Clin. Biochem. 14 (2) 72-73 (1981)

Serum Triglyceride Levels in Uremic Patients Receiving

Polyacrylonitrile +Dialysis G. SEVERINI AND A. BUONGIORNO

Laboratorio di Tecnologie Biomediche, Istituto Superiore di Sanita, Roma, Italy.

Fasting levels of serum triglycerides cholesterol and high- density lipoprotein (HDL) were studied in 20 uremic patients with persis tent high t r ig lycer ide levels receiving polyacrylonitrile dialysis. Up to the sixth month of the trial there was no change in cholesterol and high density lipoprotein; on the contrary, triglyceride levels decreased progressively and reached at the fourth month the normal range. A statistical significative difference (p > 0.01) could be detected between cuprophane and polyacrylonitrile dialysis triglyceride levels. A diffusive procedure using polyacrylonitrile is good enough to lower high triglyceride levels, hut treatment must be prolonged for four months at least.

ABNORMALITIES IN THE BLOOD CONSTITUENTS of pa- t ients receiving chronic maintenance haemodialysis have been studied by many authors. Besides the well recognized al terat ions in urea and other nitrogenous products, these patients frequently have elevated plasma tr iglyceride levels and low HDL cholesterol while their total cholesterol levels have been repor ted to be normal (1,2,3}. The pathogenesis of these changes is complex and probably a consequence of the interac- tion of a number of al tered cellular processes.

Recently it has been suggested as a possible cause of hyper t r ig lycer idemia that a defect in the action of l ipoprotein lipase may exist , and Murase(4) has demonstra ted the presence in uremic plasma of an in- hibitor of this enzyme. This inhibitor has a molecular size that places it into the range of middle molecules. The hypothesis is also confirmed by the decrease of t r iglyceride levels using a polyacrylonitrile filter in a c o n v e c t i v e p r o c e d u r e ( h e m o f i l t r a t i o n ) ( 5 , 6 , 7 ) . T h e polyacrylonitri le dialysis membrane differs from the s tandard cuprophane and cel lophane m e m b r a n e s previously used during renal haemodialysis in that it is permeable to water soluble compounds with molecular weights of up to 15000. The purpose of our study was to demonstra te if the same results could be obtained by means of a simple diffusive procedure (haemodialysis) using polyacrylonitrile.

MATERIAL AND METHODS

Twenty adults, males and females who had received conven- tional haemodialysis for at least one year and who had ages bet- ween 25 and 63 years, were studied. They were divided into two groups: Group 1°: ten control patients with high triglyceride levels

Correspondence: Severini Giancarlo, Laboratorio di Tee- nologie Biomediche, Istituto Superiore di SanitY, viale Regina Elena 299, 00161 Roma, Italy.

who were maintained by 3-4 hr cuprophane dialysis sessions per week.

Group 2°: ten test patients with high triglyceride levels who were maintained usually as for group 1, but who were put on 3-3 hr polyacrylonitrile dialysis ses- sions per week for a period of 4 months, then were returned regular cuprophane dialysis.

All patients used the same dialysis bath fluid containing (in mEq/I) Na 138; K 2.5; Ca 4; CI 107,5; Mg 1,5: acetate ion 38; and glucose 2g/].

Fasting pre-dialysis samples were withdrawn at the start of the trial, and at the second, fourth and sixth months. These were tested for serum triglycerides, total cholesterol and HDL-cholesterol levels.

Total serum cholesterol and triglyceride levels were measured enzymatically using an automated procedure CGEM- SAEC centrifugal analyzer, manufactured by Electro nucleonics inc.}. The method used for cholesterol determination was a modification of that of Allain et al. (8) according to the procedure suggested for the Spinchem Reagent for the deter-

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Fig. 1 -- Serum triglycerides, cholesterol and HDL levels /mg/dl/ in uremic pat ients receiving polyacrylonitri le dialysis. Comparison with controls.

SERUM TRIGLYCERIDE LEVELS IN UREMIC PATIENTS 73

mination of cholesterol (n ° 89607) of Smith Kline Instruments Inc.

The method used for determination of triglycerides was a modification of that of Bucolo and David (9) according to the procedure suggested for the Eskalab Triglyceride Reagent Bulk (n ° 89804) of Smith Kline. The HDL-cholesterol was deter- mined after heparin-Mn 2+ precipitation according to the pro- tocol of Lipid Research Clinic Program (10): To 2 ml of serum was added 80 ~1 of a heparin solution {5000 kilounits/liter) and immediately mixed. We then added 100 pl of MnCI 2 solution (1 mol/liter), also with immediate vortex mixing. After the sample had stood for exactly 30 min in an ice bath, the precipitate was separated by centrifugation (1500 x g, 30 min, 4°C). Cholesterol was determined in the supernate.

RESULTS AND DISCUSSION

During the t r ia l the re was no change in total cholesterol and in HDL-cholesterol levels (Fig. 1). On the cont ra ry t r ig lycer ide levels showed a different behaviour (Fig. 1): in Group 1 the re was no significative changes dur ing t r ea tmen t , while in Group 2 t r ig lycer ide levels decreased progress ive ly and reached a normal level af ter four months. Af t e r this per iod the pa t ien ts were changed to cuprophane dialysis and a recur rence of hyper t r ig lyce r idemia was observed. Abnormal i t i e s in t r ig lycer ide t r anspor t resu l t ing in e leva ted basal t r ig lycer ide levels usually resul t from increased produc- tion of t r ig lycer ide-r ich VLDL by the l iver, reduced removal by per iphera l t issues (a process media ted by the enzyme l ipoprotein lipase) or a combination of these factors (2). Signif icant ly-elevated plasma t r ig lycer ide concentrat ions have been found to pers i s t dur ing dia- lysis t r e a t m e n t and even following t ransp lan ta t ion {11). I t has been pos tu la ted tha t the l iver may respond to chronic exposure to e leva ted basal insulin levels by in- creasing hepat ic VLDL synthesis . Indeed, recen t s tudies in exper imenta l animals have shown tha t basal insulin levels cor re la te with hepat ic t r ig lycer ide pro- duction. In addition, i t appears tha t various t ryp tophan metabol i tes which are increased in uraemia, as well as ketogenic amino acids which increase in t racytoplasmic

g lycerol , may con t r i bu t e d i r e c t l y to inc reased t r ig lycer ide synthesis .

The s tud ies of Murase (4 ) s u g g e s t t ha t the t r ig lycer ide removal enzyme sys tem, involving lipopro- tein lipase, also may be compromised in uraemia (4). Ac- t iv i ty of this enzyme has been shown to be depressed to

levels seen in familial, fa t ty- induced l ipemia (type 1), a d i s o r d e r a s soc i a t e d wi th m a r k e d l y e l e v a t e d t r ig lycer ide levels and chylomicronaemia resu l t ing from an inborn L P L deficiency. Our s tudy shows tha t up to the sixth month of the t r ia l the re was no change in cholesterol levels; but on the contrary t r iglycer ide levels decreased progress ive ly and reached the normal range. A s ta t i s t ica l ly significant difference (p > 0.01) could be de tec ted be tween cuprophane- and polyacryloni t r i le- dialysis t r ig lycer ide levels. A t the second month, despi te a marked decrease, t r ig lycer ide levels were not ye t in the normal range. This sugges t s the presence in uremic plasma of an inhibitor of l ipoprotein l ipase which is in the middle molecule range. Our resul t s show tha t a diffusive procedure using polyacryloni t r i le can lower high t r ig lycer ide levels, but t r e a t m e n t mus t be prolong- ed for a t leas t four months.

REFERENCES

1. Losowsky, M.S. and Kenward, D.H. Lipid metabolism in acute and chronic renal failure. J. Lab. Cli~ Me& 71, 736-743 {1968).

2. Bagdale, J.D., Porte, D. Jr., Bierman, E.L. Hypertrigly- ceridemia: a metabolic consequence of chronic renal failure. N. EngL J. Med. 269, 181-185 (1968).

3. Brons, M., Christensen, N.C., Hordes, M. Hyperlipopro- teinemia in patients with chronic renal failure. Acta Medica Scan& 192, 119-123 (1972).

4. Murase, G. Inhibition of lipoprotein lipase by uremic plasma, a possible cause of hypertriglyceridemia. Metabolism 29, 1279-1286 (1975).

5. Henning, G. Lipid metabolism in uremia: effect of regular hemofiltration and hemodialysis treatment. J. DiaL 1, 595-605 (1977).

6. Schneider, F. Clinical experience with hemodiafiltration. Proc. Europ. DiaL TranspL Assoc. 14, 136-140 (1977).

7. Quellhorst, M. Treatment of chronic uremia by an ultrafiltration artificial kidney. First clinical experience. Proc. Europ. DiaL TranspL Assoc. 12, 314-318 (1976).

8. Allain, C.C., Pooh, L.S., Chan, C.S.G., and Fu, P.C. En- zimatic determination of total serum cholesterol. Cli~ Chem. 20, 470-475 (1974).

9. Bucolo, G. and David, H. Enzymatic determination of serum triglyceride. Clir~ Chem. 19, 476-481 (1973).

10. Lipid Research Clinics Manual of Laboratory Operations, Vol 1. Washington DC, United States Government Prin- ting Office (1974}.

11. Bagdade, J.D., Casaretto, A., and Albers, J. Effects of chronic uremia, hemodialysis and renal transplantation on plasma lipids and lipoproteins in man. J. Lab. Clin. Med. 87, 37-48 (1976).