Tracking Disease Biomarkers from PFOS Exposure in Chinese Workers by Mass Spec Metabolomics.

[NNadir]

The paper I'll discuss in this post is this one: Mass Spectrometry-Based Metabolomics Reveals Occupational Exposure to Per- and Polyfluoroalkyl Substances Relates to Oxidative Stress, Fatty Acid ?-Oxidation Disorder, and Kidney Injury in a Manufactory in China (Yao Lu, Ke Gao, Xiaona Li,§ Zhi Tang, Li Xiang, Hongzhi Zhao, Jianjie Fu, Ling Wang, Nali Zhu, Zongwei Cai,*,Yong Liang,*Yawei Wang,* and Guibin Jiang, Environ. Sci. Technol. 2019, 53, 9800?9809)

The introductory graphic:




Perfluoroalkyl substances are ubiquitous. My impression, just stumbling through the scientific literature leads me to doubt that there is anyone, save possibly some people living in remote regions of Tibet or in the mountains near Tierra del Fuego, who doesn't have detectable perfluoralkyl substances, in their blood plasma. (For one thing, they are associated with Teflon, particularly when overheated and who hasn't left a Teflon frying pan on the burner too long?) Historically, and in fact, currently, fluoroalkyl compounds are extremely useful, precisely for the same reason that they are persistent and do not actually degrade in the environment because they are inert, unreactive, and generally not subject to corrosion, under most circumstances. The main sink for them is high energy radiation, but because the main source of such radiation is UV, X-rays and gamma rays in the upper atmosphere, and because their molecular weight is generally high so that they tend to concentrate in the lower atmosphere when volatile, their atmospheric and aqueous half-lives are very, very, very long.

But they do degrade, albeit slowly, in biological systems and because of their properties, interfere in normal metabolism. The fine paper here is a study of metabolomics which is a molecular study of the transformations of molecules in physiological systems, often but not always human beings, and the effects that exogenous compounds, be they drugs, pollutants, or even foods cause in these systems.

The main tool for following metabolomics these days is mass spectrometry, a tool I didn't appreciate when I was a kid but appreciate greatly now.

The authors of this paper are located in China, and they have studied the effects of perfluoroalkyl compounds on the metabolomics of Chinese factory workers, the people who make most of our "stuff" so we can declare ourselves "green," because we would never do that kind of stuff to ourselves, because we're, um, green.

From the introduction to the paper:

Per- and polyfluoroalkyl substances (PFASs) are a group of synthetic chemicals that have received extensive attention. In 2009, perfluorooctane sulfonic acid (PFOS), its salts, and perfluorooctane sulfonyl fluoride were listed in Annex B of the Stockholm Convention.1 Subsequently, perfluorooctanoic acid (PFOA), its salts, and PFOA-related compounds in 20152 and perfluorohexane sulfonic acid (PFHxS), its salts, and PFHxSrelated compounds in 20173 were submitted to the Persistent Organic Pollutants Review Committee as Persistent Organic Pollutants candidates.

The widespread presence of PFASs has led to the concern regarding the health effects of PFAS exposure on both wildlife and human beings. Occupational workers are under greater health risks than the general population given their higher PFAS exposure levels. Our previous studies have investigated the environmental fate, as well as the human exposure conditions, including the exposure pathway, half-lives, and accumulation and elimination behavior of PFASs on occupational workers in a factory in China.4?7 Differential exposure patterns (both external and internal) between occupational workers and the general population were found. Therefore, we hypothesized that the differences in PFAS exposure would lead to discrepancies between the occupational workers and the general population at the molecular level, which may eventually indicate the corresponding health effects of occupational PFAS exposure on workers...

The authors then define metabolomics and then say this:

...With regard to the study on the environmental pollutants, metabolomics can provide new insights into the toxic effects and risk assessments of pollutants by revealing the changes in the organism at the metabolic level. It is a powerful complement to classical toxicological approaches. Several studies have adopted the metabolomics tool to assess the PFAS-induced toxicity and health effects on experimental cell and animal models.12?18 However, recent study demonstrated that known PFAS-induced toxicity mechanisms, as well as the associated health risks, might not be applicable to humans.19 Nevertheless, very few PFAS-related metabolomics studies have chosen humans as study subjects. Moreover, none of these studies have focused on the high PFAS exposure levels groups: occupational workers.20,21 ...

The authors have very nice equipment, and run their analysis on an Thermo Scientific Q Exactive Orbitrap. These instruments feature very high mass resolution, albeit at slower scan speeds which makes them less than ideal for precise quantification, meaning that they are excellent for structure elucidation or so I've been told, since personally I'm involved with triple quads as opposed to high res instruments. The GC results are run on Agilent GC with a single quad 5977A mass spectrometer. (Not particularly high resolution, but useful if you know what you're looking for.)

The graphics give a feel for what they find in their work:




The caption:

Figure 1. Scatter plots obtained from PLS-DA models: LC-MS-ESI positive-ion mode (A), LC-MS-ESI negative-ion mode (B), and GC-MS (C). The black triangles and red circles indicate for general population and occupational workers, respectively.

The caption:

Figure 2. Linear fit graphs of log ?6PFASs and log peak intensity of the 14 potential biomarkers.

The caption:

Figure 3. Box charts of log peak intensity between two groups of the 14 potential biomarkers. *p < 0.05; **p < 0.01; ***p < 0.001

Some text discussing the biomarkers monitored, molecular indicators of abnormal physiology often associated with disease states:

Regarding the biological significance of the 14 potential biomarkers, the perturbed pathways they were involved in included lipid metabolism (3-hydroxyoctanoic acid, azelaic acid, sebacic acid, gamma-CHEC, C18:1-CN, and C18:2-CN), amino acids metabolism (pyroglutamic acid, ornithine, methionine sulfoxide, and DL-2-aminooctanoic acid), purine metabolism (hypoxanthine), inositol metabolism (myo-inositol), retinol metabolism (glycerophosphocholines), and metabolism of alkaloids and their derivatives (piperine). The brief information of these metabolites is shown in Table 3. The linear fit results between the ?6PFASs level and the peak intensity of potential biomarkers can be found in Figure 2, and the box charts of peak intensity of the two groups can be found in Figure 3.

Some excerpted results:

Biological Significance of the Biomarkers. A number of 14 abnormal metabolites resulting from high PFAS exposure levels were identified in the occupational workers. Of the altered metabolites, pyroglutamic acid and ornithine were both up-regulated. Pyroglutamic acid, as the cyclic lactam of glutamic acid, is the potential precursor and reservoir of glutamate. Increased pyroglutamic acid may relate to oxidative damage in the body.29 Ornithine is an amino acid generated from arginine during the process of excreting urea in humans. Both pyroglutamic acid and ornithine are involved in the glutathione metabolism (GSH metabolism), wherein glutathione is oxidized to glutathione disulfide (GSSG) when scavenging free radicals and other reactive species through enzymatic reactions, and GSH/GSSG is the most crucial redox couple toward oxidative stress. Therefore, the disturbance of GSH metabolism indicates that the body may be under oxidative stress...30

...In the present study, the balance between methionine and methionine sulfoxide was broken, as indicated by the down-regulation of methionine sulfoxide in the workers. Gamma-carboxyethyl hydroxychroman (?-CEHC) is a potent antioxidant, and it was up regulated in the workers.33 Therefore, we speculated that high PFAS exposure level could induce oxidative stress and may activate the antioxidant defense in workers, which have also been found in in vivo and in vitro studies...3

...Two acylcarnitines, acylcarnitine C18:1 (C18:1-CN) and acylcarnitine C18:2 (C18:2-CN), both of which are attached to C-18 unsaturated fatty acids, presented an upward trend. Fatty acids and acyl carnitines are closely associated with fatty acids metabolism. Mitochondrial fatty acids ?-oxidation (FAO) is the most common and important metabolic pathway for fatty acids in human beings...

...Accumulation of acyl carnitine metabolites in the blood is commonly used for diagnosis of FAO disorders.36 On the basis of the up- or down-regulation of three fatty acids and the upregulation of two acyl carnitines in the workers’ plasma samples, we conjectured that the mitochondrial FAO processes were disturbed by high PFAS exposure levels. Furthermore, fatty acids, glucose, and proteins are three substrates for organisms to generate energy. FAO is pivotal for energy homeostasis in various organisms, especially for cardiac and skeletal muscle. Other tissues, in particular, the liver, use the FAO process product to form ketone bodies to provide energy for other tissues.37 Due to the disturbances in the FAO process, we speculate that the energy homeostasis of the workers is perturbed by occupational PFAS exposure...

...and so on...

By the way, the contamination of Chinese workers is hardly limited to polyfluorinated alkylated stuff. Although China has recently cut off the import of stuff for "green" recycling, the electronic recycling business in China has led to widespread contamination with other classes of persistent organic pollutants, for example, PBDE's and PBDD/F and PCDD, the flame retardants and related compounds in our electronic stuff.

Don't worry. Be happy. You're green, not like those Chinese.

More don't worry, be happy: They'll continue to make your "green" solar cells, even if that's not good for them either, since they are, at least we suppose they are, happy to suffer whatever it is they suffer, so people in the United States can continue to be green, green, green and more green.

Enjoy the holiday weekend.