Activation of the RAGE pathway: a general mechanism in the pathogenesis of polyneuropathies?

Identification and validation of serum amino acids as diagnostic biomarkers for diabetic peripheral neuropathy

BACKGROUND

Diabetic peripheral neuropathy (DPN) is the most prevalent complication of type 2 diabetes mellitus (T2DM). Due to a lack of specific biomarkers, the early diagnosis of this disorder is limited.

AIM

To identify and validate serum amino acids that could discriminate T2DM patients with DPN from those without DPN.

METHODS

T2DM patients with DPN, T2DM patients without DPN, and healthy controls were recruited for this study. The participants comprised two nonoverlapping cohorts: A training cohort (DPN = 84 participants, T2DM = 82 participants, normal = 50 participants) and a validation cohort (DPN = 112 participants, T2DM = 93 participants, normal = 58 participants). A prediction model of the ability of serum amino acids to distinguish DPN from T2DM was established using a logistic regression model, and area under the curve (AUC) analysis was used to evaluate the diagnostic ability of the model. In addition, the serum amino acid levels of 13 DPN patients were also detected before treatment and after 3 months of treatment.

RESULTS

A clinical detection method for the diagnosis of DPN based on a biomarker panel of three serum amino acids and diabetes duration was developed. The diagnostic model demonstrated AUC values of 0.805 (95%CI: 0.739-0.871) and 0.810 (95%CI: 0.750-0.870) in the training and verification cohorts, respectively. In the identification of T2DM patients and normal controls, the AUC values were 0.891 (95%CI: 0.836-0.945) and 0.883 (95%CI: 0.832-0.934) in the training and validation cohorts, respectively. Arginine and tyrosine levels were increased after treatment, whereas aspartic acid levels were decreased after treatment.

CONCLUSION

This study successfully identified and validated the metabolomic significance of arginine, tyrosine, and glutamic acid as potential biomarkers for diagnosing DPN. These findings are particularly valuable, as they establish a foundational step toward developing the first routine laboratory test for DPN. Moreover, the diagnostic model that was constructed in this study effectively distinguishes DPN patients from those with T2DM without neuropathy, thereby potentially facilitating early diagnosis and intervention.

Unveiling the Role of Schwann Cell Plasticity in the Pathogenesis of Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is a prevalent complication of diabetes that affects a significant proportion of diabetic patients worldwide. Although the pathogenesis of DPN involves axonal atrophy and demyelination, the exact mechanisms remain elusive. Current research has predominantly focused on neuronal damage, overlooking the potential contributions of Schwann cells, which are the predominant glial cells in the peripheral nervous system. Schwann cells play a critical role in neurodevelopment, neurophysiology, and nerve regeneration. This review highlights the emerging understanding of the involvement of Schwann cells in DPN pathogenesis. This review explores the potential role of Schwann cell plasticity as an underlying cellular and molecular mechanism in the development of DPN. Understanding the interplay between Schwann cell plasticity and diabetes could reveal novel strategies for the treatment and management of DPN.

Diabetic peripheral neuropathy based on Schwann cell injury: mechanisms of cell death regulation and therapeutic perspectives

Diabetic peripheral neuropathy (DPN) is a complication of diabetes mellitus that lacks specific treatment, its high prevalence and disabling neuropathic pain greatly affects patients' physical and mental health. Schwann cells (SCs) are the major glial cells of the peripheral nervous system, which play an important role in various inflammatory and metabolic neuropathies by providing nutritional support, wrapping axons and promoting repair and regeneration. Increasingly, high glucose (HG) has been found to promote the progression of DPN pathogenesis by targeting SCs death regulation, thus revealing the specific molecular process of programmed cell death (PCD) in which SCs are disrupted is an important link to gain insight into the pathogenesis of DPN. This paper is the first to review the recent progress of HG studies on apoptosis, autophagy, pyroptosis, ferroptosis and necroptosis pathways in SCs, and points out the crosstalk between various PCDs and the related therapeutic perspectives, with the aim of providing new perspectives for a deeper understanding of the mechanisms of DPN and the exploration of effective therapeutic targets.

Recent Advances in Biomolecular Patho-Mechanistic Pathways behind the Development and Progression of Diabetic Neuropathy

Diabetic neuropathy (DN) is a neurodegenerative disorder that is primarily characterized by distal sensory loss, reduced mobility, and foot ulcers that may potentially lead to amputation. The multifaceted etiology of DN is linked to a range of inflammatory, vascular, metabolic, and other neurodegenerative factors. Chronic inflammation, endothelial dysfunction, and oxidative stress are the three basic biological changes that contribute to the development of DN. Although our understanding of the intricacies of DN has advanced significantly over the past decade, the distinctive mechanisms underlying the condition are still poorly understood, which may be the reason behind the lack of an effective treatment and cure for DN. The present study delivers a comprehensive understanding and highlights the potential role of the several pathways and molecular mechanisms underlying the etiopathogenesis of DN. Moreover, Schwann cells and satellite glial cells, as integral factors in the pathogenesis of DN, have been enlightened. This work will motivate allied research disciplines to gain a better understanding and analysis of the current state of the biomolecular mechanisms behind the pathogenesis of DN, which will be essential to effectively address every facet of DN, from prevention to treatment.

[B vitamins and diseases of the peripheral nervous system]

Various diseases of the peripheral nervous system are associated with metabolic disorders of B vitamins. A lack of neurotropic vitamins, which began in the early stages of the development of a bacterial disease, led to its more rapid development. The article analyzes data on B vitamin deficiency in the pathogenesis of the most dangerous diseases of the peripheral nervous system. Information is provided about the dangers of the clinical use of the drug Combilipen for the treatment of such patients.

Understanding the role of hyperglycemia and the molecular mechanism associated with diabetic neuropathy and possible therapeutic strategies

Diabetic neuropathy is a neuro-degenerative disorder that encompasses numerous factors that impact peripheral nerves in the context of diabetes mellitus (DM). Diabetic peripheral neuropathy (DPN) is very prevalent and impacts 50% of diabetic patients. DPN is a length-dependent peripheral nerve lesion that primarily causes distal sensory loss, discomfort, and foot ulceration that may lead to amputation. The pathophysiology is yet to be fully understood, but current literature on the pathophysiology of DPN revolves around understanding various signaling cascades involving the polyol, hexosamine, protein-kinase C, AGE, oxidative stress, and poly (ADP ribose) polymerase pathways. The results of research have suggested that hyperglycemia target Schwann cells and in severe cases, demyelination resulting in central and peripheral sensitization is evident in diabetic patients. Various diagnostic approaches are available, but detection at an early stage remains a challenge. Traditional analgesics and opioids that can be used "as required" have not been the mainstay of treatment thus far. Instead, anticonvulsants and antidepressants that must be taken routinely over time have been the most common treatments. For now, prolonging life and preserving the quality of life are the ultimate goals of diabetes treatment. Furthermore, the rising prevalence of DPN has substantial consequences for occupational therapy because such therapy is necessary for supporting wellness, warding off other chronic-diseases, and avoiding the development of a disability; this is accomplished by engaging in fulfilling activities like yoga, meditation, and physical exercise. Therefore, occupational therapy, along with palliative therapy, may prove to be crucial in halting the onset of neuropathic-symptoms and in lessening those symptoms once they have occurred.

Clinical Pathobiochemistry of Vitamin B12 Deficiency: Improving Our Understanding by Exploring Novel Mechanisms with a Focus on Diabetic Neuropathy

Vitamin B₁₂ (B₁₂) is an essential cofactor of two important biochemical pathways, the degradation of methylmalonic acid and the synthesis of methionine from homocysteine. Methionine is an important donor of methyl groups for numerous biochemical reactions, including DNA synthesis and gene regulation. Besides hematological abnormalities (megaloblastic anemia or even pancytopenia), a deficiency in B₁₂ may cause neurological symptoms, including symptoms resembling diabetic neuropathy. Although extensively studied, the underlining molecular mechanism for the development of diabetic peripheral neuropathy (DPN) is still unclear. Most studies have found a contribution of oxidative stress in the development of DPN. Detailed immunohistochemical investigations in sural nerve biopsies obtained from diabetic patients with DPN point to an activation of inflammatory pathways induced via elevated advanced glycation end products (AGE), ultimately resulting in increased oxidative stress. Similar results have been found in patients with B₁₂ deficiency, indicating that the observed neural changes in patients with DPN might be caused by cellular B₁₂ deficiency. Since novel results show that B₁₂ exerts intrinsic antioxidative activity in vitro and in vivo, B₁₂ may act as an intracellular, particularly as an intramitochondrial, antioxidant, independent from its classical, well-known cofactor function. These novel findings may provide a rationale for the use of B₁₂ for the treatment of DPN, even in subclinical early states.

Methylglyoxal and Its Adducts: Induction, Repair, and Association with Disease

Metabolism is an essential part of life that provides energy for cell growth. During metabolic flux, reactive electrophiles are produced that covalently modify macromolecules, leading to detrimental cellular effects. Methylglyoxal (MG) is an abundant electrophile formed from lipid, protein, and glucose metabolism at intracellular levels of 1-4 μM. MG covalently modifies DNA, RNA, and protein, forming advanced glycation end products (MG-AGEs). MG and MG-AGEs are associated with the onset and progression of many pathologies including diabetes, cancer, and liver and kidney disease. Regulating MG and MG-AGEs is a potential strategy to prevent disease, and they may also have utility as biomarkers to predict disease risk, onset, and progression. Here, we review recent advances and knowledge surrounding MG, including its production and elimination, mechanisms of MG-AGEs formation, the physiological impact of MG and MG-AGEs in disease onset and progression, and the latter in the context of its receptor RAGE. We also discuss methods for measuring MG and MG-AGEs and their clinical application as prognostic biomarkers to allow for early detection and intervention prior to disease onset. Finally, we consider relevant clinical applications and current therapeutic strategies aimed at targeting MG, MG-AGEs, and RAGE to ultimately improve patient outcomes.

Diabetes, a Contemporary Risk for Parkinson's Disease: Epidemiological and Cellular Evidences

Diabetes mellitus (DM), a group of diseases characterized by defective glucose metabolism, is the most widespread metabolic disorder affecting over 400 million adults worldwide. This pathological condition has been implicated in the pathogenesis of a number of central encephalopathies and peripheral neuropathies. In further support of this notion, recent epidemiological evidence suggests a link between DM and Parkinson’s disease (PD), with hyperglycemia emerging as one of the culprits in neurodegeneration involving the nigrostriatal pathway, the neuroanatomical substrate of the motor symptoms affecting parkinsonian patients. Indeed, dopaminergic neurons located in the mesencephalic substantia nigra appear to be particularly vulnerable to oxidative stress and degeneration, likely because of their intrinsic susceptibility to mitochondrial dysfunction, which may represent a direct consequence of hyperglycemia and hyperglycemia-induced oxidative stress. Other pathological pathways induced by increased intracellular glucose levels, including the polyol and the hexosamine pathway as well as the formation of advanced glycation end-products, may all play a pivotal role in mediating the detrimental effects of hyperglycemia on nigral dopaminergic neurons. In this review article, we will examine the epidemiological as well as the molecular and cellular clues supporting the potential susceptibility of nigrostriatal dopaminergic neurons to hyperglycemia.

Peripheral Glial Cells in the Development of Diabetic Neuropathy

The global prevalence of diabetes is rapidly increasing, affecting more than half a billion individuals within the next few years. As diabetes negatively affects several physiological systems, this dramatic increase represents not only impaired quality of life on the individual level but also a huge socioeconomic challenge. One of the physiological consequences affecting up to half of diabetic patients is the progressive deterioration of the peripheral nervous system, resulting in spontaneous pain and eventually loss of sensory function, motor weakness, and organ dysfunctions. Despite intense research on the consequences of hyperglycemia on nerve functions, the biological mechanisms underlying diabetic neuropathy are still largely unknown, and treatment options lacking. Research has mainly focused directly on the neuronal component, presumably from the perspective that this is the functional signal-transmitting unit of the nerve. However, it is noteworthy that each single peripheral sensory neuron is intimately associated with numerous glial cells; the neuronal soma is completely enclosed by satellite glial cells and the length of the longest axons covered by at least 1,000 Schwann cells. The glial cells are vital for the neuron, but very little is still known about these cells in general and especially how they respond to diabetes in terms of altered neuronal support. We will discuss current knowledge of peripheral glial cells and argue that increased research in these cells is imperative for a better understanding of the mechanisms underlying diabetic neuropathy.

The Quest for more Research on Painful Diabetic Neuropathy

A 62-year-old diabetologist diagnosed himself to have diabetes type-2, with an HbA1c of 9.5. Five months after lifestyle intervention and a multi-drug approach, HbA1c was 6.3, systolic blood pressure was below 135mmHg and BMI reduced to 27. But he suffered from severe painful diabetic neuropathy. Therefore he decided to visit his friend, a famous neuroscientist at an even more famous university. He asked him several plain questions: 1. What is the natural course of painful diabetic neuropathy? 2. Why do I have, despite almost normalizing HbA1c, more problems than before? 3. Are you sure my problems are due to diabetes or should we do a nerve biopsy? 4. Are there imaging techniques helpful for the diagnosis of this diabetic complication, starting in the distal nerve endings of the foot and slowly moving ahead? 5. Can you suggest any drug, specific and effective, for relieving painful diabetic neuropathy? This review will use the experts' answers to the questions of the diabetologist, not only to give a summary of the current knowledge, but even more to highlight areas of research needed for improving the fate of patients with painful diabetic neuropathy. Based on the unknowns, which exceed the knowns in diabetic neuropathy, a quest for more public support of research is made.

Activation of RAGE/STAT3 pathway by methylglyoxal contributes to spinal central sensitization and persistent pain induced by bortezomib

Bortezomib is a first-line chemotherapeutic drug widely used for multiple myeloma and other nonsolid malignancies. Although bortezomib-induced persistent pain is easily diagnosed in clinic, the pathogenic mechanism remains unclear. Here, we studied this issue with use of a rat model of systemic intraperitoneal administration of bortezomib for consecutive 5days. Consisted with our previous study, we found that bortezomib treatment markedly induced mechanical allodynia in rats. Furthermore, we first found that bortezomib treatment significantly induced the upregulation of methylglyoxal in spinal dorsal horn of rats. Spinal local application of methylglyoxal also induced mechanical allodynia and central sensitization in normal rats. Moreover, administration of bortezomib upregulated the expression of receptors for advanced glycation end products (RAGE) and phosphorylated STAT3 (p-STAT3) in dorsal horn. Importantly, intrathecal injection of metformin, a known scavenger of methylglyoxal, significantly attenuated the upregulation of methylglyoxal and RAGE in dorsal horn, central sensitization and mechanical allodynia induced by bortezomib treatment, and blockage of RAGE also prevented the upregulation of p-STAT3, central sensitization and mechanical allodynia induced by bortezomib treatment. In addition, inhibition of STAT3 activity by S3I-201 attenuated bortezomib-induced mechanical allodynia and central sensitization. Local knockdown of STAT3 also ameliorated the mechanical allodynia induced by bortezomib administration. Our results suggest that accumulation of methylglyoxal may activate the RAGE/STAT3 signaling pathway in dorsal horn, and contributes to the spinal central sensitization and persistent pain induced by bortezomib treatment.

Association of transketolase polymorphisms with measures of polyneuropathy in patients with recently diagnosed diabetes

BACKGROUND

Shunting of glycolytic intermediates into the pentose phosphate pathway has been suggested to protect from hyperglycaemia-induced microvascular damage. We hypothesized that genetic variability in the gene encoding transketolase, a key pentose phosphate pathway enzyme, contributes to early nerve dysfunction in recent-onset diabetes.

METHODS

In this cross-sectional study, we assessed nine single nucleotide polymorphisms (SNPs) in the transketolase gene, plasma methylglyoxal concentrations, and clinical and quantitative measures of peripheral nerve function in 165 type 1 and 373 type 2 diabetic patients with a diabetes duration up to 1 year.

RESULTS

The Total Symptom Score was associated with transketolase SNPs rs7648309, rs62255988, and rs7633966, while peroneal motor nerve conduction velocity (MNCV) correlated only with rs7648309 (P < 0.01). Cold thermal detection threshold (TDT) (foot) was associated with transketolase SNPs rs11130362 and rs7648309, while warm TDT (hand) correlated with rs62255988 and rs7648309 (P < 0.01). After Bonferroni correction, the correlations of transketolase SNP rs7648309 with Total Symptom Score and rs62255988 with warm TDT (hand) remained statistically significant. Among subgroups, men with type 2 diabetes showed the strongest associations. No associations were observed between each of the nine tagged transketolase SNPs and plasma methylglyoxal concentrations.

CONCLUSIONS

The observed associations of genetic variation in transketolase enzyme with neuropathic symptoms and reduced thermal sensation in recent-onset diabetes suggest a role of pathways metabolizing glycolytic intermediates in early diabetic neuropathy. Copyright © 2016 John Wiley & Sons, Ltd.

Schwann cell interactions with axons and microvessels in diabetic neuropathy

The prevalence of diabetes worldwide is at pandemic levels, with the number of patients increasing by 5% annually. The most common complication of diabetes is peripheral neuropathy, which has a prevalence as high as 50% and is characterized by damage to neurons, Schwann cells and blood vessels within the nerve. The pathogenic mechanisms of diabetic neuropathy remain poorly understood, impeding the development of targeted therapies to treat nerve degeneration and its most disruptive consequences of sensory loss and neuropathic pain. Involvement of Schwann cells has long been proposed, and new research techniques are beginning to unravel a complex interplay between these cells, axons and microvessels that is compromised during the development of diabetic neuropathy. In this Review, we discuss the evolving concept of Schwannopathy as an integral factor in the pathogenesis of diabetic neuropathy, and how disruption of the interactions between Schwann cells, axons and microvessels contribute to the disease.

The Activation of RAGE and NF-KB in Nerve Biopsies of Patients with Axonal and Vasculitic Neuropathy

INTRODUCTION

The receptor for advanced glycation end products (RAGE) is a pattern recognition receptor expressed in tissues and cells, which plays a role in immunity. The activation of RAGE results in the translocation of nuclear factor kappa B (NF-κB) to the nucleus for expression of proinflammatory molecules. The role of the RAGE pathway in the pathogenesis of diabetic complications is well determined. We aimed to investigate the role of the RAGE pathway in axonal and vasculitic neuropathy.

METHODS

We immunoreacted nerve biopsy samples from 17 axonal neuropathy (AN), 11 vasculitic neuropathy (VN) and 12 hereditary neuropathy (as a control group) with liability to pressure palsy (HNPP) patients with antibodies to NF-κB and RAGE. Subsequently, we performed double staining with the antibodies to NF-κB or RAGE and T cells, macrophages and Schwann cells.

RESULTS

RAGE and NF-κB immunoreactivities were higher in the perivascular cuff and in endoneurial cells in VN than in AN and HNPP. Although there is no significant difference, nerve biopsies with AN showed higher NFκB and RAGE immunoreactivities than HNPP. The colocalization study showed that most of the NFκB- and RAGE-positive cells were CD8 (+) T cells in VN. In AN, all NFκB- and RAGE-positive cells were macrophages, whereas all NFκB- and RAGE-positive cells were Schwann cells in HNPP.

CONCLUSION

The activation of the RAGE pathway predominant in CD8 (+) T cells underscores its role in VN. In AN patients, the immunoreactivity to NFκB and RAGE in macrophages may support their role in axonal degeneration without inflammatory milieu.

Up-regulation of the receptor for advanced glycation end products in the skin biopsy specimens of patients with severe diabetic neuropathy

BACKGROUND AND PURPOSE

The receptor for advanced glycation end products (RAGE) may contribute to the development of diabetic neuropathy. To assess its relevance in humans, this study examined the expression of RAGE in the skin biopsy samples of patients with diabetes mellitus, and investigated its correlation with intraepidermal nerve-fiber density (IENFD) and clinical measures of neuropathy severity.

METHODS

Forty-four patients who either had type 2 diabetes or were prediabetes underwent clinical evaluation and a 3-mm skin punch biopsy. The clinical severity of their neuropathy was assessed using the Michigan Diabetic Neuropathy Score. IENFD was measured along with immunohistochemical staining for RAGE in 29 skin biopsy samples. The expression of RAGE was also quantified by real-time reverse-transcription PCR in the remaining 15 patients.

RESULTS

RAGE was localized mostly in the dermal and subcutaneous vascular endothelia. The staining was more intense in patients with a lower IENFD (p=0.004). The quantity of RAGE mRNA was significantly higher in patients with severe neuropathy than in those with no or mild neuropathy (p=0.003). The up-regulation of RAGE was related to dyslipidemia and diabetic nephropathy. There was a trend toward decreased sural nerve action-potential amplitude and slowed peroneal motor-nerve conduction with increasing RAGE expression.

CONCLUSIONS

The findings of this study demonstrate up-regulation of RAGE in skin biopsy samples from patients with diabetic neuropathy, supporting a pathogenic role of RAGE in the development of diabetic neuropathy.

Increased expression of the receptor for advanced glycation end-products in human peripheral neuropathies

BACKGROUND

Diabetic neuropathy and idiopathic neuropathy are among the most prevalent neuropathies in human patients. The molecular mechanism underlying pathological changes observed in the affected nerve remains unclear but one candidate molecule, the receptor for advanced glycation end-products (RAGE), has recently gained attention as a potential contributor to neuropathy. Our previous studies revealed that RAGE expression is higher in porcine and murine diabetic nerve, contributing to the inflammatory mechanisms leading to diabetic neuropathy. Here, for the first time, we focused on the expression of RAGE in human peripheral nerve.

METHODS

Our study utilized de-identified human sural nerve surplus obtained from 5 non-neuropathic patients (control group), 6 patients with long-term mild-to-moderate diabetic neuropathy (diabetic group) and 5 patients with mild-to-moderate peripheral neuropathy of unknown etiology (idiopathic group). By using immunofluorescent staining and protein immunoblotting we studied the expression and colocalization patterns of RAGE and its ligands: carboxymethyllysine (CML), high mobility group box 1 (HMBG1) and mammalian Diaphanous 1 (mDia1) in control and neuropathic nerves.

RESULTS

We found that in a normal, healthy human nerve, RAGE is expressed in almost 30% of all nerve fibers and that number is higher in pathological states such as peripheral neuropathy. We established that the levels of RAGE and its pro-inflammatory ligands, CML and HMBG1, are higher in both idiopathic and diabetic nerve, while the expression of the RAGE cytoplasmic domain-binding partner, mDia1 is similar among control, diabetic, and idiopathic nerve. The highest number of double stained nerve fibers was noted for RAGE and CML: ∼76% (control), ∼91% (idiopathic) and ∼82% (diabetic) respectively.

CONCLUSIONS

Our data suggest roles for RAGE and its inflammatory ligands in human peripheral neuropathies and lay the foundation for further, more detailed and clinically oriented investigation involving these proteins and their roles in disorders of the human peripheral nerve.

The effects of oxidative stress on female reproduction: a review

Oxidative stress (OS), a state characterized by an imbalance between pro-oxidant molecules including reactive oxygen and nitrogen species, and antioxidant defenses, has been identified to play a key role in the pathogenesis of subfertility in both males and females. The adverse effects of OS on sperm quality and functions have been well documented. In females, on the other hand, the impact of OS on oocytes and reproductive functions remains unclear. This imbalance between pro-oxidants and antioxidants can lead to a number of reproductive diseases such as endometriosis, polycystic ovary syndrome (PCOS), and unexplained infertility. Pregnancy complications such as spontaneous abortion, recurrent pregnancy loss, and preeclampsia, can also develop in response to OS. Studies have shown that extremes of body weight and lifestyle factors such as cigarette smoking, alcohol use, and recreational drug use can promote excess free radical production, which could affect fertility. Exposures to environmental pollutants are of increasing concern, as they too have been found to trigger oxidative states, possibly contributing to female infertility. This article will review the currently available literature on the roles of reactive species and OS in both normal and abnormal reproductive physiological processes. Antioxidant supplementation may be effective in controlling the production of ROS and continues to be explored as a potential strategy to overcome reproductive disorders associated with infertility. However, investigations conducted to date have been through animal or in vitro studies, which have produced largely conflicting results. The impact of OS on assisted reproductive techniques (ART) will be addressed, in addition to the possible benefits of antioxidant supplementation of ART culture media to increase the likelihood for ART success. Future randomized controlled clinical trials on humans are necessary to elucidate the precise mechanisms through which OS affects female reproductive abilities, and will facilitate further explorations of the possible benefits of antioxidants to treat infertility.

Cell signaling and receptors in toxicity of advanced glycation end products (AGEs): α-dicarbonyls, radicals, oxidative stress and antioxidants

Considerable attention has been paid to the toxicity of advanced glycation end products (AGEs), including relation to various illnesses. AGEs, generated nonenzymatically from carbohydrates and proteins, comprises large numbers of simple and more complicated compounds. Many reports deal with a role for receptors (RAGE) and cell signaling, including illnesses and aging. Reactive oxygen species appear to participate in signaling. RAGE include angiotensin II type 1 receptors. Many signaling pathways are involved, such as kinases, p38, p21, TGF-β, NF-κβ, TNF-α, JNK and STAT. A recent review puts focus on α-dicarbonyl metabolites, formed by carbohydrate oxidation, and imine derivatives from protein condensation, as a source via electron transfer (ET) of ROS and oxidative stress (OS). The toxic species have been related to illnesses and aging. Antioxidants alleviate the adverse effects.

Pharmacological treatment of diabetic neuropathic pain

Neuropathic pain continues to be a difficult and challenging clinical issue to deal with effectively. Painful diabetic polyneuropathy is a complex pain condition that occurs with reasonable frequency in the population and it may be extremely difficult for clinicians to provide patients with effective analgesia. Chronic neuropathic pain may occur in approximately one of every four diabetic patients. The pain may be described as burning or a deep-seated ache with sporadic paroxysms of lancinating painful exacerbations. The pain is often constant, moderate to severe in intensity, usually primarily involves the feet and generally tends to worsen at night. Treatment may be multimodal but largely involves pharmacological approaches. Pharmacological therapeutic options include antidepressants (tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors), α2δ ligands and topical (5%) lidocaine patch. Other agents may be different antiepileptic drugs (carbamazepine, lamotrigine, topiramate), topical capsaicin, tramadol and other opioids. Progress continues with respect to understanding various mechanisms that may contribute to painful diabetic neuropathy. Agents that may hold some promise include neurotrophic factors, growth factors, immunomodulators, gene therapy and poly (adenosine diphosphate-ribose) polymerase inhibitors. It is hoped that in the future clinicians will be able to assess patient pathophysiology, which may help them to match optimal therapeutic agents to target individual patient aberrant mechanisms.

Protective effects of grape seed proanthocyanidin extracts on cerebral cortex of streptozotocin-induced diabetic rats through modulating AGEs/RAGE/NF-kappaB pathway

Diabetic encephalopathy is a severe complication in patients with long-term hyperglycemia. Oxidative stress is thought to be closely implicated in this disorder, so in this study, we examined whether grape seed proanthocyanidin extract (GSPE), a naturally occurring antioxidant derived from grape seeds, could reduce the injuries in the cerebral cortex of diabetic rats by modulating advanced glycation end products (AGEs)/the receptor for AGEs (RAGE)/nuclear factor-kappa B p65 (NF-kappaB p65) pathway, which is crucial in oxidative stress. Body weight and serum AGEs were tested; cerebral cortexes were isolated for morphological observations and the pyramidal cell layers were immunohistochemically stained for the detection of RAGE, NF-kappaB p65, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) as well. For RAGE and NF-kappaB p65, quantitative reverse transcriptase coupled to polymerase chain reaction (RT-PCR) was employed for determination of mRNA levels, and western blot was used to detect protein expression. Our results showed that long term hyperglycemia in diabetic rats caused the degeneration of neurons and the up-regulation of serum AGEs, and also the up-regulation of RAGE, NF-kappaB p65, VCAM-1 and ICAM-1 in the brain. We found that GSPE treatment improved the pathological changes of diabetic rats by modulating the AGEs/RAGE/NF-kappaB p65 pathway. This study enables us to further understand the key role that the AGEs/RAGE/NF-kappaB pathway plays in the pathogenesis of diabetic encephalopathy, and confirms that GSPE might be a therapeutical means to the prevention and treatment of this disorder.

RAGE (Receptor for Advanced Glycation Endproducts), RAGE ligands, and their role in cancer and inflammation

The Receptor for Advanced Glycation Endproducts [RAGE] is an evolutionarily recent member of the immunoglobulin super-family, encoded in the Class III region of the major histocompatability complex. RAGE is highly expressed only in the lung at readily measurable levels but increases quickly at sites of inflammation, largely on inflammatory and epithelial cells. It is found either as a membrane-bound or soluble protein that is markedly upregulated by stress in epithelial cells, thereby regulating their metabolism and enhancing their central barrier functionality. Activation and upregulation of RAGE by its ligands leads to enhanced survival. Perpetual signaling through RAGE-induced survival pathways in the setting of limited nutrients or oxygenation results in enhanced autophagy, diminished apoptosis, and (with ATP depletion) necrosis. This results in chronic inflammation and in many instances is the setting in which epithelial malignancies arise. RAGE and its isoforms sit in a pivotal role, regulating metabolism, inflammation, and epithelial survival in the setting of stress. Understanding the molecular structure and function of it and its ligands in the setting of inflammation is critically important in understanding the role of this receptor in tumor biology.

Maillard products as biomarkers in cancer

Because tumors exert increased glycolysis rates, a high intracellular carbonyl stress with the formation of Maillard products may evolve. Therefore, we studied the presence of N epsilon-(carboxymethyl)lysine (CML) modification in breast cancer tissues from 20 patients and found significant cytoplasmatic staining in tumor cells that was independent of the tumor stage, tumor type, and microanatomic localization. Studying breast cancer cell lines, we also found strong cytoplasmatic CML staining that was again independent of their invasive or metastatic behavior. Our results reveal that tumor cells show a strong cytoplasmatic immunoreactivity to CML without evident association with breast carcinoma type, differentiation, tumor stage, or intratumoral localization. We conclude that CML formation is a general tumor cell-associated process.

The RAGE pathway: activation and perpetuation in the pathogenesis of diabetic neuropathy

The molecular mechanisms underlying loss of pain perception in diabetic neuropathy are poorly understood. Experimental diabetic neuropathy models recently provided evidence that engagement of the receptor for advanced glycation end products (RAGE) and RAGE-dependent sustained activation of the proinflammatory transcription factor nuclear factor kappa B might significantly contribute to reduced nociception. Most importantly, diabetes-induced loss of pain perception is largely prevented in RAGE-deficient mice compared to RAGE-bearing wild-type mice. Identifying RAGE-dependent inflammation as one pathomechanism underlying neuronal dysfunction might provide the basis for new therapeutic approaches.

The IKK-NF-kappaB pathway: a source for novel molecular drug targets in pain therapy?

Several studies indicate that the nuclear factor-kappa B (NF-kappaB) -activation cascade plays a crucial role not only in immune responses, inflammation, and apoptosis but also in the development and processing of pathological pain. Accordingly, a pharmacological intervention into this pathway may have antinociceptive effects and could provide novel treatment strategies for pain and inflammation. In this review we summarize the role of NF-kappaB in the nervous system, its impact on nociception, and several approaches that investigated the effects of various modulators of the classical I-kappaB-kinase-NF-kappaB signal transduction pathway in inflammatory nociception and neuropathic pain. The results indicate that NF-kappaB has an impact on nociceptive transmission and processing and that a number of substances that inhibit the NF-kappaB-activating cascade are capable of reducing the nociceptive response in different animal models. Therefore, a modulation of specific participants in the NF-kappaB signal transduction might exert a useful approach for the development of new painkillers.

Glucose neurotoxicity

Neurons have a constantly high glucose demand, and unlike muscle cells they cannot accommodate episodic glucose uptake under the influence of insulin. Neuronal glucose uptake depends on the extracellular concentration of glucose, and cellular damage can ensue after persistent episodes of hyperglycaemia--a phenomenon referred to as glucose neurotoxicity. This article reviews the pathophysiological manifestation of raised glucose in neurons and how this can explain the major components of diabetic neuropathy.