Hypertension

1. Hypertension Case Study for Computational Pharmacology

2. What is Hypertension • High blood pressure: blood forced through the arteries at an increased rate. • It is measured as two numbers, e.g. 120/80 mmHg. Normal blood pressure is below this value. • The first number is the systolic blood pressure. This is the maximum pressure in the arteries when heart contracts/beats. • The second number is the diastolic blood pressure. This is the minimum pressure in the arteries when heart is at rest between beats. • Until it becomes extreme, there are no symptoms. Hence, it is called the “Silent Killer.” • Severe hypertension may cause headache, sleepiness, confusion or coma.

3. Hypertension Categories • Primary/Essential hypertension is hypertension with no identifiable cause. • Secondary hypertension is caused by another disorder. For example, adrenal tumors, Cushing’s syndrome, kidney disorders, oral contraceptives and use of other drugs/chemicals. • Malignant hypertension is a very high blood pressure which causes swelling of the optic nerve. It is usually accompanied by other organ damage like heart failure, kidney failure and brain damage. It may be caused due to pregnancy. • Isolated systolic hypertension occurs in old age due to stiffening of the arteries. The systolic blood pressure remains above 160 and the diastolic below 90. • White coat hypertension is anxiety induced hypertension. • Resistant hypertension is blood pressure that cannot be reduced despite drug regime. • Renovascular, portal, renal, intracranial, pulmonary … • African Americans and Caucasian males have a higher rate of significant hypertension.

4. Complications Caused by Hypertensions • Atherosclerosis: Narrowing of the arteries. • Stroke: Hemorrhage or blood clots in brain. • Aneurysm: Widening of artery ultimately causing it to rupture. • Heart attack • Heart failure: Reduced pumping ability. • Kidney failure • Eye damage

5. Medicine Categories for Hypertension Treatment • Angiotensin-converting Enzyme (ACE) inhibitors stop the production of hormone Angiotensin II that makes the blood vessels narrow. • Angiotensin-II receptor antagonists/blockers (ARB) block the action of hormone Angiotensin II. • Beta-blockers block the effect of hormone adrenaline which relaxes heart so that it beats slowly. • Alpha-blockers cause blood vessels to relax and widen. • Calcium-channel blockers reduce muscle tension in arteries and slightly relaxes heart muscle. • Diuretics cause body to get rid of excess salt and fluids via kidneys. In some cases they relax blood vessels reducing strain on circulation.

6. Metabolism of yohimbine by human CYP450 isoforms. 1/3PharmGKB Dataset [Hypertension] • Background: • A2-adrenergic blockage has been used to investigate adrenergic dysfunction in human hypertension, • This suggests that a discrete subset of individuals are at genetic risk of hypertension with exaggerated sympathetic responses to the a2-antagonist yohimbine. • Role of pharmacokinetic determinants of yohimbine disposition is not completely understood in diverse human populations. • Objectives: • Study the in vitro metabolism of yohimbine in diverse human populations. • Conclusions: • None drawn. No associated papers either.

7. Metabolism of yohimbine by human CYP450 isoforms. 2/3PharmGKB Dataset [Hypertension] • Yohimbine at a substrate concentration from 1 to 250 uM was incubated in the pressence of microsomes from cells containing hetrologously expressed CYP450 isoforms co-expressed with CYP/NADP reductase. • NADP (Nicotinamide adenine dinucleotide phosphate) coenzyme. Coenzymes are small organinc non-protein molecules that carry chemical groups between enzymes. • Reductase is an enzyme that catalyzes reduction. • CYP2D6, CYP3A4 and CYP3A5 expressed in a baculovirus system were used at specific concentrations in the pressense of NADP, glucose-6-phosphate dehydrogenase in total volume of 0.5ml of 100mM potassium phosphate. • Reactions were performed in triplicate. Mean and standard error values of conversion rate and concentration are reported along with the clearance values.

8. Metabolism of yohimbine by human CYP450 isoforms. 3/3PharmGKB Dataset [Hypertension]

9. Pentose Phosphate PathwayRelationship with Glucose-6-phosphate dehydrogenase (G6PD) • Glucose-6-phosphate dehydrogenase (G6PD) is an enzyme in the pentose phosphate pathway. • This is a metabolic pathway that supplies reducing energy to cells by maintaining the level of the co-enzyme nicotinamide adenine dinucleotide phosphate (NADPH). • The NADPH in turn maintains the level of glutathione in these cells that helps protect the red blood cells against oxidative damage. • G6PD converts glucose-6-phosphate into 6-phosphoglucono-δ-lactone and is the rate-limiting enzyme of the pentose phosphate pathway. http://en.wikipedia.org/wiki/Glucose-6-phosphate_dehydrogenase_deficiency

10. Adrenergic Receptor 1/2 • A class of G protein-coupled receptors that are targets of the catecholamines. • Catecholamines are chemical compounds derived from the amino acid tyrosine. • Tyrosine is used by cells to synthesize proteins. • Tyrosine also plays a key role in signal transduction. • It is a precursor to a few thyroid hormones as well. • Catecholamines are water soluble and 50% bound to plasma proteins, so they circulate in blood stream. • Most abundant catecholamines include epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine. • These are produced mainly from adrenal medulla and the postganglionic fibers of the sympathetic nervous system. • Most catecholamines act as neurotrasmitters. They prepare the body for physical activity (so called fight-or-flight response). Typical effects include increase in blood pressure, heart rate and glucose level. http://en.wikipedia.org/wiki/Catecholamine

11. Adrenergic Receptor 2/2 • Many cells possess these receptors. • Agonist binding generally causes cell to respond in fight-or-flight manner. • Subtypes: • α receptors are present in smooth muscle and pre-/post-synaptic nerve terminals. These receptors bind norepinephrine and epinephrine, with higher affinity for norepinephrine. Phenylephrine is a selective agonist of this receptor. • β receptors are present in heart, cerebral cortex, lung, smooth muscle, cerebellum, and adipose tissue. These receptors are linked to Gs proteins. Agonist binding causes rise in intracellular concentration of second messenger cAMP. • These types are subdivided into sub-types based on their binding preference and location. See: http://en.wikipedia.org/wiki/Adrenergic_receptor

12. Sympathetic Nervous System • One of the two divisions of the vertebrate autonomous nervous system. • The sympathetic preganglionic neurons have their cell bodies in the toracic and lumbar regions of the spinal cord and connect to the paravertebral chain of sympathetic ganglia, innervate heart and blood vessels, swat glands, viscera and the adrenal medulla.

13. Sympathetic Nerve Pathway (Neuroeffector Junction)Simplified diagram of a sympathetic neuroeffector junction displaying genes which may be involved. • Yohimbine is a pre-synaptic alpha 2-adrenergic blocking agent. The exact mechanism for its use in impotence has not been fully elucidated. However, yohimbine may exert its beneficial effect on erectile ability through blockade of central alpha 2-adrenergic receptors producing an increase in sympathetic drive secondary to an increase in norepinephrine release and in firing rate of cells in the brain noradrenergic nuclei. • Yohimbine-mediated norepinephrine release at the level of the corporeal tissues may also be involved. • In addition, beneficial effects may involve other neurotransmitters such as dopamine and serotonin and cholinergic receptors. http://www.pharmgkb.org/search/pathway/neurotransmitter/neuroeffector.jsp

14. YohimbineDrug • Pausinystalia Yohimbe tree bark extract. • An alpha-blocker. • It increases Norepinephrine (a stress hormone from adrenal glands) levels. • Causes rapid heart rate, high blood pressure, over stimulation and anxiety. • Vasodialator, which causes increased blood flow to extremities and appendages. • Used to treat • Erectile dysfunction (male impotence), Libido (women) • Treat sexual side effects from antidepressants (serotonin reuptake inhibitor) • Nervous system dysfunction (autonomic failure) • Dry mouth

15. Yohimbine Metabolism PathwayPharmacokinetic pathway of yohimbine in a stylized human liver cell. http://www.pharmgkb.org/search/pathway/neurotransmitter/neuroeffector.jsp

16. Genetic Epidemiology of Responses to Antihypertensives (GERA)PharmGKB Dataset [Essential Hypertension] • Background: • Diuretics are commonly prescribed for treatment of hypertension, blood pressure decreases in response to diuretic therapy in some individuals but not in others. • Objective: • Determine whether measured variation in genes coding for components of the renin-angiotensin-aldosterone (RAA) system predicts interindividual differences in blood pressure response to diuretic therapy in African-Americans and non-Hispanic Whites. • Determine whether variation in genes of the RAA system predicts interindividual differences in baseline measures of the endocrine RAA system or response of these measures to diuretic therapy. • Determine whether the predictive effects of variation in genes of the RAA system on blood pressure response to diuretic therapy are mediated through their effects on baseline measures of the endocrine RAA system or response of these measures to diuretic therapy. • Conclusions: • Results of the proposed research have the potential to identify genes contributing to the etiology of inter-individual differences in blood pressure response to diuretic therapy in African-Americans and in non-Hispanic Whites. • Response to drug Hydrochlorothiazide studied, which is a diuretic. • Genes ACE, ADD1, ADRB1, ADRB2, AGT, AGTR1, CYP11B2, GNB3, LPL, NOS3, REN studied.

17. C825T Polymorphism of the G Protein Beta(3)-subunit and Antihypertensive Response to a Thiazide Diuretic 1/2 • Motivation: Fewer than 40% of treated hypertensives have their blood pressure adequately controlled. Drug provided control varies considerably and the variation is primarily due to pharmacodynamic differences and likely reflects variation in pathophysiological mechanisms. • The T allele of the C825T polymorphism of the gene encoding the β3–subunit of G proteins has been associated with increased sodium-hydrogen exchange and low renin in patients with essential hypertension. • Study its association with blood pressure response to diuretic therapy in 197 blacks and 190 non-Hispanic whites with essential hypertension. • The participants were given hydrochlorothiazide for four weeks. • TT genotype was a found to be a significant predictor of greater declines in blood pressure. Other univariate predictors of greater blood pressure included black race, female gender, higher pretreatment blood pressure, older age, lower waist-to-hip ratio, and measures of lower renin-angiotensin-aldosterone (RAA) system activity. • Result: The C825T polymophism of the G protein β3–subunit was found to be an indicator of diuretic therapy effectiveness in patients with essential hypertension. http://hyper.ahajournals.org/cgi/content/full/37/2/739

18. C825T Polymorphism of the G Protein Beta(3)-subunit and Antihypertensive Response to a Thiazide Diuretic 2/2 • The sample consisted of 197 unrelated black adults (134 women, 63 men) and 190 unrelated non-Hispanic white adults (76 women, 114 men) aged 30 to 59.9 years. • All participants were previously diagnosed with primary hypertension but otherwise in good health. • Subjects’ weight, blood pressure, and serum potassium concentrations were measured before, and after 2 and 4 weeks of diuretic therapy. At the end of diuretic-therapy, subjects’ plasma aldosterone concentration, renin activity, and serum potassium concentration were measured. • Subjects’ aldosterone and renin activity was measured in triplicate. Results were averaged. • Qualitative traits were summarized by calculating means and variances of each GNB3 genotype within each racial group. • A 1-way ANOVA was used to assess differences in means among genotypes within each racial group. • Relative frequencies of genotypes and alleles were calculated for each racial group. X2 contingency tests were used to assess differences in relative frequencies between racial groups. • Linear regression was used to assess whether variation in genotype made a statistically significant contribution to the prediction of blood pressure responses to hydrochlorothiazide. http://hyper.ahajournals.org/cgi/content/full/37/2/739

19. Hydrochlorothiazide (HCT, HCTZ, or HZT)Drug • A diuretic. Inhibits kidney’s ability to retain water. This reduces the volume of the blood, decreasing peripheral vascular resistance. • Belongs to thiazide class of diuretics, which act on the kidney to reduce sodium reabsorption in the distal convoluted tubule. • The distal convoluted tubule is responsible for regulation of potassium, sodium, calcium and pH. • This reduces the somotic pressure in the kidney causing less water to be reabsorbed by the collecting ducts. • This drug is used in the treatment of hypertension, congestive heart failure, symptomatic edema and the prevention of kidney stones. • This drug is also effective for diabetes insipidus and is sometimes used for hypercalciuria. • An occassional side effect is Hypokalemia, a potentially fatal condition in which body fails to retain sufficient potassium to maintain health. It is prevented by giving potassium supplements or combining this drug with potassium-spanning diuretic. • Other uses: Arteriosclerois, Calcium metabolism disorders, premature cardiac complexes, cardiomegaly, congestive heart failure, hypertension, renovascular hypertension, hypertrophy, left ventricular hypertrophy, kidney diseases. http://en.wikipedia.org/wiki/Hydrochlorothiazide

20. Antiarrythmic Drug PathwaysPharmacodynamic pathway of antiarrhythmic drugs in a stylized cardiac myocyte. • With each heart beat, cardic myocytes undergo excitation, contraction, relaxation, and repolarization. Impuleses generated by these proteins in each cell propagate over the whole heart to generate normal or abnormal rhythms. • The figure shows the major physiologic entities involved in the heart beat. Membrane ionic currents, pumps, and exchanges underlie excitation and repolarization, gap junction function determines impulse propagation, and contraction and relaxation reflect intracellular calcium cycling into and out of sarcoplasmic reticulum. • Each of the physiologic events reflects the expression and function of multiple genes. • Ionic currents are generated by expression of pore-forming proteins (“channels”), termed alpha subunits, along with function-modifying proteins, termed beta subunits. • Some currents require expression of more than one alpha subunit gene. • Beta subunit accomplish a range of tasks, including acting and chaperones or modifying gating. http://www.pharmgkb.org/search/pathway/antiarrhythmic/antiarrhythmic.jsp

21. Renin-Angiotensin-Aldosterone System (RAA) System • RAA System is a hormone system that helps regulate long-term blood pressure and blood volume in the body. • The system can be activated when there is a loss of blood volume or a drop in blood pressure (such as in a hemorrhage) • If the perfusion of the juxtaglomerular apparatus in the kidneys decreases, then the juxtaglomerular cells release the enzyme renin. • Renin cleaves an incative peptide called angiotensinogen, converting it into angiotensin I. • Angiotensin I is then converted to angiotensin II by angiotensin-converting enzyme (ACE), which is found mainly in lung capillaries. • Angiotensin II has a variety of effects on the body: • It is a vasoconstrictor. • In the kidneys, it constricts glomerular arterioles, having a greater effect on efferent arterioles than afferent. This raises systemic arterial blood pressure. The glomerular pressure is increased as a consequence to maintain glomerular filtration rate. • In the adrenal cortex, it acts to cause the release of aldosterone. Aldosterone acts on the tubules in the kidneys, causing them to absorb more sodium and water from the urine. It also acts on the central nervous system to increase a person’s appetite for salt, and to make them feel thirsty. • The net effect is an increase in the amount of fluid in the blood, making up for a loss in volume, and to increase blood pressure. • RAA is manipulated to treat high blood pressure • ACE inhibitors are often used to reduce the formation of angiotensin II. • Angiotensin receptor blockers (ARBs) is used to prevent angiotensin II from acting on angiotensin receptors. http://en.wikipedia.org/wiki/Renin-angiotensin_system

22. Renin-angiotensin-aldosterone (RAA) system http://en.wikipedia.org/wiki/Renin-angiotensin_system

23. The Renin-angiotensin System http://www.elsevier-international.com/e-books/viewbook.cfm?ID=146

24. Regulating Blood Pressure: The Rening-Angiotensin-Aldosterone System • When blood pressure falls (for systolic, to 100 mm Hg or lower), the kidneys release the enzyme renin into the bloodstream. • Renin splits angiotensinogen, a large protein that circulates in the bloodstream, into pieces. One piece is angiotensin I. • Angiotensin I, which is relatively inactive, is split into pieces by angiotensin-converting enzyme (ACE). One piece is angiotensin II, which is very active. • Angiotensin II, a hormone, causes the muscular walls of small arteries (arterioles) to constrict, increasing blood pressure. Angiotensin II also triggers the release of the hormone aldosterone from the adrenal glands. • Aldosterone causes the kidneys to retain salt (sodium) and excrete potassium. The sodium causes water to be retained, thus increasing blood volume and blood pressure. http://www.merck.com/mmhe/sec03/ch022/ch022a.html

25. Activating Mineralocorticoid Receptor Mutation in Hypertension Exacerbated by Pregnancy • Background: • Blood pressure is normally reduced throughout gestation. About 6% of pregnancies are complicated by the development of hypertension, raising the risk of pre-eclampsia, a hypertensive disorder of pregnancy that increases maternal and perinatal mortality. The disorder goes away promptly after the end of pregnancy. • Mutations that change renal salt reabsorption alter blood pressure. For example, heterozygous loss-of-function mutations in the mineralocorticoid receptor (MR), a member of nuclear receptor family, cause pseudohypoaldosteronism type 1 (PHA1), a disease featuring salt wasting and hypotension. • Normally, activation of MR by the steroid hormone aldosterone raises renal salt reabsorption by increasing activity of the epithelial sodium channel of the distal nephron. • Objective: • The study determines whether gain-of-function mutations in MR cause increased renal salt reabsorption and hypertension that may lead to early-onset hypertension, exacerbated in pregnancy. • Parameters: • The mineralocorticoid receptor (MR) is a protein in kidney cells that is involved in the body’s handling of salt. • The study looks at S810L mutation of MR protein, where Leucine was substituted in place of Serine at codon 810. The mutation lies in the MR homone-binding domain. • Study of 23 relatives of a 15 year old boy with severe hypertension with the mutation were studied. 11 of the relatives had severe hypertension before age 20, a rare trait in general. • Results: • Progesterone and other steroids lacking 21-hyroxyl groups normally act as MR antagonists. However with the mutation, they become potent agonists. • The clinically used drug spironolactone which is an MR antagonist, becomes a potent agonist for this modified protein. Study by Yale Medical School: Science Vol 278, July 2000 http://www.sciencemag.org/cgi/content/summary/sci;289/5476/23b

26. ACE-inhibitor PathwayNon-tissue specific cell displaying genes which may be involved in the ACE inhibitor pathway. • ACE inhibitors target the angiotensin converting enzyme resulting in downstream reduction of angiotensin and decreased aldosterone secretion. • The decrease in aldosterone decreases dodium and water reabsorption in the kidney and decreases potassium excretion. • Through their action on the bradykinin pathway they also increase production of nitric oxide and induce vasodilation. • Ref: Hydrochlorothiazide diuretic. http://www.pharmgkb.org/search/pathway/ace-inhibitor.jsp

27. Summary • Introduced to hypertension. • Essential vs. secondary hypertension. • Complications caused. • Medicinal categories treating hypertension. • Reviewed the hypertension dataset. • Yohimbine & its metabolic pathway. • Sympathatic nerve pathway. • Andrenergic receptor. • Reviewed the essential hypertension dataset. • Hydrochlorothiazide • ACE inhibitor pathway. • Antiarrythmic drug pathway. • RAA system. • Reviewed the hypertension exacerbated by pregnancy.

28. References • http://www.netdoctor.co.uk/diseases/facts/hypertension.htm • http://www.health24.com/medical/Condition_centres/777-792-815-1775,17124.asp • http://health.ucsd.edu/news/2003/02_05_Thistle.html • http://www.sciencemag.org/cgi/content/summary/289/5476/23b • http://www.emdbiosciences.com/html/emd/interactivepathways.htm • http://web.ebscohost.com.ezproxy1.lib.asu.edu/ehost/delivery?vid=17&hid=101&sid=27036987-d480-49b8-9608-e29cbf1ad9aa%40sessionmgr102 • http://content.nejm.org/cgi/content/abstract/348/6/500 • http://www.jraas.com/issue/current • http://www.nhlbi.nih.gov • http://www.merck.com/mmhe/sec03/ch022/ch022a.html • http://www.med.uc.edu/krianias/Sarcoplasmic_Reticulum.htm • http://www.4um.com/tutorial/science/pharmak.htm • http://www.georgetown.edu/faculty/ballc/webtools/web_chi_tut.html