Keith C. Falkner

Polychlorinated biphenyls, lead, and mercury are associated with liver disease in American adults: NHANES 2003-2004.

Background High-level occupational exposures to some industrial chemicals have been associated with liver diseases, including nonalcoholic fatty liver disease (NAFLD). However, the potential role of low-level environmental pollution on liver disease in the general population has not been evaluated. Objective We determined whether environmental pollutants are associated with an elevation in serum alanine aminotransferase (ALT) activity and suspected NAFLD in U.S. adults. Methods This cross-sectional cohort study evaluated adult participants without viral hepatitis, hemochromatosis, or alcoholic liver disease from the National Health and Nutrition Examination Survey (NHANES) for 2003–2004. ALT elevation was defined in men as ≥ 37 IU/L (age18–20 years) and ≥ 48 IU/L (age ≥ 21 years) and in women as ≥ 30 IU/L (age 18–20 years) and ≥ 31 IU/L (age ≥ 21 years). Adjusted odds ratios (ORs) for ALT elevation were determined across exposure quartiles for 17 pollutant subclasses comprising 111 individual pollutants present with at least a 60% detection rate. Adjustments were made for age, race/ethnicity, sex, body mass index, poverty income ratio, and insulin resistance. Individual pollutants from subclasses associated with ALT elevation were subsequently analyzed. Results The overall prevalence of ALT elevation was 10.6%. Heavy metals and polychlorinated biphenyls (PCBs) were associated with dose-dependent increased adjusted ORs for ALT elevation. Within these subclasses, increasing whole-blood levels of lead and mercury and increasing lipid-adjusted serum levels of 20 PCBs were individually associated with ALT elevation. Conclusions PCB, lead, and mercury exposures were associated with unexplained ALT elevation, a proxy marker of NAFLD, in NHANES 2003–2004 adult participants.

Toxicant-associated steatohepatitis in vinyl chloride workers.

Although nonalcoholic steatohepatitis (NASH) is typically associated with obesity, it has also been reported to occur in lean individuals exposed to industrial chemicals. Occupational exposure to vinyl chloride (VC) is a well‐documented risk factor for hemangiosarcoma, but has not previously been associated with steatohepatitis. Here we evaluate liver biopsies from 25 nonobese, highly exposed VC workers for steatohepatitis. Next, we evaluate associated metabolic and cytokine abnormalities in affected workers controlled by 26 chemical workers with no to minimal VC exposures, and 11 unexposed, healthy volunteers. Among highly exposed VC workers the prevalence of steatohepatitis was 80%. Of these, 55% had fibrosis and four had hemangiosarcoma. We have coined the term toxicant‐associated steatohepatitis (TASH) to describe this condition, which was not explained by obesity or alcohol. Although mean serum transaminases were normal in TASH, total cytokeratin 18, but not the caspase‐cleaved fragment, was elevated. Despite the absence of obesity, workers with TASH had insulin resistance with reduced adiponectin levels. TASH was also associated with markedly elevated serum tumor necrosis factor alpha and interleukins 1β, 6, and 8. Serum antioxidant activity was reduced in TASH. Conclusion: TASH occurred frequently in these nonobese VC workers with high cumulative exposures and normal liver enzymes. Elevated total cytokeratin 18 suggested the presence of necrotic cell death in TASH and may be a useful serologic biomarker. TASH was further characterized by insulin resistance, elevated proinflammatory cytokines, and impaired antioxidant defenses. The threshold VC exposure and the role of other chemical agents in TASH are as yet unknown. (HEPATOLOGY 2009.)

Hormonal regulation of hepatic enzymes involved in foreign compound metabolism.

The regulation of hepatic P450s has been the focus of numerous studies because of the importance of these proteins in endocrinology, oncology, and toxicology, as well as drug development. Considerable evidence exists demonstrating that many hepatic P450s are regulated by developmental, sex, or hormonal factors in addition to receptors that interact with foreign chemicals. The focus of work in our laboratory has been on the effects of steroid hormones, especially glucocorticoids, on expression of genes regulated by the Ah receptor. We have shown that most rat hepatic genes of the Ah receptor gene battery are regulated by glucocorticoids. We have used glucocorticoid‐deficient animal models to demonstrate that these steroids do modulate the expression (basal and inducible) of these genes in vivo. Using cultured rat hepatocytes, we have demonstrated that polycyclic aromatic hydrocarbon (PAH) induction of cytochrome P4501A1, glutathione S‐transferase Ya1, and UDP‐glucuronoeyl‐transferase 1∗6 are apparently potentiated two‐ to fourfold upon inclusion of glucocorticoids in the media to activate the glucocorticoid receptor and further, that the receptor antagonist RU 38486 reverses these phenomenon. NAD(P)H:quinone oxi‐doreductase and aldehyde dehydrogenase 3 gene expression were repressed 70‐80% by glucocorticoids in cultured hepatocytes through a glucocorticoid receptor‐mediated process as well. The effect of glucocorticoid concentration on PAH induction of glutathione S‐transferase Ya1 subunit for glucocorticoids was biphasic, but at physiological concentrations gene expression was repressed to ~20‐40% of control. At supraphysiological concentrations, glucocorticoids alone induced expression two‐ to threefold and potentiated the PAH‐inducible expression of the Ya1 subunit gene. Subsequent work in our laboratory has focused on defining the molecular basis of this hormonal regulation, specifically elucidating responsive elements responsible for the action of the glucocorticoid receptor and the mechanisms by which some of these genes are positively regulated and others are negatively regulated.—Prough, R. I., Linder, M. W., Pinaire, J. A., Xiao, G.‐H., Falkner, K. C. Hormonal regulation of hepatic enzymes involved in foreign compound metabolism. FASEB J. 10, 1369‐1377 (1996)

Drug-induced hepatotoxicity or drug-induced liver injury.

Drug-induced hepatotoxicity is underreported and underestimated in the United States. It is an important cause of acute liver failure. Common classes of drugs causing drug-induced hepatotoxicity include antibiotics, lipid lowering agents, oral hypoglycemics, psychotropics, antiretrovirals, acetaminophen, and complementary and alternative medications. Hepatotoxic drugs often have a signature or pattern of liver injury including patterns of liver test abnormalities, latency of symptom onset, presence or absence of immune hypersensitivity, and the course of the reaction after drug withdrawal.

Identification of Environmental Chemicals Associated with the Development of Toxicant-associated Fatty Liver Disease in Rodents

Background: Toxicant-associated fatty liver disease (TAFLD) is a recently identified form of nonalcoholic fatty liver disease (NAFLD) associated with exposure to industrial chemicals and environmental pollutants. Numerous studies have been conducted to test the association between industrial chemicals/environmental pollutants and fatty liver disease both in vivo and in vitro. Objectives: The objective of the article is to report a list of chemicals associated with TAFLD. Methods: Two federal databases of rodent toxicology studies—Toxicological Reference Database (ToxRefDB; Environmental Protection Agency) and Chemical Effects in Biological Systems (CEBS, National Toxicology Program)—were searched for liver end points. Combined, these 2 databases archive nearly 2,000 rodent studies. Toxicant-associated steatohepatitis (TASH) descriptors including fatty change, fatty necrosis, Oil red O-positive staining, steatosis, and lipid deposition were queried. Results: Using these search terms, 123 chemicals associated with fatty liver were identified. Pesticides and solvents were the most frequently identified chemicals, while polychlorinated biphenyls (PCBs)/dioxins were the most potent. About 44% of identified compounds were pesticides or their intermediates, and >10% of pesticide registration studies in ToxRefDB were associated with fatty liver. Fungicides and herbicides were more frequently associated with fatty liver than insecticides. Conclusion: More research on pesticides, solvents, metals, and PCBs/dioxins in NAFLD/TAFLD is warranted due to their association with liver damage.

Serum cytokeratin 18 and cytokine elevations suggest a high prevalence of occupational liver disease in highly exposed elastomer/polymer workers.

Objective: Cytokeratin 18 (CK18) is a novel serologic biomarker for occupational liver disease. The purpose of this study is to determine the prevalence of CK18 elevation in elastomer/polymer workers exposed to acrylonitrile, 1,3-butadiene, and styrene. Methods: A total of 82 chemical workers were evaluated. Cytokeratin 18 was determined by enzyme-linked immunosorbent assay and proinflammatory cytokines were measured by multi-analyte chemiluminescent detection. Results: Thirty-nine percent (32 of 82) had elevated CK18 levels, which were not explained by alcohol or obesity, except in potentially four cases. The pattern of CK18 elevation was consistent with toxicant-associated steatohepatitis (TASH) in the majority of cases (78%). Tumor necrosis factor &agr;, interleukin-6, interleukin-8, monocyte chemotactic protein-1, and plasminogen activator inhibitor-1 were increased in these workers compared with those with normal CK18 levels. Conclusions: These results suggest a high prevalence of occupational liver disease and TASH in elastomer/polymer workers with elevated proinflammatory cytokines.

Vinyl Chloride Metabolites Potentiate Inflammatory Liver Injury caused by LPS in Mice.

Vinyl chloride (VC) is a ubiquitous environmental contaminant for which human risk is incompletely understood. We have previously reported that high occupational exposure to VC directly caused liver damage in humans. However, whether VC may also potentiate liver injury from other causes is not known. C57Bl/6J mice were administered chloroethanol (CE), a major metabolite of VC, and lipopolysaccharide (LPS) 24 h after CE. Samples were harvested for determination of liver damage, inflammation, and changes in carbohydrate and lipid metabolism. In mice, CE exposure alone caused no detectable liver damage. LPS exposure caused inflammatory liver damage, oxidative stress, lipid accumulation, and glycogen depletion; the effect of all of these variables was potentiated by CE pre-exposure. In vitro experiments suggest that VC metabolite chloroacetaldehyde (CAA) directly damages mitochondria, which may explain the sensitization effect observed in vivo Moreover, co-exposure of cells to CAA and TNFα caused increased cell death, supporting the hypothesis of sensitization by VC metabolites. Taken together, these data demonstrate that exposure to VC/metabolites at levels that are not overtly hepatotoxic can potentiate liver injury caused by another hepatotoxicant. This serves as proof-of-concept that VC hepatotoxicity may be modified by an additional metabolic stress such as endotoxemia, which commonly occurs in acute (eg, sepsis) and chronic (eg, NAFLD) diseases.

Regulation of the Rat UGT1A6 by Glucocorticoids Involves a Cryptic Glucocorticoid Response Element

Glucocorticoids precociously induce fetal rat UGT1A6 and potentiate polycyclic aromatic hydrocarbon (PAH)-dependent induction of this enzyme in vivo and in isolated rat hepatocytes. To establish whether induction was due to glucocorticoid receptor (GR), luciferase reporter vectors were tested in transfection assays with HepG2 cells. Using a reporter construct containing approximately 2.26 kilobases of the 5′-flanking region of the UGT1A6-noncoding leader exon (A1*), dexamethasone increased basal activity 3- to 7-fold in cells cotransfected with an expression plasmid for GR. PAH increased gene expression 23-fold, but the presence of dexamethasone only induced PAH-dependent expression by 1.5-fold, suggesting interaction between GR and the aryl hydrocarbon (Ah) receptor. Furthermore, the GR antagonist RU 38486 [17β-hydroxy-11β-(4-dimethylamino-phenyl)-17α-(prop-1-ynyl)-estra-4,9-dien-3-one] was a partial agonist that increased, rather than inhibited, basal activity 3-fold. 5′-deletion analysis defined the 5′-boundary for a functional glucocorticoid-responsive unit between base pairs –141 and –118 relative to the transcription start site. This region contains the Ah receptor response element (AhRE), and both PAH and glucocorticoid-dependent gene activation were lost when this area was deleted. Mutation of a single base pair located in the AhRE region simultaneously reduced induction by PAH and increased glucocorticoid induction. Thus, the sequences of both the AhRE and glucocorticoid response elements seem to overlap, suggesting that Ah receptor binding may decrease glucocorticoid-dependent induction due to interactions of these two cis-acting elements. Mutation of a putative GRE located between base pair –81 and –95 reduced, but did not completely eliminate, glucocorticoid-dependent induction of the reporter, suggesting that a nonclassic mechanism of induction is involved in this response.

Activator Protein-1 Regulation of Murine Aldehyde Dehydrogenase 1a1

Previously we demonstrated that aldehyde dehydrogenase (ALDH) 1a1 is the major ALDH expressed in mouse liver and is an effective catalyst in metabolism of lipid aldehydes. Quantitative real-time polymerase chain reaction analysis revealed a ≈2.5- to 3-fold induction of the hepatic ALDH1A1 mRNA in mice administered either acrolein (5 mg/kg acrolein p.o.) or butylated hydroxylanisole (BHA) (0.45% in the diet) and of cytosolic NAD+-dependent ALDH activity. We observed ≈2-fold increases in ALDH1A1 mRNA levels in both Nrf2(+/+) and Nrf2(−/−) mice treated with BHA compared with controls, suggesting that BHA-induced expression is independent of nuclear factor E2-related factor 2 (Nrf2). The levels of activator protein-1 (AP-1) mRNA and protein, as well as the amount of phosphorylated c-Jun were significantly increased in mouse liver or Hepa1c1c7 cells treated with either BHA or acrolein. With use of luciferase reporters containing the 5′-flanking sequence of Aldh1a1 (−1963/+27), overexpression of c-Jun resulted in an ≈4-fold induction in luciferase activity, suggesting that c-Jun transactivates the Aldh1a1 promoter as a homodimer and not as a c-Jun/c-Fos heterodimer. Promoter deletion and mutagenesis analyses demonstrated that the AP-1 site at position −758 and possibly −1069 relative to the transcription start site was responsible for c-Jun-mediated transactivation. Electrophoretic mobility shift assay analysis with antibodies against c-Jun and c-Fos showed that c-Jun binds to the proximal AP-1 site at position −758 but not at −1069. Recruitment of c-Jun to this proximal AP-1 site by BHA was confirmed by chromatin immunoprecipitation analysis, indicating that recruitment of c-Jun to the mouse Aldh1a1 gene promoter results in increased transcription. This mode of regulation of an ALDH has not been described before.

Serum Cytokeratin 18 and Cytokine Elevations Suggest a High Prevalence of Occupational Liver Disease in Elastomer/Polymer Workers Highly Exposed to Acrylonitrile, Butadiene and Styrene

Objective: Occupational liver disease is likely to be under-recognized because, in many cases, routine serologic liver chemistries are not effective biomarkers. Cytokeratin 18 (CK18) is a novel serologic biomarker for occupational liver disease. We recently demonstrated that serum CK18 and pro-inflammatory cytokines were elevated in chemical workers with toxicant-associated steatohepatitis (TASH) due to high-level vinyl chloride exposures. The purpose of this study is to determine the prevalence of CK18 elevation in elastomer/polymer workers exposed to mixtures of acrylonitrile, 1,3 butadiene, and styrene. Methods: 82 chemical workers were evaluated. CK18 was determined by ELISA and pro-inflammatory cytokines were measured by multianalyte chemiluminescent detection. Results: Mean routine liver chemistries (aspartate aminotransferase, alanine aminotransferase, total bilirubin, albumin, and alkaline phosphatase) were in the normal range. In fact, only 3 of 82 total subjects had any single lab abnormality detected by these tests. However, 39% (32 of 82) had elevated CK18 levels which were not explained by alcohol or obesity, except in potentially 4 cases. The pattern of CK18 elevation was consistent with TASH in the majority of cases (78%). TNFα, IL-6, IL-8, MCP-1, and PAI-1 were increased in these workers compared to those with normal CK18 levels. Conclusions: These results suggest a high prevalence of occupational liver disease and TASH in elastomer/polymer workers with elevated pro-inflammatory cytokines. Funding Information: NIEHS (P30ES014443-01A1, T35ES014559), the NIAAA (K23AA18399-01A, 1P01AA017103-01), and NCRR (5P20RR024489-02).