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ABSTRACT |
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The following is an abstract of the article discussed in the subsequent letter:
Marshall, Sally M., Klavs W. Hansen, Ruth Østerby,
Jan Frystyk, Hans Ørskov, and Allan Flyvbjerg. Effects of heparin on renal morphology and albuminuria in experimental diabetes. Am.
J. Physiol. 271 (Endocrinol. Metab. 34):
E326-E332, 1996.Female nondiabetic and streptozotocin diabetic
Wistar rats received 200 units heparin two times daily by subcutaneous
injection for 6 mo. Mesangial volume fraction was reduced in
heparin-treated control (CH) compared with untreated control (C)
animals (CH 0.18 ± 0.02 vs. C 0.24 ± 0.02,
P < 0.05), but other histological parameters were similar.
In the heparin-treated diabetic (DH) group, wet kidney weight was
increased compared with the untreated diabetic (D) group (DH
1,156 ± 39 vs. D 1,050 ± 30 mg, P < 0.05), as were absolute, but not fractional, glomerular volume (P < 0.05)
and capillary volume (P < 0.05). Basement membrane
thickness (DH 193 ± 3 vs. D 231 ± 9 nm, P < 0.01)
and mesangial/glomerular volume fraction (P < 0.001) were
decreased. Urinary albumin excretion was increased in the
heparin-treated control animals compared with control animals [CH 980 (range 150-4,446) vs. C 221 (range 86-654) µg/24 h,
P < 0.001] and in the heparin-treated diabetic animals
compared with the diabetic animals [DH 12,785 (range
4,495-29,520) vs. D 899 (range 450-1,335) µg/24 h,
P < 0.001]. Thus the possibly deleterious increases in
glomerular capillary volume and albumin excretion may negate the
beneficial effects of heparin on mesangial and basement membrane
structures.
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LETTER |
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Heparin and Diabetic Nephropathy
To the Editor: The paper by Marshall et al. (3) is an interesting contribution to what is known about the effect of heparin and derivatives on nephropathies. Besides confirming effects on the glomerular basement membrane thickness and on the expansion of mesangial matrix (1), it shows that unfractionated commercial heparin also affects glomerular capillary volume and glomerular and overall kidney size. The latter changes may be harmful to kidney function, as occurs with increased albuminuria observed in this study in groups treated with heparin. The effect on albuminuria is puzzling, because previous investigations by us and others (see review in Ref. 1) demonstrate the reduction of albuminuria with heparin treatment in diabetic animals. We wish to raise two points.The first concerns the hypothesis of Marshall et al. (3) that an increase in the available glomerular filtration surface would explain the higher albuminuria in heparin-treated animals compared with control rats. In their heparin-treated control group, albuminuria is higher than in untreated control animals, despite there being no change in capillary glomerular volume and only a 10% higher capillary diameter (an insignificant difference) observed. This means that the filtration surface does not differ from or is even lower1 than that of controls. It is thus difficult to reconcile the fivefold increase in albuminuria in this group with the pathophysiological explanation given by Marshall et al. In forming an alternative, speculative hypothesis, it should be noted that albumin undergoes proximal tubule reabsorption. This reabsorption is also charge dependent: if heparin appears in the glomerular ultrafiltrate2 (2) (because of the high dosage used, three- to fourfold higher than the therapeutical anticoagulant dosage in humans), then its electronegative charge might bring about interference with the tubular handling of albumin, increasing albuminuria. Before concluding that heparin alters glomerular permeability to proteins, we should also recall that the hard and fast rule for evaluating glomerular permeability is still the clearance of neutral and anionic dextrans, whereas albumin urinary excretion is only an indirect indicator. We have previously demonstrated by the dextran clearance method that a chemically modified heparin prevented any disturbance in charge permselectivity of the glomerular basement membrane in experimental diabetic nephropathy (1).
Second, when we refer to heparin, we generally overlook its being a heterogeneous group of polysaccharides, with various values of sulfation, molecular weight, and different biological activities. Commercial heparins from different suppliers are similar for the anticoagulant activity but not for their many other activities. An example is antiproliferation, the best-investigated nonanticoagulation-related activity of heparin. Despite having the same anticoagulant activity, commercial heparins from different suppliers show a broad range of antimitogenicity, and some are even mitogenic (4). Furthermore, different heparin dosages may have different biological activity, so that the same heparin may be both antiproliferative and proliferative (4).
Because studies on the effect of heparin on experimental diabetic nephropathy differ in their drug formulations and dosages, contradictory results concerning albuminuria and kidney weight might be due to the different qualities and quantities of drugs in different protocols. For example, results of the study of Marshall et al. (3) differ from those of our 1994 experiment (1), which also showed no difference in kidney weight between heparin-treated and untreated diabetic and control rats.
In conclusion, we certainly agree with Marshall et al. (3) that further study is necessary before widespread clinical use of heparin in diabetic nephropathy. Improved knowledge of the structure-function relationship of heparin and glycosaminoglycans and a dose-response finding of these drugs might provide a unique opportunity to select new heparin derivatives with specific effects on diabetic nephropathy and possibly, most importantly, devoid of anticoagulant activity.
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FOOTNOTES |
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1
Roughly, if we assume that the capillary volume can
be calculated by considering this volume as corresponding to a unique cylinder and that the capillary volumes in control (c) and
heparin-treated control rats (ch) are equal, then r2c · Lc =
r2ch · Lch
(where r is the radius and L the length), so that,
because rch is ~10% higher than
rc, Lc should be 21% greater
than Lch; thus the filtration surface, i.e., the
cylinder surface (2
r · L) in
heparin-treated controls might be even lower than in control rats.
2 Unfractionated heparin is eliminated through two separate mechanisms. At lower doses, a saturable mechanism is the primary route, but at higher doses the drug is cleared by a nonsaturable mechanism (endothelial binding and cell internalization), and the renal route is the nonsaturable mechanism (2).
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REFERENCES |
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1.
Gambaro, G.,
and
B. Baggio.
Glycosaminoglycans: a new paradigm in the prevention of proteinuria and progression of glomerular disease.
Nephrol. Dial. Transplant.
11:
762-764,
1996[Medline].
2.
Kandrotas, R. J.
Heparin pharmacokinetics and pharmacodynamics.
Clin. Pharmacokinet.
22:
359-374,
1992[Medline].
3.
Marshall, S. M.,
K. W. Hansen,
R. Østerby,
J. Frystyk,
H. Ørskov,
and
A. Flyvbjerg.
Effects of heparin on renal morphology and albuminuria in experimental diabetes.
Am. J. Physiol.
271 (Endocrinol. Metab. 34):
E326-E332,
1996
4.
Wright, T. C.,
J. J. Castellot,
M. Petitou,
J.-C. Lormeau,
J. Choay,
and
M. J. Karnovsky.
Structural determinants of heparin's growth inhibitory activity.
J. Biol. Chem.
264:
1534-1542,
1989
Giovanni Gambaro Bruno Baggio Division of Nephrology Institute of Internal Medicine University Hospital 35 128 Padua, Italy |
To the Editor: We are pleased that Drs. Gambaro and Baggio
recognize the potential importance of our work, even though it is a
year since publication. They take issue with our hypothesis that the
increased albumin excretion observed in heparin-treated control and
diabetic animals may arise from an increase in the available glomerular
filtration surface. They are correct in their assertions that
glomerular capillary volume fraction and average capillary diameter
were not significantly increased in the heparin-treated nondiabetic
animals compared with their appropriate controls. We did not obtain a
direct measure of filtration surface in this series, and therefore
statements relating to its magnitude can only be tentative. Conclusions
on filtration surface area cannot be drawn from capillary length, as
Gambaro and Baggio have attempted in footnote 1, because the
ratio of capillary-mesangial interface to filtration surface is
unknown: the ratio is likely to have decreased, as did mesangial volume
fraction in the heparin-treated nondiabetic and diabetic animals. Thus
an increase in the available glomerular filtration surface
remains a possible partial explanation for our findings. Such an effect
obviously does not preclude an additional effect mediated by changes in
tubular handling of albumin. We have no information on glomerular or
tubular handling of substances other than albumin in our study.
Gambaro and Baggio also point to the differences in the physical
properties and actions of different forms of heparin. We did discuss
this briefly in our article but were constrained by issues of space. We
would agree that different preparations have very different properties.
However, several other publications in addition to our own have
reported negative or neutral effects of heparin on albumin excretion.
In type 1 diabetic patients with overt nephropathy, Tamsma et al. (3)
found no benefit of low-molecular-weight heparin treatment compared
with placebo. In an experimental model of mesangioproliferative
glomerulonephritis, administration of nonanticoagulant heparin begun
late (days 10-17) did not affect the course of the disease
(1). In streptozotocin diabetes, low-molecular-weight heparin at a dose
of 2 mg · kg body
wt In view of all of this conflicting evidence, we would wholeheartedly
echo the conclusions of Gambaro and Baggio that much more work is
needed on many fronts before heparin can be considered for routine
clinical use in diabetic nephropathy.
REPLY
Top
Abstract
Letter
References
1 · day
1 had no
effect on albumin excretion rate despite normalizing renal levels of
transforming growth factor-
1 mRNA (2). Thus several groups have
questioned the beneficial effects of a variety of different heparin
preparations.
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REFERENCES |
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1.
Burg, M.,
T. Ostendorf,
A. Mooney,
K. M. Koch,
and
J. Floege.
Treatment of experimental mesangioproliferative glomerulonephritis with nonanticoagulant heparin: therapeutic efficacy and safety.
Lab. Invest.
76:
505-516,
1997[Medline].
2.
Oturai, P., B. Rolin, and H. Vissing. Effects of heparin on kidney
TGF-1 mRNA in experimental diabetic nephropathy. Diabetes 46, Suppl. 1: 120A, 1997.
3.
Tamsma, J. T.,
F. J. van der Woulde,
and
H. H. Lemkes.
Effect of sulphated glycosaminoglycans on albuminuria in patients with overt diabetic (type 1) nephropathy.
Nephrol. Dial. Transplant.
11:
182-185,
1996[Abstract].
Sally M. Marshall Klaus W. Hansen Ruth Østerby Jan Frystyk Hans Ørskov Allan Flyvbjerg Institute of Experimental Clinical Research University of Aarhus and Medical Department M (Diabetes and Endocrinology) University Hospital DK 8000 Aarhus, Denmark |