The Influence of Repair Pathways on the Cytotoxicity and Mutagenicity Induced by the Pyridyloxobutylation Pathway of Tobacco-Specific Nitrosamines

Tobacco-specific nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N′-nitrosonornicotine (NNN), are considered to be human carcinogens. Both compounds are metabolized to pyridyloxobutylating intermediates that react with DNA to form adducts such as 7-[4-(3-pyridyl)-4-oxobut-1-yl]-guanine (7-pobG), O2-[4-(3-pyridyl)-4-oxobut-1-yl]-cytosine (O2-pobC), O2-[4-(3-pyridyl)-4-oxobut-1-yl]-2′-deoxythymidine (O2-pobdT), O6-[4-(3-pyridyl)-4-oxobut-1-yl]-2′-deoxyguanosine (O6-pobdG) and 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB)-releasing adducts. The role of specific DNA adducts in the overall genotoxic activity of the pyridyloxobutylation pathway is not known. One adduct, O6-pobdG, is mutagenic. To characterize the mutagenic and cytotoxic properties of pyridyloxobutyl DNA adducts, the impact of DNA repair pathways on the cytotoxic and mutagenic properties of the model pyridyloxobutylating agent, 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (NNKOAc) was investigated in Chinese hamster ovary (CHO) cell lines proficient or deficient in O6-alkylguanine DNA alkyltransferase (AGT), deficient in both AGT and base excision repair (BER), or deficient in both AGT and nucleotide excision repair (NER). The repair of the four pyridyloxobutyl DNA adducts was determined in the same cell lines via sensitive LC-MS/MS methods. NNKOAc was more cytotoxic in the cell lines lacking AGT, BER and NER repair pathways. It also induced more mutations in the hprt gene in the BER and NER deficient cell lines. However, AGT expression did not influence NNKOAc’s mutagenicity despite efficient repair of O6-pobdG. Analysis of the hprt mutational spectra indicated that NNKOAc primarily caused point mutations at AT base pairs. GC to AT transition mutations were a minor contributor to the overall mutation spectrum, providing a rationale for the observation that AGT does not protect against the overall mutagenic properties of NNKOAc in this model system. The only adduct affected by the absence of effective NER was O2-pobdT. Slower repair of O2-pobdT in NER deficient cells was associated with increased AT to TA transversion mutations, supporting the hypothesis that these mutations are caused by O2-pobdT. Together, these data support a hypothesis that the pyridyloxobutylation pathway generates multiple mutagenic and toxic adducts

Anthropogenic contamination of tap water, beer, and sea salt.

Plastic pollution has been well documented in natural environments, including the open waters and sediments within lakes and rivers, the open ocean and even the air, but less attention has been paid to synthetic polymers in human consumables. Since multiple toxicity studies indicate risks to human health when plastic particles are ingested, more needs to be known about the presence and abundance of anthropogenic particles in human foods and beverages. This study investigates the presence of anthropogenic particles in 159 samples of globally sourced tap water, 12 brands of Laurentian Great Lakes beer, and 12 brands of commercial sea salt. Of the tap water samples analyzed, 81% were found to contain anthropogenic particles. The majority of these particles were fibers (98.3%) between 0.1-5 mm in length. The range was 0 to 61 particles/L, with an overall mean of 5.45 particles/L. Anthropogenic debris was found in each brand of beer and salt. Of the extracted particles, over 99% were fibers. After adjusting for particles found in lab blanks for both salt and beer, the average number of particles found in beer was 4.05 particles/L with a range of 0 to 14.3 particles/L and the average number of particles found in each brand of salt was 212 particles/kg with a range of 46.7 to 806 particles/kg. Based on consumer guidelines, our results indicate the average person ingests over 5,800 particles of synthetic debris from these three sources annually, with the largest contribution coming from tap water (88%)

Replication Data for: Anthropogenic contamination of tap water, beer, and sea salt

Raw Data (including particle counts, colors and sample information) used as the basis for the peer-reviewed journal article "Anthropogenic contamination of tap water, beer, and sea salt", submitted to PLOS On

Tap v. Beer particle counts.

<p>Comparison of anthropogenic particle count in beer and its corresponding municipal tap water.</p

Beer particle colors.

<p>Color distribution of anthropogenic particles extracted from 12 brands of beer.</p

Sea salt particles.

<p>Examples of anthropogenic particles found in sea salt: (A) Fiber, 1 mm in length from Pacific Ocean sourced sea salt; (B) Fiber, 1.5 mm in length from Atlantic Ocean sourced sea salt.</p

Summary of beer results.

<p>Summary of beer results.</p