Below are the most recent studies on L-Proline and its most interesting derivatives from a healthy point of view:

Natural cryoprotectants combinations of l-proline and trehalose for red blood cells cryopreservation.
Dou M, Lu C, Sun Z, Rao W.
Cryobiology. 2019 Dec;91:23-29. doi: 10.1016/j.cryobiol.2019.11.002.

Synthesis and evaluation of the antitumor activity of Calix[4]arene l-proline derivatives.
Oguz M, Gul A, Karakurt S, Yilmaz M.
Bioorg Chem. 2020 Jan;94:103207. doi: 10.1016/j.bioorg.2019.103207.

l-Proline protects mice challenged by Klebsiella pneumoniae bacteremia.
Chen X, Qin S, Zhao X, Zhou S.
J Microbiol Immunol Infect. 2019 Jul 5. pii: S1684-1182(19)30079-9. doi: 10.1016/j.jmii.2019.05.013.

l-Proline-based-cyclic dipeptides from Pseudomonas sp. (ABS-36) inhibit pro-inflammatory cytokines and alleviate crystal-induced renal injury in mice.
Begum Ahil S, Hira K, Shaik AB, Pal PP, Kulkarni OP, Araya H, Fujimoto Y.
Int Immunopharmacol. 2019 Aug;73:395-404. doi: 10.1016/j.intimp.2019.05.044.

5-Oxo-1-[(2,3,6,7-tetramethoxy-9-phenanthrenyl)methyl]-L-proline Inhibits Hepatitis C Virus Entry.
Nguyen LP, Park C, Luong TTD, Park EM, Choi DH, Han KM, Mai HN, Nguyen HC, Lim YS, Hwang SB.
Sci Rep. 2019 May 13;9(1):7288. doi: 10.1038/s41598-019-43783-6.

Non-enzymatic Determination of L-Proline Amino Acid in Unprocessed Human Plasma Sample Using Hybrid of Graphene Quantum Dots Decorated with Gold Nanoparticles and Poly Cysteine: A Novel Signal Amplification Strategy.
Hasanzadeh M, Navay Baghban H, Shadjou N.
Anal Sci. 2018;34(3):355-362. doi: 10.2116/analsci.34.355.

Influence of the Steric Bulk and Solvent on the Photoreactivity of Ruthenium Polypyridyl Complexes Coordinated to l-Proline.
Cuello-Garibo JA, Pérez-Gallent E, van der Boon L, Siegler MA, Bonnet S.
Inorg Chem. 2017 May 1;56(9):4818-4828. doi: 10.1021/acs.inorgchem.6b02794

Vitamin C and l-Proline Antagonistic Effects Capture Alternative States in the Pluripotency Continuum.
D'Aniello C, Habibi E, Cermola F, Paris D, Russo F, Fiorenzano A, Di Napoli G, Melck DJ, Cobellis G, Angelini C, Fico A, Blelloch R, Motta A, Stunnenberg HG, De Cesare D, Patriarca EJ, Minchiotti G.
Stem Cell Reports. 2017 Jan 10;8(1):1-10. doi: 10.1016/j.stemcr.2016.11.011.

l-Proline, GABA Synthesis and Gamma Oscillations in Schizophrenia.
Volk DW, Gonzalez-Burgos G, Lewis DA.
Trends Neurosci. 2016 Dec;39(12):797-798. doi: 10.1016/j.tins.2016.10.009

Cytosolic Accumulation of L-Proline Disrupts GABA-Ergic Transmission through GAD Blockade.
Crabtree GW, Park AJ, Gordon JA, Gogos JA.
Cell Rep. 2016 Oct 4;17(2):570-582. doi: 10.1016/j.celrep.2016.09.029.

L-proline: a highly effective cryoprotectant for mouse oocyte vitrification.
Zhang L, Xue X, Yan J, Yan LY, Jin XH, Zhu XH, He ZZ, Liu J, Li R, Qiao J.
Sci Rep. 2016 Jul 14;6:26326. doi: 10.1038/srep26326.

Modulation of physicochemical and spectroscopic properties of l-serine and l-proline by propionate based food preservatives.
Banipal TS, Kaur N, Kaur J, Komal, Banipal PK.
Food Chem. 2016 Oct 15;209:220-7. doi: 10.1016/j.foodchem.2016.04.056.

Apoptosis-like death was involved in freeze-drying-preserved fungus Mucor rouxii and can be inhibited by L-proline.
Wang X, Wang Y.
Cryobiology. 2016 Feb;72(1):41-6. doi: 10.1016/j.cryobiol.2015.11.006.

L-Proline (Proline) is an amino acid ( but it is also labelled as imino acid ) present in the human body, plants and fresh fruit (hydroxy-L-proline). It is considered a non-essential amino acid synthesized from glutamic acid, but is considered an essential component of collagen and for the proper functioning of tendons and joints.

The name defines the structure of the molecule:

• proline is an amino acid that is used in protein biosynthesis.
• "L" in L-proline refers to the chirality of the molecule, which is a property of asymmetry important in several branches of science, including chemistry and biochemistry. Chirality is a geometric property of certain molecules and ions, and a chiral molecule/ion is not superimposed on its mirror image.

L-proline synthesis occurs in the body through a multi-stage process:

• Glutamate conversion: The process begins with the conversion of glutamate into glutamate semialdehyde through the enzyme glutamate 5-kinase and glutamate-5-semialdehyde dehydrogenase.
• P5C formation: Glutamate semialdehyde then spontaneously converts to pyrrolin-5-carboxylate (P5C).
• Reduction to proline: Finally, P5C is reduced to proline by the enzyme pyrrolin-5-carboxylate reductase.

Studies

In contrast to aflatoxins B1 and M1, which are part of a group of secondary metabolites of high toxicity, L-Prolin has demonstrated hepatoprotective activity in laboratory animals by reducing oxidative damage and decreasing downstream apoptosis (1).

The results of this study suggest that l-proline reduces plasma asymmetric dimethylarginine levels and improves redox status, thereby increasing nitric oxide bioavailability and counteracting the angiotensin II-induced Systolic blood pressure rise (2).

L-proline is a cryoprotectant that has no toxicity that helps cells and tissues to resist freezing in a wide range of plants and animals (3).

It's an antibacterial (4) and also chitosan/L-Prolin hydrogels could be a potential dressing material for wound tissue regeneration and repair (5). 

L-Proline, what does scientific research says

• Molecular Formula: C₅H₉NO₂
• Molecular Weight: 115.13 g/mol
• CAS: 147-85-3  4305-67-3  37159-97-0
• EC Number: 205-702-2  925-434-6
• FEMA 3319
• DSSTox Substance ID: DTXSID5044021
• Beilstein/REAXYS Number 80810
• MDL number MFCD00064318
• PubChem Substance ID 24898097
• eCl@ss 32160406
• NACRES NA.26

Synonyms:  

• (S)-Pyrrolidine-2-carboxylic acid
• (-)-(S)-Proline
• (2S)-pyrrolidine-2-carboxylic acid
• L-Prolin
• 2-pyrrolidinecarboxylic acid 

References_____________________________________________________________

 (1) l-Proline Alleviates Kidney Injury Caused by AFB1 and AFM1 through Regulating Excessive Apoptosis of Kidney Cells.  Li H, Li S, Yang H, Wang Y, Wang J, Zheng N.  Toxins (Basel). 2019 Apr 16;11(4). pii: E226. doi: 10.3390/toxins11040226.

(2) l-proline supplementation improves nitric oxide bioavailability and counteracts the blood pressure rise induced by angiotensin II in rats.  Leal J, Teixeira-Santos L, Pinho D, Afonso J, Carvalho J, de Lourdes Bastos M, Albino-Teixeira A, Fraga S, Sousa T.  Nitric Oxide. 2019 Jan 1;82:1-11. doi: 10.1016/j.niox.2018.10.007.

(3) Cryobiological Characteristics of L-proline in Mammalian Oocyte Cryopreservation.  Zhang L, Xue X, Yan J, Yan LY, Jin XH, Zhu XH, He ZZ, Liu J, Li R, Qiao J.  Chin Med J (Engl). 2016 Aug 20;129(16):1963-8. doi: 10.4103/0366-6999.187846.

(4) A Thioether-Stabilized d-Proline-l-Proline-Induced β-Hairpin Peptide of Defensin Segment Increases Its Anti-Candida albicans Ability.  Zhao B, Yang D, Wong JH, Wang J, Yin C, Zhu Y, Fan S, Ng TB, Xia J, Li Z.  Chembiochem. 2016 Aug 3;17(15):1416-20. doi: 10.1002/cbic.201600179.

(5) Biomimetic hydrogel loaded with silk and l-proline for tissue engineering and wound healing applications.  Thangavel P, Ramachandran B, Kannan R, Muthuvijayan V.  J Biomed Mater Res B Appl Biomater. 2017 Aug;105(6):1401-1408. doi: 10.1002/jbm.b.33675. 

(6) The anti-inflammatory effects of N-methyl-(2S,4R)-trans-4-hydroxy-l-proline from Syderoxylon obtusifolium are related to its inhibition of TNF-alpha and inflammatory enzymes.  de Aquino PE, Magalhães TR, Nicolau LA, Leal LK, de Aquino NC, Dos Santos SM, Neves KR, Silveira ER, Viana GS.  Phytomedicine. 2017 Jan 15;24:14-23. doi: 10.1016/j.phymed.2016.11.010.