Ill Plants containing hypoglycaemic organic sulphur compounds

Allium cepa LILIACEAE

Onion

(See also Chapters 2 and 4). Already in 1923 Collip noticed that a totally (?) depancreatized dog could be kept alive for 66 days on three injections of crude onion extract. Later, a number of research workers confirmed that the onion and its extracts have a distinct, slowly developing hypoglycaemic action and that the effect is also obtained when the extract is given by mouth (Hermann, 1956, 1958; Jain and Vyas, 1974).

The action of a petroleum ether extract of sliced dried onion was equivalent to 62% of that of a standard dose (0.5 g) of tolbutamide and further purification led to an extract equivalent to 76.6% of this standard) (Brahmachari and Augusti, 1962). Later, two active disulphides were isolated from fresh onions by steam distillation and solvent extraction. They were allyl propyl disulphide (APDS) and allicin (diallyl disulphide oxide) (Augusti and Benaim, 1974; Augusti, 1975, 1976a, b; Augusti et al., 1975).

With APDS, blood glucose and glycosuria were significantly decreased in alloxan-diabetic rabbits and glucose tolerance was also improved. In a 4-h test in fasting human subjects APDS caused a marked fall of blood sugar (hourly controls) plus an increase of serum insulin levels, whilst the free fatty acid levels remained the same. In a control trial there was no fall of blood glucose, but the serum insulin levels decreased and the free fatty acid levels increased considerably.

The authors (Augusti and Benaim, 1974; Augusti, 1976a, b) explain these results as follows. Insulin is a disulphide protein and its inactivation by compounds and albumins rich in SH groups has been established. APDS probably removes insulin-inactivating compounds by competing with insulin for the SH group(s) in these compounds, thus producing an insulin-sparing effect and preventing the increase of free fatty acids on fasting.

In clinical trials, 100 mg allicin per kg body weight produced a significant drop in fasting blood glucose levels with a concomitant rise in serum insulin levels. In 12 subjects the action lasted for about 12 h. Long-term feeding to normal rats of 100 mg of allicin per kg of body weight produced a large reduction in the lipid constituents of the blood and liver and in this respect allicin might have an advantage over tolbutamide (Augusti and Benaim, 1974). Cyanidin- and paeonidin-glycosides are also present in onion bulbs, and could well be partly responsible for the effect of the crude extract.

Table 7.3. Plants containing hypoglycaemic organic sulphur compounds

Plant Family

Part used

Possible active constituents

Observed activity

References

Allium cepah.

(Onion) Liliaceae

Bulbs

Allyl propyl disulphide (APDS),allicin (diallyl disulphide oxide) , methylalliin in fresh juice (latter also bacteriostatic) Also in bulbs: flavon glycosides; kaempferol, quercetin- and phloroglucin-derivatives

In fasting humans, APDS in doses of 0.125 g/ 50 kg produced a significant fall of hyper-glycaemia, a rise in serum insulin levels and no change in free fatty acid levels. APDS is believed to remove insulin-inactivating compounds by competing with insulin for the SH group, thus having an insulin sparing effect.

The activities of petroleum ether and ethyl ether extracts of sliced dried onion were equivalent to 62 and 76% of that of a tolbutamide standard respectively. APDS does not act in totally depancreatized rabbits

Bhandahari and Mukerje (1959) Brahmachari and Augusti (1961a, b,

1962a) Jain and Sharma (1967) Augusti and Benaim (1974) Jain and Vyas (1974) Augusti(1975,1976a, 1976b) Augusti etal. (1975) Matthew and Augusti (1975)

Allium sativum L.

(Garlic) Liliaceae

Dried flower heads

Organic sulphur compounds

The activity of an ethyl ether extract of dried A. sativum heads is 58% of that of a tolbutamide standard

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