Depletion of nitric oxide synthase-containing neurons in the diabetic retina: reversal by aminoguanidine

Abstract

The pathogenesis of diabetic retinopathy has not been fully elucidated but is thought to be related to haemodynamic changes of the retinal vasculature [1]. Many vasoactive substances influence retinal haemodynamics including nitric oxide (NO), a diffusible gas molecule, formed by three different isoforms of nitric oxide synthase (NOS) [2]. One isoform of NOS is neuronal NOS (nNOS) which is found throughout the nervous system and has been localised to specific cells of the retina including amacrine cells [3]. Previously we have shown that these nNOS-immunoreactive (nNOS-IR) amacrine cells lie in close proximity to the retinal vessels and that their processes can envelop the retinal vasculature [3]. This suggests that nitrergic innervation of the retinal vasculature might link retinal blood flow to metabolism [3] as has been proposed for the cerebral cortex [4].Given the potential role for nNOS in retinal vascular control, the first aim of this study was to deter- Diabetologia (1998) Summary A close association of neuronal nitric oxide synthase-immunoreactive (nNOS-IR) neurons with the retinal vasculature has been reported and it is proposed that activation of these neurons could be the mechanism by which retinal blood flow and metabolism are linked. Further, advanced glycation end products (AGEs) have previously been shown to be increased in the diabetic retina and aminoguanidine (AG), an inhibitor of advanced glycation, has been shown to attenuate the development of AGE accumulation as well as the progression of experimental diabetic retinopathy. This study examined the effects of short (1 and 3 weeks) and long term (32 weeks) diabetes on nNOS-containing neurons of the retina using NADPH diaphorase (NADPHd) histochemistry. In addition, the effect of aminoguanidine (an inhibitor of advanced glycation and NOS) and N G -nitro-Larginine methyl ester (L-NAME) (a non-selective NOS inhibitor) on retinal nNOS-containing neurons was examined in short and long term control and diabetic rats. In a separate study, the effect of 2,3 diamino-phenazine (NN0028) (an inhibitor of advanced glycation, but not NOS) was examined in short term (3 weeks) diabetic rats. The number of NADPHdpositive neurons per retina was reduced after one week of diabetes and remained decreased in long term diabetic rats, an effect not observed in diabetic rats rendered euglycaemic by intensified insulin treatment. Treatment of diabetic animals with aminoguanidine or NN0028 prevented the depletion in the nNOS-containing neuron number, an effect not reproduced by L-NAME. These studies suggest that the action of AG in restoring the number of nNOScontaining retinal neurons is mediated by the inhibition of AGE formation. The depletion of nNOS-containing neurons may contribute to alterations in the autoregulation of blood flow which occurs in diabetes. [Diabetologia (1998

Apoptotic death of photoreceptors in the streptozotocin-induced diabetic rat retina

“…It is also clarified that the initial phase of diabetic retinopathy is through non aminoguanidine-inhibited mechanism [42]. In con-trast, aminoguanidine has been suggested to act on restoring the number of nNOS-containing neurons in the short-term and long-term diabetic retinas, as mediated by the inhibition of AGE formation [43]. We suggest that future studies should be directed towards characterizing the mechanisms inducing the apoptosis of photoreceptors and ganglion cells.…”

Synergistic action of advanced glycation end products and endogenous nitric oxide leads to neuronal apoptosis in vitro: A new insight into selective nitrergic neuropathy in diabetes

“…Aminoguanidine, a potent inhibitor of AGE-mediated crosslinking, has been shown to prevent the development of nitrergic dysfunction in the penis [39,40] and to prevent depletion of nitrergic neurones in the retina of diabetic rats [41]. However aminoguanidine also inhibits nNOS [42] and iNOS [43].…”

Experimental diabetes induces hyperreactivity of rabbit renal artery to 5-hydroxytryptamine

“…A defective NO-dependent renal vasodilation is responsible of the increased vasoconstrictor sensitivity of the diabetic renal vasculature to adenosine (Pflueger et al, 1999). Diabetes is associated with a reduction of nNOS activity in retinal vasculature (Roufail et al, 1998), skeletal muscle (Perreault et al, 2000), mesenteric artery (Ferrer et al, 2000) and penile tissue (Cellek et al, 1999) of the streptozotocin-induced diabetic rats. In contrast, an increased activity of the nNOS pathway has been suggested to play a role in the pathogenesis of diabetic renal hemodynamic changes in the rat (Komers et al, 2000a,b).…”