The Formation of an Anti-Cancer Complex Under Simulated Gastric Conditions

Temperature, pH, and Molecular Packing Effects on the Penetration of Oleic Acid Monolayer by α-Lactalbumin

Recently, we reported on the interfacial behavior of mixed oleic acid (OA)-α-lactalbumin monolayer and its relevance in the formation of tumoricidal HAMLET (human α-lactalbumin made lethal to tumor cells)-like complex. This complex is probably formed in the gastrointestinal tract, but it has not been proved so far. The molecular base and the underlying physicochemical forces leading to such complexation remain to be known as well. There are also several other issues related with the complex stoichiometry that need to be fully explained. This study provides insight into the mechanism of temperature, pH, and physical state of monolayer-dependent binding of OA by the milk protein- apo-α-lactalbumin. Using the Langmuir and Langmuir-Blodgett approaches, we investigated the interactions between the OA monolayer and the apo-bovine α-lactalbumin (BLA III) at different pH, temperatures, and molecular packing. We found that the most favorable conditions for the formation of mixed OA-BLA III film are relevant to the gastric environment. The stabilization of OA-BLA III at the interface is associated with the conformational changes of protein in the presence of fatty acids induced by low pH and high temperature in the expanded monolayer. Our approach helps to understand the molecular mechanism of HAMLET/bovine α-lactalbumin made lethal to tumor cells formation in vivo.

BAMLET kills chemotherapy-resistant mesothelioma cells, holding oleic acid in an activated cytotoxic state

Malignant pleural mesothelioma is an aggressive cancer with poor prognosis. Here we have investigated in vitro efficacy of BAMLET and BLAGLET complexes (anti-cancer complexes consisting of oleic acid and bovine α-lactalbumin or β-lactoglobulin respectively) in killing mesothelioma cells, determined BAMLET and BLAGLET structures, and investigated possible biological mechanisms. We performed cell viability assays on 16 mesothelioma cell lines. BAMLET and BLAGLET having increasing oleic acid content inhibited human and rat mesothelioma cell line proliferation at decreasing doses. Most of the non-cancer primary human fibroblasts were more resistant to BAMLET than were human mesothelioma cells. BAMLET showed similar cytotoxicity to cisplatin-resistant, pemetrexed-resistant, vinorelbine-resistant, and parental rat mesothelioma cells, indicating the BAMLET anti-cancer mechanism may be different to drugs currently used to treat mesothelioma. Cisplatin, pemetrexed, gemcitabine, vinorelbine, and BAMLET, did not demonstrate a therapeutic window for mesothelioma compared with immortalised non-cancer mesothelial cells. We demonstrated by quantitative PCR that ATP synthase is downregulated in mesothelioma cells in response to regular dosing with BAMLET. We sought structural insight for BAMLET and BLAGLET activity by performing small angle X-ray scattering, circular dichroism, and scanning electron microscopy. Our results indicate the structural mechanism by which BAMLET and BLAGLET achieve increased cytotoxicity by holding increasing amounts of oleic acid in an active cytotoxic state encapsulated in increasingly unfolded protein. Our structural studies revealed similarity in the molecular structure of the protein components of these two complexes and in their encapsulation of the fatty acid, and differences in the microscopic structure and structural stability. BAMLET forms rounded aggregates and BLAGLET forms long fibre-like aggregates whose aggregation is more stable than that of BAMLET due to intermolecular disulphide bonds. The results reported here indicate that BAMLET and BLAGLET may be effective second-line treatment options for mesothelioma.

Gastric digestion of α-lactalbumin in adult human subjects using capsule endoscopy and nasogastric tube sampling

In the present study, structural changes in the milk protein α-lactalbumin (α-LA) and its proteolysis were investigated for the potential formation of protein-fatty acid complexes during in vivo gastric digestion. Capsule endoscopy allowed visualisation of the digestion of the test drinks, with nasogastric tubes allowing sampling of the gastric contents. A total of ten healthy volunteers had nasogastric tubes inserted into the stomach and ingested test drinks containing 50 g/l of sucrose and 25 g/l of α-LA with and without 4 g/l of oleic acid (OA). The samples of gastric contents were collected for analysis at 3 min intervals. The results revealed a rapid decrease in the pH of the stomach of the subjects. The fasting pH of 2·31 (SD 1·19) increased to a pH maxima of pH 6·54 (SD 0·29) after ingestion, with a subsequent decrease to pH 2·22 (SD 1·91) after 21 min (n 8). Fluorescence spectroscopy and Fourier transform IR spectroscopy revealed partial protein unfolding, coinciding with the decrease in pH below the isoelectric point of α-LA. The activity of pepsin in the fasting state was found to be 39 (SD 12) units/ml of gastric juice. Rapid digestion of the protein occurred: after 15 min, no native protein was detected using SDS-PAGE; HPLC revealed the presence of small amounts of native protein after 24 min of gastric digestion. Mirocam® capsule endoscopy imaging and video clips (see the online supplementary material) revealed that gastric peristalsis resulted in a heterogeneous mixture during gastric digestion. Unfolding of α-LA was observed during gastric transit; however, there was no evidence of a cytotoxic complex being formed between α-LA and OA.