Lipolysis

Lipolysis /lɪˈpɒlɪsɪs/ is the metabolic pathway through which lipid triglycerides are hydrolyzed into a glycerol and free fatty acids.

When lipase enzymes are phosphorylated, they can access lipid droplets and through multiple steps of hydrolysis, breakdown triglycerides into fatty acids and glycerol.

There, it suppresses lipolysis and decreases sympathetic nervous outflow to the fatty part of the brain matter.

[11] The regulation of this process involves interactions between insulin receptors and gangliosides present in the neuronal cell membrane.

Triglycerides present on the VLDL undergo lipolysis by the cellular lipases of target tissues, which yields glycerol and free fatty acids.

Free fatty acids not immediately taken up by cells may bind to albumin for transport to surrounding tissues that require energy.

Hepatic glycerol 3-phosphate is converted mostly into dihydroxyacetonephosphate (DHAP) and then glyceraldehyde 3-phosphate (GA3P) to rejoin the glycolysis and gluconeogenesis pathway.

Currently there are four main non-invasive body contouring techniques in aesthetic medicine for reducing localized subcutaneous adipose tissue in addition to the standard minimally invasive liposuction: low-level laser therapy (LLLT), cryolipolysis, radio frequency (RF) and high-intensity focused ultrasound (HIFU).

[17][18] However, they are less effective with shorter lasting benefits and can remove significantly smaller amounts of fat compared to traditional surgical liposuction or lipectomy.

However, future drug developments can be potentially combined with smaller procedures to augment the result.

This image illustrates the three separate steps of hydrolysis involved in lipolysis. In the first step, triacylglycerol is hydrolyzed to make diacylglycerol and this is catalyzed by adipose triglyceride lipase (ATGL). In the second step, diacylglycerol is hydrolyzed to make monoacylglycerol and this is catalyzed by hormone-sensitive lipase (HSL). In the last step, monoacylglycerol is hydrolyzed to make glycerol and this is catalyzed by monoacylglycerol lipase (MGL).
Example of a triacylglycerol
Example of a diacylglycerol
Example of a monoacylglycerol
Illustration of the activation of lipolysis in an adipocyte . Induced by high epinephrine and low insulin levels in the blood, epinephrine binds to beta-adrenergic receptors on the cell membrane of the adipocyte, which causes cAMP to be generated inside the cell.
The cAMP activates protein kinases , which phosphorylate and thus activate hormone-sensitive lipases in the adipocyte .
These lipases cleave free fatty acids from their attachment to glycerol in the lipid droplet of the adipocyte.
The free fatty acids and glycerol are then released into the blood.
The activity of hormone sensitive lipase is regulated by the circulating hormones insulin , glucagon , norepinephrine , and epinephrine .