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Phil B.FontanarosaMD, Deputy EditorIndividualAuthorStephen J.LurieMD, PhD, Fishbein FellowIndividualAuthor
To the Editor: Dr Heymsfield and colleagues1 documented the effect of exogenous leptin administration
on body weight and showed that only patients in the highest dose groups had
significant weight loss compared with those taking placebo. We suggest that
the physiological characteristics of leptin may be relevant to its pharmacokinetics.
Diurnal and ultradian oscillations are essential characteristics of
hormone secretion. Leptin is characterized by nyctohemeral rhythms, with serum
leptin concentrations being highest around midnight.2
This pattern closely resembles the circadian rhythmicity of other hormones,
such as thyrotropin and prolactin, and precedes the peak concentrations of
cortisol and growth hormone. To what extent the nocturnal increase in leptin
is related to biological activity remains to be clarified. In humans, the
nocturnal increase in leptin secretion seems to be entrained to meal timing
and most likely is related to the cumulative hyperinsulinemia from food ingestion
during the entire waking period.
Superimposed on the circadian rhythm, total circulating leptin levels
exhibit a pattern indicative of pulsatile release with a pulse duration of
approximately 30 minutes and are inversely related to rapid fluctuations in
plasma cortisol and adrenocorticotropic hormone levels.3
Pulsatility is crucial for the attainment of biological effects in several
endocrine systems (eg, luteinizing hormone-releasing hormone and growth hormone).
Thus, for maximal biological leptin effectiveness, pulsatility may be an important
requirement. In this sense, it is interesting that a high dosage need for
nonpulsatile administration of leptin has been reported. Initial animal studies
showed that a single daily leptin injection resulted in a small but significant
body weight reduction, whereas twice-daily injections yielded better results.4,5 Interestingly, constant leptin
infusion at a low dose through subcutaneously implanted minipumps resulted
in maximal weight loss.4
Due to its peptide nature, leptin had to be administered subcutaneously,
which produced significant injection site reactions.1
These adverse effects explain the rationale for a single daily administration.
However, taking into account the rhythmicity and pulsatility of leptin, it
might have been more effective to administer leptin in the evening. Even better
results might have been obtained by using subcutaneously implanted minipumps,
which could simulate a more physiological release. The beneficial effects
of exogenous leptin treatment in a leptin-deficient child using a similar
single morning administration6 may be explained
by a possible leptin receptor overexpression in congenital leptin deficiency.
In our opinion, the findings of Heymsfield et al need to be interpreted
with caution until the clinical significance of the optimal method for leptin
administration is defined.
Frühbeck G, Díez-Caballero A, Salvador J, Alvarez-Cienfuegos J. Chronobiology of Recombinant Leptin Therapy. JAMA. 2000;283(12):1567–1568. doi:10.1001/jama.283.12.1563
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