Vinpocetine is known to inhibit sodium-gated ion channels and has also been identified as a weak inhibitor (IC50 ~ 10µM) of phosphodiesterase-1 (PDE-1). These activities have been used to explain the neuroprotective and vasorelaxant properties of the molecule.
”The Researchers at University of Rochester Medical Center have now reported potent activity of vinpocetine in a mouse model of lung inflammation, showing promise for the treatment of chronic inflammatory diseases such as COPD, rheumatoid arthritis and psoriasis. The scientists have demonstrated that the mechanism of action is via inhibition of IκB kinase (IKK) resulting in suppression of the proinflammatory transcription factor, NFκB.
Since the compound has a long history of human use, the researchers hope that development of vinpocetine as an antiinflammatory therapy will be easier than for a novel molecule. The university has applied for a patent for vinpocetine for use as an IKK-inhibitor for the treatment of COPD and Yan and Berk, lead scientists of the study, have formed a start-up company, Rock Pharmaceuticals, with the hope of licensing the intellectual property rights.
Full details of the study are currently in press at PNAS, entitled “Vinpocetine inhibits inflammation via an IKK-dependent but PDE-independent mechanism”.
Systemic infection and inflammation lead to release of cytokines, such as IL-1, which activate the brain’s stress response mechanisms, producing typical symptoms such as lethargy, fever, and lack of appetite. In response to inflammation or infection, the hypothalamus releases corticotropin-releasing factor which, in turn, stimulates the pituitary gland to secrete adrenocorticotropic hormone. This then causes the adrenal glands to increase production of glucocorticoids, which both mobilise energy reserves to cope with the inflammatory insult and also act as powerful immunosuppressants, preventing excessive cytokine production and immune cell proliferation. Since cytokines are not able to freely cross the blood-brain barrier, exactly how they initiate this cascade of events has not been clear but researchers at the Salk Institute for Biological Studies have now begun to unravel the process.
It had been suggested that cytokines might interact with epithelial cells in the brain’s vasculature to produce prostanoids which act as secondary messengers transmitting the signal onwards. Epithelial cells are ideally positioned to receive inflammatory signals from circulating blood but need a very strong signal to become activated. In contrast, perivascular macrophages, a subset of brain-resident macrophages, are much more sensitive to cytokines but are not in direct contact with the bloodstream. To clarify the roles of both cell types, liposomes containing clodronate, which specifically deplete macrophages, were injected into the lateral cerebral ventricles of rats. This procedure abolished responses to IL-1 which activates prostanoid synthesis only in perivascular cells, but enhanced responses to LPS which stimulates prostanoid synthesis by both perivascular cells and endothelial cells. Resident macrophages lined up along the blood-brain barrier thus play opposing roles in the transmission of immune signals to the brain depending on the nature of the stimulus.
As well as clarifying the cellular mechanisms of CNS responses to inflammatory insults, the team hope that a better understanding of how immune signals are transmitted across the blood-brain barrier may also lead ultimately to new treatments for chronic neurodegenerative diseases such as Amyotrophic Lateral Sclerosis, Parkinson’s disease, Alzheimer’s disease and prion diseases, in which inflammation is believed to play an important role.
The study is published in the January 14th issue of Neuron.
P-glycoprotein (P-gp, ABCB1) was originally characterized by its ability to confer a multidrug-resistant phenotype to cancer cells. It was also the first drug efflux transporter to be detected on blood-brain barrier endothelial cells and is now recognized to be involved in the transport of a wide variety of substrates and drug molecules. P-gp is also expressed on cells of the immune system where it is believed to play a role in the efflux of inflammatory mediators such as steroids, prostaglandins and cytokines.
Scientists from the Netherlands have now shown that P-gp may play a key role in multiple sclerosis (MS). In MS, autoreactive myelin-specific T helper (Th) cells – which are primed in the periphery by antigen-presenting dendritic cells (DCs) – cause extensive destruction of myelin sheaths and axonal loss. The team found that both DC maturation and T-cell stimulatory capacity were severely impaired in P-gp knockout mice (Mdr1a/1b-/-) which showed less severe clinical symptoms of experimental autoimmune encephalomyelitis (EAE) following administration of recombinant myelin oligodendrocyte glycoprotein (rMOG) than wild type animals. The observed differences in clinical symptoms were associated with decreased demyelination in the brains of the knockout animals and reduced brain inflammation. Following immunisation with rMOG, secretion of Th1 cytokines, IFN-γ and TNF-α and Th2 cytokines, IL10 and IL5, by lymph node cells was significantly reduced in the Mdr1a/1b-/- mice compared with wild type animals whereas no changes were observed in the secretion of the Th17 cytokine, IL-17. Since P-gp did not affect the ability of T-cells to become activated, the authors propose that the observed differences in T-cell responses are likely mediated by regulation of cytokine secretion by DCs.
The study, which is published in PLoSone, highlights a novel immunomodulatory role for P-gp and may provide new opportunities to treat immune-related or inflammatory diseases.
Gastroesophageal reflux (GER), or acid reflux, which occurs when the lower esophageal sphincter opens spontaneously or doesn’t close properly, is experienced intermittently by most people. Gastroesophageal reflux disease (GERD) occurs when the amount of gastric juice that refluxes into the esophagus exceeds the normal limit and the esophageal mucosa is damaged, causing esophagitis. It has generally been thought that damage to the esophagus is the direct result of chemical burns by the acid in refluxed gastric juice but researchers at UT Southwestern Medical Center have now suggested that this may not be the case. The team created GERD in rats by connecting the duodenum to the esophagus, which allows stomach acid and bile to enter the esophagus, but were surprised to find that esophagitis didn’t develop for a number of weeks after the operation. If GERD is really caused by acid burns, the damage would be expected to appear much more quickly. In earlier studies, perfusion with highly concentrated acid did cause rapid damage to the esophagus, but early events in animal models designed to more closely resemble human GERD had not been investigated in detail.
In the present study, the researchers expected to see death of surface cells followed by injury to the deeper layers of the esophagus but found just the opposite. Reflux esophagitis started at postoperative day 3; at this stage there was no damage to surface epithelial cells, but lymphocytes had begun to infiltrate the submucosa and later progressed to the epithelial surface. Since damage to the deeper layers of the esophagus preceded surface erosions, the team suggest that it is infiltrating lymphocytes, rather than direct chemical burns, that cause the damage. Exposure of esophageal epithelial cells to acidified bile salts was shown to increase the secretion of cytokines interleukin-8 and interleukin-1β, and conditioned media from these cells was found to cause significant increases in the migration rates of T cells and neutrophils. Current treatments for GERD focus on reducing acid production by the stomach but the new study provides a more complex picture and suggests that treatments that modulate the immune response could also be of benefit.
Image: Flickr - Clayirving Cystic Fibrosis (CF) is an autosomal recessive genetic disorder affecting the secretory glands, resulting from mutations in the CF transmembrane conductance regulator (CFTR) gene. The disease predominantly involves the respiratory and digestive systems, with lung injuries and infections responsible for approximately 90% of the morbidity and mortality of CF patients.
CFTR encodes a chloride conducting channel and the CF-causing mutations result in reduced numbers and/or defective ion channels. Although the link between mutated CFTR and CF has been known for 20 years, the fundamental question of how this results in disease has remained elusive. Contrary to expectations, the levels of Cl– in the airways of CF patients are not very different to those found in unaffected individuals.
It is known, however, that CFTR channels are able to conduct other ions, including thiocyanate (SCN–), and new research from scientists at the Howard Hughes Medical Institute and University of Pennsylvania School of Medicine now suggests that defective SCN– transport may play a role. Thiocyanate has antioxidant properties, providing protection from reactive oxygen species (ROS) that are formed in response to infection. Transport of thiocyanate into the airway lumen results in higher concentrations in airway secretions than in plasma and is dependent on functional CFTR. In this study, the researchers showed that lactoperoxidase in the airways catalyses the conversion of SCN– to tissue-innocuous hypothiocyanite (OSCN–), consuming potentially damaging hydrogen peroxide in the process. Further, SCN– depletes harmful hypochlorite (OCl–) through competition with chloride ion for myeloperoxidase and by direct reduction.
The authors of the study, published in PNAS, suggest that as well as a potential role in the pathogenesis of CF, insufficient levels of SCN– may provide inadequate protection from hypochlorite, exacerbating inflammatory diseases.
Selective cyclooxygenase-2 (COX-2) inhibitors were developed to reduce the risk of gastrointestinal side effects associated with the older non-steroidal anti-inflammatory drugs (NSAIDs) which inhibit both COX-1 and COX-2. The withdrawal of rofecoxib (Vioxx™) in 2004 and valdecoxib (Bextra™) in 2005 because of a slightly increased risk of thrombotic events such as heart attacks and strokes after long-term treatment came as a blow to the pharmaceutical industry, doctors and patients. Since the withdrawal of rofecoxib and valdecoxib, no new anti-inflammatory drugs have been submitted to the FDA for the treatment of osteoarthritis.
Last month, however, French pharmaceutical company, NicOX, submitted an NDA for its first-in-class cyclooxygenase-inhibiting nitric oxide donator (CINOD), naproxcinod, for the treatment of osteoarthritis. Naproxcinod is a nitroxybutyl ester of the well established and well tolerated NSAID, naproxen, and is intended to overcome another drawback of NSAIDs and COX-2 inhibitors – increased blood pressure. Cleavage of naproxcinod by esterases gives naproxen, together with a nitric oxide donating moiety. Nitric oxide relaxes vascular smooth muscle cells, causing dilation of the arteries and reducing blood pressure, and has also been reported to reduce formation of thrombi. In clinical trials in patients with osteoarthritis of the knee and hip, naproxcinod met efficacy endpoints and did not cause an increase in blood pressure. Naproxcinod also showed an advantage compared with naproxen in terms of gastrointestinal side effects.
The physiological role of aldose reductase (AR) is still incompletely understood, although it has long been associated with the pathogenesis of diabetes-associated diseases such as cataract and neuropathy. In the last twenty years a number of AR inhibitors have entered clinical trials for the potential treatment of diabetic neuropathy. Whilst the compounds have generally been well tolerated, efficacy has not been clearly established (although one compound, Epalrestat, is approved in Japan for treatment of subjective neuropathy symptoms associated with diabetic peripheral neuropathy).
The rationale for use of AR inhibitors in diabetic complications is based on the ability of AR to reduce glucose to sorbitol, levels of which are elevated in tissues of diabetic patients. Although glucose does not have high affinity for AR, the pathway is believed to be relevant in hyperglycaemia.
AR is also known to reduce lipid aldehydes and their glutathione conjugates in response to reactive oxygen species (ROS). The products of the AR-catalysed reduction mediate activation of NFκB and the subsequent generation of inflammatory proteins. This observation led researchers at University of Texas Medical Branch and Louisiana State University Health Sciences Center to hypothesise that AR inhibitors may be useful in inflammatory diseases such as asthma. In a study published in PLoSone, the scientists stimulated primary human small airway epithelial cells (SAEC) with ragweed pollen extract (RWE). In this in vitro experiment, AR inhibition prevented RWE-induced apoptosis and expression of inflammatory mediators. Further, AR inhibition prevented allergic airway inflammation in mice sensitised with endotoxin-free RWE.
The results encourage exploration of AR inhibitors in inflammatory diseases such as asthma.
Since the early 1990s, when it was first suggested that the presence of the anti-oxidant, resveratrol, could explain the cardioprotective effects of red wine, the health benefits attributed to this compound have grown and grown. Based largely on studies in simple organisms and in rodents, resveratrol has been credited with cardioprotective and neuroprotective properties, as well as with anti-diabetic, anti-cancer, anti-inflammatory, and anti-ageing powers. Resveratrol has been shown to interact with numerous biochemical pathways: the anti-ageing properties of resveratrol have been linked to activation of sirtuins, and researchers at the University of Glasgow and the University of Singapore have now identified a pathway involved in its anti-inflammatory effects.
Pretreatment of human or mouse neutrophils with resveratrol was found to significantly block oxidative burst, leukocyte migration, degranulation, and inflammatory cytokine production caused by the inflammatory mediator, C5 anaphylatoxin. The anti-inflammatory activity of resveratrol was attributed to its ability to inhibit sphingosine kinase (IC50 ~20µM) and so prevent activation of phospholipase D. Resveratrol also blocked ERK1/2 phosphorylation independently of sphingosine kinase. In further studies, prior injection of resveratrol reduced the inflammatory response of mice to challenge with C5 anaphylatoxin. The authors suggest that inhibition of sphingosine kinase by resveratrol could provide an effective treatment for systemic sepsis, appendicitis, and peritonitis, which are currently very difficult to treat. The study is published in the August print issue of FASEB Journal.
Given the profusion of biochemical targets that are being uncovered for resveratrol, it will be very interesting to see whether analogues that are being optimised specifically for one pathway retain the full activity of the parent compound in selected animal studies.
The incidence of gastroesophageal reflux disease (GERD) has increased significantly in the United States since the 1970s. The chronic inflammation associated with GERD can lead to the development of Barrett’s oesophagus, a precancerous condition that, in rare cases, leads to oesophageal adenocarcinoma. Despite extensive epidemiological investigation, the cause of GERD and the reasons underlying the increase in prevalence remain unclear. Researchers at the University of New York Langone Medical Center have now shown, however, that the condition is linked to a global alteration of the microbiome in the oesophagus. The team collected and sequenced bacteria from the oesophagus of patients with oesophagitis or Barrett’s oesophagus and compared these with samples from healthy individuals. Although it wasn’t possible to obtain a detailed picture of species present in low abundance, they found that streptococci predominated in healthy patients whereas samples from patients with oesophagitis or Barrett’s oesophagus were more diverse and contained more Gram-negative bacteria.
The study examined samples from only 34 individuals and it is not yet known whether the changes in bacterial populations seen in GERD patients are cause or effect, but if the changes in the microbiome can be shown by further studies to play a causal role in pathogenesis, it may be possible to design new treatments to treat this increasingly common disease.
Crohn’s disease is an inflammatory disease of the gastrointestinal tract that causes abdominal pain, diarrhea and vomiting. First described by Burrill Bernard Crohn and co-workers in 1932, the disease is believed to be an autoimmune disorder but the precise causes are unknown. Treatment options focus on management of acute symptoms and maintenance of remission, since no known cure is available.
Crohn himself was convinced that the disease was caused by Mycobacterium paratuberculosis (MAP), the same pathogen responsible for the related Johne’s disease in cattle. Whilst his research was unable to establish the involvement of MAP, the theory has received more attention in recent years.
New research from McGill University Health Centre (MUHC), Quebec, has established a link between the human NOD2 gene and mycobacteria. Mutations in NOD2 have been observed in approximately 25% of Crohn’s disease patients, but the nature of the effect of these mutations has not been understood. Normally, NOD2 codes for a receptor that recognises invading bacteria, triggering an immune response. The MUHC study demonstrates that the NOD2 receptor preferentially recognises a peptide, N-glycolylated peptidoglycan-derived muramyl dipeptide (MDP), which is only found in mycobacteria. When mycobacteria invade the human body, they cause an immediate and very strong immune response via the NOD2 receptor. This new discovery, published in the Journal of Experimental Medicine, associates the predisposition for Crohn’s disease with both the NOD2 mutation and the presence of mycobacteria, but researchers must still determine the precise combination of these factors to understand how the disease develops.
In a separate study, researchers from Case Western Reserve University School of Medicine have identified a novel link between ITCH, a gene known to regulate inflammation in the body and NOD2. ITCH,which encodes an E3 ubiquitin ligase, can cause a variety of inflammatory diseases when malfunctioning. The team at Case Western found that ITCH also influences NOD2-induced inflammation. These findings, to be published in the August 11th issue of Current Biology, suggest a common pathophysiology exists between multiple inflammatory diseases. The unexpected finding of the interaction between these genes offers the possibility of new drug targets for intervention in Crohn’s disease.