Tubular Release of N-acetylglucosaminidase Into Glomerular Filtrate is Minimally Related to Cadmium-Induced Nephron Destruction

Exposure to even low levels of the environmental pollutant cadmium (Cd), increases the risk of kidney damage. The body burden of Cd at which kidney damage occurs is not, however, reliably defined. Here, multiple-regression and mediation analyses were applied to data from 737 non-diabetic Thai nationals, of which 32.2% had hypertension and 9.1% had an estimated glomerular filtration rate (eGFR) ≤ 60 mL/min/1.73 m2 (low eGFR). The excretion rates of Cd (ECd) and N-acetyl-β-D-glucosaminidase (ENAG), a marker of tubular injury, were normalized to creatinine clearance (Ccr) as ECd/Ccr and ENAG/Ccr. Doubling ECd/Ccr increased the risks of having a low eGFR [POR = 2.71 (95% CI:1.97, 3.74), p < 0.001] and severe tubular injury [POR = 4.80 (95% CI: 1.35, 17.1), p = 0.015]. ENAG/Ccr was strongly associated with ECd/Ccr in both men (β = 0.447, p <0.001) and women (β = 0.394, p <0.001), while showing a moderate inverse association with eGFR only in women (β = −0.178, p = 0.002). A moderate association of ENAG/Ccr and ECd/Ccr was found in the low- (β = 0.287, p = 0.001), and the high-Cd body burden groups (β = 0.145, p = 0.004), but ENAG/Ccr was inversely associated with eGFR only in the high-Cd body burden group (β = −0.223, p <0.001). These findings together with an insignificant mediated effect suggested that Cd-induced injury that causes release of NAG plays little or no role in the nephron destruction that reduces GFR.