Paclitaxel-induced epithelial damage and ectopic MMP-13 expression promotes neurotoxicity in zebrafish

Oxidative stress-dependent MMP-13 activity underlies glucose neurotoxicity

BACKGROUND

A complication of diabetes is neuropathy, a condition of sensory axon degeneration that originates in the epidermis. The mechanisms remain unknown but reactive oxygen species (ROS) have been implicated in this condition. In this study, we assessed the role of ROS and a candidate downstream target, MMP-13 in glucose-induced sensory axon degeneration in zebrafish and mice.

METHODS

The effects of glucose on metabolism and sensory axon degeneration were assessed using qPCR and live imaging. ROS were analyzed using pentafluorobenzene-sulfonyl fluorescein and activation of the NF-κB stress response was determined using Tg(NF-κB:GFP) zebrafish. The role of MMP-13 and ROS in glucose-dependent axon degeneration was determined in zebrafish following treatment with the antioxidant, N-acetylcysteine and the MMP-13 inhibitor, DB04760. Neuropathic mice fed on a high-fat/high-sugar diet were treated with the MMP-13 inhibitor, CL-82198 to assess sensory recovery.

RESULTS

Glucose treatment of zebrafish induced metabolic changes that resemble diabetes. Sensory axon degeneration was mediated by ROS-induced MMP-13 and prevented upon antioxidant treatment or MMP-13 inhibition. MMP-13 inhibition also reversed neuropathy in diabetic mice.

CONCLUSION

We demonstrate that zebrafish are suitable to study glucose-induced neurotoxicity. Given the effects in zebrafish and mice, MMP-13 inhibition may be beneficial in the treatment of human diabetic neuropathy.

Drug Discovery in Fish, Flies, and Worms

Nonmammalian model organisms such as the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and the zebrafish Danio rerio provide numerous experimental advantages for drug discovery including genetic and molecular tractability, amenability to high-throughput screening methods and reduced experimental costs and increased experimental throughput compared to traditional mammalian models. An interdisciplinary approach that strategically combines the study of nonmammalian and mammalian animal models with diverse experimental tools has and will continue to provide deep molecular and genetic understanding of human disease and will significantly enhance the discovery and application of new therapies to treat those diseases. This review will provide an overview of C. elegans, Drosophila, and zebrafish biology and husbandry and will discuss how these models are being used for phenotype-based drug screening and for identification of drug targets and mechanisms of action. The review will also describe how these and other nonmammalian model organisms are uniquely suited for the discovery of drug-based regenerative medicine therapies.

A Mechanistic Understanding of Axon Degeneration in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapeutic agents cause many short and long term toxic side effects to peripheral nervous system (PNS) that drastically alter quality of life. Chemotherapy-induced peripheral neuropathy (CIPN) is a common and enduring disorder caused by several anti-neoplastic agents. CIPN typically presents with neuropathic pain, numbness of distal extremities, and/or oversensitivity to thermal or mechanical stimuli. This adverse side effect often requires a reduction in chemotherapy dosage or even discontinuation of treatment. Currently there are no effective treatment options for CIPN. While the underlying mechanisms for CIPN are not understood, current data identify a “dying back” axon degeneration of distal nerve endings as the major pathology in this disorder. Therefore, mechanistic understanding of axon degeneration will provide insights into the pathway and molecular players responsible for CIPN. Here, we review recent findings that expand our understanding of the pathogenesis of CIPN and discuss pathways that may be shared with the axonal degeneration that occurs during developmental axon pruning and during injury-induced Wallerian degeneration. These mechanistic insights provide new avenues for development of therapies to prevent or treat CIPN.

Chemotherapy-induced peripheral neuropathy: A current review

Chemotherapy-induced peripheral neuropathy (CIPN) is a common dose-limiting side effect experienced by patients receiving treatment for cancer. Approximately 30 to 40% of patients treated with neurotoxic chemotherapy will develop CIPN, and there is considerable variability in its severity between patients. It is often sensory-predominant with pain and can lead to long-term morbidity in survivors. The prevalence and burden of CIPN late effects will likely increase as cancer survival rates continue to improve. In this review, we discuss the approach to peripheral neuropathy in patients with cancer and address the clinical phenotypes and pathomechanisms of specific neurotoxic chemotherapeutic agents. Ann Neurol 2017;81:772-781.

Neurotoxic mechanisms of paclitaxel are local to the distal axon and independent of transport defects

Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting side effect of paclitaxel and other chemotherapeutic agents. Paclitaxel binds and stabilizes microtubules, but the cellular mechanisms that underlie paclitaxel's neurotoxic effects are not well understood. We therefore used primary cultures of adult murine dorsal root ganglion neurons, the cell type affected in patients, to examine leading hypotheses to explain paclitaxel neurotoxicity. We address the role of microtubule hyperstabilization and its downstream effects. Paclitaxel administered at 10-50nM for 1-3days induced retraction bulbs at the tips of axons and arrested axon growth without triggering axon fragmentation or cell death. By correlating the toxic effects and microtubule stabilizing activity of structurally different microtubule stabilizing compounds, we confirmed that microtubule hyperstabilization, rather than an off-target effect, is the likely primary cause of paclitaxel neurotoxicity. We examined potential downstream consequences of microtubule hyperstabilization and found that changes in levels of tubulin posttranslational modifications, although present after paclitaxel exposure, are not implicated in the paclitaxel neurotoxicity we observed in the cultures. Additionally, defects in axonal transport were not implicated as an early, causative mechanism of paclitaxel's toxic effects on dorsal root ganglion neurons. By using microfluidic chambers to selectively treat different parts of the axon with paclitaxel, we found that the distal axon was primarily vulnerable to paclitaxel, indicating that paclitaxel acts directly on the distal axon to induce degenerative effects. Together, our findings point to local effects of microtubule hyperstabilization on the distal-most portion of the axon as an early mediator of paclitaxel neurotoxicity. Because sensory neurons have a unique and ongoing requirement for distal growth in order to reinnervate the epidermis as it turns over, we propose that the ability of paclitaxel to arrest their growth accounts for the selective vulnerability of sensory neurons to paclitaxel neurotoxicity.

Chemotherapy-induced peripheral neuropathy: an update on the current understanding

Chemotherapy-induced peripheral neuropathy is a common side effect of selected chemotherapeutic agents. Previous work has suggested that patients often under report the symptoms of chemotherapy-induced peripheral neuropathy and physicians fail to recognize the presence of such symptoms in a timely fashion. The precise pathophysiology that underlies chemotherapy-induced peripheral neuropathy, in both the acute and the chronic phase, remains complex and appears to be medication specific. Recent work has begun to demonstrate and further clarify potential pathophysiological processes that predispose and, ultimately, lead to the development of chemotherapy-induced peripheral neuropathy. There is increasing evidence that the pathway to neuropathy varies with each agent. With a clearer understanding of how these agents affect the peripheral nervous system, more targeted treatments can be developed in order to optimize treatment and prevent long-term side effects.