pulmonary toxicology disposition metabolism and enzyme kinetics l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Pulmonary Toxicology : Disposition, Metabolism and Enzyme Kinetics PowerPoint Presentation
Download Presentation
Pulmonary Toxicology : Disposition, Metabolism and Enzyme Kinetics

Loading in 2 Seconds...

play fullscreen
1 / 40

Pulmonary Toxicology : Disposition, Metabolism and Enzyme Kinetics - PowerPoint PPT Presentation


  • 141 Views
  • Uploaded on

Pulmonary Toxicology : Disposition, Metabolism and Enzyme Kinetics. Anthony J. Hickey, Ph.D., D.Sc. School of Pharmacy, UNC-Chapel Hill, NC. Introduction Lung Deposition Clearance Mechanisms Mucociliary Transport Cell Transport Absorption Lung Cells Enzyme Expression Metabolism

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Pulmonary Toxicology : Disposition, Metabolism and Enzyme Kinetics' - wyndham


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
pulmonary toxicology disposition metabolism and enzyme kinetics

Pulmonary Toxicology : Disposition, Metabolism and Enzyme Kinetics

Anthony J. Hickey, Ph.D., D.Sc.

School of Pharmacy, UNC-Chapel Hill, NC

slide2
Introduction
  • Lung Deposition
  • Clearance Mechanisms
    • Mucociliary Transport
    • Cell Transport
    • Absorption
  • Lung Cells
  • Enzyme Expression
  • Metabolism
  • Conclusion
slide3

Nasal

Passages

G

I

T

r

a

c

t

B

l

o

o

d

T-B Airways

Pulmonary

Parenchyma

Lymph

Nodes

slide4

Mucus

blanket

Cilia

Columnar

epithelial

cells

slide5

100

10

1

0.1

MICE

RATS

PEOPLE

DOGS AND GUINEA PIGS

100 200 300

FRACTION CLEARED PER DAY (X103)

DAYS AFTER INHALATION

slide8

Passive Diffusion

Facilitated Diffusion

Active Transport

slide9

100

10-1

10-2

10-3

10-4

10-5

RAT

RABBIT

DOG

SHEEP

FETAL LAMB

MAN, AEROSOL

DOG, AEROSOL

101 102 103 104 105 106

CLEARANCE (min-1)

MOLECULAR WEIGHT (daltons)

Effros and Mason, 1985

slide10
Introduction
  • Lung Deposition
  • Clearance Mechanisms
    • Mucociliary Transport
    • Cell Transport
    • Absorption
  • Lung Cells
  • Enzyme
    • Action
    • Expression
    • Distribution
  • Conclusion
slide12

k1

k3

E + S ES E + P

k2

The rate of first-order kinetic reaction:

One-substrate mechanism:

slide13

Dependence of initial rate of

  • reactant concentration for a simple
  • first- or second-order chemical reaction.
  • Dependence of initial rate of
  • substrate concentration for a typical
  • enzyme-catalyzed reaction.
slide15

Catalytic cycle of microsomal carboxylesterase (left) and microsomal epoxide hydrolase (right), two α/β-hydrolase fold enzymes.

slide16

OH

SH

DRUG

DRUG

DRUG

NH3+

CO2-

Drug and Xenobiotic Metabolism

Glucuronic Acid

Carboxyamide

PHASE I

PHASE II

Functionalization

Conjugation

SO4-

Glutathione

Cytochrome P450s

Monooxygenases

Dehydrogenases

Oxidases

Esterases

Glucuronosyltransferases

Sulfotransferases

Acetyltransferases

Methyltransferases

Glutathione S-Transferases

MDR1 (P-Glycoprotein)

EXCRETION

Courtesy: Matt Redinbo

enzymatic systems in the respiratory tract
Enzymatic Systems in the Respiratory Tract
  • Phase I
    • CYP-450s
    • Flavin containing mono-oxygenases (FMA)
    • Monoamine oxidase (MAO)
    • Aldehyde dehydrogenase
    • NADPH cP450 reductase
    • Esterases
    • Epoxide hydrolase
enzymatic systems in the respiratory tract18
Enzymatic Systems in the Respiratory Tract
  • Phase II conjugating enzymes
    • Glutathione S-transferase (GST)
    • Sulfotransferase
    • N-acetyltransferase
    • methyltransferase
slide23

Summary of Expression of Xenobiotic-Metabolizing Enzymes in

Human Lung —Phase I Enzymes

- weak negative evidence, +/- conflicting evidence, + weak positive evidence, ++ moderate positive evidence, +++ strong evidence, ? no report

Zhang, J. Y.; Fen Wang, Y.; Prakash, C., Current Drug Metabolism 2006, 7, 939-948.

slide24

Summary of Expression of Xenobiotic-Metabolizing Enzymes in Human Lung —Phase II Enzymes

- weak negative evidence, +/- conflicting evidence, + weak positive evidence, ++ moderate positive evidence, +++ strong evidence, ? no report

Zhang, J. Y.; Fen Wang, Y.; Prakash, C., Current Drug Metabolism 2006, 7, 939-948.

distribution of enzymes
Distribution of Enzymes
  • Upper respiratory tract
    • Olfactory epithelium:
      • CYP450 & NADPH
      • CYP450 levels < liver, but activities >> than liver
      • Epoxide hydrolase, carboxylesterase, aldehyde dehydrogenase activity > respiratory
      • Phase II enzymes: GST, glucoronyl transferases, sulfotransferases
distribution of enzymes26
Distribution of Enzymes
  • Lower respiratory tract
  • Tracheobronchial region
    • CYP450 throughout
    • FMO absent in larynx and trachea
  • Bronchiolar region
    • Clara cells:
      • CYP450 isozymes
      • NADPH cP450 reductase
      • FMO, GST, UDP-GT, and epoxide hydrolase
    • Type II pneumocytes
      • CYP450 isozymes
      • NADPH cP450 reductase
distribution of enzymes27
Distribution of Enzymes
  • Alveolar Macrophages:
    • No CYP450
  • Type I cells
    • No metabolic activity
    • Susceptible to toxicity e.g. butylated hydroxytoluene is severely toxic to Type I cells
slide28
Introduction
  • Lung Deposition
  • Clearance Mechanisms
    • Mucociliary Transport
    • Cell Transport
    • Absorption
  • Lung Cells
  • Enzyme
    • Action
    • Expression
    • Distribution
  • Conclusion
pulmonary enzyme systems
Pulmonary Enzyme Systems
  • CYP450 mono-oxygenase
    • Metabolism of endogenous FA’s, steroids, and lipid soluble xenobiotics
    • Note: some metabolism leads to bioactivity or carcinogens (e.g. benzo[a]pyrene)
  • NADPH Cytochrome P450 reductase
    • Identical to hepatic enzyme
    • Activates toxicity of paraquat and nitrofurantion (reduction of nitro grp  free radical  regenerates parent drug and superoxide anion  lipid peroxidation and depletion of cellular NADPH)
structures of some acute pulmonary toxins
Structures of Some Acute Pulmonary Toxins

J.J. Fenton, Toxicology: A Case-Oriented Approach, CRC Press, Boca Raton, FL 2002.

diesel exhaust particles
Diesel Exhaust Particles

Solid carbon core (primary particle size of

10-80 nm, agglomerates of 50-1000 nm).

Adsorbed hydrocarbons.

Liquid condensed hydrocarbon particles.

Sulfates, nitrates, metals, or trace elements.

Adapted from Marano, et al. (2002). Cell Biol Toxicol. 18(5): 315-320.

ros formation
ROS Formation

DEP

Redox

Cycling

PAHs

Quinones

CYP1A1

ROS

ROS

NQO-1

Also from:

-activated macrophages

-recruited neutrophils

Hydroquinone

slide33

Role of epoxide hydrolase in the inactivation of benzo[a]pyrene 4,5-oxide and in the conversion of benzo[a]pyrene to its tumorigenic diolepoxide.

slide34

Two-Electron Reduction of Menadione to a Hydroquinone, and Production of Reactive Oxygen Species During its One-Electron Reduction to a Emiquinone Radical

Casarett and Doull’s Toxicology: The Basic Science of Poisons,

C.D. Klaassen Ed., 6th Ed. McGraw-Hill, New York, NY 2001.

slide35

Hierarchical Oxidative Stress Response

High

GSH/GSSG

Ratio

Low

GSH/GSSG

Ratio

Level of

Oxidative

Stress

Normal

Antioxidant

Defense

Inflammation

Toxicity

Cell or Tissue Response

Adapted from Xiao, et al. (2003). J Biol Chem. 278(50).

slide36

Comparative Metabolism of Trichloroethylene (TCE)in Mouse Hepatocytes and Lung Clara Cells

Green, T., Environ Health Perspect 2000, 108 Suppl 2, 261-4.

slide37

The Relevance of Clara Cell in Assessing Human Risks of Toxicity: Noticing Specie Differences

  • Different expression levels of CYP2E1 between species:

mouse > rat > human

TCE metabolism is 600-fold less in human lung than in mouse lung, due to lack of expression of CYP2E1 in any cell type.

  • Number and morphology differences of Clara Cells between species
  • Implication of involvement of alveolar type II cells

A large number of mouse lung tumors express alveolar type II surfactant apoprotein.

Green, T., Environ Health Perspect 2000, 108 Suppl 2, 261-4.

macrophages as a host cell for infectious microorganisms
Macrophages as a host cell for infectious microorganisms

Mycobacterium

tuberculosis

Toxoplasma

gondii

pH

NO

NO2-

NO3-

H2O2

OH

O2

O2

NH4+

NADPH

SOD

O2-

Lysosomal

enzymes

NADP

NH4+

GL

ST

LAM

conclusion
Conclusion

Particle deposition and distribution from the lungs is mediated by a number of mechanisms

Conventional enzyme kinetic analysis may be used to characterize activity in lung tissue (fluids or cells).

There are a number of cell types throughout the respiratory tract exhibiting differential enzyme expression and activity.

Local metabolism of xenobiotics may result in toxicity (metabolism of drugs may result in efficacy or inactivation).

Pathogens act, in part, by suppressing metabolism