The haptoglobin phenotype influences the risk of cutaneous squamous cell carcinoma in kidney transplant patients

Unlocking the link between haptoglobin polymorphism and noninfectious human diseases: insights and implications

Haptoglobin (Hp) is a polymorphic protein that was initially described as a hemoglobin (Hb)-binding protein. The major functions of Hp are to scavenge Hb, prevent iron loss, and prevent heme-based oxidation. Hp regulates angiogenesis, nitric oxide homeostasis, immune responses, and prostaglandin synthesis. Genetic polymorphisms in the Hp gene give rise to different phenotypes, including Hp 1-1, Hp 2-1, and Hp 2-2. Extensive research has been conducted to investigate the association between Hp polymorphisms and several medical conditions including cardiovascular disease, inflammatory bowel disease, cancer, transplantation, and hemoglobinopathies. Generally, the Hp 2-2 phenotype is associated with increased disease risk and poor outcomes. Over the years, the Hp 2 allele has spread under genetic pressures. Individuals with the Hp 2-2 phenotype generally exhibit lower levels of CD163 expression in macrophages. The decreased expression of CD163 may be associated with the poor antioxidant capacity in the serum of subjects carrying the Hp 2-2 phenotype. However, the Hp 1-1 phenotype may confer protection in some cases. The Hp1 allele has strong antioxidant, anti-inflammatory, and immunomodulatory properties. It is important to note that the benefits of the Hp1 allele may vary depending on genetic and environmental factors as well as the specific disease or condition under consideration. Therefore, the Hp1 allele may not necessarily confer advantages in all situations, and its effects may be context-dependent. This review highlights the current understanding of the role of Hp polymorphisms in cardiovascular disease, inflammatory bowel disease, cancer, transplantation, hemoglobinopathies, and polyuria.

Cutaneous squamous cell carcinoma arising in immunosuppressed patients: a systematic review of tumor profiling studies

As solid organ transplantation becomes more prevalent, more individuals are living as members of the immunosuppressed population with an elevated risk for cutaneous squamous cell carcinoma (cSCC). Although great progress has been made in understanding the pathogenesis of cSCC in general, little is known about the drivers of tumorigenesis in immunosuppressed patients and organ-transplant recipients, specifically. This systematic review sought to synthesize information regarding the genetic and epigenetic alterations as well as changes in protein and mRNA expression that place this growing population at risk for cSCC, influence treatment response, and promote tumor aggressiveness. This review will provide investigators with a framework to identify future areas of investigation and clinicians with additional insight into how to best manage these patients.

Haptoglobin polymorphism and prostate cancer mortality

Prostate cancer is a common malignancy in men worldwide and it is known that oxidative stress is a risk factor for cancer development. A common functional haptoglobin (Hp) polymorphism, originating from a duplication of a gene segment spanning over two exons, results in three distinct phenotypes with different anti-oxidative capacities: Hp1-1, Hp1-2, and Hp2-2. The aim of the study was to investigate the relationship between this Hp polymorphism and prostate cancer mortality. The study was performed on 690 patients with histologically confirmed prostate cancer, recruited between January 2004 and January 2007. Hp genotypes were determined by a TaqMan fluorogenic 5′-exonuclease assay. Hp1-1 was present in 76 (11%), Hp1-2 in 314 (45.5%), and Hp2-2 in 300 (43.5%) patients. During a median follow-up of 149 months, 251 (35.3%) patients died. Hp genotypes were not significantly associated with higher overall mortality (HR 1.10; 95% CI 0.91–1.33; p = 0.34). This remained similar in a multivariate analysis including age at diagnosis, androgen deprivation therapy, and risk group based on PSA level, GS, and T stage (HR 1.11; 95% CI 0.91–1.34; p = 0.30). We conclude that the common Hp polymorphism does not seem to be associated with overall mortality in prostate cancer patients.

Haptoglobin 2-2 Genotype, Patient, and Graft Survival in Renal Transplant Recipients

BACKGROUND

Cardiovascular disease is the leading cause of death in renal transplant recipients. An association between haptoglobin genotype 2-2 and cardiovascular disease has been found in patients with diabetes mellitus and liver transplant recipients. To date, the role of haptoglobin genotype after renal transplantation has not been studied.

METHODS

In this single-center retrospective cohort study of 1975 adult Norwegian transplant recipients, who underwent transplantation between 1999 and 2011, we estimated the risk of all-cause and cardiovascular mortality and overall and death-censored graft loss for patients with haptoglobin genotype 2-2 compared to genotype 2-1 or 1-1, after adjustment for confounders and competing risks.

RESULTS

We found no associations between haptoglobin genotype 2-2 and cardiovascular mortality (subdistributional hazard ratio 1.08, 95% confidence interval 0.78-1.49; P = .63). We also failed to detect any association between haptoglobin 2-2 genotype and all-cause mortality, overall graft loss, and death-censored graft loss. Similar results were found in the subpopulation of transplant recipients with diabetes.

CONCLUSION

In this large cohort of kidney transplant recipients, we could not demonstrate any association between haptoglobin 2-2 genotype and patient or graft survival after renal transplantation.

Circulating Haptoglobin and Metabolic Syndrome in Renal Transplant Recipients

Haptoglobin (Hp) is an acute phase protein that has recently been linked to components of the metabolic syndrome (MetS). We aimed to evaluate Hp as marker of MetS, and to assess its association with long-term outcome in renal transplant recipients (RTR). We measured plasma Hp in a prospective cohort of 699 stable RTR and 149 healthy controls. Median plasma Hp concentration in RTR was 1.4 [interquartile range (IQR), 1.0–1.8] g/L, which was higher compared to 1.1 [0.9–1.4] g/L in controls (P < 0.001). Hp was independently associated with the MetS (β = 0.10) (P = 0.005). During follow-up of 5.4 [4.8–6.1] years, 150 (21%) recipients died, of whom 60 (9%) due to cardiovascular causes, and 83 (12%) RTR developed graft failure. High (≥2.0 g/L) and low (≤0.9 g/L) plasma Hp were associated with increased risk of mortality (HR’s 2.3 [1.3–4.1] and 1.9 [1.0–3.5], resp.), predominantly cardiovascular. The association of high Hp lost significance upon adjustment for inflammation markers (HR 1.5 [0.8–2.7]), while low Hp was independently associated with mortality (HR 2.2 [1.2–4.0]). Hp was not associated with graft failure (P = 0.49). In conclusion, plasma Hp is independently associated with MetS in RTR. Importantly, high and low Hp are associated with increased mortality risk, independent of MetS.

Haptoglobin Phenotypes and Susceptibility to Schistosoma Parasites Infection in Central Sudan

Haptoglobin (Hp) is an acute phase protein that binds the free hemoglobin (Hb), thus preventing iron loss and renal damage. Hp also has antioxidative and immunomodulatory properties. Three Hp phenotypes have been identified in human: Hp1-1, Hp2-1, and Hp2-2. Hp polymorphisms have been related to susceptibility of various diseases. In this study, we aimed to assess the possible association of Hp phenotypes polymorphism to Schistosoma parasites infection in central Sudan. We have investigated the Hp phenotypes polymorphism distribution in the serum of 125 (93 S. mansoni, 13 S. haematobium and 19 infected with both "co-infection") parasitologically confirmed infected individuals and 208 healthy individuals served as control. Hp phenotypes have been determined by polyacrylamide gel electrophoresis followed by benzidine staining. Our study revealed that Hp1-1 percentage frequency was significantly higher in infected individuals than healthy control individuals 51% and 26% respectively. Our data suggest that Hp1-1 phenotype may upsurge the susceptibility to Schistosoma parasites infection in central Sudan.

Haptoglobin

Haptoglobin (Hp) is an abundant human plasma protein that tightly captures hemoglobin (Hb) during hemolysis. The Hb-Hp complex formation reduces the oxidative properties of heme/Hb and promotes recognition by the macrophage scavenger receptor CD163. This leads to Hb-Hp breakdown and heme catabolism by heme oxygenase and biliverdin reductase. Gene duplications of a part of or the entire Hp gene in the primate evolution have led to variant Hp gene products that collectively may be designated "the haptoglobins (Hps)" as they all bind Hb. These variant products include the human-specific multimeric Hp phenotypes in individuals, which are hetero- or homozygous for an Hp² gene allele. The Hp-related protein (Hpr) is another Hp duplication product in humans and other primates. Alternative functions of the variant Hps are indicated by numerous reports on association between Hp phenotypes and disease as well as the elucidation of a specific role of Hpr in the innate immune defense. Recent Advances: Recent functional and structural information on Hp and receptor systems for Hb removal now provides insight on how Hp carries out essential functions such as the Hb detoxification/removal, and how Hpr, by acting as an Hp-lookalike, can sneak a lethal toxin into trypanosome parasites that cause mammalian sleeping sickness. Critical Issues and Future Directions: The new structural insight may facilitate ongoing attempts of developing Hp derivatives for prevention of Hb toxicity in hemolytic diseases such as sickle cell disease and other hemoglobinopathies. Furthermore, the new structural knowledge may help identifying yet unknown functions based on other disease-relevant biological interactions involving Hps. Antioxid. Redox Signal. 26, 814-831.

Association of haptoglobin phenotypes with the development of Kaposi's sarcoma in HIV patients

Kaposi's sarcoma (KS) is a rare cutaneous tumor caused by human herpes virus-8 (HHV-8) infection that preferentially develops in case of severe immunosuppression, such as in HIV/AIDS disease. Haptoglobin (Hp), a polymorphic multifunctional plasma protein, exerts several immunomodulatory effects and is characterized by a genetic polymorphism leading to three major phenotypes (Hp 1-1, Hp 2-1 and Hp 2-2). This study investigated the influence of Hp genetic polymorphism on the development of KS in HIV-positive patients. 661 HIV patients were enrolled in the study with a median age of 35 years and a median follow-up time of 57 months. Hp phenotyping was performed using hemoglobin-supplemented starch gel electrophoresis. In case of low Hp concentration high pressure gel permeation chromatography (HPGPC) was used. The Hp 1-1 phenotype was associated with a significant higher risk of KS compared to the combined group of Hp 2-1 and Hp 2-2 patients (p < 0.0005) which remained significant after adjustment for possible confounding variables (age, gender and AIDS status) (p < 0.001). In contrast, the Hp 2-1 phenotype carried the lowest risk. These findings point to the involvement of Hp phenotypes in the pathogenesis of KS, which may be due to a difference in skin immunosurveillance between the Hp phenotypes.