This review was written for and published in our local Parkinson support
group paper. I thought it might be relevant to the topic discussed here
recently namely PD and diabetes. Although I have been retired for sveral
years, I feel I still qualify as a research chemist.
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ASPARTAME

        A question arose through Internet as to whether the
ingestion of aspartame, the generic name for NUTRASWEET, has
any effect on the therapeutic efficacy of Sinemet in Parkinson
patients.  One contributor to Internet denounced aspartame for
a multidude of ills and sins of the world except for the Viet
Nam, Korean, and World War II.

        Chemically, aspartame is the methyl ester of a dipeptide
and has a nutritive value of 4 calories per gram, but is about
160 times as sweet as sucrose (table sugar). It was first
approved by the FDA in 1974 as a sugar substitute for table
use, and as a sweeetener in various products, and later in
carbonated beverages.  Formal objections based on safety issues
were evaluated thoroughly and at length, but the government
concluded that the proposed food additive use is safe under the
proposed usage.  It has become a major ingredient in diet sodas
and many other dietetic drinks and food preparations. The
quantities of the substance that can be consumed can be quite
significant when compared to the dosage amounts of Sinemet: for
instance, one glass of soda contains about 160mg of aspartame.
However, 3 Oz or 100Gm (1Gm=1,000mg) of beef or other protein
food is enormous in comparison.

        Aspartame is easily hydrolyzed (broken down) into two
different amino acids, aspartic acid  and phenylalanine.  This
hydrolysis occurs in vivo (in the body) as the substance is
metabolized but can also be achieved in vitro by boiling it in
a liquid, which is why it is not to be used in cooking, and
likewise occurs in the early stage of metabolism.  Aspartic
acid and phenylalanine obtained from aspartame are identical to
those derived from any protein and likewise should compete with
Sinemet for the active receptor sites in the brain, if taken
within at least one half hour, the recommended interval, from
dosing time. However, a brief note in the Winter '93-'94 APDA
Bulletin reported no adverse effect in a double blind study
with aspartame and L-dopa by Dr. P.J. Karsteadt and J.H. Pincus
of the Georgetown University Hospital  (Neurology, 43:611-613,
1993).

        It would be good to know there is no adverse effect from
aspartame on Sinemet, even at a high dietary level, no matter
what the age of the patient nor the elapsed time since the
onset of Parkinson's disease.  However, this study does not
give enough information to provide this assurance.  The premise
that ingestion of large neutral amino acids within a specific
time frame of dosing with Sinemet may affect the response to
the drug, and consequently, motor performance, is an important
one to examine.  This study  consisted of administering 600mg
or 1200mg of aspartame, intended to bracket a high, but larger
amount than ordinarily consumed to a group of 18 patients from
45 to 75 years, a range of 30 years.  These patients had been
ill from 4 to 30 years.  Various physico-chemical tests were
used to measure disability, dyskinesia, walking, and blood
levels at various times after administration.

   There is no way to know from this paper whether the patients
were assigned in a balanced way to the two groups, but the
particular measures of motor performance and disability could
be expected to vary by age and extent of illness.  Thus, if one
group consisted of the younger and also the less able patients,
it could be that the group would not show changes across the
course of the study.  That would not, however, account for
differences or lack thereof in plasma phenylalanine. It should
be noted that the higher exposed group did show differences in
this measure.

        The authors' concluded that the aspartame has no adverse
effects on Parkinson patients even at high levels of
consumption.  Yet, the study does not include enough people,
nor even enough in subgroups like the aged or more disabled, to
conclude that there is no effect at the lower amount tested.
Further repeated intake (e.g., several diet sodas a day) might
produce a different motor performance profile and level of
plasma phenylalanine.  Therefore, it is suggested that it would
be prudent to treat aspartame like any protein and avoid it at
least within half an hour before and after a dose of Sinemet.

                                                                       Michel
Margosis