Vitamin-B 12 (Cyanocobalamin)-An Update

Vitamin-B 12 (Cyanocobalamin)-An Update

Cyanocobalamin (B12) is a cobalt-containing coordination compound produced by intestinal micro-organisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. INTRINSIC FACTOR is important for the assimilation of vitamin B 12.

Vitamin B12 may be found in liver, kidney, fish, and fortified milk and helps convert folic acid into its active form. Vitamin B12 is essential to synthesize DNA and promotes cellular division and is required for hematopoiesis (development of red blood cells in bone marrow) and to maintain the integrity of the nervous system. 

Vitamin B12 is absorbed in the intestine with the aid of an intrinsic factor produced by gastric parietal cells. Once absorbed, vitamin B12 binds to the transcobalamin II protein and is then transferred to tissues. Vitamin B12 is stored in the liver for up to three years during which time it is slowly excreted in urine. 

Vitamin B12 deficiency is common in patients who are strict vegetarians and in patients who have malaborption syndromes (cancer, celiac disease), gastrectomy, Crohn’s disease, and liver and kidney diseases. Vitamin B12 (cyanocobalmin) administered both orally and parenterally is equally effective in treating anemia from vitamin B12 deficiency. 

However, use of parenteral cyanacobalamin is the most common method of vitamin B12 replacement because it may be more reliable and practical. Subcutaneous or intramuscular administration is appropriate. Vitamin B12 is absorbed completely following parenteral administration, whereas oral vitamin B12 is absorbed poorly via the GI tract. 

Furthermore, use of parenteral vitamin B12 to treat megaloblastic anemia may circumvent the need to perform a Schilling test to diagnose lack of intrinsic factor. A typical cyanocobalmin dosing regimen is 800 to 1000 mcg/day for 1 to 2 weeks, followed by 100 to 1000 mcg/day every week until the Hgb/Hct normalizes and maintenance of 100 to 1000 mcg monthly for life. However, a number of dosing regimens exist. In addition, a number of oral vitamin B12 preparations are available, including many over-the-counter formulations. 

A common oral dosing regimen is from 1000 to 2000 mcg/day. If parenteral cyanocobalmin is used initially, oral vitamin B12 can be useful as maintenance therapy. Typically, the response to therapy is quick. Neurologic symptoms and megaloblastic cells disappear within a few days, and hemoglobin levels increase after a week of therapy.Vitamin B12 generally is well tolerated and exhibits minimal adverse effects. Injection-site pain, pruritus, rash, and diarrhea have been reported. Drug interactions have been observed with omeprazole and ascorbic acid that decrease oral absorption.

   

RECOMBINANT DNA TECHNOLOGY

Recombinant DNA technology, joining together of DNA molecules from two different species that are inserted into a host organism to produce new genetic combinations that are of value to science, medicine, agriculture, and industry. Since the focus of all genetics is the gene, the fundamental goal of laboratory geneticists is to isolate, characterize, and manipulate genes. Although it is relatively easy to isolate a sample of DNA from a collection of cells, finding a specific gene within this DNA sample can be compared to finding a needle in a haystack. Consider the fact that each human cell contains approximately 2 metres (6 feet) of DNA. Therefore, a small tissue sample will contain many kilometres of DNA. However, recombinant DNA technology has made it possible to isolate one gene or any other segment of DNA, enabling researchers to determine its nucleotide sequence, study its transcripts, mutate it in highly specific ways, and reinsert the modified sequence into a living organism.

DNA Cloning

In biology a clone is a group of individual cells or organisms descended from one progenitor. This means that the members of a clone are genetically identical, because cell replication produces identical daughter cells each time. The use of the word clone has been extended to recombinant DNA technology, which has provided scientists with the ability to produce many copies of a single fragment of DNA, such as a gene, creating identical copies that constitute a DNA clone. In practice the procedure is carried out by inserting a DNA fragment into a small DNA molecule and then allowing this molecule to replicate inside a simple living cell such as a bacterium. The small replicating molecule is called a DNA vector (carrier). The most commonly used vectors are plasmids (circular DNA molecules that originated from bacteria), viruses, and yeast cells. Plasmids are not a part of the main cellular genome, but they can carry genes that provide the host cell with useful properties, such as drug resistance, mating ability, and toxin production. They are small enough to be conveniently manipulated experimentally, and, furthermore, they will carry extra DNA that is spliced into them.

Creating the clone

The steps in cloning are as follows. DNA is extracted from the organism under study and is cut into small fragments of a size suitable for cloning. Most often this is achieved by cleaving the DNA with a restriction enzyme. Restriction enzymes are extracted from several different species and strains of bacteria, in which they act as defense mechanisms against viruses. They can be thought of as “molecular scissors,” cutting the DNA at specific target sequences. The most useful restriction enzymes make staggered cuts; that is, they leave a single-stranded overhang at the site of cleavage. These overhangs are very useful in cloning because the nucleotides will pair with other overhangs made using the same restriction enzyme. So, if the donor DNA and the vector DNA are both cut with the same enzyme, there is a strong possibility that the donor fragments and the cut vector will splice together because of the complementary overhangs. The resulting molecule is called recombinant DNA. It is recombinant in the sense that it is composed of DNA from two different sources. Thus, it is a type of DNA that would be impossible naturally and is an artifact created by DNA technology.

Isolating the clone

In general, cloning is undertaken in order to obtain the clone of one particular gene or DNA sequence of interest. The next step after cloning, therefore, is to find and isolate that clone among other members of the library. If the library encompasses the whole genome of an organism, then somewhere within that library will be the desired clone. There are several ways of finding it, depending on the specific gene concerned. Most commonly, a cloned DNA segment that shows homology to the sought gene is used as a probe. For example, if a mouse gene has already been cloned, then that clone can be used to find the equivalent human clone from a human genomic library. Bacterial colonies constituting a library are grown in a collection of Petri dishes. Then a porous membrane is laid over the surface of each plate, and cells adhere to the membrane. The cells are ruptured, and DNA is separated into single strands—all on the membrane. The probe is also separated into single strands and labeled, often with radioactive phosphorus. A solution of the radioactive probe is then used to bathe the membrane. The single-stranded probe DNA will adhere only to the DNA of the clone that contains the equivalent gene. The membrane is dried and placed against a sheet of radiation-sensitive film, and somewhere on the films a black spot will appear, announcing the presence and location of the desired clone. The clone can then be retrieved from the original Petri dishes.

DNA sequencing

Once a segment of DNA has been cloned, its nucleotide sequence can be determined. The nucleotide sequence is the most fundamental level of knowledge of a gene or genome. It is the blueprint that contains the instructions for building an organism, and no understanding of genetic function or evolution could be complete without obtaining this information.

Uses
Knowledge of the sequence of a DNA segment has many uses, and some examples follow. First, it can be used to find genes, segments of DNA that code for a specific protein or phenotype. If a region of DNA has been sequenced, it can be screened for characteristic features of genes. For example, open reading frames (ORFs)—long sequences that begin with a start codon (three adjacent nucleotides; the sequence of a codon dictates amino acid production) and are uninterrupted by stop codons (except for one at their termination)—suggest a protein-coding region. Also, human genes are generally adjacent to so-called CpG islands—clusters of cytosine and guanine, two of the nucleotides that make up DNA. If a gene with a known phenotype (such as a disease gene in humans) is known to be in the chromosomal region sequenced, then unassigned genes in the region will become candidates for that function. Second, homologous DNA sequences of different organisms can be compared in order to plot evolutionary relationships both within and between species. Third, a gene sequence can be screened for functional regions. In order to determine the function of a gene, various domains can be identified that are common to proteins of similar function. For example, certain amino acid sequences within a gene are always found in proteins that span a cell membrane; such amino acid stretches are called transmembrane domains. If a transmembrane domain is found in a gene of unknown function, it suggests that the encoded protein is located in the cellular membrane. Other domains characterize DNA-binding proteins. Several public databases of DNA sequences are available for analysis by any interested individual.

Methods
The two basic sequencing approaches are the Maxam-Gilbert method, discovered by and named for American molecular biologists Allan M. Maxam and Walter Gilbert, and the Sanger method, discovered by English biochemist Frederick Sanger. In the most commonly used method, the Sanger method, DNA chains are synthesized on a template strand, but chain growth is stopped when one of four possible dideoxy nucleotides, which lack a 3′ hydroxyl group, is incorporated, thereby preventing the addition of another nucleotide. A population of nested, truncated DNA molecules results that represents each of the sites of that particular nucleotide in the template DNA. These molecules are separated in a procedure called electrophoresis, and the inferred nucleotide sequence is deduced using a computer.

Absorption of Drugs

 And

General definitions in Pharmacology

I. GENERAL DEFINITIONS

•  Pharmacology is the study of the interaction of chemicals with living systems.
•    Drugs are chemicals that act on living systems at the chemical (molecular) level.
• Medical pharmacology is the study of drugs used for the diagnosis, prevention, and treatment of disease.
• Toxicology is the study of the untoward effects of chemical agents on living systems. It is usually considered an area of pharmacology
• Pharmacodynamic properties of a drug describe the action of the drug on the body, including receptor interactions, dose-response phenomena, and mechanisms of therapeutic and toxic action.
• Pharmacokinetic properties describe the action of the body on the drug, including absorption, distribution, metabolism, and excretion. Elimination of a drug may be achieved by metabolism or by excretion.

  

  
  

THE NATURE OF DRUGS

A.    Size. The great majority of drugs lie in the range from molecular weight 100 to 1,000. Drugs in this range are large enough to allow selectivity of action and small enough to allow adequate movement within the various compartments in the body.

B.      Chemistry and reactivity. Drugs may be small, simple molecules (amino acids, simple amines, organic acids, alcohols, esters, ions, etc.), carbohydrates, lipids, or even proteins. Binding of drugs to their receptors. the specific molecules in a biologic system that mediate drug effects, is usually by noncovalent bonds (hydrogen bonds, van de Waals attractions, and ionic bonds), and less commonly by covalent bonds. Weaker, noncovalent bonds require a better fit of the drug to the receptor binding site and, usually, a reversible type of action. Very strong bonding, eg, covalent bonds, usually involves less selectivity and an irreversible interaction.

C.     Shape. The overall shape of a drug molecule is important for the fit of the drug to its receptor. Between a quarter and a half of all drugs in use exist as stereoisomers. In most cases the stereoisomers are chiral enantiomers. Enantiomers are mirrored image twin molecules that result from the presence of an asymmetric carbon, or in a few cases, other asymmetric atoms in their structures. Chiral enantiomers often differ in their ability to bind to and alter the function of receptors. They also can differ in their rates of elimination and in their toxicity.

PHARMACOKINETIC

Pharmacokinetics concerns the effects of the body on the administered drug. It can be pictured as the processes of absorption, distribution, and elimination. Elimination includes both metabolism and excretion. All of these processes involve movement of drug molecules through various body compartments and across the barriers separating those compartments.

 A. Absorption of Drugs. Drugs usually enter the body at sites remote from the target tissue and are carried by the circulation to the intended site of action. Before a drug can enter the bloodstream, it must be absorbed from its site of administration. The rate and efficiency of absorption differs depending on the route of administration. Common routes of administration of drugs and some of their features include:

Oral (swallowed). Maximum convenience but may be slower and less complete than parenteral (non-oral) routes. Dissolution of solid formulations (eg, tablets) must occur first. The drug must survive exposure to stomach acid. This route of administration is subject to the first pass effect (metabolism of a significant amount of drug in the gut wall and the liver, before it reaches the systemic circulation).

Sublingual (under the tongue). Permits direct absorption into the systemic venous circulation thus avoiding the first pass effect. May be fast or slow depending on the physical formulation of the product. Nitroglycerin is administered by this route in the treatment of angina.

Rectal (suppository). Same advantage as sublingual route; larger amounts are feasible. Useful for patients who cannot take oral medications (eg, because of nausea and vomiting).

Intramuscular. Absorption is sometimes faster and more complete than after oral administration. Large volumes (eg, 5 - 10 mL) may be given. Requires an injection. Generally more painful than subcutaneous injection. Vaccines are usually administered by this route.

Subcutaneous. Slower absorption than intramuscular. Large volumes are not feasible. Requires an injection. Insulin is administered by this route.

Inhalation. For respiratory diseases, this route deposits drug close to the target organ; when used for systemic administration (e.g., nicotine Susan Masters, PhD 63 in cigarettes, inhaled general anesthetics) it provides rapid absorption because of the large surface area available in the lungs.

Topical. Application to the skin or mucous membrane of the nose, throat, airway, or vagina for a local effect. It is important to note that topical drug administration can result in significant absorption of drug into the systemic circulation. Drugs used to treat asthma are usually administered this way.

Transdermal. application to the skin for systemic effect. Transdermal preparations generally are patches that stick to the skin and are worn for a number of hours or even days. To be effective by the transdermal route, drugs need to be quite lipophilic. Nicotine is available as a transdermal patch for those who are trying to stop cigarette smoking.

Intravenous. Instantaneous and complete absorption (by definition, 100%); potentially more dangerous because the systemic circulation is transiently exposed to high drug concentrations.

Microbiology

 (General principles of microbial concepts)

Microorganisms:

Microorganisms (Latin micro = small) are living beings so small (< 40 µm or 0.04 mm) that they are not visible by the naked eye. Microorganisms related to human health include certain bacteria, viruses, fungi and parasites.

Types of Microorganisms:

Microorganisms can be, according to their characteristics, divided into several groups:

• bacteria, viruses, certain fungi and parasites
• pathogenic (capable of causing disease), non-pathogenic, and opportunistic (causing disease when they have an opportunity, like in people with low immune system)
• acellular (without cell, like viruses), unicellular (bacteria, yeasts and certain parasites), or multi-cellular (molds)

 1. Bacteria

Bacteria are unicellular organisms, about few microns in size (1 micron (µm) = 1/1,000 of a millimetre), consisting of DNA, cytoplasm, structures needed for metabolism and reproduction, cell membrane, cell wall and capsule .Certain bacteria use flagella, tail-like appendages, to propel themselves.

  Bacterial structure

                                                                        

Bacteria multiply asexually by dividing into two daughter cells

                                                                

Bacteria can be divided into several groups:

• Spheres or cocci (like Staphylococcus aureus), rods or bacilli (like Lactobacillus acidophilus), spirals or spirochetes (like Treponema pallidum); bacterial shape can help in their recognizing under the microscope
• Aerobic bacteria, like Mycobacterium tuberculosis, need oxygen to thrive, while  anaerobic, like Clostsridium difficile, do not. Facultative anaerobic bacteria, like Pseudomonas aureginosa, can live in aerobic and anaerobic environment.
• Gram positive (G+) bacteria, like Streptococcus, and Gram negative (G-) bacteria, like Klebsiella
• Pathogenic and non-pathogenic bacteria

Certain bacteria can form endospores, a kind of encapsulated bunkers within a bacteria that enable vital parts of bacteria to survive in harsh conditions, like freezing or boiling water, dessication, lack of nutrients, etc. Some bacteria can survive weeks, and some millions of years in this form.

In the human body, bacteria usually cause localized infections, like pneumonia or skin infections. Bacterial infections can be diagnosed by growing a bacterial culture from a sample of infected body fluid (e.g. urine, blood), stool, discharge (e.g. sputum) or tissue (e.g. mucosal layer of the stomach). Most of bacterial infections can be successfully treated by anti-bacterial drugs – antibiotics.

Examples of bacteria pathogenic for a human are:

• Staphylococcus aureus, causing skin infections, pneumonia, and infection of the heart valves, etc.
• Streptococcus pyogenes, causing “strep throat”, cellulitis, etc.
• Neisseria gonorrheae, causing gonorrhea
• Salmonella, causing diarrhea in food poisoning
• Helicobacter pylori, causing chronic gastritis
• Mycoplasma, causing atypical pneumonia

Examples of non-pathogenic bacteria:

• Staphylococcus epidermidis, a part of normal skin flora
• Lactobacillus acidophilus, a part of normal intestinal flora

Examples of opportunistic bacteria:

• Certain intestinal bacteria, like Escherichia coli and Enterobacter live in the human intestine without causing any symptoms, but in a person with lowered immune system they may overgrow and cause a bowel infection.

2. Viruses

Viruses are simple microorganisms, containing only DNA or RNA molecule and capsule. They cannot survive outside the host for long periods, so they are mainly transmitted by blood-to-blood or stool-to-mouth route. In the human body, they have to invade the cells to multiply

Virus cycle: entry of herpes simplex virus (HSV) into the cell (on the left), multiplying within the cell and release (right) from the cell 

Viruses usually cause systemic infections, affecting the whole body. Examples of viruses, pathogenic for a human:

• Rhinovirus, causing common cold
• Influenzavirus, causing flu, bird flu, swine flu
• Herpes simplex virus causing herpes labialis (cold sore) or herpes genitalis
• HIV, causing AIDS
• Ebolavirus, causing hemorrhagic fever

Viruses can be diagnosed by finding specific antibodies in the sample of blood (serologic tests). Vaccination against several virus infections is possible; only few viral infections can be treated by anti-viral medications, though.

3. Fungi

Fungi are widely present in the environment and also on the human skin, gut and vagina.

Fungi are subdivided on the basis of their life cycles, the presence or structure of their fruiting body and the arrangement of and type of spores (reproductive or distributional cells) they produce.

The three major groups of fungi are:

·         multicellular filamentous moulds

·         macroscopic filamentous fungi that form large  fruiting bodies. Sometimes the group is referred  to as ‘mushrooms’, but the mushroom is just the part of the fungus we see above ground which is also known as the fruiting body.

·         single celled microscopic yeasts

4. Parasites

Human intestinal parasites are either one-cell organisms or intestinal worms that live in the small or large intestine and use the stool or blood from intestinal wall as a source of food.

One-cell organisms, like Giardia lamblia, also called Giardia duodenale 

 1),Cryptosporidium (crypto) and Cyclospora, utilize nutrients from the stool. They belong to a living kingdom Protozoa (Gk. protos = first; zoa = animals). They may cause inflammation of thesmall intestine thus hampering absorption of nutrients. Entamoeba hystolytica lives predominantly in the colon.

Intestinal Worms (Helminths):

Intestinal worms (helminths), like roundworms (hookworms), whipworms,  Ascaris andTrichinella), tapeworms and flukes, are few millimeters to several meters in size, they eat the bowel content or suck the blood from the intestinal wall and can cause about the same symptoms as one-cell parasites.

 

Beneficial Microorganisms

Microorganisms, like certain bacteria and yeasts, living on the human skin or in the nose, mouth, throat, small and large intestine and vagina, are part of the normal human flora; they prevent overgrowth of harmful microorganisms. Some of these microbes, when overgrow, may become pathogenic, though.

Harmful or Pathogenic Microorganisms

Pathogenic means capable of causing disease. An actual harmful effect of a microbe to the body depends on:

• Microbial virulence - a relative ability of a microbe to cause a disease; for example, a certain, highly virulent subtype of influenza virus may cause a bird flu, which is deadly in a high percent, while “usual” influenza virus is not.
• Invasion through the body’s barriers; staph bacteria might not cause any harm to a person with an intact skin, but can cause a severe infection of a skin wound.
• Amount of microbes; eating few bites of food contaminated with staph bacteria may go unnoticed, while eating the whole portion of the same food may cause a severe food poisoning.
• Body’s defense (immune) system; patients with a weak immune system, like those receiving corticosteroids, often get oral thrush (candida infection of the mouth), while otherwise healthy people do not.

 Physiology of Nervous system

The nervous system has two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The central system is the primary control center for the body and is composed of the brain and spinal cord. The peripheral system consists of a network of nerves that connects the rest of the body to the CNS.

The two systems work together to collect information from inside the body and from the environment outside it. The systems process the collected information and then dispatch instructions to the rest of the body, making it respond.

In most cases, the brain is the destination for information gathered by the rest of the nervous system. Once data arrives, the brain sorts and files it before sending out any necessary commands.

The brain is divided into many different sections, including the cerebrum and brain stem. These parts handle pieces of the brain’s overall workload, including storing and retrieving memory and making body movements smooth.

Although the brain is the control center, its job would not be possible without the spinal cord, which is the major conduit for information traveling between brain and body.

Peripheral system nerves branch from either the brain stem or the spinal cord. Each nerve is connected to a particular area of the torso or limbs and is responsible for communication to and from those regions.

The PNS can also be divided into smaller pieces: the somatic and autonomic systems. The somatic involves parts of the body a person can command at will, and the autonomic helps run involuntary functions such as pumping blood.

Information conveyed through the nervous system moves along networks of cells called neurons. These neurons can only send information one way. Those transmitting to the brain are sensory neurons; those that transmit from the brain are known as motor neurons.

The nervous system can suffer from a number of afflictions, including cancer. Other problems include multiple sclerosis, in which damaged nerves prevent signals from traveling along them, and meningitis, which causes an inflammation of the membranes surrounding the brain and spinal cord.