Oxidative stress response in canine in vitro liver, kidney and intestinal models with seven potential dietary ingredients.

In vitro cell culture systems are a useful tool to rapidly assess the potential safety or toxicity of chemical constituents of food. Here, we investigated oxidative stress and organ-specific antioxidant responses by 7 potential dietary ingredients using canine in vitro culture of hepatocytes, proximal tubule cells (CPTC), bone marrow-derived mesenchymal stem cells (BMSC) and enterocyte-like cells (ELC). Cellular production of free radical species by denatonium benzoate (DB), epigallocatechin gallate (EPI), eucalyptol (EUC), green tea catechin extract (GTE) and sodium copper chlorophyllin (SCC), tetrahydroisohumulone (TRA) as well as xylitol (XYL) were continuously measured for reactive oxygen/nitrogen species (ROS/RNS) and superoxide (SO) for up to 24h. DB and TRA showed strong prooxidant activities in hepatocytes and to a lesser degree in ELC. DB was a weak prooxidant in BMSC. In contrast DB and TRA were antioxidants in CPTC. EPI was prooxidant in hepatocytes and BMSC but showed prooxidant and antioxidant activity in CPTC. SCC in hepatocytes (12.5mg/mL) and CPTC (0.78mg/mL) showed strong prooxidant and antioxidant activity in a concentration-dependent manner. GTE was effective antioxidant only in ELC. EUC and XYL did not induce ROS/RNS in all 4 cell types. SO production by EPI and TRA increased in hepatocytes but decreased by SCC in hepatocytes and ELC. These results suggest that organ-specific responses to oxidative stress by these potential prooxidant compounds may implicate a mechanism of their toxicities.

Considering new methodologies in strategies for safety assessment of foods and food ingredients.

Toxicology and safety assessment are changing and require new strategies for evaluating risk that are less depending on apical toxicity endpoints in animal models and relying more on knowledge of the mechanism of toxicity. This manuscript describes a number of developments that could contribute to this change and implement this in a stepwise roadmap that can be applied for the evaluation of food and food ingredients. The roadmap was evaluated in four case studies by using literature and existing data. This preliminary evaluation was shown to be useful. However, this experience should be extended by including examples where experimental work needs to be included. To further implement these new insights in toxicology and safety assessment for the area of food and food ingredients, the recommendation is that stakeholders take action in addressing gaps in our knowledge, e.g. with regard to the applicability of the roadmap for mixtures and food matrices. Further development of the threshold of toxicological concern is needed, as well as cooperation with other sectors where similar schemes are under development. Moreover, a more comprehensive evaluation of the roadmap, also including the identification of the need for in vitro experimental work is recommended.

Safety assessment of potential food ingredients in canine hepatocytes.

This research aimed to develop in vitro methods to assess hazard of canine food ingredients. Canine hepatocytes were harvested and cell viability of clove-leaf oil (CLO), eugenol (EUG), lemongrass oil (LGO), guanosine monophosphate (GMP), inosine monophosphate (IMP), sorbose, ginger-root extract (GRE), cinnamon-bark oil (CBO), cinnamaldehyde (CINA), thymol oil (TO), thymol (THYM), and citric acid were assessed with positive controls: acetaminophen (APAP), aflatoxin B1 and xylitol. Molecular Toxicology PathwayFinder array (MTPF) analyzed toxicity mechanisms for LGO. LC50 for APAP was similar among human (3.45), rat (2.35), dog (4.26 mg/ml). Aflatoxin B1 had an LC50 of 4.43 (human), 5.78 (rat) and 6.05 (dog) µg/ml; xylitol did not decrease viability. LC50 of CLO (0.185 ± 0.075(SD)), EUG (0.165 ± 0.112), LGO (0.220 ± 0.012), GRE (1.54 ± 0.31) mg/ml; GMP (166.03 ± 41.83), GMP + IMP (208.67 ± 15.27) mM; CBO (0.08 ± 0.03), CINA (0.11 ± 0.01), TO (0.21 ± 0.03), THYM (0.05 ± 0.01), citric acid (1.58 ± 0.08) mg/ml, while sorbose was non-toxic. LGO induced upregulation of 16 and down-regulation of 24 genes, which CYP and heat shock most affected. These results suggest that in vitro assays such as this may be useful for hazard assessment of food ingredients for altered hepatic function.

Species-specific kinetics and zonation of hepatic DNA synthesis induced by ligands of PPARalpha.

Peroxisome proliferator-activated receptor alpha (PPARalpha) ligands evoke a profound mitogenic response in rodent liver, and the aim of this study was to characterize the kinetics of induction of DNA synthesis. The CAR ligand, 1,4-bis[2-(3,5-dichoropyridyloxy)]benzene, caused induction of hepatocyte DNA synthesis within 48 h in 129S4/SvJae mice, but the potent PPARalpha ligand, ciprofibrate, induced hepatocyte DNA synthesis only after 3 or 4 days dosing; higher or lower doses did not hasten the DNA synthesis response. This contrasted with the rapid induction (24 h) reported by Styles et al., 1988, Carcinogenesis 9, 1647-1655. C57BL/6 and DBA/2J mice showed significant induction of DNA synthesis after 4, but not 2, days ciprofibrate treatment. Alderley Park and 129S4/SvJae mice dosed with methylclofenapate induced hepatocyte DNA synthesis at 4, but not 2, days after dosing and proved that inconsistency with prior work was not due to a difference in mouse strain or PPARalpha ligand. Ciprofibrate-induced liver DNA synthesis and growth was absent in PPARalpha-null mice and are PPARalpha dependent. In the Fisher344 rat, hepatocyte DNA synthesis was induced at 24 h after dosing, with a second peak at 48 h. Lobular localization of hepatocyte DNA synthesis showed preferential periportal induction of DNA synthesis in rat but panlobular zonation of hepatocyte DNA synthesis in mouse. These results characterize a markedly later hepatic induction of panlobular DNA synthesis by PPARalpha ligands in mouse, compared to rapid induction of periportal DNA synthesis in rat.

Peroxisome proliferator activated receptor alpha regulates a male-specific cytochrome P450 in mouse liver.

We set out to find if the strain-specific, male-specific hepatic expression of Cyp4a protein in mouse was due to expression of Cyp4a12 and to understand the genetic basis for reported differences in expression. 12-Lauric acid hydroxylase (LAH) activity was found to show higher levels in male ddY, but not C57Bl/6, mouse liver microsomes. The expression of Cyp4a12 mRNA was studied using RNAase protection assays in male and female liver and kidney of nine mouse strains. Cyp4a12 was found to be highly expressed in male liver and kidney, but at much lower levels in female liver and kidney, in all strains studied. Western blotting with an antibody specific for Cyp4a12 confirmed that Cyp4a12 was expressed in a male specific fashion in C57Bl/6 mouse liver. RNAase protection analysis for Cyp4a10 and 14 in ddY mice revealed that neither of these genes showed male-specific expression. To further investigate genetic factors that control male-specific Cyp4a12 expression, PPARalpha+/+ and -/- mice were studied, showing that total P450 and 12-LAH activity was male-specific in +/+, but not -/- mice. RNAase protection assays were used to confirm that Cyp4a12 was lower in -/- mice. However, the male-specific Slp and MUP-1 genes retained hepatic male-specific levels of expression in +/+ and -/- mice, showing that the decrease in Cyp4a12 was not a general effect on male-specific expression. Thus, PPARalpha has a specific effect on constitutive expression of Cyp4a12.