Diabete mellito, aspetti biochimico-molecolari

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Diabete mellito, aspetti biochimico-molecolari
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Diabete mellito

• Un gruppo eterogeneo di malattie caratterizzate
  da un metabolismo anormale dei CARBOIDRATI,
  causato da un DEFICT DI INSULINA assoluto (tipo
  1) o relativo (tipo 2), che provoca IPERGLICEMIA

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Rischi associati al diabete mellito
Nathan, N Engl J Med 1993
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Prevalenza e incremento dei diabetici nel mondo
2000 151 milioni 2010 221 milioni
Incremento 46
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Epidemiologia

• Prevalenza in Italia circa 2 milioni (3,5 )
  Tipo 1 circa 5
• Tipo 2 circa 90
• Incidenza Nord-Italia 5-6/100.000 nuovi
  casi/anno
• Prevalenza nel mondo
• 2001 circa 140.000.000
• 2025 circa 300.000.000

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Frequenza del diabete e dellintolleranza al
glucosio in funzione delletà
Garancini et al, 1995
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Segni, sintomi e conseguenze dellipoglicemia
Sfumata sintomatologia neurologica
Controregolazione
Sintomi da neuroglicopenia
Letargia
Coma
Convulsioni
Danni cerebrali permanenti
Morte
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Diabete tipo 1, sviluppo
induzione
attivazione e "homing" sulle cellule b
distruzione
Markers - antigeni HLA classe II DR3, DR4 (DR2
protettivo) - anticorpi anticellule - anticorpi
antiinsulina
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Stages in Development of Type 1 Diabetes
GENETICALLY AT RISK
MULTIPLE ANTIBODY POSITIVE
LOSS OF FIRST PHASE INSULIN RESPONSE
BETA CELL MASS
GENETIC PREDISPOSITION
INSULITIS BETA CELL INJURY
PRE-DIABETES
DIABETES
TIME
NEWLY DIAGNOSED DIABETES
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Diabete di tipo 1
Portatori di alleli HLA DR3-DR4 rischio 6-7
Parente di I grado (senza conoscere genotipo)
rischio 3-6 Parente di I grado (con assetto
genetico noto) rischio 6-16
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Possibile patogenesi del Diabete di tipo 2
Ambiente
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Caratteristiche cliniche del LADA(Latent
Autoimmune Diabetes of the Adult)

• Prevalenza circa il 10 del diabete delladulto
• Età desordio generalmente superiore ai 35 anni
• Quadro desordio lento od attenuato
• Sviluppo graduale di insulino-dipendenza
• Frequente presenza di anticorpi antiGAD

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Diabete Gestazionale

• Prevalenza oltre 5 delle gravidanze
• Definizione
• Intolleranza ai CHO di vario grado e severità,
  con
• inizio o primo riscontro durante la gravidanza
• Screening OGCT (50g)
• Diagnosi OGTT (100 o 75g)
• Classificazione dopo il parto
• NGT, IFG, IGT, Diabete

Lapolla, 2001
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Altre condizioni patologiche a rischio di
evoluzione a diabete mellito

• Ridotta tolleranza al glucosio (IGT impaired
  glucose tolerance)
• Alterata glicemia a digiuno (IFG impaired
  fasting glucose)

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Glicemia - variazioni giornaliere
M. Luzzana, 1999
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Sticking to membranes. Hexokinases associate with
various cellular membranes, and this association
affects their activity. These enzymes are not
only involved in glucose sensing and metabolism
but also in signal transduction. This duality is
achieved by switching between a bound and unbound
form that interacts with different proteins, such
as regulatory DNA-protein complexes in the
nucleus. Receptors for hexokinases (purple) must
be present to enable differential targeting of
these enzymes to different subcellular locations.
Hexokinases associate with membranes of
subcellular compartments, such as the endoplasmic
reticulum (ER) and mitochondria.
Frommer et al, Science 2003
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Brain glucose sensing mechanism and glucose
homeostasis Luc Pénicaud, Corinne Leloup, Anne
Lorsignol, Thierry Alquier and Elise
Guillod Current Opinion in Clinical Nutrition and
Metabolic Care 2002, 5539543
Purpose of review Glucose homeostasis must be
finely regulated. Changes in glucose levels
elicit a complex neuroendocrine response that
prevents or rapidly corrects hyper- or
hypoglycemia. It is well established that
different parts of the brain, particularly the
hypothalamus and the brain stem, are important
centres involved in the monitoring of glucose
status and the regulation of feeding. The
pioneering work of Mayer, including his proposal
of the glucostatic theory, has recently received
experimental support from the molecular,
electro-physiological and physiological
fields. Recent findings Making the analogy with
the b cell of the islet of Langerhans, it has
been proposed that glucose sensing could be
assured in some cells of the brain by proteins
such as glucose transporter 2, glucokinase and
the ATP-dependent potassium channel. Furthermore,
some pathological conditions such as diabetes and
obesity have been shown to alter this glucose
sensing system. Summary These findings could lead
to a better understanding of metabolic disorders,
with hypoglycemia possibly being the most
deleterious.Brain glucose sensing mechanism and
glucose homeostasis.
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trasportatori del glucosio

• GLUT1 RBC/epatociti 492 aa 1p35-31.3
• GLUT2 b-cell/fegato 524 aa 3q26
• GLUT3 cervello 496 aa 12p13
• GLUT4 insulin-resp. 509 aa 17p13
• GLUT5 intestino 501 aa 1p31
• GLUT6 pseudogene
• GLUT7 reticolo endoplasmico epatociti

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Figure 1 (A) Schematic representation of human
PG. Tissue-specific post-translational processing
of PG in the pancreas (B) and small intestine
(C). The numbers indicate positions of amino acid
residues and cleavage sites. Relative presence of
glucagon and GLP-1 derived from the
post-translational processing of preproglucagon
molecule in the pancreas (D) and small intestine
(E). In the pancreas, PG is cleaved to produce
GRPP, glucagon, IP-1 and MPGF. All of these
products are present in approximately equimolar
amounts and are secreted synchronously. In
addition to these predominant products, small
amounts of a peptide corresponding to the GLP-1
domain are also formed. This molecule, which is
probably biologically inactive, corresponds to
PG(72107), but small amounts of PG(72108) are
also formed. GLP-1 regulates glucose homeostasis
719 EUROPEAN JOURNAL OF ENDOCRINOLOGY (2000)
143 www.eje.org
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Figure 2 Schematic representation of GLP-1 action
on target tissues. The role of GLP-1 on muscle
and adipose tissues is represented with a
question mark next to the proposed enhancement of
insulin sensitivity based on the yet
controversial findings reported.
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SEVERAL BIOLOGICAL FEATURES of glucagon-like
peptide 1 (GLP-1) have led to propose this
peptide hormone as an ideal candidate for the
treatment of diabetes(1). GLP-1 lowers
postprandial hyperglycemia via three independent
mechanisms increases insulin secretion, inhibits
glucagon release, and inhibits gastrointestinal
motility. Perhaps even more important is the
observation that the insulin secretory action of
GLP-1 is regulated by the plasma concentration of
glucose, virtually preventing the possibility of
developing reactive hypoglycemia while inducing
the release of insulin (2). Finally, it is of
significant clinical relevance the observation
that GLP-1 retains its glucose lowering activity
in patients with diabetes, even many years after
clinical onset of the disease, when islet -cells
are no longer responsive to other pharmacological
insulin-secreting agents (3).
secretion. Indeed, GLP-1 also affects the
expression of insulin and other -cell-specific
genes whose products are involved in the
regulation of glucose utilization (4, 5). The
mechanism by which GLP-1 modulates the
-cell-specific gene expression has only in part
been elucidated, and it is known to require the
activation of the homeodomain transcription
factor IDX-1 (6).
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FIG. 1. Islets cell morphology. Human islets
were cultured for 1, 3, and 5 d in M199 medium,
with 6 mM glucose, 10 FCS, and 0.1 mM
diprotin-A and in the presence, or absence, of
GLP-1 (10 nM, added every 12 h). Human islets on
d 1, control (A) and GLP-1-treated islets (B) d
3, control (C) and GLP-1 treated (D) and d 5,
control (E) and GLP-1 treated (F). Pictures are
representative of islets morphology as observed
by culturing human islets from three independent
donors.
Endocrinology 2003144(12)51495158
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Trasduzione segnale insulinico
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Trasduzione del segnale insulinico
Glut-4
pp-120 IRS-1 IRS-2 IRS-3 IRS-4
Prot SH2 PI-3 chinasi
MAPK PKB SgK
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Kulkarni, Science 2004
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J. Risley, 1999 - http//opbs.okstate.edu/
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1370aa 2a, 2 b NPEY motif gt 60 mutazioni note
J. Risley, 1999 - http//opbs.okstate.edu/
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J. Risley, 1999 - http//opbs.okstate.edu/
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Mutations in this gene were first reported in
1988 Kadowaki (1988) Science 240, 787Yoshimasa
(1988) Science 240, 784Moller (1988) N Engl J
Med 319, 1526
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Basi biochimiche delle complicanze diabetiche
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Brownlee M. Biochemistry and molecular cell
biology of diabetic complications. Nature.
414(6865)813-20, 2001 Dec 13 Diabetes-specific
microvascular disease is a leading cause of
blindness, renal failure and nerve damage, and
diabetes-accelerated atherosclerosis leads to
increased risk of myocardial infarction, stroke
and limb amputation. Four main molecular
mechanisms have been implicated in
glucose-mediated vascular damage. All seem to
reflect a single hyperglycaemia-induced process
of overproduction of superoxide by the
mitochondrial electron-transport chain. This
integrating paradigm provides a new conceptual
framework for future research and drug discovery.
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Collagene Cristallino Albumina Emoglobina LDL
A. Lapolla et al. / Clinical Biochemistry 38
(2005) 103115
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A. Lapolla et al. / Clinical Biochemistry 38
(2005) 103115
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A. Lapolla et al. / Clinical Biochemistry 38
(2005) 103115
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Possibile utilizzo degli AGE

• Misura del controllo glico-metabolico a lungo
  termine
• early glycation
• Glicoalbumina
• HbA1c
• intermediate glycation
• Metil-gliossale
• Misura del grado di modificazioni tissutali in
  relazione al rischio delle complicanze
• AGE
• Pentosidina libera
• Misura effetto terapie

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Alcuni prodotti di glicazione intermedi e tardivi
(AGE)
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Administering the soluble form of the glycation
product receptor seems to stop the accelerated
atherosclerosis. Nature 4 1025, 1998.
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Ruboxistaurin is an orally active, b specific PKC
inhibitor which seems to be well tolerated and
normalises retinal blood flow in diabetic
patients with retinopathy.
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interrupting the overproduction of superoxide
by the mitochondrial electron-transport chain
would normalize polyol pathway flux, AGE
formation, PKC activation, hexosamine pathway
flux and NF-  B activation. But it might be
difficult to accomplish this using conventional
antioxidants, as these scavenge reactive oxygen
species in a stoichiometric manner. Thus,
although long-term administration of a
multi-antioxidant diet inhibited the development
of early diabetic retinopathy in rats96, and
vitamin C improved endothelium-dependent
vasodilation in diabetic patients97, low-dose
vitamin E failed to alter the risk of
cardiovascular and renal disease in patients with
diabetes
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Marcatori genetici del diabete di tipo 2
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Cambiamenti morofologici nel pancreas in diverse
condizioni
Rhodes CJ, Science 2005307
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Modello dinamico per i cambiamenti della massa
beta cellulare
t1/2 delle beta-cell 60 d
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Fattori che scatenano lapoptosi delle
beta-cellule nel DM t2

• Iperglicemia cronica
• Iperlipidemia cronica
• Stress ossidativo
• Diverse citochine
• Sviluppo di stress del reticolo endoplasmico
• Alterazioni di IRS-2

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Meccanismi potenziali che scatenano la
degradazione di IRS-2 e lapoptosi delle
beta-cellule
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CONCLUDENDO

• IRS-2 ha importanza rilevante nel pathway
  insulinico nei tessuti insulino-responsivi.
• Una sua diminuzione causa insulino-resistenza.
• Cè correlazione tra i meccanismi molecolari che
  controllano la sensibilità insulinica e quelli
  che promuovono la sopravvivenza ß cellulare.

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Insulino-resistenza

• Tutti i geni di proteine coinvolte nella
  trasduzione del segnale insulinico sono
  potenzialmente coinvolti
• Mutazioni del recettore
• Varianti IRS-1
• Mutazioni PI-3 chinasi (?)
• Ridotta attivazione della via IR/IRS/PI3K
• Mutazioni di altri fattori (PPARg2
  peroxisome-proliferator-activated receptor)
• Riduzione della attivazione della eNOS

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Some developing countries face the paradox of
families in which the children are underweight
and the adults are overweight. This combination
has been attributed by some people to
intrauterine growth retardation and resulting low
birth weight, which apparently confer a
predisposition to obesity later in life through
the acquisition of a thrifty phenotype that,
when accompanied by rapid childhood weight gain,
is conducive to the development of insulin
resistance and the metabolic syndrome.
n engl j med 3563 www.nejm.org january 18, 2007
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ORahilly, Science 2005
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References recenti
Raeder et al. Mutations in the CEL VNTR causes a
syndrome of diabetes and pancreatic exocrine
disfunction. Nature Genetics 20063854-62
Grant et al. Variant of transcription 7-like 2
(TCF7L2) gene confers risk of type 2 diabetes.
Nature Genetics 2006.
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Frayling T. Nature Review Genetics September 2007