We investigated the influence of salivary leptin, purified by affinity chromatography, on the proliferation of human oral keratinocytes. Furthermore we determined the time-and dose-dependency of the incubation with salivary leptin on the production of epidermal growth factor (EGF) and keratinocyte growth factor (KGF), which are growth factors relevant to keratinocyte proliferation. The analysis was performed both intra-and extracellularly. The relationship between the three cytokines in cell proliferation was studied by successive blocking with specific antibodies. The incubation of oral keratinocytes with recombinant and native leptin led to a significantly increased, dose-dependent cell proliferation (P,0·001). A further significant increase in proliferation was observed after incubating the cells with sterile filtered saliva (P,0·001). The increase in proliferation could not be observed by simultaneous incubation with salivary leptin and specific antibodies against either leptin or KGF (P,0·001). We found a significant dose-dependency between leptin incubation and production of KGF and EGF at the RNA and protein level. Both cytokines were expressed intracellularly and released into the culture medium, where they could be quantified by ELISA. Furthermore, there was a dose-and time-dependent increase in the phosphorylation of STAT-1 and STAT-3, indicating that Ob-R b (the long form of the leptin receptor) expressed by the keratinocytes is functional. It is conceivable that the leptin-induced proliferation in keratinocytes is mediated by this signalling pathway. This is the first study to show a physiological role of salivary leptin as a growth factor for keratinocyte proliferation in the oral cavity. We could demonstrate its influence on the production of other growth factors essential for this proliferative effect. Based on the findings of our study we assume an important role for salivary leptin in wound healing within the vulnerable oral cavity.
The response of insulin, human growth hormone (hGH), cortisol, leptin and ghrelin, in addition to various metabolic parameters, was measured at 10 minute intervals following the oral ingestion of a standardised physiological dose of essential amino acids (AA). Twenty-eight healthy male, fasted volunteers (aged 18-40 yrs, BMI 18·0-24·5 kg/m 2 ) took part in the study; 13 volunteers in the AA group, nine subjects in an iso-caloric control group, and a further six subjects served as fasting controls.Twenty minutes after ingestion, insulin reached peak concentrations that were up to 500% higher than basal values (P,0·0001). The AA group and iso-caloric control group showed a similar insulin response.AA ingestion led to an increase in hGH secretion with maximum concentrations being 2100 1013% higher than the basal values (P,0·0001). In contrast, no changes in hGH concentrations were observed in the iso-caloric controls; in the fasting controls only a slight increase in hGH was found towards the end of the fasting period.While cortisol decreased significantly (P,0·01) during the study in the AA group, neither control group showed a significant change in this parameter.Changes in leptin levels remained insignificant in all three groups, whereas ghrelin showed a different profile in each of the three groups, i.e. a continuous rise towards the end of the study period (P,0·001) in the AA group, a less significant effect for the fasting group, and no effect at all in the iso-caloric control group.There was no significant correlation between the concentrations or the area under curve of the hormones measured in any of the groups.The endocrine data provided in this study indicate that a single bolus of essential AA in fasted individuals is associated with both anabolic and catabolic hormonal responses.
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