Unique advantages of dynamic l-[¹¹C]methionine PET/CT for assessing the rate of skeletal muscle protein synthesis: A pilot trial in young men

by Koichiro Sumi, Kana Yamazaki, Ryuichi Nishii, Misato Sakuda, Kentaro Nakamura, Kinya Ashida, Kentaro Tamura, Tatsuya Higashi

Although the standard method to evaluate skeletal muscle protein synthesis (MPS) is muscle biopsy, the method is invasive and problematic for multisite use. We conducted a small pilot study in volunteers to investigate changes in MPS according to skeletal muscle site using a noninvasive method in which 6 healthy young men were given yogurt (containing 20 g milk protein) or water, and 1 h later, l-[¹¹C]methionine ([¹¹C]Met) was administered intravenously. Dynamic PET/CT imaging of their thighs was performed for 60 min. The influx constant K_i of [¹¹C]Met in skeletal muscle protein was calculated as an index of MPS using a Patlak plot, and found to be 0.6%–28% higher after ingesting yogurt than after water in 5 of the 6 volunteer participants, but it was 34% lower in the remaining participant. Overall, this indicated no significant increase in K_i after ingesting milk protein. However, when the quadriceps and hamstring muscles were analyzed separately, we found a significant difference in K_i. This demonstrates the potential of visualizing MPS by calculating the K_i for each voxel and reconstructing it as an image, which presents unique advantages of [¹¹C]Met PET/CT for evaluating MPS, such as site-specificity and visualization.