This document discusses metabolic syndrome, which is a cluster of risk factors for heart disease that includes diabetes, obesity, high cholesterol, and high blood pressure. It notes the increasing prevalence of metabolic syndrome in children and adolescents. While there is no consensus on diagnosing metabolic syndrome in younger populations, most agree that having two or more of the following constitutes metabolic syndrome: insulin resistance, elevated cholesterol/triglycerides, low HDL, obesity, and high blood pressure. The document focuses on insulin resistance as a unifying mechanism, exploring its relationship to excess fat, especially visceral fat, and adipocytokines like adiponectin that impact inflammation and insulin sensitivity.

1. Metabolic Syndrome (1)
Dr. Yousef M. Elshrek

2. • The metabolic syndrome is a cluster of the most
dangerous heart attack risk factors: diabetes and
raised fasting plasma glucose, abdominal
obesity, high cholesterol and high blood
pressure.
• In recent years, there has been a greater
concern about the presence of obesity
and metabolic syndrome in children and
adolescents.
• However, there is no consensus
regarding the diagnosis of metabolic
syndrome in children and adolescents.

3. • It is evident that each component of
the syndrome must be identified as
early as possible in order to prevent
definitive lesions.
• The question is how to do this and
which cut-offs must be adopted for
this diagnosis.
• Pediatric
Metabolic
Syndrome
(PMETs) does not have a clear
definition.

4. • Most institutions agree that it can be
diagnosed when a patient has two or
more of the following:
1. insulin resistance and impaired glucose
tolerance,
2. elevated cholesterol and triglycerides,
3. low circulating amounts of highdensity lipoproteins,
4. obesity
(especially
around
the
abdomen),
5. and/or high blood pressure.

5. Insulin Resistance and Glucose
Intolerance
• the world die from complications associated
with diabetes.
• In countries with a high diabetes incidence,
such as those in the Pacific and the Middle East,
as many as one in four deaths in adults aged
between 35 and 64 years is due to the disease,
(e. g. Obesity distribution in Libya reached 41%
among women, and 21% among men, at the
same time the body mass index reached 26.4%
for males and 29.0% for females. Main while,
overweight reached 57.5% and 69.8% for males
and female respectively).

6. • Type 2 diabetes, which accounts
for 90 per cent of all diabetes, has
become one of the major causes of
premature illness and death,
mainly through the increased risk
of CVD which is responsible for up
to 80 per cent of these deaths.
6b,

7. • Insulin is the most potent anabolic hormone
in the body, exerting a plethora of effects on
lipid and protein metabolism, ion an amino
acid transport, cell cycle proliferation, cell
differentiation and nitric oxide synthesis .
• The majority of persons with Metabolic
Syndrome also have insulin resistance.
• Insulin resistance and/or associated
hyperinsulinemia are believed to be the
direct cause of other Metabolic Syndrome
risk factors .

8. • Insulin resistance is accepted as the most unifying
pathophysiologic mechanism underlying the
cluster of characteristics of Metabolic Syndrome
and is usually caused by a defect in insulin action
within target organs and tissues that results in
compensatory hyperinsulinemia
• Several possible mechanisms of insulin resistance
have been proposed: pre-receptor, receptor and
post-receptor mechanism.
• The most studied pathway that appears to be
absolutely necessary for mediating metabolic
effects of insulin involves the phosphorylation of
the insulin receptor substrate (IRS) 1 and 2 and
activation of phosphatidylinosital (PI) 3-kinase.

9. • This pathway also contributes to the mitogenic (Causing
mitosis or transformation ) aspects of insulin activity.
• Under normal conditions in endothelial cells (A tissue
consisting of a single layer of cells that lines the blood and
lymph vessels, heart, and some other cavities ) , insulin is
antiatherogenic (Protects against atherogenesis and
Atherogenic means tending to promote the formation of
fatty plaques in the arteries ) , and stimulates nitric oxide
(a potent vasodilator*) production and decreases the
expression of adhesion molecules thereby protecting cells
from excessive interaction with circulating monocytes**.
• In the insulin resistant state, the PI 3-kinase pathway is
impaired and insulin is no longer antiatherogenic
-------------------------------------------------------------------• *Vasodilators are medicines that act directly on muscles in
blood vessel walls to make blood vessels widen (dilate).
• ** A large phagocytic white blood cell with a simple oval
nucleus and clear, grayish cytoplasm.

10. • A
second
pathway
involves
the
phosphorylation activation of Ras, Raf,
MEK* and mitogen activated protein
(MAP) kinases (Erk 1 and 2)**.
• This second pathway contributes solely to
the nuclear and mitogenic effects of insulin
and does not convey the metabolic action of
insulin.
_______________________________________
*It will be explained latter in detail
**It will be also explained latter in detail

11. • This pathway is unimpaired in insulin resistance
and is more strongly activated by compensatory
hyperinsulinemia leading to increased activity of
growth promoting agents.
• Over stimulation of this pathway is perhaps the
source of the proatherogenic mechanism.
• Insulin resistance is enhanced by excess adipose
tissue, in particular abdominal adiposity.
• Excess adipose tissue releases non - esterfied
fatty acids (NEFA).
• A high NEFA level overloads muscle and liver
with lipid and enhances insulin resistance.

12. • Free fatty acids are also produced through the
lipolysis of lipoproteins by the action of
lipoprotein lipase, the stimulation of which is
influenced by insulin.
• Insulin also inhibits lipolysis in adipose tissue.
• When insulin resistance develops, increased
lipolysis in adipose tissue produces more fatty
acids, further inhibiting the antilipolytic effect
of insulin and creates additional lipolysis
• Over production of toxic metabolites that
contribute to defective insulin signaling and
insulin resistance can result from intracellular
accumulation of free fatty acids.

13. • High plasma levels of free fatty acids
accompanied by fatty acid overloaded muscle
cells contributes to the development of fatty
liver as excess free fatty acids are directed to
the liver.
• Hyperinsulinemia may increase the production
of very low-density lipoprotein triglycerides
and thus raise triglycerides. Insulin resistance
can raise blood pressure.
• Insulin resistance generally rises with body fat
content, but a broad range of insulin resistance
exists at any given body fat level .

14. • Visceral or omental( See
the figures) fat appears to
be the most detrimental
and contributes most to
the
development
of
lipotoxicity in peripheral
tissues by the secretion of
adipocytokines.

15. • Several of these adipocytokines*: adiponectin,
resisting, leptin, tumor necrosis factor-alpha and
interlukin-6 are implicated in insulin resistance.
• Leptin is secreted by adipocytes and secretion is
regulated by the size of fat stores.
• Leptin receptors are located mostly in the
hypothalamus and the brain stem and signals
through these receptors controls satiety, energy
expenditure and neuroendocrine function.
• Most overweight and obese individuals have
elevated levels of leptin that do not suppress
appetite, or in other words, leptin resistance.
Leptin resistance is thought to be a
fundamental pathology in obesity.

16. • For example, circulating levels of adiponectin ** seem to
correlate with hyperinsulinemia and insulin resistance
• Adiponectin is an anti-inflammatory cytokine that is
produced by adipocytes. Adiponectin not only enhances
insulin sensitivity, but also inhibits several steps in the
inflammatory process.
• ______________________________________________________________
*Adipocytokines, are soluble mediators derived mainly from adipocytes
(fat cells), in the interaction between adipose tissue, inflammation and
immunity. The adipocytokines adiponectin and leptin have emerged as the
most abundant adipocyte products, thereby redefining adipose tissue as a
key component not only of the endocrine system, but also of the immune
system.
• **Adiponectin (also referred to as GBP-28, apM1, AdipoQ and Acrp30) is a
protein which in humans is encoded by the ADIPOQ gene. It is involved in
regulating glucose levels as well as fatty acid breakdown.

17. • It also inhibits hepatic gluconeogenic enzymes
and the rate of endogenous glucose production
in the liver.
• It increases glucose transport in muscle and
enhances fatty acid oxidation.
• There is an association between insulin
resistance and asymmetric dimethylarginine
(ADMA is an endogenous inhibitor of nitric
oxide synthase and there is relationship
between insulin resistance and endothelial
dysfunction.

18. • ADMA is known to be elevated in
syndromes
associated
with
vascular
diseases.
• Also, ADMA is known to correlate with NO
mediated vasodilation and with adherence
of monocytes to the endothelium.
• Measurements of ADMA and insulin
sensitivity via the insulin suppression test
indicate that ADMA concentrations are
elevated in insulin sensitive individuals,
both normal and hypertensive.

19. • This relationship was further validated
when pharmacological intervention
with rosiglitazone enhanced insulin
sensitivity and reduced ADMA
concentrations.
• ADMA may be yet another metabolic
contributor to endothelial damage and
increased risk for cardiovascular
disease in insulin resistance.

20. • In the post-menopausal women with Metabolic
Syndrome, leptin and resistin will be elevate
where as adiponectin is decreased.
• In addition, BMI correlated strongly with markers
of insulin resistance and adipocytokine levels.
• The relation between impaired fasting glucose or
impaired glucose tolerance and insulin resistance
is well supported.
• To compensate for defects in insulin activity,
insulin secretion or clearance needs to be modified
to sustain normal glucose levels.
• Hyperglycemia is the end result if these
mechanisms fail

21. • Hyperglycemic induced endothelium damage
takes place by five major molecular
mechanisms
all
of
which
result
in
overproduction of superoxide by the
mitochondrial electron transport chain.
• The formation of these reactive oxygen species
can lead to endothelial dysfunction and
decreased nitric oxide and prostacyclin
production.
• Reactive oxygen species can increase the
formation of vasoconstrictor prostanoids* and
endothelin and promote atherosclerotic plague
formation.
________________________________________
•
*Prostanoids are a subclass of eicosanoids consisting of the prostaglandins (mediators of inflammatory
and anaphylactic reactions), the thromboxanes (mediators of vasoconstriction), and the prostacyclins
(active in the resolution phase of inflammation.)

22. • Increased vascular permeability is also a
consequence of hyperglycemia induced
reactive oxygen species formation and is
responsible for the expression of
endothelial mitogen vascular endothelial
growth factor, which promotes diabetic
microangiopathy.*
__________________________________________________________
• *Microangiopathy (or microvascular disease, or small vessel disease)
is an angiopathy (i.e. disease of blood vessels) affecting small blood
vessels in the body.[1] It can be contrasted to macroangiopathy. The
term cerebral small vessel disease refers to a group of pathological
processes with various aetiologies that affect the small arteries,
arterioles, venules, and capillaries of the brain. Age-related and
hypertension-related small vessel diseases and cerebral amyloid
angiopathy are the most common forms.

23. • Since insulin resistance increases a person's
risk for developing cardiovascular disease
and Type 2 diabetes, several researchers
have proposed measures of insulin
resistance in obese individuals with and
without Metabolic Syndrome.
• Some investigators found that plasma
triglyceride concentration, the ratio of
triglyceride to HDL cholesterol and insulin
concentrations were the most useful
metabolic markers for determining insulin
resistance.

24. • Tumor necrosis factor-alpha has also been
implicated in the development of obesity and
insulin resistance.
• Elevated levels of tumor necrosis factor-alpha
are positively correlated with insulin resistance
and chronic exposure of tumor necrosis factoralpha induces insulin resistance.
• Tumor necrosis factor-alpha may also impair
insulin receptor tyrosine kinase activity and
lead to impaired downstream insulin signaling .
• Tumor necrosis factor-alpha also impairs
insulin signaling by increasing serum nonesterfied fatty acids, which can induce insulin
resistance in many tissues

25. • Interleukin-6 is also associated with insulin resistance
and obesity and its expression and concentration are
positively correlated with obesity, impaired glucose
tolerance and insulin resistance.
• Interleukin 6 (IL-6) is an interleukin that acts as both
a pro-inflammatory cytokine and an antiinflammatory myokine.
• In humans, it is encoded by the IL6 gene.
• In addition, plasma concentrations of interleukin-6
predict the development of type 2 diabetes
• Interleukin-6 decreases insulin signaling in peripheral
tissues by decreasing the expression of insulin
receptor signaling components .
• Interleukin-6 has recently been revealed to be an
important factor in the chronic inflammatory state
and hepatic insulin resistance in obesity

26. • Plasminogen activator inhibitor-1 is a regulator
protein in the coagulation cascade and elevated
levels in obese states are a known risk factor for
thrombosis, as it decreases the generation of
plasmin and thus decreases fibrinolysis.
• High levels of plasminogen activator inhibitor-1
along with obesity-induced increases in clotting
factors and platelet activation create a
hypercoagulable state, atherogenesis and
increase cardiovascular risk.
• Plasminogen activator inhibitor-1 has also been
implicated in the accumulation of visceral fat

27. • Resistin (resistance to insulin) expression is 15fold greater in visceral as compared to
subcutaneous fat in rodents and is potentially
linked to obesity with insulin resistance.
• However, numerous epidemiological studies in
humans have failed to link resistin expression
in adipose tissue or circulating resistin levels
with adiposity or insulin resistance

28. Ras-Raf-MEK-ERK-MAPK pathway
Transcription Factors

29. • Introduction
• Cellular growth and differentiation are controlled
by multiple extracellular signals, many of which
activatedthe Ras/mitogen-activated protein (MAP
or ERK) kinase cascade.
• This pathway is conserved trough evolution and
transfer information from the environment (growth
factors, mitogens and antigen receptors, by GPCR
activation, by stress and inflammatory stimulus, by
UV, FASL activation) to the nucleus through a three
levels pathway that involves the sequential
phosphorylation of three kinases: MAPK kinase
kinase (MAPKKK), MAPK kinase (MAPKK) and
MAPK:

30. • This pathway is conserved trough evolution and
transfer information from the environment
(growth factors, mitogens and antigen receptors,
by GPCR activation, by stress and inflammatory
stimulus, by UV, FASL activation) to the nucleus
through a three levels pathway that involves the
sequential phosphorylation of three kinases:
1.
2.
3.
MAPK kinase kinase (MAPKKK),
MAPK kinase (MAPKK)
and MAPK:

32. Yeast

33. Vertebrate

34. MAPKKK
• Ras directly interacts with and activates Raf.
• Raf phosphorylates and activates MEK, which in
turn phosphorylates and activates ERKs.
• The receptor tyrosine kinase effector, Raf, named
for Rapidly Accelerated Fibrosarcoma, was
discovered over two decades ago by two groups
independently as a retroviral oncogene, v-Raf or vMIL, possessing a serine/threonine kinase activity.
• This serine/threonine kinase was later found to
function in the linear Ras-Raf-MEK-ERK mitogen
activated protein kinase (MAPK) pathway with an
intricate regulation.

36. • The Ras-Raf-MEK-ERK mitogen activated protein
kinase (MAPK) pathway is activated by growth
factors, mitogens and antigen receptors, by
GPCR activation, by stress and inflammatory
stimulus, by UV, FASL activation directly and by
the activation of G-coupled receptor that
switches on Calmoduline signal Ca++citoplasmatic-dependent induced by PLC.
• For these reasons the activation of MAPK
pathway is an indicator of a "good state" of the
cell because it is involved in pro-proliferation
and pro-survival response.

37. Raf kinases functions
• Besides their established role in
tumorigenesis, Raf proteins and the MAPK
pathway have been shown to play key
roles in various “normal” physiological
processes
1.
2.
3.
as diverse as cellular metabolism,
cell cycle progression,
cell death and neurological function.

39. Raf kinase signaling
• RAS GTPases are activated by the majority of
growth factor receptors and bind and recruit
Raf to the cell membrane upon activation.
• The central components of Raf, MEK and ERK
signaling
are
then
sequentially
phosphorylated and activated by each other.
• More than 70 nuclear and non-nuclear
effector molecules of the mitogenic cascade
have been identified so far.

41. • In addition, Raf kinase signaling in a cascadeindependent fashion has been described.
• This includes the activation of the NF-kB
transcription factor, the prevention of
apoptosis by antagonizing proapoptotic
factors such as
1. MST2, the mammalian sterile 20-like kinase,
ASK1, the apoptosis signal-regulating
kinase1,
2. and BAD, the BCL-2-antagonist of cell death,
and finally the positive regulation of cell
migration via the Rho effector kinase Rok-a.

42. • The regulation of Raf kinase activity is quite
complex, far from being fully understood.
• The key feature involves assembly of the
cascade at the membrane from preexisting
modules (Ras module, Raf module, KSR module).
• This process is paralleled by an intricate pattern
of phosphorylation and dephosphorylation
events leading to conformational changes of
signaling molecules.

43. • Within this signaling zoo along the mitogenic
cascade, there is still more room for novel
players.
• They are definitely more than just additional
signaling proteins and contribute significantly
to our understanding how Raf kinase
signaling really works.
• Homo- and heterodimerization of Raf kinases
clearly exist, and that heterodimerization can
be Ras induced.

44. • The kinetics of this process depends on the
presence of individual Raf isoenzymes and on
the engagement of various positive and
negative feedback loops.
• Primarily the phosphorylation status and the
localization of Raf kinases determine the
association with interacting partners, such as
chaperones, other kinases, prolyl isomerases,
phosphatases, scaffolding proteins and also
lipids and vice versa.

45. • In addition, it was shown that Raf
heterodimerization is regulated by 14-33 proteins, mitogens and the Mixedlineage kinase 3 and is also stabilized by
MEK inhibition.
• Several
authors
described
that
heterodimerization is involved in the
activation of C-RAF by B-RAF, but that
wild-type and mutant B-RAF use
different activation mechanisms

46. • Whereas wild-type B-RAF activates C-RAF via
RAS-induced heterodimerization, mutant B-RAF
heterodimerizes with and activates C-RAF in a
RAS-independent manner, thereby generating a
novel B-RAF > C-RAF > MEK > ERK pathway that
is active in normal as well as in transformed
cells.
• Whether signaling via this pathway just reflects
some sort of crossactivation of Raf isoforms or
whether it leads to a different set of effector
functions in comparison to the classical RAF >
MEK > ERK cascade remains to be determined in
future.

47. Role of Raf in Cancer
• Since its first isolation as a potential
cellular oncogene, many studies involving
Raf were focused on its role in cancer.
• These included examining both its direct
role in cancer and its involvement in
mediating transformation by its upstream
effectors, especially Ras and growth factor
receptors.

48. Raf Regulation
• Most of understanding of Raf regulation
comes from studies using C-Raf, though
several fundamental studies using B-Raf have
also provided significant input to view of this
complex process.
• C-Raf is a 648 amino acid protein migrating
on SDS/PAGE as a ~75 kDa polypeptide.
• There are several regions conserved among
all Raf proteins designated CR1, CR2, and
CR3.

49. • This interaction is stabilized by the binding of
a 14-3-3 dimer at two C-Raf phosphorylated
sites, S259 and S621.
• As to the Raf activation process following the
interaction with active Ras, the common
thinking is that C-Raf undergoes a series of
phosphorylation and dephosphorylation
events that result in a stably active form.
• This aspect of Raf regulation turned out to
be a highly challenging task to tackle and
remains only partially resolved.

50. • The transforming v-Raf form contains a
deletion of CR1 and CR2, resulting in a
constitutively active form of Raf.
• Thus, the N-terminal half of Raf is considered
to be a negative regulatory domain which
helps in maintaining Raf in an inactive state
in the absence of stimulation.
• The common view is that the catalytic
domain of Raf is folded and bound to the Nterminal regulatory domain.