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REVIEW ARTICLE
A ticking clock links metabolic pathways and organ systems
function in health and disease
Manlio Vinciguerra •Maria Florencia Tevy •
Gianluigi Mazzoccoli
Received: 16 January 2013 / Accepted: 19 March 2013
ÓSpringer-Verlag Italia 2013
Abstract Rhythmic variations with 24-h periodicity
hallmark homeostatic regulation, metabolic processes and
organ systems function, driven by a circadian timing sys-
tem composed of central and peripheral oscillators. Recent
reports suggest that disrupted circadian rhythmicity of
physiology and behavior severely alters body homeostasis.
Nuclear receptors and transcriptional regulators sense
hormonal and metabolic cues and manage the rhythmic
patterns of chromatin remodelling and gene expression,
playing a key role in the cross talk between the circadian
clock circuitry, the metabolic pathways and the organ
systems. The alteration of this cross talk contributes to the
pathophysiology of metabolic, degenerative, immune-
related and neoplastic diseases.
Keywords Circadian rhythm Clock gene
Neuroendocrine-immune system Metabolism
Introduction
Living organisms on Earth including humans may be
deemed as complex hierarchical multi-component systems
facing environmental conditions that change over time,
exposing internal equilibrium to failures of different types
and physiological challenges that may be episodic/unex-
pected or periodic/predictable. The biological processes
underlying body homeostasis maintenance must afford
adaptive responses to sporadic events, and anticipatory
adjustments to expected fluctuations, providing selective
advantage [1]. In this context, organismal regulatory
phenomena are characterized by time-related variations
realizing a multifrequency/multiphase array of rhythms,
prevalently with 24-h periodicity and defined circadian
(from the Latin circa, about and dies, a day) [1]. They are
synchronized by a timing system comprising central oscil-
lators in the hypothalamic suprachiasmatic nuclei (SCN)
and subsidiary oscillators in peripheral tissues, functioning
as cellular biological clocks, and driven by the SCN through
the anatomic hardwire of neural circuits and the diffuse
modulation of humoral mediators, but also entrainable by
local signals, such as metabolite flux related to feeding [1].
The master pacemaker is timed by photic cues conveyed by
the retinohyopthalamic tract, entraining the circadian
rhythmicity of body physiology and behavior to the daily
geophysical cycles of alternating light and darkness [2].
A proper temporal organization of homeostatic processes
along with neuroendocrine-immune and organ systems
function is critical for the preservation of health, and recent
reports have put in evidence that alteration of the biological
clocks and/or desynchronization related to altered behav-
ioral cycles of sleep/wake, rest/activity and fasting/feeding,
and caused by exposure to electric light at night with
intentional sleep restriction, may underlie the elevated and
increasing risk of cancer worldwide [3]. Besides, alteration
of the circadian timing system contributes to metabolic
derangement [4], and the epidemic of metabolic syndrome,
obesity and diabetes mellitus is attaining outstanding
relevance, impacting on cardiovascular risk in the general
M. Vinciguerra
Division of Medicine, Institute of Liver and Digestive Health,
University College London, Royal Free Campus, London, UK
M. F. Tevy G. Mazzoccoli (&)
Division of Internal Medicine and Chronobiology Unit,
Department of Medical Sciences, IRCCS Scientific Institute and
Regional General Hospital ‘‘Casa Sollievo della Sofferenza,’’
Opera di Padre Pio da Pietrelcina, Cappuccini Avenue,
71013 San Giovanni Rotondo, FG, Italy
e-mail: g.mazzoccoli@operapadrepio.it
123
Clin Exp Med
DOI 10.1007/s10238-013-0235-8
population and representing an important challenge for the
health-care systems. The recognition of the relevance of
circadian rhythmicity in human physiology calls for new
therapeutic strategies addressing the role played by
disruption of the circadian clock circuitry in the patho-
physiology of metabolic, as well as degenerative, immune-
related and neoplastic diseases [5,6].
The molecular clockwork
A molecular clockwork goes ticking in every single cell,
functioning through a feedback loop of transcription/
translation involving a set of genes, called clock genes,
encoding transcription factors (CLOCK/NPAS2 and
BMAL1-2) that heterodimerize and activate expression of
genes encoding circadian proteins (PER 1-3 and CRY 1-2),
which in turn inhibit clock gene transcription [7]. The
heterodimeric transcriptional complex also activates the
expression of the genes encoding the nuclear receptors
REVERBa/band RORa/c, which play negative and posi-
tive transcriptional roles, respectively, and steer amplitude
and robustness of oscillation in this autoregulatory tran-
scriptional feedback mechanism that completes a cycle in
approximately 24 h [8,9]. The heterodimers, the nuclear
receptors and the circadian proteins also drive the expres-
sion of clock-controlled genes encoding transcription fac-
tors (HLF, TEF, DBP, E4BP4, DEC1-2), which entrain
transcriptional processes to environmental cues and syn-
chronize gene expression and epigenetic modification in
metabolic pathways with energy balance, redox state and
fasting/feeding-rest/activity cycles through interaction with
nutrient sensors [1,10]. A critical and somehow essential
role in the circadian oscillatory functioning of the molecular
clock is played by rhythmic post-translational modifications
operated predominantly by processes of phosphorylation,
catalyzed by casein kinases, AMP-activated protein kinase
and glycogen synthase kinase-3b, and through sumoylation
and ubiquitylation [1]. An additional mechanism of circa-
dian transcriptional regulation is represented by epigenetic
modifications represented by chromatin remodelling
through acetylation/deacetylation processes. CLOCK
directly acetylates and the type III nicotinamide adenine
dinucleotide (NAD?)-dependent histone/protein deacetyl-
ase SIRT1 deacetylates BMAL1, counteracting the acety-
lating action exerted by CLOCK. SIRT1 links metabolism
and circadian rhythmicity gauging cellular redox and met-
abolic status: NAD?biosynthesis from tryptophan is cat-
alyzed by the nicotinamide phosphoribosyltransferase
(NAMPT/visfatin), whose expression is controlled by the
biological clock and drives circadian oscillations of NAD?,
which operates as a metabolic oscillator, and influencing
SIRT1 deacetylating activity regulates the circadian
synthesis of its own rate-limiting enzyme [11]. The clock
gene machinery controls basic cell processes, such as cell
cycle, proliferation, differentiation, DNA damage repair,
apoptosis, whose deregulation is involved in carcinogenesis.
A circadian pattern of expression characterizes approxi-
mately 5–20 % of the transcriptome, diverging greatly
among tissues and reaching 80 % in the liver, and the clock-
controlled transcription factors drive the expression of
tissue-specific output genes involved in the regulation of
transcriptional networks that direct tissue/organ functions in
liver, kidney, adipose tissue, immune and hematopoietic
system, cardio-vascular apparatus [10] (Fig. 1).
Circadian rhythms in the neuroendocrine regulation
of immune function
Circadian rhythmicity characterizes oscillations of neuro-
endocrine function and innate/adaptive immune response,
driven by neural and humoral outputs from the SCN, which
regulate hormone secretion and well-timed trafficking of
leukocytes [12], and self-sustained biological clocks tick-
ing in the immune effectors, which organize their tasks.
Several transcription factors encoded by clock-controlled
genes are engaged in the control of the innate immune
response [10], the molecular oscillators drive the produc-
tion of cytolytic factors in natural killer cells [13], and gate
the response timing to immune challenges such as bacterial
lipopolysaccharide stimulation in macrophages [14]. In
turn, immunological factors such as TNF-aand IL-1b
feedback on the circadian clock circuitry influencing the
cross talk between the circadian and the neuroendocrine-
immune system pathways [15]. Circadian variations have
been found in immune system variables, including daily
rhythms in circulating leukocytes and serum cytokines
concentration [16], and circadian control of the antigen-
specific immune response and T cell proliferation regula-
tory mechanisms has been put in evidence [13]. Circadian
T cell immune responses are timed by a self-sustained
oscillator, and the transcriptional processes are connected
to rhythmicity of cell processes driven by the molecular
clockwork through the nuclear factor jB (NF-jB) pathway
[16]. On the other hand, experiments performed in animals
with clock gene mutations have highlighted different
immune phenotypes and evidenced altered expression of
immune-related genes and immune cells function, with
reduced leukocyte levels and altered circadian rhythmicity
of variation in the peripheral blood [13,17,18]. Mouse
lymph nodes exhibit rhythmic clock gene expression, and T
cells from lymph nodes collected over 24 h show a circa-
dian variation in proliferation after stimulation via the T
cell receptor, which is dampened in mice with Clock gene
mutation [13]. In humans, the total number of lymphocytes
Clin Exp Med
123
in the peripheral blood changes rhythmically over 24 h
with a nocturnal zenith, and opposing rhythms characterize
the nycthemeral oscillations of specific lymphocyte sub-
sets, with effector cytotoxic function peaking during the
day and memory function peaking at night [13]. The cir-
cadian timing system drives immune system function also
controlling the oscillatory secretion of neuroendocrine
hormones with immunomodulatory action (cortisol peaking
in the early morning, melatonin, growth hormone, prolactin
and thyroid-stimulating hormone peaking at night), and
directing the sleep/wake cycle. Sleep at night shifts
monocyte cytokine production to type 1 proinflammatory
pattern inducing predominance of T helper (Th1)-mediated
adaptive response, respect to anti-inflammatory type 2
cytokines that stimulate Th2-mediated immunity, and type
1–type 2 cytokine equilibrium is modulated by cross-
inhibition and regulated by the neuroendocrine system
[13].
The dynamic process of Th cell differentiation is
specifically and progressively influenced by fine tuning
of transcriptional control and gene expression patterns
[19], and several transcription factors encoded by
clock-controlled genes are engaged in the control of the
adaptive immune response [10]. For instance, the tran-
scription factors DEC1 and DEC2 oscillate with circadian
rhythmicity in peripheral blood mononuclear cells [20],
playing a key role in Th cell function and fate: DEC1
influences T lymphocyte activation, whereas DEC2 is
expressed principally during Th2 differentiation [21]. Th2
responses are also regulated by the highly expressed tran-
scription factor E4BP4, which controls cytokine production
and effector function in Th2 cells [22].
The biological clock and the connection
between immunity and metabolism
A crucial role in the multidirectional communication
among the circadian clock circuitry, the metabolic path-
ways and the neuroendocrine-immune system is played by
the nuclear receptors, comprising a superfamily of ligand
activated proteins expressed with different rhythmicity in
many tissues, capable to bind a number of molecules, such
as metabolites and hormones, and to influence gene
Fig. 1 The molecular clockwork. The biological oscillator is oper-
ated by an intracellular mechanism composed of a set of interlocking
transcription–translation feedback loops in which the expression of
clock genes is suppressed periodically by their protein products and
complete one cycle in approximately 24 h. The period genes (Per1-3)
and cryptochrome genes (Cry1-2) represent the core of the negative
limb in the feedback loop and are activated by the transcription
factors CLOCK and BMAL1, which heterodimerize and bind to
E-box enhancer elements in their promoters. The Per and Cry mRNAs
then give rise to PER and CRY proteins that are phosphorylated (Ph)
by casein kinase (CK), form a repression complex that translocates
back into the nucleus, interact directly with CLOCK and BMAL1 and
hinder their transcriptional activity. Otherwise, PER and CRY are,
respectively, targeted by CK and AMP kinase (AMPK) for degrada-
tion. CLOCK and BMAL1 also activate the expression of REV-
ERBs, which activate E4BP4 transcription and negatively control the
rhythmic transcription of Bmal1 impeding RORs binding at the
response elements, the nuclear receptor PPAR, the transcription
factors DBP, HLF, TEF, DEC and the clock-controlled genes, which
drive cell, tissue and organ functions
Clin Exp Med
123
expression through the modification of their transcriptional
activity after ligand binding [23]. The core clock genes
drive expression of nuclear receptors for several molecules,
such as fatty acids, cholesterol, oxysterols, androgens,
estrogens, glucocorticoids [10], and the circadian protein
PER2 is able to bind rhythmically at the promoters of
nuclear receptors target genes, co-regulating their tran-
scription and coordinating the biological oscillator with
metabolite/sensing, hormone/binding and transcriptional
processes [23]. The clock gene machinery also drives daily
variations in levels and responsiveness of pattern recogni-
tion receptors for pathogen-associated molecules such as
toll-like receptor 9, whose expression is driven through
binding of the transcriptional heterodimer CLOCK/
BMAL1 on TLR9 gene promoter, inducing circadian
rhythmic functional changes of TLR9-dependent cytokine
response engaged in the pathophysiological mechanisms
involved in septic shock, influencing clinical severity and
prognostic outcome [24].
The core clock genes also drive a number of transcrip-
tion factors, such as IRF-1, STAT 1-4, GATA-3, NF-AT,
NF-jB and AP 1-2 [10], implicated in the control of
inflammatory gene expression and differentiation/function
of immune cells, through regulation of cytokine production
and recruitment of costimulatory molecules influencing
immune responses. The rapid reprogramming of tran-
scriptional circuits upon inflammatory cytokine signaling
drives the acute phase response, a manifestation of innate
immunity involved in tissue homeostasis and defence.
Elevated levels of acute phase proteins together with lipid
and bile acid sensing nuclear receptors impinge on meta-
bolic and inflammatory/anti-inflammatory pathways
involved in derangements of cholesterol metabolism and
lipoprotein properties, atherogenesis and metabolic disor-
ders [25]. Liver X receptor (LXR, binding oxysterols),
peroxisome proliferator-activated receptors (PPARs, bind-
ing fatty acids), liver receptor homolog-1 (LRH-1, binding
phosphatidylinositols) and farnesoid X receptor (FXR,
binding bile acids) operate transcriptional interference with
the signal-dependent activation of proinflammatory tran-
scription factors, such as NF-jB, STATs and AP1, inhib-
iting the activities of other classes of transcription factors
in a ligand-dependent manner, and repressing inflammatory
gene expression by a mechanism defined transrepression
[25]. This mechanism does not require DNA binding by the
nuclear receptor and results in the elimination from geno-
mic binding sites of the nuclear receptor–proinflammatory
transcription factor complexes [25]. Animal studies have
shown that the inflammatory response is influenced by
REV-ERBaand RORapresent in vascular smooth muscle
cells, where IL-6 and cyclooxygenase-2 expression
levels are up-regulated by REV-ERBa. Besides, in
primary human macrophages present in the vascular wall,
REV-ERBaexpression is transcriptionally activated by
LXR, which controls cholesterol homeostasis, inflamma-
tion and the immune response through activation of TLR4
expression. TLR4 in turn is negatively regulated by binding
of REV-ERBato a response element site in its promoter
overlapping with the LXR response element site [11].
Furthermore, the clock gene machinery and PPARs are
strictly interconnected: PER2 negatively regulates expres-
sion of PPARcand inhibits PPARcrecruitment to target
promoters, PPARcpositively regulates Bmal1 transcrip-
tion, a reciprocal positive regulation of expression between
BMAL1 and PPARahas been put in evidence, and
CLOCK directly controls the circadian expression of Ppara
[11]. Interestingly, PPARs influence T lymphocyte differ-
entiation, proliferation, function and cytokine secretion,
independently from ligand binding [26], and self-sustained
biological clocks have been evidenced in human peripheral
blood mononuclear cells, with circadian rhythmicity of
expression of the core clock genes [20]. On the other hand,
RORaand RORct are involved in the differentiation pro-
cess of Th17 cells, which intervene in immune responses
against extracellular bacteria and fungi and contribute to
the initiation of organ-specific autoimmune diseases [27].
Cholesterol sulfate and derivatives are potential ligands of
RORa, which has also been proposed as the nuclear
mediator of melatonin signalling, entailing the pineal
monoamine as a key regulator of the molecular switch
leading to the reciprocally restricted generation of Th17
and T regulatory cells, essential to maintain self-tolerance
[28]. RORais also important for the differentiation and
expansion of the nuocytes, cytokine-secreting cells that
share a developmental lineage with natural helper cells and
innate helper cells and are strongly involved in type 2
immune responses mediated diseases, such as asthma and
allergy [29]. Furthermore, RORais expressed by IgA(?)
memory B cells and is involved in the preservation of
subset integrity and function in class-specific memory B
cells [30]. Interestingly, chronodisruption, represented by
desynchronization with respect to the daily light/dark cycle
of humoral and behavioral rhythms, is accompanied by
severe alteration of melatonin and cortisol secretion pat-
terns, inadequate pancreatic insulin secretion and increased
post-prandial plasma glucose concentrations, as evidenced
by experiments of forced desynchronization and prolonged
sleep restriction in humans [4,31,32]. The differentiation
of Th17 cells and Foxp3(?) T regulatory cells is also
modulated by the transcription factor aryl hydrocarbon
receptor (AHR), which manages biochemical effects of
exogenous and endogenous toxic molecules [33]. AHR
displays circadian variation of expression levels, driving
time-related pharmacological and immunomodulatory
effects of AHR agonists, represented by environmental
pollutants and metabolic by products [11].
Clin Exp Med
123
The circadian cross talk between the homeostatic
processes
The circadian timing system, the metabolic network and
the neuroendocrine-immune system interact on a complex
level integrating mutually environmental cues and physi-
ological signals originated from body tissues. The nuclear
receptors provide reciprocal communications among sev-
eral biological phenomena through nutrient and hormone
sensing, recruitment of coactivator/corepressor complexes
and modulation of numerous transcriptional circuits. These
interconnections may influence the cross talk among cir-
cadian, metabolic and neuroendocrine-immune pathways
in different tissues and may modulate the well-timed
functioning of homeostatic processes [1,11,13].
The circadian clock circuitry and lipid metabolism
The circadian clock circuitry drives the metabolic path-
ways controlling chromatin remodelling and transcriptional
circuits in metabolically active tissues, such as liver,
muscle, adipose tissue, and clock gene mutations and/or
hystone modification disorders in animal models determine
different metabolic phenotypes. In fact, in mouse liver, it
has been evidenced that histone deacetylation is charac-
terized by circadian rhythmicity related to histone deace-
tylase 3 (HDAC3) recruitment to the genome and
colocalization with REV-ERBanear genes regulating lipid
metabolism, and when HDAC3 and REV-ERBs are not
present the 24-h periodicity of gene expression disappears,
causing remarkable consequences on hepatic lipid metab-
olism and liver steatosis [34,35]. Furthermore, considering
that the expression of several genes encoding enzymes
involved in lipid metabolism is driven by the clock gene
machinery, the dysregulation of the circadian clock cir-
cuitry and/or incoordination with feeding times cause
improper expression patterns with fatty acid flux pertur-
bation, lipotoxicity, non-alcoholic fatty liver disease,
obesity, metabolic syndrome, diabetes mellitus, cardio-
vascular disease and atherothrombosis [11].
In this respect, studies performed in both rodents and
humans have shown that the hepatic clock gene machinery
controls both bile acid and lipid biosynthesis, driving
the circadian variation of expression of genes encoding
among the others 3-hydroxy-3-methylglutaryl coenzyme A
reductase, fatty acid and acyl-CoA synthase, fatty acid
transport proteins, lipolytic enzymes, apolipoproteins,
lipoprotein receptors [11]. In particular, RORaand REV-
ERBacontrol plasma triglyceride turnover driving, with
positive and negative roles, respectively, the expression of
the gene encoding apolipoprotein C-III. Synthesis, catab-
olism and export of cholesterol are tightly regulated to
maintain steady levels of this indispensible, but potentially
harmful molecule, transcriptionally regulated by sterol
regulatory element-binding proteins (SREBPs) that induce
cholesterol biosynthesis and uptake when intracellular
levels fall, and LXR that promotes cholesterol export and
elimination when intracellular cholesterol is excessive [11].
REV-ERBadrives bile acid synthesis interacting with
SREBPs and controlling oscillations of their quantity and
activity. In turn, expression of Cyp7a1, encoding the rate-
limiting enzyme in bile acid synthesis, is driven positively
by LXR binding with oxysterols and negatively by FXR
binding with bile acids, oscillates with circadian rhyth-
micity, and participates in the feeding-related synchroni-
zation of peripheral clocks and metabolic oscillators via
nutritional and hormonal cues [11]. Adipose tissue pro-
duces adipokines such as leptin and adiponectin that in
humans are expressed with circadian rhythmicity, modulate
insulin sensitivity and regulate energy balance influencing
feeding/fasting behavior. Obesity is characterized by dis-
ruption of adipokines 24-h profiles, accompanied by an
important component of the inflammatory response, the
endoplasmic reticulum stress within adipose tissue. A
characteristic of obesity is represented by decreased SIRT1
expression in adipose tissue together with macrophage
recruitment. SIRT1 down-regulation induces histone
hyperacetylation and ectopic inflammatory gene expres-
sion, playing a key role in macrophage influx into adipose
tissue during overnutrition and high-fat diet in rodents and
humans, and fostering the progression to metabolic dys-
function [36,37]. The expanded visceral adipose tissue
releases free fatty acids, TNF-a, IL-6, CC chemokine
ligand 2, which are implicated in the development of
insulin resistance and atherosclerosis [11], and as stated
above immune mediators and cytokines feedback with a
negative action on core clock components [15]. Lipids,
cytokines and metabolic stress pathways trigger a low-
grade chronic inflammatory condition defined ‘‘metaflam-
mation’’ that impinges on cell, tissue and organ function,
including adipocytes and macrophages, and leads to unfa-
vorable metabolic and inflammatory derangement influ-
encing lipoprotein properties, cholesterol metabolism and
atherogenesis [25].
The circadian clock circuitry and glucose metabolism
The circadian clock circuitry also controls glucose
metabolism by means of circadian genes and proteins and
through hormones (cortisol, melatonin) and autonomic
nerves from the SCN, which modulate nycthemeral chan-
ges in insulin sensitivity and insulin secretory capacity of
endocrine pancreas. A number of studies performed in
animal models have shown that insulin secretion is
Clin Exp Med
123
coordinated with the sleep/wake cycle by self-sustained
oscillators in the Langerhans islets bcells, and the clock
gene machinery drives the circadian rhythmicity of
expression changes of genes encoding enzymes and
transporters involved in glucose homeostasis [11]. CLOCK
controls hepatic glycogen synthesis, CRY 1 and CRY2
regulate hepatic gluconeogenesis, and clock gene muta-
tions settle on disparate metabolic phenotypes: liver-spe-
cific Bmal1 disruption causes hypoglycemia specifically
during the inactivity phase, and impaired glucose tolerance,
reduced insulin secretion, and defects in size and prolif-
eration of pancreatic islets worsening with age characterize
Clock
D19/D19
and pancreas-specific Bmal1
–/–
mutant mice
[11]. Besides, in humans, single nucleotide polymorphisms
within the genes encoding CRY2 and the MT
2
melatonin
receptor (MTNR1B) have been found capable to influence
fasting blood glucose concentrations in genome-wide
association studies [11].
The circadian timing system from health to disease
The breakdown of the array of rhythms or a change of their
functional interactions may lead to distortion of body
rhythmicity with tainted communication among circadian
and metabolic pathways, immune cell functions, cytokine/
chemokine production and neuroendocrine secretion
influencing metabolism and immunomodulation, fostering
illness-related or aging-related pathological processes.
Circadian rhythmicity characterizes fluctuations of
symptomatology in acute and chronic inflammatory dis-
eases, as exemplified by recrudescence in the early morn-
ing of joint pain, morning stiffness, and functional
disability in patients with rheumatoid arthritis. The daily
oscillation of symptom intensity is related to nycthemeral
variation of cytokine levels (in particular TNF-aand
IFN-c), endogenous l-opiatergic agonists (b-endorphin),
hormones (ACTH, cortisol, melatonin), neurotransmitters
and neuropeptides released by peripheral and autonomic
nervous system fibers, immunologic parameters (immuno-
globulins and immune-competent cells) [38,39].
Among the age-related diseases, Alzheimer’s dementia
is one of the most costly degenerative diseases in devel-
oped countries and is characterized by amyloid-b(Ab)
accumulation in the brain extracellular space, a process
related to level changes in brain interstitial fluid, neuronal
activity and the sleep-wake cycle, and preceding clinical
onset by several years. Animal studies have put in evidence
that sleep restriction significantly increases Abplaque
formation [40], and in turn, plaque formation alters the
sleep-wake cycle and diurnal fluctuation of Abin mice and
humans, suggesting that the sleep-wake cycle may play a
role in the pathogenesis of Alzheimer’s diseases [41].
Summary
Chronodisruption and desynchronization of the internal
clocks contribute to the alteration of the organismal time
structure causing functional disorders and modifications of
the anatomic integrity, as demonstrated by epidemiological
studies reporting an increased risk of metabolic, degenera-
tive, immune-related and neoplastic diseases in relationship
to protracted exposure to light at night or long-term rotating
night shifts/work schedules associated with sleep curtail-
ment and/or mistiming. The increasing interest in circadian
physiology and genetics opens new frontiers in the study of
disease mechanisms and compels accurate knowledge of
the fourth dimension of the biological processes in the
evaluation of new therapeutic approaches. As perspective
endeavor, it will be worth considering the alteration of the
temporal structure of body homeostasis among the patho-
physiological bases of disease, with the aim to (1) develop
pharmacological agents influencing the circadian timing
system and the molecular clockwork to recover disarray; (2)
redirect and reinforce the circadian clock circuitry by means
of natural entraining factors such as feeding time and light
exposure; (3) set up suitable chronomodulated drug delivery
systems to improve treatment of symptoms and therapy of
diseases related to chronodisruption.
Acknowledgments We apologize for not comment on all the rele-
vant studies and not citing all pertinent references due to space lim-
itations. This work was supported by ‘‘Italian Ministry of Health’’
grant RC1203ME46 through Department of Medical Sciences, Divi-
sion of Internal Medicine and Chronobiology Unit, IRCCS Scientific
Institute and Regional General Hospital ‘‘Casa Sollievo della Sof-
ferenza,’’ Opera di Padre Pio da Pietrelcina, San Giovanni Rotondo
(FG), Italy.
Conflict of interest The authors declare that there is no conflict of
interest with respect to the authorship and/or publication of this
article.
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