Antisence Technology

Antisense Technology:

—  The  general concept for  antisense  technology  was created in the mid of 19^th century(1978).

—  Scientist coined the term “Antisense” because the mRNA sequence is known as the “sense” sequence. Since this technology blocks the mRNA it became known as “Antisense”.

      In principle, antisense technology is supposed to prevent protein production from a targeted gene.

Antisense oligonucleotides:

—  Antisense  oligonucleotides are single strands of DNA  or RNA that are complimentary to the chosen sequence.

—  In the case of antisense RNA they prevent protein translation of certain messenger RNA strands by binding to them.

—  Antisense DNA can be used to target a specific, complimentary(coding or  non coding) RNA.

—  If binding takes places this DNA/RNA hybrid can be degraded by the enzyme RNase H.

A case study in antisense technology;

The Flavr Savr Tomato:

Tomatoes allowed to completely ripen on the vine develop their full color, flavor and softness characteristics in great demand by consumers. But for shipping purposes, commercially grown tomatoes must be picked before they get too soft, resulting in hard, bland-tasting tomatoes at the market. The agricultural biotechnology company Calgene (California) used antisense technology to inhibit the production of the fruit-softening enzyme polygalacturonase which breaks down a cell wall polysaccharide. This resulted in a 90% reduction in polygalacturonase activity and a significantly longer ripening period. The “Flavr Savr” tomatoes could be left on the vine longer  to develop  color and flavor without getting as soft as normal tomatoes.  But they could still be shipped without being damaged and they would eventually soften at the market or at home. But, the Flavr Savr tomato  was only produced commercially for a few  years because the variety  used for genetic engineering  had inferior agronomic characteristics (too small, low yield). DNA Plant Technologies later introduced an antisense engineered tomato (“Endless Summer”) which inhibited ethylene production, but withdrew the product after a patent fight with Monsanto and take-over by another company.

 

 

 

 

 

 

Hypovolemic Shock

 Shock:

It is a situation in which a general disorder of blood flow exists where in tissue perfusion and oxygen delivery are reduced to a level below those required to meet metabolic demands despite the operation of various compensatory mechanism.
Shock is also the term given to the clinical condition in which the patient is pale, cold and sweaty, the pulse is rapid, of low volume and the arterial BP is relatively low, often less than 80 mmHg.

Role of Kidneys in Hypovolemic Shock:
 

Fall in MAP perfusing the kidneys and stimulation of sympathetic nerves, stimulate JGA leading to release of renin.

Renin converts Angiotensinogen to Angiotensin –I which is converted to Angiotensin- II.

Angiotensin- II causes

  i)    constriction of arterioles leading to increase ­ in TPR.

  ii)   release of aldosterone from adrenal cortex which helps in reabsorption of Na+ in the kidneys

  iii)  causes release of ADH which helps in the

            reabsorption of water from the kidney

  iv)  stimulates thirst center in the hypothalamus

           which increases water intake

     Overall effect is increase­ TPR, ­ increase BV, increase ­SV leading to an increase in BP

 

ØDecrease in MAP leads to ­ sympathetic discharge to kidneys which causes

   a) decrease in Renal blood flow (normal blood flow is 20-25% of CO)- diverting blood to increase circulating BV.

  b) decrease in GFR leading to decreased urine output

  c)  Stimulates JGA causing ­ secretion of

          renin.

Ø Increased release of erythropoietin

Overall effect is an­ increase in BV, ­increase in BP, increase in ­ RBC production.

 

 

Stages of Shock:

Stage I  - Stage of compensated, reversible hypotensive shock. This shock occurs when there is decrease in circulating blood volume by 10% or less.

Stage II  -  Stage of decompensated hypotension but potentially reversible shock. This stage of shock results when there is decrease in blood volume of not more than 35-40% and arterial BP does not fall below 50 mmHg.

Stage III  -  Irreversible stage of shock due to microcirculatory failure leading to cellular injury and death. In this stage arterial BP continues to fall to a critical level- usually about 45mmHg or below; at which vital organ perfusion is reduced and a vicious circle of deterioration of functions ensues i.e. shock it self causes shock.

 

Management Principles for Shock
“VIP” 

Ventilation:  To ensure adequate pulmonary exchange of oxygen and carbon dioxide.      Supplement oxygen , some may need mechanical ventilator.

Infusion:  To ensure adequate intravascular volume -  intravenous fluids, blood.

Pump:  To ensure cardiovascular competence:

      give Inotropes and vasopressors

                                   ­ 

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Infective endocarditis

It is an infecion of heart valves or the endocardium due infectious agents, mostly bacteria (septicemia).
The valves of the heart do not receive any dedicated blood supply, i.e defence mechanism can not directly reach the heart valves.
Predesposing factors:
vValvular heart disease
v Rheumatic heart disease
v Congenital heart disease
v Mitral valve prolapse
v Prosthetic devices( valves, pace makers)
v Intravenous drug use

Pathogenesis:
qPatients at risk are those who have pre- existing cardiac disease. In 1/3rd cases normal heart beat are also affected.
qInoculation of bacteria colonizing a mucosal  or peripheral tissue site into the bloodstream
qTransient bacteremia of a serum-resistant pathogen capable of adhering to a cardiac valvular surface
q Turbulent blood flow across the valve
qBacterial adherence to cardiac valvular surface
qPathogen - host tissue interaction resulting in vegetation formation and local tissue damage

Laboratory Diagnosis:
Blood culture
v Most important diagnostic test
v Positive in 90% of cases
v 5ml for children and 10 ml for adult in 3 separate samplings within in 1-24 hours from different peripheral site is recommended
v Samples should be taken before initiating antibiotic therapy
v Culture should be grown both aerobically &  anaerobically for at least 3 wks.

Treatment:

vMedical care
v Aim: Complete eradication of organism i.e. suitable antibiotic according to culture sesitivity with proper dose.
v Prolonged parenteral therapy essential usually least 4weeks and preferably 8 weeks.
v Therapy tailored according to the etiological agent & the type of endocarditis
*** For unknown organism penicillin and gentamicin
v  Surgery may be required if heart valves are damaged
v  Prosthetic valve infection with MRSA is frequently fatal and should       be treated with a combination of vancomycin, rifampin and gentamicin