**7. Clinical implications**

tubulointerstitial damage [19]. In another study considering cultured mesangial and vascular smooth muscle cells, AT II via AT1R signaling was shown to stimulate TLR-4 expression that was considered to promote cellular oxidative injury, apoptosis, and inflammation [20]. T cells were considered to show the pro-inflammatory effects of AT II via AT1R and endogenous RAS, which has been disclosed to modulate T-cell proliferation, cytoskeletal rearrangements,

AT II is considered to stimulate the production of molecular oxygen species that trigger mitochondrial dysfunction and cellular injury [21]. AT II via AT1R stimulation has been shown to activate NAD(P)H oxidase to produce ROS, resulting in oxidative stress damage [21]. It has been proposed that ROSs are the most prominent molecular species involved in the aging process [22]. ROSs have been revealed to contribute significantly to various age-associated organ failures, including hypertension, cardiovascular diseases, and renal damage [22]. Hence, AT II is considered to be involved in organ senescence related to its ability to mediate the release of oxidant species [23]. Recent studies have disclosed that AT II-induced ROS production leads to functional and structural changes of blood vessels that result in vascular senescence and age-related vascular diseases [23]. Previous studies related to the long-term effects of AT II inhibition by either ACEi or ARBs disclosed protective effects on the cardiovascular system of rats and revealed the prolongation of the life span of rats [24, 25]. Another study disclosed that old mice lacking AT1R did not develop age-related cerebral circulation damage caused by the accumulation of oxygen radicals [26]. The inhibition of RAS has been disclosed to reverse age-related advanced myocardiac hypertrophy and fibrosis in old hypertensive rats, and the protective effect presumably was considered to involve the suppression of AT II-mediated oxidative stress, as disclosed by

reduced expression of NAD(P)H oxidative components in the hearts of aged rats [26].

**6. Further mechanisms of angiotensin II-induced inflammation:** 

Co-stimulatory effects of angiotensinogen, AT I, and AT II on the proliferation of T and NK cells have been revealed [27]. T and NK cells were considered to have RAS elements, and they have been synthesizing AT II at the sites of inflammation creating a potential inflammatory amplification system [27, 28]. Th1 immune response has been disclosed to be crucial in the

However, the interaction of AT II with Th1/Th2 cytokines during the development of inflammation is considered debatable. Recent studies have demonstrated the presence of RAS elements in human T and NK cells that they were capable to synthesize their own AT II [29]. Renin-induced inflammation has been related to the binding of AT II to the renin receptor in T cells, NK cells, and DC [29]. AT 2R which was previously considered to antagonize the actions of the AT1R and having beneficial effects in hypertension, cell growth, vascular remodeling, proliferation, and

**human T and natural killer cells**

pathogenesis of inflammatory vascular diseases [28].

migration, and release of specific cytokines and chemokines [20].

**5. Angiotensin II: role in immunosenesence**

112 Renin-Angiotensin System - Past, Present and Future

New medical applications of RAS antagonists as anti-inflammatory and immunomodulatory agents without significant side-effects are being considered in the treatment of autoimmune diseases [31, 32].

### **7.1. Captopril suppresses inflammation in endotoxin-induced uveitis in rats**

It has been suggested that ACEi captopril has a strong anti-ocular inflammatory effect in endotoxin-induced uveitis (EIU) [33]. Captopril has been shown to suppress the NF-κB activation in the iris and ciliary body cells by inhibiting the production of AT II [34]. The inhibitory effect of captopril on leucocyte infiltration, protein leakage, and other inflammatory markers in the aqueous humor including TNF-α, PGE-2, MCP-1, NO have also been revealed [35].

TNF-α is an inflammatory cytokine, which plays an important role in the recruitment of inflammatory cells, synthesis of other inflammatory cytokines, eicosanoids, and NO [35]. Anti TNF-α therapy has been used for the treatment of Behcet's disease [36]. The transcription of TNF-α was shown to be under the control of NF-κB [35, 36]. It has previously been disclosed that ACE inhibitors suppress TNF-α synthesis *in vivo* and *in vitro* and captopril was shown to successfully down regulate TNF-α in the aqueous humor by interfering the positive loop between TNF-α and NF-κB [36]. PGE2 and NO in the aqueous humor were considered to have profound effects on local inflammatory processes mainly by increasing vascular permeability and breaking down the blood-aqueous barrier in uveitis [37]. Their concentrations in the aqueous humor were disclosed to be down-regulated by captopril treatment [37]. Inhibition of both TNF-α and PGE2/NO pathways by captopril has been shown to improve EIU in rabbits [38]. Another inflammatory marker MCP-1, which is under NF-κB control, is considered as an important mediator of monocyte infiltration. MCP-1 has been shown to be over expressed in human eyes during acute anterior uveitis as well as in the rat EIU model [38]. The results of the recent studies have disclosed that captopril successfully down-regulated MCP-1 levels in anterior chamber, and it showed its anti-inflammatory properties by affecting monocyte recruitment in EIU in rats [34, 37, 38].

The beneficial effect of AT II blockers on tissue inflammation was also considered to be related to the blockage of Ang II-mediated activation of Toll-like receptors (TLRs) [39]. Drugs that limit AT II synthesis and its biological activity, ACEi lisinopril, or ARB Candesartan were disclosed to result in the suppression of Th1 and Th17 cytokine release and the induction of powerful antigen-specific regulatory T cells (Treg) through the modulation of the NF-κB pathway [40]. Administration of ARB was disclosed to suppress EAU and reduce the severity of myocardial lesions in EAM by inhibiting antigen-specific T-cell activation and contributing to the shift of Th1–Th2 immune response [41]. Chronic treatment with ACEi or ARB has been shown to reduce kidney damage associated with age, and the beneficial effect of RAS inhibition was considered to be related to the preservation of renal mitochondria [40]. Enalapril and losartan treatments have been shown to prevent the age-associated decline in the renal mitochondrial capacity for energy production and to attenuate the age-associated increase in mitochondrial oxidant production [40]. RAS inhibition was disclosed to exert a similar protective effect in the liver from aged rats through the maintenance of an adequate mitochondrial function by enhancing expression of genes responsible for mitochondrial respiration and biogenesis [41]. Aging is considered to be the result of chronic inflammation, and the use of RAS inhibitors or genetic deletion of AT1R was considered to extend the life span [41].

### **7.2. Oral delivery of ACE2/Ang-(1–7) bioencapsulated in plant cells protects against experimental uveitis and autoimmune uveoretinitis**

Improving the systemic and local activity of the protective axis of the RAS by oral delivery of ACE2 and Ang-(1–7) bioencapsulated in plant cells has been considered as a therapeutic option for the ocular inflammation. Increased levels of ACE2 and Ang-(1–7) were observed in the retinal circulation after oral administration of ACE2 and Ang-(1–7) expressing plant cells [42]. Oral feeding of mice with bioencapsulated ACE2/Ang-(1–7) was shown significantly to reduce the incidence of EIU [42]. Treatment with bioencapsulated ACE2/Ang-(1–7) in mice disclosed dramatical decrease of cellular infiltration and retinal vasculitis in EAU [42]. It has been concluded that enhancing the protective axis of RAS by oral delivery of ACE2/Ang-(1–7) bioencapsulated in plant cells provide an innovative, highly efficient, and cost-effective therapeutic strategy for ocular inflammatory diseases [42].
