Since Reis and colleagues first discovered agmatine and ADC activity in the mammalian brain , agmatine has been widely studied. It is known to have various biological actions through multiple molecular targets, exhibiting affinity not only to α2-adrenoceptors and I1- and I2-imidazoline receptors but also to β-adrenoceptors and 5-HT3 serotonin, nicotinic cholinergic NMDA, D2-dopamine, κ-opioid, and adenosine A1 receptors [10–12]. Agmatine also inhibits iNOS/nNOS and monoamine oxidase [10, 14, 15]. As well, agmatine reduces heart rate and blood pressure , stimulates insulin and β-endorphin release, leading to increased cellular glucose uptake [33, 34], and accelerates glomerular ultrafiltration . Agmatine protects systemic organs, especially against oxidative stress. Additionally, it shows cardioprotective and renoprotective effects on ischemic insult [36, 37], and it directly protects mitochondria from ROS [38, 39]. In the CNS, agmatine shows neuroprotective effects on various neuronal injuries: reduces the infarct size and edema after cerebral ischemia [17, 18, 40], attenuates brain damage and reactive gliosis caused by trauma [41, 42], and also decreases traumatic/ischemic spinal cord injuries [43, 44]. Agmatine also decreases neuropathic pain and convulsive events [45, 46], attenuates opioid dependence and alcohol withdrawal anxiety [47, 48], and it improves motor and cognitive functions in Parkinson's and Alzheimer's disease, respectively [49, 50]. Even in the eyes, agmatine lowers intraocular pressure and protects retinal ganglion cells [51, 52]. Taken together, agmatine seems to be a miracle cure rather than a specific drug.
In routine clinical settings, exogenous drug administration may be the most straightforward therapeutic strategy. However, exogenous drug administration is not always the best approach for real patients. Taken orally, agmatine is readily distributed throughout the body [53, 54] and can even cross the blood–brain barrier [55, 56]. Moreover, its reported half-life in the body is about 2 hrs . The various functions of agmatine have pros and cons. In addition to neuronal effects, agmatine also has cardiovascular, endocrinal, renal, gastric, and growth effects . Therefore, taken orally, agmatine may cause unwanted systemic responses. Thus, it is important to focus on the action of the drug at the site of injury and extend its duration of action. In this regard, in the ophthalmologic field, a topical agmatine ophthalmic solution has been formulated to preserve the optic nerves against glaucomatous damage . Agmatine eye drops effectively lower intraocular pressure and protect retinal ganglion cells from chronic ocular pressure injuries. Along the same lines, investigators have attempted to develop a distinctive method for increasing endogenous agmatine production via a recombinant retroviral vector system containing the hADC gene. The hADC gene can be effectively delivered into mouse fibroblast NIH3T3 cells , primary mouse cortical neural stem cells , and human bone marrow mesenchymal stem cells . Different types of transformed cells synthesize agmatine when they are exposed to hydrogen peroxide, resulting in resistance against oxidative stress. Irrespective of the cell type in an oxidative stressed environment, intracellular agmatine concentration is boosted by about 2 to 5-fold in hADC-overexpressing cells compared to no treatment control cells, as determined by HPLC [23–25]. While in normal culture conditions, agmatine synthesis is significantly increased in cortical neural stem cells  but not fibroblasts or mesenchymal stem cells [23, 25]. It is not yet clear why the activity of an introduced hADC gene differs according to cell type, especially in non-stressful conditions; nonetheless, it is assumed that agmatine controls the expression of the introduced hADC gene. If normal cells use little agmatine, the transformed cells are presumed not to utilize the introduced ADC without harmful stimuli. However, if normal cells actively use agmatine, the transformed cells are presumed to utilize the introduced ADC. When cells are attacked, all the cell types seem to use the introduced ADC.
In this investigation, we focused on cortical astrocytes, which have recently came to the forefront due to their suspected roles in many CNS injuries, including cerebral ischemia [2, 3]. Our results showed that intracellular levels of agmatine, as well as its precursor arginine and byproduct putrescine, are definitively increased (about 11-fold compared to the control, p < 0.001) in normal and oxidative stressed conditions upon hADC gene transduction, as measured by HPLC. Simultaneously, cell viability was determined by Hoechst /PI double nuclear staining and the LDH assay. hADC-overexpressing cells remained viable and healthy under oxidative stress conditions induced by OGD for 4 hrs. This astrocyte-rescuing property was gradually potentiated as restoration time proceeded for up to 10 hours. In addition, the neuroprotective effect of endogenous agmatine seemed to be related to iNOS intracellular signaling and the activity of MMPs, as assessed by RT-PCR, Western immunoblots, and immunofluorescence. Our present and previous findings are similar to those of other groups in regards to iNOS [15, 58–60] and MMPs [61, 62], respectively. As MMPs are upregulated by ischemic insult and degrade the basement membrane of brain microvessels , their suppression via ADC gene transduction may reduce ischemic injuries. Our retroviral system to deliver the hADC gene to target cells cannot be directly applied to non-dividing cells. Accordingly, another vector system using the Lentivirus is currently under development. It may be directly applied to non-dividing CNS neurons, specifically through in vivo transduction.