Weight gain is a common harmful side effect of atypical antipsychotics used for schizophrenia treatment. Conversely, treatment with the novel phosphodiesterase-10A (PDE10A) inhibitor MK-8189 in clinical trials led to significant weight reduction, especially in patients with obesity. This study aimed to understand and describe the mechanism underlying this observation, which is essential to guide clinical decisions.
We hypothesized that PDE10A inhibition causes beiging of White Adipose Tissue (WAT), leading to weight loss. Magnetic Resonance Imaging (MRI) methods were developed, validated and applied in a Diet Induced Obesity mouse model treated with a PDE10A inhibitor THPP-6 or vehicle for measurement of fat content and vascularization of adipose tissue.
Treated mice showed significantly lower fat fraction in white and brown adipose tissue, and increased perfusion and vascular density in WAT vs. vehicle, confirming the hypothesis, and matching the effect of CL-316,243, a compound known to cause adipose tissue beiging. The in vivo findings were validated by qPCR revealing upregulation of Upc1 and Pcg1-α genes, known markers of WAT beiging, and angiogenesis marker Vegf-A in the THPP-6 group.
This work provides a detailed understanding of the mechanism of action of PDE10A inhibitor treatment on adipose tissue and body weight, and will be valuable to guide both the use of MK-8189 in schizophrenia and the potential application of the target for weight loss indication.

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