Targeting the Liver with Nucleic Acid Therapeutics for the Treatment of Systemic Diseases of Liver Origin

Systemic diseases of liver origin (SDLO) are complex diseases in multiple organ systems, such as cardiovascular, musculoskeletal, endocrine, renal, respiratory, and sensory organ systems, caused by irregular liver metabolism and production of functional factors. Examples of such diseases discussed in this article include primary hyperoxaluria, familial hypercholesterolemia, acute hepatic porphyria, hereditary transthyretin amyloidosis, hemophilia, atherosclerotic cardiovascular diseases, α-1 antitrypsin deficiency-associated liver disease, and complement-mediated diseases. Nucleic acid therapeutics use nucleic acids and related compounds as therapeutic agents to alter gene expression for therapeutic purposes. The two most promising, fastest-growing classes of nucleic acid therapeutics are antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs). For each listed SDLO disease, this article discusses epidemiology, symptoms, genetic causes, current treatment options, and advantages and disadvantages of nucleic acid therapeutics by either ASO or siRNA drugs approved or under development. Furthermore, challenges and future perspectives on adverse drug reactions and toxicity of ASO and siRNA drugs for the treatment of SDLO diseases are also discussed. In summary, this review article will highlight the clinical advantages of nucleic acid therapeutics in targeting the liver for the treatment of SDLO diseases. SIGNIFICANCE STATEMENT: Systemic diseases of liver origin (SDLO) contain rare and common complex diseases caused by irregular functions of the liver. Nucleic acid therapeutics have shown promising clinical advantages to treat SDLO. This article aims to provide the most updated information on targeting the liver with antisense oligonucleotides and small interfering RNA drugs. The generated knowledge may stimulate further investigations in this growing field of new therapeutic entities for the treatment of SDLO, which currently have no or limited options for treatment.

OUES from submaximal cardiopulmonary exercise

Introduction

Cardiopulmonary exercise testing (CPEX) provides valuable diagnostic and prognostic cardiopulmonary function data. However, in clinical setting a maximal test is not always achievable. The Oxygen Efficiency Uptake Slope (OUES) has been proposed as a possible submaximal measure of cardiopulmonary function as it remains relatively stable during the final quartile of the exercise test. This study explored the validity of OUES as a surrogate marker for cardiopulmonary function in the event of a submaximal test.

Methods

Four groups of subjects [128 healthy controls (73 M), 44 asymptomatic hypertensive (HT) patients (26 M), 67 adult cardiac congenital heart disease (ACHD) patients (44 M) and 35 Heart Failure with preserved Ejection Fraction (HFpEF) (10M) patients] were recruited after informed consent. All subjects underwent clinical assessment, resting ECG, blood pressure and spirometry prior to a treadmill CPEX to volitional exhaustion and a respiratory exchange ratio (RER) of at least 1.1 using the same testing protocol. Peak VO2 (ml/min) was recorded from the last 5s of the maximal test (RER=1.1) and OUES was calculated from complete (RER=1.1) and truncated (RER=0.9) gas exchange data. The linear relationships between absolute peak VO2 and OUES from complete and truncated gas exchange data were assessed using Pearson's correlation coefficient. Subsequently, the two correlations obtained in each patient group were compared. Statistical significance was set at p<0.01.

Results

Mean and 95% confidence intervals of the peak VO2 for males and females in each decile of life examined in the 4 subject groups are shown in the Figure. Peak VO2 values achieved in each of the patient groups were significantly lower when matched for age and sex compared to healthy participants (HT p=0.006, ACHD patients p<0.001 and HFpEF patients p<0.001).

In all 4 groups there was a good correlation between absolute peak VO2 and the OUES at RER 1.1 (healthy volunteers r=0.910, p<0.001, HT r=0.899, p<0.001, ACHD r=0.816, p<0.001 and HFpEF r=0.846, p<0.001). Correlations were inferior for absolute peak VO2 and OUES at RER 0.9 (healthy volunteers r=0.74, p<0.001, HT r=0.780, p<0.001, ACHD r=0.651, p<0.001 and HFpEF r=0.817, p<0.001). Correlations between absolute peak VO2 vs OUES at RER of 1.1 and 0.9 were significantly different only for healthy controls (p=0.001, Z-score = −4.649), but not for HT (p=0.05, Z-score = −1.909), ACHD (p=0.04, Z-score = −2.080) or HFpEF (p=0.7, Z-score = −0.377) patients.

Conclusion

Our data support the use of submaximal OUES at an RER of 0.9 as a surrogate marker for absolute peak VO2 obtained at an RER of 1.1, especially in patients, in whom it can often be difficult to achieve maximal exercise.

Funding Acknowledgement

Type of funding sources: None.