The naked mole-rat has a functional purinergic pain pathway despite having a non-functional peptidergic pain pathway

P2X3 and P2X2/3 receptors inhibition produces a consistent analgesic efficacy: A systematic review and meta-analysis of preclinical studies

BACKGROUND

P2X3 and P2X2/3 receptors are promising therapeutic targets for pain treatment and selective inhibitors are under evaluation in ongoing clinical trials. Here we aim to consolidate and quantitatively evaluate the preclinical evidence on P2X3 and P2X2/3 receptors inhibitors for pain treatment.

METHODS

A literature search was conducted in PubMed, Scopus and Web-of-Science on August 5, 2023. Data was extracted and meta-analyzed using a random-effects model to estimate the analgesic efficacy of the intervention; then several subgroup analyses were performed.

RESULTS

67 articles were included. The intervention induced a consistent pain reduction (66.5 [CI95% = 58.5, 74.5]; p < 0.0001), which was highest for visceral pain (114.3), followed by muscle (79.8) and neuropathic pain (71.1), but lower for cancer (64.1), joint (57.5) and inflammatory pain (49.0). Further analysis showed a greater effect for mechanical hypersensitivity (70.4) compared to heat hypersensitivity (64.5) and pain-related behavior (54.1). Sex (male or female) or interspecies (mice or rats) differences were not appreciated (p > 0.05). The most used molecule was A-317491, but other such as gefapixant or eliapixant were also effective (p < 0.0001 for all). The analgesic effect was higher for systemic or peripheral administration than for intrathecal administration. Conversely, intracerebroventricular administration was not analgesic, but potentiated pain.

CONCLUSION

P2X3 and P2X2/3 receptor inhibitors showed a good analgesic efficacy in preclinical studies, which was dependent on the pain etiology, pain outcome measured, the drug used and its route of administration. Further research is needed to assess the clinical utility of these preclinical findings.

PROTOCOL REGISTRATION

PROSPERO ID CRD42023450685.

Phenylpropanoid-enriched broccoli seedling extract can reduce inflammatory markers and pain behavior

BACKGROUND

Pain is a worldwide problem requiring an effective, affordable, non-addictive therapy. Using the edible plant broccoli, a growth protocol was developed to induce a concentrated combinatorial of potential anti-inflammatories in seedlings.

METHODS

A growth method was utilized to produce a phenylpropanoid-rich broccoli sprout extract, referred to as Original Extract (OE). OE was concentrated and then resuspended for study of the effects on inflammation events. A rabbit disc model of inflammation and degeneration, and, a mouse model of pain behavior were used for in vivo and in vitro tests. To address aspects of mammalian metabolic processing, the OE was treated with the S9 liver microsome fraction derived from mouse, for use in a mouse in vivo study. Analytical chemistry was performed to identify major chemical species. Continuous variables were analyzed with a number of methods including ANOVA, and two-tailed t tests, as appropriate.

RESULTS

In a rabbit spine (disc) injury model, inflammatory markers were reduced, and levels of regenerative markers were increased as a result of OE treatment, both in vivo and in vitro. In a mouse pain behavioral model, after treatment with S9 liver microsome fraction, the resultant extract significantly reduced early and late pain behavior in response to a pain stimulus. The OE itself reduced pain behavior in the mouse pain model, but did not achieve the level of significance observed for S9-treated extract. Analytical chemistry undertaken on the extract constituents revealed identities of the chemical species in OE, and how S9 liver microsome fraction treatment altered species identities and proportions.

CONCLUSIONS

In vitro and in vivo results indicate that the OE, and S9-treated OE broccoli extracts are worthwhile materials to develop a non-opiate inflammation and pain-reducing treatment.

The naked truth: a comprehensive clarification and classification of current 'myths' in naked mole-rat biology

The naked mole-rat (Heterocephalus glaber) has fascinated zoologists for at least half a century. It has also generated considerable biomedical interest not only because of its extraordinary longevity, but also because of unusual protective features (e.g. its tolerance of variable oxygen availability), which may be pertinent to several human disease states, including ischemia/reperfusion injury and neurodegeneration. A recent article entitled 'Surprisingly long survival of premature conclusions about naked mole-rat biology' described 28 'myths' which, those authors claimed, are a 'perpetuation of beautiful, but falsified, hypotheses' and impede our understanding of this enigmatic mammal. Here, we re-examine each of these 'myths' based on evidence published in the scientific literature. Following Braude et al., we argue that these 'myths' fall into four main categories: (i) 'myths' that would be better described as oversimplifications, some of which persist solely in the popular press; (ii) 'myths' that are based on incomplete understanding, where more evidence is clearly needed; (iii) 'myths' where the accumulation of evidence over the years has led to a revision in interpretation, but where there is no significant disagreement among scientists currently working in the field; (iv) 'myths' where there is a genuine difference in opinion among active researchers, based on alternative interpretations of the available evidence. The term 'myth' is particularly inappropriate when applied to competing, evidence-based hypotheses, which form part of the normal evolution of scientific knowledge. Here, we provide a comprehensive critical review of naked mole-rat biology and attempt to clarify some of these misconceptions.

The Somatosensory World of the African Naked Mole-Rat

The naked mole-rat (Heterocephalus glaber) is famous for its longevity and unusual physiology. This eusocial species that lives in highly ordered and hierarchical colonies with a single breeding queen, also discovered secrets enabling somewhat pain-free living around 20 million years ago. Unlike most mammals, naked mole-rats do not feel the burn of chili pepper's active ingredient, capsaicin, nor the sting of acid. Indeed, by accumulating mutations in genes encoding proteins that are only now being exploited as targets for new pain therapies (the nerve growth factor receptor TrkA and voltage-gated sodium channel, Na_V1.7), this species mastered the art of analgesia before humans evolved. Recently, we have identified pain-insensitivity as a trait shared by several closely related African mole-rat species. In this chapter we will show how African mole-rats have evolved pain insensitivity as well as discussing what the proximate factors may have been that led to the evolution of pain-free traits.

Cholesterol-rich naked mole-rat brain lipid membranes are susceptible to amyloid beta-induced damage in vitro

Naked mole-rats are extraordinarily long-lived rodents that offer unique opportunities to study the molecular origins of age-related neurodegenerative diseases. Remarkably, they do not accumulate amyloid plaques, even though their brains contain high concentrations of amyloid beta (Aβ) peptide from a young age. Therefore, they represent a particularly favourable organism to study the mechanisms of resistance against Aβ neurotoxicity. Here we examine the composition, phase behaviour, and Aβ interactions of naked mole-rat brain lipids. Relative to mouse, naked mole-rat brain lipids are rich in cholesterol and contain sphingomyelin in lower amounts and of shorter chain lengths. Proteins associated with the metabolism of ceramides, sphingomyelins and sphingosine-1-phosphate receptor 1 were also found to be decreased in naked mole-rat brain lysates. Correspondingly, we find that naked mole-rat brain lipid membranes exhibit a high degree of phase separation, with the liquid ordered phase extending to 80% of the supported lipid bilayer. These observations are consistent with the 'membrane pacemaker' hypothesis of ageing, according to which long-living species have lipid membranes particularly resistant to oxidative damage. We also found that exposure to Aβ disrupts naked mole-rat brain lipid membranes significantly, breaking the membrane into pieces while mouse brain derived lipids remain largely intact upon Aβ exposure.