Of Mice and Methamphetamine

Diabetes drug being tested for addiction.

It’s a mouthful: peroxisome proliferator activated receptor gamma (PPAR-gamma). 

Peroxisomes are specialized subunits inside cells that help metabolize various substances, including fatty acids and certain toxins. A blockbuster member of this drug family—Avandia—is a much disputed but immensely lucrative diabetes medicine that may cause heart failure.

(Partial Agonist Ppar Gamma Cocrystal)--------->

PPAR gamma agonists belong to a class of drugs known as thiazolidinediones. Clinical research has pointed toward additional therapeutic applications for thiazolidinediones in the areas of inflammation and cancer. The only approved use for thiazolidinediones is in the treatment of diabetes, but the drug class has also been studied for treatment of polycystic ovary syndrome, psoriasis, autism—and now drug addictions. A PPAR compound will soon undergo testing under the auspices of the Omeros Corporation, with funding from the National Institute on Drug Abuse (NIDA).

Omeros says it has developed a novel drug “for the prevention and treatment of addiction to substances of abuse, such as opioids nicotine and alcohol, as well as other compulsive behaviors, including eating disorders.” Phase 2 clinical studies on opiate addiction by Dr. Sandra D. Comer and associates at the New York State Psychiatric Institute will begin soon, according to an Omeros press release.

Such claims add up to a tall order for any anti-craving drug. In fact, no drug currently exists for the treatment of so wide a spectrum of addictive disorders. Nonetheless, Omeros claims to have demonstrated a previously unknown link between a variant of this family of diabetes medications and addiction.

The heart problems linked to the PPAR marketed as Avandia may be a special case. According to an article by Gardiner Harris in the New York Times, based on government reports obtained by the newspaper: “If every diabetic now taking Avandia were instead given a similar pill named Actos, about 500 heart attacks and 300 cases of heart failure would be averted every month because Avandia can hurt the heart. Avandia, intended to treat Type 2 diabetes, is known as rosiglitazone and was linked to 304 deaths during the third quarter of 2009.” Actos, another thiazolidinedione, has not been linked to any heart trouble.

 GlaxoSmithKline is disputing the findings. A number of other pharmaceutical houses—AstraZeneca, and Eli Lilly among them—discontinued their first generation PPAR drugs. The derivative marketed as Avandia is not the compound under study by Omeros.

There is little clinical evidence to bolster the PPAR theory. A recent Spanish study suggested the possibility that PPAR gene variants may be associated with higher alcohol consumption in a small sampling of Mediterranean drinkers.

The most comprehensive study may be a 2007 paper in Neuropsychopharmacology by Takehiko and coworkers, demonstrating that PPARs can have an effect on behavioral sensitization to methamphetamine in mice.

Behavioral sensitization is the name for the progressive increase in meth-driven locomotor activity over time. The researchers found that a PPAR variant “plays an inhibitory role in the expression” of sensitization to methamphetamine. The action takes place in the brain’s nucleus accumbens, where repeated hits of meth cause an increase in PPAR expression, according to the researchers: “These results indicate that [an isotope of PPAR] in the reward system is involved in behavioral sensitization to METH.”

What is the mechanism of action? The researchers speculate that upregulation and activation of PPAR in the meth-crazy mice may be due in part to an inflammatory response. PPAR, in theory, exerts anti-inflammatory activity in brain cells.  And psychostimulants, according to the researchers, “upregulate the expression of target genes via activation of inflammatory-responsive transcriptional factors.”

Maeda, T., Kiguchi, N., Fukazawa, Y., Yamamoto, A., Ozaki, M., & Kishioka, S. (2006). Peroxisome Proliferator-Activated Receptor Gamma Activation Relieves Expression of Behavioral Sensitization to Methamphetamine in Mice Neuropsychopharmacology, 32 (5), 1133-1140 DOI: 10.1038/sj.npp.1301213

Graphics Credit: http://www.prostaglandinresearch.com