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Luis Mata

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University of Santiago de Compostela

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The University of Auckland

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Papers by Luis Mata

Antibacterial Residue Excretion via Urine as an Indicator for Therapeutical Treatment Choice and Farm Waste Treatment

Antibiotics, 2021

Many of the infectious diseases that affect livestock have bacteria as etiological agents. Thus, ... more Many of the infectious diseases that affect livestock have bacteria as etiological agents. Thus, therapy is based on antimicrobials that leave the animal’s tissues mainly via urine, reaching the environment through slurry and waste water. Once there, antimicrobial residues may lead to antibacterial resistance as well as toxicity for plants, animals, or humans. Hence, the objective was to describe the rate of antimicrobial excretion in urine in order to select the most appropriate molecule while reducing harmful effects. Thus, 62 pigs were treated with sulfamethoxypyridazine, oxytetracycline, and enrofloxacin. Urine was collected through the withdrawal period and analysed via LC-MS/MS. Oxytetracycline had the slowest rate of degradation (a half-life time of 4.18 days) and the most extended elimination period in urine (over 2 months), followed by enrofloxacin (a half-life time of 1.48 days, total urine elimination in ca. 3 weeks) and sulfamethoxypyridazine (a half-life time of 0.49 da...

Optimization and Validation of a New Microbial Inhibition Test for the Detection of Antimicrobial Residues in Living Animals Intended for Human Consumption

Foods, 2021

Even though antibiotics are necessary in livestock production, they can be harmful not only due t... more Even though antibiotics are necessary in livestock production, they can be harmful not only due to their toxicity, but also in view of their contribution to the emergence of antimicrobial resistance. Screening tests based on microbial growth inhibition appeared to be useful tools to prevent its entry into the food chain. They have nevertheless been traditionally carried out post mortem, leading to great economical loss and harm to the environment in case a positive sample is found. Hence, the objective was to evaluate the use of a screening test as an ante mortem alternative for the detection of antibiotic residues in meat: thus, Explorer®-Blood test was optimized and validated. After adapting the procedure for matrix preparation, the assay parameters were assessed from 344 antibiotic-free blood serum samples. Limits of Detection (LoDs) were defined by spiking blood serum with several of the most common antimicrobials used in veterinary practice. LoDs were similar to those obtained ...

Is Blood a Good Indicator for Detecting Antimicrobials in Meat? Evidence for the Development of In Vivo Surveillance Methods

Antibiotics, 2020

The introduction of antimicrobial residues in the food chain has a significant impact on human he... more The introduction of antimicrobial residues in the food chain has a significant impact on human health. An innovative solution to avoid their presence in meat is the adaptation of current control methods for use with in vivo matrixes. Thus, the aim was to obtain paired blood and muscle samples from pigs treated with some of the main antimicrobials currently used in veterinary medicine (oxytetracycline, sulfamethoxypyridazine, enrofloxacin, amoxicillin), and to compare their rate of depletion in both matrixes. Antimicrobial concentrations in paired samples of blood and muscle were determined by liquid chromatography with tandem mass spectrometry (LC–MS/MS) or high performance liquid chromatography with fluorescence detection (HPLC-FLD). A comparison between values obtained in muscle and blood showed a similar distribution in both matrixes for oxytetracycline; for sulfamethoxypyridazine, a similar decrease rate but a concentration three times higher in blood compared to muscle was foun...

Changes in the Distribution of Cadmium and Lead in Human and Bovine Milk Induced by Heating or Freezing

Journal of Food Protection, 1996

The percentage of cadmium or lead present in the fat fraction of bovine milk is not affected by h... more The percentage of cadmium or lead present in the fat fraction of bovine milk is not affected by heating or freezing. In human skimmed milk, cadmium is mainly associated with a fraction with molecular weight lower than 10,000. Storage at −20°C for 10 days does not have any effect on the distribution of cadmium when milk is incubated with this metal before freezing. This treatment causes only a small increase in the amount of cadmium associated with the low molecular weight fraction when the metal is added after freezing. In bovine milk, 64% of cadmium is associated with a fraction with molecular weight above 70,000. Freezing causes a 37% decrease of the cadmium present in this fraction when the metal is added after thawing. When bovine milk was incubated with cadmium before freezing there was not a marked change in its distribution as when added after thawing. Heating at 63°C for 30 min caused a slight decrease in the amount of cadmium present in the casein fraction. The distribution...

Distribution of Added Lead and Cadmium in Human and Bovine Milk

Journal of Food Protection, 1995

Distribution of added lead and cadmium to bovine and human milk and whey has been studied. In bov... more Distribution of added lead and cadmium to bovine and human milk and whey has been studied. In bovine milk, about 97 and 89% of lead and cadmium, respectively, were recovered in the casein fraction obtained by enzymatic coagulation. However, only 6% of lead and 41% of cadmium were found in the same fraction separated by acid precipitation, indicating that the distribution of both metals is very different depending on the method used for milk fractionation. Moreover, gel filtration of bovine and human skimmed milk and whey after addition of lead and cadmium was carried out. Most of the lead was associated to the casein fraction after gel filtration of skimmed milk, whereas in the chromatography of whey, lead was eluted with the low molecular weight fraction in both species. However, a different pattern in the distribution of cadmium has been observed in the two species studied. In contrast to the binding of cadmium to the low molecular weight fraction in human skimmed milk and whey, i...

Experimental evidence for the essential role of the C-terminal residue in the strict aminopeptidase activity of the thiol aminopeptidase PepC, a bacterial bleomycin hydrolase

Biochemical Journal, 1997

PepCs isolated from lactic acid bacteria and bleomycin hydrolases of eukaryotic organisms are str... more PepCs isolated from lactic acid bacteria and bleomycin hydrolases of eukaryotic organisms are strict aminopeptidases which belong to the papain family of thiol peptidases. The structural basis of the enzymic specificity of the lactococcal PepC has been investigated by site-directed mutagenesis. The deletion of the C-terminal residue (Ala-435) abolished the aminopeptidase activity, whereas this deletion led to a new peptidase specificity. The enzymic properties of wild-type and mutant PepCs demonstrate that the terminal α-carboxy group plays a key role in the strict aminopeptidase activity.

Single laboratory validation of A ready-to-Use phosphatase inhibition assay for detection of okadaic acid toxins

A phosphatase inhibition assay for detection of okadaic acid (OA) toxins in shellfish, OkaTest, w... more A phosphatase inhibition assay for detection of okadaic acid (OA) toxins in shellfish, OkaTest, was single laboratory validated according to international recognized guidelines (AOAC, EURACHEM). Special emphasis was placed on the ruggedness of the method and stability of the components. All reagents were stable for more than 6 months and the method was highly robust under normal laboratory conditions. The limit of detection and quantification were 44 and 56 µg/kg, respectively; both below the European legal limit of 160 µg/kg. The repeatability was evaluated with 2 naturally contaminated samples. The relative standard deviation (RSD) calculated was 1.4% at a level of 276 µg/kg and 3.9% at 124 µg/kg. Intermediate precision was estimated by testing 10 different samples (mussel and scallop) on three different days and ranged between 2.4 and 9.5%. The IC 50 values of the phosphatase used in this assay were determined for OA (1.2 nM), DTX-1 (1.6 nM) and DTX-2 (1.2 nM). The accuracy of the method was estimated by recovery testing for OA (mussel, 78-101%; king scallop, 98-114%), DTX-1 (king scallop, 79-102%) and DTX-2 (king scallop, 93%). Finally, the method was qualitatively compared to the mouse bioassay and LC-MS/MS.

Development of a Simple Enzyme Immunoassay for the Determination of Ovine Luteinizing Hormone

Veterinary Research Communications, 2007

Deletion of the four C-terminal residues of PepC converts an aminopeptidase into an oligopeptidase

Protein Engineering, Design and Selection, 1999

The aminopeptidase PepC is a cysteine peptidase isolated from lactic acid bacteria. Its structura... more The aminopeptidase PepC is a cysteine peptidase isolated from lactic acid bacteria. Its structural and enzymatic properties closely resembles those of the bleomycin hydrolases, a group of cytoplasmic enzymes isolated from eukaryotes. Previous biochemical and structural data have shown that the C-terminal end of PepC partially occupies the active site cleft. In this work the substrate specificity of PepC was engineered by deletion of the four C-terminal residues. The mutant PepC∆ ∆432-435 cleaved peptide substrates as an oligopeptidase while the aminopeptidase specificity was totally abolished. The substrate size dependency indicated that PepC∆ ∆432-435 possesses an extended binding site able to accommodate four residues of the substrate on both sides of the cleaved bond. The activity of PepC∆ ∆432-435 towards tryptic fragments of casein revealed a preference for peptides with hydrophobic amino acids at positions P2 and P3 and for Gly, Asn and Gln at position P1. PepC∆ ∆432-435 was shown to be highly sensitive to the thiol peptidase inhibitors leupeptin or E64 which are inefficient towards the wild-type PepC. In conclusion, deletion of the four C-terminal residues in PepC produces a new enzyme with properties resembling those of an endopeptidase from the papain family.

Quantitative Determination of the Okadaic Acid Toxins Group by a Colorimetric Phosphatase Inhibition Assay: Interlaboratory Study

Journal of AOAC INTERNATIONAL, 2013

An interlaboratory collaborative study to validate a colorimetric phosphatase inhibition assay fo... more An interlaboratory collaborative study to validate a colorimetric phosphatase inhibition assay for quantitative determination of the okadaic acid (OA) toxins group in molluscs, OkaTest, was conducted. Eight test materials, including mussels, scallops, clams, and cockles, were analyzed as blind duplicates. Blank samples and materials containing different OA toxin levels ranging from 98 to 275 μg/kg OA equivalents were included. The study was carried out by a total of 16 laboratories from 11 different countries. Values obtained for repeatability relative standard deviations (RSDr) ranged from 5.4 to 11.2% (mean 7.5%). Reproducibility RSD (RSDR) values were between 7.6 and 13.2% (mean 9.9%). The Horwitz ratio (HorRat) values ranged between 0.4 and 0.6. A recovery assay was also carried out using a sample spiked with OA. A mean recovery of 98.0% and an RSD of 14.5% were obtained. The results obtained in this validation study indicate that the colorimetric phosphatase inhibition assay, O...

A multi-laboratory evaluation of a clinically-validated incurred quality control material for analysis of allergens in food

Food Chemistry, 2014

A dessert matrix previously used for diagnosis of food allergies was incurred with pasteurised eg... more A dessert matrix previously used for diagnosis of food allergies was incurred with pasteurised egg white or skimmed milk powder at 3, 6, 15 and 30 mg allergen protein per kg of dessert matrix and evaluated as a quality control material for allergen analysis in a multi-laboratory trial. Analysis was performed by immunoassay using five kits each for egg and milk (based on casein) and six 'other' milk kits (five based on b-lactoglobulin and one total milk). All kits detected allergen protein at the 3 mg kg À1 level. Based on ISO criteria only one egg kit accurately determined egg protein at 3 mg kg À1 (p = 0.62) and one milk (casein) kit accurately determined milk at 6 (p = 0.54) and 15 mg kg À1 (p = 0.83), against the target value. The milk ''other'' kits performed least well of all the kits assessed, giving the least precise analyses. The incurred dessert material had the characteristics required for a quality control material for allergen analysis.

Evaluation of indirect competitive and double antibody sandwich ELISA tests to determine β-lactoglobulin and ovomucoid in model processed foods

Food and Agricultural Immunology, 2008

Performance of a New Microbial Test for Quinolone Residues in Muscle

Food Analytical Methods, 2010

Interaction of Mercury with Human and Bovine Milk Proteins

Bioscience, Biotechnology, and Biochemistry, 1997

Cadmium uptake by Caco-2 cells. Effect of some milk components

Chemico-Biological Interactions, 1996

The effect of some milk components on the cellular uptake of cadmium has been studied using a hum... more The effect of some milk components on the cellular uptake of cadmium has been studied using a human intestinal cell line (Caco-2). Cadmium uptake by Caco-2 cells increased with the concentration of this metal in the culture medium, in a saturable way. These cells were exposed to different concentrations of cadmium and the synthesis of metallothionein was studied by a cadmium-saturation method. The levels of metallothionein increased with the cadmium concentration in the medium up to 20 pM of metal. Supplementation of the culture medium with lO?/ bovine milk caused a 25% decrease in the uptake of cadmium with respect to that internalized by the cells maintained in the culture medium alone. However, the uptake of cadmium from the medium supplemented with 100/o human milk was similar to that with serum-free medium. &Lactoglobulin interacted with cadmium when studied by equilibrium dialysis, showing a stoichiometric binding constant of 5 x lo4 Vmol. Interaction of lactoferrin with cadmium, however, was negligible. When Caco-2 cells were incubated in culture medium containing lactoferrin, cadmium uptake decreased with respect to that observed incubating the cells in a medium containing 8-lactoglobulin or in the free-protein medium. The inhibitory effect of lactoferrin on the uptake of cadmium might be due to a reduction of the cell surface charge, through its binding to the membrane.

Antibacterial Residue Excretion via Urine as an Indicator for Therapeutical Treatment Choice and Farm Waste Treatment

Antibiotics, 2021

Many of the infectious diseases that affect livestock have bacteria as etiological agents. Thus, ... more Many of the infectious diseases that affect livestock have bacteria as etiological agents. Thus, therapy is based on antimicrobials that leave the animal’s tissues mainly via urine, reaching the environment through slurry and waste water. Once there, antimicrobial residues may lead to antibacterial resistance as well as toxicity for plants, animals, or humans. Hence, the objective was to describe the rate of antimicrobial excretion in urine in order to select the most appropriate molecule while reducing harmful effects. Thus, 62 pigs were treated with sulfamethoxypyridazine, oxytetracycline, and enrofloxacin. Urine was collected through the withdrawal period and analysed via LC-MS/MS. Oxytetracycline had the slowest rate of degradation (a half-life time of 4.18 days) and the most extended elimination period in urine (over 2 months), followed by enrofloxacin (a half-life time of 1.48 days, total urine elimination in ca. 3 weeks) and sulfamethoxypyridazine (a half-life time of 0.49 da...

Optimization and Validation of a New Microbial Inhibition Test for the Detection of Antimicrobial Residues in Living Animals Intended for Human Consumption

Foods, 2021

Even though antibiotics are necessary in livestock production, they can be harmful not only due t... more Even though antibiotics are necessary in livestock production, they can be harmful not only due to their toxicity, but also in view of their contribution to the emergence of antimicrobial resistance. Screening tests based on microbial growth inhibition appeared to be useful tools to prevent its entry into the food chain. They have nevertheless been traditionally carried out post mortem, leading to great economical loss and harm to the environment in case a positive sample is found. Hence, the objective was to evaluate the use of a screening test as an ante mortem alternative for the detection of antibiotic residues in meat: thus, Explorer®-Blood test was optimized and validated. After adapting the procedure for matrix preparation, the assay parameters were assessed from 344 antibiotic-free blood serum samples. Limits of Detection (LoDs) were defined by spiking blood serum with several of the most common antimicrobials used in veterinary practice. LoDs were similar to those obtained ...

Is Blood a Good Indicator for Detecting Antimicrobials in Meat? Evidence for the Development of In Vivo Surveillance Methods

Antibiotics, 2020

The introduction of antimicrobial residues in the food chain has a significant impact on human he... more The introduction of antimicrobial residues in the food chain has a significant impact on human health. An innovative solution to avoid their presence in meat is the adaptation of current control methods for use with in vivo matrixes. Thus, the aim was to obtain paired blood and muscle samples from pigs treated with some of the main antimicrobials currently used in veterinary medicine (oxytetracycline, sulfamethoxypyridazine, enrofloxacin, amoxicillin), and to compare their rate of depletion in both matrixes. Antimicrobial concentrations in paired samples of blood and muscle were determined by liquid chromatography with tandem mass spectrometry (LC–MS/MS) or high performance liquid chromatography with fluorescence detection (HPLC-FLD). A comparison between values obtained in muscle and blood showed a similar distribution in both matrixes for oxytetracycline; for sulfamethoxypyridazine, a similar decrease rate but a concentration three times higher in blood compared to muscle was foun...

Changes in the Distribution of Cadmium and Lead in Human and Bovine Milk Induced by Heating or Freezing

Journal of Food Protection, 1996

The percentage of cadmium or lead present in the fat fraction of bovine milk is not affected by h... more The percentage of cadmium or lead present in the fat fraction of bovine milk is not affected by heating or freezing. In human skimmed milk, cadmium is mainly associated with a fraction with molecular weight lower than 10,000. Storage at −20°C for 10 days does not have any effect on the distribution of cadmium when milk is incubated with this metal before freezing. This treatment causes only a small increase in the amount of cadmium associated with the low molecular weight fraction when the metal is added after freezing. In bovine milk, 64% of cadmium is associated with a fraction with molecular weight above 70,000. Freezing causes a 37% decrease of the cadmium present in this fraction when the metal is added after thawing. When bovine milk was incubated with cadmium before freezing there was not a marked change in its distribution as when added after thawing. Heating at 63°C for 30 min caused a slight decrease in the amount of cadmium present in the casein fraction. The distribution...

Distribution of Added Lead and Cadmium in Human and Bovine Milk

Journal of Food Protection, 1995

Distribution of added lead and cadmium to bovine and human milk and whey has been studied. In bov... more Distribution of added lead and cadmium to bovine and human milk and whey has been studied. In bovine milk, about 97 and 89% of lead and cadmium, respectively, were recovered in the casein fraction obtained by enzymatic coagulation. However, only 6% of lead and 41% of cadmium were found in the same fraction separated by acid precipitation, indicating that the distribution of both metals is very different depending on the method used for milk fractionation. Moreover, gel filtration of bovine and human skimmed milk and whey after addition of lead and cadmium was carried out. Most of the lead was associated to the casein fraction after gel filtration of skimmed milk, whereas in the chromatography of whey, lead was eluted with the low molecular weight fraction in both species. However, a different pattern in the distribution of cadmium has been observed in the two species studied. In contrast to the binding of cadmium to the low molecular weight fraction in human skimmed milk and whey, i...

Experimental evidence for the essential role of the C-terminal residue in the strict aminopeptidase activity of the thiol aminopeptidase PepC, a bacterial bleomycin hydrolase

Biochemical Journal, 1997

PepCs isolated from lactic acid bacteria and bleomycin hydrolases of eukaryotic organisms are str... more PepCs isolated from lactic acid bacteria and bleomycin hydrolases of eukaryotic organisms are strict aminopeptidases which belong to the papain family of thiol peptidases. The structural basis of the enzymic specificity of the lactococcal PepC has been investigated by site-directed mutagenesis. The deletion of the C-terminal residue (Ala-435) abolished the aminopeptidase activity, whereas this deletion led to a new peptidase specificity. The enzymic properties of wild-type and mutant PepCs demonstrate that the terminal α-carboxy group plays a key role in the strict aminopeptidase activity.

Single laboratory validation of A ready-to-Use phosphatase inhibition assay for detection of okadaic acid toxins

A phosphatase inhibition assay for detection of okadaic acid (OA) toxins in shellfish, OkaTest, w... more A phosphatase inhibition assay for detection of okadaic acid (OA) toxins in shellfish, OkaTest, was single laboratory validated according to international recognized guidelines (AOAC, EURACHEM). Special emphasis was placed on the ruggedness of the method and stability of the components. All reagents were stable for more than 6 months and the method was highly robust under normal laboratory conditions. The limit of detection and quantification were 44 and 56 µg/kg, respectively; both below the European legal limit of 160 µg/kg. The repeatability was evaluated with 2 naturally contaminated samples. The relative standard deviation (RSD) calculated was 1.4% at a level of 276 µg/kg and 3.9% at 124 µg/kg. Intermediate precision was estimated by testing 10 different samples (mussel and scallop) on three different days and ranged between 2.4 and 9.5%. The IC 50 values of the phosphatase used in this assay were determined for OA (1.2 nM), DTX-1 (1.6 nM) and DTX-2 (1.2 nM). The accuracy of the method was estimated by recovery testing for OA (mussel, 78-101%; king scallop, 98-114%), DTX-1 (king scallop, 79-102%) and DTX-2 (king scallop, 93%). Finally, the method was qualitatively compared to the mouse bioassay and LC-MS/MS.

Development of a Simple Enzyme Immunoassay for the Determination of Ovine Luteinizing Hormone

Veterinary Research Communications, 2007

Deletion of the four C-terminal residues of PepC converts an aminopeptidase into an oligopeptidase

Protein Engineering, Design and Selection, 1999

The aminopeptidase PepC is a cysteine peptidase isolated from lactic acid bacteria. Its structura... more The aminopeptidase PepC is a cysteine peptidase isolated from lactic acid bacteria. Its structural and enzymatic properties closely resembles those of the bleomycin hydrolases, a group of cytoplasmic enzymes isolated from eukaryotes. Previous biochemical and structural data have shown that the C-terminal end of PepC partially occupies the active site cleft. In this work the substrate specificity of PepC was engineered by deletion of the four C-terminal residues. The mutant PepC∆ ∆432-435 cleaved peptide substrates as an oligopeptidase while the aminopeptidase specificity was totally abolished. The substrate size dependency indicated that PepC∆ ∆432-435 possesses an extended binding site able to accommodate four residues of the substrate on both sides of the cleaved bond. The activity of PepC∆ ∆432-435 towards tryptic fragments of casein revealed a preference for peptides with hydrophobic amino acids at positions P2 and P3 and for Gly, Asn and Gln at position P1. PepC∆ ∆432-435 was shown to be highly sensitive to the thiol peptidase inhibitors leupeptin or E64 which are inefficient towards the wild-type PepC. In conclusion, deletion of the four C-terminal residues in PepC produces a new enzyme with properties resembling those of an endopeptidase from the papain family.

Quantitative Determination of the Okadaic Acid Toxins Group by a Colorimetric Phosphatase Inhibition Assay: Interlaboratory Study

Journal of AOAC INTERNATIONAL, 2013

An interlaboratory collaborative study to validate a colorimetric phosphatase inhibition assay fo... more An interlaboratory collaborative study to validate a colorimetric phosphatase inhibition assay for quantitative determination of the okadaic acid (OA) toxins group in molluscs, OkaTest, was conducted. Eight test materials, including mussels, scallops, clams, and cockles, were analyzed as blind duplicates. Blank samples and materials containing different OA toxin levels ranging from 98 to 275 μg/kg OA equivalents were included. The study was carried out by a total of 16 laboratories from 11 different countries. Values obtained for repeatability relative standard deviations (RSDr) ranged from 5.4 to 11.2% (mean 7.5%). Reproducibility RSD (RSDR) values were between 7.6 and 13.2% (mean 9.9%). The Horwitz ratio (HorRat) values ranged between 0.4 and 0.6. A recovery assay was also carried out using a sample spiked with OA. A mean recovery of 98.0% and an RSD of 14.5% were obtained. The results obtained in this validation study indicate that the colorimetric phosphatase inhibition assay, O...

A multi-laboratory evaluation of a clinically-validated incurred quality control material for analysis of allergens in food

Food Chemistry, 2014

A dessert matrix previously used for diagnosis of food allergies was incurred with pasteurised eg... more A dessert matrix previously used for diagnosis of food allergies was incurred with pasteurised egg white or skimmed milk powder at 3, 6, 15 and 30 mg allergen protein per kg of dessert matrix and evaluated as a quality control material for allergen analysis in a multi-laboratory trial. Analysis was performed by immunoassay using five kits each for egg and milk (based on casein) and six 'other' milk kits (five based on b-lactoglobulin and one total milk). All kits detected allergen protein at the 3 mg kg À1 level. Based on ISO criteria only one egg kit accurately determined egg protein at 3 mg kg À1 (p = 0.62) and one milk (casein) kit accurately determined milk at 6 (p = 0.54) and 15 mg kg À1 (p = 0.83), against the target value. The milk ''other'' kits performed least well of all the kits assessed, giving the least precise analyses. The incurred dessert material had the characteristics required for a quality control material for allergen analysis.

Evaluation of indirect competitive and double antibody sandwich ELISA tests to determine β-lactoglobulin and ovomucoid in model processed foods

Food and Agricultural Immunology, 2008

Performance of a New Microbial Test for Quinolone Residues in Muscle

Food Analytical Methods, 2010

Interaction of Mercury with Human and Bovine Milk Proteins

Bioscience, Biotechnology, and Biochemistry, 1997

Cadmium uptake by Caco-2 cells. Effect of some milk components

Chemico-Biological Interactions, 1996

The effect of some milk components on the cellular uptake of cadmium has been studied using a hum... more The effect of some milk components on the cellular uptake of cadmium has been studied using a human intestinal cell line (Caco-2). Cadmium uptake by Caco-2 cells increased with the concentration of this metal in the culture medium, in a saturable way. These cells were exposed to different concentrations of cadmium and the synthesis of metallothionein was studied by a cadmium-saturation method. The levels of metallothionein increased with the cadmium concentration in the medium up to 20 pM of metal. Supplementation of the culture medium with lO?/ bovine milk caused a 25% decrease in the uptake of cadmium with respect to that internalized by the cells maintained in the culture medium alone. However, the uptake of cadmium from the medium supplemented with 100/o human milk was similar to that with serum-free medium. &Lactoglobulin interacted with cadmium when studied by equilibrium dialysis, showing a stoichiometric binding constant of 5 x lo4 Vmol. Interaction of lactoferrin with cadmium, however, was negligible. When Caco-2 cells were incubated in culture medium containing lactoferrin, cadmium uptake decreased with respect to that observed incubating the cells in a medium containing 8-lactoglobulin or in the free-protein medium. The inhibitory effect of lactoferrin on the uptake of cadmium might be due to a reduction of the cell surface charge, through its binding to the membrane.