Effects of Tourniquet Ischemia on Current Perception Thresholds in Healthy Volunteers

Abstract: The neuroselective effects of tourniquet isch‐ emia/compression in healthy volunteers were evaluated using the automated electrodiagnostic sensory Nerve Conduction Threshold (sNCT) test. The sNCT evaluation generates reliable, painless Current Perception Threshold (CPT) measures. Standardized CPT measures using constant alternating current sinusoid waveform stimulus at 3 different frequencies 5 Hz, 250 Hz, and 2 kHz (NeurometerEG CPT/C Neurotron, Inc. Baltimore, MD) were obtained from 10 individuals at baseline and after 5, 10, 15, and 20 minutes of tourniquet ischemia and 30 minutes post‐tourniquet release. The data were analyzed to determine the significance of any changes in CPTs. Increases in CPTs after 15 and 20 minutes of tourniquet ischemia at 2000 Hz and 250 Hz reached statistical significance. There were no significant changes in 5 Hz CPT measures. The results of this study demonstrate the ability of the sNCT test to quantify previously described differential neuroselective effects of tourniquet ischemia on sensory nerve function. Demonstration of statistically significant increases in CPT values at 2000 Hz and 250 Hz secondary to tourniquet ischemia, with no change in 5 Hz CPT values, is consistent with the understanding that 2000 Hz sine wave stimuli activate the large myelinated sensory fibers, 250 Hz sine wave stimuli activate small myelinated sensory fibers, and 5 Hz sine wave stimuli activate small unmyelinated sensory fibers.     

Homologous recombination is a highly conserved determinant of the synergistic cytotoxicity between cisplatin and DNA topoisomerase I poisons

Phase I and II clinical trails are currently investigating the antitumor activity of cisplatin and camptothecins (CPTs; DNA topoisomerase I poisons), based on the dramatic synergistic cytotoxicity of these agents in some preclinical models. However, the mechanistic basis for this synergism is poorly understood. By exploiting the evolutionary conservation of DNA repair pathways from genetically tractable organisms such as budding and fission yeasts to mammalian cells, we demonstrate that the synergism of CPT and cisplatin requires homologous recombination. In yeast and mammalian cell lines defective for RAD52 and XRCC2/3, respectively, the combination of these agents proved antagonistic, while greater than additive activity was evident in isogenic wild-type cells. Homologous recombination appears to mediate a similar interaction of X-rays and CPT, but antagonizes the synergism of cytarabine (Ara-C) with CPT. These findings suggest that homologous recombination comprises an evolutionarily conserved determinant of cellular sensitivity when CPTs are used in combination with other therapeutics.     

Recent Progress on C‐4‐Modified Podophyllotoxin Analogs as Potent Antitumor Agents

Podophyllotoxin (PPT), as well as its congeners and derivatives, exhibits pronounced biological activities, especially antineoplastic effects. Its strong inhibitory effect on tumor cell growth led to the development of three of the most highly prescribed anticancer drugs in the world, etoposide, teniposide, and the water‐soluble prodrug etoposide phosphate. Their clinical success as well as intriguing mechanism of action stimulated great interest in further modification of PPT for better antitumor activity. The C‐4 position has been a major target for structural derivatization aimed at either producing more potent compounds or overcoming drug resistance. Accordingly, numerous PPT derivatives have been prepared via hemisynthesis and important structure–activity relationship (SAR) correlations have been identified. Several resulting compounds, including GL‐331, TOP‐53, and NK611, reached clinical trials. Some excellent reviews on the distribution, sources, applications, synthesis, and SAR of PPT have been published. This review focuses on a second generation of new etoposide‐related drugs and provides detailed coverage of the current status and recent development of C‐4‐modified PPT analogs as anticancer clinical trial candidates.     

Pregnancy-related Increases in Sensory Perception Thresholds Are Not Correlated with Serum Progesterone Levels

Background: Why pregnant women require smaller doses of anesthetic agents still remains speculative. One hypothesis proposes that pregnancy raises sensory perception thresholds, perhaps through a progesterone‐mediated effect. This study was undertaken in order to quantify any changes in sensory perception thresholds after parturition and to correlate these changes with the expected decrease in postpartum serum progesterone levels. Methods: Nineteen gravid women scheduled to undergo an elective Cesarean section consented to participate. Sensory current perception threshold (CPT) testing was performed before and 7 days after an elective Cesarean section. CPT was defined as the minimum amount of constant current stimulation that can be reproducibly detected at a particular frequency. CPT values were determined on the distal phalanx of the nondominant index finger at 2000 Hz, 250 Hz, and 5 Hz monofrequency stimulation. Seven women permitted serum progesterone level determinations at the prepartum and the postpartum CPT testing sessions. Results: Parturition resulted in a statistically significant decrease in the sensory CPT at all 3 frequencies tested, (p < 0.05). However, there was no significant correlation between the postpartum reduction in serum progesterone levels and the observed postpartum decrease in CPT for any frequency, (r < 0.5). Conclusions: CPTs are significantly reduced after parturition. However, this reduction does not appear to be significantly correlated with the reduction in serum progesterone levels.     

Constant current sine wave transcutaneous nerve stimulation for the evaluation of peripheral neuropathy

We have evaluated various forms of peripheral neuropathy with a new device which emits a constant sinusoid stimulus at varying frequencies to quantitate current perception thresholds (CPTs). In normal individuals, CPT measures increase with increasing stimulation frequency, are highest on the toe and lowest on the face. There is a significant effect of age and sex on threshold perception. In patients with neuropathy, there is a marked increase in thresholds on hands and feet, as well as a lesser but still significant increase of facial CPTs. Thresholds furthermore correlated with clinical severity in a group of patients with diabetic neuropathy. Facial thresholds were markedly elevated in the patients with moderate to severe neuropathy, suggesting that the device is sensitive to the systemic nature of peripheral neuropathy. The authors believe the device will be a useful tool in screening for sensory neurologic abnormalities.     

Evaluation of allodynia and pain associated with postherpetic neuralgia using current perception threshold testing

OBJECTIVES: Postherpetic neuralgia has various clinical features, and the implicated pathophysiologic mechanisms are controversial. This study was carried out to clarify the roles of peripheral sensory nerves in the production of allodynia and ongoing pain. Current perception threshold (CPT) testing was used to evaluate the sensory function. METHODS: The intensities of ongoing pain and dynamic allodynia were assessed using a numeric rating scale (0-10). Assessment of sensory nerve function was performed by a series of 2,000-, 250-, and 5-Hz stimuli using CPT testing. These measurements were made in ipsilateral and contralateral area. RESULTS: CPTs at all frequencies in the ipsilateral area were significantly higher than those in the contralateral area. There were significant and inverse correlations between the intensity of allodynia and CPTs at all frequencies. No correlation was found between the intensity of ongoing pain and CPTs at any frequency. There was no correlation between the intensity of ongoing pain and the intensity of dynamic allodynia. CONCLUSIONS: The intensity of dynamic allodynia in postherpetic neuralgia correlates with the preserved functions of Abeta, Adelta, and C fibers. In contrast, the intensity of ongoing pain does not correlate with either the preserved function of C fibers or the intensity of dynamic allodynia. Therefore, it is suggested that postherpetic neuralgia might be a pain syndrome including both peripheral and central mechanisms.     

Mapping diabetic sensory neuropathy by current perception threshold testing

Detailed clinical neurological examinations were conducted on 44 nondiabetic volunteers and 59 diabetic subjects. The examinations focused particularly on sensory symptomatic and physical evaluation. Standardized assessment of symptoms and physical testing of light touch, pain, vibratory, and thermal sensation was performed at the hand, wrist, elbow, foot, ankle, and knee. A total symptom score and physical score were defined by summing test scores at each site. Current perception threshold (CPT) testing that used constant sine-wave-alternating current was conducted at the same anatomic sites. CPT correlations with the physical score gave r values of .55 for 5 Hz, .60 for 250 Hz, and .62 for 2000 Hz (n = 618). Correlations with the symptom score were not as strong: r = .45 for 5 Hz, .46 for 250 Hz, and .51 for 2000 Hz. The correlation with symptom score was due primarily to a strong relationship for the symptom of numbness (r = .53 for all 3 frequencies). Correlations with pain and paresthesia were much lower. CPTs for diabetic subjects at the three frequencies were higher at most locations than for the nondiabetic volunteers. However, CPTs were no different from normal values in diabetic subjects without evidence of neuropathy. CPT testing appears to be a useful technique for assessment of diabetic sensory neuropathy.     

Evaluation of the pathophysiology of classical trigeminal neuralgia by blink reflex study and current perception threshold testing

We recruited 49 patients with classical trigeminal neuralgia (TN) according to the latest guidelines of the International Classification of Headache Disorders, and divided them into an acute (≤30 days onset; 13 patients) and a chronic (>30 days onset; 36 patients) group. We used blink reflex study and current perception threshold (CPT) testing to evaluate the painful facial areas and contralateral non-painful areas of patients with classical TN. CPT 5 Hz examinations, which correlate with unmyelinated fiber function, showed significantly decreased CPTs in the acute stage (11.62 ± 6.99 vs. 18.69 ± 9.66, P = 0.025), but significantly increased CPTs in the chronic stage (26.67 ± 18.65 vs. 19.69 ± 13.70, P = 0.010) on the painful side when compared with the contralateral non-painful side. However, CPTs at 250 Hz (Aδ) and 2000 Hz (Aβ) examinations did not show significant differences between the painful and non-painful sides. In contrast, only three (3/49) patients showed an abnormal trigeminal nerve stimulation on the ipsilateral painful side by blink reflex study. The findings suggest that classical TN is not a simple large-myelinated nerve fiber dysfunction but a more complex process with a main dysfunction of unmyelinated nerve fibers.     

Marine natural products as anticancer drugs

The chemical and biological diversity of the marine environment is immeasurable and therefore is an extraordinary resource for the discovery of new anticancer drugs. Recent technological and methodologic advances in structure elucidation, organic synthesis, and biological assay have resulted in the isolation and clinical evaluation of various novel anticancer agents. These compounds range in structural class from simple linear peptides, such as dolastatin 10, to complex macrocyclic polyethers, such as halichondrin B; equally as diverse are the molecular modes of action by which these molecules impart their biological activity. This review highlights several marine natural products and their synthetic derivatives that are currently undergoing clinical evaluation as anticancer drugs.     

Cyclooxygenase inhibitors: Scope of their use and development in cancer chemotherapy

The traditional nonsteroidal anti‐inflammatory drugs (NSAIDs) exert their effect by inhibition of cyclooxygenase‐1 (COX‐1) as well as COX‐2 enzymes. As COX‐1 is responsible for maintaining normal biological functions, the nonselective inhibition of these enzymes caused side effects including gastrointestinal (GI) problems. Recently developed selective COX‐2 inhibitors could reduce these adverse effects, but the evidence of cardiovascular side effects including an increased risk of myocardial infarction began to emerge, and some of the COX‐2 inhibitors were eventually withdrawn from the market and this led to the downfall of this research. So, the discovery of novel COX‐2 inhibitors with their safety profile became the biggest challenge in pharmaceutical research. However, recent mechanistic and clinical studies revolutionized this area by indicating the fact that COX‐2 is involved in apoptosis resistance, angiogenesis, and tumor progression. Epidemiological data suggest that selective COX‐2 inhibitors might prevent the development of cancers. Moreover, COX‐2 is found to be overexpressed in many cancers thus making it an attractive therapeutic target for the prevention and treatment of a number of malignancies. The purpose of this review is to focus on the medicinal chemistry aspects of COX‐2 inhibitors in cancer chemotherapy and recent reports on these inhibitors as anticancer agents. We attempted to cover only the COX inhibitors that showed anticancer activity, although a number of potent COX‐2 inhibitors have been reported without their anticancer effects. Furthermore, structure–activity relationships (SAR) of different classes of compounds for COX‐2 inhibition as well as anticancer activity, and their future applications are discussed. © 2009 Wiley Periodicals, Inc. Med Res Rev, 31, No. 2, 161–201, 2011     

Measuring attitudes toward participation in cancer treatment and cancer prevention trials: the Attitudes Toward Cancer Trials Scales (ACTS)

This investigation aimed to develop psychometric instruments that measure attitudes toward participating in cancer treatment trials (CTs) and cancer prevention trials (CPTs), that is, the Attitudes Toward Cancer Trials Scales (ACTS). A conceptualized construct of attitudes toward CTs and CPTs guided the writing of items for psychometric measurement. An expert panel assessment condensed reduced items to 116, and these were formatted into a self-report written survey. Data collection occurred within multiple settings, targeting an ethnically diverse sample (N = 312). Item and principal component analyses empirically supported the Attitudes Toward Cancer Trials Scales (ACTS), a 2-dimensional instrument containing an 18-item CT scale (four components) and a 16-item CPT scale (3 components) with Cronbach's alpha values of .86 and .89, respectively. Four components comprised the CT scale: personal benefits, personal barriers and safety, personal and social value, and trust in the research process. Three components comprised the CPT scale: personal barriers and safety, altruism, and personal value. Early evidence of the internal consistency reliability and construct validity of the ACTS was provided by the sample.     

DNA repair enzyme, O6-methylguanine DNA methyltransferase, modulates cytotoxicity of camptothecin-derived topoisomerase I inhibitors

Two camptothecin-resistant cell lines, CPT30 and KB100, were established and characterized previously in our laboratory. Because enhanced sensitivity to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and decreased expression of O(6)-methylguanine-DNA methyltransferase (MGMT) protein were observed in these lines, we hypothesized that MGMT may be a determinant of cytotoxicity associated with camptothecin-derived DNA topoisomerase I inhibitors (CPTs). We used the Tet-On system to induce expression of MGMT in Chinese hamster ovary (CHO) cells and RNA interference to knock down MGMT expression in human nasopharyngeal carcinoma HONE-1 cells in order to identify any correlations between MGMT expression and CPTs cytotoxicity. CHO-derived Tet-On-inducible cells (S12+) showed MGMT overexpression and statistically significant more resistance to BCNU, camptothecin, 7-ethyl-10-hydrocamptothecin (SN38), and topotecan than parental CHO cells (p < 0.05), but there was less resistance to CPTs than to BCNU. Knockdown of MGMT expression with small interfering RNA in HONE-1 cells conferred increased sensitivity to BCNU and CPTs compared with mock control. Furthermore, alteration of MGMT expression coincides with CPT-induced cell death and poly(ADP-ribose) polymerase cleavage. There were no differences in protein levels and catalytic activity of topoisomerase I between MGMT-proficient and MGMT-deficient cells from the Tet-On-inducible and small interfering RNA (siRNA) systems. Resistance to CPTs coincided with decreased amounts of protein-linked DNA breaks generated by CPTs in MGMT-proficient cells and vice versa in MGMT-deficient cells. Our data indicate that MGMT can modulate cytotoxicity of CPT-derived topoisomerase I inhibitors.     

Heparosan‐Derived Heparan Sulfate/Heparin‐Like Compounds: One Kind of Potential Therapeutic Agents

Heparan sulfate (HS) is a highly sulfated glycosaminoglycan and exists in all animal tissues. HS and heparin are very similar, except that heparin has higher level of sulfation and higher content of iduronic acid. Despite the fact that it is a century‐old drug, heparin remains as a top choice for treating thrombotic disorders. Pharmaceutical heparin is derived from porcine intestine or bovine lung via a long supply chain. This supply chain is vulnerable to the contamination of animal pathogens. Therefore, new methods for manufacturing heparin or heparin‐like substances devoid of animal tissues have been explored by many researchers, among which, modifications of heparosan, the capsular polysaccharide of Escherichia coli K5 strain, is one of the promising approaches. Heparosan has a structure similar to unmodified backbone of natural HS and heparin. It is feasible to obtain HS or heparin derivatives by modifying heparosan with chemical or enzymatic methods. These derivatives display different biological activities, such as anticoagulant, anti‐inflammatory, anticancer, and antiviral activities. This review focuses on the recent studies of synthesis, activity, and structure‐activity relationship of HS/heparin‐like derivatives prepared from heparosan.     

Observational Learning and Pain-Related Fear: An Experimental Study With Colored Cold Pressor Tasks

The primary aim of the current study was to experimentally test whether pain-related fear can be acquired through observational learning, whether extinction occurs after actual exposure to the aversive stimulus, and whether pain-related fear was associated with increased pain ratings. During an observation phase, female volunteers watched a video showing models performing cold pressor tasks (CPT), of which the color served as a conditioned stimulus (CS). In a differential fear conditioning paradigm, each of 2 colors were either paired with models’ painful (CS+) or neutral (CS−) facial expressions. Exposure consisted of participants performing CPTs of both colors (10°C). Self-reported fear of pain and expected pain ratings were obtained after the observation period, while actual pain and avoidance measures were obtained during and after exposure. Results show that after observing another person performing the CPT associated with the painful faces, subjects report more fear of pain and expect more intense and unpleasant pain as compared with the CPT associated with the neutral faces. This effect of observational learning on pain-related fear persisted until after exposure. During and after exposure no stimulus-type effect for pain ratings was found. This study provides preliminary evidence for observational learning of pain-related fear in humans.

Perspective

Fear of pain can be more disabling than pain itself, and is a risk factor for chronic pain. Knowledge about the acquisition of pain-related fear may help to develop novel pain management programs. This study is one of the first to demonstrate the effects of observational learning on pain-related fear.     

Preclinical to clinical development of the novel camptothecin nanopharmaceutical CRLX101

Camptothecin (CPT) is a potent broad-spectrum anticancer agent that acts through inhibition of topoisomerase 1. Clinical development of CPT was unsuccessful due to poor drug solubility, insufficient in vivo stability of the active form, and toxicity. In order to address these issues, a polymeric nanoparticle comprised of cyclodextrin-poly(ethylene glycol) copolymer (CDP) conjugated to CPT (CRLX101) has been developed and Phase 2 clinical studies are ongoing. Camptothecin is conjugated to the polymer in its active form at 10-12 wt.% loading. CRLX101 self-assembles in solution into nanoparticles with an apparent solubility increase of > 1000-fold as compared to the parent drug camptothecin. Preclinical studies exhibited CRLX101 pharmacokinetics superior to the parent drug. Drug concentration in tumor relative to plasma and other major organs is consistent with the enhanced permeation and retention (EPR) anticipated from a nanoparticle. Significant anti-tumor activity was observed that is superior when compared to irinotecan across a broad range of xenograft models. Pharmacokinetic data are consistent with the prolonged half-life and increased AUC. The CRLX101 preclinical and clinical data confirm that CDP can address not only solubility, formulation, toxicity, and pharmacokinetic challenges associated with administration of CPT, but more importantly, can impart unique biological properties, that enhance pharmacodynamics and efficacy of camptothecin.     

Effect of X‐ray irradiation on pharmacokinetics of irinotecan hydrochloride and expression of CES1 and CYP3A1 in rats

Concurrent chemoradiation with irinotecan hydrochloride (CPT‐11) is accepted for cancer treatment. However, the effects of X‐ray irradiation on chemotherapeutics in the plasma remain unclear. We evaluated the pharmacokinetics of CPT‐11 in rats after exposure to X‐ray irradiation and examined the changes of protein and mRNA expression of CES1 and CYP3A1. The X‐ray irradiation with 1 Gy and 5 Gy was delivered to the whole body of rats. CPT‐11 at 30 and 60 mg/kg, respectively, was intravenously infused 24 h after irradiation. CPT‐11 was determined by RP‐HPLC in plasma. ELISA and PCR were used to analyze the protein and mRNA expression of CES1 and CYP3A1, respectively. Compared with control rats, the X‐ray irradiation decreased the AUC of CPT‐11 (30 mg/kg) by 15.6% at 1 Gy and 39.0% at 5 Gy and increased the CL by 60.0% at 5 Gy. The X‐ray irradiation could also decrease the AUC of CPT‐11 (60 mg/kg) and increase the CL. In addition, the protein and mRNA expression of CES1 and CYP3A1 were increased significantly in rats after irradiation. This study found significant changes in the pharmacokinetics of CPT‐11 in rats after exposure to X‐ray irradiation, and they might be due to significant increases in the expressions of CYP3A1 and CES1. The pharmacokinetics of CPT‐11 should be rechecked, and the optimal CPT‐11 dose should be reevaluated during concurrent chemoradiation therapy.     

Tumor-targeted bioconjugate based delivery of camptothecin: design, synthesis and in vitro evaluation.

Camptothecin (CPT) presents numerous challenges associated with optimal transport and delivery including variability in clinically observed effects, low target tissue concentrations and severe and unpredictable toxicity. The objective of the present study was to optimize the delivery of CPT by targeting it to cancer cells using an endogenous receptor system. A novel CPT bioconjugate was synthesized using carbodiimide chemistry with a linear poly(ethylene glycol) (PEG) and amino acid glycine as the spacer and linker respectively. Folic acid was used as the targeting ligand to take advantage of folate receptor mediated endocytosis. The bioconjugate was extensively characterized using MALDI, proton NMR, FT-IR and amino acid analysis. Furthermore, the bioconjugate was evaluated in vitro for specific targeting to folate receptor-expressing KB cells, a human nasopharyngeal carcinoma. Finally, the delivery system was evaluated for cytotoxicity using a MTT based assay. The results indicate significantly higher efficacy of the bioconjugate in comparison to CPT. A control conjugate without PEG demonstrated no improvement in efficacy over untargeted CPT emphasizing the importance of spacer between the anticancer compounds and targeting moiety. This bioconjugate represents the 'first-in-series' of targeted bioconjugates and serves as prototype for improving tumor cell concentration and efficacy.     

Molecular targeting of BCL2 and BCLXL proteins by synthetic BCL2 homology 3 domain peptide enhances the efficacy of chemotherapy

Chemotherapeutic agents are known to induce programmed cell death or apoptosis. The activation of cellular antiapoptotic defense that prevents the translation of drug-induced damage into cell death is the key factor in cellular antiapoptotic resistance that decreases the chemotherapeutic effectiveness of a broad spectrum of anticancer drugs. A novel proapoptotic anticancer drug delivery system (DDS) was designed to simultaneously induce apoptosis and suppress antiapoptotic cellular defense. The system includes three main components: 1) anticancer drug camptothecin (CPT) as an apoptosis inducer, 2) synthetic BCL2 homology 3 domain (BH3) peptide as a suppressor of cellular antiapoptotic defense, and 3) poly(ethylene glycol) (PEG) polymer as a carrier. The above DDS was studied in vitro using A2780 human ovarian carcinoma cells and in vivo on nude mice bearing xenografts of human ovarian tumor. The results obtained in both series of experiments corroborate each other. They show that the designed DDS provided intracellular delivery of active components and suppressed cellular antiapoptotic defense, leading to the more pronounced induction of caspase-dependent signaling pathway of apoptosis compared with CPT alone and simple CPT-PEG conjugate. Including BH3 peptide in complex DDS decreased apoptotic cellular defense, substantially increased toxicity of the whole complex, and provided high antitumor activity. Therefore, the proposed novel multicomponent proapoptotic anticancer drug delivery system has high potential to enhance the efficacy of chemotherapy.     

Therapeutic potential of nucleic acid‐binding isoquinoline alkaloids: Binding aspects and implications for drug design

Isoquinoline alkaloids represent a group of natural products with remarkable importance in the contemporary biomedical research and drug discovery programs. Several members of this group exhibit immense pharmacological and biological properties, including potential anticancer properties. Although the molecular targets of these alkaloids are not yet clearly delineated, extensive research in this area continues to build up new data that are clinically exploitable. The gross structural features of many of the members DNA interaction are more or less clear, but the mystery still remains on many aspects of their binding, including specificity and energetics. RNA‐binding aspects of these alkaloids are being elucidated. More recent advancements in analytical instrumentation have enabled clearer elucidation and correlation of the structural and energetic aspects of the interaction. In this review, we report up‐to‐date details of the interaction of berberine, palmatine, and jatrorrhizine of the protoberberine group, sanguinarine from the benzophananthridine group, and several of their synthetic derivatives, such as coralyne, berberrubine, palmatrubine, and jatrorubin with nucleic acids have been reviewed. These studies, taken together up to now, have led to interesting knowledge on the mode, mechanism, specificity of binding, and correlation between structural aspects and energetics enabling a complete set of guidelines for design of new drugs. In contemporary research, several derivatives of these natural alkaloids are being prepared and investigated in several laboratories for ultimate discovery of new compounds that can be used as effective therapeutic agents. © 2010 Wiley Periodicals, Inc. Med Res Rev 31:821‐862, 2011     

Conventional versus acupuncture-like transcutaneous electrical nerve stimulation on cold-induced pain in healthy human participants: effects during stimulation

Objectives: To compare the hypoalgesic effects of conventional transcutaneous electrical nerve stimulation (TENS) (high frequency, low intensity) and acupuncture‐like TENS (AL‐TENS, low frequency, high intensity) on cold‐induced pain. Design: Randomized controlled parallel group study comparing the effects of strong non‐painful AL‐TENS, conventional TENS and placebo (no current) TENS on cold‐pressor pain threshold (CPT) and pain intensity. Two baseline (pre‐intervention) measures and three during intervention measures of CPT and cold pain intensity (four point category scale) were recorded. Setting: Physiology laboratory in Leeds Metropolitan University. Participants: One hundred and twenty‐one healthy participants. Interventions: Each participant received one of three TENS interventions over their flexor digitorum profundus: (i) high pulse rate TENS with a strong non‐painful paraesthesia (conventional), (ii) low‐rate burst mode TENS that caused strong non‐painful phasic muscle twitching (acupuncture like) or (iii) no current (placebo) TENS. Main outcome measure: Difference between conventional TENS and AL‐TENS in cold pain threshold relative to pre‐TENS baseline after 25 min of stimulation. Results: No differences were detected for CPT or cold pain intensity during conventional TENS compared with AL‐TENS. When compared with placebo TENS, the confidence intervals for the ratio of intervention CPT to baseline CPT, for both AL‐TENS (0·966, 1·424) and conventional TENS (0·948, 1·401), were close to the positive side of one, although neither reached statistical significance. Conclusions: Unlike some previous studies, the present study detected no differences in hypoalgesia between AL‐TENS, conventional TENS and placebo (no current) TENS during stimulation.