Can eye lens proteins be used to determine birth year?

1. Can eye lens proteins be used to determine birth year? Radiocarbon Dating of the human eye lens crystallines reveal proteins without carbon turnover throughout life Jace James & Lauren Erland

2. Lens Crystalline Proteins • Long lived proteins found in the lens of the eye • Maintains transparency of the lens • Prevent protein aggregation • Elongation of compact fibres of crystalline proteins results in lens formation

3. 14C Dating of Lens Crystalline Proteins • Large accumulation of 14C in the atmosphere after development and testing of nuclear bombs during and after World War II • Levels are much lower in marine environments

4. Assumptions • Lens crystallines formed as a single event in the year of birth and do not degrade with age • Zero turnover • Primarily terrestrial diet • Globally everyone has approximately the same diet

5. Lens Crystallines formed as a single event and show zero turnover • Cataracts • Deamidation • Solubility • Vitamin C

6. Cataracts • Age-related, protein aggregation disease • Denaturation & insolubilization of lens proteins • Factors promoting cataract formation • UV light & ionizing radiation • Diabetes, hypertension and advanced age • Heavy smoking • Change from a reducing to an oxidizing environment environment results in protein unfolding • Addition of oxygen atoms due to hydroxide radicals • Majority of the proteins in the nuclei of advanced ARN cataract lenses undergoing are due to extensive modification and protein unfolding

7. Deamidation • Modifications that disrupt the order of crystallines • Deamidation • Truncation • Methylation • Oxidation • Disulfide bond formation • Glycation • Racemization • Modification significantly decreases the amount of intact crystallines even in young adults • Deamidation • is the most abundant modification • >60% • Amide group removed • Leads to protein instability

8. Solubility • Amount of insoluble protein increases almost linearly with age • In ARN cataract, insoluble even in 8 M urea • increases progressively • ~ 50% total nuclear protein. • It has been estimated that all people will suffer from cataract if they live long enough • Proteins do change!

9. Vitamin C • Vitamin C and its degradation products induce protein modifications in vivo via non-enzymatic glycation • Vitamin C levels are particularly high in the lens • Degradation products damage proteins via formation of advanced glycation end products.

10. Primarily terrestrial diet “Consumption of fish would have a significant effect on the 14C content of the lenses because the 14C content is smaller than that in the atmosphere” • Humans use organic carbon as their carbon source • All carbon in our bodies is derived from the food we eat • Diet completely determines the 14C content in our tissues • Seafood accounts for 14-16% animal protein consumed globally • >1 billion rely on fish as their primary source of animal protein

11. Global Fish Consumption (WHO)

12. Data Collection & Analysis • 13 people of varying ages • All from Denmark • Small sample size, limited population • Cannot accurately predict age of those born before nuclear testing caused atmospheric build up of 14C • 1950’s • WWII

13. Other problems… “It was our experience that the lens could be removed up to three days post-mortem. After this period, post-mortem degradation and putrefaction made it impossible to extract the lens, as it became more and more fluid and not intact in its capsule” • Cannot be used on corpses more than 3 days old • Often months or years before a body is discovered • Practicality for forensic use?

14. Other Methods of Age Determination • Teeth • Dentine • Aspartic acid racemization • Radiocarbon dating • Skeleton • Partial or whole • Can optimize techniques based on suspected age • Ie child, adult • In both cases age can be determined from a whole or partial skeleton or a (partially) decomposed body

15. Can only use this method of age determination for people living in Denmark, born after WWII, who do not eat fish and seafood… … And cannot be used it if the victim has been dead more than three days… … or had a history of lens degrading diseases.