Leptin Mediates Obesity Hypertension – End Of Story!

Some times you think that a scientific question has long been adequately answered when someone comes along and puts any remaining doubts to rest.

This happened last week, when Stephanie Simonds and an international group of researchers, in a paper published in Cell, present a rather elegant and sophisticated range of studies clearly demonstrating that the adipocyte-derived hormone leptin is a key mediator of hypertension in diet-induced (and probably other types of) obesity.

The reason I thought that this question had already long been put to rest was due to a series of rather convincing animal and human studies published in the early 2000s (some of which I was directly involved in) that nicely demonstrated a) that obesity in hypertension is largely mediated by an increase in (renal) sympathetic activity; b) that leptin stimulates sympathetic activity and sodium retention; c) in dogs and humans leptin concentrations are closely correlated with sympathetic nerve activity and blood pressure. We’ve also known that obese mice lacking leptin or its receptor do not develop hypertension despite considerable weight gain.

If anyone should have any remaining questions, these are now answered in the paper by Simonds and colleagues which uses an array of experiments involving animals deficient in leptin or leptin receptors, humans with loss-of-function mutations in leptin and the LepR and show that leptin’s effects on blood pressure are mediated by neuronal circuits in the dorsomedial hypothalamus (DMH), an effect that is prevented or reversed by blocking leptin with a specific antibody, antagonist, or inhibition of the activity of LepR-expressing neurons in the DMH. 

All of this is interesting and highlights the fact that adipose tissue is far more than a simple storage organ for fat but rather a tissue that plays an active role in the regulation of a wide range of bodily functions.

Leptin alone, just one of the many hormones secreted by fat cells (often collectively referred to as adipokines), has been shown to play an important role in appetite and energy regulation, immune function and bone development.

As for bringing us a step closer to obesity treatments, the study suggests that it may not be easily possible to harness leptin as a treatment for weight loss, as one expected side effect would be an increase in blood pressure and heart rate – effects that have limited the clinical tolerability of other “sympathomimetic” drugs.

@DrSharma
Edmonton, AB