Phillip J. Albrecht

Pathologic alterations of cutaneous innervation and vasculature in affected limbs from patients with complex regional pain syndrome.

Abstract Complex regional pain syndromes (CRPS, type I and type II) are devastating conditions that can occur following soft tissue (CRPS type I) or nerve (CRPS type II) injury. CRPS type I, also known as reflex sympathetic dystrophy, presents in patients lacking a well‐defined nerve lesion, and has been questioned as to whether or not it is a true neuropathic condition with an organic basis. As described here, glabrous and hairy skin samples from the amputated upper and lower extremity from two CRPS type I diagnosed patients were processed for double‐label immunofluorescence using a battery of antibodies directed against neural‐related proteins and mediators of nociceptive sensory function. In CRPS affected skin, several neuropathologic alterations were detected, including: (1) the presence of numerous abnormal thin caliber NF‐positive/MBP‐negative axons innervating hair follicles; (2) a decrease in epidermal, sweat gland, and vascular innervation; (3) a loss of CGRP expression on remaining innervation to vasculature and sweat glands; (4) an inappropriate expression of NPY on innervation to superficial arterioles and sweat glands; and (5) a loss of vascular endothelial integrity and extraordinary vascular hypertrophy. The results are evidence of widespread cutaneous neuropathologic changes. Importantly, in these CRPS type I patients, the myriad of clinical symptoms observed had detectable neuropathologic correlates.

Voltage-gated sodium channel expression in rat and human epidermal keratinocytes: evidence for a role in pain.

Abstract Keratinocytes are implicated in sensory transduction and can influence nociception, but whether these contribute to chronic pain is not known. In neurons, voltage‐gated sodium channels (Nav) are involved in neuropathic pain and are activated by depolarization. Since keratinocytes can also show changes in membrane potential, we used RT‐PCR, in situ hybridization, and immunohistochemistry to investigate the expression of sodium channels in these cells. Nav1.1, Nav1.6, and Nav1.8 were localized within keratinocytes in rat epidermis. In addition, sodium channels contribute to the release of ATP from rat keratinocytes in response to increased [K+]o, implicating sodium channels in keratinocyte ligand release and nociception. To examine whether keratinocytes may contribute to human pain states, we analyzed sodium channel expression in human skin biopsies from subjects with complex regional pain syndrome Type 1 (CRPS) and post‐herpetic neuralgia (PHN) using immunohistochemistry. Control skin exhibited immunolabeling for Nav1.5, Nav1.6 and Nav1.7. In contrast, painful skin from CRPS and PHN subjects displayed Nav1.1, Nav1.2, and Nav1.8 immunolabeling, in addition to substantially increased signal for Nav1.5, Nav1.6, Nav1.7. These observations lead us to propose that pathological increases in keratinocyte sodium channel expression may contribute to pain by increasing epidermal ATP release, resulting in excessive activation of P2X receptors on primary sensory axons. Consistent with this hypothesis, animal models of neuropathic pain exhibit increases in subcutaneous ATP release and activity of primary sensory neurons, and peripheral administration of P2X antagonists has been shown to reduce neuropathic pain in humans.

Differential hypertrophy and atrophy among all types of cutaneous innervation in the glabrous skin of the monkey hand during aging and naturally occurring type 2 diabetes

Diabetic neuropathy (DN) is a common severe complication of type 2 diabetes. The symptoms of chronic pain, tingling, and numbness are generally attributed to small fiber dysfunction. However, little is known about the pathology among innervation to distal extremities, where symptoms start earliest and are most severe, and where the innervation density is the highest and includes a wide variety of large fiber sensory endings. Our study assessed the immunochemistry, morphology, and density of the nonvascular innervation in glabrous skin from the hands of aged nondiabetic rhesus monkeys and from age‐matched monkeys that had different durations of spontaneously occurring type 2 diabetes. Age‐related reductions occurred among all types of innervation, with epidermal C‐fiber endings preferentially diminishing earlier than presumptive Aδ‐fiber endings. In diabetic monkeys epidermal innervation density diminished faster, became more unevenly distributed, and lost immunodetectable expression of calcitonin gene‐related peptide and capsaicin receptors, TrpV1. Pacinian corpuscles also deteriorated. However, during the first few years of hyperglycemia, a surprising hypertrophy occurred among terminal arbors of remaining epidermal endings. Hypertrophy also occurred among Meissner corpuscles and Merkel endings supplied by Aβ fibers. After longer‐term hyperglycemia, Meissner corpuscle hypertrophy declined but the number of corpuscles remained higher than in age‐matched nondiabetics. However, the diabetic Meissner corpuscles had an abnormal structure and immunochemistry. In contrast, the expanded Merkel innervation was reduced to age‐matched nondiabetic levels. These results indicate that transient phases of substantial innervation remodeling occur during the progression of diabetes, with differential increases and decreases occurring among the varieties of innervation. J. Comp. Neurol. 501:543–567, 2007.

Loss of Bardet–Biedl syndrome proteins causes defects in peripheral sensory innervation and function

Reception and interpretation of environmental stimuli is critical for the survival of all organisms. Here, we show that the ablation of BBS1 and BBS4, two genes mutated in Bardet–Biedl syndrome and that encode proteins that localize near the centrioles of sensory neurons, leads to alterations of s.c. sensory innervation and trafficking of the thermosensory channel TRPV1 and the mechanosensory channel STOML3, with concomitant defects in peripheral thermosensation and mechanosensation. The thermosensory phenotype is recapitulated in Caenorhabditis elegans, because BBS mutants manifest deficient thermosensory responses at both physiological and nociceptive temperatures and defective trafficking of OSM-9, a polymodal sensory channel protein and a functional homolog of TRPV1 or TRPV4. Our findings suggest a hitherto unrecognized, but essential, role for mammalian basal body proteins in the acquisition of mechano- and thermosensory stimuli and highlight potentially clinical features of ciliopathies in humans.

Opioids Activate Brain Analgesic Circuits Through Cytochrome P450/Epoxygenase Signaling

To assess the importance of brain cytochrome P450 (P450) activity in μ opioid analgesic action, we generated a mutant mouse with brain neuron–specific reductions in P450 activity; these mice showed highly attenuated morphine antinociception compared with controls. Pharmacological inhibition of brain P450 arachidonate epoxygenases also blocked morphine antinociception in mice and rats. Our findings indicate that a neuronal P450 epoxygenase mediates the pain-relieving properties of morphine.

Dorsal Root Ganglion Infiltration by Macrophages Contributes to Paclitaxel Chemotherapy-Induced Peripheral Neuropathy

UNLABELLED Chemotherapy-induced peripheral neuropathy (CIPN) is a disruptive and persistent side effect of cancer treatment with paclitaxel. Recent reports showed that paclitaxel treatment results in the activation of Toll-like receptor 4 (TLR4) signaling and increased expression of monocyte chemoattractant protein 1 (MCP-1) in dorsal root ganglion cells. In this study, we sought to determine whether an important consequence of this signaling and also a key step in the CIPN phenotype was the recruitment and infiltration of macrophages into dorsal root ganglia (DRG). Here, we show that macrophage infiltration does occur in a time course that matches the onset of the behavioral CIPN phenotype in Sprague-Dawley rats. Moreover, depletion of macrophages by systemic administration of liposome-encapsulated clodronate (clophosome) partially reversed behavioral signs of paclitaxel-induced CIPN as well as reduced tumor necrosius factor α expression in DRG. Intrathecal injection of MCP-1 neutralizing antibodies reduced paclitaxel-induced macrophage recruitment into the DRG and also blocked the behavioral signs of CIPN. Intrathecal treatment with the TLR4 antagonist lipopolysaccharide-RS (LPS-RS) blocked mechanical hypersensitivity, reduced MCP-1 expression, and blocked the infiltration of macrophages into the DRG in paclitaxel-treated rats. The inhibition of macrophage infiltration into DRG after paclitaxel treatment with clodronate or LPS-RS prevented the loss of intraepidermal nerve fibers (IENFs) observed after paclitaxel treatment alone. These results are the first to indicate a mechanistic link such that activation of TLR4 by paclitaxel leads to increased expression of MCP-1 by DRG neurons resulting in macrophage infiltration to the DRG that express inflammatory cytokines and the combination of these events results in IENF loss and the development of behavioral signs of CIPN. PERSPECTIVE This paper shows that activation of innate immunity by paclitaxel results in a sequence of signaling events that results in the infiltration of the dorsal root ganglia by activated macrophages. Macrophages appear to drive the development of behavioral hypersensitivity and the loss of distal epidermal nerve fibers, and hence play an important role in the mechanism of paclitaxel-related neuropathy.

Multimodal Analgesia for Chronic Pain: Rationale and Future Directions

Chronic pain is a multifaceted disease requiring multimodal treatment. Clinicians routinely employ various combinations of pharmacologic, interventional, cognitive-behavioral, rehabilitative, and other nonmedical therapies despite the paucity of robust evidence in support of such an approach. Therapies are selected consistent with the biopsychosocial model of chronic pain, reflecting the subjective nature of the pain complaint, and the myriad stressors that shape it. Elucidating mechanisms that govern normal sensation in the periphery has provided insights into the biochemical, molecular, and neuroanatomic correlates of chronic pain, an understanding of which is leading increasingly to mechanism-specific multidrug therapies. Peripheral and central neuroplastic reorganization underlying the disease of chronic pain is influenced by patient-specific emotions, cognition, and memories, further impairing function and idiosyncratically defining the illness of chronic pain. Clinical perceptions of these and related subjective elements associated with the suffering of chronic pain drive psychosocial treatments, including, among other options, relaxation therapies, coping skills development, and cognitive-behavioral therapy. Treatment selection is thus guided by comprehensive assessment of the phenomenology and inferred pathophysiology of the pain syndrome; patient goals, preferences, and expectations; behavioral, cognitive, and physical function; and level of risk. Experiential, practice-based evidence may be necessary for improving patient care, but it is insufficient; certainly, well-designed studies are needed to support therapeutic decision making. This review will discuss the biochemical basis of pain, factors that govern its severity and chronicity, and foundational elements for current and emerging multimodal treatment strategies.

Air-Stimulated ATP Release from Keratinocytes Occurs through Connexin Hemichannels

Cutaneous ATP release plays an important role in both epidermal stratification and chronic pain, but little is known about ATP release mechanisms in keratinocytes that comprise the epidermis. In this study, we analyzed ATP release from cultured human neonatal keratinocytes briefly exposed to air, a process previously demonstrated to trigger ATP release from these cells. We show that exposing keratinocytes to air by removing media for 15 seconds causes a robust, long-lasting ATP release. This air-stimulated ATP release was increased in calcium differentiated cultures which showed a corresponding increase in connexin 43 mRNA, a major component of keratinocyte hemichannels. The known connexin hemichannel inhibitors 1-octanol and carbenoxolone both significantly reduced air-stimulated ATP release, as did two drugs traditionally used as ABC transporter inhibitors (glibenclamide and verapamil). These same 4 inhibitors also prevented an increase in the uptake of a connexin permeable dye induced by air exposure, confirming that connexin hemichannels are open during air-stimulated ATP release. In contrast, activity of the MDR1 ABC transporter was reduced by air exposure and the drugs that inhibited air-stimulated ATP release had differential effects on this transporter. These results indicate that air exposure elicits non-vesicular release of ATP from keratinocytes through connexin hemichannels and that drugs used to target connexin hemichannels and ABC transporters may cross-inhibit. Connexins represent a novel, peripheral target for the treatment of chronic pain and dermatological disease.

Absence of pain with hyperhidrosis: A new syndrome where vascular afferents may mediate cutaneous sensation

ABSTRACT Congenital absence of pain perception is a rare phenotype. Here we report two unrelated adult individuals who have a previously unreported neuropathy consisting of congenital absence of pain with hyperhidrosis (CAPH). Both subjects had normal intelligence and productive lives despite failure to experience pain due to broken bones, severe cold or burns. Functional assessments revealed that both are generally hypesthetic with thresholds greater than two standard deviations above normal for a several of modalities in addition to noxious stimuli. Sweating was 3 to 8‐fold greater than normal. Sural nerve biopsy showed that all types of myelinated and unmyelinated fibers were severely reduced. Extensive multi‐antibody immunofluorescence analyses were conducted on several skin biopsies from the hands and back of one CAPH subject and two normal subjects. The CAPH subject had all normal types of immunochemically and morphologically distinct sensory and autonomic innervation to the vasculature and sweat glands, including a previously unknown cholinergic arterial innervation. Virtually all other types of normal cutaneous C, Aδ and Aβ‐fiber endings were absent. This subject had no mutations in the genes SCN9A, SCN10A, SCN11A, NGFB, TRKA, NRTN and GFRA2. Our findings suggest three hypotheses: (1) that development or maintenance of sensory innervation to cutaneous vasculature and sweat glands may be under separate genetic control from that of all other cutaneous sensory innervation, (2) the latter innervation is preferentially vulnerable to some environmental factor, and (3) vascular and sweat gland afferents may contribute to conscious cutaneous perception.

Skin Matters: A Review of Topical Treatments for Chronic Pain. Part Two: Treatments and Applications

In Part One of this two-part series, we discussed skin physiology and anatomy as well as generalities concerning topical analgesics. This modality of therapy has lesser side effects and drug–drug interactions, and patients tolerate this form of therapy better than many oral options. Unfortunately, this modality is not used as often as it could be in chronic pain states, such as that from neuropathic pain. Part Two discusses specific therapies, local anesthetics, and other drugs, as well as how a clinician might use specific aspects of a patient’s neuropathic pain presentation to help guide them in the selection of a topical agent.