Methylglyoxal (MGO) is a metabolite of glucose. MGO binds to and modifies arginine, lysine, and cysteine residues in proteins, which leads to formation of a variety of advanced glycation end-products (AGEs) such as argpyrimidine and Nε-(carboxyethyl)lysine. The concentration of MGO significantly increases in plasma from diabetic patients. Increased plasma MGO level seems to be associated with diabetic microvascular complications. In addition, MGO accumulates in large vascular tissues from spontaneous hypertensive rats, which is associated with increased blood pressure. Although it is logical to hypothesize that MGO could directly affect vascular reactivity, available reports are very limited. Our group has examined effects of MGO on vascular reactivity (contraction and relaxation) and explored underlying mechanisms. In this review article, we summarized our recent findings on 1) short-term effects of MGO, 2) long-term effects of MGO, and 3) effects of MGO accumulation in arterial walls on vascular reactivity. These findings may provide further mechanistic insights into the pathogenesis of diabetes-related macrovascular complications including hypertension.
Angiotensin II plays an important role in regulating blood pressure. Moreover, angiotensin II directly promotes organ damage by inducing expression of various genes, such as transforming growth factor (TGF)-β and matrix metalloproteinase (MMP)-9 precursors. Blockade of angiotensin II has been shown to not only lower blood pressure, but also to prevent cardiovascular and renal dysfunction and fibrosis. Inhibition of TGF-β and MMP-9 has also been shown to prevent cardiovascular and renal damage. A mast cell–produced enzyme, chymase, generates angiotensin II and also converts precursors of TGF-β and MMP-9 to their active forms. Chymase also strongly promotes accumulation of inflammatory cells. These multiple functions of chymase may play an important role in the development and promotion of various diseases. In fact, chymase inhibitors have been shown to prevent nonalcoholic steatohepatitis, intestinal inflammation, and adhesion formation after surgery and cardiovascular and renal damage. On the other hand, chymase inhibitors, unlike angiotensin-converting enzyme inhibitors and angiotensin II blockers, have no blood pressure-lowering effect despite blocking angiotensin II formation. Thus, chymase inhibitors may be useful for preventing damage to various organs via multiple mechanisms without lowering blood pressure.
Alzheimer’s disease (AD) is an age-related neurodegenerative disorder, accompanied by neuronal loss and the formation of senile plaques in the brain. Glial cells, such as microglia, have been shown to be activated and induce chronic inflammatory responses in AD brain. The endoplasmic reticulum (ER) functions to facilitate protein folding. However, ER stress occurs when cells are exposed to stress. Mounting evidence suggests that ER stress is involved in the pathology of AD. Meanwhile, recent findings suggested crosstalk between ER stress and immune function. However, the mechanisms linking the progression of AD with ER and immunological stress are still not clear. In the present paper, we review and discuss recent results regarding the mechanism of AD pathogenesis, focusing on ER stress and immunological stress.
Endoplasmic reticulum (ER)-associated degradation (ERAD) is a protective mechanism against ER stress in which unfolded proteins accumulated in the ER are selectively transported to the cytosol for degradation by the ubiquitin–proteasome system. We cloned the novel ubiquitin ligase HRD1, which is involved in ERAD, and showed that HRD1 promoted amyloid precursor protein (APP) ubiquitination and degradation, resulting in decreased generation of amyloid β (Aβ). In addition, suppression of HRD1 expression caused APP accumulation and promoted Aβ generation associated with ER stress and apoptosis. Interestingly, HRD1 levels were significantly decreased in the cerebral cortex of patients with Alzheimer’s disease (AD), and the brains of these patients experienced ER stress. Our recent study revealed that this decrease in HRD1 was due to its insolubilization; however, controversy persists about whether the decrease in HRD1 protein promotes Aβ generation or whether Aβ neurotoxicity causes the decrease in HRD1 protein levels. Here, we review current findings on the mechanism of HRD1 protein loss in the AD brain and the involvement of HRD1 in the pathogenesis of AD. Furthermore, we propose that HRD1 may be a target for novel AD therapeutics.
Pathological hallmarks of Alzheimer’s disease (AD) include senile plaques, neurofibrillary tangles (NFTs), synaptic loss, and neurodegeneration. Senile plaques are composed of amyloid-β (Aβ) and are surrounded by microglia, a primary immune effector cell in the central nervous system. NFTs are formed by the intraneuronal accumulation of hyperphosphorylated tau, and progressive synaptic and neuronal losses closely correlate with cognitive deficits in AD. Studies on responsible genes of familial AD and temporal patterns of pathological changes in brains of patients with Down’s syndrome (Trisomy 21), who invariably develop neuropathology of AD, have suggested that Aβ accumulation is a primary event that influences other AD pathologies. Although details of the interaction between AD pathologies remain unclear, experimental evidences to discuss this issue have been accumulated. In this paper, we review and discuss recent findings that link the AD pathologies to each other. Further studies on the interaction between pathologies induced in AD brain may contribute to provide deep insight into the pathogenesis of AD and to develop novel therapeutic, prophylactic, and early diagnostic strategies for AD.
Alzheimer’s disease (AD) is a neurodegenerative disease of the brain associated with irreversible cognitive decline, memory impairment, and behavioral changes. Postmortem brains of AD patients reveal neuropathologic features, in particular the presence of senile plaques (SPs) and neurofibrillary tangles (NFTs), which contain β-amyloid peptides and highly phosphorylated tau proteins. Currently, AD can only be definitively confirmed by postmortem histopathologic examination of SPs and NFTs in the brain. Therefore, SPs and NFTs in the brain may be useful as biomarkers for the differential diagnosis of AD; the detection of individual SPs and NFTs in vivo by positron-emission tomography (PET) or single-photon emission computed tomography (SPECT) should improve diagnosis and also accelerate discovery of effective therapeutic agents for AD. Many PET/SPECT imaging probes for SPs have already been developed. Several of the PET probes have been shown in clinical trials to be useful for the imaging of β-amyloid plaques in living brain tissue. More recently, the development of PET/SPECT probes for in vivo imaging of NFTs is an active area of study in the field of molecular imaging because the appearance of NFT pathology correlates well with clinical severity of dementia. We will review current research on the development of PET/SPECT imaging probes for in vivo detection of SPs and NFTs and their application to diagnosis and therapy of AD.
Recent advances in clinical molecular and genetic studies on Alzheimer’s disease (AD) are summarized here. Cerebrospinal fluid (CSF) Aβ42 and tau are the most sensitive biomarkers for the diagnosis of AD and prediction of its onset following mild cognitive impairment (MCI). Based on this progress, new diagnostic criteria for AD dementia, MCI due to AD, and preclinical AD were proposed by the National Institute of Aging (NIA) and Alzheimer’s Association (AA) in April 2011. In these new criteria, progress in CSF biomarker and amyloid imaging studies over the past 10 years has added to critical information. The marked contributions of basic and clinical studies have established clinical evidence supporting these markers. Based on this progress, essential curative therapy for AD is urgently expected.
This study aimed to investigate whether oxidative stress contributes to retinal cell death in a mouse model of photoreceptor degeneration induced by N-methyl-N-nitrosourea (MNU). We measured in vitro MNU-induced radical production in retinal cell cultures of murine 661W photoreceptor–derived cells; RGC-5, a mouse ganglion cell line; and primary retinal cells. The addition of MNU induced oxidative radical generation in 661W and primary retinal cells, but not in RGC-5 cells. Edaravone, a free radical scavenger, at 1 μM reduced MNU-induced radical production in 661W and primary retinal cells. To induce in vivo retinal photoreceptor degeneration in mice, we administered 60 mg/kg MNU by intraperitoneal injection. We intravenously administered 1 mg/kg edaravone immediately and at 6 h after the MNU injection. Retinal photoreceptor degeneration was evaluated by measuring the thickness of the outer nuclear layer (ONL) by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining and by oxidative stress markers. MNU caused photoreceptor cell loss at 7 days after administration. Edaravone inhibited ONL thinning and reduced TUNEL-positive cells and the oxidative stress markers. These findings indicate that MNU leads to selective photoreceptor degradation via oxidative stress in vitro and in vivo and may help to understand the pathogenic mechanism of retinitis pigmentosa.
Many stimuli such as ischemia, hypoxia, heat shock, amino acid starvation, and gene mutation, exhibit a cellular response called endoplasmic reticulum (ER) stress. ER stress induces expression of a series of genes, leading to cell survival or apoptosis. Previously, we found that in an animal model of hearing loss caused by acute mitochondrial dysfunction, several ER stress markers including C/EBP homologous protein were induced in the cochlear lateral wall. To elucidate the mechanism of hearing loss caused by ER stress, we established a novel animal model of hearing loss by perilymphatic perfusion of tunicamycin, an ER stress activator that inhibits N-acetylglucosamine transferases. Subacute and progressive hearing loss was observed at all sound frequencies studied, and stimulation of ER stress marker genes was noted in the cochlea. The outer hair cells were the most sensitive to ER stress in the cochlea. Electron microscopic analysis demonstrated degeneration of the subcellular organelles of the inner hair cells and nerve endings of the spiral ganglion cells. This newly established animal model of hearing loss from ER stress will provide additional insight into the mechanism of sensorineural hearing loss.
The endothelium in rat mesenteric vascular beds has been demonstrated to regulate vascular tone by releasing mainly endothelium-derived hyperpolarizing factor (EDHF), which is involved in the activation of K+ channels and gap-junctions. However, it is unclear whether the endothelial system in mouse resistance arteries contributes to regulation of the vascular tone. The present study was designed to investigate the role of the endothelium using acetylcholine and A23187 (Ca2+ ionophore) in mesenteric vascular beds isolated from male C57BL/6 mice and perfused with Krebs solution to measure perfusion pressure. In preparations with active tone produced by methoxamine in the presence of guanethidine, injections of acetylcholine, A23187, and sodium nitroprusside (SNP) caused a concentration-dependent decrease in perfusion pressure due to vasodilation. The vasodilator responses to acetylcholine and A23187, but not SNP, were abolished by endothelium dysfunction and significantly inhibited by Nω-nitro-L-arginine methyl ester (nitric oxide synthase inhibitor) and tetraethylammonium (K+-channel inhibitor) but not glibenclamide (ATP-sensitive K+-channel inhibitor). Indomethacin (cyclooxygenase inhibitor) significantly blunted only A23187-induced vasodilation, while 18α-glycyrrhetinic acid (gap-junction inhibitor) attenuated only acetylcholine-induced vasodilation. These results suggest that the endothelium in mouse mesenteric arteries regulates vascular tone by prostanoids, EDHF, and partially by nitric oxide, different from the endothelium of rat mesenteric arteries.
Microinjection of the α2-adrenoceptor agonist clonidine into the hypothalamic periventricular nuclei (PVN) induces the pressor response associated with bradycardia in freely-moving conscious rats. This study investigated the involvement of γ-aminobutyric acid nerves (GABAergic nerves) and glutamatergic nerves in the cardiovascular response to microinjection of clonidine in the PVN. Male Wistar rats were chronically implanted with a microinjection cannula into the PVN and an arterial catheter into the abdominal aorta through the femoral artery. Blood pressure and heart rate were measured under a conscious unrestrained state. PVN injection of clonidine induced a dose-dependent pressor response concomitant with bradycardia. PVN pretreatment with GABA, muscimol (GABAA-receptor agonist), or bicuculline (GABAA-receptor antagonist) significantly inhibited the pressor response to PVN-injected clonidine without affecting bradycardia. PVN pretreatment with baclofen (GABAB-receptor agonist), 2-hydroxysaclofen (GABAB-receptor antagonist), or kynurenic acid (non-selective NMDA-type glutamate–receptor and ionotropic glutamate–receptor antagonist) did not affect the pressor response to PVN-injected clonidine. These results suggest that clonidine induces a pressor response by stimulating the presynaptic α2-adrenoceptor of GABAergic nerves in the PVN, thereby inhibiting GABAergic nerve activity.
Pruritus is a severe symptom that is difficult to treat in atopic dermatitis patients. Red ginseng (RG), a natural medicine, has various biological activities such as anti-inflammatory effects. In this study, we examined the efficacy of RG extract (RGE) and its mechanism on experimental atopic dermatitis in mice. The effects of RGE on vascular permeability and itching were first evaluated. Histamine-induced permeability and itching were significantly inhibited by embrocation with RGE as well as diphenhydramine, an antihistamine drug. Next, we assessed the therapeutic effect of topical RGE in a mouse model of atopic dermatitis. Dermatitis was induced by repeated application of 2,4-dinitrofluorobenzene (DNFB) acetone solution to the mouse ear. The effects of tacrolimus (a calcineurin blocker), dexamethasone (a corticosteroid), and RGE on dermatitis and associated scratching behavior were compared. Repeated DNFB application caused frequent scratching behaviors and ear swelling. Topical treatment with tacrolimus, dexamethasone, and RGE for 8 days before the final challenge with DNFB significantly inhibited ear swelling. Tacrolimus and RGE significantly inhibited scratching behavior, whereas dexamethasone failed to do so. DNFB-induced nerve growth factor expression and nerve fiber extension were significantly attenuated by tacrolimus and RGE, but not by dexamethasone. RGE may have the potential for treatment of atopic dermatitis.