Evaluation of PIG-A-mutated granulocytes and ex-vivo binucleated micronucleated lymphocytes frequencies after breast cancer radiotherapy in humans

The PIG-A gene mutation assay in human biomonitoring and disease

The blood cell phosphatidylinositol glycan class A (PIG-A) gene mutation assay has been extensively researched in rodents for in vivo mutagenicity testing and is now being investigated in humans. The PIG-A gene is involved in glycosyl phosphatidylinositol (GPI)-anchor biosynthesis. A single mutation in this X-linked gene can lead to loss of membrane-bound GPI anchors, which can be enumerated via corresponding GPI-anchored proteins (e.g., CD55) using flow cytometry. The studies published to date by different research groups demonstrate a remarkable consistency in PIG-A mutant frequencies. Moreover, with the low background level of mutant erythrocytes in healthy subjects (2.9-5.56 × 10-6 mutants), induction of mutation post genotoxic exposure can be detected. Cigarette smoking, radiotherapy, and occupational exposures, including lead, have been shown to increase mutant levels. Future applications of this test include identifying new harmful agents and establishing new exposure limits. This mutational monitoring approach may also identify individuals at higher risk of cancer development. In addition, identifying protective agents that could mitigate these effects may reduce baseline somatic mutation levels and such behaviors can be encouraged. Further technological progress is required including establishing underlying mechanisms of GPI anchor loss, protocol standardization, and the development of cryopreservation methods to improve GPI-anchor stability over time. If successful, this assay has the potential be widely employed, for example, in rural and low-income countries. Here, we review the current literature on PIG-A mutation in humans and discuss the potential role of this assay in human biomonitoring and disease detection.

PIG-A gene mutation as a mutagenicity biomarker among coke oven workers

PIG-A gene mutations can be detected in humans, and PIG-A assays can potentially predict the risk of exposure to carcinogens. However, extensive, population-based studies to validate this are lacking. We studied a cohort of occupational coke oven workers with chronic high exposure to carcinogenic polycyclic aromatic hydrocarbons, which are well-studied genotoxins classified by the IARC as carcinogenic to humans. Peripheral blood erythrocytes of workers were assessed for gene mutations using a PIG-A assay, and chromosome damage using the cytokinesis-block micronucleus test with lymphocytes. Two sample populations from a non-industrialized city and new employees in industrial plants were selected as controls. We observed a significantly elevated PIG-A mutation frequency (MF) and increased frequencies of micronuclei (MN) and nuclear buds (NBUDs) in coke oven workers, compared with levels in the control groups. We found that the coke oven workers with different lengths of service had a relatively high mutation frequency. Overall, the study findings showed that occupational exposure of coke oven workers increases the genetic damage and the PIG-A MF could be a potential biomarker for risk assessment of carcinogen exposure.

PIG-A gene mutation as a genotoxicity biomaker in polycyclic aromatic hydrocarbon-exposed barbecue workers

Background

The PIG-A gene mutation assay is a valuable tool for measuring in vivo gene mutations in blood cells. The human PIG-A assay, used as a potential genotoxicity biomarker, is minimally invasive, sensitive, and cost-efficient; however, the relationship between carcinogen exposure and PIG-A mutations is not well understood.

Methods

We investigated the genotoxic effect of red blood cells using PIG-A assay and lymphocyte cytokinesis-block micronucleus test in barbecue restaurant workers (N = 70) exposed to polycyclic aromatic hydrocarbons (PAHs) and self-identified healthy control subjects (N = 56). Urinary PAH metabolites were measured to evaluate internal exposure levels.

Results

Multivariate Poisson regression showed that the PAH-exposed workers exhibited significantly higher PIG-A mutant frequency (MF) (8.04 ± 6.81 × 10^− 6) than did the controls (5.56 ± 5.26 × 10^− 6) (RR = 0.707, 95% CI: 0.615–0.812, P < 0.001). These results indicate that PAH exposure is a risk factor for elevated PIG-A MF. The frequencies of micronuclei (MN) and nuclear buds (NBUD) in the PAH-exposed workers (MN: 3.06 ± 2.07 ‰, NBUD: 1.38 ± 1.02 ‰) were also significantly higher than in the controls (MN: 1.46 ± 0.64 ‰, P < 0.001; NBUD: 0.70 ± 0.60 ‰, P < 0.001). Additionally, PIG-A MFs showed better associations with several urinary hydroxylated PAH metabolites (P_2-OH-Flu = 0.032, r_2-OH-Flu = 0. 268; P_2-OH-Phe = 0.022, r_2-OH-Phe = 0.286; P_3-OH-Phe = 0.0312, r_3-OH-Phe = 0.270; P_4-OH-Phe = 0.018, r_4-OH-Phe = 0.296), while the increase in MN, NPB, and NBUD frequencies was not associated with any OH-PAH metabolites; and high-PAH-exposed workers showed the highest PIG-A MFs. Furthermore, there was a significant association between PIG-A MF and PAH exposure levels (Chi-square test for trend, P = 0.006).

Conclusions

Our results indicate that an increase in PIG-A MF in barbecue workers could reflect the response to PAH exposure, providing evidence of its potential as a genotoxicity biomarker in human risk assessment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41021-021-00230-1.