Focal cerebral ischemia elicits various types of neuronal injuries including neurodegeneration, motor dysfunction and cognitive impairment. Necrosis takes place in neurons and supporting glia because of severe oxygen and glucose shortage [1,2]. The penumbra is at the peripheral zone of this core injury and can be salvageable if collateral arteries provide blood into this region [3]. However, if the blockage of the main cerebral artery persists, penumbral cells will undergo necrosis. The clinical point of stroke intervention is to improve neuronal injury and reduce the effects of ischemia. Once neural cells get damaged, recovery is difficult, therefore it is important to protect ischemic situations during stroke.

Human serum albumin (HSA) is produced in the liver and has multifunctional roles [4]. HSA is soluble and a monomeric human protein that transports hormones, free fatty acids and other compounds. It also works as a pH buffer and maintains osmotic pressure [5]. The role of albumin in neuroprotection has been studied over many years [6]. Much research have demonstrated the effectiveness of albumin administration in diminishing brain infarction volumes and brain edema, as well as compromise blood brain barrier permeability [7,8,9]. HSA also specifically inhibits endothelial cell apoptosis and histopathological damages [10,11]. High-dose albumin therapy ameliorates neurological function and improves the reduced local perfusion of blood flow in the ischemic brain [12]. HSA is typically administered through intravenous injection (I.V.); although I.V injection is a direct and effective way of delivering materials into the body, it requires the use of needles. Thus, if oral administration of HSA is evinced to bring about similar protection effects as I.V. injections, then it can be developed into a more generalized intervention that can be applied to individuals of all ages.

In our previous study, we have shown that optical recordings of intrinsic signals (ORIS) can be utilized to monitor hemodynamic alterations in a MCAO model. We reported that the hemodynamic response of the ischemia region to electrical stimulation was drastically decreased, and ORIS measurements were tightly correlated with the severity of ischemia [13]. ORIS is a relatively easy technique to assess the levels of cerebral perfusion and is readily applicable to monitor the effects of HSA oral administration.

Albumin therapy is known to reduce brain edema and improve local vascular perfusion. It acts similarly to an antioxidant and is more powerful than vitamin E [15], without any observable side effects in humans [7,8,9]. Additionally, albumin provides essential fatty acids to the injured brain [16,17]. When albumin concentrations in both plasma and interstitial fluids are high, the protein scavenge for radical oxygen and bind to free fatty acids and metal ions, thus obstructing the oxidative process of lipid peroxidation. Albumin can also inhibit copper-ion-dependent lipid peroxidation binding to copper ions. Albumin can retard the formation of highly reactive hydroxyl radical species by acting as a multiple binding site that traps free radicals [18]. In functional association with changes in redox status, the structure and beneficial antioxidant properties of albumin adjust accordingly. Albumin essentially constitutes the major plasmic target protein of oxidant stress [17]; it is the main target of reactive oxygen species (ROS) and may function to prevent oxidative damage by sequestering and reducing ROS in stroke models [19]. In addition, the ROS-sensitivity of albumin stems from its cysteine and methionine residues that have ROS-scavenging capacities [20]. These effects of albumin can thus improve reperfusion injuries in a stroke model.

Transient ischemic stroke provokes the huge loss of phospholipid-acyl groups. As such, albumin provides essential fatty acids like DHA, which can be a crucial element in facilitating neuronal membrane repair [3] and proper physical conformations of ion channels, receptors, transporters and neuroprotectin D1 (NPD1) precursors [9,21,22]. NPD1 is related to the reduction of neuroinflammation and activation of antiapoptotic pathways. Thus, albumin can provide protective effects to the ischemic brain.

Thus far, HSA is commonly injected intravenously to patients, including stroke patients [23]. Intravenous injections assuredly deliver materials into the vascular system, but it can be difficult in some situations such as in repeated and long term treatment. IV is an invasive method for drug medication due to its side effects such as infection [24]. On the other hand, oral administration can be easier than intravenous injections, especially if everyday treatment or preventive intervention are necessary. In addition, oral administration can be easily applied for long term medication. However, oral administration may have less availability for absorption to target sites unlike intravenous injections, such that high doses of HSA solution may be needed for MCAO models.

We found that oral administration of HSA has effects on cerebral perfusion and infarct size. We demonstrated that oral administration of HSA has neuroprotective effects on focal cerebral ischemia. MCAO animals with a two-week oral administration of HSA showed a different general spreading pattern and large maximum amplitude of cerebral blood volume (CBV) changes near the direct cortical stimulation site compared to the group given a control substance. In the normal cortex, direct electrical stimulation delivered into the cortical tissue results in notable subsequent increases in CBV along the ipsilateral hemisphere of the stimulation. In our previous study, the direct electrical stimulation caused dramatic reduction in CBV following electrical stimulation in the sensory cortex of animals MCAO. The MCAO animal with saline administration showed similar patterns with those from our previous study that were without any given treatment [13]. However, CBV changes of the albumin group exhibited gradual increases following direct electrical stimulation, suggesting that their cortical tissue is capable of perfusing cortical blood more than the saline group. In addition, the infarction size of animals that were orally administrated with HSA is significantly smaller than that of the saline group. The albumin group also showed minimal necrosis of the ipsilateral hemisphere whereas the saline group had drastic necrosis due to MCAO. These results indicate that HSA may prevent neuronal apoptosis and conserve neuronal membranes from focal cerebral ischemia. We also found that a two-week oral administration of HSA improved neurological deficits caused by MCAO. In particular, from days 4 through 10 post-MCAO, the modified NSS of the albumin group was lower than that of the saline group, suggesting that HSA delivers protective effects on multiple levels of the neurosystem, including behavior and cortical perfusion. In fact, improved cortical perfusion may lead to better cognitive function. Lastly, the gradual and stable weight gain of the albumin group may also imply less stress from focal cerebral diseases than the saline group.

The question remains as to how HSA can affect neuronal damage after the process of digestion. HAS digestion is still not well understood; it is however known to be divided at residue 307 to produce two fragments by limited pepsin digestion [25]. This degradation may result in greater exposure of the ligand domain that binds free fatty acids [20], which in turn protects neuronal cells [26]. In addition, the products from HSA degradation, such as amino acids, are harmless and can be preferentially taken in by damaged tissues for nutrition [27,28]. Because of these properties of HSA, the protein can have beneficial effects at sites of inflammation, which are representative of the damages at focal ischemia in organ and cells [29,30]. On the other hand, HSA that is not digested can circulate in the blood and act as neuroprotectants. Cortical neurons take up albumin directly when the blood-brain barrier is perturbed during focal ischemia. It has also been indicated that albumin may have neuroprotective effects through direct cellular uptake [31]. Given these evidence, oral administration of HSA may thus have neuroprotective effects following focal ischemia. Thus, our current study strongly suggest that a simple oral administration of HSA may have neuroprotective effects against focal cerebral ischemia in a MCAO animal model.