L14 - L17 Flashcards
Mechanism for Active B12 Absorption
- through ileum
- Vit B12 released from food & bound to haptocorrin (transcobalamin 1) produced in salivary glands
- Haptocorrin takes B12 to duodenum and is degraded by proteases, releasing B12
- B12 then captured by Gastric Intrinsic Factor (glycoprotein produced by parietal cells).
- goes through intestine & is endocytosed by cubam in terminal ileum - Intrinsic factor is degraded in enterocyte releasing B12 which gets released in blood by ABC transporter where it binds to transcobalamin II
Plasma Transport of Vit B12 & Cellular Uptake
- B12 transported in plasma binded to transcobalamin 1,2 or 3
- uptake when transcobalamin binds to its receptor CD320 and is endocytosed. transcobalamin degraded yielding B12
- Excess B12 is stored in liver
Pernicious Anaemia
(Autoimmune atrophic gastritis)
Destruction of gastric parietal cells and the associated lack of intrinsic factor
- immune response attacks H+/K+ ATPase
- also caused by antibodies directed against intrinsic factor
Consequences of Vitamin B12 Deficiency
- normal serum conc. B12 is 115-100pmol/L
Megaloblastic anaemia - main symptom
Neurological - Paraesthesia, ataxia, sensory weakness
Digestive - Hunters collitis
Cardiovascular - angina, thrombosis
degeneration of spinal cord
- myelin sheath degeneration
Drug Induced B12 Deficiency
- PPI & H2 antagonists
- Oral Contraceptive
- Metformin
- Cholchicine
PPI & H2 antagonists - Less stomach acid so less B12 release from food not broken down
Oral Contraceptives - reduces transcobalamin levels
Metformin - reduces B12 absorption
Cholchicine
- impairs or inhibits receptors in terminal ileum
Treatment of B12 Deficiency
- lifelong treatment
Oral - cyanocobalamin
parenteral - hydroxocobalamin
- must be parenteral if intrinsic factor deficient or surgically removed stomach because B12 will be degraded in stomach
Sources of B9
- folate/folic acid
- dark green vegetables
- cooking destroys B9 in vegetables
RDA 200mcg / day
400mcg supplement given in pregnancy
Absorption of Folate
- requirements
- natural folates are conjugated into polyglutamyl chain
- folate must be in monoglutamate form to be absorbed
- glutamic acid residue on folate is cleaved off by folate conjugase.
Absorption of Folate Steps
- most absorption occurs in proximal small intestine (in duodenum or jejunum) some in colon
- Polyglutamic Folate made into monoglutamic by folate conjugase. absorbed from lumen by PCFT& RFC - folate is exchanged for organic phosphate (OP)
- Enterocytes have folate receptors and internalise it by receptor mediated endocytosis. enterocyte exports it as folate or metabolises it to 5-MTHF
- exported to blood via Organic Anion Transporter & circulates in blood (some is albumin-bound)
- Cellular uptake again by PCFT, RFT, & Folate receptors
Symptoms & Treatment for Folate Deficiency
- (can cause megaloblastic anaemia)
Symptoms:
- sore tongue + swallowing pains
- nausea, vomiting, diarrhoea
- dementia, depression
Treatment: oral folic acid 1-4 months
- oral route is sufficient even with malabsorption patients
Pharmaceutical Analysis
- determines quality of drug via analytical chemistry
Step 1 : analysis of pharmaceutical product, make sure contents are correct
- UV/Vis Spectrophotometry
- High-pressure Liquid chromatography
Step 2 : Analysis of solid product, is the material the required product
- infrared Spectroscopy
- X-ray Diffraction
Spectroscopy
- energy gain through levels of excitation
- microwave causes rotational energy from dipoles absorbing energy
- infrared wavelengths cause vibrational energy when bonds absorb energy and vibrate
Diffraction
- process
- light shined onto diffraction grate, separating polychromatic light into different wavelengths
- sample cuvette with drug in it is moved into the wavelength of light to be used, rest is blocked out
- PMT detects amount of light coming through cuvette
we can work out how much light was absorbed by drug
Quantitative analysis
- Beer Lambert Law
- more drug = more absorption
- light scattering must be avoided, sample must be homogenous (no undissolved drug or bubbles)
Infrared Spectroscopy
< 800nm is “fingerprint” region - you can compare against different molecules unique IR region
- IR has less energy than UV/Vis
- causes rotational and vibrational energy level shifts
Gestational Diabetes
Gestational Diabetes
- can affect up to 25% of pregnant women
- usually develops in 2nd trimester
- possibly due to hormone changes which may block insulin action
Diagnosing Diabetes
- Fasting glucose test
- Fasting Glucose Test
- no food/drink for 8-10hrs before (except water)
- normal range 3.9 - 5.4mmol/L
- pre-diabetic 5.5 - 6.9, diabetic : >7mmol/L
Diagnosing Diabetes
- Oral Glucose Tolerance Test
- Oral Glucose Tolerance test
75g glucose dissolved in water
- 7.9 - 11 mmol/L impaired glucose tolerance
> 11.1 mmol/L indicates diabetes
Diagnosing Diabetes
- HbA1c Test
- not for type 1
HbA1c - haemoglobin A (HbA) and glucose
- gives measure of glucose levels over last 3-4 months
> 48mmol/mol - diabetes
42 - 47mmol/mol - diabetes risk
Acute Symptoms of Diabetes
- increased urination, dehydration
- tiredness, hunger
- glucose levels high, kidney can’t absorb
-unabsorbed glucose in urine draws H2O - increased urination, dehydration & blurred vision
- tiredness, hunger and weight loss as glucose is not stored as energy source so fat stores are broken down
- damage to blood vessels limits flow of oxygen needed for repair - slows healing
Diabetic Ketoacidosis
- chronic Type 1 diabetes complication
- metabolic changes in T2 usually not severe enough to cause DKA
- body can’t use glucose as energy source which increases release of Free Fatty Acids from adipocytes
- FFA’s made into ketones by the liver (acetoacetate) which serves as energy source but it makes blood acidic
- liver keeps secreting glucose which causes dehydration further lowering blood pH which can be deadly
Treatment of DKA
Treatment: fluid replacement, insulin, mineral replacement
- usually develops at time of diabetes diagnosis or during illness/ during growth spurt
Chronic Diabetes Complications
- retinopathy
- nephropathy
- neuropathy
- diabetic foot
Diabetic Retinopathy - damage to vessels in eye (leading cause of blindness)
Diabetic Nephropathy - microvascular liver damage
Diabetic Neuropathy - sensory loss by hyperglycaemia and damage to blood vessels
Diabetic Foot - damage to blood vessels leads to slower healing because less oxygen. can lead to amputation
Insulin Signalling
- PKB Activation
- insulin binding to receptor causes autophosphorylation (receptor is a kinase)
- IR phosphorylates Tyrosine residues on IRS proteins causing phosphoinositide 3-kinase to bind to IRS
- this causes PIP2 -> PIP3. binding to PIP3 activates PDK 1 which activates PKB
- activated PKB diffuses through cell wall and activates glucose transport and glycogen synthesis
Glucose Uptake Pathway into Adipocytes & Muscle
- insulin signalling
- blood glucose rise = insulin release
- AS160 phosphorylated by PKB, inactivating it, releasing GLUT-4 from vesicles
- allows GLUT4 to bind to plasma membrane, increasing glucose transporter levels at surface
- Glucose binds to GLUT-4 and is taken into cell
Insulin Signalling
- Repression of Gluconeogenesis
- Fox01 is transcription factor for gluconeogenic genes
- insulin signalling = PKB activation.
PKB phosphorylates Fox01 in cytosol - prevents Fox01 entering nucleus as gluconeogenic transcription factor
- leads to loss of gluconeogenic gene expression in liver = less glucose production
Type 1 Diabetes
- Autoimmune condition resulting in destruction of
beta-cells, insulin deficiency & hyperglycaemia
Causes :
- HLA1 area of genome is susceptible to T1 D
- autoantibodies against beta-cell antigens
- glutamic acid decarboxylase-65 (GAD-65), Insulin, IA-2
- presence of 2 of these autoantibodies increases TD 1 risk within next 10yrs to 75%
Inhibition of Insulin Signalling Pathways
- PTP1B Pathway
- PKC Pathway
PTP1B Pathway:
- PTP1B activates PKC
- PKC phosphorylates serine residues on IRS
- prevents IR phosphorylating tyrosine residues on IRS
Obesity Leading to Insulin Resistance
- DAG & Ceramide Pathway
- triglycerides exceed storage capacity in adipose cells. fat accumulates in muscle + liver
- DAG & Ceramide formed from fatty acids
- They cause serine residue phosphorylation on IRS
Obesity Leading to Insulin Resistance
- TNF-a Pathway
- Obese patients release more pro-inflammatory cytokines like TNF-a
- TNF-a causes expression of PTP1B which dephosphorylates Insulin receptor
Obesity Leading to Insulin Resistance
- Adiponectin
- Adiponectin secreted from adipocytes and promotes insulin sensitivity
- obese patients produce less adiponectin leading to insulin resistance
