Neuroprotective Effects Of Humanin And S14G-HN On Inflammatory Damage Induced By β-amyloid Protein And Intracerebral Hemorrhage

Background and PurposeThe incidence rate of Alzheimer's disease (AD) and intracerebral hemorrhage (ICH) is increasing with the aging of population, which have been common diseases that severely influence the middle-aged and older population. The pathogenesis for AD and ICH remains unclear so far, and there have no specific treatment for these disorders. Recent studies have shown that inflammation predominately contributes to the pathophysiological process of AD and ICH. Thus, it is necessary to explore the specific-clinical measurements for these diseases. Humanin (HN) is a newly identified 24-residue peptide with neuroprotective action. Increasing studies revealed that HN and HN derivative peptides, known as S14G-HN (HNG), may antagonize against neurotoxicity induced by all known various insults of AD, and the bioactivity of HNG is 1000 times more potent than HN. In recent years, the researches that aim at the neuroprotective effects of HN draw more and more attention to it in the field of neuroscience. For example, HNG has been demonstrated to protect against cerebral ischemia/reperfusion injury in vivo. However, the exact mechanisms by which HN and HNG exert their neuroprotective actions are not well understood. The purpose of the present study is to determine whether HN and HNG can antagonize against inflammatory damage induced byβ-amyloid protein (Aβ), and whether HNG can play a neuroprotective action in ICH.Methods and Results(1)Effective inhibitory function of HN and HNG for inflammatory damage induced by Aβ. By stereotacticly injecting Aβ25～35 into the right hippocampus CA1 region of mouse, we established experimental AD models to determine whether HN and HNG can antagonize against inflammatory damage induced by Aβ. Our data showed that the numbers of GFAP positive astrocytes in ipsilateral hippocampus were evidently decreased in each HN- and HNG- treatment group than in control groups at 3, 7, and 14 days (P<0.01, respectively), and these effects exhibited a dose-dependent relationship. The numbers of GFAP positive astrocytes in 100μmol/L HN- treatment group were markedly decreased than that in 10μmol/L HN-treatment group, while similar results were found in HNG-treatment groups. These findings indicated that HN and HNG effectively inhibited GFAP expresson caused by Aβin vivo, suggesting that HN and HNG exert neuroprotective action for AD by one approach to protest against inflammation.(2) Eevolution of inflammatory reaction, brain edema and neurological deficits in rats with intracerebral hemorrhage. ICH rat models were established by stereotacticly injecting autologous whole blood (75μl) into the right caudate nucleus, and the inflammatory reaction, brain edema and neurological deficits were examined during natural course. We found that following the course of ICH, numerous GFAP-immunoreactive astrocytes, OX42-immunoreactive microglia, and MPO-immunoreactive neutrophil leukocyte distributed around the hematoma at 6 hours, and reached the peak at 72 hours, and recovered to that of control group after two weeks; TUNEL positive cells appeared at 12 hours, and markedly increased at 72 hours, and decreased at 7 days, but its amount in ICH group was also more than that in control group at 14 days. Brain edema in hematoma peripheral area including striatum and cerebral cortex was detected at 3 hours, and developed progressively to reach the peak at 24 hours. After sustaining 72 hours, the brain edema decreased gradually and recovered to that of control group at one week. The contralateral brain was also involved lightly increasing edema, but recovered rapidly to that in control group at 3 day. No edema was found in cerebellum each group. There was a negative correlation between neurological deficits and brain edema of cortex and striatum. These findings suggested that the inflammation and brain edema after ICH formed and developed at early phase, and the strong effective measurements for preventing inflammation and edema should be carried out during 24-72 hours.(3) Neuroprotective effects of HNG on inflammatory reacton caused by ICH in rats. The HNG (5μl) was injected into lateral cerebral ventricle of rats with ICH, and glia and apoptostic cell were examined by immunohistochemistry following 72 hours after operation. We found that the amount of GFAP-immunoreactive astrocytes, OX42-immunoreactive microglia, and TUNEL-positive cells around the hematoma decreased obviously in HNG-treatment group than in control group. These findings suggested that HNG exert neuroprotective function for ICH by inhibiting inflammatory response and antiapoptosis, thus, we speculate that HNG could be a novel neuroprotective agent against ICH. SummaryBased on these experimental findings, we conclude that (1) we firstly revealed that HN and HNG effectively inhibited GFAP expresson caused by Aβin vivo, suggesting that HN and HNG exert neuroprotective action for AD by one approach to protest against inflammation; (2) inflammation and brain edema after ICH could developed at early phase, and the strong effective measurements for preventing inflammation and edema should be carried out during 24-72 hours; (3) HNG exerted neuroprotective function for ICH by inhibiting inflammatory response and antiapoptosis, and HNG could be a novel neuroprotective agent against ICH. Togethre, these findings provide experimental evidences for further understanding of the exct mechanisms of HN and HNG.