Background: Inflammatory pain can be effectively controlled by an interaction of opioid receptors on peripheral sensory nerve terminals with opioid peptides released from immune cells upon stressful stimulation. To define the source of opioid peptide production, we sought to identify and quantify populations of opioid-containing cells during the course of Freund's complete adjuvant-induced hind paw inflammation in the rat. In parallel, we examined the development of stress-induced local analgesia in the paw. Methods: At 2, 6, and 96 h after Freund's complete adjuvant inoculation, cells were characterized by flow cytometry using a monoclonal pan-opioid antibody (3E7) and antibodies against cell surface antigens and by immunohistochemistry using a polyclonal antibody to beta-endorphin. After magnetic cell sorting, the beta-endorphin content was quantified by radioimmunoassay. Pain responses before and after cold water swim stress were evaluated by paw pressure thresholds. Results: In early inflammation, 66% of opioid peptide-producing (3E7+) leukocytes were HIS48+ granulocytes. In contrast, at later stages (96 h), the majority of 3E7+ immune cells were ED1+ monocytes or macrophages (73%). During the 4 days after Freund's complete adjuvant inoculation, the number of 3E7+ cells increased 5.6-fold (P < 0.001, Kruskal-Wallis test) and the beta-endorphin content in the paw multiplied 3.9-fold (P < 0.05, Kruskal-Wallis test). In parallel, cold water swim stress-induced analgesia increased by 160% (P < 0.01, analysis of variance). Conclusions: The degree of endogenous pain inhibition is proportional to the number of opioid peptide-producing cells, and distinct leukocyte lineages contribute to this function at different stages of inflammation. These mechanisms may be important for understanding pain in immunosuppressed states such as cancer, diabetes, or AIDS and for the design of novel therapeutic strategies in inflammatory diseases.

Giant cell arteritis (GCA) is a systemic vasculitis preferentially affecting large and medium-sized arteries. Inflammatory infiltrates in the arterial wall induce luminal occlusion with subsequent ischemia and degradation of the elastic membranes, allowing aneurysm formation. To identify pathways relevant to the disease process, differential display–PCR was used. The enzyme aldose reductase (AR), which is implicated in the regulation of tissue osmolarity, was found to be upregulated in the arteritic lesions. Upregulated AR expression was limited to areas of tissue destruction in inflamed arteries, where it was detected in T cells, macrophages, and smooth muscle cells. The production of AR was highly correlated with the presence of 4-hydroxynonenal (HNE), a toxic aldehyde and downstream product of lipid peroxidation. In vitro exposure of mononuclear cells to HNE was sufficient to induce AR production. The in vivo relationship of AR and HNE was explored by treating human GCA temporal artery–severe combined immunodeficiency (SCID) mouse chimeras with the AR inhibitors Sorbinil and Zopolrestat. Inhibition of AR increased HNE adducts twofold and the number of apoptotic cells in the arterial wall threefold. These data demonstrate that AR has a tissue-protective function by preventing damage from lipid peroxidation. We propose that AR is an oxidative defense mechanism able to neutralize the toxic effects of lipid peroxidation and has a role in limiting the arterial wall injury mediated by reactive oxygen species.

Different sensory profiles in diabetic distal symmetrical sensory-motor polyneuropathy (DSPN) may be associated with pain and the responsiveness to analgesia. We aimed to characterize sensory phenotypes of patients with painful and painless diabetic neuropathy and to assess demographic, clinical, metabolic, and electrophysiological parameters related to the presence of neuropathic pain in a large cohort of well-defined DSPN subjects. This observational cross-sectional multi-center cohort study (performed as part of the ncRNAPain EU consortium) of 232 subjects with nonpainful (n = 74) and painful (n = 158) DSPN associated with diabetes mellitus of type 1 and 2 (median age 63 years, range 21-87 years; 92 women) comprised detailed history taking, laboratory tests, neurological examination, quantitative sensory testing, nerve conduction studies, and neuropathy severity scores. All parameters were analyzed with regard to the presence and severity of neuropathic pain. Neuropathic pain was positively correlated with the severity of neuropathy and thermal hyposensitivity (P < 0.001). A minority of patients with painful DSPN (14.6%) had a sensory profile, indicating thermal hypersensitivity that was associated with less severe neuropathy. Neuropathic pain was further linked to female sex and higher cognitive appraisal of pain as assessed by the pain catastrophizing scale (P < 0.001), while parameters related to diabetes showed no influence on neuropathic pain with the exception of laboratory signs of nephropathy. This study confirms the value of comprehensive DSPN phenotyping and underlines the importance of the severity of neuropathy for the presence of pain. Different sensory phenotypes might be useful for stratification of patients with painful DSPN for analgesic treatment and drug trials.

—Giant cell arteritis (GCA) is an inflammatory vasculopathy in which T cells and macrophages infiltrate the wall of medium and large arteries. Clinical consequences such as blindness and stroke are related to arterial occlusion. Formation of aortic aneurysms may result from necrosis of smooth muscle cells and fragmentation of elastic membranes. The molecular mechanisms of arterial wall injury in GCA are not understood. To identify mechanisms of arterial damage, gene expression in inflamed and unaffected temporal artery specimens was compared by differential display polymerase chain reaction. Genes differentially expressed in arterial lesions included 3 products encoded by the mitochondrial genome. Immunohistochemistry with antibodies specific for a 65-kDa mitochondrial antigen revealed that increased expression of mitochondrial products was characteristic of multinucleated giant cells and of CD68+ macrophages that cluster in the media and at the media-intima junction. 4-Hydroxy-2-nonenal adducts, products of lipid peroxidation, were detected on smooth muscle cells and on tissue infiltrating cells, in close proximity to multinucleated giant cells and CD68+ macrophages. Also, giant cells and macrophages with overexpression of mitochondrial products were able to synthesize metalloproteinase-2. Our data suggest that in the vascular lesions characteristic for GCA, a subset of macrophages has the potential to support several pathways of arterial injury, including the release of reactive oxygen species and the production of metalloproteinase-2. This macrophage subset is topographically defined and is also identified by overexpression of mitochondrial genes. Because these macrophages have a high potential to promote several mechanisms of arterial wall damage, they should be therapeutically targeted to prevent blood vessel destruction.

Recent studies have provided evidence of pathology and functional abnormalities of small nerve fibers as a potential correlate of pain in the fibromyalgia syndrome. Here, we aimed to quantify dermal unmyelinated nerve fiber diameter at the electron microscopic level to find a potential morphological correlate of the functional disturbance. Thirty-two patients with fibromyalgia syndrome, 12 patients with small fiber neuropathy, and 24 healthy controls were prospectively recruited. Skin biopsies of the distal and proximal legs and index finger were taken and processed for immunofluorescence and for electron microscopy. We determined the diameter of small unmyelinated nerve fibers by measuring ten transversely cut axons of each biopsy. The mean axon diameter was reduced in patients with fibromyalgia syndrome compared with patients with small fiber neuropathy and controls (P < 0.05). Furthermore, we confirmed previous findings of disturbed small fiber function in quantitative sensory testing and of reduced intraepidermal nerve fiber density in patients with fibromyalgia. Our study provides further evidence of small fiber pathology in fibromyalgia syndrome and discloses differences compared with small fiber neuropathy, indicating that different pathomechanisms may lead to small fiber loss in the 2 disorders.