Elsevier

Peptides

Volume 26, Issue 4, April 2005, Pages 647-652
Peptides

A comparison of leptin and ghrelin levels in plasma and saliva of young healthy subjects

https://doi.org/10.1016/j.peptides.2004.11.008Get rights and content

Abstract

In the last 10 years, saliva has been increasingly used as a diagnostic fluid and in predictions of disease progression. Leptin and ghrelin are synthesized in several tissues including the salivary glands. The action of ghrelin is antagonistic to that of leptin. This study was undertaken to measure and compare the saliva ghrelin–leptin and plasma ghrelin–leptin levels in healthy young subjects. In 30 healthy subjects, after an overnight fast, saliva and plasma leptin levels were measured using the ELISA method while saliva and plasma immunoreactive ghrelin levels were measured using a commercial radioimmunoassay (RIA). The latter uses 125I-labeled bioactive ghrelin as a tracer and a rabbit polyclonal antibody raised against full-length octanoylated human ghrelin (Phoenix, Europe, Karlsruhe, Germany). The results of this investigation revealed that saliva leptin levels (6.19 ± 2.10 μg/l) were lower than plasma levels (7.39 ± 3.23 μg/l) while saliva ghrelin levels (188.5 ± 84.7 pg/ml) were higher than plasma levels (126.4 ± 38.5 pg/ml), when male and female subjects were considered together. Saliva leptin levels (5.93 ± 1.94 μg/l) were lower than plasma levels (6.22 ± 2.92 pg/ml) while saliva ghrelin levels (190.3 ± 80.2 pg/ml) were higher than plasma levels (120.4 ± 35.7 pg/ml) in young males. Saliva leptin levels (6.47 ± 2.29 μg/l) were lower than plasma levels (8.73 ± 3.14 μg/l) while saliva ghrelin levels (183.2 ± 90.2 pg/ml) were higher than plasma levels (129.3 ± 42.8 pg/ml) in young females, and both saliva and plasma leptin levels were slightly lower in male subjects in comparison with female subjects. Also, Immunohistochemistry study indicated that ghrelin positivity was found in ductus epithelium of salivary gland. We have demonstrated for the first time that saliva ghrelin levels were higher than in plasma while saliva leptin levels were almost the same as in plasma. Measurements of ghrelin and leptin in saliva is non-invasive, simple, and generally much preferred by patients and thus may be an acceptable alternative to plasma sampling.

Introduction

The use of saliva rather than blood for diagnosis has been increased as a diagnostic fluid in the last decade [38]. These include hormones (e.g. DHEA and cortisol), toxins (e.g. heavy metals, such as Pb and Cd) [25], various drugs and their metabolites (e.g. cotinine), measures of mucosal function (e.g. immunoglobulins and enzymes) [39] and leptin [13], [32].

Leptin, which is the product of the obese gene with a single-chain structure and a molecular mass of 16 kDa [6], [20], and expressed predominantly in adipose tissue, is potentially relevant for control of feeding but also to cardiovascular function, insulin secretion, angiogenesis, immune response, bone formation, and haematopoiesis [6], [20]. It is synthesized in the placenta, granulocytes, stomach, and was also recently found to be present in saliva [13], [32]. Leptin and ghrelin (or motilin-related) are complementary, yet antagonistic [4]. Leptin inhibits while ghrelin stimulates appetite in male rats [4], [7] and in human [21] probably by modulating the neuropeptide Y and agouti-related peptide signaling in the hypothalamus [4], [7], [16], [21].

Recently, Tomasetto et al. identified it separately from the stomach as the motilin-related peptide [41], with structural and effect-related similarities to the duodenal hormone motilin that has a key role in the regulation of gastrointestinal motility [10], [41]. Motilin and ghrelin were also known to have a GH-releasing effect [10], [21], [41]. Both stimulate food intake in animals and humans [1], [4], [7], [12], [21], [47]. Based on structural and effect-related similarities, motilin and motilin-related peptide (MTLRP)/ghrelin receptors belongs to the same protein family with gastrin, secretin, pancreatic polypeptide (PP), insulin, epidermal growth factor (EGF), and tachykinin families [23], [36] and shows the same amino acid sequence as ghrelin [21].

With recent discovery of leptin (‘satiety hormone’) [6] and ghrelin (‘hunger hormone’) [22], that are involved in control of appetitive. Interest in these hormones has gained an increase and a number of research activities have been directed at understanding of these peptide hormones. Human ghrelin is a novel peptide hormone, which is predominantly synthesized in the stomach [22], but it is also synthesized in several other tissues, including in the central nervous system, kidney, heart, parathyroid glands, small and large intestine, α-cells of pancreatic islet [46], placenta [8]. It stimulates growth hormone (GH) secretion and acts as a signal for the regulation of food intake and energy expenditure and fat accumulation, and thereby contribute to the control of body weight gain [44]. Circulating ghrelin levels are elevated after fasting [9], and lean people tend to have high circulating ghrelin concentrations [14], and exerts orexigenic effects [2], [21]. Thus, defective ghrelin signaling from the stomach could contribute to abnormalities in growth, energy balance, and associated gastrointestinal and neuroendocrine functions [21].

Ghrelin also indicated to have stimulatory effects on plasma epinephrine [31]. This is consistent with the effects of hexarelin (HEX), a synthetic GH-releasing peptide in patients with chronic heart failure (CHF) [27], [29]. Previous studies have exhibited that GH and its mediator, IGF-1, induce myocardial growth and increase myocardial contractility [33]. Thus, ghrelin may have beneficial effects in patients with CHF via its GH-releasing effects [5], [27], [40]. Stimulation of GHS-R by hexarelin, a synthetic GHS, has been showed to prevent cardiac damage after ischemia-reperfusion in hypophysectomized rats [42].

To the best of our knowledge, although ghrelin is discovered in 1999, no data on saliva ghrelin levels in human are available at present. Therefore, the aim of this study was to measure and compare the saliva ghrelin–leptin and plasma ghrelin–leptin levels in healthy young subjects and evaluate whether the saliva and plasma levels are correlated.

Section snippets

Subjects, sample collection, preparation, storage and analysis

We studied 14 female and 16 male medical students in age of 19 (±0.0) at F.U. School of Medicine. All subjects were healthy and matched for age and body mass index (BMI). Exclusion criteria were as follows: pregnancy, use of any drugs, BMI >25 kg/m2, alcohol consumption of >1 drinks per day, diabetes (even family history), use of tobacco products (former and current), regular intense exercise (>15 min of aerobics three times per week), chronic medical illness, and family history of obese. None of

Discussion

In the last 10 years, the use of saliva, rather than blood for diagnosis, has become somewhat of a translational research success story [11], [14], [15]. Because the collection of saliva is non-invasive, and generally much preferred by individuals [15]. In the present study, we examined saliva leptin and ghrelin levels. We found that saliva leptin concentrations were slightly lower than in plasma [6.19 ± 2.1 μg/l versus 7.39 ± 3.23 μg/l, respectively] as has been showed by others [13], [32],

Acknowledgements

We thank Bora Ozkan and the students of Medical School of Firat University for their participation, Michael Lin for technical assistance, Phoenix Pharmaceuticals Inc., USA, and Dr. Benjamin Stark for some grammar works at IIT, Chicago, USA.

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    This work was presented as a poster at the 18th meeting of the Turkish Biochemical Societies held in Trabzon, Turkey, 15–19 May 2004.

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