Short‐term subcutaneous insulin treatment delays but does not prevent diabetes in NOD mice

Abstract

Despite encouraging results in the NOD mouse, type 1 diabetes prevention trials using subcutaneous insulin have been unsuccessful. To explain these discrepancies, 3-weekold NOD mice were treated for 7 weeks with subcutaneous insulin at two different doses: a high dose (0.5 U/mouse) used in previous mouse studies; and a low dose (0.005 U/mouse) equivalent to that used in human trials. Effects on insulitis and diabetes were monitored along with immune and metabolic modifications. Low-dose insulin did not have any effect on disease incidence. High-dose treatment delayed but did not prevent diabetes, with reduced insulitis reappearing once insulin discontinued. This effect was not associated with significant immune changes in islet infiltrates, either in terms of cell composition or frequency and IFN-γ secretion of islet-reactive CD8 + T cells recognizing the immunodominant epitopes insulin B 15-23 and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) [206][207][208][209][210][211][212][213][214] . Delayed diabetes and insulitis were associated with lower blood glucose and endogenous C-peptide levels, which rapidly returned to normal upon treatment discontinuation. In conclusion, high-but not low-dose prophylactic insulin treatment delays diabetes onset and is associated with metabolic changes suggestive of β-cell "rest" which do not persist beyond treatment. These findings have important implications for designing insulin-based prevention trials.Keywords: Insulin r NOD mouse r Prevention r T cells r Type 1 diabetes IntroductionType 1 diabetes (T1D) is an autoimmune disease in which failures in central and peripheral tolerance mechanisms lead to T-cellmediated destruction of insulin-producing β cells. Several β-cell Ags have been identified, among which insulin and its precursor (pre)proinsulin ((pre)PI) are major targets of islet-reactive T cells, both in humans [1] and in NOD mice [2]. This led to the Correspondence: Dr. Roberto Mallone e-mail: roberto.mallone@inserm.fr hypothesis that subcutaneous insulin administration could prevent disease, the rationale of which is twofold. First, insulin administration could induce a state of "β-cell rest" that would make β cells less vulnerable to metabolic stress, apoptosis [3], and possibly to immune-mediated destruction [4]. Second, repeated subcutaneous insulin injections could act as a vaccination protocol potentially restoring immune tolerance [5]. The relative role of these two putative mechanisms remains unsettled.Studies in the NOD mouse showed that subcutaneously administered insulin, started prior to disease development, is capable of preventing insulitis and diabetes [6]. This observation prompted the Diabetes Prevention Trial-Type 1 (DPT-1) [7] Eur. J. Immunol. 2012. 42: 1553-1561 developing disease [8]. However, both trials were unsuccessful, as no difference in T1D incidence was observed between insulinand placebo-treated individuals [7,8].It is still not clear why this translation from animal studies to human clinical trials fail...

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“…1% dose of INS used for intensive glycemic control in mice. This dose was selected in correspondence to the dose used in human trials and based on the dose used in insulin tolerance tests 44, 46, 47. We found that one-time injection of low-dose INS could transiently reduce hyperglycemia in T1D mice (Fig.…”

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“…Only the high dose achieved some effects: it delayed but did not prevent diabetes onset, it reduced insulitis, and suppressed C-peptide secretion. However, all these effects were only transient and rapidly lost upon (83).…”

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