“…Protein-free media (PFM) was Fibrolife basal media (Lifeline Cell Technology, Walkersville, MD) supplemented with 10 mM HEPES (Sigma, St. Louis, MO), 1× non-essential amino acids (Sigma), 1 mM sodium pyruvate (Sigma), 2 mM glutamine (Lonza, Basel, Switzerland), 100 U/ml penicillin and 100 µg/ml streptomycin (Lonza). Serum-free media (SFM) was PFM further supplemented with 10 µg/ml recombinant human insulin (Sigma), 5 µg/ml recombinant human transferrin (Sigma), and 550 µg/ml filter-sterilized human albumin (isolated and checked for purity as previously described (48)), fish skin gelatin (Sigma), or skim milk powder (EMD Millipore, Billerica, MD). Protein supplements were checked for concentration using absorbance at 280 nm.…”