Nádia Maria Martins

Cisplatin-induced nephrotoxicity and targets of nephroprotection: an update

Cisplatin is a highly effective antitumor agent whose clinical application is limited by the inherent nephrotoxicity. The current measures of nephroprotection used in patients receiving cisplatin are not satisfactory, and studies have focused on the investigation of new possible protective strategies. Many pathways involved in cisplatin nephrotoxicity have been delineated and proposed as targets for nephroprotection, and many new potentially protective agents have been reported. The multiple pathways which lead to renal damage and renal cell death have points of convergence and share some common modulators. The most frequent event among all the described pathways is the oxidative stress that acts as both a trigger and a result. The most exploited pathways, the proposed protective strategies, the achievements obtained so far as well as conflicting data are summarized and discussed in this review, providing a general view of the knowledge accumulated with past and recent research on this subject.

Carvedilol protects against cisplatin-induced oxidative stress, redox state unbalance and apoptosis in rat kidney mitochondria.

Cisplatin is a highly effective chemotherapeutic agent which causes severe nephrotoxicity. Studies have suggested that reactive oxygen species, mainly generated in mitochondria, play a central role in cisplatin-induced renal damage. A wide range of antioxidants have been evaluated as possible protective agents against cisplatin-induced nephrotoxicity; however a safe and efficacious compound has not yet been found. The present study is the first to evaluate the protective potential of carvedilol, a beta-blocker with strong antioxidant properties, against the mitochondrial oxidative stress and apoptosis in kidney of rats treated with cisplatin. The following cisplatin-induced toxic effects were prevented by carvedilol: increased plasmatic levels of creatinine and blood urea nitrogen (BUN); lipid peroxidation, oxidation of cardiolipin; oxidation of protein sulfhydryls; depletion of the non-enzymatic antioxidant defense and increased activity of caspase-3. Carvedilol per se did not present any effect on renal mitochondria. It was concluded that carvedilol prevents mitochondrial dysfunction and renal cell death through the protection against the oxidative stress and redox state unbalance induced by cisplatin. The association of carvedilol to cisplatin chemotherapy was suggested as a possible strategy to minimize the nephrotoxicity induced by this antitumor agent.

Carvedilol protects against the renal mitochondrial toxicity induced by cisplatin in rats.

The clinical use of cisplatin is highly limited by its nephrotoxicity, which has been associated with mitochondrial dysfunction. We investigated the protective effect of carvedilol, an antihypertensive with strong antioxidant properties, against the nephrotoxicity induced by cisplatin in rats. Carvedilol was able to counteract the renal damage by preventing the mitochondrial dysfunction induced by cisplatin. The mitochondrial eletrochemical potential, calcium uptake, respiration and the phosphorylative capacity were preserved by the co-administration of carvedilol. The mechanism of protection probably does not involve alterations in the cellular and sub-cellular distribution of cisplatin. The study suggests that carvedilol is a potential drug for the adjuvant nephroprotective therapy during cisplatin chemotherapy.

Involvement of oxidative stress in the hepatotoxicity induced by aromatic antiepileptic drugs

The use of the classic aromatic antiepileptic drugs (AAEDs) has recently been expanded to a broad spectrum of psychiatric and neurological disorders. However, the clinical use of these drugs is limited by several adverse effects, mainly idiosyncratic hepatotoxicity. AAED-induced hepatotoxicity has been attributed to a defective detoxification by the epoxide hydrolase and accumulation of arene oxides. The underlying mechanism has been proposed as immune-mediated, but direct toxicity has also been suggested. In general, idiosyncratic drug-induced hepatotoxicity may be mediated, at least in part, by oxidative stress. On the other hand, the oxidative stress induced by the AAED metabolites has not been demonstrated yet. Therefore, in the present study we have evaluated the induction of oxidative stress by three classical AAEDs: carbamazepine, phenytoin and phenobarbital as well as by their metabolites. The toxic effects of the metabolites were evaluated by incubating the drug with rat liver microsomes. The AAED-induced oxidative stress was demonstrated by the increased malondialdehyde levels, oxidation of cardiolipin; oxidation of sulfhydryl proteins and alteration of the cellular redox status. Results suggest that the hepatotoxicity associated with AAED might be mediated by the oxidative stress induced by the drugs metabolites.

Caffeic acid phenethyl ester (CAPE) protects PC12 cells from MPP+ toxicity by inducing the expression of neuron-typical proteins.

Neurite loss is an early event in neurodegenerative diseases; therefore, the regeneration of the network of neurites constitutes an interesting strategy of treatment for such disorders. Neurotrophic factors play a critical role in neuronal regeneration, but their clinical use is limited by their inability to cross the blood brain barrier. Oxidative and inflammatory events are implicated in neurodegeneration and antioxidant compounds have been suggested as potential neuroprotectors. The protective potential of CAPE (caffeic acid phenethyl ester) has been shown in different models of neurotoxicity (in vitro and in vivo) and it has been associated with immune-modulatory, antioxidant and anti-inflammatory properties; however, other mechanisms might be involved. The present study demonstrates that CAPE protects PC12 cells from the cellular death induced by the dopaminergic neurotoxin MPP(+) by increasing the network of neurites. Results showed that CAPE induced the formation, elongation and ramification of neurites in PC12 cells non-stimulated with NGF (nerve growth factor) and inhibited the shortage of neurites induced by the dopaminergic neurotoxin. These effects were associated with increased expression of neuron-typical proteins responsible for axonal growth (GAP-43) and synaptogenesis (synaptophysin and synapsin I). It is noteworthy that, unlike neurotrophins, CAPE would be able to cross the blood brain barrier and exert its neurotrophic effects in the brain. This study corroborates the therapeutic potential of CAPE in neurodegenerative diseases while proposes the involvement of neuroplasticity in the mechanism of neuroprotection.

The neuroprotection of cannabidiol against MPP⁺-induced toxicity in PC12 cells involves trkA receptors, upregulation of axonal and synaptic proteins, neuritogenesis, and might be relevant to Parkinson's disease.

Cannabidiol (CBD) is a non-psychoactive constituent of Cannabis sativa with potential to treat neurodegenerative diseases. Its neuroprotection has been mainly associated with anti-inflammatory and antioxidant events; however, other mechanisms might be involved. We investigated the involvement of neuritogenesis, NGF receptors (trkA), NGF, and neuronal proteins in the mechanism of neuroprotection of CBD against MPP(+) toxicity in PC12 cells. CBD increased cell viability, differentiation, and the expression of axonal (GAP-43) and synaptic (synaptophysin and synapsin I) proteins. Its neuritogenic effect was not dependent or additive to NGF, but it was inhibited by K252a (trkA inhibitor). CBD did not increase the expression of NGF, but protected against its decrease induced by MPP(+), probably by an indirect mechanism. We also evaluated the neuritogenesis in SH-SY5Y cells, which do not express trkA receptors. CBD did not induce neuritogenesis in this cellular model, which supports the involvement of trkA receptors. This is the first study to report the involvement of neuronal proteins and trkA in the neuroprotection of CBD. Our findings suggest that CBD has a neurorestorative potential independent of NGF that might contribute to its neuroprotection against MPP(+), a neurotoxin relevant to Parkinsons disease.

A tripeptide isolated from Bothrops atrox venom has neuroprotective and neurotrophic effects on a cellular model of Parkinson’s disease

Parkinsons disease (PD) is the second most common neurodegenerative disorder; however, there is no treatment able to prevent the loss of dopaminergic neurons or its consequences. Trophic factors such as NGF and BDNF has positive effects on different disorders of the brain, including neurodegeneration. Additionally, studies have suggested the use of venom peptides as a therapeutic strategy for neurological disorders. Therefore, in the present study, we investigated the neuroprotective activity of a peptide isolated from Bothrops atrox venom and its trophic ability by using a cellular model of dopaminergic neurotoxicity induced by 1-methyl-4-phenylpyridinium (MPP(+)) in PC12 cells. We showed that it decreased the activities of the apoptotic proteases caspase-9 (mitochondrial) and caspase-3 (executor) and increased cell viability and proliferation in this model. Additionally, it increased neuritogenesis in non-treated PC12 cells (neuronal model) as well as in PC12 cells treated with the dopaminergic neurotoxin. The amino acid sequence of the peptide was identified as Glutamic acid-Valine-Tryptophan (Glu-Val-Trp). These findings suggest that this tripeptide has the potential to protect against the dopaminergic neurons loss and that trophic stimulation of neuroplasticity might be involved in its mechanism of neuroprotection.

Low-molecular-mass peptides from the venom of the Amazonian viper Bothrops atrox protect against brain mitochondrial swelling in rat: Potential for neuroprotection

The neurodegenerative diseases are important causes of morbidity and mortality in Western countries. Common mechanisms of toxicity involving mitochondrial damage have been suggested; however, a definitive treatment has not yet been found. Therefore, there has been great interest in the development of mitochondria-targeted protective compounds for the treatment of neuropathies. Animal toxins represent a promising source of new molecules with neuroprotective activity and potential to originate new drugs. We present here the effects of a low-molecular-mass peptides fraction (Ba-V) from Bothrops atrox snake venom, on rat brain mitochondrial function. Ba-V did not induce the mitochondrial swelling and moreover, was as effective as cyclosporin A (CsA) to inhibit the calcium/phosphate-induced swelling, which indicates its potential to prevent the mitochondrial permeability transition (MPT). The membrane electrochemical potential, the oxygen consumption during states-3 and -4 respirations as well as the respiratory control ratio (RCR) were not affected by Ba-V. Additionally, Ba-V did not induce reactive oxygen species (ROS) generation. Interestingly, Ba-V did not protect against the generation of ROS induced by t-BOH, which suggests a protection mechanism other than ROS scavenging. Given the important role of the mitochondrial damage and, more specifically, of MPT, in the development of neuropathies, Ba-V might be useful in the future strategies for the treatment of these diseases.

Non-cytotoxic Concentration of Cisplatin Decreases Neuroplasticity-Related Proteins and Neurite Outgrowth Without Affecting the Expression of NGF in PC12 Cells

Cisplatin is the most effective and neurotoxic platinum chemotherapeutic agent. It induces a peripheral neuropathy characterized by distal axonal degeneration that might progress to degeneration of cell bodies and apoptosis. Most symptoms occur nearby distal axonal branches and axonal degeneration might induce peripheral neuropathy regardless neuronal apoptosis. The toxic mechanism of cisplatin has been mainly associated with DNA damage, but cisplatin might also affect neurite outgrowth. Nevertheless, the neurotoxic mechanism of cisplatin remains unclear. We investigated the early effects of cisplatin on axonal plasticity by using non-cytotoxic concentrations of cisplatin and PC12 cells as a model of neurite outgrowth and differentiation. PC12 cells express NGF-receptors (trkA) and respond to NGF by forming neurites, branches and synaptic vesicles. For comparison, we used a neuronal model (SH-SY5Y cells) that does not express trkA nor responds to NGF. Cisplatin did not change NGF expression in PC12 cells and decreased neurite outgrowth in both models, suggesting a NGF/trkA independent mechanism. It also reduced axonal growth (GAP-43) and synaptic (synapsin I and synaptophysin) proteins in PC12 cells, without inducing mitochondrial damage or apoptosis. Therefore, cisplatin might affect axonal plasticity before DNA damage, NGF/trkA down-regulation, mitochondrial damage or neuronal apoptosis. This is the first study to show that neuroplasticity-related proteins might be early targets of the neurotoxic action of cisplatin and their role on cisplatin-induced peripheral neuropathy should be investigated in vivo.