Effects of adenosine agonists and an antagonist on excitatory transmitter release from the ischemic rabbit hippocampus

Therapeutic Potential of Non-Psychotropic Cannabidiol in Ischemic Stroke

Cannabis contains the psychoactive component delta⁹-tetrahydrocannabinol (delta⁹-THC), and the non-psychoactive components cannabidiol (CBD), cannabinol, and cannabigerol. It is well-known that delta⁹-THC and other cannabinoid CB₁ receptor agonists are neuroprotective during global and focal ischemic injury. Additionally, delta⁹-THC also mediates psychological effects through the activation of the CB₁ receptor in the central nervous system. In addition to the CB₁ receptor agonists, cannabis also contains therapeutically active components which are CB₁ receptor independent. Of the CB₁ receptor-independent cannabis, the most important is CBD. In the past five years, an increasing number of publications have focused on the discovery of the anti-inflammatory, anti-oxidant, and neuroprotective effects of CBD. In particular, CBD exerts positive pharmacological effects in ischemic stroke and other chronic diseases, including Parkinson’s disease, Alzheimer’s disease, and rheumatoid arthritis. The cerebroprotective action of CBD is CB₁ receptor-independent, long-lasting, and has potent anti-oxidant activity. Importantly, CBD use does not lead to tolerance. In this review, we will discuss the therapeutic possibility of CBD as a cerebroprotective agent, highlighting recent pharmacological advances, novel mechanisms, and therapeutic time window of CBD in ischemic stroke.

General versus specific actions of mild-moderate hypothermia in attenuating cerebral ischemic damage

Mild or moderate hypothermia is generally thought to block all changes in signaling events that are detrimental to ischemic brain, including ATP depletion, glutamate release, Ca(2+) mobilization, anoxic depolarization, free radical generation, inflammation, blood-brain barrier permeability, necrotic, and apoptotic pathways. However, the effects and mechanisms of hypothermia are, in fact, variable. We emphasize that, even in the laboratory, hypothermic protection is limited. In certain models of permanent focal ischemia, hypothermia may not protect at all. In cases where hypothermia reduces infarct, some studies have overemphasized its ability to maintain cerebral blood flow and ATP levels, and to prevent anoxic depolarization, glutamate release during ischemia. Instead, hypothermia may protect against ischemia by regulating cascades that occur after reperfusion, including blood-brain barrier permeability and the changes in gene and protein expressions associated with necrotic and apoptotic pathways. Hypothermia not only blocks multiple damaging cascades after stroke, but also selectively upregulates some protective genes. However, most of these mechanisms are addressed in models with intraischemic hypothermia; much less information is available in models with postischemic hypothermia. Moreover, although it has been confirmed that mild hypothermia is clinically feasible for acute focal stroke treatment, no definite beneficial effect has been reported yet. This lack of clinical protection may result from suboptimal criteria for patient entrance into clinical trials. To facilitate clinical translation, future efforts in the laboratory should focus more on the protective mechanisms of postischemic hypothermia, as well as on the effects of sex, age and rewarming during reperfusion on hypothermic protection.

Concentrations of extracellular free zinc (pZn)e in the central nervous system during simple anesthetization, ischemia and reperfusion

"Free Zn2+" (rapidly exchangeable Zn2+) is stored along with glutamate in the presynaptic terminals of specific specialized (gluzinergic) cerebrocortical neurons. This synaptically releasable Zn2+ has been recognized as a potent modulator of glutamatergic transmission and as a key toxin in excitotoxic neuronal injury. Surprisingly (despite abundant work on bound zinc), neither the baseline concentration of free Zn2+ in the brain nor the presumed co-release of free Zn2+ and glutamate has ever been directly observed in the intact brain in vivo. Here, we show for the first time in dialysates of rat and rabbit brain and human CSF samples from lumbar punctures that: (i) the resting or "tonic" level of free Zn2+ signal in the extracellular fluid of the rat, rabbit and human being is approximately 19 nM (95% range: 5-25 nM). This concentration is 15,000-fold lower than the "300 microM" concentration which is often used as the "physiological" concentration of free zinc for stimulating neural tissue. (ii) During ischemia and reperfusion in the rabbit, free zinc and glutamate are (as has often been presumed) released together into the extracellular fluid. (iii) Unexpectedly, Zn2+ is also released alone (without glutamate) at a variable concentration for several hours during the reperfusion aftermath following ischemia. The source(s) of this latter prolonged release of Zn2+ is/are presumed to be non-synaptic and is/are now under investigation. We conclude that both Zn2+ and glutamate signaling occur in excitotoxicity, perhaps by two (or more) different release mechanisms.

Nucleotides modulate renal ischaemia-reperfusion injury by different effects on nitric oxide and superoxide

1. The present study investigated the effects of kidney ischaemia duration on nitric oxide (NO) and superoxide (O2-) generation at reperfusion and the role of xanthine and adenosine as mediators of NO/O2- generation. 2. The effect of the duration of ischaemia on renal nucleotide levels was studied in two ischaemic groups (10 and 30 min). The role of adenosine and xanthine was studied in ischaemic-reperfused groups (subjected to 10 and 30 min ischaemia and 60 min reperfusion). 3. Tissue levels of adenosine decreased significantly after 30 min ischaemia, whereas xanthine/hypoxanthine levels increased concomitantly with renal dysfunction and histological damage. 4. Nitric oxide production increased significantly after 10 min ischaemia and 60 min reperfusion, whereas lipoperoxidation increased significantly after 30 min ischaemia and 60 min reperfusion. The administration of theophylline (40 mg/kg, i.p.) reversed the early increase in NO production. 5. Xanthine supplementation decreased renal function and increased lipoperoxidation. 6. In conclusion, NO/O2- production and the subsequent renal injury/dysfunction may be modified by changes in the adenosine and xanthine levels of the injured kidney, although the present data show a significant in vivo role only for xanthine.

Neuroprotection role of adenosine under hypothermia in the rat global ischemia involves inhibition of not dopamine release but delayed postischemic hypoperfusion

Adenosine (ADO) has an important role in the ischemic brain as an endogenous neuroprotective factor. On the other hand, intraischemic hypothermia ameliorates ischemic neuronal injury. To investigate the effect of ADO during intraischemic mild hypothermia, the extracellular concentration of ADO, its metabolites, dopamine (DA), and local cerebral blood flow were measured in rat striatum during and after 20 min of global ischemia. Additionally, the histopathological outcome was estimated after 48 h of recirculation. Three experimental groups were used: (1) a normothermic group (NT) maintained at 37 degrees C during and after ischemia; (2) a hypothermic group (HT), exposed to intraischemic hypothermia (32.0 degrees C) and postischemic normothermia; and (3) a hypothermia plus theophylline group (HT+T), with the same temperature conditions as in the HT group, combined with intravenously administration of theophylline (10 mg/kg), an antagonist of adenosine receptor, which was given 10 min before ischemia. The level of ADO in HT was significantly higher than ADO levels in NT. In contrast, ischemic DA release was significantly inhibited in HT compared with NT. Theophylline administration had no effect on intraischemic hypothermia induced modulation of extracellular ADO and DA concentration. The postischemic delayed hypoperfusion was ameliorated in HT, and theophylline eliminated this effect in HT+T. A protective effect on histopathological outcome was observed in HT and HT+T. These results suggest that ADO plays an essential role in the inhibition of postischemic delayed hypoperfusion, but this effect is not crucial role in the protective effect induced by intraischemic hypothermia.

Effects of adenosine on ischaemia-reperfusion injury associated with rat pancreas transplantation

BACKGROUND

During cold preservation, cellular consumption of adenosine triphosphate leads to the accumulation of nucleotides and nucleosides. The precise role of adenosine in modulating the inflammatory response of cold-preserved pancreas after reperfusion remains to be elucidated. The aim of this study was to assess the influence of adenosine on the inflammatory response associated with the process of ischaemia-reperfusion in rat pancreas transplantation.

METHODS

The effect of adenosine from preservation solution on the levels of high-energy nucleotides and their breakdown products after cold ischaemic preservation was determined. In addition, the inflammatory response associated with the process of ischaemia-reperfusion in pancreas transplantation was quantified with and without pretreatment with the adenosine antagonist theophylline, and during preservation of the organ in University of Wisconsin solution with and without adenosine.

RESULTS

Adenosine from preservation solution is able to modify the nucleotide and nucleoside content of preserved pancreas, indicating that adenosine is incorporated and metabolized in tissue. Administration of the adenosine antagonist to transplanted rats moderated the increases in nitrite and nitrate, myeloperoxidase activity and lipoperoxidation levels in the pancreas.

CONCLUSION

Adenosine in the preservation solution may enhance the inflammatory response in rat pancreas transplantation.