Effect of insulin on the lysosomal function of rat aortic smooth muscle cells and subcutaneous fibroblasts in tissue culture

Beta-N-acetyl-glucosaminidase: possible role in ocular neovascularization

The possibility that lysosomal enzymes might be involved as angiogenic factors in ocular neovascularization (NV) was investigated. Beta-N-acetyl-glucosaminidase (NAGase) activity, and that of two other glycosidases, were present in the retinal derived protein fraction (RDPF) reported by others to be angiogenic. NAGase, but not the other glycosidases, was inhibited by vitreous. NAGase exhibited the same stability characteristics as RDPF. In diabetic rats there was a significant rise in vitreous but a fall in retinal NAGase activity. The sera of these animals, however, showed elevation in the activities of all five glycosidases. Preliminary experiments indicate that only the intermediate isoenzyme of NAGase, putatively insulin dependent, is elevated in the eyes of these diabetic rats. NAGase was also specifically elevated in the intraocular fluid from monkey eyes with retinal vein occlusion (RVO), and markedly so if NV was present. These results suggest the involvement of NAGase in the neovascular process in the eye.

The effects of glucose and insulin on beta-hexosaminidase in cultured fibroblasts from diabetic and non-diabetic subjects

The effects of glucose and insulin in culture medium on the release and cellular content of beta-hexosaminidase were studied in fibroblast cultures obtained from patients with type II diabetes and from control subjects. The release of beta-hexosaminidase was (positively) correlated to extracellular glucose concentration. The cellular activity was not influenced by glucose. Insulin had no effect on the cellular activity or the release of beta-hexosaminidase. The results were similar for both cell types. It is proposed that increased plasma levels of lysosomal hydrolases (e.g. beta-hexosaminidase) from human diabetics might be due to increased release from cells exposed to elevated glucose concentrations.