Lanthanum chloride precipitation-based toxicoproteomic analysis of 3-monochloropropane-1,2-diol toxicity in rat kidney reveals involvement of extracellular signal-regulated kinase 2.

The heat-induced food contaminant 3-monochloropropane-1,2-diol (3-MCPD) and its fatty acid esters exert nephrotoxicity in rodents. Previous studies including a non-targeted toxicoproteomics approach using samples from a 28-day oral toxicity study in rats with 10 mg/kg body weight (b.w.) of 3-MCPD, an equimolar dose of 53 mg/kg b.w. 3-MCPD dipalmitate and a lower dose of 13.3 mg/kg b.w. of 3-MCPD dipalmitate, revealed substance-induced alterations in metabolic pathways, especially for glycolysis and energy metabolism. In order to obtain deeper insight into mechanisms of 3-MCPD toxicity, samples from the above-mentioned study were reanalyzed using a lanthanum chloride precipitation-based toxicoproteomics approach in order to increase the yield of phosphorylated proteins, crucial players in cellular signaling. A comparison of standard 2D-gel-based proteomics and lanthanum chloride precipitation was performed, thus providing a comprehensive case study on these two methods using in vivo effects of an important food toxicant in a primary target organ. While resulting in similar 2D-gel electrophoresis pherograms and spot counts, data analysis demonstrated that lanthanum precipitation yielded more significantly deregulated proteins thus considerably improving our knowledge on 3-MCPD-dependent proteomic alterations in the kidney. 3-MCPD-induced deregulation of the phosphorylated, active version of extracellular signal-regulated kinase 2 (ERK2) in rat kidney was demonstrated using mass spectrometry and immunohistochemistry. In summary, this paper for the first time links 3-MCPD effects to deregulation of the ERK/mitogen-activated protein kinase signaling pathway in rat kidney and demonstrates that lanthanum chloride precipitation is suited to support the gain of mechanistic knowledge on organ toxicity using 2D-gel-based proteomics.

Proteomic analysis of 3-MCPD and 3-MCPD dipalmitate-induced toxicity in rat kidney.

3-Chloropropane-1,2-diol (3-MCPD) and its fatty acid esters are formed during thermal treatment of fat-containing foodstuff in the presence of salt. Toxicological studies indicate a carcinogenic potential of 3-MCPD, pointing to the kidney as the main target organ. It is assumed that the toxicological property of 3-MCPD esters is constituted by the release of 3-MCPD during digestion. In a repeated-dose 28-day oral toxicity study using Wistar rats, animals were treated with equimolar doses of either 3-MCPD (10 mg/kg body weight) or 3-MCPD dipalmitate (53 mg/kg body weight). A lower dose of 3-MCPD dipalmitate (13.3 mg/kg body weight) was also applied. No histopathologically visible toxicity was observed in the study. To address molecular mechanisms leading to toxicity of 3-MCPD and its esters, kidney samples were analyzed by a comparative, two-dimensional gel electrophoresis/mass spectrometry proteomic approach. After either 3-MCPD or 3-MCPD dipalmitate treatment, alterations in proteins related to various metabolic pathways, including carbohydrate, amino acid, and fatty acid metabolism, were detected. These findings confirm and complement previous data on the inhibition of glucose metabolism by 3-MCPD. Altogether, broad overlap of 3-MCPD- and 3-MCPD dipalmitate-induced proteomic changes was observed. Further analyses revealed that the observed induction of glutathione S-transferase pi 1 (Gstp1) occurred at the transcriptional level and was not related to nuclear factor (erythroid-derived 2)-like 2 activation. Overall, the results indicate common mechanisms of toxicity for 3-MCPD and its dipalmitate ester. Furthermore, data suggest Gstp1 as a sensitive marker for early 3-MCPD-induced effects in rat kidney.

Analysis of 3-MCPD- and 3-MCPD dipalmitate-induced proteomic changes in rat liver.

3-Monochloropropane-1,2-diol (3-MCPD) and 3-MCPD fatty acid esters are process contaminants in foodstuff which are generated during thermal treatment. Long-term exposure to 3-MCPD or 3-MCPD esters causes toxicity especially in kidney and testis. 3-MCPD esters are efficiently hydrolyzed in the gastrointestinal tract, suggesting that their toxicity is mediated by free 3-MCPD. Combined exposure to free 3-MCPD and 3-MCPD released from 3-MCPD esters might lead to dietary consumption above the tolerable daily intake of 2 µg/kg body weight/day. Suspected mechanisms of 3-MCPD toxicity include the inhibition of glycolysis and oxidative stress. Here, a comparative proteomic approach was followed to analyze the effects of 3-MCPD or 3-MCPD dipalmitate in livers from rats exposed to 10 mg/kg body weight 3-MCPD, an equimolar dose of 3-MCPD dipalmitate, or a 4-fold lower dose of the ester during a 28-day repeated-dose feeding study. Early cellular changes were monitored in the absence of overt toxicity. A comprehensive view of 3-MCPD- or 3-MCPD dipalmitate-triggered proteomic changes in rat liver links to previously proposed mechanisms of toxicity and substantially extends our knowledge on molecular hepatic effects of 3-MCPD. Organ-independent marker proteins altered upon 3-MCPD exposure, for example DJ-1/PARK7, were identified by comparison of the proteomic patterns of kidney, testis and liver.

Proteomic analysis of 3-MCPD and 3-MCPD dipalmitate toxicity in rat testis.

Thermal treatment of foodstuff containing fats and salt promotes the formation of 3-chloropropane-1,2-diol (3-MCPD) and its fatty acid esters. 3-MCPD-exposed rats develop testicular lesions and Leydig cell tumors. 3-MCPD and 3-MCPD ester toxicity is thought to be caused by 3-MCPD and its metabolites, since 3-MCPD esters are hydrolyzed in the gut. Inhibition of glycolysis is one of the few known molecular mechanisms of 3-MCPD toxicity. To obtain deeper insight into this process, a comparative proteomic approach was chosen, based on a 28-days repeated-dose feeding study with male Wistar rats. Animals received equimolar doses of 3-MCPD or 3-MCPD dipalmitate. A lower dose of 3-MCPD dipalmitate was also administered. Absence of histopathological changes supported an analysis of early cellular disturbance. Testes were analyzed by two-dimensional gel electrophoresis followed by mass-spectrometric protein identification. Data provide a comprehensive overview of proteomic changes induced by 3-MCPD and 3-MCPD dipalmitate in rat testis in an early phase of organ impairment. Results are compatible with known 3-MCPD effects on reproductive function, substantially extend our knowledge about cellular responses to 3-MCPD and support the hypothesis that toxicity of 3-MCPD and 3-MCPD esters is mediated via common effectors. DJ-1 was identified as a candidate marker for 3-MCPD exposure.

Determination of osteocalcin in meat and bone meal of bovine and porcine origin using matrix-assisted laser desorption ionization/time-of-flight mass spectrometry and high-resolution hybrid mass spectrometry.

A method has been developed for determining the origin of meat and bone meal (MBM) by detecting species-specific osteocalcin (OC) using matrix-assisted laser desorption ionization/time-of-flight (MALDI/TOF) and high-resolution hybrid mass spectrometry (HR-Q/TOF MS). The analysis is based on the detection of typical species-specific OC and its tryptic peptide fragments which differ in mass due to differences in the amino-acid sequences between species. After dissolving the MBM samples in EDTA buffer, purification after ultrafiltration was performed using two methods: solid-phase extraction using Zip-Tip C(18) or size exclusion coupled with reverse-phase chromatography. Fractions containing partially purified intact OC were analyzed using LC-Q/TOF and MALDI/TOF mass spectrometry. Species-specific OC was detected at the typical protonated and doubly protonated molecular ions. Furthermore, typical porcine- and bovine-derived tryptic fragments from MBM were detected after enzymatic digestion. In order to determine the underlying amino-acid sequences and to confirm the assignment to OC-derived peptides, MS/MS analysis was carried out. In conclusion, we were able to detect OC in bovine and porcine MBM with high sensitivity and the MS-based method described here by which total OC mass and marker peptides of digested OC are recorded can be used as an alternative approach to detect genus-specific differences in MBM and can be applied as a confirmatory method to mainly immunological osteocalcin screening methods.