Assessing Chronic Heavy Metal Exposure by Analysis of Human Cataract Specimens and the Relationship to Metabolic Profiles.

Abstract

Purpose: With age, the mammalian lens forms successive layers of crystallin protein fibers which infoliate with lens growth and development. As heavy metals generally bind to tissue protein, heavy metals are posited to sequester within the lens with age. Therefore, this study aims to compare heavy metals in human crystalline lens of older adults to known physiologic blood and urine levels and assess the association between concentrations in the lens and metabolic biomarkers.

Methods: Consecutive lens specimens obtained during cataract surgery by phacoemulsification were subjected to atomic spectrometry for heavy metal content. A one-sample t-test compared heavy metals in lens to known physiologic blood and urine concentrations. Linear regression models assessed the association between heavy metals and biomarkers of metabolic function. Linear discriminant analysis assessed the classification of gender and smoking status based on multiple and individual heavy metals.

Results: All heavy metal levels were elevated in lens specimens compared to blood and urine with the exception of iron (p < 0.0001). Lens titanium and copper were positively associated with blood-urea nitrogen (Titanium: $\hat{\beta }$ = 1.14, p = 0.04, Copper: $\hat{\beta }$ = 1.12, p = 0.03. Lens copper was positively associated with creatinine ($\hat{\beta }$ = 1.10; p = 0.02), but negatively associated with glomerular filtration rate ($\hat{\beta }$ = 0.89; p = 0.02). Lens chromium and lead were positively associated with albumin (Chromium: $\hat{\beta }$ = 1.03, p = 0.03; Lead: $\hat{\beta }$ = 1.02, p = 0.04). Lens nickel was positively associated with bilirubin ($\hat{\beta }$ = 1.14; p = 0.03). Classification based on multiple or individual heavy metals for gender and smoking status was not statistically significant.

Conclusions: Our results suggest the human crystalline lens accumulates heavy metals with age and demonstrate the correlation between abnormality of metabolic function and heavy metal deposition in older adult lens.