2 September 2019

S-methylcysteine sulfoxide – the Kale anaemia factor

Natural toxin

S-methylcysteine sulfoxide – the primary factor causing haemolytic anaemia in ruminant livestock after feeding excessive amounts of Brassica species.

Plants of the genus Brassica, including cabbage, kale, forage rape, forage turnips and others produce S-methylcysteine sulfoxide (SMCO) and glucosinolates as secondary metabolites. Both metabolites act as defense against fungi, microorganisms and insects. Upon mechanical disruption or wounding of the plant, cysteine sulfoxide lyase is released and breaks down SMCO into ammonia, pyruvate and methanesulphenic acid, which then prevent infection of the plant.

Figure 1: Cattle grazing on Brassica.

After consuming cabbage for five to six months per year over several years, cattle and sheep were described as having poor productivity. Symptoms in cattle included high aborted levels, low conception rates, poor body condition, anaemia and low milk production. In sheep, symptoms including sway lamb backs, enlarged thyroids and anaemia were observed. In a case study by Taljaard, 1993, SMCO and glucosinolates were identified as potential causative agents. Later, SMCO was associated with haemolytic anaemia and determined as the so called kale factor. SMCO-caused haemolysis includes symptoms such as weakness, anaemia, elevation of heart and respiration rate, fall in performance, and in severe cases haemoglobinuria and massive and fatal prehepatic icterus.

Figure 2: Structure of S-methylcysteine sulfoxide. Click image for 3D interactive model.

SMCO enters the organism through ingestion of plant tissue containing the compound. In ruminants, SMCO is then transported to the rumen and converted to the haemolysin dimethyl disulfide (DMDS) via enzymatic rumen fermentation. DMDS is the causative agent responsible for SMCO toxicity, as it is rapidly absorbed into the blood where it causes haemolytic anaemia. Even though the enzyme responsible for SMCO metabolism in ruminants was also found in the human gastrointestinal tract, no obvious adverse effects have been observed so far. In fact, SMCO was shown to exhibit anticarcinogenic, anti-diabetic and cardiovascular effects, which may cause beneficial effects in humans if SMCO-containing plants are consumed in moderate amounts.



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