Patterns of cutaneous nerve fibre loss and regeneration in type 2 diabetes with painful and painless polyneuropathy.

AIMS/HYPOTHESIS: The determinants and mechanisms of the development of diabetic sensorimotor polyneuropathy as a painful (DSPN+p) or painless (DSPN-p) entity remain unclear. We examined the degree of cutaneous nerve fibre loss and regeneration in individuals with type 2 diabetes with DSPN+p or DSPN-p compared with individuals with recent-onset type 2 diabetes and corresponding healthy volunteers. METHODS: In this cross-sectional study, skin biopsies taken from the distal lateral calf were obtained from individuals with recent-onset type 2 diabetes (n = 32) from the German Diabetes Study, with DSPN+p (n = 34) and DSPN-p (n = 32) from the PROPANE study, and volunteers with normal glucose tolerance (n = 50). Double immunofluorescence staining for protein gene product 9.5 (PGP9.5) (pan-neuronal marker) and growth-associated protein 43 (GAP-43) (nerve regeneration marker) was applied to assess intraepidermal nerve fibre density (IENFD) and length (IENFL) and dermal nerve fibre length (DNFL). DSPN was diagnosed using the modified Toronto Consensus (2011) criteria, while neuropathic pain was assessed using an 11-point Numerical Rating Scale. RESULTS: After adjustment for age, sex, BMI and HbA1c, IENFD and IENFL were reduced for both markers in individuals with recent-onset diabetes and both DSPN groups compared with control participants (all p < 0.05), but did not differ between the DSPN groups. The DNFL GAP-43/PGP9.5 ratio was higher in the DSPN+p and DSPN-p groups compared with control participants (1.18 ± 0.28 and 1.07 ± 0.10 vs 1.02 ± 0.10; p ≤ 0.05) and in the DSPN + p group compared with DSPN-p (p < 0.05). Correlation analyses showed distinct inverse associations between the DNFL GAP-43/PGP9.5 ratio and PGP9.5 positive IENFD as well as DNFL (IENFD: ß = -0.569, DNFL: ß = -0.639; both p < 0.0001) in individuals with type 2 diabetes, but not in the control group. A similar pattern was found for correlations between the DNFL GAP-43/PGP9.5 ratio and peripheral nerve function tests. CONCLUSIONS/INTERPRETATION: Dermal nerve fibre regeneration is enhanced in DSPN, particularly in DSPN+p, and increases with advancing intraepidermal nerve fibre loss. These data suggest that, despite progressive epidermal fibre loss, dermal nerve repair is preserved, particularly in DSPN+p, but fails to adequately counteract epidermal neurodegenerative processes.

Overexpression of cutaneous mitochondrial superoxide dismutase in recent-onset type 2 diabetes.

AIMS/HYPOTHESIS: Oxidative stress and microvascular damage have been implicated in the pathogenesis of diabetic neuropathy, with manganese superoxide dismutase 2 (SOD2) responsible for superoxide detoxification in mitochondria. We hypothesised that patients with recently diagnosed type 2 diabetes would show an altered cutaneous expression of SOD2 and endothelial cell area. METHODS: In this cross-sectional study, we assessed skin biopsies using immunohistochemistry, peripheral nerve function and heart rate variability in 69 participants of the German Diabetes Study with recently diagnosed type 2 diabetes and 51 control individuals. RESULTS: Subepidermal SOD2 area in the distal leg was increased by ~60% in the diabetic group vs the controls (0.24 ± 0.02% vs 0.15 ± 0.02%; p = 0.0005) and was correlated with an increasing duration of diabetes (r = 0.271; p = 0.024) and with the low frequency/high frequency ratio (ß = 0.381; p = 0.002) as an indicator of sympathovagal balance. The area of the subepidermal endothelial cells (measured by CD31 staining) did not differ between the groups. CONCLUSIONS/INTERPRETATION: Cutaneous antioxidative defence is enhanced in relation to the duration of diabetes and is linked to a cardiac sympathovagal imbalance towards a sympathetic predominance in individuals with recently diagnosed type 2 diabetes without evidence of endothelial cell damage. Whether cutaneous SOD2 levels can predict the development of diabetic neuropathy remains to be determined in prospective studies.

Augmented Corneal Nerve Fiber Branching in Painful Compared With Painless Diabetic Neuropathy.

CONTEXT: The factors that determine the development of diabetic sensorimotor polyneuropathy (DSPN) as a painful or painless entity are unknown. OBJECTIVE: We hypothesized that corneal nerve pathology could be more pronounced in painful DSPN, indicating predominant small nerve fiber damage. DESIGN AND METHODS: In this cross-sectional study, we assessed 53 patients with painful DSPN, 63 with painless DSPN, and 46 glucose-tolerant volunteers by corneal confocal microscopy (CCM), nerve conduction (NC), and quantitative sensory testing. DSPN was diagnosed according to modified Toronto Consensus criteria. A cutoff at 4 points on the 11-point rating scale was used to differentiate between painful and painless DSPN. RESULTS: After adjustment for age, sex, body mass index, and smoking, corneal nerve fiber density, corneal nerve fiber length, and corneal nerve branch density (CNBD) were reduced in both DSPN types compared with the control group (P < 0.05). Only CNBD differed between the groups; it was greater in patients with painful DSPN compared with those with painless DSPN [55.8 (SD, 29.9) vs 43.8 (SD, 28.3) branches/mm2; P < 0.05]. Several CCM measures were associated with NC and cold perception threshold in patients with painless DSPN (P < 0.05) but not those with painful DSPN. CONCLUSION: Despite a similarly pronounced peripheral nerve dysfunction and corneal nerve fiber loss in patients with painful and painless DSPN, corneal nerve branching was enhanced in those with painful DSPN, pointing to some susceptibility of corneal nerve fibers toward regeneration in this entity, albeit possibly not to a sufficient degree.

Differential associations of lower cardiac vagal tone with insulin resistance and insulin secretion in recently diagnosed type 1 and type 2 diabetes.

OBJECTIVE: It is unclear to which extent altered insulin sensitivity/secretion contribute to the development of diabetic cardiovascular autonomic neuropathy (CAN) characterized by diminished heart rate variability (HRV). We hypothesised that lower HRV is differentially associated with measures of insulin resistance and insulin secretion in recent-onset type 1 and type 2 diabetes. MATERIALS/METHODS: This cross-sectional study included participants from the German Diabetes Study with type 1 (n=275) or type 2 diabetes (n=450) with known diabetes duration ≤1year and glucose-tolerant controls (n=81). Four time domain and frequency domain HRV measures each, reflecting vagal and/or sympathetic modulation were determined over 3h during a hyperinsulinaemic-euglycaemic clamp. Insulin sensitivity was calculated as the M-value, while insulin secretion was determined by glucagon-stimulated incremental C-peptide (ΔC-peptide). RESULTS: After adjustment for sex, age, BMI, smoking, and HbA1c, both M-value and ΔC-peptide were lower in the diabetes groups compared to controls (P<0.05). In multiple linear regression analyses after Bonferroni correction, vagus-mediated HRV indices were positively associated with M-value in both diabetes types (P<0.05) and inversely associated with ΔC-peptide only in participants with type 1 diabetes (P<0.05). In type 2 diabetes, the low-frequency/high-frequency (LF/HF) power as an indicator of sympathovagal balance was weakly inversely associated with M-value. CONCLUSIONS: Insulin resistance may contribute to the development of early cardiovagal suppression rather than sympathetic predominance in both diabetes types, while in type 1 diabetes a lower glucagon-stimulated insulin secretion is linked to a possibly compensatory higher parasympathetic tone. Whether interventions aimed at reducing insulin resistance could also reduce the risk of CAN remains to be established.

Proinflammatory Cytokines Predict the Incidence and Progression of Distal Sensorimotor Polyneuropathy: KORA F4/FF4 Study.

OBJECTIVE: Experimental and epidemiological studies have implicated inflammatory processes in the pathogenesis of distal sensorimotor polyneuropathy (DSPN), but prospective studies are lacking. We hypothesized that biomarkers of inflammation predict the development and progression of DSPN in a population-based cohort. RESEARCH DESIGN AND METHODS: This study was based on participants aged 62-81 years from the Cooperative Health Research in the Region of Augsburg (KORA) F4/FF4 cohort, with a mean follow-up of 6.5 years. The predictive value of systemic levels of eight biomarkers of inflammation was assessed for incident DSPN in 133 incident case subjects and 397 individuals without incident DSPN, and for DSPN progression in 57 patients with prevalent DSPN at both time points. RESULTS: Higher hs-CRP, interleukin (IL)-6, tumor necrosis factor (TNF)-α, IL-1 receptor antagonist (IL-1RA), and soluble intercellular adhesion molecule (sICAM-1) and lower adiponectin levels were associated with incident DSPN in age- and sex-adjusted analysis; IL-18 and omentin were not. IL-6 (odds ratio 1.31 [95% CI 1.00-1.71]) and TNF-α (odds ratio 1.31 [95% CI 1.03-1.67]) remained associated with incident DSPN after adjusting for known DSPN risk factors. The addition of both cytokines to a clinical risk model improved model fit and reclassification. sICAM-1 and IL-1RA were positively associated with progression of DSPN. CONCLUSIONS: Systemic subclinical and vascular inflammation predicted both the onset and progression of DSPN over 6.5 years in an older general population. Thus modulation of inflammatory processes may be relevant to prevent and/or treat diabetic neuropathy.

Differential Patterns of Impaired Cardiorespiratory Fitness and Cardiac Autonomic Dysfunction in Recently Diagnosed Type 1 and Type 2 Diabetes.

OBJECTIVE: Both impaired cardiorespiratory fitness (CRF) and heart rate variability (HRV) are predictors of mortality, but their relative roles in recent-onset diabetes are unknown. We determined to which extent CRF and HRV are reduced and interrelated in recent-onset diabetes. RESEARCH DESIGN AND METHODS: Participants from the German Diabetes Study with type 1 (n = 163) or type 2 (n = 188) diabetes with known diabetes duration <1 year and two age-matched glucose-tolerant control groups (n = 40 each) underwent spiroergometry and HRV assessment during a hyperinsulinemic-euglycemic clamp. RESULTS: Compared with control subjects, patients with type 2 diabetes showed reduced VO2max (median [1st-3rd quartiles] 19.3 [16.5-22.9] vs. 25.6 [20.7-29.9] mL/kg body weight/min; P < 0.05), diminished VCO2max (23.0 [19.1-26.8] vs. 30.9 [24.5-34.4] mL/kg body weight/min; P < 0.05), blunted heart rate recovery after 2 min (-29.0 [-35.0 to -23.0] vs. -36.0 [-42.8 to -28.0] beats/min; P < 0.05), and reduced HRV in four of nine indices, whereas patients with type 1 diabetes had unaltered CRF but reduced HRV in three of nine indices (P < 0.05), indicating diminished vagal and sympathetic HRV modulation. HRV measures correlated with VO2max in patients with type 1 diabetes (r >0.34; P < 0.05) but not in those with type 2 diabetes. CONCLUSIONS: CRF is reduced in recently diagnosed type 2 diabetes but preserved in type 1 diabetes, whereas cardiac autonomic function is reduced in both diabetes types but is strongly associated with CRF only in type 1 diabetes. These results support the therapeutic concept of promoting physical fitness in the early course of diabetes.

Lower serum extracellular superoxide dismutase levels are associated with polyneuropathy in recent-onset diabetes.

Increased oxidative stress is implicated in the pathogenesis of experimental diabetic neuropathy, but translational evidence in recent-onset diabetes is scarce. We aimed to determine whether markers of systemic oxidative stress are associated with diabetic sensorimotor polyneuropathy (DSPN) in recent-onset diabetes. In this cross-sectional study, we measured serum concentrations of extracellular superoxide dismutase (SOD3), thiobarbituric acid reactive substances (TBARS), and reduced glutathione (GSH) in 107 type 1 and 215 type 2 diabetes patients from the German Diabetes Study baseline cohort and 37 glucose-tolerant individuals (controls). DSPN was defined by electrophysiological and clinical criteria (Toronto Consensus, 2011). SOD3 and GSH concentrations were lower in individuals with type 1 and type 2 diabetes compared with concentrations in controls (P<0.0001). In contrast, the TBARS concentration was higher in participants with type 1 diabetes and type 2 diabetes compared with levels in controls (P<0.0001). In addition, the SOD3 concentration was higher in participants with type 1 diabetes compared to concentrations in those with type 2 diabetes (P<0.0001). A low SOD3 concentration was associated with DSPN in individuals with type 1 diabetes (ß=-0.306, P=0.002), type 2 diabetes (ß=-0.164, P=0.017), and in both groups combined (ß=-0.206, P=0.0003). Lower SOD3 concentrations were associated with decreased motor nerve conduction velocity (NCV) in men and, to a lesser degree, with reduced sensory NCV in women with diabetes. In conclusion, several biomarkers of oxidative stress are altered in recent-onset diabetes, with only a lower SOD3 concentration being linked to the presence of DSPN, suggesting a role for reduced extracellular antioxidative defense against superoxide in the early development of DSPN.

Inflammatory markers are associated with cardiac autonomic dysfunction in recent-onset type 2 diabetes.

OBJECTIVE: Cardiovascular autonomic neuropathy is a common but underestimated diabetes-related disorder. Associations between cardiovascular autonomic dysfunction and subclinical inflammation, both risk factors of diabetic comorbidities and mortality, have been proposed in non-diabetic populations, while data for type 1 and type 2 diabetes are conflicting. Our aim was to investigate associations between inflammation-related biomarkers and cardiac autonomic dysfunction in patients with diabetes. METHODS: We characterised the associations between seven biomarkers of subclinical inflammation and cardiac autonomic dysfunction based on heart rate variability and cardiovascular autonomic reflex tests (CARTs) in 161 individuals with type 1 and 352 individuals with type 2 diabetes (time since diagnosis of diabetes <1 year). Analyses were adjusted for age, sex, anthropometric, metabolic and lifestyle factors, medication and cardiovascular comorbidities. RESULTS: In individuals with type 2 diabetes, higher serum interleukin (IL)-18 was associated with lower vagal activity (p≤0.015 for association with CARTs), whereas higher levels of total and high-molecular-weight adiponectin showed associations with very low frequency power, an indicator of reduced sympathetic activity (p≤0.014). Higher levels of soluble intercellular adhesion molecule-1 were associated with indicators of both lower vagal (p=0.025) and sympathetic (p=0.008) tone, soluble E-selectin with one indicator of lower vagal activity (p=0.047). Serum C-reactive protein and IL-6 were also related to cardiac autonomic dysfunction, but these associations were explained by confounding factors. No consistent associations were found in individuals with type 1 diabetes. CONCLUSIONS: Biomarkers of inflammation were differentially associated with diminished cardiac autonomic dysfunction in recent-onset type 2 diabetes.

Adiponectin, markers of subclinical inflammation and nerve conduction in individuals with recently diagnosed type 1 and type 2 diabetes.

OBJECTIVE: Subclinical inflammation has been implicated in the development of diabetic sensorimotor polyneuropathy (DSPN), but studies using electrophysiological assessment as outcomes are scarce. Therefore, we aimed to investigate associations of biomarkers reflecting different aspects of subclinical inflammation with motor and sensory nerve conduction velocity (NCV) in individuals with diabetes. DESIGN AND METHODS: Motor and sensory NCV was assessed in individuals with recently diagnosed type 2 (n=352) or type 1 diabetes (n=161) from the baseline cohort of the observational German Diabetes Study. NCV sum scores were calculated for median, ulnar and peroneal motor as well as median, ulnar and sural sensory nerves. Associations between inflammation-related biomarkers, DSPN and NCV sum scores were estimated using multiple regression models. RESULTS: In type 2 diabetes, high serum interleukin (IL)-6 was associated with the presence of DSPN and reduced motor NCV. Moreover, higher levels of high-molecular weight (HMW) adiponectin, total adiponectin and their ratio were associated with prevalent DSPN and both diminished motor and sensory NCV, whereas no consistent associations were observed for C-reactive protein, IL18, soluble intercellular adhesion molecule-1 and E-selectin. In type 1 diabetes, only HMW and total adiponectin showed positive associations with motor NCV. CONCLUSIONS: Our results point to a link between IL6 and both DSPN and slowed motor NCV in recently diagnosed type 2 diabetes. The reverse associations between adiponectin and NCV in type 1 and type 2 diabetes are intriguing, and further studies should explore whether they may reflect differences in the pathogenesis of DSPN in both diabetes types.