Wellness-enhancing effects of the canine growth hormone releasing hormone therapy mediated by plasmid and electroporation in healthy old dogs

Min-Ok Ryu¹Sung-Moon Kim²J Joseph Kim³Hyun Namkung¹Hokyoung Jung⁴Hee Jin Nam²Charles Reed⁵Ga-Hyun Lim¹Eun Jin Kim^2*Hwa-Young Youn^1*

• ¹College of Veterinary Medicine, Seoul National University, Seoul, Republic of Korea
• ²Plumbline Life Sciences, Inc, Seoul, Republic of Korea
• ³AGENTA therapeutics, Blue Bell, United States
• ⁴HONGCHEON CTCVAC Co., Ltd., Hongcheon, Republic of Korea
• ⁵Independent consultant/contractor, Souderton, United States

Aging leads to increased disease susceptibility and weakened immunity, a condition known as immunosenescence. The growth hormone-releasing hormone (GHRH)/growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis plays a key role in both somatic growth and immune modulation. This study evaluated the clinical and immunological effects of a canine GHRH-encoding plasmid delivered by electroporation in 30 healthy senior dogs (aged 10–16 years). Dogs received a single intramuscular injection and were monitored over 180 days. Significant improvements were observed in clinical scores, with 90% of dogs showing increased well-being based on owner-assessed measures including appetite, activity, and exercise tolerance. Limb thickness, used as a surrogate for muscle mass, significantly increased in both hindlimbs by day 180. While mean serum IGF-1 concentrations did not change overall, post-hoc stratification revealed that dogs with low baseline IGF-1 (<90 ng/ml) showed substantial increases, whereas those with high baseline levels tended to decrease. This bidirectional modulation suggests feedback-sensitive regulation of the GHRH-GH-IGF-1 axis. Flow cytometry demonstrated increases in total CD3+ T cells, as well as naïve CD4+ and CD8+ T cell subsets, indicating a potential delay in immunosenescence. The therapy was well-tolerated, with no serious adverse effects reported; hematologic abnormalities and gastrointestinal symptoms were transient and resolved without intervention. These findings suggest that GHRH-encoding plasmid therapy may improve clinical condition and modulate immune function in aging dogs, warranting further investigation into its long-term efficacy and potential applications.