Novel treatment and insight for irradiation-induced injuries: Dibucaine ameliorates irradiation-induced testicular injury by inhibiting fatty acid oxidation in primary Leydig cells

BACKGROUND

Male infertility is a worldwide problem but few treatments, especially irradiation-induced testicular injury. The aim of this research was to investigate novel drugs for the treatment of irradiation-induced testicular injury.

METHODS

We administered dibucaine (0.8 mg/kg) intraperitoneally to male mice (6 mice per group) after five consecutive daily 0.5 Gy whole-body irradiation, and evaluated its ameliorating efficacy by testicular HE staining and morphological measurements. Drug affinity responsive target stability assay (Darts) were used to find target protein and pathway; mouse primary Leydig cells were isolated and to explore the mechanism (Flow cytometry, Western blot, and Seahorse palmitate oxidative stress assays); finally rescue experiments were completed by combining dibucaine with fatty acid oxidative pathway inhibitors and activators.

RESULTS

The testicular HE staining and morphological measurements in dibucaine treatment group was significantly better than that in irradiation group (P < 0.05); sperm motility and mRNA levels of spermatogenic cell markers were also higher than those in the latter (P < 0.05). Darts and Western blot results showed that dibucaine targets CPT1A and downregulate fatty acid oxidation. Flow cytometry, Western blot, and Palmitate oxidative stress assays of primary Leydig cells demonstrated that dibucaine inhibits fatty acid oxidation in Leydig cells. Dibucaine combined with etomoxir/baicalin confirmed that its inhibition of fatty acid oxidation was beneficial in ameliorating irradiation-induced testicular injury.

CONCLUSIONS

In conclusion, our data suggest that dibucaine ameliorates irradiation-induced testicular injury in mice by inhibiting fatty acid oxidation in Leydig cells. This will provide novel ideas for the treatment of irradiation-induced testicular injury.

Pre-clinical evaluation of new dibucaine formulations for preventive analgesia

We have previously developed ammonium sulphate gradient loaded liposomes to encapsulate dibucaine. Thus, the purpose of this study was to evaluate the pre-clinical safety and effectiveness of this novel ionic liposomal formulation of dibucaine (DBC), as described in previous work. Effectiveness was evaluated in vivo on Wistar rats (n = 8) that received plain DBC or liposomal DBC (DBC_LUV). Control empty liposomes (without DBC) or saline were also used as control. Sciatic nerve block was performed using the formulations or controls (0.4 mL). A hindpaw incision-based postoperative pain model was used to evaluate mechanical hypersensitivity with von Frey filaments. To verify antiinflamatory activity protein levels of TNF-α, IL-1β, substance P and CGRP were measured by ELISA in the hindpaw tissue after 1 and 6 hours of the incision. To corroborate drug safety, sciatic nerve Schwann cell cultures were treated with the aforementioned formulations and assessed for cell viability (MTT assay) and death (flow cytometry assay). Histopathology of the tissues surrounding the sciatic nerve region was also assessed 2 and 7 days after treatment. All animals presented post incisional hypersensitivity and DBC_LUV showed longer analgesic effect (p < 0.001). DBC_LUV reduced TNF-α and CGRP levels (p < 0.05). Histopathological evaluation showed greater inflammatory reaction after the administration of control liposomes when compared to DBC (p < 0.05). There was no difference in Schwann cell viability and death between plain and encapsulated DBC. DBC_LUV was safe and enhanced anaesthesia duration due to slow release of dibucaine from ammonium sulphate gradient loaded liposomes.

History of T-cain: a local anesthetic developed and manufactured in Japan

In many anesthesia textbooks written in English, lidocaine, tetracaine, bupivacaine, ropivacaine, and chloroprocaine are listed as useful local anesthetics for spinal anesthesia. In contrast, T-cain is not included in these lists, even though it has been reported to be suitable for spinal anesthesia in Japan. T-cain was developed as a local anesthetic in the early 1940s by Teikoku Kagaku Sangyo Inc. in Itami, Japan, by replacing a methyl group on tetracaine (Pantocaine(®)) with an ethyl group. T-cain was clinically approved for topical use in Japan in November 1949, and a mixture of dibucaine and T-cain (Neo-Percamin S(®)) was approved for spinal use in May 1950. Simply because of a lack of foreign marketing strategy, T-cain has never attracted global attention as a local anesthetic. However, in Japan, T-cain has been used topically or intrathecally (as Neo-Percamin S(®)) for more than 60 years. Other than the side effects generally known for all local anesthetics, serious side effects have not been reported for T-cain. In fact, several articles have reported that T-cain decreases the neurotoxicity of dibucaine. In this historical review, the characteristics of T-cain and its rise to become a major spinal anesthetic in Japan are discussed.