Deoxysphingoid bases as plasma markers in Diabetes mellitus

BACKGROUND: Sphingoid bases are formed from the precursors L-serine and palmitoyl-CoA-a reaction which is catalyzed by the serine-palmitoyltransferase (SPT). SPT metabolizes, besides palmitoyl-CoA also other acyl-CoAs but shows also variability towards the use of other amino acid substrates. The enzyme is also able to metabolize alanine, which results in the formation of an atypical deoxy-sphingoid base (DSB). This promiscuous activity is greatly increased in the case of the sensory neuropathy HSAN1, and pathologically elevated DSB levels have been identified as the cause of this disease. Clinically, HSAN1 shows a pronounced similarity to the diabetic sensory neuropathy (DSN), which is the most common chronic complication of diabetes mellitus. Since serine and alanine metabolism is functionally linked to carbohydrate metabolism by their precursors 3-phosphoglycerate and pyruvate, we were interested to see whether the levels of certain sphingoid base metabolites are altered in patients with diabetes. RESULTS: In a case-control study we compared plasma sphingoid base levels between healthy and diabetic individuals. DSB levels were higher in the diabetic group whereas C16 and C18 sphingoid bases were not significantly different. Plasma serine, but not alanine levels were lower in the diabetic group. A subsequent lipoprotein fractionation showed that the DSBs are primarily present in the LDL and VLDL fraction. CONCLUSION: Our results suggest that DSBs are a novel category of plasma biomarkers in diabetes which reflect functional impairments of carbohydrate metabolism. Furthermore, elevated DSB levels as we see them in diabetic patients might also contribute to the progression of the diabetic sensory neuropathy, the most frequent complication of diabetes

The SPTLC3 Subunit of Serine Palmitoyltransferase Generates Short Chain Sphingoid Bases*

The enzyme serine palmitoyltransferase (SPT) catalyzes the rate-limiting step in the de novo synthesis of sphingolipids. Previously the mammalian SPT was described as a heterodimer composed of two subunits, SPTLC1 and SPTLC2. Recently we identified a novel third SPT subunit (SPTLC3). SPTLC3 shows about 68% identity to SPTLC2 and also includes a pyridoxal phosphate consensus motif. Here we report that the overexpression of SPTLC3 in HEK293 cells leads to the formation of two new sphingoid base metabolites, namely C16-sphinganine and C16-sphingosine. SPTLC3-expressing cells have higher in vitro SPT activities with lauryl- and myristoyl-CoA than SPTLC2-expressing cells, and SPTLC3 mRNA expression levels correlate closely with the C16-sphinganine synthesis rates in various human and murine cell lines. Approximately 15% of the total sphingolipids in human plasma contain a C16 backbone and are found in the high density and low density but not the very low density lipoprotein fraction. In conclusion, we show that the SPTLC3 subunit generates C16-sphingoid bases and that sphingolipids with a C16 backbone constitute a significant proportion of human plasma sphingolipids

Mobilization of hematopoietic progenitor cells with standard or reduced dose filgrastim after vinorelbine in multiple myeloma patients. a randomized prospective single center phase II study

Vinorelbine combined with filgrastim (r-metHuG-CSF) at a dose of 10 µg/kg of body weight (BW) per day is a reliable and well tolerated regimen for mobilization of hematopoietic progenitor cells (HPC) in patients with multiple myeloma. This prospective randomized phase 2 study was initiated to assess the feasibility of a reduced filgrastim dosage. Vinorelbine was combined with either standard dosed filgrastim (10 µg/kg body weight (BW) per day) or reduced dosed filgrastim (5 µg/kg BW per day). Leukapheresis sessions were planned to start at day 8 and were continued until the predefined target amount of 4 x 106 HPC/kg BW was collected. The study demonstrated the feasibility of vinorelbine combined with reduced daily filgrastim with a mean of 1.29 leukapheresis sessions necessary per patient (95% confidence interval 0.95-1.7). All patients could start leukapheresis as planned at day 8, and the collection success rate was 100% for the whole patient collective after a maximum of two leukapheresis sessions. No statistically significant differences with regard to the amount of HPC collected between the two groups were observed (p=0.99). Accordingly, no differences were seen with regard to length of hospitalization for autotransplant (p=0.34), duration of neutrophil (p=0.93) and platelet engraftment (p=0.42). Patients receiving reduced dose filgrastim reported significantly lower peak pain values in a numerical analogue scale (p=0.01), and the costs were significantly lower than in the patients undergoing standard dosed chemo-mobilization (p=0.001). Vinorelbine 35 mg/m2 plus filgrastim 5 µg /kg BW once per day until completion of HPC collection is feasible and appears to be advantageous with respect to the severity of pain intensity and treatment costs