Effects of photobiomodulation therapy on the local experimental envenoming by Bothrops leucurus snake

Highlights

• Bothrops leucurus venom caused hypernociception, edema, hemorrhage, and myotoxicity.

• Photobiomodulation therapy reduced the hypernociception caused by the venom.

• Photobiomodulation therapy reduced the edema caused by the venom.

• Venom-induced hemorrhage was not influenced by photobiomodulation therapy.

• Venom-induced myotoxicity was delayed by photobiomodulation therapy.

Abstract

Bothrops leucurus is the major causative agent of snakebites in Brazil's Northeast. The systemic effects of its venom are effectively neutralized by antivenom therapy, preventing bitten patients' death. However, antivenom fails in neutralizing local effects that include intense pain, edema, bleeding, and myonecrosis. Such effects can lead to irreversible sequels, representing a clinically relevant issue for which there is no current effective treatment. Herein, the effects of photobiomodulation therapy (PBMT) were tested in the local actions induced by B. leucurus venom (BLV) in mice (n = 123 animals in 20 experimental groups). A continuous emission AlGaAs semiconductor diode laser was used in two wavelengths (660 or 780 nm). Mechanical nociceptive thresholds were assessed with the electronic von Frey apparatus. Local edema was determined by measuring the increase in paw thickness. Hemorrhage was quantified by digital measurement of the bleeding area. Myotoxicity was evaluated by serum creatine kinase (CK) activity and histopathological analysis. PBMT promoted anti-hypernociception in BLV-injected mice; irradiation with the 660 nm laser resulted in faster effect onset than the 780 nm laser. Both laser protocols reduced paw edema formation, whether irradiation was performed immediately or half an hour after venom injection. BLV-induced hemorrhage was not altered by PBMT. Laser irradiation delayed, but did not prevent myotoxicity caused by BLV, as shown by a late increase in CK activity and histopathological alterations. PBMT was effective in the control of some of the major local effects of BLV refractory to antivenom. It is a potential complementary therapy that could be used in bothropic envenoming, minimizing the morbidity of these snakebite accidents.

Introduction

Snakebite envenoming is a world health issue indexed by the World Health Organization in the list of neglected tropical diseases [1]. The incidence of snakebites is higher in the tropical and subtropical areas of the globe, affecting mostly the poorest population living in developing countries [2]. Snakes from the genus Bothrops (Viperidae, Crotalinae) have a wide geographic distribution, occurring throughout the Americas from northeastern Mexico down to Argentina [3]. In Brazil, Bothrops spp. are accountable for the majority of venomous snakebites, comprising thousands of cases annually [4]. Among the species found in this country, Bothrops leucurus (white-tailed jararaca) is spread throughout Brazil's northeastern region, where it stands out as the main causative agent of snakebites [[5], [6], [7], [8]].

Bothropic envenoming (i.e. envenoming caused by Bothrops snakes) is characterized by both systemic and local effects. Systemically, the venom triggers hemodynamic disturbs [9] and nephrotoxicity [10], which are the major causes of death by Bothrops snakebite [11,12]. Locally, there is an intense inflammatory response marked by excruciating pain, edema, bleeding, and myonecrosis [[5], [6], [7],9,11]. The current treatment for snakebites is based on antivenom therapy, which is remarkably efficient, as shown by the significant decrease in lethality rates promoted by it [13]. Nevertheless, the local disturbs induced by bothropic venom are poorly neutralized by antivenom [14,15]. Experimental data show that even when antivenom is administered immediately after venom inoculation, the local effects persist [16]. Even though such disturbs are not life-threatening, they are liable for the high morbidity of the accidents, leading to extensive tissue loss, amputations, and disabling sequels that affect patients' life quality and economic productivity [17,18].

By virtue of this therapeutic gap, efforts have been made in attempt to elucidate the pathophysiology of the local effects of bothropic venom [19,20], laying ground for the proposal of complementary therapies aiming such effects [[21], [22], [23]]. One of the strategies proposed for the control of local alterations in bothropic envenoming is photobiomodulation therapy (PBMT) [[24], [25], [26], [27]]. PBMT, formerly known as low-level laser therapy (LLLT), has been studied for over fifty years, showing remarkable efficacy in the treatment of inflammatory conditions and in the repair of muscle damage [28]. Nevertheless, the therapeutic effects of PBMT are inconsistent across studies performed with different Bothrops species. While PBMT promotes an anti-inflammatory effect against B. jararacussu venom [25], the same is not true for B. moojeni [24]. Moreover, PBMT promotes a quick anti-myotoxic effect against B. moojeni venom [26], but not against B. jararacussu venom [27]. These differences could be attributed to the interspecific differences in venom composition, which varies greatly among the species of the genus Bothrops [29].

Considering that each Bothrops sp. has unique toxins and venom composition, the efficacy of a given treatment cannot be extrapolated to all congener species. Although some studies have shown the therapeutic effects of PBMT in bothropic envenoming, it is still unknown whether this therapy is suitable for patients bitten by B. leucurus, one of the major medically important snakes in Brazil. Therefore, the present work aimed to investigate the therapeutic potential of PBMT in the local effects experimentally induced by Bothrops leucurus venom (BLV).