[Functional significance of adenosine receptors in the eye and their dysregulation in pseudoexfoliation syndrome]

Adenosine: The common target between cancer immunotherapy and glaucoma in the eye

Adenosine, an endogenous purine nucleoside, is a well-known actor of the immune system and the inflammatory response both in physiologic and pathologic conditions. By acting upon particular, G-protein coupled adenosine receptors, i.e., A1, A2- a & b, and A3 receptors mediate a variety of intracellular and immunomodulatory actions. Several studies have elucidated Adenosine's effect and its up-and downstream molecules and enzymes on the anti-tumor response against several types of cancers. We have also targeted a couple of molecules to manipulate this pathway and get the immune system's desired response in our previous experiences. Besides, the outgrowth of the studies on ocular Adenosine in recent years has significantly enhanced the knowledge about Adenosine and its role in ocular immunology and the inflammatory response of the eye. Glaucoma is the second leading cause of blindness globally, and the recent application of Adenosine and its derivatives has shown the critical role of the adenosine pathway in its pathophysiology. However, despite a very promising background, the phase III clinical trial of Trabodenoson failed to achieve the non-inferiority goals of the study. In this review, we discuss different aspects of the abovementioned pathway in ophthalmology and ocular immunology; following a brief evaluation of the current immunotherapeutic strategies, we try to elucidate the links between cancer immunotherapy and glaucoma in order to introduce novel therapeutic targets for glaucoma.

Asymmetric dimethylarginine is not elevated in exfoliation syndrome but symmetric dimethylarginine is related to exfoliative glaucoma

BACKGROUND

Hyperhomocysteinemia (HH), oxidative stress and endothelial dysfunction are all implicated as possible pathogenetic factors in exfoliation syndrome (XFS) and exfoliative glaucoma (XFG). Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide and plasma level of ADMA is often elevated in HH. Thus the present study was undertaken to study plasma levels of ADMA with concomitant measurement of symmetric dimethylarginine (SDMA) and L-arginine (L-Arg) in XFS and XFG.

METHODS

This cross-sectional, prospective study involved 36 XFS patients, 11 of them having XFG, and 36 age- and gender-matched controls. Fasting plasma ADMA, SDMA and L-Arg levels of participants were determined. A special view was created how plasma L-Arg, ADMA and SDMA correlate to plasma homocysteine (P-Hcy). In addition, the influence of P-Hey values derived from our previous study on the above mentioned parameters were evaluated by cut-off values of P-Hcy, 12 micromol/l for women and 14.5 micromol/l for men. RESULTS The mean plasma ADMA, SDMA and L-Arg levels were 0.41, 0.49 and 62.9 micromol/l in the XFS/XFG group, and 0.41, 0.44 and 69.7 micromol/l in the control group, respectively. As all parameters within the XFS and control group were compared, no statistical significance was stated. On the other hand, a positive correlation was observed between plasma SDMA and P-Hcy in XFGs (P = 0.002), and additionally, also a statistically significant difference was in plasma SDMA between the two groups sorted by cut-off levels of P-Hcy 0.49 +/- 0.15 vs. 0.36 +/- 0.04 micromol/l, above and below cut-off levels, respectively (P = 0.001), but not between ADMA in a respective assay. The mean values of L-Arg were 64.6 +/- 17.2 vs. 74.8 +/- 13.3 microg/l, respectively (P = 0.031). In the XFS subgroup, on the contrary, there was no positive correlation between P-Hcy and plasma SDMA.

CONCLUSIONS

A positive correlation of plasma SDMA in respect to P-Hcy in XFGs and increase of SDMA in mild or intermediate hyperhomocysteinemia may indicate SDMA as a marker of developing XFG in hyperhomocysteinemic