Preclinical evidence for mitochondrial DNA as a potential blood biomarker for chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a serious dose-limiting side effect of several first-line chemotherapeutic agents including paclitaxel, oxaliplatin and bortezomib, for which no predictive marker is currently available. We have previously shown that mitochondrial dysfunction is associated with the development and maintenance of CIPN. The aim of this study was to evaluate the potential use of mitochondrial DNA (mtDNA) levels and complex I enzyme activity as blood biomarkers for CIPN. Real-time qPCR was used to measure mtDNA levels in whole blood collected from chemotherapy- and vehicle-treated rats at three key time-points of pain-like behaviour: prior to pain development, at the peak of mechanical hypersensitivity and at resolution of pain-like behaviour. Systemic oxaliplatin significantly increased mtDNA levels in whole blood prior to pain development. Furthermore, paclitaxel- and bortezomib-treated animals displayed significantly higher levels of mtDNA at the peak of mechanical hypersensitivity. Mitochondrial complex I activity in whole blood was assessed with an ELISA-based Complex I Enzyme Activity Dipstick Assay. Complex I activity was not altered by any of the three chemotherapeutic agents, either prior to or during pain-like behaviour. These data demonstrate that blood levels of mtDNA are altered after systemic administration of chemotherapy. Oxaliplatin, in particular, is associated with higher mtDNA levels before animals show any pain-like behaviour, thus suggesting a potential role for circulating mtDNA levels as non-invasive predictive biomarker for CIPN.

Detection of extended-spectrum β-lactam, AmpC and carbapenem resistance in Enterobacteriaceae in beef cattle in Great Britain in 2015

AIMS

This study investigated the occurrence and genetic diversity of Enterobacteriaceae with extended-spectrum β-lactamase (ESBL)-, AmpC- and carbapenemase-mediated resistance in British beef cattle, and related risk factors.

METHODS AND RESULTS

Faecal samples (n = 776) were obtained from farms in England and Wales (n = 20) and Scotland (n = 20) in 2015. Isolates from selective agars were identified by MALDI ToF mass spectrometry. Selected isolates were characterized by multiplex PCR (bla_{CTX -M,} bla_{OXA ,} bla_SHV and bla_TEM genes), whole-genome sequencing (WGS), minimum inhibitory concentrations and pulsed-field gel electrophoresis. None of the faecal samples yielded carbapenem-resistant Escherichia coli. Ten (25%) of the farms tested positive for ESBL-producing CTX-M Enterobacteriaceae, 15 (37·5%) of the farms were positive for AmpC phenotype E. coli and none were positive for carbapenem-resistant E. coli. WGS showed a total of 30 different resistance genes associated with E. coli, Citrobacter and Serratia from ESBL agars, and colocation of resistance genes with bla_{CTX -M1} . Buying bulls and bringing in fattening cattle from another farm were identified as significant risk factors for positive samples harbouring CTX-M Enterobacteriaceae or AmpC phenotype E. coli respectively.

CONCLUSIONS

Beef cattle on a proportion of farms in GB carry ESBL-producing Enterobacteriaceae. Factors, such as operating as a closed herd, may have an important role in reducing introduction and transmission of resistant Enterobacteriaceae. The results indicate management factors may play an important role in impacting ESBL prevalence. In particular, further study would be valuable to understand the impact of maintaining a closed herd on reducing the introduction of resistant Enterobacteriaceae.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study showing the presence of ESBL-producing Enterobacteriaceae in British beef cattle.

Characterization of a rat model of bortezomib-induced painful neuropathy

Background and Purpose

Bortezomib (Velcade®) is a breakthrough treatment for multiple myeloma, significantly improving patient survival. However, its use is limited by painful neuropathy often resulting in dose reduction/cessation of first‐line treatment due to lack of treatment. The aim of this study was to characterize a clinically relevant rat model of bortezomib‐induced painful neuropathy, using established evoked measures and novel ethological techniques, to aid drug discovery.

Experimental Approach

Adult male Sprague–Dawley rats were injected i.p. with 0.1 and 0.2 mg·kg⁻¹ bortezomib, or its vehicle, on days 0, 3, 7 and 10. Multiple behavioural approaches were utilized: mechanical hypersensitivity, cold allodynia, heat hypersensitivity, motor co‐ordination, burrowing and voluntary wheel running. At maximal bortezomib‐induced mechanical hypersensitivity, 200 mg·kg⁻¹ ethosuximide/vehicle and 100 mg·kg⁻¹ phenyl N‐tert‐butylnitrone (PBN)/vehicle were administered i.p. in separate experiments, and mechanical hypersensitivity assessed 1, 3 and 24 h later.

Key Results

Bortezomib induced dose‐related mechanical hypersensitivity for up to 80 days. Bortezomib induced short‐term cold allodynia, but no significant change in heat hypersensitivity, motor co‐ordination, voluntary wheel running and burrowing behaviour compared to vehicle‐treated controls. Systemic PBN and ethosuximide significantly ameliorated bortezomib‐induced mechanical hypersensitivity.

Conclusions and Implications

These data characterize a reproducible rat model of clinical‐grade bortezomib‐induced neuropathy demonstrating long‐lasting pain behaviours to evoked stimuli. Inhibition by ethosuximide and PBN suggests involvement of calcium and/or ROS in bortezomib‐induced painful neuropathy. These drugs could be used as preclinical positive controls to assess novel analgesics. As ethosuximide is widely used clinically, translation to the clinic to treat bortezomib‐induced painful neuropathy may be possible.

Oxidative stress in the development, maintenance and resolution of paclitaxel-induced painful neuropathy

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ROS levels assessed in peripheral and central sensory neurons following paclitaxel.

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Increased ROS levels seen in non-peptidergic neurons prior to paclitaxel-induced pain.

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Elevated ROS levels in spinal neurons, but not microglia/astrocytes, after paclitaxel.

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Assayed activity of main antioxidant enzymes during paclitaxel-evoked pain timecourse.

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Inadequate antioxidant response suggests elevated ROS sustains paclitaxel-evoked pain.

Paclitaxel is a first-line chemotherapeutic with the major dose-limiting side effect of painful neuropathy. Previous preclinical studies indicate mitochondrial dysfunction and oxidative stress are associated with this disorder; however no direct assessment of reactive oxygen species (ROS) levels and antioxidant enzyme activity in sensory neurons following paclitaxel has been undertaken. As expected, repeated low doses of systemic paclitaxel in rats induced long-lasting pain behaviour with a delayed onset, akin to the clinical scenario. To elucidate the role of ROS in the development and maintenance of paclitaxel-induced painful neuropathy, we have assessed ROS and antioxidant enzyme activity levels in the nociceptive system in vivo at three key behavioural time-points; prior to pain onset (day 7), peak pain severity and pain resolution. In isolated dorsal root ganglia (DRG) neurons, ROS levels were unchanged following paclitaxel-exposure in vitro or in vivo. ROS levels were further assessed in DRG and spinal cord in vivo following intrathecal MitoTracker®RedCM-H₂XRos administration in paclitaxel-/vehicle-treated rats. ROS levels were increased at day 7, specifically in non-peptidergic DRG neurons. In the spinal cord, neuronally-derived ROS was increased at day 7, yet ROS levels in microglia and astrocytes were unaltered. In DRG, CuZnSOD and glutathione peroxidase (GPx) activity were increased at day 7 and peak pain time-points, respectively. In peripheral sensory nerves, CuZnSOD activity was increased at day 7, and at peak pain, MnSOD, CuZnSOD and GPx activity were increased. Catalase activity was unaltered in DRG and saphenous nerves. These data suggest that neuronally-derived mitochondrial ROS, accompanied with an inadequate endogenous antioxidant enzyme response, are contributory factors in paclitaxel-induced painful neuropathy.