De Novo Lipogenesis: Fatty Acid Synthesis Explained

What Is De Novo Lipogenesis?

De novo lipogenesis (abbreviated DNL) refers to the biochemical synthesis of new fatty acids from non-lipid precursors – primarily carbohydrates, but also amino acids and other substrates. The term comes from Latin and literally means “new formation” (de novo) of fats (lipogenesis). It is a natural metabolic pathway found in virtually all mammals and occurs mainly in the liver and adipose (fat) tissue.

Biological Background and Occurrence

In humans, de novo lipogenesis takes place primarily in liver cells (hepatocytes). To a lesser extent, it also occurs in fat cells (adipocytes) and in the mammary gland during lactation. Under normal dietary conditions, DNL in humans is relatively low when energy intake is balanced. However, it increases significantly when carbohydrate or total caloric intake chronically exceeds energy expenditure.

Mechanism of De Novo Lipogenesis

The process proceeds through several biochemical steps:

• Glycolysis: Glucose is broken down into pyruvate.
• Acetyl-CoA formation: Pyruvate is converted to acetyl-CoA inside the mitochondria.
• Citrate transport: Acetyl-CoA enters the citric acid cycle and is converted to citrate, which is then exported from the mitochondria into the cytoplasm.
• Malonyl-CoA synthesis: The enzyme acetyl-CoA carboxylase (ACC) converts acetyl-CoA to malonyl-CoA – the first and rate-limiting step of fatty acid synthesis.
• Fatty acid synthesis: The fatty acid synthase complex (FAS/FASN) elongates the carbon chain stepwise until palmitate (C16:0) is produced – the primary end product of DNL.
• Further processing: Palmitate can subsequently be elongated or desaturated into longer-chain or unsaturated fatty acids.

Regulation of De Novo Lipogenesis

DNL is regulated by a variety of hormonal and nutrient-dependent signaling pathways:

• Insulin: Promotes DNL by activating the transcription factor SREBP-1c (sterol regulatory element-binding protein 1c), which upregulates genes involved in fatty acid synthesis.
• Glucose and fructose: High concentrations of these sugars stimulate DNL directly. Fructose is considered a particularly potent activator because it rapidly replenishes the acetyl-CoA pool.
• AMPK (AMP-activated protein kinase): Inhibits DNL during low-energy states by inactivating acetyl-CoA carboxylase.
• Glucagon and catecholamines: Inhibit DNL via activation of AMPK and suppression of SREBP-1c.

De Novo Lipogenesis and Nutrition

The type and quantity of nutrients consumed significantly affects DNL activity:

• High-carbohydrate diets: Consistently high carbohydrate intake, especially from simple sugars like sucrose and fructose, strongly activates DNL.
• Caloric surplus: Any energy intake exceeding expenditure – regardless of macronutrient source – promotes de novo fatty acid synthesis.
• Low-carbohydrate or ketogenic diets: Markedly reduce DNL by limiting the availability of acetyl-CoA for lipogenesis.

Clinical Significance

Chronically elevated de novo lipogenesis is associated with several metabolic disorders:

• Non-alcoholic fatty liver disease (NAFLD/MASLD): In individuals with obesity and insulin resistance, hepatic DNL is substantially increased and contributes significantly to liver fat accumulation.
• Metabolic syndrome: Elevated DNL activity correlates with hypertriglyceridemia, visceral obesity, and insulin resistance.
• Type 2 diabetes mellitus: Increased hepatic fat export raises VLDL-triglyceride levels in the blood and worsens insulin sensitivity.
• Obesity: Chronic caloric surplus stimulates DNL and contributes to increases in fat mass over time.

Therapeutic Approaches

Given the clinical relevance of de novo lipogenesis, several strategies are being investigated to modulate its activity:

• Dietary interventions: Reducing fructose, sucrose, and overall caloric intake to lower hepatic DNL.
• Pharmacological inhibitors: Agents such as ACC inhibitors (e.g., firsocostat) are being evaluated in clinical trials for NAFLD.
• FASN inhibitors: Inhibitors of fatty acid synthase are under investigation in both metabolic medicine and oncology, as many tumor cells exhibit elevated DNL.
• Exercise and physical activity: Activates AMPK and thereby suppresses DNL.

De Novo Lipogenesis in Oncology

An emerging area of research concerns the role of de novo lipogenesis in cancer cells. Many tumor cells show markedly elevated FASN expression and increased lipogenic activity. This is interpreted as an adaptation to the high biosynthetic demands of rapidly dividing cells, closely related to the concept of the Warburg effect. Accordingly, FASN inhibitors are being explored as potential anticancer agents.

References

1. Strable, M. S. & Ntambi, J. M. (2010): Genetic control of de novo lipogenesis: Role in diet-induced obesity. Critical Reviews in Biochemistry and Molecular Biology, 45(3), 199–214. DOI: 10.3109/10409231003667500
2. Loomba, R. et al. (2021): De novo lipogenesis as a key driver of nonalcoholic fatty liver disease. Journal of Hepatology, 76(3), 700–710. DOI: 10.1016/j.jhep.2021.07.005
3. Hanahan, D. & Weinberg, R. A. (2011): Hallmarks of Cancer: The Next Generation. Cell, 144(5), 646–674. DOI: 10.1016/j.cell.2011.02.013