have achieved only limited success in the treatment of carcinomas due largely to their lack of specificity for cells of tumorigenic origin. It is important, therefore, to investigate treatment strategies aimed at novel cellular targets that are sufficiently different between normal cells and cancer cells so as to provide a basis for selective tumor cell killing. Delocalized lipophilic cations (DLCs) are concentrated by cells and into mitochondria in response to negative inside transmembrane potentials. The higher plasma and/or mitochondrial membrane potentials of carcinoma cells compared to normal epithelial cells account for the selective accumulation of DLCs in carcinoma mitochondria. Since most DLCs are toxic to mitochondria at high concentrations, their selective accumulation in carcinoma mitochondria and consequent mitochondrial toxicity provide a basis for selective carcinoma cell killing. Several of these compounds have already displayed some degree of efficacy as chemotherapeutic agents in vitro and in vivo. The effectiveness of DLCs can also be enhanced by their use in photochemotherapy or combination drug therapy. Discovery of the biochemical differences that account for the higher membrane potentials in carcinoma cells is expected to lead to the design of new DLCs targeted specifically to those differences, resulting in even greater selectivity and efficacy for tumor cell killing.

Regional mitochondrial respiratory activity in Huntington's disease brain

This study investigated mitochondrial respiratory activity in Huntingtons disease (HD) brain. Mitochondrial membranes from caudate and cortex of HD and non‐HD autopsied brains were assayed for succinate oxidation, cytochrome oxidase activity, and cytochromes b, cc1, and aa3. There was a significant decrease in HD caudate mitochondrial respiration, cytochrome oxidase activity, and cytochrome aa3, whereas cytochromes b and cc1 were normal. These findings are consistent with the hypothesis that mitochondrial dysfunction may contribute to the localized hypometabolism and progressive atrophy of the HD caudate.

Antipsychotic Drugs: Comparison in Animal Models of Efficacy, Neurotransmitter Regulation, and Neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D2 receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

Postnatal development of rat liver mitochondria: State 3 respiration, adenine nucleotide translocase activity, and the net accumulation of adenine nucleotides☆

The postnatal maturation of respiratory activity was studied in mitochondria isolated from livers of newborn rats that had been Caeserean delivered on the 22nd day of gestation. At birth, the State 3 respiratory rate with glutamate + malate (68.1 ± 8.4 ng atoms O/min/ mg protein) was much lower than the 2,4-dinitrophenol-uncoupled rate (112.7 ± 13.3 ng atoms O/min/mg protein). During the first hour of postnatal life, the State 3 rate increased to nearly equal the uncoupled rate, which did not change significantly. The State 4 rate and ADPO ratio did not change. After 1 h postnatal, when State 3 respiration had increased 1.6-fold, the total adenine nucleotide content (ATP + ADP + AMP) had increased 1.8-fold, and adenine nucleotide translocase activity had increased 1.5-fold. However, the total adenine nucleotide content and translocase activity continued to increase between 1 and 4.5 h postnatal in parallel with each other, but long after State 3 respiration had developed maximally. The ability of newborn liver mitochondria to accumulate adenine nucleotides in relation to the maturation of State 3 respiration was studied in vitro. Mitochondria incubated with 1 mm ATP at 30 °C for 10 min doubled their total adenine nucleotide content, and this was correlated with a doubling of the State 3 respiratory rate. The net accumulation of adenine nucleotides was inhibited 76 ± 1.8% by 100 μmN-ethylmaleimide and to a lesser extent (57 ± 0.5%) by 50 μm atractyloside. It was concluded that the accumulation of intramitochondrial adenine nucleotides, via the net uptake of ATP or ADP, probably accounted for the postnatal maturation of adenine nucleotide translocase activity and State 3 respiration. The data suggested that the translocase rate varied as a function of a much greater range of intramitochondrial adenine nucleotide contents than did the overall State 3 rate. The low rate of ADP-stimulated respiration at birth may have been limited by the rate of translocase-mediated exchange of newly synthesized ATP for external ADP, and/or by the absolute size of the exchangeable internal adenine nucleotide pool, which may have been submaximal for the F1-ATPase.

Rhodamine 123 inhibits bioenergetic function in isolated rat liver mitochondria

Rhodamine 123 accumulates in the mitochondria of living cells and exhibits selective anticarcinoma activity. The biochemical basis of toxicity was investigated by testing the effect of the dye on isolated rat liver mitochondria. Much lower concentrations of rhodamine 123 were required to inhibit ADP-stimulated respiration and ATP synthesis in well-coupled energized mitochondria than were required to inhibit uncoupled respiration and uncoupler-stimulated ATP hydrolysis. The amount of rhodamine 123 associated with the mitochondria was several-fold greater under energized as compared to non-energized conditions, which may explain why coupled functions appeared to be more sensitive than uncoupled functions to inhibition at low concentrations of rhodamine 123. It was concluded that the site of rhodamine 123 inhibition is most likely the F0F1 ATPase complex and possibly electron transfer reactions as well.

Mechanism and regulation of the mitochondrial ATP-Mg/Pi carrier

The mitochondrial ATP-Mg/Pi carrier functions to modulate the matrix adenine nucleotide pool size (ATP + ADP + AMP). Micromolar Ca2+ is required to activate the carrier. Net adenine nucleotide transport occurs as an electroneutral divalent exchange of ATP-Mg2− for HPO42−. A steady-state adenine nucleotide pool size is attained when the HPO42− and ATP-Mg2− matrix/cytoplasm concentration ratios are the same. This means that ATP-Mg2− can be accumulated against a concentration gradient in proportion to the [HPO42−] gradient that is normally maintained by the Pi/OH− carrier. In liver, changes in matrix adenine nucleotide concentrations that are brought about by the ATP-Mg/Pi carrier can affect the activity of adenine nucleotide-dependent enzymes that are in the mitochondrial compartment. These enzymes in turn contribute to the overall regulation of bioenergetic function, flux through the gluconeogenesis and urea synthesis pathways, and organelle biogenesis. The ATP-Mg/Pi carrier is distinct from other mitochondrial transport systems with respect to kinetics and to substrate and inhibitor sensitivity. It is the only carrier regulated by Ca2+. This carrier is present in kidney and liver mitochondria, but not in heart.

In vitro alteration of the size of the liver mitochondrial adenine nucleotide pool: Correlation with respiratory functions☆

Abstract Mitochondrial respiration was studied as a function of the total adenine nucleotide content of rat liver mitochondria. The adenine nucleotide content was varied by treating isolated mitochondria with pyrophosphate or by incubating pyrophosphate-treated mitochondria with ATP. Mitochondria with at least 4 nmol adenine nucleotides/mg protein maintained at least 80% of the State 3 activity of control mitochondria, which had approximately 10 nmol/mg protein. However, State 3 decreased rapidly once the adenine nucleotide content fell below 4 nmol/mg protein. Between 2 and 4 nmol adenine nucleotides/mg, State 3 was not limited by the maximal capacity of electron flow as measured by the uncoupled respiration. However, at very low adenine nucleotide levels (

Female role in sperm storage in the red flour beetle, Tribolium castaneum

This study clarifies the role of female-controlled processes contributing to sperm storage in the red flour beetle, Tribolium castaneum. Evidence presented indicates that sperm motility is not affected by extreme hypoxia produced by anesthetization of the female with either carbon dioxide or nitrogen. Sperm location and motility in low-oxygen environments did not differ from that of sperm in reproductive tracts immersed in fully aerated saline. Sperm motility was unaffected by exposure to potassium cyanide, an aerobic respiratory system poison, but was inhibited by exposure to iodoacetic acid, a glycolysis poison. Based on the retention of sperm motility under extreme hypoxia, female control over sperm storage was then examined. Both anesthetized females and dead females had fewer stored sperm after mating than unanesthetized control females. These results suggest that female T. castaneum play an active role in moving sperm from the site of deposition into storage.

Mitochondrial tRNAthr mutation in fatal infantile respiratory enzyme deficiency

The mitochondrial DNA (mtDNA) of two unrelated infants with lethal respiratory chain defects was studied using denaturing gradient gel analysis. This analysis revealed melting behavior differences suggesting a point mutation(s) in a restriction fragment containing the apocytochrome b and tRNA(thr) genes. Sequencing revealed that patient 1 had an A to G mutation at nt 15924 which is the last base pair of the anticodon stem adjacent to the anticodon loop of tRNA(thr). Patient 2 had an A to G mutation at nt 15923 which is the last base of the anticodon loop. The results suggest that mtDNA mutations affecting the anticodon loop structure of tRNA(thr) cause mitochondrial disease that is fatal in infancy.

Differential effects of typical and atypical neuroleptics on mitochondrial function in vitro.

A series of typical (chlorpromazine, haloperidol and thioridazine) and atypical (risperidone, quetiapine, clozapine and olanzapine) antipsychotics were tested for effects on integrated bioenergetic functions of isolated rat liver mitochondria. Polarographic measurement of oxygen consumption in freshly isolated mitochondria showed that electron transfer activity at respiratory complex I is inhibited by chlorpromazine, haloperidol, risperidone, and quetiapine, but not by clozapine, olanzapine, or thioridazine. Chlorpromazine and thioridazine act as modest uncouplers of oxidative phosphorylation. The typical neuroleptics inhibited NADH-coenzyme Q reductase in freeze-thawed mitochondria, which is a direct measure of complex I enzyme activity. The inhibition of NADH-coenzyme Q reductase activity by the atypicals risperidone and quetiapine was 2-4 fold less than that for the typical neuroleptics. Clozapine and olanzapine had only slight effects on NADH-coenzyme Q reductase activity, even at 200 μM. The relative potencies of these neuroleptic drugs as inhibitors of mitochondrial bioenergetic function is similar to their relative potencies as risk factors in the reported incidence of extrapyramidal symptoms, including tardive dyskinesia (TD). This suggests that compromised bioenergetic function may be involved in the cellular pathology underlying TD.