fourth important cation , Second most abundant cation in intracellular fluid after K+., co- factor for more than 300 enzymes , functions of magnesium,Mg-ATP substrate , Mg-GTP substrate, ATP metabolism, muscle contraction and relaxation,normal neurological function and release of neurotransmitters are Mg dependent, green leafy vegetables are particularly rich in magnesium. Absorption in intestine and re absorption in Kidney .Paracellular -Claudin-16/-19, TRPM 6/ 7. Factor affecting for absorption and res absorption ,Action potential conduction in nodal tissue. Neuromuscular Irritability,As Constituent of Bones and Teeth: Hypomagnesemia Causes of Hypomagnesemia -Decreased intake, Redistribution from extracellular to intracellular, Increased losses -Renal Gastrointestinal. hypermagnesemia. sing and symptom of Mg deficiency, familial hypomagnesemia . Hypomagnesemia clinical manifestation, endocrinological manifestation , biochemical manifestation, method of estimations , calmagite , methylbule, Xylidyl blue, forzaman dye, enzymatic method, Magnesium Tolerance Test

1. Hari Sharan Makaju
M.Sc. Clinical Biochemistry
1st year

2. Outlines
■ Introduction
■ Distribution
■ Sources
■ Absorption
■ Function
■ Clinical aspects

3. Magnesium
■ Fourth most abundant cation in the body
– after sodium, potassium, and calcium
■ Second most abundant cation in intracellular fluid after
K+.
■ Mg++ is needed in many enzymatic reactions
■ Magnesium dependent:
– ATP metabolism, muscle contraction and relaxation,
normal neurological function and release of
neurotransmitters
■ Magnesium binds to other nucleotide phosphates and to
nucleic acids
■ Required for DNA replication, transcription, and
translation.

4. DISTRIBUTION
■ A normal 70 kg adult body contains about 25 g of
magnesium:
–˜ 55% resides in the skeleton
– ˜ 45% in soft tissues
– ˜ 1% in extracellular fluids
■ One third of skeletal magnesium is
exchangeable
– thought to serve as a reservoir for maintaining the
extracellular magnesium concentration.

5. Distribution
Within the cell
■ Most of the magnesium is bound to proteins and
negatively charged molecules
– 80% of cytosolic magnesium is bound to ATP
■ Mg ATP is the substrate for numerous enzymes.
■ The nucleus, mitochondria, and endoplasmic
reticulum contain significant amounts of
magnesium.
■ Approx. 0.5 to 5.0% of the total cellular magnesium
is free.
■ In cells varies from 2.4 to 7.3 mg/dL or 1 to 3
mmol/L

6. Distribution
Extracellular magnesium
■ Accounts for about 1% of total body magnesium
– About 55% of the magnesium in plasma is
free,
– 30% is associated with proteins (primarily
albumin),
– 15% is complexed with phosphate, citrate,
and other anions

7. Sources
■ Widely distributed in foods of both plant and
animal origin
■ As chlorophyll is the magnesium chelate of
porphyrin, green leafy vegetables are
particularly rich in magnesium
 Vegetables, grains, legumes and nuts (and some fish and seafood)
generally have a higher magnesium content (60-2700 mg/kg)
compared to animal products such as meat and dairy (<280 mg/kg)
 Refined wheat, barley, rye or rice flour have less magnesium compared
to whole grain products

8. Sources

9. Recommended Dietary
AllowanceLife Stage Age Males (mg/day) Females (mg/day)
Infants 0-6 months 30 (AI*) 30 (AI)
Infants 7-12 months 75 (AI) 75 (AI)
Children 1-3 years 80 80
Children 4-8 years 130 130
Children 9-13 years 240 240
Adolescents 14-18 years 410 360
Adults 19-30 years 400 310
Adults 31 years and older 420 320
Pregnancy 18 years and younger - 400
Pregnancy 19-30 years - 350
Pregnancy 31 years and older - 360
Breast-feeding 18 years and younger - 360
Breast-feeding 19-30 years - 310
Breast-feeding 31 years and older - 320
*Adequate Intake

10. Increased Magnesium Requirements

11. Absorption
■ Absorbed mostly in the small intestine and some
extent in the large intestine .
■ There are two pathways
– Paracellular
– Transcellular
Fed Fractional Absorption
7 mg 65-75%
36 mg 11-14%

12. Absorption
Paracellular absorption
 Passive transport which is
responsible for 80–90% of
uptake
 The exact mechanism for
paracellular transport is not
known
 But has been attributed to
high luminal magnesium
concentration and tight
junction permeability
regulated by Claudin-16
and -19.

13. Absorption
Transcellular absorption
■ Facilitated by transient receptor
potential channel melastatin member 6
(TRPM6) and TRPM7 Mg2+ channels
■ TRPM7 is ubiquitously expressed
among tissues,
■ TRPM6 is found
– along the full length of the intestine
(with the highest expression in the colon
and caecum),
– along the kidney nephron(predominantly
in distal convoluted tubules),
– lung and testis tissues
■ Penner and Fleig (2007) have found
that TRPM6 and TRPM7 are suppressed
by elevated cytoplasmic free Mg2+ and
Mg ATP, suggesting that cytosolic Mg2+
is an important regulator of channel
function
CNNM-4
Members of the Cyclin M :CNNM-4

14. Factor affecting absorption■ Size of Mg load:
– Absorption is doubled when normal dietary Mg requirement is
doubled and vice versa.
■ Dietary calcium:
– Increased absorption in calcium deficient diets.
– Decreased absorption occurs in presence of excess of Ca.
■ Common transport mechanism from intestinal tract for both Ca
and Mg suggested.
■ Motility and mucosal state:
– In hurried bowel, absorption is decreased.
– Absorption decreases in damaged mucosal state.
■ Vitamin D, Parathyroid hormone and growth hormone :
– Helps in increased absorption.
■ Other factors
– High protein intake and neomycin therapy increases
absorption.
– Fatty acids, phytates and phosphates decrease absorption.

15. Renal Reabsorption
■ Kidney plays a crucial role in the maintenance
of Mg2+ balance filtering approximately 2000-
2400 mg of magnesium per day
■ 95-97% of filtered magnesium is reabsorbed in
the renal tubules
– 10-25% of the filtered magnesium is absorbed in
the Proximal tubule
– Thick ascending limb of the loop of Henle, (TAL) :-
50 - 70% of total reabsorption
– Distal convoluted tubules(DCT) -: 5 -10% of
reabsorption magnesium
■ 3-5% is excreted in the urine i.e.~100 mg [3]

16. Renal Reabsorption
■ TAL - facilitated by
claudin 16 and claudin
19
■ Required 2 conditions
■ First is a lumen positive
transepithelial voltage
■ Second is paracellular
permeability for the
divalent cations.
Na+–K+–2Cl-cotransporter: (NKCC2)
renal outer medullary K : (ROMK) channel

17. Renal Reabsorption
■ ‘Fine-tuning’ of Mg2+
reabsorption takes place along
DCT
■ Reabsorbed by an active
transcellular transport via
TRPM6
■ The voltage-gated K+ channel
Kv1.1 provides the driving force
for Mg2+ transport across the
apical
■ Epidermal growth factor
regulates active.
■ At the basolateral membrane,
extrusion of Mg2+ occurs
against a steep
electrochemical gradient via a
recently identified
magnesium/sodium exchanger
SLC41A1 family .
Transient receptor potential channel melastatin 6
:-TRPM 6
SLC-41A1

18. Factors Affecting Renal Excretion
■ Calcium intake:
– Increased dietary calcium produced increased excretion of Mg.
■ Parathormone (PTH):
– Diminishes excretion.
■ Antidiuretic hormone (ADH) & Aldosterone :
– Increases Mg excretion
■ Thyroid hormones:
– 80 per cent greater excretion in hyperthyroidism.
■ Alcohol ingestion:
– Oral ingestion of as little as 1.0 ml of 95 per cent alcohol per kg,
increases urinary excretion 2 to 3-fold.
– The increased excretion partially accounts for Mg-deficiency in
chronic alcoholics with Delirium tremens.
■ Administration of acidifying substances (NH4Cl) is followed
by increased urinary elimination of Mg

19. Excretion
■ Faeces:
– 60 to 80 per cent of orally taken Mg is lost in
faeces.
■ Urine:
– Dependent on renal handling of the ion.
– In a normal healthy adult with normal diet 3 to
17 mEq are excreted daily(3-5%)
■ Sweat loss:
– 0.75 mEq of Mg is lost daily in perspiration in
normal health with normal diet.

20. 20-25%
50-60%
25-30%

21. Representative fluxes (mmol/24 h) in a healthy adult (70 kg body weight)
for magnesium.

22. Functions
Role in Enzyme Action
■ Cofactor for more than 300 enzymes in the body.
■ Required for formation of substrates of enzymes (e.g., Mg-
ATP, , GTP-Mg is a substrate for numerous enzymes that
require ATP)
– Enzyme substrate (ATP-Mg, GTP-Mg)
■ Kinases B
– Hexokinase
– Creatine kinase
– Protein kinase
■ ATPases or GTPases
– Na + /K + ATPase
– Ca2+ ATPase
■ Cyclases
– Adenylate cyclase
– Guanylate cyclase

23. Functions
Role in Enzyme Action
 Magnesium is an allosteric activator of many enzyme
systems.
 Examples of enzymes that require magnesium for
action:
 Phosphofructokinase
 Creatine kinase
 5 -Phosphoribosyl-pyrophosphate synthetase
 Adenylate cyclase
 Na + /K + ATPase
 Ca2+ ATPase

24. Functions
■ Membrane function
– Cell adhesion
– Transmembrane electrolyte flux
■ Transport of potassium and calcium which are essential
for the conduction of nerve impulses, muscle
contraction, maintaining vasomotor tone and for normal
heart rhythm.
■ Structural function
– Proteins
– Polyribosomes
– Nucleic acids
– Multiple enzyme complexes
– Mitochondria

25. Functions

26. Functions
Calcium antagonist
■ Muscle contraction/relaxation
– In muscle contraction, for example, magnesium
stimulates calcium re-uptake by the calcium-activated
ATPase of the sarcoplasmic reticulum
■ Neurotransmitter release
– Magnesium also influences neurotransmitter release at
the neuromuscular junction
– by competitively inhibiting the entry of calcium into the
presynaptic nerve terminal.
■ Action potential conduction in nodal tissue
– A decrease in the serum magnesium concentration
– Lowers the threshold of axonal stimulation
– Increases nerve conduction velocity.

27. Function
Neuromuscular Irritability:
■ Mg exerts an effect on neuromuscular irritability similar to
that of Ca++,
– High levels depress nerve conduction and low levels
may produce tetany (hypomagnesaemic tetany).
■ Reducing the serum magnesium concentration results in
increased neuromuscular excitability.
As Constituent of Bones and Teeth:
■ About 70 per cent of body magnesium is present as apatite
in bones, dental enamel and dentin

28. Hypomagnesemia (below 1.2 mg/dL)
■ Magnesium deficiency can thus result in a variety of
metabolic abnormalities and clinical consequences
■ Hypomagnesemia is common in patients in hospitals.
– 10% of patients admitted to city hospitals and as
many as 65% of patients in intensive care units may
be hypomagnesemic
■ Causes of Hypomagnesemia
– Decreased intake,
– Redistribution from extracellular to intracellular,
– Increased losses
– Renal
– Gastrointestinal

29. Hypomagnesemia
Decreased Intake
 Decreased Dietary consumption
 Alcohol Dependence
 Hypomagnesemia develops in people with chronic
alcohol abuse
 Parenteral Nutrition
 Approximately 48% of the population in the United
States have been shown to consume less than the
daily magnesium requirement.

30. Hypomagnesemia
Redistribution from Extracellular to Intracellular Compartment:
■ Recovery from starvation (Refeeding Syndrome)
– Not clear mechanism.
– It is possibly related to the intracellular movement of magnesium
with carbohydrate feeding and preexisting low magnesium status
■ Hungry Bone Syndrome
– Causes hypomagnesemia by increased uptake of magnesium by
renewing bone after parathyroidectomy or thyroidectomy
■ Treatment of Diabetic Ketoacidosis
– Diabetic ketoacidosis also causes hypomagnesemia by driving
magnesium into the cells
■ Acute Pancreatitis
– Pancreatitis causes hypomagnesemia by saponification of
magnesium in necrotic fat

32. Hypomagnesemia
Gastrointestinal Losses:
■ Diarrhea
■ Vomiting
■ Nasogastric suction
■ Malabsorption
■ Small bowel bypass surgery
■ Proton Pump Inhibitors
– may be excessive gut loss rather than
malabsorption

33. Hypomagnesemia
Renal Losses:
■ Familial:
– Bartter syndrome,
– Gitelman syndrome
– Familial hypomagnesemia with hypercalciuria and
nephrocalcinosis (FHHNC)
■ Acquired:
– Medications: Thiazide Diuretic, Aminoglycoside
Antibiotics, Amphotericin B, Cisplatin, Pentamidine,
Tacrolimus, Cyclosporine
– Alcohol Dependence,
– Hypercalcemia

34. Acquired Hypomagnesemia
NKCC2
NCCT

35. Acquired Hypomagnesemia
■ Aminoglycosides including
amikacin and gentamicin are well
known to induce
hypomagnesemia,
– Hypothesized to occur via
binding to and activation of
the CaSR.
■ CaSR reduce ROMK activity,
hence reduce the favorable
potential
difference necessary for optimal
paracellular Mg2+ reabsorption at
the TAL.
■ Activation of CaSR by
extracellular calcium upregulates
claudin-14, which in turn interacts
with the claudin-16/claudin-19
complex and inhibits its cation
permeability

36. Disorders Renal
segment
Gene Protein Serum
Mg
Urine
Mg
Other
symptoms
Pattern of
inheritances
Familial
hypomagnesaemia
with hypercalciuria
and nephrocalcinosis
TAL Claudin-16 and
-19
Nephrocalcinosis
and visual
impairment
AR
Bartter’s syndrome TAL Na-K -Cl
cotransporter,
Barttin,
ClC-Kb Cl
channel,
ROMK K channel
Hypokalaemic
alkalosis,
elevated renin
and aldosterone
AR
Hypomagnesaemia
with secondary
hypocalcemia
DCT TRPM 6 Epileptic
seizures, muscle
spasms and
mental
retardation
AR
Gitelman syndrome DCT Na–Cl
cotransporter
Muscle
weakness,
tetany and
fatigue
AR
Isolated dominant
hypomagnesaemia
DCT FXYD2
(Na 1/K 1-
ATPase-Protein)
Convulsions AD
Isolated autosomal
recessive
hypomagnesaemia
DCT EGF Epileptic
seizures and
mental
retardation
AR
Human genetic magnesium transport disorders

38. Clinical manifestations of
hypomagnesemia■ Neuromuscular/Nervous System:
– Tremor, Fasciculations, Tetany, Headaches, Seizures, Fatigue,
Generalized Fatigue, Asthenia
■ Cardiovascular system :
– Atherosclerotic Vascular Disease/Coronary Artery Disease
– Arrhythmias: Torsades de pointes, PR prolongation,
progressive QRS widening and diminution of T-waves
– Hypertension
– Congestive Heart Failure
■ Osteoporosis
■ Asthma
■ Nephrolithiasis

40. Endocrine Manifestations
Altered Glucose Homeostasis/Diabetic
Complications
■ Required for glucose utilization and insulin
signaling
■ Magnesium depletion is common in both
insulin resistant individual and in diabetics
■ Low intracellular magnesium levels will
result in defective tyrosine kinase activation
and reduced insulin receptor activation and
signaling
■ Magnesium improves the ability of b-cells to
compensate for variations in insulin
sensitivity in non-diabetic individuals
■ Magnesium may help lower blood glucose
levels via increased GLUT4 mRNA
expression, independent to insulin secretion
■ American Diabetes Association published a
consensus statement in 1992 suggesting
that diabetic patients with
hypomagnesemia
should receive magnesium
supplementation.

41. Biochemical Manifestations
Hypokalemia
– Hypokalemia is a common finding in patients with
hypomagnesemia.
– Potassium depletion in these cases cannot be resolved until
magnesium is replete.
■ Mechanism for the hypokalemia in magnesium deficiency can be
secondary to multiple mechanisms
■ Regulating the activity of the ROMK
■ Other possible mechanisms are likely linked to the
dependence
of sodium-potassium+-ATPase, Sodium/Potassium co-
transport, and other transport processes on magnesium.

42. Hypokalemia
■ Regulating the activity of the ROMK
■ A high intracellular magnesium level blocks the ROMK channel pore
and prevents potassium efflux.
■ Therefore, low intracellular magnesium will cause potassium efflux
and result in hypokalemia.
Low Mg++

43. Hypocalcemia
■ Symptomatic hypocalcemia is seen more commonly in
patients with moderate to severe magnesium deficiency.
■ Hypocalcemia with magnesium deficiency cannot be
treated or corrected with calcium, vitamin D, or both.
■ Magnesium therapy alone will resolve the hypocalcemia.
■ Different mechanisms have been hypothesized for
hypocalcemia in magnesium deficiency.
– Impaired secretion of PTH, end-organ resistance for
PTH, increase in metabolism of PTH, decrease in 1,25
dihydoxy-vitamin D,
Biochemical Manifestations

45. Hypermagnesemia
■ Symptomatic hypermagnesemia is almost always
caused by excessive intake
– Antacids
– Purgative
– Parenterally
– Treatment of pregnancy-induced hypertension
– Treatment of magnesium deficiency
■ Impaired renal excretion of magnesium
– Acute kidney injury and chronic kidney disease
– Familial hypocalciuric hypercalcemia
– Lithium treatment

46. Hypermagnesemia
■ Depression of the neuromuscular system is the most
common manifestation of magnesium intoxication.
■ Deep tendon reflexes disappear at a serum
magnesium concentration above 5 to 9 mg/dL
■ Depressed respiration and apnea, caused by voluntary
muscle paralysis,
– may occur at serum magnesium concentrations
greater than 10 to 12 mg/dL .
■ Hypermagnesemia induces a decrease in the serum
concentration of calcium, presumably
– because of the inhibition of both PTH secretion and
end-organ action of PTH by magnesium.

47. Magnesium and addiction
■ Stress increases the vulnerability of an
individual to addiction and low magnesium
status increases the risk of relapse
■ Magnesium supplementation:
– decreases dopamine synthesis and release
in brain
– decreases the activity of glutamate NMDA
receptors
– increases glutamate metabolism (as the
main excitatory amino acid involved in
addiction) by enhancing glutamate
decarboxylase activity
– increases GABA activity

49. Indication for measurement of
Magnessium
■ Following myocardial infarction
■ Refractory cardiac dysrhythmias
■ Alcoholism
■ Hypokalemia, particularly if refractory to treatment
■ Patients receiving diuretic drugs, digoxin, cyclosporine
■ Severe or prolonged diarrhea
■ Patients receiving parenteral nutrition
■ Unexplained hypocalcaemia, hyponatremia or or
chemotherapy for malignant disease hypophosphataemia

50. Methods of Estimations
■ Measured by various techniques
– Photometry
– Fluorometry
– Flame emission spectroscopy,
– Atomic absorption spectrometry
■ Photometric methods are most commonly used
■ AAS is considered the reference method, it is rarely
used today

51. Photometric Methods
■ Calmagite method
Principle
■ Calmagite [1-(1-hydroxy-4-methyl-2-phenylazo)-2-naphthol- 4-
sulfonic acid] , a metallochromic indicator, forms a colored
complex (reddish violet) with magnesium in alkaline solution,
which is measured at 530 to 550 nm.
■ Ethylene glycol tetra-acetic acid (EGTA), specifi calcium-chelating
agent
– Added to reduce interference by calcium.
■ Reagents may include potassium cyanide
– to prevent formation of heavy metal complexes
■ Polyvinylpyrrolidone and surfactants
– to reduce interference from protein and lipemia

52. Methylthymol blue
■ Methylthymol blue forms a blue complex with magnesium,
which is measured around 600 nm
– EGTA is added to reduce interference by calcium.
Xylidyl blue
■ Magon, or xylidyl blue [1-azo-2-hydroxy-3
(2,4dimethylcarboxanilido)-naphthalene-1′-(2
ydroxybenzene)] ,binds magnesium in alkaline solution,
causing a spectral shift and forming a red complex.
■ Absorbance most often has been measured around 600
nm.
– Calcium interferences are reduced by EGTA
– Protein interferences are reduced by dimethyl sulfoxide,

53. Formazan dye
■ A formazan dye [1,5-bis(3,5-dichloro-2-hydroxyphenyl)-
3-formazan carbonitrile] forms a complex with
magnesium at alkaline pH, which has been measured
at 630 nm by thin-film reflectance photometry.
– N,N′-[1,2-ethanediylbis(oxy- 2,1 phenylene)bis(N-
carboxymethyl)] glycine is used to chelate calcium.
– This thin-film reflectance method shows relatively
little interference from icteric, lipemic, and
hemolyzed specimen

54. Enzymatic methods
■ Have been developed with hexokinase or another enzyme
that uses Mg2 +-ATP as a substrate.
■ The rate of the enzyme-catalyzed reaction is dependent on
the concentration of magnesium.
■ When hexokinase is used with glucose-6-phosphate
dehydrogenase, the rate of the dehydrogenase reaction is
monitored by measuring the formation of NADPH monitored
at 340 nm.
■ Glucose + Mg2 +-ATP Glucose 6-Phosphate +ADP
■ Glucose 6-Phosphate+NADP+ Gluconolactone - 6-
Phosphate
+NADPH + H+
Hexokinase
G6PDH

55. Atomic Absorption Spectrometry
■ Atomic Absorption Spectrometry
■ Provide greater accuracy and precision for
magnesium measurements than do photometric.
■ After dilution with lanthanum oxide solution ,
specimen are subjected to AAS determination
■ Specimen are reacted at high temperature
,reducing the ionic magnesium and converting it
into atomic Magnesium vapor and the light
absorbed by the Magnesium at its characteristic
wavelength of 285.2 nm is quantified.

56. Free (Ionized) Magnesium
■ In the 1990s - Instruments for the measurement of free magnesium
were developed.
■ These instruments use ISEs with neutral carrier ionophores, including
ETH5220, ETH7025, or a proprietary ionophore.
■ Current ionophores or electrodes have insufficient selectivity for
magnesium over calcium.
■ Thus it is necessary to determine the two ions simultaneously in each
sample and to correct the result for Ca2 + interference.
■ Also pH should be measured simultaneously, as the binding of Mg in
plasma is pH dependent

57. Magnesium Tolerance Test
■ Magnesium status of an individual is best measured by a
parenteral magnesium load test
– also known as a magnesium tolerance test
■ In this test, the percentage magnesium retention is assessed
after an intravenous magnesium load.
– After baseline collection of 24 hour urine, 0.1 mmol/kg body weight
of magnesium is administered intravenously in 5% dextrose
– Another 24 hour urine collection is carried out.
– In individuals with adequate magnesium stores, 60 to 80% of the
magnesium load is excreted within 24 hours.
■ Urine specimens should be collected in acid
– (e.g., HCl, 6 mol/L, with 20 to 30 mL added to the container for a 24
hour collection)
■ To prevent precipitation of magnesium complexes.

58. SUGGESTED PROTOCOL FOR USE OF
MAGNESIUM TOLERANCE TEST
I. Collect baseline 24-h urine for magnesium/creatinine ratio.
II. Infuse 0.2 mEq (2.4 mg) elemental magnesium per kilogram of
lean body weight in 50 ml of 5% dextrose over 4 h.
III. Collect urine (starting with infusion) for magnesium and creatinine
for 24 h.
IV. Percentage magnesium retained is calculated by the following
formula:
Criteria for Mg deficiency
.50% retention at 24 h = definite deficiency
.25% retention at 24 h = probable deficiency

59. Thank YOU

60. References
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