The pathophysiology of elevated vitamin B12 in clinical practice.

Hypercobalaminemia (high serum vitamin B12 levels) is a frequent and underestimated anomaly. Clinically, it can be paradoxically accompanied by signs of deficiency, reflecting a functional deficiency linked to qualitative abnormalities, which are related to defects in tissue uptake and action of vitamin B12. The aetiological profile of high serum cobalamin predominantly encompasses severe disease entities for which early diagnosis is critical for prognosis. These entities are essentially comprised of solid neoplasms, haematological malignancies and liver and kidney diseases. This review reflects the potential importance of the vitamin B12 assay as an early diagnostic marker of these diseases. A codified approach is needed to determine the potential indications of a search for high serum cobalamin and the practical clinical strategy to adopt upon discovery of elevated cobalamin levels. While low serum cobalamin levels do not necessarily imply deficiency, an abnormally high serum cobalamin level forms a warning sign requiring exclusion of a number of serious underlying pathologies. Functional cobalamin deficiency can thus occur at any serum level.

Polyphenols can inhibit furin in vitro as a result of the reactivity of their auto-oxidation products to proteins.

UNLABELLED: Methods using fluorogenic peptide substrates have been proposed for screening of proprotein convertase (PC) inhibitors and they are attractive since they offer the advantage of being sensitive, cost-effective and susceptible to miniaturization. Several polyphenols, including epigallocatechin gallate ((-)EGCG), the main component of green tea, and quercetin, widely distributed in fruit and vegetables, however, led to false positive results when fluorogenic peptide substrates were used. Processing of genuine furin substrates was not inhibited by these polyphenols. In the present study, these discordant effects of (-)EGCG on the PC furin were studied. While quercetin can form aggregates in solution, aggregate-based promiscuous inhibition could be ruled out as underlying mechanism for (-)EGCG. Hydrogen peroxide production, from auto-oxidation, was too low to be a major factor but appeared associated to furin inhibition, suggesting a role for other auto-oxidation products. Since the instability of catechins is related to their electrophilic character, we tested the nucleophilic substance glutathione for stabilization. Indeed glutathione reduced furin inhibition and (-)EGCG binding to furin and serum albumin as shown by redox-cycling staining. Catechins, therefore, seem to form reactive compounds and this should be taken into account in screening assays. Adding glutathione to the detergent-based assay, as used in these studies to measure furin processing activity, strongly reduced inhibition by a number of polyphenols (catechins, gallic acid and quercetin), while the effect on the genuine inhibitor nona-D-arginine remained unchanged. IN CONCLUSION: the combined use of detergent and glutathione in the screening assay for furin inhibitors improves the predictive value.

Limitations of inhibitory activities of polyphenols on furin-mediated substrate processing.

Recently, selected polyphenols were reported to exert proprotein convertase (PC) inhibitory activities on in vitro cleavage of a fluorogenic peptide substrate and it was concluded that this anti-protease activity might be responsible for the reported anti-cancer properties of these polyphenols. This prompted investigations to identify PC inhibiting polyphenols that could affect IGF-1R-mediated tumorigenesis since pro-IGF-1R is bioactivated by PCs like furin. Initial screening of polyphenols for their impact on in vitro cleavage of fluorogenic peptide substrate Pyr-RTKR-AMC by human furin (hfurin(573)) indeed revealed varying inhibitory effects. (-)EGCG, chrysin, and quercetin, were subsequently evaluated using uncleaved diphtheria toxin as substrate in vitro. However, none displayed any inhibitory impact on processing. Binding of (-)EGCG to both furin and the diphtheria toxin protein was demonstrated. Subsequently, it was found that for seven polyphenols tested, addition of casein or gamma globulin led to reduction or even annihilation of in vitro Pyr- RTKR-AMC cleavage inhibition. No such effect was seen with the furin inhibitor nona-D-arginine. Western blot studies to investigate possible effects of selected polyphenols on processing in cells of the tumorigenesis-linked proproteins pro-IGF-1R and pro-GPC3 also revealed no inhibitory effects. In conclusion, our results confirm the reported PC inhibitory effects of polyphenols on fluorogenic peptide substrate cleavage in vitro. However, the data show that polyphenolic inhibitory effects on hfurin(573)-mediated in vitro fluorogenic peptide substrate cleavage cannot be extrapolated to similar effects on processing of genuine proproteins, whether in vitro or in cells. This undermines the anti-protease rationale for the reported polyphenolic anti-cancer properties.

Curcumin for monoclonal gammopathies. What can we hope for, what should we fear?

Over the last decades there has been an increasing interest in a possible role of curcumin on cancer. Although curcumin is considered safe for healthy people, conclusive evidence on the safety and efficacy of curcumin for patients with monoclonal gammopathies is, so far, lacking. The present paper reviews the literature on molecular, cellular and clinical effects of curcumin in an attempt to identify, reasons for optimism but also for concern. The results of this critical evaluation can be useful for both patient- selection and monitoring in the context of clinical trials. Curcumin might be helpful for some but certainly not for all patients with monoclonal gammopathies. It is important to avoid unnecessary detrimental side effects in some in order to safeguard curcumin for those that could benefit. Parameters for patient monitoring, that can be used as early warning signs and as indicators of a favorable development have therefore been suggested.

Curcumin for the prevention of progression in monoclonal gammopathy of undetermined significance: A word of caution.

A recent pilot study found that curcumin, in certain patients with monoclonal gammopathy of undetermined significance (MGUS), decreases the paraprotein load and the urinary N-telopeptide of type 1 collagen bone turnover marker. While this result is encouraging, the easy availability of the food component turmeric, containing curcumin, may lead to intake by MGUS patients without medical supervision. Curcumin is generally considered safe. Nevertheless, it is known that curcumin inhibits interleukin-12 production in dendritic cells, thereby dampening the Th1 response. It is also well established that Th1 cells are protective against invading pathogens and tumors. The present study describes a case in which bronchitis developed upon turmeric intake for gastrointestinal complaints. While one case does not provide proof of curcumin toxicity, a thorough literature overview suggests that turmeric may have an immunosuppressive effect, notably in patients with a compromised immune system. A warning against the use of turmeric or curcumin without medical supervision in immunocompromised patients seems therefore very opportune. Patients with MGUS, in whom the levels of non-affected immunoglobulins are reduced, should be carefully monitored for toxicity when curcumin is administered.