Adipokines: The Peptides Fat Tissue Sends Out
Peptide Hormone Systems
600+ adipokines
White adipose tissue secretes over 600 identified bioactive molecules, including peptide hormones that regulate metabolism, inflammation, and cardiovascular function.
Multiple reviews, 2024-2025
Multiple reviews, 2024-2025
View as imageFor most of medical history, fat tissue was considered inert storage. That changed in 1994, when Jeffrey Friedman's lab discovered leptin, a peptide hormone secreted by adipocytes that signals to the brain to reduce appetite. The discovery revealed that adipose tissue is an active endocrine organ, secreting hundreds of peptide hormones, cytokines, and signaling molecules collectively called adipokines. These molecules regulate metabolism, inflammation, insulin sensitivity, cardiovascular function, and reproductive health. For the broader context of how gut peptide hormones communicate between organs, adipokines represent the fat tissue arm of a body-wide peptide signaling network.
When adipose tissue expands in obesity, adipokine secretion changes dramatically. Some adipokines increase (leptin, resistin, chemerin, visfatin), while others decrease (adiponectin, omentin). This imbalance contributes directly to the metabolic dysfunction associated with obesity: insulin resistance, chronic low-grade inflammation, endothelial dysfunction, cardiovascular disease, and certain cancers. Understanding adipokines explains why obesity is not just a matter of excess weight but a state of fundamentally altered hormonal signaling that affects nearly every organ system.
Key Takeaways
- Adipose tissue is an endocrine organ secreting over 600 bioactive molecules, including peptide hormones called adipokines
- Leptin signals satiety to the brain, but obesity causes leptin resistance, not leptin deficiency (levels are elevated in obese individuals)
- Adiponectin is the most abundant adipokine and has anti-inflammatory, insulin-sensitizing, and cardioprotective effects, but its levels decrease in obesity
- Tirzepatide synergizes with leptin signaling to enhance weight loss and restore metabolic homeostasis in animal models (Sun et al., 2025)
- GLP-1 receptor agonists modulate adipokine profiles, with adiponectin increases linked to their metabolic benefits (Al-Halawani et al., 2025)
- Apelin, visfatin, and resistin are newer adipokines with distinct roles in cardiovascular function, wound healing, and insulin resistance
Leptin: The Satiety Signal That Fails in Obesity
Leptin is a 167-amino-acid peptide hormone produced primarily by white adipocytes. Circulating leptin levels are proportional to fat mass: the more body fat, the more leptin in the blood. Leptin crosses the blood-brain barrier and binds to leptin receptors (LepR) in the hypothalamus, where it suppresses appetite and increases energy expenditure.
The discovery of leptin initially generated excitement about a potential obesity cure. If leptin signals satiety, perhaps obese individuals lacked it and could be treated with exogenous leptin. This logic held for the rare individuals with genetic leptin deficiency, who respond dramatically to leptin replacement. But for the vast majority of obese individuals, the problem is leptin resistance, not deficiency. Their leptin levels are elevated, often dramatically so, but the hypothalamic response is blunted.
Solheim et al. identified specific hypothalamic PNOC/NPY neurons as mediators of leptin-controlled energy homeostasis, providing new mechanistic insight into the neural circuits through which leptin acts and potentially where resistance develops.[1]
The interaction between leptin and GLP-1 receptor agonists is an active area of research. Sun et al. demonstrated that tirzepatide synergizes with leptin signaling on weight loss and restoring metabolic homeostasis in diet-induced obesity models, suggesting that dual GIP/GLP-1 agonism may partially overcome leptin resistance.[2] Fu et al. found that combining leptin with liraglutide improved glucose metabolism in insulin-dependent diabetes models beyond what either agent achieved alone.[3] Petelakova et al. explored the additive effects of leptin combined with palm-LEAP2(1-14) on ameliorating obesity-induced metabolic stress in ob/ob mice, showing that multi-peptide approaches may be more effective than single-agent therapies.[4]
Jiang et al. reported a concerning finding: repeated withdrawal of a GLP-1 receptor agonist induced hyperleptinemia and deteriorated metabolic health in obese subjects, suggesting that the leptin system's response to GLP-1 drug discontinuation may contribute to weight regain.[5]
Adiponectin: The Protective Peptide That Decreases in Obesity
Adiponectin is the most abundant peptide hormone in the bloodstream, circulating at concentrations of 5-30 micrograms per milliliter, roughly 1,000-fold higher than most other hormones. It is produced exclusively by adipocytes but, paradoxically, its levels decrease as fat mass increases. Obese individuals have lower adiponectin levels than lean individuals.
Adiponectin has insulin-sensitizing, anti-inflammatory, anti-atherogenic, and cardioprotective effects. It enhances fatty acid oxidation in muscle and liver through AMPK activation, suppresses hepatic glucose production, reduces inflammatory cytokine release from macrophages, and protects vascular endothelium from oxidative damage. Adiponectin circulates in three forms: trimers (low molecular weight), hexamers (medium molecular weight), and multimers (high molecular weight), with the high-molecular-weight form considered the most biologically active for insulin sensitization. Low adiponectin levels are independently associated with insulin resistance, type 2 diabetes, cardiovascular disease, and metabolic syndrome. The negative correlation between adiponectin and fat mass creates a damaging feedback loop: as obesity increases, adiponectin decreases, removing its protective metabolic effects and accelerating further metabolic decline.
Al-Halawani et al. found that adiponectin may play a crucial role in the metabolic effects of GLP-1 receptor agonist treatment, with improvements in adiponectin levels correlating with the metabolic benefits observed during therapy.[6] This suggests that part of how GLP-1 drugs improve metabolic health may be mediated through restoring healthier adipokine profiles, not just through direct appetite suppression or insulin secretion.
Vatankhah et al. demonstrated that exenatide (a GLP-1 receptor agonist) improved ovarian adiponectin system expression in polycystic ovary syndrome (PCOS), linking adipokine modulation to reproductive health benefits.[7] Jung et al. similarly found that glycemic improvement with low-dose dulaglutide was associated with leptin and obestatin modulation, further establishing the connection between incretin therapy and adipokine profiles.[8]
Apelin: The Cardiovascular Adipokine
Apelin is a peptide adipokine with potent cardiovascular effects. Multiple forms exist (apelin-13, apelin-17, apelin-36), all derived from a 77-amino-acid precursor. Apelin binds to the APJ receptor (now called the apelin receptor) expressed in the heart, blood vessels, brain, and adipose tissue.
In the cardiovascular system, apelin promotes vasodilation, reduces blood pressure, and has positive inotropic effects on the heart (increasing contractile force without increasing heart rate). Yan et al. showed that apelin-13 in the paraventricular nucleus of the hypothalamus attenuates myocardial ischemia through V1a vasopressin receptors, demonstrating a central nervous system pathway through which this adipokine protects the heart.[9]
Apelin levels increase in early obesity but decline in severe obesity and obesity-associated cardiovascular disease. This biphasic pattern suggests that apelin may represent a compensatory protective mechanism that eventually fails as adipose tissue dysfunction progresses. The decline in apelin in advanced obesity removes one of the body's natural vasodilatory and cardioprotective signals, potentially contributing to the increased cardiovascular risk seen in severe obesity. Synthetic apelin analogs are under investigation as potential cardiovascular therapeutics, though none have reached late-stage clinical trials. For more on how cardiovascular peptides regulate blood pressure and heart function, see our dedicated article. ANP, the atrial natriuretic peptide, works through complementary pathways to apelin in maintaining cardiovascular homeostasis.
Visfatin, Resistin, and Other Adipokines
Beyond the major adipokines, fat tissue secretes dozens of additional peptide signals:
Visfatin (also known as nicotinamide phosphoribosyltransferase/NAMPT) is produced by visceral adipose tissue and has insulin-mimetic properties. Joo et al. explored the wound healing properties of peptides derived from visfatin's active sites, demonstrating that fragments of this adipokine have biological activity independent of the full-length protein.[10] This is particularly relevant because it suggests that enzymatic degradation of visfatin may produce bioactive peptide fragments with their own signaling functions.
Resistin was named for its role in inducing insulin resistance. In humans, resistin is produced mainly by macrophages within adipose tissue rather than by adipocytes directly. Elevated resistin levels correlate with inflammatory markers and are associated with type 2 diabetes, atherosclerosis, and non-alcoholic fatty liver disease.
Omentin-1 is an anti-inflammatory adipokine produced by visceral (but not subcutaneous) fat. Its levels decrease in obesity and insulin resistance. Omentin-1 enhances insulin signaling and promotes endothelial function.
Chemerin is a chemoattractant peptide that recruits immune cells (particularly macrophages and dendritic cells) to adipose tissue. Chemerin levels increase with BMI and are associated with metabolic syndrome. It may be a key link between obesity and chronic inflammation, as macrophage infiltration of adipose tissue is a hallmark of obesity-associated metabolic dysfunction. As fat mass expands, chemerin draws more immune cells into adipose tissue, which then produce pro-inflammatory cytokines that further dysregulate insulin signaling.
Asprosin is a recently discovered adipokine (2016) that acts on the liver to stimulate glucose production. It rises between meals and falls after eating, functioning as a fasting-induced hormonal signal. Asprosin levels are elevated in obesity and insulin resistance. Anti-asprosin antibodies have reduced appetite and blood glucose in animal models, making it a potential therapeutic target for both obesity and type 2 diabetes.
Irisin is technically a myokine (muscle-derived) that also acts on adipose tissue, inducing "browning" of white fat cells. Browning converts energy-storing white adipocytes into energy-burning beige adipocytes, increasing thermogenesis. Irisin levels increase with exercise, providing one mechanism through which physical activity improves metabolic health beyond caloric expenditure. The discovery of irisin reinforced the concept that muscle and fat tissue communicate through peptide signals in both directions.
The GLP-1 Drug Connection
The interaction between GLP-1-based therapies and adipokine signaling is increasingly recognized as clinically important. GLP-1 receptor agonists and dual GIP/GLP-1 agonists like tirzepatide do not just reduce appetite; they reshape the endocrine output of adipose tissue.
Mi et al. developed a mesoporous polydopamine encapsulation system for tirzepatide retention in inguinal white adipose tissue (iWAT), demonstrating enhanced weight loss through sustained local drug presence in fat depots.[11] This approach targets adipose tissue directly, potentially modulating local adipokine production in ways that systemic administration does not.
The broader implication is that weight loss drugs may have effects beyond caloric reduction. By changing the hormonal output of adipose tissue (increasing adiponectin, normalizing leptin signaling, modifying chemerin and resistin levels), these drugs may address the metabolic dysfunction of obesity at its endocrine source. This is distinct from simple caloric restriction, which also changes adipokine levels but through a different mechanism. The clinical significance extends to conditions beyond obesity itself: adipokine dysregulation is implicated in PCOS, non-alcoholic fatty liver disease, atherosclerosis, and certain cancers. If GLP-1-based therapies normalize adipokine profiles, their benefits may extend to these obesity-associated conditions through endocrine mechanisms rather than weight loss alone.
The concept of fat tissue as an endocrine organ also explains why body fat distribution matters more than total fat mass for metabolic health. Visceral (abdominal) adipose tissue produces a more pro-inflammatory adipokine profile than subcutaneous fat. Visceral fat releases more resistin, chemerin, and IL-6, and less adiponectin, than subcutaneous fat. This is why individuals with the same BMI but different fat distribution patterns can have very different metabolic risk profiles.
For more on how neuropeptides in the brain integrate adipokine signals with appetite and energy regulation, see our article on brain peptide signaling. The complete catalog of body peptide hormones, including all known adipokines, is covered in Every Peptide Hormone in Your Body.
The Bottom Line
Adipokines are peptide hormones and signaling molecules secreted by adipose tissue that regulate metabolism, inflammation, insulin sensitivity, and cardiovascular function. Leptin signals satiety but becomes ineffective in obesity due to resistance. Adiponectin is protective but decreases as fat mass increases. Apelin, visfatin, resistin, and newer adipokines each contribute distinct functions. GLP-1 receptor agonists and tirzepatide modulate adipokine profiles, with emerging evidence that this modulation contributes to their metabolic benefits beyond appetite suppression.