Progressive
chronic kidney disease (CKD) is common in
lysinuric protein intolerance (LPI), a primary inherited aminoaciduria characterized by massive
Lysine excretion in urine. However, by which mechanisms
Lysine may cause kidney damage to tubule cells is still not understood. This study determined whether
Lysine overloading of human proximal tubular cells (HK-2) in culture enhances apoptotic cell loss and its associated mechanisms. Overloading HK-2 with
Lysine levels reproducing those observed in urine of patients affected by LPI (10 mM) increased apoptosis (+30%; p < 0.01 vs.C), as well as Bax and Apaf-1 expressions (+30-50% p < 0.05), while downregulated Bcl-2 (-40% p < 0.05). Apoptosis induced by high
Lysine was no longer observed after addition of
caspase-9 and
caspase-3 inhibitors while
caspase-8 inhibitor had no protective effect. High
Lysine induced elevations in ROS generation and
NADPH oxidase subunits mRNAs (p22 (
phox) +106 ± 23%, p67 (
phox) +108 ± 22% and gp91 (
phox) +75 ± 4% p < 0.05-0.01). In addition, the
NADPH oxidase inhibitor DPI prevented both ROS production and apoptosis. Treating HK-2 with
antioxidants, such as
Cysteine and its analog,
N-acetyl-L-cysteine (NAC), rescued the HK-2 from apoptosis induced by
Lysine. In summary, our data show that high
Lysine in vitro increases the permissiveness of proximal tubule kidney cells to apoptosis by triggering a pathway involving
NADPH oxidase signaling. This event may represent a key cellular effect in the increasing the susceptibility of human tubular cells to apoptosis when the tubules cope with a high
Lysine load. This effect is instrumental to renal damage and
disease progression in patients with LPI.