Chronic exposure to the nephrotoxic metal pollutant, cadmium (Cd), has been associated with the pathogenesis of hypertension, but so far, the mechanism has not been well defined. We hypothesize that exposure to Cd causes a decline in the glomerular filtration rate (GFR), which in turn, causes a rise in blood pressure. Data were collected from 447 Thai subjects with a mean age of 51.1 years, of which 48.8% had hypertension, 15.4% had diabetes and 6.9% had an estimated GFR (eGFR) below 60 mL/min/1.73m2 (low eGFR). The mean blood Cd and mean urinary Cd concentrations were 2.75 and 4.23 µg/L, respectively. Prevalence odds ratio (POR) for hypertension rose twofold in those with a medium Cd burden and blood Cd levels of 0.61-1.69 µg/L. In the hypertensive group, the eGFR was inversely associated with age (β =−0.517), the Cd excretion rate (β = −0.177), and diabetes (β = −0.175). Mean eGFR in those with hypertension was 7.5 mL/min/1.73m2 lower than those who were normotensive with the same Cd body burden. In addition, higher systolic blood pressure (SBP) values were associated with older age (β = 0.243), higher BMI (β = 0.113), lower eGFR (β = −0.106) and diabetes (β = 0.216). Mean SBP in those who had low eGFR and medium and heavy Cd body burden was 9.5 mmHg higher than those with the same Cd body burden and a normal eGFR. Thus, chronic environmental exposure to Cd that produces urinary and blood Cd levels of 0.57-0.61 µg/L, increases the risk of hypertension, and this could be mediated by a declining GFR.

Cadmium (Cd) is a pervasive, toxic environmental pollutant that preferentially accumulates in tubular epithelium of the kidney. Current evidence suggests that the cumulative burden of Cd here leads to progress loss of the glomerular filtration rate (GFR). In this study, we have quantified changes in estimated GFR (eGFR) and albumin excretion (Ealb) in according to levels of blood Cd ([Cd]b) and excretion of Cd (ECd) after adjustment for confounders. ECd and Ealb were normalized to creatinine clearance (Ccr) as ECd/Ccr and Ealb/Ccr. Among 482 residents of Cd-polluted and non-polluted regions of Thailand, 8.1% had low eGFR and 16.9% had albuminuria, (Ealb/Ccr)×100 ≥ 20 mg/L filtrate. In the low Cd burden group, (ECd/Ccr) ×100 < 1.44 µg/L filtrate, eGFR did not correlate with ECd/Ccr (β = 0.007), while an inverse association with ECd/Ccr was found in the medium (β =−0.230) and high-burden groups (β =−0.349). Prevalence odds ratios (POR) for low eGFR were increased in the medium (POR 8.26) and high Cd burden groups (POR 3.64). Also, eGFR explained a significant proportion of Ealb/Ccr variation among those with middle (η2 0.093) and high [Cd]b tertiles (η2 0.132), but did not with low tertile (η2 0.001). With adjustment of eGFR, age and BMI, POR values for albuminuria were increased in the middle (POR 2.36) and high [Cd]b tertiles (POR 2.74) and those with diabetes (POR 6.02) and hypertension (2.05). These data argue that ECd/Ccr of 1.44 µg/L filtrate (0.01−0.02 µg/g creatinine) could determine a Cd threshold level from which protective exposure guidelines should be formulated.

Excretion of β2-microglobulin (β2M) above 300 µg/g creatinine, termed tubulopathy, was regarded as the critical effect of chronic exposure to the metal pollutant cadmium (Cd). However, current evidence suggests that Cd may induce nephron atrophy, resulting in a reduction in the estimated glomerular filtration rate (eGFR) below 60 mL/min/1.73 m2. Herein, these pathologies were investigated in relation to Cd exposure, smoking, diabetes and hypertension. Data were from 448 residents of Cd-polluted and non-polluted regions of Thailand. The body burden of Cd, indicated by the mean Cd excretion (ECd) normalized to creatinine clearance (Ccr) as (ECd/Ccr) ×100 in women and men did not differ (3.21 vs. 3.12 µg/L filtrate). The prevalence odds ratio (POR) for tubulopathy and a reduced eGFR were increased by 1.9-fold and 3.2-fold for every 10-fold rise in Cd body burden. In women only, a dose-effect relationship was seen between β2M excretion (Eβ2M/Ccr) and ECd/Ccr (F = 3.431, η2 0.021). In men, Eβ2M/Ccr was associated with diabetes (β = 0.279). In both genders, eGFR was inversely associated with Eβ2M/Ccr. The respective covariate- adjusted mean eGFR values were 16.5 and 12.3 mL/min/1.73 m2 lower in women and men who had severe tubulopathy; (Eβ2M/Ccr) ×100 ≥ 1000 µg/L filtrate. These findings indicate that women were particularly susceptible to the nephrotoxicity of Cd, and that the increment of Eβ2M/Ccr could be attributable mostly to Cd-induced impairment in tubular reabsorption of the protein together with Cd-induced nephron loss, evident from an inverse relationship between Eβ2M/Ccr and the eGFR.