Differential analysis of effect of high glucose level in the development of neuropathy in a tissue culture model of diabetes mellitus: role of hyperosmolality.

To analyse the contributions of metabolic toxicity of high glucose level and accompanying hyperosmolality to the development of diabetic neuropathy, mouse dorsal root ganglion (DRG) cultures were used. DRGs from postnatal day 7 mice were embedded in collagen gel and incubated in RPMI 1640 culture medium with increasing concentrations of glucose or equimolar amounts of mannitol which would create similar osmolalities. Outgrowth of axons from the peripheral nerve attached to DRG and migration of cells into the gel were quantified. The extent of cell death, apoptosis and mitosis among the migrating cells and apoptosis among DRG neurons following exposure to high glucose or mannitol were also evaluated. The growth of axons was almost equally affected by increasing concentrations of glucose or mannitol up to 395 mOsm/kg H (2)O. Number of migrating cells was close to control values with mannitol between 340-395 mOsm/kg H (2)O while high concentrations of glucose always decreased it. Exposure to high glucose or mannitol led to increased proportions of dead and apoptotic migrating cells and apoptotic DRG neurons. Mitotic activity was also negatively affected by high glucose or mannitol. While glucose proved significantly more detrimental to migrating cells than mannitol in the latter tests, the extent of apoptosis was similar among DRG neurons in both conditions. In conclusion, the contribution of hyperosmolality to the development of neuropathy in high glucose condition appears to be quite significant. The peripheral nerve cells and neurons, however, are differentially affected by hyperosmolality and metabolic toxicity of high glucose.