Skip to main page content
U.S. flag

An official website of the United States government

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2022 Mar 10;14(6):1162.
doi: 10.3390/nu14061162.

Neuroprotective Effects of Nicotinamide (Vitamin B3) on Neurodegeneration in Diabetic Rat Retinas

Kyoung In Jung  1 , Jeong-Sun Han  1 , Chan Kee Park  1
Affiliations

Neuroprotective Effects of Nicotinamide (Vitamin B3) on Neurodegeneration in Diabetic Rat Retinas

Kyoung In Jung et al. Nutrients. .

Abstract

The loss of inner retinal neurons is an initial event in diabetic retinopathy. In diabetic retinas, oxidative stress is increased, which could lead to increased oxidative DNA damage. Nicotinamide is a precursor to nicotinamide adenine dinucleotide, which contributes to the DNA damage response. We investigated whether nicotinamide plays a neuroprotective role in diabetic retinal neurodegeneration in terms of DNA repair. Male Sprague Dawley rats with streptozotocin-induced diabetes were orally administered nicotinamide (500 mg/kg/day) for 4 or 12 weeks. Oxidative stress exhibited by dihydroethidium was upregulated at 4 and 12 weeks after onset of diabetes, and nicotinamide treatment reduced oxidative stress at 4 weeks after induction of diabetes. Oxidative DNA damage measured by 8-hydroxy-2'-deoxyguanosine (8-OHdG) increased at 4 and 12 weeks after induction of diabetes and decreased following nicotinamide treatment. The elevated expression of glial fibrillary acidic protein (GFAP) induced by diabetes was attenuated by nicotinamide treatment. In Western blot analysis, the increased expression of cleaved PARP-1 in diabetes was attenuated by nicotinamide treatment at 12 weeks after induction of diabetes. The diabetes-induced apoptosis of inner retinal cells detected by the TUNEL assay was reduced by nicotinamide treatment. In conclusion, nicotinamide attenuated retinal neurodegeneration in diabetes, probably by reducing oxidative DNA damage and supporting DNA repair.

Keywords: DNA repair; apoptosis; diabetic retinopathy; neuroprotection; nicotinamide; retinal ganglion cell.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Timetable of the experimental design. Serum glucose values were assessed at 3 days after induction of diabetes. From the day when diabetes was confirmed, the rats in the nicotinamide group were given 500 mg/kg/day oral administration of nicotinamide in drinking water for 4 weeks or 12 weeks. NAM, nicotinamide; STZ, streptozotocin.
Figure 2
Figure 2
Representative posterior eyecup image stained with DAPI for analysis. Each eyecup was split into 2 mid-central (1.5 mm from the optic nerve) and 2 peripheral regions (3.5 mm from the optic nerve) for image assay.
Figure 3
Figure 3
Body weight and blood glucose level. Body weight was lighter in the diabetes group than in the normal control group from one week to twelve weeks after streptozotocin injection, regardless of drug treatment (all p < 0.05). Blood glucose was elevated in the diabetic rats compared to the normal control rats from one week to twelve weeks after onset of diabetes (all p < 0.05). NAM, nicotinamide. *, significant difference exists between groups (p < 0.05).
Figure 4
Figure 4
Dihydroethidium (DHE) staining, which detects superoxide (A–D). Four and twelve weeks after induction of diabetes, retinas showed extensively increased staining for DHE spanning the vertical retinal section (both p < 0.001). Nicotinamide treatment reduced DHE expression at 4 weeks after onset of diabetes (p < 0.001). DHE, dihydroethidium; DM, diabetes mellitus; NAM, nicotinamide. Scale bar = 20 μm. GCL, ganglion cell layer. INL, inner nuclear layer. ONL, outer nuclear layer. *, significantly different as indicated (p < 0.05).
Figure 5
Figure 5
Oxidative DNA damage. 8-Hydroxy-2′-deoxyguanosine (OHdG) expression was observed in the ganglion cell layer (GCL) at 4 weeks after injection of streptozotocin. 8-OHdG immunostaining was extended to the inner nuclear layer at 12 weeks after onset of diabetes (A,C). Nicotinamide treatment attenuated increased 8-OHdG labeling by diabetes at 4 and 12 weeks after induction of diabetes (p = 0.002, 0.005, respectively; (B,D)). Scale bar = 20 μm. DM, diabetes mellitus; NAM, nicotinamide. GCL, ganglion cell layer. INL, inner nuclear layer. ONL, outer nuclear layer. *, significantly different as indicated (p < 0.05).
Figure 6
Figure 6
Glial activation. Glial fibrillary acidic protein (GFAP) immunofluorescence staining was increased, extending to the outer nuclear layer compared to the normal control group at 4 and 12 weeks after onset of diabetes (A,C). Nicotinamide treatment significantly attenuated GFAP expression at 4 and 12 weeks after induction of diabetes (Both p < 0.001; (B,D)). Scale bar = 20 μm. DM, diabetes mellitus; NAM, nicotinamide. GCL, ganglion cell layer. INL, inner nuclear layer. ONL, outer nuclear layer. *, significantly different as indicated (p < 0.05).
Figure 7
Figure 7
(A) Poly(ADP-ribose)polymerase (PARP)-1 immunofluorescence staining. The proportion of PARP-1-positive cells was elevated in the diabetes group compared to the normal control group at 4 weeks and 12 weeks after onset of diabetes (both p < 0.001). An increased expression of PARP-1 in diabetic conditions was decreased by nicotinamide treatment at 12 weeks after induction of diabetes (p < 0.001). (B) Western blotting of poly(ADP-ribose)polymerase (PARP)-1. There was no significant difference in the expression of full-length PARP-1 according to the presence of diabetes or nicotinamide treatment at 4 or 12 weeks after onset of diabetes (p = 0.228, p = 0.103, respectively) Cleaved PARP-1 expression was elevated in the diabetes group compared to the normal control group at 4 and 12 weeks after induction of diabetes (p = 0.002, p < 0.001, respectively). Elevated expression of cleaved PARP-1 was reduced by nicotinamide treatment 12 weeks after onset of diabetes (p < 0.001). Scale bar = 20 μm. DM, diabetes mellitus; NAM, nicotinamide. GCL, ganglion cell layer. INL, inner nuclear layer. ONL, outer nuclear layer. *, significantly different as indicated (p < 0.05).
Figure 8
Figure 8
Apoptosis in the diabetic retina. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells were observed in the ganglion cell layer (GCL) and colocalized with anti-NeuN antibody at 4 and 12 weeks after induction of diabetes (A,C). The percentage of TUNEL-positive cells was higher in diabetic retinas than in the normal control (p = 0.002, p < 0.001) at 4 and 12 weeks, respectively, after onset of diabetes (B,D). The proportion of apoptotic cells in diabetic retinas was reduced by administration of nicotinamide at 4 and 12 weeks after induction of diabetes (p = 0.002, p < 0.001, respectively). Scale bar = 20 μm. DM, diabetes mellitus; NAM, nicotinamide. INL, inner nuclear layer. ONL, outer nuclear layer. *, significantly different as indicated (p < 0.05).
Figure 9
Figure 9
Electron microscopy of cross-sections through the region surrounding the distal myelinated optic nerve demonstrated that axons with normal axoplasm were surrounded by myelin sheaths in the normal control eyes (A). In the diabetic retinas, myelin sheaths were thinned and unorganized, and axoplasm was sparse compared to the control retinas (B). In the retinas of diabetes model mice that underwent nicotinamide treatment, myelin sheaths and axoplasm were relatively preserved (C). Scale bars = 0.5 μm. NAM, nicotinamide. Red asterisk, axoplasm. Red arrow, myelin sheaths.
Figure 10
Figure 10
Hypothetical overview of oxidative DNA damage, DNA repair, and effects of nicotinamide (precursor of NAD+) supplementation on retinal neurodegeneration.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Antonetti D.A., Klein R., Gardner T.W. Diabetic retinopathy. N. Engl. J. Med. 2012;366:1227–1239. doi: 10.1056/NEJMra1005073. - DOI - PubMed
    1. Cheung N., Mitchell P., Wong T.Y. Diabetic retinopathy. Lancet. 2010;376:124–136. doi: 10.1016/S0140-6736(09)62124-3. - DOI - PubMed
    1. Simo R., Simo-Servat O., Bogdanov P., Hernandez C. Neurovascular Unit: A New Target for Treating Early Stages of Diabetic Retinopathy. Pharmaceutics. 2021;13:1320. doi: 10.3390/pharmaceutics13081320. - DOI - PMC - PubMed
    1. Stitt A.W., Curtis T.M., Chen M., Medina R.J., McKay G.J., Jenkins A., Gardiner T.A., Lyons T.J., Hammes H.P., Simo R., et al. The progress in understanding and treatment of diabetic retinopathy. Prog. Retin. Eye Res. 2016;51:156–186. doi: 10.1016/j.preteyeres.2015.08.001. - DOI - PubMed
    1. Park H.Y., Kim I.T., Park C.K. Early diabetic changes in the nerve fibre layer at the macula detected by spectral domain optical coherence tomography. Br. J. Ophthalmol. 2011;95:1223–1228. doi: 10.1136/bjo.2010.191841. - DOI - PubMed