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Peritoneal Dialysis International, Vol. 22, pp. 48–52 Printed in Canada. All rights reserved.
Copyright 2002 International Society for Peritoneal Dialysis LACK OF ISOPRENE OVERPRODUCTION DURING PERITONEAL DIALYSIS
Enrico Capodicasa,1 Gianfranco Trovarelli,2 Federica Brunori,2 Luigi Vecchi,3 Carmen Carobi,3 Gianna E. De Medio,3 Maria A. Pelli,4 and Umberto Buoncristiani3 Department of Clinical and Experimental Medicine,1 Institute of Biochemistry and Medical Chemistry,2 Perugia University Medical School; Nephrology and Dialysis Unit,3 Silvestrini General Hospital; Department of Emergency and General Surgery,4 Perugia University Medical School, Perugia, Italy ♦ Objective: Isoprene is the constitutive unit of iso-
alysis patients include continuous versus intermit- prenoid lipids and sterols. However, it is also a potential
tent dialysis, biocompatibility and safety of the pro- toxic and carcinogenic agent. Recent findings of a marked
cedure, contamination, adequacy in removing small and prolonged isoprene overproduction induced by hemo-
and large solutes, hemodynamic stability, anticoagu- dialysis sessions raises the question of isoprene behav-
lation, long-term prognosis, and the incidence of some ior in patients on peritoneal dialysis.

diseases, including myocardial infarction and cere- Design: A study with repeated measures per patient
and healthy control.
brovascular accidents, infections, amyloidosis, cancer.
Setting: Nephrology and Dialysis Unit and Perugia Uni-
(1–11). Evaluating differences in changes associated versity Medical School.
with the type of dialysis may be of interest in patho- ♦ Patients: Sixteen consecutive patients on regular con-
physiological and clinical settings.
tinuous ambulatory peritoneal dialysis (CAPD) were evalu-
A new metabolic aspect described to date only in ated. Endogenous isoprene was analyzed using gas
HD patients is the increased breath isoprene exhala- chromatographic assay of breath isoprene, collected at
tion observed in regular 4-hour (0800 hours, 1200 set times before and after dialysis fluid exchange.
hours,) three-times-weekly maintenance HD (12).
Results: No significant variations were found in breath
Breath isoprene was increased in all patients. The isoprene concentrations in the different samples from
overproduction was HD-induced, became evident in each patient, and levels were almost stable within the
the postdialysis period, and followed a biphasic pat- normal range of healthy controls.
Conclusion: These results show that CAPD, unlike
tern with significantly increased overproduction also hemodialysis, has little or no effect on isoprene and iso-
persisting the morning after, on the non-HD day (13).
prenoid-related lipid turnover. This lack of increased en-
This behavior pattern could have clinical and biologi- dogenous isoprene synthesis, in addition to being a
cal value because cells depend on isoprenoids derived distinctive metabolic feature of CAPD, could have impor-
from mevalonate for growth, differentiation, and tant pathophysiological and clinical implications.
maintenance of homeostatic functions (14); moreover,isoprene is thought to have carcinogenic and toxic effects (15–18). There are no data on the behaviorpatterns of breath isoprene during PD.
Extracorporeal dialysis, or hemodialysis (HD), and The aim of this study was to evaluate breath iso- peritoneal dialysis (PD) — most often continu- prene patterns in patients undergoing CAPD.
ous ambulatory peritoneal dialysis (CAPD) — are twomodalities of treatment for end-stage renal disease PATIENTS AND METHODS
considered alternatives, even though there may beremarkable differences in efficacy, physiology, contra- indications, and complications. Problem areas for di- Sixteen consecutive patients (8 men and 8 women; Correspondence to: E. Capodicasa, Department of Clini- mean ± SD age 62.2 ±13 years, range 29 – 77 years) cal and Experimental Medicine, Perugia University Schoolof Medicine, Policlincio Montelkuce, via Brunamonti, 06100 on stable CAPD were evaluated. All patients were treated with standard PD solutions, with lactate as buffer and glucose as osmotic agent at different con- Received 4 April 2001; accepted 16 July 2001.
centrations according to individual need. Mean du- ration of dialysis treatment was 30.4 ± 20.2 months Water removal is required to avoid aluminum column (range 9 – 79 months). Each patient had 3 daytime deactivation and to prevent ice formation in the trap.
exchanges and 1 nighttime exchange. Detailed infor- During thermal desorption (280°C, 6 minutes, helium mation on the 16 patients included in the study is flow 15 mL/min), the desorbed compounds were con- centrated in a cryogenic trap (–100°C) by liquid ni-trogen. Finally, flash heating sent the volatiles to the Al O /KCl column (25 m, 0.32 mm, 5.0 µm; Varian– Chrompack). The temperature program was 50°C for Isoprene concentration in exhaled breath was de- 2 minutes, increased 8°C/minute to 190°C, and final termined by gas chromatographic analysis as reported isotherm 15 minutes. Helium pressure was 80 kPa by elsewhere (12). Briefly, 1-L Tedlar bags (SKC Inc., flame ionization detector (250°C). A software program Eighty Four, Pennsylvania, USA) were used for col- (Mosaic, Varian–Chrompack) running on a personal lecting breath. The first 500 mL was split off (dead computer was used to analyze chromatograms and space) and only the end of the alveolar breath was collected. New and used bags were purged by heliumflow. All bags were tested before sampling. Fixed amounts of breath samples (100 mL) were absorbedon to a glass tube filled with preconditioned Exhaled breath was collected from the 16 patients Carbosieve, Carbotrap, and Carbotrap C (Varian– (group A) immediately before and after the drainage Chrompack Italy, Turin, Italy) by suction pump phase of the first two daytime exchanges, and at the (25/30 mL/min). Thermo desorption cold trap unit end of the first and second hours of the dwell period (TCT) samples tubes were placed on a TCT/purge and between the two. In a previous study performed in trap injection (PTI) CP 4001 injector (Varian– HD patients, the first breath isoprene increase was Chrompack) and processed automatically. A gentle detected at the end of dialysis, but became more evi- preflush (53°C, 4 minutes, helium flow 15 mL/minute) dent half an hour later; therefore, in one subgroup of was used to remove the remaining nonadsorbed gas.
6 patients (group A2), refilling after the first drain- CIN = chronic interstitial nephritis; PKD = polycystic kidney disease; CGN = chronic glomerulonephritis; HNS = hyperten-sive nephrosclerosis.
Stay-Safe, Fresenius Medical Care Science and Product Consulting, Bad Homburg, Germany; Fres/S.S3/99, Fresenius;Dianectan S, Laboratoire Aguettan, Lyon, France; Baxter T, Baxter Healthcare Corp. (Renal division), McGaw Park, Illi-nois, USA; Bieffe, Bieffe Medital S.p.a., Milan, Italy; Periline, Haemopharm Health Care, Milan, Italy.
age was delayed for 30 minutes, after which anothersample was collected. In a second subgroup of 4 pa-tients (group A3), who were followed up for 24 hours,exhaled breath was also collected before and after thethird and fourth exchanges.
Data are reported as mean ±SD. Analysis of vari- ance was done and significance of differences wasassessed by t-test for paired data analysis; a p valueless than 0.05 was assumed significant.
Figure 2 — Breath isoprene during continuous ambulatoryperitoneal dialysis with delayed refilling. In this subset of In the first part of the study, breath isoprene con- patients (group A2; n = 6), abdominal refilling after the first centration was evaluated in samples collected from drainage was postponed 30 minutes, at which time an extra the 16 patients in group A during the first morning sample was collected (t1D). Isoprene levels are reported as cycle [i.e., before (time 0) and soon after the first peri- toneal drainage; 1 and 2 hours after the first perito-neal refilling; and before and soon after the second Finally, Figure 3 shows the behavior pattern in the peritoneal drainage]. Figure 1 shows breath isoprene 4 patients (group A3) in whom the breath isoprene con- concentrations at these different sample times. At centration was measured in all four exchanges. Again, time 0, isoprene concentration was 5.52 ± 2.25 nmol/L, no significant differences were found, but there was a that is, almost identical to the level found in healthy tendency toward a decrease during the diurnal hours subjects with normal renal function in our laboratory in accord with the circadian rhythm of this hydrocarbon [breath isoprene levels in 89 healthy controls ranged in normal subjects. Isoprene was not present in fluid from 1.4 to 10.8 nmol/L (5.06 ± 2.24 nmol/L)]. Con- used for dialysis and the isoprene concentration in centrations remained almost stable without signifi- ambient air was negligible (data not shown).
cant variation over time in samples collected from thesame patient.
DISCUSSION
Figure 2 shows no variations in isoprene concen- tration occurring in the 6 patients in group A2 after This is the first time that breath isoprene produc- refilling was postponed for 30 minutes.
tion has been evaluated in PD patients.
Breath isoprene levels were not significantly dif- ferent from the normal healthy control values before,during, and after a peritoneal exchange. These find-ings suggest that, in CAPD patients, an isoprene en-dogenous overproduction does not occur, unlike in HDpatients, in whom isoprene overproduction persists,for many hours after dialysis ends, in a biphasic be-havior pattern with concentrations remaining high the next morning (a nondialysis day) (12,13).
The reasons for this different behavior are not known. An endogenous product of lipid metabolism,isoprene in man is believed to derive from the syn-thetic mevalonate pathway leading to sterols and iso- prenoid lipids (Figure 4). This metabolic pathwayappears to be strictly regulated at the level of meva- Figure 1 — Breath isoprene during continuous ambulatory lonic acid (MVA) (19–22), a low molecular weight, peritoneal dialysis. Breath samples were collected water-soluble substance, levels of which are increased immediately before first morning drainage (t0), soon after in the plasma of uremic patients before a HD session first morning drainage (t1), 1 hour after first peritoneal refilling (t2), 2 hours after first peritoneal refilling (t3), On the contrary, isoprene (molecular weight 68.12, immediately before second drainage (t4), and soon aftersecond drainage (t5). Isoprene levels are reported as melting point –146°C, boiling point 34°C), a volatile liposoluble substance, is not removed by HD but is Figure 3 — Time course of breath isoprene during continuous ambulatory peritoneal dialysis. In this subset of patients(group A3; n = 4), breath isoprene concentration was measured at specific time points for all four exchanges of the day.
Isoprene levels are reported as mean percentage values ±SD.
determining the different breath isoprene behaviorpattern in HD and CAPD patients.
The first hypothesis is that, in a short space of time, HD removes great quantities of MVA, and conse-quently the MVA-regulated inhibitory mechanism,and initiates enzymatic induction mechanisms, whichcould result, after the end of the dialysis session, inthe increased respiratory exhalation of isoprene inthe biphasic behavior pattern described elsewhere(13). In CAPD patients, the slower and continuousremoval of hydrosoluble isoprene precursors does notpromote a clear isoprene overproduction.
Alternatively, intermediate mechanisms inducing isoprene overproduction may involve factors relatedto biocompatibility, to hemodynamic stress, or to otherunknown factors associated with hemodialytic proce-dures per se.
Variations in alveolar respiration do not seem to play a major role in isoprene emission: in breathsamples from dialyzed patients, no significant varia-tions were found in alveolar levels of other volatilehydrocarbons (e.g., ethane, pentane, isopentane, pro-pane, butane, and isobutane) (data not shown).
Whatever the causal mechanism(s), patients on HD, unlike those on CAPD, incur an increased iso-prene biosynthesis and a prolonged overexposure con-sequent to repeated dialysis sessions.
Thus, variations in isoprene respiratory exhalation could reflect the effect of the dialysis session on lipid Figure 4 — Branched pathway of mevalonate metabolism metabolism in uremic patients and could have reper- cussions in terms of cellular and cardiovascular easily exhaled with alveolar air, in which it can be physiopathology. High isoprene levels have been re- measured noninvasively by gas chromatography.
ported in patients with acute myocardial infarction Differences in continuous and intermittent dialy- (24). Furthermore, isoprene itself is acknowledged to sis treatments probably play an important role in have a possible direct pathogenic role. In fact, chemi- cally, isoprene [H C=CHC(CH )=CH ] is an analogue 10. Drueke TB. Beta2-microglobulin and amyloidosis.
of butadiene, which is reputed to be a toxic, mutagenic, Nephrol Dial Transplant 2000; 15(Suppl 1):17–24.
and carcinogenic agent (15–17). In experimental mod- 11. Zima T, Mestek O, Nemecek K, Bartova V, Fialova J, els, even episodic exposure to isoprene has increased Tesar V, et al. Trace elements in hemodialysis and con- the incidence of various neoplasias, even many years tinuous ambulatory peritoneal dialysis patients. BloodPurif 1998; 1:253–60.
after exposure (18). This hydrocarbon is thus the ob- 12. Capodicasa E, Trovarelli G, De Medio GE, Pelli MA, ject of growing interest as a potentially harmful nox- Lippi G, Verdura C, et al. Volatile alkanes and increased concentrations of isoprene in exhaled air during hemo- In conclusion, the lack of an increase in isoprene levels during CAPD appears to be not only a distinc- 13. Trovarelli G, Brunori F, De Medio GE, Timio M, Lippi tive feature of this type of dialysis, but also a meta- G, Pelli MA, et al. Onset, time course, and persistence bolic phenomenon that deserves further investigation of increased haemodialysis-induced breath isoprene and that could be of remarkable physiological, clini- cal, and prognostic interest in these patients.
14. Vishnuvardhan D, Beinfeld MC. Lovastatin is a potent inhibitor of cholecystokinin secretion in endocrine ACKNOWLEDGMENTS
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the English version of this paper, and Fortuna Gino 16. Bolt HM. Butadiene and isoprene: future studies and Girolamo and Marinacci Giuliana for their technical implications. Toxicology 1996; 113:356–60.
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