Cholesterol homeostasis and cell proliferation by mitogenic homologs: insulin, benzo-α-pyrene and UV radiation

Cholesterol and Cytokines: Molecular Links to Atherosclerosis and Carcinogenesis

An increase of cholesterol concentration within the artery obstructs arterial blood flow once it deposits alongside the arterial wall. This results in atherosclerosis. Carcinogenesis causes a quicker clearance of vascular cholesterol to meet the demands of tumour cell development. Both illnesses have an increased concentration of pro-inflammatory cytokines in the blood. To search the comparative characteristics of cholesterol and pro-inflammatory cytokines in the pathogenesis of atherosclerosis and carcinogenesis, a comprehensive online survey using MEDLINE, Scopus, PubMed, and Google Scholar was conducted for relevant journals with key search term cholesterol and cytokines in atherosclerotic and cancerous patients. According to reports, hypercholesterolaemia related dyslipidemia causes atherosclerosis in blood arteries and hypercholesterolaemia in cell nucleus is a reason for developing carcinogenesis. It is also noted that pro-inflammatory cytokines are involved in both of the aforementioned pathogenesis. Changes in anti-inflammatory cytokines are only the characteristic features of each kind. Thus, Cholesterol and pro-inflammatory cytokines are intensely interlinked in the genesis of atherosclerotic and carcinogenic consequences.

Exposure to Benzo(a)pyrene promotes proliferation and inhibits differentiation of stromal cells in mice during decidualization

The environmental pollutant Benzo(a)pyrene (BaP) has an adverse effect on the reproductive performance of mammals. We previously showed that BaP treatment during early pregnancy damages endometrial morphology and impairs embryo implantation. Endometrial decidualization at the implantation site (IS) after embryo implantation is crucial for pregnancy maintenance and placental development. The balance between proliferation and differentiation in endometrial stromal cells (ESCs) is a crucial event of decidualization, which is regulated by the cell cycle. Here, we report that abnormal decidualization caused by BaP is associated with cell cycle disturbance of stromal cells. The mice in the treatment group were gavaged with 0.2 mg/kg/day BaP from day 1-8 of pregnancy, while those in control were gavaged with corn oil in parallel. BaP damaged the decidualization of ESCs and reduced the number of polyploid cells. Meanwhile, BaP up-regulated the expression of Ki67 and PCNA, affecting the differentiation of stromal cells. The cell cycle progression analysis during decidualization in vivo and in vitro showed that BaP induced polyploid cells deficiency with enhanced expressions of CyclinA(E)/CDK2, CyclinD/CDK4 and CyclinB/CDK1, which promote the transformation of cells from G₁ to S phase and simultaneously activate the G₂/M phase. The above results indicated that BaP exposure accelerates cell cycle progression, promotes ESC proliferation, inhibits differentiation, and impedes proper decidualization and polyploidy development. Thus, the imbalance of ESC proliferation and differentiation would be an important mechanism for BaP-induced defective decidualization.

Atherosclerosis and carcinoma: Two facets of dysfunctional cholesterol homeostasis

Although cholesterol is an essential and necessary component for biological systems; inappropriate accumulation of cholesterol in blood vessels and intracellular territory is also detrimental to living things. On one hand, cholesterol is the acting precursor of many metabolic regulators, a component of the structural veracity and scaffold fluidity of biomembranes, an insulator of electrical transmission in nerves and many more; on the other hand, its deposition in blood vessels induces atherosclerotic plaque and cardiovascular complications with the consequences of heart attack and stroke. It is also an emerging fact that cholesterol is a prelate in the cell nucleus for cell proliferation and any oddity in this venture may be the cause of tumorigenesis. Hence, cholesterol homeostasis is a very crucial element in issues of health management. Cholesterol is now a global target for maintaining quality health, particularly to control the two giants of the present world health tragedy: atherosclerosis and carcinoma, which appear to be the two facets of dysfunctional cholesterol homeostasis.

Cholesterol: A Prelate in Cell Nucleus and its Serendipity

Cholesterol is a chameleon bio-molecule in cellular multiplex. It acts as a prelate in almost every cellular compartment with its site specific characteristics viz. regulation of structural veracity and scaffold fluidity of bio-membranes, insulation of electrical transmission in nerves, controlling of genes by making steroid endocrines, acting as precursors of metabolic regulators and many more with its emerging prophecy in the cell nucleus to drive new cell formation. Besides the crucial legacy in cellular functionality, cholesterol is ostracized as a member of LDL particle, which has been proved responsible to clog blood vessels. LDL particles get deposited in the blood vessels because of their poor clearance owing to the non-functioning LDL receptor on the vessel wall and surrounding tissues. Blocking of blood vessel promotes heart attack and stroke. On the other hand, cholesterol has been targeted as pro-cancerous molecule. At this phase again cholesterol is biphasic. Although cholesterol is essential to construct nuclear membrane and its lipid-rafts; in cancer tumour cells, cholesterol is not under the control of intracellular feedback regulation and gets accumulated within cell nucleus by crossing nuclear membrane and promoting cell proliferation. In precancerous stage, the immune cells also die because of the lack of requisite concentration of intracellular and intranuclear cholesterol pool. The existence of cholesterol within the cell nucleus has been found in the nuclear membrane, epichromosomal location and nucleoplasm. The existence of cholesterol in the microdomain of nuclear raft has been reported to be linked with gene transcription, cell proliferation and apoptosis. Hydrolysis of cholesterol esters in chromosomal domain is linked with new cell generation. Apparently, Cholesterol is now a prelate in cell nucleus too ------ A serendipity in cellular haven.

Toxicity and DNA repair in normal human keratinocytes co-exposed to benzo[a]pyrene and sunlight

Skin has the potential to be exposed to both solar UV radiation and polycyclic aromatic hydrocarbons, especially in occupational environments. In the present work, we investigated how benzo[a]pyrene (B[a]P) modulates cellular phototoxicity and impacts formation and repair of pyrimidine dimers induced by simulated sunlight (SSL) in normal human keratinocytes (NHK). We were especially interested in determining whether the aryl hydrocarbon receptor (AhR) was involved since it was recently shown to negatively impact repair. Addition of 1 μM B[a]P after exposure to 2 minimal erythemal doses of SSL had little impact on NHK. The inverse protocol involving incubation with B[a]P followed by irradiation led to a strong increase in phototoxicity. Repair of DNA photoproducts was drastically impaired. Using agonists and antagonists of AhR allowed us to conclude that this factor was not involved in these results. Observation of a strong increase in the level of the oxidative marker 8-oxo-7,8-dihydroguanine in the protocol involving B[a]P treatment followed by exposure to SSL strongly suggested that a photosensitized oxidative stress was responsible for cell death and inhibition of DNA repair. Accordingly, both adverse effects were diminished with a lower concentration of B[a]P and a lower SSL dose, leading to less oxidative stress.

Differential Response of B Cells to an Immunogen, a Mitogen and a Chemical Carcinogen in a Mouse Model System

Background: B cells are specific antibody generating cells which respond to foreign intruders in the circulation. The purpose of this study was to compare the relative immunogenic potentials of three well established agent types viz. an immunogen, a mitogen and a carcinogen, by following B cell responses to their presence in a mouse model system. Methods: Mice were treated with tetanus toxoid (immunogen), poke weed mitogen (typical mitogen), and benzo-α- pyrene (carcinogen) and generated B cell populations were determined in isolated splenic lymphocytes (splenocytes) by flow cytometry using specific anti-B cell marker antibodies. Flow cytometric estimation of LDL receptor (LDLR) expression, along with associated B cell markers, was also conducted. Kit based estimation of serum IgG, western blotting for LDLR estimation on total splenocytes and spectrometry for cholesterol and serum protein estimation were further undertaken. Student’s T-tests and one way ANOVA followed by the Bonferroni method were employed for statistical analysis. Results: The mitogen was found to better stimulate B cell marker expression than the immunogen, although the latter was more effective at inducing antibody production. The chemical carcinogen benzo-α-pyrene at low concentration acted potentially like a mitogen but almost zero immunity was apparent at a carcinogenic dose, with a low profile for LDLR expression and intracellular cholesterol. Conclusion: The findings in our study demonstrate an impact of concentration of BaP on generation of humoral immunity. Probably by immunosuppression through restriction of B-cell populations and associated antibodies, benzo-α-pyrene may exerts carcinogenicity. The level of cholesterol was found to be a pivotal target.