Systemic inflammation induced from remote extremity trauma is a critical driver of secondary brain injury

Blast exposure, commonly experienced by military personnel, can cause devastating life-threatening polysystem trauma. Despite considerable research efforts, the impact of the systemic inflammatory response after major trauma on secondary brain injury-inflammation is largely unknown. The aim of this study was to identify markers underlying the susceptibility and early onset of neuroinflammation in three rat trauma models: (1) blast overpressure exposure (BOP), (2) complex extremity trauma (CET) involving femur fracture, crush injury, tourniquet-induced ischemia, and transfemoral amputation through the fracture site, and (3) BOP+CET. Six hours post-injury, intact brains were harvested and dissected to obtain biopsies from the prefrontal cortex, striatum, neocortex, hippocampus, amygdala, thalamus, hypothalamus, and cerebellum. Custom low-density microarray datasets were used to identify, interpret and visualize genes significant (p < 0.05 for differential expression [DEGs]; 86 neuroinflammation-associated) using a custom python-based computer program, principal component analysis, heatmaps and volcano plots. Gene set and pathway enrichment analyses of the DEGs was performed using R and STRING for protein-protein interaction (PPI) to identify and explore key genes and signaling networks. Transcript profiles were similar across all regions in naïve brains with similar expression levels involving neurotransmission and transcription functions and undetectable to low-levels of inflammation-related mediators. Trauma-induced neuroinflammation across all anatomical brain regions correlated with injury severity (BOP+CET > CET > BOP). The most pronounced differences in neuroinflammatory-neurodegenerative gene regulation were between blast-associated trauma (BOP, BOP+CET) and CET. Following BOP, there were few DEGs detected amongst all 8 brain regions, most were related to cytokines/chemokines and chemokine receptors, where PPI analysis revealed Il1b as a potential central hub gene. In contrast, CET led to a more excessive and diverse pro-neuroinflammatory reaction in which Il6 was identified as the central hub gene. Analysis of the of the BOP+CET dataset, revealed a more global heightened response (Cxcr2, Il1b, and Il6) as well as the expression of additional functional regulatory networks/hub genes (Ccl2, Ccl3, and Ccl4) which are known to play a critical role in the rapid recruitment and activation of immune cells via chemokine/cytokine signaling. These findings provide a foundation for discerning pathophysiological consequences of acute extremity injury and systemic inflammation following various forms of trauma in the brain.

Effects of a Subanesthetic Ketamine Infusion on Inflammatory and Behavioral Outcomes after Closed Head Injury in Rats

Traumatic brain injury (TBI) affects millions of people annually, and most cases are classified as mild TBI (mTBI). Ketamine is a potent trauma analgesic and anesthetic with anti-inflammatory properties. However, ketamine's effects on post-mTBI outcomes are not well characterized. For the current study, we used the Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA), which replicates the biomechanics of a closed-head impact with resulting free head movement. Adult male Sprague-Dawley rats sustained a single-session, repeated-impacts CHIMERA injury. An hour after the injury, rats received an intravenous ketamine infusion (0, 10, or 20 mg/kg, 2 h period), during which locomotor activity was monitored. Catheter blood samples were collected at 1, 3, 5, and 24 h after the CHIMERA injury for plasma cytokine assays. Behavioral assays were conducted on post-injury days (PID) 1 to 4 and included rotarod, locomotor activity, acoustic startle reflex (ASR), and pre-pulse inhibition (PPI). Brain tissue samples were collected at PID 4 and processed for GFAP (astrocytes), Iba-1 (microglia), and silver staining (axonal injury). Ketamine dose-dependently altered locomotor activity during the infusion and reduced KC/GRO, TNF-α, and IL-1β levels after the infusion. CHIMERA produced a delayed deficit in rotarod performance (PID 3) and significant axonal damage in the optic tract (PID 4), without significant changes in other behavioral or histological measures. Notably, subanesthetic doses of intravenous ketamine infusion after mTBI did not produce adverse effects on behavioral outcomes in PID 1-4 or neuroinflammation on PID 4. A further study is warranted to thoroughly investigate beneficial effects of IV ketamine on mTBI given multi-modal properties of ketamine in traumatic injury and stress.

Effects of an intravenous ketamine infusion on inflammatory cytokine levels in male and female Sprague-Dawley rats

Background

Ketamine, a multimodal dissociative anesthetic drug, is widely used as an analgesic following traumatic injury. Although ketamine may produce anti-inflammatory effects when administered after injury, the immunomodulatory properties of intravenous (IV) ketamine in a non-inflammatory condition are unclear. In addition, most preclinical studies use an intraperitoneal (IP) injection of ketamine, which limits its clinical translation as patients usually receive an IV ketamine infusion after injury.

Methods

Here, we administered sub-anesthetic doses of a single IV ketamine infusion (0, 10, or 40 mg/kg) to male and female Sprague–Dawley rats over a 2-h period. We collected blood samples at 2- and 4-h post-ketamine infusion to determine plasma inflammatory cytokine levels using multiplex immunoassays.

Results

The 10 mg/kg ketamine infusion reduced spontaneous locomotor activity in male and female rats, while the 40 mg/kg infusion stimulated activity in female, but not male, rats. The IV ketamine infusion produced dose-dependent and sex-specific effects on plasma inflammatory cytokine levels. A ketamine infusion reduced KC/GRO and tumor necrosis factor alpha (TNF-α) levels in both male and female rats, interleukin-6 (IL-6) levels in female rats, and interleukin-10 (IL-10) levels in male rats. However, most cytokine levels returned to control levels at 4-h post-infusion, except for IL-6 levels in male rats and TNF-α levels in female rats, indicating a different trajectory of certain cytokine changes over time following ketamine administration.

Conclusions

The current findings suggest that sub-anesthetic doses of an IV ketamine infusion may produce sex-related differences in the effects on peripheral inflammatory markers in rodents, and further research is warranted to determine potential therapeutic effects of an IV ketamine infusion in an inflammatory condition.

Is Prehospital Ketamine Associated With a Change in the Prognosis of PTSD?

INTRODUCTION

Ketamine is an alternative to opioids for prehospital analgesia following serious combat injury. Limited research has examined prehospital ketamine use, associated injuries including traumatic brain injury (TBI) and PTSD outcomes following serious combat injury.

MATERIALS AND METHODS

We randomly selected 398 U.S. service members from the Expeditionary Medical Encounter Database who sustained serious combat injuries in Iraq and Afghanistan, 2010-2013. Of these 398 patients, 213 individuals had charted prehospital medications. Clinicians reviewed casualty records to identify injuries and all medications administered. Outcomes were PTSD diagnoses during the first year and during the first 2 years postinjury extracted from military health databases. We compared PTSD outcomes for patients treated with either (a) prehospital ketamine (with or without opioids) or (b) prehospital opioids (without ketamine).

RESULTS

Fewer patients received prehospital ketamine (26%, 56 of 213) than only prehospital opioids (69%, 146 of 213) (5%, 11 of 213 received neither ketamine nor opioids). The ketamine group averaged significantly more moderate-to-serious injuries, particularly lower limb amputations and open wounds, compared with the opioid group (Ps < .05). Multivariable regressions showed a significant interaction between prehospital ketamine (versus opioids) and TBI on first-year PTSD (P = .027). In subsequent comparisons, the prehospital ketamine group had significantly lower odds of first-year PTSD (OR = 0.08, 95% CI [0.01, 0.71], P = .023) versus prehospital opioids only among patients who did not sustain TBI. We also report results from separate analyses of PTSD outcomes among patients treated with different prehospital opioids only (without ketamine), either morphine or fentanyl.

CONCLUSIONS

The present results showed that patients treated with prehospital ketamine had significantly lower odds of PTSD during the first year postinjury only among patients who did not sustain TBI. These findings can inform combat casualty care guidelines for use of prehospital ketamine and opioid analgesics following serious combat injury.

An Analysis of Prolonged, Continuous Ketamine Infusions

INTRODUCTION

Opioids carry high risk of dependence, and patients can rapidly build tolerance after repetitive dosing. Low-dose ketamine is an analgesic agent alternative that provides more hemodynamic stability. We sought to describe the effects of prolonged ketamine use in non-burn patients.

MATERIALS AND METHODS

We queried the electronic health system at the Brooke Army Medical Center for patient encounters with ketamine infusions lasting >72 hours. We abstracted data describing demographics, vital signs, ketamine infusion dose and duration, and discharge diagnoses potentially relevant to ketamine side effects.

RESULTS

We identified 194 subjects who met the study inclusion criteria. The median age was 39 years, most were male (67.0%), and most were primarily admitted for a non-trauma reason (59.2%). The mean ketamine drip strength was 43.9 mg/h (95% CI, 36.7-51.1; range 0.1-341.6) and the mean drip length was 130.8 hours (95% CI, 120.3-141.2; range 71-493). Most subjects underwent mechanical ventilation (56.1%) at some point during the infusion and most survived to hospital discharge (83.5%). On a per-day basis, the average heart rate was 93 beats per minute, systolic blood pressure was 128 mmHg, diastolic blood pressure was 71 mmHg, oxygen saturation was 96%, and respiratory rate was 22 respirations per minute.

CONCLUSIONS

We demonstrate that continuous ketamine infusions provide a useful adjunct for analgesia and/or sedation. Further development of this adjunct modality may serve as an alternative agent to opioids.