Synergistic Effect of β-Lapachone and Aminooxyacetic Acid on Central Metabolism in Breast Cancer

The compound β-lapachone, a naturally derived naphthoquinone, has been utilized as a potent medicinal nutrient to improve health. Over the last twelve years, numerous reports have demonstrated distinct associations of β-lapachone and NAD(P)H: quinone oxidoreductase 1 (NQO1) protein in the amelioration of various diseases. Comprehensive research of NQO1 bioactivity has clearly confirmed the tumoricidal effects of β-lapachone action through NAD+-keresis, in which severe DNA damage from reactive oxygen species (ROS) production triggers a poly-ADP-ribose polymerase-I (PARP1) hyperactivation cascade, culminating in NAD+/ATP depletion. Here, we report a novel combination strategy with aminooxyacetic acid (AOA), an aspartate aminotransferase inhibitor that blocks the malate-aspartate shuttle (MAS) and synergistically enhances the efficacy of β-lapachone metabolic perturbation in NQO1+ breast cancer. We evaluated metabolic turnover in MDA-MB-231 NQO1+, MDA-MB-231 NQO1-, MDA-MB-468, and T47D cancer cells by measuring the isotopic labeling of metabolites from a [U-13C]glucose tracer. We show that β-lapachone treatment significantly hampers lactate secretion by ~85% in NQO1+ cells. Our data demonstrate that combinatorial treatment decreases citrate, glutamate, and succinate enrichment by ~14%, ~50%, and ~65%, respectively. Differences in citrate, glutamate, and succinate fractional enrichments indicate synergistic effects on central metabolism based on the coefficient of drug interaction. Metabolic modeling suggests that increased glutamine anaplerosis is protective in the case of MAS inhibition.

Impact of Pharmacological Inhibition of Hydrogen Sulphide Production in the SOD1G93A-ALS Mouse Model

A number of factors can trigger amyotrophic lateral sclerosis (ALS), although its precise pathogenesis is still uncertain. In a previous study done by us, poisonous liquoral levels of hydrogen sulphide (H₂S) in sporadic ALS patients were reported. In the same study very high concentrations of H₂S in the cerebral tissues of the familial ALS (fALS) model of the SOD1G93A mouse, were measured. The objective of this study was to test whether decreasing the levels of H₂S in the fALS mouse could be beneficial. Amino-oxyacetic acid (AOA)—a systemic dual inhibitor of cystathionine-β-synthase and cystathionine-γ lyase (two key enzymes in the production of H₂S)—was administered to fALS mice. AOA treatment decreased the content of H₂S in the cerebral tissues, and the lifespan of female mice increased by approximately ten days, while disease progression in male mice was not affected. The histological evaluation of the spinal cord of the females revealed a significant increase in GFAP positivity and a significant decrease in IBA1 positivity. In conclusion, the results of the study indicate that, in the animal model, the inhibition of H₂S production is more effective in females. The findings reinforce the need to adequately consider sex as a relevant factor in ALS.

The therapeutic potential of cystathionine β-synthetase/hydrogen sulfide inhibition in cancer

SIGNIFICANCE

Cancer represents a major socioeconomic problem; there is a significant need for novel therapeutic approaches targeting tumor-specific pathways.

RECENT ADVANCES

In colorectal and ovarian cancers, an increase in the intratumor production of hydrogen sulfide (H2S) from cystathionine β-synthase (CBS) plays an important role in promoting the cellular bioenergetics, proliferation, and migration of cancer cells. It also stimulates peritumor angiogenesis inhibition or genetic silencing of CBS exerts antitumor effects both in vitro and in vivo, and potentiates the antitumor efficacy of anticancer therapeutics.

CRITICAL ISSUES

Recently published studies are reviewed, implicating CBS overexpression and H2S overproduction in tumor cells as a tumor-growth promoting "bioenergetic fuel" and "survival factor," followed by an overview of the experimental evidence demonstrating the anticancer effect of CBS inhibition. Next, the current state of the art of pharmacological CBS inhibitors is reviewed, with special reference to the complex pharmacological actions of aminooxyacetic acid. Finally, new experimental evidence is presented to reconcile a controversy in the literature regarding the effects of H2S donor on cancer cell proliferation and survival.

FUTURE DIRECTIONS

From a basic science standpoint, future directions in the field include the delineation of the molecular mechanism of CBS up-regulation of cancer cells and the delineation of the interactions of H2S with other intracellular pathways of cancer cell metabolism and proliferation. From the translational science standpoint, future directions include the translation of the recently emerging roles of H2S in cancer into human diagnostic and therapeutic approaches.

Effects of hydrogen sulfide on a rat model of sepsis-associated encephalopathy

To investigate the interaction and involvement of sodium hydrosulfide (NaHS), a H(2)S donor, on hippocampus of rats suffering from sepsis-associated encephalopathy, rats were subjected to cecal ligation and puncture (CLP)-induced sepsis. Adult male Sprague-Dawley rats were randomly divided into four groups: Sham group, CLP group, CLP+NaHS group and CLP+aminooxyacetic acid (AOAA, an inhibitor of H(2)S formation) group. The four groups were observed at 3, 6, 9, 12 h after treatment. We examined hippocampal H(2)S synthesis and the expression of cystathionine-β-synthetase (CBS), a major enzyme involved in the H(2)S synthesis in hippocampus. CBS expression was detected by reverse transcription polymerase chain reaction (RT-PCR). The concentrations of inflammatory cytokines (TNF-α, IL-1β) were determined in hippocampus by using enzyme-linked immunosorbent assay (ELISA). Neuronal damage was studied by histological examination of hippocampus. In CLP group, H(2)S synthesis was significantly increased in hippocampus compared with sham group and it peaked 3 h after CLP (P<0.05). Sepsis also resulted in a significantly upregulated CBS mRNA in hippocampus. The levels of TNF-α and IL-1β in the hippocampus were substantially elevated at each time point of measurement (P<0.05), and they also reached a peak value at about 3 h. Administration of NaHS significantly aggravated sepsis-associated hippocampus inflammation, as evidenced by TNF-α and IL-1β activity and histological changes in hippocampus. In septic rats pretreated with AOAA, sepsis-associated hippocampus inflammation was reduced. It is concluded that the rats subjected to sepsis may suffer from brain injury and elevated pro-inflammatory cytokines are responsible for the process. Furthermore, administration of H(2)S can increase injurious effects and treatment with AOAA can protect the brain from injury.

Gamma-aminobutyric acid and mefloquine-induced seizures in mice

The role of GABAergic mechanism in the convulsant effect of mefloquine was investigated in mice. Mefloquine dose dependently induced tonic seizures in mice. Aminooxyacetic acid, diaminobutyric acid and muscimol significantly protected mice against mefloquine-induced seizures by significantly delaying the onset and decreasing the incidence of the seizures. Bicuculline and picrotoxin significantly enhanced the seizure producing effect of mefloquine and also significantly antagonised the protective effect of muscimol against the seizures. Phenobarbitone and diazepam effectively protected mice against mefloquine-induced seizures. Phenytoin did not alter mefloquine-induced seizures. These data indicate that GABA mechanisms might be involved in seizures produced by mefloquine in mice.

Aminooxyacetic acid-induced accumulation of GABA enhances clonidine hypotension

The effect of 2-oxoglutarate aminotransferase inhibitor, aminooxyacetic acid (AOAA) on hypotension induced by clonidine in spontaneously hypertensive rats (SHR) was examined. AOAA given 15 min before clonidine significantly intensified clonidine--induced reduction of blood pressure. This effect reached its maximum within 120 min after AOAA administration, when AOAA itself had no influence on blood pressure. Our data suggest that the activation of functional state of GABAergic system by GABA accumulation potentiates clonidine hypotension.

The synergistic protective effect of propranolol & aminooxyacetic acid against picrotoxin-induced myoclonus in rats

The effect of propranolol was assessed against myoclonus induced by picrotoxin (a known GABA antagonist) in a dose of 3 mg/kg and allylglycine (the inhibitor of GABA synthesis and release) in a dose of 150 mg/kg. A dose-dependent (0.5-2 mg/kg) protective effect was found against both models. Pretreatment of rats with a GABA-reducing dose (100 mg/kg, nonmyoclonic) of allylglycine produced no change in the effect of propranolol against picrotoxin-induced myoclonus. Propranolol thus inhibited myoclonic responses when both the receptor activity and the functional pool of GABA were impaired, suggesting that it produces as antimyoclonic action without the involvement of GABA. However, the drug seems to show a synergistic action with GABA-ergic agents, as greater protection was observed in rats treated concurrently with propranolol and amino-oxyacetic acid, an inhibitor of GABA degradation.

Evaluation of amino-oxyacetic acid as a palliative in tinnitus

Amino-oxyacetic acid (AOAA) was evaluated as a palliative in tinnitus. Sixty-six patients with tinnitus presumed to be of cochlear origin were given either a placebo or 75 mg of AOAA four times a day for 1 week. Response was evaluated by both audiometric measurement of tinnitus loudness and subjective rating by patients of change or no change in tinnitus severity. Because loudness measurements and self-rating have not been shown to be independent, and since the aim of clinical treatment of tinnitus is the alleviation of subjective distress, greater weight was given to the patient's self-rating. A total of 21% of all patients reported a subjective decrease in tinnitus severity, usually within 3 to 4 days after the start of AOAA use. Patients with tinnitus caused by presbycusis or Meniere's disease were the most likely to respond to AOAA treatment with a reduction in tinnitus severity, whereas those with drug-induced tinnitus were the least likely to respond. Nausea and dysequilibrium were the most common side effects of AOAA use. Of the 21% of patients who responded to AOAA, 71% developed some type of side effect. Amino-oxyacetic acid produces a reduction in the severity of tinnitus in about 20% of patients; however, the incidence of side effects makes the drug unacceptable for clinical use.

The superiority of the Goodwin procedure over the traditional procedure in measuring the loudness level of tinnitus

The results of two procedures for measuring the loudness level of tinnitus will be presented. The traditional procedure yielded significantly smaller loudness matches, when expressed in decibel sensation level (i.e., dB SL), than did the Goodwin procedure. The Goodwin procedure is more sensitive to pharmacologically induced changes in tinnitus loudness than is the traditional procedure. The Goodwin method correlates well with changes in patient's subjective rating of tinnitus severity. The Goodwin match has a larger reliability coefficient. Nonlinear correlation also indicates that the Goodwin procedure is superior to the traditional method.

Synergistic anticonvulsant action of diazepam & clonazepam with amino-oxyacetic acid against isoniazid-induced convulsions in rats

The protective effect of two benzodiazepine compounds, diazepam and clonazepam was tested against isoniazid (INH)- induced convulsions in rats pretreated with the gamma-amino-butyric acid (GABA) transaminase inhibitor viz., aminooxyacetic acid (AOAA), and the result was compared with that produced by the two drugs independently. Rats treated 6 h and not 30 min previously with AOAA showed a dose-dependent inhibition of INH-induced convulsions. In these animals both diazepam and clonazepam showed a greater protective effect than that produced by them alone. It is suggested from these findings that, even if their anticonvulsant mechanisms are distinct, with or without the involvement of GABA, AOAA and the benzodiazepine compounds seem to act synergistically against INH-induced convulsions.

[Experimental study of the antiepileptic activity of fenibut and its combinations with sodium valproate and aminooxyacetic acid]

The antiepileptic activity of GABA-mimetics (phenibut, sodium valproate and aminooxyacetic acid/AOAA/) was studied in experiments on the model of hippocampal penicillin-induced epilepsy in rats. The effects of the drugs were studied in experiments with a mirror epileptogenic focus which forms in the hippocampus contralateral to the penicillin-damaged hippocampus. All the drugs suppressed the activity of the epileptogenic focus after injections in the focus region. At systemic administration of the drugs the antiepileptic activity was found only with sodium valproate and AOAA. Phenibut enhanced the antiepileptic effect of sodium valproate and the toxic effects of AOAA at parenteral administration.

Amino-oxyacetic acid as a palliative in tinnitus

Amino-oxyacetic acid, previously shown to cause a reversible loss of hearing sensitivity and a reduction in endocochlear potential, was tried as a palliative in human tinnitus. Because the drug seemed to have a cochlear site of action, patients were selected for the study if their audiograms were indicative of cochlear lesions and if there was a reduction in tinnitus following intravenous lidocaine (lidocaine positive). Ten such patients received either 50 or 75 mg of amino-oxyacetic acid four times a day orally for one week or placebo administered in a random, crossover, double-blind design. Of these ten, three reported subjective lessening of tinnitus. One of those three and two others not reporting subjective lessening of tinnitus showed a substantial improvement in speech discrimination scores while receiving amino-oxyacetic acid but not placebo. One additional patient who did not receive lidocaine also reported a subjective lessening of tinnitus. Four patients who were lidocaine negative showed neither subjective nor objective improvement in tinnitus after treatment with amino-oxyacetic acid.

Aminooxyacetic acid provides transient protection against seizures induced by hyperbaric oxygen

In an attempt to demonstrate a protective effect against convulsions induced by hyperbaric oxygen (OHP), aminooxyacetic acid (AOAA at 2.5 mg/kg) was administered subcutaneously to 60 white leghorn cockerels (aged 21-28 days) at periods of 1-72 h before exposure to OHP. A transient protection was noted 1-8 h after administration of the AOAA. This took the form of a 51-67% increase in the latent period before OHP induced convulsions began. By 12 h after injection, the protective effect had disappeared. Thereafter a phase of increased susceptibility to hyperbaric oxygen commenced. This phase lasted for at least a further 60 h.

Failure of aminooxyacetic acid therapy in Huntington disease

Seven patients with Huntington disease were treated with aminooxyacetic acid (AOAA), an inhibitor of gamma-aminobutyric acid aminotransferase (GABA-T), in an effort to alleviate symptoms by increasing brain GABA content. AOAA was given orally in a placebo-controlled crossover trial in which patients, relatives, and three of the evaluating physicians remained blind. Toxic symptoms occurred in all seven patients when AOAA dosage was increased beyond 2 mg per kilogram per day, and included drowsiness, ataxia, seizures, and psychotic behavior. In five patients who took AOAA for 4 months, no clinical improvement was observed. Biochemical monitoring showed that less inhibition of hepatic GABA-T enzyme activity was achieved than in patients treated with large doses of isoniazid. Results of this trial neither support nor exclude the possible therapeutic usefulness of increasing brain GABA content in Huntington disease.

A gerbil model of cerebral ischemia suitable for drug evaluation

Cerebral ischemia was produced in the Mongolian gerbil by bilateral occlusion of the carotid arteries. Although the cerebral ischemia so produced was not total, a mortality rate of 100% was obtained if the occlusion was maintained for 60 min in gerbils weighing 45--55 gm. Few deaths were observed after 50 min of bilateral carotid arterial occlusion. Test drugs were administered, after the removal of the arterial clips, to groups of gerbils to determine the mortality rate associated with each drug. Isoproterenol 50 mg/kg, amphetamine 5.0 mg/kg, and methylprednisolone 35 mg/kg improved survival after cerebral ischemia. Atropine 1 mg/kg, thiosemicarbazide 4 mg/kg, aminooxyacetic acid 100 mg/kg, theophylline 100 mg/kg, and phenytoin 50 mg/kg were associated with a reduced survival after cerebral ischemia. The known tendency of the gerbil to exhibit spontaneous seizures and the frequency and severity of the observed post-ischemic seizures suggest that the lethality of prolonged cerebral ischemia may be, in part, related to seizures triggered by the cerebral ischemia.

Effect of amino-oxyacetic acid (AOAA) on focal penicillin seizures

The biochemical and behavioral effects of the anticonvulsant amino-oxyacetic acid (AOAA) have been studied in a model of focal penicillin seizures in rats. At 20 mg/Kg AOAA treatment results in a progressive 11 fold increase in GABA levels in cortex over three hours. There is a decrease in aspartate, ketoglutarate, alanine and glutamine, and an initial decrease followed by an increase in pyruvate and glutamate. These results reflect a functional inhibition of several B-6 dependent aminotransferase enzymes. When rats are pretreated 30 min before the onset of focal penicillin seizures there is a 60% reduction in the number of discharges and a 34% reduction in seizure duration. Pretreatment beyond 75 min results in progressively less anticonvulsant effect, such that seizures eventually become more severe than control. There is an increase in the number and duration of discharges, seizure spikes become complex, and tonic-clonic events develop. Penicillin seizures do not cause a change in levels of GABA, but result in a decrease in glutamate within the focus. AOAA pretreatment initially prevents this decrease in glutamate but later accentuates it. The biochemical effects of AOAA are complex, but biphasic anticonvulsant properties coincide in time with a change in the balance of excitatory and inhibitory amino acids in the seizure focus.

Protection against high-pressure oxygen seizures by amino-oxyacetic acid

A variety of autonomic blocking agents, general anesthetics, and anticonvulsants have been shown to offer protection from seizures caused by hyperbaric oxygen. Amino-oxyacetic acid (AOAA) has been shown to offer rats only minimal protection from such seizures. This study investigated whether AOAA protected cats and mice from hyperbaric-oxygen-induced seizures. Cats and mice were exposed to 100% oxygen at 5 ATA until seizures occurred or for a period of up to 60 min. Approximately half of the animals were pretreated with AOAA either 30 or 240 min before oxygen exposure. Results showed that the interval between exposure and grand mal seizures increased significantly in cats pretreated 30 or 240 min before exposure with 17 to 25 mg/kg AOAA; the number of cats remaining seizure-free for 60 min also increased markedly. However, mice received little protection even at doses up to 40 mg/kg. At higher doses the AOAA itself caused seizures even in the absence of hyperbaric oxygen.

gamma-Aminobutyric acid (Gaba) and the dopamine hypothesis of schizophrenia

gamma-Aminobutyric acid (Gaba) has been shown to influence dopamine activity in the brain. The author suggests that Gaba could be involved in the hypothesized dopamine hyperactivity in schizophrenia. He discusses pharmacological interventions that may raise Gaba-mediated function in the brain and states that further development of Gaba analogues seems clearly indicated. It is conceivable, he concludes, that these compounds could enhance the antipsychotic activity of dopamine receptor blockers, which could lead to the use of lower doses and therefore fewer extrapyramidal side effects.

[Antagonistic effect of sodium hydroxybutyrate on several effects of aminoxyacetic acid]

A well-known protective effect of aminooxyacetic acid against thiosemicarbazide convulsions was confirmed; it was shown that a similar, although somewhat weaker activity, was exerted by sodium hydroxybutyrate. Surprisingly, the effect of aminooxyacetic acid was diminished by sodium hydroxybutyrate. Sodium hydroxybutyrate in combination with aminooxyacetic acid decreased the protective activity of the latter against thiosemicarbazide convulsions and diminished the extent of GABA accumulation characteristic of aminooxyacetic acid action. This effect is attributed to the competition between the aminooxyacetic acid, sodium hydroxybutyrate and GABA for alpha-ketoglutarate-GABA-transaminase and possible for the GABA-ergic receptor.