Leptin: Hormone Functions and Effects

Leptin

• Leptin is a hormone produced by white adipocytes.
• Leptin is a signal of inadequate food intake.
• Leptin levels decrease during fasting, low-calorie dieting, or uncontrolled type 1 diabetes.
• Leptin levels increase with increasing adiposity.
• Leptin resistance may be a primary cause of obesity.
• The receptors that bind leptin decrease in obesity leading to leptin resistance.
• Leptin receptors are found in many organs including the liver, skeletal muscles, pancreatic beta cells, and even adipose cells.
• Leptin is an insulin-sensitizer.
• Leptin can decrease glucagon synthesis and secretion, decrease hepatic glucose production, and increase insulin hepatic extraction.
• Leptin can decrease lipogenesis in adipose tissue and increase lipolysis.
• Leptin inhibits insulin biosynthesis and secretion from pancreatic β-cells.
• Insulin stimulates leptin secretion from adipose tissue.
• Leptin and insulin are part of a regulatory feedback loop known as the adipo-insular axis.

Adiponectin

• Adiponectin is an adipocytokine that influences insulin sensitivity and atherogenesis.
• Adiponectin mediates its effects through binding to receptors AdipoR1 and AdipoR2.
• Adiponectin levels are lower in obesity.
• Lower adiponectin levels are associated with insulin resistance, dyslipidemia, and atherosclerosis in humans.
• Adiponectin levels increase with weight loss and improve insulin sensitivity.
• Adiponectin suppresses the action of inflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha).
• Adiponectin improves dyslipidemia and other cardiovascular disease risk factors.
• Adiponectin is thought to have anti-tumor effects.
• Adiponectin may inhibit leptin-induced tumor proliferation.
• Low adiponectin levels have been associated with several types of cancer, including breast, gastric, lung, prostate, and others.
• Adiponectin enhances insulin sensitivity through increased fatty acid oxidation in skeletal muscle and inhibition of hepatic glucose production.

Leptin

• Leptin is a hormone secreted by white adipocytes (fat cells).
• It is encoded by the ob gene.
• Leptin plays a crucial role in regulating appetite and energy expenditure.
• It signals the brain about energy stores and influences feeding behavior.
• During fasting or calorie restriction, leptin levels decrease, stimulating hunger and reducing energy expenditure.
• Conversely, leptin levels increase with increased adiposity (fat storage).
• Leptin resistance is a potential mechanism for the development of obesity.
• This occurs when the body's cells become less responsive to the effects of leptin.
• Reduced levels of soluble leptin receptors (SLRs) in obese individuals may contribute to leptin resistance.
• Leptin's role extends beyond the brain, affecting organs like the liver, skeletal muscles, and pancreatic beta cells.
• It influences glucose and lipid metabolism, promoting insulin sensitivity and affecting insulin secretion.
• Leptin is a key player in the adipoinsular axis, a hormonal feedback loop between adipose tissue and the pancreas.

Adiponectin

• Adiponectin is another hormone produced by adipose tissue, having significant metabolic effects.
• It interacts with receptors AdipoR1 and AdipoR2, activating signaling pathways like AMPK and PPAR-α.
• Adiponectin levels are typically lower in obese individuals, linked to insulin resistance, dyslipidemia, and atherosclerosis.
• Weight loss can increase adiponectin levels, improving insulin sensitivity.
• Adiponectin possesses anti-inflammatory properties, counteracting the effects of TNF-alpha.
• It promotes cardiovascular health by positively influencing dyslipidemia and immune function.
• Adiponectin has potential anti-tumor effects, possibly by inhibiting leptin-induced tumor proliferation.
• Reduced adiponectin levels are associated with an increased risk of certain cancers.
• Adiponectin enhances insulin sensitivity by promoting fatty acid oxidation in skeletal muscle and suppressing hepatic glucose production.