An article published last year described a new appetite suppressing peptide hormone, obestatin (see previous blog and reference here). One interesting feature about this peptide is that it appears to be derived from the same precursor as ghrelin, the hunger hormone elevated in PWS. Thus ghrelin and obestatin were proposed to originate from the same molecule, but have opposing effects - a Yin and Yang of the appetite world.Since that first description of obestatin, there has been some controversy in the literature about the exact role of obestatin and its significance in suppressing appetite, and some newer studies have failed to support a role for obestatin in suppressing appetite. While the exact role of obestatin in controlling appetite and weight remains to be determined, Park and co-workers show in a new paper that children with PWS do not seem to have elevated levels of obestatin in their blood, despite having high levels of ghrelin. (Park WH et al, Obestatin is not elevated or correlated with insulin in children with Prader-Willi Syndrome. J Clin Endrocrinol Metab 2006).
These researchers have examined ghrelin levels before in people with PWS, and here they look at ghrelin, obestatin and insulin levels in 15 children with PWS and 18 controls. They find, as expected, total and acetylated ghrelin are high in children with PWS. For both those with PWS and controls, insulin levels are inversely related to ghrelin levels - this is also an expected result since it has been previously proposed that insulin regulates ghrelin in this manner. As has also been reported, after drinking glucose, insulin levels were lower in kids with PWS compared to controls. But there was much less difference between controls and those with PWS when it came to obestatin. There were no significant differences in obestatin levels in the blood in those with PWS or controls after glucose was given, nor did there seem to be a strong relationship between the levels of obestatin and insulin in either group. The authors conclude that obestatin is not elevated in PWS, nor does obestatin appear to be regulated in the same manner as ghrelin. At this time, then, there does not seem to be strong reason to suspect that obestatin plays a critical role in the excessive appetite associated with PWS.