Cholesterol and repair processes in arteriosclerosis

Extracellular cholesterol oxidase production by Streptomyces aegyptia, in vitro anticancer activities against rhabdomyosarcoma, breast cancer cell-lines and in vivo apoptosis

In recent years, microbial cholesterol oxidases have gained great attention due to its widespread use in medical applications for serum cholesterol determination. Streptomyces aegyptia strain NEAE-102 exhibited high level of extracellular cholesterol oxidase production using a minimum medium containing cholesterol as the sole source of carbon. Fifteen variables were screened using Plackett–Burman design for the enhanced cholesterol oxidase production. The most significant variables affecting enzyme production were further optimized by using the face-centered central composite design. The statistical optimization resulted in an overall 4.97-fold increase (15.631 UmL⁻¹) in cholesterol oxidase production in the optimized medium as compared with the unoptimized medium before applying Plackett Burman design (3.1 UmL⁻¹). The purified cholesterol oxidase was evaluated for its in vitro anticancer activities against five human cancer cell lines. The selectivity index values on rhabdomyosarcoma and breast cancer cell lines were 3.26 and 2.56; respectively. The in vivo anticancer activity of cholesterol oxidase was evaluated against Ehrlich solid tumor model. Compared with control mice, tumors growth was significantly inhibited in the mice injected with cholesterol oxidase alone, doxorubicin alone and cholesterol oxidase/doxorubicin combination by 60.97%, 72.99% and 97.04%; respectively. These results demonstrated that cholesterol oxidase can be used as a promising natural anticancer drug.

Purification and characterization of the enzyme cholesterol oxidase from a new isolate of Streptomyces sp

An extracellular cholesterol oxidase (cho) enzyme was isolated from the Streptomyces parvus, a new source and purified 18-fold by ion exchange and gel filtration chromatography. Specific activity of the purified enzyme was found to be 20 U/mg with a 55 kDa molecular mass. The enzyme was stable at pH 7.2 and 50 °C. The enzyme activity was inhibited in the presence of Pb(2+), Ag(2+), Hg(2+), and Zn(2+) and enhanced in the presence of Mn(2+). The enzyme activity was inhibited by the thiol-reducing reagents (DTT, β-mercaptoethanol), suggesting that disulfide linkage is essential for the enzyme activity. The enzyme activity was found to be maximum in the presence of Triton X-100 and X-114 detergents whereas sodium dodecyl sulfate fully inactivated the enzyme. The enzyme showed moderate stability towards all organic solvents except acetone, benzene, chloroform and the activity increased in the presence of isopropanol and ethanol. The K(m) value for the oxidation of cholesterol by this enzyme was 0.02 mM.

Heterologous expression of cholesterol oxidase in Bifidobacterium longum under the control of 16S rRNA gene promoter of bifidobacteria

We have constructed a constitutive high-level-expression vector for the genus Bifidobacterium and used it to express cholesterol oxidase from Streptomyces coelicola. The promoter region of the 16S rRNA gene was amplified by inverse PCR and used for the construction of pBES16PR. The optimal ribosome-binding site (RBS) for Bifidobacterium was incorporated in pBES16PR. In order to test the efficacy of this expression vector, we constructed pBES16PR-CHOL with the structural gene for cholesterol oxidase under the control of the 16S rRNA promoter, and used it to transform Bifidobacterium longum. The gene was successfully expressed and high level of cholesterol oxidase activity was obtained in B. longum. This is the first report of an expression vector for the genus Bifidobacterium using a 16S rRNA gene promoter and successful expression of cholesterol oxidase.

Degradation of cholesterol by Bacillus subtilis SFF34 isolated from Korean traditional fermented flatfish

AIMS

To examine cholesterol degradation by Bacillus subtilis SFF34.

METHODS AND RESULTS

Cholesterol degradation and cholesterol oxidase production by B. subtilis SFF34 were investigated in a medium containing 0.2% cholesterol. In addition, the oxidized product of cholesterol by the purified cholesterol oxidase was detected using a gas chromatograph. Cholesterol oxidase production reached its maximal level (3.14 U ml(-1) after 24 h of incubation in the cholesterol medium. The residual cholesterol content reduced to 0.98 mg g(-1) after 60 h of cultivation in the cholesterol medium. Two cholesterol oxidases were purified from the culture supernatant fluid and their reaction product against cholesterol was identified as 4-cholesten-3-one.

CONCLUSIONS

B. subtilis SFF34 degraded cholesterol and produced a high level of extracellular cholesterol oxidase.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacillus subtilis will be very useful for the reduction of cholesterol in many fermented foods and as a source of cholesterol oxidase.

Another cholesterol hypothesis: cholesterol as antioxidant

Current emphasis on cholesterol as agency if not cause of human atherosclerosis and subsequent cardiovascular disease ignores the essentiality of cholesterol in life processes. Additionally ignored is the ubiquitous presence of low levels of oxidized cholesterol derivatives (oxysterols) in human blood and select tissues, oxysterols also implicated in atherosclerosis. Whereas such oxysterols may be regarded putatively as agents injurious to the aorta, an alternative view of some of them is here proposed: that B-ring oxidized oxysterols of human blood represent past interception of blood and tissue oxidants in vivo by cholesterol as an ordinary aspect of oxygen metabolism. Such interception and subsequent efficient hepatic metabolism of oxysterols so formed, with biliary secretion and fecal excretion, constitute as in vivo antioxidant system. Whether cholesterol, oxysterols, oxidized lipoproteins, or oxidants in blood, singly or in concert, cause or exacerbate human atherosclerosis remains to be understood.

Adaptive changes in aging and arteriosclerosis--role of cholesterol

The "lipid theory" assumes that cholesterol has a causal part in the development of arteriosclerosis; however, in view of the fact that cholesterol has always accompanied life processes, the "lipid theory" contradicts the evolutionary principle of "teleonomy" which predicts that long lasting metabolic effects must have beneficial consequences. Support for the theory was claimed from the correlation between high serum cholesterol and arteriosclerotic complications, from observations in cholesterol fed animals and from cardiac lesions in familial hypercholesterolemia. However, correlations do not prove causality; whether the animal experiments and the observations in familial hypercholesterolemia are pertinent is questionable. Therefore, the possibility was considered that the cholesterol changes are an adaptive mechanism. This is supported by the "normal" cholesterol content of the early lesion, by the stabilization of the DNA helix by cholesterol in appropriate concentration, by the beneficial effects of cholesterol-rich granulomata; by recent reliable "intervention" trials with low cholesterol diets and by the observation that persons dying from ischemic heart disease (having high serum cholesterol) live at least as long as those dying from other causes. Furthermore, studies with serum cholesterol lowering drugs are difficult to interpret and often misleading. The symptomatology of the serum cholesterol changes in arteriosclerosis suggests that they belong to the adaptive aging phenomenon. This would be in line with evolutionary thinking.

A tentative molecular-biological hypothesis for arteriosclerosis

In view of the fact that complications of arteriosclerosis are the most frequent causes of death in industrialized societies, its etiology is of enormous interest. The widely held lipid theory (detrimental effects of cholesterol) has been attacked because it cannot account for such facts as the homeostatic relationship of endogenous and exogenous cholesterol: for the "normal" cholesterol content of the early atheroma; for the distribution of the lesions, their spotty occurrence and their "programmed" appearance. Arteriosclerosis is part of the normal processes of aging which are related to molecular-biological changes. Autoimmune processes and the effects of extrachromosomal organisms of the genome (viruses, plasmids, viroids) are clinically of interest. Arteriosclerotic lesions are probably influenced by autoimmune processes; the variability and specificity of the non-chromosomal organisms may explain the location of the lesions; the end of the incubation period of the organisms may be responsible for the programmed appearance of clinical symptoms. The lipid changes are probably part of the adaptive mechanisms counteracting the rapid destruction of the vessels following the DNA alterations. Arteriosclerosis is part of normal evolution.

Biological autoxidation. II. Cholesterol esters as inert barrier antioxidants. Self-assembly of porous membrane sacs. An hypothesis

The antioxidation defenses recognized thus far appear too weak. Needed are inert barriers to encapsulate foci of activated oxygen (FAOs) and contain their spreading. These capsules must: 1. self-assemble nonenzymatically and spontaneously in face of adversity; 2. resist oxidation and dissolution in water; and 3. be moderately fluid and elastic enough to withstand flexing by tissues. Evidence shows activated oxygen: a. is produced by common cholesterolester (CE)-raising agents; b. boosts accumulation of CEs; and c. splits low-density lipoproteins (LDL), thus releasing CE-rich coalescence-prone lipid micelles. I am proposing that CEs, combined with polar lipids, are uniquely suited to form inert-lipid antioxidation barriers (ILABs). Porous ILAB capsules self-assemble from lipid micelles released by oxidatively degraded LDL. The capsules are thermodynamically unstable but elastic, durable and capable of self-repair through oxidation of ambient LDL. All capsules tend to contract into spheres. Enclosed needle-like "foreign bodies", such as asbestos, puncture the contracting capsules. Hence the odd bulbous architecture of asbestos bodies. ILABs protect from--and their failure initiates and promotes--carcinogenesis and atherosclerosis. ILABs may be mediators of membrane biogenesis. The loss of arterial flexibility in atherosclerosis protects ILAB capsules from breakage.