Melittin, a honeybee venom derived peptide for the treatment of chemotherapy-induced peripheral neuropathy

Cancer continues to be the leading cause of morbidity and mortality in the globe [1, 2] with mortality increases of about 25.0% since the 1990s and estimates as much as ≥ 23 million annually by 2030 [3, 4]. Most of the cancer patients are either treated with curative or palliative chemotherapy throughout the treatment. While chemotherapy has significantly enhanced survival rates in several cancer forms, chemotherapy-induced peripheral neuropathy (CIPN) is a common and serious clinical problem that affects many patients receiving cancer treatment.

Based on the particular chemotherapeutic compounds, there can be different types of neuropathies: large and small fiber, sensory and/or motor, demyelinating and axonal, cranial, and autonomic [5]. Chemotherapy’s effects on the nervous system vary across different types of medications in which drug’s physical and chemical properties, whether used in single or combined doses have a significant role [6]. The prevalence of CIPN is based on the person, with rates reported ranging from 19% to over 85% [7] and it is the largest for platinum-based medications (70–100%) followed by taxanes (11–87%), ixabepilone (60–65%), and thalidomide and its analogs (20–60%), (6). Toxicity can occur either with a large single dosage or after combined exposure. The signs observed differ in severity, duration, and range from intense temporary warm stimuli to persistent peripheral nerve changes caused by severe pain and lasting nerve damage. Recent reports placed the prevalence of CIPN at about 68.1% when assessed in the first month following chemotherapy, 60% at third months, and 30% after sixth months [8]. Chemotherapeutics, such as oxaliplatin and paclitaxel, are major sources of neuropathic pain caused by the medication. CIPN results in impairment in the quality of life of cancer survivors patients and often lead to change in either the drug dosages or combinations especially in patients with acute neuropathy. CIPN is seen as an acceptable, unavoidable complication of chemotherapy by caregivers, and is also necessary to save the life of patients [9]. In contrast, CIPN was seen by cancer patients as an often difficult chemotherapeutic complication affecting their quality of life [10]. CIPN put up to delay functional recovery, decrease treatment tolerability causing symptom distress in cancer patient [9]. Clinical symptoms of CIPN mainly involve sensory axonal neuropathy with occasionally motor and autonomic indulgence affecting predominantly the arm and leg of the patients. Usually, sensory fibers are mostly affected but sometimes cause a sensorimotor pattern by cytostatic agents. Typical symptoms include numbness, paraesthesia, lancinating pain, abnormal gait, and motor weakness. It is important to keep in mind that CIPN will extend beyond antineoplastic therapy for several years and is associated with an elevated risk of falls [11]. Hence, cancer-related neuropathy is considered a major adverse outcome for cancer patients. No drug can currently be proposed as a gold standard to either prevent CIPN or treat its symptoms, and the only preventive strategy remains to modify the chemotherapeutic drug dose. According to the American Society of Clinical Oncology (ASCO), clinicians may offer duloxetine along with tricyclic antidepressants, gabapentin, or pregabalin to manage CIPN-induced symptoms. However, these agents do not affect motor symptoms or negative sensory symptoms [12, 13]. Therefore, a curative medication needs to be established that can be used to treat this complication. The review summarises the numerous research groups' attempts to subdue the chemotherapy-induced neuropathy using melittin and reflects on the potential strategies of resolving haemolysis caused by melittin.

CIPN can induce severe pain and impairment leading to significant loss of functional ability and reduced quality of life. Neurotoxic chemotherapy can cause peripheral nerve structural damage resulting in aberrant somatosensory processing of the peripheral and central nervous system [14]. It is rare to reach the firing threshold in normal primary afferent neurons without the input of a stimulus. However, after nerve injury it is believed that most damaged axons and related cell bodies in the diagnosis-related groups experience an increase in their intrinsic electrical excitability. As a consequence, they start generating impulse discharge spontaneously or with only minimal stimulation associated with the site of injury resulting in excessive spontaneous and stimulus-related electrical impulses feeding into the central nervous system [15]. There are four main substance groups namely platinum-based antineoplastic agents, taxanes, epothilones and immunomodulatory drugs that cause damage to peripheral sensory, motor and autonomic neurons, which result in the development of CIPN. Following are the mechanisms of CIPN induced by these drugs.

The majority of drug-induced peripheral neuropathies (DIPN) cause damage to the dorsal root ganglia and account for just 4% of all neuropathies, but DIPN can occur in 60% of patients undergoing chemotherapy [24, 25]. At present, the expert opinion of the American Society for Clinical Oncology’s 2014 Practice Guide has suggested that no agents can be approved for the prevention of CIPN and offers only modest support for treatment with a serotonin-norepinephrine reuptake inhibitor, duloxetine [11]. Unfortunately, duloxetine is associated with adverse effects (nausea, dizziness, and insomnia), and the prescription of the medication must be carefully controlled by a doctor [13]. As an alternative to duloxetine, tropical agents are sometimes recommended but have only symptomatic relief. Ketamine, baclofen, and amitriptyline topical application improved tingling sensory subscales but did not improve numbness, thermal pain, or functional abilities [26]. Due to a related overlapping process of mitotoxicity as part of pathophysiology, it is probable that a single pharmacological therapy may be possible for all CIPNs [27]. The existing medications approved for CIPN are only marginally successful in the management of symptoms of neuropathy. In fact, after the discontinuation of the medications, symptoms reappear. It has witnessed that presently available medications for the disease provide only short-term symptomatic relief and have significant adverse side effects. Unfortunately, there is no standard treatment procedure regarding CIPN prevention, mitigation, and management.

Honey bee venom (HBV) is a colourless, acidic liquid (pH 4.5–5.5) and the most valuable product of the honeybee. Its potential therapeutic value has been attributed to many diseases, particularly in rheumatic and arthritic conditions. HBV has at least 28 different active compounds with distinct health benefits. Several studies identified these compound’s biological properties and the health benefits of each ingredient. However, melittin is the main vital pharmacological component of HBV accounting for 40–50% dry weight of the venom [28]. It is a peptide with 26 amino acid residues and because of its amphiphilic nature, it is water-soluble [29]. If the allergenic components and histamine are removed, it is a safer product than whole bee venom [30, 31].

Melittin has many therapeutic values such as anti-viral, anti-bacterial, anti-fungal, anti-parasitic, anti-cancer and neuroprotective effect [32‐35]. It strengthens muscle control, suppresses the development of pro-inflammatory cytokines, increases the expression of muscle regeneration factors (MyoD, myogenin, and α-SMA) and improved histological changes of damaged tissue in animal model of muscle contusion (Fig. 4) [36, 37]. In the studies conducted using different animal models of pain, HBV acupuncture has been reported to have a potent analgesic effect [34, 36, 38] and two studies have suggested that bee venom acupuncture treatment can help to reduce peripheral neuropathy caused by chemotherapy. Although there is no clinical trial evaluating the impact of melittin on humans, Park et al. examined the efficacy and protection of the sweet bee venom pharmacoacupuncture on five patients with peripheral neuropathy (CIPN) caused by chemotherapy [39, 40]. The graphic comparison scale of patients and the CIPN classification of the world health organization (WHO) as the primary outcomes shown that the treatment is effective without causing significant adverse effects such as allergic reaction. Since sweet bee venom therapy uses melittin, the discovery indicates that melittin can be used safely for future patients. When administered 20 min before treatment, prazosin (α1-adrenergic receptor antagonist, 30 μg, i.t.) or idazoxan (α2-adrenergic receptor antagonist, 50 μg, i.t.) blocked melittin analgesia on mechanical and cold allodynia. This suggested involvement in the melittin analgesic effects of both the spinal α1- and 2 adrenergic receptors [35]. Bee venom acupuncture combined with morphine has prolonged analgesic effects, in comparison to BVA or morphine alone. Similarly, it has shown that BVA could enhance the analgesic effect of clonidine injection in the persistent constriction-caused neuropathic pain model [41]. Whole honeybee venom attributes to allergic reaction whereas melittin is free from such action.

Because of its intense surface action on lipid membranes accompanied by the release of inflammatory mediators and the activation of primary nociceptor cells [34], melittin has thus far been considered a pain-producing agent. Subcutaneous injection of melittin on the back surface of rat’s hind paw actually produced spontaneous paw flinching reflex and an increase in the incidence of spontaneous spinal wide dynamic range (WDR) neuron discharges on the hind paw’s cutaneous receptive area. In contrast, subcutaneous melittin administration on the ST36 acupuncture point did not produce unwanted unpredictable behaviour. Injecting melittin at ST36 will contribute to more analgesic effect than systemic administration and the adverse effect associated with the melittin produced by injecting it through systemic injection such as intraperitoneal or intravenous can be avoided. Moreover, it did not generate spontaneous discharge of wide dynamic neuron that was stated to respond to the sensitive hind paw. Analgesic impact of acupuncture or electroacupuncture on ST36 was induced by triggering the descending pain inhibitory system [35], melittin injection on ST36 may also have triggered the descending noradrenergic inhibitory system. Melittin’s cytotoxicity depends on its dosage, considering its sensitivity to the erythrocyte membrane, low-dose intradermal, or subcutaneous injection of melittin may also be a safe method for haemolysis prevention [42].

Despite having a strong effective report against chemotherapeutic-induced neuropathy, melittin was ruled out from clinical applicability since it induces haemolysis which might lead to rhabdomyolysis and acute renal failure resulting in a broad range of clinical signs starting from local oedemic swelling of skin to a life-threatening systemic anaphylactic shock [43]. These toxic features of melittin are indeed assumed as restricting factors for its use in cancer therapy [44]. Other reasons such as toxicity, lack of precision, degradation, systemic inefficiency, and limited bioavailability are also concerns for its therapeutic application [44‐46]. To overcome these problems, various approaches including nanotechnology, gene therapy, and immunoconjugate were tried on melittin [30, 38]. However, the problem still persists and continues to be challenging [47]. Novel approaches are indeed necessary to tackle side effects associated with melittin treatments. In our study with melittin, we found that melittin-induced haemolysis in human RBCs can be inhibited by α-crystallin (human eye lens proteins). This study gives hope to use an appropriate amount of combination of melittin with α-crystallin to use it for therapeutic application without the problem of haemolysis.

Haemolysis is one of the major side effects of melittin which limits its usage in treating various diseases including chemotherapeutic-induced neuropathy. It was found that α-Crystallin (eye lens protein) can subdue the melittin-induced haemolysis in human RBC which indicates that melittin in combination with α-Crystallin can be useful in treating chemotherapeutic-induced neuropathy.

Crystallins are water-soluble chaperone proteins found in the lenses of all vertebrate eyes at high levels [48]. There are three classes of crystallins found in the human eye, namely α, β, and γ, which make up to more than 90% of the lens’ proteins [49]. α-Crystallin accounts for about 35% of all proteins of the vertebrate lens and is known to have chaperone-like properties and is a representative member of the small heat shock proteins (sHsp) [50‐52]. It is understood that α-crystallin exhibits many physiological roles, i.e. preventing denatured protein precipitation and enhancing cellular tolerance to stress that are essential for maintenance of lens transparency and the prevention of cataract. Moreover, subunits of α-crystallin can inhibit cellular aggregation and protein inactivation in different stress states. It was discovered that melittin interacts with α crystallin with amino acid residues 13–21 and 71–88 of αA-crystallin and residues 70–78 of αB-crystallin [52].

Whole honeybee venom and melittin are effective in treating few diseases. Particularly, in case of chemotherapy-induced neuropathy, melittin ameliorated the condition by improving mechanical hyperalgesia, cold allodynia and spinal wide dynamic range. Despite that, their usage has often been limited due to its side effects, mainly haemolysis. Since it is demonstrated that α-crystallin can inhibit melittin-induced haemolysis, it is plausible that this combination if used in appropriate ratios in the treatment of chemotherapeutic-induced neuropathy may have therapeutic benefit. Therefore, there is a need to further investigate the proposed combinational therapy with respect to its efficacy and safety.