In This Issue of Diabetes Free

A hybrid insulin peptide formed by the fusion of C-peptide and chromogranin A (HIP9) appears to have a pathogenic role in the development of type 1 diabetes, according to Callebaut et al. (p. 743). Specifically, HIP9 appears to drive T-cell responses in individuals with a haplotype that is usually considered to have no risk for the disease, potentially explaining why disease rates are increasing, particularly in individuals without high-risk HLA haplotypes. The findings come from a study that initially focused on isolating an HIP9-specific T-cell clone via single-cell sorting followed by a series of assays to sort through the haplotypes that were most likely linked. After successfully isolating the clone, the authors found that the response was restricted by HLA-DRB1*11, which is considered a nonrisk allele. The authors then used tetramer-based assays on peripheral blood mononuclear cells from individuals with and without type 1 diabetes to confirm they could detect HIP9 responses in peripheral blood. The authors then compared HIP9 responses in 11 individuals with diabetes and 11 individuals without diabetes. All individuals were DRB1*11 positive. They found that individuals with diabetes had significantly higher HIP9 frequencies than individuals without diabetes. They also found a significant correlation between HIP9 frequency and age at diagnosis, with younger age corresponding to higher frequencies. The authors propose that further studies with larger cohorts of low-risk individuals would be helpful to verify the relationship with age, although these might be challenging because of low prevalence of the allele. “We were surprised to discover that responses to this hybrid insulin peptide were restricted by a nonrisk HLA allele, since we had previously speculated that having a high-risk HLA might be required,” said author Eddie A. James. “Nonrisk HLA alleles have a greater propensity for generating regulatory T cells that respond to conventional peptides, but this might not occur for hybrid peptides.”

Cardiovascular autonomic neuropathy (CAN) appears to be a strong independent predictor of kidney function decline in both type 1 and type 2 diabetes, according to Tang et al. (p. 751). Specifically, participants in two prior diabetes-related trials who had evidence of CAN at baseline experienced significantly more rapid glomerular filtration rate decline over several years of follow-up compared with individuals who did not have CAN. The associations remained (largely) significant after adjustment for confounding factors, setting up CAN as an independent predictor of kidney failure in both types of diabetes and potentially also as a target for novel therapies. The findings come from post hoc analyses of the Preventing Early Renal Loss in Diabetes (PERL) trial, which enrolled people with type 1 diabetes, and the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial, which enrolled individuals with type 2 diabetes. Both studies collected a wide array of clinical data, including serial assessments of estimated glomerular filtration rates (eGFR) to evaluate diabetic kidney disease and electrocardiogram-derived indices of heart rate variability to evaluate CAN. The authors found that CAN was associated with a more negative decline in eGFR during follow-up, increased odds of rapid eGFR decline, and higher risk for ≥40% eGFR loss. After adjusting for potential confounders (e.g., baseline GFR and albuminuria), the associations remained significant. Based on the findings, the authors propose that specific measures of CAN derived from electrocardiograms might be a useful addition to known clinical risk factors for rapid kidney function loss. “The fact that this biomarker now can be routinely assessed through a simple electrocardiogram makes its use in clinical practice feasible,” said author Rodica Pop-Busui. “CAN is another biomarker that we have at our disposal to select patients with type 1 or type 2 diabetes who should be targeted with aggressive renoprotective treatments,” added author Alessandro Doria.

The sodium-glucose cotransporter 2 (SGLT2) inhibitor canagliflozin appears to be able to provide a protective effect to proximal tubular cells of the kidney via a mechanism that goes beyond its glucose-lowering effect. According to Nakatsuka et al. (p. 763), the mechanism centers on the 78-kDa glucose-regulated protein, or GRP78, and integrin β1 and their interaction with SGLT2 in kidney cells. Using a combination of mouse and cell studies, the authors investigated GRP78 and its potential role in kidney function. Observations, including positive renal outcomes, from prior trials with SGLT2 inhibitors prompted the authors to hypothesize that unknown mechanisms may exist that go beyond their glucose-lowering properties. They found that in kidneys from mice with streptozotocin-induced diabetes, GRP78, SGLT2, and integrin β1 on plasma membrane fractions were all increased compared with nondiabetic controls, but they were suppressed by canagliflozin (an SGLT2 inhibitor). There was also altered subcellular localization of GRP78 and integrin β1 in mice with diabetes that promoted epithelial mesenchymal transition and fibrosis (i.e., elements of kidney disease). Again, canagliflozin could mitigate these effects. In cultured HK2 cells, the authors found high glucose conditions resulted in reduced intracellular GRP78 but increased secretion rates and epithelial mesenchymal transition-like changes, effects that canagliflozin could abolish. Further in vitro experiments with recombinant GRP78 revealed potential inflammation in tubular cells that canagliflozin reversed. Mechanistic studies then pointed to a variety of effects of canagliflozin on entities such as sarco/endoplasmic reticulum Ca²⁺-ATPase, p65NFkB, and Akt and related pathways that ultimately pointed toward kidney protective mechanisms of canagliflozin that go beyond glucose lowering. Commenting further, author Atsuko Nakatsuka said, “We have discovered a novel mechanism of action of canagliflozin mediated by GRP78. We hope that this finding will be translated into clinical practice.”

An antibody called mAb43 appears to prevent and reverse new-onset type 1 diabetes, at least in mice prone to diabetes, according to Kasinathan et al. (p. 806). Specifically, it seems that the antibody acts against zinc transporter 8 (ZnT8), which is a major autoantigen present on the surface of β-cells, and effectively blocks autoantibodies from recognizing them. Given that the approach masks rather than modifies features of β-cells, the authors propose that the approach is likely to be clinically relevant (and safe) in humans despite the differences in immune systems compared with mice. The findings come from a series of experiments with nonobese diabetic (NOD) mice as well as isolated cell lines and specifically looked at the in vivo consequences of β-cell masking with mAb43 and the longer-term efficacy/safety of repeated dosing in NOD mice. Initial immunofluorescence experiments with live primary human islet cells confirmed the binding of the antibody to ZnT8 on the β-cell surface and its rapid internalization. In 10-week-old NOD mice, weekly administration of mAb43 up to 35 weeks resulted in nearly all mice maintaining euglycemia, while control NOD mice all developed diabetes. Delayed administration of the antibody resulted in prolonged but not indefinite protection against diabetes, and discontinuation of treatment at various stages resulted in mice gradually developing diabetes. Diving deeper, further experiments revealed preservation of β-cell mass with the treatment and that it progressively reduced insulitis severity over time. Notably, the mice also exhibited insulin autoantibody negativity that was lost following treatment cessation. Perhaps most significantly, the treatment could also result in remission from diabetes after onset. Subsequent mechanistic studies suggested the masking suppresses an immunological cascade involving B-cell antigens and ultimately T-cell.mediated destruction of β-cells. Commenting further, author Dax Fu said, “As an islet-specific autoantibody, mAb43 opens a new avenue of research to explore autoantibodies transmitted maternally or administered systemically as a safe therapeutic option.”