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Biotechnology Application in Medicine: Genetically Engineered Insulin, Gene Therapy and Molecular Diagnosis, Practice Problems and FAQs

Biotechnology Application in Medicine: Genetically Engineered Insulin, Gene Therapy and Molecular Diagnosis, Practice Problems and FAQs

We have all been vaccinated with vaccines against infectious diseases such as measles, polio, hepatitis, etc. Have you ever wondered how these vaccines are prepared? You must also be aware that diabetic patients with high blood sugar level have to regularly inject insulin into their body to keep the sugar level in control. How are the insulin injections prepared?

Application of biotechnology in medicine

The answer to this lies in the branch of biology that utilises modern technology for industrial scale production of biological products from living organisms. This branch of biology is known as biotechnology and has massive application in the field of medicines. Biotechnology has opened the avenue of treating fatal diseases such as Severe Combined Immunodeficiency (SCID), leukaemia, etc. which were earlier untreatable. Come let us learn about these life changing innovations in the field of biotechnology.

Genetically Engineered Insulin

Diabetes is a disease that is caused by high blood sugar levels due to lack of insulin in the body. Insulin helps in utilisation of glucose in the body and hence reduces blood glucose (sugar) levels.

There are two types of diabetes, Type I and Type II. In type I, pancreas does not function properly whereas, in type II the human body becomes resistant to insulin. So in type I diabetes, the malfunctioning of pancreas is a result of loss of beta cells. The decrease in beta cells decreases insulin production leading to an increase of blood sugar level. This type I diabetes is treated by providing insulin from the outside. The external insulin is considered as an artificial insulin which is derived from two sources, either from animal source or microbial source. 

Insulin Produced from Animal

In earlier times, insulin was extracted from pancreas of slaughtered pigs and cattle. This is because the insulin extracted from these animals were nearly identical to that of human insulin. The insulin was further purified to remove impurities and packaged for use.

 Insulin obtained from animal

Disadvantages of Animal Insulin

The major disadvantage of this animal insulin is that it leads to allergy or hypersensitive immune responses in some of the patients which makes it difficult for patients to use this animal insulin on a regular basis. 

Moreover, the yield of animal insulin was quite low. Due to low production, a lot of cattle and pig pancreas had to be extracted and processed to yield very less insulin. This process made these insulin injections much expensive and inaccessible to poorer patients.

Microbial Insulin Production

The insulin is produced from microbes by using recombinant DNA technology. The recombinant DNA technology is a technique that involves the introduction of genes of interest into a plasmid. This recombinant plasmid is further introduced into microbes where it multiplies and forms multiple copies of genes of interest which expresses itself within the microbial host. As microbes multiply rapidly, a large quantity of the protein expressed by the gene of interest can be obtained in a shorter time period. The plasmid is hence said to be a vector which helps in carrying the gene of interest within the host microbial cell.

The gene of insulin obtained from humans is inserted into a plasmid vector which is then inserted into E.Coli. However, the insulin produced by this method is non-functional.

Insulin production using rDNA technology

Structure of Insulin

The human insulin consists of a polypeptide chain A and a polypeptide chain B. These two chains are linked together with the help of disulfide bonds. These collectively form a functional insulin. In mammals, insulin is synthesised as a prohormone (proinsulin) which is non-functional. It contains an extra stretch of C peptide, which is present between A chain and B chain. The proinsulin undergoes maturation during which C peptide is removed and A and B chains are joined. This results in functional insulin.

insulin

To produce functional insulin, genes of A and B chains are separately inserted into different plasmid vectors. This forms recombinant plasmids. The recombinant plasmids are then introduced into different E.Coli cells. The transformed E.Coli produces A and B chain peptides, respectively. These chains are extracted and combined with the help of disulfide bonds to form a functional human insulin.

Recombinant insulin production

In 1983, Eli Lilly, an American company first produced genetically engineered insulin. It was marketed under the name Humulin.

Humulin

Why isn't Insulin Taken Orally?

Insulin is administered as a subcutaneous injection (under the skin). A fat layer is present beneath the skin from where insulin is absorbed slowly. It is not taken as oral medicine because proteolytic enzymes present in the gastrointestinal tract degrade the hormone, which is a peptide, into fragments. This makes the insulin ineffective.

Gene Therapy

Gene therapy is a type of treatment of diseases done by repairing or reconstructing the defective genes. The method of gene therapy helps to correct the genetic defect in an embryo or child. The mutated cell is treated by transferring the functional gene from a healthy cell into a mutated cell. The gene of interest is isolated from the healthy cell and incorporated within a vector. The most commonly used vector in gene therapy is the viral vector because it can easily inject its genetic material into the host cell. The recombinant viral vector then injects the gene of interest into the host cell.

Gene therapy

Adenosine Deaminase Deficiency

The gene therapy was first used to treat ADA deficiency which is a genetic disorder. In ADA deficiency, the gene coding for ADA enzyme undergoes deletion mutations and therefore, ADA enzyme is not produced. 

Adenosine Deaminase Deficiency

The adenosine deaminase enzyme is responsible for eliminating a molecule called deoxyadenosine. It is produced when DNA is broken down. Adenosine deaminase enzyme converts deoxyadenosine, a toxic molecule to lymphocytes, to another molecule called deoxyinosine, which is not harmful to lymphocytes.

Since this enzyme is missing in ADA deficient patients, the concentration of deoxyadenosine increases. The excess of deoxyadenosine results in severe damage to lymphocytes. This ultimately affects the immune system of the patient. Hence, the condition is known as severe combined immunodeficiency disease (SCID). 

Presence or absence of ADA enzyme

The common early treatments for ADA deficiency are enzyme replacement therapy and bone marrow transplant. 

Enzyme replacement therapy

ADA enzyme is deficient in ADA deficient patients. To treat this, enzyme replacement therapy is a simple treatment in which a patient is injected with functional ADA enzyme. This method seems very simple and easy but it has many limitations:

Limitations of ERT

  • This method requires frequent injections sometimes even twice a week.
  • ERT requires constant monitoring of a patient in order to adjust doses according to the patient's conditions.
  • It is an expensive treatment because a single dose of injection can cost in lakhs.
  • It does not cure ADA completely because after sometime patient might not respond to the injection

 Enzyme replacement therapy

Bone Marrow Transplant

Bone marrow transplantation is a surgical procedure of transferring bone marrow from a donor to a recipient. In this procedure, healthy stem cells from bones are transferred to the defective one. These stem cells can divide and differentiate into healthy lymphocytes, thus treating the immunodeficiency.

Procedure of BMT

The first step in bone marrow transplant is to collect the bone marrow cells from a suitable donor. This procedure is known as bone marrow harvest. Meanwhile the recipient is given chemotherapy to kill faulty marrow cells. The harvested bone marrow cells are then injected into the recipient's body. The recipient is kept under observation to check for side effects. These bone marrow cells repopulate recipient’s bone marrow and lymphocyte production goes up. 

 Bone marrow transplant

Limitations of BMT

There are several disadvantages of bone marrow transplant:

  • There is a lack of suitable donors.
  • It is a surgical procedure and involves several difficulties and complications.
  • This treatment is so expensive and it does not cure ADA permanently.

Gene Therapy

In modern times, gene therapy is being used for the treatment of SCID. Gene therapy is classified into two different types on the basis of the type of cells involved - somatic gene therapy and germline gene therapy. 

Somatic Gene Therapy

In somatic gene therapy, a person's own lymphocytes are involved. This saves an immense amount of time that is required to find a suitable donor. The lymphocytes are extracted from the patient's blood. A retroviral vector is used that contains ADA complementary DNA. This is because retrovirus uses reverse transcription machinery to synthesise a double stranded gene of interest, which is a functional ADA gene. The lymphocytes and vectors are incubated together. This results in transformed lymphocytes. These transformed lymphocytes are then multiplied. These modified lymphocytes are finally injected into the patient’s body.

Somatic gene therapy

Limitations of Somatic Gene Therapy

  • The lifespan of modified lymphocytes is limited.
  • Patient requires the periodic infusion of modified lymphocytes.

Germline Gene Therapy

In germline gene therapy, normal genes are extracted from the donor and introduced into the eggs or sperm of parents. The normal genes can also be introduced into the fertilised egg or early embryo of the offspring.

Germline gene therapy

Advantages of Germline Gene Therapy

Germline gene therapy is referred to as permanent cure because embryonic cells produce hematopoietic cells that produce lymphocytes without genetic defect. This occurs throughout the lifespan of an individual.

Difference Between Somatic and Germline Gene Therapy

Somatic Gene Therapy

Germline Gene Therapy

Healthy cells are transferred into the somatic cells.

Healthy genes are transferred into gametic or embryonic cells.

This cannot be inherited by upcoming generations.

This can be inherited by upcoming generations.

Affects target cells only.

Affects all cells.

Done multiple times because the results are not long lasting.

Done once in a lifetime due to long lasting effects.

Molecular Diagnosis

Biotechnology is used for molecular diagnosis in which these methods detect and measure the presence of biomolecules, such as DNA, RNA and proteins, associated with a specific disease. 

Earlier, conventional methods were used such as urine test or serum test to diagnose the type of disease. These methods are done with the onset of early symptoms. In these methods, urine or blood samples are taken from the body and then tested for disease causing microbes. The sensitivity of conventional methods is low in case of low concentration of pathogens and these methods are time consuming. To overcome these drawbacks, molecular diagnosis is done using Polymerase Chain Reaction. It helps in predicting the accurate disease.

Polymerase Chain Reaction or PCR is a method used to amplify DNA molecules and thus helps in detecting the gene of interest even if it is present in very low concentrations.

Detection of Cancer

PCR is used for the detection of cancer. There are a number of carcinogens that are present in our environment, such as UV rays, cigarettes etc. These carcinogens cause mutations in the gene that cause uncontrolled growth of cells which are termed as cancer. The mutated genes in the body can be identified using PCR techniques.

Mutation causing cancer

Detection of Genetic Disorder

Genetic disorders can be diagnosed using PCR. If the DNA consists of a mutated gene, PCR will amplify these genes by using specific probes. These probes have a sequence complementary to the mutated gene. If the DNA does not contain any mutated genes, then the gene specific probe (which is complementary to the mutated gene) will not bind to the DNA. Hence, no PCR products will be obtained

Detection of genetic disorder

Detection of HIV

HIV infection is diagnosed using PCR. The first step in the detection of HIV is to extract the RNA of the virus. The complementary DNA (cDNA) sequence is obtained from it. This cDNA is used to prepare probes that are specific to HIV. 

Preparation of cDNA from RNA of virus

If the patient is infected with HIV, the DNA will contain the HIV specific gene. The probe will bind to it and make multiple copies of the gene. It confirms that the patient is AIDS positive.

Detection of HIV

Practice Problems of Biotechnology Application in Medicine

Ques:- Why is insulin not administered orally to a diabetic patient?

A. Insulin can harm digestive tract if taken orally
B. Insulin is a peptide hormone
C. Insulin will lead to sudden hypoglycemia if taken orally
D. Insulin will break down in buccal cavity only

Solution: The structure of insulin is composed of two polypeptides, A and B chains. These chains are linked together by disulphide bridges. It cannot be administered orally to diabetic patients. This is because the proteolytic enzymes of the gut digest the insulin hormone which is a peptide in nature. Insulin is therefore taken via injection.

Hence, the correct option is b.

Ques:- Identify the method which is not used for treating SCID.

A. Bone marrow transplantation
B. Enzyme replacement therapy
C. Gene therapy
D. Antibody therapy

Solution: The appropriate approach to treat SCID is to provide functional adenosine deaminase enzymes that will break down the toxic molecule into non-toxic one. This can be done through following procedures:

  • Bone marrow transplantation: The surgical procedure through which the stem cells from bone marrow are transferred from donor to recipient.
  • Enzyme replacement therapy: The patient is injected with frequent doses of functional ADA enzyme.
  • Gene therapy: The method through which normal genes or cells are introduced in the patient.

Hence, the correct option is d.

Ques:-Study the following statements (A-D).

  1. Insulin is synthesised as a prohormone in mammals.
  2. Functional insulin consists of three polypeptide chains.
  3. Humulin is synthesised using Escherichia coli.
  4. Insulin helps in the process of gluconeogenesis.

How many of the above statements are true?

A. Three
B. Four
C. Two 
D. One

Solution: In mammals, insulin is produced by the beta cells of pancreas. It is produced in an inactive form called proinsulin in which an extra stretch of C peptide is present between the A and B chains. It undergoes maturation and forms functional insulin. During this process, C peptide is removed and A and B chains are joined with the help of disulfide bridges.

Humulin is the human insulin produced with the help of recombinant DNA technology by Eli Lilly company. It is produced by using a laboratory strain of Escherichia coli. Humulin possesses the same number of amino acids which is present in human insulin. Hence, the correct option is c.

Ques:- Which of the following parts of the proinsulin hormone is removed to form functional insulin hormone?

b


A. a
B. b
C. c
D. Both b and c

Solution: The given figure represents the structure of non functional insulin, called proinsulin. ‘a’ represents the A polypeptide chain, ‘b’ represents the C peptide and ‘c’ represents the B polypeptide chain of insulin. This proinsulin undergoes maturation during which removal of C peptide takes place. The A and B chains are then joined together with disulfide bridges and it is known as functional insulin. Thus, part ‘b’ is removed from proinsulin to produce functional hormone. Hence, the correct option is b.

NAME IMAGE

Frequently Asked Questions of Biotechnology Application in Medicine

Ques:- What is the use of biotechnology in medicine?

Answer: Biotechnology is used in the field of medicine in the following ways:

  • It is used in the production of genetically engineered insulin.
  • It is used in gene therapy. For example, gene therapy is given in the case of adenosine deaminase deficiency which is a genetic disorder.
  • It is used in the molecular diagnosis of various diseases like cancer, AIDS and genetic disorders.

Ques:- What is gene therapy?

Answer: Gene therapy is a type of treatment of diseases done by repairing or reconstructing the defective genes. The method of gene therapy helps to correct the genetic defect in an embryo or child. Gene therapy is of two types based on the type of cells involved in it. These are:

  • Somatic gene therapy: The healthy cells are transferred to the somatic cells.
  • Germline gene therapy: The healthy cells are transferred to the gametic or embryonic cells.

Ques:- What are the limitations of somatic gene therapy?

Answer: The disadvantages of somatic gene therapy are -

  • The lifespan of modified lymphocytes is limited.
  • Patient requires the periodic infusion of modified lymphocytes.

Ques:- What are the advantages of germline gene therapy?
Answer: Germline gene therapy is referred to as a permanent cure of ADA deficiency because healthy cells are incorporated into the embryonic cells or gametic cells. The embryonic cells produce hematopoietic cells that produce lymphocytes without genetic defects. This occurs throughout the lifespan of an individual.

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