Bvr. Sastry et Me. Hemontolor, Influence of nicotine and cotinine on retinal phospholipase A(2) and its significance to macular function, J OCUL PH T, 14(5), 1998, pp. 447-458
The macula is a constituent of the sensory retina that is necessary for sha
rp contrast and color vision. A significant relationship has been found bet
ween tobacco smoking and age-related macular degeneration. Opsin, rhodopsin
and phospholipase A(2) (PLA(2)) are located in excitable membranes of reti
na which are enriched with polyunsaturated fatty acids (PUFA). A question m
ay arise as to whether nicotine and its major metabolite cotinine influence
PLA(2) so that arachidonic acid (AA) and proinflammatory prostaglandins (P
G) are produced in the retina. Therefore, the effects of nicotine and cotin
ine on the retinal. PLA(2) were studied.
PLA(2) activity of rat retinal sonicates was assayed using 1-palmitoyl-2[1-
C-14]arachidonyl-Phosphatidylethanolamine (PE, 2.2 nmol) as a substrate in
Tris buffer (10 mM, pH 7.4) at 37 degrees C with and without nicotine or co
tinine in the assay medium. These studies gave the following results: (I) R
at retinal PLA(2) activity was 4.2 +/- 0.8 pmol PE hydrolyzed/100 ng protei
n/hr. (2) Nicotine in low concentrations (1-150 nM) activated PLA(2) (EC50
5nM). (3) Cotinine also activated PLA(2) (EC50 300 nM). (4) Only high conce
ntrations of nicotine (> 1.0 mu M) and cotinine (> 25 mu M) exhibit inhibit
ion of PLA(2). (5) All three known PLA(2) inhibitors, mepacrine, 4-bromophe
nacyl bromide and bromoacetylcholine bromide (IC50: 0.5mM, 88 mu M, 30mM, r
espectively) inhibited retinal PLA(2) activity. These observations suggest
that polyunsaturated fatty acids are cleaved, and arachidonic acid, the pre
cursor for prostaglandins and related pro-inflammatory mediators, is libera
ted by nicotine and cotinine. Oxidative stress (reduced levels of antioxida
nts), vascular insufficiency, as well as activation of PLA(2) by nicotine a
nd cotinine may contribute for retinal degeneration in smokers during aging
.