Transcript Proteinuria 2012 Engl

Proteinuria
Plasma proteins - essential components of any
living being
The kidneys play a major role in the retention of
plasma proteins
glomerular filtration barrier
renal tubules reabsorption of the passing through glomerular
filtration barrier proteins
Proteinuria
The glomerular capillary wall - charge and size-selective
properties
high-molecular-weight (HMW) plasma proteins can not enter the urinary
space
only a tiny fraction of albumin, globulin, and other large plasma
proteins cross
LMW proteins (<20,000 Da) cross capillary wall
they are normally reabsorbed by the proximal tubule
Proteinuria
Most healthy individuals
excrete 30 and 130 mg/day of protein
the upper limit of normal total urine protein excretion - 150 to 200 mg/day for
adults
the upper limit of normal albumin excretion - 30 mg/day
Proteinuria
Normal tubular protein secretion  a very small amount of
protein that normally appears in the urine
Tamm-Horsfall protein (uromodulin) HMW glycoprotein (23 × 106 Da)
formed on the epithelial surface of the thick ascending limb of the loop of Henle
and early distal convoluted tubule
binds and inactivates the cytokines interleukin-1 and tumor necrosis factor
Immunoglobulin A (IgA)
Urokinase
Proteinuria
Normal urine protein excretion
up to 150 mg/d
the detection of abnormal quantities or types of protein in the urine - an
early sign of significant renal or systemic disease
Normal urine albumin excretion
less than 5 mg/L
low levels of albumin excretion = microalbuminuria
linked to the identification of the early stages of diabetic kidney disease
Microalbuminuria
excretion of 30-300 mg/d or 20-200 µg/min
too small to be detected by routine dipstick screening
Proteinuria
Abnormal amounts of protein in the urine – three/four
mechanisms
glomerular proteinuria
disruption of the capillary wall barrier  a large amount of HMW plasma
proteins that overwhelm the limited capacity of tubular reabsorption and cause
protein to appear in the urine
tubular proteinuria
tubular damage or dysfunction inhibit the normal resorptive capacity of the
proximal tubule increased amounts of mostly LMW proteins appear in the
urine
increased production of normal or abnormal plasma proteins can be
filtered at the glomerulus and overwhelms the resorptive capacity of the
proximal tubule (!!)
–rarely - increased urine protein due to increased tubular production of
protein
Proteinuria
β2-Microglobulin
an LMW (11.8-kDa) protein
identified as the light chain of class I major histocompatibility antigens (e.g.,
human leukocyte antigens [HLAs] A, B, and C)
freely filtered at the glomerulus  avidly taken up and catabolized by the
proximal tubule
detectable urinary levels of β2-microglobulin - associated with many
pathologic conditions involving the proximal tubule
•aminoglycoside
•Balkan endemic nephropathy
•heavy metal nephropathies
•radiocontrast nephropathy
•kidney transplant rejection
•useful in distinguishing upper from lower urinary tract infection.
Proteinuria
Bence Jones protein
immunoglobulin light chains filtered at the glomerulus
plasma cell dyscrasias may produce monoclonal proteins, immunoglobulin, free
light chains, and a combination of these
the detection of urine immunoglobulin light chains can be the first clue to a
number of important clinical syndromes associated with plasma cell
dyscrasias that involve the kidney
plasma cell dyscrasias may also manifest as proteinuria or albuminuria
when the glomerular deposition of light chains causes disruption of the
normally impermeable capillary wall (!!)
Proteinuria
Selective or nonselective proteinuria
glomerular proteinuria can be further characterized as selective or
nonselective
a clearance ratio of immunoglublin G (IgG; an HMW protein)–to-albumin that
is less than 0.10 = selective proteinuria
more often seen in patients with minimal change disease
predicts a good response to treatment with corticosteroids
IgG-to-albumin clearance ratios greater than 0.50 = nonselective pattern
the cost of the protein separation procedures has limited their widespread
clinical use
Proteinuria
Glomerular proteinuria / tubular proteinuria
higher amounts of albumin and HMW proteins suggest glomerular
proteinuria
nephrotic range >3 g/24 hr  certain glomerular source
isolated increases in LMW protein fractions are more suggestive of tubular
proteinuria
it is unusual for tubular proteinuria to exceed 1 to 2 g/day
only a small fraction of protein excretion due to tubular damage should be
albumin
tubular proteins are heterogeneous; α2-microglobulin is often a major
constituent
Proteinuria
Techniques to Measure Urine Protein
in random samples
in timed or untimed overnight samples
in 24-hour collections
source of error - inaccurate urine collection particularly 24-hour
collections
Proteinuria
Techniques to Measure Urine Protein
Tests to accurately quantitate total protein concentration in urine
rely on precipitation(sulfosalicylic acid is added to a sample of urine, and the
turbidity is measured with a photometer or a nephelometer )
Tests to estimate total protein concentration in urine
chemically impregnated plastic strips (dipstick)
Proteinuria
Techniques to Measure Urine Protein
Tests to accurately quantitate total protein concentration in urine
(precipitation)
proteins detected: γ-globulin light chains, albumin
the method is more sensitive to albumin than to globulins
trichloroacetic acid can be used in place of sulfosalicylic acid to increase the
sensitivity to γ-globulin (eg for Bence Jones protein)
Tests to estimate total protein concentration in urine(dipstick)
pH-sensitive colorimetric indicator that changes color when negatively charged
proteins bind to it
positively charged proteins are less detected  immunoglobulin light chains may
escape urine dipstick detection even when present in large amounts in the urine
sensitive to very small urine protein concentrations -the lower limit of detection 1020 mg/dL (could be Tamm-Horsfall protein )
Proteinuria
Techniques to Measure Urine Protein
quantitative determinations of albuminas gold standards
Radioimmunoassay
Immunoturbimetric technique
Enzyme-linked immunosorbent assay (ELISA)
Proteinuria
Techniques to Measure Urine Protein
Screening methods
dipstick = qualitative or semiquantitative for total protein excretion and
microalbuminuria
sensitivity and specificity - markedly influenced by fluid intake, state of diuresis, and
the resulting urine concentration
protein-to-creatinine or albumin-to-creatinine ratio in random, or timed urine
collections
there is a high degree of correlation between 24-hour urine protein excretion and
protein-to-creatinine ratios in random, single-voided urine samples in patients with a
variety of kidney diseases
Proteinuria
Techniques to Measure Urine Protein
Screening methods - protein-to-creatinine or albumin-to-creatinine ratio
more quantitative than a simple dipstick screening procedure
a protein-to-creatinine ratio of greater than 3.0 or 3.5 mg/mg or less than 0.2
mg/mg indicates protein excretion rates of greater than 3.0 or 3.5 g/24 hr or
less than 0.2 g/24 hr
Proteinuria
Analytic tools - to separate and identify individual urinary proteins
agarose gel electrophoresis
column gel chromatography
polyacrylamide gel electrophoresis
immunoelectrophoresis
isoelectric focusing
proteomic techniques employing mass spectrometry
peptide mass fingerprinting
have been used in clinical laboratories
to determine the selectivity of urine protein
to identify monoclonal immunoglobulin heavy and light chains
Proteinuria
β2-Microglobulin
commonly measured in urine using radioimmunoassay or ELISA
Bence Jones protein
immunoglobulin light chains may not be detected by dipstick
a proteinuria or albuminuria may also exists when the glomerular
deposition of light chains causes disruption of the normally impermeable
capillary wall
monoclonal proteins are best detected using serum and urine
immunoelectrophoresis
the diagnosis of a plasma cell dyscrasia can be suspected when a tall, narrow
band on electrophoresis suggests the presence of a monoclonal γ-globulin or
immunoglobulin light chain
Proteinuria
Screening methods  established diagnosis of kidney disease
Measuring the amount of urine protein (usefull in IgA
nephropathy, membranous nephropathy, type I
membranoproliferative glomerulonephritis, nephrotic syndrome,
mild renal insufficiency )
additional prognostic information
can be used to monitor the response to immunosuppressive therapy
Proteinuria
There are variations of concentration of albumin in the urine
with: physical activity level, acute illnesses or fevers, menstruation,
pregnancy, vaginal discharge, diet, blood pressure, volume status, degree
of glycemic control, and urine collection method (eg, 24 h, overnight or
timed, short-term)
Albumin excretion - 25% higher during the day than overnight, with a
day-to-day variation of 40%
before a patient is classified as having microalbuminuria - at
least 3 urine samples over a 6-month period that satisfy the above
range criterion are recommended
Proteinuria
The presence of abnormal amounts or types of protein in the urine
reflects :
A defective glomerular barrier  abnormal amounts of proteins of
intermediate molecular weight enter the Bowman space
Tubular diseases  inability of the kidneys to normally reabsorb the
proteins through the renal tubules
Overproduction of plasma proteins pass through the normal glomerular
basement membrane (GBM)  enter the tubular fluid in amounts that exceed
the capacity of the normal proximal tubule to reabsorb them
Proteinuria
Symptoms
in most patients - asymptomatic proteinuria
detected upon screening
in patients with hypertension, diabetes
frequently in the absence of serious underlying renal disease
Proteinuria
The more common and benign causes of proteinuria
transient proteinuria
associated with physical exertion and fever
orthostatic proteinuria (albuminuria < 1 g/d, normal renal
function)
typically - in tall thin adolescents or adults younger than 30 years, +/severe lordosis
overnight urine collection shows normal protein excretion (ie, <50 mg
during 8-h period)
nonrenal disease (proteinuria < 1 g/d, normal renal function)
severe cardiac failure, sleep apnea
Proteinuria
Microalbuminuria (30-300 mg/d or 20-200 µg/min) frequently
observed in association with:
Hypertension
Early stages of diabetic nephropathy
Proteinuria
Proteinuria in significant glomerular disease
in excess of 500 mg/d
particularly associated with:
Changes in urine appearance: red/smoky, frothy
Edema: ankle, periorbital, labial, scrotal
Elevated blood pressure
Elevated cholesterol, lipiduria, hypoalbuminemia
Active urine sediment (dysmorphic red blood cells,+/-red cell casts)
Abnormal renal function
Proteinuria
Proteinuria in significant glomerular disease
Joint discomfort, skin rash, eye symptoms, or symptoms of Raynaud
syndrome
Multisystem disease : systemic lupus erythematosus, rheumatoid
arthritis
History of kidney disease (including pregnancy related)
Medication, including over-the-counter or herbal remedies
Past health problems, such as jaundice, tuberculosis, malaria, syphilis,
endocarditis
Systemic symptoms, such as fever, night sweats, weight loss, or bone
pain
Risk factors for HIV or hepatitis
Symptoms that suggest complication(s) of nephrotic syndrome
Loin pain, abdominal pain, breathlessness, pleuritic chest pain, rigors
Associated upper respiratory tract infection
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
1. glomerulosclerosis is explained by the
hyperfiltration theory
2. tubulointerstitial injury is olso induced by
proteinuria; this is a final common pathway to
eventual kidney failure
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
Albumin - Albumin-bound fatty acids
albumin = a major components in proteinuric
urine
albumin-bound fatty acids = important mediators
of tubulointerstitial injury  apoptosis in
proximal tubular cells
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
Tubulointerstitial injury induced by proteinuria
molecular and cell biological changes
 up-regulation of certain proinflammatory and
profibrogenic gene: MCP-1, osteopontin
 transdifferentiation of tubular cells into
myofibroblasts fibrosis of the kidney
 a large number of apoptotic cells in the
tubulointerstitial compartment
 apoptosis of tubular cells  atubular glomeruli and
decreases the number of functional nephrons
How dose proteinuria damage the kidney?
Tubulointerstitial injury induced by proteinuria
=
atubular glomeruli and interstitial fibrosis
How dose proteinuria damage the kidney?
What mediates tubular and interstitial damage
induced by proteinuria?
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
Effects of filtered macromolecules on tubular cells
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
Various components in proteinuric urine damages tubular
cells directly:
growth factors
transferrin
albumin
albumin-bound fatty acids
complement components in proteinuric urine
How dose proteinuria damage the kidney?
Protein overload in tubular cells is also associated with
ammonium production
Complement component C3 modified by ammonia =
amidated C3  amidated C3 forms the alternative
pathway convertase of the complement cascade
Preferential secretion of ammonia into the tubular
lumen  inappropriate activation of the alternative
pathway at the brush border in proteinuric conditions
How dose proteinuria damage the kidney?
Complement components in proteinuric urine =
crucial mediator of tubulointerstitial damage
complement is activated in urine of patients with
various glomerular diseases
the degree of intratubular complement activation
correlated with the level of non-selective proteinuria
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
accumulation of inflammatory cells around tubules of
high filtered protein load
C3 staining in the brush border or within the
cytoplasm at sites of high protein reabsorption
!! renoprotective effects of ACE inhibitor by limiting
tubular activation of complement
How dose proteinuria damage the kidney?
proteinuria  tubular injury
fibrotic changes  duration of proteinuria, quantity of
proteinuria, quality of proteinuria, other factors
other factors: hypertension, smoking, aging, chronic hypoxia
How dose proteinuria damage the kidney?
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How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
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How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
How dose proteinuria damage the kidney?
Podocytes
Podocytes
Podocytes
Podocytes
Podocytes
there are quite a number of podocyte diseases =
podocytopathies
in the podocytopathies the orderly structure of
the podocytes and the foot processes interlinked
by the slit diaphragms is lost (effacement of the
podocytes
Podocytes
the filtration barrier = an amazing structure
filtering something like 200-500 l plasma per
day and producing something like 200 l of
primary urine
the podocyte which is really standing or sitting
on top of the capillaries is one of the key players
there in the final regulation of the passage of
the proteins or actually preventing the leakage
of the proteins
Podocytes
there is a number of molecules located in the slit
diaphragm domain
transmembrane
or intracellular
these molecules adjust the shape of the podocyte
foot processes
Podocytes
Nephrin - neph-1, neph-2, filtrin, hemoglobulin group
of molecules, an immunoglobulin family of cell adhesion
proteins
They are clustering together with podocin for the
functionality of the slit diaphragm
The nephrin molecules extend from neighbouring
podocytes and foot processes and induce the interaction
between the different podocyte foot processes
Nephrin really forms the framework of the slit
diaphragm
Podocytes
The nephrin damage determines lack of normal foot
processes and the filtration slit organisation
Specific administration or generation of specific
nephrin antibodies lead to proteinuria
In diabetes and diabetic nephropathy there are found
circulating anti-nephrin antibodies many months before
the actual attack to the kidney
Proteinuria
Microalbuminuria
an independent predictor of cardiovascular disease
an independent predictor all-cause mortality in both diabetic and
nondiabetic men and women
a stronger indicator for future cardiovascular events than systolic BP or
serum cholesterol
Detecting microalbuminuria is an important screening tool to
identify people
who are at high risk for cardiovascular events and progression of kidney
disease
who need more intensive therapy compared with subjects with normal
albumin excretion rates
Proteinuria
According to the American Diabetes Association (ADA), the gold
standard for measuring urine albumin excretion is a 24-h urine
collection
A more convenient method to detect microalbuminuriais the
albumin (g)/creatinine (mg) ratio (ACR) measured in a random
urine specimen
Currently, the National Kidney Foundation recommends the use of
spot urine ACR obtained under standardized conditions (first
voided, morning, midstream specimen) to detect microalbuminuria
The ACR is a more convenient test for patients and may be less
prone to errors due to improper collection methods and variations in
24-h protein excretion compared with a random urine specimen
Proteinuria
The ADA and the National Kidney Foundation define
microalbuminuria as an ACR between 30 to 300 g/mg in both men
and women
Proteinuria
Proteinuria
How dose proteinuria damage the kidney?
Proteinuria