The leptin/adiponectin ratio: Potential implications for peritoneal dialysis

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1 & 2008 International Society of Nephrology The leptin/adiponectin ratio: Potential implications for peritoneal dialysis D Teta 1, M Maillard 1, G Halabi 1 and M Burnier 1 1 Division of Nephrology, Department of Internal Medicine, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland Leptin and adiponectin are adipokines with respective pro-atherogenic and anti-atherogenic properties, defining the plasma leptin/adiponectin ratio as a novel marker for atherosclerosis. In non-renal patients, both hyperleptinemia and hypoadiponectinemia are associated with cardiovascular complications. In peritoneal dialysis (PD) patients, the leptin/ adiponectin ratio is markedly elevated, which is consistent with their increased cardiovascular risk. As glucose metabolism regulates adipokines, we hypothesized that glucose and/or other PD fluid components may affect adipokine production balance. This review summarizes the available data arising from research in this area. In 3T3-L1 adipocytes, glucose-based PD4 1.36% significantly increased leptin secretion vs amino-acid-based (AA) and icodextrin (ICOD)-based PD fluids. In contrast, adiponectin secretion was significantly reduced by PD4 1.36% vs glucose-free dialysates. Glucose concentration in PD fluids was shown to determine leptin secretion. Preliminary data from PD patients showed that a single 6-h dwell with PD4 3.86% glucose acutely increased plasma leptin vs AA (Po0.05). The reduction in glucose load in a standard PD regimen was associated with an improvement in the plasma leptin/ adiponectin ratio at 6 months. ph-neutral PD fluids increased leptin secretion in vitro vs acidic PD fluids, without effect on adiponectin. Whether this effect may have an impact on plasma leptin levels in PD patients is unknown. In conclusion, glucose-based PD fluids worsen the adipokine production balance in vitro while glucose-free solutions improve it. In PD patients, hypertonic glucose-based PD fluids may increase plasma leptin levels. Glucose-sparing PD regimens appear to improve the leptin/adiponectin ratio. However, their potential to reduce cardiovascular complications needs to be demonstrated. ; doi: /sj.ki KEYWORDS: adipokines; adiponectin; cardiovascular risk; leptin; peritoneal dialysis; plasma ratio Correspondence: D Teta, Division of Nephrology, Department of Internal Medicine, Centre Hospitalier Universitaire Vaudois (CHUV), Bugnon 17, Lausanne 1011, Switzerland. Daniel.Teta@chuv.ch The adipose tissue is now recognized as an active endocrine organ, involved in the regulation of energy homeostasis and metabolism. 1 Adipocytes secrete a number of hormones and cytokines, namely adipokines, including leptin, adiponectin, tumor necrosis factor-a, interleukin-6, resistin, and visfatin, which are implicated in important pathophysiological mechanisms determining health and disease. Leptin and adiponectin have well-defined actions in humans. Leptin is a 167-amino-acid (AA)-circulating protein encoded by the ob gene, which signals the body s nutritional status to the brain to regulate energy balance. 2 Leptin also has distinct cytokine properties, such as the stimulation of inflammation and modulation of the immune system. 3 Adiponectin is a 244-AA protein produced by the apm1 gene, which has insulinsensitizing, anti-inflammatory, and anti-atherogenic properties. 4 In patients with end-stage renal disease (ESRD), adipokines accumulate in plasma, mainly because of the loss of renal clearance. 5,6 However, an important determinant of plasma levels of adipokines is fat mass, even in patients with various stages of renal insufficiency. 5,6 Plasma leptin level is strongly correlated with fat mass. 7 Thus, ESRD patients have hyperleptinemia, which is further magnified by high fat mass. 8 In contrast, plasma adiponectin level is inversely correlated with adipose tissue mass, 9 and patients with ESRD display moderate hyperadiponectinemia, which may be mitigated in obese patients. Other factors such as gender, sex hormone levels, and factors associated with ESRD such as inflammation, hyperinsulinemia, and acidosis, may superimpose modulation of either leptin and/or adiponectin 13,14 production to determine final plasma levels. Peritoneal dialysis (PD) is characterized by gain of fat mass, extraordinarily raised plasma leptin 15 and moderate hyperadiponectinemia 6 and, thus, represents a distinct condition for the study of adipokine metabolism. Glucose metabolism is a major factor regulating both leptin 16 and adiponectin. 17 As glucose is a key element in the composition of most PD fluids, we hypothesized that glucose-based PD solutions and/or a regimen high in glucose may regulate plasma levels of leptin and adiponectin in these patients. Because adipokines have pleiotropic actions, that is, on insulin sensitivity, inflammation, immunity, and atherosclerosis, the adipokine balance in PD may thus have an impact on patient outcome. S112

2 The aims of this article are the following: (1) to review the biological and clinical actions of adipokines, with a focus on the cardiovascular system; (2) to introduce the notion of the leptin/adiponectin ratio as a novel marker for cardiovascular risk; and (3) to discuss the effects of PD fluids on adipokine production balance in vitro and on leptin/adiponectin ratio in PD patients. It is hypothesized that modulation of the adipokine profile by using a glucose-sparing PD regimen could reduce cardiovascular risk in PD patients. LEPTIN AND ADIPONECTIN ACTIONS ON THE CARDIOVASCULAR SYSTEM Leptin as a pro-atherogenic molecule Leptin was first described as the monogenic mutation responsible for the morbidly obese phenotype observed in the ob/ob mouse. 18 After secretion from adipose tissue into plasma, this 16-kDa protein crosses the blood-brain barrier and interacts with specific leptin receptors (Ob-Rb) in the hypothalamus to limit food intake. 2 Leptin also increases energy expenditure through a stimulatory effect on the sympathetic nervous system. 19 Obese patients have high not low leptin levels, suggesting that obesity may be associated with leptin resistance. 7 However, leptin sensitivity may be restored when plasma leptin is reduced, for instance, after weight loss. 20 Leptin has effects well beyond the regulation of energy balance. The discovery of Ob-Rb receptors in peripheral tissues such as T cells 21 and vascular endothelial cells 22 has indeed ascribed to leptin a status of pleiotropic adipokine. In particular, leptin has distinct pathophysiological effects on the cardiovascular system, which may be important in hyperleptinemic states such as in PD, in light of the high cardiovascular mortality of these patients. Leptininduced cardiovascular actions have been summarized in two recent reviews. 23,24 Experimental and clinically relevant data are detailed in the following paragraph. Leptin injected acutely in mice activates sympathetic outflow via both central and peripheral mechanisms. 25 Chronic intravenous infusion of leptin over 1 week increases blood pressure and heart rate in conjunction with overt weight loss, 26 indicating that leptin per se induces a sympathetic effect independent of fat mass accumulation. The above experimental findings are supported by epidemiological evidence that leptin and arterial pressure are correlated, although modestly, even after adjustment for adiposity. 27 An independent association between leptin levels and heart rate was found in heart transplant recipients with sympathetic denervation, 28 suggesting a direct effect of leptin on heart rate, presumably through cardiac leptin receptors. Angiotensin II has been shown to increase leptin synthesis in cultured adipocytes 29 and in rats in vivo, 30 which suggests that angiotensin II and leptin could synergically interact to promote hypertension. Leptin directly acts on the vasculature. In vitro experiments have shown that leptin induces proliferation of rat vascular smooth muscle cells, 31 osteogenic transformation of cultured vascular cells prone to develop calcified lesions, 32 regeneration of endothelial cells after intimal injury, 33 and stimulation of oxidative stress. 22 In vivo, leptin may exert a direct vasodilatory action through nitric oxide-dependent and independent effects. However, the sympathetically mediated pressor effect of leptin predominates over its vasodilatory effect. 23 Leptin is a pro-coagulant factor. In ob/ob mice, thrombi from arterial lesions are unstable compared with those in littermate controls, and leptin replacement normalizes thrombi formation. 34 Leptin may also modulate fibrinolysis since plasma leptin was significantly associated with decreased plasminogen activator inhibitor-1 activity even after adjustments for adiposity and age. 35 Along with the above experimental data, there is increasing epidemiological evidence linking leptin and cardiovascular markers and/or clinical end points. Leptin was independently associated with decreased arterial distensibility in healthy adolescents within a wide range of body mass indexes. 36 In hypertensive men, myocardial wall thickness was associated with high plasma leptin, independently of body composition and blood pressure. 37 Leptin was independently associated with coronary calcification in a cohort of type II diabetic patients. 38 Leptin also has been associated with myocardial infarction and stroke. 39,40 Finally, in the prospective West of Scotland Coronary Prevention Study (WOSCOPS), leptin independently increased the relative risk for a first myocardial infarction. 41 Adiponectin as an anti-atherogenic molecule Adiponectin is a 30-kDa adipocyte complement-related protein encoded by the adipose most abundant gene transcript 1 (apm1), which has distinct insulin-sensitizing effects. 42 Adiponectin circulates in human plasma as a hexamer of relatively low molecular weight, and as a larger multimeric structure of high molecular weight (HMW) at high concentrations ranging from 0.5 to 20 mgml 1 that is 0.01% of the total plasma protein pool. 42 It is thought that the HMW adiponectin complex is the active form of this protein, and that the ratio HMW/total adiponectin (HMW þ low molecular weight) is more accurate than total adiponectin in predicting insulin sensitivity. 43 In contrast to most adipose tissue-derived proteins such as leptin, plasma adiponectin has a paradoxical negative correlation with fat mass. 9 Adiponectin release is significantly lower from omental than subcutaneous adipose tissue (Johnson J et al. Obes Res 2003; 11: A34; abstract), which is consistent with the higher cardiovascular risk observed in men and in clinical situations in which truncal (that is, visceral) obesity is predominant. The insulin-sensitizing effects of adiponectin are mediated through adiponectin receptors 1 and 2, which are primarily expressed in skeletal muscle and in the liver, respectively. Receptors are indeed markedly expressed in pancreatic b-cells, 44 macrophages, atherosclerotic lesions 45 and the brain, 46 reflecting pleiotropic actions of adiponectin, such as for leptin. Beyond its primary insulin-sensitizing effect, the interest in adiponectin derives from its potential protective role for S113

3 the cardiovascular system. Adiponectin inhibits endothelial cell production of adhesion molecules in vitro, thus suppressing the attachment of monocytes, an early event occurring in the atherosclerotic process. 4 In addition, adiponectin has direct anti-inflammatory actions, since it reduces the production and activity of tumor necrosis factor-a; 47 conversely, tumor necrosis factor-a downregulates adiponectin production. 48 Neointimal thickening of damaged arteries was exacerbated in adiponectin-deficient mice and was inhibited by exogenous adiponectin, 49 suggesting that adiponectin may play a role in the intimal proliferation observed after angioplasty. In line with experimental data, low plasma adiponectin concentrations have been reported in patients with coronary artery disease, 50 obesity, 9 essential hypertension, 51 and type II diabetes mellitus. 52 Furthermore, low levels of adiponectin were found to predict later development of type II diabetes, 53 myocardial infarction, 54 and coronary heart disease. 55 THE LEPTIN/ADIPONECTIN RATIO As shown above, there is clear biological evidence that leptin and adiponectin have opposite effects on the cardiovascular system, including directly on blood vessels. Clinical studies linking adipokines and outcome are not overwhelming, but the evidence we have so far indicates that both hyperleptinemia and hypoadiponectinemia are associated with a worse cardiovascular outcome. In line with this view, it was reported that the leptin/adiponectin ratio is correlated with pulse wave velocity to a greater extent than plasma leptin and adiponectin alone. 56 Another recent study showed that the leptin/adiponectin ratio could serve as a clinical marker for atherosclerosis in type II diabetic subjects, as it was a strong indicator of increased carotid intima-media thickness. 57 Although further epidemiological evidence is needed to consolidate the notion of leptin/adiponectin ratio, these preliminary observations suggest that patients exhibiting a high plasma ratio may be prone to cardiovascular events. The leptin/adiponectin ratio in PD patients Plasma leptin levels in patients treated by PD are considerably higher than those observed in hemodialysis patients and in patients with chronic renal failure under conservative treatment. 15 PD-associated hyperleptinemia is out of proportion to fat accumulation observed under this treatment and reaches a 5- to 20-fold increment vs controls. 15 Furthermore, plasma leptin is already elevated a few days after PD treatment is started, 58 which suggests that specific factors associated with the PD procedure itself may stimulate leptin production in these patients. Compared to leptin, plasma adiponectin is only modestly increased in PD patients, by about two- to threefold vs controls. 6 Unlike leptin, plasma adiponectin level did not differ between patients on hemodialysis and those on PD in a cross-sectional study. 6 However, sequential longitudinal measurements of plasma adiponectin over time in PD patients are not available. Thus, in spite of elevations of both plasma leptin and adiponectin, the leptin/adiponectin ratio in PD patients is markedly elevated, essentially because of severe hyperleptinemia. In men from WOSCOPS, the risk of a first myocardial infarction was increased by 26% for each standard deviation increase in plasma leptin. 41 If this epidemiological association would be applicable to PD patients, PD-associated hyperleptinemia would increase the risk of such an event by more than 600%. It is emphasized that leptin insensitivity observed in obesity-associated hyperleptinemia should not discount the importance of this issue. Leptin resistance in murine obesity models has actually been shown to be restricted to the metabolic effects of leptin, sparing its cardiovascular sympathetic actions. 59 Selective leptin resistance may therefore explain why excess leptin may contribute to cardiovascular complications despite metabolic resistance in hyperleptinemic states such as in PD. In a small retrospective study, plasma leptin was associated with total cholesterol and triglycerides. 60 In addition, leptin level was shown to correlate with hemostatic parameters and platelet aggregation in PD patients. 61 These findings suggest that leptin may be interpreted as a cardiovascular risk factor in this setting. However, there are currently no data linking leptin and clinical events in the field of PD. In non-renal patients, low plasma adiponectin is consistently associated with higher cardiovascular risk. This evidence may question the role of increased adiponectinemia in triggering cardiovascular events in PD. However, in spite of modest hyperadiponectinemia associated with ESRD, Zoccali et al. 62 have shown that patients on hemodialysis with plasma adiponectin lower than 11.6 mgl 1 had a worse 3-year survival compared to patients with higher levels. Plasma adiponectin remained inversely correlated with typical cardiovascular risk factors such as plasma glucose, triglycerides, insulin, and low-density lipoprotein-cholesterol. 62 So, the relationship between plasma adiponectin and cardiovascular damage in ESRD appears to be reset at a higher level. 63 As an exception, plasma adiponectin measured retrospectively from patients with chronic kidney disease stages 3 or 4 entering a prospective study designed to address renal progression, was unexpectedly found to correlate positively with mortality. 64 However, this study suffered numerous limitations, including technical issues (plasma was frozen up to 15 years before assay), which may have precluded reasonable interpretations. To sum up, the available data suggest that the dramatically high plasma leptin/adiponectin ratio in PD may have implications for patient outcomes. Strategies to reduce hyperleptinemia and induce higher adiponectinemia, in order to improve this ratio, may therefore be developed to reduce cardiovascular risk in these patients. How PD solutions affect adipokine production Many factors associated with PD, such as accumulation of fat mass, hyperinsulinemia, and increased levels of inflammatory markers, for example tumor necrosis factor-a, are known to upregulate leptin 7,10,11 and downregulate adiponectin. 9,13,14 S114

4 It is thus conceivable that, beyond the role of ESRD in retaining adipokines, the magnitude of hyperleptinemia is exacerbated, whereas that of hyperadiponectinemia is mitigated by PD. A role for PD fluids in determining plasma levels of adipokines in this context is appealing. Studies from adipocyte cultures in vitro and in animals have shown that glucose metabolism is a major regulator of both leptin and adiponectin production, in part through mechanisms involving the hexosamine signalling pathway. 16,17 Most PD solutions contain glucose. During the dwell, the solutes contained in PD fluids are transferred by passive diffusion through the peritoneal barrier. 65 As a result, different cell types located in the submesothelial space, that is resident fibroblasts and macrophages, have been shown to be activated by the chemical components of PD fluids. 66 We hypothesized that glucose from PD fluids is transported through the mesothelial cell layer and interacts with adipose cells from the omentum to impact leptin and adiponectin production (Figure 1). It is also possible that adipokine production from subcutaneous adipocytes is affected by systemic chemical modifications induced by PD fluid components. In the following section, the available data regarding the effects of PD fluids on adipokine production in vitro from cultured adipocytes and in vivo in PD patients are discussed. EFFECTS OF PD SOLUTIONS ON LEPTIN AND ADIPONECTIN PRODUCTION Studies in vitro Effect of glucose-based vs glucose-free PD fluids. 3T3-L1 adipocytes in culture were exposed to a 50:50 mixture of PD dialysis solution and M199 with 10% fetal bovine serum, as described previously. 67 Commercial glucose-based and glucose-free, lactate-buffered PD fluids from Baxter Healthcare were compared. Solutions were Dianeal s PD4 glucose 1.36% (PD4 1.36%), AA-based Nutrineal s, and icodextrinbased Extraneal s (ICOD). The control solution (C) was culture medium M199. PD4 1.36% increased leptin secretion from 3T3-L1 adipocytes in culture at 48 h vs C (Po0.001) (Figure 2). Adiponectin secretion was on the contrary reduced by PD4 1.36% (Po0.05 vs C) (Figure 3). In contrast, glucose-free dialysates AA and ICOD did not affect leptin and adiponectin secretion vs C. Effect of glucose concentration per se on leptin secretion. Filtersterilized dialysates (Lab-D) of identical electrolyte composition and ph to PD4 1.36% were generated to enable D-glucose concentration of the final test medium to be varied. 67 When glucose concentration was increased from 2.75 to 40 mm in Lab-D, we observed a dose-dependent increase in leptin concentrationinthecellsupernatantsbyupto110712% at 48 h (Po0.001) (Figure 4). Leptin mrna content was upregulated byhighglucose dialysates(po0.05, glucose 20 and 40 vs 2.75 mm) at 24 h, preceding the effect on leptin secretion. Osmolality and glucose degradation products (GDPs) had no effect on leptin secretion. 67 Omental adipose tissue (Adipokine secretion) PD fluids Mesothelium Figure 1 Interactions between PD fluids, omental adipocytes and adipokines. Normal visceral peritoneal morphology showing a thin mesothelial cell layer lying on a thick sheet of omental adipose tissue. PD fluids are transferred by diffusion through the mesothelium, and therefore may interact with omental adipocytes, which synthesize adipokines. Picture at 10 original magnification; courtesy of Dr P Furness, Department of Histopathology, Leicester General Hospital, UK. Leptin (pg per well per 48 h) PD4 ICOD AA C Figure 2 Effect of glucose-based and glucose-free PD fluids on leptin secretion. 3T3-L1 adipocytes in six-well plates were incubated for 48 h in PD4 (glucose 1.36%), ICOD and AA-based PD fluids. M199 was used as the control solution (C). Solutions were diluted 50:50 with M199. Results shown are means7s.e.m. of three independent experiments (pool of culture wells for each set of conditions). **Po0.001 vs C. Taken together, our data in 3T3-L1 adipocytes show that glucose-based PD fluids stimulate leptin secretion through a transcriptional effect, which is readily explained by glucose concentration per se. The mechanisms involved in the downregulation of adiponectin production by glucose-based PD fluids observed in this model have not been investigated. As opposed to leptin, it was evidenced that the activation of the hexosamine signalling pathway resulted in decreased serum adiponectin levels in mice. 17 It is thus speculated that high extracellular glucose concentrations may lead to increased glucose availability in this pathway, to reduce adiponectin production. Effects of ph-neutral PD fluids. We previously showed that a low ph inhibits leptin production in vitro 68 and S115

5 Adiponectin (ng per well per 48 h ) PD4 ICOD AA C Figure 3 Effect of glucose-based and glucose-free PD fluids on adiponectin secretion. 3T3-L1 adipocytes in six-well plates were incubated for 48 h in PD4 (glucose 1.36%), ICOD, and AA-based PD fluids. M199 was used as the control solution (C). Solutions were diluted 50:50 with M199. Results shown are means7s.e.m. of three independent experiments (pool of culture wells for each set of conditions). *Po0.05 vs C. Leptin (pg per well per 48 h) Glucose (mm) Figure 4 Effect of glucose concentration in dialysates on leptin secretion. 3T3-L1 adipocytes in six-well plates were incubated in laboratory-manufactured PD fluids at various glucose concentrations. Solutions were diluted 50:50 with M199. The final glucose concentration in the test media was as shown. Results shown are those obtained at 48 h of incubation (means7s.e.m. of three independent experiments; pool of culture wells for each set of conditions). **Po0.001 vs 2.75 mm glucose. systemically in uremic rats. 12 Thus, we hypothesized that ph-neutral PD fluids may impact on adipokine production from cultured adipocytes. The effects of conventional acidic PD fluids (PD-Acid, Stay-Safe s, ph: 5.5), and ph-neutral solutions, either lactate-buffered (PD-Bal, Stay-Safe Balance s, ph: 7.0) or bicarbonate-buffered (PD-Bic, Bicavera s, ph: 7.4) from Fresenius Medical Care, Bad Homburg, Germany, were studied as described earlier. 69 Compared with PD-Acid, ph-neutral dialysates PD-Bal and PD-Bic produced an increase in leptin secretion of 2572 and 4374% at 48 h (Po0.05 and o0.01, respectively). Adiponectin secretion was not affected by ph-neutral PD fluids. Further experiments have shown that the % plasma leptin variation AA PD4 3.86% C (no fluid) Min Figure 5 Acute effect of PD4 3.86% on plasma leptin. PD patients (n ¼ 5) were subjected to a 6-h dwell with sequentially a high glucose-containing PD fluid (PD4 3.86%), an AA PD fluid, and no PD fluid (C). Patients fasted overnight and during the protocol. Leptin was assayed in plasma after 3 and 6 h (enzyme-linked immunosorbent assay). Mean7s.e.m. % of plasma leptin changes vs initial values are shown. *Po0.05 vs C and AA. leptin-stimulating effect of ph-neutral PD fluids was due to ph and not to the type of buffer. 69 Studies in PD patients Acute effects of PD fluids on plasma adipokines. After an overnight fast, five patients underwent an acute 6-h dwell with 2 l of a hypertonic glucose-based PD fluid (Dianeal PD4 3.86%). During a second session, they were subjected to an identical volume of a glucose-free AA-based dialysate (Nutrineal, AA). In a third session, they were observed with no dwell (control, C). Patients fasted during the procedures. Each investigational session was separated by at least 1 week. Preliminary results are presented in Figure 5. A significant decline in plasma leptin was observed at 6 h in C, reflecting the effect of prolonged fasting. Leptin response to AA did not differ from C. In contrast, PD4 3.86% increased plasma leptin by approximately 12% despite prolonged fasting. When PD4 3.86% and AA were compared, a 39% increase in plasma leptin was seen with PD4 3.86% (Po0.05, Wilcoxon s test). Plasma adiponectin was not affected by C and/or both PD fluids (Teta D et al. Acute effect of PD fluids on adipokine profile in PD patients. Congress of the American Society of Nephrology 2007; poster presentation). These results are in line with those reported in rats subjected to PD exchanges with high glucose-based dialysates, in which a strong increase in plasma leptin was seen. 70 Contrary to these findings, Pérez Fontán et al. 71 reported that an exchange with PD4 3.86% was associated with a small but significant decline in plasma leptin of approximately 10%. No other PD fluid was tested in the latter study. However, dwell time in that study was considerably shorter than in ours, 2 vs 6 h. Glucose-based PD fluids may require several hours to induce upregulation of leptin mrna in cultured adipocytes (Teta D et al., unpublished data). It is therefore possible that the use of a very short dwell in that study may have limited the potential to detect leptin de novo synthesis. A study investigating the adipokine acute kinetics under various PD exchanges is currently underway in our center. S116

6 Effects of PD regimen on plasma adipokines long term. Plasma adipokines are more likely to vary after changes in PD regimen for longer periods. A recent observation actually reported that the replacement of a single exchange from glucose-based to ICOD solutions in a standard continuous ambulatory peritoneal dialysis regimen was associated with a 100% decrease in plasma leptin and a 50% increase in plasma adiponectin at 6 months. 72 Although this effect appears to be remarkable, prospective studies expressly designed to test this issue are necessary in order to avoid the role of potential confounders such as body composition and inflammation, which are known to affect plasma adipokines. DISCUSSION AND OUTLOOK PD fluids clearly affect the adipokine balance. Glucosecontaining PD fluids upregulate leptin and downregulate adiponectin production from 3T3-L1 adipocytes. Glucose concentration in PD fluids is an essential determinant of leptin secretion in this model. Data on adiponectin secretion in vitro are limited. In particular, the range of glucose concentrations in which the adiponectin-suppressing effect is operative needs further investigation. In PD patients, high glucose-containing PD fluids acutely induce plasma leptin at 6 h, thus worsening the already high PD-associated leptin/adiponectin ratio. Conversely, reduction of glucose load in a standard continuous ambulatory peritoneal dialysis regimen is associated with a decrease in leptin and an increase in adiponectin plasma levels long term, thus, improving the leptin/adiponectin ratio. The potential relevance of bioactive forms of adipokines in plasma, for example, HMW-adiponectin rather than total adiponectin, needs to be clarified. The role of ph-neutral PD fluids is intriguing, since they increase leptin without affecting adiponectin production in vitro. Thus, these solutions may potentially worsen the adipokine production balance. It is conceivable that a local (intraperitoneal) leptin-stimulating effect by adipocytes exposed to ph-neutral solutions may reflect a state of better biocompatibility, which may ultimately serve to improve local host defense. It has to be emphasized that ph-neutral PD fluids tested in our experiments were either purely lactate or purely bicarbonate-buffered solutions. Combination lactate-bicarbonate buffers have not been tested in vitro. However, the prototype of such a combination, that is, Physioneal s did not induce plasma leptin acutely in preliminary observations (Teta D et al., unpublished data). Nevertheless, a potential increase in plasma leptin over time in patients treated by various ph-neutral solutions needs to be verified. In conclusion, glucose-based PD fluids aggravate the adipokine production balance from cultured adipocytes and may increase plasma leptin/adiponectin ratio in PD patients. 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