Changes in the skeletal muscle transcriptome due to the intramuscular administration of lidocaine in wether lambs

Lidocaine is a commonly used local anesthetic that deadens tissues by blocking sodium channels in nociceptor neurons, thus preventing the transmission of pain signals to the brain. For medical and research purposes, lidocaine can be administered at the biopsy site to reduce discomfort during the procedure. These biopsy samples may be used to study the transcriptome under the assumption that lidocaine-treated tissue accurately reflects the genomic activity of untreated tissue. This study aimed to investigate how intramuscular lidocaine injections influence skeletal muscle gene expression in sheep with the goal of understanding how these transcriptomic changes could affect the interpretation and reliability of studies involving lidocaine or similar interventions. Approximately 10 minutes before euthanasia, the left biceps brachii muscle from each of 6 wether lambs was injected (IM; 20G hypodermic needle) at a depth of 3 cm with 2 mL of 2 percent lidocaine (20 mg/mL); the right biceps brachii was untreated. At necropsy, muscle samples were collected from the injection sites and contralateral limbs and flash-frozen. In an additional set of 4 wethers, lidocaine-treated and untreated biceps brachii and vastus intermedius muscles were collected. RNA was isolated and sequenced (Illumina 2x150 paired-end) to a targeted depth of 20 million reads per sample. Sequences were mapped to ARS_UI_Ramb_v2.0 and quantified. Matched pair analysis was performed in edgeR. No genes were consistently differentially expressed in both muscle types, indicating that the biceps brachii and the vastus intermedius responded differently to lidocaine administration, perhaps reflecting their distinct physiological roles. Lidocaine did influence the individual transcriptome of each muscle. The anti-inflammatory effects of lidocaine were evident in both muscle types, including the downregulation of immune-associated transcription factors and other genes. Lidocaine had an influence of varying magnitude and direction on other broad categories of genes, including those associated with muscle contractility, tissue repair, and structural integrity, which could affect transcriptome studies of muscle growth and development. Pathway analysis further revealed that lidocaine impacted signaling mechanisms for cellular connectivity and structural components. This study demonstrates that administering lidocaine to deaden muscle tissues results in a clear alteration of the gene expression of the tissue profiles, highlighting the importance of considering the potential influence of lidocaine in transcriptome analyses and recommending the use of complementary physiological measures to validate transcriptomic findings; this approach can help ensure that observed gene expression changes are accurately attributed to experimental conditions rather than the effects of lidocaine itself.