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Abstract

Plasma membranes isolated from pig liver contained almost no acid sphingomyelinase but significant neutral magnesium-dependent sphingomyelinase that was activated by phosphatidylserine. We report here the purification to apparent homogeneity of neutral sphingomyelinase of about 87 kDa from liver plasma membranes. The purified enzyme strictly required magnesium and had a neutral optimal pH. In contrast with neutral sphingomyelinase purified from other sources (such as brain), the enzyme purified from from liver plasma membrane was not inhibited by GSH and, strikingly, it was not activated by phosphatidylserine. Liver sphingomyelinase was inhibited by several lipophilic antioxidants in a dose-dependent way. Ubiquinol-10 was more effective than alpha-tocopherol, alpha-tocopherylquinone, alpha-tocopherylquinone, and ubiquinone-10, and inhibition was noncompetitive. Differential inhibition of neutral sphingomyelinase by antioxidants did not correlate with different levels of protection against lipid peroxidation. The purified sphingomyelinase was not inhibited significantly by ubiquinone-10 and ubiquinol- 10, but ubiquinol-0 and ubiquinone-0 inhibited by 30 and 60% respectively. Our results demonstrate a direct inhibitory effect of ubiquinol on the plasma membrane n-SMase and support the participation of this molecule in the regulation of ceramide-mediated signaling.

Diverse Roles of Ceramide in the Progression and Pathogenesis of Alzheimer’s Disease

“…A previous report suggested that an isolated compound, scyphostatin, has a structural resemblance to ceramide and may inhibit N-sphingomyelinase [ 88 ]. Moreover, some other N-sphingomyelinase inhibitor analogs have been developed, namely spiroexpoxide, [ 89 ] manumycin A, [ 90 ] alutenusin, [ 91 ] and ubiquinol [ 92 ].…”

Sphingomyelinases: enzymology and membrane activity

“…These results suggest that caveolar nSMase may be involved in TNF‐α signalling. Working on a different system, namely pig liver plasma membranes, Martin et al [54] isolated a Mg 2+ ‐dependent nSMase that was not inhibited by glutathione but was inhibited by ubiquinol and other lipophilic antioxidants. Also relevant in this context is the somewhat forgotten report of a latent nSMase in chicken erythrocyte membranes [55].…”

Small Molecule Inhibitors Targeting Biosynthesis of Ceramide, the Central Hub of the Sphingolipid Network

“…108 Another hydroquinone-based compound, ubiquinol (72) (CoQ 10 H 2 , Figure 23), was reported to inhibit Mg 2+ -dependent nSMase of pig liver plasma membranes (>90% inhibition at 100 μM following 15 min preincubation) in a noncompetitive manner with respect to sphingomyelin. 109 Subsequent studies releveled that inhibition by ubiquinol ( 72) is time-dependent, displaying a greater degree of potency when preincubated for 60 min. 110 Furthermore, CoQ 6 H 2 (73) (Figure 23) was found to have the optimal isoprenoid side chain length for nSMase inhibition among several homologs.…”

“…Compound 71 (Figure ), the corresponding quinolone derivative of 69 , was also found to potently inhibit nSMase of rat brain microsomes with a IC 50 value of 0.8 μg/mL (4.2 μM) . Another hydroquinone-based compound, ubiquinol ( 72 ) (CoQ 10 H 2 , Figure ), was reported to inhibit Mg 2+ -dependent nSMase of pig liver plasma membranes (>90% inhibition at 100 μM following 15 min preincubation) in a noncompetitive manner with respect to sphingomyelin . Subsequent studies releveled that inhibition by ubiquinol ( 72 ) is time-dependent, displaying a greater degree of potency when preincubated for 60 min .…”