Probucol-Induced α-Tocopherol Deficiency Protects Mice against Malaria Infection

The emergence of malaria pathogens having resistance against antimalarials implies the necessity for the development of new drugs. Recently, we have demonstrated a resistance against malaria infection of α-tocopherol transfer protein knockout mice showing undetectable plasma levels of α-tocopherol, a lipid-soluble antioxidant. However, dietary restriction induced α-tocopherol deficiency is difficult to be applied as a clinical antimalarial therapy. Here, we report on a new strategy to potentially treat malaria by using probucol, a drug that can reduce the plasma α-tocopherol concentration. Probucol pre-treatment for 2 weeks and treatment throughout the infection rescued from death of mice infected with Plasmodium yoelii XL-17 or P. berghei ANKA. In addition, survival was extended when the treatment started immediately after parasite inoculation. The ratio of lipid peroxidation products to parent lipids increased in plasma after 2 weeks treatment of probucol. This indicates that the protective effect of probucol might be mediated by the oxidative stressful environment induced by α-tocopherol deficiency. Probucol in combination with dihydroartemisin suppressed the proliferation of P. yoelii XL-17. These results indicated that probucol might be a candidate for a drug against malaria infection by inducing α-tocopherol deficiency without dietary α-tocopherol restriction.     

Enhancement of lipid peroxidation and its amelioration by vitamin E in a subject with mutations in the SBP2 gene

Selenocysteine (Sec) insertion sequence-binding protein 2 (SBP2) is essential for the biosynthesis of Sec-containing proteins, termed selenoproteins. Subjects with mutations in the SBP2 gene have decreased levels of several selenoproteins, resulting in a complex phenotype. Selenoproteins play a significant role in antioxidative defense, and deficiencies in these proteins can lead to increased oxidative stress. However, lipid peroxidation and the effects of antioxidants in subjects with SBP2 gene mutations have not been studied. In the present study, we evaluated the lipid peroxidation products in the blood of a subject (the proband) with mutations in the SBP2 gene. We found that the proband had higher levels of free radical-mediated lipid peroxidation products, such as 7β-hydroxycholesterol, than the control subjects. Treatment of the proband with vitamin E (α-tocopherol acetate, 100 mg/day), a lipid-soluble antioxidant, for 2 years reduced lipid peroxidation product levels to those of control subjects. Withdrawal of vitamin E treatment for 7 months resulted in an increase in lipid peroxidation products. Collectively, these results clearly indicate that free radical-mediated oxidative stress is increased in the subject with SBP2 gene mutations and that vitamin E treatment effectively inhibits the generation of lipid peroxidation products.     

Presence of immunoreactive endothelin in human plasma

A highly specific and sensitive radioimmunoassay has been established for measurement of human endothelin (hET) in human plasma. After extraction of plasma with an octyl-silica column, this assay allowed for detection of immunoreactive (IR) hET as low as 0.2 fmol/ml. In 16 healthy subjects, the mean concentration of plasma IR-hET was 0.6 fmol/ml. Reverse-phase HPLC coupled with radioimmunoassay revealed two major IR-hET components, one corresponding to authentic hET(1-21) and another with more hydrophilicity than hET(1-21). These data indicate that ET is a circulating vasoconstrictor hormone in man.     

Effect of endothelin-1 on release of arginine-vasopressin from perifused rat hypothalamus

Endothelin-1 (ET-1) is an endothelium-derived vasoconstrictor peptide with potent pressor activity. We studied the effect of ET-1 on release of arginine-vasopressin (AVP) from perifused rat hypothalamus. ET-1 (10(-10) to 10(-8) M) significantly stimulated AVP release. The ET-1-induced AVP release was completely blocked in the presence of nicardipine. Our results suggest a possible involvement of ET in the regulation of AVP release.     

Biosynthesis and secretion of salusin-alpha from human cells

Salusins originally identified using bioinformatics analyses have been shown to act on the cardiovascular and endocrine systems. Although the hypotensive activity of salusin-alpha is limited, it exerts a significant anti-atherosclerotic effect via suppression of foam cell formation in human monocyte-derived macrophages by down-regulating acyl-CoA:cholesterol acyltransferase-1. Furthermore, serum salusin-alpha levels show a close negative correlation with the severity of atherosclerotic diseases. However, biosynthesis and secretion of salusin-alpha peptide from cultured mammalian cells have not been demonstrated to date. We examined the expression, synthesis and release of salusin-alpha in human-derived cell lines. Preprosalusin mRNA and protein were detected ubiquitously in all cells tested, whereas the processing of preprosalusin into salusin-alpha peptide is dependent upon each cell type. Immunohistochemical study revealed the most abundant salusin-alpha-like immunoreactivity to be present in HeLa cells which released salusin-alpha-like immunoreactivity into the culture supernatant. Analysis of extracted conditioned media from HeLa cells by reverse-phase high performance liquid chromatography coupled with radioimmunoassay detection revealed a single immunoreactive component that co-eluted with authentic salusin-alpha. These results present the first evidence that salusin-alpha is biosynthesized and released from human-derived cells.     

Adrenomedullin is an autocrine/paracrine growth factor for rat vascular smooth muscle cells

Adrenomedullin is a potent vasodilator peptide secreted by vascular endothelial and smooth muscle cells. Adrenomedullin stimulates the proliferation of quiescent rat vascular smooth muscle cells (VSMCs) via p42/p44 ERK/MAP kinase activation. Recently, receptor-activity-modifying proteins (RAMPs) have been shown to transport calcitonin-receptor-like-receptor (CRLR) to the cell surface to present either as CGRP receptor or adrenomedullin receptor. We investigated whether adrenomedullin acts as an autocrine/paracrine growth factor for cultured rat VSMCs and whether coexpressions of RAMP isoform and CRLR may mediate p42/p44 ERK/MAP kinase activation by adrenomedullin. Adrenomedullin dose-dependently stimulated the proliferation of quiescent rat VSMCs, and this effect was inhibited by an adrenomedullin receptor antagonist, a MAP kinase kinase inhibitor and phosphatidylinositol 3-kinase inhibitors. Addition of either CGRP(8-37) or anti-adrenomedullin antibody to exponentially growing rat VSMCs inhibited the serum-induced cell proliferation, suggesting its role as an autocrine/paracrine growth factor. Cotransfection of RAMP2 or RAMP3 with CRLR into rat VSMCs potentiated activation of cAMP activity, but not of p42/p44 ERK/MAP kinase activity in response to adrenomedullin. Our results suggest that adrenomedullin is an autocrine/paracrine growth factor for rat VSMCs via p42/p44 ERK/MAP kinase and phosphatidylinositol 3-kinase pathways and that it is not mediated by human RAMP-CRLR receptors.     

Cytokine-induced release of endothelin-1 from porcine renal epithelial cell line.

To elucidate the mechanism by which endothelin-1 (ET-1) is released from renal epithelial cells, we have investigated the effects of several compounds on release of ET-1-like immunoreactivity (LI) from LLCPK1 cell line. Thrombin, transforming growth factor-beta, cytokines (tumor necrotizing factor-alpha, interleukin-1 beta), and phorbol ester stimulated ET-1-LI release in a time- and dose-dependent manner. The cytokine-induced ET-1-LI release was not affected by indomethacin. Northern blot analysis using cDNA for porcine preproET-1 as a probe revealed a single major band corresponding to the size of ET-1 mRNA in LLCPK1. These data indicate that the preproET-1 gene is also expressed in renal epithelial cells and the release of ET-1 from renal cells is regulated by the similar mechanism to that from endothelial cells.