Plasma total cysteine (tCys) concentrations are associated with BMI. To study the relationship between tCys and BMI, we monitored the changes in serum concentrations of tCys and metabolically related compounds in sixty obese patients (BMI 50–60 kg/m2) from before to 1 year after either gastric bypass surgery (mean 30 % weight loss) or duodenal switch surgery (mean 41 % weight loss). A total of fifty-eight healthy persons (BMI 17–31 kg/m2) served as controls. Before surgery, obese patients had modestly (approximately 17 %) higher mean serum tCys, and markedly (>2-fold) higher glutamate concentrations, than controls (P ≤ 0·001 for both). Serial examinations after surgery revealed that gastric bypass patients had no change in tCys concentrations (P = 0·22), while duodenal switch patients showed a modest (approximately 12 %) but significant decrease in tCys (P < 0·001). Total homocysteine concentrations increased in duodenal switch patients but not in gastric bypass patients. Independent of surgery type, serum concentrations of methionine and cystathionine decreased (P < 0·05 for both), while serum glutathione and taurine remained stable. Glutamate concentrations declined, as did γ-glutamyltransferase activity (P < 0·001 for both). These results show that despite 30 % weight loss, and decreases in methionine, cystathionine and glutamate, there was no significant change in serum tCys in patients after gastric bypass surgery. The decrease in tCys in patients undergoing duodenal switch could be related to malabsorption. The present findings do not suggest that BMI is a causal determinant of plasma tCys.

This paper demonstrates that the activities of glycogen phosphorylase (GP), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are reduced in adult worms of the filarial nematode Litomosoides carinii recovered from pyri-doxine-deficient cotton rats when compared to worms recovered from pyridoxine-sufficient controls. GP, ALT and AST activities were determined in adult worms L. carinii recovered from cotton rat hosts over a 20-week experimental period. Activities of GP, ALT and AST in the parasite showed a direct correlation with the dietary pyridoxine intake of their host. Throughout the experiment, enzyme activities were significantly lower (P < 0·001) in worms from rats fed a pyridoxine-free diet ad libitum that in worms from rats fed either a stock colony diet, a pyridoxine-free diet ad libitum with daily supplementation of 100 μg pyridoxine or limited amounts of pyridoxine-free diet with daily supplementation of 100 μg pyridoxine. The lower than normal activity of GP, ALT, AST and other enzymes dependent on the biologically active derivative of pyridoxine, the coenzyme pyridoxal-5-phosphate (PLP), interferes with the protein, carbohydrate and lipid metabolism of L. carinii and may in part cause the reduced establishment, development and growth of the parasite in pyridoxine-deficient hosts.

Pyridoxine (vitamin B6) deficiency was induced in cotton rats which were then infected with the filarial parasite Litomosoides carinii. Embryogenesis was assessed microscopically in worms taken from pyridoxine deficient cotton rats and from various categories of control animals. Embryogenesis was retarded in worms from pyridoxine deficient hosts and more abnormal embryos were present in such worms than in those from control animals.

Vector-borne nematodes of the Order Filarioidea produce chronic, debilitating human infections which are usually non-fatal but are associated with a high degree of severe morbidity. Weight loss often accompanies infection and is probably a consequence of the increased energy cost associated with filarial fever, lymphangitis and lymphadenitis. In onchocerciasis, weight loss is associated with heavy worm loads as assessed by abundant nodules and large numbers of skin microfilariae. Experimental infections using rodent filariae have confirmed these observations and have also shown that low protein diets render hosts more susceptible to infection; nevertheless, parasite growth and embryogenesis is retarded in stunted female worms from protein deficient animals. In the absence of appropriate evidence, studies of experimental filariasis suggest that human protein-energy malnutrition may delay the development of stage-specific acquired immunity with a corresponding prolongation of patency. Epidemiological and experimental evidence shows that filarial nematodes acquire certain nutrients directly from their hosts. Of major importance in this respect is vitamin A which is taken up preferentially by human and rodent filariae; in humans, symptoms of hypovitaminosis A often accompany infection and could be an aggravating factor in onchocerciasis. Filariae also appear to require other specific nutrients such as iodine, thiamine and pyridoxine; dietary levels of these nutrients affect the host-parasite relationships in filariasis and pyridoxine seems to be of particular importance in this respect. Filarial parasites obviously compete with their hosts for available nutrients and, in the real world, human filariasis is often associated with a deterioration in the plane of nutrition of infected individuals.

Four trials were carried out to determine the optimal level of dietary pyridoxine (vitamin B6) and its interaction with riboflavin (vitamin B2) in early-weaned piglets. In Trial 1, twelve piglets were tube-fed graded supplements of B6, 0, 10, 50 or 100 mg/kg. The level of 50 mg/kg maximized B6 in red blood cells (P<0·05). In Trial 2, thirty-six piglets were tube-fed with four combinations of B6 (0 v. 50 mg/kg) and B2 (0 v. 25 mg/kg). The B6 supplement increased (P<0·01) B6 in red blood cells. C-peptide and insulin responses to intravenous glucose tended (P<0·08) to or decreased (P<0·03) with B2 while no effect was observed on glucose. After gastro-enteral glucose, dietary B2 depressed C-peptide and insulin responses in B6-unsupplemented piglets and increased them in B6-supplemented piglets (P<0·03). The glucose response tended to be higher in B6-supplemented piglets (P<0·06). Trials 3 and 4 were carried out in commercial conditions using either B6 and/or B2 supplements given during 2 weeks after weaning (Trial 3) or a B6 supplement alone (50 mg/kg) given between 2 (weaning) and 10 weeks of age. Despite a marked and persistent increase (P<0·01) of B6 in red blood cells in B6-supplemented piglets, the effect on growth performance was either none (P>0·39; Trial 3) or marginally lower (<−2 %; P<0·03; Trial 4). In conclusion, it appears that a dietary supplement of 50 mg/kg B6 saturated the red blood cell pool in B6 and influenced, along with B2, the glucose homeostasis through the entero-insular axis. Nevertheless, such metabolic effects are not reflected on growth performance.

Using a high protein diet (483 g/kg), two trials were carried out to assess any potential benefit which may result from the supplementation of diets for fingerling and grower class gilthead seabream with pyridoxine at levels which were below, matched and far exceeded the minimum dietary requirement. At the level of supplementation below the minimal requirement (lowest level) the responses from the practical diet almost matched the responses from the diet containing an amount of pyridoxine corresponding to the published minimum requirement for the species and no significant improvement in performance was recorded in response to increasing supplement level. However, despite the absence of a marked effect on overall performance, a small potential for increased activity of alanine aminotransferase was recorded amongst grower class fish given diets containing the lowest supplement. The proximate composition of the grower class fish was unaffected by the level of pyridoxine supplementation though marginal increases in the lipid content of the fingerlings were observed. At the haematological level, haematocrit, total haemoglobin and the plasma concentrations of glucose and protein were also unaffected. However, on the application of an acute stressor (repeated netting), significant alterations in haematocrit and plasma glucose concentration reflecting dietary pyridoxine supplement were recorded.

A study was undertaken to ascertain the effect of pyridoxine in diets of varying protein to energy ratio (P: E) for Mediterranean gilthead seabream fry (Sparus aurata) with respect to protein utilization. Diets were formulated to provide three levels of added pyridoxine (0·5, 5·0 and 50·0 mg/kg), at two protein levels (320 or 470 g/kg) whilst maintaining a similar gross isocalorific profile at 20 MJ/kg. Feeding level was proportionately 0·02 of the fish body weight per day, resulting in the following effects after a 70-day feeding trial. Low P: E ratio diets (15 g/MJ) did not perform as well as high P: E diets (24 g/MJ), with respect to growth related indices. Higher inclusions of pyridoxine into diets of equal P: E ratios, caused elevations in food conversion efficiency, protein efficiency ratio and apparent net protein utilization. A marked improvement of growth rate concomitant with pyridoxine level only occurred in the high P: E diets. It was concluded that incremental additions of pyridoxine in the diet, increased the efficiency of protein utilization for all diets tested. However, the protein sparing effect oflipid was not achieved for the low protein diets indicating the relatively high requirement for protein in the growth of the juvenile seabream.