Oxidative stress in early diabetic nephropathy: fueling the fire Glucotoxicity pathways in diabetic nephropathy

1. Diabetic nephropathy
B.DEVADATHA
M.Sc IInd YEAR BMB
DEPT. OF BIOCHEMISTRY & MOLECULAR
BIOLOGY
PONDICHERRY UNIVERSITY

2. Figure 2 TNF signaling cascades have a pivotal role in diabetic nephropathy
Navarro-González, J. F. et al. (2011)
Inflammatory molecules and pathways in the pathogenesis of diabetic nephropathy
Nat. Rev. Nephrol. doi:10.1038/nrneph.2011.51

3. Oxidative stress in early diabetic nephropathy: fueling the fire
Dhruv K. Singh, Peter Winocour & Ken Farrington
Abstract
Diabetic nephropathy is a major microvascular complication of diabetes mellitus
and the most common cause of end-stage renal disease worldwide. The
treatment costs of diabetes mellitus and its complications represent a huge
burden on health-care expenditures, creating a major need to identify modifiable
factors concerned in the pathogenesis and progression of diabetic nephropathy.
Chronic hyperglycemia remains the primary cause of the metabolic, biochemical
and vascular abnormalities in diabetic nephropathy. Promotion of excessive
oxidative stress in the vascular and cellular milieu results in endothelial cell
dysfunction, which is one of the earliest and most pivotal metabolic
consequences of chronic hyperglycemia. These derangements are caused by
excessive production of advanced glycation end products and free radicals and
by the subjugation of antioxidants and antioxidant mechanisms. An increased
understanding of the role of oxidative stress in diabetic nephropathy has lead to
the exploration of a number of therapeutic strategies, the success of which has so
far been limited. However, judicious and timely use of current therapies to
maintain good glycemic control, adequate blood pressure and lipid levels, along
with lifestyle measures such as regular exercise, optimization of diet and smoking
cessation, may help to reduce oxidative stress and endothelial cell dysfunction
and retard the progression of diabetic nephropathy until more definitive therapies
become available.

4. TNF, a type II transmembrane protein, is processed by
TACE, which cleaves the 26 kDa membrane-bound form of TNF to
the soluble 17 kDa form. TNF signaling occurs primarily via
TNFR1, which is ubiquitously expressed. Binding of soluble TNF to
this receptor can induce either stimulation of gene expression or
induction of apoptosis. Both processes are initiated by binding of
the adaptor protein TRADD, which binds directly to the TNFR1
death domain. When FADD (another adaptor protein) binds to
TRADD, the signaling cascade eventually results in apoptosis.
However, when TRADD binding is followed by TRAF2 and RIP
binding, gene expression is stimulated through the activation of
various downstream signaling pathways, including those mediated
by NFκB (the major pathway activated by TNF), c-Jun N-terminal
kinases or p38 MAPK. Abbreviations: FADD, Fas-associated death
domain; IκB, inhibitor of NFκB; MAPK, mitogen-activated protein
kinase; NFκB, nuclear factor κB; RIP, receptor-interacting protein;
TACE, TNF-converting enzyme; TNF, tumor necrosis factor;
TNFR1, TNF receptor 1; TRADD, TNF-receptor type 1-associated
death domain protein; TRAF2, TNF receptor-associated factor 2

5. Figure 5 Effects of oxidative stress in early diabetic nephropathy

6. Figure 4 Glucotoxicity pathways in diabetic nephropathy

7. Organ damage can be triggered by both extracellular and intracellular
hyperglycemia. Increased extracellular glucose leads to
nonenzymatic glycosylation of proteins and subsequent formation of
advanced glycation end products (AGE) that interact with the receptor
for AGE (RAGE) on the plasma membrane and promote the
production of reactive oxygen species (ROS). Increased intracellular
glucose drives mitochondrial activity, increases the activity of protein
kinase C (PKC) and NADPH oxidase and promotes flux through the
polyol pathway, all of which effect cellular metabolism and phenotype.
Excessive ROS production in the vasculature drives changes in cell
phenotype that are mediated by a range of signaling pathways and
transcription factors. Kidney cells also undergo cell-specific and
organ-specific phenotypic changes as a result of hyperglycemiamediated ROS production. Abbreviations: AP1, activator protein 1;
AR, aldose reductase; CCL2, CC-chemokine ligand 2 (also known as
MCP1); CDC42, cell division cycle 42; EGR1, early growth response
protein 1; ERK, extracellular signal-regulated kinase; JAK, Janusactivated kinase; JNK, Jun N-terminal kinase; MAPK, mitogenactivated protein kinase; NFκB, nuclear factor κB; PI3K,
phosphatidylinositol 3-kinase; RNS, reactive nitrogen species; SDH,
sorbitol dehydrogenase; STAT, signal transducer and activator of
transcription. Adapted wit

8. Figure 3 Reactive oxygen and reactive nitrogen species
Figure 3 Reactive oxygen and reactive nitrogen species

9. Some of the prominent ROS include free radicals such as superoxide (˙O2−)
and hydroxyl (˙OH) and nonradical molecules such as hydrogen peroxide
(H2O2) and hypochlorous acid (HOCl). These oxidative molecules with an
unpaired electron in the outer orbit are highly reactive and bring about adverse
changes, when in contact with other cell structures and molecules. In addition
to ROS, another group of oxidant species, the reactive nitrogen species
(RNS), are major contributors to oxidative stress. The most important RNS is
peroxynitrite (OONO−), which is formed as a result of the reaction of superoxide
with nitric oxide.69 Adapted with permission from Macmillan Publishers ©
Lambeth, J. D. Nat. Rev. Immunol. 4, 181–189 (2004).

10. Figure 3 Leukocyte infiltration into the diabetic kidney
Navarro-González, J. F. et al. (2011)
Inflammatory molecules and pathways in the pathogenesis of diabetic nephropathy Nat. Rev. Nephrol.
doi:10.1038/nrneph.2011.51

11. E-selectin, ICAM-1 and VCAM-1 are cell adhesion molecules that
mediate binding of epithelial cells to each other, to other cell types (such
as mesangial cells) and to the extracellular matrix. These proteins also
actively control transmigration of leukocytes into renal tissue via the
adhesion cascade. Circulating leukocytes move towards the
endothelium and are captured (tethering). Leukocytes initially adhere
transiently and roll along the endothelium. When the endothelium is
activated, rolling of leukocytes is substantially slower than the
movement of freely circulating leukocytes (slow rolling). Leukocyte
activation is induced both directly by E-selectin-mediated slow rolling,
and indirectly by signals transmitted through adjacent receptors.
Leukocyte arrest is mediated by firm binding to adhesion molecules,
including E-selectin, ICAM-1 and VCAM-1. Adherent leukocytes then
undergo transmigration. Interactions between leukocyte integrins and
their ligands also stimulate endothelial cells, further promoting leukocyte
transmigration through transcellular or paracellular pathways and
inducing the formation of endothelial-cell projections that express high
levels of ICAM-1 and/or VCAM-1. Leukocytes infiltrating the renal tissue
initiate changes that are potentially harmful for the kidney.
Abbreviations: ICAM-1, intercellular adhesion molecule 1; VCAM-1,
vascular cell adhesion protein 1.

12. Figure 4 NFκB signaling pathways in diabetic nephropathy
Navarro-González, J. F. et al. (2011) Inflammatory molecules and pathways in the pathogenesis of diabetic
nephropathy Nat. Rev. Nephrol. doi:10.1038/nrneph.2011.51

13. NFκB is a transcriptional regulator expressed in the cytoplasm
of almost all cell types, where its activity is controlled by IκBs, a
family of regulatory proteins. IκBs bind to the p52 subunit of
NFκB, which prevents the complex from entering the nucleus.
NFκB activation is tightly regulated by signals that degrade IκB.
In renal cells, these signals include ligand binding to TNF type 1
and type 2 receptors, T-cell receptors, B-cell receptors, and Tolllike receptor–IL-1 receptor superfamily members. Such signals
activate a multisubunit IκB kinase complex that phosphorylates
IκB. Phosphorylated IκB undergoes proteasomal
degradation, which enables free NFκB to translocate to the
nucleus, bind to promoter and enhancer sites, and activate
transcription. In patients with diabetic nephropathy, NFκB
signaling results in increased transcription of target genes that
encode chemokines, effector molecules of
immunity, inflammatory cytokines, and cell adhesion molecules
(which perpetuate inflammatory responses), as well as other
molecules relevant for this complication (e.g. metalloproteinases
and tissue factor). Abbreviations: IκB, inhibitor of NFκB;
NFκB, nuclear factor κB; TNF, tumor necrosis factor