Alpha2-adrenoreceptor agonist, dexmedetomidine, alters acute gene expression after global ischemia in gerbils

Transcriptomic response of brain tissue to focused ultrasound-mediated blood-brain barrier disruption depends strongly on anesthesia

Focused ultrasound (FUS) mediated blood-brain barrier disruption (BBBD) targets the delivery of systemically-administered therapeutics to the central nervous system. Preclinical investigations of BBBD have been performed on different anesthetic backgrounds; however, the influence of the choice of anesthetic on the molecular response to BBBD is unknown, despite its potential to critically affect interpretation of experimental therapeutic outcomes. Here, using bulk RNA sequencing, we comprehensively examined the transcriptomic response of both normal brain tissue and brain tissue exposed to FUS-induced BBBD in mice anesthetized with either isoflurane with medical air (Iso) or ketamine/dexmedetomidine (KD). In normal murine brain tissue, Iso alone elicited minimal differential gene expression (DGE) and repressed pathways associated with neuronal signaling. KD alone, however, led to massive DGE and enrichment of pathways associated with protein synthesis. In brain tissue exposed to BBBD (1 MHz, 0.5 Hz pulse repetition frequency, 0.4 MPa peak-negative pressure), we systematically evaluated the relative effects of anesthesia, microbubbles, and FUS on the transcriptome. Of particular interest, we observed that gene sets associated with sterile inflammatory responses and cell-cell junctional activity were induced by BBBD, regardless of the choice of anesthesia. Meanwhile, gene sets associated with metabolism, platelet activity, tissue repair, and signaling pathways, were differentially affected by BBBD, with a strong dependence on the anesthetic. We conclude that the underlying transcriptomic response to FUS-mediated BBBD may be powerfully influenced by anesthesia. These findings raise considerations for the translation of FUS-BBBD delivery approaches that impact, in particular, metabolism, tissue repair, and intracellular signaling.

Molecular targets and mechanism of action of dexmedetomidine in treatment of ischemia/reperfusion injury

Dexmedetomidine (DEX), a highly specific α2-adrenergic agonist, which exhibits anaesthetic-sparing, analgesia and sympatholytic properties. DEX modulates gene expression, channel activation, transmitter release, inflammatory processes and apoptotic and necrotic cell death. It has also been demonstrated to have protective effects in a variety of animal models of ischemia/reperfusion (I/R) injury, including the intestine, myocardial, renal, lung, cerebral and liver. The broad spectrum of biological activities associated with DEX continues to expand, and its diverse effects suggest that it may offer a novel therapeutic approach for the treatment of human diseases with I/R involvement.

The protective effects of dexmedetomidine on the liver and remote organs against hepatic ischemia reperfusion injury in rats

AIM

To investigate the protective effects of dexmedetomidine against hepatic ischemia/reperfusion (IR) injury and hepatic IR induced remote organ injury.

METHODS

Forty Wistar albino rats were divided into the following four groups: sham, dexmedetomidine, IR, and IR + dexmedetomidine. Hepatic ischemia was created by the Pringle maneuver for 30 min followed by a 30 min reperfusion period in the IR and IR + dexmedetomidine groups. The dexmedetomidine and IR + dexmedetomidine groups were administered dexmedetomidine (100 μg/kg, single dose) intraperitoneally after the anesthesia insult. Blood samples and hepatic, renal, and lung tissue specimens were obtained to measure serum and tissue total oxidative activity (TOA), total antioxidant capacity (TAC), paraoxonase (PON-1), and oxidative stress index (OSI) after 60 min in all groups.

RESULTS

According to the biochemical analyses of the samples taken from the serum and the liver, lung, and kidney tissues, when comparing the sham group and the IR group, TOA and OSI values were higher in the IR group, while TAC and PON-1 values were lower (p < 0.05). It was observed that TOA and OSI values were significantly lower, while TAC and PON-1 values increased with dexmedetomidine treatment (p < 0.05). In addition, dexmedetomidine ameliorated hepatic histopathological changes inducing IR, but there were no significant histopathological changes in the remote organs.

CONCLUSION

This study demonstrated that dexmedetomidine markedly reduced the oxidative stress in serum, liver, and remote organs induced by hepatic IR injury, and ameliorated the histopathological damage in the liver.

The effects of dexmedetomidine on mesenteric arterial occlusion-associated gut ischemia and reperfusion-induced gut and kidney injury in rabbits

OBJECTIVE

We assessed the antioxidant activity of dexmedetomidine (Dex) administered during the ischemic period in a rabbit model of mesenteric ischemia/reperfusion (I/R) injury using biochemical and histopathological methods.

METHODS

A total of 24 male New Zealand white rabbits weighing between 2.5 and 3.0 kg were randomly divided into three groups: the sham group (Group S, n = 8), the I/R group (Group I/R, n = 8), and the I/R plus Dex treatment group (Group Dex, n = 8). In the I/R group, ischemia was achieved with 60 min of mesenteric occlusion. The sham group provided normal basal values. The rabbits in Group I/R were operated to achieve I/R. Group Dex received intravenous Dex 30 min after the commencement of reperfusion (10 μg/kg Dex was infused within 10 min, and then a maintenance dose of 10 μg/kg/h Dex was infused intravenously). For the measurement of tissue malondialdehyde, total antioxidant status, total oxidant status, lipid hydroperoxide levels, superoxide dismutase, catalase, and myeloperoxidase activity levels in the renal tissue samples of animals, the rabbits in each group were sacrificed 3 h after reperfusion. The histopathological examination scores were determined using the intestinal and renal tissues.

RESULTS

The mean malondialdehyde, total oxidant status, myeloperoxidase, and lipid hydroperoxide levels were significantly higher in Group I/R than in Groups S and Dex (P < 0.05). There also were significant decreases in the mean total antioxidant status, catalase, and superoxide dismutase activities in Group I/R compared with Groups S and Dex (P < 0.05). The histopathological examination scores of the intestinal and renal tissues were significantly higher in Group I/R compared with Groups S and Dex (P < 0.05).

CONCLUSION

Dex treatment may have biochemical and histopathological benefits by preventing I/R-related cellular damage of intestinal and renal tissues as shown in an experimental mesenteric ischemia model. The preference to use Dex for anesthesia during the mesenteric ischemia procedure may attenuate I/R injury in intestinal and renal tissues.

The effects of dexmedetomidine dosage on cerebral vasospasm in a rat subarachnoid haemorrhage model

We investigated the effect of two different doses of dexmedetomidine on vasospasm in a rat model of subarachnoid haemorrhage (SAH). SAH was induced by injecting 0.3 mL blood into the cisterna magna in all rat groups except the control (Group C). At 1 hour and 24 hours after SAH, 5 microg/kg dexmedetomidine was given to group D5, and 10 microg/kg dexmedetomidine was given to group D10. No medication was administered to the haemorrhage group (Group H). Malondialdehyde (MDA) and paraoxonase (PON) levels were measured at 48 hours after SAH. Mean wall thickness (MWT), mean luminal diameter (MLD), and proliferating cell nuclear antigen (PCNA) expression of the basilar artery were evaluated. MDA levels and MWT were lower in the dexmedetomidine groups. The lowest MDA levels and MWT were found in Group D10. The MLD was lowest in Group H. PCNA expression was observed only in Group D10. We concluded that dexmedetomidine reduces oxidative stress and vasospasm following SAH in a dose-dependent manner.

Alpha2 adrenoreceptor agonist regulates protein kinase C-induced heat shock protein 27 phosphorylation in C6 glioma cells

Dexmedetomidine (Dexmd), a potent and highly specific alpha(2) adrenoreceptor agonist, is an efficient therapeutic agent for sedation. Dexmd has been recently reported to have a neuroprotective effect. Heat shock protein (HSP) 27, a low-molecular weight HSP has been shown to be expressed following cerebral ischemia in astrocytes but not in neurons. HSP27 expression is involved in ischemic tolerance of the brain. This study investigated the effect of Dexmd on HSP27 in rat C6 glioma cells. 12-O-tetradecanoylphorbol-13-actate (TPA), a direct activator of protein kinase C (PKC), stimulated the phosphorylation of HSP27 at Ser82, but not Ser15 in a time-dependent manner. Prostaglandin (PG) E(1) or PGE(2) which activates the adenylyl cyclase-cAMP system as well as forskolin and dibutyryl-cAMP, suppressed the TPA-induced phosphorylation of HSP27. Dexmd reversed the suppression of HSP27 phosphorylation by the adenylyl cyclase-cAMP system. Therefore, these results strongly suggest that Dexmd reverses the suppression of HSP27 phosphorylation by the adenylyl cyclase-cAMP system activation through the inhibition of its system in C6 cells. alpha(2) Adrenoreceptor agonists may therefore show a neuroprotective effect through the modification of HSP27 phosphorylation induced by PKC activation.

Endogenous alpha2-adrenergic receptor-mediated neuroprotection after severe hypoxia in preterm fetal sheep

Central alpha-adrenergic receptor activity is important for fetal adaptation to hypoxia before birth. It is unclear whether it is also important during recovery. We therefore tested the hypothesis that an infusion of the specific alpha(2)-adrenergic receptor antagonist idazoxan (1 mg/kg/h i.v.) from 15 min to 4 h after profound hypoxia induced by 25 min umbilical cord occlusion in fetal sheep at 70% of gestation (equivalent to the 28-32 weeks in humans) would increase neural injury. After 3 days' recovery, idazoxan infusion was associated with a significant increase in neuronal loss in the hippocampus (P<0.05), expression of cleaved caspase-3 (P<0.05), and numbers of activated microglia (P<0.05). There was no significant effect on other neuronal regions or on loss of O4-positive premyelinating oligodendrocytes in the subcortical white matter. Idazoxan was associated with an increase in evolving epileptiform electroencephalographic (EEG) transient activity after occlusion (difference at peak 2.5+/-1.0 vs. 11.7+/-4.7 counts/min, P<0.05) and significantly reduced average spectral edge frequency, but not EEG intensity, from 54 until 72 h after occlusion (P<0.05). Hippocampal neuronal loss was correlated with total numbers of epileptiform transients during idazoxan infusion (P<0.01; r(2)=0.7). In conclusion, endogenous inhibitory alpha(2)-adrenergic receptor activation after severe hypoxia appears to significantly limit evolving hippocampal damage in the immature brain.

alpha2-Adrenoceptor agonists: shedding light on neuroprotection?

Although alpha(2)-adrenoceptor agonists are widely used for analgesia, anxiolysis, sedation, sympatholysis and as anaesthetic-adjuncts for many years, their potential use as neuroprotectants has so far been confined to laboratory experiments. Despite the large body of evidence from both in vivo and in vitro studies, their exact neuroprotective mechanisms remain elusive. Herein, we review the available literature pertaining to the neuroprotective effect of alpha(2)-adrenoceptor agonists and the possible biochemical and physiological cascades involved in their mechanisms of action. The remarkable safety profile of alpha(2)-adrenoceptor agonists and their high potency of neuroprotection should prompt clinical trials to evaluate their neuroprotective efficacy in humans.