Telomere length in human adults and high level natural background radiation

Abstract

Background: Telomere length is considered as a biomarker of aging, stress, cancer. It has been associated with many chronic diseases such as hypertension and diabetes. Although, telomere shortening due to ionizing radiation has been reported in vitro, no in vivo data is available on natural background radiation and its effect on telomere length.

Methodology/principal findings: The present investigation is an attempt to determine the telomere length among human adults residing in high level natural radiation areas (HLNRA) and the adjacent normal level radiation areas (NLNRA) of Kerala coast in Southwest India. Genomic DNA was isolated from the peripheral blood mononuclear cells of 310 individuals (HLNRA: N = 233 and NLNRA: N = 77). Telomere length was determined using real time q-PCR. Both telomere (T) and single copy gene (S) specific primers were used to calculate the relative T/S and expressed as the relative telomere length. The telomere length was determined to be 1.22+/-0.15, 1.12+/-0.15, 1.08+/-0.08, 1.12+/-0.11, respectively, among the four dose groups (</=1.50, 1.51-3.00, 3.01-5.00 and >5.00 mGy per year), which did not show any dose response. The results suggested that the high level natural chronic radiation did not have significant effect on telomere length among young adult population living in HLNRA, which is indicative of better repair of telomeric ends. No significant difference in telomere length was observed between male and female individuals. In the present investigation, although the determination of telomere length was studied among the adults with an age group between 18 to 40 years (mean maternal age: 26.10+/-4.49), a negative correlation was observed with respect to age. However, inter-individual variation was (0.81-1.68) was clearly observed.

Conclusions/significance: In this preliminary investigation, we conclude that elevated level of natural background radiation has no significant effect on telomere length among the adult population residing in HLNRAs of Kerala coast. To our knowledge, this is the first report from HLNRAs of the world where telomere length was determined on human adults. However, more samples from each background dose group and samples from older population need to be studied to derive firm conclusions.

Figure 1. Telomere length in adults with respect to various background dose levels.

(The line graph represents the relative telomere length (T/S ratio) in five different background dose groups (≤1.5, 1.51–3.0, 3.01–5.0, >5.00 mGy/year). For each point, error bars indicate the standard error of the mean (SEM). N (Number of individuals studied in each dose group) is given in table 1).

Figure 2. Telomere length among male and female adults with respect to various background dose levels.

[(≤1.50 mGy/year: 34 males+43 females, 1.51–3.0 mGy/year: 67 males+80 females, 3.01–5.0 mGy/year: 23 males+27 females, >5.00 mGy/year: 17 males +19 females)].

Figure 3. Telomere length in male and female adults with respect to age.