C-peptide improves neuropathy in type 1 diabetic BB/Wor-rats

Department of Pathology, Wayne State University, School of Medicine, Detroit, MI 48201, USA.
Diabetes/Metabolism Research and Reviews (Impact Factor: 3.55). 01/2007; 23(1):63-70. DOI: 10.1002/dmrr.672
Source: PubMed


The spontaneously diabetic BB/Wor-rat is a close model of human type 1 diabetes and develops diabetic polyneuropathy (DPN) similar to that seen in type 1 patients. Here we examine the therapeutic effects of C-peptide, delivered as continuous infusion or once daily subcutaneous injections on established DPN.
Diabetic rats were treated from four to seven months duration of diabetes with full continuous replacement dose of rat C-peptide via (a) osmopumps (OS), (b) full replacement dose (HSC) or (c) one-third of full replacement dose (LSC) by once daily injections.
Diabetic rats treated with OS showed improvements in motor nerve conduction velocity (p < 0.001), sural nerve myelinated fibre number (p < 0.005), size (p < 0.05), axonal area (p < 0.001), regeneration (p < 0.001) and overall neuropathy score (p < 0.001). The progressive decline in sensory nerve conduction velocity was fully prevented. The frequencies of Wallerian degeneration were decreased (p < 0.005). HSC-treated rats showed prevention of further progression of DPN (p < 0.001), whereas LSC-treated rats showed a milder progression of DPN (p < 0.001) compared to untreated rats as assessed by neuropathy score.
We conclude that (1) C-peptide is effective in the treatment of established DPN, (2) its effect is dose-dependent and (3) replacement by continuous infusion is the most effective administration of C-peptide.

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    • "C-peptide substitution in type 1 BB/Wor-rats prevents the degenerative processes of the paranode and the node of Ranvier [99] and intervention with C-peptide repairs the paranodal apparatus as evidenced by an increased number of intercalated internodes [17]. It therefore appears as if these functionally significant lesions in type 1 DPN relate to abnormalities in insulin-signaling. "
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    ABSTRACT: Diabetic polyneuropathy (DPN) occurs more frequently in type 1 diabetes resulting in a more severe DPN. The differences in DPN between the two types of diabetes are due to differences in the availability of insulin and C-peptide. Insulin and C-peptide provide gene regulatory effects on neurotrophic factors with effects on axonal cytoskeletal proteins and nerve fiber integrity. A significant abnormality in type 1 DPN is nodal degeneration. In the type 1 BB/Wor-rat, C-peptide replacement corrects metabolic abnormalities ameliorating the acute nerve conduction defect. It corrects abnormalities of neurotrophic factors and the expression of neuroskeletal proteins with improvements of axonal size and function. C-peptide corrects the expression of nodal adhesive molecules with prevention and repair of the functionally significant nodal degeneration. Cognitive dysfunction is a recognized complication of type 1 diabetes, and is associated with impaired neurotrophic support and apoptotic neuronal loss. C-peptide prevents hippocampal apoptosis and cognitive deficits. It is therefore clear that substitution of C-peptide in type 1 diabetes has a multitude of effects on DPN and cognitive dysfunction. Here the effects of C-peptide replenishment will be extensively described as they pertain to DPN and diabetic encephalopathy, underpinning its beneficial effects on neurological complications in type 1 diabetes.
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    ABSTRACT: Diabetic polyneuropathy (DPN) is the most common late complication of diabetes mellitus. The underlying pathogenesis is multifaceted, with partly interrelated mechanisms that display a dynamic course. The mechanisms underlying DPN in type 1 and type 2 diabetes mellitus show overlaps or may differ. The differences are mainly due to insulin deficiency in type 1 diabetes which exacerbates the abnormalities caused by hyperglycaemia. Experimental DPN in rat models have identified early metabolic abnormalities with consequences for nerve conduction velocities and endoneurial blood flow. When corrected, the early functional deficits are usually normalised. On the other hand, if not corrected, they lead to abnormalities in lipid peroxidation and expression of neurotrophic factors which in turn result in axonal, nodal and paranodal degenerative changes with worsening of nerve function. As the structural changes progress, they become increasingly less amendable to metabolic interventions. In the past several years, experimental drugs--such as aldose reductase inhibitors, antioxidants and protein kinase C inhibitors--have undergone clinical trials, with disappointing outcomes. These drugs, targeting a single underlying pathogenetic factor, have in most cases been initiated at the advanced stage of DPN. In contrast, substitution of acetyl-L-carnitine (ALC) or C-peptide in type 1 DPN target a multitude of underlying mechanisms and are therefore more likely to be effective on a broader spectrum of the underlying pathogenesis. Clinical trials utilising ALC have shown beneficial effects on nerve conduction slowing, neuropathic pain, axonal degenerative changes and nerve fibre regeneration, despite relatively late initiation in the natural history of DPN. Owing to the good safety profile of ALC, early initiation of ALC therapy would be justified, with potentially greater benefits.
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