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BRIEF REPORT |
Department of Psychiatry, University of Naples, Largo Madonna delle Grazie, 80138 Naples, Italy
Address all correspondence and requests for reprints to: Palmiero Monteleone, M.D., Department of Psychiatry, University of Naples, Largo Madonna delle Grazie, 80138 Naples, Italy. E-mail: monteri{at}tin.it.
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Abstract |
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Methods: In the present study, we measured circulating blood levels of obestatin and ghrelin and assessed their relationships with anthropometric and clinical measures in 20 AN patients, 21 BN patients, and 20 appropriate healthy controls.
Results: Compared with healthy women, patients with BN showed no significant differences in plasma obestatin and ghrelin concentrations and in the ghrelin/obestatin ratio, whereas underweight AN patients displayed significantly increased circulating levels of both obestatin (P < 0.009) and ghrelin (P < 0.002) and an increased ghrelin/obestatin ratio (P < 0.04). Moreover, in AN women, positive correlations emerged between the ghrelin/obestatin ratio and current body weight and body mass index.
Conclusions: Underweight AN patients are characterized by increased concentrations of ghrelin and obestatin and a higher ghrelin to obestatin ratio. No changes in circulating ghrelin or obestatin as well as in ghrelin to obestatin ratio seem to occur in acutely ill patients with BN. Although those changes likely reflect the physiological state of symptomatic AN individuals, they may also contribute to the pathophysiology of the disorder.
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Introduction |
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Ghrelin has been suggested to be involved in the pathophysiology of anorexia nervosa (AN) and bulimia nervosa (BN). Indeed, baseline plasma ghrelin concentrations and plasma ghrelin responses to calorie ingestion have been found to be deranged in both underweight AN subjects and symptomatic BN patients (5).
Based on the above reported connection between ghrelin and obestatin, it seems plausible that obestatin may be a further candidate to the pathophysiology of eating disorders. Therefore, to shed light on the putative role of obestatin in AN and BN, we measured circulating blood levels of obestatin and ghrelin and assessed their relationships with anthropometric and clinical measures in patients with AN or BN and in appropriate healthy controls.
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Patients and Methods |
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Control women were recruited among medical students; they had no current or past DSM-IV Axis I disorder, as assessed by the SCID-I nonpatient edition (7), were regularly menstruating, and had normal eating habits; all of them were drug-free for more than 8 wk.
Female controls and patients who were normally menstruating were tested in the follicular phase of their menstrual cycle (d 5–10 from menses).
The local ethic committee approved the study and collection of blood samples from healthy controls; subjects gave written informed consent before study participation.
All subjects underwent a blood sample collection by venipuncture between 0800 and 0900 h after an overnight fast; blood was collected in tubes containing disodium EDTA and aprotinin (500 U/ml) and was immediately centrifuged. Plasma was separated and stored at –80 C until assayed.
Ghrelin was measured by a commercial ELISA kit (Phoenix Pharmaceuticals Inc., Burlingame, CA); intra- and interassay coefficients of variation (CV) were less than 5% and less than 9%, respectively. Obestatin was measured by a commercial ELISA kit (Peninsula Laboratories Inc., San Carlos, CA); intra- and interassay CV were less than 5% and less than 9%, respectively. Leptin was determined by a commercial ELISA kit (Alexis Biochemicals, Laufelfingen, Switzerland); intra- and interassay CV were 6.1 and 8.5%, respectively. The ghrelin to obestatin ratio was calculated (8).
The BMDP statistical software package (9) was used for data analysis. There was no significant deviation from normality in obestatin, ghrelin, and ghrelin/obestatin ratio values in each group as assessed by means of the Shapiro Wilk normality test. One-way ANOVA and the Pearson’s correlation test were used where appropriate.
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Results |
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) but significantly lower leptin levels [F(1,38) = 47.22; P < 0.0001] (Table 1
), whereas BN women had similar circulating levels of obestatin [74.9 ± 22.4 vs. 68.3 ± 14.8 pg/ml; F(1,39) = 1.15; P = 0.2], ghrelin [217.4 ± 111.8 vs. 221.1 ± 95.6 pg/ml; F(1 39) = 1.01; P = 0.9] (Fig. 1) and leptin [F(1,39) = 0.68; P = 0.4] (Table 1). The ghrelin/obestatin ratio was significantly higher in AN women [F(1,38) = 4.31, P < 0.045] but not in BN patients [F(1,39) = 0.42; P = 0.5] (Fig. 1). No significant difference in plasma obestatin, ghrelin, and leptin levels as well as in the ghrelin/obestatin ratio emerged between AN-R and AN-BP patients.
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Discussion |
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Literature studies are consistent with present findings on ghrelin and leptin changes in AN and BN patients (5), although decreased leptin concentrations in BN were detected in a previous study of ours (10). Differences in the severity and/or length of the patients’ illness have been suggested to explain this discrepancy (10). To the best of our knowledge, no study reported on obestatin levels in symptomatic BN patients, whereas, according to our results, Harada et al. (11) and Nakahara et al. (12) showed increased plasma obestatin and ghrelin concentrations in small groups of AN patients compared with age-matched healthy women. None of these two studies, however, calculated the ghrelin/obestatin ratio and assessed its relationships with nutritional parameters.
Zhang et al. (2) initially suggested a role of obestatin as an antagonist of the ghrelin actions in energy homeostasis. These observations have been confirmed by some authors but questioned by others (3, 4), and controversies still exist on the definite effects of obestatin on food intake/energy balance as well as on the measurements of the hormone levels in the human blood (13). Nonetheless, if one assumes the suggested role of obestatin as an antagonist of ghrelin actions, one would expect opposite changes of these peptides in pathological conditions characterized by alterations in energy balance. Therefore, in underweight AN patients, decreased levels of obestatin would be expected. Present findings and literature data show that this is not the case. On the other hand, in obese patients who show decreased fasting plasma ghrelin levels (8, 14) and were expected to have enhanced obestatin, circulating obestatin concentrations have been found to be reduced by most although not all of the authors (8, 15). Therefore, present findings and literature data show parallel changes in ghrelin and obestatin secretion in pathological conditions characterized by energy imbalance, suggesting that dysregulated metabolic states may potentially affect the preproghrelin gene expression and/or the splicing of its products and that the conclusive effect on food intake and energy homeostasis could depend upon the ratio between ghrelin and obestatin peptides.
Therefore, it might be hypothesized that in underweight AN subjects, an enhanced expression of the preproghrelin gene leads to an enhanced production of ghrelin and obestatin, which likely does not occur on a one to one ratio, with the consequent increase in the ghrelin/obestatin ratio. Mechanisms responsible for such an imbalance of ghrelin to obestatin production are not clear, because little is known about the posttranslational cleavage of the preproghrelin peptide. Nonetheless, the increased ghrelin to obestatin ratio would result in a potentiation of the peripheral orexigenic signal, which aims to oppose the patient’s over-control on her food intake. This hypothesis seems to be corroborated by the finding of significant positive correlations between the ghrelin/obestatin ratio and BW measures in our AN group, which may suggest that when the hunger signal of ghrelin is stronger than the satiety signal of obestatin, as expressed by higher values of the ghrelin/obestatin ratio, then AN patients are able to reach higher BW likely because of an increased drive to eat. Recently, in a family trios study assessing the transmission of two single-nucleotide polymorphisms (SNP) of the preproghrelin gene in AN probands, it has been found that patients carrying the obestatin Gln90Leu SNP had a lower lifetime BMI compared with the homozygotes for the wild allele (16). Although the functional significance of this SNP is not known, one could speculate that if it was responsible for enhanced obestatin secretion/activity, the association with a lower lifetime BMI might strengthen our hypothesis that the balance between ghrelin and obestatin activities is crucial for BW regulation in AN.
A potential limitation of our study is that we measured total obestatin, that is both amidated and nonamidated peptide, and total ghrelin, that is both acyl- and desacyl-ghrelin. Amidation of obestatin is likely essential for its biological activity as well as acylation of ghrelin. Because desacyl-ghrelin, similarly to obestatin, provides opposing effects to acyl-ghrelin on appetite and gastrointestinal motility (17), different results might emerge if the two forms of peptides are measured. A second limitation of the present study is represented by the low number of AN-R patients with respect to AN-BP individuals. Because in AN-BP subjects, ghrelin concentrations have been reported to be higher than in AN-R ones (18), we cannot exclude that the prevalence of binge-purging subjects in our sample might cause higher ghrelin/obestatin ratio. However, other studies failed to find increased levels of ghrelin in binge-purging anorexics compared with restricted ones (19, 20), and we could not detect any significant difference in hormone levels between the two subtypes of AN individuals.
In conclusion, this study shows that underweight AN patients are characterized by increased concentrations of ghrelin and obestatin and a higher ghrelin to obestatin ratio, which was positively correlated with BW measures. Although these changes likely reflect the physiological state of symptomatic AN individuals, they may also contribute to the pathophysiology of the disorder. No changes in circulating ghrelin or obestatin as well as in ghrelin to obestatin ratio seem to occur in acutely ill patients with BN.
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Footnotes |
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First Published Online August 26, 2008
Abbreviations: AN, Anorexia nervosa; AN-BP, AN binge and/or purge; AN-R, AN food restrictor; BN, bulimia nervosa; BMI, body mass index; BW, body weight; CV, coefficient of variation; SNP, single-nucleotide polymorphism.
Received May 27, 2008.
Accepted August 14, 2008.
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