Factors that impact symptomatic diabetic peripheral neuropathy in placebo-administered patients from two 1-year clinical trials

How inflammation dictates diabetic peripheral neuropathy: An enlightening review

BACKGROUND

Diabetic peripheral neuropathy (DPN) constitutes a debilitating complication associated with diabetes. Although, the past decade has seen rapid developments in understanding the complex etiology of DPN, there are no approved therapies that can halt the development of DPN, or target the damaged nerve. Therefore, clarifying the pathogenesis of DPN and finding effective treatment are the crucial issues for the clinical management of DPN.

AIMS

This review is aiming to summary the current knowledge on the pathogenesis of DPN, especially the mechanism and application of inflammatory response.

METHODS

We systematically summarized the latest studies on the pathogenesis and therapeutic strategies of diabetic neuropathy in PubMed.

RESULTS

In this seminal review, the underappreciated role of immune activation in the progression of DPN is scrutinized. Novel insights into the inflammatory regulatory mechanisms of DPN have been unearthed, illuminating potential therapeutic strategies of notable clinical significance. Additionally, a nuanced examination of DPN's complex etiology, including aberrations in glycemic control and insulin signaling pathways, is presented. Crucially, an emphasis has been placed on translating these novel understandings into tangible clinical interventions to ameliorate patient outcomes.

CONCLUSIONS

This review is distinguished by synthesizing cutting-edge mechanisms linking inflammation to DPN and identifying innovative, inflammation-targeted therapeutic approaches.

Corneal Confocal Microscopy Identifies People with Type 1 Diabetes with More Rapid Corneal Nerve Fibre Loss and Progression of Neuropathy

There is a need to accurately identify patients with diabetes at higher risk of developing and progressing diabetic peripheral neuropathy (DPN). Fifty subjects with Type 1 Diabetes Mellitus (T1DM) and sixteen age matched healthy controls underwent detailed neuropathy assessments including symptoms, signs, quantitative sensory testing (QST), nerve conduction studies (NCS), intra epidermal nerve fiber density (IENFD) and corneal confocal microscopy (CCM) at baseline and after 2 years of follow-up. Overall, people with type 1 diabetes mellitus showed no significant change in HbA1c, blood pressure, lipids or neuropathic symptoms, signs, QST, neurophysiology, IENFD and CCM over 2 years. However, a sub-group (n = 11, 22%) referred to as progressors, demonstrated rapid corneal nerve fiber loss (RCNFL) with a reduction in corneal nerve fiber density (CNFD) (p = 0.0006), branch density (CNBD) (p = 0.0002), fiber length (CNFL) (p = 0.0002) and sural (p = 0.04) and peroneal (p = 0.05) nerve conduction velocities, which was not related to a change in HbA1c or cardiovascular risk factors. The majority of people with T1DM and good risk factor control do not show worsening of neuropathy over 2 years. However, CCM identifies a sub-group of people with T1DM who show a more rapid decline in corneal nerve fibers and nerve conduction velocity.

Is Nerve Electrophysiology a Robust Primary Endpoint in Clinical Trials of Treatments for Diabetic Peripheral Neuropathy?

There is currently no FDA-approved disease-modifying therapy for diabetic peripheral neuropathy (DPN). Nerve conduction velocity (NCV) is an established primary endpoint of disease-modifying therapies in DPN and clinical trials have been powered with an assumed decline of 0.5 m/s/year. This paper sought to establish the time-dependent change in NCV associated with a placebo, compared to that observed in the active intervention group. A literature search identified twenty-one double-blind, randomised controlled trials in DPN of ≥1 year duration conducted between 1971 and 2021. We evaluated changes in neurophysiology, with a focus on peroneal motor and sural sensory NCV and amplitude in the placebo and treatment groups. There was significant variability in the change and direction of change (reduction/increase) in NCV in the placebo arm, as well as variability influenced by the anatomical site of neurophysiological measurement within a given clinical trial. A critical re-evaluation of efficacy trials should consider placebo-adjusted effects and present the placebo-subtracted change in NCV rather than assume a universal annual decline of 0.5 m/s/year. Importantly, endpoints such as corneal confocal microscopy (CCM) have demonstrated early nerve repair, whilst symptoms and NCV have not changed, and should thus be considered as a viable alternative.

Activators and Inhibitors of Protein Kinase C (PKC): Their Applications in Clinical Trials

Protein kinase C (PKC), a family of phospholipid-dependent serine/threonine kinase, is classed into three subfamilies based on their structural and activation characteristics: conventional or classic PKC isozymes (cPKCs; α, βI, βII, and γ), novel or non-classic PKC isozymes (nPKCs; δ, ε, η, and θ), and atypical PKC isozymes (aPKCs; ζ, ι, and λ). PKC inhibitors and activators are used to understand PKC-mediated intracellular signaling pathways and for the diagnosis and treatment of various PKC-associated diseases, such as cancers, neurological diseases, cardiovascular diseases, and infections. Many clinical trials of PKC inhibitors in cancers showed no significant clinical benefits, meaning that there is a limitation to design a cancer therapeutic strategy targeting PKC alone. This review will focus on the activators and inhibitors of PKC and their applications in clinical trials.

Pathogenesis, diagnosis and clinical management of diabetic sensorimotor peripheral neuropathy

Diabetic sensorimotor peripheral neuropathy (DSPN) is a serious complication of diabetes mellitus and is associated with increased mortality, lower-limb amputations and distressing painful neuropathic symptoms (painful DSPN). Our understanding of the pathophysiology of the disease has largely been derived from animal models, which have identified key potential mechanisms. However, effective therapies in preclinical models have not translated into clinical trials and we have no universally accepted disease-modifying treatments. Moreover, the condition is generally diagnosed late when irreversible nerve damage has already taken place. Innovative point-of-care devices have great potential to enable the early diagnosis of DSPN when the condition might be more amenable to treatment. The management of painful DSPN remains less than optimal; however, studies suggest that a mechanism-based approach might offer an enhanced benefit in certain pain phenotypes. The management of patients with DSPN involves the control of individualized cardiometabolic targets, a multidisciplinary approach aimed at the prevention and management of foot complications, and the timely diagnosis and management of neuropathic pain. Here, we discuss the latest advances in the mechanisms of DSPN and painful DSPN, originating both from the periphery and the central nervous system, as well as the emerging diagnostics and treatments.

Malfunctioning CD106-positive, short-term hematopoietic stem cells trigger diabetic neuropathy in mice by cell fusion

Diabetic neuropathy is an incurable disease. We previously identified a mechanism by which aberrant bone marrow-derived cells (BMDCs) pathologically expressing proinsulin/TNF-α fuse with residential neurons to impair neuronal function. Here, we show that CD106-positive cells represent a significant fraction of short-term hematopoietic stem cells (ST-HSCs) that contribute to the development of diabetic neuropathy in mice. The important role for these cells is supported by the fact that transplantation of either whole HSCs or CD106-positive ST-HSCs from diabetic mice to non-diabetic mice produces diabetic neuronal dysfunction in the recipient mice via cell fusion. Furthermore, we show that transient episodic hyperglycemia produced by glucose injections leads to abnormal fusion of pathological ST-HSCs with residential neurons, reproducing neuropathy in nondiabetic mice. In conclusion, we have identified hyperglycemia-induced aberrant CD106-positive ST-HSCs underlie the development of diabetic neuropathy. Aberrant CD106-positive ST-HSCs constitute a novel therapeutic target for the treatment of diabetic neuropathy.

Katagi et al. show that abnormal bone marrow-derived cells originated from hematopoietic stem cells (CD106-positive short-term HSCs) aberrantly fuse with neurons to develop diabetic neuropathy. This study suggests that the pathological abnormality is memorized in the bone marrow and that it cannot be erased by conventional therapy.

Rate of neuropathic progression in hereditary transthyretin amyloidosis with polyneuropathy and other peripheral neuropathies: a systematic review and meta-analysis

Background

We aimed to compare neuropathic progression rate between hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN) and other peripheral neuropathies, including diabetic peripheral neuropathy (DPN) and Charcot-Marie-Tooth disease (CMT).

Methods

Literature searches identified studies reporting neuropathic progression, measured by Neuropathy Impairment Score (NIS) or NIS-Lower Limbs (NIS-LL). Our study also included unpublished data from a clinical registry of patients who were diagnosed with different peripheral neuropathies and seen at the Oregon Health & Science University (OHSU) during 2016–2020. Meta-analysis and meta-regression models examined and compared annual progression rates, calculated from extracted data, between studies of ATTRv-PN and other peripheral neuropathies.

Results

Data were synthesized from 15 studies in which NIS and/or NIS-LL total scores were assessed at least twice, with ≥12 weeks between assessments, among untreated patients with ATTRv-PN or other peripheral neuropathies. Meta-analysis models yielded that the annual progression rate in NIS total scores was significantly different from zero for studies in ATTRv-PN and CMT (11.77 and 1.41; both P < 0.001), but not DPN (− 1.96; P = 0.147). Meta-regression models showed significantly faster annual progression in studies in ATTRv-PN, which statistically exceeded that in other peripheral neuropathies by 12.45 points/year for NIS, and 6.96 for NIS-LL (both P < 0.001).

Conclusions

Peripheral nervous function deteriorates more rapidly in patients with ATTRv-PN than for other peripheral neuropathies. These findings may improve understanding of the natural history of neuropathy in ATTRv-PN, facilitate early diagnosis, and guide the development of assessment tools and therapies specifically targeting neuropathic progression in this debilitating disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02094-y.

The time to develop treatments for diabetic neuropathy

BACKGROUND

Diabetic neuropathy is a multifaceted condition affecting up to 50% of individuals with long standing diabetes. The most common presentation is peripheral diabetic sensory neuropathy (DPN).

METHODS

We carried out a systematic review of papers dealing with diabetic neuropathy on Pubmed in addition to a targeted Google search.Search terms included small fiber neuropathy,diffuse peripheral neuropathy, quantitative sensory testing, nerve conduction testing, intra-epidermal nerve fiber density, corneal confocal reflectance microscopy, aldose reductase inhbitors, nerve growth factor, alpha-lipoic acid, ruboxistaurin, nerve growth factor antibody, and cibinetide.

RESULTS

Over the past half century, there have been a number of agents undergoing unsuccessful trials for treatment of DPN.There are several approved agents for relief of pain caused by diabetic neuropathy, but these do not affect the pathologic process.

EXPERT OPINION

The failure to find treatments for diabetic neuropathy can be ascribed to (1) the complexity of design of studies and (2) the slow progression of the condition, necessitating long duration trials to prove efficacy.We propose a modification of the regulatory process to permit early introduction of agents with demonstrated safety and suggestion of benefit as well as prolongation of marketing exclusivity while long term trials are in progress to prove efficacy.

γ-Linolenic Acid versus α-Lipoic Acid for Treating Painful Diabetic Neuropathy in Adults: A 12-Week, Double-Placebo, Randomized, Noninferiority Trial

BACKGROUND

This study was a multicenter, parallel-group, double-blind, double-dummy, randomized, noninferiority trial to evaluate the efficacy and safety of γ-linolenic acid (GLA) relative to α-lipoic acid (ALA) over a 12-week treatment period in type 2 diabetes mellitus (T2DM) patients with painful diabetic peripheral neuropathy (DPN).

METHODS

This study included 100 T2DM patients between 20 and 75 years of age who had painful DPN and received either GLA (320 mg/day) and placebo or ALA (600 mg/day) and placebo for 12 weeks. The primary outcome measures were mean changes in pain intensities as measured by the visual analogue scale (VAS) and the total symptom scores (TSS).

RESULTS

Of the 100 subjects who initially participated in the study, 73 completed the 12-week treatment period. Per-protocol analyses revealed significant decreases in the mean VAS and TSS scores compared to baseline in both groups, but there were no significant differences between the groups. The treatment difference for the VAS (95% confidence interval [CI]) between the two groups was -0.65 (-1.526 to 0.213) and the upper bound of the 95% CI did not exceed the predefined noninferiority margin (δ₁=0.51). For the TSS, the treatment difference was -0.05 (-1.211 to 1.101) but the upper bound of the 95% CI crossed the noninferiority margin (δ₂=0.054). There were no serious adverse events associated with the treatments.

CONCLUSION

GLA treatment in patients with painful DPN was noninferior to ALA in terms of reducing pain intensity measured by the VAS over 12 weeks.

In-vivo reflectance confocal microscopy of Meissner's corpuscles in diabetic distal symmetric polyneuropathy

OBJECTIVE

To evaluate in-vivo reflectance confocal microscopy (RCM) of Meissner's corpuscles (MC) in diabetic distal symmetric polyneuropathy (DSP).

METHODS

Forty-three adults with diabetes and 21 control subjects underwent RCM of MC density at the fingertip of digit V, thenar eminence (TE), and arch of the foot, ankle skin biopsy for epidermal nerve fiber density (ENFD), electrophysiological studies, monofilament threshold testing, and timed vibration at the toe. Subjects with diabetes were subdivided into groups with and without clinical DSP using the American Academy of Neurology (AAN) case definition and neuropathy outcomes were compared across groups.

RESULTS

Both diabetic groups (with and without AAN clinical DSP criteria) had objective evidence of peripheral sensory involvement using conventional sensory measures, although those with clinical DSP criteria had greater abnormalities. MC densities were lower in the entire diabetic group at the TE and digit V relative to controls. MC densities at all imaging sites were associated with corresponding conventional sensory measures. MC densities were reduced in subjects without AAN clinical DSP criteria at the TE and digit V compared to controls whereas conventional upper limb sensory measures did not differ between these groups.

CONCLUSIONS

In-vivo RCM of MC density at digit V is a non-invasive, painless, objective marker in diabetes that offers a window into early large fiber sensory nerve terminal loss. Further studies are needed to determine whether RCM of MCs can identify quantitative changes in DSP associated with disease progression or treatment.

Safety and efficacy of ranirestat in patients with mild-to-moderate diabetic sensorimotor polyneuropathy

We examined the efficacy and safety of ranirestat in patients with diabetic sensorimotor polyneuropathy (DSPN). Patients (18-75 years) with stable type 1/2 diabetes mellitus and DSPN were eligible for this global, double-blind, phase II/III study (ClinicalTrials.gov NCT00927914). Patients (n = 800) were randomized 1 : 1 : 1 to placebo, ranirestat 40 mg/day or 80 mg/day (265 : 264 : 271). Change in peroneal motor nerve conduction velocity (PMNCV) from baseline to 24 months was the primary endpoint with a goal improvement vs. placebo ≥1.2 m/s. Other endpoints included symptoms, quality-of-life, and safety. Six hundred thirty-three patients completed the study. The PMNCV difference from placebo was significant at 6, 12, and 18 months in both ranirestat groups, but <1.2 m/s. The mean improvement from baseline at 24 months was +0.49, +0.95, and +0.90 m/s for placebo, ranirestat 40 mg and 80 mg, respectively (NS). The treatment difference vs. placebo reached significance when ranirestat groups were combined in a post hoc analysis (+0.44 m/s; p = 0.0237). There was no effect of ranirestat on safety assessments, secondary or exploratory endpoints vs. placebo. Ranirestat was well tolerated and improved PMNCV, but did not achieve any efficacy endpoints. The absence of PMNCV worsening in the placebo group underscores the challenges of DSPN studies in patients with well-controlled diabetes.

Electrophysiologic testing in diabetic neuropathy

Electrophysiologic studies provide objective data concerning nerve and muscle function. This information enables the diagnosis of disease states and monitoring of disease progression. This chapter describes the changes in electrophysiologic function in both prediabetes and diabetes and discusses the utility of this testing in patients with diabetes. Both the strengths and limitations of electrophysiology are discussed.

Wherefore Art Thou, O Treatment for Diabetic Neuropathy?

As of March 2016, we continue to advocate the diagnosis of diabetic neuropathy using a simple foot examination or monofilament, which identifies only those with severe neuropathy and hence risk of foot ulceration. Given the fact that the 5-year mortality rate of diabetic patients with foot ulceration is worse than that of most common cancers, surely we should be identifying patients at an earlier stage of neuropathy to prevent its progression to a stage with such a high mortality? Of course, we lament that there is no licensed treatment for diabetic neuropathy. Who is to blame? As researchers and carers, we have a duty of care to our patients with diabetic neuropathy. So, we have to look forward not backwards, and move away from our firmly entrenched views on the design and conduct of clinical trials for diabetic neuropathy. Relevant organizations such as Neurodiab, the American Diabetes Association and the Peripheral Nerve Society have to acknowledge that they cannot continue to endorse a bankrupt strategy. The FDA needs an open and self-critical dialogue with these organizations, to give pharmaceutical companies at least a fighting chance to deliver effective new therapies for diabetic neuropathy.

The Perfect Clinical Trial

Multiple phase III clinical trials have failed to show disease-modifying benefits for diabetic sensorimotor polyneuropathy (DSP) and this may be due to the design of the clinical trials. The perfect clinical trial in DSP would enroll sufficiently large numbers of patients having early or minimal disease, as demonstrated by nerve conduction studies (NCS). These patients would be treated with an intervention given at an effective and well-tolerated dose for a sufficient duration of time to show change in the end points selected. For objective or surrogate measures such as NCS and for some small fiber measures, the duration needed to show positive change may be as brief as 6-12 months, but subsequently, trials lasting 5-8 years will be required to demonstrate clinical benefits.

Treating Diabetic Neuropathy: Present Strategies and Emerging Solutions

Diabetic peripheral neuropathies (DPN) are a heterogeneous group of disorders caused by neuronal dysfunction in patients with diabetes. They have differing clinical courses, distributions, fiber involvement (large or small), and pathophysiology. These complications are associated with increased morbidity, distress, and healthcare costs. Approximately 50% of patients with diabetes develop peripheral neuropathy, and the projected rise in the global burden of diabetes is spurring an increase in neuropathy. Distal symmetrical polyneuropathy (DSPN) with painful diabetic neuropathy, occurring in around 20% of diabetes patients, and diabetic autonomic neuropathy (DAN) are the most common manifestations of DPN. Optimal glucose control represents the only broadly accepted therapeutic option though evidence of its benefit in type 2 diabetes is unclear. A number of symptomatic treatments are recommended in clinical guidelines for the management of painful DPN, including antidepressants such as amitriptyline and duloxetine, the γ-aminobutyric acid analogues gabapentin and pregabalin, opioids, and topical agents such as capsaicin. However, monotherapy is frequently not effective in achieving complete resolution of pain in DPN. There is a growing need for head-to-head studies of different single-drug and combination pharmacotherapies. Due to the ubiquity of autonomic innervation in the body, DAN causes a plethora of symptoms and signs affecting cardiovascular, urogenital, gastrointestinal, pupillomotor, thermoregulatory, and sudomotor systems. The current treatment of DAN is largely symptomatic, and does not correct the underlying autonomic nerve deficit. A number of novel potential candidates, including erythropoietin analogues, angiotensin II receptor type 2 antagonists, and sodium channel blockers are currently being evaluated in phase II clinical trials.

A meta-analysis of randomized double-blind clinical trials in CMT1A to assess the change from baseline in CMTNS and ONLS scales after one year of treatment

CMT1A is the most common inherited peripheral neuropathy. There is currently no approved treatment. We performed a meta-analysis including four randomized, double-blind, Placebo-controlled clinical trials to assess the disease progression after one year under Placebo, Ascorbic Acid (AA) or PXT3003, a combination of three repurposed drugs. We observed a weak deterioration in patients under Placebo, well below the reported natural disease progression. Patients treated with AA were stable after one year but not significantly different from Placebo. Patients undergoing PXT3003 treatment showed an improvement in CMTNS and ONLS, statistically significant versus Placebo and potentially precursory of a meaningful change in the disease course.

Nociception at the diabetic foot, an uncharted territory

The diabetic foot is characterised by painless foot ulceration and/or arthropathy; it is a typical complication of painless diabetic neuropathy. Neuropathy depletes the foot skin of intraepidermal nerve fibre endings of the afferent A-delta and C-fibres, which are mostly nociceptors and excitable by noxious stimuli only. However, some of them are cold or warm receptors whose functions in diabetic neuropathy have frequently been reported. Hence, it is well established by quantitative sensory testing that thermal detection thresholds at the foot skin increase during the course of painless diabetic neuropathy. Pain perception (nociception), by contrast, has rarely been studied. Recent pilot studies of pinprick pain at plantar digital skinfolds showed that the perception threshold was always above the upper limit of measurement of 512 mN (equivalent to 51.2 g) at the diabetic foot. However, deep pressure pain perception threshold at musculus abductor hallucis was beyond 1400 kPa (equivalent to 14 kg; limit of measurement) only in every fifth case. These discrepancies of pain perception between forefoot and hindfoot, and between skin and muscle, demand further study. Measuring nociception at the feet in diabetes opens promising clinical perspectives. A critical nociception threshold may be quantified (probably corresponding to a critical number of intraepidermal nerve fibre endings), beyond which the individual risk of a diabetic foot rises appreciably. Staging of diabetic neuropathy according to nociception thresholds at the feet is highly desirable as guidance to an individualised injury prevention strategy.

Blockade of PKCβ protects against remote organ injury induced by intestinal ischemia and reperfusion via a p66shc-mediated mitochondrial apoptotic pathway

Intestinal ischemia-reperfusion (I/R) is a serious clinical dilemma with high morbidity and mortality. Remote organ damage, especially acute lung injury and liver injury are common complications that contribute to the high mortality rate. We previously demonstrated that activation of PKCβII is specifically involved in the primary injury of intestinal I/R. Considering the tissue-specific features of PKC activation, we hypothesized that some kind of PKC isoform may play important roles in the progression of secondary injury in the remote organ. Mice were studied in in vivo model of intestinal I/R. The activation of PKC isoforms were screened in the lung and liver. Interestingly, we found that PKCβII was also activated exclusively in the lung and liver after intestinal I/R. PKCβII suppression by a specific inhibitor, LY333531, significantly attenuated I/R-induced histologic damage, inflammatory cell infiltration, oxidative stress, and apoptosis in these organs, and also alleviated systemic inflammation. In addition, LY333531 markedly restrained p66shc activation, mitochondrial translocation, and binding to cytochrome-c. These resulted in the decrease of cytochrome-c release and caspase-3 cleavage, and an increase in glutathione and glutathione peroxidase. These data indicated that activated PKC isoform in the remote organ, specifically PKCβII, is the same as that in the intestine after intestinal I/R. PKCβII suppression protects against remote organ injury, which may be partially attributed to the p66shc-cytochrome-c axis. Combined with our previous study, the development of a specific inhibitor for prophylaxis against intestinal I/R is promising, to prevent multiple organ injury.

High-dosage ascorbic acid treatment in Charcot-Marie-Tooth disease type 1A: results of a randomized, double-masked, controlled trial

IMPORTANCE

No current medications improve neuropathy in subjects with Charcot-Marie-Tooth disease type 1A (CMT1A). Ascorbic acid (AA) treatment improved the neuropathy of a transgenic mouse model of CMT1A and is a potential therapy. A lower dosage (1.5 g/d) did not cause improvement in humans. It is unknown whether a higher dosage would prove more effective.

OBJECTIVE

To determine whether 4-g/d AA improves the neuropathy of subjects with CMT1A.

DESIGN

A futility design to determine whether AA was unable to reduce worsening on the CMT Neuropathy Score (CMTNS) by at least 50% over a 2-year period relative to a natural history control group.

SETTING

Three referral centers with peripheral nerve clinics (Wayne State University, Johns Hopkins University, and University of Rochester).

PARTICIPANTS

One hundred seventy-four subjects with CMT1A were assessed for eligibility; 48 did not meet eligibility criteria and 16 declined to participate. The remaining 110 subjects, aged 13 to 70 years, were randomly assigned in a double-masked fashion with 4:1 allocation to oral AA (87 subjects) or matching placebo (23 subjects). Sixty-nine subjects from the treatment group and 16 from the placebo group completed the study. Two subjects from the treatment group and 1 from the placebo group withdrew because of adverse effects.

INTERVENTIONS

Oral AA (4 g/d) or matching placebo.

MAIN OUTCOMES AND MEASURES

Change from baseline to year 2 in the CMTNS, a validated composite impairment score for CMT.

RESULTS

The mean 2-year change in the CMTNS was -0.21 for the AA group and -0.92 for the placebo group, both better than natural history (+1.33). This was well below 50% reduction of CMTNS worsening from natural history, so futility could not be declared (P > .99).

CONCLUSIONS AND RELEVANCE

Both treated patients and those receiving placebo performed better than natural history. It seems unlikely that our results support undertaking a larger trial of 4-g/d AA treatment in subjects with CMT1A.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00484510.

Ruboxistaurin for the treatment of diabetic peripheral neuropathy: a systematic review of randomized clinical trials

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes mellitus. Protein kinase C (PKC) inhibitor's has been thought to be a potential disease modifying drug's in DPN as it slows or reverse neuropathy's progression. To assesses the efficacy and safety of ruboxistaurin on the progression of symptoms, signs, or functional disability in DPN.

METHODS

A systematic review of the literature databases like PubMed, ProQuest, EBSCO, EMBASE, and Cochrane Central was performed up to August 2012. We included randomized controlled trials (RCTs) comparing PKC inhibitor ruboxistaurin (RBX) with control and lasting at least 6 months. Our primary outcome measure was change in neurological examination, measured by neurological total symptom score (NTSS) and vibration detection threshold (VDT). Secondary outcome measures were total quality of life (QoL), skin microvascular blood flow and others.

RESULTS

Six RCTs were included in review. Change in neurological function assessed by NTSS was reported in six studies, out of which significant difference between the RBX and placebo group seen in four studies favouring treatment group while remaining two studies reported no significant difference. VDT was assessed in only one study in which no significant difference seen between RBX and placebo group. Two studies reported significant improvement in QoL data. Safety data was reported in only two studies in which none of side effect was related to RBX.

CONCLUSION

RBX had effects on DPN in some studies, but the evidence is not enough for meta-analysis and firm conclusion.

Corneal confocal microscopy to assess diabetic neuropathy: an eye on the foot

Accurate detection and quantification of human diabetic peripheral neuropathy are important to define at-risk patients, anticipate deterioration, and assess new therapies. Easily performed clinical techniques such as neuro-logical examination, assessment of vibration perception or insensitivity to the 10 g monofilament only assess advanced neuropathy, i.e., the at-risk foot. Techniques that assess early neuropathy include neurophysiology (which assesses only large fibers) and quantitative sensory testing (which assesses small fibers), but they can be highly subjective while more objective techniques, such as skin biopsy for intra-epidermal nerve fiber density quantification, are invasive and not widely available. The emerging ophthalmic technique of corneal confocal microscopy allows quantification of corneal nerve morphology and enables clinicians to diagnose peripheral neuropathy in diabetes patients, quantify its severity, and potentially assess therapeutic benefit. The present review provides a detailed critique of the rationale, a practical approach to capture images, and a basis for analyzing and interpreting the images. We also critically evaluate the diagnostic ability of this new noninvasive ophthalmic test to diagnose diabetic and other peripheral neuropathies.

Inflammation: therapeutic targets for diabetic neuropathy

There are still no approved treatments for the prevention or of cure of diabetic neuropathy, and only symptomatic pain therapies of variable efficacy are available. Inflammation is a cardinal pathogenic mechanism of diabetic neuropathy. The relationships between inflammation and the development of diabetic neuropathy involve complex molecular networks and processes. Herein, we review the key inflammatory molecules (inflammatory cytokines, adhesion molecules, chemokines) and pathways (nuclear factor kappa B, JUN N-terminal kinase) implicated in the development and progression of diabetic neuropathy. Advances in the understanding of the roles of these key inflammatory molecules and pathways in diabetic neuropathy will facilitate the discovery of the potential of anti-inflammatory approaches for the inhibition of the development of neuropathy. Specifically, many anti-inflammatory drugs significantly inhibit the development of different aspects of diabetic neuropathy in animal models and clinical trials.

Guidelines in the management of diabetic nerve pain: clinical utility of pregabalin

Diabetic peripheral neuropathy is a common complication of diabetes. It presents as a variety of syndromes for which there is no universally accepted unique classification. Sensorimotor polyneuropathy is the most common type, affecting about 30% of diabetic patients in hospital care and 25% of those in the community. Pain is the reason for 40% of patient visits in a primary care setting, and about 20% of these have had pain for greater than 6 months. Chronic pain may be nociceptive, which occurs as a result of disease or damage to tissue with no abnormality in the nervous system. In contrast, neuropathic pain is defined as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system." Persistent neuropathic pain interferes significantly with quality of life, impairing sleep and recreation; it also significantly impacts emotional well-being, and is associated with depression, anxiety, and noncompliance with treatment. Painful diabetic peripheral neuropathy is a difficult-to-manage clinical problem, and patients with this condition are more apt to seek medical attention than those with other types of diabetic neuropathy. Early recognition of psychological problems is critical to the management of pain, and physicians need to go beyond the management of pain per se if they are to achieve success. This evidence-based review of the assessment of the patient with pain in diabetes addresses the state-of-the-art management of pain, recognizing all the conditions that produce pain in diabetes and the evidence in support of a variety of treatments currently available. A search of the full Medline database for the last 10 years was conducted in August 2012 using the terms painful diabetic peripheral neuropathy, painful diabetic peripheral polyneuropathy, painful diabetic neuropathy and pain in diabetes. In addition, recent reviews addressing this issue were adopted as necessary. In particular, reports from the American Academy of Neurology and the Toronto Consensus Panel on Diabetic Neuropathy were included. Unfortunately, the results of evidence-based studies do not necessarily take into account the presence of comorbidities, the cost of treatment, or the role of third-party payers in decision-making. Thus, this review attempts to give a more balanced view of the management of pain in the diabetic patient with neuropathy and in particular the role of pregabalin.

H-reflex and clinical examination in the diagnosis of diabetic polyneuropathy

OBJECTIVES

To determine among adult patients with type-2 diabetes mellitus the proportion diagnosed with diabetic polyneuropathy (DPN) by clinical evaluation and by the Hoffmann reflex (H-reflex). In addition, the predictive value of the H-reflex in the diagnosis of DPN was evaluated.

METHODS

Studies were carried out on 150 adult patients referred for neuropathy screening. Diagnostic criteria for DPN were at least two abnormalities in clinical neurophysiological examinations and electrophysiological testing (H-reflex and nerve conduction velocity). Logistic regression analysis was performed to identify unique contributions of study characteristics to positive versus negative outcomes.

RESULTS

H-reflex was absent in 39.3% (59/150) and latency was prolonged in 43.3% (65/150) of patients. Ulnar nerve motor branch nerve conduction showed prolonged latency in 9.3% (14/150) of patients. Logistic regression analysis indicated that the H-reflex was significantly associated with positive outcomes.

CONCLUSION

The H-reflex could have a predictive value in DPN, providing more quantitative information regarding diagnosis than conventional nerve conduction studies.

Reproducibility of peroneal motor nerve conduction measurement in older adults

OBJECTIVE

While neuropathy is common in the elderly, nerve conduction (NC) reproducibility in older adults is not well-established. We sought to evaluate intraobserver reproducibility of peroneal motor NC measures in a diverse sample of older adults.

METHODS

We measured peroneal motor NC amplitude and velocity in a subset of participants (mean age=82.9±2.7, n=62, 50% female, 51.6% black, 35.5% DM) in the Health, Aging, and Body Composition Study. Using coefficients of variation (CVs), intraclass correlation coefficients (ICCs), and Bland Altman Plots, we compared two sets of measurements taken by the same examiner hours apart on the same day.

RESULTS

Low CVs (2.15-4.24%) and moderate to high ICCs (0.75-0.99) were observed. No systematic variation was found across measures. Despite small numbers in some subgroups, we found no differences in reproducibility by diabetes, race or study site.

CONCLUSION

NC measures have moderate to high intraobsever reproducibility in older adults and are not affected by diabetes, race, or gender.

SIGNIFICANCE

These data provide evidence to support use of these measures in aging research.

A longitudinal study of sensory biomarkers of progression in patients with diabetic peripheral neuropathy using skin biopsies

We aimed to identify biomarkers in skin punch biopsies that could be used to monitor progression of diabetic peripheral neuropathy (DPN), and, in future studies, to assess the efficacy of agents that may reduce progression. Patients with DPN were studied with clinical assessments, skin biopsies, quantitative sensory testing (QST), histamine-induced skin flare, nerve conduction studies and contact heat-evoked potentials (CHEPS). Skin biopsies were performed on two visits with a 6 month interval (n=29 patients) to quantify intraepidermal (IENF) and subepidermal (SENF) nerve fibres immunoreactive for: protein gene product 9.5 (PGP9.5), a pan-neuronal marker; transient receptor potential cation channel vanilloid 1 (TRPV1), the heat and capsaicin receptor; and growth associated protein-43 (GAP-43), a marker of regenerating fibres. The IENF were counted along the length of four non-consecutive sections, and results were expressed as fibres per millimetre length of section. SENF were measured by image analysis, and the area of highlighted immunoreactivity was obtained as a percentage (% area) of the field scanned. QST, skin flare and CHEPS were also performed at the two visits. We found that IENF and SENF were significantly reduced for both PGP9.5 and TRPV1 between the first and second skin biopsy over 6months. The annual rate ± standard error of the mean of IENF loss was 3.76 ± 1.46 fibres/mm for PGP9.5, and 3.13 ± 0.58 fibres/mm for TRPV1. The other tests did not show significant changes. Strongly positive GAP-43 nerve fibres were found in deep dermis in the patients with diabetes, even in those with an absence of IENF. We conclude that PGP9.5 and TRPV1 IENF and SENF in skin biopsies are useful markers of progression in DPN, whereas GAP-43 SENF could potentially help detect nerve regeneration in severe neuropathy.

α-Lipoic Acid, Diabetic Neuropathy, and Nathan’s Prophecy

Both oral and intravenous administration of alpha-lipoic acid (ALA) has been investigated as add-on treatment for diabetic peripheral neuropathy. The recent Neurological Assessment of Thioctic Acid in Diabetic Neuropathy (NATHAN) 1 trial has shown that 4-year oral ALA administration is of some value in achieving a clinically meaningful improvement and a slight delay in the progression of neuropathic deficits among patients with mild/moderate diabetic peripheral neuropathy. Despite these promising results, important questions remain to be answered, mainly appropriate patient selection and optimal treatment duration. Moreover, a cost-benefit analysis would be useful.

Cilostazol in Diabetic Neuropathy

Peripheral neuropathy remains a major chronic complication of diabetes mellitus. Its pathogenesis mainly involves chronic glucose toxicity and nerve ischemia. Preclinical studies have shown that cilostazol, a reversible selective inhibitor of phosphodiesterase-3A with antiplatelet, antithrombotic, and vasodilatory properties, exerts beneficial effects on nerve function in experimental diabetes. Clinical data, however, is sparse. Two recent randomized placebo-controlled clinical trials showed that cilostazol did not improve diabetic neuropathy in humans. Hence, more data is needed to confirm or refute the poor clinical efficacy of cilostazol. Importantly, future studies should include larger patient series, provide longer follow-up data, and employ more accurate diagnostic tools.

Diabetic neuropathy: cellular mechanisms as therapeutic targets

In patients with diabetes, nerve injury is a common complication that leads to chronic pain, numbness and substantial loss of quality of life. Good glycemic control can decrease the incidence of diabetic neuropathy, but more than half of all patients with diabetes still develop this complication. There is no approved treatment to prevent or halt diabetic neuropathy, and only symptomatic pain therapies, with variable efficacy, are available. New insights into the mechanisms leading to the development of diabetic neuropathy continue to point to systemic and cellular imbalances in metabolites of glucose and lipids. In the PNS, sensory neurons, Schwann cells and the microvascular endothelium are vulnerable to oxidative and inflammatory stress in the presence of these altered metabolic substrates. This Review discusses the emerging cellular mechanisms that are activated in the diabetic milieu of hyperglycemia, dyslipidemia and impaired insulin signaling. We highlight the pathways to cellular injury, thereby identifying promising therapeutic targets, including mitochondrial function and inflammation.

Efficacy and safety of antioxidant treatment with α-lipoic acid over 4 years in diabetic polyneuropathy: the NATHAN 1 trial

OBJECTIVE

To evaluate the efficacy and safety of α-lipoic acid (ALA) over 4 years in mild-to-moderate diabetic distal symmetric sensorimotor polyneuropathy (DSPN). RESEARCH DESIGN AND METHODS In a multicenter randomized double-blind parallel-group trial, 460 diabetic patients with mild-to-moderate DSPN were randomly assigned to oral treatment with 600 mg ALA once daily (n = 233) or placebo (n = 227) for 4 years. Primary end point was a composite score (Neuropathy Impairment Score [NIS]-Lower Limbs [NIS-LL] and seven neurophysiologic tests). Secondary outcome measures included NIS, NIS-LL, nerve conduction, and quantitative sensory tests (QSTs).

RESULTS

Change in primary end point from baseline to 4 years showed no significant difference between treatment groups (P = 0.105). Change from baseline was significantly better with ALA than placebo for NIS (P = 0.028), NIS-LL (P = 0.05), and NIS-LL muscular weakness subscore (P = 0.045). More patients showed a clinically meaningful improvement and fewer showed progression of NIS (P = 0.013) and NIS-LL (P = 0.025) with ALA than with placebo. Nerve conduction and QST results did not significantly worsen with placebo. Global assessment of treatment tolerability and discontinuations due to lack of tolerability did not differ between the groups. The rates of serious adverse events were higher on ALA (38.1%) than on placebo (28.0%).

CONCLUSIONS

Four-year treatment with ALA in mild-to-moderate DSPN did not influence the primary composite end point but resulted in a clinically meaningful improvement and prevention of progression of neuropathic impairments and was well tolerated. Because the primary composite end point did not deteriorate significantly in placebo-treated subjects, secondary prevention of its progression by ALA according to the trial design was not feasible.

Olive (Olea europaea L.) leaf extract attenuates early diabetic neuropathic pain through prevention of high glucose-induced apoptosis: in vitro and in vivo studies

AIM OF STUDY

Since the leaves of olive have been recommended in the literature as a remedy for the treatment of diabetes and they also contain antioxidant agents, we decided to investigate the possible effects of olive leaf extract (OLE) on in vitro and in vivo models of diabetic pain neuropathy.

MATERIALS AND METHODS

The high glucose-induced cell damage in naive and NGF-treated Pheochromocytoma (PC12) cells and streptozotocin-induced diabetic rats were used. Tail-flick test was used to access nociceptive threshold. Cell viability was determined by MTT assay. Biochemical markers of neural apoptosis were evaluated using immunoblotting.

RESULTS

We found that elevation of glucose (4 times of normal) sequentially increases functional cell damage and caspase-3 activation in NGF-treated PC12 cells. Incubation of cells with OLE (200, 400 and 600 μg/ml) decreased cell damage. Furthermore, the diabetic rats developed neuropathic pain which was evident from decreased tail-flick latency (thermal hyperalgesia). Activated caspase 3 and Bax/Bcl2 ratio were significantly increased in spinal cord of diabetic animals. OLE treatment (300 and 500 mg/kg per day) ameliorated hyperalgesia, inhibited caspase 3 activation and decreased Bax/Bcl2 ratio. Furthermore, OLE exhibited potent DPPH free radical scavenging capacity.

CONCLUSION

The results suggest that olive leaf extract inhibits high glucose-induced neural damage and suppresses diabetes-induced thermal hyperalgesia. The mechanisms of these effects may be due, at least in part, to reduce neuronal apoptosis and suggest therapeutic potential of olive leaf extract in attenuation of diabetic neuropathic pain.

Short-term metabolic change is associated with improvement in measures of diabetic neuropathy: a 1-year placebo cohort analysis

AIMS

Randomized clinical trials have frequently shown improvement in diabetic sensorimotor polyneuropathy in placebo-treated participants, counter to the prevailing concept that it deteriorates with time. We aimed to determine the variables associated with this paradoxical nerve function improvement.

METHODS

Participants with diabetic sensorimotor polyneuropathy randomized to placebo in a multi-centre, double-blind study were evaluated for the primary outcome of 1-year change in the summed sensory nerve conduction velocity of the bilateral sural and non-dominant median nerves. Association with clinical and biochemical variables measured at 13 time points were examined.

RESULTS

The 134 participants had mild to moderate diabetic sensorimotor polyneuropathy of 4.6 years' duration and mean 1-year improvement of 2.0 ± 8.0 m/s. Primary outcome measures were available for 122 participants (91%). In multivariate analyses, the change in HbA(1c) and serum triglycerides from baseline to 2 months demonstrated the strongest association, even independent of baseline and end-of-study levels. According to quintiles of change, we determined thresholds: participants with salutary improvement in HbA(1c) (exceeding a drop of -0.8%) or whose triglycerides did not increase (by 0.32 mmol/l or more) experienced significant improvement (2.9 m/s), while those with salutary levels of both these variables had an exaggerated improvement (5.1 m/s). In comparison, those with non-salutary changes in both variables experienced a loss of -4.9 m/s (ANOVA P=0.0014).

CONCLUSIONS

In mild to moderate diabetic sensorimotor polyneuropathy, short-term improvements in glycaemic control and serum triglyceride levels have an independent, additive and durable effect on restoration of nerve function.

Research design considerations for confirmatory chronic pain clinical trials: IMMPACT recommendations

There has been an increase in the number of chronic pain clinical trials in which the treatments being evaluated did not differ significantly from placebo in the primary efficacy analyses despite previous research suggesting that efficacy could be expected. These findings could reflect a true lack of efficacy or methodological and other aspects of these trials that compromise the demonstration of efficacy. There is substantial variability among chronic pain clinical trials with respect to important research design considerations, and identifying and addressing any methodological weaknesses would enhance the likelihood of demonstrating the analgesic effects of new interventions. An IMMPACT consensus meeting was therefore convened to identify the critical research design considerations for confirmatory chronic pain trials and to make recommendations for their conduct. We present recommendations for the major components of confirmatory chronic pain clinical trials, including participant selection, trial phases and duration, treatment groups and dosing regimens, and types of trials. Increased attention to and research on the methodological aspects of confirmatory chronic pain clinical trials has the potential to enhance their assay sensitivity and ultimately provide more meaningful evaluations of treatments for chronic pain.

Ruboxistaurin: PKC-beta inhibition for complications of diabetes

Diabetes mellitus is the most common cause of blindness among working-age adults, with a prevalence of 7 - 8% of adults in the USA, and is one of the most common causes of renal failure requiring kidney transplant and the most common cause of non-traumatic lower limb amputation in developed nations [1] . The role of the intracellular signaling enzyme protein kinase C (PKC) in the development of diabetic complications has become a field of intense research interest. An inhibitor of the PKC-beta isoform ruboxistaurin (RBX) has in vitro and in vivo benefits in ameliorating disturbances of cell regulation and blood flow related to hyperglycemia. The benefit of RBX for peripheral neuropathy has not been successfully demonstrated in Phase III trials. Although there was a beneficial effect of RBX on nephropathy in a pilot study, there has been no further clinical development for this indication. The major cause of visual disability - diabetic macular edema - seems to respond to RBX treatment with both anatomic and functional benefits. The manufacturer, Eli Lilly Co., has received an approvable letter from the FDA for the prevention of vision loss in patients with diabetic retinopathy with RBX, pending results of additional clinical trials for this indication.

Randomized placebo-controlled double-blind clinical trial of cannabis-based medicinal product (Sativex) in painful diabetic neuropathy: depression is a major confounding factor

OBJECTIVE

To assess the efficacy of Sativex, a cannabis-based medicinal extract, as adjuvant treatment in painful diabetic peripheral neuropathy (DPN).

RESEARCH DESIGN AND METHODS

In this randomized controlled trial, 30 subjects with painful DPN received daily Sativex or placebo. The primary outcome measure was change in mean daily pain scores, and secondary outcome measures included quality-of-life assessments.

RESULTS

There was significant improvement in pain scores in both groups, but mean change between groups was not significant. There were no significant differences in secondary outcome measures. Patients with depression had significantly greater baseline pain scores that improved regardless of intervention.

CONCLUSIONS

This first-ever trial assessing the efficacy of cannabis has shown it to be no more efficacious than placebo in painful DPN. Depression was a major confounder and may have important implications for future trials on painful DPN.

The Utah Early Neuropathy Scale: a sensitive clinical scale for early sensory predominant neuropathy

Early neuropathy is often sensory predominant and prominently involves small-diameter nerve fibers. Established neuropathy examination scales such as the Michigan Diabetic Neuropathy Scale (MDNS) and the Neuropathy Impairment Score-Lower Leg (NIS-LL) focus primarily on large-fiber sensory and motor function. Here, we validate the Utah Early Neuropathy Scale (UENS), a physical examination scale specific to early sensory predominant polyneuropathy. Compared with other scales, the UENS emphasizes severity and spatial distribution of pin (sharp) sensation loss in the foot and leg and focuses less on motor weakness. UENS, MDNS, and NIS-LL were compared in 215 diabetic or prediabetic subjects, with (129) or without neuropathy (86), and repeated in 114 neuropathy subjects after 1 year of follow-up. Neuropathy severity was also evaluated with nerve conduction studies, quantitative sensory testing, quantitative sudomotor axonal reflex testing, and intraepidermal nerve fiber density determination. The UENS had a high degree of interrater reliability (interclass correlation of 94%). UENS correlated significantly to MDNS and NIS-LL (p < 0.01), and more significantly than MDNS or NIS-LL to confirmatory tests. In this cohort, UENS had a superior profile to receiver operating characteristic analysis across a range of scores, with a sensitivity (92%) higher than MDNS (67%) or NIS-LL (81%), without sacrificing specificity. UENS more closely correlated with change in ancillary and small-fiber neuropathy measures over 1 year follow-up than did MDNS or NIS-LL. UENS is a sensitive and reproducible clinical measure of sensory and small-fiber nerve injury and may be useful in trials of early neuropathy.

Selective PKC beta inhibition with ruboxistaurin and endothelial function in type-2 diabetes mellitus

PURPOSE

Type-2 diabetes mellitus increases risk of atherosclerotic cardiovascular disease. However, the mechanisms linking hyperglycemia and atherosclerosis remain poorly understood. One proposed mechanism involves endothelial dysfunction via activation of protein kinase C beta (PKC beta). Prior studies demonstrate beneficial effects of PKC beta inhibition on microvascular parameters, but, to date, no study has examined the effect on macrovascular atherosclerotic readouts.

METHODS

The goal of this double-masked, placebo-controlled trial in type-2 diabetes was to assess the effect of the PKC beta-specific inhibitor, ruboxistaurin (32 mg/day for 6 weeks) on ultrasound assessed brachial artery flow mediated dilatation (FMD), a surrogate of macro vascular endothelial function, and urinary isoprostanes, indices of oxidant stress.

RESULTS

Compared to placebo, ruboxistaurin tended to improve FMD (difference in 6-week change in FMD, mean +/- SD millimeter) at one (0.13 +/- 0.26 mm, p = 0.08) and 5 min (0.12 +/- 0.21 mm, p = 0.02) after cuff deflation, but had no effect on nitroglycerin-mediated dilatation or urinary isoprostanes.

CONCLUSIONS

This proof of concept trial is the first to suggest that specific inhibition of PKC beta may improve macro vascular endothelial function in type-2 diabetes. Larger trials including clinical endpoints are warranted to determine the potential efficacy of PKC beta inhibition in reducing atherosclerotic cardiovascular complications in diabetes mellitus.

Diabetic neuropathy: mechanisms to management

Neuropathy is the most common and debilitating complication of diabetes and results in pain, decreased motility, and amputation. Diabetic neuropathy encompasses a variety of forms whose impact ranges from discomfort to death. Hyperglycemia induces oxidative stress in diabetic neurons and results in activation of multiple biochemical pathways. These activated pathways are a major source of damage and are potential therapeutic targets in diabetic neuropathy. Though therapies are available to alleviate the symptoms of diabetic neuropathy, few options are available to eliminate the root causes. The immense physical, psychological, and economic cost of diabetic neuropathy underscore the need for causally targeted therapies. This review covers the pathology, epidemiology, biochemical pathways, and prevention of diabetic neuropathy, as well as discusses current symptomatic and causal therapies and novel approaches to identify therapeutic targets.

PKCbeta modulates ischemia-reperfusion injury in the heart

Protein kinase C-betaII (PKCbetaII) is an important modulator of cellular stress responses. To test the hypothesis that PKCbetaII modulates the response to myocardial ischemia-reperfusion (I/R) injury, we subjected mice to occlusion and reperfusion of the left anterior descending coronary artery. Homozygous PKCbeta-null (PKCbeta(-/-)) and wild-type mice fed the PKCbeta inhibitor ruboxistaurin displayed significantly decreased infarct size and enhanced recovery of left ventricular (LV) function and reduced markers of cellular necrosis and serum creatine phosphokinase and lactate dehydrogenase levels compared with wild-type or vehicle-treated animals after 30 min of ischemia followed by 48 h of reperfusion. Our studies revealed that membrane translocation of PKCbetaII in LV tissue was sustained after I/R and that gene deletion or pharmacological blockade of PKCbeta protected ischemic myocardium. Homozygous deletion of PKCbeta significantly diminished phosphorylation of c-Jun NH(2)-terminal mitogen-activated protein kinase and expression of activated caspase-3 in LV tissue of mice subjected to I/R. These data implicate PKCbeta in I/R-mediated myocardial injury, at least in part via phosphorylation of JNK, and suggest that blockade of PKCbeta may represent a potent strategy to protect the vulnerable myocardium.