OAT and Insulin resistance: L-ornithine is further broken down by ornithine aminotransferase (OAT) to produce polyamines (putrescine, spermidine, and spermine) that contribute to β-cell dysfunction, insulin resistance, and pro-inflammatory responses, or by ornithine decarboxylase (ODC) to produce L-proline, which mediates β-cell dysfunction and insulin resistance.