Epidemiology and burden of diabetes nephropathy

Diabetes complications, epidemiology

1. 1
Diabetic Nephropathy

2. 2
•Diabetic nephropathy is the leading cause of chronic
renal failure in the industrialised world.
•It is also one of the most significant long-term
complications in terms of morbidity and mortality for
individual patients with diabetes.
•Diabetes is responsible for 30-40% of all end-stage
renal disease (ESRD) cases in the United States.
•Although both type 1 diabetes mellitus (insulin-
dependent diabetes mellitus [IDDM]) and type 2
diabetes mellitus (non–insulin-dependent diabetes
mellitus [NIDDM]) lead to ESRD, the great majority of
patients are those with NIDDM.

3. 3
•The glomeruli and kidneys are typically normal or
increased in size initially, thus distinguishing diabetic
nephropathy from most other forms of chronic renal
insufficiency, wherein renal size is reduced (except
renal amyloidosis and polycystic kidney disease).

4. 4
Signs and Symptoms
•Approximately 25% to 40% of patients with DM 1
ultimately develop diabetic nephropathy (DN), which
progresses through five predictable stages.

5. 5
Stage 1 (very early diabetes)
•Increased demand upon the kidneys is indicated by an
above-normal glomerular filtration rate (GFR).
•Hyperglycemia leads to increased kidney filtration
(see later)
•This is due to osmotic load and to toxic effects of high
sugar levels on kidney cells
•Increased Glomerular Filtration Rate (GFR) with
enlarged kidneys

6. 6
Stage 2 (developing diabetes)
•Clinically silent phase with continued hyper filtration
and hypertrophy
•The GFR remains elevated or has returned to normal,
but glomerular damage has progressed to significant
microalbuminuria (small but above-normal level of the
protein albumin in the urine).
•Significant microalbuminuria will progress to end-stage
renal disease (ESRD).
•Therefore, all diabetes patients should be screened for
microalbuminuria on a routine basis.

7. 7
Stage 3 (overt, or dipstick-positive diabetes)
•Glomerular damage has progressed to clinical
albuminuria.
•Basement membrane thickening due to AGEP
•The urine is "dipstick positive," containing more than
300 mg of albumin in a 24-hour period.
•Hypertension (high blood pressure) typically develops
during stage 3.

8. 8
Stage 4 (late-stage diabetes)
•Glomerular damage continues, with increasing amounts
of protein albumin in the urine.
•The kidneys’ filtering ability has begun to decline
steadily, and blood urea nitrogen (BUN) and creatinine
(Cr) has begun to increase.
•The glomerular filtration rate (GFR) decreases about
10% annually. Almost all patients have hypertension at
stage 4.

9. 9
Stage 5 (end-stage renal disease, ESRD)
•GFR has fallen to <10 ml/min and renal replacement
therapy (i.e., haemodialysis, peritoneal dialysis, kidney
transplantation) is needed.

10. 10

11. 11

12. 12

13. 13
CAPILLARY ENDOTHELIUM
BASEMENT MEMBRANE
FOOT PROCESSES OF PODOCYTES
FILTRATION SLIT
FENESTRATION

14. 14
NORMAL GBM. LEFT - a single glomerulus. There are
one million of these in each kidney. RIGHT - a close up of
the GBM (G) around part of one tiny blood vessel in a
glomerulus (red circle in left hand diagram)

15. 15
Glomerular Histology: 
•The glomerular capillary wall is composed of an
endothelial cell layer (blood side), a thick basement
membrane, and epithelial cell layer (urine side).
 
(i) Glomerular Endothelium
•The glomerular endothelium is fenestrated. The
fenestrae (0.07 to 0.1 mm-micrometers- in maximal
diameter) allow the passage of electrolytes, proteins,
and globulin.
•However, platelets (3 mm), red cells (7 mm) and
neutrophils (15 mm) can't pass through the endothelial
layer.

16. 16
(ii) Glomerular Basement Membrane (GBM):
•The GBM is a tri-laminar structure, 0.3 microns in
thickness, composed of collagen, proteoglycans and
laminin.
•It is product of the fusion of the endothelial and
epithelial basement laminae.
•The dense central GBM area, or lamina densa, is due
to the overlapping of the two laminae.
 
•Around 50% of the GBM is collagen IV.

17. 17
•The negative charge of the GBM has been attributed to
the presence of the heparan sulphate proteoglycan
(HSPG) called perlecan.
•These negatively charged molecules are geometrically
arranged in clusters separated by about 0.003 µm from
each other.
•This anionic molecular sieve restricts the passage of
molecules according to size and charge.
•Water, salts, glucose, amino acids and neutral, or
cationic, molecules with radii less that 0.0035 µm are
filtered with relative ease.
•The albumin molecule measures 0.0035 µm and is
negatively charged. Therefore its filtration is restricted.

18. 18
•Presence of protein in the urine is a sign that either the
charge or the distance between the anionic clusters, or
both, are pathologically altered.
•The presence of red cells in the glomerular urine, is
certain indication of GBM ruptures.
•Other classical constituents of the basement membrane
are type IV collagen, laminin, and entactin.

19. 19
Glomerular mesangium:
•The intra-capsular glomerular capillary network is kept
together by the mesangium that is is composed of
mesangial cells type I and II, and other tissue matrix.
•Mesangial type I cells are monocytes with phagocytic
functions. These cells can extend cytoplasmic
projections into the glomerular capillary.
•They also "clean" the mesangium of materials that leak
from the capillary lumen into the matrix. These cells are
stimulated by cytokines to produce free radicals and
cytotoxic peptides.

20. 20
•Mesangial type II cells are myofibroblasts with the
ability to contract upon ADH and angiotensin
stimulation.
•Their contraction causes a reduction of the effective
glomerular filtration area.
•Mesangial Matrix is a tissue mesh composed of
different types of collagens (I, III, IV), laminin and
proteoglycans.

21. 21
Three major histologic changes occur in the
glomeruli of persons with diabetic nephropathy.
1.Mesangial expansion is directly induced by
hyperglycemia, perhaps via increased matrix
production or glycosylation of matrix proteins.
2.GBM thickening occurs.
3.Glomerular sclerosis is caused by intraglomerular
hypertension (induced by renal vasodilatation or from
ischemic injury induced by hyaline narrowing of the
vessels supplying the glomeruli).

22. 22
Glomerular Hyper filtration
•Glucose provides an osmotic diuretic effect
•Result is increased renal filtration, leading to
glomerular hypertrophy
•Glomerular pressure increases
•Kidney responds with hypertrophy of epithelium and
endothelium
•Accelerates glomerular cell failure
•Result is premature glomerulosclerosis

23. 23
Metabolic Perturbations
•Oxidant Stress - related to glomerular hypertrophy
and abnormal metabolism
•Non-enzymatic glycosylation of macromolecules -
particularly basement membrane (BM)
•Activation of glucose metabolizing enzymes
•Cytokine and other humoral imbalances

24. 24
Non enzymatic Glycosylation
•Biochemical studies have shown that basement
membranes in diabetes include excess amounts of
type IV collagen, the main component of basement
membranes, and decreased amounts of
proteoglycans
•Both changes decrease the permeability of
capillaries and disturb leukocyte diapedesis, oxygen
diffusion, nutrition and metabolic waste removal.
•Altered charge on BM may explain albuminuria
•Macrophage receptor activation leads to IL1, TNF
production which stimulates matrix
•AGEP formation leads to abnormal collagen,
increased toxic oxygen species

25. 25
Humoral Imbalances in DM Nephropathy
•Insulin Deficiency
•Elevated Glucagon Concentrations
•Increased Transforming Growth Factor (TGF)-ß
•Increased angiotensin II
•Abnormally regulated thromboxanes and endothelins
•Abnormal insulin like growth factor (IGF)-1
•Elevated platelet derived growth factor (PGDF)

26. 26
Role of TGF-ß
•Stimulates extracellular matrix synthesis
•Inhibits extracelluular matrix degradation
•Up regulates protease inhibitors; down regulates
matrix degrading enzymes
•Stimulates synthesis of integrins (matrix receptors)
•Key role in glomerular and tubuloepithelial
hypertrophy, basement membrane thickening, and
mesangial matrix expansion
•TGF-ß has been implicated in a number of chronic,
scarring diseases

27. 27

28. 28
•Angiotensin II and Thrombospondin (TSP1) can both
stimulate the production of transforming growth factor-β
(TGF-β) by tubuloepithelial cells and fibroblasts.
•TGF-β, in turn, causes proliferation of fibroblasts and
tubuloepithelial cells.
•TGF-β ultimately increases extracellular matrix proteins,
likely by several mechanisms.
•TGF-β stimulates production of several growth factors
including basis fibroblast growth factor (bFGF) and
platelet derived growth factor (PDGF) that stimulate the
formation of extracellular matrix (ECM) proteins.

29. 29
Ultrastructural changes of the glomerular
basement membrane in diabetic nephropathy
revealed by newly devised tissue negative
staining method.
•The normal human GBM showed a fine meshwork
structure consisting of fibrils forming the small pores.
•The diameter of these pores was slightly smaller than
that of human albumin molecules.
•The GBM in patients with diabetic nephropathy
showed irregular thickening.
•At higher magnification, unknown cavities and tunnel
structures, which were not seen in normal controls,
were observed in the thickened GBM.

30. 30
•In some portions, these cavities presented a
honeycomb-like appearance.
•The diameters of the cavities and tunnels were far
larger than the dimensions of albumin molecules.
•These enlarged structures are believed to allow serum
protein molecules to pass through the GBM from the
capillary lumen to the urinary space.
•These results suggest that the cause of massive
proteinuria in diabetic nephropathy is the disruption of
the size barrier of the GBM.

31. 31
Glomerular and vascular pathology is linked to
hyperglycemia.
•Changes in glomerular basement membrane structure
occur very early in diabetic nephropathy, before even
microalbuminuria is apparent.
•Collagen IV deposition is directly stimulated by
hyperglycaemia and increased urinary levels indicate
changes in the glomerular basement membrane.
•Contributing factors include the formation of advanced
glycosylation end products (AGEs) due to non-
enzymatic glycosylation of capillary basement
membranes, as a consequence of long-term
hyperglycaemia.

32. 32
•Non-enzymatic glycosylation has recently attracted
increasing interest as a crucial pathophysiologic event
behind all these hyperglycaemia-related alterations and
in the pathophysiology of the development of diabetic
complications.
•Proteins and lipids exposed to aldose sugars go
through reactions which are not enzyme-dependent,
and generation of reversible Schiff bases or Amadori
products take place.
•Later, through further molecular rearrangements,
irreversible advanced glycosylation end products
(AGEs) are formed.
•This process also takes place during normal ageing, but
in diabetes their formation is accelerated to an extent
related to the level and duration of hyperglycaemia.

33. 33
•Hence large studies have shown a delay in onset or
slowing of the progression of these complications if
near normo-glycaemia can be maintained.
•The glycated proteins cross-link, contributing to
basement membrane (and mesangial) thickening,
(culminating in the kidney in nodular
glomerulosclerosis), as well as loss of the normal
selective permeability (leading to proteinuria, retinal
hard exudates and microhaemorrhages).

34. 34
•The potential pathophysiological significance of AGEs is
associated with their accumulation in plasma, cells and
tissues and their contribution to the formation of cross-
links, generation of reactive oxygen intermediates and
interactions with particular receptors on cellular surfaces
•AGEs have direct effects on the host response by
affecting tissue structures, e.g. by increasing collagen
cross-links, which is followed by changes in collagen
solubility and turnover.
•Thickening of basement membranes is partly due to
glycosylation of membrane proteins or entrapment of
glycosylated serum proteins into basement membrane
•It is evident that AGEs can interact with cell functions,
tissue remodelling and inflammatory reactions in several
different ways.

35. 35

36. 36

37. 37
•When Ang II is increased, greater AT1 receptor-
mediated constriction of efferent than afferent arterioles
increases single nephron glomerular filtration rate and
raises intraglomerular pressure, causing glomerular
hypertension.
•Sustained or severe increases in intraglomerular
pressure can lead to GBM damage, glomerular
endothelial dysfunction, and ultimately, extravasation of
protein into Bowman’s capsule.
•In addition to hypertension, conditions like diabetes that
are associated with increased oxidative stress
(increased formation of reactive oxygen species)
independent of hypertension and glyco-oxidative
modification of proteins (AGEs) comprising the
glomerular basement membrane can lead to
extravasation of protein.

38. 38

39. 39
•Glomerular hypertension can lead to injury to the
glomerular basement membrane causing it to leak
plasma proteins into the urine.
•Attempts by the proximal tubules to reabsorb this filtered
protein causes injury to the tubular cells, activates an
inflammatory response, and is associated with the
development of lipid metabolic abnormalities that create
further oxidative stress on the already compromised
glomerulus.
•The resultant tubular inflammatory response and renal
microvascular injury activate pathways that lead to
fibrosis and scarring of both glomerular and tubular
elements of the nephron.

40. 40
•An additional consequence of glomerular hypertension
and resultant reduction in glomerular filtration rate
(GFR) activates growth factors and cytokines that
promote an influx of monocytes and macrophages into
the vessel wall and into the renal interstitium, and also
causes the differentiation of renal cells into fibroblasts.
•Monocytes, macrophages and fibroblasts are capable of
producing those growth factors and cytokines that
activate pathways leading to expansion of extracellular
matrix, fibrosis and loss of both tubular and glomerular
structures.

41. 41
•Collagen IV is the principal component of the glomerular
basement membrane and it is released into the urine
during its turnover.
•Increased urinary levels of collagen IV are found in
several conditions where glomerular injury is found,
particularly in diabetic nephropathy.
•Collagen IV is too large to cross the glomerular
membrane (MW 540 000) and so urinary collagen IV is a
specific sensitive indicator of changes to the structure of
extracellular matrix of the kidney.
•Unlike serum creatinine, that measures changes in
glomerular function, increased levels of urinary collagen
IV indicate that damage is occurring to the renal tissue.
•Urinary collagen IV is a very early and specific biomarker
for pathological changes to the glomerular membrane,
particularly in diabetic nephropathy.