alpha-D-mannopyranosylmethyl-p-nitrophenyltriazene inhibition of rat liver alpha-D-mannosidases

Tension-type headache

Tension-type headache (TTH) is the most prevalent neurological disorder worldwide and is characterized by recurrent headaches of mild to moderate intensity, bilateral location, pressing or tightening quality, and no aggravation by routine physical activity. Diagnosis is based on headache history and the exclusion of alternative diagnoses, with clinical criteria provided by the International Classification of Headache Disorders, third edition. Although the biological underpinnings remain unresolved, it seems likely that peripheral mechanisms are responsible for the genesis of pain in TTH, whereas central sensitization may be involved in transformation from episodic to chronic TTH. Pharmacological therapy is the mainstay of clinical management and can be divided into acute and preventive treatments. Simple analgesics have evidence-based effectiveness and are widely regarded as first-line medications for the acute treatment of TTH. Preventive treatment should be considered in individuals with frequent episodic and chronic TTH, and if simple analgesics are ineffective, poorly tolerated or contraindicated. Recommended preventive treatments include amitriptyline, venlafaxine and mirtazapine, as well as some selected non-pharmacological therapies. Despite the widespread prevalence and associated disability of TTH, little progress has been made since the early 2000s owing to a lack of attention and resource allocation by scientists, funding bodies and the pharmaceutical industry.

Dissecting glycoprotein biosynthesis by the use of specific inhibitors

It is possible to interfere with different steps in the dolichol pathway of protein glycosylation and in the processing of asparagine-linked oligosaccharides. Thus some clues about the role of protein-bound carbohydrate can be obtained by comparing the biochemical fates and functions of glycosylated proteins with their non-glycosylated counterparts, or with proteins exhibiting differences in the type of oligosaccharide side chains. Cells infected with enveloped viruses are good systems for studying both aspects of protein glycosylation, since they contain a limited number of different glycoproteins, often with well-defined functions. Tunicamycin, an antibiotic, as well as several sugar analogues have been found to act as inhibitors of protein glycosylation by virtue of their anti-viral properties. They interfere with various steps in the dolichol pathway resulting in a lack of functional lipid-linked oligosaccharide precursors. Compounds that interfere with oligosaccharide trimming represent a second generation of inhibitors of glycosylation. They are glycosidase inhibitors that interfere with the processing glucosidases and mannosidases and, as a result, the conversion of high-mannose into complex-type oligosaccharides is blocked. Depending upon the compound used, glycoproteins contain glucosylated-high-mannose, high-mannose or hybrid oligosaccharide structures instead of complex ones. The biological consequences of the alterations caused by the inhibitors are manifold: increased susceptibility to proteases, improper protein processing and misfolding of polypeptide chains, loss of biological activity and alteration of the site of virus-budding, to name but a few.

Inhibition of glycoprotein oligosaccharide processing in vitro and in influenza-virus-infected cells by alpha-D-mannopyranosylmethyl-p-nitrophenyltriazene

The effects of alpha-D-mannopyranosylmethyl-p-nitrophenyltriazene (MMNT) on mannosidases involved in asparagine-linked oligosaccharide processing were investigated. MMNT was found to inhibit the activity of rat liver Golgi alpha-mannosidase I in a concentration-dependent manner (50% inhibition with 0.18 mM-MMNT), whereas rat liver endoplasmic-reticulum alpha-mannosidase appeared to be resistant (less than 5% inhibition at 1 mM-MMNT). Jack-bean alpha-mannosidase was also sensitive to inhibition by MMNT (50% inhibition with 0.32 mM-MMNT). Treatment of influenza-virus-infected chick-embryo cells with 1 mM-MMNT led to a decrease in the formation of complex-type asparagine-linked oligosaccharides and an accumulation of high-mannose-type oligosaccharides with the composition Man8(GlcNAc)2 and Man7(GlcNAc)2 on the viral glycoproteins. The biological activities of influenza-virus haemagglutinin and neuraminidase synthesized in the presence of 1 mM-MMNT remained unchanged, but the virus was less infectious than the control.