In Search of New Classes of Antibiotics

Over the history of medicine, the development of antibiotics (1930 – 1980) to combat virulent and dangerous infections has saved countless lives and helped avoid the onset of dangerous pandemics.  The use of these antibiotics has been of immense value in increasing the longevity of human populations.

Antibiotics currently fit into five classes as described in the following table –

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.

However, no new classes of antibiotics have been developed since 1980 and the overuse of the standard antibiotics has led to the insidious development of antibiotic –resistant strains of disease like tuberculosis (TB) and gonorrhea.  From a public health perspective, it is of enormous importance to encourage the development of new classes of antibiotics with unique modes of action.

Nature of the Resistance of Flavivirus Infection to Host Cell Defenses

Flaviviruses (FVs) represent a family of viral pathogens responsible for human life-threatening diseases such as Dengue Fever, West Nile, Yellow Fever and Japanese Encephalitis.   The infectious agent within this family of viruses is single-stranded RNA.  During the process of infection (through arthropod vectors), the viral genome (gRNA) is successfully replicated and  subgenomic flaviviral  RNAs (sfRNAs) are also produced.  In animal studies, it has been demonstrated that these sfRNAs are an integral part of the disease process.  It is interesting to note that these sfRNAs are produced as a result of the incomplete degradation of gRNA by the host-derived exonuclease Xm1 – an enzyme that is a part of the host cell defense against infection.  In this scenario, host cell defenses inadvertently play a crucial role in producing disease.

This resistance to complete degradation of gRNA by Xm1 has been shown to be due to specific RNA sequences that are referred to as Xm1-resistant RNAs (xrRNAs).  It is therefore of interest to more fully understand the molecular structure of xrRNAs and, therefore, elucidate the nature of the resistance to the action of Xm1.

Dr. Erich G. Chapman and his colleagues at the Department of Biochemistry and Molecular Genetics, School of Medicine, University of Colorado at Denver focused their research efforts on establishing the unique and precise structural aspects of xrRNAs  that make them impervious  to Xm1-mediated degradation.

As a result of their extensive analysis they were able to show that the three-dimensional structure of xrRNAs consist of a “ringlike” conformation that prevents Xm1 from breaking down sfRNAs.  In addition, the investigators purposefully disrupted this structure and effectively prevented the formation of sfRNAs during infection.  This is an important finding; for, it helps clarify the mechanism of FV infections that impact many individuals throughout the world.

Therapeutic Cloning

In April of 2014, a major breakthrough was established in human stem cell research.  In that month two laboratories independently reported the successful production of human embryonic stem (ES) cells derived from skin cells cultured in the laboratory ( in-vitro).  This a significant achievement in that an application of this technique could be exceedingly useful in the production of replacement tissues in-vitro for the treatment of such diseases as  juvenile (type 1)diabetes and Parkinson’s disease – both of which arise from the precipitous loss of the cells required to manufacture insulin and dopamine, respectively.  The added benefit of such an approach is that since the cells can be derived from the patient being treated, graft rejection is no longer an issue.

The cloning technique that was employed is referred to as somatic cell nuclear transfer (SCNT); an analogous method was used to clone the now famous sheep, Dolly.  It was subsequently applied to cloning cattle, mice dogs and other animals.  There is no desire among members of the scientific community to apply this approach to cloning humans but rather to produce early-stage human embryos from which ES cells could be derived.   Heretofore, human cells have been problematic in regards to cloning.

Dr. Dong Ryul Lee and his colleagues at CHA University in Seoul, Korea successfully created human ES cells from the skin cells of two individuals – men ranging in ages from 35 to 75 years old.  Later in April of the same year, Dr. Dieter Egli and his collaborators from the New York Stem Cell Foundation (NYSCF) Research Institute used the skin cells of a young woman patient suffering from type 1 diabetes to also produce ES cells and then induced these cells to become insulin-producing cells.  Following this momentous result, the investigative team then introduced these insulin-producing  cells into experimental mice where it was shown that the hormone insulin was made in-vivo.  This latter finding has yet to be published.

The overall technique that was employed in Egli’s laboratory is briefly described below –

·         DNA is removed from an unfertilized human egg cell (oocyte)

·         The DNA from skin cells grown in-vitro from a patient with type 1 diabetes is transferred to the oocyte that had its own DNA removed

·         If the transfer is successful, the oocyte begins to divide

·         At a very early point in cell division – the Blastocyst stage – ES cells are harvested

·         Finally, these cells are coaxed into differentiating into insulin-producing pancreatic cells.

These results are very exciting; however, the possible application to human disease faces considerable obstacles that need to be addressed.  Nonetheless, it is a significant step in the goal to successfully treat implacable diseases such as type 1 diabetes and Parkinson’s through tissue –replacement therapies. 

Antibiotic Treatment for Yaws – A Plan to Eradicate the Disease

Yaws is an infectious disease that is prevalent among human populations in the tropical regions.  It is a disfiguring ailment that impacts hundreds of thousands of individuals.   There are not many fatalities associated with yaws; however, it produces considerable suffering among those afflicted, especially children.  The primary symptoms include serious skin ulcers especially on the face, back, buttocks and legs.  It has been reported that approximately 100,000 new cases show up every year, of which 75% are children.  Although most suffers heal over time with no chronic side effects, about 10% suffer from erosion of connective tissues including cartilage and bone.

The pathogen responsible for yaws is Treponema pallidum - an organism closely related to the infectious agent that causes syphilis.  However, unlike syphilis, yaws is not sexually transmitted.  Yaws is readily treated by the use of antibiotics.  An attempt was made in 1952 to completely eradicate this disease using benzathine penicillin in over 46 countries.  As a result of this intensive effort, disease incidence had dropped by 95 percent, but by the 1970s, the disease began to return and ultimately reached current levels.

In 2012, a new plan has emerged, sponsored by the World Health Organization (WHO), to eradicate the disease – referred to as the Morges Plan.  The ambitious strategy involved is to use the relatively inexpensive antibiotic azithromycin requiring only one oral dose.  In addition to administering this drug to those individuals infected, the plan is to include at least 90% of the population in the infected areas.  This strategy is designed to treat not only those individuals who are clearly ill but also those with latent infection and who are asymptomatic.

Epidemiologists are hopeful that this scheme might prove successful, but are also aware of the many obstacles that have to be overcome including the magnitude of the administrative task involved, the scope of the project and its cost. 

The Role of Dopamine Deficiency in Obesity

Dopamine, a potent neural transmitter found in the human brain, has been implicated in a variety of reward circuits including eating.  It has been well established that the production of dopamine in the dorsal striatum of the brain markedly increases during feeding in both rodents and humans.  Controlled levels of dopamine production are also required for normal eating behavior.  These finding are consistent with the known role that dopamine plays in the reward circuitry of the brain. 

Given this critical role played by dopamine in relation to eating behavior, it has been suggested that overeating may be a compensation for a diminished function in regard to the reward circuitry dependent upon dopamine levels.  In fact, dopamine receptor deficiency has been reported in studies involving obese patients.  This is certainly consistent with significantly reduced response to food stimuli in individuals suffering from obesity.  Additionally, rats that were purposefully depleted of dopamine receptors demonstrated obsessive feeding behavior.

The physiological mechanism linking incessant high-fat intake to dopamine deficiency has been unclear.   Dr. Luis A. Tellez and his colleagues at the John B Pierce Laboratory in New Haven, CT focused their research in an attempt to elucidate the physiological mechanism linking obesity and dopamine levels in the brain.  In their experimental approach, they administered oleoylethanolamine to mice fed a diet rich in fat.  Oleoylethanolamine is, in fact, a lipid messenger whose production is suppressed in individuals subjected to high-fat dietary intake.  Upon administration of this lipid messenger, the experimental mice demonstrated increased levels of dopamine release.   Exposure of these mice to oleoylethanolamine also reinstated normal eating habits.

From these data, the authors of this report concluded that high-fat dietary intake as evidence of gastrointestinal malfunction seems to play a pivotal role in dopamine deficiency and, most importantly, restoring gut-related lipid messenger may  increase the reward feedback mechanism in regard to the intake of healthier lower-fat food.    

Mechanism of Immune Reponses Related to Allergic Airway Diseases such as Asthma

Asthma is a chronic condition that adversely impacts the airway passages. This disease presents as episodic events typified by difficulty in breathing as a result of obstruction of the airways as well as inflammatory responses. This condition is provoked by response of the immune system to allergens. The inflammatory response manifests itself by the enhanced production of interleukin-4 (IL-4), increased activity of a particular subset of T helper lymphocytes (TH2) and serum immunoglobulins. A link has also been established between proteinases – enzymes that cleave proteins, the immune Toll-like receptor 4 (TLR4) and asthma. These proteinases that have been shown to initiate TH2-mediated allergic reactions are secreted by fungi, pollen and dust mite antigens.

 A full understanding of the underlying factors that trigger asthmatic episodes would, of course, be invaluable in developing therapeutic strategies to treat this illness. Dr. Valentine Ongeri Millien and colleagues from the Translational and Molecular Medicine Program at Baylor College of Medicine at Houston Texas have made some important discoveries in this light. The research efforts of this investigative team have established that airway- derived proteinases trigger allergic disease and innate immunity against fungal infection. Furthermore, they have shown that these particular outcomes were a direct result of the breakdown of fibrinogen, an essential clotting factor, by these proteinases. It is the products of this breakdown that bind to TLR4 on both epithelial cells that line the airways and to macrophages – a type of circulating cell of the immune system that has the role of ingesting invading infectious agents. From these results, it seems apparent that inflammation of the airways that is characteristic of asthma is a direct result of the immune antifungal defense strategy.

The Elucidation of this mechanism may prove to be invaluable in terms of developing therapeutic strategies for the treatment of allergen-induced pulmonary diseases such as asthma. In fact, this group when on to show that the use of hirudin, a drug that functions as a potent protease inhibitor, can lessen the severity of allergic lung disease. This may prove to be a very important finding.

The Role of Pathogens in Tumorigenesis

The Role of Pathogens in Tumorigenesis