Type 1 diabetes mellitus in the SARS-CoV-2 pandemic: Oxidative stress as a major pathophysiological mechanism linked to adverse clinical outcomes

Recent reports have demonstrated the association between type 1 diabetes mellitus (T1DM) and increased morbidity and mortality rates during coronavirus disease (COVID-19) infection, setting a priority of these patients for vaccination. Impaired innate and adaptive immunity observed in T1DM seem to play a major role. Severe, life-threatening COVID-19 disease is characterized by the excessive release of pro-inflammatory cytokines, known as a “cytokine storm”. Patients with T1DM present elevated levels of cytokines including interleukin-1a (IL), IL-1β, IL-2, IL-6 and tumor necrosis factor alpha (TNF-α), suggesting the pre-existence of chronic inflammation, which, in turn, has been considered the major risk factor of adverse COVID-19 outcomes in many cohorts. Even more impor-tantly, oxidative stress is a key player in COVID-19 pathogenesis and determines disease severity. It is well-known that extreme glucose excursions, the prominent feature of T1DM, are a potent mediator of oxidative stress through several pathways including the activation of protein kinase C (PKC) and the increased production of advanced glycation end products (AGEs). Additionally, chronic endothelial dysfunction and the hypercoagulant state observed in T1DM, in combination with the direct damage of endothelial cells by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), may result in endothelial and microcirculation impairment, which contribute to the pathogenesis of acute respiratory syndrome and multi-organ failure. The binding of SARS-CoV-2 to angiotensin converting enzyme 2 (ACE2) receptors in pancreatic b-cells permits the direct destruction of b-cells, which contributes to the development of new-onset diabetes and the induction of diabetic ketoacidosis (DKA) in patients with T1DM. Large clinical studies are required to clarify the exact pathways through which T1DM results in worse COVID-19 outcomes. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Whispering gallery mode resonances in thermally poled borosilicate glass optical microcavities

Three-dimensional control in the tuning of the linear and nonlinear properties of optical materials can catalyse the design of new photonic devices. Glasses being the backbone materials for drawing optical fibres, are inherently centrosymmetric, so their nonlinear dielectric susceptibility χ(2) is zero; thermal poling has been used for breaking the symmetry of such amorphous matrixes

Whispering gallery mode resonances in thermally poled borosilicate glass hetero-fibers

Whispering gallery mode (WGM) resonances in radially, thermally poled glass hetero-fibers, are investigated for the first time. Upon radially oriented thermal poling, both TE and TM polarized responses undergoing a spectral 'cleaning' process, namely higher-order radial modes are being suppressed, or even fully annihilated, compared to the spectral behavior of the pristine fibers. Second-harmonic generation (SHG) microscopy, Energy Dispersive X-Ray Spectroscopy (EDX) and micro-Raman (μ-Raman) measurements were conducted in order to reveal the spatial profile of the structural and optical changes introduced to the thermally poled hetero-fibers, and correlate them with the WGM spectral measurements. The specific selective, mode cleaning behavior is attributed to refractive index changes generated in proximity to the fiber's circumference, which are associated with radially-symmetric ionic re-distribution. The thermally poled hetero-fiber WGM cavities have been rigorously simulated using the finite element method, the calculated modal eigenstates and transmission spectra, further confirm the specific mode selection mechanism, introduced by the azimuthally symmetric thermal, poling process