Wednesday, October 21, 2020

The Role of Microglia in Alzheimer's and Parkinson's Diseases

 

Alzheimer’s and Parkinson’s are diseases that directly impact and impair brain functions. They are degenerative and devastating illnesses that result in severe dementia in the case of Alzheimer’s and a serious degradation of motor control in the case of Parkinson’s disease. There is no cure in either case and no known biomarkers that could predict onset of these conditions. There is a type of cell resident in the brain referred to as microglia that function as amyloid phagocytes – they are cells capable of monitoring the local environment and can ingest and clear amyloid protein.

It seems that in addition to this known role, microglia may play an additional and essential role in maintaining neuronal function and homeostasis. In fact, the build up of amyloid protein in brain tissue may not be the primary cause of dementia that is the result of neuronal dysfunction and cognitive decline in neurodegenerative disease – some centenarians have been found to display good cognitive health and a build up of amyloid proteins in their brain tissue. It seems that accumulated patient data demonstrate that some aging individuals with accumulated amyloid protein show cognitive dysfunction while others do not. It is important from a therapeutic standpoint to understand the nature of this difference.

Several genetic studies indicate that microglia may provide the answer to this difference in health outcomes. According to Soyon Hong from the UK Dimentia Research Institute at University College, London, “Emerging data in developing, adult, and diseased brains collectively suggest that microglia are critical to neuronal homeostasis and health. These observations raise the question of whether, and which, microglia-neuron interactions may be impaired in Alzheimer’s disease (AD) and Parkinson’s disease (PD) to confer neurodegeneration. Insight into this question will enable the development of methods to assess and modulate microglia-neuron interactions in the aging brain and allow for a desperately needed expansion of focus from clearing amyloids alone to monitoring neuronal health in biomarker and target engagement efforts.”

It seems that in addition to their role in clearing pathogens and amyloid protein and responding to the presence of injury and dying neurons present in the environment of the brain, microglia are involved in monitoring changes in neuronal activity and the modulation of such distinct functions as memory and learning. In AD, for example, synaptic loss and dysfunction have been shown to be associated with the disruption of cognitive ability in patients. It is, therefore, of great importance to understand the underlying mechanisms that are responsible for this degenerative process and the role that microglia play in maintaining synaptic integrity.

Thursday, July 2, 2020

Evidence for the Role of Dramatically Increased Numbers of Megakaryocytes Associated with Blood Clots in COVID-19

Disturbing new evidence is emerging from the post-mortems of patients who have died from COVID-19 disease that demonstrates the presence of blood clots (thrombi). These thrombi have been shown in this extensive study to be present in major organs and systems including the lungs, heart, kidney, and brain. 

In addition, a particular cell type referred to as a megakaryocyte has also been found associated with these thrombi. Platelets (thrombocytes) are often associated with thrombi. Platelets, themselves, are generated from so-called progenitor, promegakaryocytes that reside and multiply within the bone marrow. Megakaryocytes are formed from promegakaryocytes and from these megakaryocytes are formed that ultimately break up to produce platelets (see diagram below) that are released into the blood and tissues. The fact that megakaryocytes are evidenced in higher than usual numbers in tissues such as lung, heart, kidney, and brain in patients with COVID-19 disease is a cause for concern.





According to an abstract published by Lancet – a prestigious medical publication – and authored by Amy V. Rapkiewicz, “In seven patients (four female), regardless of anticoagulation status, all autopsies demonstrated platelet-rich thrombi in the pulmonary, hepatic, renal, and cardiac microvasculature. Megakaryocytes were seen in higher than usual numbers in the lungs and heart. Two cases had thrombi in the large pulmonary arteries, where casts conformed to the anatomic location. Thrombi in the IVC were not found, but the deep leg veins were not dissected. Two cases had cardiac venous thrombosis with one case exhibiting septal myocardial infarction associated with intramyocardial venous thrombosis, without atherosclerosis.” In addition, The presence of circulating megakaryocytes on autopsy in various organs was also found and thoroughly studied.

The fact that thrombi have been found in the post-mortems of a significant number of patients who died of COVID-19 disease can account for systemic organ failure in vital organs such as lung, kidneys and heart and such a set of conditions could easily lead to subsequent death.

These data are exceedingly troubling and leaves researchers with a profound question – how does COVID-19 infection trigger such a disastrous response?

The Apparent Efficacy of the Steroid Drug Dexamethasone as Therapy for COVID-19 Patients

As medical professionals, epidemiologists, immunologists, and molecular biologists work in the midst of the COVID-19 pandemic, many aspects of the biology of this virus are being studied and as a result, new understandings are emerging.

It seems that patients with advanced disease that require intervention using a ventilator may be suffering from a hyper-active immune response. In such cases, the use of steroid-based anti-inflammatory drugs may prove efficacious.

An extremely encouraging report from the highly respected Science journal, Nature, has shown the results of a trial study using the proven steroid drug Dexamethasone.

According to the report, the results have indicated that, “An inexpensive and commonly used steroid can save the lives of people seriously ill with COVID-19, a randomized, controlled clinical trial in the United Kingdom has found. The drug, called dexamethasone, is the first shown to reduce deaths from the coronavirus that has killed more than 440,000 people globally. In the trial, it cut deaths by about one-third in patients who were on ventilators because of coronavirus infection.”

This study was expansive involving 2100 participants who received the drug at what is considered a low to moderate dose – 6 milligrams (mg.) per day for 10 consecutive days. The results from the patients were then compared to the results from 4300 patients who received standard care for COVID-19 infection.

Although the drug had no noticeable impact on patients showing no severe symptoms, the positive effect was most striking on patients on ventilators and even on those undergoing just oxygen therapy (not on ventilators) where the rate of death was reduced by 20%.

These are, indeed, encouraging results.

Tuesday, June 9, 2020

The Respiratory Syncytial Virus (RSV) and Pulmonary Disease

Respiratory Syncytial Virus Infection (RSV)According to the Center for Disease Control (CDC), “Respiratory syncytial virus, or RSV (see image below), is a common respiratory virus that usually causes mild, cold-like symptoms. RSV is an RNA virus and a member of the pneumoviridae family of viruses belonging to the genus orthopneumovirus. Most people recover in a week or two, but RSV can be serious, especially for infants and older adults.”

According the National Institutes of Health (NIH), “It is one of the most commons causes of infant viral death worldwide. In fact, RSV is the most common cause of bronchiolitis (inflammation of the small airways in the lung) and pneumonia (infection of the lungs) in children younger than 1 year of age in the United States. It is also a significant cause of respiratory illness in older adults.”
 


RSV infects cells of the mucosal lining of the respiratory tract resulting in the fusion of the infected cells to form a syncytium – a cytoplasmic mass containing a multiplicity of nuclei. It is a major cause of lower respiratory tract infections and hospital visits during infancy and childhood.

A further characterization of the virus is described by an article from the NIH, “The RNA of RSV contains 10 genes encoding 11 proteins. The envelope of the virus is formed by four proteins associated with the lipid bilayer: the matrix (M) protein, the small hydrophobic (SH) protein, and the two glycosylated surface proteins: the fusion (F) and the attachment glycoprotein (G). F and G proteins are crucial for virus infectivity and pathogenesis since the G protein is responsible for the attachment of the virus to respiratory epithelial cells, while the F protein determines the entry of the virus, by fusing viral and cellular membranes, as well as the subsequent insertion of the viral RNA into the host cell inducing the formation of the characteristic syncytia. Moreover, the F and G proteins stimulate the neutralizing antibody immune response by the host.

"The G protein is a type II glycoprotein synthesized as a polypeptide composed by 300 amino acids (depending on the viral strain) with a single C-terminal hydrophobic domain and a large number of glycan added [20]. Three types of epitopes have been identified in the G protein by murine monoclonal antibodies: (I) conserved epitopes, detectable in all viral strains; (II) group-specific epitopes, expressed only by to the same antigenic group and (III) strain-specific epitopes, that are present only in specific strains of the same antigenic group and expressed in the C-terminal hypervariable region of the G protein ectodomain [21].

"The F protein is a type I glycoprotein which has a structure comparable to the F proteins of other Pneumoviridae (e.g., metapneumovirus) and Paramyxoviridae (e.g., parainfluenza virus type 5) viruses. The F glycoprotein derives from an inactive precursor containing three hydrophobic peptides: (I) the N-terminal signal peptide, which mediates translocation of the nascent polypeptide into the lumen of the endoplasmic reticulum; (II) the transmembrane region near the C-terminus, which links F protein to the cell and viral membranes; and (III) the so-called fusion peptide, which inserts into the target cell membrane and determines the fusion process. The binding of prefusion F protein to the cell surface is followed by its activation and conformational changes, which leads to the fusion of the virion membrane with the host cell membrane.”

These details regarding the molecular biology of RSV is vitally important in establishing the mode of infection and suggests approaches to the development of suitable therapies and the creation of an effective vaccine. For example, a detailed understanding of the molecular structure of the attachment glycoprotein G as described above is of immense importance in regards to establishing methodologies to prevent attachment of the virus to host cells and thereby curtailing infection including the potential for the production of a vaccine for this purpose.

Monday, June 1, 2020

Promising News Regarding Cellular Immunity and COVID-19

As medical professionals, epidemiologists, immunologists, and molecular biologists work in the midst of the COVID-19 pandemic, many aspects of the biology of this virus are being studied and as a result, a new understanding is emerging.

As a result of these efforts some promising aspects of the immunological response have been revealed. Primary among the results of these accumulated data is the fact that individuals infected with this virus harbor T-cells – an important subset of circulating lymphocytes that play a critical role in the human immunological response – that actively target the virus and may assist in recovery. In addition, it seems that some individuals who have never been infected with COVID-19, have these cellular defenses – suggesting that this potential immunological defense arose; because they were previously infected with other coronaviruses that cause the common cold. 


Helper T Cells

These findings provide suggestive evidence that the potent T cell responses that were shown to exist may play an important role in long-term protective immunity. In addition, a more complete understanding of how the human body responds to this particular virus will undoubtedly enhance the search for an effective prophylactic vaccine.

There are more than 100 COVID-19 vaccines in various stages of development focusing on a wide rage of modalities. Within the arsenal of the so-called “adaptive” arm of the human immune system are circulating B and T lymphocytes. The B cells are responsible for the production of antibodies against particular targets. The mechanism that the immune system employs in this regard is that the B cell produced in response to exposure to the virus is to attach itself to the viral particle and prevent it from entering healthy tissue cells. This role can be exploited in the development of a vaccine. In addition, to this part of the natural arsenal against infection, there are circulating T cells that can activate and enhance B cell response. In addition to these players, there are killer T cells that actually target and destroy tissue cells that have been infected. Given the interrelationship of these defense mechanisms, there is a correlation between the severity of the disease and the strength of the T cell responses.

Shane Crotty and Alessandro Sette – immunologists from the La Jolla Institute of Immunology – determined what proteins from the surface of COVID-19 particles were most likely to stimulate immune response and subsequently exposed cells grown in culture (in-vitro) from 10 patients who had recovered from mild cases of COVID-19 to these virally-derived protein pieces. In all the samples studied, the patients carried helper T cells that were specific for the COVID-19 spike protein – the predominant protein of the viral surface that is involved in targeting tissue cells. In addition, 70% of the patients studied showed the presence of virus-specific killer T cells. Whether these patients also acquired long term immunity is not completely clear. These data, however, are very encouraging.

Although not unambiguous, these results are of great interest and suggest that an effective vaccine against COVID-19 infection needs to stimulate the production of helper T cells.

Saturday, May 2, 2020

The Mode of Action of the Anti-viral Drug Remdesivir

Currently, the United States along with many parts of the world is being severely impacted by the COVID-19 pandemic. As discussed in more detail in previous reports, COVID-19 is an RNA virus that was previously resident in another mammalian species and underwent a genetic modification that allowed it to cross species to humans – a not uncommon event among viral pathogens. The current genetic evidence is strongly suggestive that the mammalian species from where the virus originated was the bat. 

Recent clinical trials have demonstrated that the anti-viral drug remdesivir has some efficacy in the treatment of the illness brought about by COVID-19 infection. Remdesivir is a nucleoside analog (structure shown below)


Structure of Remdesivir



Inside the target host cell – lung tissue as an example – this substance functions as an inhibitor of the process that is involved in viral replication. The drug’s specific target tin RdRp (see diagram below) – the protein complex that the coronavirus uses to replicate its RNA genome.

Structure of RdRp

According to a report presented by E.S. Amirian, “After the host metabolizes remdesivir into active nucleoside triphosphate (NTP), the metabolite competes with adenosine triphosphate (ATP; the natural nucleotide normally used in this process) for incorporation into the nascent RNA strand – effectively substituting the drug metabolite for ATP. The incorporation of this substitute into the new strand results in premature termination of RNA synthesis, halting the growth of the RNA strand after a few more nucleotides are added. Although coronaviruses (CoVs) have a proofreading process that is able to detect and remove other nucleoside analogs, rendering them resistant to many of these drugs, remdesivir seems to outpace this viral proofreading activity, thus maintaining antiviral activity. Unsurprisingly, Agostini et al. reported that a mutant murine hepatitis virus (MHV) devoid of proofreading ability was more sensitive to remdesivir.”

Since viruses are prone to mutations, it is also possible that that mutations could spontaneously occur that would effectively improve proofreading and result in remdesivir resistance. In addition, it also quite possible that the effectiveness of this anti-viral drug could be due to additional factors that are currently unknown.

At the present time, in-vitro and clinical trials have yielded strong suggestive evidence that remdesivir may provide a clinical route to a therapy that could be applied to COVID-19 patients. Ongoing studies are also investigating the possibility of finding additional drugs that could provide a synergistic effect to further improve positive outcomes.

This line of investigation together with a fast-track search for an effective vaccine may ultimately safe countless lives worldwide. These scientific investigations highlight the intrinsic and inestimable value that the ongoing scientific studies contribute to humanity and its future.

Saturday, April 11, 2020

NIH Clinical Trial of Investigational Vaccine for COVID-19 Begins

"The following article has been take from the National Institutes of Health (NIH) website: http://www.nih.gov describing a study enrolling Seattle-based healthy adult volunteers. 

The image below shows a spike protein of SARS-CoV-2—also known as 2019-nCoV (COVID-19). The spike protein enables the virus to enter and infect human cells. On the virus model, the virus surface is covered with spike proteins that enable the virus to enter and infect human cells. For more information, visit NIH




"A Phase 1 clinical trial evaluating an investigational vaccine designed to protect against coronavirus disease 2019 (COVID-19) has begun at Kaiser Permanente Washington Health Research Institute (KPWHRI) in Seattle. The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, is funding the trial. KPWHRI is part of NIAID’s Infectious Diseases Clinical Research Consortium. The open-label trial will enroll 45 healthy adult volunteers ages 18 to 55 years over approximately 6 weeks. The first participant received the investigational vaccine today.

"The study is evaluating different doses of the experimental vaccine for safety and its ability to induce an immune response in participants. This is the first of multiple steps in the clinical trial process for evaluating the potential benefit of the vaccine.

"The vaccine is called mRNA-1273 and was developed by NIAID scientists and their collaborators at the biotechnology company Moderna, Inc., based in Cambridge, Massachusetts. The Coalition for Epidemic Preparedness Innovations (CEPI) supported the manufacturing of the vaccine candidate for the Phase 1 clinical trial.

'Finding a safe and effective vaccine to prevent infection with SARS-CoV-2 is an urgent public health priority,' said NIAID Director Anthony S. Fauci, M.D. 'This Phase 1 study, launched in record speed, is an important first step toward achieving that goal.'

"Infection with SARS-CoV-2, the virus that causes COVID-19, can cause a mild to severe respiratory illness and include symptoms of fever, cough and shortness of breath. COVID-19 cases were first identified in December 2019 in Wuhan, Hubei Province, China. As of March 15, 2020, the World Health Organization (WHO) has reported 153,517 cases of COVID-19 and 5,735 deaths worldwide. More than 2,800 confirmed COVID-19 cases and 58 deaths have been reported in the United States as of March 15, according to the Centers for Disease Control and Prevention (CDC).

"Currently, no approved vaccines exist to prevent infection with SARS-CoV-2.

"The investigational vaccine was developed using a genetic platform called mRNA (messenger RNA). The investigational vaccine directs the body’s cells to express a virus protein that it is hoped will elicit a robust immune response. The mRNA-1273 vaccine has shown promise in animal models, and this is the first trial to examine it in humans.

"Scientists at NIAID’s Vaccine Research Center (VRC) and Moderna were able to quickly develop mRNA-1273 because of prior studies of related coronaviruses that cause severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). Coronaviruses are spherical and have spikes protruding from their surface, giving the particles a crown-like appearance. The spike binds to human cells, allowing the virus to gain entry. VRC and Moderna scientists already were working on an investigational MERS vaccine targeting the spike, which provided a head start for developing a vaccine candidate to protect against COVID-19. Once the genetic information of SARS-CoV-2 became available, the scientists quickly selected a sequence to express the stabilized spike protein of the virus in the existing mRNA platform.

"The Phase 1 trial is led by Lisa A. Jackson, M.D., senior investigator at KPWHRI. Study participants will receive two doses of the vaccine via intramuscular injection in the upper arm approximately 28 days apart. Each participant will be assigned to receive a 25 microgram (mcg), 100 mcg or 250 mcg dose at both vaccinations, with 15 people in each dose cohort. The first four participants will receive one injection with the low dose, and the next four participants will receive the 100 mcg dose. Investigators will review safety data before vaccinating the remaining participants in the 25 and 100 mcg dose groups and before participants receive their second vaccinations. Another safety review will be done before participants are enrolled in the 250 mcg cohort.

"Participants will be asked to return to the clinic for follow-up visits between vaccinations and for additional visits across the span of a year after the second shot. Clinicians will monitor participants for common vaccination symptoms, such as soreness at the injection site or fever as well as any other medical issues. A protocol team will meet regularly to review safety data, and a safety monitoring committee will also periodically review trial data and advise NIAID. Participants also will be asked to provide blood samples at specified time points, which investigators will test in the laboratory to detect and measure the immune response to the experimental vaccine.

“This work is critical to national efforts to respond to the threat of this emerging virus,” Dr. Jackson said. “We are prepared to conduct this important trial because of our experience as an NIH clinical trials center since 2007.”

"Adults in the Seattle area who are interested in joining this study should visit https://corona.kpwashingtonresearch.org. For more information about the study, visit ClinicalTrials.gov and search identifier NCT04283461.

"NIAID conducts and supports research — at NIH, throughout the United States, and worldwide — to study the causes of infectious and immune-mediated diseases, and to develop better means of preventing, diagnosing and treating these illnesses. News releases, fact sheets and other NIAID-related materials are available on the NIAID website.

"About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.

"Adults in the Seattle area who are interested in joining this study should visit https://corona.kpwashingtonresearch.org/. People who live outside of this region will not be eligible to participate in this trial."

The mode of action of mRNA vaccines is to introduce a messenger RNA (mRNA) into the individual recipient that codes for the production of a unique protein that is part of the structure of the pathogen being targeted. In this case the pathogen is COVID-19 and the protein is referred to as spike (see image above). Once spike is made by the individual vaccinated, that should alert the immune system to recognize an essential protein on COVID 19 and prepares the body if and when it is actually exposed to the virus. This methodology would obviate the need to introduce a weakened (attenuated) form of COVID-19 as part of a vaccine.  This kind of approach holds a lot of promise.