Disease relevance of fructoselysine

• These data show that FL and Maillard products in skin correlate with functional abnormalities in other tissues and suggest that protein glycation and oxidation (glycoxidation) may be implicated in the development of diabetic retinopathy and early nephropathy [1].
• Identification of a pathway for the utilization of the Amadori product fructoselysine in Escherichia coli [2].
• The mice grow normally and are apparently healthy, and levels of protein-bound and free fructoselysine are elevated in several tissues of importance to diabetic complications [3].

High impact information on fructoselysine

• We measured the initial Amadori adduct, fructoselysine (FL); two Maillard products, N epsilon-(carboxymethyl) lysine (CML) and pentosidine; and fluorescence (excitation = 328 nm, emission = 378 nm) in skin collagen from 39 type 1 diabetic patients (aged 41.5 +/- 15.3 [17-73] yr; duration of diabetes 17.9 +/- 11.5 [0-46] yr, [mean +/- SD, range]) [1].
• Alternatively, FL may be cleaved oxidatively to form N(epsilon)-(carboxymethyl)lysine (CML), while glycated hydroxylysine, an amino-acid unique to collagen, may yield N(epsilon)-(carboxymethyl)hydroxylysine (CMhL) [4].
• Unlike FN3K, FN3K-RP did not phosphorylate fructoselysine, 1-deoxy-1-morpholino-fructose, or lysozyme glycated with glucose [5].
• Escherichia coli was found to grow on fructoselysine as an energetic substrate at a rate of about one-third of that observed with glucose [2].
• The proteins encoded by YhfQ and YhfN were overexpressed in E. coli, purified, and shown to catalyze the ATP-dependent phosphorylation of fructoselysine to a product identified as fructoselysine 6-phosphate by 31P NMR (YhfQ), and the reversible conversion of fructoselysine 6-phosphate and water to lysine and glucose 6-phosphate (YhfN) [2].

Biological context of fructoselysine

• CML may be formed by oxidation of fructoselysine (FL), the Amadori adduct formed on nonenzymatic glycosylation of lysine residues in protein, or by reaction of ascorbate with protein under autoxidizing conditions [6].
• We now show that a third enzyme encoded by this operon catalyses the metal-dependent reversible interconversion of fructoselysine with its C-3 epimer, psicoselysine [7].

Anatomical context of fructoselysine

• Moreover, analysis of the fructoselysine 3-phosphate content of haemoglobin from diabetic subjects suggests that, in addition to FN3K, another deglycating mechanism may be operative in human erythrocytes [8].
• The monocyte-like cell lines Mono Mac 6 (MM6) and U937 bind Amadori-modified proteins via fructoselysine (FL)-specific sites with molar masses of 110, 150 and 200 kDa, which can specifically be isolated by an affinity method with magnetobeads coated with glycated polylysine [9].
• Nucleophosmin is a component of the fructoselysine-specific receptor in cell membranes of Mono Mac 6 and U937 monocyte-like cells [9].

Associations of fructoselysine with other chemical compounds

• We have measured FL, pentosidine, fluorescence (excitation = 328 nm, emission = 378 nm), CML, and CMhL in insoluble skin collagen from 14 insulin-dependent diabetic patients before and after a 4-mo period of intensive therapy to improve glycemic control [4].
• Specific HPLC methods were used to quantify the Amadori product fructoselysine and the AGE compounds pentosidine and pyrraline in acid or enzymatic hydrolysates [10].
• The paper reports results from balance trials with a total of 42 volunteers testing glycated casein samples containing the Maillard-(Amadori-) product fructoselysine (= FL, analysed as furosine) [11].
• Selective fortification of lysinoalanine, fructoselysine and N epsilon-carboxymethyllysine in casein model systems [12].

Gene context of fructoselysine

• The physiological function of fructosamine-3-kinase may be to initiate a process leading to the deglycation of fructoselysine and of glycated proteins [13].
• Our results indicate that the lens content of FL increases significantly between infancy and about age 5 but that there is only a slight, statistically insignificant increase in FL between age 5 and 80 (mean +/- SD = 1.4 +/- 0.4 mmol of FL/mol of Lys) [14].
• No growth on fructoselysine or psicoselysine was observed with Tn5 mutants in which the putative transporter (FrlA) or fructoselysine 6-phosphate deglycase (FrlB) had been inactivated, indicating the importance of the frl operon for the metabolism of both substrates [7].

Analytical, diagnostic and therapeutic context of fructoselysine

• Their levels were not correlated with fructoselysine levels and were similar in diabetic and non-diabetic patients on hemodialysis, indicating that their increase was not driven by glucose [15].
• Experiments with rats and human volunteers have shown that the fructoselysine moiety is poorly digested and absorbed and apparently not metabolized but soon excreted via the kidneys [16].

References