Effects of chronic guanosine treatment on hippocampal damage and cognitive impairment of rats submitted to chronic cerebral hypoperfusion

Abstract

Chronic cerebral hypoperfusion contributes to a cognitive decline related to brain disorders. Its experimental model in rats is a permanent bilateral common carotid artery occlusion (2VO). Overstimulation of the glutamatergic system excitotoxicity due to brain energetic disturbance in 2VO animals seems to play a pivotal role as a mechanism of cerebral damage. The nucleoside guanosine (GUO) exerts extracellular effects including antagonism of glutamatergic activity. Accordingly, our group demonstrated several neuroprotective effects of GUO against glutamatergic excitotoxicity. Therefore, in this study, we evaluated a chronic GUO treatment effects in rats submitted to 2VO. We evaluated the animals performance in the Morris water maze and hippocampal damage by neurons and astrocytes immunohistochemistry. In addition, we investigated the cerebrospinal fluid (CSF) brain derived neurotrophic factor (BDNF) and serum S100B levels. Additionally, the purine CSF and plasma levels were determined. GUO treatment did not prevent the cognitive impairment promoted by 2VO. However, none of the 2VO animals treated with GUO showed differences in the hippocampal regions compared to control, while 20% of 2VO rats not treated with GUO presented loss of pyramidal neurons and increased glial labeling cells in CA1 hippocampal region. In addition, we did not observe differences in CSF BDNF nor serum S100B levels among the groups. Of note, both the 2VO surgery and GUO treatment changed the purine CSF and plasma profile. In conclusion, GUO treatment did not prevent the cognitive impairment observed in 2VO animals, but our data suggest that GUO could be neuroprotective against hippocampal damage induced by 2VO.

Intranasal guanosine administration presents a wide therapeutic time window to reduce brain damage induced by permanent ischemia in rats

“…Previously, we reported that chronic oral GUO treatment was also able to increase ADO plasma levels [7]. Some works in the literature have focused attention on the interplay of extracellular ADO and GUO levels.…”

“…Determination of the purines concentration in CSF, blood plasma, and brain structures was performed using the methodology of HPLC described previously [7]. The injected sample volume was 0.02 ml.…”

“…Blood plasma GUO and HYP levels were not possible to be detected due to its value not reaching the HPLC inferior detection limits (data not shown). This inability seems to be related specifically to the use of TFA 7 % in purines extraction protocol, as GUO plasma levels could be observed using different extraction compounds [7,16,25,26]. Notably, we chose TFA 7 % based on a pilot experiment which we tested different chemicals to homogenize brain tissue and blood samples to obtain the highest radioactivity extraction derived from [ 3 H] GUO (TCA 10 %, TFA 7 %, ACN, methanol, perchloric acid; data not shown).…”

“…As GLU is the main excitatory neurotransmitter in the CNS, and excessive GLU signaling (excitotoxicity) is involved with several brain diseases [5,6], the neuroprotective potential of GUO against excitotoxicity has been investigated. Accordingly, the exogenous administration of GUO has shown neuroprotective effects on CNS injury in several animal models linked to excitotoxicity events, including models of dementia [7], seizures [8,9], neuropathic pain [10], stroke [11][12][13][14][15], and hepatic encephalopathy [16].…”

“…Certainly, GUO effects seem to be directly mediated by action on the brain, as intracerebroventricular or intracortical GUO infusion in experimental models of excitotoxicity have demonstrated neuroprotection [8,13]. Nevertheless, most of the neuroprotective effects exerted by GUO were observed after its systemic (intraperitoneal [IP] or oral) administration [7,[9][10][11][12][13][14][15][16]. In this regard, systemic administration routes present important limitations for protocols with endogenous drugs that aim to reach the brain but can be metabolized in the systemic pathway, which is the case for GUO.…”