# Effects of Workers Exposure to Nanoparticles Studied by NMR Metabolomics
## 3 Results and Discussion
### Analysis of Blood Plasma
Excessive concentrations of oxalate causerolithiasis and nephracalcinosis [48]. The excessive oxidation of glyoxylate to oxalate by lactate dehydrogenase is prevented by reduction of cytosolic and mitochondrial glyoxylate to glycolate by cytosolic glyoxylate reductase [48]. The post-shift group also manifested increased concentrations of myo-inositol. This metabolite has an important omoregulatory role and is involved in the running of a wide range of cell functions, including cell growth and survival [49; 50], which could explain why myo-inositol is increased in the acute state. Several studies have reported alterations in the myo-inositol levels after exposure to NPs in rats [43] or mouse fibroblast cells L929 [51]. The decreased tryptophan concentration in the post-shift group could be explained by its transformation to kynure acid via the kynure pathway (pathway tryptophan metabolism in Figure S8c in Supplementary Materials). Kynure acid has a protective effect against oxidative stress and lung inflammation induced by exposure to NPs [52]. Furthermore, the kynure pathway was previously associated with the elevated levels of cytokines [53], which is consistent with the results of our previous study [12; 13]. A decreased concentration of tryptophan was also observed in rat blood serum after exposure to TiO\({}_{2}\) NPs [52], which is in agreement with the findings in workers exposed to nanoTiO\({}_{2}\), and similar oxidative stress effects [54; 55]. The levels of several metabolites associated with the synthesis of glutathione were found altered, namely cystine, glutamate and 2-hydroxybutyrate. Glutathione as a major antioxidant is synthesized from cysteine, glutamate and glycine. Cysteine is transformed to glutathione in response to oxidative stress. This is reflected in decreased levels of cystine, an oxidized dimer form of cysteine. The availability of cysteine was reported as the rate-limiting step in the glutathione synthesis where cysteine is supplied via the cystine-glutamate antiporter system [49; 56]. Elevated levels of glutamate in the pre- and post-shift group indicate that glutamate is exchanged for cystine in the antiporter system [49]. The elevated levels of glutamate also affect several other metabolic pathways, such as glutamine and glutamate metabolism, alanine, aspartate and glutamate metabolism, arginine and proline metabolism, histidine metabolism and butanoate metabolism, as is shown in the metabolic pathway analysis via MetaboAnalyst (Figure S8a,b in Supplementary Materials). Alterations in glutamate levels have also been observed in several studies focusing on NPs' impact on rats [26; 43; 51]. The utilization of glutamate in glutathione biosynthesis leads to higher demands on glutamate and increases glutamine transformation into glutamate via the glutamine and glutamate metabolism pathway. This is documented by decreased levels of glutamine in both pre- and post-shift groups compared to the control group. Together with glutamate, glutamine is also involved in the pathway of alanine, aspartate and glutamate metabolism, which was also found altered according to metabolic pathway analysis (Figure S8a,b in Supplementary Materials). Glutamine and glutamate were also found affected in the study of [PERSON] et al. [57], in which the effect of TiO\({}_{2}\) and CeO\({}_{2}\) nanomaterials on human liver HepG2 cells was examined. A significant decrease in glutamine was observed, similar to observations from our study. Nevertheless, a decrease in glutamate was observed, on the contrary to our study, indicating that glutamate was involved at least partially in a different way. 2-Hydroxybutyrate is a reduction product of 2-ketobutyrate, which is produced during the transformation of cystathionine to cysteine within the methionine degradation pathway [58].