The role of novel inflammation-associated biomarkers in diabetic peripheral neuropathy.

Diabetic neuropathy is one of the commonest complications of diabetes mellitus. Its most frequent form is diabetic peripheral neuropathy (DPN). Currently, there is no established and widely used biomarker for diagnosis and clinical staging of DPN. There is accumulating evidence that low-grade systemic inflammation is a key element in its pathogenesis. In this context, several clinical studies have so far identified potential biomarkers of DPN. These studies have enrolled both subjects with type 1 diabetes mellitus (T1DM) and subjects with type 2 diabetes mellitus (T2DM), including children with T1DM and elderly T2DM subjects. They have also evaluated participants with prediabetes. Potential biomarkers include a wide spectrum of cytokines, chemokines and immune receptors, notably interleukins (IL), mostly IL-1, IL-6 or IL-10, as well as mediators of the tumour necrosis factor-α (TNF-α) related pathway. Cell-ratios, such as neurtrophil-to-lymphocyte ratio (NLR), have yielded promising results as well. Other works have focused on adipokines and identified several signalling molecules (adiponectin, neuregulin 4, isthmin-1 and omentin) as promising biomarkers of DPN. Finally, epigenetic biomarkers have been investigated. Further experience is being gathered with the use of biomarkers in specific age groups and in the discrimination between painless and painful DPN. Prospective studies appear promising in monitoring of DPN progression, but experience is rather limited. Finally, certain cut-off values have been proposed for DPN screening, but these need confirmation. Future large-scale studies are now required to validate biomarkers and to investigate their potential clinical utility.