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Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304\(\pm\)0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of \(\pm\)0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies.
Depression is a common psychiatric disorder among geriatric patients that decreases the quality of life and increases morbidity and mortality. Vitamin D as a neuro-steroid hormone might play a role in the onset and treatment of depression. In the present study, the association between depressive symptoms and vitamin D concentration in serum was evaluated. 140 patients of a psychogeriatric day-care unit were included. The geriatric depression scale (GDS) and the Hamilton depression rating scale (HDRS) were assessed at the beginning and end of treatment, GDS scores additionally 6 weeks after discharge from the day-care unit. Vitamin D levels were measured at the beginning of the treatment, routinely. Patients with levels below 30 µg/L were treated with 1000 IU vitamin D per day. There was no association between the severity of depressive symptoms and the concentration of vitamin D at the beginning of the treatment. Patients with higher vitamin D levels showed a stronger decline of depressive symptoms measured by the GDS during their stay in the day-care unit. We provide evidence that vitamin D serum levels might influence antidepressant therapy response in a geriatric population. Prospective studies are necessary to determine which patients may profit from add-on vitamin D therapy.