SRE/AIW/18.4.74
DARK TOBACCO CIGARETTES
Summary
Although a number of studies have been undertaken,
there is relatively little information on dark
tobacco cigarettes.
Apart from the interest in cigar tobaccos, this
may be partly due
to the local 'native' nature of dark tobaccos,
which are often
produced from local, or locally naturalised, seed
lines.
Mouse-skin studies show that condensate from dark
tobaccos, including cigar tobacco manufactured
into cigarettes,
are at least as tumorigenic and often more
tumorigenic than that
from flue-cured Burley and oriental tobaccos.
Following a long-term inhalation experiment,
assessed on
the basis of the severity of laryngeal lesions in
hamsters,
Dontenwill concluded that smcke from a "black"
cigarette was
biologically very much less active than smoke from
the reference
cigarette; the latter being a 'standard' German
blend. It should
be noted, however, that the reduction in
biological activity could
be accounted for almost e-.ntirelv by a lower
accumulated dose from
the "black" cigarette due to a shorter exposure
time 'and the lower
delivery of smoke. A similar reason may also be
advanced for the
marked reductions found for filter tip versions of
the reference
blend.
Because of the publicity which has surrounded the
work of
Passey and his colleagues, this must also be
included in a
bonsideration of dark tobacco cigarettes.
Nevertheless, the studies,
which were undertaken under poor experimental
conditions, have been
severely criticised and do not add materially to
our knowledge of
dark tobacco cigarettes.
In conclusion, the hypothesis that smoke from dark
cigarettes is "safer" than that from flue-cured or
blended cigarettes
is certainly not supported by the results of the
mouse-skin painting
experiments and the Dontenwill inhalation study
appears to provide
only shaky supporting evidence. On the present
evidence, it is 1~;
suggested that any concept of a lower risk
attached to dark C:)
cigarettes canr in a given population, only be
associated with a
reduced level of inhalation faccuumulated dose)
from such products. r\-)
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DARK TOBACCO CIGARETTES
a) . Study of Ciqar Tobacco Condensate
Following reports from Croninger (1) and Homburger
(2),
which suggested, but did not prove statistically,
that cigar smoke
condensate was more carcinogenic than that from
cigarette smoke,
Davies and Day (3) re-examined the position.
The results obtained after 116 weeks showed that
the
condensate from the cigar was more carcinogenic
than that of
the cicarette manufactured from cigar tobacco or
from flue-cured
tobacco. There was no significant difference in
carcinogenicity
to mouse-skin of the condensates from the two
cigarettes. The
differences in mortality rates were small and the
results were
not affected by age-standardisation.
b) Comparison of Tobacco Types
In a further TRC experiment, a number of different
types of tobacco, including an air-cured fermented
(Paraguay)
tobacco, --yere examined. The tumorigenic ratios
and 95% confidence
limits for the condensates from the various
cigarettes compared
with the flue-cured "control" (T4) were:
SaiPple T16 Air-cured fermented 1.38 (1.14 - 1.65)
T17 Burley 1.07 (0.89 - 1.29)
T18 Oriental 1.11 (0.92 - 1.33)
T19 indian sun-cured 1.55 (1.29 - 1.90)
T20 Indian flue-cured 1.22 (1.02 - 1.47)
These results show that condensate fro-m air-cured
fermented tobacco is more tumorigenic than the
flue-cured control.
Condensate from Indian sun-cured is also more
tumorigenic, while
that from Indian flue-cured tobacco is just
significantly more
tumorigenic than the control. The differences for
Burley and
Oriental tobaccos are not significant.
Subsequently, Imperial Tobacco Ltd. have compared
condensates from Gauloises and other continental
brands with
Embassy cigarettes. Full details are not
available, but at 92
weeks, it was clear that condensate from Gauloises
Caporal plain
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was very much more tumorigenic than that of
Embassy filter.
The ranking was :
Gauloises'> Belga Rouge -filter > Nazionali
Esportazione
Embassy
c) Inhalation Study Dontenivill et al. (4)
In this long-term experiment, smoke from a "black"
cigarette manufactured from a blend of Burley
(15%), Maryland (6%),
and dark tobaccos was compared with a "standard"
German blend and
various other cigarettes.
Comparison of the various cigarettes was based on
the
seveje laryngeal changes found following exposure
of hamsters to
30 cigarettes twice a day for up to two years. On
this basis,
smoke from the "black" cigarette was found to have
only 33% (stage 5)
or 12% (stage 6) of the activity of the reference
cigarette,
ie. a 67-88% reduction in activity .
Apart from the absence of suitable methods for the
analysis
of such experiments, two main fac-,~crs should be
considered in
attempting to put these reslilts into perspective.
1. Cellulose acetate cr paper filter versions of
the
reference cigarette also led to a cunsiderable
reduction in activity;
56-60% (stage 5) and 76-99% (stage 6)
respectively.
2. The condensate from the "black" cigarette was
nearly 40% lower than that from the reference
cigarette and the
exposure time was also 20% lowe:c. Similarly,
condensate deliveries
from the filter cigarettes were 30 and 33% lower
than that of the
reference ciaarette.
Since the above reduction in condensate delivery
and
exposure tiine for the "black" cigarette compared
with the
re-Eerence cigarette obviously reduce the total
accumulated dose
to the respiratory system, it is considered that
the mar!-ed
reduction in biological response should be treated
with considerablg='
caution.
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Other Inhalation Studies Passey et al. (5)
In two experiments, groups of 12 rats were exposed
to
smoke under what can only be considered ;,.s
poc.,- experimental
conditions. In one experiment, cigarette smoke
.:as compared with
smoke from cigarettes manufactured from cigar
tobacco (TRC C2).
A commercial cigar tobacco cigarette (Calypso) and
a cigarette
manufactured from Burley tobacco (TRC T17) were
included in the
second experiment. The rats exposed to smoke from
flue-cured
tobacco died early and with enlarged and severely
diseased lungs.
The conclusions drawnwere that smoke from
flue-cured .
cigarettes is more dangerous to man and to animals
than that from
air-cured tobaccos and that this is related to the
method of
curing (and the sugar content) of the tobaccos.
These experiments have been criticised severely
because
the pathological findings of the rats which died
suddenly could
be related to an inflammatory condition not
regularly encountered
in man: Passey himself stated that chronic
respiratory disease
and bronchiectasis were endemic in the strain of
rats used Zor
their studies. Passey also undertook some limited
mouse-skin
painting experiments.
Passey's studies have become linked to lung cancer
(because of a limited mouse-skin study) and also
to a theory of
lung cancer induction advanced by Braven and
Fenner M: the
lattcr because of Passay's contention that the
sugar conLe-nt of
the tobacco was an important factor. In the same
review (6), it
is argued that, although the studies of Passey may
conceivably
have some relevance to chronic inflammatory lung
disease in man,
there are no grounds for regarding them as
relevant to lung cancer.
The link with sugar content and Braven and
Fenner's
work is also criticised, since there is no
evidence that cystein
offers protection from cancer iniucing effects of
chemical agents.
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1 . Croninger, A.B. et al.
2. Homburger, F. et al
3. Davies R.F. et al.
4. Donten-dill, W. et al.
5. Passey, R.D. et al
6. Editorial
7. Braven, J. et al.
8. Fenner, M.L. et al.
Cancer ReL. 1956. 18, 1263
J. Natn. Cancer Inst. 1963, 31, 1445
Br. J. Cancer, 1969, 23, 363
J. Natn. Cancer Inst. 1973, 51, 1781
Br. med. J. 1971, IV, 198
Lancet, 1973, 187
Br. J. Cancer, 1967, 21, 623
Br. J. Cancer, 1968, 22, 474
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APPENDIX
Details of Cigarettes and Cig-ars used in TRC
Cigar Study
Table 1
Code L,~ngth Circum Weight I Butt Puff NVWSC (4)
Leng Lin No.
(mm) (mm) (g) (mm) (mg)
CIM 83 33.7 1.86 25 19.8 37.8
C2(1) 70 25.1 0.94 20 8.4 19.4
T4 (3 70 25.3 1.09 20 10.9 26.3
(1) Composite blend cigar tobacco; granulated
wrapper and
binder of natural leaf.
(2) Blend as C1 cut at 50 cpi for cigarette
manufacture
(3) Composite blend of flue-cured tobacco.
(4) Non volatile whole smoke condensate.
:zmoking conditions : Duff volume 25 ml
duration 2 seconds
one puff per minute
Table 2
Summary of results from Dontenwill Inhalation
Study
Sample Condensate Relative Laryngeal Changes
ExDosure Relative Potency
Factor
Dry Factor Stage 5 Stage 6
(mg/cig)
Ccntrol (1) 33.7 1.0 1.0 1.0 1.0
"Black" (2) 20.9 0.62 0.8 0.33 0.12
Control 23.5 0.70 1.0 0.44 0.06
Acetate Filter
Control 22.7 0.67 1.1 0.40 0.24
Paper Filter
(1) German blend: 551. flue-cured, 35% oriental
and 10% Burley
(2) Black cigarette: 15% Burley, 6% Maryland, 6%
Java,
19% cigar tobacco, 54% other dark tobacco (-n
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