What is Metreleptin?
Metreleptin (brand name MYALEPT in the US, MYALEPTA in Europe) is a recombinant 147-amino-acid analogue of human leptin approved by the FDA on February 25, 2014 for the metabolic complications of leptin deficiency in patients with congenital or acquired generalized lipodystrophy.
It is the only approved leptin replacement therapy worldwide and is administered as a once-daily subcutaneous injection.
Background — Leptin and Lipodystrophy
Leptin is a 16 kDa adipocyte-secreted hormone discovered in 1994 (Friedman et al.) that signals adipose mass to the hypothalamus and regulates energy balance, glucose homeostasis, and reproductive function. In states of low fat mass (anorexia, lipodystrophy), leptin drops to undetectable levels — producing severe metabolic dysregulation.
Generalized lipodystrophy is a rare disorder (congenital or acquired) characterized by near-total absence of subcutaneous adipose tissue. Without functional adipocytes:
- Leptin is undetectable
- Hyperphagia and severe insulin resistance develop
- Ectopic fat deposits in liver and muscle
- Severe hypertriglyceridemia and pancreatitis risk
- Diabetes refractory to conventional therapy
Metreleptin replaces the missing leptin signal, partially correcting the metabolic phenotype.
Structure
Metreleptin is recombinant human leptin produced in E. coli, identical in amino acid sequence to native leptin except for an additional methionine residue at the N-terminus (a residual methionine from the recombinant expression initiator that does not affect function).
Mechanism of Action
- Leptin receptor (ObR/LepR) binding in the hypothalamus, suggesting central effects on appetite and energy expenditure
- Suppression of hyperphagia — reduces food intake
- Improved insulin sensitivity — particularly hepatic glucose output and lipid metabolism
- Reduced hepatic and ectopic fat — likely via effects on hepatic lipid handling
- Reduced serum triglycerides — often dramatically (some patients move from >2000 mg/dL to normal)
- Hypothalamic-pituitary-gonadal restoration — in some patients with lipodystrophy-related amenorrhea
In contrast to common obesity (where leptin levels are high but receptor signaling is desensitized), in lipodystrophy leptin levels are pathologically low — making leptin replacement effective.
Clinical Evidence
Pivotal NIH study (NEJM 2002):
- Open-label studies in patients with severe lipodystrophy
- HbA1c reductions of 1-2%
- Triglyceride reductions of 50-75% in many patients
- Marked reduction in liver volume and hepatic steatosis
These uncontrolled studies in a small population provided the basis for FDA approval under the orphan drug pathway.
Approval History
- February 25, 2014 — FDA approval (Myalept) for generalized lipodystrophy
- 2018 — EMA approval (Myalepta), extending to partial lipodystrophy in some cases
Place in Therapy
Metreleptin is reserved for patients with generalized lipodystrophy and severe metabolic complications. It is not indicated for common obesity because high endogenous leptin in obesity reflects leptin resistance, not deficiency, and leptin replacement does not produce meaningful weight loss in obese non-lipodystrophic patients.
It is administered as a once-daily SC injection, with dose adjusted based on metabolic response.
Safety Profile
Adverse events:
- Hypoglycemia (especially when used alongside insulin)
- Headache, fatigue
- Anti-metreleptin antibodies (~50% of patients) — most are non-neutralizing; rare neutralizing antibodies can cause loss of efficacy or worsened lipodystrophy phenotype
- T-cell lymphoma reports — boxed warning, primarily in acquired lipodystrophy patients with HIV-1; uncertain causal relationship
REMS Program
Metreleptin requires participation in a Risk Evaluation and Mitigation Strategy (REMS) program because of the lymphoma signal and antibody concerns. Prescribers must be certified, and patients enrolled in the program with annual safety monitoring.
Why It Matters
Metreleptin is one of the few approved peptide hormone replacement therapies for an ultra-rare disorder. It demonstrated proof-of-concept that peptide hormone replacement can transform the metabolic phenotype of patients with severe genetic deficiency, paralleling the approach of palopegteriparatide in hypoparathyroidism and lonapegsomatropin in growth hormone deficiency.