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42

 Functional Assessment of Urinary Neuro-biogenic Amines—A COMPREHENSIVE GUIDE

While there is currently no method

to evaluate or control the attachment

of methyl groups to DNA, evaluation

of oxidative stress and the methylation

pathway (genetics and function) is avail-

able through laboratory testing. Click on

the links below for more information

about the tests.

DNA Methylation Pathway DNA Oxidative Damage Assay Methylation Profile; plasma Glutathione;

erythrocytes

Toxic Exposures

The delicate balance of neurotrans-

mitter signaling may be disrupted by ex-

posure to neurotoxic elements or chemi-

cals. Life in modern society ensures daily

exposure to a variety of neuroactive and

neurotoxic substances. Exposure to tox-

icants may:

induce epigenetic changes

alter enzyme functions

exhaust anti-oxidant reserves

overwhelm detoxification pathways

Behavior changes in humans may oc-

cur for a variety of reasons, and toxicant

exposures are known to induce behavior

changes in humans (behavioral toxicity).

Observing behavior changes in animals

is a routine part of the assessment of po-

tentially toxic substances. The neurotox-

icity of many substances such as meth-

yl mercury, lead and manganese were

originally identified not because of their

observed effects on laboratory animals,

but because their adverse effects on hu-

man brain function have been well-doc-

umented in historical accounts.

Urinary neurotransmitters are being

used to evaluate workers exposed to

toxic chemicals and elements. A 2006

study of welders exposed to manga-

nese demonstrated cognitive and be-

havioral changes along with decreased

levels of urinary serotonin metabolites.

BHMT

Methionine

SAMe

CBS

SUOX

AHCY

MTR

MTHFR

5, 10

Methylene THF

dUMP

5 Methyl

THF

Homocysteine

Sulfate

Thymidine

synthesis

DNA

RNA

Protein

Lipids

SAH

TMG

methyltransferases

MTRR

Cystathionine

Taurine

Glutathione

Cysteine

Sulfite

adenosine

DMG

SHMT

B12

FIGURE 11.

Methionine metabolism and the transsulfuration

pathway (also called the “methylation pathway”)