C-peptide replacement therapy as an emerging strategy for preventing diabetic vasculopathy

Dammarenediol-II Prevents VEGF-Mediated Microvascular Permeability in Diabetic Mice

Diabetic retinopathy is a major diabetic complication predominantly caused by vascular endothelial growth factor (VEGF)-induced vascular permeability in the retina; however, treatments targeting glycemic control have not been successful. Here, we investigated the protective effect of dammarenediol-II, a precursor of triterpenoid saponin biosynthesis, on VEGF-induced vascular leakage using human umbilical vein endothelial cells (HUVECs) and diabetic mice. We overproduced the compound in transgenic tobacco expressing Panax ginseng dammarenediol-II synthase gene and purified using column chromatography. Analysis of the purified compound using a gas chromatography-mass spectrometry system revealed identical retention time and fragmentation pattern to those of authentic standard dammarenediol-II. Dammarenediol-II inhibited VEGF-induced intracellular reactive oxygen species generation, but it had no effect on the levels of intracellular Ca(2+) in HUVECs. We also found that dammarenediol-II inhibited VEGF-induced stress fiber formation and vascular endothelial-cadherin disruption, both of which play critical roles in modulating endothelial permeability. Notably, microvascular leakage in the retina of diabetic mice was successfully inhibited by intravitreal dammarenediol-II injection. Our results suggest that the natural drug dammarenediol-II may have the ability to prevent diabetic microvascular complications, including diabetic retinopathy.

Type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is an expanding global health problem, closely linked to the epidemic of obesity. Individuals with T2DM are at high risk for both microvascular complications (including retinopathy, nephropathy and neuropathy) and macrovascular complications (such as cardiovascular comorbidities), owing to hyperglycaemia and individual components of the insulin resistance (metabolic) syndrome. Environmental factors (for example, obesity, an unhealthy diet and physical inactivity) and genetic factors contribute to the multiple pathophysiological disturbances that are responsible for impaired glucose homeostasis in T2DM. Insulin resistance and impaired insulin secretion remain the core defects in T2DM, but at least six other pathophysiological abnormalities contribute to the dysregulation of glucose metabolism. The multiple pathogenetic disturbances present in T2DM dictate that multiple antidiabetic agents, used in combination, will be required to maintain normoglycaemia. The treatment must not only be effective and safe but also improve the quality of life. Several novel medications are in development, but the greatest need is for agents that enhance insulin sensitivity, halt the progressive pancreatic β-cell failure that is characteristic of T2DM and prevent or reverse the microvascular complications. For an illustrated summary of this Primer, visit: http://go.nature.com/V2eGfN.

C-peptide as a Therapy for Kidney Disease: A Systematic Review and Meta-Analysis

C-peptide has intrinsic biological activity and may be renoprotective. We conducted a systematic review to determine whether C-peptide had a beneficial effect on renal outcomes. MEDLINE, EMBASE, and the Cochrane Central Databases were searched for human and animal studies in which C-peptide was administered and renal endpoints were subsequently measured. We identified 4 human trials involving 74 patients as well as 18 animal studies involving 35 separate experiments with a total of 641 animals. In humans, the renal effects of exogenously delivered C-peptide were only studied in type 1 diabetics with either normal renal function or incipient nephropathy. Pooled analysis showed no difference in GFR (mean difference, -1.36 mL/min/1.73 m2, p = 0.72) in patients receiving C-peptide compared to a control group, but two studies reported a reduction in glomerular hyperfiltration (p<0.05). Reduction in albuminuria was also reported in the C-peptide group (p<0.05). In diabetic rodent models, C-peptide led to a reduction in GFR (mean difference, -0.62 mL/min, p<0.00001) reflecting a partial reduction in glomerular hyperfiltration. C-peptide also reduced proteinuria (mean difference, -186.25 mg/day, p = 0.05), glomerular volume (p<0.00001), and mesangial matrix area (p<0.00001) in diabetic animals without affecting blood pressure or plasma glucose. Most studies were relatively short-term in duration, ranging from 1 hour to 3 months. Human studies of sufficient sample size and duration are needed to determine if the beneficial effects of C-peptide seen in animal models translate into improved long-term clinical outcomes for patients with chronic kidney disease. (PROSPERO CRD42014007472)

Therapeutic Effects of PPAR α on Neuronal Death and Microvascular Impairment

Peroxisome-proliferator activated receptor-alpha (PPARα) is a broadly expressed nuclear hormone receptor and is a transcription factor for diverse target genes possessing a PPAR response element (PPRE) in the promoter region. The PPRE is highly conserved, and PPARs thus regulate transcription of an extensive array of target genes involved in energy metabolism, vascular function, oxidative stress, inflammation, and many other biological processes. PPARα has potent protective effects against neuronal cell death and microvascular impairment, which have been attributed in part to its antioxidant and anti-inflammatory properties. Here we discuss PPARα's effects in neurodegenerative and microvascular diseases and also recent clinical findings that identified therapeutic effects of a PPARα agonist in diabetic microvascular complications.

Circulating Dipeptidyl Peptidase-4 Activity is Associated with Diabetic Retinopathy in Type 1 Diabetic Patients

Purpose

Diabetic retinopathy (DR) is the most frequent complication among patients with type 1 diabetes mellitus (T1DM). Dipeptidyl peptidase–4 (DPP4) is a protease with elevated activity in patients with T1DM. Several studies indicate that DPP4 inhibitors might have beneficial effect on nonproliferative retinopathy (NPR) development as well as on its progression to proliferative retinopathy (PR). We aimed to explore the relationship between serum DPP4 activity and DR in patients with T1DM.

Methods

This cross-sectional study recruited 44 patients with T1DM. The DPP4 activity was measured by colorimetric assay in a microplate reader. Photodocumented retinopathy status was made according to the EURODIAB protocol.

Results

A total of 28 (63.6%) patients were men, mean age 45.36 years, diabetes duration 23.71 years, glycated hemoglobin A1c (HbA1c) 7.4%. Patients were stratified into 2 groups according to retinopathy prevalence. Group 1 comprised 14 (31.85%) patients with DR absence while the second group consisted of 30 (68.15%) patients with both PR and NPR. Group 1 had lower fasting serum DPP4 activity (25.85 vs 33.84 U/L, p<0.001) when compared to the second group. In the binary logistic regression model adjusted for age, sex, diabetes duration, and HbA1c level, DPP4 activity was associated with DR prevalence (odds ratio 1.887 [1.073-3.321]).

Conclusions

Serum DPP4 activity may be independently associated with both DR types in patients with T1DM. Further study is warranted to elucidate whether there is an association between DPP4 activity and DR severity and/or progression.