Glutamine

S. aureus strains were grown overnight at 37°C in tryptic soy broth (TSB; OXOID, Basingstoke, UK) under vigorous shaking (115 rpm) in a water bath. The cultures were then diluted into 10 mL pre-warmed Roswell Park Memorial Institute 1640 (RPMI) medium supplemented with 2 mM glutamine (GE Healthcare/PAA, Little Chalfont, United Kingdom) to an optical density at 600 nm (OD₆₀₀) of 0.1 and cultivation was continued under the same conditions. Exponentially growing cells with an OD₆₀₀ of ±0.5 were again diluted into 15 mL of fresh pre-warmed RPMI 1640 medium to a final OD₆₀₀ of 0.1 and their cultivation was continued until an OD₆₀₀ of ±1.2 was reached, which corresponds to the stationary growth phase. Then, cells were separated from the growth medium by centrifugation, and proteins in the growth medium were precipitated overnight at 4°C using 10% trichloroacetic acid (Sigma-Aldrich, St. Louis, USA). The precipitated proteins were collected by centrifugation, washed once with ice-cold acetone, dried at room temperature, and stored at −20°C until further use.

The human cell line SH-SY5Y was maintained at humidified air (95%), 5% CO₂, 37 °C, and cultured in DMEM/F12 (Life Technologies, Darmstadt, Germany) supplemented with 10% FCS and 1% Glutamine (GE Healthcare, Piscataway, NJ, USA).

The human neuroblastoma cell line SH-SY5Y was maintained at humidified air (95 %), 5 % CO₂, 37 °C, and cultured in DMEM/F12 (Life Technologies, Darmstadt, Germany) supplemented with 10 % FCS and 1 % Glutamine (both GE Healthcare, Piscataway, NJ, USA). For assay conditions, cells were seeded at a density of 30,000 cells per well of a white glas-bottom 96 well plate (Greiner Bio-One GmbH, Frickenhausen, Germany) in OptiMEM (Life Technologies, Darmstadt, Germany). After 24 h incubation period, culture supernatant was aspirated and exchanged by 50 µl fresh OptiMEM or OptiMEM supplemented with A-beta peptides in NH₄OH/PBS at the indicated concentration or with solvent. Cells were incubated for 24 h; subsequently, 5 µl cell supernatant for LDH release assay were pipetted to a clear 96 well plate and assay was performed as recommended by the manufacturer (Biovision, Milpitas, CA, USA). 5 µl MTT (5 mg/ml, Sigma Aldrich, St. Louis, MO, USA) were added per well to the cells. Development of formazane crystals was controlled by light microscopy and crystals lysed after 1 h of incubation [humidified air (95 %), 5 % CO₂ and 37 °C] with 200 µl 0.1 N HCl in isopropanol per well by vigorous pipetting. Then, absorption was measured at 595 and 620 nm in a plate reader (Asys Hitech Expert 96, Biochrom, Cambridge, UK) and viability calculated by A₅₉₅–A₆₂₀ in % of control (solvent-treated cells).

N-Cetyltrimethylammonium bromide (CTAB), tetraethyl orthosilicate (TEOS), sodium hydroxide (NaOH), 3-aminopropyltriethoxysilane (APTES), pyruvic acid (PA), N-hydroxysuccinimide (NHS), 1-ethyl-3-(3-(dimethylamino) propyl) carbodiimide hydrochloride (EDC), (2-thienylmethyl)hydrazine hydrochloride, (5,6-dimethylthieno[2,3-d]pyrimidin-4-yl)hydrazine, trifluoroacetic acid (TFA), triethylamine (TEA), ethanol, 2-propanol from Carl Roth (Carl Roth GmbH & Co. KG, Karlsruhe, Germany), dichloro(p-cymene)ruthenium(II) dimer, phosphate buffered saline (PBS), toluene and crystal violet (CV) were purchased from Sigma-Aldrich (Merck KGaA, Darmstadt, Germany). Dulbecco’s Modified Eagle Medium (DMEM) was purchased from Biowest (Riverside, CA, USA). For in vitro experiments nutrition medium RPMI 1640, FCS (fetal calb serum), penicillin/streptomycin and phosphate buffer saline (PBS) were obtained from Capricorn scientific GmbH (Ebsdorfergrund, Germany), glutamine and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) from GE healthcare (Chicago, IL, USA) and Biomol GmbH (Hamburg, Germany), respectively.