Subcutaneous Ghrelin Enhances Acute Food Intake in Malnourished Patients Who Receive Maintenance Peritoneal Dialysis: A Randomized, Placebo-Controlled Trial
Katie Wynne*,
Kalli Giannitsopoulou*,
Caroline J. Small*,
Michael Patterson*,
Gary Frost*,
Mohammad A. Ghatei*,
Edwina A. Brown,
Stephen R. Bloom* and
Peter Choi
* Department of Metabolic Medicine, Faculty of Medicine, Imperial College London, Hammersmith Hospital; and Directorate of Renal and Transplant Medicine, Hammersmith Hospitals NHS Trust, Charing Cross Hospital, London, United Kingdom
Address correspondence to: Dr. Peter Choi, Renal Services, Ground Floor Pilot Wing, Charing Cross Hospital, Fulham Palace Road, London W6 8RF, UK. Phone: +44-208-846-1754; Fax: +44-208-846-7589; E-mail: p.choi{at}imperial.ac.uk
Received for publication January 11, 2005.
Accepted for publication March 29, 2005.
Anorexia and malnutrition confer significant morbidity and mortalityto patients with end-stage kidney disease but are resistantto therapy. The aim of this study was to determine whether subcutaneousadministration of ghrelin, an appetite-stimulating gut hormone,could enhance food intake in patients who are receiving maintenanceperitoneal dialysis and have evidence of malnutrition. The principaloutcome measure was energy intake during a measured study meal.Secondary outcome measures were BP and heart rate and 3-d foodintake after intervention. Nine peritoneal dialysis patientswith mild to moderate malnutrition (mean serum albumin 28.6± 5.0 g/L, total cholesterol 4.4 ± 0.6 mmol/L,subjective global assessment score of 5.7 ± 1.7) weregiven subcutaneous ghrelin (3.6 nmol/kg) and saline placeboin a randomized, double-blind, crossover protocol. Administrationof subcutaneous ghrelin significantly increased the group meanabsolute energy intake, compared with placebo, during the studymeal (690 ± 190 versus 440 ± 250 kcal; P = 0.0062).When expressed as proportional energy increase for each individual,ghrelin administration resulted in immediate doubling of energyintake (204 ± 120 versus 100%; P = 0.0319). Administrationof ghrelin maintained a nonsignificant increase in energy intakeover 24 h after intervention (2009 ± 669 versus 1579± 330 kcal) and was not followed by subsequent underswing(1790 ± 370 versus 1670 ± 530 and 1880 ±390 versus 1830 ± 530 kcal on days 2 and 3, respectively).Ghrelin administration resulted in a significant fall in meanarterial BP (P = 0.0030 by ANOVA). There were no significantadverse events during the study. Subcutaneous ghrelin administrationenhances short-term food intake in dialysis patients with mildto moderate malnutrition.
End-stage kidney disease is a chronic condition associated witha high prevalence of nutritional dysfunction (1). This malnutritionis resistant to intervention (2) and is a major predictor ofmorbidity and mortality in patients who receive both peritonealdialysis (PD) and hemodialysis (3,4). There is a linear correlationbetween body mass index (BMI) and survival in dialysis patients(5), to the extent that the usual association of increased mortalitywith obesity is reversed in patients who receive renal replacementtherapy (6). Nutritional parameters that have been correlatedindependently with increased mortality and morbidity includelow serum albumin (4,7,8), low serum cholesterol (7,9), anda low measured subjective global assessment score of nutrition(4,10).
Malnutrition in chronic kidney disease is multifactorial, butreduced protein and energy intake play an important role (1).Patients with kidney failure experience a complex anorexic syndromethat is evident early in the course of the disease, before therequirement for dialysis (11), including patients with a GFR>50 ml/min per 1.73 m2 (12). Reduced dietary energy and proteinintake is common in patients who are on maintenance PD and hemodialysis(1), and inadequate dietary intake correlates with poor nutritionaloutcomes (13). The effects of diminished dietary energy intakein some PD patients may be offset by increased glucose absorptionfrom peritoneal dialysate (14). Proposed mechanisms for anorexiainclude derangement of gut hormones, reduced gastric emptying,and the anorectic effects of cytokines and uremic toxins (1).
The hormone ghrelin, principally secreted from the stomach (15),is thought to function as an appetite enhancer (16). Ghrelinis also important in long-term body weight regulation, as circulatingghrelin levels are inversely correlated with energy balance(17) and chronic ghrelin administration results in weight gainin animal models (18). Ghrelin mediates its orexigenic actionvia the type 1a growth hormone secretagogue receptor (15). Ligationof this receptor also results in release of growth hormone,although the appetite-enhancing effect of ghrelin is independentof growth hormone (19). The activity of ghrelin is dependenton acylation of the third serine residue (20). Secreted acylatedghrelin exerts orexigenic effect but is rapidly converted inthe circulation to deacylated ghrelin, which does not activatethe type 1a growth hormone secretagogue receptor and is notknown to exhibit orexigenic effect or endocrine activity (15,20).
Intravenous infusion of ghrelin stimulates appetite in healthyvolunteers (21) and cancer patients (22). Therefore, we hypothesizedthat subcutaneously administered ghrelin could enhance acutefood intake among PD patients with evidence of malnutritionand provide the potential for practical therapeutic intervention.
Patients
Malnourished patients, between the ages of 18 and 55 yr, wererecruited from the PD unit of Hammersmith Hospitals NHS Trust,which forms part of the West London Renal Centre. Thirty-eighteligible patients were invited to participate; 11 were interviewed,and nine patients consented to trial participation. The trialwas performed between January and July 2004. Patients were definedas malnourished when they demonstrated two of three qualifyingcriteria: Serum albumin <35 g/L by Bromcresol Purple (normalrange 35 to 48) with normal C-reactive protein, serum cholesterol<4.5 mmol/L, or subjective global assessment (SGA) score6/7 (23). A modified seven-point SGA score (severe malnutrition1 to 2; mild to moderate malnutrition 3 to 5; mild malnutritionto well nourished 6 to 7) was used (4). Patients with a historyof diabetes or coronary or cerebrovascular disease were excludedto minimize risk for intercurrent events. Factors that couldconfound food intake analysis, such as psychologic food aversion,abdominal discomfort during PD exchanges, dialysis fills <1L, and recent initiation of PD (<6 mo), were also exclusioncriteria. The Riverside Medical Ethics Committee approved theprotocol (reference number 3721). Participants gave writtenconsent, and the study was performed in accordance with theDeclaration of Helsinki.
Protocol
The study was performed as a randomized, double-blind, placebo-controlled,crossover protocol in a dedicated clinical trials unit at CharingCross Hospital. Before initiation, patients attended a shamstudy session to acclimatize to study conditions and to ensurepalatability of the study meal, which was assessed using a nine-pointhedonistic scale. On subsequent study visits, patients receivedan injection of 3.6 nmol/kg subcutaneous ghrelin or saline inrandom order, separated by at least 7 d. A subcutaneous doseof 3.6 nmol/kg ghrelin was chosen as the smallest effectivedose from a dose-response pilot study performed in healthy volunteers(Dr. N. Neary and Dr. M. Druce, Department of Metabolic Medicine,Imperial College London, UK, personal communication, November2003). An independent physician performed the randomizationof injection sequence.
On the day before each study meal, patients refrained from alcoholand strenuous exercise, consumed a standard-calorie prefastmeal, and then fasted overnight from 9 p.m. On each study day,patients received their injection at 11.30 a.m. and were providedwith their selected meal in excess at 12:00 p.m. The patientswere placed in isolation and requested to eat until they feltcomfortably full. The study meal, of known caloric content,was weighed before and after ad libitum feeding to measure energyintake. Each individual received an identical meal at each studyvisit. The average calorie density of meals was 620 kcal/100g. Water intake was also measured during this period. Throughoutthe study, participants were encouraged to relax by readingor watching films. Clocks were removed from the study room tolimit the effect of meal anticipation on appetite sensation.Visual analogue scales, 100 mm in length, were recorded at baselineand subsequently every 30 min to evaluate subjective feelingsof hunger, nausea, and meal palatability. BP and heart ratewere measured and serial blood samples were taken for hormoneassays at baseline and at 15, 30, 60, 75, and 90 min after injection.All blood samples were collected from an antecubital fossa cannulainto lithium/heparin tubes (LIP Ltd., Cambridge, UK) that contained2000 kallikrein inhibitor units of aprotinin (Trasylol; Bayer,Newbury, UK) and stored on ice. After centrifugation, plasmawas separated immediately and stored at 20°C untilanalysis. Diaries of food consumption were recorded by eachparticipant for 72 h after each study visit. Study participantsreceived careful guidance regarding completion of their fooddiaries, and caloric intake was estimated by decoding diarieswith Dietplan-5 (Forestfield Software, Horsham, West Sussex,UK) nutritional analysis software.
Materials
The synthesized human ghrelin (GSSFLSPEHQRVQQRKESKKPPAKLQPR;Bachem St. Helens, UK) was sterile on culture after 7 d, andthe limulus amoebocyte assay for pyrogen was negative (Associatesof Cape Cod, Liverpool, UK). A 10-fold dose (36 nmol/kg) ofghrelin was administered to C57BL/6 mice for toxicity testing;behavioral observation and blinded histologic examination revealedno abnormalities. The orexigenic bioactivity of synthesizedhuman ghrelin was confirmed by administration to a cohort ofmale Wistar rats. On each study day, a blinded physician preparedthe injections by the addition of sterile water to freeze-driedvials of ghrelin or saline. The participants received 0.2 mlof the dissolved substance into their abdominal subcutaneoustissue with the use of a 27-gauge needle.
Hormone Measurements
Total ghrelin, insulin, and peptide YY were measured using establishedin-house RIA (2426). All samples were assayed in duplicateand within one assay to eliminate interassay variation. Theghrelin assay cross-reacted fully with acylated and deacylatedhuman ghrelin but did not cross-react with any other gastrointestinalor pancreatic peptide hormones. Briefly, antiserum (SC-10368)was obtained from Santa Cruz Biotechnology (Santa Cruz, CA)and used at a final dilution of 1:50,000. The 125I ghrelin wasprepared with Bolton & Hunter reagent (Amersham International,Little Chalfont, UK) and purified by RP-HPLC using a lineargradient from 10 to 40% acetonitrile and 0.05% TFA over 90 min.The specific activity of ghrelin label was 48 Bq/fmol. The assaywas performed in total volume of 0.7 ml of 0.06 M phosphatebuffer (pH 7.2) that contained 0.3% BSA and was incubated for3 d at 4°C before separation of free and bound antibodyby charcoal absorption. The ghrelin assay was able to detectchanges of 8 pmol/L (95% confidence interval [CI]) with an intra-assayvariation of 9.5%. The insulin assay was able to detect changesof 6 pmol/L (95% CI) with an intra-assay variation of 5.4%.The peptide YY assay was able to detect changes of 2 pmol/L(95% CI) with an intra-assay variation of 5.8%. A commerciallyavailable assay was used to measure plasma leptin (Linco Research,St. Charles, MO). Growth hormone was analyzed using an Advantageautomated chemiluminescent immunoassay (Nichols Institute Diagnostics,San Juan Capistrano, CA), and glucose levels were measured byan Olympus AU640 clinical chemistry analyzer (Melville, NY).
Statistical Analyses
Blinded analysis of food diary data was performed using Dietplan-5nutritional analysis software. Statistical comparisons betweentreatments for food intake, preprandial visual analogue scores,and hormone levels were made using nonparametric paired t test.Comparison of repeated measurements of BP and subjective measuresof nausea and fatigue were performed by two-way ANOVA. Statisticalanalysis was performed with Prism software (version 3.0; GraphPadSoftware, San Diego, CA). All values are expressed as mean ±SE.
Five female and four male patients, mean age 49.8 ± 1.7yr, agreed to participate in the study, and all nine completedthe protocol. Demographic and nutritional parameters are displayedin Table 1. All patients were in a clinically stable condition.Mean serum albumin for the group was 28.6 ± 1.7 g/L,with mean total cholesterol of 4.4 ± 0.2 mmol/L and meanSGA score of 5.7 ± 1.7. Six participants fulfilled allqualifying criteria for malnutrition, and three individualsfulfilled two of three criteria. No patient had a serum albuminwithin the normal range, although all patients had a C-reactiveprotein level within the normal range. The mean BMI was 24.7± 1.5 kg/m2.
Table 1. Study participants demographic and nutritional parametersa
The National Kidney Foundations Dialysis Outcomes QualityInitiative (27) and the UK Renal Associations targetcreatinine clearance of 60 L/wk per 1.73 m2 (28) was achievedby all patients. Mean duration of PD was 42.7 ± 12.2mo, and no patient had experienced peritonitis within 6 mo ofthe trial. Throughout the study period, there were no changesin dialysis delivery between the study interventions for anypatient. Specifically, each patient presented for his or herstudy meals with identical dialysate volume and glucose concentrations.There was no deviation from study timings, and each study participantreceived his or her meals at identical intervals after his orher last instillation of dialysis fluid.
Administration of subcutaneous ghrelin increased energy intakeduring the study meal in eight of nine patients (Figure 1A).Significant differences in group mean absolute energy intakewere observed between administration of subcutaneous salineand ghrelin (440 ± 250 versus 690 ± 190 kcal,respectively; P = 0.0062; Figure 1A). When expressed as proportionalenergy increase for each individual, ghrelin administrationresulted in doubling of energy intake (100 versus 204 ±120%; P = 0.0319; Figure 1B). There were no significant differencesin water intake after saline or ghrelin administration (132± 26 versus 165 ± 46 ml; P = 0.4573).
Figure 1. Energy intake after administration of subcutaneous saline or 3.6 nmol/kg ghrelin. (A) Absolute energy intake for individual participants during study meals, with mean absolute energy intake represented by the bold line. Data were analyzed by nonparametric paired t test. (B) Proportional increase in energy intake for each participant during study meals, with mean absolute energy intake represented by the bold line. Energy intake after saline injection was ascribed a value of 100%. Data were analyzed by nonparametric paired t test.
Visual analogue scores of subjective parameters of appetitewere recorded before and after administration of the study injection(Figure 2). Administration of ghrelin was associated with changesin visual analogue scores, which were consistent with a subjectiveincrease in preprandial appetite (Figure 2, A through D). However,in comparison with changes observed after saline administration,the observed differences in appetite scores after ghrelin administrationdid not achieve statistical significance for the subjectivescores of hunger (saline 9 ± 3 mm versus ghrelin 14 ±4 mm; P = 0.2668; Figure 2A), desire to eat (saline 6 ±5 mm versus ghrelin 11 ± 4 mm; P = 0.4905; Figure 2B),fullness (saline 4 ± 4 mm versus ghrelin 10 ±5 mm; P = 0.0972; Figure 2C), and expected food consumption(saline 4 ± 3 mm versus ghrelin 12 ± 3 mm; P =0.2014; Figure 2D).
Figure 2. Subjective measures of appetite, nausea, and fatigue after administration of subcutaneous saline (dotted line) or 3.6 nmol/kg ghrelin (solid line). (A through F) Change from baseline values of visual analogue scores. Patients recorded their subjective assessment in response to a questionnaire asking (A) "How hungry do you feel?" (B) "How pleasant would it be to eat?" (C) "How full do you feel?" (D) How much do you think you can eat?" (E) "How nauseated do you feel?" (F) "How sleepy do you feel?" The injection was administered at 0 min, and the study meal was provided at 30 min.
There was a nonsignificant trend for enhanced meal enjoymentafter ghrelin administration when assessed by postprandial foodpalatability score (saline 57 ± 8 mm versus ghrelin 65± 7 mm; P = 0.0921). Throughout the study period, therewere no significant differences in nausea (P = 0.2171 by ANOVA;Figure 2E) or fatigue (P = 0.9294 by ANOVA; Figure 2F) betweensaline and ghrelin administration.
Blinded analysis of food diaries, completed by the patientsover the 3 d after injection, suggested that increased energyintake after ghrelin administration was maintained over 24 h,although this was nonsignificant (saline 1579 ± 130 kcalversus ghrelin 2009±250 kcal; P = 0.0645; Figure 3).Importantly, the increase in energy intake after ghrelin administrationwas not followed by an underswing (saline 1670 ± 210kcal versus ghrelin 1790 ± 140 kcal; saline 1830 ±220 kcal versus ghrelin 1880 ± 150 kcal on days 2 and3, respectively; Figure 3).
Figure 3. Energy intake calculated from diaries of food consumption, up to 72 h after administration of subcutaneous saline or 3.6 nmol/kg ghrelin.
Patients with end-stage kidney disease demonstrated significantlyhigher circulating leptin levels (214.3 ± 4.6 pmol/L)than 16 BMI-matched healthy subjects (80.0 ± 2.0; P <0.0001). Baseline hormonal analysis also revealed that studyparticipants had significantly higher endogenous total plasmaghrelin immunoreactivity (1076 ± 92 pmol/L) than BMI-matchedhealthy control subjects (738 ± 104 pmol/L; P = 0.0330).After administration of subcutaneous ghrelin, the patientstotal plasma ghrelin immunoreactivity increased, reached a plateauat 30 min (mean 12737 ± 3300 pmol/L; range 142125787pmol/L), and started to fall after 75 min (Figure 4). As expected,growth hormone concentrations also increased from baseline (2.6± 0.6 IU/L) and peaked at 30 min (70.3 ± 13.0IU/L), indicating that the administered exogenous ghrelin wasbioactive (Figure 4).
Figure 4. Plasma ghrelin immunoreactivity (solid line) and growth hormone levels (dotted line) after ghrelin administration. The injection was administered at 0 min, and the study meal was provided at 30 min.
Administration of ghrelin was not associated with changes inpreprandial insulin levels (saline 86.2 ± 25.5 pmol/Lversus ghrelin 82.3 ± 14.7 pmol/L; P = 0.7957), preprandialglucose concentration (saline 4.33 ± 0.09 mmol/L versusghrelin 4.56 ± 0.12 mmol/L; P = 0.2209), or peptide YYlevels (saline 54.4 ± 8.4 pmol/L versus ghrelin 51.3± 8.4 pmol/L; P = 0.6571) 30 min after injection. Administrationof ghrelin was associated with a significant decline in meanarterial pressure from a baseline 110.4 ± 6.5 mmHg (P= 0.0030 by ANOVA; Figure 5A), diastolic BP from mean baseline88.6 ± 4.2 mmHg (P = 0.0039 by ANOVA; Figure 5D), anda nonsignificant trend toward fall in systolic BP from meanbaseline 132.1 ± 9.4 mmHg (P = 0.0747 by ANOVA; Figure5C). The change in BP was evident within 15 min of ghrelin administrationand was maintained for the 90-min observation period. No symptomatichypotension occurred during the study. Administration of ghrelinwas not associated with a change in pulse rate (P = 0.2358 byANOVA; Figure 5B). There were no adverse events during the studyperiod.
Figure 5. BP during the study meal, after administration of saline (dotted line) or 3.6 nmol/kg subcutaneous ghrelin (solid line). The change from participants baseline mean arterial BP, pulse rate, and systolic and diastolic BP is shown in A, B, C, and D, respectively. All data were analyzed by a two-way ANOVA.
Subcutaneous ghrelin administration resulted in a two-fold increasein short-term energy intake for each individual in a cohortof mildly to moderately malnourished PD patients. The mean absoluteenergy intake for the group increased from 440 ± 80 to690 ± 60 kcal after a 10-fold increase in circulatingghrelin levels. The immediate increase in energy intake at thestudy meal was followed by a trend toward increased energy intakeover the following 24 h (Figure 3). Importantly, there was nosubsequent compensatory reduction in energy intake over thefollowing 72 h, which would negate any potential therapeuticbenefit of chronic administration.
We demonstrated elevated endogenous total ghrelin levels inthis cohort of PD patients, compared with BMI-matched healthyindividuals, in agreement with observations by Perez-Fontanet al. (29) and Ayala et al. (30). Although there are high endogenouslevels of total ghrelin, dietary energy intake is paradoxicallyreduced in PD patients. There are a number of possible explanations.First, this may reflect other abnormalities of appetite signaling,which are present in patients with kidney disease. For example,the current study also demonstrated elevated circulating leptinlevels in PD patients, in keeping with previous observations(31,32), and inappropriately elevated leptin concentrationsare associated with weight loss (33). Dialysis patients alsodisplay abnormally high concentrations of other anorectic gutpeptides that may contribute to appetite loss and gastrointestinaldysfunction, including motilin, somatostatin, peptide YY, vasoactiveintestinal peptide, pancreatic polypeptide (34), and cholecystokinin(35). Second, recent evidence suggests that the ratio of deacylatedto acylated ghrelin is disordered in kidney disease and is amore potent driver of renal anorexia than total ghrelin immunoreactivity(36).
Despite the disordered endocrine system demonstrated in patientswith kidney disease, this study demonstrates that the orexigeniceffect of exogenous ghrelin administration is retained in patientswith kidney disease and that there is no apparent ghrelin resistanceassociated with elevated total endogenous ghrelin levels. Indeed,we demonstrated a greater increase in food intake than previoustrials of intravenously administered ghrelin to healthy individualsand anorexic cancer patients (21,22). This may reflect the highcirculating total ghrelin levels achieved and subsequent correctionof a disordered deacylated to acylated ghrelin ratio.
A significant fall in mean and diastolic BP was observed duringstudy sessions, without symptomatic hypotension or reflex tachycardia.This effect seemed additive to the patients ongoing antihypertensivetherapy, which was not altered during the study; eight of ninepatients were regularly taking antihypertensive medication,five of these requiring multiple therapy. A reduction in BPwas seen throughout the study meal period and is in accordancewith previous observations concerning the beneficial effectsof intravenous ghrelin on BP and cardiac output in healthy volunteersand patients with heart failure (37,38). There is a close associationbetween malnutrition and cardiovascular death in patients withend-stage kidney disease (39). In addition, emerging data alsosuggest an anti-inflammatory role for ghrelin (40). Ghrelinreceptor ligation on T cells and monocytes inhibits the expressionof proinflammatory anorectic cytokines such as IL-1, IL-6, andTNF- and is hypothesized to provide a link between the metabolicaxis and immune system (41). Epidemiologic data reveal an intimaterelationship among inflammation, malnutrition, and cardiovascularoutcomes (42,43). Thus, a therapy that is able to improve energyintake, reduce inflammation, and enhance cardiovascular functionwould be of great value to patients with kidney disease.
This study was designed as a short-term, single-dose analysisof the effects of ghrelin administration to establish efficacy.Patients with established cardiovascular disease were excludedto minimize adverse events; thus, few patients with severe wastingnutritional deficiency were eligible. However, it is these patientswho are most likely to derive the greatest clinical benefitfrom treatment, and further investigation is needed to establishthe efficacy of exogenous ghrelin within this high-risk group.Nonetheless, we have shown clearly that subcutaneous ghrelinadministration is able to increase substantially acute spontaneousenergy intake in mildly to moderately malnourished patientswho receive maintenance PD. Long-term ghrelin administrationmay have the potential to improve nutritional parameters andpatient outcomes. Longer term studies are now required.
Acknowledgments
We thank Dr. Nicola Neary and Dr. Maralyn Druce for sharingunpublished pilot data. We also thank Professor Malcolm Alisonfor reviewing murine histology during toxicology testing. Weare indebted to the patients who agreed to participate in thestudy.
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Fung F, Sherrard DJ, Gillen DL, Wong C, Kestenbaum B, Seliger S, Ball A, Stehman-Breen C: Increased risk for cardiovascular mortality among malnourished end-stage renal disease patients.
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Li WG, Gavrila D, Liu X, Wang L, Gunnlaugsson S, Stoll LL, McCormick ML, Sigmund CD, Tang C, Weintraub NL: Ghrelin inhibits proinflammatory responses and nuclear factor-kappaB activation in human endothelial cells.
Circulation 109
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Dixit VD, Schaffer EM, Pyle RS, Collins GD, Sakthivel SK, Palaniappan R, Lillard JW Jr, Taub DD: Ghrelin inhibits leptin- and activation-induced proinflammatory cytokine expression by human monocytes and T cells.
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Qureshi AR, Alvestrand A, Vino-Filho JC, Gutierrez A, Heimburger O, Lindholm B, Bergstrom J: Inflammation, malnutrition, and cardiac disease as predictors of mortality in hemodialysis patients.
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Received for publication January 11, 2005.
Accepted for publication March 29, 2005.
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