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Naqibullah Jogezai
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Date Posted: 03:06:01 12/23/05 Fri
Author Host/IP: ntc.net.pk/202.83.175.123
In reply to:
Naqibullah Jogezai
's message, "Re: More Information About Biotechnology" on 03:04:47 12/23/05 Fri
>>>
>>>Welcome to BioTech! Our goal is to enrich the
>public's
>>>knowledge of biology and chemistry. We aim to serve
>>>everyone from high school students to professional
>>>researchers. For more information
>>>
>>>
>>>What is "BioTech"?
>>>Located in Jinna Town Quetta at University of BUITMS,
>>>BioTech is a hybrid biology/chemistry educational
>>>resource and research tool on the World Wide Web.
>>>BioTech is intended to be a learning tool that will
>>>attract students and enrich the public's knowledge of
>>>biology issues in the world today. At the same time,
>>>BioTech is also a research tool for those already
>>>involved in the broad subject of biology. By
>providing
>>>information about resources, as well as avenues for
>>>further exploration, we intend to open the doors of
>>>biology resources to post-secondary students,
>>>researchers, and faculty.
>>>Our Mission:
>>>Our mission is to make BioTech as useful a tool to a
>>>high school student as it is to a postdoctoral
>fellow.
>>>We aim to educate those who may not have as much
>>>experience with biology and biotechnology while at
>the
>>>same time providing quick access to biology-related
>>>resources for those who are dealing with much more
>>>specific and detailed information. We do not wish to
>>>exclude anyone from this project -- we will assist
>>>those who need assistance and merely open doors for
>>>those who are interested in finding information on
>>>their own.
>>>Our Goal:
>>>Our goal is to utilize the skyrocketing success of
>the
>>>World Wide Web as a means of bringing information
>>>about the broad scope of biology into view of as many
>>>people from many educational levels as possible. We
>>>intend to educate, facilitate, inform, and direct
>>>attention to as many sources of biology-related
>>>information as possible.Biotechnology:
>>A new era for plant pathology
>>and plant protection.
>>
>>Plant biotechnology ushers in a new era for plant
>>scientists working to maintain healthy plants,
>>optimize crop yields, and minimize pesticide usage.
>>One of the ultimate aims of agricultural biotechnology
>>is to feed an expanding world population. A recent
>>survey by The Economist shows that the world
>>population has increased by 90% in the past 40 years
>>while food production has increased by only 25% per
>>head. With an additional 1.5 billion mouths to feed by
>>2020, farmers worldwide will have to produce 39% more
>>grain (The Economist, March 25, 2000). These survey
>>results aptly describe the food production challenges
>>facing the global community of farmers and consumers
>>in the new millennium and the dimension of the debate
>>on the risks and benefits of developing genetically
>>engineered crop plants to meet the increasing global
>>food demand while preserving the environment.
>>
>>Genetic engineering has the potential to provide a
>>cornucopia of beneficial plant traits, particularly an
>>enhanced ability to withstand or resist attack by
>>plant pathogens. New approaches to plant disease
>>control are particularly important for pathogens that
>>are difficult to control by existing methods. The
>>percentage of crop losses caused by plant pathogens,
>>insect pests, and weeds, has steadily increased to 42%
>>worldwide, accounting for $500 billion dollars worth
>>of damage (Oerke et al., 1994). In the United States
>>alone, crop losses due to plant pathogens amount to
>>$9.1 billion dollars, while worldwide, plant diseases
>>reduce crop productivity by 12% (Food and Agriculture
>>Organization, 1993). Worldwide, pesticide applications
>>costing $26 billion dollars annually are applied to
>>manage pest losses. Genetically engineered plants
>>resistant to plant pathogens can prevent crop losses
>>and reduce pesticide usage. This feature article
>>provides a current perspective on four major areas of
>>research and application of plant genetic engineering
>>for resistance to plant pathogens.
>>
>> Enhancing resistance with plant genes: Scientists
>>from all over the world are investigating the
>>biochemical nature of, and the signals involved in, a
>>plant’s reactions to pathogen invasion and disease
>>development. Plant resistance genes and the genes
>>involved in resistance reactions are being identified
>>and engineered into crop plants to protect them
>>against plant diseases. This rapidly advancing field
>>of investigation is described in this feature under
>>Enhancing a plant’s resistance with genes from the
>>plant kingdom.
>>
>> Pathogen derived resistance: Plants can be protected
>>from diseases with transgenes (genes that are
>>engineered into plants) that are derived from the
>>pathogens themselves, a concept referred to as
>>pathogen-derived resistance. For example, plant viral
>>transgenes can protect plants from infection by the
>>virus from which the transgene was derived. Genetic
>>engineering of plants for viral resistance is a
>>thriving area of research and is described in this
>>feature with special emphasis on research being done
>>at Cornell University, Geneva, NY, under Genetic
>>engineering: A novel and powerful tool to combat plant
>>virus diseases.
>>
>> Antimicrobial proteins: Another area of
>>investigation involves peptides and proteins with
>>antimicrobial properties that when produced by plants
>>have the potential to strengthen plant resistance to
>>fungal and bacterial plant pathogens. Fungi, insects,
>>animals, and humans all contain genes encoding
>>antimicrobial compounds. This use of antimicrobials to
>>improve plant resistance to pathogens is described in
>>this feature with special emphasis on research being
>>done at Cornell University, Geneva, NY, under Using
>>antimicrobial proteins to enhance plant resistance.
>>
>> Plantibodies: Although plants have mechanisms to
>>protect themselves against pathogen attack, in
>>contrast to animals, there is no "immune system" per
>>se in plants. With the advent of genetic engineering,
>>plants can be engineered to express an antibody
>>against a protein crucial for pathogenesis resulting
>>in a level of immunity or resistance to the pathogen.
>>This promising approach is described under
>>Plantibodies: an animal strategy imported to the plant
>>kingdom to fight back pathogens.
>>
>>Biotechnology is now a lightning rod for visceral
>>debate, with opposing camps making strong claims of
>>promise and peril. The debate involves not only
>>scientific but also political, socio-economic,
>>ethical, and philosophical issues (Wambugu 1999, Hails
>>2000, Ferber 1999, Trewavas 1999, Sagar et al. 2000).
>>
>>This feature article provides a glimpse of the
>>application of biotechnology to plant improvement. The
>>dawn of a new era in plant pathology and plant
>>protection is upon us. Biotechnology has rewritten the
>>scope of scientific investigation, broadened the
>>avenues to resistant plants, and challenged us to take
>>safe and careful steps. Like any other new technology,
>>much still needs to be done before the full potential
>>of agricultural biotechnology is realized. As more and
>>more plant biotechnology products become available,
>>studies to evaluate the risks associated with
>>biotechnology must be intensified. Findings from such
>>studies must be easily accessible to the general
>>public. The risks associated with this technology must
>>be addressed and the benefits should be kept in mind.
>>We are confronted with biotechnology’s vast
>>perspective and this astounding view has expanded the
>>very foundation of our understanding of life.
>Recombinant DNA is DNA that has been created
>artificially. DNA from two or more sources is
>incorporated into a single recombinant molecule.
>Treat DNA from both sources with the same restriction
>endonuclease (BamHI in this case).
>BamHI cuts the same site on both molecules
>5' GGATCC 3'
>3' CCTAGG 5'
>The ends of the cut have an overhanging piece of
>single-stranded DNA.
>These are called "sticky ends" because they are able
>to base pair with any DNA molecule containing the
>complementary sticky end.
>In this case, both DNA preparations have complementary
>sticky ends and thus can pair with each other when
>mixed.
>DNA ligase covalently links the two into a molecule of
>recombinant DNA.
>To be useful, the recombinant molecule must be
>replicated many times to provide material for
>analysis, sequencing, etc. Producing many identical
>copies of the same recombinant molecule is called
>cloning. Cloning can be done in vitro, by a process
>called the polymerase chain reaction (PCR). Here,
>however, we shall examine how cloning is done in vivo.
>
>Cloning in vivo can be done in
>unicellular prokaryotes like E. coli
>unicellular eukaryotes like yeast and
>in mammalian cells grown in tissue culture.
>In every case, the recombinant DNA must be taken up by
>the cell in a form in which it can be replicated and
>expressed. This is achieved by incorporating the DNA
>in a vector. A number of viruses (both bacterial and
>of mammalian cells) can serve as vectors. But here let
>us examine an example of cloning using E. coli as the
>host and a plasmid as the vector.
>
>Plasmids
>Plasmids are molecules of DNA that are found in
>bacteria separate from the bacterial chromosome. They:
>are small (a few thousand base pairs)
>usually carry only one or a few genes
>are circular
>have a single origin of replication
>Plasmids are replicated by the same machinery that
>replicates the bacterial chromosome. Some plasmids are
>copied at about the same rate as the chromosome, so a
>single cell is apt to have only a single copy of the
>plasmid. Other plasmids are copied at a high rate and
>a single cell may have 50 or more of them.
>
>Genes on plasmids with high numbers of copies are
>usually expressed at high levels. In nature, these
>genes often encode proteins (e.g., enzymes) that
>protect the bacterium from one or more antibiotics.
>
>Plasmids enter the bacterial cell with relative ease.
>This occurs in nature and may account for the rapid
>spread of antibiotic resistance in hospitals and
>elsewhere. Plasmids can be deliberately introduced
>into bacteria in the laboratory transforming the cell
>with the incoming genes.
>
>An Example
>(courtesy of David Miklos and Greg Freyer of the Cold
>Spring Harbor Laboratory, who used these plasmids as
>the basis of a laboratory introduction to recombinant
>DNA technology that every serious biology student —
>high school or college — should experience!)
>pAMP
>4539 base pairs
>a single replication origin
>a gene (ampr)conferring resistance to the antibiotic
>ampicillin (a relative of penicillin)
>a single occurrence of the sequence
>5' GGATCC 3'
>3' CCTAGG 5'
>that, as we saw above, is cut by the restriction
>enzyme BamHI
>a single occurrence of the sequence
>5' AAGCTT 3'
>3' TTCGAA 5'
>that is cut by the restriction enzyme HindIII
>Treatment of pAMP with a mixture of BamHI and HindIII
>produces:
>a fragment of 3755 base pairs carrying both the ampr
>gene and the replication origin
>a fragment of 784 base pairs
>both fragments have sticky ends
>pKAN
>4207 base pairs
>a single replication origin
>a gene (kanr) conferring resistance to the antibiotic
>kanamycin.
>a single site cut by BamHI
>a single site cut by HindIII
> Treatment of pKAN with a mixture of BamHI and HindIII
>produces:
>a fragment of 2332 base pairs
>a fragment of 1875 base pairs with the kanr gene (but
>no origin of replication)
>both fragments have sticky ends
>These fragments can be visualized by subjecting the
>digestion mixtures to electrophoresis in an agarose
>gel. Because of its negatively-charged phosphate
>groups, DNA migrates toward the positive electrode
>(anode) when a direct current is applied. The smaller
>the fragment, the farther it migrates in the gel.
>Ligation Possibilities
>If you remove the two restriction enzymes and provide
>the conditions for DNA ligase to do its work, the
>pieces of these plasmids can rejoin (thanks to the
>complementarity of their sticky ends).
>
>Mixing the pKAN and pAMP fragments provides several
>(at least 10) possibilities of rejoined molecules.
>Some of these will not produce functional plasmids
>(molecules with two or with no replication origin
>cannot function).
>
>
>One interesting possibility is the joining of
>
>the 3755-bp pAMP fragment (with ampr and a replication
>origin) with the
>1875-bp pKAN fragment (with kanr)
>Sealed with DNA ligase, these molecules are
>functioning plasmids that are capable of conferring
>resistance to both ampicillin and kanamycin. They are
>molecules of recombinant DNA.
>
>Because the replication origin, which enables the
>molecule to function as a plasmid, was contributed by
>pAMP, pAMP is called the vector.
>
>Transforming E. coli
> Treatment of E. coli with the mixture of religated
>molecules will produce some colonies that are able to
>grow in the presence of both ampicillin and kanamycin.
>A suspension of E. coli is treated with the mixture of
>religated DNA molecules.
>The suspension is spread on the surface of agar
>containing both ampicillin and kanamycin.
>The next day, a few cells — resistant to both
>antibiotics — will have grown into visible colonies
>containing billions of transformed cells.
>Each colony represents a clone of transformed cells.
>However, E. coli can be simultaneously transformed by
>more than one plasmid, so we must demonstrate that the
>transformed cells have acquired the recombinant
>plasmid.
>
>Electrophoresis of the DNA from doubly-resistant
>colonies (clones) tells the story.
>
>Plasmid DNA from cells that acquired their resistance
>from a recombinant plasmid only show only the 3755-bp
>and 1875-bp bands (Clone 1, lane 3).
>Clone 2 (Lane 4) was simultaneous transformed by
>religated pAMP and pKAN. (We cannot tell if it took up
>the recombinant molecule as well.)
>Clone 3 (Lane 5) was transformed by the recombinant
>molecule as well as by an intact pKAN.
>Cloning other Genes
>The recombinant vector described above could itself be
>a useful tool for cloning other genes. Let us assume
>that within its kanamycin resistance gene (kanr) there
>is a single occurrence of the sequence
>5' GAATTC 3'
>3' CTTAAG 5'
>This is cut by the restriction enzyme EcoRI, producing
>sticky ends.
>If we treat any other sample of DNA, e.g., from human
>cells, with EcoRI, fragments with the same sticky ends
>will be formed. Mixed with EcoRI-treated plasmid and
>DNA ligase, a small number of the human molecules will
>become incorporated into the plasmid which can then be
>used to transform E. coli.
>
>But how to detect those clones of E. coli that have
>been transformed by a plasmid carrying a piece of
>human DNA?
>
>The key is that the EcoRI site is within the kanr
>gene, so when a piece of human DNA is inserted there,
>the gene's function is destroyed.
>
>
>All E. coli cells transformed by the vector, whether
>it carries human DNA or not, can grow in the presence
>of ampicillin. But E. coli cells transformed by a
>plasmid carrying human DNA will be unable to grow in
>the presence of kanamycin.
>
>So,
>Spread a suspension of treated E. coli on agar
>containing ampicillin only
>grow overnight
>with a sterile toothpick transfer a small amount of
>each colony to an identified spot on agar containing
>kanamycin
>(do the same with another ampicillin plate)
>Incubate overnight
>All those clones that continue to grow on ampicillin
>but fail to grow on kanamycin (here, clones 2, 5, and
>8) have been transformed with a piece of human DNA.
>
>Some recombinant DNA products being used in human
>therapy
>Using procedures like this, many human genes have been
>cloned in E. coli or in yeast. This has made it
>possible — for the first time — to produce unlimited
>amounts of human proteins in vitro. Cultured cells (E.
>coli, yeast, mammalian cells) transformed with the
>human gene are being used to manufacture:
>
>insulin for diabetics
>factor VIII for males suffering from hemophilia A
>factor IX for hemophilia B
>human growth hormone (GH)
>erythropoietin (EPO) for treating anemia
>three types of interferons
>several interleukins
>granulocyte-macrophage colony-stimulating factor
>(GM-CSF) for stimulating the bone marrow after a bone
>marrow transplant
>granulocyte colony-stimulating factor (G-CSF) for
>stimulating neutrophil production, e.g., after
>chemotherapy and for mobilizing hematopoietic stem
>cells from the bone marrow into the blood.
>tissue plasminogen activator (TPA) for dissolving
>blood clots
>adenosine deaminase (ADA) for treating some forms of
>severe combined immunodeficiency (SCID)
>angiostatin and endostatin for trials as anti-cancer
>drugs
>parathyroid hormone
>leptin
>hepatitis B surface antigen (HBsAg) to vaccinate
>against the hepatitis B virus
Recombinant DNA Technology in the Synthesis of Human Insulin
--------------------------------------------------------------------------------
The nature and purpose of synthesising human insulin.
Since Banting and Best discovered the hormone, insulin in 1921.(1) diabetic patients, whose elevated sugar levels (see fig. 1) are due to impaired insulin production, have been treated with insulin derived from the pancreas glands of abattoir animals. The hormone, produced and secreted by the beta cells of the pancreas' islets of Langerhans,(2) regulates the use and storage of food, particularly carbohydrates.
Fig. 1
Fluctuations in diabetic person's blood glucose levels, compared with healthy individuals. Source: Hillson,R. - Diabetes: A beyond basics guide, pg.16.
Although bovine and porcine insulin are similar to human insulin, their composition is slightly different. Consequently, a number of patients' immune systems produce antibodies against it, neutralising its actions and resulting in inflammatory responses at injection sites. Added to these adverse effects of bovine and porcine insulin, were fears of long term complications ensuing from the regular injection of a foreign substance,(3) as well as a projected decline in the production of animal derived insulin.(4) These factors led researchers to consider synthesising Humulin by inserting the insulin gene into a suitable vector, the E. coli bacterial cell, to produce an insulin that is chemically identical to its naturally produced counterpart. This has been achieved using Recombinant DNA technology. This method (see fig. 2) is a more reliable and sustainable(5) method than extracting and purifying the abattoir by-product.
Fig. 2
An overview of the recombination process. Source: Novo - Nordisk promotional brochure,pg 6.
Understanding the genetics involved.
The structure of insulin.
Chemically, insulin is a small, simple protein. It consists of 51 amino acid, 30 of which constitute one polypeptide chain, and 21 of which comprise a second chain. The two chains (see fig. 3) are linked by a disulfide bond.(6)
Fig. 3
Source: Chance, R. and Frank B. - Research, development, production and safety of Biosynthetic Human Insulin.
Inside the Double Helix.
The genetic code for insulin is found in the DNA at the top of the short arm of the eleventh chromosome. It contains 153 nitrogen bases (63 in the A chain and 90 in the B chain).DNA Deoxyribolnucleic Acid), which makes up the chromosome, consists of two long intertwined helices, constructed from a chain of nucleotides, each composed of a sugar deoxyribose, a phosphate and nitrogen base. There are four different nitrogen bases, adenine, thymine, cytosine and guanine.(7) The synthesis of a particular protein such as insulin is determined by the sequence in which these bases are repeated (see fig. 4).
Fig. 4
DNA strand with the specific nucleotide sequence for Insulin chain B. Source: Based on the diagram in Watson, J.D., Gilman, M., Witkovski, J., Zoller, M. - Recombinant DNA, pg 22.
Insulin synthesis from the genetic code.
The double strand of the eleventh chromosome of DNA divides in two, exposing unpaired nitrogen bases which are specific to insulin production (see fig. 5).
Fig. 5
Unravelling strand of the DNA of chromosome 11, with the exposed nucleotides coding for the B chain of Insulin. Source: Based on the diagram in Watson, J.D., Gilman, M., Witkovski, J., Zoller, M. - Recombinant DNA, pg 22.
Using one of the exposed DNA strands (see fig.6) as a template, messenger RNA forms in the process of transcription (see fig. 7).
Fig 6
A single strand of DNA coding for Insulin chain B. Source: Novo-Nordisk promotional brochure, pg 13.
Fig. 7
The (m) RNA strand. Source: Novo-Nordisk promotional brochure, pg 13.
The role of the mRNA strand, on which the nitrogen base thymine is replaced by uracil, is to carry genetic information, such as that pertaining to insulin,from the nucleus into the cytoplasm, where it attaches to a ribosome (see fig. 8).
Fig. 8
Process of translation at the Ribosome. Source: Novo-Nordisk promotional brochure, pg 13.
The nitrogen bases on the mRNA are grouped into threes, known as codons. Transfer RNA (tRNA) molecules, three unpaired nitrogen bases bound to a specific amino acid, collectively known as an anti-codon (see fig.9) pair with complementary bases (the codons) on the mRNA.
Fig. 9
Source: Novo-Nordisk promotional brochure, pg 13.
The reading of the mRNA by the tRNA at the ribosome is known as translation. A specific chain of amino acids is formed by the tRNA following the code determined by the mRNA. The base sequence of the mRNA has been translated into an amino acid sequence which link together to form specific proteins such as insulin.
The Vector (Gram negative E. coli).
A weakened strain of the common bacterium, Escherrichia coli (E. coli) (see fig. 10), an inhabitant of the human digestive tract, is the 'factory' used in the genetic engineering of insulin.
Fig. 10
The insulin is introduced into an E. coli cell such as this. Source: Novo-Nordisk promotional brochure, pg 16 .
When the bacterium reproduces, the insulin gene is replicated along with the plasmid,(8) a circular section of DNA (see fig. 11). E. coli produces enzymes that rapidly degrade foreign proteins such as insulin. By using mutant strains that lack these enzymes, the problem is avoided.(9)
Fig. 11
Electron micrograph of the Vector's plasmid. Source: Watson, J.D., Gilman, M., Witkovski, J., Zoller, M. - Recombinant DNA, pg 73.
In E. coli, B-galactosidase is the enzyme that controls the transcription of the genes. To make the bacteria produce insulin, the insulin gene needs to be tied to this enzyme.
Inside the genetic engineer's toolbox.
Restriction enzymes, naturally produced by bacteria, act like biological scalpels(10) (see fig.12), only recognising particular stretches of nucleotides, such as the one that codes for insulin.(11)
Fig 12
An analogous look at Restriction enzymes. Source: CSIRO Research of Australia No. 8.
This makes it possible to sever certain nitrogen base pairs and remove the section of insulin coding DNA from one organism's chromosome so that it can manufacture insulin (See fig. 13). DNA ligase is an enzyme which serves as a genetic glue, welding the sticky ends of exposed nucleotides together.
Fig. 13
Source: Watson, J.D., Gilman, M., Witkovski., Zoller, M. - Recombinant DNA, pg 78.
Manufacturing Humulin.
The first step is to chemically synthesise the DNA chains that carry the specific nucleotide sequences characterising the A and B polypeptide chains of insulin (see fig. 14).
Fig. 14
Human insulin structure. Amino acid RNA to DNA conversion. Source: Genetic Engineering Activities, pg 176.
The required DNA sequence can be determined because the amino acid compositions of both chains have been charted. Sixty three nucleotides are required for synthesising the A chain and ninety for the B chain, plus a codon at the end of each chain,signalling the termination of protein synthesis. An anti-codon, incorporating the amino acid, methionine, is then placed at the beginning of each chain which allows the removal of the insulin protein from the bacterial cell's amino acids. The synthetic A and B chain 'genes' (see fig. 15) are then separately inserted into the gene for a bacterial enzyme, B-galactosidase, which is carried in the vector's plasmid. At this stage, it is crucial to ensure that the codons of the synthetic gene are compatible with those of the B-galactosidase.
Fig. 15
Source: Watson, J.D., Gilman, M.,Witkovski., Zoller, M. - Recombinant DNA, pg 456.
The recombinant plasmids are then introduced into E. coli cells. Practical use of Recombinant DNA technology in the synthesis of human insulin requires millions of copies of the bacteria whose plasmid has been combined with the insulin gene in order to yield insulin. The insulin gene is expressed as it replicates with the B-galactosidase in the cell undergoing mitosis (see fig. 16).
Fig. 16
The process of mitosis. Source: Novo-Nordisk promotional brochure, pg 11.
The protein which is formed, consists partly of B-galactosidase, joined to either the A or B chain of insulin (see fig.17). The A and B chains are then extracted from the B-galactosidase fragment and purified.
Fig. 17
Source: Watson, J.D., Gilman, M., Witkovski, J., Zoller, M. - Recombinant DNA, pg 456.
The two chains are mixed and reconnected in a reaction that forms the disulfide cross bridges, resulting in pure Humulin - synthetic human insulin (see fig. 18).
Fig. 18
Human insulin molecule. Source: Source: Watson, J.D., Gilman, M., Witkovski, J., Zoller, M. - Recombinant DNA, pg 456.
Biological implications of genetically engineered Recombinant human insulin.
Human insulin is the only animal protein to have been made in bacteria in such a way that its structure is absolutely identical to that of the natural molecule. This reduces the possibility of complications resulting from antibody production. In chemical and pharmacological studies, commercially available Recombinant DNA human insulin has proven indistinguishable from pancreatic human insulin.(12) Initially the major difficulty encountered was the contamination of the final product by the host cells, increasing the risk of contamination in the fermentation broth. This danger was eradicated by the introduction of purification processes. When the final insulin product is subjected to a battery of tests, including the finest radio-immuno assay techniques,(13) no impurities can be detected.(14) The entire procedure is now performed using yeast cells as a growth medium, as they secrete an almost complete human insulin molecule with perfect three dimensional structure. This minimises the need for complex and costly purification procedures.
The issue of hypoglycaemic complications in the administration of human insulin.
Since porcine insulin was phased out, and the majority of insulin dependent patients are now treated with genetically engineered recombinant human insulin, doctors and patients have become concerned about the increase in the number of hypoglycaemic episodes experienced.(15) Although hypoglycaemia can be expected occasionally with any type of insulin, some people with diabetes claim that they are less cognisant of attacks of hypoglycaemia since switching from animal derived insulin to Recombinant DNA human insulin.(16) In a British study, published in the 'Lancet", hypoglycaemia was induced in patients using either pork or human insulin, The researchers found "no significant difference in the frequency of signs of hypoglycaemia between users of the two different types of insulin."(17)
An anecdotal report from a British patient who had been insulin dependent for thirty years, stated that she began experiencing recurring, unheralded hypoglycaemia only after substituting Recombinant DNA human insulin for animal derived insulin. After switching back to pork insulin to ease her mind, she hadn't experienced any unannounced hypoglycaemia. Eli Lilly and Co., a manufacturer of human insulin, noted that a third of people with diabetes, who have been insulin dependent for over ten years, "lose their hypoglycaemic warning signals, regardless of the type of insulin they are taking."(18)
Dr Simon P. Wolff of the University College of London said in an issue of Nature , "As far as I can make out, there's no fault (with the human insulin)." He concluded, "I do think we need to have a study to examine the possible risk."(19)
Although the production of human insulin is unarguable welcomed by the majority of insulin dependent patients, the existence of a minority of diabetics who are unhappy with the product cannot be ignored. Although not a new drug, the insulin derived from this new method of production must continue to be studied and evaluated, to ensure that all its users have the opportunity to enjoy a complication free existence.
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