Prospective analysis of plasma amyloid beta and postoperative delirium in the Interventions for Postoperative Delirium: Biomarker-3 study.

BACKGROUND: The effect of postoperative delirium on the amyloid cascade of Alzheimer's dementia is poorly understood. Using early postoperative plasma biomarkers, we explored whether surgery and delirium are associated with changes in amyloid pathways. METHODS: We analysed data from 100 participants in the Interventions for Postoperative Delirium: Biomarker-3 (IPOD-B3) cohort study in the USA (NCT03124303 and NCT01980511), which recruited participants aged >65 yr undergoing non-intracranial surgery. We assessed the relationship between the change in plasma amyloid beta ratio (AßR; Aß42:Aß40) and delirium incidence (defined by the 3-Minute Diagnostic Confusion Assessment Method) and severity (quantified by the Delirium Rating Scale-Revised-98, the study's primary outcome). We also tested the relationship between plasma amyloid beta and intraoperative variables. RESULTS: Across all participants, the plasma AßR increased from the preoperative period to postoperative Day 1 (Wilcoxon P<0.001). However, this increase was not associated with delirium incidence (Wilcoxon P=0.22) or peak severity after adjusting for confounders (log[incidence rate ratio]=0.43; P=0.14). Postoperative Day 1 change in plasma AßR was not associated with postoperative Day 1 change in plasma tau, neurofilament light, or inflammatory markers (interleukin [IL]-1ß, IL-1Ra, IL-2, IL-4, IL-6, IL-8, IL-10, and IL-12), or with operative time or low intraoperative arterial pressure. CONCLUSIONS: Perioperative changes in plasma amyloid do not appear to be associated with postoperative delirium. Our findings do not support associations of dynamic changes in amyloid with postoperative delirium. CLINICAL TRIAL REGISTRATION: .NCT03124303 and NCT01980511.

Sevoflurane dose and postoperative delirium: a prospective cohort analysis.

BACKGROUND: Recent trials are conflicting as to whether titration of anaesthetic dose using electroencephalography monitoring reduces postoperative delirium. Titration to anaesthetic dose itself might yield clearer conclusions. We analysed our observational cohort to clarify both dose ranges for trials of anaesthetic dose and biological plausibility of anaesthetic dose influencing delirium. METHODS: We analysed the use of sevoflurane in an ongoing prospective cohort of non-intracranial surgery. Of 167 participants, 118 received sevoflurane and were aged >65 yr. We tested associations between age-adjusted median sevoflurane (AMS) minimum alveolar concentration fraction or area under the sevoflurane time×dose curve (AUC-S) and delirium severity (Delirium Rating Scale-98). Delirium incidence was measured with 3-minute Diagnostic Confusion Assessment Method (3D-CAM) or CAM-ICU. Associations with previously identified delirium biomarkers (interleukin-8, neurofilament light, total tau, or S100B) were tested. RESULTS: Delirium severity did not correlate with AMS (Spearman's ρ=-0.014, P=0.89) or AUC-S (ρ=0.093, P=0.35), nor did delirium incidence (AMS Wilcoxon P=0.86, AUC-S P=0.78). Further sensitivity analyses including propofol dose also demonstrated no relationship. Linear regression confirmed no association for AMS in unadjusted (log (IRR)=-0.06 P=0.645) or adjusted models (log (IRR)=-0.0454, P=0.735). No association was observed for AUC-S in unadjusted (log (IRR)=0.00, P=0.054) or adjusted models (log (IRR)=0.00, P=0.832). No association of anaesthetic dose with delirium biomarkers was identified (P>0.05). CONCLUSION: Sevoflurane dose was not associated with delirium severity or incidence. Other biological mechanisms of delirium, such as inflammation and neuronal injury, appear more plausible than dose of sevoflurane. CLINICAL TRIAL REGISTRATION: NCT03124303, NCT01980511.

Postoperative delirium and changes in the blood-brain barrier, neuroinflammation, and cerebrospinal fluid lactate: a prospective cohort study.

BACKGROUND: Case-control studies have associated delirium with blood-brain barrier (BBB) permeability. However, this approach cannot determine whether delirium is attributable to high pre-existing permeability or to perioperative changes. We tested whether perioperative changes in cerebrospinal fluid/plasma albumin ratio (CPAR) and plasma S100B were associated with delirium severity. METHODS: Participants were recruited to two prospective cohort studies of non-intracranial surgery (NCT01980511, NCT03124303, and NCT02926417). Delirium severity was assessed using the Delirium Rating Scale-98. Delirium incidence was diagnosed with the 3D-Confusion Assessment Method (3D-CAM) or CAM-ICU (CAM for the ICU). CSF samples from 25 patients and plasma from 78 patients were analysed for albumin and S100B. We tested associations between change in CPAR (n=11) and S100B (n=61) and delirium, blood loss, CSF interleukin-6 (IL-6), and CSF lactate. RESULTS: The perioperative increase in CPAR and S100B correlated with delirium severity (CPAR ρ=0.78, P=0.01; S100B ρ=0.41, P<0.001), delirium incidence (CPAR P=0.012; S100B P<0.001) and CSF IL-6 (CPAR ρ=0.66 P=0.04; S100B ρ=0.75, P=0.025). Linear mixed-effect analysis also showed that decreased levels of S100B predicted recovery from delirium symptoms (P=0.001). Linear regression demonstrated that change in plasma S100B was independently associated with surgical risk, cardiovascular surgery, blood loss, and hypotension. Blood loss also correlated with CPAR (ρ=0.64, P=0.04), S100B (ρ=0.70, P<0.001), CSF lactate (R=0.81, P=0.01), and peak delirium severity (ρ=0.36, P=0.01). CONCLUSION: Postoperative delirium is associated with a breakdown in the BBB. This increased permeability is dynamic and associated with a neuroinflammatory and lactate response. Strategies to mitigate blood loss may protect the BBB.

A 'toothache tree' alkylamide inhibits Aδ mechanonociceptors to alleviate mechanical pain.

In traditional medicine, the 'toothache tree' and other plants of the Zanthoxylum genus have been used to treat inflammatory pain conditions, such as toothache and rheumatoid arthritis. Here we examined the cellular and molecular mechanisms underlying the analgesic properties of hydroxy-α-sanshool, the active alkylamide produced by Zanthoxylum plants. Consistent with its analgesic effects in humans, sanshool treatment in mice caused a selective attenuation of mechanical sensitivity under naïve and inflammatory conditions, with no effect on thermal sensitivity. To elucidate the molecular mechanisms by which sanshool attenuates mechanical pain, we performed single fibre recordings, calcium imaging and whole-cell electrophysiology of cultured sensory neurons. We found that: (1) sanshool potently inhibits Aδ mechanonociceptors that mediate both sharp acute pain and inflammatory pain; (2) sanshool inhibits action potential firing by blocking voltage-gated sodium currents in a subset of somatosensory neurons, which express a unique combination of voltage-gated sodium channels; and (3) heterologously expressed Nav1.7 is most strongly inhibited by sanshool as compared to other sodium channels expressed in sensory neurons. These results suggest that sanshool targets voltage-gated sodium channels on Aδ mechanosensory nociceptors to dampen excitability and thus induce 'fast pain' analgesia.

TRPA1 mediates mechanical sensitization in nociceptors during inflammation.

Inflammation is a part of the body's natural response to tissue injury which initiates the healing process. Unfortunately, inflammation is frequently painful and leads to hypersensitivity to mechanical stimuli, which is difficult to treat clinically. While it is well established that altered sensory processing in the spinal cord contributes to mechanical hypersensitivity (central sensitization), it is still debated whether primary afferent neurons become sensitized to mechanical stimuli after tissue inflammation. We induced inflammation in C57BL/6 mice via intraplantar injection of Complete Freund's Adjuvant. Cutaneous C fibers exhibited increased action potential firing to suprathreshold mechanical stimuli. We found that abnormal responses to intense mechanical stimuli were completely suppressed by acute incubation of the receptive terminals with the TRPA1 inhibitor, HC-030031. Further, elevated responses were predominantly exhibited by a specific subgroup of C fibers, which we determined to be C-Mechano Cold sensitive fibers. Thus, in the presence of HC-030031, C fiber mechanical responses in inflamed mice were not different than responses in saline-injected controls. We also demonstrate that injection of the HC-030031 compound into the hind paw of inflamed mice alleviates behavioral mechanical hyperalgesia without affecting heat hyperalgesia. Further, we pharmacologically anesthetized the TRPA1-expressing fibers in vivo by co-injecting the membrane-impermeable sodium channel inhibitor QX-314 and the TRPA1 agonist cinnamaldehyde into the hind paw. This approach also alleviated behavioral mechanical hyperalgesia in inflamed mice but left heat hypersensitivity intact. Our findings indicate that C-Mechano Cold sensitive fibers exhibit enhanced firing to suprathreshold mechanical stimuli in a TRPA1-dependent manner during inflammation, and that input from these fibers drives mechanical hyperalgesia in inflamed mice.

Impaired sensory nerve function and axon morphology in mice with diabetic neuropathy.

Diabetes is the most prevalent metabolic disorder in the United States, and between 50% and 70% of diabetic patients suffer from diabetes-induced neuropathy. Yet our current knowledge of the functional changes in sensory nerves and their distal terminals caused by diabetes is limited. Here, we set out to investigate the functional and morphological consequences of diabetes on specific subtypes of cutaneous sensory nerves in mice. Diabetes was induced in C57Bl/6 mice by a single intraperitoneal injection of streptozotocin. After 6-8 wk, mice were characterized for behavioral sensitivity to mechanical and heat stimuli followed by analysis of sensory function using teased nerve fiber recordings and histological assessment of nerve fiber morphology. Diabetes produced severe functional impairment of C-fibers and rapidly adapting Aß-fibers, leading to behavioral hyposensitivity to both mechanical and heat stimuli. Electron microscopy images showed that diabetic nerves have axoplasm with more concentrated organelles and frequent axon-myelin separations compared with control nerves. These changes were restricted to the distal nerve segments nearing their innervation territory. Furthermore, the relative proportion of Aß-fibers was reduced in diabetic skin-nerve preparations compared with nondiabetic control mice. These data identify significant deficits in sensory nerve terminal function that are associated with distal fiber loss, morphological damage, and behavioral hyposensitivity in diabetic C57Bl/6 mice. These findings suggest that diabetes damages sensory nerves, leading to functional deficits in sensory signaling that underlie the loss of tactile acuity and pain sensation associated with insensate diabetic neuropathy.

Physiological basis of tingling paresthesia evoked by hydroxy-alpha-sanshool.

Hydroxy-alpha-sanshool, the active ingredient in plants of the prickly ash plant family, induces robust tingling paresthesia by activating a subset of somatosensory neurons. However, the subtypes and physiological function of sanshool-sensitive neurons remain unknown. Here we use the ex vivo skin-nerve preparation to examine the pattern and intensity with which the sensory terminals of cutaneous neurons respond to hydroxy-alpha-sanshool. We found that sanshool excites virtually all D-hair afferents, a distinct subset of ultrasensitive light-touch receptors in the skin and targets novel populations of Abeta and C fiber nerve afferents. Thus, sanshool provides a novel pharmacological tool for discriminating functional subtypes of cutaneous mechanoreceptors. The identification of sanshool-sensitive fibers represents an essential first step in identifying the cellular and molecular mechanisms underlying tingling paresthesia that accompanies peripheral neuropathy and injury.