Synthetic dipeptides──a new dimension in clinical nutrition

Recent investigations clearly indicate that certain amino acids previously considered as non-essential are conditionally indispensable substrates in various diseased states: Hypermetabolic and hypercatabolic situations are accomPanied by a marked depression of the intracellular glutamine mpl. This depletion of glutamine stores leads to severe complications, such as infection, poor wound healing, impaired immunity, increased intestinal permeability, and finally multiple organ failure. In the liver tissue of fetuses and preterm and term infants the endogenous synthesis of the sulfur containing amino acid cysteine is impaired due to low or undetectable activity of the key enzyTne cystathionase. tow intracellular concentrations of taurine are a typical feature in chronic renal failure and presumably associated with muscle fatigue. Under certain pathologica1 conditions like phenylketonuria, liver and kidney diseases, and in premature infants the aromatic amino acid tyrosine is considered conditionally indispensable due to impaired synthesis from phenylalanine. These data strongly support the notion that glutarnine, cysteine/cystine, taurine, and tyrosine should be essential parts of artificial nutrition in various diseased states. However, unfavourable physica1/chemical properties as well as metabolic limitations hamper their use as parenteral substrates in routine clinical setting. Glutamine quantitatively decomposes in aqueous solutions during heat sterilization and long-term storage to yield pyroglutamic acid and amrnonia. In addition, provision of free glutamine in adequate amounts to patients is always associated with a high water load due to its limited solubi1ity. Tyrosine and cystine are poorly soluble (only 0. 4 and 0. 1g/L H20, respective ly);cysteine rapidly oxidizes to yield cystine. Parenteral free taurine might not be available for the depleted intracellular compartment because of a low transport rate due to the very high intracellular/extracellular transmembrane gradient.Synthesis and characterization of synthetic dipeptides These obvious drawbacks have initiated an intensive research for alternative substrates which can be used as amino acid sources in parenteral and enteral nutrition. In cooperation with our industry partners (Dequssa AG, Fresenius Kabi) we successfully developed in our working group chemical /biotechnological methocls for the synthesis of glu tamine -, cystine -, tyrosine- and taurine- containing dipeptides/conjugates. All synthetic peptides were highly soluble and showed purity degrees better than 99 %. Carefully controlled studies confirmed the stability of the peptides during sterilization and storage. In the meantime, the synthetic process has been scaled up for selected peptides (glutarnine and tyrosine dipeptides) to yield industrial quantities. Dpeptide utilization- experimental studiesBasic studies with various synthetic glutamine-, tyrosine’ and cystine-containing dipeptides provide convincing evidence that thesesubstrates are rapidly cleared from plasma after parenteral administration without accumulating in tissues and with minimal losses inurine. The presence of membran-bound as well as tissue free extracellular hydroase activity facilitates a prompt and quantitative pep-tide hydroysis,the liberated amino acids being available for protein sguthesis and/or g6neration of energy.InpePtide utilization-human studiesHuman studies in healthy volunteers demonstrated that the synthetic glutamine dipePtides L-alanyl-L-glutamine (Ala-Gln, pre-Sen in rspePtivenR) and glycyl-L-glutamine (Gly-Gln,present in Glamin’) as well as the synthetic tyrosine dipeptide g1ycyl-L-tyro-sine(GlyTgr, present in Glamin’) are rapidly hydroyzed after bolus injection (elimination half lives 3. 3, 7. 8, and 3. 8 min, respec-tivdy)’ Continuous infuSion of a commercial amino acid soution supplemented with Ala-Gln or Gly-Gln was not accompanied by anyside efhets,and no complaints were reported. lnfusion of peptide-supplemented solutions resulted in a prompt increase in alanine, glu-tamine, t^ne,and glycine

Recent investigations clearly indicate that certain amino acids previously considered as non-essential are conditionally indispensable substrates in various diseased states: Hypermetabolic and hypercatabolic situations are accomPanied by a marked depression of the intracellular glutamine mpl. This depletion of glutamine stores leads to severe complications, such as infection, poor wound healing, impaired immunity, increased intestinal permeability, and finally multiple organ failure. In the liver tissue of fetuses and preterm and term infants the endogenous synthesis of the sulfur containing amino acid cysteine is impaired due to low or undetectable activity of the key enzyTne cystathionase. tow intracellular concentrations of taurine are a typical feature in chronic renal failure and presumably associated with muscle fatigue. Under certain pathologica1 conditions like phenylketonuria, liver and kidney diseases, and in premature infants the aromatic amino acid tyrosine is considered conditionally indispensable due to impaired synthesis from phenylalanine. These data strongly support the notion that glutarnine, cysteine/cystine, taurine, and tyrosine should be essential parts of artificial nutrition in various diseased states. However, unfavourable physica1/chemical properties as well as metabolic limitations hamper their use as parenteral substrates in routine clinical setting. Glutamine quantitatively decomposes in aqueous solutions during heat sterilization and long-term storage to yield pyroglutamic acid and amrnonia. In addition, provision of free glutamine in adequate amounts to patients is always associated with a high water load due to its limited solubi1ity. Tyrosine and cystine are poorly soluble (only 0. 4 and 0. 1g/L H20, respective ly);cysteine rapidly oxidizes to yield cystine. Parenteral free taurine might not be available for the depleted intracellular compartment because of a low transport rate due to the very high intracellular/extracellular transmembrane gradient.Synthesis and characterization of synthetic dipeptides These obvious drawbacks have initiated an intensive research for alternative substrates which can be used as amino acid sources in parenteral and enteral nutrition. In cooperation with our industry partners (Dequssa AG, Fresenius Kabi) we successfully developed in our working group chemical /biotechnological methocls for the synthesis of glu tamine -, cystine -, tyrosine- and taurine- containing dipeptides/conjugates. All synthetic peptides were highly soluble and showed purity degrees better than 99 %. Carefully controlled studies confirmed the stability of the peptides during sterilization and storage. In the meantime, the synthetic process has been scaled up for selected peptides (glutarnine and tyrosine dipeptides) to yield industrial quantities. Dpeptide utilization- experimental studiesBasic studies with various synthetic glutamine-, tyrosine' and cystine-containing dipeptides provide convincing evidence that thesesubstrates are rapidly cleared from plasma after parenteral administration without accumulating in tissues and with minimal losses inurine. The presence of membran-bound as well as tissue free extracellular hydroase activity facilitates a prompt and quantitative pep-tide hydroysis,the liberated amino acids being available for protein sguthesis and/or g6neration of energy.InpePtide utilization-human studiesHuman studies in healthy volunteers demonstrated that the synthetic glutamine dipePtides L-alanyl-L-glutamine (Ala-Gln, pre-Sen in rspePtivenR) and glycyl-L-glutamine (Gly-Gln,present in Glamin') as well as the synthetic tyrosine dipeptide g1ycyl-L-tyro-sine(GlyTgr, present in Glamin') are rapidly hydroyzed after bolus injection (elimination half lives 3. 3, 7. 8, and 3. 8 min, respec-tivdy)' Continuous infuSion of a commercial amino acid soution supplemented with Ala-Gln or Gly-Gln was not accompanied by anyside efhets,and no complaints were reported. lnfusion of peptide-supplemented solutions resulted in a prompt increase in alanine, glu-tamine, t^ne,and glycine concentr