Tenofovir (TFV) is an antiviral drug approved for treating Human Immunodeficiency Virus (HIV) and Hepatitis B. TFV is administered orally as the prodrug tenofovir disoproxil fumarate (TDF) which then is deesterified to the active drug TFV. TFV induces nephrotoxicity characterized by renal failure and Fanconi Syndrome. The mechanism of this toxicity remains unknown due to limited experimental models. This study investigated the cellular mechanism of cytotoxicity using a human renal proximal tubular epithelial cell line (HK-2). HK-2 cells were grown for 48 h followed by 24 to 72 h exposure to 0–28.8 μM TFV or vehicle, phosphate buffered saline (PBS). MTT (MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) and Trypan blue indicated that TFV diminished cell viability at 24–72 h. TFV decreased ATP levels at 72 h when compared to vehicle, reflecting mitochondrial dysfunction. TFV increased the oxidative stress biomarkers of protein carbonylation and 4-hydroxynonenol (4-HNE) adduct formation. Tumor necrosis factor alpha (TNFα) was released into the media following exposure to 14.5 and 28.8 μM TFV. Caspase 3 and 9 cleavage was induced by TFV compared to vehicle at 72 h. These studies show that HK-2 cells are a sensitive model for TFV cytotoxicity and suggest that mitochondrial stress and apoptosis occur in HK-2 cells treated with TFV.

Tenofovir disproxil fumarate (Viread) is a highly effective HIV antiviral drug approved for treating infections with Human Immunodeficiency Virus (HIV) and Hepatitis B. It is one of the first line drugs used to treat HIV and is efficacious in both novel and treatment‐experienced HIV patients. Tenofovir is administered orally as the prodrug tenofovir disoproxil fumarate (TDF), which is deesterified to the active drug tenofovir. However, renal damage is a major adverse effect associated with its use. Tenofovir can induce decreased glomerular filtration rate (GFR), renal failure, and Fanconi Syndrome. The exact mechanism of this toxicity remains unknown, largely due to limited experimental models. Our laboratory has established that clinically relevant concentrations of tenofovir are toxic within 72 h. The purpose of this study was to investigate the cellular mechanism of cytotoxicity in a human renal proximal tubular epithelial cell line (HK‐2). Tenofovir (TFV) is the active form and was used for all studies. HK‐2 cells were seeded and grown to confluency for 48 h followed by a 72 h exposure to 0–30 uM tenofovir. The vehicle was phosphate buffered saline (PBS). Cell viability was assessed using the MTT assay. Tenofovir induced a loss of cell viability when compared to vehicle within 48–72h but did not alter MTT following a 24 h exposure. Mitochondrial dysfunction was assessed by measuring ATP and ADP levels. A 72 h exposure to tenofovir drastically reduced (p<0.05) ATP levels compared to vehicle control. Oxidative stress was assessed using OxyBlot and showed an increase in protein carbonylation after 72 h exposure to 5–30 uM tenofovir. Oxidative stress induced by tenofovir was sufficient to induce an increase in 4‐hydroxynonenal (4‐HNE) adducted proteins and 3‐nitrotyrosine (3‐NT) addition to proteins. Tenofovir also activated cleavage of Caspase 3 and 9 relative to vehicle. These studies suggest that mitochondrial stress and apoptosis occur in HK‐2 cells treated with tenofovir.Support or Funding InformationSupported by NASA West Virginia Space Grant Consortium Graduate Fellowship to Rachel Murphy.