Step 1: Understanding the Concept:
PPAR-\(\alpha\) is a nuclear receptor that, once activated, switches on genes controlling fatty acid oxidation and lipoprotein lipase activity. Drugs that turn on this receptor form their own class, separate from bile acid sequestrants and cholesterol absorption inhibitors.
Step 2: Key Fact:
Gemfibrozil belongs to the fibrate class of drugs, and fibrates are defined by their action as PPAR-\(\alpha\) agonists. Activating this receptor raises fatty acid breakdown and lipoprotein lipase activity, lowering triglycerides and raising HDL cholesterol.
Step 3: Detailed Explanation:
Ezetimibe blocks intestinal cholesterol absorption through the NPC1L1 transporter, unrelated to any nuclear receptor.
Niacin acts through the GPR109A receptor on fat cells to reduce lipolysis, a different pathway entirely.
Colesevelam binds bile acids in the gut, forcing the liver to use more cholesterol, again with no PPAR-\(\alpha\) involvement.
Only gemfibrozil's mechanism runs through PPAR-\(\alpha\) activation.
Step 4: Final Answer:
The PPAR-\(\alpha\) agonist among the options is Gemfibrozil.