Associations between multiple neurological biomarkers and distal sensorimotor polyneuropathy: KORA F4/FF4 study.

AIMS: The aim of this study was to assess associations between neurological biomarkers and distal sensorimotor polyneuropathy (DSPN). MATERIALS AND METHODS: Cross-sectional analyses were based on 1032 participants aged 61-82 years from the population-based KORA F4 survey, 177 of whom had DSPN at baseline. The prevalence of type 2 diabetes was 20%. Prospective analyses used data from 505 participants without DSPN at baseline, of whom 125 had developed DSPN until the KORA FF4 survey. DSPN was defined based on the examination part of the Michigan Neuropathy Screening Instrument. Serum levels of neurological biomarkers were measured using proximity extension assay technology. Associations between 88 biomarkers and prevalent or incident DSPN were estimated using Poisson regression with robust error variance and are expressed as risk ratios (RR) and 95% CI per 1-SD increase. Results were adjusted for multiple confounders and multiple testing using the Benjamini-Hochberg procedure. RESULTS: Higher serum levels of CTSC (cathepsin C; RR [95% CI] 1.23 (1.08; 1.39), pB-H = 0.044) and PDGFRα (platelet-derived growth factor receptor A; RR [95% CI] 1.21 (1.08; 1.35), pB-H = 0.044) were associated with prevalent DSPN in the total study sample. CDH3, JAM-B, LAYN, RGMA and SCARA5 were positively associated with DSPN in the diabetes subgroup, whereas GCP5 was positively associated with DSPN in people without diabetes (all pB-H for interaction <0.05). None of the biomarkers showed an association with incident DSPN (all pB-H>0.05). CONCLUSIONS: This study identified multiple novel associations between neurological biomarkers and prevalent DSPN, which may be attributable to functions of these proteins in neuroinflammation, neural development and myelination.

Association of transketolase polymorphisms with diabetic polyneuropathy in the general population: The KORA F4 study.

AIMS: We recently reported that genetic variability in the TKT gene encoding transketolase, a key enzyme in the pentose phosphate pathway, is associated with measures of diabetic sensorimotor polyneuropathy (DSPN) in recent-onset diabetes. Here, we aimed to substantiate these findings in a population-based KORA F4 study. MATERIALS AND METHODS: In this cross-sectional study, we assessed seven single nucleotide polymorphisms (SNPs) in the transketolase gene in 952 participants from the KORA F4 study with normal glucose tolerance (NGT; n = 394), prediabetes (n = 411), and type 2 diabetes (n = 147). DSPN was defined by the examination part of the Michigan Neuropathy Screening Instrument (MNSI) using the original MNSI > 2 cut-off and two alternative versions extended by touch/pressure perception (TPP) (MNSI > 3) and by TPP plus cold perception (MNSI > 4). RESULTS: After adjustment for sex, age, BMI, and HbA1c, in type 2 diabetes participants, four out of seven transketolase SNPs were associated with DSPN for all three MNSI versions (all p ≤ 0.004). The odds ratios of these associations increased with extending the MNSI score, for example, OR (95% CI) for SNP rs62255988 with MNSI > 2: 1.99 (1.16-3.41), MNSI > 3: 2.27 (1.26-4.09), and MNSI > 4: 4.78 (2.22-10.26); SNP rs9284890 with MNSI > 2: 2.43 (1.42-4.16), MNSI > 3: 3.46 (1.82-6.59), and MNSI > 4: 4.75 (2.15-10.51). In contrast, no associations were found between transketolase SNPs and the three MNSI versions in the NGT and prediabetes groups. CONCLUSIONS: The link of genetic variation in transketolase enzyme to diabetic polyneuropathy corroborated at the population level strengthens the concept suggesting an important role of pathways metabolising glycolytic intermediates in the evolution of diabetic polyneuropathy.

Association of dietary patterns with diabetes-related comorbidities varies among diabetes endotypes.

BACKGROUND AND AIMS: Differences of dietary pattern adherence across the novel diabetes endotypes are unknown. This study assessed adherence to pre-specified dietary patterns and their associations with cardiovascular risk factors, kidney function, and neuropathy among diabetes endotypes. METHODS AND RESULTS: The cross-sectional analysis included 765 individuals with recent-onset (67 %) and prevalent diabetes (33 %) from the German Diabetes Study (GDS) allocated into severe autoimmune diabetes (SAID, 35 %), severe insulin-deficient diabetes (SIDD, 3 %), severe insulin-resistant diabetes (SIRD, 5 %), mild obesity-related diabetes (MOD, 28 %), and mild age-related diabetes (MARD, 29 %). Adherence to a Mediterranean diet score (MDS), Dietary Approaches to Stop Hypertension (DASH) score, overall plant-based diet (PDI), healthful (hPDI) and unhealthful plant-based diet index (uPDI) was derived from a food frequency questionnaire and associated with cardiovascular risk factors, kidney function, and neuropathy using multivariable linear regression analysis. Differences in dietary pattern adherence between endotypes were assessed using generalized mixed models. People with MARD showed the highest, those with SIDD and MOD the lowest adherence to the hPDI. Adherence to the MDS, DASH, overall PDI, and hPDI was inversely associated with high-sensitivity C-reactive protein (hsCRP) among people with MARD (ß (95%CI): -9.18 % (-15.61; -2.26); -13.61 % (-24.17; -1.58); -19.15 % (-34.28; -0.53); -16.10 % (-28.81; -1.12), respectively). Adherence to the PDIs was associated with LDL cholesterol among people with SAID, SIRD, and MOD. CONCLUSIONS: Minor differences in dietary pattern adherence (in particular for hPDI) and associations with markers of diabetes-related complications (e.g. hsCRP) were observed between endotypes. So far, evidence is insufficient to derive endotype-specific dietary recommendations. TRIAL REGISTRATION: Clinicaltrials.gov: NCT01055093.

Serum neurofilament light chain: a novel biomarker for early diabetic sensorimotor polyneuropathy.

AIMS/HYPOTHESIS: No established blood-based biomarker exists to monitor diabetic sensorimotor polyneuropathy (DSPN) and evaluate treatment response. The neurofilament light chain (NFL), a blood biomarker of neuroaxonal damage in several neurodegenerative diseases, represents a potential biomarker for DSPN. We hypothesised that higher serum NFL levels are associated with prevalent DSPN and nerve dysfunction in individuals recently diagnosed with diabetes. METHODS: This cross-sectional study included 423 adults with type 1 and type 2 diabetes and known diabetes duration of less than 1 year from the prospective observational German Diabetes Study cohort. NFL was measured in serum samples of fasting participants in a multiplex approach using proximity extension assay technology. DSPN was assessed by neurological examination, nerve conduction studies and quantitative sensory testing. Associations of serum NFL with DSPN (defined according to the Toronto Consensus criteria) were estimated using Poisson regression, while multivariable linear and quantile regression models were used to assess associations with nerve function measures. In exploratory analyses, other biomarkers in the multiplex panel were also analysed similarly to NFL. RESULTS: DSPN was found in 16% of the study sample. Serum NFL levels increased with age. After adjustment for age, sex, waist circumference, height, HbA1c, known diabetes duration, diabetes type, cholesterol, eGFR, hypertension, CVD, use of lipid-lowering drugs and use of non-steroidal anti-inflammatory drugs, higher serum NFL levels were associated with DSPN (RR [95% CI] per 1-normalised protein expression increase, 1.92 [1.50, 2.45], p<0.0001), slower motor (all p<0.0001) and sensory (all p≤0.03) nerve conduction velocities, lower sural sensory nerve action potential (p=0.0004) and higher thermal detection threshold to warm stimuli (p=0.023 and p=0.004 for hand and foot, respectively). There was no evidence for associations between other neurological biomarkers and DSPN or nerve function measures. CONCLUSIONS/INTERPRETATION: Our findings in individuals recently diagnosed with diabetes provide new evidence associating higher serum NFL levels with DSPN and peripheral nerve dysfunction. The present study advocates NFL as a potential biomarker for DSPN.

Hyperbaric oxygen rapidly improves tissue-specific insulin sensitivity and mitochondrial capacity in humans with type 2 diabetes: a randomised placebo-controlled crossover trial.

AIMS/HYPOTHESIS: Hyperbaric oxygen (HBO) therapy may improve hyperglycaemia in humans with type 2 diabetes, but underlying mechanisms are unclear. Our objective was to examine the glucometabolic effects of HBO on whole-body glucose disposal in humans with type 2 diabetes. METHODS: In a randomised placebo-controlled crossover trial located at the German Diabetes Center, 12 male individuals with type 2 diabetes (age 18-75 years, BMI <35 kg/m2, HbA1c 42-75 mmol/mol [6-9%]), randomly allocated by one person, underwent 2-h HBO, once with 100% (240 kPa; HBO) and once with 21% oxygen (240 kPa; control, CON). Insulin sensitivity was assessed by hyperinsulinaemic-euglycaemic clamps with D-[6,6-2H2]glucose, hepatic and skeletal muscle energy metabolism were assessed by 1H/31P-magnetic resonance spectroscopy, while high-resolution respirometry measured skeletal muscle and white adipose tissue (WAT) mitochondrial capacity. All participants and people assessing the outcomes were blinded. RESULTS: HBO decreased fasting blood glucose by 19% and increased whole-body, hepatic and WAT insulin sensitivity about one-third (p<0.05 vs CON). Upon HBO, hepatic γ-ATP concentrations doubled, mitochondrial respiratory control doubled in skeletal muscle and tripled in WAT (p<0.05 vs CON). HBO increased myocellular insulin-stimulated serine-473/threonine-308 phosphorylation of Akt but decreased basal inhibitory serine-1101 phosphorylation of IRS-1 and endoplasmic reticulum stress (p<0.05 vs CON). CONCLUSIONS/INTERPRETATION: HBO-mediated improvement of insulin sensitivity likely results from decreased endoplasmic reticulum stress and increased mitochondrial capacity, possibly leading to low-dose reactive oxygen species-mediated mitohormesis in humans with type 2 diabetes. TRIAL REGISTRATION: ClinicalTrials.gov NCT04219215 FUNDING: German Federal Ministry of Health, German Federal Ministry of Education and Research, North-Rhine Westfalia Ministry of Culture and Science, European-Regional-Development-Fund, German-Research-Foundation (DFG), Schmutzler Stiftung.

High-intensity interval training for 12 weeks improves cardiovascular autonomic function but not somatosensory nerve function and structure in overweight men with type 2 diabetes.

AIMS/HYPOTHESIS: It remains unclear whether and which modality of exercise training as a component of lifestyle intervention may exert favourable effects on somatosensory and autonomic nerve tests in people with type 2 diabetes. METHODS: Cardiovascular autonomic and somatosensory nerve function as well as intraepidermal nerve fibre density (IENFD) were assessed in overweight men with type 2 diabetes (type 2 diabetes, n = 20) and male glucose-tolerant individuals (normal glucose tolerance [NGT], n = 23), comparable in age and BMI and serving as a control group, before and after a supervised high-intensity interval training (HIIT) intervention programme over 12 weeks. Study endpoints included clinical scores, nerve conduction studies, quantitative sensory testing, IENFD, heart rate variability, postural change in systolic blood pressure and spontaneous baroreflex sensitivity (BRS). RESULTS: After 12 weeks of HIIT, resting heart rate decreased in both groups ([mean ± SD] baseline/12 weeks: NGT: 65.1 ± 8.2/60.2 ± 9.0 beats per min; type 2 diabetes: 68.8 ± 10.1/63.4 ± 7.8 beats per min), while three BRS indices increased (sequence analysis BRS: 8.82 ± 4.89/14.6 ± 11.7 ms2/mmHg; positive sequences BRS: 7.19 ± 5.43/15.4 ± 15.9 ms2/mmHg; negative sequences BRS: 12.8 ± 5.4/14.6 ± 8.7 ms2/mmHg) and postural change in systolic blood pressure decreased (-13.9 ± 11.6/-9.35 ± 9.76 mmHg) in participants with type 2 diabetes, and two heart rate variability indices increased in the NGT group (standard deviation of R-R intervals: 36.1 ± 11.8/55.3 ± 41.3 ms; coefficient of R-R interval variation: 3.84 ± 1.21/5.17 ± 3.28) (all p<0.05). In contrast, BMI, clinical scores, nerve conduction studies, quantitative sensory testing, IENFD and the prevalence rates of diabetic sensorimotor polyneuropathy and cardiovascular autonomic neuropathy remained unchanged in both groups. In the entire cohort, correlations between the changes in two BRS indices and changes in [Formula: see text] over 12 weeks of HIIT (e.g. sequence analysis BRS: r = 0.528, p=0.017) were observed. CONCLUSIONS/INTERPRETATION: In male overweight individuals with type 2 diabetes, BRS, resting heart rate and orthostatic blood pressure regulation improved in the absence of weight loss after 12 weeks of supervised HIIT. Since no favourable effects on somatic nerve function and structure were observed, cardiovascular autonomic function appears to be more amenable to this short-term intervention, possibly due to improved cardiorespiratory fitness.

Differences in the prevalence of erectile dysfunction between novel subgroups of recent-onset diabetes.

AIMS/HYPOTHESIS: In men with diabetes, the prevalence of erectile dysfunction increases with advanced age and longer diabetes duration and is substantially higher in men with type 2 diabetes than those with type 1 diabetes. This study aimed to evaluate the prevalence of erectile dysfunction among the five novel subgroups of recent-onset diabetes and determine the strength of associations between diabetes subgroups and erectile dysfunction. METHODS: A total of 351 men with recent-onset diabetes (<1 year) from the German Diabetes Study baseline cohort and 124 men without diabetes were included in this cross-sectional study. Erectile dysfunction was assessed with the International Index of Erectile Function (IIEF) questionnaire. Poisson regression models were used to estimate associations between diabetes subgroups (each subgroup tested against the four other subgroups as reference) and erectile dysfunction (dependent binary variable), adjusting for variables used to define diabetes subgroups, high-sensitivity C-reactive protein and depression. RESULTS: The prevalence of erectile dysfunction was markedly higher in men with diabetes than in men without diabetes (23% vs 11%, p = 0.004). Among men with diabetes, the prevalence of erectile dysfunction was highest in men with severe insulin-resistant diabetes (SIRD) (52%), lowest in men with severe autoimmune diabetes (SAID) (7%), and intermediate in men with severe insulin-deficient diabetes (SIDD), mild obesity-related diabetes (MOD) and mild age-related diabetes (MARD) (31%, 18% and 29%, respectively). Men with SIRD had an adjusted RR of 1.93 (95% CI 1.04, 3.58) for prevalent erectile dysfunction (p = 0.038). Similarly, men with SIDD had an adjusted RR of 3.27 (95% CI 1.18, 9.10) (p = 0.023). In contrast, men with SAID and those with MARD had unadjusted RRs of 0.26 (95% CI 0.11, 0.58) (p = 0.001) and 1.52 (95% CI 1.04, 2.22) (p = 0.027), respectively. However, these associations did not remain statistically significant after adjustment. CONCLUSIONS/INTERPRETATION: The high RRs for erectile dysfunction in men with recent-onset SIRD and SIDD point to both insulin resistance and insulin deficiency as major contributing factors to this complication, suggesting different mechanisms underlying erectile dysfunction in these subgroups.

Effect of obesity on the associations of 25-hydroxyvitamin D with prevalent and incident distal sensorimotor polyneuropathy: population-based KORA F4/FF4 study.

BACKGROUND/OBJECTIVES: The association between vitamin D and DSPN has been investigated in cross-sectional studies in individuals with diabetes. However, evidence from prospective and population-based studies is still lacking. Also, the potential modifying effect of obesity and glucose tolerance has not been investigated. Therefore, we examined the cross-sectional and prospective associations of serum 25(OH)D with DSPN and assessed possible effect modifications. SUBJECTS/METHODS: The study included individuals aged 62-81 years who participated in the German KORA F4 (2006-2008) and FF4 (2013-2014) studies. DSPN was assessed using the Michigan Neuropathy Screening Instrument. Cross-sectional analyses (n = 1065; 33% of the participants had obesity) assessed the associations of baseline 25(OH)D with prevalent DSPN, while prospective analyses (n = 422) assessed the associations of 25(OH)D with incident DSPN. RESULTS: No association was found between 25(OH)D and prevalent DSPN in the total sample after adjustment for age, sex, season of blood sampling, BMI, metabolic variables, lifestyle factors, and comorbidities. However, a decrease by 10 nmol/L in 25(OH)D was associated with prevalent DSPN (RR (95% CI) 1.08 (1.01, 1.16)) in individuals with obesity but not in normal-weight individuals (RR (95% CI) 0.97 (0.92, 1.02), pinteraction = 0.002). No evidence for effect modification by glucose tolerance was found (p > 0.05). In the prospective analysis, 25(OH)D levels in the first and second tertiles were associated with higher risk of DSPN (RR (95% CI) 1.18 (1.02; 1.38) and 1.40 (1.04; 1.90)) compared to the third tertile after adjustment for age, sex, season of blood sampling, and BMI. There was no evidence for effect modification by obesity or glucose tolerance categories. CONCLUSIONS: Our study did not show consistent evidence for cross-sectional and prospective associations between serum 25(OH)D levels and DSPN in the total study population of older individuals. However, there was evidence for an association between lower serum 25(OH)D levels and higher prevalence of DSPN in individuals with obesity.

Progression and regression of nerve fibre pathology and dysfunction early in diabetes over 5 years.

It has traditionally been suggested that the early development of diabetic sensorimotor polyneuropathy (DSPN) is characterized by predominant and progressive injury to small nerve fibres followed by large fibre impairment. We alternatively hypothesized that small and large fibre damage due to DSPN in type 1 and type 2 diabetes could develop in parallel and may not only be progressive but also reversible. Participants from the German Diabetes Study baseline cohort with recent-onset type 1/type 2 diabetes (n = 350/570) and age-matched glucose-tolerant control individuals (Control 1/Control 2: n = 114/190) were assessed using nerve conduction studies, thermal detection thresholds, vibration perception thresholds, neuropathy symptom scores, neuropathy disability scores and intraepidermal nerve fibre density (IENFD) in skin biopsies (type 1/type 2 diabetes: n = 102/226; Control 1/Control 2: n = 109/208). Subsets of participants with type 1/type 2 diabetes were followed for 5 years (n = 184/307; IENFD subset: n = 18/69). DSPN was defined by the Toronto Consensus criteria. At baseline, DSPN was present in 8.1% and 13.3% of the type 1 and type 2 diabetes groups, respectively. The most frequently abnormal tests in the lower limbs below or above the 2.5th and 97.5th centiles of the controls were the IENFD (13.7%) and individual nerve conduction studies (up to 9.4%) in type 1 diabetes participants and IENFD (21.8%), malleolar vibration perception thresholds (17.5%), and individual nerve conduction studies (up to 11.8%) in those with type 2 diabetes, whereas thermal detection threshold abnormalities did not differ between the control and diabetes groups. After 5 years, the highest progression rates from the normal to the abnormal range in type 2 diabetes participants were found for IENFD (18.8%) by -4.1 ± 2.8 fibres/mm, malleolar vibration perception threshold (18.6%) by 9.1 ± 20.2 µm and nerve conduction studies (15.0%) by 3.7 ± 1.5 points, while vice versa the highest regression rates were observed for neuropathy disability scores (11.2%) by -3.1 ± 1.3 points, sural nerve amplitudes (9.1%) by 4.7 ± 3.0 µV, IENFD (8.7%) by 1.4 ± 1.3 fibres/mm, and neuropathy symptom scores (8.2%) by -5.8 ± 1.6 points. In type 1 diabetes participants, no major progression was seen after 5 years, but subclinical DSPN regressed in 10.3%. These findings point to early parallel damage to both small and large nerve fibres in well-controlled recent-onset type 2 and, to a lesser extent, type 1 diabetes. After 5 years, peripheral nerve morphology and function and clinical measures progress to the abnormal range in type 2 diabetes, but initial nerve alterations are also reversible to a meaningful degree.

Peripheral Ion Channel Gene Screening in Painful- and Painless-Diabetic Neuropathy.

Neuropathic pain is common in diabetic peripheral neuropathy (DN), probably caused by pathogenic ion channel gene variants. Therefore, we performed molecular inversion probes-next generation sequencing of 5 transient receptor potential cation channels, 8 potassium channels and 2 calcium-activated chloride channel genes in 222 painful- and 304 painless-DN patients. Twelve painful-DN (5.4%) patients showed potentially pathogenic variants (five nonsense/frameshift, seven missense, one out-of-frame deletion) in ANO3 (n = 3), HCN1 (n = 1), KCNK18 (n = 2), TRPA1 (n = 3), TRPM8 (n = 3) and TRPV4 (n = 1) and fourteen painless-DN patients (4.6%-three nonsense/frameshift, nine missense, one out-of-frame deletion) in ANO1 (n = 1), KCNK18 (n = 3), KCNQ3 (n = 1), TRPA1 (n = 2), TRPM8 (n = 1), TRPV1 (n = 3) and TRPV4 (n = 3). Missense variants were present in both conditions, presumably with loss- or gain-of-functions. KCNK18 nonsense/frameshift variants were found in painless/painful-DN, making a causal role in pain less likely. Surprisingly, premature stop-codons with likely nonsense-mediated RNA-decay were more frequent in painful-DN. Although limited in number, painful-DN patients with ion channel gene variants reported higher maximal pain during the night and day. Moreover, painful-DN patients with TRP variants had abnormal thermal thresholds and more severe pain during the night and day. Our results suggest a role of ion channel gene variants in neuropathic pain, but functional validation is required.

Association of cardiac autonomic dysfunction with higher levels of plasma lipid metabolites in recent-onset type 2 diabetes.

AIMS/HYPOTHESIS: Emerging evidence suggests that in addition to hyperglycaemia, dyslipidaemia could represent a contributing pathogenetic factor to diabetic neuropathy, while obesity and insulin resistance play a role in the development of diabetic cardiac autonomic neuropathy (CAN) characterised by reduced heart rate variability (HRV), particularly in type 2 diabetes. We hypothesised that distinct lipid metabolites are associated with diminished HRV in recent-onset type 2 diabetes rather than type 1 diabetes. METHODS: We analysed 127 plasma lipid metabolites (11 acylcarnitines, 39 NEFA, 12 sphingomyelins (SMs), 56 phosphatidylcholines and nine lysophosphatidylcholines) using MS in participants from the German Diabetes Study baseline cohort recently diagnosed with type 1 (n = 100) and type 2 diabetes (n = 206). Four time-domain HRV indices (number of normal-to-normal (NN) intervals >50 ms divided by the number of all NN intervals [pNN50]; root mean square of successive differences [RMSSD]; SD of NN intervals [SDNN]; and SD of differences between adjacent NN intervals) and three frequency-domain HRV indices (very-low-frequency [VLF], low-frequency [LF] and high-frequency [HF] power spectrum) were computed from NN intervals recorded during a 3 h hyperinsulinaemic-euglycaemic clamp at baseline and in subsets of participants with type 1 (n = 60) and type 2 diabetes (n = 95) after 5 years. RESULTS: In participants with type 2 diabetes, after Bonferroni correction and rigorous adjustment, SDNN was inversely associated with higher levels of diacyl-phosphatidylcholine (PCaa) C32:0, PCaa C34:1, acyl-alkyl-phosphatidylcholine (PCae) C36:0, SM C16:0 and SM C16:1. SD of differences between NN intervals was inversely associated with PCaa C32:0, PCaa C34:1, PCaa C34:2, PCae C36:0 and SM C16:1, and RMSSD with PCae C36:0. For VLF power, inverse associations were found with PCaa C30:0, PCaa C32:0, PCaa C32:1, PCaa C34:2 and SM C16:1, and for LF power inverse associations were found with PCaa C32:0 and SM C16:1 (r = -0.242 to r = -0.349; p ≤ 0.0005 for all correlations). In contrast, no associations of lipid metabolites with measures of cardiac autonomic function were noted in participants recently diagnosed with type 1 diabetes. After 5 years, HRV declined due to ageing rather than diabetes, whereby prediction analyses for lipid metabolites were hampered. CONCLUSIONS/INTERPRETATION: Higher plasma levels of specific lipid metabolites are closely linked to cardiac autonomic dysfunction in recent-onset type 2 diabetes but not type 1 diabetes, suggesting a role for perturbed lipid metabolism in the early development of CAN in type 2 diabetes. Graphical abstract.

A gain-of-function sodium channel ß2-subunit mutation in painful diabetic neuropathy.

Diabetes mellitus is a global challenge with many diverse health sequelae, of which diabetic peripheral neuropathy is one of the most common. A substantial number of patients with diabetic peripheral neuropathy develop chronic pain, but the genetic and epigenetic factors that predispose diabetic peripheral neuropathy patients to develop neuropathic pain are poorly understood. Recent targeted genetic studies have identified mutations in α-subunits of voltage-gated sodium channels (Navs) in patients with painful diabetic peripheral neuropathy. Mutations in proteins that regulate trafficking or functional properties of Navs could expand the spectrum of patients with Nav-related peripheral neuropathies. The auxiliary sodium channel ß-subunits (ß1-4) have been reported to increase current density, alter inactivation kinetics, and modulate subcellular localization of Nav. Mutations in ß-subunits have been associated with several diseases, including epilepsy, cancer, and diseases of the cardiac conducting system. However, mutations in ß-subunits have never been shown previously to contribute to neuropathic pain. We report here a patient with painful diabetic peripheral neuropathy and negative genetic screening for mutations in SCN9A, SCN10A, and SCN11A-genes encoding sodium channel α-subunit that have been previously linked to the development of neuropathic pain. Genetic analysis revealed an aspartic acid to asparagine mutation, D109N, in the ß2-subunit. Functional analysis using current-clamp revealed that the ß2-D109N rendered dorsal root ganglion neurons hyperexcitable, especially in response to repetitive stimulation. Underlying the hyperexcitability induced by the ß2-subunit mutation, as evidenced by voltage-clamp analysis, we found a depolarizing shift in the voltage dependence of Nav1.7 fast inactivation and reduced use-dependent inhibition of the Nav1.7 channel.

Myeloperoxidase, superoxide dismutase-3, cardiometabolic risk factors, and distal sensorimotor polyneuropathy: The KORA F4/FF4 study.

BACKGROUND: Oxidative stress has been proposed as important pathomechanism of cardiometabolic diseases and distal sensorimotor polyneuropathy (DSPN). However, the relevance of biomarkers of oxidative stress has not been investigated in this context. Therefore, this study aimed to assess the association of the prooxidant myeloperoxidase (MPO) and the antioxidant extracellular superoxide dismutase (SOD3) with cardiometabolic risk factors and with prevalence and incidence of DSPN. METHODS: Cross-sectional analyses comprised 1069 participants (40.3% with prediabetes and 20.5% with type 2 diabetes) of the population-based Cooperative Health Research in the Region of Augsburg (KORA) F4 study (2006-2008), 181 of whom had DSPN at baseline. Prospective analyses included 524 individuals without DSPN at baseline who also participated in the KORA FF4 study (2013-2014), 132 of whom developed DSPN during the 6.5-year follow-up. Serum MPO and SOD3 were measured by ELISA, and their association with cardiometabolic risk factors and DSPN were estimated by using linear and logistic regression analyses. RESULTS: Higher MPO and SOD levels showed multiple positive associations with cardiometabolic risk factors including age, indices of obesity, insulin resistance, serum lipids, renal dysfunction, and biomarkers of inflammation. Higher MPO levels were associated with prevalent DSPN (fully adjusted OR 1.38 [95% CI 1.10; 1.72] per doubling of MPO). Higher baseline SOD3 levels were related to incident DSPN (age and sex-adjusted OR 2.14 [1.02; 4.48] per doubling of SOD3), which was partially explained by cardiometabolic risk factors. CONCLUSIONS: Systemic levels of both pro- and antioxidant enzymes appear involved in cardiometabolic risk and development of DSPN.

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.

Cardiorespiratory Fitness and Cardiac Autonomic Function in Diabetes.

PURPOSE OF REVIEW: This review summarizes the current knowledge on the relationship of physical activity, exercise, and cardiorespiratory fitness (CRF) with cardiovascular autonomic neuropathy (CAN) based on epidemiological, clinical, and interventional studies. RECENT FINDINGS: The prevalence of CAN increases with age and duration of diabetes. Further risk factors for CAN comprise poor glycemic control, dyslipidemia, abdominal obesity, hypertension, and the presence of diabetic complications. CAN has been also linked to reduced CRF. We recently showed that CRF parameters (e.g., maximal oxidative capacity or oxidative capacity at the anaerobic threshold) are associated with cardiac autonomic function in patients recently diagnosed with type 1 or type 2 diabetes. Exercise interventions have shown that physical activity can increase cardiovagal activity and reduce sympathetic overactivity. In particular, long-term and regularly, but also supervised, performed endurance and high-intense and high-volume exercise improves cardiac autonomic function in patients with type 2 diabetes. By contrast, the evidence in those with type 1 diabetes and also in individuals with prediabetes or metabolic syndrome is weaker. Overall, the studies reviewed herein addressing the question whether favorably modulating the autonomic nervous system may improve CRF during exercise programs support the therapeutic concept to promote physical activity and to achieve physical fitness. However, high-quality exercise interventions, especially in type 1 diabetes and metabolic syndrome including prediabetes, are further required to better understand the relationship between physical activity, fitness, and cardiac autonomic function.

Differential associations between selenoprotein P and distal sensorimotor polyneuropathy in people with and without diabetes: KORA F4/FF4 study.

BACKGROUND: Oxidative stress is a risk factor for distal sensorimotor polyneuropathy (DSPN). Selenoprotein P is a protein with antioxidant properties but has not been investigated in the context of DSPN. This study aimed to assess the associations between selenoprotein P and DSPN in people without and with type 2 diabetes (T2D). METHODS: Cross-sectional and prospective analyses were based on 1053 (including 217 with T2D) and 513 participants (including 79 with T2D), respectively, aged 61-82 years from the population-based KORA F4 survey. DSPN at baseline (KORA F4) and in the follow-up survey KORA FF4 was defined based on the Michigan Neuropathy Screening Instrument. Serum levels of full-length selenoprotein P were quantified by ELISA. Associations between selenoprotein P and prevalent or incident DSPN were estimated using logistic regression analysis adjusting for multiple confounders. RESULTS: Selenoprotein P levels were not associated with prevalent DSPN in the total sample. However, there was a significant interaction by diabetes status. Higher levels of selenoprotein P were associated with lower odds of prevalent DSPN in individuals without T2D (fully adjusted model: OR 0.825 [95 % CI 0.682, 0.998], p = 0.0476), but not in those with T2D (OR [95 % CI] 1.098 [0.829, 1.454], p = 0.5132; pinteraction = 0.0488). Selenoprotein P levels were not associated with incident DSPN over a follow-up of 6.5 years. CONCLUSION: In individuals without T2D from the older general population, lower selenoprotein P levels were associated with a higher prevalence of DSPN. Whether the antioxidant properties of selenoprotein P are responsible for the observed associations remains to be elucidated in future research.

Analysis of type 2 diabetes heterogeneity with a tree-like representation: insights from the prospective German Diabetes Study and the LURIC cohort.

BACKGROUND: Heterogeneity in type 2 diabetes can be represented by a tree-like graph structure by use of reversed graph-embedded dimensionality reduction. We aimed to examine whether this approach can be used to stratify key pathophysiological components and diabetes-related complications during longitudinal follow-up of individuals with recent-onset type 2 diabetes. METHODS: For this cohort analysis, 927 participants aged 18-69 years from the German Diabetes Study (GDS) with recent-onset type 2 diabetes were mapped onto a previously developed two-dimensional tree based on nine simple clinical and laboratory variables, residualised for age and sex. Insulin sensitivity was assessed by a hyperinsulinaemic-euglycaemic clamp, insulin secretion was assessed by intravenous glucose tolerance test, hepatic lipid content was assessed by 1 H magnetic resonance spectroscopy, serum interleukin (IL)-6 and IL-18 were assessed by ELISA, and peripheral and autonomic neuropathy were assessed by functional and clinical measures. Participants were followed up for up to 16 years. We also investigated heart failure and all-cause mortality in 794 individuals with type 2 diabetes undergoing invasive coronary diagnostics from the Ludwigshafen Risk and Cardiovascular Health (LURIC) cohort. FINDINGS: There were gradients of clamp-measured insulin sensitivity (both dimensions: p<0·0001) and insulin secretion (pdim1<0·0001, pdim2=0·00097) across the tree. Individuals in the region with the lowest insulin sensitivity had the highest hepatic lipid content (n=205, pdim1<0·0001, pdim2=0·037), pro-inflammatory biomarkers (IL-6: n=348, pdim1<0·0001, pdim2=0·013; IL-18: n=350, pdim1<0·0001, pdim2=0·38), and elevated cardiovascular risk (nevents=143, pdim1=0·14, pdim2<0·00081), whereas individuals positioned in the branch with the lowest insulin secretion were more prone to require insulin therapy (nevents=85, pdim1=0·032, pdim2=0·12) and had the highest risk of diabetic sensorimotor polyneuropathy (nevents=184, pdim1=0·012, pdim2=0·044) and cardiac autonomic neuropathy (nevents=118, pdim1=0·0094, pdim2=0·06). In the LURIC cohort, all-cause mortality was highest in the tree branch showing insulin resistance (nevents=488, pdim1=0·12, pdim2=0·0032). Significant gradients differentiated individuals having heart failure with preserved ejection fraction from those who had heart failure with reduced ejection fraction. INTERPRETATION: These data define the pathophysiological underpinnings of the tree structure, which has the potential to stratify diabetes-related complications on the basis of routinely available variables and thereby expand the toolbox of precision diabetes diagnosis. FUNDING: German Diabetes Center, German Federal Ministry of Health, Ministry of Culture and Science of the state of North Rhine-Westphalia, German Federal Ministry of Education and Research, German Diabetes Association, German Center for Diabetes Research, European Community, German Research Foundation, and Schmutzler Stiftung.

Environmental risk factors of incident distal sensorimotor polyneuropathy: Results from the prospective population-based KORA F4/FF4 study.

Distal sensorimotor polyneuropathy (DSPN) is a common condition in older populations with high prevalence of obesity and type 2 diabetes. We hypothesised that the risk of DSPN is increased by multiple ubiquitous environmental risk factors, particularly in people with obesity. This study was based on 423 individuals aged 62-81 years without DSPN who participated in the population-based Cooperative Health Research in the Region of Augsburg (KORA) F4 survey (2006-2008) in Southern Germany. During 6.5 years of follow-up, 188 participants developed clinical DSPN as assessed by the Michigan Neuropathy Screening Instrument. Environmental exposures, including air temperature, surrounding greenness (assessed with the normalized difference vegetation index [NDVI]), long-term road traffic noise and air pollution, were assessed at participants' residences. The cumulative risk index (CRI) evaluated the joint effects of co-occurring exposures on DSPN risk based on effect estimates from multi-exposure Poisson regression models. The models were adjusted for age, sex, height, waist circumference, smoking, alcohol consumption, physical activity, education and neighbourhood socioeconomic status. In the entire cohort, the co-occurrence of an interquartile range (IQR) decrease in temperature of the warm season and NDVI in a 100-m buffer and of an IQR increase in night-time average traffic noise and in annual average particle number concentration (PNC) was positively associated with incident DSPN (CRI [95 % CI] 1.39 [1.02, 1.91]). Effect estimates for exposure combinations were generally higher in individuals with obesity (CRI 1.34-2.01) than in those without obesity (CRI 0.90-1.33). The four-exposure model showed a twofold increased risk of DSPN among obese (CRI [95 % CI] 2.01 [1.10, 3.67]), but not among non-obese individuals (CRI [95 % CI] 1.18 [0.83, 1.67]). Thus, ubiquitous environmental exposures jointly augment the risk of DSPN in the older population. Lower air temperature in the warm season, less greenness, and higher noise levels and ultrafine particle concentrations identified people with obesity as a particularly vulnerable subgroup.

Intramyocellular Triglyceride Content During the Early Course of Type 1 and Type 2 Diabetes.

Intramyocellular lipid content (IMCL) is elevated in insulin-resistant humans, but it changes over time, and relationships with comorbidities remain unclear. We examined IMCL during the initial course of diabetes and its associations with complications. Participants of the German Diabetes Study (GDS) with recent-onset type 1 (n = 132) or type 2 diabetes (n = 139) and glucose-tolerant control subjects (n = 128) underwent 1H-MRS to measure IMCL and muscle volume, whole-body insulin sensitivity (hyperinsulinemic-euglycemic clamps; M-value), and cycling spiroergometry (VO2max). Subgroups underwent the same measurements after 5 years. At baseline, IMCL was ∼30% higher in type 2 diabetes than in other groups independently of age, sex, BMI, and muscle volume. In type 2 diabetes, the M-value was ∼36% and ∼62% lower compared with type 1 diabetes and control subjects, respectively. After 5 years, the M-value decreased by ∼29% in type 1 and ∼13% in type 2 diabetes, whereas IMCL remained unchanged. The correlation between IMCL and M-value in type 2 diabetes at baseline was modulated by VO2max. IMCL also associated with microalbuminuria, the Framingham risk score for cardiovascular disease, and cardiac autonomic neuropathy. Changes in IMCL within 5 years after diagnosis do not mirror the progression of insulin resistance in type 2 diabetes but associate with early diabetes-related complications. ARTICLE HIGHLIGHTS: Intramyocellular lipid content (IMCL) can be elevated in insulin-resistant humans, but its dynamics and association with comorbidities remain unclear. Independently of age, sex, body mass, and skeletal muscle volume, IMCL is higher in recent-onset type 2, but not type 1 diabetes, and remains unchanged within 5 years, despite worsening insulin resistance. A degree of physical fitness modulates the association between IMCL and insulin sensitivity in type 2 diabetes. Whereas higher IMCL associates with lower insulin sensitivity in people with lower physical fitness, there is no association between IMCL and insulin sensitivity in those with higher degree of physical fitness. IMCL associates with progression of microalbuminuria, cardiovascular disease risk, and cardiac autonomic neuropathy.

Diagnostic Tools, Biomarkers, and Treatments in Diabetic polyneuropathy and Cardiovascular Autonomic Neuropathy.

The various manifestations of diabetic neuropathy, including distal symmetric sensorimotor polyneuropathy (DSPN) and cardiovascular autonomic neuropathy (CAN), are among the most prevalent chronic complications of diabetes. Major clinical complications of diabetic neuropathies, such as neuropathic pain, chronic foot ulcers, and orthostatic hypotension, are associated with considerable morbidity, increased mortality, and diminished quality of life. Despite the substantial individual and socioeconomic burden, the strategies to diagnose and treat diabetic neuropathies remain insufficient. This review provides an overview of the current clinical aspects and recent advances in exploring local and systemic biomarkers of both DSPN and CAN assessed in human studies (such as biomarkers of inflammation and oxidative stress) for better understanding of the underlying pathophysiology and for improving early detection. Current therapeutic options for DSPN are (I) causal treatment, including lifestyle modification, optimal glycemic control, and multifactorial risk intervention, (II) pharmacotherapy derived from pathogenetic concepts, and (III) analgesic treatment against neuropathic pain. Recent advances in each category are discussed, including non-pharmacological approaches, such as electrical stimulation. Finally, the current therapeutic options for cardiovascular autonomic complications are provided. These insights should contribute to a broader understanding of the various manifestations of diabetic neuropathies from both the research and clinical perspectives.