Urineprint of high-altitude: Insights from analyses of urinary biomarkers and bio-physical-chemical features of extracellular vesicles

Humans exposed to altitude hypoxia experience dysfunctions of the urinary system. As a non-invasive, easily manageable and informative biological sample, urine represents a relevant matrix for detecting clinical impairments of urinary system, as well as alterations of other systems and extracellular vesicles (EVs) biology during high-altitude expeditions. Nevertheless, gaps exist in the comprehensive assessment of dysfunction, molecular burden and EVs biology due to high-altitude acute exposure. This study aimed to find a biophysical and biochemical signature of urinary EVs for hypoxia-induced changes in urinary function, putatively accompanied by an oxinflammatory burden. Urine samples of 15 participants were sampled at low and high-altitude during an Alpine project (7 women and 8 men, aged 24-to-63 years and with BMI 17.93-to-30.76 kg/m²) and analysed for: creatinin and albumin, lipid peroxidation, IL6, NO derivatives; atomic force microscopy and Raman spectroscopy were carried out after urinary EVs were isolated through sucrose-gradient ultracentrifugation. Albumin-to-creatinin ratio increased at high altitude, as did IL6 and 8-isoprostane. AFM showed a globular and flattened shape of EVs, although several samples were characterized by a lot of contaminants and EVs lost their prototypal spherical shape; EVs comprehensively maintained their morphology at high altitude. Raman spectroscopy revealed some typical phospholipidic-like pattern, often masked by contaminants of spectra that most often refer to high-altitude samples. Collectively, short-term exposure to altitude hypoxia increased renal concentrating ability, produced non-pathological impairment or renal function, and triggered an oxyinflammatory burden with heterogeneous response of NO system. The combination of AFM and Raman spectroscopy revealed that EVs collected at high altitude more likely are fused together and incorporated into a sediment matrix, and contain contaminants peaks that make the purification process less efficient. The combination of analytical procedures as in the present study offers novel possibilities to detect the biological and clinical effects of high altitude on renal system.