Adipotide (FTPP)

Adipotide (FTPP — Fat-Targeted Proapoptotic Peptide) is a chimeric research peptide combining two functional domains joined by a Gly-Gly flexible linker: the CKGGRAKDC white adipose tissue vascular homing sequence and the all-D-amino acid KLAKLAKKLAKLAK proapoptotic sequence. Together, these domains create a compound that selectively delivers a mitochondria-disrupting proapoptotic signal specifically to blood vessel endothelial cells of white adipose tissue (WAT), exploiting the surface expression of prohibitin on WAT endothelium as the molecular targeting mechanism.

The homing domain CKGGRAKDC was identified through in vivo phage display screening by Kolonin et al. (Nature Medicine, 2004). In this technique, a diverse library of phage particles displaying random peptide sequences on their coat proteins was injected intravenously into mice, and phage that selectively accumulated in white adipose tissue vasculature — over heart, lung, brain, kidney, and other vascular beds — were recovered and sequenced. The CKGGRAKDC sequence was consistently enriched in WAT vasculature across multiple selection rounds, establishing it as a WAT-selective vascular homing sequence. The cysteine residues form a disulphide bridge creating a constrained cyclic structure that maintains the CKGGRAKDC binding geometry.

Barnhart et al. (Cell Metabolism, 2011) identified prohibitin as the molecular target of CKGGRAKDC on WAT endothelium through photoaffinity crosslinking — using a photoactivatable CKGGRAKDC derivative to covalently capture interacting proteins, followed by mass spectrometry identification of prohibitin as the primary binding partner. Prohibitin (PHB1) normally functions as an inner mitochondrial membrane chaperone protein involved in respiratory chain assembly and membrane protein quality control. Its aberrant surface expression on WAT endothelial cells — accessible to circulating peptides and absent from most other vascular beds — creates the tissue-selective targeting exploited by Adipotide. The mechanism driving this unusual surface prohibitin localisation specifically in WAT endothelium remains an active research question.

The proapoptotic domain KLAKLAKKLAKLAK uses all D-amino acids — making it completely resistant to intracellular proteolytic degradation throughout the cytoplasmic transit to the mitochondria. The amphipathic alpha-helical structure of this D-amino acid sequence inserts into the inner mitochondrial membrane, disrupting membrane potential, triggering cytochrome c release to the cytoplasm, and activating the intrinsic caspase cascade (caspase-9, then effector caspases-3/7). This mitochondria-targeting mechanism relies on the strongly negative inner mitochondrial membrane potential (approximately -180 mV) to concentrate the cationic amphipathic helix at the inner membrane, providing an additional layer of specificity within cells that have internalised the Adipotide construct.

In vitro research applications for Adipotide use primary human adipose microvascular endothelial cells (hAMECs) isolated from adipose tissue biopsies as the primary WAT endothelial model, with human umbilical vein endothelial cells (HUVECs) or dermal microvascular endothelial cells as non-adipose comparison controls. Key experiments include: fluorescently labelled CKGGRAKDC binding assays comparing WAT versus non-WAT endothelium by confocal microscopy and flow cytometry; prohibitin surface expression characterisation by non-permeabilised cell immunostaining; full Adipotide dose-response proapoptotic studies (annexin V/PI flow cytometry, caspase-3/7 activity); and adipose tissue explant culture experiments examining vessel integrity markers.

Critical controls for Adipotide research include: scrambled CKGGRAKDC sequence control (confirming sequence-specific binding); KLAKLAK without homing domain at matched concentrations (confirming targeting is required for selectivity); and prohibitin shRNA knockdown cells (confirming prohibitin dependence of CKGGRAKDC binding).

Full sequence: CKGGRAKDC-GG-D(KLAKLAK)2. MW: approximately 2.8 kDa. Store lyophilised at -20°C. For laboratory and analytical research purposes only.