High-dose propofol triggers short-term neuroprotection and long-term neurodegeneration in primary neuronal cultures from rat embryos

S100 and S100β: biomarkers of cerebral damage in cardiac surgery with or without the use of cardiopulmonary bypass

OBJECTIVE

The present study is to describe the clinical impact of S100 and S100β for the evaluation of cerebral damage in cardiac surgery with or without the use of cardiopulmonary bypass (CPB).

METHODS

Quantitative results of S100 and S100β reported in the literature of the year range 1990-2014 were collected, screened and analyzed.

RESULTS

Cerebrospinal fluid and serum S100 levels showed a same trend reaching a peak at the end of CPB. The cerebrospinal fluid/serum S100 ratio decreased during CPB, reached a nadir at 6 h after CPB and then increased and kept high untill 24 h after CPB. Serum S100 at the end of CPB was much higher in infant than in adults, and in on-pump than in off-pump coronary artery bypass patients. ∆S100 increased with age and CPB time but lack of statistical significances. Patients receiving an aorta replacement had a much higher ∆S100 than those receiving a congenital heart defect repair. Serum S100β reached a peak at the end of CPB, whereas cerebrospinal fluid S100 continued to increase and reached a peak at 6 h after CPB. The cerebrospinal fluid/serum S100β ratio decreased during CPB, increased at the end of CPB, peaked 1 h after CPB, and then decreased abruptly. The increase of serum S100β at the end of CPB was associated with type of operation, younger age, lower core temperature and cerebral damages. ∆S100β displayed a decreasing trend with age, type of operation, shortening of CPB duration, increasing core temperature, lessening severity of cerebral damage and the application of intervenes. Linear correlation analysis revealed that serum S100β concentration at the end of CPB correlated closely with CPB duration.

CONCLUSION

S100 and S100β in cerebrospinal fluid can be more accurate than in the serum for the evaluations of cerebral damage in cardiac surgery. However, cerebrospinal fluid biopsies are limited. But serum S100β and ∆S100β seem to be more sensitive than serum S100 and ∆S100. The cerebral damage in cardiac surgery might be associated with younger age, lower core temperature and longer CPB duration during the operation. Effective intervenes with modified CPB circuit filters or oxygenators and supplemented anesthetic agents or priming components may alleviate the cerebral damage.

Endoplasmic reticulum stress is involved in the neuroprotective effect of propofol

Propofol is a common clinically used intravenous anaesthetic agent with antioxidative property. It has been thought to have neuroprotection in vitro and in vivo. However, the underlying mechanisms remain unclear. Endoplasmic reticulum (ER) stress plays an important role in regulating the signaling pathways concerning cell death and survival. Therefore, we wondered whether the neuroprotective effects of propofol are associated with its regulation on ER stress. In this study, we found that propofol up-regulated BiP and attenuated tunicamycin-induced neural cell death. Propofol pretreatment also inhibited tunicamycin-induced up-regulation of C/EBP homologous protein (CHOP). We also found that propofol or tunicamycin alone increased the levels of spliced XBP1 (XBP1s) and cleaved activating transcription factor 6 (ATF6), an active form of ATF6. However, pretreatment with propofol attenuated the levels of phosphorylated protein kinase receptor-like ER kinase, phosphorylated elF2α, ATF4, and caspase-3, but failed to affect the increase of cleaved ATF6 and XBP1s, induced by tunicamycin. Knockdown endogenous BiP with siRNA abolished the suppression of propofol on tunicamycin-mediated activation of CHOP and caspase-3. Meanwhile, knockdown BiP attenuated the protective effects of propofol on the neural cells exposed to tunicamycin. These data suggest that ER stress is involved in the neuroprotection of propofol via differentially regulating the unfolded protein response pathway, in which BiP plays an important role in initiating the adaptive ER stress and inhibiting the apoptotic ER stress.

Behavioral and toxicological effects of propofol

There is increasing concern about abuse of propofol, a widely-used surgical anesthetic and sedative that is currently not a controlled substance. The purpose of this study was to establish a rat model of the psychoactive effect of subanesthetic doses of propofol that could be useful for confirming abuse liability and for studying mechanisms of propofol abuse. Sprague-Dawley rats were trained to discriminate propofol (10 mg/kg, intraperitoneally) from vehicle (2% methylcellulose). Carisoprodol (100 mg/kg), chlordiazepoxide (10 mg/kg), and dizocilpine (0.1 mg/kg) were tested for substitution for the discriminative-stimulus effects of propofol (10 mg/kg), whereas pentylenetetrazol (10 mg/kg) was tested for antagonism of the discriminative-stimulus effects. Propofol (10 mg/kg) was tested for substitution in rats trained to discriminate carisoprodol from vehicle. Carisoprodol produced 59% propofol-appropriate responding, chlordiazepoxide produced 65% propofol-appropriate responding, and dizocilpine produced 34% propofol-appropriate responding. Pentylenetetrazol decreased propofol-appropriate responding to 41%. Propofol produced 52% carisoprodol-appropriate responding. Mortality rate during training of propofol (10 mg/kg) was 38%. Postmortem examination revealed cardiovascular abnormalities similar to those observed in propofol-infusion syndrome in humans. The results demonstrate that propofol can be trained as a discriminative stimulus. Its discriminative-stimulus effects were more similar to compounds promoting γ-aminobutyric acid-A receptor activity than to a compound inhibiting N-methyl-d-aspartate receptor activity. As propofol has discriminative-stimulus effects similar to known drugs of abuse, and occasions a high-mortality rate, its potential for continued abuse is of particular concern.