Replacing C-Peptide in Type 1 Diabetes Improved Nerve Function in a Randomized Controlled Trial | Research

The takeaway

Six months of C-peptide replacement therapy improved sensory nerve conduction velocity, clinical neurological scores, and vibration perception in type 1 diabetic patients with neuropathy.

1.0 m/s nerve speed improvement
C-peptide-treated patients with less severe neuropathy showed significant improvement in sensory nerve conduction velocity versus placebo after just 6 months

What the researchers found

C-peptide replacement therapy for 6 months improved sensory nerve conduction velocity (SCV) in type 1 diabetic patients with neuropathy. Both dose groups (1.5 mg/day and 4.5 mg/day) showed similar improvement. In the less severely affected patients (SCV < 2.5 SD below normal at baseline, n=70), SCV improved by 1.0 m/s compared to placebo (p<0.014). The proportion of patients showing SCV improvement >1.0 m/s was significantly greater in C-peptide groups versus placebo (p<0.03). Clinical neurological impairment scores and vibration perception also improved (p<0.011 and p<0.002 respectively). These improvements occurred independently of blood sugar control, which changed similarly across all groups.

Why it matters

Diabetic neuropathy is the most common complication of type 1 diabetes, causing numbness, pain, and loss of sensation in the extremities, with no approved disease-modifying treatment. C-peptide — a natural byproduct of insulin production that is completely absent in type 1 diabetes — showed the ability to actually improve nerve function, not just slow deterioration. This is the first randomized controlled trial showing that replacing a missing peptide can reverse neuropathy damage.

The numbers in context

n=139 completed · 6-month treatment · 1.5 or 4.5 mg/day SC · SCV improved 1.0 m/s vs. placebo (p<0.014 in less severe) · NIA score improved (p<0.011) · Vibration perception improved (p<0.002) · 86% had clinical neuropathy at baseline · Mean diabetes duration 30.6 years

How the study worked

Exploratory, double-blinded, randomized, placebo-controlled trial at five centers in Sweden. 139 type 1 diabetes patients with peripheral neuropathy completed the protocol. Three groups: C-peptide 1.5 mg/day (replacement dose, four subcutaneous injections daily), C-peptide 4.5 mg/day (3× replacement), or placebo. Neurological examination and neurophysiological measurements (nerve conduction velocity, vibration perception, clinical impairment scores) were performed at baseline and 6 months.

What this study cannot tell us

Described as 'exploratory,' suggesting it was powered for signal detection rather than definitive efficacy. The four-times-daily injection regimen is burdensome. The higher dose (4.5 mg/day) didn't show greater benefit than the replacement dose, raising questions about the dose-response relationship. Six months may be too short to see full nerve regeneration effects. The study was published in 2007, and C-peptide has not progressed to approval despite these promising results.

How to read the evidence

This is a randomized, double-blind, placebo-controlled trial — the gold standard of clinical evidence. However, it was described as 'exploratory' and had a moderate sample size (n=139). The five-center design in Sweden adds credibility but limits ethnic/geographic generalizability.

When this study was published

Published in 2007, this study is nearly two decades old. Despite positive results, C-peptide has not progressed to regulatory approval. More recent research continues to explore C-peptide's biological activities, but the lack of commercial development remains a notable gap.

The bigger picture

For decades, C-peptide was considered biologically inert — just a byproduct of insulin production. This trial is part of the evidence that overturned that view, showing C-peptide has its own biological functions, particularly in protecting nerves and blood vessels. Despite promising results, C-peptide replacement has not reached FDA approval, partly due to the commercial challenges of developing a therapy for a relatively small patient population. The story of C-peptide illustrates how a 'waste product' peptide can turn out to have important therapeutic potential.

Questions still open

Why hasn't C-peptide replacement progressed to approval despite positive trial results from nearly two decades ago?
Would longer treatment periods (beyond 6 months) produce greater nerve function improvement or even nerve regeneration?
Could C-peptide be combined with insulin in a single formulation to simplify delivery for type 1 diabetes patients?

Common questions

What is C-peptide and why are type 1 diabetes patients missing it?

C-peptide is a small peptide released alongside insulin when the pancreas processes proinsulin. In type 1 diabetes, the immune system destroys the insulin-producing beta cells, so patients lose both insulin and C-peptide. While insulin is replaced with injections, C-peptide has never been replaced — until studies like this one showed it actually has important biological functions, particularly for nerve health.

If C-peptide worked in this trial, why isn't it available as a treatment?

Despite positive results, C-peptide replacement faced commercial challenges: it would need to be injected four times daily alongside insulin, the type 1 diabetes population is smaller than type 2, and the patent landscape was complicated. The company developing it (Creative Peptides/Cebix) eventually ended development. However, the scientific evidence supporting C-peptide's nerve-protective effects remains robust.

Read the original research

C-Peptide replacement therapy and sensory nerve function in type 1 diabetic neuropathy.

Diabetes care, 30(1), 71-6

View on PubMed ↗

Citation

Ekberg, Karin; Brismar, Tom; Johansson, Bo-Lennart; Lindström, Per; Juntti-Berggren, Lisa; Norrby, Anders; Berne, Christian; Arnqvist, Hans J; Bolinder, Jan; Wahren, John. (2007). C-Peptide replacement therapy and sensory nerve function in type 1 diabetic neuropathy.. Diabetes care, 30(1), 71-6.