Delirium, sigma-1 receptors, dopamine, and glutamate: how does haloperidol keep the genie in the bottle?*

Reactivity to neural tissue epitopes, aquaporin 4 and heat shock protein 60 is associated with activated immune-inflammatory pathways and the onset of delirium following hip fracture surgery

OBJECTIVES

Activation of the immune-inflammatory response system (IRS) and a deficiency in the compensatory immunoregulatory system (CIRS), neuronal injuries, and alterations in the glutamate receptor (GlutaR), aquaporin-4 (AQP4) and heat shock protein 60 (HSP60) are involved in delirium. Increased serum levels of neurofilament protein (NFP), glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP) are biomarkers of neuronal injury. This investigation delineates whether elevated IgA/IgG reactivity against those self-antigens is associated with delirium severity and IRS activation.

METHODS

We measured peak Delirium Rating Scale (DRS) scores on days 2 and 3 following surgery in 59 hip fractured older adults, and IgA and IgG antibody levels against MBP, NFP, GFAP and myelin oligodendrocyte glycoprotein (MOG), metabotropic glutamate receptors mGluRs 1 and 5, N-Methyl-D-Aspartate receptor (NMDAR) GLU₁ (NR₁) and GLU₂ (NR₂), APQ4 and HSP60.

RESULTS

The IgA antibody levels against those self-antigens, especially GFAP, MBP and HSP60, strongly predict peak DRS scores on days 2 and 3 post-surgery. IgA reactivity against NMDAR and baseline DRS scores explained 40.6% of the variance in peak DRS scores, while IgA against NMDAR, IgG against MBP and age explained 29.1% of the variance in the IRS/CIRS ratio. There was no correlation between DRS scores and IgG directed against other self-antigens.

CONCLUSIONS

Increased IgA levels against neuronal self-antigens, AQP4 and HSP60 are risk factors for delirium. Polyreactive antibody-associated breakdown of immune tolerance, IRS activation and injuries in the neuronal cytoskeleton, oligodendrocytes, astrocytes, glial cells, and myelin sheath are involved in the pathophysiology of delirium.

Effects of Dexmedetomidine Combined with Sufentanil on Postoperative Delirium in Young Patients After General Anesthesia

Background

This study was designed to evaluate the effects of combined usage of dexmedetomidine (DEX) and sufentanil on young patients with postoperative delirium (POD) after general anesthesia.

Material/Methods

We randomized 100 young patients with POD into 4 groups: Group D, Group S, Group DS1, and Group DS2, with loading and maintenance doses of DEX and/or sufentanil administered according to the experimental protocol. Hemodynamic variables, standard visual analogue scale (VAS) scores, sedation agitation scale (SAS) scores, stress hormones, and inflammatory biomarkers were assessed at 5 time-points: baseline (T₁); 1 h (T₂), 2 h (T₃), 4 h (T₄), and 8 h (T₅) after completion of the loading dose.

Results

At T₃–T₅, hemodynamic indicators in group D were obviously higher than in the other groups (P<0.05). At T₂–T₅, the VAS and SAS scores were noticeably lower than those at T₁ in each group (P<0.05). The VAS and SAS scores were remarkably higher in group D than those in the other groups (P<0.05). Compared with DS1, the incidence of respiratory distress decreased and the incidence of POD increased in group DS2. Compared to T₁, plasma concentrations of epinephrine, norepinephrine, IL-6, and TNF-α all decreased at T₂ and T₅ (P<0.05).

Conclusions

DEX and sufentanil decrease the incidence of POD, ameliorate the abnormities of hemodynamic indicators, and decrease VAS scores, SAS scores, stress hormones, and inflammatory biomarkers, but increase the incidence of respiratory distress. DEX combined with sufentanil may play a synergistic reaction in causing respiratory distress, but remarkably decreases the incidence of POD.

Sigma-1 receptors and animal studies centered on pain and analgesia

INTRODUCTION

Neuropathic pain is difficult to relieve with standard analgesics and tends to be resistant to opioid therapy. Sigma-1 receptors activated during neuropathic injury may sustain pain. Neuropathic injury activates sigma-1 receptors, which results in activation of various kinases, modulates the activity of multiple ion channels, ligand activated ion channels and voltage-gated ion channels; alters monoamine neurotransmission and dampens opioid receptors G-protein activation. Activation of sigma-1 receptors tonically inhibits opioid receptor G-protein activation and thus dampens analgesic responses. Therefore, sigma-1 receptor antagonists are potential analgesics for neuropathic and adjuvants to opioid therapy.

AREAS COVERED

This article reviews the importance of sigma-1 receptors as pain generators in multiple animal models in order to illustrate both the importance of these unique receptors in pathologic pain and the potential benefits to sigma-1 receptor antagonists as analgesics.

EXPERT OPINION

Sigma-1 receptor antagonists have a great potential as analgesics for acute neuropathic injury (herpes zoster, acute postoperative pain and chemotherapy induced neuropathy) and may, as an additional benefit, prevent the development of chronic neuropathic pain. Antagonists are potentially effective as adjuvants to opioid therapy when used early to prevent analgesic tolerance. Drug development is complicated by the complexity of sigma-1 receptor pharmacodynamics and its multiple targets, the lack of a specific sigma-1 receptor antagonist, and potential side effects due to on-target toxicities (cognitive impairment, depression).