Microglial inflammation modulates opioid analgesic tolerance.

As we all know, opioids are the drugs of choice for treating severe pain. However, very often, opioid use leads to tolerance, dependence, and hyperalgesia. Therefore, understanding the mechanisms underlying opioid tolerance and designing strategies for increasing the efficacy of opioids in chronic pain are important areas of research. Microglia are brain macrophages that remove debris and dead cells from the brain and participate in immune defense of the central nervous system during an insult or injury. However, recent studies indicate that microglial activation and generation of proinflammatory molecules (e.g., cytokines, nitric oxide, eicosanoids, etc.) in the brain may contribute to opioid tolerance and other side effects of opioid use. In this review, we will summarize the evidence and possible mechanisms by which proinflammatory molecules produced by activated microglia may antagonize the analgesic effect induced by opioids, and thus, lead to opioid tolerance. We will also delineate specific examples of studies that suggest therapeutic targets to counteract the development of tolerance clinically using suppressors of microglial inflammation.

Smooth or Risky Revisit of an Old Malaria Drug for COVID-19?

Hydroxychloroquine (HCQ) is an old medication for malaria. In addition to handling this parasitic disease, HCQ is also used to treat a number of autoimmune disorders including rheumatoid arthritis and systemic lupus erythematosus when other medications are not effective. Recently a new viral infection (COVID-19) is rocking the entire world so much that it has already taken more than 200,000 lives throughout the world within the last two months and the World Health Organization was forced to declare it as a pandemic on March 11, 2020. Interestingly, some reports indicate that this wonder drug may be also beneficial for COVID-19 and accordingly, many clinical trials have begun. Here, we discuss different modes of action (anti-inflammatory, antioxidant, inhibition of endosomal acidification, suppression of angiotensin-converting enzyme 2 or ACE2 glycosylation, etc.) of HCQ that might be responsible for its possible anti-COVID-19 effect. On the other hand, this review also makes an honest attempt to delineate mechanisms (increase in vasoconstriction, inhibition of autophagy, depletion of T cells, etc.) indicating how it may aggravate certain conditions and why caution should be taken before granting widespread repurposing of HCQ for COVID-19. Graphical Abstract.

Low-Dose Aspirin Upregulates Tyrosine Hydroxylase and Increases Dopamine Production in Dopaminergic Neurons: Implications for Parkinson's Disease.

Increasing the function of residual dopaminergic neurons in the nigra of PD patients is an important area of research as it may eventually compensate the loss. Although tyrosine hydroxylase (TH) is the rate-limiting enzyme in the dopamine (DA) biosynthesis pathway, there are no effective drugs/molecules to upregulate TH and increase the production of DA in nigral dopaminergic neurons. This study underlines the importance of aspirin in stimulating the expression of TH and increasing the level of DA in dopaminergic neurons. At low doses, aspirin increased the expression of TH and the production of DA in mouse MN9D dopaminergic neuronal cells. Accordingly, oral administration of aspirin increased the expression of TH in the nigra and upregulated the level of DA in striatum of normal C57/BL6 mice and aged A53T α-syn transgenic mice. Oral aspirin also improved locomotor activities of normal mice and A53T transgenic mice. While investigating mechanisms, we found the presence of cAMP response element (CRE) in the promoter of TH gene and the rapid induction of cAMP response element binding (CREB) activation by aspirin in dopaminergic neuronal cells. Aspirin treatment also increased the level of phospho-CREB in the nigra of C57/BL6 mice. The abrogation of aspirin-induced expression of TH by siRNA knockdown of CREB and the recruitment of CREB to the TH gene promoter by aspirin suggest that aspirin stimulates the transcription of TH in dopaminergic neurons via CREB. These results highlight a new property of aspirin in stimulating the TH-DA pathway, which may be beneficial in PD patients. Graphical Abstract ᅟ.