Abstract
Background:
Research has shown that disturbances in sphingolipid metabolic homeostasis are significant contributors to Diabetic Peripheral Neuropathy (DPN). Ceramides and their metabolites are cell signaling molecules involved in islet cell function, insulin resistance, β-cell apoptosis, and neurodegeneration. However, diabetes-related abnormalities in sphingolipid metabolism in peripheral nerves have received little attention in the scientific literature.
Methods:
Neuroblastoma cells (Neuro2a) were exposed to high glucose (50 mM). Alpha-lipoic acid (ALA; 50 μM) and docosahexaenoic acid (DHA; 50 μM) were considered therapeutic interventions. Myelin-specific and neurotrophin gene expression was also studied in Schwann cells (IMS32) and in DPN induced in mice with streptozotocin (150 mg/kg).
Results:
High glucose reduced cell viability, compromised membrane integrity, and induced apoptosis, as revealed by MTT, propidium iodide, and Annexin V/PI assays. RT-qPCR analysis showed significantly higher mRNA levels of genes that regulate the de novo, salvage, and sphingomyelinase pathways. Bioactive sphingolipids (ceramide, sphingosine, ceramide-1-P, and sphingosine-1-P) were found elevated by ELISA. The apoptotic (AIF, Bak, Bax, Cas-3, Cas-9, and p53) and inflammatory (IL-6, IL-1β, TNF-α, iNOS, and NF-κB) genes were upregulated, while Bcl-2 was downregulated. mRNA expression of myelin-specific proteins and neurotrophic factors was also reduced in the sciatic nerves of DPN mice and HG-treated IMS32 cells. DHA and ALA were found to normalize nearly all anomalies induced by hyperglycemia.
Discussion:
The genes regulating the de novo, salvage, and sphingomyelinase pathways were differentially modulated in diabetic conditions. We suggest that targeting those genes would be a safer approach to ameliorate ceramide-mediated nerve damage in diabetes. Myelin-specific genes, including NT-3, NT-4, NGF-β, BDNF, CNTF, and GDNF, were downregulated in the sciatic nerve of neuropathic animals. Treatment with ALA and DHA proved beneficial in reversing the conditions; hence, supplementation with ALA and DHA, in addition to the standard anti-diabetic treatment regimen, is suggested.
Conclusion:
These findings suggest significant implications of hyperglycemia on sphingolipid metabolic impairment, which, in turn, impacts cell integrity and viability, myelin stability, and neurodegeneration.