The presence of multiple forms of cytochrome P-450 in human hepatic microsomes
was demonstrated. Different forms of cytochrome P-450 showed different activities
The following important problems to be resolved for further development of
clinical pharmacology were proposed.
I) Alterations ofcytochrome P-450 under pathological and nonphysiological states.
2) Effects ofdrugs, diets and environmental chemicais.
3) Quantitative species differences in cytochrome P-450.
4) Quantitative and qualitative determinations ofgenetic differences.
5) Evaluation ofracial differences through international cooperation in the exchange
Alvares, A. P., Schilling, G., Levin, W., Kuntzman , R., Brand, L. & Mark, L. C. (1969).
Cytochromes P-450 and bs in human liver microsomes. Clin. Pharmac. Ther., 10,
Beaune, P. H., Remers, P. &Dansette, P. (1980). Partial purification ofhuman liver cytochrome
P-450 . In Microsomes, Drug Oxidations and Chemical Carcinogenesis ed. Coon, M. J.,
Conney, A. H., Estabrook, R. W., Gelboin, H. V., Gillette, J. R. &ü 'Brien, P. J., in press.
Guengerich, F. P. (1979). Isolation and purification of cytochrome P-450 , and the existence of
multiple forms. Pharmac. Ther., 6,99-121.
Ishii, K., Ando, M., Kamataki, T. & Kato, R. (1980). Metabolie activation of mutagenic
tryptophan pyrolysis products (Trp-P-I and Trp-P-2) by a purified cytochrome P-450-
cytochrome P-450 and NADPH-cytochrome c(P-450) reductase from human liver
microsomes. Biochem. Pharmac ., 28, 1993-2000.
Kaschnitz, R. M. & Coon, M. J. (1975). Drug and fatty acid hydroxylation by solubilized human
liver microsomal cytochrome P-450-phospholipid requirement. Biochem. Pharmac.. 24,
Kato, R. (1977). Drug metabolism under pathological and abnormal physiological states in
animals and man. Xenobiot .. 7,25-92 .
Kuntzman, R., Lu, A. Y. H., West, S., Jacobson, M. & Conney, A. H. (1971). The importance of
cytochrome P-450 and P-448 in determining the specificity of the reconstituted liver
In Microsomes and Drug Oxidations ed. Ullrich, V., Roots, 1.,Hildebrandt, A., Estabrook,
R. W. & Conney,A. H. pp. 735-747. NewYork: Pergamon Press.
Lu, A. Y. H. & Levin, W. (1974). The resolution and reconstitution of the liver microsomal
monooxygenase system and drug-induced spectral interactions in human liver
microsomes. Chem-Biol.Interactions, 9,205-216.
Ryan, D., Lu, A. Y. H., Kawalek, J., West, S. B. & Levin, W. (1975). Highly purified
cytochrome P-448 and P-450 from rat liver microsomes. Biochem. Biophys. Res.
PURIFICATION OF HEPATIC CYTOCHROME P-450 85
Wang, P., Mason , P. S. & Guengerich, F. P. (1980). Purification of human liver cytochrome
P-450 and comparison to the enzyme isolated from rat Iiver. Arch. Biochem. Biophys., 199,
Yamazoe, Y., Ishii, K., Kamataki, T., Kato , R. & Sugimura, T. (1980). Isolation and
characterization of active metabolites oftryptophan-pyrolysate mutagen, Trp-P-2, formed
by rat Iiver microsomes. Chem.-Biol. Interactions, 30, 125-138.
To describe all the phenomena of ageing in a relatively short space is an
impossibility. This paper will, therefore , describe a group of clinically relevant
changes, indulge in a little theorizing and conclude with a reference to the major
syndromes of geriatric medicine.
The general shape and configuration ofthe human frame depends to a large extent
on its muscular covering. Muscles are composed of non-mitotic cells and these
structures achieve their optimum size and strength when the individual reaches full
maturity in the middle twenties. Thereafter, the more robustly physical the life-style,
the bulkier the muscles remain, manual workers and athletes often maintaining their
size and strength into the sixth decade. Eventually, for everyone , there is a slow
atrophy, which may be due to primary degeneration ofmuscle cells or due to loss of
anterior horn cells responsible for motor units (Tomlinson & Irving, 1977). Wasting
of muscles is accompanied by replacement with an increasing quantity of adipose
tissue, which not only compensates for the loss ofbulk, but may create new bulges in
Lean body mass is made up of muscles, liver, brain and kidneys, its total weight
diminishing by 20-30% between the ages of 30 and 80 years. Novak (1972), studied
215 men and 305 women volunteers between the ages ofl8 and 85 years, determining
total body potassium by counting naturally radioactive 4°K in the whole body
counter. Total body potassium was reduced with age in men from 56 to 43 mmol kg-1
and, in women, from 46 to 38 mmol kg-1
• Fat increased with age in men from 18%to
36%, while fat free mass and cellular mass diminished from 82% to 64% and from
65% to 36% respectively (Figure I). Similar but less striking changes occurred in
women, the process commencing in borh sexes about the age of 45. The same type of
loss occurs from the organs which combine with muscle to constitute lean body mass.
Only the lungs appear to be spared, liver, brain, kidneys, spleen and pancreas all
showing a significant loss over life-span (Rossman, 1979).
The reduction in lean body mass results in a progressive decrease in total body
protein. The total albumin pool is reduced in the elderly by about 20%, the serum
concentration decreasing slowly from the fifth decade. Levels of albumin in the
serum depend on a homeostatic mechanism operating in the liver, osmotic pressure
variations in the plasma 'causing that organ to produce more or less albumin as
required. One reason for the reduced albumin pool may be that this mechanism
becomes less etTective with increasing age (Yan & Franks, 1968).
In the skeleton one fmds a similar picture. Garn (1978) has reported that bone loss
has been quantified in both men and women in a number of ways. Derived from
hundreds of skeletons, thousands of absorptiometric assessments and hundreds of
thousands of radiographs, all measurements state the same message. Over the years
from maturity through the ninth decade , there is a 12% loss oftissue bone in the male
and a 25% loss oftissue bone in the female. It is interesting to note that femoral, tibial
calculations, Garn (1978) believes that bone lass begins at the age of39 years. In other
words, from the fifth decade onwards there is a steady slow lass of bone substance
from both men and women although, unfortunately, the latter with a smaller initial
bone mass lose substantiallv more than their male counterparts.
reprodueed by permission (Cape, 1978).
One ofthe first systems , in which ageing changes were examined, was the excretion
of urine through the kidneys . In what has become a classic piece of research and one
of the first to demonstrate unequivocally that ageing per se can cause significant and
consistent changes in function of a particular organ system , Davies & Shock's study
ofrenal function was published in 1950. Seven groups, each of9-12 men from each
decade from the 3rd to 9th were studied. No subject had evidence ofprevious renal ,
cerebrovascular, or coronary artery disease, was hypertensive or had any recent
alteration in body weight. The authors studied inulin and Diodrast clearances which
represent the filtration through the glomeruli and the excretion through the tubules.
Their results indicated that, by the age of 80 years, the average clearances were
& Shock (1976) have reported on a longitudinal study of almost 300 men, whose
creatinine clearances were estimated on three occasions, 18-24 months apart, over a
period oflO years. Similar results were obtained.
Figure 2a InulincIearanceat varyingages.
Figure2b lodopyracet (Diodrast) clearance at varying ages. Number of subjects at each age
noted.(Reproduced by permission: Davies& Shock, 1950).
Du nnill & Halley (1973) counted glomeruli in eighteen individuals whose ages
ranged from one day to seventy three years, and divided them into two groups
according to age. The Irrst cons isted of thirteen individuals, aged 38 years or
under, with a glomerular count of 870 ,000 to 1,090 ,000 , and the second, five
individuals, whose ages were greater than 38 years , with counts of 650,000 to
790 ,000 . This somewhat lim ited direct evidence goes some way to confirrn the
suspicion that the reduction in renal function of the healthy elderly person results
To sum up, studies on muscles, bone and most organs ofthe body demonstrate that
with age there is a physical loss of tissue mass varying in amount from 7% to 30%.
'The old man is only half the man he used to be'. T hese quantitative cha nges are
accompanied by qua litati ve alterations in the tissues . As a result of these, their
reaction to a variety of pharmacological or humoral agents may be altered. One
example is the efTect ofinsulin on glucose levels. Andres (1971) cites nine large studies
to demonstrate that the blood glucose level one hour after a 50 g oral bolus ranges
from 100 mg 100 mi-I at age 20 to 170 mg 100 ml! at age 75 years. There are
variations in the findi ngs ofdifTerent workers in the United States, Australia, Sweden
and England but the trend is unequivocal. For each decade of life the blood glucose
level at one hour rises by 10 ± 4 mg 100ml-l
To investigate th is ph enomenon, Sm ith & Hall (1973) studied fifty three very old
subjects (ages between 86 and 95). A randomly selected group of patients awaiting
discharge from a geriatr ic ward were given a standard glucose tolerance test after
three days of a fixed carbohydr ate diet (300 g da ily). T he results obtained have been
represented graphicall y in Figur e 3. The continuous line shows the mean results from
--....-.......... /- ....... , I \
! 120-35 19 _________ \ Female 42-59 21
- --I 185-95 34 (Norma' GTI) _ .- Old 85-96 13 (Abnormal GTIj
Figure 3a Glucose tolerance curves in young wornen, postrnenopausal wornen, and very
elderly subjects ofboth sexeswho weregiven 50 gglucose.
Figure3b Production of insulin in response to 50 g glucose given orally to individuals at
varyingages. Based on data ofSrnith & Hall (1973); reproduced by permission (Cape, 1978).
a group of nineteen women (mean age 30) who had been delivered of a baby of
normal birth weight within the previous two years. The second control group
fifty three elderly subjects, thirty four had a normal glucose tolerance, apart from a
delayed peak at one hour . A small group of six had a probable diabetic curve,
uppermost, while the third group of thirteen fell into an intermediate range. When
insulin levels were examined, it can be seen that insulin production is comparable in
the first thirty minutes although it is a little less in the very old, who continue to
increase their output to peak at one hour for the thirty four 'normals', two hours for
the six 'diabetic' and ninety minutes for the intermediate group. Smith & Hall
suggest that either insulin is less biologically active or isineffective because of an as
yet unknown antagon ist prevent ing it from fulfilling its normal action. This lauer
may not be an inherent property ofthe old person's insulin, but rather be a reduction
of responsiveness by target tissues, due to loss of insulin receptor sites. This indicates
a qualitative change in the tissues.
While there is no loss oflung weight and pC02 and blood pH levels are not affected
by age, p02 does tend to fall slowly. The major reason for this is that less air is moved
in and out ofthe lung bases at age 80 than at age 20 years, a phenomenom which can
be noted with a stethoscope . Holland, Milic-Emili, Macklem & Bates (1968)
concluded that the loss of elastic lung recoil and an increased tendency to airway
collapse result in airway closure during part or all of the breathing cycle in the
dependent lung zones of the elderly. The ratio of ventilation to perfusion in these
areas thus falls, leading to a lowering ofarterial oxygenation, the main effect ofwhich
is to reduce the amount and pace ofactivity in the older person.
Comments
Post a Comment
اكتب تعليق حول الموضوع