Neuron-associated macrophage proliferation in the sensory ganglia is associated with peripheral nerve injury-induced neuropathic pain involving CX3CR1 signaling.

Resident macrophages are distributed across all tissues and are highly heterogeneous due to adaptation to different tissue-specific environments. The resident macrophages of the sensory ganglia (sensory neuron-associated macrophages, sNAMs) are in close contact with the cell body of primary sensory neurons and might play physiological and pathophysiological roles. After peripheral nerve injury, there is an increase in the population of macrophages in the sensory ganglia, which have been implicated in different conditions, including neuropathic pain development. However, it is still under debate whether macrophage accumulation in the sensory ganglia after peripheral nerve injury is due to the local proliferation of resident macrophages or a result of blood monocyte infiltration. Here, we confirmed that the number of macrophages increased in the sensory ganglia after the spared nerve injury (SNI) model in mice. Using different approaches, we found that the increase in the number of macrophages in the sensory ganglia after SNI is a consequence of the proliferation of resident CX3CR1+ macrophages, which participate in the development of neuropathic pain, but not due to infiltration of peripheral blood monocytes. These proliferating macrophages are the source of pro-inflammatory cytokines such as TNF and IL-1b. In addition, we found that CX3CR1 signaling is involved in the sNAMs proliferation and neuropathic pain development after peripheral nerve injury. In summary, these results indicated that peripheral nerve injury leads to sNAMs proliferation in the sensory ganglia in a CX3CR1-dependent manner accounting for neuropathic pain development. In conclusion, sNAMs proliferation could be modulated to change pathophysiological conditions such as chronic neuropathic pain.

PD-1/PD-L1 Inhibition Enhances Chemotherapy-Induced Neuropathic Pain by Suppressing Neuroimmune Antinociceptive Signaling.

Cytotoxic agents synergize with immune checkpoint inhibitors and improve outcomes for patients with several cancer types. Nonetheless, a parallel increase in the incidence of dose-limiting side effects, such as peripheral neuropathy, is often observed. Here, we investigated the role of the programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) axis in the modulation of paclitaxel-induced neuropathic pain. We found that human and mouse neural tissues, including the dorsal root ganglion (DRG), expressed basal levels of PD-1 and PD-L1. During the development of paclitaxel-induced neuropathy, an increase in PD-L1 expression was observed in macrophages from the DRG. This effect depended on Toll-like receptor 4 activation by paclitaxel. Furthermore, PD-L1 inhibited pain behavior triggered by paclitaxel or formalin in mice, suggesting that PD-1/PD-L1 signaling attenuates peripheral neuropathy development. Consistent with this, we observed that the combined use of anti-PD-L1 plus paclitaxel increased mechanical allodynia and chronic neuropathy development induced by single agents. This effect was associated with higher expression of inflammatory markers (Tnf, Il6, and Cx3cr1) in peripheral nervous tissue. Together, these results suggest that PD-1/PD-L1 inhibitors enhance paclitaxel-induced neuropathic pain by suppressing PD-1/PD-L1 antinociceptive signaling.

Inducible nitric oxide synthase (iNOS) mediates ethanol-induced redox imbalance and upregulation of inflammatory cytokines in the kidney.

Overexpression of the inducible isoform of the enzyme nitric oxide synthase (iNOS) has been associated to pathological processes in the kidney. Ethanol consumption induces the renal expression of iNOS; however, the contribution of this enzyme to the deleterious effects of ethanol in the kidney remains elusive. We examined whether iNOS plays a role in the renal dysfunction and oxidative stress induced by ethanol consumption. With this purpose, male C57BL/6 wild-type (WT) or iNOS-deficient (iNOS-/-) mice were treated with ethanol (20% v/v) for 10 weeks. Treatment with ethanol increased the expression of Nox4 as well as the concentration of thiobarbituric acid reactive substances and the levels of tumor necrosis factor α in the renal cortex of WT but not iNOS-/- mice. Augmented serum levels of creatinine and increased systolic blood pressure were found in WT and iNOS-/- mice treated with ethanol. WT mice treated with ethanol showed increased production of reactive oxygen species and myeloperoxidase activity, but these responses were attenuated in iNOS-/- mice. We concluded that iNOS played a role in ethanol-induced oxidative stress and pro-inflammatory cytokine production in the kidney. These are mechanisms that may contribute to the renal toxicity induced by ethanol.

Verapamil decreases calpain-1 and matrix metalloproteinase-2 activities and improves hypertension-induced hypertrophic cardiac remodeling in rats.

AIMS: Increased activity of calpain-1 and matrix metalloproteinase (MMP)-2 was observed in different models of arterial hypertension and contribute to thicken the left ventricle (LV) walls and to hypertrophy cardiac myocytes. MMP-2 activity may be regulated by calpain-1 via bioactive molecules activation such as transforming growth factor (TGF)-ß in cardiovascular diseases. This study analyzed whether calpain-1 causes cardiac hypertrophy and dysfunction by modulating the expression and activity of MMP-2 in renovascular hypertension. MAIN METHODS: Male Wistar rats were submitted to two kidneys, one clip (2K1C) model of hypertension or sham surgery and were treated with verapamil (VRP, 8 mg/kg/bid) by gavage from the second to tenth week post-surgery. Systolic blood pressure (SBP) was weekly assessed by tail-cuff plethysmography and morphological and functional parameters of LV were analyzed by echocardiography. MMP-2 activity was analyzed by in situ and gelatin zymography, while calpain-1 activity by caseinolytic assay. MMP-2, calpain-1, TGF-ß and MMP-14/TIMP-2 levels were identified in the LV by western blots. Fluorescence assays were performed to evaluate oxidative stress, MMP-2 and calpain-1 levels. KEY FINDINGS: SBP increased in 2K1C rats and was unaltered by VRP. However, VRP notably ameliorated hypertension-induced increase in LV thickness. VRP decreased hypertension-induced enhances in calpain-1 and MMP-2 activities, oxidative stress and mature TGF-ß levels. Treatment with VRP also decreased the accentuated MMP-14/TIMP-2 levels in 2K1C. SIGNIFICANCE: Treatment with VRP decreases calpain-1 and MMP-2 activities and also reduces TGF-ß and MMP-14/TIMP-2 levels in the LV of hypertensive rats, thus contributing to ameliorate cardiac hypertrophy.