Association of arterial stiffness and neuropathy in diabetes: a systematic review and meta-analysis

Evidence is still emerging on the relationships of arterial stiffness with cardiac autonomic neuropathy (CAN) and peripheral neuropathy (PN). To our knowledge no systematic reviews or meta-analyses of these associations have been published. The purpose of our review was to assess the association of arterial stiffness with each type of neuropathy. Medline and Embase were systematically searched for observational studies of arterial stiffness and neuropathy.The systematic review of 60 studies (25 for CAN and 37 for PN), 59 including people with diabetes, showed arterial stiffness overall was higher in people with neuropathy than people without neuropathy. Forty-three studies were included in the meta-analysis. For CAN (19 studies), arterial stiffness was increased in people with neuropathy compared with without, as measured by pulse wave velocity (PWV) (mean difference: 1.32 m/s, 95% CI 0.82 to 1.81, p<0.00001), pulse pressure (PP) (mean difference: 6.25 mmHg, 95% CI 4.51 to 7.99, p<0.00001) or augmentation index (mean difference: 5.52%, 95% CI 3.46 to 7.58, p<0.0001). For PN (26 studies), arterial stiffness was increased in people with neuropathy compared with those without, as measured by PWV (mean difference: 1.22 m/s, 95% CI 0.87 to 1.58, p<0.00001) or PP (mean difference: 4.59 mmHg, 95% CI 2.96 to 6.22, p<0.00001). Only two cohort studies were located so the temporality of the association between arterial stiffness and neuropathy remains unclear. Increased arterial stiffness is associated with CAN and PN.PROSPERO registration number: CRD42019129563.

What factors modify the effect of monthly bolus dose vitamin D supplementation on 25-hydroxyvitamin D concentrations?

The increasing use of vitamin D supplements has stimulated interest in identifying factors that may modify the effect of supplementation on circulating 25-hydroxyvitamin D (25(OH)D) concentrations. Such information is of potential interest to researchers, clinicians and patients when deciding on bolus dose of vitamin D supplementation. We carried out a large randomized controlled trial of 5110 adults aged 50-84 years, of European/Other (84%), Polynesian (11%) and Asian (5%) ethnicity, to whom we gave a standard dose of vitamin D₃ supplements (200,000 IU initially, then 100,000 IU monthly) which was taken with high adherence. All participants provided a baseline blood sample, and follow-up blood samples were collected at 6 months and annually for 3 years in a random sample of 441 participants, and also at 2 years in 413 participants enrolled in a bone density sub-study. Serum 25(OH)D was measured by LC/MSMS. Mixed model analyses were carried out on all 854 participants providing follow-up blood samples in multivariable models that included age, sex, ethnicity, body mass index (kg/m²), tobacco smoking, alcohol intake, physical activity, sun exposure, season, medical prescription of high-dose vitamin D₃ (Cal.D.Forte tablets), asthma/COPD and the study treatment (vitamin D or placebo). The adjusted mean difference in 25(OH)D in the follow-up points between vitamin D supplementation and placebo groups was inversely related (all p for interaction <0.05) to baseline 25(OH)D, BMI, and hours of sun exposure, and higher in females, elders, and those with high frequency of alcohol, medical prescription of vitamin D, and asthma/COPD. The mean difference was not significantly related to ethnicity (p = 0.12), tobacco (p = 0.34), and vigorous activity (p = 0.33). In summary, these data show that vitamin D status, BMI, sun exposure hours, sex and asthma/COPD modify the 25(OH)D response to vitamin D supplementation. By contrast, ethnicity, tobacco smoking, and vigorous activity do not.

Ras/MEK but not p38 signaling mediates NT-3-induced neurite extension from spiral ganglion neurons

Neurotrophin (NT)-3 is expressed in the neuronal target tissue of the developing rat cochlea and has been shown to promote the survival and neurite outgrowth of spiral ganglion (SG) neurons, suggesting a role for this protein during the innervation of the organ of Corti. In other neurons, NT-3 can mediate neuritogenesis and survival via a number of intracellular signal pathways. To date, the intracellular transduction pathways involved in the mediation of NT-3 effects have not been investigated in SG neurons. To determine whether the activities of NT-3 on SG neurons are dependent on the activation of mitogen-activated protein kinase kinases (MEK)/extracellular-signal-regulated kinases (ERK), Ras, and/or p38, SG explants from postnatal-day 4 rats were cultured with NT-3 and increasing concentrations of the MEK inhibitor U0126, the Ras farnesyl-transferase inhibitor (FTI)-277, and the p38 inhibitor SB203580. After fixation and immunocytochemical labeling, neurite growth was evaluated. A dose-dependent decrease of the effects of NT-3 on length and number of processes was observed in the U0126- and FTI-277-treated SG neurons. In contrast, SB203580 had no significant effect on NT-3-mediated stimulation of neurite growth, in terms of either number or length. The results suggest that NT-3 effects on SG neurons are mediated primarily by the Ras/MEK/ERK signaling pathway.