Abstract
A brief episode of transient ischemia (TI) can confer cerebral ischemic tolerance against a subsequent severer TI under standard condition. The brain under obesity’s conditions is more sensitive to ischemic injury. However, the impact of a brief episode of TI under obesity’s conditions has not been fully addressed yet. Thus, the objective of this study was to determine the effect of a brief TI in the hippocampus of high-fat diet (HFD)-induced obese gerbils and related mechanisms. Gerbils were maintained on HFD or normal diet (ND) for 12 weeks and subjected to 2 min TI. HFD gerbils were heavier, with higher blood glucose, serum total cholesterol, triglycerides, and leptin levels. Massive loss of pyramidal neurons occurred in the hippocampal cornu ammonis 1 (CA1) field of HFD animals at 5 days after 2 min of TI, but 2 min of TI did not elicit death of pyramidal neurons in ND gerbils. The HFD group showed significantly increased levels of oxidative stress indicators (dihydroethidium and 4-hydroxynonenal) and proinflammatory cytokines (tumor necrosis factor-α and interleukin-1β) and microglial activation in pre- and/or post-ischemic phases compared to the ND group. Levels of mammalian target of rapamycin (mTOR) and phosphorylated-mTOR in the CA1 field of the HFD group were also significantly higher than the ND group. On the other hand, inhibition of mTOR activation by rapamycin (an allosteric mTOR inhibitor) significantly attenuated neuronal death induced by HFD, showing reduction of HFD-induced increases of oxidative stress indicators and proinflammatory cytokines, and microglia activation. Taken together, a brief episode of TI can evoke neuronal death under obesity’s conditions. It might be closely associated with an abnormal increase of mTOR activation-mediated, severe oxidative stress and neuroinflammation in pre- and/or post-ischemic phases.
Highlights
Transient ischemia (TI) in the whole brain, following a complete interruption of blood flow can lead to irreversible neuronal damage/death in vulnerable brain areas [1,2]
Obesity is a condition characterized by an excessive accumulation of body fat that can lead to Obesity is a condition characterized by an excessive accumulation of body fat that can lead to metabolic abnormalities, such as hyperlipidemia, hypercholesterolemia, and hyperglycemia, all of metabolic abnormalities, such as hyperlipidemia, hypercholesterolemia, and hyperglycemia, all of which can affect the pathophysiology of ischemic insults [33,34]
We set up a high-fat diet (HFD)-induced which can affect the pathophysiology of ischemic insults [33,34]
Summary
Transient ischemia (TI) in the whole brain, following a complete interruption of blood flow can lead to irreversible neuronal damage/death in vulnerable brain areas [1,2]. Extensive loss of pyramidal neurons in the CA1 occurs typically over several days after TI. It can result in hippocampal-dependent cognitive deficits [3,4]. Many studies have suggested that oxidative stress and neuroinflammation are crucial factors involved in ischemia-induced neuronal death [5,6,7], underlying mechanisms related to this phenomenon have not been clearly established yet. Researchers have demonstrated that a brief duration (1–3 min) of TI can prevent neuronal death in CA1 against a subsequent, longer TI that can result in massive loss of CA1 pyramidal neurons in rats [10,11], mice [12], and gerbils [13,14]
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