Structural and Functional Integrity of Human Serum Albumin: Analytical Approaches and Clinical Relevance in Patients with Liver Cirrhosis

Bibliographic info

• Authors: Marina Naldi, Maurizio Baldassarre, Marco Domenicali, Manuela Bartolini, Paolo Caraceni
• Journal: Journal of Pharmaceutical and Biomedical Analysis, 2017, vol. 144, pp. 138–153
• Institution: University of Bologna, Italy

Key question

What is the comprehensive analytical landscape for characterizing HSA structural integrity and PTMs, and what are the clinical implications of these alterations in liver cirrhosis?

Methods

• Type: Comprehensive review article (systematic narrative)
• Scope: All major analytical techniques for HSA structural characterization; clinical significance of each PTM type in cirrhosis

Content overview

HSA structure and synthesis

• 585 amino acids; MW 66,438 Da; 3 domains (I, II, III); 35 Cys (34 in disulfide bonds, 1 free at Cys34)
• Synthesized by hepatocytes; 10–15 g/day; half-life 16–20 days
• Preproalbumin → proalbumin → albumin (processing in ER and Golgi)
• Synthesis inhibited by proinflammatory cytokines (relevant in cirrhosis)

PTMs reviewed

PTM	Mechanism	Key residue(s)	Δmass	Disease relevance
Cysteinylation (HNA1)	Disulfide with free cysteine	Cys34	+119 Da	Dominant in cirrhosis; marker of reversible oxidative stress
Sulfinylation (HNA2 partial)	Irreversible oxidation → sulfenic/sulfinic acid	Cys34	+16/+32 Da	Irreversible loss of antioxidant capacity
Sulfonic acid (HNA2 full)	Further irreversible oxidation	Cys34	+48 Da	Severe oxidative damage; survival marker
Glycation	Non-enzymatic Amadori reaction with reducing sugars	Lys525, Lys439, Lys281, Lys199; N-terminus	+162 Da per hexose	Metabolic disease; biphasic pattern in CLD
AGEs (advanced glycation)	Further oxidative steps from glycation	Lys, Arg	variable	Chronic diabetes, uremia
Truncation	Enzymatic cleavage at N/C terminus	N-terminus: −Asp (−115 Da)	−115 Da	CLD; consumed by homodimerization
Dehydroalanine	Dehydration of Cys34 (under alkaline conditions)	Cys34	−18 Da	⚠️ Processing artifact or in vivo?
Dimerization	Disulfide at free Cys34 between two monomers	Cys34	~2× monomer	ACLF marker (→ baldassarre-2016-dimers)
Nitrosylation	Reaction with NO	Cys34, Tyr	variable	Inflammation, sepsis
Deamidation	Spontaneous; Asn/Gln → Asp/Glu	Asn, Gln	+1 Da	Aging, storage artifact
Carbamylation	Cyanate from urea cycle or smoking	Lys, N-terminus	+43 Da	Uremia, renal disease

Analytical methods

Technique	What it measures	Strengths	Limitations
IEC-UV (Ion-exchange chromatography)	HMA/HNA1/HNA2 fractions (Cys34 state only)	Established; no MS needed; clinical routine possible	Only 3 fractions; no multi-PTM isoforms; no structural details
CZE (Capillary zone electrophoresis) ± MS	Cys34 state; glycation	Fast; can be coupled to MS	Lower resolution for complex isoforms
RP-LC-MS Top-down	Full isoform landscape (7+ isoforms)	Gold standard; multi-PTM resolution	Requires HR-MS; LC optimization needed
RP-LC-MS Bottom-up	Site-level PTM confirmation	Comprehensive; finds novel PTMs	Sample prep intensive; loses isoform context
MALDI-TOF	Intact mass	Quick; confirms major isoforms	Lower accuracy; difficult quantification
EPR spin-probe	Binding function (fatty acid sites)	Functional; not structural	No PTM specificity

Clinical relevance of isoforms in cirrhosis

• HNA1 + HNA2 levels increase progressively from compensated → decompensated → ACLF
• Native HSA decline = structural surrogate for effective albumin concept
• Glycation inverse correlation with severity (as in domenicali-2014)
• Dimerization (from baldassarre-2016-dimers): adds to functional deficiency
• Combined structural damage = “effective albumin” deficit (formalized in baldassarre-2021-ealb)

Connections

• HSA — comprehensive structural/functional reference
• Cysteinylation — HNA1/HNA2 nomenclature fully reviewed here; definitive reference
• Glycation — multi-site glycation + AGEs reviewed
• Oxidation — all Cys34 oxidative states and their mass signatures
• Top-down proteomics — gold standard method for isoform profiling validated
• Bottom-up proteomics — site-level PTM confirmation role
• domenicali-2014 — the main clinical paper this review is built around
• baldassarre-2016-dimers — dimerization data incorporated
• oettl-2013 — HNA2 survival prediction; IEC method
• spinella-2016-review — parallel review focused more on functional/therapeutic aspects

My notes

• This is the analytical methods reference for the field. It is the definitive summary of what can be detected, by which technique, and what it means clinically.
• Key for our pipeline: IEC and EPR detect Cys34 redox fractions only (HMA/HNA1/HNA2) — our RP-LC-HR-MS top-down approach provides far more structural detail (full isoform landscape including glycation, truncation combinations).
• Table 1 in this paper (analytical approaches per PTM type) is a critical resource for designing any new assay or cross-platform comparison.
• The dehydroalanine (−18 Da) modification at Cys34 is worth investigating as a potential isoform in the ALBOM panel — it was detectable by TD approach rahali-2022 as well.