Diabetes is linked to increased oxidative stress which damages cells. High blood glucose in diabetes leads to free radical production through several mechanisms like glucose auto-oxidation and protein glycation. This oxidative stress damages biomolecules like DNA, proteins and lipids in cells like pancreatic beta cells and tissues like retina, nerves and kidneys. It also decreases the body's antioxidant defenses. This cellular damage underlies diabetes and its complications like retinopathy, neuropathy and nephropathy through multiple pathways involving nuclear factor kappa B and protein kinase C activation. Chronic hyperglycemia continuously increases oxidative stress in diabetes and its complications.

1. Prepared by,
Dhanushya .G,
I M.Pharmacy ,
Department of Pharmacology,
PSG College of Pharmacy
ROLE OF FREE RADICALS IN
DIABETES
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2. CONTENT
1.Free radicals
2.Oxidative stress & Diabetes
3.Diabetes
3.1.Mechanism of OS in Diabetes
4.Post diabetic-complications
4.1.Mechanism of OS in Post-diabetic complications
5.Specific Complications & Mechanisms
6.Reference
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3. 1.FREE RADICALS
 Free radicals are oxygen containing unstable
molecules with uneven no.of electrons.These
radicals are highly reactive since they are
unpaired.
 These electrons like to be in pairs,so they
scavenge the body to seek out electrons to
become a pair.
 When these free radicals & anti-oxidants are out
of balance, it leads to Oxidative stress.
 The Oxidative stress causes cell & tissue damage
leading to a no.of diseases overtime.
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4. 2.OXIDATIVE STRESS &
DIABETES
 Increase in Oxidative stress(OS) is linked with
diabetes & post-diabetic complications.
 OS leads to
Oxidation of major biomolecules inside the cell
Alteration in cell signaling mechanism,cell
permeability,basic genetic mechanism.
 In diabetes,
Type-I pancreatic cells are damaged decreased
production/utilization of insulin hyperglycemia.
Type II Intracellular glucose concentration rises
post-diabetic complications.
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6. 3.DIABETES
Type I diabetes Type II diabetes
 Insulin –dependent/
Juvenile-onset
diabetes
 Autoimmune disorder
in which T cells attack
the b-cells
loss of b-cells in the
islets of Langerhans
 Environmental &
genetic factors are
involved
 Insulin-independent/
Adult-onset diabetes
 Lack of insulin
sensitivity in glucose-
utilizing cells
 Associated with
modern lifestyle
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7. DIABETES
a)Mechanism for b-cell
damage/function
1.Damage to macromolecules
PROTEIN DAMAGE
- Protein
molecules are found in cell
membrane 8 cytosol of
cells.
- Its function is
based upon its type of
folding.
- ROS tend to
modify its folding by
oxidizing its amino acid
residues.
Eg:Cysteine,Methionine
- It also results in
partial unfolding of
proteins.
NUCLEIC ACID DAMAGE
- NO & ROS
damage the nuclear&
mitochondrial DNA in b-
cells.
- ROS & reactive
nitrogen species(RNS)
cause breakage of the
DNA strands and can also
cause base substitution.
Eg:convertion of guanine
to 8-oxo,2’-
deoxyguanosine(8-
oxodG)which is a
biomarker for oxidative
DNA damage.
LIPID DAMAGE
- ROS oxidize
lipids via Lipid
peroxidation
- Mutagenic lipids
are produced: Epoxides,
hydroperoxides,alkoxyl &
peroxyl radicals and enals.
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8. 2.Poor antioxidative potential of
b-cells
B-cells are responsible fro sensing glucose level & secreting insulin.
ROS & RNS damage b-cells specifically due to their low antioxidative
state.
The level of free radical quenching (anti-oxidant) enzymes-
catalase,glutathione peroxidase & superoxide dismutase in low in b-cells.
As the OS rises,inflammatory process is initiated.
Immune cells like macrophages infiltrate the islets of Langerhans &
generate ROS- NO,H2O2
It cause deleterious effects on b-cells.
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9. 3.Triggers to inflammatory
pathway
The pathogenesis of type I diabetes involves an
interplay between the cells of immune system & the b-cell.
The prediabetic phase of the disease is characterized
by macrophages & T cells,resulting in insulitis.
Cytokines play a major role in prediabetic situation.the
local release of cytokines-IL 1β,IFN-γ, TNF-α induce the
onflammatory pathways in b-cells leading to insulin deficiency
& hyperglycemia.
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10. August 23
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4.ER stress pathway
ER stress is associated with diabetes.
Prolonged episodes of ER stress lead to the
death of b-cells.
A mixture of pro-inflammatory mediators
(cytokines) activate ER stress in b-cells.
Cytokines activate ER stress by decreasing the
Ca pump SERCA2B leads to depletion in the ER calcium
stores.

11. b)Mechanism for decrease in insulin
secretion:
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 The secretion of insulin is regulated by
mitochondrial glucose metabolism.
 ROS- H2O2 increase intracellular calcium,
decreases ATP/ADP ratio & inhibits glucose-
stimulated insulin secretion in response to a
glucose stimulus.
 OS to mitochondria leads to decreased insulin
secretion
 ER stress is also involved in decreased insulin
secretion.It can activate NF-KB which promotes
defects in insulin secretion.

12. 4.POST-DIABETIC
COMPLICATIONS
 Chronic increase in blood glucose level in both
type I diabetes & type II diabetes leads to various
post-diabetic complications.
 Increased concentration of glucose
increase in OS.
 The cells in retina ,nerves & kidney being more
fragile due to weak antioxidative state lose their
ability to fight the OS.
 Complications are:
Retinopathy
Neuropathy
Nephropathy
Macrovascular complications August 23
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13. 4.1.MECHANISM OF OS IN POST-
DIABETIC COMPLICATIONS
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 Excess generation of highly ROS & RNS- key component in
development of complications invoked by hyperglycemia.
 ROS directly oxidize & damage DNA,protein & lipids
diminish their metabolic functions.
 ROS activate a no.of cellular stress-sensitive pathways
cellular damage
 Mechanism involved in generation of ROS by hyperglycemia:
 Oxidative phosphorylation
 Glucose auto-oxidation
 Increased lipoxygenase expression
 Changes in regulation & expression of
o nitric oxide synthase(NOS) isoforms(eNOS,iNOS,nNOS)
o ONOO- production

14. a)Mechanism involved in damage
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• Modification of enzymes:
• ROS on interaction with enzymes leads to formation of abnormal
products
• Eg: Peroxynitrite on reaction with proteins inhibit their function &
attack iron-sulfur centres of enzyme to release iron atoms & inhibit
their activity.
• Nonenzymatic glycation :
• Metal-catalysed glucose autooxidation – glucose toxicity.
• It is non-enzymatic glycation process that occurs due to high
glucose concentration in blood & cells.
• This is due to ROS-superoxide & hydroxyl formation through
transition
• Modification of transcription factors:
• ROS attacks transcription factors and change their genetic
mechanism.
• Oxidative modification leads to
• Decreased expression of apoptosis inhibitory factor,complex I,Bcl-
2
• Increased expression of Stress proteins- proapoptotic(COX
Modification of proteins

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• DNA modification is the most important consequence of OS.
• In diabetes, DNA strand breaks have been observed.
• Serum 8-OHdG(a modified nucleic acid due to OS) – increased in
diabetic patients which plays a major role in mutagenesis. It is
found to be in large amounts in retinopathy,neuropathy &
nephropathy.
Modification of DNA
• In type 2 diabetes,a correlation exists between fasting plasma FFA
& ratio of reduced/oxidized(endogenous antioxidant).
• Elevated FFA has adverse effects on mitochondrial function.
• It impairs endogenous antioxidant defenses by reducing
intracellular glutathione.
Modification of Lipids
• Increase in FFA leads to decrease in GSH level
• Decrease in GSH levels in cells renders it susceptible to oxidative
injury.
Decrease in antioxidant content

16. b)Pathways involved:
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Polyol
pathway
s
• Increase in glucose leads to activation of polyol pathway.
• Glucose is reduced to sorbitol which depletes NADPH,a
cofactor to generate GSH,an antioxidant.
Hexos-
amine
pathway
• Excessive flux of glucose/FFA into cells-activates this pathway
• Fructose generated via polyol pathway on further conversions
yields uridine diphosphate – N-acetylglucosamine attacks
serine & threonine residues of transcription factors
overexpression of TGF & PAF-1
NF-KB
pathway
• Mediates immune & inflammatory responses & apoptosis.

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JNK/SAPK
& p38
pathway
• These are members of complex superfamily of MAP
serine/threonine protein kinases which are stress activated
• These are responsive to exo- & endogenous stress-inducing
stimuli-hyperglycemia,ROS,cytokines
• This pathway leads to apoptosis
PKC
pathway
• Family of 11 isoforms.
• Linked with OS
• Hyperglycemia stimlates DAG formation which activates the
isoforms which affects the balance of gene expression & induces
OS
Inflammatio
n
• All the above pathways leads to inflammation.
• ROS leads to inflammation which further adds up to increase in
ROS.
• Two main inflammatory agents- C-reactive protein & TNF-α

18. 5.SPECIFIC COMPLICATIONS &
MECHANISMS
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 A cyclic relationship exists between DM & OS
triggers deleterious cellular processes.
1.NEUROPATHY:
 Its incidence increases with duration of diabetes
 Accelerated by poor control of glucose level.
 Neurons are lost & their ability to regenerate is impaired
 Mechanism:
 Proteins & lipids are important in structural & functional
aspects.Modified proteins are unable to perform axonal transport
& signaling.
 Loss of function in neurons promotes necrosis & apoptosis.
 Neuropathy – denegeration & regeneration occur simultaneously
 Schwann cells involved in regeneration are affected in OS due to
hyperglycemia.

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2.NEPHROPATHY:
 Advanced glycation end products (AGEs) is increased.
 Chemical pathways leading to AGE formation & RAS
system interact via generation of free radicals.
 RAS system blocks up- & downstream pathways
leading to tissue injury
 AGE-dependent pathways development of
tubulointerstitial fibrosis.
3.RETINOPATHY:
 ROS formation in retinal mitochondria is due to
hyperglycemia & increased FFAs.
 Mitochondria – main site for generation of ROS,thus
damage their DNA.
 Eyes are vascularised tissue & full of capillaries.The
capillaries are made of endothelial cells- destroyed by
repeated attacks of high blood glucose loss
of sight.

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4.DIABETES & MACROVASCULAR DYSFUNCTION:
 Macrovascular complications are associated with
diabetes.
 The endothelial cells lining the arterial vasculature
balances thrombosis & fibrinolysis.This balance is linked
to NO production by eNOS. Imbalance between these
two results in peripheral arterial disease(PAD) in which
C-reactive protein(CRP) acts as a biomarker.
 Hyperglycemia affects the endothelial cells & eNOS
activity.
 Insulin resistance – loss of normal NO homeostasis &
produce ROS.
 High glucose concentration affects vascular smooth
muscle cell(VSMC) accelerates atherosclerosis
& plaque destabilization

21. 6.REFERENCE
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 Free Radicals in Human Health and
Disease,2015, Vabhi Rani,Umesh Chand Singh
Yadav