The Multiple Chemicals and Actions Model of carcinogenesis. A possible new approach to developing prevention strategies for environmental carcinogenesis

Occupational exposure of workers to pesticides: Toxicogenetics and susceptibility gene polymorphisms

Farm workers are often exposed to pesticides, which are products belonging to a specific chemical group that affects the health of agricultural workers and is mostly recognized as genotoxic and carcinogenic. The exposure of workers from Piauí, Brazil, to these hazardous chemicals was assessed and cytogenetic alterations were evaluated using the buccal micronucleus assay, hematological and lipid parameters, butyrylcholinesterase (BChE) activity and genetic polymorphisms of enzymes involved in the metabolism of pesticides, such as PON1, as well as of the DNA repair system (OGG1, XRCC1 and XRCC4). Two groups of farm workers exposed to different types of pesticides were evaluated and compared to matched non-exposed control groups. A significant increase was observed in the frequencies of micronuclei, kariorrhexis, karyolysis and binucleated cells in the exposed groups (n = 100) compared to controls (n = 100). No differences were detected regarding the hematological parameters, lipid profile and BChE activity. No significant difference was observed either regarding DNA damage or nuclear fragmentation when specific metabolizing and DNA repair genotypes were investigated in the exposed groups.

Tracheal Morphologic and Protein Alterations FollowingShort-Term Cigarette Mainstream Smoke Exposure to Rats

A short-term 5-day nose-only cigarette smoke exposure study was conducted in Fisher 344 rats to identify smoke-induced tracheal protein changes. Groups of 10 male and female 5 week old rats were assigned to 1 of 4 exposure groups. Animals received filtered air, or 75, 200 or 400 mg total particulate matter (TPM)/m³ of diluted 3R4F Kentucky reference cigarette mainstream smoke. Exposures were conducted for 3 hrs/day, for 5 consecutive days. Tracheas from half the rats were processed for pathology, and tracheas from the other half of the rats frozen immediately for proteomics. We hypothesized that smoke will activate tracheal inflammatory, apoptotic, proliferative, and stress-induced pathways. Mucosal epithelial toxicity from the inhaled material was evidenced by cilia shortening and loss of tracheal mucosal epithelium in smoke-exposed animals. Mucosal thinning occurred in all smoke-exposed groups with hyperplastic reparative responses in the 200 and 400 mg TPM/m³ groups. Tracheal lysates from control vs. treated animals were screened for 800 proteins using antibody-based microarray technology and subsequently the most changed proteins evaluated by Western blot. Tracheal proteins expressed at high levels that were markedly increased or decreased by smoke exposure depended on dose and gender and included caspase 5, ERK 1/2 and p38. Signaling pathways common between the morphologic and protein changes were stress, apoptosis, cell cycle control, cell proliferation and survival. Changes in identified proteins affected by smoke exposure were associated with tracheal mucosal pathology, may induce functional tracheal changes, and could serve as early indicators of tracheal damage and associated disease.

Proteomic analyses of lung lysates from short-term exposure of Fischer 344 rats to cigarette smoke

A short-term 5 day mainstream cigarette smoke exposure study was conducted in Fischer 344 rats to identify changes in lung proteins. Groups of 10 male and female rats at 5 weeks of age were assigned to one of four exposure groups. Animals received either nose-only filtered air (Air Control) or 75, 200, or 400 mg total particulate matter (TPM)/m(3) of diluted cigarette smoke. Exposures were conducted for 3 h per day, for 5 consecutive days. One lung per animal was frozen in liquid nitrogen and processed for proteomic analyses. Lung lysates from control verses treated animals were screened with 650 antibodies for changes in signaling protein levels and phosphorylation using antibody microarray technology, and then over 100 of the top protein hits were assessed by immunoblotting. The top smoke-altered proteins were further evaluated using reverse lysate microarrays. Major protein changes showed medium to strong bands on Western blots, depended on dose and gender, and included protein-serine kinases (Cot/Tpl2, ERK1/2, GSK3α/β, MEK6, PKCα/γ, RSK1), protein phosphatases (PP4/A'2, PP1Cβ), and other proteins (caspase 5, CRMP2, Hsc70, Hsp60, Rac1 and STAT2). The most pronounced changes occurred with 75 mg TPM/m(3) exposed females and 200 mg TPM/m(3) exposed males. Smoke-altered proteins regulate apoptosis, stress response, cell structure, and inflammation. Changes in identified proteins may serve as early indicators of lung damage.

Effects of short-term cigarette smoke exposure on Fischer 344 rats and on selected lung proteins

A short-term 5-day cigarette smoke exposure study was conducted in Fischer 344 rats to identify smoke-induced lung protein changes. Groups of 10 male and 10 female rats at 5 weeks of age were randomly assigned to one of four exposure groups. Animals received filtered air (control) or 75, 200, or 400 mg total particulate matter (TPM)/m(3) of diluted Kentucky reference 3R4F cigarette smoke. Nose-only exposures were conducted for 3 hours/day for 5 consecutive days. Mean body weights were significantly reduced only in male rats exposed to 400 mg TPM/m(3). Body weight gains were significantly reduced in 200- and 400-mg TPM/m(3)-exposed males and in all smoke-exposed females compared with controls. Alveolar histiocytosis increased slightly in all smoke exposed-females and 200- and 400-mg TPM/m(3)-exposed males. Cyclooxygenase-2 staining increased at 400 mg TPM/m(3). Matrix metalloproteinase-12 staining of alveolar macrophages and bronchiolar epithelia increased in smoke-exposed animals, especially 400-mg TPM/m(3)-exposed females. Protein kinase C-alpha staining increased in macrophages at 200- and 400-mg TPM/m(3) doses. c-Jun NH(2)-terminal kinases staining decreased in smoke-exposed tissues. The identified changed proteins play roles in inflammation, transformation, proliferation, stress activation, and apoptosis.

Background, approaches and recent trends for setting health-based occupational exposure limits: a minireview

The setting of occupational exposure limits (OELs) are founded in occupational medicine and the predictive toxicological testing, resulting in exposure-response relationships. For compounds where a No-Observed-Adverse-Effect-Level (NOAEL) can be established, health-based OELs are set by dividing the NOAEL of the critical effect by an overall uncertainty factor. Possibly, the approach may also be used for carcinogens if the mechanism is epigenetic or the genetic effect is secondary to effect from reactions with proteins such as topoisomerase inhibitors, and mitotic and meiotic spindle poisons. Additionally, the NOAEL approach may also be used for compounds with weak genotoxic effect, playing no or only a minor role in the development of tumours. No health-based OEL can be set for direct-acting genotoxic compounds where the life-time risks may be estimated from the low-dose linear non-threshold extrapolation, allowing a politically based exposure level to be set. OELs are set by several agencies in the US and Europe, but also in-house in major chemical and pharmaceutical companies. The benchmark dose approach may in the future be used where it has advantage over the NOAEL approach. Also, more attention should be devoted to sensitive groups, toxicological mechanisms and interactions as most workplace exposures are mixtures.