SLU-PP-332

SLU-PP-332 is not a peptide, whatever shelf it is sold from. It is a small synthetic molecule of 290.3 daltons with no amino acids in it and no peptide bonds, built by chemists from an earlier GlaxoSmithKline compound called GSK4716. What it does is switch on a family of proteins that sit inside the cell nucleus and turn genes on, the estrogen related receptors, and the genes they turn on are the ones for building new mitochondria, the compartments in a cell that turn food into usable energy, and for burning fat. Sellers call it exercise in a bottle. The mouse work behind that phrase is real, and every mouse in it got the compound injected into the abdominal cavity, the space the organs sit in. Most of what is sold is a capsule you swallow.

The receptors it acts on, written ERR alpha, ERR beta and ERR gamma, switch on the genes for building new mitochondria, for burning fat, and for the chemical loop that turns food into cellular fuel. They are called orphan receptors because no natural substance that switches them on has been identified, and despite the name they are not estrogen receptors. SLU-PP-332 turns all three on and is too blunt a tool to separate them, which its own authors say in print. Two things are worth keeping apart here. The idea that these receptors are essential for muscle adapting to aerobic exercise, which is the whole basis of the exercise mimetic pitch, comes from genetics rather than from this drug. And the fifty fold gain in potency the chemists got at the alpha receptor when they redesigned GSK4716 was measured in cells, not in an animal.

This entry does not survey what buyers say they are after, so what follows is the pitch and the finding each piece of it traces to. It is sold for endurance and for fat under the phrase exercise in a bottle. The endurance claim traces to six male mice given 50 mg per kilogram into the abdominal cavity for six days, which ran about 70 percent longer on a treadmill than six mice given a dummy injection. The fat claim traces to twenty week old males fattened for eight weeks on a 60 percent fat diet and then dosed for 28 days, seven per group, which put on less than 0.5 grams of fat against about 5 grams in the untreated group. That is fat gained, not fat lost, and on ordinary chow the same dosing moved body weight not at all.

Two mistakes, and they stack. The first is reading oral activity onto this molecule. The scientists who made it wrote that SLU-PP-332 lacks oral bioavailability, meaning it does not get from the gut into the blood, and the orally available compound they describe is SLU-PP-915, a chemically distinct molecule with a different name. Most of what is sold is a capsule, so the product and the sentence that undermines it are both in print, and the sentence was written by the people who invented the thing. The second mistake is treating the number on the bottle as information. One seller lists capsules at 250 micrograms and another at 50 milligrams under the same compound name, two hundred fold apart on the label, and a buyer cannot fix that by being careful because there is no correct number to be careful about. The 400 to 800 mg a day that circulates for the swallowed route is roughly where a body surface area conversion of the mouse dose lands, about 570 mg a day for a 70 kilogram adult, which is arithmetic rather than evidence, and arithmetic applied to a route its own inventors say does not work.

I could find no published human safety data of any kind. The only toxicity assessment I found is ten days long, in mice given 50 mg per kilogram twice daily into the abdomen, reporting normal blood counts, normal electrolytes and a normal level of creatine kinase, an enzyme that leaks out of damaged muscle. That is an observation inside a study about performance, not a toxicology package, and mice have been dosed for longer with no formal toxicology endpoints attached, six weeks in the heart failure study, which did report increased survival, and eight weeks in the kidney one. I could find no repeat dose toxicology study, no test of whether the compound damages DNA, and no safety pharmacology work of the kind that precedes a first human dose. One thing a reader should have alongside that emptiness: the same receptor has been pursued in the opposite direction, and a 2023 medicinal chemistry review covers compounds designed to turn the alpha receptor down, describing it as strongly expressed in breast cancer cells with high levels linked to poor outcomes in one subtype, triple negative breast cancer. Whether that matters to someone taking a compound that turns the same receptor up is not established, and I found no study addressing it. An empty file is not a clean one. Seller pages list fatigue, stomach upset, sleep changes and injection site reactions, and those are unsourced reports rather than trial findings.