Ketamine-induced attenuation of reactive oxygen species in zebrafish is prevented by acetyl l-carnitine in vivo

Neonatal Anesthesia and Oxidative Stress

Neonatal anesthesia, while often essential for surgeries or imaging procedures, is accompanied by significant risks to redox balance in the brain due to the relatively weak antioxidant system in children. Oxidative stress is characterized by concentrations of reactive oxygen species (ROS) that are elevated beyond what can be accommodated by the antioxidant defense system. In neonatal anesthesia, this has been proposed to be a contributing factor to some of the negative consequences (e.g., learning deficits and behavioral abnormalities) that are associated with early anesthetic exposure. In order to assess the relationship between neonatal anesthesia and oxidative stress, we first review the mechanisms of action of common anesthetic agents, the key pathways that produce the majority of ROS, and the main antioxidants. We then explore the possible immediate, short-term, and long-term pathways of neonatal-anesthesia-induced oxidative stress. We review a large body of literature describing oxidative stress to be evident during and immediately following neonatal anesthesia. Moreover, our review suggests that the short-term pathway has a temporally limited effect on oxidative stress, while the long-term pathway can manifest years later due to the altered development of neurons and neurovascular interactions.

Zebrafish (Danio rerio): A potential model to assess developmental toxicity of ketamine

Ketamine is a non-competitive antagonist of NMDA glutamate receptor. It is used as an anesthetic, analgesic, sedative, and anti-depressive agent in clinical practice and also an illegal recreational drug. The increasing use has contributed to the measurable levels of ketamine in both wastewaters and hospital effluents, thereby classified as an emergent contaminant. Lately, the potential toxicity of ketamine has raised serious concerns about its iatrogenic or illicit use during pregnancy, neonatal and childhood stages. However, to assess its long-term toxicity potentially by the use of early life stages in human and rodents is limited. In this regard, the zebrafish has been considered as excellent model organism for biosafety assessments of ketamine due to it boasts an in vivo model with the advantages of an in vitro assay. In this review, we summarize the current understanding of the reported toxicity studies with ketamine in early life stage of zebrafish. The adverse effects of ketamine are known to cause overall developmental and multi-organ toxicity, including cardio-, neuro-, and skeletal toxicity. Furthermore, multiple mechanisms are found to be responsible for perpetrating toxicity of ketamine. The current findings confluence to emphasize the zebrafish embryo as an appealing model system for developmental toxicity testing in higher vertebrates.

Acetyl l-carnitine protects adipose-derived stem cells against serum-starvation: regulation on the network composed of reactive oxygen species, autophagy, apoptosis and senescence

Adipose-derived stem cells (ADSCs) play an important role in cell therapy and regenerative medicine. However, local nutritional deficiency often limits therapeutical effect of the transplanted cells. Acetyl l-carnitine (ALC) is a common energy metabolism regulator and free radical scavenger. This study investigated the effect of ALC on ADSCs exposed to severe serum-deprivation and explored the relative machanisms. Treating with 1 mM ALC improved proliferation and alleviated senescence of starved cells, accompanied with reduced reactive oxygen species (ROS) and increased protein expression of SOD1 and catalase. In addition, ALC inhibited apoptosis but increased starvation-induced autophagy, which might be related to the regulation of phases of dissociation of Bcl-2-Beclin1 and Bcl-2-Bax complexes. Evidence obtained by replacing ALC with N-acetylcysteine (N-AC) suggested that ROS might be the central inducer of autophagy, apoptosis and senescence. There was a difference between ALC and N-AC in the protection mechanism, that was, compared with N-AC, ALC maintained autophagy well at the same time as anti-oxidation. Inhibition of autophagy by 3-methyladenine (3-MA) partially offset the protective effect of ALC. However, despite low-level ROS and enhanced autophagy, ALC with high concentration (10 mM) markedly aggravated cell apoptosis and senescence, thus losing cytoprotection and even causing damage.

Ketamine: Neuroprotective or Neurotoxic?

Ketamine, a non-competitive N-methyl-D-aspartate receptor (NMDAR) antagonist, has been employed clinically as an intravenous anesthetic since the 1970s. More recently, ketamine has received attention for its rapid antidepressant effects and is actively being explored as a treatment for a wide range of neuropsychiatric syndromes. In model systems, ketamine appears to display a combination of neurotoxic and neuroprotective properties that are context dependent. At anesthetic doses applied during neurodevelopmental windows, ketamine contributes to inflammation, autophagy, apoptosis, and enhances levels of reactive oxygen species. At the same time, subanesthetic dose ketamine is a powerful activator of multiple parallel neurotrophic signaling cascades with neuroprotective actions that are not always NMDAR-dependent. Here, we summarize results from an array of preclinical studies that highlight a complex landscape of intracellular signaling pathways modulated by ketamine and juxtapose the somewhat contrasting neuroprotective and neurotoxic features of this drug.

Effect of ketamine on gene expression in zebrafish embryos

Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist. Used as an anesthetic, potential neurotoxic and cardiotoxic effects of ketamine in animal models have been reported. The underlying mechanisms of ketamine-induced toxicity are not clear. The zebrafish is an ideal model for toxicity assays because of its predictive capability in chemical testing, which compares well with that of mammalian models. To gain insight into potential mechanisms of ketamine effects, we performed real-time quantitative polymerase chain reaction-based gene expression array analyses. Gene expression analysis was conducted for multiple genes (a total of 84) related to 10 major signaling pathways including the transforming growth factor β (TGFβ), Wingless and Int-1 (Wnt), nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB), Janus kinase/signal transducers and activators of transcription (JAK/STAT), p53, Notch, Hedgehog, peroxisome proliferator-activated receptor (PPAR), oxidative stress, and hypoxia pathways. Our results show that ketamine altered the expression of specific genes related to hypoxia, p53, Wnt, Notch, TGFβ, PPAR, and oxidative stress pathways. Thus, we can further focus on these specific pathways to elucidate the mechanisms by which ketamine elicits a toxic response.

Target specific tight junction modulators

Intercellular tight junctions represent a formidable barrier against paracellular drug absorption at epithelia (e.g., nasal, intestinal) and the endothelium (e.g., blood-brain barrier). In order to enhance paracellular transport of drugs and increase their bioavailability and organ deposition, active excipients modulating tight junctions have been applied. First-generation of permeation enhancers (PEs) acted by unspecific interactions, while recently developed PEs address specific physiological mechanisms. Such target specific tight junction modulators (TJMs) have the advantage of a defined specific mechanism of action. To date, merely a few of these novel active excipients has entered into clinical trials, as their lack in safety and efficiency in vivo often impedes their commercialisation. A stronger focus on the development of such active excipients would result in an economic and therapeutic improvement of current and future drugs.

Effects of acetyl L-carnitine on zebrafish embryos: Phenotypic and gene expression studies

Acetyl L-carnitine (ALCAR), a dietary supplement and an antioxidant, plays a vital role in the bioenergetic process that produces ATP. Although there are reports on antioxidant toxicity, there is no information on the potential toxicity of ALCAR. Here, using zebrafish embryos, we explored whether ALCAR modulated ATP synthesis, generation of reactive oxygen species (ROS) and expression of specific genes related to major signaling pathways that control metabolism, growth, differentiation, apoptosis and oxidative stress. First, we show that ALCAR elicits a physiologic response, as ATP levels increased after ALCAR treatment. Simultaneously, an increase in the expression of ROS, a by-product of ATP synthesis, was observed in the ALCAR-treated embryos. Consistent with higher ROS expression, the level of cysteine, a precursor of glutathione, was significantly reduced. ALCAR did not have any drastic effect on overall development and heart rate. Polymerase chain reaction-based gene expression array analyses showed no significant change in the expression of 83 genes related to 10 major signaling pathways including: the transforming growth factor β (TGFβ), Wingless and Int-1 (Wnt), nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB), Janus kinase/signal transducers and activators of transcription (JAK/STAT), p53, Notch, Hedgehog, Peroxisome proliferator-activated receptor (PPAR), oxidative stress, and hypoxia pathways. Our results show that the expression of 83 genes related to these major signaling pathways did not change significantly.

N-acetylcysteine prevents verapamil-induced cardiotoxicity with no effect on the noradrenergic arch-associated neurons in zebrafish

There is a strong association between calcium channel blockers (CCBs) and heart failure. CCB toxicity is very common due to overdose and underlying medical conditions. CCBs also have been shown to affect the nervous system. Recently, we demonstrated that the antioxidant N-acetylcysteine (NAC) prevented ketamine-induced cardiotoxicity, developmental toxicity and neurotoxicity. Functionally, we attributed NAC's beneficial effect to its ability to increase cellular calcium. Here, we hypothesized that if there was an involvement of calcium in NAC's preventative effects on ketamine toxicity, NAC might also ameliorate toxicities induced by verapamil, an L-type CCB used to treat hypertension. Using zebrafish embryos, we show that in the absence of NAC, verapamil (up to 100 μM) dose-dependently reduced heart rate and those effects were prevented by NAC co-treatment. Furthermore, a 2-h treatment with NAC rescued reduction of heart rate induced by pre-treatment of 50 and 100 μM of verapamil for 18 h. Verapamil up to 100 μM and NAC up to 1.5 mM did not have any adverse effects on the expression of tyrosine hydroxylase in the noradrenergic neurons of the arch-associated cluster (AAC) located near the heart. NAC did not change cysteine levels in the embryos suggesting that the beneficial effect of NAC on verapamil toxicity may not involve its antioxidant property. In our search for compounds that can prevent CCB toxicity, this study, for the first time, demonstrates protective effects of NAC against verapamil's adverse effects on the heart.

Nifedipine toxicity is exacerbated by acetyl l-carnitine but alleviated by low-dose ketamine in zebrafish in vivo

Calcium channel blocker (CCB) poisoning is a common and sometimes life-threatening emergency. Our previous studies have shown that acetyl l-carnitine (ALCAR) prevents cardiotoxicity and developmental toxicity induced by verapamil, a CCB used to treat patients with hypertension. Here, we tested whether toxicities of nifedipine, a dihydropyridine CCB used to treat hypertension, can also be mitigated by co-treatment with ALCAR. In the zebrafish embryos at three different developmental stages, nifedipine induced developmental toxicity with pericardial sac edema in a dose-dependent manner, which were surprisingly exacerbated with ALCAR co-treatment. Even with low-dose nifedipine (5 μm), when the pericardial sac looked normal, ALCAR co-treatment showed pericardial sac edema. We hypothesized that toxicity by nifedipine, a vasodilator, may be prevented by ketamine, a known vasoconstrictor. Nifedipine toxicity in the embryos was effectively prevented by co-treatment with low (subanesthetic) doses (25-100 μm added to the water) of ketamine, although a high dose of ketamine (2 mm added to the water) partially prevented the toxicity.As expected of a CCB, nifedipine either in the presence or absence of ketamine-reduced metabolic reactive oxygen species (ROS), a downstream product of calcium signaling, in the rapidly developing digestive system. However, nifedipine induced ROS in the trunk region that showed significantly stunted growth indicating that the tissues under stress potentially produced pathologic ROS. To the best of our knowledge, these studies for the first time show that nifedipine and the dietary supplement ALCAR together induce adverse effects while providing evidence on the therapeutic efficacy of subanesthetic doses of ketamine against nifedipine toxicity in vivo.