SLU-PP-332

What is SLU-PP-332?

SLU-PP-332 is a synthetic compound developed at Saint Louis University (SLU) that agonizes estrogen-related receptors (ERRs), a family of orphan nuclear receptors involved in mitochondrial biogenesis and oxidative metabolism. ERRs (ERR-alpha, ERR-beta, and ERR-gamma) are transcription factors that regulate genes responsible for fatty acid oxidation, mitochondrial function, and energy homeostasis in metabolically active tissues, particularly skeletal muscle, heart, and brown adipose tissue.

The compound emerged from research by Dr. Thomas Bhurre's laboratory at SLU, where high-throughput screening identified SLU-PP-332 as a potent and selective ERR agonist. In preclinical studies published in 2023, mice treated with SLU-PP-332 showed dramatic improvements in exercise endurance (running 70% longer and 45% further than untreated controls) without any exercise training. The compound increased the proportion of fatigue-resistant type IIa and type I muscle fibers while enhancing mitochondrial respiratory capacity.

SLU-PP-332 differs from other exercise mimetics (like AICAR, which activates AMPK) by targeting the transcriptional program that controls muscle fiber type specification. ERR activation upregulates PGC-1alpha target genes, promoting a shift from glycolytic fast-twitch fibers toward oxidative slow-twitch fibers. This muscle remodeling is normally achieved only through sustained endurance training. The compound is being investigated for applications in muscle wasting, metabolic syndrome, and conditions where exercise is limited.

Mechanism of Action

SLU-PP-332 acts at the transcriptional level, reprogramming gene expression in muscle tissue to mimic the molecular adaptations normally triggered by endurance exercise.

ERR Activation & Target Gene Expression

Estrogen-related receptors are orphan nuclear receptors (no known endogenous ligand) that bind to ERR response elements (ERREs) in the promoter regions of genes involved in oxidative metabolism. SLU-PP-332 binds to the ligand-binding domain of ERR-alpha, ERR-beta, and ERR-gamma, stabilizing the active conformation and promoting transcription of target genes including those encoding mitochondrial respiratory chain components, fatty acid oxidation enzymes, and the transcriptional coactivator PGC-1alpha [2].

Muscle Fiber Type Conversion

The most striking effect of SLU-PP-332 is the shift in muscle fiber composition. Skeletal muscle contains a spectrum of fiber types: type I (slow oxidative), type IIa (fast oxidative), type IIx (fast intermediate), and type IIb (fast glycolytic). ERR activation promotes conversion from type IIb/IIx toward type IIa and type I fibers. These oxidative fibers have higher mitochondrial density, greater capillary supply, and are resistant to fatigue. This conversion normally requires months of endurance training [1].

Mitochondrial Biogenesis

ERR-gamma is a master regulator of mitochondrial function in metabolically active tissues. SLU-PP-332 activation of ERR-gamma upregulates nuclear-encoded mitochondrial genes, increasing mitochondrial density and respiratory capacity in muscle fibers. This is mechanistically linked to PGC-1alpha co-activation — the same pathway activated by exercise, caloric restriction, and cold exposure [3].

Metabolic Reprogramming

Beyond structural changes in muscle, ERR activation shifts substrate utilization from glucose toward fatty acids. This metabolic reprogramming increases fat oxidation capacity, reduces reliance on glycogen (extending endurance), and may improve metabolic flexibility. In obese mouse models, ERR agonism has been associated with reduced body weight and improved insulin sensitivity, though these effects have not been studied with SLU-PP-332 specifically.

Dosing Considerations

SLU-PP-332 is a relatively new research compound with no human clinical trials. All dosing information is derived from preclinical mouse studies and allometric scaling estimates.

Reconstitution Guide

Reconstitute lyophilized SLU-PP-332 with bacteriostatic water. As a newer compound, dissolution characteristics may vary. Never shake the vial.

1. Remove the plastic cap from the vial and wipe the rubber stopper with an alcohol swab. Allow to dry completely.
2. Draw 1 mL of bacteriostatic water into a sterile syringe. For a 5 mg vial, this yields a concentration of 5 mg/mL.
3. Insert the needle through the rubber stopper at a slight angle. Inject the water slowly against the inner wall of the vial — do not spray directly onto the powder.
4. Allow the vial to sit for 2–3 minutes. Gently roll the vial between your palms if needed. Do not shake or vortex.
5. The solution should be clear. Discard if you observe any cloudiness, particulate matter, or discoloration.

Injection Technique

SLU-PP-332 is administered via subcutaneous injection. Standard SubQ peptide injection technique applies.

1. Clean the injection site with an alcohol swab and allow it to air dry completely (approximately 30 seconds). Common sites: lower abdomen (2 inches from navel), upper thigh.
2. Draw the dose. Insert the needle into the vial through the rubber stopper. Invert the vial and draw the calculated number of units slowly. Tap the syringe to move any air bubbles to the top, then push them out gently.
3. Pinch the skin at the injection site to create a fold of subcutaneous tissue. Insert the needle at a 45-degree angle in a quick, smooth motion. Release the skin fold.
4. Inject slowly. Depress the plunger steadily over 5–10 seconds. Withdraw the needle at the same angle it was inserted. Apply gentle pressure with a clean swab if needed.

Storage & Stability

Limited stability data is available for SLU-PP-332 as a newer research compound. Conservative storage practices are recommended.

Side Effects & Considerations

SLU-PP-332 has very limited safety data. All information is derived from preclinical mouse studies. No human safety or toxicology data exists.

Preclinical Safety Data

• No reported toxicity in mouse models at studied doses (10–50 mg/kg IP, twice daily).
• No observed adverse behavioral effects or weight loss in treated mice.
• Mice maintained normal food intake and activity levels outside of exercise testing.

Theoretical Considerations

• ERR-gamma is highly expressed in heart tissue. Cardiac effects of sustained ERR agonism are unknown and represent a theoretical safety concern that has not been adequately studied.
• Long-term effects of pharmacologically forced muscle fiber type conversion are unknown. Whether this adaptation is fully reversible upon discontinuation has not been established.
• ERR activation affects mitochondrial function broadly. Effects on non-muscle tissues (liver, kidney, brain) at systemic doses are not characterized.
• No reproductive or developmental toxicity studies have been conducted.
• No drug interaction studies have been performed.

Related Compounds

Researchers studying SLU-PP-332 often investigate these related compounds:

Literature & Citations

1. Kim W, Sung J, Bhurre T, et al. SLU-PP-332 is a novel ERR agonist that enhances exercise capacity. Presented at ACS Spring Meeting. 2023.
2. Rangwala SM, Wang X, Calvo JA, et al. Estrogen-related receptor gamma is a key regulator of muscle mitochondrial activity and oxidative capacity. J Biol Chem. 2010;285(29):22619-22629. PubMed
3. Fan W, Evans R. PPARs and ERRs: molecular mediators of mitochondrial metabolism. Curr Opin Cell Biol. 2015;33:49-54. PubMed
4. Narkar VA, Downes M, Yu RT, et al. AMPK and PPARdelta agonists are exercise mimetics. Cell. 2008;134(3):405-415. PubMed
5. Gan Z, Rumsey J, Hazen BC, et al. Nuclear receptor/microRNA circuitry links muscle fiber type to energy metabolism. J Clin Invest. 2013;123(6):2564-2575. PubMed
6. Villena JA, Kralli A. ERRalpha: a metabolic function for the oldest orphan. Trends Endocrinol Metab. 2008;19(8):269-276. PubMed