BIOCHEMICAL SOClETY TRANSACTlONS
Investigation of human mitochondrial myopathies by phosphorus magnetic
GEORGE K. RADDA, DORIS J. TAYLOR and
DOUGLAS L. ARNOLD
Department of Biochemistry, University of Oxford, South
Parks Road, Oxford OX1 3Q0: U.K., and Clinical Magnetic
Resonance Laboratory, Radcliffe Infirmav, Woodstock
Road, Oxford OX2 6HE, U.K.
The investigation of human muscle disease by phosphorus
(3'P) magnetic resonance spectroscopy began in Oxford in
1981 (Ross et al., 1981). Since then we have investigated
over 300 patients. many of them several times, with a
variety of primary muscle disorders or systemic disorders
that are reflected in muscle metabolism (for summaries,
see Radda et al., 1984; Radda & Taylor, 1985). We devel-
oped a relatively simple protocol in which the energetics
of the flexor digitorum superficialis muscle is examined by
placing the forearm of the subject inside a 1.9 T super-
conducting magnet of a Fourier transform n.m.r. spec-
trometer. Signals from phosphocreatine (PCr), ATP, Pi and
hexose monophosphates are recorded with the aid of a
carefully positioned surface-coil and intracellular pH is
derived from the chemical shift of the Pi resonance. A
patient examination takes between 30 and 45 min during
which approx. 30n.m.r. spectra are accumulated at rest,
during a 7 min two-stage exercise period and during a 10
to 15 inin recovery phase (Taylor et al., 1983).
We measure a set of characteristic parameters in normal
individuals and can use these to characterize and quantify
different types of abnormalities, several of which are
associated with mitochondrial myopathies. We use the
following 'normal' indices:
(i) At rest, intracellular pH and the relative concen-
trations of PCr, Pi and ATP are essentially invariant from
normal individual to individual. From these values we
calculate the concentration of free ADP assuming that
creatine kinase is at equilibrium and obtain a low and
relatively constant value for ADP concentration (6 t 3 pM).
The (phosphorylation potential)-' (i.e. [ATP] / [ADP] x
[Pi]) at rest is 2.8 f 1.3 x 106M-l in normal subjects
(Arnold et al., 1985).
(ii) During aerobic, dynamic exercise there is a charac-
teristic relationship between the decrease in PCr and intra-
cellular pH (Taylor et al., 1983).
(iii) During recovery, the rate of PCr resynthesis has a
t1,* of 52 t 16s and represents the rate of oxidative phos-
phorylation. The PCr resynthesis rate also refects the rate
of pH recovery (Arnold et al., 1984), the latter being
relatively slow, and is likely to be a measure of H+ export
from the muscle cell.
(iv) The rapid decrease of ADP concentration to its
resting level (within 2 min) is also characteristic.
We have studied 12 patients with evidence of mito-
chondrial myopathies in whom the clinical manifestations
ranged from mild external opthalmoplegia without symp-
toms or signs of limb weakness to severe generalized weak-
ness and exercise intolerance (Arnold et al., 1985).
At rest, an n.m.r. abnormality could be demonstrated in
11 of the 12 patients, 10 having evidence of a reduced
muscle energy state with at least one of the following
Abbreviation used: PCr, phosphocreatine.
abnormalities: low phosphorylation potential, low [PCr] ,
high [ADP] or high [Pi]. Two patients had abnormal
resting muscle intracellular pH.
Evidence of impaired rephosphorylation of ADP to
ATP during recovery from exercise was found in approxi-
mately half the patients. In three patients the rephosphory-
lation was affected severely enough to alter PCr resynthesis
significantly (c.f. Radda et al., 1982). In these subjects
ADP recovery was also slow. Additionally ADP recovery
was slow in three patients whose PCr recovery times were
within normal limits. These observations show that at the
early stages of ATP resynthesis (represented by the decrease
in [ADP] ), the increased demand for oxidative phosphory-
lation puts a greater stress on mitochondrial function and
therefore abnormalities are more readily detected.
An interesting observation was that although severe
lactic acidosis (i.e. increase in blood lactate) was produced
by exercise in most of our patients, the intracellular pH
changes were not very significant and the rate of pH recovery
where it could be measured was shown to be more rapid
than in normal subjects. This suggests some adaptation of
the acid-extrusion mechanism in order to remove rapidly the
damagingly large amounts of intracellular lactate produced.
We finally mention that one of the patients examined
also showed cerebral involvement, and 31P n.m.r. nieasure-
ments on the brain of this patient also showed an elevated
[Pi] and decreased phosphorylation potential (D. J . Hayes,
D. Hilton-Jones, D. L. Arnold, J. Duncan & G. K. Radda.
31P n.m.r. in vivo thus appears to provide reasonable
sensitivity and specificity in the diagnosis of human mito-
chondrial myopathies. This non-invasive technique has a
role in defining the pathophysiology of these conditions
and may prove useful in evaluating therapeutic interventions.
The authors are grateful to their colleagues in the Clinical
Magnetic Resonance Laboratory. especially Dr. P. J. Bore and Ilr.
P. Styles, whose help with these studies has been invaluablc. We
wish to thank Dr. J. Morgan-Hughes. Dr. B. 1). Ross, Dr. J. Hockaday,
Dr. N. Hyman and Dr. C. Davis for allowing us to investigate their
patients and for making available results of clinical investigations.
Dr. B. D. Ross and Dr. D. Hilton-Jones gave additional clinical
assistance. Technical help was provided by Miss J. Ilarlcy and
Mrs. Y. Green. This work was supported by grants from the British
Heart Foundation and the Medical Research Council. D.L.A. is
grateful to the Medical Research Council of Canada for personal
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