The detrimental association between fear of falling and motor performance in older cancer patients with chemotherapy-induced peripheral neuropathy.

BACKGROUND: Cancer patients with chemotherapy-induced peripheral neuropathy (CIPN) are at increased risk of falls and developing fear of falling (FoF). Although FoF may continue to impair motor performance and increase the risk of falling even further, this association remains unexplored in CIPN. RESEARCH QUESTION: Does high FoF in patients with CIPN further deteriorate motor performance beyond the impairment from CIPN-related sensory deficits? METHODS: In this secondary analysis of data collected from two clinical trials, gait parameters during habitual walking condition and postural sway parameters during 30-second quiet standing (eye-open and eyes-closed) were compared among older participants (≥ 65 years) with CIPN and high FoF (CIPN FoF+; n=16), older participants with CIPN and low FoF (CIPN FoF-; n=19) and normal older controls (i.e., non-cancer, non-diabetic, non-neurologic, and non-orthopedic; n=16). We measured gait and postural sway parameters using wearable sensors (BioSensics, Newton, MA, USA), and FoF severity using the Falls Efficacy Scale-International. RESULTS: The largest between-group differences were found in gait speed. The CIPN FoF + group had significantly slower gait speed (0.78 ± 0.21 m/s) than the CIPN FoF- (0.93 ± 0.17 m/s) and normal control groups (1.17 ± 0.13 m/s) (all p < .05; effect sizes = 0.79 and 2.23, respectively). We found a significant association between gait speed and FoF severity (R2 = 0.356; p < .001) across all participants with CIPN. Among participants with CIPN, no significant differences in postural sway parameters were found between the CIPN FoF+and CIPN FoF- groups. SIGNIFICANCE: Our results suggest that gait performance further deteriorates in patients with CIPN and high FoF beyond the impairment from CIPN-related sensory deficits. Our results also suggest further research is needed regarding FoF, and fall risk, as FoF is a simple tool that healthcare providers can use in clinical practice.

A YoeB toxin cleaves both RNA and DNA.

Type II toxin-antitoxin systems contain a toxin protein, which mediates diverse interactions within the bacterial cell when it is not bound by its cognate antitoxin protein. These toxins provide a rich source of evolutionarily-conserved tertiary folds that mediate diverse catalytic reactions. These properties make toxins of interest in biotechnology applications, and studies of the catalytic mechanisms continue to provide surprises. In the current work, our studies on a YoeB family toxin from Agrobacterium tumefaciens have revealed a conserved ribosome-independent non-specific nuclease activity. We have quantified the RNA and DNA cleavage activity, revealing they have essentially equivalent dose-dependence while differing in requirements for divalent cations and pH sensitivity. The DNA cleavage activity is as a nickase for any topology of double-stranded DNA, as well as cleaving single-stranded DNA. AtYoeB is able to bind to double-stranded DNA with mid-micromolar affinity. Comparison of the ribosome-dependent and -independent reactions demonstrates an approximate tenfold efficiency imparted by the ribosome. This demonstrates YoeB toxins can act as non-specific nucleases, cleaving both RNA and DNA, in the absence of being bound within the ribosome.

Identifying a Molecular Mechanism That Imparts Species-Specific Toxicity to YoeB Toxins.

The ribosome-dependent E. coli (Ec) mRNase toxin YoeB has been demonstrated to protect cells during thermal stress. Agrobacterium tumefaciens (At), a plant pathogen, also encodes a YoeB toxin. Initial studies indicated that AtYoeB does not impact the growth of Ec, but its expression is toxic to the native host At. The current work examines this species-specific effect. We establish the highly similar structure and function of Ec and AtYoeB toxins, including the ability of the AtYoeB toxin to inhibit Ec ribosomes in vitro. Comparison of YoeB sequences and structures highlights a four-residue helix between ß-strands 2 and 3 that interacts with mRNA bases within the ribosome. This helix sequence is varied among YoeB toxins, and this variation correlates with bacterial classes of proteobacteria. When the four amino acid sequence of this helix is transplanted from EcYoeB onto AtYoeB, the resulting chimera gains toxicity to Ec cells and lessens toxicity to At cells. The reverse is also true, such that EcYoeB with the AtYoeB helix sequence is less toxic to Ec and gains toxicity to At cultures. We suggest this helix sequence directs mRNA sequence-specific degradation, which varies among proteobacterial classes, and thus controls growth inhibition and YoeB toxicity.

Expression of different ParE toxins results in conserved phenotypes with distinguishable classes of toxicity.

Toxin-antitoxin (TA) systems are found on both chromosomes and plasmids. These systems are unique in that they can confer both fatal and protective effects on bacterial cells-a quality that could potentially be harnessed given further understanding of these TA mechanisms. The current work focuses on the ParE subfamily, which is found throughout proteobacteria and has a sequence identity on average of approximately 12% (similarity at 30%-80%). Our aim is to evaluate the equivalency of chromosomally derived ParE toxin activity depending on its bacterial species of origin. Nine ParE toxins were analyzed, originating from six different bacterial species. Based on the resulting toxicity, three categories can be established: ParE toxins that do not exert toxicity under the experimental conditions, toxins that exert toxicity within the first four hours, and those that exert toxicity only after 10-12 hr of exposure. All tested ParE toxins produce a cellular morphologic change from rods to filaments, consistent with disruption of DNA topology. Analysis of the distribution of filamented cells within a population reveals a correlation between the extent of filamentation and toxicity. No membrane septation is visible along the length of the cell filaments, whereas aberrant lipid blebs are evident. Potent ParE-mediated toxicity is also correlated with a hallmark signature of abortive DNA replication, consistent with the inhibition of DNA gyrase.

The toxin from a ParDE toxin-antitoxin system found in Pseudomonas aeruginosa offers protection to cells challenged with anti-gyrase antibiotics.

Toxin-antitoxin systems are mediators of diverse activities in bacterial physiology. For the ParE-type toxins, their reported role of gyrase inhibition utilized during plasmid-segregation killing indicates they are toxic. However, their location throughout chromosomes leads to questions about function, including potential non-toxic outcomes. The current study has characterized a ParDE system from the opportunistic human pathogen Pseudomonas aeruginosa (Pa). We identified a protective function for this ParE toxin, PaParE, against effects of quinolone and other antibiotics. However, higher concentrations of PaParE are themselves toxic to cells, indicating the phenotypic outcome can vary based on its concentration. Our assays confirmed PaParE inhibition of gyrase-mediated supercoiling of DNA with an IC50 value in the low micromolar range, a species-specificity that resulted in more efficacious inhibition of Escherichia coli derived gyrase versus Pa gyrase, and overexpression in the absence of antitoxin yielded an expected filamentous morphology with multi-foci nucleic acid material. Additional data revealed that the PaParE toxin is monomeric and interacts with dimeric PaParD antitoxin with a KD in the lower picomolar range, yielding a heterotetramer. This work provides novel insights into chromosome-encoded ParE function, whereby its expression can impart partial protection to cultures from selected antibiotics.