Keratinocyte Biomarkers Distinguish Painful Diabetic Peripheral Neuropathy Patients and Correlate With Topical Lidocaine Responsiveness

Abstract

This study investigated quantifiable measures of cutaneous innervation and algesic keratinocyte biomarkers to determine correlations with clinical measures of patient pain perception, with the intent to better discriminate between diabetic patients with painful diabetic peripheral neuropathy (PDPN) compared to patients with low-pain diabetic peripheral neuropathy (lpDPN) or healthy control subjects. A secondary objective was to determine if topical treatment with a 5% lidocaine patch resulted in correlative changes among the quantifiable biomarkers and clinical measures of pain perception, indicative of potential PDPN pain relief. This open-label proof-of-principle clinical research study consisted of a pre-treatment skin biopsy, a 4-week topical 5% lidocaine patch treatment regimen for all patients and controls, and a post-treatment skin biopsy. Clinical measures of pain and functional interference were used to monitor patient symptoms and response for correlation with quantitative skin biopsy biomarkers of innervation (PGP9.5 and CGRP), and epidermal keratinocyte biomarkers (Nav1.6, Nav1.7, CGRP). Importantly, comparable significant losses of epidermal neural innervation (intraepidermal nerve fibers; IENF) and dermal innervation were observed among PDPN and lpDPN patients compared with control subjects, indicating that innervation loss alone may not be the driver of pain in diabetic neuropathy. In pre-treatment biopsies, keratinocyte Nav1.6, Nav1.7, and CGRP immunolabeling were all significantly increased among PDPN patients compared with control subjects. Importantly, no keratinocyte biomarkers were significantly increased among the lpDPN group compared with control. In post-treatment biopsies, the keratinocyte Nav1.6, Nav1.7, and CGRP immunolabeling intensities were no longer different between control, lpDPN, or PDPN cohorts, indicating that lidocaine treatment modified the PDPN-related keratinocyte increases. Analysis of the PDPN responder population demonstrated that increased pretreatment keratinocyte biomarker immunolabeling for Nav1.6, Nav1.7, and CGRP correlated with positive outcomes to topical lidocaine treatment. Epidermal keratinocytes modulate the signaling of IENF, and several analgesic and algesic signaling systems have been identified. These results further implicate epidermal signaling mechanisms as modulators of neuropathic pain conditions, highlight a novel potential mode of action for topical treatments, and demonstrate the utility of comprehensive skin biopsy evaluation to identify novel biomarkers in clinical pain studies.

Cutaneous targets for topical pain medications in patients with neuropathic pain: individual differential expression of biomarkers supports the need for personalized medicine

“…Currently, the full range of functions for CGRP receptor activation in keratinocytes remains largely unexplored; however, recent evidence suggests a role for keratinocyte CGRP in the pain associated with diabetic peripheral neuropathy (PDPN). 4,34 Mixed results were found for both GABA B and TrpV1 keratinocyte labeling, demonstrating the equally differential individual labeling patterns. Baclofen has been used topically with variable benefit, 1,39 and topical capsaicin has been used for some chronic pain conditions, particularly PHN, 14,46,51,75 and both are associated with activity directly on nerve fibers.…”

Integrative miRNA–mRNA profiling of human epidermis: unique signature of SCN9A painful neuropathy

“…NEDD4 is known to participate in the regulation of axonal growth, neuronal hyperexcitability 63 , 86 and Nav1.7 modulation. 63 , 87-89 To investigate its effect on Nav1.7, which has been previously proposed as a potential biomarker for painful neuropathy, 90 we performed IFA in skin biopsy sections from 11 NavNP patients carrying W1538R, L1267V, D1908G and/or V991L/M932L haplotypes and in 18 HC ( Supplementary Table 7 ). Remarkably, Nav1.7 signal intensity was significantly increased in patients’ keratinocytes as compared to HC ( P = 8.798 × 10 −5 , interobserver agreement P < 0.001), with a sensitivity of 81.8% and a specificity of 100%.…”

Cutaneous nerve fiber and peripheral Nav1.7 assessment in a large cohort of patients with postherpetic neuralgia

“… 17 Previous trials in diabetic polyneuropathy, however, have demonstrated that patients experiencing pain showed a higher degree of IENF degeneration, functional sensory loss, as well as different keratinocyte biomarker patterns compared with nonpainful neuropathy patients. 2 , 33 , 45 …”

“…Following procedures previously published, 2 , 37 quantification of Nav1.7 among keratinocytes was assessed from the standardized Nav1.7 epifluorescence images of the full width and thickness of the epidermis captured from each of the 5 sections from each biopsy. Standard image analysis tools (Photoshop, Adobe Systems, San Jose, CA) to quantify the average pixel intensity (API) from specific-sized sampling masks and identical standardized camera sensitivity and exposure times were used for all sections.…”

“…17 Previous trials in diabetic polyneuropathy, however, have demonstrated that patients experiencing pain showed a higher degree of IENF degeneration, functional sensory loss, as well as different keratinocyte biomarker patterns compared with nonpainful neuropathy patients. 2,33,45 These findings have to be interpreted in the light of different pathophysiological mechanisms causing neuropathic pain. In a subgroup of patients, nociceptive fibers in the skin are relatively preserved and show signs of peripheral sensitization (ie, irritable nociceptors), which is associated with pain.…”