Deciphering the Hepatic Endocannabinoidome: Analytical Innovations, Cellular Pathophysiology, and Sex-Dimorphic Dimorphism in Liver Disease Pharmacotherapy

Abstract

The endocannabinoid system (ECS) and its extended metabolic network, the endocannabinoidome (eCBome)—comprising $N$-acylethanolamines (NAEs), monoacylglycerols (MAGs), and their primary metabolic enzymes—serve as master homeostatic regulators of hepatic energy metabolism and inflammatory cascades. Recent methodological breakthroughs in high-resolution liquid chromatography-tandem mass spectrometry (LC-MS/MS) and supercritical fluid chromatography have transformed our capacity to quantify faint lipidomic shifts within the diseased liver parenchyma. At the cellular level, dysregulated eCBome signaling orchestrates the progression of metabolic dysfunction-associated steatohepatitis (MASH), alcohol-related liver disease (ALD), and fibrosis through cannabinoid receptor 1 (CB1)-mediated lipogenesis, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction in hepatocytes, alongside localized hepatic stellate cell (HSC) activation. Conversely, activation of cannabinoid receptor 2 (CB2) and peroxisome proliferator-activated receptor alpha (PPARα) mitigates immunometabolic injury. Crucially, eCBome regulation exhibits profound sexual dimorphism governed by circulating sex steroids, differential expression of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), and estrobolome crosstalk. This article provides a molecular synthesis of analytical lipidomics in liver disease, detailing cell-specific eCB signaling mechanisms and emphasizing the imperative of sex-and-gender-based analysis (SGBA) for precision pharmacotherapy.

Introduction & Cellular Mechanisms

The pathogenesis of chronic liver diseases, spanning MASH, ALD, cirrhosis, and hepatocellular carcinoma (HCC), is fundamentally tied to dysregulated lipid homeostasis and unresolved inflammation. Historically characterized by the canonical endogenous ligands $N$-arachidonoylethanolamine (anandamide, AEA) and 2-arachidonoylglycerol (2-AG), the liver eCBome has expanded to encompass a complex lipidome of over 100 non-cannabinoid congener molecules, including $N$-oleoylethanolamine (OEA), $N$-palmitoylethanolamine (PEA), and fatty acid esters of hydroxy fatty acids (FAHFAs).

To capture the fleeting dynamics of these bioactive lipophilic mediators, modern analytical platforms rely on advanced matrix-matched extraction protocols (such as modified Folch or solid-phase extraction [SPE]) coupled with ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) operating in electrospray ionization (ESI) mode. These methodologies achieve picomolar sensitivity, overcoming challenges associated with rapid enzymatic turnover and isobaric lipid interference.

```
┌────────────────────────────────────────┐
│ Hepatic Endocannabinoidome │
│ (AEA, 2-AG, OEA, PEA, FAHFAs, etc.) │
└───────────────────┬────────────────────┘
│
┌────────────────────────────┴────────────────────────────┐
▼ ▼
┌──────────────────────┐ ┌──────────────────────┐
│ Hepatocyte Injury │ │ HSC & Kupffer │
│ & Metabolic Shift │ │ Activation │
└──────────┬───────────┘ └──────────┬───────────┘
│ │
┌─────────┴──────────┐ ┌─────────┴──────────┐
│ • CB1 Activation │ │ • CB1: Pro-fibrotic│
│ • SREBP-1c / ACC1 │ │ (TGF-β / Smad3) │
│ • ER Stress / ROS │ │ • CB2: Anti-fibrotic│
│ • Mitochondrial │ │ & Anti-inflamm. │
│ Dysfunction │ │ • PPARα: β-Oxid. │
└────────────────────┘ └────────────────────┘
```

The localized physiological activity of the eCBome within the hepatic sinusoids is executed through a network of cell-type-specific receptors and signaling pathways:

1. Hepatocyte Metabolic Dysfunction: Pathological overexpression or hyper-activation of hepatic CB1 receptors drives *de novo* lipogenesis (DNL) by upregulating transcriptional factors including sterol regulatory element-binding protein 1c (SREBP-1c), carbohydrate-responsive element-binding protein (ChREBP), acetyl-CoA carboxylase-1 (ACC1), and fatty acid synthase (FAS). Simultaneously, CB1 signaling inhibits AMP-activated protein kinase (AMPK) activity and downregulates carnitine palmitoyltransferase-1 (CPT-1), blunting mitochondrial fatty acid $\beta$-oxidation.
2. Organelle Stress Cascades: Sustained CB1 stimulation induces severe endoplasmic reticulum (ER) stress, activating the protein kinase RNA-like ER kinase (PERK)-eIF2$\alpha$-CHOP axis. This pathway exacerbates hepatocyte ballooning and apoptotic cell death. Furthermore, eCB imbalance disrupts mitochondrial cristae architecture, uncouples oxidative phosphorylation, and elevates mitochondrial reactive oxygen species (mROS) production.
3. Hepatic Stellate Cell (HSC) Transdifferentiation: In quiescent HSCs, differential receptor expression dictates cellular fate. Activation of CB1 by elevated local AEA or 2-AG accelerates transdifferentiation into collagen-producing myofibroblasts via the TGF-$\beta1$/Smad3 and ERK1/2 signaling pathways. Conversely, activation of CB2 receptors triggers apoptosis in activated HSCs and suppresses extracellular matrix (ECM) deposition.
4. Kupffer Cell and Macrophage Polarisation: Non-canonical pathways, mediated by PPAR$\alpha$, G protein-coupled receptor 55 (GPR55), and transient receptor potential vanilloid 1 (TRPV1), interact with CB2 to polarize hepatic macrophages from a pro-inflammatory M1 phenotype (driven by NF-$\kappa$B, TNF-$\alpha$, and IL-1$\beta$) toward a pro-resolving, tissue-repairing M2 phenotype.

Sex-Dimorphic Regulation & Translational Implications

Biological sex is a critical deterministic factor in hepatic lipid handling, inflammatory trajectory, and fibrosis progression. Sexual dimorphism within the eCBome accounts for the differential susceptibility and progression patterns observed between biological males and females in MASH and ALD.

```
17β-Estradiol (E2) Testosterone
│ │
┌─────────┴─────────┐ ┌─────────┴─────────┐
▼ ▼ ▼ ▼
FAAH Activity NAPE-PLD Tone MAGL Activity CB1 Expression
[Suppressed] [Up-regulated] [Up-regulated] [Up-regulated]
│ │ │ │
▼ ▼ ▼ ▼
Higher OEA/PEA Sustained Rapid 2-AG Enhanced DNL
Preservation Anti-inflammatory Degradation & ER Stress
(PPARα Active) Tone (Pro-inflammatory) (MASH Risk)
```

1. Hormonal Modulation of Enzymatic Machinery

Estrogenic signaling exerts direct transcriptional control over primary eCB metabolic enzymes. $17\beta$-estradiol ($E_2$), acting via Estrogen Receptor Alpha ($ER\alpha$), suppresses the transcription and enzymatic activity of fatty acid amide hydrolase (FAAH) in premenopausal females. This down-regulation preserves endogenous levels of OEA and PEA, which serve as endogenous agonists for PPAR$\alpha$, enhancing mitochondrial $\beta$-oxidation and down-regulating pro-inflammatory cytokine transcription. Conversely, androgenic signaling upregulates monoacylglycerol lipase (MAGL) and hepatic CB1 expression, accelerating the conversion of 2-AG to arachidonic acid—the precursor for pro-inflammatory eicosanoids—thereby predisposing males to accelerated steatosis and inflammatory recruitment.

2. Dimorphic Receptor Distribution and Signaling Cascades

Females consistently exhibit a higher baseline hepatic CB2-to-CB1 receptor expression ratio compared to age-matched males. Elevated CB2 expression exerts a protective effect against fibrogenic transformation, blunting activated HSC proliferation and suppressing macrophage IL-6/TNF-$\alpha$ secretion. Following menopause, or under condition of ovariectomy, the loss of $E_2$-mediated inhibition leads to an abrupt up-regulation of hepatic CB1 expression and decreased FAAH baseline levels, aligning female metabolic risk profiles with those of males.

3. Precision Medicine and Diagnostic Biomarker Profiling

The integration of Sex-and-Gender-Based Analysis (SGBA) into analytical lipidomics is essential for establishing clinically valid diagnostic and therapeutic benchmarks:

Quantification and Normalization: Mass spectrometry analytical pipelines must incorporate sex-stratified reference intervals for circulating and tissue levels of AEA, 2-AG, OEA, and PEA. Failure to stratify by biological sex risks masking key therapeutic windows or lipidomic biomarkers of liver injury.

Targeted Therapeutic Interventions: Pharmacological strategies utilizing peripherally restricted CB1 inverse agonists or dual FAAH/MAGL inhibitors require sex-dosed optimization. Female cohorts demonstrate distinct pharmacodynamics due to variations in subcutaneous body fat distribution, CYP-mediated hepatic drug metabolism, and fluctuating endogenous lipid tone across the estrous/menstrual cycle.

Conclusions & Clinical Outlook

The evolution of targeted lipidomics has elevated the endocannabinoidome from a secondary signaling network to a central driver of hepatic immunometabolism. The structural complexity and localized action of eCBome mediators necessitate analytical precision, primarily achieved through advanced LC-MS/MS methodologies. Clinically, translating these analytical advances into effective hepatology therapeutics requires a structural shift toward precision biomedicine that fully integrates biological sex as a key variable.

Future drug discovery must prioritize non-systemic, peripherally restricted CB1 modulators, cell-type-targeted delivery systems (e.g., HSC-targeted lipid nanoparticles), and dual-action eCBome enzyme inhibitors. Integrating sex-stratified clinical trial designs with longitudinal lipidomic profiling will be essential to establish personalized, highly effective pharmacotherapies for metabolic and fibrotic liver diseases.

Key Insights

High-Precision Lipidomic Architecture: UHPLC-MS/MS platforms enable high-resolution quantification of the hepatic endocannabinoidome, revealing how subtle alterations in AEA, 2-AG, OEA, and PEA drive the clinical progression of MASH, ALD, and liver fibrosis.

Cell-Type-Specific Signaling Networks: Pathological CB1 activation drives hepatocyte lipogenesis, ER stress, and HSC-mediated fibrogenesis, whereas counter-regulatory CB2 and PPAR$\alpha$ signaling attenuates inflammation and promotes fibrosuppression.

Sex-Dimorphic Therapeutic Imperative: $17\beta$-estradiol and testosteronic regulation of FAAH, MAGL, and receptor density generate distinct male and female metabolic trajectories, necessitating sex-stratified lipidomic biomarkers and pharmacotherapies.

References

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