# AOD-9604 and the hGH Fragment 176-191 Explained

> The hGH fragment 176-191 is the C-terminal tail of growth hormone that AOD-9604 is modelled on. Antilipogenic in fat cells, receptor-sparing, and the source of its fat-metabolism design.

Where the molecule comes from, what its parent region does, and why the fragment leaves the growth signal behind.

## In plain English

AOD-9604 is built from the tail end of growth hormone — a stretch of the hormone known as the hGH fragment 176-191 (sometimes written HGH frag 176-191). Growth hormone is a big molecule that does many jobs. Decades of work found that its fat-handling job lives in this small tail region, separate from its growth job.

So AOD-9604 copies just the tail. It keeps the part that affects fat and drops the part that drives growth. In fat cells, that tail slows the building of new fat (antilipogenic) and, in animals, helps shift cells toward burning fat. Because it is only the tail, it does not plug into the growth hormone receptor (the cell's port for the whole hormone), and it does not raise IGF-1, the growth signal. That is the entire design idea: fat effects without growth-hormone effects. Whether that idea produces real fat loss in people is a separate question — and the human trials say it did not.

## HGH frag 176-191: the structure

The hGH fragment 176-191 is the C-terminal region of human growth hormone. AOD-9604 is the engineered version of it: a 16-amino-acid peptide (a hexadecapeptide) modelled on hGH residues 177-191, with a tyrosine added at the N-terminus in place of the native phenylalanine [3]. Two cysteines form an intramolecular disulfide bridge that mirrors the cystine loop of the parent hormone.

Reported sequence: Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe (YLRIVQCRSVEGSCGF). Molecular formula C78H123N23O23S2; molecular weight about 1815.1 Da; CAS 221231-10-3. Identifiers: PubChem CID 71300630; FDA UNII 7UP768IP4M; DrugBank DB06388. Names you will see for the same molecule: AOD9604, AOD 9604, Tyr-hGH(177-191), and "hexadecapeptide AOD9604."

## What the parent region does

The functional claim for this region is old and well-characterised. Human growth hormone and its C-terminal part-sequence inhibit acetyl-CoA carboxylase — the rate-limiting enzyme in fatty-acid synthesis — by interacting with fat-cell and liver-cell membranes and releasing a second messenger that phosphorylates the enzyme [2]. The synthetic 177-191 sequence reproduced the antilipogenic activity of intact hGH, with no significant lipolytic effect by the glycerol-release assay [3]. Metabolic studies confirmed the synthetic C-terminal domain as the seat of the hormone's fat-metabolism activity [12].

The contrast with the full hormone is the point. Synthetic C-terminal fragments spanning residues 172-191 through 178-191 also carry glucose effects — a transient blood-glucose rise and a more sustained insulin rise, with the 178-191 fragments reducing insulin sensitivity [13]. AOD-9604's design keeps the fat activity while steering clear of the growth-hormone receptor entirely, so it does not raise IGF-1 [1].

## Fragment versus hormone, and versus secretagogues

Two distinctions keep the hGH fragment 176-191 from being confused with its neighbours. First, it is a fragment, not growth hormone: it is a short piece of the hormone, not the whole thing, and it does not act on the growth hormone receptor. Second, it is not a secretagogue: it does not signal the pituitary to release more growth hormone, which is what CJC-1295, ipamorelin, and sermorelin do. AOD-9604 works downstream, in the fat cell, on the metabolic machinery the C-terminal region touches — and it does so without the IGF-1 rise those other peptides aim for.

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A brushed-steel worksheet on the AOD-9604 record — the antilipogenic fragment logged first, the receptor-sparing design stated as the design it is, and the failed human weight-loss trial left in plain steel; no clinic behind the console and nothing here dosed, compounded, prescribed, or sold.