Anthrax Toxin

Introduction

Pain is a response and signal to organisms that there is damage to the body. This could be due to an infection, tissue damage or organ damage. Different types of pain medication have been manufactured in the last decade. This includes the artificial manufacture of opioids, non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, using pathogens like bacteria and other substances. Bacteria have been investigated for managing and treating pain, with varying levels of effectiveness.

Research by Yang et al. (2021) has shown that bacteria can interact with organisms and communicate with the nervous system, leading to analgesia (pain relief). Bacteria can also activate nociceptors, receptors that respond to pain, to alert the organism of damage. These nociceptors can also detect bacterial processes that release pain-producing toxins. Yang et al.’s research specifically looked at the bacterial toxin Bacillus anthracis (Figure 1). It is a significant factor in the spread of anthrax, an infectious disease, and their experiments showed that it can lead to analgesia, as Bacillus anthracis and nociceptors can work together to suppress pain.

The experiment

The experiment by Yang et al. looked at different methods to target and suppress specific nociceptive neurons to decrease pain in mammals using bacteria.

The study focused on the interactions between nociceptors and Bacillus anthracis. The researchers found that Bacillus anthracis toxin was made up of three substances: protective antigen (PA), lethal factor (LF), and edema factor (EF), as shown in Figure 2. They created edema toxin (ET) using PA and EF, and administered the ET to mice via the intrathecal route (through the spinal canal, also shown in Figure 2). The scientists used different doses of PA, LF and EF. The intrathecal route was used to limit the diffusion of ET to the spinal cord and sensory neurons, preventing ET from moving into other organs.

The researchers then analysed the mouse neurons to compare the sequences before and after the experiments and determine the effectiveness of the treatments. The results indicated high levels of ANTXR2 receptors (high-affinity receptors for anthrax toxins), meaning the response to pain was faster.

The results

The researchers examined the mechanical sensitivity and thermal latency. Mechanical sensitivity is the ability to differentiate between and respond to mechanical stimuli, and thermal latency is the ability to differentiate between and respond to heat stimuli.

In mammals, signs of pain can be quantified using these indicators. The higher the threshold, the lower the pain. The threshold levels of these factors were compared up to 24 hours after the injections of the PA, PA + LF and PA + EF, as shown in Figure 3.

Figure 3: Line graphs showing the results of the intrathecal injections. (A) Line graph of mechanical sensitivity thresholds after intrathecal administration. (B) Line graph of thermal sensitivity thresholds after intrathecal administration. (C) Line graph of mechanical sensitivity thresholds on the day and 24 hours after the second injection.

After administration of the injections via the intrathecal route, thresholds of mechanical sensitivity, Figure 3A, were increased significantly for several hours. The injection of PA + EF resulted in the highest threshold, remaining at 1.0 g 6 hours post-injection, compared to the injections of PA and PA + LF, which both had a threshold of below 0.5 g 6 hours post-injection.

The thresholds of thermal latency, shown in Figure 3B, also increased significantly for several hours. Again, the injection of PA + EF resulted in the highest latency, remaining for more than 20 seconds 6 hours post-injection, compared to the injections of PA and PA + LF, which both had a latency of below 20 seconds 6 hours post-injection.

The results from Figures 3A and 3B suggest that the injections of PA + EF were the most effective in increasing the thresholds of both mechanical sensitivity and thermal latency.

A second injection of ET was administered, and thresholds of mechanical sensitivity were again elevated, as shown in Figure 3C. After the second injection, the effects of pain relief were more potent. In the graph, at D2, the threshold of mechanical sensitivity 6 hours after the second injection was above 1.5 g for mice given ET, compared to below 1.0 g 6 hours after the first injection for mice given ET. This could be due to the upregulation of the ANTXR2 receptors induced by ET. Upregulation is when hormone secretion is suppressed, and the number of receptors (in this case, ANTXR2) increases, causing a faster response to the stimulus (in this case, pain). This suggests that ET can result in pain receptors being affected, leading to a faster analgesic response.

The researchers concluded that this experiment did result in analgesia in mice as ET targeted specific nociceptors. The results from this experiment are significant because they indicate that pain behaviour can be blocked by intrathecal administration of a harmful bacterial toxin such as Bacillus anthracis.

Conclusion

Yang et al. (2021) found that the injection of the ET via the intrathecal route results in blocked pain behaviour in mice. The experiment is significant as it has shown that a harmful toxin can have positive effects. However, it is difficult to know if the effects will be replicated in humans as human trials have not yet been carried out.

In addition, the sample size was very small, with a maximum of eight mice observed after each injection. This could result in high variability (the data points would be more spread out from the mean and, therefore, less consistent) and inconclusive results.

Nevertheless, with further study, experimentation, and refinement of the ET via the intrathecal method, new therapies for people with pain, especially chronic pain, could be created in the future. Different dosages of the ET could be experimented upon to see whether a higher dosage has better results, with a bigger sample size, and human trials. The results from Yang et al. (2021) showed that intrathecal ET injections are promising, and if successful in humans, this method would ease the burden on healthcare systems worldwide.

Written by Naoshin Haque

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