The Toxicologist - Society of Toxicology

1707 RELEVANCE OF CIRCADIAN DISRUPTION AND
CIRCADIAN INDUCTION FOR CANCER CONTROL.
F. Levi. Rhythmes Biologiques et Cancer, INSERM, Villejuif, France. Sponsor: H. Zarbl.
The circadian timing system drives daily changes in xenobiotic metabolism and
detoxification, cell cycle events, DNA repair, apoptosis, and angiogenesis. As a result
the main hallmarks of cancer, including inflammation, are under circadian
control. Cancer promotion and/or progression are accelerated in rodents with circadian
disruption resulting from ablation of the suprachiasmatic nuclei, the central
pacemaker; chronic jet lag; or clock gene mutation. Circadian disruption is also involved
in chemical carcinogenesis. Cancer patients with circadian disruption display
poor survival, as compared with those with robust circadian rhythms, despite
similar clinical characteristics. Clock genes are down-regulated in most experimental
and human cancers and impairment of tumor molecular clocks can accelerate
cancer growth. Circadian induction in tumor tissue with defective circadian clocks
using timed seliciclib or meals slows tumor growth in mice. Meal timing induces
the rhythmic expression of over 400 genes for tumor growth in a pancreatic tumor.
We show that the circadian amplitude of core body temperature is critical for circadian
induction in tumor and implicates cell stress signaling pathways in tumor
transcriptome entrainment. Circadian timing can also modify the tolerability and
efficacy of anticancer drugs in patients. Improved efficacy correlates with the respective
times of best tolerability, due to (a) inherently poor circadian entrainment
of tumors and (b) persistent circadian entrainment of healthy tissues. Conversely,
host clocks are disrupted whenever anticancer drugs are administered at their most
toxic time, while speeding cancer processes. Mathematical and systems biology approaches
currently develop and integrate theoretical, experimental, and technological
tools in order to further optimize and personalize the circadian administration
of cancer treatments. The detection of early warning signals (temperature and restactivity)
may provide relevant decision making information for the personalization
of cancer chronotherapeutics.
1708 METHYLSELENOCYSTEINE RESETS THE RHYTHMIC
EXPRESSION OF CIRCADIAN AND GROWTH
REGULATORY GENES DISRUPTED BY
NITROSOMETHYLUREA IN VIVO.
M. Fang and H. Zarbl. Environmental and Occupational Health Sciences Institiute,
Robert Wood Johnson Medical School, Piscataway, NJ.
The role of Selenium (Se) in chemoprevention of mammary carcinomas was first
suggested by animal studies performed by Ip and coworkers who showed that feeding
carcinogen-treated rats garlic grown in selenium enriched soil, dramatic reduced
tumor incidence. Subsequent studies demonstrated that methylselenocysteine
(MSC), the active form of Se, mediates its effects at the post-initiation stage of
carcinogenesis. However, the in vivo mechanisms of MSC-mediated chemoprevention
are still poorly understood at the molecular level. To investigate how a dietary
MSC is able to reduce the incidence of mammary carcinoma in pubescent female
Fischer 344 (F344) rats exposed to N’-nitoso-N’-methyurea (NMU), we used
DNA microarrays and qPCR to compare gene expression profiles in mammary tissue
of NMU-treated F344 rats fed a MSC-enriched diet (3 ppm Se) to that of rats
on a standardized diet (0.1 ppm Se). Unexpectedly, the most dramatic effect of dietary
MSC supplementation was on the genes involved in the network of circadian
rhythm, providing the first evidence for the link between circadian rhythm and
chemoprevention. Exposure to a single carcinogenic dose of the alkylating agent,
NMU, resulted in a persistent disruption in the rhythmic expression of several circadian
genes, including Period 2 (Per2), Rev-ErbA α, the Melatonin Receptor 1α
(MTNR1A), as well as estrogen receptor beta (ERβ), in contrast, dietary MSC significantly
restored or enhanced the circadian expression of these genes during the
early stage of mammary tumoregenesis. At meantime, dietary MSC also promotes
circadian expression of genes essential to normal mammary cell growth and differentiation
(ER[|#61472#|]b, Trp53, p21, Gadd45[|#61537#|]), suggesting an important
role of enhanced-circadian rhythm on inhibition of tumoregenesis.
Analysis of tumors that arising in animals fed a MSC-enriched diet showed that
these tumors lost MSC-induced expression of circadian genes compared to normal
mammary glands, indicating that circadian gene expression was incompatible with
NMU-induced mammary carcinogenesis.
1709 MACROPHAGES: REGULATORS OF TOXICITY AND
DISEASE PATHOGENESIS.
D. Laskin and A. Gow. Pharmacology and Toxicology, Rutgers University,
Piscataway, NJ.
Macrophages function as control switches of the immune system, providing a balance
between pro- and anti-inflammatory responses. To accomplish this, they develop
into different subsets: classically (M1) or alternatively (M2) activated
368 SOT 2011 ANNUAL MEETING
macrophages. Whereas M1 macrophages display a cytotoxic, proinflammatory phenotype,
M2 macrophages, suppress immune and inflammatory responses and participate
in wound repair and angiogenesis. Critical to the actions of these divergent
or polarized macrophage subpopulations is the regulated release of inflammatory
mediators. When properly controlled, classically activated M1 macrophages effectively
destroy invading pathogens, tumor cells, and foreign materials. However,
when M1 activation becomes uncontrolled, these cells release excessive quantities of
cytotoxic mediators that contribute to disease pathogenesis. The activity of M1
macrophages is countered by alternatively activated M2 macrophages which release
mediators that down regulate M1 cells, and stimulate growth, extracellular matrix
turnover, and tissue repair. Aberrant functioning of M2 macrophages can lead to fibrosis
and tumor metastasis and progression. Ultimately, it is the balance in the
production of mediators by these two cell types that determines the outcome of the
tissue response to chemical toxicants and disease progression. These different models
will be presented to illustrate this divergent role of macrophages in disease
pathogenesis and toxicity.
1710 MACROPHAGES AND HEPATOTOXICITY: A BATTLE
OF FORCES.
D. Laskin 1 , C. Gardner 1 ,Y. Liu 1 and J. Laskin 2 . 1 Pharmacology and Toxicology,
Rutgers University, Piscataway, NJ and 2 UMDNJ-RWJ Medical School, Piscataway, NJ.
Accumulating evidence suggests that macrophages are key in acetaminophen
(APAP) hepatotoxicity. However, their role in the pathogenic process depends on
the timing of their appearance in the liver, and the inflammatory mediators they
encounter which direct their functional responses. Initially, macrophages responding
to stimuli such as LPS, HMGB1 and/or TNFα release proinflammatory cytokines
and cytotoxic mediators contributing to toxicity. Later in the pathogenic
process, following exposure to IL-10 or IL-4/IL-13, they function to down regulate
inflammation and initiate wound repair. These activities appear to be mediated by
distinct subpopulations of macrophages exhibiting a classically (M1) or alternatively
(M2) activated phenotype. This is supported by findings that APAP intoxication
results in early accumulation of macrophages in the liver expressing M1 markers
(e.g., TNFα, inducible nitric oxide synthase) followed by cells expressing M2
markers (e.g., arginase, galectin). Additionally, the appearance of M1 and M2
macrophage subpopulations correlates with evidence of oxidative stress and liver injury
(reduced GSH, elevated serum transaminases) and tissue repair (hepatocyte
proliferation, expression of the growth factors, CTGF and TGFβ), respectively. It
appears that the switch in macrophage phenotype from M1 to M2 is a consequence
of a changing cytokine environment. This is consistent with findings that the M2
chemokines and macrophage activators, MCP-1/CCR-2, IL-10 and IL-4/IL-13,
are upregulated in the liver during the initial stages of APAP-induced tissue repair.
Whereas pretreatment of animals with gadolinium chloride, an M1 inhibitor, protects
against APAP induced hepatotoxicity, clodronate liposomes, which suppress
M2 cells, exacerbates tissue injury. These data demonstrate that macrophages with
distinct phenotypes play different roles in APAP hepatotoxicity; moreover the outcome
of the response depends on the balance between these cell populations (NIH
GM034310, ES005022 AR055073, ES004738, CA132624).
1711 LUNG MACROPHAGE RESPONSES TO BIOACTIVE
ENGINEERED NANOMATERIALS (ENM) INVOLVES
ACTIVATION OF THE NLRP3 INFLAMMASOME.
A. Holian and C. Migliaccio. Center for Environmental Health Sciences, University
of Montana, Missoula, MT.
Exposure to ENM can lead to lung inflammation and fibrosis. The mechanisms
underlying the development of these pathologies, and the characteristics that separate
bioactive from benign ENM have not been established. Evidence suggests that
cells of the innate immune system initiate and sustain chronic inflammation required
for the development of pulmonary fibrosis. Alveolar and interstitial
macrophages are the primary innate immune cells in the lung; subpopulations of
these cells have been implicated in the development of chronic inflammation and
fibrosis. A key pathway in the macrophage initiation of inflammation is the NLRP3
inflammasome. Activation of the NLRP3 inflammasome results in activated caspase-1
and cleavage of the pro-IL-1β family of cytokines into bioactive forms.
Excessive and sustained productions of IL-1β, and possibly IL-18, appear to be responsible
for chronic inflammation. Utilizing C57Bl/6 and Balb/c strains of mice,
we evaluated the responses of a series of well-characterized multi-walled carbon
nanotubes and titanium dioxide ENM by using in vitro (isolated AM) and in vivo
systems. Our studies demonstrate that bioactive (causing lung inflammation and
pathology) ENM consistently induce activation of the NLRP3 inflammasome by
classically activated macrophages. In contrast, benign ENM cause little or no activation
of the NLRP3 inflammasome. The results indicate that inflammasome activation
can be predicted by shape and composition. Thus, long durable ENM and