How the Ebola Virus Gains Entry into its Target Cell

Many viruses that have been studied require a specific cell surface receptor in order to gain entry to their target cell(s).  To this date, no specific cell surface receptor has been identified for the Ebola virus.   The Ebola virus is responsible for a highly infectious disease referred to as hemorrhagic fever in humans.  However, important strides have been made in understanding the mechanism of Ebola virus infection.

Once the Ebola virus successfully binds specifically to its host cell, it is engulfed by a process known as micropinocytosis that encapsulates the virus in a cell organelle referred to as endosome – a membrane-bound vesicle.  While within this environment, the virus’ surface glycoproteins are cleaved through the action of a protease (an enzyme that degrades proteins).

The process by which the virus is ultimately released from the endosome into the intracellular environment remains to be completely characterized.  However Dr. Yasuteru Sakurai and his colleagues from the Texas Biomedical Research Institute in San Antonio Texas have elucidated an important step in this process.  Through exhaustive and painstaking studies they have shown that endosomal calcium channels – two-pore channels (TPCs) are necessary for the release of the Ebola virus from the endosome that holds it.

More importantly, from a therapeutic standpoint, the investigators used a number of research techniques to disrupt TPC function including gene knockout – where the gene responsible for the production of TPC protein is rendered dysfunctional  - and were able to effectively disrupt virus trafficking and, thereby, prevent infection.  Finally the use of Tetrandrine -  a calcium channel blocker possessing anti-inflammatory, immunologic and antiallergenic effects - inhibited infection of human macrophages; these cells have been shown to be the primary target of the Ebola virus in an in-vitro setting.

These are important findings for a number of reasons.  They demonstrate that TPC-related proteins play an essential role in the Ebola virus infection process.  In addition, their preliminary results using Tetrandrine illustrate how this information may be used to develop effective strategies against hemorrhagic fever. 

Revolutionary Advances in Genomic Engineering

The area of study encompassed by genomic engineering has made so many technological advances that the modification of genomes – including the human genome – has rapidly come within the reach of those adequately trained in the techniques and methodologies of molecular biology.

There have been two extraordinary technological advances in the field of molecular biology that have made the ability to modify specific genes a reality.  First of all, the complete sequencing of the human genome in 2003 has made it possible to identify the genes implicated in many cellular and disease processes.  Secondly, the use of cluster regularly interspaced short palindromic repeats (CRISPRs) together with Cas9 has made it possible to specifically engineer the modification of literally any targeted gene.   Cas genes code for proteins that are directly related to CRISPR activity.

The CRISPR-Cas9 system was discovered in prokaryotic cells, bacteria for example.  It has been shown that this system provides protection from foreign genetic elements such as plasmids and phages- phages are viruses that target prokaryotic cells - that often attack prokaryotic cells.  This system has been likened to acquired immunity found in more complex organisms such as human.

CRISPRs are found in approximately 40% of sequenced bacteria genomes.  CRISPRs are, in fact, composed of segments of prokaryotic DNA made up of short repetitions of base sequences followed by segments of so-called, "spacer DNA."   These spacer segments seem to result from the cell’s previous exposure to an invading organism and serve as a template for the production of RNA transcription products that interact with Cas gene – related proteins in a system designed to inactivate invading phages or plasmids.

Since 2013, the CRISPR-Cas9 system has been adapted for use in the specific editing of genes.  When a specifically engineered CRISPR-Cas9 system is introduced into a host mammalian cell such as human it can alter a target gene in a very specific way.  This was amply demonstrated when researches at MIT effectively used this approach to effectively cure mice of a rare genetic liver disorder.   

This is such a powerful technique carrying with it such profound implications for the future of genetic engineering that in January of 2015 a group of those scientists intimately associated with these studies met in Napa, California at the Innovative Genomics Initiative (IGI) Forum on Bioethics to discuss the scientific, medical, legal and ethical implications of their work.

A Possible New Treatment Option for Patients with Acute Myeloid Leukemia (AML)

AML is the most common form of adult leukemia accounting for some twenty-five percent of adult patients with leukemia.  The standard protocol for treatment involves a shot-gun approach using non- selective chemotherapy to induce successful remission.   Although this clinical methodology has shown to be effective for most patients, other avenues of treatment are needed for those who prove refractory to the standard approach and to those patients who cannot endure high dose chemotherapy.

The biology of cancer cells has progressed dramatically since the complete sequencing of the human genome.  As a result, it has been clearly established that cancer is the result of genetic mutations that involve either/or those genes referred to as proto-oncogenes involved in normal cell division and tumor suppressor genes involved in the normal suppression of cell division The new era of cancer treatment involves the development of methodologies to specifically target these mutations either by developing specialized drugs to target these changes or mobilizing the immune system through targeted immunotherapy.

Dr. Anuradha Illendula and his colleagues from the Department of Molecular Physiology and Biological Physics at the University of Virginia in Charlottesville, using the mouse animal model,  have developed a small molecule referred to as AI-10-49 that effectively binds to a transcription factor subunit referred to as core bind factor β (CBFβ).

Molecular Structure of AI-10-49 -

  

   

These investigators were able to show that the use of A!-10-49 not only prolonged the survival of mice transplanted with leukemic cells without any observable toxic effects but was also able to inhibit the proliferation of a sub-type of human AML cells grown in culture.  These findings are of particular importance for this approach may serves as a model for development of drugs specifically targeting "uninhibited cell division resulting from genetically altered transcription factor function."

Extreme Winter Weather in the Lower Latitudes and Warming of the Arctic Ocean

For the past two winters, the continental United States has experienced harsh weather conditions with unusual amounts of precipitation in the form of snow.  Meteorologists have established that arctic-born weather has been directed to the Northeastern, Midwestern and even Southeastern continental United States as a result of a shift in the direction, depth and pattern of the jet stream described as “wavy.”

Dr. Jennifer Francis, a climatologist, and her colleagues at Rutgers University in collaboration with Dr. Steven Vavrus from the University of Wisconsin at Madison have published data establishing a connection between warming in the Arctic Ocean and the extreme winter weather in the lower latitudes. 

  

Ordinarily sea ice exerts an influence on global temperature by its ability to reflect back solar radiation into space on account of its whiteness through what is referred to as the albedo effect.  However, as a result of the gradual warming of the planet due to the accumulation of greenhouse gases, the temperature in the Arctic has increased at twice the rate as the rest of the earth.   This increased temperature is accelerating the melting of Artic sea ice.  As this sea ice melts, it reduces the albedo effect and results in increased warming and therefore the further melting of sea ice.  This cycle of increased warming is referred to as negative feedback.

 

It seems that this warming trend in the Arctic has disrupted normal climate conditions in the following way - cold air that is usually contained within the Arctic region by so-called “polar vortex winds” has moved southward into the mid-latitudes as a result of the high pressure that is a direct consequence of the enhanced melting of the sea ice.   Accordingly, the lower latitudes have experienced unusually extreme winter weather.

If this explanation is proven to be correct for seasonal aberrations in weather in the lower latitudes, then these changes would suggest a permanent alteration in weather patterns for the regions impacted.

The Frequency of Various Types of Cancers Explained

For more than a century, the medical world has known that certain kinds of cancers are far more prevalent than others.   The question, of course, that comes to mind is why is this so?  There has been much speculation concerning the answer to this important question.

Drs. Cristian Tomasetti and Bert Vogelstein form the Division of Biostatistics and Bioinformatics at the Department of Oncology at the Sidney Kimmel Cancer Center at John Hopkins University School of Medicine and the Department of Biostatistics at the John Hopkins Bloomberg School of Public Health in Baltimore MD conducted an exhaustive statistical analysis of patient data.  The following represents a summary of their results.

 The table below shows the relative lifetime risk of a number of different types of cancers.

Cancer by Tissue Type	Percentage of Lifetime Risk of Cancer
Lung	6.9
Thyroid	1.08
Brain and Nervous System	.6
Pelvic Bone	.003
Laryngeal Cartilage	.00072

Although some of these differences can be associated with certain risk factors such a smoking and alcohol use, ultraviolet light exposure and human papilloma virus (HPV) infection, such etiology only applies to specific populations.  In addition, environmental factors cannot explain the wide differences found in lifetime risks involving cancers of the alimentary tract – esophagus .51%, large intestine 4 82%, small intestine .20% and stomach .86%.

    

Interestingly, cancers of small intestine are three times less common than brain cancers even though the epithelial cells of the small intestine are far more exposed to environmentally dangerous substances than brain cells that are protected by the so-called blood –brain barrier.

Another factor that is often cited to explain differences in risk of various cancers is inherited genetic variation.  The statistical data shows, however, that this risk factor accounts for only between 5 and 10 percent of the etiology of cancer.

Therefore, there must be another cause that accounts for the wide variability shown in the table above.  The investigators went on to demonstrate that a very close correlation (81%) exists between the lifetime risk for a given cancer and the, “total number of divisions of the normal self-renewing cells (stem cells) maintaining the tissue’s homeostasis.”   From this perspective, it is the probability of sustaining deleterious random genetic mutations that transform a cell into a cancerous state that increases with the number of cell divisions of tissue-specific stem cells.

 

This may prove to be a very important finding in regards to understanding the etiology of cancer. 

A Promising New Class of Antibiotics

As mentioned in an earlier report, the current classes of antibiotics (See table below) being utilized to fight infection are no longer effective in regards to certain diseases, especially since many pathogenic organisms have developed an effective immunity against them. 

Classes of Antibiotics Currently in Use -

Class	Mode of Action	Example
Β-lactam	Inhibits bacterial cell wall biosynthesis	Penicillin
Aminoglycoside	Inhibits protein synthesis in Gram-negative bacteria  such as Streptomyces griseus	Neomycin
Macrolide	Inhibits protein synthesis in Gram-positive bacteria such as Streptococcus pneumoniae by preferentially binding to the  50S component of the bacterial ribosome	Erythromycin
Tetracycline	Inhbits protein synthesis by preferentially binding to the  30S component of the bacterial ribosome	Tetracycline
Fluoroquinolone	Irreversibly binds to and inactivates key enzymes that maintain bacterial DNA	Norfloxacin

Note: Antibiotics are of no use in treating viral infections since the biology of the virus is markedly different than that of bacterial agents.

There is, however, some basis for renewed optimism in regard to this global public health concern.  Most antibiotics currently being utilized are natural products produced by cultured soil micro-organisms.  For varied reasons, some economic in nature, the synthetic production of antibiotics has been unable to adequately supply new and effective classes of antibiotics.  Uncultured bacteria, on the other hand, although large in number, have been an untapped resource for new antibiotics.

Dr  Losee Ling and his colleagues at the Novobiotic Team,  NovoBiotic Pharmaceuticals, LLC.  767C Concord Ave, Cambridge, MA have developed specific methodologies to grow uncultured organisms thereby opening up a vast new resource.  As a result of an exhausted screening of uncultured bacteria,  they discovered a new antibiotic that they have called teixobactin (see the structure below).

Teixobactin acts by inhibiting cell wall synthesis.  It  accomplishes this by binding to highly conserved constituents of the bacterial cell wall and, in this way, effectively interfering with cell wall synthesis resulting in bacterial cell death.  The investigators were able to demonstrate that no resistant strains were produced when teixobactin was used to undermine the growth of both Staphylococcus aureus and Mycobacterium tuberculosis- pathogens responsible for Staphylococcus infections and Tuberculosis, respectively .   According to Dr. Ling, “The properties of this compound suggest a path towards developing antibiotics that are likely to avoid development of resistance.”

This is a very exciting development in regards to global public health.

How Cells Overcome Oxidative Stress

At some point in the evolutionary past, living organisms began to use molecular oxygen in cellular respiratory metabolic pathways and therefore gained access to increased amounts of energy to support life.  This was especially important in the evolution of complex multi-cellular organisms.    Along with this new capability came the issue of dealing with the harmful by-products of oxidative respiration.  The most detrimental of these are reactive oxygen species (ROS) that are produced in the mitochondria – those organelles that generate most of the energy required for cellular processes within eukaryotic cells.

ROS can produce oxidative damage and have been shown to be involved in a number of serious human pathologies including Alzheimer’s, cancer, diabetes and Parkinson’s.  These reactive molecular species are also involved in cellular senescence and cell death.

In response to this threat - referred to as oxidative stress - cells have developed mechanisms designed to minimize the damage.   the ROS defense system localized in the mitochondria transforms highly reactive and potentially destructive superoxide anions (O₂^--)  to hydrogen peroxide (H₂O₂) that is subsequently broken down to water by ubiquitous peroxidase enzymes that use reduced glutathione (GSH) as their substrate.  Given the essential role that GSH plays in this mechanism, it is crucial that appropriate levels of this substance are maintained.   A key enzyme that is employed in providing high levels of GSH is the nicotinamide nucleotide transhydrogenase (TH) enzyme.

Dr. Leung and his colleagues at the Department of Integrative Structure and Computational Biology at the Scripps Research Institute in La Jolla CA studied the three dimensional structure of TH and elucidated its mechanism of action.  This kind of information is important in so far as it increases the overall understanding of how cells cope with oxidative stress.