Examination of the exposome in an animal model: The impact of high fat diet and rat strain on local and systemic immune markers following occupational welding fume exposure.

The goal of this study was to investigate the impact of multiple exposomal factors (genetics, lifestyle factors, environmental/occupational exposures) on pulmonary inflammation and corresponding alterations in local/systemic immune parameters. Accordingly, male Sprague-Dawley (SD) and Brown Norway (BN) rats were maintained on either regular (Reg) or high fat (HF) diets for 24wk. Welding fume (WF) exposure (inhalation) occurred between 7 and 12wk. Rats were euthanized at 7, 12, and 24wk to evaluate local and systemic immune markers corresponding to the baseline, exposure, and recovery phases of the study, respectively. At 7wk, HF-fed animals exhibited several immune alterations (blood leukocyte/neutrophil number, lymph node B-cell proportionality)-effects which were more pronounced in SD rats. Indices of lung injury/inflammation were elevated in all WF-exposed animals at 12wk; however, diet appeared to preferentially impact SD rats at this time point, as several inflammatory markers (lymph node cellularity, lung neutrophils) were further elevated in HF over Reg animals. Overall, SD rats exhibited the greatest capacity for recovery by 24wk. In BN rats, resolution of immune alterations was further compromised by HF diet, as many exposure-induced alterations in local/systemic immune markers were still evident in HF/WF animals at 24wk. Collectively, HF diet appeared to have a greater impact on global immune status and exposure-induced lung injury in SD rats, but a more pronounced effect on inflammation resolution in BN rats. These results illustrate the combined impact of genetic, lifestyle, and environmental factors in modulating immunological responsivity and emphasize the importance of the exposome in shaping biological responses.

Inhalation of iron-abundant gas metal arc welding-mild steel fume promotes lung tumors in mice.

Welding fumes were reclassified as a Group 1 carcinogen by the International Agency for Research on Cancer in 2017. Gas metal arc welding (GMAW) is a process widely used in industry. Fume generated from GMAW-mild steel (MS) is abundant in iron with some manganese, while GMAW-stainless steel (SS) fume also contains significant amounts of chromium and nickel, known carcinogenic metals. It has been shown that exposure to GMAW-SS fume in A/J mice promotes lung tumors. The objective was to determine if GMAW-MS fume, which lacks known carcinogenic metals, also promotes lung tumors in mice. Male A/J mice received a single intraperitoneal injection of corn oil or the initiator 3-methylcholanthrene (MCA; 10 µg/g) and, one week later, were exposed by whole-body inhalation to GMAW-MS aerosols for 4 hours/day x 4 days/week x 8 weeks at a mean concentration of 34.5 mg/m3. Lung nodules were enumerated by gross examination at 30 weeks post-initiation. GMAW-MS fume significantly increased lung tumor multiplicity in mice initiated with MCA (21.86 ± 1.50) compared to MCA/air-exposed mice (8.34 ± 0.59). Histopathological analysis confirmed these findings and also revealed an absence of inflammation. Bronchoalveolar lavage analysis also indicated a lack of lung inflammation and toxicity after short-term inhalation exposure to GMAW-MS fume. In conclusion, this study demonstrates that inhalation of GMAW-MS fume promotes lung tumors in vivo and aligns with epidemiologic evidence that shows MS welders, despite less exposure to carcinogenic metals, are at an increased risk for lung cancer.

Renal disease in rats with type 2 diabetes is associated with decreased renal nitric oxide production.

AIMS/HYPOTHESIS: In several other models of chronic renal disease, decreases in renal nitric oxide activity and nitric oxide synthase (NOS) protein abundance have been demonstrated. Here, we studied diabetic obese Zucker (ZDF Gmi fa/fa) rats that develop severe hyperglycaemia and renal disease, together with their lean control animals, to determine if renal nitric oxide deficiency also occurs in this model. METHODS: Obese Zucker rats aged 10 to 12 weeks were maintained on Purina 5008 diet until 4, 8, or 11 months of age and compared with similarly maintained, 4- and 11-month-old lean Zucker rats. NOS activity and abundance of endothelial NOS (eNOS) and neuronal NOS (nNOS) were measured on homogenates of kidney cortex. Blood was analysed for glucose, lipids, creatinine, and blood urea nitrogen and kidney tissue was obtained for histology. RESULTS: Obese rats exhibited severe hyperglycaemia from 4 months of age and developed increasing hyperlipidaemia, proteinuria, and decreasing renal function with age compared to lean counterparts. At 4 months cortical NOS activity and nNOS abundance were lower in obese rats than in lean ones. At 11 months NOS activity remained depressed and nNOS abundance had declined further in obese rats. Glomerulosclerosis in the obese rats was mild at 4 months, becoming severe by 11 months. Lean rats had only mild age-dependent increases in glomerular injury. CONCLUSIONS/INTERPRETATION: The chronic renal disease that occurs in hyperglycaemic, obese Zucker rats is associated with decreased renal cortical nitric oxide production and increasing renal injury, although the changes do not resemble those of diabetic nephropathy in man.

The nitric oxide pathway is amplified in venular vs arteriolar cultured rat mesenteric endothelial cells.

To determine if there are differences in nitric oxide activity between pre- and postcapillary microvessels, we studied cultured rat mesenteric arteriolar and venular endothelial cells (RMAEC, RMVEC). We measured expression of endothelial nitric oxide synthase (eNOS), the activity of eNOS, and L-arginine transport in live RMAEC and RMVEC and the L-arginine content of RMAEC and RMVEC lysates. The abundance of eNOS was significantly greater in RMVEC vs RMAEC; this was also true for freshly harvested, pooled microvessels. Baseline NOS activity was higher in RMVEC than in RMAEC. NG-monomethyl-L-arginine (L-NMA; 5 mM) inhibited NOS activity by approximately 70-80% in both RMAEC and RMVEC, indicating that metabolism of l-arginine is largely via NOS. Intracellular L-arginine levels were higher in RMVEC vs RMAEC and well above the eNOS Km in both cell types. L-arginine levels increased with L-NMA in both RMAEC and RMVEC, presumably due to reduced substrate utilization. Since L-arginine transport was not higher in RMVEC vs RMAEC, this may reflect higher intracellular arginine synthesis. A higher intrinsic level of baseline NO production in the postcapillary microvascular endothelium may reflect both the contribution of venular derived NO to control of arteriolar tone and a key role of venular-derived NO in local thrombosis control.

Uremic levels of BUN do not cause nitric oxide deficiency in rats with normal renal function.

In vitro, 7 days of high blood urea nitrogen (BUN) inhibits endothelial L-arginine transport and nitric oxide synthase (NOS) activity. The present study investigates whether 7 days of high BUN in vivo influences renal hemodynamics, blood pressure (BP), and/or the nitric oxide (NO) system. Normal rats were fed low-nitrate food containing 30% urea for 7 days, which increased BUN (15 +/- 1 to 69 +/- 4 mg/100 ml, P < 0.001). High BUN did not reduce 24-hour urinary nitrite/nitrate excretion (a measure of total NO production). Baseline BP and renal hemodynamics were unaffected by high BUN as were the pressor and renal vasoconstrictor responses to acute NOS inhibition with N(G)-nitro-L-arginine-methyl ester. In addition, high BUN had no impact on renal cortical L-arginine concentration, density of either endothelial NOS or neuronal NOS protein, or renal cortical NOS activity. NOS activity in the brain cerebellum was also unaffected. In conclusion, high BUN did not lead to vasoconstriction or NO deficiency in rats with normal renal function. Further studies are needed to evaluate the effect of high BUN on the NO system in rats with progressive renal functional insufficiency.