Extended Duration of Hyperglycemia Result in Human-Like Corneal Nerve Lesions in Mice With Alloxan- and Streptozotocin-Induced Type 1 Diabetes

Abstract

PURPOSE. Previous experimental studies assessing corneal nerves as a measure of the severity of diabetic peripheral neuropathy have yielded discordant results; this may have been due to the effect of the short duration of the induced diabetes. We investigated whether increases in the duration of hyperglycemia result in the development of corneal lesions in a mouse model of alloxan (AL)-or streptozotocin (STZ)-induced type 1 diabetes. We further determined whether corneal nerve fiber density, intraepidermal nerve fiber density (IENFD), and sural nerve morphology can be used as morphologic markers of diabetic peripheral neuropathy in rodent models. METHODS. A total of 30 female ICR mice were divided into three groups: those with STZinduced (STZ group) and AL-induced (AL group) diabetes, and a control group. Hyperglycemia was maintained in diabetic mice for 35 weeks. Animals were euthanized at 41 weeks of age. RESULTS. Subbasal nerve plexus density (SBNPD) and terminal epithelial nerve density (TEND) in the cornea, as well as IENFD, were significantly lower, and mean sural nerve axon sizes were smaller in mice in the STZ and AL groups than in the control group. There were significant correlations between IENFD and SBNPD, and between IENFD and TEND. CONCLUSIONS. These results indicate that the TEND and SBNTD of the cornea may be useful morphologic markers for diabetic peripheral neuropathy.

Hyperglycemia Suppresses Age-Related Increases in Corneal Peripheral Sensory Nerves in Wistar Bon Kobori (WBN/Kob) Rats

“…20,21 Recently, we reported that, following long-term (35 weeks) hyperglycemia, mice with STZ-induced and alloxan-induced type 1 diabetes exhibited significant reductions in corneal sensory nerve fiber density. 22 Our findings suggested that extended exposure to hyperglycemia could cause corneal lesions in mice with STZ-induced or alloxan-induced type 1 diabetes. STZ-induced diabetic rats and mice show rapid and overt hyperglycemia, slow nerve conduction, and a mild degree of axonal atrophy.…”

“…Male WBN/Kob rats exhibit diabetic symptoms from approximately 30 weeks of age (initial diabetic stage), and their diabetic condition progresses until approximately 90 weeks of age (long-lasting diabetic stage). 22 In the present study, WBN/ Kob rats were separated into four groups (n ¼ 7 per group): (1) 36-week male rats, (2) 36-week female rats, (3) 90-week male rats, (4) 90-week female rats. As the mother strain of WBN/Kob rats was not available, we used female rats as age-matched and nondiabetic controls.…”

“…Histological and morphometrical analysis was performed as in a prior report. 22 Briefly, the rats were killed by exsanguination, and foot pads were collected from the plantar surface of the hind paw. The sections were fixed, sectioned (80-lm sections), stained with a pan-neuronal marker (rabbit polyclonal antiprotein gene product 9.5 (PGP9.5) antibody [dilution, 1:200, Z5116; Dako, Santa Clara, CA, USA]), and visualized with Alexa Fluor 488-conjugated secondary antibody (Invitrogen, Carlsbad, CA, USA) using the method described in a prior report.…”

“…The sections were fixed, sectioned (80-lm sections), stained with a pan-neuronal marker (rabbit polyclonal antiprotein gene product 9.5 (PGP9.5) antibody [dilution, 1:200, Z5116; Dako, Santa Clara, CA, USA]), and visualized with Alexa Fluor 488-conjugated secondary antibody (Invitrogen, Carlsbad, CA, USA) using the method described in a prior report. 22 Negative control staining was also performed as in the prior report. 22 The IENFD was measured as in the prior report.…”

“…22 Negative control staining was also performed as in the prior report. 22 The IENFD was measured as in the prior report. 22…”