Determination of Threshold Levels

1
Determination of Threshold Levels of Sour Gas
and H2S on the Mammalian Brain
Funding Agreement Number 2001-01 BC Oil and Gas
Commission Sheldon H. Roth Faculty of
Medicine University of Calgary
2
Objectives of Study

• to determine threshold levels of hydrogen
  sulphide (H2S), sour gas and H2S/organic compound
  mixtures
• i.e. the Lowest Observable Adverse Effect Levels
  (LOAELs) and the No Observable Adverse Effect
  Levels (NOAELs)
• to evaluate the differences of effects between
  H2S alone and as a component of sour gas on in
  vivo and in vitro mammalian central nervous
  systems (CNS)

3
Hydrogen Sulphide (H2S)

• extremely toxic gas
• environmental industrial pollutant
• produced by variety of human and natural
  processes
• produced endogenously in mammals

4
Hydrogen Sulphide

• colourless
• heavier than air
• flammable
• characteristic rotten egg odour
• odor threshold 0.5 ppb
• olfactory fatigue gt 100 ppm
• ATSDR 1999
• H2S Health Research Risk Assessment Symposium
  2000

5
H2S exposure

• one of the leading causes of sudden accidental
  death in the workplace
• affects many organ systems (broad spectrum
  toxicant)
• effects dependent on concentration, duration and
  rate of exposure
• organs with high O2 demand - most susceptible

6
Broad spectrum effects of H2S

• nervous system (brain)
• lung
• heart
• reproductive developing systems
• eye
• metabolic systems
• smell (olfactory)

7
Dose Response of H2S
Roth Env Epidemiol Toxicol 1999
8
Effects of H2S (low level exposure)

• eye, nose throat irritation
• headache, sinus, etc
• nausea
• hoarseness, cough
• nasal congestion
• shortness of breath
• stress
• drowsiness
• Schiffman
• H2S Health Research Risk Assessment Symposium
  2000

9
Effects of H2S exposure on the nervous system
(brain)

• mental depression
• irritability
• loss of memory
• lethargy
• dizziness
• loss of appetite
• fatigue
• headache

memory
Fundamentals of Neuroscience 1999
10
hippocampus

• functions of the hippocampus
• memory storage
• cognitive function
• sensory processing
• voluntary movements

Amaral Witter, 1989
11
Recording from hippocampus
placement of stimulating recording electrodes
PS amplitude of population spike
12
Methods

• prepare rat hippocampal slices
• place slices in recording chamber
• activate excitatory synaptic inputs to CA1
  pyramidal neurons
• record field potentials (PS) of CA1 neurons
• apply H2S gas (in nitrogen)
• analyze data using custom software

13
Monitor
Interscan Corporation 4000 Series Compact
Portable Analyzer 0-1999 ppb 1 ppb
resolution electrochemical voltammetry sensor
14
control experiments nitrogen
15
Exposure to 50 ppm H2S
16
Exposure to 25 ppm H2S
25 ppm H2S
17

18
Exposure to 1 ppm H2S
1 ppm H2S
19


20
500 ppb H2S
21
Dose response curve - H2S
22
Inhibition of Respiratory Mechanisms
cytochrome c oxidase whole brain IC50 0.13 µM
Nicholson et al J Toxicol Environ Health A 1998
23
J Toxicol Environ Health A 1998
24
Conclusions

• long-lasting synaptic enhancement occurs
  following exposure to low levels of H2S
• effects appear to be concentration-dependent
• inhibition of respiratory enzymes (cytochrome
  oxidase, carbonic anhydase) confirmed
• effects may account for symptoms such as anxiety
  and cognitive impairment

25
Acknowledgements

• Investigators
• Ron Bennington
• James Brooks
• Russell Nicholson (SFU)
• Lisa Partlo
• R.S. Sainsbury
• Barbara Skrajny
• Lisa Strosher
• Steven Ip
• Ricardo Bonafine
• Peter OBrien (U of T)
• D.P. Archer

• Funding
• BC Oil Gas Commission
• Medical Research Council of Canada
• Alberta Heritage for Medical Research
• University of Calgary

26
Future Experiments

• H2S experiments in ppb range
• S. Ip
• Sour gas experiments
• S. Ip
• whole animal (in vivo) studies
• Dr. R. Bonafine
• further studies on respiratory enzymes
• Dr. P. OBrien University of Toronto

27
Sour Gas
28